WEBVTT 00:00.290 --> 00:01.130 Hello everyone. 00:01.130 --> 00:04.910 Welcome back to the CFD using Openfoam course beginners to intermediate. 00:05.510 --> 00:07.100 This is the third class. 00:07.100 --> 00:13.430 In this class, we'll be seeing how to use Block mesh tool to generate further complicated mesh using 00:13.430 --> 00:15.380 another tool called Snappy Hex Mesh. 00:16.190 --> 00:18.680 So snappy hex mesh is dependent on block mesh. 00:19.220 --> 00:26.030 So we have to use block mesh in certain way to use it for snappy x mesh that we will be looking, and 00:26.030 --> 00:32.230 how to set up a snappy hex mesh and what actually snappy hex mesh is, and how to create complex meshes 00:32.230 --> 00:33.430 using snappy hex mesh. 00:33.430 --> 00:37.780 Then we will look at a command called check mesh to check the quality of our mesh. 00:38.830 --> 00:45.970 Okay, so the block mesh is used to create the background mesh in case of uh, snappy hex mesh. 00:45.970 --> 00:47.500 So what is background mesh? 00:47.500 --> 00:48.220 We will look that. 00:48.220 --> 00:55.620 So the mesh must consist purely of hexes like we should have a pure cube or pure cuboid, just like 00:55.620 --> 00:58.800 how we created the rectangular cavity in the previous tutorial. 00:59.460 --> 01:02.550 So the cell aspect ratio should be approximately one. 01:02.550 --> 01:03.840 That is the ideal condition. 01:03.840 --> 01:10.320 So it is good to maintain that and at least near the surfaces at which the subsequent snapping procedure 01:10.320 --> 01:14.790 is applied, which if you did not understand now, you will understand later. 01:14.790 --> 01:21.270 But if you are good with meshing in general, you will understand what snapping is so near the areas 01:21.270 --> 01:23.220 where there will be snapping towards the surface. 01:23.220 --> 01:29.070 We have to keep the cell aspect ratio as one and towards the convergence of the snapping. 01:29.070 --> 01:35.880 If the procedure is slow, it could lead to the possibility of failure and we are not wanting to do 01:35.880 --> 01:36.180 that. 01:36.180 --> 01:42.340 So we have to make sure that the aspect ratio is one and there must be at least one interaction, sorry, 01:42.340 --> 01:48.040 intersection of a cell edge with the cell surface that is, a mesh of one cell will not work. 01:48.040 --> 01:53.290 So it has to intersect with some cell edges with the cell surface. 01:53.290 --> 02:00.010 If everything till now goes through your head, don't worry, you will understand right when we get 02:00.010 --> 02:01.870 into the presentation. 02:02.350 --> 02:06.540 Okay, now let's assume that we have an STL surface okay. 02:06.540 --> 02:07.920 This car is the STL. 02:07.920 --> 02:11.250 We are interested in simulating flow over a car. 02:12.090 --> 02:12.510 Okay. 02:12.510 --> 02:17.010 Now the gray area is your fluid domain and we have the STL surface okay. 02:17.010 --> 02:19.470 STL is basically surface geometry. 02:19.470 --> 02:20.490 So we have it. 02:20.490 --> 02:25.380 We are interested in mesh in the gray area, not the white area because we are interested in flow over 02:25.380 --> 02:25.800 the car. 02:26.520 --> 02:32.420 Okay, now the block mesh will act as the background mesh which will create the the outer box. 02:32.420 --> 02:34.250 Like you see this black box. 02:34.910 --> 02:39.080 The black mesh will create these blocks and it will have some subdivisions over there. 02:40.010 --> 02:44.240 It also contains the boundary patch such as inlet, outlet and walls. 02:44.240 --> 02:48.290 Let's say that this patch has to be inlet and this has to be outlet. 02:48.290 --> 02:50.690 Then we will define that in the block mesh itself. 02:50.690 --> 02:55.840 We are not going to do using snap hex mesh, because snap hex mesh is going to deal only with the surface. 02:56.500 --> 03:01.030 Okay, then the block mesh will enclose the entire STL and can act as the fluid domain. 03:01.030 --> 03:04.450 If the mesh is required around the model and inside the block mesh. 03:04.480 --> 03:11.680 So what this means is that now we have created this black box is generated enclosing the STL surface. 03:11.680 --> 03:19.460 So this block mesh has created a fluid domain which is the gray area which encloses the surface. 03:19.460 --> 03:21.440 So this grey area is the fluid domain. 03:22.160 --> 03:29.060 And this is essential only if we want to make a mesh which is outside the surface. 03:29.060 --> 03:34.790 But if this is this surface is like a pipe, then it does not have to be this big. 03:34.790 --> 03:38.600 It can just enclose the pipe and we can generate the mesh inside the pipe. 03:38.600 --> 03:42.520 Then the SDL will act as the enclosure, not the block mesh. 03:42.550 --> 03:49.810 Okay, so only when the, uh, mesh is, uh, required outside the surface, then we need block mesh 03:49.810 --> 03:52.990 bigger than the STL and it will act as the fluid domain. 03:52.990 --> 03:55.180 You will understand it when we actually do it. 03:56.140 --> 04:01.480 Okay, then the purpose of Snappy Mesh is that it is advanced mesh generation tool for very complex 04:01.480 --> 04:03.430 geometry like this aircraft. 04:03.550 --> 04:09.390 So this is generated by, uh, fuzzy Lab, which is at IIT Bombay. 04:09.900 --> 04:11.100 I used to work there. 04:11.100 --> 04:19.710 So one of the, uh, research researchers generated this mesh for the Sukhoi 30 MKI Mach one aircraft. 04:19.710 --> 04:24.840 So we were interested in simulating flow over the aircraft. 04:24.840 --> 04:26.820 So this is just the surface mesh? 04:26.820 --> 04:31.280 Actually, the mesh lies, uh, in the fluid domain, but we can view the surface mesh. 04:31.580 --> 04:32.780 Okay, that's what this image is. 04:32.780 --> 04:37.250 The point is, we can generate mesh for highly complicated surfaces, too. 04:37.280 --> 04:39.320 That's what I wanted to say. 04:39.320 --> 04:43.190 And the capabilities is it can handle complex geometries. 04:43.310 --> 04:48.860 It can handle refinement features like if you want to refine just one region, you can't do that. 04:48.860 --> 04:52.580 And mesh quality improvement can be done through an iterative process. 04:53.660 --> 04:56.270 Snappy workflow is like follows. 04:56.270 --> 05:01.970 First, we will be importing the STL file into a folder called Try surface, which will reside under 05:01.970 --> 05:06.110 constant directory like how we have Polymesh adjacent to Polymesh. 05:06.110 --> 05:10.610 We will create a new folder called try surface and put the necessary STL file inside that. 05:10.610 --> 05:17.150 Then we will be extracting the surface feature using a feature called Surface Feature Extract or surface 05:17.150 --> 05:23.070 feature extract is the command to extract the surfaces from the STL and save it into dot e mesh file, 05:23.070 --> 05:24.870 which is openfoam understandable. 05:25.020 --> 05:27.450 Then we will create a castellated mesh. 05:27.450 --> 05:32.970 If you are good with meshing and the techniques used in it, you will understand what castellated mesh 05:32.970 --> 05:39.780 is and we, the snap mesh will initially create a castellated mesh using snapping and refinement. 05:39.780 --> 05:45.080 Then it will adjust the mesh to conform the surface geometry through further snapping. 05:45.080 --> 05:50.390 And then if you want layer additions like boundary layers, five layers or six layers through layer 05:50.390 --> 05:54.380 thickness for wireless, then you can add layers also. 05:54.380 --> 05:56.420 So that can also be done in snaps mesh. 05:56.780 --> 06:00.020 So now we will see how actually snap mesh works. 06:00.020 --> 06:03.860 Now the blocks which you are seeing is generated by the block mesh. 06:03.890 --> 06:05.450 That is the background mesh. 06:05.450 --> 06:10.300 Then we have the car which is overlapping with the mesh, but we are interested in mesh outside the 06:10.300 --> 06:11.290 car, not inside it. 06:11.290 --> 06:11.650 Right. 06:11.650 --> 06:14.500 So this is the first scenario where we have the setup. 06:14.770 --> 06:16.870 We have a block mesh and we have an STL file. 06:17.920 --> 06:25.060 Then the snap mesh process will start to split the cells near the surface. 06:25.060 --> 06:25.330 Okay. 06:25.330 --> 06:28.300 The feature edge is what we say for the surface. 06:28.300 --> 06:36.180 So wherever there is a feature edge the snappy mesh solve, uh, algorithm will split the cells to refine 06:36.180 --> 06:39.030 it so that we can capture it accurately. 06:39.030 --> 06:41.460 It will do for all the feature edges. 06:41.460 --> 06:43.740 So it will look something like this. 06:43.740 --> 06:44.100 Okay. 06:44.100 --> 06:49.890 It has, uh, divided the blocks into smaller blocks to capture the features. 06:50.730 --> 06:55.610 Then it will remove whatever is residing inside the cell SDL surface. 06:55.610 --> 06:57.080 We are not interested in that right? 06:57.080 --> 07:03.170 We are interested only in the mesh outside it, so it will remove or delete all the cells inside the, 07:03.500 --> 07:05.090 uh, SDL surface. 07:05.240 --> 07:08.540 Then it will start snapping to surfaces. 07:08.540 --> 07:10.340 As you can see, this is not very good. 07:10.340 --> 07:14.630 The car wheel is circular, but we are getting mesh inside also, and it's not very nice. 07:14.630 --> 07:22.660 So the process of snapping will start and it will confirm the mesh and it will snap to the surface, 07:22.660 --> 07:26.470 and it will not have anything outside or inside the surface. 07:26.470 --> 07:28.300 So it will be on the surface. 07:28.300 --> 07:29.020 Exactly. 07:29.020 --> 07:31.510 So this is what snapping does. 07:31.810 --> 07:33.040 Uh, snapping does. 07:33.040 --> 07:38.890 And we will start adding mesh layers wherever it is necessary so we can control the mesh layer where 07:38.890 --> 07:39.820 it is necessary. 07:39.820 --> 07:40.750 We can do that. 07:41.560 --> 07:45.720 So this is the entire process of how snappy hex mesh works. 07:45.750 --> 07:52.320 Now, for example, we will mesh a simple cylindrical pipe using a pipe geometry pipe. 07:52.320 --> 07:52.980 Dostal. 07:52.980 --> 07:57.240 You will have the STL file already in the resources so you can download and use it. 07:57.240 --> 08:03.630 So first we will set up the file called surface feature extracted, because that is what is going to 08:04.050 --> 08:09.450 extract the feature from STL and put it into r dot m s e mesh. 08:09.540 --> 08:11.790 That's what Openfoam can understand. 08:12.780 --> 08:13.080 Okay. 08:13.080 --> 08:15.750 This is how the surface feature extract dict looks. 08:15.750 --> 08:19.920 So I will open the file itself so you can understand it better. 08:19.920 --> 08:22.680 Now I am in the terminal. 08:23.190 --> 08:26.370 I will go to the class three. 08:26.670 --> 08:30.390 We have the pipe external folder as the first tutorial. 08:30.600 --> 08:32.380 So I will enter that. 08:32.410 --> 08:36.130 Okay, we have constant perform and system. 08:36.130 --> 08:37.480 We are not going to set up the case. 08:37.480 --> 08:45.700 Run it so we don't have the zero file now okay now I will first run the block mesh okay. 08:45.700 --> 08:46.750 We have the block mesh. 08:46.870 --> 08:49.060 Now to open this exact location. 08:49.180 --> 08:53.740 We can do this command explorer dot x space dot and hit enter. 08:54.310 --> 08:55.990 It will open the exact location. 08:56.000 --> 08:58.640 you can see C3 Won by Paxton. 08:59.090 --> 09:02.600 I'll open the parameter file to view the mesh generated by block mesh. 09:04.250 --> 09:06.830 Yeah, this is the mesh we have. 09:06.860 --> 09:07.400 Okay. 09:08.720 --> 09:11.660 This will act as the background mesh. 09:12.170 --> 09:17.690 Now what we are going to do is we are going to mesh up pipe. 09:17.780 --> 09:26.800 As I said under uh, constant folder, we have tri surface and we have pipe dot STL. 09:26.980 --> 09:29.890 I'll click on okay and apply. 09:30.700 --> 09:33.760 Now you can see this is the pipe we are going to work with. 09:34.570 --> 09:37.210 I will put it in wireframe so you can see it better. 09:37.240 --> 09:40.090 So this is the background mesh and this is the pipe. 09:40.090 --> 09:42.310 Now we are interested in meshing around the pipe. 09:43.150 --> 09:44.760 Please don't ask me why we are doing it. 09:44.760 --> 09:46.860 We are just doing it for learning purpose. 09:47.460 --> 09:49.860 So we are not going to run any simulation. 09:49.860 --> 09:52.260 We are going to mesh around the pipe. 09:52.560 --> 10:00.090 Okay, so by the block mesh we have inlet outlet upper and lower. 10:00.720 --> 10:02.760 And we also have front and back. 10:04.200 --> 10:06.030 This is what we have okay. 10:06.240 --> 10:09.110 And I will close this. 10:09.950 --> 10:12.320 I will go system under this. 10:12.320 --> 10:16.760 We will be able to find the surface feature, extract it I will open that. 10:18.440 --> 10:21.320 So you can see that we have sourced pipes. 10:21.560 --> 10:24.200 So what is the location by the way. 10:24.200 --> 10:25.820 You will not have this file when you get it. 10:25.820 --> 10:29.090 So you will just have polymesh and tri surface. 10:29.090 --> 10:35.980 The Polymesh will contain the mesh from block mesh and this dry surface will have only dot STL. 10:36.010 --> 10:41.650 Okay, so we have this STL which we created using any CAD software I created using FreeCAD. 10:41.680 --> 10:44.770 I have put it here so you will get it through the resources. 10:45.010 --> 10:46.780 So it is inside dry surface. 10:46.780 --> 10:49.210 And notice that's is capital. 10:49.630 --> 10:54.460 Okay now we are sourcing that name pipe dot STL. 10:54.520 --> 10:57.340 The extraction method is always extract from surface. 10:57.340 --> 10:58.750 This include angle. 10:58.750 --> 11:00.280 We are setting it to 150. 11:00.280 --> 11:05.140 If it is zero it will select no h and if it is 180 it will select all h. 11:05.140 --> 11:07.570 So h is basically triangulated surface. 11:07.570 --> 11:09.130 So it also has edges. 11:09.970 --> 11:13.810 And uh we are giving 150 to be okayish. 11:13.810 --> 11:15.670 It will select everything in a cylinder. 11:15.670 --> 11:21.830 For highly complex surface we might need 180 degrees and subset of features. 11:21.830 --> 11:26.120 We will set non-manifold edges as no and open edges as yes. 11:26.120 --> 11:29.000 It is always safe to keep it in this setting. 11:29.000 --> 11:33.890 If you want to know more about this, you can read the documentation and you can explore. 11:34.430 --> 11:41.120 Nothing wrong, but I always like to keep my non-manifold edges as no and open edges as yes. 11:41.360 --> 11:44.150 And you have to set right obj as yes. 11:44.150 --> 11:45.790 Okay, I will save this file. 11:46.450 --> 11:57.970 And the next command which we have to do is extract sorry surface feature extract. 11:58.090 --> 12:02.650 Notice that every other word has the first letter as capital I'll hit enter. 12:03.100 --> 12:06.430 You should be seeing end without any error or warning. 12:06.940 --> 12:12.960 Now what this will do is it will create this folder called Extended Feature Edge Mesh. 12:12.960 --> 12:15.390 And it has written all these files. 12:15.390 --> 12:17.490 So this is what write obj does. 12:17.520 --> 12:18.210 Okay. 12:18.390 --> 12:20.370 And um this is fine. 12:20.370 --> 12:24.840 Now we also have the pipe dot extended feature edge mesh file. 12:24.840 --> 12:26.460 But we're not interested in that. 12:26.460 --> 12:30.180 If you go to try surface we pasted only dot stl file here. 12:30.180 --> 12:31.950 But it also has dot image file. 12:31.950 --> 12:33.950 That is what is needed actually. 12:34.190 --> 12:38.540 Okay, now we are ready to do snappy hex mesh. 12:40.040 --> 12:40.550 Okay. 12:40.700 --> 12:42.320 So snappy hex mesh data. 12:42.350 --> 12:45.260 It has these three parameters as the main thing. 12:45.260 --> 12:47.720 So castellated mesh it has to be true. 12:47.720 --> 12:49.370 Otherwise you are not going to get the mesh. 12:49.370 --> 12:51.170 Snap has to be true. 12:51.170 --> 12:53.330 Otherwise you are not going to get a smooth mesh. 12:53.360 --> 12:54.170 Add layers. 12:54.170 --> 12:55.820 It can be true or false. 12:55.820 --> 12:58.780 It depends on what your necessity is, okay? 12:59.260 --> 13:03.370 And by default we will be giving five dot style. 13:03.370 --> 13:09.490 In this case, if you are having any other dot style, it has to match with the name under tri surface 13:09.490 --> 13:09.880 folder. 13:09.880 --> 13:14.050 So you are giving it here and the type will be tri surface mesh. 13:14.050 --> 13:17.950 The name is pipe this pipe under name. 13:17.950 --> 13:19.270 It is user defined. 13:19.270 --> 13:21.600 You can keep anything that you want Okay. 13:21.600 --> 13:23.760 It is not a syntax you can keep. 13:23.760 --> 13:28.950 Whatever you want and feature will be given through file pipe dot image. 13:28.950 --> 13:32.640 This is what the surface feature extract has uh generated. 13:32.640 --> 13:36.210 And we are setting it to level six for very good refinement. 13:36.210 --> 13:40.710 It can be three, four, five, six anything, but generally three is okayish okay. 13:40.710 --> 13:42.030 And six will be very good. 13:42.030 --> 13:43.710 You can also go above that. 13:43.710 --> 13:50.780 There is no limit but generally six is very fine and three is coarse or a decent mesh. 13:52.070 --> 13:57.200 And the next thing is refinement surfaces where we are selecting this pipe. 13:57.530 --> 13:57.770 Right. 13:57.770 --> 14:02.450 So this pipe is same as what you defined in here the name. 14:02.450 --> 14:09.320 So it has to match okay the pipe and the level I have set it to 5 to 6 minimum and maximum refinement 14:09.320 --> 14:09.740 level. 14:09.740 --> 14:14.740 So it will see how the surface is and it will choose whether to do minimum or maximum. 14:14.740 --> 14:15.850 So it can be same. 14:15.850 --> 14:21.850 Also five five also be given six six can also be given and the patch info will be type pipe. 14:22.630 --> 14:24.400 And in groups it is pipe. 14:24.400 --> 14:30.940 So as we were seeing in Paraview we have empty patch as well as uh walls patch. 14:31.000 --> 14:33.460 We can also do pipe. 14:33.460 --> 14:35.040 We can give our own group. 14:35.040 --> 14:36.360 If there are like many pipes. 14:36.360 --> 14:38.070 In the same case, we can do pipes. 14:38.070 --> 14:39.900 Okay, this will be in the patch info. 14:40.500 --> 14:42.930 Then we have to give location and mesh. 14:42.930 --> 14:45.210 So this is what is most important. 14:45.210 --> 14:50.370 I will try to explain it through visualization. 14:53.070 --> 14:56.190 So we have our block mesh here. 14:56.790 --> 14:59.770 And I will also load the try surface here. 15:01.330 --> 15:02.710 Our STL file. 15:03.040 --> 15:04.750 Yeah we have it okay. 15:04.750 --> 15:10.420 So if I want the mesh outside the surface I have to choose a point outside the surface. 15:10.420 --> 15:12.370 But it has to be inside the block mesh. 15:12.370 --> 15:19.360 You can turn on data access grid and see what are the points on x, y and z. 15:19.360 --> 15:26.730 So the point if it lies outside the pipe, but inside the block mesh, it will generate the block mesh 15:26.730 --> 15:27.840 as the fluid domain. 15:27.960 --> 15:34.710 But if your point lies inside the surface of the pipe, uh, then the mesh will be inside the pipe. 15:34.740 --> 15:37.230 The second tutorial will be on inside the pipe. 15:37.230 --> 15:39.150 So for now we are doing outside the pipe. 15:39.870 --> 15:50.330 So if you see the part we are choosing zero comma 0.5 comma zero uh, which is around in x, it is zero 15:50.450 --> 15:54.740 y, it is 0.5. 15:54.740 --> 15:56.480 And is it is it is zero. 15:56.480 --> 16:00.290 So zero, 0.5 and zero. 16:00.290 --> 16:02.660 It is slightly above the pipe. 16:02.960 --> 16:07.640 It is almost same on the surface of the pipe, but uh, it is outside the pipe. 16:07.640 --> 16:12.190 So it is going to generate the mesh outside the pipe and nothing inside. 16:12.190 --> 16:13.630 So inside will be hollow. 16:14.560 --> 16:15.040 Okay. 16:15.040 --> 16:17.680 And the next feature is add layer controls. 16:17.680 --> 16:24.850 If you set the initial conditions to false for add layers in this region, then you don't have to set 16:24.850 --> 16:26.860 up anything under Add Layers control function. 16:26.860 --> 16:30.580 But if you are setting it to true then you can add the end face layers. 16:30.880 --> 16:36.030 You have to choose the name of the uh region, which in this case is pipe. 16:36.090 --> 16:38.730 So now we will run snappy hex mesh. 16:38.730 --> 16:44.400 So that commands to do it is first we will do block mesh, then the surface feature extract which two 16:44.430 --> 16:45.570 we have already done. 16:45.570 --> 16:50.580 Then we have to run the command snappy hex mesh uh hyphen override. 16:50.580 --> 16:55.350 But before that we will look at the actual file instead of just screenshots. 16:56.130 --> 17:02.210 So it is under snappy hex mesh dict If you go here we have the same file here. 17:02.720 --> 17:03.200 Okay. 17:04.010 --> 17:09.860 And we also have these things called maximum local cells set to 100,000. 17:09.860 --> 17:12.740 Maximum global cells is set to 2 million. 17:12.740 --> 17:14.360 So these are like limits. 17:14.360 --> 17:18.590 You can play over it but pretty much you can leave it default in most cases. 17:19.040 --> 17:24.970 And we have seen this I have set level three because level six is going to take a lot of time. 17:25.450 --> 17:26.680 Uh, that's why I said two three. 17:26.680 --> 17:29.650 But if you want to increase six then it's fine. 17:29.740 --> 17:31.540 Then for uh, refinement levels. 17:31.540 --> 17:36.640 Also, I said to three and four because it will do it faster and resolve angles. 17:36.640 --> 17:37.870 This is very important. 17:37.870 --> 17:44.320 Unlike, uh surface which are extracted, the more the angle the better the capturing. 17:44.320 --> 17:47.970 But in this case, lesser the angle, better the capturing. 17:47.970 --> 17:49.650 So it is to resolve sharp angles. 17:49.650 --> 17:51.240 So usually 30 is fine. 17:51.240 --> 17:54.990 It's not good to go like 10 or 5 in general. 17:54.990 --> 17:56.490 So that is decent. 17:57.240 --> 17:58.890 And we have refinement reasons. 17:59.010 --> 18:01.020 We will cover this in a later tutorial. 18:01.020 --> 18:04.380 So this is not getting used in our case. 18:04.380 --> 18:04.860 Okay. 18:05.400 --> 18:08.730 Uh, so you can pretend that this doesn't exist here. 18:08.730 --> 18:12.320 And the location and meshes also set in the snap controls. 18:12.320 --> 18:19.490 It has a lot of parameters, but pretty much you can leave it default in a beginner level or intermediate 18:19.490 --> 18:19.700 level. 18:19.700 --> 18:26.630 If you want to do very fine level of meshing, then you can maybe play with this and add layer controls. 18:26.630 --> 18:32.060 Also has this expansion ratio, final layer thickness, minimum thickness and at what parameters it 18:32.060 --> 18:32.660 has to grow. 18:32.660 --> 18:36.970 So you can check these commands on what these parameters are actually. 18:36.970 --> 18:39.670 So that is why these come commands exist. 18:39.670 --> 18:46.000 You can read and understand what each of these parameters do, and you can play with the values accordingly. 18:46.750 --> 18:49.420 Now we have something called mesh quality controls. 18:49.420 --> 18:56.980 So it is including a file called mesh quality dict which is also in the systems folder. 18:56.980 --> 19:01.560 You can always copy paste this mesh quality dict Mostly this is perfectly fine. 19:01.560 --> 19:03.570 You don't have to change anything in this. 19:03.870 --> 19:09.870 So we are going to leave it and after this it can be always default. 19:09.870 --> 19:11.280 You don't have to change it. 19:11.520 --> 19:12.990 Pretty much most of the time. 19:13.200 --> 19:13.590 Okay. 19:13.590 --> 19:16.830 Now we will run snappy hex mesh. 19:16.860 --> 19:17.310 Okay. 19:17.310 --> 19:22.920 So the command is snappy hex mesh and always do overwrite. 19:23.690 --> 19:29.810 It is not mandatory to do this space hyphen override, but what this will do is since we are running 19:29.810 --> 19:31.640 multiple iterations, right. 19:31.640 --> 19:37.910 So you can see here we have refinement levels. 19:37.910 --> 19:43.520 So for each refinement level it will try to write it in a new time step file. 19:43.550 --> 19:44.870 We are not interested in doing that. 19:44.870 --> 19:46.910 So we are writing the command overwrite. 19:46.910 --> 19:50.170 So it will override the, uh, polymesh itself. 19:50.170 --> 19:53.650 So we will have consistent mesh under Polymesh folder itself. 19:53.770 --> 19:57.580 So I'll hit enter and it will start to do the meshing. 20:01.060 --> 20:02.620 Now the mesh is over. 20:02.620 --> 20:12.930 So now you can see that in the poly mesh we have more files not just boundary faces points and owner 20:12.930 --> 20:13.440 and neighbour. 20:13.440 --> 20:14.580 We have more. 20:14.580 --> 20:17.130 We also got a new file called sets. 20:17.130 --> 20:21.660 So if I go to boundary now we have five. 20:21.660 --> 20:23.460 Like we also have pipe. 20:23.460 --> 20:25.260 Previously we had only four. 20:25.260 --> 20:26.550 Now we also have pipe. 20:26.550 --> 20:28.770 This is what snappy hex mesh has added. 20:28.800 --> 20:30.600 Now we will actually view the mesh. 20:30.600 --> 20:31.380 I'll go here. 20:31.380 --> 20:33.930 Hide the pipe with para dot form. 20:33.930 --> 20:35.550 I'm going to give refresh. 20:35.720 --> 20:38.120 You can see it has pipe in it. 20:38.720 --> 20:38.930 Okay. 20:38.930 --> 20:40.970 We have generated the mesh of the pipe. 20:41.780 --> 20:43.370 So this is the background mesh. 20:43.370 --> 20:44.960 It stays consistent. 20:44.960 --> 20:46.790 It doesn't it doesn't change. 20:46.790 --> 20:53.360 Now I can go here and select inlet outlet and pipe alone okay. 20:53.360 --> 20:54.200 We have the inlet. 20:54.200 --> 20:55.460 We have the outlet. 20:55.460 --> 20:57.020 And we also have the pipe. 20:58.010 --> 21:00.720 Yeah it is a decent enough mesh. 21:00.720 --> 21:04.440 It's not good to run simulation, but to learn a meshing it is fine. 21:04.500 --> 21:09.930 So as you can see, this is almost, uh, all quad, all hexahedral. 21:09.930 --> 21:11.970 This is what snappy hex mesh does. 21:12.120 --> 21:14.520 So the hex means hexahedral. 21:14.520 --> 21:15.810 Mostly it is Hexahedral. 21:15.810 --> 21:18.030 Sometimes it fails and makes tetra. 21:18.360 --> 21:21.990 But 99% it is hexahedral. 21:23.550 --> 21:29.900 Okay, we have this pipe if you want to see a slice of it, you can also do that. 21:29.900 --> 21:31.040 I'll create a slice. 21:31.040 --> 21:35.750 To create a slice you can click on this button and hide the show plane. 21:35.750 --> 21:36.410 Apply. 21:37.100 --> 21:43.130 So you can see we have the pipe only as a line because we have removed internal mesh I'll select internal 21:43.130 --> 21:43.640 mesh. 21:46.490 --> 21:48.820 And select the slice surface with edges. 21:49.180 --> 21:52.120 As you can see, this is what we have got. 21:54.340 --> 21:57.760 We have the layers also good amount of layers. 21:57.850 --> 21:58.750 We have the mesh. 21:58.750 --> 22:00.190 This is a very coarse mesh. 22:00.190 --> 22:02.470 If you want to work on the refinement levels it's up to you. 22:02.470 --> 22:08.920 But I am saying that when you once you start refining the mesh, it is going to take a lot of time. 22:08.920 --> 22:11.920 So for tutorial purpose I have kept it very low. 22:11.920 --> 22:14.380 You can go up to six seven refinements also. 22:15.280 --> 22:15.490 Okay. 22:15.490 --> 22:18.760 Now we have done the pipe meshing outside the pipe. 22:18.760 --> 22:21.370 But what if we want to do inside the pipe. 22:21.400 --> 22:24.430 The procedure remains literally the same. 22:24.430 --> 22:24.880 Okay. 22:24.880 --> 22:28.750 So I'm going to go to the internal pipe case. 22:28.750 --> 22:30.100 We have the block mesh. 22:30.100 --> 22:33.310 We have surface mixer extract snap x mesh. 22:33.640 --> 22:37.490 And we will pretend that this doesn't exist already. 22:38.330 --> 22:40.790 So initially, you will have only this. 22:40.970 --> 22:45.560 Okay, so we have the try surface and inside that we have the pipe dot STL. 22:46.040 --> 22:48.710 And we have these files also. 22:49.430 --> 22:56.420 Now the method to do as you know already is go to the right location. 22:58.850 --> 23:02.650 Check if it is the right location then run block mesh. 23:02.890 --> 23:09.160 Get a good end and do surface feature extract. 23:09.820 --> 23:11.080 Get a good end. 23:11.290 --> 23:17.500 Ensure that it has created the extended feature edge mesh folder and the dot mesh. 23:17.860 --> 23:20.770 And we already set up the snappy hex mesh. 23:20.770 --> 23:22.480 But there is a slight change. 23:22.480 --> 23:25.350 As I said, the location in mesh is going to change. 23:26.190 --> 23:35.310 Previously it was zero comma 0.5 comma zero, but now it is one comma, 0.25 comma 0.25, because that 23:35.310 --> 23:39.840 is going to reside inside the pipe and not on the block mesh. 23:39.840 --> 23:41.280 So I will show you. 23:46.770 --> 23:49.430 You can see the block mesh is exactly the same. 23:49.430 --> 23:50.660 There is no change at all. 23:51.140 --> 23:57.650 But the point which I have chosen, it lies inside the pipe somewhere in the middle. 23:57.650 --> 24:01.580 It need not be exactly middle, it just has to reside inside the pipe. 24:01.640 --> 24:05.900 Then the entire mesh is going to be inside the pipe and not on the block mesh. 24:05.900 --> 24:09.920 Okay, but the problem is it is not going to do the inlet outlet and all. 24:09.920 --> 24:12.650 It's going to be getting completely removed. 24:12.650 --> 24:18.280 We will look how to do that also in a later tutorial, but for now this is fine. 24:22.840 --> 24:29.260 Now the next thing is we run snappy hex mesh override. 24:29.500 --> 24:38.160 If you want to play, uh, and learn what the command without uh, override does, then you can just 24:38.160 --> 24:41.160 run snappy hex mesh and see what it does to the time step. 24:41.430 --> 24:44.790 Apart from the zero time step, it will also have other time steps. 24:44.790 --> 24:48.210 If you want to play around that, you are free to do. 24:53.220 --> 24:56.460 Or the meshing is over very fast. 24:58.050 --> 25:00.090 Go here and give refresh. 25:00.090 --> 25:01.940 As you can see, this is our only mesh. 25:02.600 --> 25:03.980 This is all that we have. 25:04.160 --> 25:09.020 I'll close this and open it again so you can see the boundary conditions also properly. 25:10.880 --> 25:14.150 You see we have one pipe here, nothing else. 25:17.750 --> 25:24.050 This is what the inside the location will do. 25:28.000 --> 25:28.240 Okay. 25:29.080 --> 25:30.670 We have this mesh. 25:35.200 --> 25:36.880 So this is the internal mesh. 25:36.970 --> 25:44.080 So now you understood how to make snaps mesh outside as well as inside the geometry. 25:44.080 --> 25:49.330 This works pretty much with every geometry, even if it is an aircraft or a ship. 25:49.330 --> 25:49.950 It works. 25:49.950 --> 25:56.100 Okay, so you can, uh, try to download some STL files from Grabcad or any online sources. 25:56.100 --> 26:01.800 Or if you are good at designing, you can design your own STL files and try to do this. 26:03.780 --> 26:07.050 Uh, so we will now do check mesh quality command. 26:07.050 --> 26:09.210 So it will ensure the accuracy. 26:09.210 --> 26:16.640 The, uh, it will check the accuracy of the mesh that is generated by this mesh or any mesh. 26:16.640 --> 26:19.040 Even if you do just the block mesh, you can do this. 26:19.040 --> 26:22.970 And it can be helpful in identifying potential problems in the mesh. 26:22.970 --> 26:25.310 So the command is just check mesh. 26:25.310 --> 26:30.290 So now since we have all the mesh we will do check mesh. 26:30.620 --> 26:37.340 You see it has given all the necessary details right from at what time it has checked the number of 26:37.340 --> 26:42.720 points or faces, number of cells and how many hexahedral is there? 26:42.720 --> 26:44.130 How many prism is there? 26:44.130 --> 26:45.960 How many wedge or pyramid is there? 26:45.960 --> 26:46.200 What? 26:46.200 --> 26:48.120 How many polyhedral is there? 26:48.120 --> 26:56.100 And breakdown of the polyhedral number of faces like four face thing is 16 and six face thing is 118. 26:56.100 --> 27:00.630 So all these data you get this is very highly informative. 27:00.630 --> 27:04.970 And the topology like what are the patch names and what is the face? 27:05.540 --> 27:11.570 Uh, how many faces it has, how many points it has and how is the surface like is it okay on the topology. 27:11.960 --> 27:14.630 Is it closely seeing a closed singly connected. 27:14.630 --> 27:19.820 So these are the things which are uh known from this check mesh command. 27:19.940 --> 27:23.630 And it also gives us simply mesh okay or mesh problems. 27:23.630 --> 27:28.120 If there is some problem it will say what problem it face like one error or two error. 27:28.120 --> 27:30.190 Then you can check what problem it has. 27:30.190 --> 27:33.400 It says okay for boundary openness. 27:33.580 --> 27:35.770 It says okay for couple point location. 27:35.770 --> 27:39.430 For maximum skewness it is saying okay non orthogonality check. 27:39.430 --> 27:40.090 It is saying okay. 27:40.090 --> 27:42.520 So you can see the cell volume is okay. 27:42.520 --> 27:43.900 Phase area magnitude is okay. 27:43.900 --> 27:49.090 If something is not okay it will say one error and you can go back and check which is not fine okay. 27:49.090 --> 27:56.670 So this is the, uh, purpose of doing check mesh command and it will basically say skewness aspect 27:56.670 --> 28:00.450 ratio non orthogonality and mesh consistency checks. 28:00.450 --> 28:07.290 So it will give you an understanding on the common issue and their implication on the mesh and how it 28:07.290 --> 28:09.780 will affect your uh final simulation result. 28:09.960 --> 28:13.470 So tips for resolving common mesh is also found online. 28:13.470 --> 28:16.700 You can check the documentation on how to resolve certain things. 28:16.700 --> 28:22.340 Let's say if you are facing non orthogonality errors then you can uh, check the documentation and see 28:22.340 --> 28:23.390 how to resolve it. 28:24.230 --> 28:25.610 It is case by case thing. 28:25.610 --> 28:27.950 So we can't generally say how it is. 28:27.950 --> 28:36.500 So you have to learn by practicing snap x mesh and refining snap X mesh will generally resolve most 28:36.500 --> 28:38.750 of the errors, but sometimes it also needs some. 28:39.520 --> 28:45.430 personalized curation on the mesh and how it is generated on certain surfaces, and how much refined 28:45.430 --> 28:45.820 it is. 28:45.820 --> 28:52.240 So it all comes with practice and experience on how to make a better snappy hex mesh. 28:52.630 --> 28:55.000 So this is how our final mesh looked. 28:55.450 --> 28:56.980 And you have a task now. 28:56.980 --> 29:01.810 So create a new mesh where the mesh is inside the pipe using the same STL. 29:01.810 --> 29:11.460 But now you have to create, uh, how to say, uh, boundary layers inside the pipe. 29:11.520 --> 29:15.000 So we did not have the boundary layers when we did this. 29:15.000 --> 29:18.030 So you have to create boundary layers inside the pipe. 29:18.210 --> 29:19.470 And that is your task. 29:19.470 --> 29:21.210 You can practice it on your own. 29:22.380 --> 29:22.650 Okay. 29:22.650 --> 29:25.320 So if you have any questions feel free to contact me. 29:25.350 --> 29:26.820 See you in the next video. 29:26.820 --> 29:27.690 Thank you.