WEBVTT 1 00:00:00.000 --> 00:00:05.420 I'd like to start by acknowledging that today we are gathered on the traditional country of the Kaurna people of the Adelaide Plains. 2 00:00:06.480 --> 00:00:08.940 I'd also like to introduce myself a little bit further. 3 00:00:09.040 --> 00:00:13.740 I have a company called Bridge8, which is a foresight and science communications consultancy. 4 00:00:13.860 --> 00:00:18.160 So the sort of work that we do is using futures to understand the way that the world could be, 5 00:00:18.860 --> 00:00:21.440 and using science to understand the way that the world works. 6 00:00:21.720 --> 00:00:26.520 And so I'm particularly excited to introduce you to Laura Brooks today, 7 00:00:26.620 --> 00:00:29.820 because when I first met Laura a week ago when we were planning this session, 8 00:00:30.000 --> 00:00:34.620 I said to her, you know, what is your motivation for what you do and why you do it? 9 00:00:35.520 --> 00:00:40.400 I really got this feeling that what pushes Laura is understanding the way the world works. 10 00:00:40.600 --> 00:00:45.320 So taking those fundamental ideas and knowledge of the world we live in and the world around us, 11 00:00:45.780 --> 00:00:50.240 transferring those to real world scenarios and seeing the direct applications of that 12 00:00:50.240 --> 00:00:54.180 to design things in a better way and to make the world work in a better way. 13 00:00:54.260 --> 00:00:56.940 So I'm really excited to be able to introduce Laura to you today. 14 00:00:57.780 --> 00:00:59.300 So a little bit more about Laura. 15 00:01:00.000 --> 00:01:03.840 Laura is a lecturer in the School of Mechanical Engineering at the University of Adelaide. 16 00:01:04.480 --> 00:01:08.360 She has a Bachelor of Engineering with Honours and PhD from the University of Adelaide. 17 00:01:08.560 --> 00:01:13.680 She was awarded the prestigious Fulbright Scholarship to research underwater sound transmission 18 00:01:13.680 --> 00:01:16.720 at Scripps Institution of Oceanography in California. 19 00:01:17.620 --> 00:01:21.680 And she has completed a postdoctoral appointment at Victoria University in Wellington, New Zealand. 20 00:01:22.140 --> 00:01:27.400 Her research has included underwater acoustics, micro-seismes and flow-induced noise. 21 00:01:27.700 --> 00:01:29.980 And in order to design for reducing the noise, 22 00:01:30.000 --> 00:01:33.720 her current interests include acoustic signal processing techniques 23 00:01:33.720 --> 00:01:38.600 and fundamental understanding of the noise-producing mechanisms of flow over bodies. 24 00:01:38.740 --> 00:01:41.640 Bodies like aircraft, wind turbines and submarines. 25 00:01:42.100 --> 00:01:45.360 So I'd now like you to welcome Laura to explain what that's all about 26 00:01:45.360 --> 00:01:47.500 and give you an insight into her work and her study. 27 00:01:47.660 --> 00:01:48.180 Thank you. 28 00:01:51.460 --> 00:01:54.300 Thank you for your kind introduction, Kristen. 29 00:01:54.660 --> 00:01:59.980 Okay, I think Kristen's actually been through my journey from where I started. 30 00:02:00.000 --> 00:02:04.240 As an undergraduate student at the university to where I am now as a lecturer. 31 00:02:04.640 --> 00:02:09.580 I've been fortunate to be involved in research in quite a few different areas 32 00:02:09.580 --> 00:02:12.440 in the short period for which I have been a researcher. 33 00:02:13.100 --> 00:02:15.260 Today I'm just going to talk about two of those areas. 34 00:02:16.180 --> 00:02:18.900 Ocean acoustics, which is what my PhD focused on. 35 00:02:20.000 --> 00:02:22.100 And aeroacoustics, which is what I'm working on now. 36 00:02:22.240 --> 00:02:25.160 Just due to time limitations, we'll skip over the seismics. 37 00:02:25.260 --> 00:02:26.300 But that was cool fun as well. 38 00:02:27.540 --> 00:02:27.940 Okay. 39 00:02:28.000 --> 00:02:28.160 Okay. 40 00:02:28.620 --> 00:02:29.980 Some of you here probably know a lot. 41 00:02:30.000 --> 00:02:32.040 About acoustics, some not so much. 42 00:02:32.560 --> 00:02:35.280 Acoustics is quite simply the study of sound. 43 00:02:35.600 --> 00:02:38.640 And when we think of sound transmission through a fluid, 44 00:02:38.780 --> 00:02:41.600 so through something like the air or through water, 45 00:02:41.880 --> 00:02:46.040 it is simply a fluctuation about the ambient pressure. 46 00:02:46.280 --> 00:02:49.920 So at the moment we're standing here, we're surrounded by air pressure, 47 00:02:50.060 --> 00:02:52.020 which is about 101 kilopascals. 48 00:02:52.140 --> 00:02:58.560 As I speak to you, the pressure goes up and down ever so very slightly about that value. 49 00:02:59.420 --> 00:02:59.980 Now, I'm going to talk about the 50 00:02:59.980 --> 00:03:00.000 sound transmission. 51 00:03:00.000 --> 00:03:01.860 Now, sound travels as a longitudinal wave. 52 00:03:02.100 --> 00:03:04.100 It's this picture down here. 53 00:03:05.000 --> 00:03:11.720 And what that's showing is that we get particles which will compress and then expand as a sound 54 00:03:11.720 --> 00:03:13.160 wave transmits through it. 55 00:03:13.520 --> 00:03:18.540 However, when we think about sound, we often picture it as a sine wave. 56 00:03:18.680 --> 00:03:20.480 So that thing that we've drawn at the top there. 57 00:03:20.980 --> 00:03:25.040 What we have is our ambient pressure, which is the dashed dot line around the middle. 58 00:03:25.260 --> 00:03:29.320 And then we have the sound will increase above that and then decrease below it. 59 00:03:29.320 --> 00:03:30.420 And then we have the amplitude. 60 00:03:30.420 --> 00:03:36.980 The sound has an associated amplitude, which is simply the, I guess, the peak, peak value. 61 00:03:37.440 --> 00:03:40.660 And the amplitude is simply how loud is the sound. 62 00:03:41.440 --> 00:03:44.060 It also has something called wavelength. 63 00:03:44.460 --> 00:03:48.340 And wavelength is the distance, I guess, between two points of the same phase. 64 00:03:48.620 --> 00:03:53.800 For simplicity, we can think of that as the distance between two compressions or the distance 65 00:03:54.320 --> 00:03:55.800 between two expansions. 66 00:03:56.560 --> 00:03:59.300 Something else that I'll introduce at the moment is frequency. 67 00:03:59.300 --> 00:04:02.520 Frequency, because I'll be talking about that a little bit throughout today's session. 68 00:04:03.260 --> 00:04:05.080 Frequency, you can think of like pitch. 69 00:04:05.320 --> 00:04:08.620 So if you think of musical instruments, you think of a piccolo. 70 00:04:08.700 --> 00:04:11.480 That has a very high pitch or very high frequency. 71 00:04:12.200 --> 00:04:16.240 If you think of a double bass, that is a very low pitch or a low frequency. 72 00:04:18.080 --> 00:04:22.160 Frequency is simply defined as the speed of sound divided by the wavelength. 73 00:04:23.040 --> 00:04:28.700 So the speed of sound, the speed of sound in air, for example, is about 340 metres per 74 00:04:29.300 --> 00:04:30.300 But it's not constant. 75 00:04:30.420 --> 00:04:33.980 It depends on things such as temperature and other values as well. 76 00:04:34.440 --> 00:04:36.120 In the ocean, it's a lot faster. 77 00:04:36.680 --> 00:04:37.960 But that's what sound is. 78 00:04:38.100 --> 00:04:40.200 And it is really a simple thing. 79 00:04:40.220 --> 00:04:40.820 It's just a wave. 80 00:04:41.000 --> 00:04:45.900 But it's a lot more complex when you try to apply it to a real world environment to see 81 00:04:45.900 --> 00:04:46.440 what's happening. 82 00:04:49.360 --> 00:04:54.540 So first of all, we're going to talk about ocean acoustics, which is sound propagation 83 00:04:55.280 --> 00:04:55.860 through the ocean. 84 00:04:57.260 --> 00:04:59.220 Now why is this important to us? 85 00:04:59.220 --> 00:05:03.120 If you go swimming and you duck in under the water, you can't really hear much. 86 00:05:03.560 --> 00:05:06.080 However, there's actually a lot of noise in the ocean. 87 00:05:06.400 --> 00:05:12.160 There's noise created by shipping, noise created by waves and wind events, noise created by 88 00:05:12.160 --> 00:05:12.500 animals. 89 00:05:12.720 --> 00:05:15.700 You get little snapping shrimp on the bottom of the deep ocean floor. 90 00:05:15.860 --> 00:05:21.240 You get whales and other ocean mammals communicating via sound. 91 00:05:21.720 --> 00:05:23.000 And it is very loud there. 92 00:05:23.100 --> 00:05:26.300 It doesn't couple well into the human ear, so we can't really hear it. 93 00:05:26.340 --> 00:05:27.760 But I won't go into those details. 94 00:05:28.060 --> 00:05:29.200 So what is sound? 95 00:05:29.200 --> 00:05:32.700 And why do we care about the transmission of sound in the ocean? 96 00:05:33.440 --> 00:05:37.680 Now if we think about how we communicate up here in the air. 97 00:05:37.760 --> 00:05:40.160 If I want to talk to you where you are now. 98 00:05:40.520 --> 00:05:41.860 Okay, I'm using a microphone. 99 00:05:41.940 --> 00:05:42.900 But I could just talk. 100 00:05:43.000 --> 00:05:46.600 And you would listen to the sound waves directly from how I'm speaking. 101 00:05:47.140 --> 00:05:51.220 However, if you were standing on the other side of a football field and I tried to talk 102 00:05:51.220 --> 00:05:53.940 to you without a microphone, it would be very hard to hear me. 103 00:05:54.300 --> 00:05:59.040 Sound cannot travel very far through air before the amplitude becomes too small to hear. 104 00:05:59.100 --> 00:05:59.180 And that's not very good. 105 00:05:59.820 --> 00:06:01.860 If we want to communicate long distances 106 00:06:01.860 --> 00:06:05.460 we use, I guess, waves from the electromagnetic spectrum 107 00:06:05.460 --> 00:06:06.840 so we can use light waves 108 00:06:06.840 --> 00:06:11.260 or more often we'll use, I guess, radio frequencies 109 00:06:11.260 --> 00:06:14.040 We can use those to transmit stuff wherever we want 110 00:06:14.920 --> 00:06:16.360 In the ocean it's the opposite 111 00:06:16.920 --> 00:06:20.720 Again, if you go swimming and you dive down a few metres 112 00:06:20.720 --> 00:06:22.760 you find that it gets dark very quickly 113 00:06:22.760 --> 00:06:25.460 Light doesn't travel very far through the water 114 00:06:25.460 --> 00:06:29.800 before it becomes too small a signal to be able to be useful for anything 115 00:06:30.400 --> 00:06:33.140 Similar with other electromagnetic waves 116 00:06:33.140 --> 00:06:35.660 We can't use radio waves to communicate 117 00:06:36.240 --> 00:06:38.020 So instead we use sound waves 118 00:06:38.020 --> 00:06:42.240 because sound waves in the water are kind of like the opposite to up here on Earth 119 00:06:42.240 --> 00:06:45.160 Sound can travel really, really large distances 120 00:06:45.160 --> 00:06:47.920 and still be loud enough to be useful 121 00:06:49.460 --> 00:06:52.260 So it's efficient sound transmission for large distances 122 00:06:53.020 --> 00:06:54.720 We also are lucky in that 123 00:06:54.720 --> 00:06:55.440 sound waves are not so big 124 00:06:55.440 --> 00:06:58.760 Sound does travel at about 1500 metres per second in water 125 00:06:58.760 --> 00:07:01.220 so about five times faster than on air 126 00:07:01.220 --> 00:07:04.520 so we can communicate a bit more quickly over distances 127 00:07:07.900 --> 00:07:12.940 And we already know that marine mammals have, I guess, discovered this fact 128 00:07:12.940 --> 00:07:16.540 and been able to evolve and adapt themselves to use sound 129 00:07:16.540 --> 00:07:18.700 for these very purposes of communication 130 00:07:20.460 --> 00:07:25.420 However, if we want to communicate or use sound in water 131 00:07:25.440 --> 00:07:30.340 for other purposes such as, I guess, sonar and things like that 132 00:07:30.340 --> 00:07:36.420 we need to have a very good understanding of how the ocean environment is actually affecting the sound 133 00:07:37.140 --> 00:07:42.300 Because we can turn on a source somewhere and we can go somewhere else in the water and receive that source 134 00:07:42.840 --> 00:07:45.000 but if we don't know anything about the environment in between 135 00:07:46.120 --> 00:07:48.660 the information we're going to get will be very confusing 136 00:07:52.040 --> 00:07:55.420 So there's lots of things that influence, I guess, how sound is produced and how it's used and all that kind of stuff 137 00:07:55.440 --> 00:08:00.080 So we're going to have a little bit of a look at how the environment can do that today 138 00:08:00.820 --> 00:08:04.140 First of all we'll talk about something called the sound speed profile 139 00:08:05.380 --> 00:08:09.660 The sound speed in air on Earth doesn't change very much 140 00:08:09.660 --> 00:08:12.580 It changes a little bit with temperature but it's approximately constant 141 00:08:13.680 --> 00:08:18.380 However, sound speed is actually a function of temperature, salinity and depth 142 00:08:19.040 --> 00:08:21.220 or temperature, salinity and pressure 143 00:08:21.780 --> 00:08:24.440 Pressure and depth are related in the ocean 144 00:08:25.260 --> 00:08:28.700 and it actually increases with all three of those 145 00:08:28.700 --> 00:08:33.840 So if we consider a deep ocean, we consider up near the top of the ocean 146 00:08:33.840 --> 00:08:36.520 we have water which is being heated by the sun 147 00:08:36.520 --> 00:08:39.860 so the temperature of that water is a lot warmer 148 00:08:40.540 --> 00:08:44.900 Hence we actually have an increased sound speed near the surface of the ocean 149 00:08:45.560 --> 00:08:51.000 As we start to go down a little bit, we'll find that our temperature will drop off very quickly 150 00:08:51.500 --> 00:08:53.560 That's what we call our main thermocline 151 00:08:53.560 --> 00:08:55.520 Thermo being for temperature 152 00:08:55.520 --> 00:09:01.440 As we go down deeper still, our temperature does no longer change very much 153 00:09:01.440 --> 00:09:02.700 However, we're getting deeper 154 00:09:02.700 --> 00:09:07.400 So the water pressure increases and thus the sound speed increases again 155 00:09:07.400 --> 00:09:12.720 So we can actually end up with very complex sound speed profiles in our water column 156 00:09:13.560 --> 00:09:16.960 And this is only one example of many different profiles that we can have 157 00:09:19.380 --> 00:09:23.300 Okay, so we can see we have a varying sound speed profile 158 00:09:23.560 --> 00:09:25.060 But how does this, what does this mean? 159 00:09:25.120 --> 00:09:26.780 Why does this matter for acoustic communication? 160 00:09:27.800 --> 00:09:31.920 I guess if we look at something that we can actually visualise 161 00:09:31.920 --> 00:09:33.940 and that's light passing through a prism 162 00:09:34.560 --> 00:09:37.260 A lot of you I guess would have done physics in high school 163 00:09:37.260 --> 00:09:41.800 or have gone along to science events where you've seen white light pass through a prism 164 00:09:42.560 --> 00:09:47.960 And you probably remember from that that you're able to extract all of the different colours in a rainbow on the other side 165 00:09:48.700 --> 00:09:52.580 What's actually happening is that the speed of light is different in the air 166 00:09:52.580 --> 00:09:54.900 than it does in the prism, is in the prism 167 00:09:54.900 --> 00:09:58.920 And as the light moves from the air into the prism 168 00:09:58.920 --> 00:10:03.920 It's actually being bent or refracted a certain amount 169 00:10:04.580 --> 00:10:08.220 And the amount that it's bent depends upon the frequency of the light 170 00:10:08.220 --> 00:10:10.740 Or as we think about it, the colour 171 00:10:11.580 --> 00:10:14.160 Colour is simply a different frequency for a different colour 172 00:10:14.160 --> 00:10:17.160 And as it comes out the other side it's being bent some more 173 00:10:17.900 --> 00:10:20.360 And again we can still see the colours are separated 174 00:10:23.260 --> 00:10:24.720 Sound is very similar 175 00:10:24.720 --> 00:10:29.680 If you pass sound through different areas with different sound speeds 176 00:10:29.680 --> 00:10:34.040 You will bend it and you will bend it different amounts depending upon the frequency 177 00:10:36.760 --> 00:10:42.080 So okay we can understand the sound speed profile is going to affect our sound propagation 178 00:10:43.340 --> 00:10:46.960 Another thing which affects it is the sea surface and the sea floor 179 00:10:47.580 --> 00:10:51.400 Because if we think of sound in the ocean and we send out a signal 180 00:10:51.400 --> 00:10:55.300 Not always but often, particularly in shallow water 181 00:10:55.300 --> 00:11:00.780 It will interact with the sea floor on the way to wherever we are trying to receive the signal 182 00:11:03.340 --> 00:11:06.820 And depending upon I guess what the sea floor is constructed of 183 00:11:06.820 --> 00:11:08.780 It's going to interact in a different way 184 00:11:09.400 --> 00:11:11.360 And thus the signal that we receive will be different 185 00:11:11.360 --> 00:11:14.140 So if we send out one signal here and receive it here 186 00:11:14.140 --> 00:11:16.840 And we bounce the path along the sea floor 187 00:11:17.400 --> 00:11:19.740 Then the sound that we receive depends upon 188 00:11:19.740 --> 00:11:22.600 What the sediment the sea floor is made out of 189 00:11:22.600 --> 00:11:24.600 Is it sand, is it silt, is it mud 190 00:11:24.600 --> 00:11:27.580 How deep are those layers, are there multi layers 191 00:11:27.580 --> 00:11:31.120 Is there anything else on the sea floor of interest that we want to see 192 00:11:33.460 --> 00:11:39.660 So we can appreciate I guess that there's a lot of different ways in which sound can transmit through the ocean 193 00:11:39.660 --> 00:11:43.160 In the shallow water we could have almost a constant speed profile 194 00:11:43.740 --> 00:11:48.980 Or we can have on the right there a profile where our sound 195 00:11:48.980 --> 00:11:50.980 Is refracted slightly downwards 196 00:11:50.980 --> 00:11:54.060 And it interacts a lot with the sea surface and the sea floor 197 00:11:54.060 --> 00:11:56.060 So for shallow water propagation 198 00:11:56.060 --> 00:11:59.240 The sea floor is a very important entity 199 00:11:59.240 --> 00:12:02.260 We need to be able to relate the parameters of the sea floor 200 00:12:02.260 --> 00:12:05.740 To the sound and how it affects the sound 201 00:12:06.380 --> 00:12:11.980 In deep water we don't always interact with the sea floor and the sea surface 202 00:12:13.240 --> 00:12:15.320 Because we have the varying sound speed 203 00:12:15.320 --> 00:12:18.960 In the ocean sound will be I guess bent down 204 00:12:18.980 --> 00:12:21.980 And it will be bent towards locations of lower sound velocity 205 00:12:22.980 --> 00:12:26.620 So if we have a source at the location of our lower sound velocity 206 00:12:26.620 --> 00:12:28.460 And a shallow source angle 207 00:12:28.980 --> 00:12:32.380 We can actually find that the acoustic signal will travel 208 00:12:32.980 --> 00:12:33.900 In an acoustic channel 209 00:12:35.040 --> 00:12:39.460 Through our ocean without interacting with the sea surface and the sea floor 210 00:12:39.980 --> 00:12:43.160 And the good thing about that is we don't then have to account well for the sea floor 211 00:12:43.160 --> 00:12:45.780 And we can transmit really really long distances 212 00:12:45.780 --> 00:12:47.740 With a really high signal 213 00:12:49.000 --> 00:12:50.980 Now for me I'm interested in all of this 214 00:12:50.980 --> 00:12:53.200 But I guess the things I've mainly been looking at 215 00:12:53.200 --> 00:12:57.380 Have been shallow water sound 216 00:12:57.380 --> 00:12:58.600 And I've been looking at well 217 00:12:58.600 --> 00:13:01.700 What do we need to know about the environment 218 00:13:01.700 --> 00:13:05.380 In order to understand how it's affecting the sound 219 00:13:05.380 --> 00:13:06.840 And the signals it's going to receive 220 00:13:06.840 --> 00:13:09.620 So what do we need to know about the sound speed profile 221 00:13:09.620 --> 00:13:12.540 What do we need to know about the sea surface and the sea floor 222 00:13:13.540 --> 00:13:15.460 And we can think from I guess a perspective 223 00:13:15.460 --> 00:13:18.620 If we want to communicate in the ocean 224 00:13:18.620 --> 00:13:21.880 Or if we want to have improved sonar performance 225 00:13:22.540 --> 00:13:26.020 The better the model that we have of our ocean environment 226 00:13:26.620 --> 00:13:27.800 The better that we can do that 227 00:13:30.400 --> 00:13:32.520 So I won't go into too much detail about 228 00:13:32.520 --> 00:13:36.340 I guess the details of what we've done in that area 229 00:13:36.340 --> 00:13:40.460 Because I mean it really does fall in that main scope of what we're trying to do and why 230 00:13:40.460 --> 00:13:44.320 But I will just briefly I guess give you a bit of a taste of what we physically did 231 00:13:44.980 --> 00:13:47.980 So back in 2006 in August September 232 00:13:48.680 --> 00:13:50.180 We went up to Massachusetts 233 00:13:50.180 --> 00:13:53.440 And went out on our research vessel NOR 234 00:13:53.440 --> 00:13:55.940 Which is this fellow on the left here 235 00:13:55.940 --> 00:13:58.280 That's the day before we went out it was being loaded up 236 00:13:58.280 --> 00:14:00.340 And we went out for two and a half weeks 237 00:14:00.340 --> 00:14:01.860 To do some acoustics experiments 238 00:14:03.360 --> 00:14:06.420 This is where we were so off the east coast of the US 239 00:14:06.860 --> 00:14:09.380 On the New Jersey shelf just on the edge of that 240 00:14:10.700 --> 00:14:12.820 And what we do when we want to do these experiments 241 00:14:12.820 --> 00:14:17.580 Is we have to have ways I guess of receiving signals in the ocean 242 00:14:17.580 --> 00:14:18.600 So that we can measure the sound 243 00:14:18.620 --> 00:14:21.600 And we basically drop into the ocean 244 00:14:22.720 --> 00:14:23.920 Acoustic arrays 245 00:14:23.920 --> 00:14:29.020 So these are arrays meaning that we have lots of single recording elements 246 00:14:29.620 --> 00:14:32.420 And each of those recording elements is called a hydrophone 247 00:14:32.420 --> 00:14:35.060 So it works basically the same as a microphone 248 00:14:35.620 --> 00:14:38.100 But hydro meaning that it works under water 249 00:14:38.620 --> 00:14:41.540 And we can record signals on all of those simultaneously 250 00:14:41.540 --> 00:14:46.320 And then we go to a computer and use lots and lots of complex mathematics 251 00:14:46.320 --> 00:14:47.440 And signal processing 252 00:14:47.440 --> 00:14:50.080 To be able to relate what we've received 253 00:14:50.080 --> 00:14:53.960 To I guess the acoustic sounds that we're actually trying to listen to 254 00:14:53.960 --> 00:14:57.060 And again relate that to the sound speed profile 255 00:14:57.060 --> 00:14:59.520 The ocean floor and things like that 256 00:15:00.120 --> 00:15:03.520 This little figure up on the right there is just a little aside 257 00:15:05.760 --> 00:15:08.420 This array that we have there actually recorded 258 00:15:08.420 --> 00:15:11.200 Probably about 90% of the data that I used in my PhD 259 00:15:11.200 --> 00:15:17.200 And when our dedicated group went to pick it back up off the sea floor 260 00:15:17.200 --> 00:15:18.840 They actually snapped a line attached to it 261 00:15:18.840 --> 00:15:20.700 And it was lying on the sea floor 262 00:15:20.700 --> 00:15:22.520 And they weren't sure if they were ever going to get it back again 263 00:15:22.520 --> 00:15:25.420 They sent down a claw and thankfully got it first go 264 00:15:25.920 --> 00:15:28.620 But they had to manually haul it up quite a bit 265 00:15:28.620 --> 00:15:30.020 Before they could put it back on a winch 266 00:15:30.020 --> 00:15:32.140 And this is them at 2 or 3 in the morning 267 00:15:32.140 --> 00:15:34.780 Working hard to make sure that we got our data back 268 00:15:34.780 --> 00:15:36.840 But they did an excellent job and thanks to that 269 00:15:36.840 --> 00:15:38.280 We were able to do really well 270 00:15:39.580 --> 00:15:42.500 Now this here, I'm not going to go into too much detail of the figures 271 00:15:42.500 --> 00:15:46.200 But the idea is that on this particular array 272 00:15:46.220 --> 00:15:51.600 Of hydrophones I was looking at sound from sources that we were towing 273 00:15:52.280 --> 00:15:53.500 Sources that we were lowering 274 00:15:53.500 --> 00:15:55.160 And also just ambient noise 275 00:15:55.160 --> 00:15:57.360 So when we had our sources turned off 276 00:15:57.360 --> 00:16:01.220 There was noise from other shipping and ocean waves and things like that 277 00:16:01.220 --> 00:16:05.380 And from those I was trying to determine acoustic propagation paths 278 00:16:05.380 --> 00:16:08.040 Between all the different hydrophones 279 00:16:08.040 --> 00:16:10.660 And relate that to the ocean environment 280 00:16:11.220 --> 00:16:12.800 And from these three figures here 281 00:16:12.800 --> 00:16:15.320 You can kind of see that there's some, I guess 282 00:16:15.320 --> 00:16:17.680 Some characteristics which are similar in all three 283 00:16:18.320 --> 00:16:21.200 So I was able to use different kind of sources 284 00:16:21.200 --> 00:16:23.640 And account for the type of source I was using 285 00:16:23.640 --> 00:16:25.220 To pull out the same information 286 00:16:27.500 --> 00:16:30.520 I would like to go into more detail on the ocean acoustics 287 00:16:30.520 --> 00:16:33.440 But there might be some of you that are here to listen to the air acoustics 288 00:16:33.440 --> 00:16:35.340 So I'll move on to that area 289 00:16:36.360 --> 00:16:38.400 And if you've got any questions about the ocean acoustics 290 00:16:38.400 --> 00:16:39.760 We can have a chat about that afterwards 291 00:16:41.200 --> 00:16:45.040 Okay, so in ocean acoustics I was, we're interested in using sound 292 00:16:45.040 --> 00:16:47.760 For communication, sonar, things like that 293 00:16:48.860 --> 00:16:50.840 Now I'm looking at aeroacoustics 294 00:16:50.840 --> 00:16:54.400 Which is, I guess, encompasses noise generated 295 00:16:55.040 --> 00:16:57.600 By the flow of fluids over bodies 296 00:16:57.600 --> 00:17:01.520 So for example when you have an aeroplane flying through the air 297 00:17:02.040 --> 00:17:05.220 You can have noise generated by the flow of the air over the wings 298 00:17:06.040 --> 00:17:07.720 If you have a wind turbine 299 00:17:07.720 --> 00:17:10.220 Like we have on the right hand side up here 300 00:17:10.220 --> 00:17:14.680 You'll have noise generated as the turbine blades rotate through the air 301 00:17:15.440 --> 00:17:16.600 Similarly for submarines 302 00:17:16.600 --> 00:17:19.540 They have protrusions, control surfaces, etc 303 00:17:19.540 --> 00:17:21.760 There will be noise produced from that 304 00:17:22.280 --> 00:17:24.900 For varying reasons we would like to reduce this noise 305 00:17:24.900 --> 00:17:29.940 Whether it be to, well just to reduce annoyance 306 00:17:29.940 --> 00:17:32.620 Because these might not be very nice if you live near an airport 307 00:17:33.300 --> 00:17:34.280 Potentially for health 308 00:17:34.280 --> 00:17:37.360 If you are very close to something which is producing a lot of noise 309 00:17:37.360 --> 00:17:39.220 That can have a lot of negative effects on you 310 00:17:39.220 --> 00:17:42.680 And also I guess for defence reasons 311 00:17:43.940 --> 00:17:45.020 Defence obviously is a very important part of the system 312 00:17:45.040 --> 00:17:47.380 So we would like to be able to have things that you can't hear 313 00:17:47.380 --> 00:17:49.780 So that they can undertake covert operations 314 00:17:51.280 --> 00:17:55.680 Now in order to be able to design these things to produce very little noise 315 00:17:55.680 --> 00:17:58.680 First of all we need to understand exactly 316 00:17:58.680 --> 00:18:03.760 How is this entity creating noise in these conditions 317 00:18:03.760 --> 00:18:07.360 And only when we understand exactly how it's creating noise 318 00:18:08.040 --> 00:18:10.440 Can we redesign it to create less noise 319 00:18:14.020 --> 00:18:15.020 So I won't go into too much detail on this 320 00:18:15.020 --> 00:18:18.740 But what we have here is a 321 00:18:18.740 --> 00:18:23.020 I guess a cartoon of a wind turbine 322 00:18:23.020 --> 00:18:24.880 The end of a wind turbine blade 323 00:18:25.580 --> 00:18:28.340 And I'll just very quickly walk you through some 324 00:18:28.340 --> 00:18:30.920 Noise sources that we can get from this scenario 325 00:18:31.720 --> 00:18:35.180 So we have air hitting what we call the leading edge 326 00:18:35.180 --> 00:18:37.400 So the front of the wind turbine blade 327 00:18:37.400 --> 00:18:41.020 And now that air has some turbulence associated with it 328 00:18:41.020 --> 00:18:44.180 So what that means is that it fluctuates about a bit 329 00:18:44.180 --> 00:18:45.000 In a very small amount of time 330 00:18:45.000 --> 00:18:45.680 In a random fashion 331 00:18:46.500 --> 00:18:50.620 And that turbulence is an excellent generator of sound 332 00:18:50.620 --> 00:18:53.480 As that turbulence interacts with the leading edge 333 00:18:54.000 --> 00:18:55.080 We can get sound produced 334 00:18:55.820 --> 00:18:59.680 The air will then also flow over the blade itself 335 00:18:59.680 --> 00:19:05.100 And as the turbulent part of the air in the boundary layer 336 00:19:05.100 --> 00:19:07.980 Which is the, I guess the layer right on top of the blade 337 00:19:07.980 --> 00:19:09.860 Interacts with the trailing edge 338 00:19:09.860 --> 00:19:14.060 We can actually get very high sound 339 00:19:14.060 --> 00:19:15.140 Produced from that 340 00:19:15.140 --> 00:19:16.360 We get a diffraction mechanism 341 00:19:17.060 --> 00:19:19.540 That means that trailing edge noise can be one of the most dominant 342 00:19:20.400 --> 00:19:24.120 Sources of noise production from air acoustic applications 343 00:19:25.300 --> 00:19:27.760 Also we can get vortices produced 344 00:19:27.760 --> 00:19:31.540 For example on the edge of the turbine blade here 345 00:19:32.060 --> 00:19:35.160 We can actually get little vortices which are like swirling motion 346 00:19:35.160 --> 00:19:38.360 Kind of like what you get if you take the plug out of your bathtub 347 00:19:38.360 --> 00:19:40.020 And you see the water swirl down 348 00:19:40.020 --> 00:19:44.040 And these vortices themselves will generate a lot of noise 349 00:19:44.060 --> 00:19:46.160 At certain frequencies 350 00:19:46.160 --> 00:19:51.200 So there's a big, I guess myriad of noise producing sources on a turbine 351 00:19:52.560 --> 00:19:55.080 The motor itself can also produce noise 352 00:19:55.080 --> 00:19:57.480 But that's not something that I've personally looked at 353 00:19:57.480 --> 00:20:01.420 And it's also something that they've, other people have been able to deal with in the past 354 00:20:01.420 --> 00:20:04.240 And already wind turbines that are produced today 355 00:20:04.240 --> 00:20:06.440 Have a lot less noise from that area 356 00:20:09.480 --> 00:20:13.020 So in order to be able to understand 357 00:20:13.020 --> 00:20:17.040 Where this noise is coming from and how it's being generated 358 00:20:17.040 --> 00:20:21.660 Rather than just simply going out and measuring noise from a wind turbine or an aeroplane 359 00:20:21.660 --> 00:20:23.840 We often have to take a few steps back 360 00:20:23.840 --> 00:20:26.200 And we have to look at something very fundamental 361 00:20:27.020 --> 00:20:28.960 Under controlled laboratory conditions 362 00:20:28.960 --> 00:20:32.440 So that we can really tap into one mechanism at a time 363 00:20:33.020 --> 00:20:36.600 So something that we've been looking at is just the trailing edge noise mechanism 364 00:20:36.600 --> 00:20:37.840 That I've been talking about 365 00:20:37.840 --> 00:20:42.000 And what we do is we do most of our work in a big box 366 00:20:42.000 --> 00:20:44.360 Which is this thing here 367 00:20:45.300 --> 00:20:49.300 And this box is what's effectively an anechoic chamber 368 00:20:50.000 --> 00:20:54.780 You can see it has lots of foam wedges on its roof and walls and even on its floor 369 00:20:54.780 --> 00:20:57.380 And what these do is absorb sound 370 00:20:58.000 --> 00:20:59.900 So that you've basically got an echo free environment 371 00:20:59.900 --> 00:21:03.960 So you've really only got a direct acoustic path between two points 372 00:21:03.960 --> 00:21:06.520 You don't have bounces off the wall or anything like that 373 00:21:07.760 --> 00:21:10.640 Then what we do is we put a wind tunnel through this box 374 00:21:10.640 --> 00:21:15.100 So we have a fan and we blow air out here 375 00:21:16.260 --> 00:21:21.700 And then what we can do is we can put whatever piece we're looking at in front of that air 376 00:21:21.700 --> 00:21:26.060 So up on the top right hand side we've got a simple flat plate that we've put in there 377 00:21:26.640 --> 00:21:31.500 Now the idea is that in real life with your aeroplane for example 378 00:21:31.500 --> 00:21:35.240 Your aeroplane moves and your air is approximately stationary 379 00:21:35.240 --> 00:21:36.500 Not really but approximately 380 00:21:37.640 --> 00:21:39.700 Whilst in here the plate is stationary 381 00:21:39.700 --> 00:21:40.900 And the air moves 382 00:21:40.900 --> 00:21:44.340 It's the opposite effect but exactly the same thing is happening 383 00:21:44.340 --> 00:21:46.800 And noise will be generated in exactly the same way 384 00:21:47.560 --> 00:21:50.560 Now to give you a bit of an idea of what I guess 385 00:21:51.360 --> 00:21:55.080 Aeroacoustic or aerodynamically generated noise sounds like 386 00:21:55.700 --> 00:22:01.360 What we've got here are two signals for this particular case 387 00:22:01.360 --> 00:22:04.080 The first signal which is green on the bottom there 388 00:22:04.700 --> 00:22:08.800 Is what we have when we don't have anything in there 389 00:22:08.800 --> 00:22:11.020 We just have our air turned on but we don't have our body 390 00:22:11.020 --> 00:22:12.740 So if we can have that plate, thank you 391 00:22:13.960 --> 00:22:18.600 Okay you can hear very very slightly that there is some noise happening 392 00:22:18.600 --> 00:22:21.140 And there is already aerodynamic noise being generated 393 00:22:21.700 --> 00:22:24.080 But as soon as we put the plate in we get the other noise 394 00:22:25.020 --> 00:22:27.000 You can hear we've got a lot more noise 395 00:22:27.480 --> 00:22:34.300 And so yes the air is reacting with the plate and creating a lot of noise 396 00:22:37.800 --> 00:22:38.580 Okay so 397 00:22:39.220 --> 00:22:44.360 We've done some work looking at how I guess the trailing edge has been creating the noise 398 00:22:44.360 --> 00:22:47.760 And under different conditions we've been able to pinpoint a few different mechanisms 399 00:22:47.760 --> 00:22:50.720 And then we've gone away and we're now looking at 400 00:22:50.720 --> 00:22:54.520 Well we think we have a good understanding of how this noise is being produced 401 00:22:54.520 --> 00:22:56.440