Mesh generation

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Mesh generation.

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In this video, we will generate a mesh.

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We will modify mesh settings and we will use local mesh control.

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In Fusion 360, let's carry on with our motorcycle rear set.

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At this point, we have three simulation models and each of these has a simulation study.

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This means that each of those studies will have its own mass generation.

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So for the purposes of this video we're going to focus on frame mount only.

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The reason we're going to focus on frame mount only is because it allows us to explore these mesh generation tools,

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without having to solve the mesh for all of the different studies.

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It's important to note that generating the mesh isn't strictly required to solve,

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as it happens at the time of solve if it hasn't already been generated.

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But previously generating a mesh before you solve allows you to make adjustments before committing to a solve process.

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To get started, you'll notice in the browser there's something called mesh.

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There's an i icon next to it which is hidden by default because no mesh has been generated yet.

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And a pencil icon to the right that allows you to edit mesh settings.

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For our purposes let's right click and select generate mesh.

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It will use the default settings in the simulation study and it will generate an initial mesh.

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When we look at this mesh, it's fairly coarse and it might be fine in some cases, but there might be areas of interest that we want to look at,

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and if we zoom in, you'll notice around the circular boss here that the mesh elements are not matching that circular profile,

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on the inside or outside or in the fillet areas.

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So when we think about how a mesh is generated, we need to understand what it's used for.

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When we solve the simulation study, the mesh elements are going to be carrying the load.

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So when we take a look at the constraints and the loads applied to a design,

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for example our fixed constraints and our pin constraints as well as our remote force.

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These are going to be transmitted through the mesh elements as they go through the design.

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The finer the mesh elements.

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The more accurate the results will be up to a certain point.

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So let's talk about how we can edit our mesh element sizes.

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We can do this by using the pencil icon next to mesh in the browser.

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We can right click and look at mesh settings or we can go to manage and take a look at our mesh settings in the overall settings section.

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You'll notice that we have mesh and adaptive mesh refinement.

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At the very top the study type is listed as static stress but we can actually change it from here if we wish to go to a nonlinear static stress,

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for example, keeping all of our setup information but for the purposes of this video, we're going to focus on mesh adjustments.

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We'll talk about adaptive mesh refinement and we'll use local mesh control.

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By default the average element size is model based and it has a 10% element size on the slider.

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We can reduce this down and we can get a finer mesh element.

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If we go below a certain point around 2 or 3%, we will often get a warning telling us that,

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below 3% a fine mesh will increase to high memory consumption.

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So we're going to say yes and I'm going to regenerate this mesh.

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Once we regenerate the mesh, we should see much smaller mesh element sizes but you'll notice that it took quite a bit longer.

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Now when we look at our mesh, those smaller mesh element sizes will give us more accurate results in general.

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Again, there is a point where the computation time is not going to increase the accuracy of the results,

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and in some instances it's not going to help at all depending on the design itself.

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So now that we've seen what a fine mesh looks like, let's go back to our mesh settings,

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and let's take a look at some of our other settings that we have in the advanced settings section.

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The element order set to linear or parabolic has an effect on the number of nodes that are used to create the mesh elements.

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While they're all triangular mesh elements,

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the parabolic mesh will have more points or nodes that are used to help conform that mesh to curved surfaces.

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You'll also note that there is a create curved mesh elements.

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This will help it again conform to those curved surfaces and give us a more accurate result.

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This will come at a cost though because the calculation time for those mesh elements especially in complex designs, will take longer.

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We also have other options such as turn angle, adjacent mesh size and max aspect ratio.

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These will make more sense once we start using our local mesh controls.

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For now, let's leave them how they're set by default and say Ok.

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Once we've made changes, it will now give us a warning telling us that the mesh is out of date.

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I'm going to generate this one more time before using my local mesh controls.

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Now you can see we have a much larger mesh element size more in line with our original mesh.

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I'm going to zoom into this fillet area and I'm going to go back to manage and I want to take a look at local mesh control.

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Local mesh control allows us to select edges or faces and we can have localized control of those mesh elements.

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We can select an entire body.

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So if we're working on a multi part assembly and we want to focus on a specific body, we can use that entire body selection.

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From here I'm going to set the mesh element size to 1 mm and I'm going to say Ok.

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Once again, the mesh is out of date so we need to regenerate it.

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What this allows us to do is determine the size of those mesh elements in one specific area of interest,

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and then Fusion 360 will automatically change the mesh elements around it to blend back out to the universal settings.

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Now that we've created a general mesh and we've used local mesh control,

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let's go back to our mesh settings and let's talk about some of those advanced settings that might have an effect here.

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When we take a look at the aspect ratio and the adjacent mesh sizes, these are going to affect the size difference between mesh elements.

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Because we're dealing with extremely small mesh elements and that fillet, we might want to change the adjacent size ratio.

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So that way we have smaller mesh elements blending out into the general mesh settings.

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Let's generate this mesh one last time before we talk about our last option, which is the adaptive mesh refinement.

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So now that we've modified those adjacent size ratios, you can see that we have smaller mesh elements as they blend out to those larger ones.

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Lastly, let's talk about adaptive mesh refinement.

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This adaptive refinement allows us to improve the mesh based on some computed results.

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So when we take a look at this, there are some things that we need to understand.

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The refinement control can be used based on von Mises first principle, third principle or total displacement.

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When we take a look at these different values, there are obviously different things that we need to consider.

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The Von Mises stress, for example is the equivalent stress in any of the given mesh elements.

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So if we have a yield strength that we're looking at, for example 200 M. P. a.

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That is where we would expect permanent deformation to happen and we can see that when we're looking at the VM or the von Mises stress plot.

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If we were to tailor the adaptive mesh refinement to the first principal stresses, those are looking at the tension in the model,

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and if we were to set it to third principle then it's looking at the compression,

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and when we're talking about using these for the baseline accuracy, what it's doing is it's refining the mesh, it's calculating those values.

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It's looking at those results and then it's adjusting the mesh and calculating it again.

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So when we're talking about the refinement control and we look at low, medium, high or custom,

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what we're actually doing is we're altering the number of refinements,

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and we're modifying the convergence tolerance and the portion of the elements to refine.

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So what actually happens is if we have stress concentration in a certain area,

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then it's going to be focusing on that area as well as slightly around it based on the portion of element sizes to refine.

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So it continues to refine those and it's looking for that convergence tolerance,

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whether or not the stress from the previous iteration of mesh is close enough to the stress of this next iteration.

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You can go into custom and you can have a large number of mesh refinements, but ultimately there is going to be a computation limit,

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if you use too much mass refinement or if the design has extremely sharp corners where the stress risers are, those things will never converge.

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So again, there is a limit.

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You don't want to simply go to infinity with these refinements, but it can be a helpful tool to look at.

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The last point about adaptive mesh refinement it's important to understand that we can use it for our example because we have a single load case.

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As soon as we have multiple load cases, it can no longer use adaptive mesh refinement,

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because it's not going to calculate for all of those different load cases, it can only look at one.

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So keeping those in mind, there are helpful tools to play with.

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For our example, we're going to focus on frame mount only, using that local mesh control in this fillet and modifying some of those settings.

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But again, make sure that you save often and make sure that you save this design before moving on.