WEBVTT 00:00:19.039 --> 00:00:29.818 Okay Thanksgiving Yeah. I'm very glad to be here. This is a very, very interdisciplinary and interesting summer 00:00:29.818 --> 00:00:39.746 school apologies for not being able to attend the very first part. But I was on holidays with my wife. And if I 00:00:39.746 --> 00:00:46.629 cancelled those holidays, I would have probably reached the limits of life of my marriage. So apologies for that. 00:00:46.640 --> 00:00:59.529 Another apology is I am an engineer how many engineers are in the room. Okay? Okay, very good. So what we 00:00:59.529 --> 00:01:08.981 are going to talk about is is, again, a very interdisciplinary subject, which is and you will have the view from 00:01:08.981 --> 00:01:18.330 from an engineer like me. So I'm trying to convince you today that limits of life, non dimensional analysis 00:01:18.330 --> 00:01:26.970 studies that really belong today to the ecology and the science really actually have a very important engineering 00:01:26.970 --> 00:01:36.109 application. I started working on eco hydraulics, so they interact for me. Will give a better definition later on. 00:01:36.109 --> 00:01:44.838 But for me, the way I intend it is the interaction between hydraulics and fish. That is what I do. And that is 00:01:44.838 --> 00:01:53.401 what we are going to talk today. It is not the case is a much wider subject. But again, I was saying I started 00:01:53.401 --> 00:02:02.239 working on these, say, five, six years ago, when I went to Southampton, and I started working with a fish biologist, a 00:02:02.239 --> 00:02:09.879 fish biologist, who works in Faculty of Engineering, which is quite unusual. His name is Paul Camp. And we started 00:02:09.879 --> 00:02:16.580 chatting together. I was literally dragged into into the subject. And I really loved it. It is a fascinating subject. 00:02:16.590 --> 00:02:23.630 But again, it is very interdisciplinary. I was doing the hydrogennamics part. I do fluid mechanics in my in my research. 00:02:23.639 --> 00:02:31.313 So my knowledge of biology, of biology, physiology I learned it a little bit, but clearly I always needed 00:02:31.313 --> 00:02:39.993 Paul to back me up. I'm going to show you something today about fish biology and fish physiology. But I mean, it is not 00:02:39.993 --> 00:02:49.382 exactly my subject, but I'll try to call it as good as I can we have three hours to spend today. Gabby called them 00:02:49.382 --> 00:02:59.754 a lecturing marathon so the lectures are split in two slots. There is one slot this morning when that will cover 00:02:59.754 --> 00:03:08.178 general definition of life in moving fluids and will be essentially a background lecture covering all the topics 00:03:08.178 --> 00:03:16.889 then we will be needed to better understand the lecture this morning this afternoon. Sorry Which, is about 00:03:16.889 --> 00:03:25.882 research some sort of research topics. I'm working on, and I would like to to share with you. So again, this morning we 00:03:25.882 --> 00:03:33.374 are going to talk about and life in moving through it. There would be a first subslot, which I call the lecture 00:03:33.374 --> 00:03:38.079 one. I which is an introduction to eco hydraulics and some typical subjects. 00:03:38.430 --> 00:03:45.359 In the second part, after a break, we will talk about swimming and living in complex environments. 00:03:45.719 --> 00:03:54.483 I think the first sub slot is going to be shorter, then the second will will play it by the year. Okay, but feel free to 00:03:54.483 --> 00:04:00.550 ask questions to interrupt me any time. If you have curiosities on anything else? no problem at all. 00:04:00.800 --> 00:04:13.352 So an introduction to and fish locomotion. What is eco hydraulics? well as the word suggests, this is an 00:04:13.352 --> 00:04:21.900 interdisciplinary subject. The interface between ecology and hydraulics. Essentially, we are trying to investigate how 00:04:21.900 --> 00:04:31.350 hydrogennamics, mainly an open channel flows influence ecosystems, essentially and I really like the definition of 00:04:31.350 --> 00:04:38.020 catapulties who say the deals with the trilogy of of subjects. 00:04:38.279 --> 00:04:46.320 One is an ecosystem restoration including a dumb removal and wetland station. Dumb removal now is a hot topic. 00:04:46.329 --> 00:04:52.657 Nobody really knows how to remove efficiently and sustainable of dams @unoise@ uh, because they represent um um, a 00:04:52.657 --> 00:04:59.373 barrier for fish migration. For other, many other problems. They @unoise@ they. Need to be removed in many parts of the 00:04:59.373 --> 00:05:06.329 world, like in Brazil, in Canada, there are works in the U S. There are um works in that in that field. 00:05:06.610 --> 00:05:13.777 The other typical subject is ecological flows essentially, it is the way of defining what is the flow that 00:05:13.777 --> 00:05:20.782 organisms like in rivers what defines good ecosystems ecosystem from an either dynamic point of view. And then 00:05:20.782 --> 00:05:29.358 there is the last subject, which is today's focus, which is passage systems for migration of fish, another aquatic 00:05:29.358 --> 00:05:39.113 organism. Forget about the other aquatic organisms. We were going to talk about about fish. That is what this lecture 00:05:39.113 --> 00:05:50.363 will will actually cover. And there you go. You probably all know better than me. Fish migrates and move in rivers or 00:05:50.363 --> 00:05:53.840 from the ocean to the rivers and vice versa. 00:05:54.199 --> 00:06:03.914 And the the big issue as I was introducing earlier on is the rivers are heavily fragmented, did by Manmaid structures 00:06:03.914 --> 00:06:15.509 okay. Weirs, dams, and these structures represent barriers to their movement so that we are essentially impeding 00:06:15.509 --> 00:06:24.450 fish to in fisher production. So they are not able to reach the habitat they they use for spawning and and so 00:06:24.450 --> 00:06:32.978 forth. And this is a big problem in is causing the depression of fish stocks around the world, the stocks of wheels are 00:06:32.978 --> 00:06:40.458 are depleting really, really, really fast which is a big problem commercially as well as from an ecosystem point 00:06:40.458 --> 00:06:49.434 of view it is ah, it is a big problem, especially felt and well founded in Northern Europe, not so much now in 00:06:49.434 --> 00:06:58.057 Italy, where I work. Ah, we are a bit behind. But ah, it is gaining momentum also also also there. Um, there is a 00:06:58.057 --> 00:07:06.250 picture here on the on your right hand side here, showing some salmons jumping over a waterfall. So you may say, okay, 00:07:06.250 --> 00:07:13.745 these barriers, you know, the fish are very, very strong. They can jump and overcome them. Well, certainly they cannot 00:07:13.745 --> 00:07:21.650 overcome dance like these. These are really, really large and represent imperable barriers for, for, for fish. 00:07:21.850 --> 00:07:30.582 As you know, dams are used very often for either power purposes. So whenever fish migrating either upstream or might get 00:07:30.582 --> 00:07:38.758 it in downstream. So upstream means going from the ocean to the to the spawning habitat upstream indeed, or or swimming 00:07:38.758 --> 00:07:47.456 from upstream to a meaning towards " ah " towards the ocean. That is um. Whenever they do that, they actually Ah. They 00:07:47.456 --> 00:07:56.405 encounter threats because they might actually take the spillways and make a big, a big jump here that would kill them, 00:07:56.405 --> 00:08:05.355 or they actually may swim through the through the turbines of the of the hydropower station, and which would most likely 00:08:05.355 --> 00:08:12.147 kill them as well. So besides representing a barrier, they are also a threat another typical structure that 00:08:12.147 --> 00:08:20.986 represent a barrier are weirs. This is we are in on the river paw in Tuin, where I live. And as you can see, on the 00:08:20.986 --> 00:08:30.118 downstream side of the weird. There are very a fast and shallow currents that prevent fish to actually swim so 00:08:30.118 --> 00:08:39.548 they are not even able to overcome this sort of obstacles. These structures cannot be well at the time at the moment 00:08:39.548 --> 00:08:47.103 cannot be easily removed, because they, they serve important purposes. As I say, dams are used to produce electricity, 00:08:47.103 --> 00:08:56.900 and we are really thirsty for energy worldwide. We are are used for usually purposes. So they are used to measure 00:08:56.900 --> 00:09:04.820 discharge in rivers, which is extremely important for water management purposes. So some of them that are worldwide. 00:09:04.830 --> 00:09:12.688 Some of them are recognized to be redundant so they can be removed so diminishes that would diminish the 00:09:12.688 --> 00:09:20.613 fragmentation of the old river, but some others cannot be removed. So we need to find solutions that allow these 00:09:20.613 --> 00:09:29.739 structures to be fish friendly. Essentially, we need to provide passage for for fish. There is a nice sort of sketch 00:09:29.739 --> 00:09:31.959 here that explains the problem. 00:09:32.320 --> 00:09:42.006 Every time we have a barrier, which, like in this case, in here, we need to provide ways for the fish to overcome the 00:09:42.006 --> 00:09:49.665 barrier. Imagine, let us assume this is we are talking about upstream migrations of fish. Come here and want to go 00:09:49.665 --> 00:09:58.300 upstream against the floor. There are two ways. Essentially, broadly speaking, although this is a bit brutal, but either 00:09:58.300 --> 00:10:10.960 we build a a natural sort of a natural canal that a bypass it allows to to link the upstream in the downstream part of 00:10:10.960 --> 00:10:20.075 the other around the barrier, or we actually can build a concrete structures, essentially some baffled channels were 00:10:20.075 --> 00:10:29.696 usually quite steep, where these buffals, these roughness elements, are used to decrease the float and to increase the 00:10:29.696 --> 00:10:40.598 flow depths, and therefore to allow the fish to swim, to rise these. They are called or fish passes in 00:10:40.598 --> 00:10:50.964 the design of this passes the questions and the problems we have to address are, first of all, how do we attract fish to 00:10:50.964 --> 00:10:52.259 the fish pass. 00:10:53.000 --> 00:11:02.120 That is how, how, how can we let them know? look, you have to go there, not there go there. You know, when we 00:11:02.120 --> 00:11:10.482 drive we have signs in the road. That is easy, but fish don't recognize exactly arrows and stuff. So we need to attract 00:11:10.482 --> 00:11:17.637 them there. And how do we design fish passes? that is another engineering questions, meaning okay usually 00:11:17.637 --> 00:11:24.724 these barriers are associated with head difference, which are quite substantial, as we have seen in the dumb picture 00:11:24.724 --> 00:11:33.597 earlier on. So usually we have to build, like in this case, if you look on the right inside, you know, channels 00:11:33.597 --> 00:11:40.560 buffal channels that are quite steep. So presumably they will be characterized with the high velocities. Can fish 00:11:40.560 --> 00:11:49.471 sustain these high velocities? can they actually swim into into these flows? how does turbulence and the mean flow and 00:11:49.471 --> 00:11:58.848 the of the flow within the channel effect swimming form so that they can actually rise. Shall I do it a 00:11:58.848 --> 00:12:07.466 longer fish pass but less steep or a steeper fish pass, but short. So that depends on the stamina of the fish on 00:12:07.466 --> 00:12:16.285 the fitness of the fish water temperature and many other things. That is a very difficult ecological engineering 00:12:16.285 --> 00:12:17.870 problem. 00:12:20.639 --> 00:12:30.704 We have to address, which really pertains very well with issues related to dumb and hydropower is, how do we repel fish 00:12:30.704 --> 00:12:41.321 from dangerous areas. We have seen that we have to track fish to fish, pass but we also have to find ways to repel 00:12:41.321 --> 00:12:49.548 fish from the denters are, is like spillways like intakes for the turbines, or like screens. Screens are essentially 00:12:49.548 --> 00:12:59.827 filters that that allow do not allow debris and other things to go into the water intakes of the turbines. These 00:12:59.827 --> 00:13:06.952 screens are extremely dangerous. I'll show you some pictures this afternoon. I suppose where eels and many fish 00:13:06.952 --> 00:13:15.448 get impinged, and they are not able to swim back so that is a killer for for fish. We have find ways to repell 00:13:15.448 --> 00:13:18.460 fish from screens, from spillways and so forth. 00:13:19.669 --> 00:13:28.764 In summary, it is a big problem in order to adapt problems of fish pass to allow fish migration and fish movement. We 00:13:28.764 --> 00:13:37.129 need to understand what attracts and water repels fish while migrating. And this belong to the world of fish behavior, 00:13:37.129 --> 00:13:45.383 animal behavior in general, and in this context, there is quite a strong literature now and evidence that 00:13:45.383 --> 00:13:54.072 hydrogennamics flu and seem to play really a key role in determining the fish behavior at these small scales, in 00:13:54.072 --> 00:14:01.160 proximity of these structures. Fish behavior is dictated by many things. You know, they are living organisms. So there 00:14:01.160 --> 00:14:08.255 are curious fish. There are less cutest fish, scary scared fish @unoise@ if we are hungry and they are looking for food 00:14:08.255 --> 00:14:14.711 @unoise@ uh fish are tired, the fish are very fit. So everything @unoise@ uh fish behavior in general is extremely 00:14:14.711 --> 00:14:17.610 complex and depends on a huge number of variables. 00:14:17.950 --> 00:14:26.903 As far as migration is concerned, however, it seems the hydrogennamics plays a key role the way they respond to 00:14:26.903 --> 00:14:35.408 hydrogennamics determine determines where they go essentially, and whether they go to the fish pass, or whether they get 00:14:35.408 --> 00:14:44.808 trimmed into the turbines % um the second. Okay, there should be a two here. Not one, but doesn't matter. How do we 00:14:44.808 --> 00:14:52.553 facilitate swimming in fish passes. And this belonged to the world of fish locomotion, which is belongs to a huge 00:14:52.553 --> 00:15:01.945 literature. Okay, there is a lot since 40s. I suppose there were maybe the sixties there were. There were models trying 00:15:01.945 --> 00:15:12.614 to reproduce and to understand fish locomotion and more for biometric purposes and to to get inspired design underwater 00:15:12.614 --> 00:15:14.859 vehicles and so forth. 00:15:14.970 --> 00:15:20.990 But it also has applications, as we have seen in ecological contacts. 00:15:21.159 --> 00:15:30.369 And we will see that swimming in fish passes is not only about mean velocities. Okay, you know, @unoise@ Ah, you have 00:15:30.369 --> 00:15:38.837 learned probably. Ah, you know, from your background, or in the summer school, the drag of of any object really is is it 00:15:38.837 --> 00:15:47.135 depends on the square of the velocity. If we are in the. Let us call inertia regime but it is not only that 00:15:47.135 --> 00:15:54.028 turbulence size of a this influence or may not influence. We still don't know the the swimming performance of fish. We 00:15:54.028 --> 00:16:01.195 will see some examples this morning so we have fish behavior and fish locomotion has two microscopic areas 00:16:01.195 --> 00:16:10.129 of study to address the problem of fish pass. And there there you go @unoise@ um. When I say fish behavior, I just want 00:16:10.129 --> 00:16:16.970 to stress the fact that, ah, some species migrate and move individually. Some others migrate and move collectively. 00:16:17.399 --> 00:16:25.694 And ah, fish behavior at the collective scale is, is, is, is yet another discipline of of Ah complexity sciences 00:16:25.694 --> 00:16:34.636 @unoise@ um collective behavior is that there is a lot to talk about. There is no time to talk about collective 00:16:34.636 --> 00:16:43.173 behavior in Ah today. But I do work on that un collective behavior of fish. It is a fascinating subject. So if you are 00:16:43.173 --> 00:16:52.930 curious to know more about that. We can talk later on, going back to the microscopic picture. We have fish behavior and 00:16:52.930 --> 00:17:02.021 fish locomotion to address the problem of fish pass. We need two more mm. Let us say a knowledge of of two more Ah 00:17:02.021 --> 00:17:12.098 variables. One is, of course, hydrogennamics and turbulence plays a key role, and the other one is flow sensing, as we 00:17:12.098 --> 00:17:22.481 will see in a few minutes. Fishes are living a sensors of pressure and velocity. It is really incredible how they are 00:17:22.481 --> 00:17:31.610 able to sense the flow around them, and clearly what they sense laughter, so dictate the behavior so. Whatever 00:17:31.610 --> 00:17:39.617 they they feel influence their choice of what to do. And this is fairly, fairly intuitive. Hydrogennamics, of course, 00:17:39.617 --> 00:17:45.484 influences fish locomotion and fish locomotion, meaning swimming ability, swimming performance, and that clearly 00:17:45.484 --> 00:17:55.549 influences fish behavior as well. A fish will never go to to a fast current if he is not able to sustain the current. 00:17:56.019 --> 00:18:05.918 Hydrogennamics also influences flow sensing so this let us call them physiological sensor they have in 00:18:05.918 --> 00:18:14.955 their body. @unoise@ can be um can be fooled by turbines. Okay, so turbans is a noisy represent a noisy signal for 00:18:14.955 --> 00:18:21.728 them that can prevent them to actually detect meanwhileastic gradients @unoise@ or or microscopic properties of the flow 00:18:21.728 --> 00:18:28.753 around them that actually would drive their decision that that behavior so. Hydrogennamics in general can be 00:18:28.753 --> 00:18:36.782 can influence a lot flow senses and in turn, free fish behavior. So this big picture is a system of interconnected 00:18:36.782 --> 00:18:46.183 blocks. This morning, in this first slot, we are going to talk, learn a little bit @unoise@ ah. More about the fish 00:18:46.183 --> 00:18:55.781 locomotion and and flow sensing by fish @unoise@ ok i'm going to go really. I would say a very intuitive level. We 00:18:55.781 --> 00:19:04.739 will keep it very, very, very easy and sweet okay, let us talk about fish locomotion. Well, this is a huge world. 00:19:04.750 --> 00:19:14.121 Uh. Fish fishes come with different size, shape, uh swimming abilities and so forth, but overall < laugh > Let us take 00:19:14.121 --> 00:19:26.017 this as A as A as a template for fish. You know of this, of these shape. There is a in here in the tale of 00:19:26.017 --> 00:19:38.172 the fish the coward Finn is used as an air foil as a sail. Let us say so. The the zigzaging of the of the tail and 00:19:38.172 --> 00:19:49.155 the cattle fen generates these lifts and drug forces moving that vary in direction and magnitude during the excursion of 00:19:49.155 --> 00:20:00.171 the in its Ah zigzagin pattern. And overall, these lifts and rock forces generate a positive thrust that overcomes 00:20:00.171 --> 00:20:10.309 the drag of the fish, which is mainly skin fiction. When a swains there there is no if if the 00:20:10.309 --> 00:20:17.774 fish was steady and straight you would see no separation of the boundary layers. So the only source of drug or 00:20:17.774 --> 00:20:25.612 flow resistance would be the friction between the skin of the fish and the flow itself okay so overall this 00:20:25.612 --> 00:20:34.186 catalyst is responsible for the movement of fish along a longitude in a direction of a velocity. You @unoise@ % um the 00:20:34.186 --> 00:20:46.220 lateral fines or the other fines are usually used as to stabilize the fish in in water so that is how it works. 00:20:46.839 --> 00:20:56.179 The interesting bit is um. These movements of the are used then to uh, generate different swimming activities. 00:20:56.190 --> 00:21:06.501 Okay, you can discern between cruising activity, which is, uh, when the fish, uh, can swim for hours, maintaining this 00:21:06.501 --> 00:21:16.494 regime of swimming for hours. And this swimming cause no major physiological change in the organisms, in the fish 00:21:16.494 --> 00:21:24.806 itself. So sort of a walk then there is the burst activity, the burst activity, which is ecologically, extremely 00:21:24.806 --> 00:21:33.401 um, eh important, and most important for an engineering point of view is when the fish essentially mm runs, goes really, 00:21:33.401 --> 00:21:39.950 really fast to overcome some very fast current, or to escape from a predator, for example. 00:21:40.250 --> 00:21:48.541 And this requires a sustain and intense effort that cannot be maintained, usually for more than @unoise@ um few seconds 00:21:48.541 --> 00:21:55.947 to tens of seconds. Okay, that depends on many, many things. We are going to see this very, very soon @unoise@ among, 00:21:55.947 --> 00:22:01.958 which there is also water temperature. Sure @unoise@ ah, usually when it is very, very cold. Fish are more lazy when it 00:22:01.958 --> 00:22:08.799 is hotter @unoise@ the water is is warmer sorry. They are much more active and able to do @unoise@ ah to to swim a lot 00:22:08.799 --> 00:22:18.092 faster. There is something in between called sustained activity which, has a very blurry definition, and it is not 00:22:18.092 --> 00:22:28.237 very relevant. In my opinion, what really I'm interested in, and I think has a lot of ecological and engineering value 00:22:28.237 --> 00:22:36.807 is the definition of birth activity or maximum speed. Ok this is important for the design of fish passes that are 00:22:36.807 --> 00:22:43.894 usually characterized by very steep slopes and fast currents. So that is what we need to to know about fish. What is the 00:22:43.894 --> 00:22:51.444 maximum speed they can, they can reach. And for how long if I know their maximum speed, and for how long they can 00:22:51.444 --> 00:22:59.919 sustain it. I've got speed times time. I've got a length. I can design the lens of my of my fish pass. I know that most 00:22:59.919 --> 00:23:08.733 fishes will be able to to rise and and overcome the obstacle. The fish pass is his helping to overcome. So what the term 00:23:08.733 --> 00:23:16.476 is maximum speed limits in different fish species. A big question. There is a lot of literature on these. And while 00:23:16.476 --> 00:23:24.327 reviewing the material for the Summer School, I encountered this very, very recent paper published in Nature Ecology by 00:23:24.327 --> 00:23:34.099 a German group actually? well, it is mixed. I think there is also U K University and somebody else. I don't remember. It 00:23:34.099 --> 00:23:43.323 is quite a few authors involved, and it is very, very interesting they pose the questions in general, the largest 00:23:43.323 --> 00:23:52.440 animals are not the fastest. A lion in faster than than an elephant. So why? and the question is, eh makes sense? 00:23:52.440 --> 00:24:00.799 because if you think about it, you know, the largest animals have larger muscles. They are bigger, they have more power. 00:24:00.799 --> 00:24:10.717 So in principle, they should run faster than smaller animals. And usually this maximum theoretical velocity. V has an 00:24:10.717 --> 00:24:20.246 alometric relationship with mass. It is a power law, essentially, where A and beer, two coefficients that depends on on, 00:24:20.246 --> 00:24:23.859 on, on, on the species and so forth. 00:24:24.349 --> 00:24:33.065 The explanation they give for this country. Intuitive result is is based on on the acceleration on the stamina, 00:24:33.065 --> 00:24:40.714 essentially, of of animals. A mouse is able to reach to saturate his velocity very quickly, can accelerate very, very 00:24:40.714 --> 00:24:47.277 click quickly reach ex maximum velocity and keep it an elephant, although, has aoretical velocity, which is really, 00:24:47.277 --> 00:24:56.917 really high, because it is very powerful. As many muscles accelerates very, very slowly. It gets tired for you can 00:24:56.917 --> 00:25:07.039 actually reach the the, the, the symptomatic velocity. Okay, so it is a trade off between power and and stamina, 00:25:07.039 --> 00:25:17.219 essentially. And they developed a nice model, quite simple, and they tested it against different species flying, running 00:25:17.219 --> 00:25:27.026 and swimming. And they all show this maximum. Okay, flying. They have the maximum speeds on the Y axis. Here you have 00:25:27.026 --> 00:25:37.042 the speed on the X axis, you have the body mass. Okay, so essentially there is a maximum meaning that the largest, the 00:25:37.042 --> 00:25:45.576 biggest animals are not the fastest @unoise@ the intermediate animals are actually the fastest for Uh flying. Uh 00:25:45.576 --> 00:25:55.680 mammals, reptiles, and also for swimming animals like like fish. You can see that there is clearly a maximum around, 00:25:55.680 --> 00:26:06.745 say, one hundred kilograms like tuna in the sea are really, really fast, or a marine I think they can go up to 00:26:06.745 --> 00:26:16.468 fifteen meters per second. That is very, very, very fast. And when I read this paper, I found it really, really 00:26:16.468 --> 00:26:26.817 fascinating and very, very ah. Let us say um, um, I'm consistent with this summer school But I was surprised 00:26:26.817 --> 00:26:36.535 that this study did not include or mention another very interesting study by and vase of two thousand and eight, 00:26:36.535 --> 00:26:46.716 where they actually um did um an analysis very complicated one using air for a theory, trying to find the limits, the 00:26:46.716 --> 00:26:56.233 speed limits of fish and the results of their analysis is fascinating. They say that small swimmers say one meter long 00:26:56.233 --> 00:27:05.652 are limited by power as before. So the largest fish, in principle, have more muscles so they can go faster. Small fish, 00:27:05.652 --> 00:27:11.580 they don't have enough power. They are very, very small, so they reach lower velocities. 00:27:12.359 --> 00:27:22.648 Large swimmers who, in principle, have really large masses of very strong muscles and have a lot of of stored power in 00:27:22.648 --> 00:27:32.469 their body are actually limited by , which is fascinating essentially when a fish starts sweeping the the fin if it 00:27:32.469 --> 00:27:34.340 sweeps it too fast. 00:27:36.140 --> 00:27:40.780 The water around the fin itself will experience really high velocities. 00:27:41.170 --> 00:27:47.250 And if you remember the theorem in fluid dynamics. If you have really high velocities. 00:27:47.420 --> 00:27:57.245 What happens is the pressure drops right now. You can boy water either increase in the the temperature of it, or by 00:27:57.245 --> 00:28:05.143 decreasing a lot. The the water pressure. Whenever this pressure goes beyond a certain limit, bubbles that forms from 00:28:05.143 --> 00:28:08.879 nuclei that are naturally present. Water starts to expand. 00:28:09.480 --> 00:28:17.915 And whenever these bubbles travels in the flow and reach some areas where the pressure is restored, they start 00:28:17.915 --> 00:28:26.039 oscillating. These bubbles um behave. The behavior of bubbles is is explained by the really place the equation it. 00:28:26.049 --> 00:28:32.347 Is a complicated differential equation although an ordinary differential equation, which is good. But anyway, they 00:28:32.347 --> 00:28:35.879 are very nonlinear oscillators that eventually lead to collapse. 00:28:36.180 --> 00:28:44.441 When a bubble collapses, collapses really violently inside the bubble. You may have pressures up to one thousand 00:28:44.441 --> 00:28:53.531 atmospheres. Cavitation is used for for many purposes. Usually like to avoid it because these 00:28:53.531 --> 00:29:01.600 habitation bubbles are able to break propellers like in these pictures. You see, this is the damage of cavitation. 00:29:01.599 --> 00:29:09.265 Around is a shape propeller so they can really break everything. And so they can really break and damage fish tails, 00:29:09.265 --> 00:29:17.367 essentially. And there are some pictures which I couldn't find. Unfortunately, apologies for that of of tails. I think 00:29:17.367 --> 00:29:20.369 of tuna fish being damaged by habitation. 00:29:20.579 --> 00:29:26.894 Tuna can afford to reach habitation because they have bonytails, so they don't have nerve systems, but they don't feel 00:29:26.894 --> 00:29:36.070 pain. But dolphins really do feel pain in the in their tail so they avoid to actually trigger calvation, because that 00:29:36.070 --> 00:29:44.539 would really, really hurt. So for tuna, cavitation is a problem. You set salimi for this, for the speed velocity. 00:29:44.549 --> 00:29:51.791 Because whenever you have around eh um eh any airfall or any propeller @unoise@ the deficiency essentially of the 00:29:51.791 --> 00:30:02.118 propeller decreases a lot. You reach a solid. What is called the , stall where where where were thrust diminishes a 00:30:02.118 --> 00:30:13.798 lot @unoise@ um. So my question when I was reading this paper on the one hand, you have the velocity and acceleration, a 00:30:13.798 --> 00:30:23.713 concept developed by by here and and co workers. And they and they say that that explains this maximum in the in, the 00:30:23.713 --> 00:30:33.002 speed versus body mass diagram. I wonder whether plays a role in that. It was not mentioned. But I think, uh, I 00:30:33.002 --> 00:30:42.715 think it would um regarding what I'm working on in hydraulics we are working essentially in this tale 00:30:42.715 --> 00:30:50.903 of the curve, because we deal mainly with fresh water. Well, @unoise@ eh in this lecture, we will deer mainly on fresh 00:30:50.903 --> 00:30:58.112 waterfish. So we are here. We don't reach the size of of whales and @unoise@ and so forth eh. In rivers like in the 00:30:58.112 --> 00:31:07.625 oceans @unoise@ so. This is not um a big deal, but um, definitely as a general concept, in my opinion, so should 00:31:07.625 --> 00:31:16.085 be ah taken um should be taken into account. Let me just go back to the previous light. An interesting thing is that 00:31:16.085 --> 00:31:23.477 cavitation sets speed limits, especially when fish is swing close to the surface. So say, adept the tar less than ten, 00:31:23.477 --> 00:31:30.918 fifteen meters where pressures are low. If you go deeper in the ocean. Clearly you, the fisher, experience very, very 00:31:30.918 --> 00:31:38.349 high pressures. And habitation is limited, because it is very difficult to boil water. So perhaps deep inside the ocean, 00:31:38.349 --> 00:31:47.274 fish can go really, really fast, but close to the surface, to death, that are we interest for, also for freshwater 00:31:47.274 --> 00:31:58.041 problems. Definitely cavitation can represent a phenomenon dictating Eh speed limits @unoise@ @unoise@ and this is 00:31:58.041 --> 00:32:08.322 about it for fish locomotion. We will see this afternoon how fish behaves and deals with with turbulent flows % um % uh 00:32:08.322 --> 00:32:17.994 later on four or something we will go into detail on that. Now let me just keep going with the description 00:32:17.994 --> 00:32:27.523 of background material. And let us talk now a little bit about flow sensing, flow sensing by fish is is incredible. In 00:32:27.523 --> 00:32:37.051 my opinion, and I have taken this paragraph from a paper by Horse Blackman and Zelly Cross, black man. He is a 00:32:37.051 --> 00:32:44.683 scientist based near in Germany. In born, I was lucky enough to go to one of his seminars is an excellent scientist 00:32:44.683 --> 00:32:54.975 working on the on the mechanical sensory system of fishes. And it is really fascinating what it does @unoise@ ah and eh 00:32:54.975 --> 00:33:03.662 during this seminar. Um, I was really fascinated. So I, I dig deeper into the into the topic and found out really 00:33:03.662 --> 00:33:10.953 interesting things. Essentially, as you can see from this thick picture fishes that the surface, the skin of of fishes 00:33:10.953 --> 00:33:20.305 is covered by um. Some little dots in here that represents, Ah, well, they are they are called and are 00:33:20.305 --> 00:33:30.083 spread around the body, mostly into this line, which is called the latter line. And all these as are used to sense 00:33:30.083 --> 00:33:39.968 the flow to measure pressure and velocity around around the fish. And there are so many and mostly concentrated in the 00:33:39.968 --> 00:33:50.349 head divide in superficial new must where there are some cupola here. Essentially, these are sort of slender 00:33:50.349 --> 00:33:59.213 objects essentially protruding into the flow, or, let us say, into the boundary layer forming around the fish 00:33:59.213 --> 00:34:05.820 itself. We are talking about microscopic scales here. So they are really, really, really small and when they are 00:34:05.820 --> 00:34:12.917 exposed to the flow, they bend and they send a signal to the nerve central nerve system, which analyzes the signal and 00:34:12.917 --> 00:34:37.747 dictates. Okay, here there is a high velocity or a high sheer stress, perhaps more appropriately. And the other building 00:34:37.747 --> 00:35:47.385 block of the of the lateral line is called the canal so. In the fish body there are some only small canals a bit 00:35:47.385 --> 00:35:56.885 larger, then the near the superficial nerves. Uh, these are literally um essentially. You, have two holes which 00:35:56.885 --> 00:36:03.440 are connected to the outside. Sorry by a by an under skin canal. 00:36:03.889 --> 00:36:11.660 And uh, the water inside this microscopic canal is driven by the pressure difference between one hole and the other. 00:36:12.000 --> 00:36:21.339 And this pressure difference? Ah, drive the floor inside @unoise@ um inside the the the canal and the . So the 00:36:21.339 --> 00:36:30.130 sensor characteristic sensor of the fish starts not bending, because there is a bit more a blunt structure, but slides 00:36:30.130 --> 00:36:38.626 okay. And the degree to which these the lights depends on the floor velocity, an intern on the pressure 00:36:38.626 --> 00:36:47.518 difference. So in general, you may say, superficial neuromasts, which from now on we will call S. N are sensors for 00:36:47.518 --> 00:36:52.160 velocities or for boundary layer philosophy, which is a big problem. 00:36:52.389 --> 00:37:00.305 Can we see why canal are censored for pressure pressure differences okay that inter turbulent waters, 00:37:00.305 --> 00:37:09.470 or even in cal waters can be very, very small and they are actually able really to detect really small variations. 00:37:09.940 --> 00:37:19.079 Ok for example, you can have hydrogennamic stimuli by insects moving on on the surface of a lake. Fish are 00:37:19.079 --> 00:37:29.767 able to actually detect them and go and catch them. All right, or add this generated by self generated eddies, or it is 00:37:29.767 --> 00:37:41.118 generated by other fish in in close proximity. This is a picture of the superficial you see these these 00:37:41.118 --> 00:37:54.132 small dots in here. And there is also @unoise@ there. Are also stained canal in here as you can see the poor 00:37:54.132 --> 00:38:02.150 associated with canal neuromas is slightly larger than the superficial itself. There is this. 00:38:02.590 --> 00:38:11.299 Perhaps we could switch off the light here. Uh, there is this nice picture of of, uh, I think this is a Mm. Well, I 00:38:11.299 --> 00:38:21.062 can't remember what sort of fish what species thanks disease. But you can see all the in the fish skin 00:38:21.062 --> 00:38:31.112 figure B you can see the canal neuromas just a larger diameter @unoise@ than the superficial um eh than the 00:38:31.112 --> 00:38:32.069 superficial . 00:38:32.559 --> 00:38:42.689 Um, again the superficial neurons work as a @unoise@ with bending moments essentially and measured the velocity, as we 00:38:42.689 --> 00:38:53.090 say that the cupola inside the water, the canal neuromas, which is slightly larger, instead glides. And there are these 00:38:53.090 --> 00:39:02.089 this hair bundle now. We are going deeper into the physiology of fish, which I am not really confident with, 00:39:02.089 --> 00:39:09.450 but essentially they are responsible for generating the signal that then is transferred to the central nerve system, and 00:39:09.450 --> 00:39:21.604 and as analyzed by the fish to work out the velocity field. Um now, the distribution number and size of superficial and 00:39:21.604 --> 00:39:35.055 canal that is incredibly a lot among fish species. Understanding why is definitely a very active area of 00:39:35.055 --> 00:39:45.102 research. There is an example here of three species and you can see the number and the distribution of the canal 00:39:45.102 --> 00:39:56.553 neuromas is is really, really, really high. However, there is a speculation saying that it seems that a fish with 00:39:56.553 --> 00:40:05.274 superficial neuromas. Abundance lives in calm water. Let us say lakes, something like that, um? whereas fish with 00:40:05.274 --> 00:40:12.060 abundance of canal like well are associated with um turbulent and faster waters. 00:40:12.449 --> 00:40:22.921 The literature on this is contradictory. Somebody says," It is true. Somebody else finds no whatsoever link between 00:40:22.921 --> 00:40:29.080 habitat and characteristics of the latter, a line to me. 00:40:29.500 --> 00:40:36.986 I don't really have an explanation. While superficial neuromas are more useful in calm waters than Ah than canal 00:40:36.986 --> 00:40:42.136 my interpretation is that ah um superficial neuramas measure @unoise@ @unoise@ @unoise@ @unoise@ @unoise@ @unoise@ 00:40:42.136 --> 00:40:47.973 @unoise@ @unoise@ @unoise@ @unoise@ @unoise@ @unoise@ @unoise@ @unoise@ @unoise@ let us go back to these slides are 00:40:47.973 --> 00:40:54.219 mediated by the boundary layer. Okay, so around the fish, whenever the fish moves, there is a boundary layer forming. 00:40:54.230 --> 00:41:00.621 And what they measure, since they are really, really small, is developed in the boundary leaves. So the result is sort 00:41:00.621 --> 00:41:08.766 of a filter effect of what is really going on outside canal measure pressure differences I don't know if you 00:41:08.766 --> 00:41:17.166 are familiar with boundary layer theory, but in a thin boundary layer. The fact that the boundary layer is very, very 00:41:17.166 --> 00:41:25.059 thin, dictates the fact that the pressure over the direction perpendicular to the surface locally is actually constant. 00:41:25.070 --> 00:41:32.277 Okay? so whatever they measure is is very much linked to what is actually going on outside the boundary leaves, or what 00:41:32.277 --> 00:41:40.612 they really, really want to measure. So to me, kind of makes sense that fish want to live in the inter turbulent waters 00:41:40.612 --> 00:41:49.023 have developed a system of canal which is more sorry. A number of neurons that is more skewed towards canal 00:41:49.023 --> 00:41:55.854 rather than a superficial enormous. But that is my interpretation. It could be totally, totally. It is the 00:41:55.854 --> 00:42:03.019 interpretation, again, of a free dynamicist, which should be integrated within Ah biological framework, which Ah, which 00:42:03.019 --> 00:42:14.377 is something that is as I said," Ah, ah, an active Ah research area. Ah, how are we doing with time? Hm @unoise@ almost 00:42:14.377 --> 00:42:25.023 there % um anyway. There is a general pan in terms of density, it seems that they are more concentrated towards 00:42:25.023 --> 00:42:35.153 the head of the fish, and then they slowly decrease in density along the body of the fish itself. This is of great 00:42:35.153 --> 00:42:46.803 interest, not only for for ecological purposes. Many scientists are trying to reproduce the latter. A line of fish 00:42:46.803 --> 00:42:58.962 so that they can use it in underwater systems to detect obstacles and so forth. Instead of essentially 00:42:58.962 --> 00:43:07.851 and let me just stress something which is very, very fascinating. Fish use the latter line for many purposes so 00:43:07.851 --> 00:43:16.589 they essentially detect what is going on from a point of view around them to detect praise or predators, to 00:43:16.589 --> 00:43:24.168 communicate, to do schooling schooling. It means essentially when there will, when they want to stay together, to feel 00:43:24.168 --> 00:43:33.246 to to % uh to % um to follow each other in a coordinated manner, and also for object discrimination. So incredibly fish, 00:43:33.246 --> 00:43:43.384 if you put a blindfish or a fish in total darkness within a bath and you put a lot of obstacles the fish 00:43:43.384 --> 00:43:51.826 starts doing some tail beats most the water round. Get the signal back from a free, dynamic perspective and has a 00:43:51.826 --> 00:43:59.691 sort of an hydrogennamic picture of the obstacle around the fish. And there is an ice. Hopefully it will go. Video 00:43:59.691 --> 00:44:11.620 @unoise@ of a blind cave fish. This is a blindfish that was that was immersed in this bucket essentially, and scientists 00:44:11.620 --> 00:44:21.500 monitored its movements. It is completely bad. You can't see. But as you can see, well, it seems that there is touching 00:44:21.500 --> 00:44:33.569 the the obstacles, but actually is not. So he is able to avoid them just by self propelling, and he never hurts himself 00:44:33.569 --> 00:44:52.703 and to me that is really, really incredible. The latter line is a system. There you go, which is Key. Ah, for the 00:44:52.703 --> 00:45:04.601 for the health of fish. Whenever you um you um um I the you switch off the latter line, you can do that. But I 00:45:04.601 --> 00:45:11.519 think with with some anesthetics, biologists can do that. The fish are not able really to discriminate what is what is 00:45:11.519 --> 00:45:23.199 around them. So you really impede their life heavily um and as we will see, understanding how the latter line works. 00:45:23.210 --> 00:45:34.505 What exactly is the signature felt by the fish as we will see this afternoon has huge implications, even from an 00:45:34.505 --> 00:45:45.286 engineering point of view, slightly off topic we talked about flow sensing site is also very much used by 00:45:45.286 --> 00:45:55.881 fish. And this summer school, well, this lecture is a bit a mix of hydrogennamics and fish biology, and how hydrogen it 00:45:55.881 --> 00:46:04.584 has shaped fish, perhaps. And what is really, really interesting is that, well, the the position of eyes in fish um is 00:46:04.584 --> 00:46:12.085 is really, really clever. So whenever a fish move, uh due to the movement itself. There is a pressure field 00:46:12.085 --> 00:46:19.837 generating around the fish. We will have some high pressure around the head and a little bit low pressure close to the 00:46:19.837 --> 00:46:31.641 tail. High pressure has the potential of distorting the the the essentially the the eyes of the fish, and and therefore 00:46:31.641 --> 00:46:40.451 the vision of fish. But nature really shaped the position of of the eyes in proximity of the efficient of where 00:46:40.451 --> 00:46:47.775 the efficient of pressure of the fish is actually zero Cp. The coefficient of pressure is nothing but the difference 00:46:47.775 --> 00:46:54.769 between the the pressure and @unoise@ eh pressure infinities. The background pressure @unoise@ normalized by the Ah, the 00:46:54.769 --> 00:47:03.263 the kinetic energy @unoise@ ah, the kinetic head, essentially of the current, where the fish is a old imposition, or the 00:47:03.263 --> 00:47:11.992 the velocity itself of the fish. If the the water is standing. So whenever the Cp is zero, that means essentially the 00:47:11.992 --> 00:47:20.048 pressure in proximity of of the fish surface is equal to the background pressure. And that is where the eyes of the fish 00:47:20.048 --> 00:47:30.348 are located. So their vision is not @unoise@ % eh % eh is not % um @unoise@ ah distorted a while % uh swimming @unoise@ 00:47:30.348 --> 00:47:40.271 @unoise@ % um this is a list of reference that I've used to this to do this. First slot of lecture they represent 00:47:40.271 --> 00:47:49.364 by no means a completely treachery word, but the review, but they can be considered as a seed to branch out, okay? and 00:47:49.364 --> 00:48:00.229 and read more and learn more about all these topics that we have covered as far as I understand now, it is time for a 00:48:00.229 --> 00:48:09.355 for a break ten minutes break but if there are questions be @unoise@ unhappy to discuss of course, all 00:48:09.355 --> 00:48:19.341 curiosities or or or anything all good to start for the recording videos. Yeah, okay right well 00:48:19.341 --> 00:48:31.572 come back we are now going to the second slot of these morning lectures @unoise@ Which, is about swimming and living in 00:48:31.572 --> 00:48:33.239 complex environments. 00:48:33.400 --> 00:48:45.170 So if we go back to the initial big picture of of of um of the first of the first slot um. Now we have learned a little 00:48:45.170 --> 00:48:54.282 bit more about fish locomotion. We have learned um how fish sends the flow, what remains to be addressed is a little bit 00:48:54.282 --> 00:49:01.635 of hydrogennamics. Um, eh. So what is actually in rivers? what? what? what? Uh? what sort of what is the environment 00:49:01.635 --> 00:49:03.090 that they live in. 00:49:04.139 --> 00:49:12.160 And rivers are definitely either. They have very complex environments @unoise@ ah this is a nice picture of 00:49:12.160 --> 00:49:20.201 a river in New Zealand @unoise@ And. Ah you, can see it is. It is a mandering river that Ah will show clearly strong the 00:49:20.201 --> 00:49:29.004 grades. So there will be an in the in the mean flow @unoise@ uh. And obviously, most rivers are a flow in 00:49:29.004 --> 00:49:37.670 the turbulent regime. Um and turbulence is very, very < laugh > complex phenomenon. I perhaps I shouldn't use the 00:49:37.670 --> 00:49:45.615 word complex, complex sciences. Now it is something else. It belongs to the world of collective behavior and and the 00:49:45.615 --> 00:49:52.110 emergence of microscopic Uh phenomena out of the interaction of individual elements. Perhaps I should say complicated. 00:49:52.119 --> 00:49:59.809 Okay, so it is < laugh > Turbine is complicated, is it? it is also complex in, in, in, according to you, to some theory. 00:49:59.809 --> 00:50:08.197 But what I'm talking here today is about complicated things, things that give headaches let. Us start with 00:50:08.197 --> 00:50:16.837 turbulence here. There is a little bit of material that perhaps is is redundant. I think you have had the chance to 00:50:16.837 --> 00:50:25.097 learn what and the phenomenology during previous lecture. So I'll go a little bit fast, but an open channel floor 00:50:25.097 --> 00:50:32.925 is a high Reynolds number flow, so it is exposed to the dynamic instabilities that generate this building block of 00:50:32.925 --> 00:50:41.309 turbines, which are eddies or scales of motion eddies in general extract energy from the mean flow. So it turbines is 00:50:41.309 --> 00:50:48.189 dissipative phenomenon, and eventually dissipates this energy into heat through the energy cascade, going from large 00:50:48.189 --> 00:50:56.119 vortices to small vortages. I'm not going to go farther into this, because I assume you know, that. 00:50:56.250 --> 00:51:06.588 And the if we, if we take a pictorial view of turbulence based on the on on on spectrum of inspector. We can identify 00:51:06.588 --> 00:51:13.777 three ranges of turbulence going from the large scale ladies, which contains most of the energy, and then through an 00:51:13.777 --> 00:51:20.606 intermediate range, which is called the inertia sub range @unoise@ @unoise@ where ah, the scales of motion lose 00:51:20.606 --> 00:51:29.721 memory of day of the large scales in the flow but. Still this, cosity is not important and then at a high 00:51:29.721 --> 00:51:38.184 wave number. So it is very small scales. Viscosity kicks in, energy anticipated into it, a hit um. The intermediate 00:51:38.184 --> 00:51:46.050 range is usually called inertia sub range. And Ah, farther down in the wave number, there is this dissipation range. 00:51:46.070 --> 00:51:54.398 They are both kind of predictable. Theoretically, there are some issues here at the head overlap which we have 00:51:54.398 --> 00:52:02.323 worked on, but we, we have good predictions based on theoretical princess pose. What really gives problems are the large 00:52:02.323 --> 00:52:08.457 the energy containing eddies. And this larger, this influence essentially fish locomotion. Okay, you can. And this is 00:52:08.457 --> 00:52:16.280 pretty easy to imagine a vortex of this size. Well, whenever you have fish of a certain size, and four clients, which is 00:52:16.280 --> 00:52:23.633 just the length of the fish. The ed this that will influence its swimming ability will be an idea of the same size, 00:52:23.633 --> 00:52:29.729 roughly or larger. So we are definitely in the energy containing regime. When we talk about fish turbines interaction. 00:52:29.739 --> 00:52:39.289 And unfortunately for us, these large scale ladies are unpredictable. Our our case dependent any rivers you may have all 00:52:39.289 --> 00:52:50.496 sorts of Ed is generated by different. The um @unoise@ um by different % um @unoise@ ah ah ah 00:52:50.496 --> 00:53:00.105 conditions @unoise@ and. This is ah, ah, large. It is generated by river confluence, which is, you know, it is a kind of 00:53:00.105 --> 00:53:08.610 mixing layer type of turbans @unoise@ that influences the the Ah, the dispersion of of Ah of sediment @unoise@ % um. 00:53:08.610 --> 00:53:20.989 Then you have, we may have % uh wakes around obstructions that are, uh, heavily family rivers. This can be man made 00:53:20.989 --> 00:53:29.126 structures like, uh, like bridges with column, while cylindrical elements protruding the free surface. This give rise of 00:53:29.126 --> 00:53:38.963 very coherent voices @unoise@ % um @unoise@ % uh that % um % uh, that form in procrastinity of the linders. And 00:53:38.963 --> 00:53:46.824 this is very, very topical in fish research. We will see that most experiments are done in wake turbulence, because that 00:53:46.824 --> 00:53:58.834 triggers a special behavior of fish. There was rocks and logs in torrents that fish use as a refuge, or that fish 00:53:58.834 --> 00:54:08.882 exploit to minimize energy consumption and to hold station @unoise@ the the simplest let. Us consider the simplest case 00:54:08.882 --> 00:54:16.480 of a straight, rectangular channel that you can have in a flum. So in a laboratory okay, I'm talking about this 00:54:16.480 --> 00:54:25.251 because most experiments on fish are done in the lab. And so @unoise@ the turbulence properties that are that are 00:54:25.251 --> 00:54:33.155 um investigated belongs to, you know, are essentially within the context of of wall turbines, because open 00:54:33.155 --> 00:54:42.816 channels usually have the depths, which is much smaller than the width of the channel where they flow so most of 00:54:42.816 --> 00:54:51.988 the turbines is generated by, essentially, by the the friction between water and and the bed of the channel. And this 00:54:51.988 --> 00:54:58.959 may be a simplistic view, but actually generates very complicated turbulence. We still don't understand. And this 00:54:58.959 --> 00:55:07.039 worries me a lot, because if we don't understand turbulence in a laboratory where everything is is controlled. There is 00:55:07.039 --> 00:55:14.200 a straight channel, shallow water. Everything is nice. I mean, think about trying to model and understand these rivers 00:55:14.200 --> 00:55:25.252 here. I mean, it worries me a lot but that is what we have. And in so in a name, in the digitalized case of 00:55:25.252 --> 00:55:33.504 a straight, open channel flow, uniform flow, the energy containing Andes in rivers somewhat relate to what are called 00:55:33.504 --> 00:55:41.542 turbulence can it is a very colic phenomenon, but not completely covered. There are some coherent 00:55:41.542 --> 00:55:48.006 structures. That is what they are called that are responsible for figuring most of transport phenomena. Okay, momentum, 00:55:48.006 --> 00:55:56.768 scalar and so forth. As you probably have learned in in past lectures, in this in the summer school and this high 00:55:56.768 --> 00:56:05.005 pin had. These are coherent structures that scale somewhat linearly from from the bed. They grow in size when 00:56:05.005 --> 00:56:16.031 when you go ah away from the bed, and they really have the shape of an Ipain. These are flow visualization 00:56:16.031 --> 00:56:24.667 from America, simulations of of past papers. Uh, okay. The visualization is a complicated uh issue. Um essentially, uh, 00:56:24.667 --> 00:56:33.245 there are techniques based on the balustrade in Tensor. But that does doesn't matter that are allowed to find diseases 00:56:33.245 --> 00:56:42.556 of, of, of, of swearing, essentially the swirling property of um, of of of an Eddie and eh, eh, and how these 00:56:42.556 --> 00:56:50.843 distributes. So they captured the coherence of of this um of lamps, of fluids that that share the same swearly swearing 00:56:50.843 --> 00:57:00.267 power in a very, very intuitive way and there are nice nice this is a high pink forest that was 00:57:00.267 --> 00:57:08.731 captured by a ah woo and moan in two thousand and nine, which is really impressive. In a flat boundary layer. Red means 00:57:08.731 --> 00:57:16.680 very high longitude of the lost is blue or lower velocity. And you can really see that these hypothesis is 00:57:16.680 --> 00:57:26.674 forming in the near wall region or in the nearby region. In case of of open China flows, then organize it into pockets 00:57:26.674 --> 00:57:35.326 essentially a brutal description of all turbulence can be said that is made by individual hypothesis that then 00:57:35.326 --> 00:57:43.977 organizes into packets so in many urbanities that these packets have a coherence themselves and form what are 00:57:43.977 --> 00:57:53.496 called a class of large scales. So large scales are assist packets of these , which is really the building 00:57:53.496 --> 00:58:03.649 block of energy containing Aids in open China. Well, in any world flows. Really, these large scale motions well. 00:58:03.659 --> 00:59:05.189 Let, us say this large scale ladies divides in large pockets of Europeans are independent on the what is called the 00:59:05.189 --> 00:59:38.617 submergence duration between floor depths and the diameter of spheres. Very large scale motion seems to be very much 00:59:38.617 --> 00:59:46.443 dependent according to different um submergence conditions. Okay, which correspond to different symbols in here. Um the 00:59:46.443 --> 00:59:56.996 this. I mean, it is probably a little bit of topic today. But I thought it was interesting. Ah, to show you that. I 00:59:56.996 --> 01:00:06.552 mean, there are scales that are up to fifty times the flow depth so. If you have a river one meter deep. You have 01:00:06.552 --> 01:00:13.939 scales of turbines that are along fifty meters long. Why? what is the origin of these skills. 01:00:14.150 --> 01:00:22.708 But what I really would like you to remember just for this lecture is that these large scale ladies Lsm 01:00:22.708 --> 01:00:30.264 doesn't really matter scales with the flu depth okay so they are x times the floor depths. That is 01:00:30.264 --> 01:00:37.918 what matters for fish research but just to give you a word of caution. These scales are not fully understood. The 01:00:37.918 --> 01:00:45.808 scaling of these edges is not fully understood. Actually, Cameron and and coworkers from Aberdeen suggests that the size 01:00:45.808 --> 01:00:55.225 of the very large scale motions depends not much on the ration between the floor depths and and roughness diameter. So 01:00:55.225 --> 01:01:06.156 they are often a case, but rather on the on, the width of the channel and the floor depths, which is @unoise@ why i 01:01:06.156 --> 01:01:15.176 Don't know don't ask me, because I don't have an answer, but it is an open question. It is very interesting. It is 01:01:15.176 --> 01:01:24.689 fascinating. Clearly, what is spotted here is just a maximum of these curves. Okay, because the size of the very 01:01:24.689 --> 01:01:33.812 large scale motions varies across the, across the vertical, the vertical axis. Okay, why should it scale with the 01:01:33.812 --> 01:01:42.298 whist of the channel I don't know I thought that perhaps another landscape that may get into the equation 01:01:42.298 --> 01:01:51.995 should be the the fetch over which the the boundary layer develops if I have one meter flow depths, then I need a 01:01:51.995 --> 01:01:59.715 flu. That is at least well. Much more than fifty meters long to observe this. This structure. So @unoise@ perhaps, 01:01:59.715 --> 01:02:07.206 depending on on where you measure things change. But I'm this is just speculation @unoise@ my own speculation 01:02:07.206 --> 01:02:15.256 @unoise@ Um. There you go. These are, ah, a visualization of these very large scale motions, they look like," Ah, 01:02:15.256 --> 01:02:23.339 @unoise@ i. Don't know elongated sausages really. They are really sort of mandering structures. You see, these are the 01:02:23.339 --> 01:02:31.864 core bar here indicates velocity longitude in our velocity fluctuations. These stripes in here are different 01:02:31.864 --> 01:02:40.595 experiments. Let us focus on this experiment in here, which has the higher domain that the larger domain you see stripes 01:02:40.595 --> 01:02:48.841 of high momentum and low momentum here that are really, really, really long and mandatory. And that is what very large 01:02:48.841 --> 01:02:57.920 scale motions look like. They are elongated structures, uh, moving um around, um. And obviously this is a is a top view. 01:02:57.929 --> 01:03:07.063 Okay, these weaves are from, from, uh, from above. Imagine that this is your flu, and you are putting a camera on top 01:03:07.063 --> 01:03:16.135 and observing how these scales develop. Ok, so big big big head is um another thing that I need to introduce 01:03:16.135 --> 01:03:24.410 to interpret the results that I will present. Well, not a result, but the the topic that I will present this afternoon 01:03:24.410 --> 01:03:31.569 is the concept of secondary currents @unoise@ in open China flows, which is, in my opinion, @unoise@ ah a peculiarity 01:03:31.569 --> 01:03:39.663 of, of, of, of, of, of, open China flows themselves, essentially what you have. It doesn't really matter if you have a 01:03:39.663 --> 01:03:43.109 or a tangular channel or any other shape. 01:03:43.670 --> 01:03:48.979 You always have effects of the sidewalks containing the floor. 01:03:49.130 --> 01:03:57.256 This side was generate some sort of turbulence turban and anthropy that is responsible to generate this 01:03:57.256 --> 01:04:06.666 secondary currents that look like cells in light, but in the mean flu so you observe this is secondary cells in 01:04:06.666 --> 01:04:14.269 the mean flow. So it is not directly related to the turbulent properties. I'm saying directly because they are in 01:04:14.269 --> 01:04:21.113 directly related to therapy. So we will see why in a second, the secondary currents are characterized well. Essentially, 01:04:21.113 --> 01:04:31.062 they influence the friction over the the walls of the channels, or whatever you have up going flows. You have a minimum 01:04:31.062 --> 01:04:41.432 infection wherever the flows go down here you have a maximum infliction. This is a crush section of the channel flies is 01:04:41.432 --> 01:04:53.006 entering into the plane of the of the screen in here, the origin of this secondary current is still, it is still under 01:04:53.006 --> 01:05:03.979 investigation. There are different ways to interpret their their appearance. And one way to do that is to write down the 01:05:03.979 --> 01:05:06.070 transport of electricity equation. 01:05:06.289 --> 01:05:13.407 Well, longitude in Alabama, vorticity, so theorticity that has a direction perpendicular vector is perpendicular to the 01:05:13.407 --> 01:05:21.780 screen and vorticity is something that fies locally how much the flow is is swearing essentially okay 01:05:21.780 --> 01:05:31.828 which, is what a secondary current is it is just a cell that is rotating if you write down this equation, you see 01:05:31.828 --> 01:05:39.782 that the source term into the equation depends on the friends, between the the variants of the vertical velocity 01:05:39.782 --> 01:05:47.667 component and the balance of the of the latal balustic component the difference between the two. The anisotropy 01:05:47.667 --> 01:05:55.361 gets a source there and generates laundry to the which in my opinion is really fascinating. This secondary 01:05:55.361 --> 01:06:04.832 current seems to be very, very similar in structure to those very large scale motions that I will show you earlier on 01:06:04.832 --> 01:06:14.984 but the link and relation between the two is not fully understood. What really fascinates me is that these mean 01:06:14.984 --> 01:06:18.960 flow properties, % um comes from turbulence. 01:06:19.519 --> 01:06:26.416 So essentially secondary flows are, in my opinion, well, we are talking about secondary flows in straight 01:06:26.416 --> 01:06:32.639 channels. Are mean flow characteristic of Turban flows. If you don't have turbulence. They don't appear and, 01:06:32.639 --> 01:06:39.499 in my example are really, my opinion, are the secondary flows are an example in their energy cascade. If you 01:06:39.499 --> 01:06:47.092 remember at the beginning, you know, the energy cascading therapist goes from larger this to small ladies, and then the 01:06:47.092 --> 01:06:55.627 energy energies squared that is what it is. The energy is taken by the main floor and dissipated into hit 01:06:55.627 --> 01:07:03.590 right that is the energy cascade turbines go to the influences. Give me some energy. I'll dissipated in secondary 01:07:03.590 --> 01:07:08.070 currents world you have turbulence that is generating meaningful. 01:07:08.920 --> 01:07:18.792 So it is a consistent with an embarrassment in energy cascade, which personally I don't fully understand but. As 01:07:18.792 --> 01:07:27.477 far as this lecture is concerned, secondary currents do exist. I have mentioned myself that have been measured in the 01:07:27.477 --> 01:07:36.639 field in many laboratory apparatus, and they are typical in open channel flows. But the truth is, they appear in any 01:07:36.639 --> 01:07:45.572 fluid, dynamic facility Er, than it is now. They are. They are discovering them in winters and said," , and I've 01:07:45.572 --> 01:07:54.260 got people now putting stripes of of roughness into into wind tunnels and say," Look, I've got the secondary flows. I 01:07:54.260 --> 01:08:02.260 said," this has been known in open channel for since the'80s, people do not communicate even the same discipline. 01:08:02.269 --> 01:08:09.762 But anyway, that doesn't really matter what really matters today. Swimming in turbine floors. So now we have learned a 01:08:09.762 --> 01:08:18.269 little bit what characterized turbulence in the field, in reverse, even in a the simple, simplest example of an open 01:08:18.269 --> 01:08:27.238 China flow in a laboratory which usually has rectangular channels and shallow water. So now we know what we are dealing 01:08:27.238 --> 01:08:37.219 with when we put essentially a fish in the flu okay, um. Now, when I started thinking about the material for this 01:08:37.219 --> 01:08:43.949 for the summer school." I said," I remembered this paper again by Vladimir in two thousand and three. 01:08:44.210 --> 01:08:54.256 That time he was in New Zealand. And uh, I thought he was very, very well. It is an excellent paper as usual from 01:08:54.256 --> 01:09:01.357 blood and uh, um. And it is a very nice example where swimming performance is put is put in the context of dimensional 01:09:01.357 --> 01:09:05.543 analysis. @unoise@ ah um and ah, eh eh eh 01:09:05.543 --> 01:09:09.232 01:09:09.232 --> 01:09:12.921 01:09:12.921 --> 01:09:16.609 i really thought it was consistent 01:09:16.609 --> 01:09:23.742 with the top is covering this in the school. And, uh, and a very good example to explain how, uh, what are the problems 01:09:23.742 --> 01:09:30.603 related to understanding a swimming performance interval and floors. Okay, so it is just an example. We will go through 01:09:30.603 --> 01:09:37.912 this. There are many other papers, and we will see that they should actually contradictory results so you will see 01:09:37.912 --> 01:09:45.218 today I will not give you answers we will present only open questions. Essentially, if you in this science, very 01:09:45.218 --> 01:09:54.864 little is known. I would say it is in its infancy. But anyway, let us go back to the question, how does wall 01:09:54.864 --> 01:09:58.889 generated bed generated turbans are fact swim in performance. 01:09:59.180 --> 01:10:09.777 So in this paper, they have used a species which is specific in New Zealand, which is the galaxies we don't find 01:10:09.777 --> 01:10:18.070 here in Europe, but obviously New Zealand has a strong ecological relevance @unoise@ pardon me a second @unoise@ 01:10:18.070 --> 01:10:26.781 @unoise@ and um what they decided to do is @unoise@ right, i? Want to know how turbines affect swimming performance. So 01:10:26.781 --> 01:10:34.377 I'll do time to fatigue tests @unoise@ this time to fatigue tests is uh, uh. I mean, involved putting um, establishing a 01:10:34.377 --> 01:10:39.979 flow in the flow with a given Mim put in the fish inside in the water. 01:10:40.100 --> 01:10:48.740 There is a very precise protocol to do that. But let us leave it aside for a moment and measure the time it takes for 01:10:48.740 --> 01:10:57.980 the fish to get to get really tired and impinged in a screen, usually put downstream to to catch the fish when he 01:10:57.980 --> 01:11:06.014 is too tired, essentially. K so again, you put the fish in the floor, you time it, you see how long it can swim at a 01:11:06.014 --> 01:11:09.219 given flow velocity. That is a time to fatigue test. Nothing else. 01:11:10.220 --> 01:11:17.631 They have done that. They used this flu, a very small flum. To be honest, they kept their flow depth constant. They put 01:11:17.631 --> 01:11:24.275 a couple of screens to contain the fish while swimming. And they have used two treatments. Essentially, they have done 01:11:24.275 --> 01:11:32.720 experiments with putting some sort of rough walls in the lateral sorry. They put some roughness in the lateral walls. 01:11:32.729 --> 01:11:42.863 And then they did an experiment with smooth walls and they views a large number of fish to have some sort of 01:11:42.863 --> 01:11:49.384 statistically relevant results. Statistically robust results and fish were of different dimensions. A left stands 01:11:49.384 --> 01:11:54.859 for four lengths. There is nothing but the length of the fish from the snout to tail, nothing else. 01:11:55.279 --> 01:12:04.989 And the size of the fish was five to nine centimeters a sanction. You saw small fish in a small flum seems to be fine. 01:12:05.000 --> 01:12:13.595 They also measure the turbulence characteristics of the floor inside the . This tactics section, which are 01:12:13.595 --> 01:12:20.654 obviously heterogeneous, because these screens are essentially grades that create some sort of great turbines 01:12:20.654 --> 01:12:29.478 right downstream, then the flow gets influenced totally by the roughness, or by the the the walls containing the water 01:12:29.478 --> 01:12:29.919 itself. 01:12:30.340 --> 01:12:38.106 So turbulence, properties, the main floor properties vary a little bit along the along the test section. They monitored 01:12:38.106 --> 01:12:46.522 them very, very carefully and just to give you an idea of what we are dealing with. I'm going to show you these 01:12:46.522 --> 01:12:53.772 plots. A K is the turbulent kinetic energy the turmoilant can take energy we probably know just to refresh. It is 01:12:53.772 --> 01:13:04.151 the energy of the turbulent fluctuations. So it is the sum of the of the viruses, of all the velocity fluctuations in 01:13:04.151 --> 01:13:13.720 the in the test section, field symbols are associated with smooth wall channel. Experiments were empty symbols with the 01:13:13.720 --> 01:13:22.911 raft channel. So you can see that the rough channels has. In general, these are turbulent kinetic energy versus mean 01:13:22.911 --> 01:13:29.271 longitudinal velocity, which varies in different locations. You can tell that overall, within the test section, the 01:13:29.271 --> 01:13:35.336 microscopic differ between the two treatment is that one is more turbulent or more energy is contained into terminus 01:13:35.336 --> 01:13:42.358 than the other, so that they could isolate the fact of turbulent and see whether the time to fatigue or fish depended 01:13:42.358 --> 01:13:52.124 if there was a difference between the two treatments. So it was a very good idea, um? and so they did 01:13:52.124 --> 01:14:04.490 @unoise@ and they came up with this with these interesting results. What you are seeing is is a plot of the velocity of 01:14:04.490 --> 01:14:13.294 of water, which they demonstrated essentially coincides with the fish. So I mean well, the relative the lost 01:14:13.294 --> 01:14:21.257 your fish with respect to water. Ok so overall, the velocity of fish with respect to water was the mean of 01:14:21.257 --> 01:14:27.240 water because the fish was old in station all the time, essentially moving very little. Yeah, so that is it. 01:14:27.539 --> 01:14:37.823 And on the X axis, we have the time to fatigue. So the time it takes for the given of the float to the fish to get 01:14:37.823 --> 01:14:49.198 impinged to the downstream screen. So when it gets too tired. And they have seen to have shown two important two main 01:14:49.198 --> 01:14:59.889 results. The first is about scale effects. It seems that all the large, forgiven hue for a game v. Even velocity of the 01:14:59.889 --> 01:15:08.358 flow. Larger fish have time to fatigue that are larger than smaller fish. And this makes sense is consistent with the 01:15:08.358 --> 01:15:17.135 introductory lecture earlier on a larger fish has more mass, has more power. It can sustain a high flow for longer. Very 01:15:17.135 --> 01:15:25.568 simple. Conversely, smaller fish has less power and can sustain the same velocity for shorter times now as you can 01:15:25.568 --> 01:15:35.202 see this time to fatigue is, uh, consider only the data in this area, because this is where we go from seconds to 01:15:35.202 --> 01:15:42.829 minutes, which is the time interval, which is consistent with the definition of Barst velocity of maximum velocity came. 01:15:42.840 --> 01:15:50.589 What we addressed at the beginning. So those velocities that the fish can sustain for short time. That is what we 01:15:50.589 --> 01:15:57.738 are interested in ecologically. And from an engineering point of view, these other experimental points belong to this 01:15:57.738 --> 01:16:05.270 prolonged swimming activity, which is something in between the cruising and and the burst, which is unknown territory. 01:16:05.279 --> 01:16:08.340 So they, they were kind of neglected. 01:16:08.909 --> 01:16:17.022 So I was saying," There is this first result about scale effects and this is interestingly, is the authors argue 01:16:17.022 --> 01:16:25.569 that this is due to physiological effects of power and mass which we have already discussed. There is also Reno's 01:16:25.569 --> 01:16:35.859 number of fact, you probably know that the resistant coefficient of the body immersed in a moving Floyd so the 01:16:35.859 --> 01:16:43.186 friction factor, the the drug efficient decreases with increasing Reynolds. Number Yeah, so at lower 01:16:43.186 --> 01:16:50.089 Reynolds number, you have higher and therefore smaller fish which are have a lower range of 01:16:50.089 --> 01:16:56.647 number, because simply because they are smaller, they are exposed to a higher drug efficient so this contributes 01:16:56.647 --> 01:17:02.170 them to get them tired earlier than larger fish that instead had a larger reinous number. 01:17:02.350 --> 01:17:09.193 But overall, these results show that what really matters is the size of the fish so. At length for example, 01:17:09.193 --> 01:17:12.610 which, is a good proxy for for mass and for power. 01:17:13.029 --> 01:17:19.372 And Reynolds number, whenever the number kicks in. It means that because the effects are relevant okay 01:17:19.372 --> 01:17:27.276 so this cost the plays are all the size of the fish do play a role the second results which was very, very 01:17:27.276 --> 01:17:34.543 surprising is that these experimental results are not shown. No turbulence effects whatsoever. So there is no 01:17:34.543 --> 01:17:42.928 certification of data points between turbulent so smooth. Sorry, very turbulent. Which means the rough fall, the rough 01:17:42.928 --> 01:17:50.584 wall experiment, and the less urbanet let us call it, which is the smooth wall experiment. There is no certification of 01:17:50.584 --> 01:17:57.310 data. The points are mixed which, suggests the fact that turbulence has no act, at least turbulence 01:17:57.310 --> 01:18:04.376 intensity, which varied a lot between the two treatments seems to have no effect on the swimming performance of these 01:18:04.376 --> 01:18:14.291 pieces. And this is a little bit in contrast with um, some previous literature by Pavlov Ah two thousand although 01:18:14.291 --> 01:18:23.467 the original paper was in Russian, which I cannot read @unoise@ Ah mid nineties. I don't remember, but they have shown 01:18:23.467 --> 01:18:30.900 @unoise@ that actually for another fish Ah, whose Latin name I don't remember @unoise@ ah um the 01:18:30.900 --> 01:18:32.669 turmoil did have an effect. 01:18:32.810 --> 01:18:40.615 So is it species dependent the other issues that these experiments by Pablo Vital were carried out um in a 01:18:40.615 --> 01:18:48.421 different way, not with the time to fatigue test, but with what is called a critical velocity test, which is not 01:18:48.421 --> 01:18:56.508 directly comparable with this test. So bottom line is it is an open question. This bed generated turbulence that we have 01:18:56.508 --> 01:19:05.474 learned that we have described a few minutes ago. Does it or does does not. It doesn't extend an effect on swimming 01:19:05.474 --> 01:19:10.740 performance or not, not clear. It is definitely not clear. 01:19:11.619 --> 01:19:21.269 The authors went on, ended some uh um we. Will come back to this point later on. But anyway, the the authors 01:19:21.269 --> 01:19:29.362 decided to to use these wealth of experimental data to do, to do some to to build a predictive formula linking velocity 01:19:29.362 --> 01:19:37.496 with time to fatigue, and all the other relevant variables in the problem so. If you remember, we said, it seems 01:19:37.496 --> 01:19:45.315 that the time to fatigue and the birth speed depends on viscosity because the results are dependent on 01:19:45.315 --> 01:19:53.402 number on there you go. So birth speed depends on Wisconsin burst length, time to fatigue. As we know from the 01:19:53.402 --> 01:20:02.311 previous graph. And a little bit of inertia. So they put gravity into the into the equation after dimension analysis, 01:20:02.311 --> 01:20:10.455 using the bucking and theorem. They developed a functional series of non-dimensional groups, which are related by 01:20:10.455 --> 01:20:18.847 functional relationship F and the dimension analysis shows that the the birth speed is normalized, forming a 01:20:18.847 --> 01:20:28.638 non-dimensional group, which is essentially the squared of the number of the fish fruit number is is a scale 01:20:28.638 --> 01:20:37.612 normalized by the square root of gravity, multiplied by a characteristic lane scale. This is the square of it. And this 01:20:37.612 --> 01:20:46.962 is a function of the number nicely and another non-dimensional parameter we Ah has no name. I 01:20:46.962 --> 01:20:55.875 would interpret it as the ratio between gravity and . The mean acceleration of the fish swimming in the chamber. It 01:20:55.875 --> 01:20:57.780 does in Ebay. 01:20:58.819 --> 01:21:05.813 They did an incomplete similarity assumption following bar and blood, uh theory, and they related the fish fruit number 01:21:05.813 --> 01:21:15.419 to um a number through a power law with an exponent. It needs to be found empirically. There is no way to find 01:21:15.419 --> 01:21:24.417 this exponents theoretically, and a function F associated with this. No name, dimensional number. And they did some sort 01:21:24.417 --> 01:21:32.914 of empirical fitting. And they came up with this @unoise@ with these ah with this law that allows to collapse the data 01:21:32.914 --> 01:21:40.811 fairly, fairly well and this is this is interesting because they have now developed an equation that can be 01:21:40.811 --> 01:21:48.253 used for fish management and fish pass design. So once you have your velocity in the channel, which is your design 01:21:48.253 --> 01:21:55.058 parameters, you decide," Okay, I want to design the channels that its steepness and the roughness that I put in 01:21:55.058 --> 01:22:03.892 determines this will last to you. Then I go to this graph. I know that the the time to fatigue. I know the size of the 01:22:03.892 --> 01:22:14.039 fish can work out whether the fish pass is well designed or not. So very, very useful @unoise@ % um development out of 01:22:14.039 --> 01:22:23.102 dimensional analysis and experiments on fish um going back to the previous question on why no turbulence effects are 01:22:23.102 --> 01:22:33.469 shown in the experiments. The authors, let us say they put on the table values various hypothesis, and they 01:22:33.469 --> 01:22:42.089 actually say that uh, um. Essentially in the experiments they have done. They have varied only the turbulence intensity. 01:22:42.100 --> 01:22:50.527 So the the strength of the fluctuations in the floor. That is what that means. Okay, @unoise@ they did not body the size 01:22:50.527 --> 01:22:56.945 of their this, because the flow depths was kept constant. If you remember these large scale motions, these large scale 01:22:56.945 --> 01:23:02.904 ladies that really influenced him in performance, scaled with the flow depths, so between one treatment and the other, 01:23:02.904 --> 01:23:06.039 presumably the scale of the large edges was the same. 01:23:06.750 --> 01:23:17.206 And in the fluid mechanics literature. Whenever you investigate the fact of turbulence on on the drag on a body. You 01:23:17.206 --> 01:23:28.071 body two things the size of the is and the intensity of the had is okay. Fish makes no exception, apparently. And so 01:23:28.071 --> 01:23:37.172 they say," Okay, this study is probably incomplete, because we didn't test different diseases. And they say there should 01:23:37.172 --> 01:23:46.759 be a wider range of experiments covering a wider range of an Un. Dimensional number built as the ratio between their 01:23:46.759 --> 01:23:55.361 delines and the size of the fish which, makes sense I liked it, but my criticism on that. Actually, they did 01:23:55.361 --> 01:24:03.181 because Ok, the Ed is in the floor were always the same , but the fish changed it in size. Actually, there was the 01:24:03.181 --> 01:24:10.188 worst five centimeters fish and ten centimeters fish yet. There is no effect of turbulence on their time to 01:24:10.188 --> 01:24:10.560 fatigue. 01:24:11.079 --> 01:24:21.089 So either we need to explore a wider range. But uh, I'm not sure um, or perhaps Turban simply has no effects, which is 01:24:21.089 --> 01:24:29.234 country intuitive. If you think about it, um, okay, I'm talking about that generated term. So the turbulent boundary 01:24:29.234 --> 01:24:38.580 layers, the turbans in here wakes. Mixing layers may have a completely different uh, uh effects. But as far as bed 01:24:38.580 --> 01:24:49.855 generated turban is concerned, there seems to be no effect on on fish swimming performance. We have touched bed 01:24:49.855 --> 01:24:59.929 generated turbulence. What about wakes? so the the terminus generated by downstream of of objects. You know, does it 01:24:59.929 --> 01:25:09.483 influence swimming performance or behavior of fish. This is what I'm going to talk next. And this is the topic that was 01:25:09.483 --> 01:25:17.123 addressed by James Leye, who is a big name in this field, who did very nice experiment showing really fascinating 01:25:17.123 --> 01:25:25.909 results and what he did he said," Okay, let us start from the simplest case of a wake generated by a cylinder 01:25:25.909 --> 01:25:35.193 actually used a half cylinders just fix the separation point. That means the size of the Addis was always . It did 01:25:35.193 --> 01:25:45.144 not depend on the rein of numbers, essentially so. I put this half cylinder within established some 01:25:45.144 --> 01:25:55.843 waterfalls. He put a in his co work. So of course, I think trouts in the and started monitoring the behavior 01:25:55.843 --> 01:26:05.338 well the behavior the swimming kinematics of these trouts, or the oscillations of the body or the of the and so 01:26:05.338 --> 01:26:05.770 forth. 01:26:06.329 --> 01:26:17.086 And % um, he varied a lot the size between a solidaration between the fish body lenses and the diameter of the of the 01:26:17.086 --> 01:26:25.806 cylinder so that he could generate different editing frequencies and decides at the size, okay? @unoise@ @unoise@ but 01:26:25.806 --> 01:26:36.131 ok, Forget about all these details. What was really, really interesting to observe is that fish fishes tend to 01:26:36.131 --> 01:26:46.077 stay to hold station. Let us say one or two body lens downstream of the cylinders, away from the low pressure region, 01:26:46.077 --> 01:26:54.940 where the forward there is Redesseparation, synchronizing the tail beat to the the shedding. So there was this at 01:26:54.940 --> 01:27:02.657 this cylinder here, generating these eddies and the fish was doing zigzaging among the eddies @unoise@ okay @unoise@ and 01:27:02.657 --> 01:27:11.998 what he observed is that the muscular activity of the fish while staying in this in this wake was almost zero, like the 01:27:11.998 --> 01:27:18.089 fish could be dead and do that and use no energy whatsoever to hold position. 01:27:19.390 --> 01:27:27.307 And fish actually do that, even in Ah, in rivers. So when they are tired, they go, they, they, they find a log or an 01:27:27.307 --> 01:27:34.284 object that generates these eddies. And the rest I stay there. It is fascinating. Now, @unoise@ this. Is a peculiar um 01:27:34.284 --> 01:27:43.409 behavior of fish, which is actually dictated by the latter. A line without the latter a line they struggle to do it. 01:27:43.739 --> 01:27:51.646 Clearly, fish could save energy, even staying in the, in the, in the, in the section region just downstream of the of 01:27:51.646 --> 01:27:59.290 the of the cylinder, like the cyclist too, during a race. Okay, you want to to save some energy. You stay in the wake of 01:27:59.290 --> 01:28:06.234 the person in front of you. But that is not the case. That is not what is making them saving energy is really the 01:28:06.234 --> 01:28:12.734 interaction between dead is generated by the slender and the kinematics and the swimming of the of the fish, which is 01:28:12.734 --> 01:28:21.329 tuned to see to essentially do Islam among eddies. So exploit the idea to save energy and the way this is explained is 01:28:21.329 --> 01:28:30.870 as following. Imagine a figure. Well, the panel A of this figure that is a counter clockwise, a eddy, which is shed by 01:28:30.870 --> 01:28:31.699 the cylinder. 01:28:32.510 --> 01:28:41.083 The green hour, or determines the the, the, the direction of the incident floated, the fish experiences, which will hit 01:28:41.083 --> 01:28:50.521 while the fish will adjust, having an angle of attack. This angle of attack will determine the fish will impose to the 01:28:50.521 --> 01:28:58.992 fish. Essentially a drug force here. These are here, which is parallel to the incident flow and a lift force which 01:28:58.992 --> 01:29:01.239 is perpendicular to the incident flow. 01:29:01.409 --> 01:29:10.744 These forces gave a net green. I'm a bit color blood. This is green, right? Yeah, thank you the green force 01:29:10.744 --> 01:29:20.013 there, which is the the sum of the drug and lift force that have a component upwards and an analogy to deny component, 01:29:20.013 --> 01:29:29.904 which is just enough to win the drug experienced by the fish. So essentially here the fish is moved only upwards 01:29:29.904 --> 01:29:40.978 it stays in the same laundry to the opposition, but is moving airports when the Ade travels, and is essentially next to 01:29:40.978 --> 01:29:52.670 the fish the incident flow is in this direction, identified by the gray arrow. And at this very small angle of 01:29:52.670 --> 01:30:02.247 attacks you have. Ah, you have a essentially very small drug and large lift, which determine a force, a total 01:30:02.247 --> 01:30:11.556 force that has only a vertical component. So again, the fish tends to go down and again when the clockwise heady is, is 01:30:11.556 --> 01:30:19.848 shed again. This process is exactly the same. There is a lift force. It is just the the signs are opposite on the floor, 01:30:19.848 --> 01:30:28.048 where the fish tends to go down and then up again, depending on their on the @unoise@ on the on the um the 01:30:28.048 --> 01:30:35.753 porticity ah sign of of the Ed. So that is, that is the the, the current apologies to explain this behavior. What is 01:30:35.753 --> 01:30:45.135 really fascinating is that the fish can adjust the angle of attack, and to essentially generate the system of drug and 01:30:45.135 --> 01:30:54.052 lift forces to hold position spending almost no energy whatsoever which is which is truly fascinating. I think I 01:30:54.052 --> 01:31:08.142 have. Yeah, I do a video showing you some experiment that I meant. This is the James Leo website, where you can find all 01:31:08.142 --> 01:31:09.539 this uniform flow. 01:31:09.800 --> 01:31:14.580 So this is the car mongating there you go. 01:31:15.350 --> 01:31:23.683 That is how the fish moves and this is the fish footprint overlap to some measurements of the flowfield 01:31:23.683 --> 01:31:31.176 measurement. That is what the fish does. Essentially, they do Islam among edges and what is really interesting is 01:31:31.176 --> 01:31:35.579 this video of a dead trout in flowing water. 01:31:37.449 --> 01:31:41.379 And there you go. This is no flow." 01:31:41.600 --> 01:32:02.694 and the floor kicks in @unoise@ when the flow kicks in come on, you can tell is dead @unoise@ the dead fish start to 01:32:02.694 --> 01:32:20.355 anyway which is which is very strong proof that there is no energy. Spain, that is simply because the fish is dead 01:32:20.355 --> 01:32:29.560 okay @unoise@ okay @unoise@ now so. We have learned how fish exploit vortices or turbulence to save energy, gee? 01:32:29.569 --> 01:32:36.560 and this is one of the few results. Actually, we know clearly whenever we deal with such coherence at this. 01:32:36.939 --> 01:32:43.489 Everything is a lot easier when we go back to the bed generated turbines. We have we. Have large scale motions 01:32:43.489 --> 01:32:50.239 that are packets of edges, then very large scale motions, outer layers. Log layer is a lot more complicated, but in this 01:32:50.239 --> 01:32:58.233 case it is. It is a, I think it is a nice study to show how clever are fish to exploit turbulence, and and Ah, how 01:32:58.233 --> 01:33:02.160 capable is the latter line. Ah, to actually detect these flow fields. 01:33:03.060 --> 01:33:11.057 Fish, again, are extremely good experimentalists. Fluid are experimental is because they really can measure flow fields 01:33:11.057 --> 01:33:20.176 and exploit them. Ah, to save energy. Okay, again, not much. Now we are. We are not gonna talk much about, ah, 01:33:20.176 --> 01:33:29.411 turbulence, but just mean flow properties of of the of um, that that can be exploited by fish to save energy. One of 01:33:29.411 --> 01:33:37.160 these energy saving strategies called entertainment, and is always associated again with the flowfield generated % uh by 01:33:37.160 --> 01:33:46.631 a half cylinder @unoise@ or a semi eh infinite body like this, with @unoise@ with the round head okay similar to 01:33:46.631 --> 01:33:56.964 this @unoise@ this half sealing the above so this is the work by Horse Black Man that I mentioned later on, and and co 01:33:56.964 --> 01:34:04.972 workers, and again, likely out they did experiments with some fish. They put this house cylinder or this other element 01:34:04.972 --> 01:34:12.583 in a flum, and they observed fish behavior, and they, they, they just checked wherefish, like to stay and they 01:34:12.583 --> 01:34:20.920 observed that fish really liked to stay in proximity of these half cylinder, not too far with an angle it would be 01:34:20.920 --> 01:34:29.546 a little bit of an angle of attacked with respect of the of the mean flow. And they did also some numerical simulations 01:34:29.546 --> 01:34:37.192 but also measurements, detailed measurements of the floor field when the fish is actually staying in this 01:34:37.192 --> 01:34:45.239 position, and what they notice that the fish stays there, and the muscular activity, again, is very, very much reduced. 01:34:45.250 --> 01:34:53.780 So it is definitely an energy saving strategy. And what happens here is that the flow in proximity of the of the slender 01:34:53.780 --> 01:35:02.079 is slightly deflected, which contribute to generate an angle of attack of the the air foiled fish. Let us call it. 01:35:02.409 --> 01:35:12.391 And the interaction between this flow and the fish with this anglovak that generates some sort of a system of lift and 01:35:12.391 --> 01:35:21.038 drag forces, as usual, which generates a total force upwards, indicated by . However, this so in principle, this 01:35:21.038 --> 01:35:31.073 should move away the fish if we should not be able to hold the position. What happens is that this force is 01:35:31.073 --> 01:35:38.494 counterbalanced by the very low very low pressure generated here, because here the floor is going is squeezed 01:35:38.494 --> 01:35:42.789 between the half cylinder and the fish, so accelerating the middle. 01:35:43.479 --> 01:35:52.118 High levels in low pressure, so low. Ah, Ah, Ah. So essentially this, this total force is counterbalance, but is that is 01:35:52.118 --> 01:36:01.010 low pressure in in here. So the the fish is actually able to stay to to old position in there. Unfortunately, the the 01:36:01.010 --> 01:36:09.174 shading of the of the of the half cylinder makes this position a little bit unstable, so the fish would stay there for a 01:36:09.174 --> 01:36:17.678 bit, but then it would be dragged away by an eddy because, you know, you have Ed is moving % Ah at theading around which 01:36:17.678 --> 01:36:24.612 Ah, which makes the stability of fish challenging. So that is why they did the same infinite body experiment where the 01:36:24.612 --> 01:36:31.471 fish could stay in proximity of this half selling their heads, but without their shedding. Then they noticed that the 01:36:31.471 --> 01:36:41.085 fish again liked really to stay sort of in a similar position, uh? and it was a lot more stable um um. And this is 01:36:41.085 --> 01:36:47.362 called " and train." and please remember this word. It will be very, very useful for this afternoon, when we talk about 01:36:47.362 --> 01:36:49.409 my own research, we will need that. 01:36:49.880 --> 01:37:00.689 So far, we have seen and entertainment as strategies for energy and energy saving toward station. 01:37:00.829 --> 01:37:09.861 The last one is called bow wake riding, and was observed by Leo once again. And essentially, what happens is that if you 01:37:09.861 --> 01:37:17.794 have a flow going upwards again in the flow, and there is dissolved cylinder that behaves simply as an obstacle. Fish 01:37:17.794 --> 01:37:28.463 really tended to stay just in front of the of the of the cylinder, and it really showed a reduced muscle or activity. So 01:37:28.463 --> 01:37:37.844 in simple words that reduced energy expenditure as well. The reason why is not entirely clear to me. Um, they justify 01:37:37.844 --> 01:37:46.420 that. Because here, there is due to the impinging flow in proximity of the cylinder. There is a reduced velocity and so 01:37:46.420 --> 01:37:53.988 reduced drug @unoise@ % uh that. Is what they say I don't think this. This gives the complete picture but 01:37:53.988 --> 01:38:02.790 that is what we know what happens for sure is that in front of the cylinder the tail beat frequency, the muscular 01:38:02.790 --> 01:38:10.636 activity of the fish, and therefore damage expenditure is definitely low. So to summarize, after Leo, two thousand a 01:38:10.636 --> 01:38:20.299 beautiful review of Leo. Two thousand and seven. We have three energy saving strategies that are known at the moment. Um 01:38:20.299 --> 01:38:32.839 with respect to a fish swimming in a uniform floor, a fish that does bow wake riding um entertainment or 01:38:32.839 --> 01:38:41.809 experiences uh much less um energy expenditure. Please do remember these these aspects, because we will be used 01:38:41.809 --> 01:38:50.971 this afternoon to, uh, talk about, uh, um, space use and habitat selection in trouts um in my own uh " research. Again, 01:38:50.971 --> 01:39:00.099 this is a list of reference that you can consult to to go a little bit, uh, to dig deeper in what we have just discuss. 01:39:00.109 --> 01:39:07.680 And that is it for this morning. If there are questions, I'm happy to discuss.