Harmonic Response - Problem Description
Tutorial 10: Advanced Automeshing - Example 3 - -Using Custom Settings
The Custom Settings of the Surface Automeshing tool can manipulate the resultant surface mesh. To access Custom Settings,
1. Choose Tools/Automeshing/Surface Mesh.
2. Click the Sizes tab.
3. Click the Custom button.
The dialog box should look like Figure 10.15 below.
Figure 10.15 - Custom Settings in the Surface Meshing dialog box
Length Ratio
The Length Ratio setting can be used to specify the minimum edge length of any created element (with exception of elements that connect closely spaced vertices). By default the Length Ratio is 0.1, which mean that the minimum element size created will be limited to 10% of the value specified for the Maximum Edge Length. To highlight the use of this setting:
1. Undo the previous mesh.
2. Enter 10 in the Maximum Edge Length % box.
3. Enter 0.01 In the Length Ratio box.
4. Click Mesh.
Figure 10.16 below shows the result.
Figure 10.16 - Resultant Mesh with Maximum Edge Length of 10% and Length Ratio of 0.01
This combination of settings allows for relatively large and small elements to be created in one mesh. As you can see from Figure 10.16 above, the curvature of the holes is captured well with the small elements, which quickly grow into larger elements with distance away from the holes.
Maximum Increase
The change in element size across faces of geometry can be controlled with the Maximum Increase setting. This defines the percentage difference in edge length that is allowed between neighbouring elements.
Increasing this value gives a faster transition in element size from small geometric features to larger ones.
Reducing this value maintains a more gradual transition between element sizes.
A small Maximum Increase value will produce a better quality mesh, but introduce more elements. To demonstrate the use of this setting:
1. Undo the previous mesh.
3. Enter 8 in the Maximum Increase box.
4. Click Mesh.
5. Click Close.
Figure 10.17 below shows the result.
Figure 10.17 - Resultant Mesh with Maximum Increase of 8%
The effect of this setting is more prominent when compared to the mesh in Figure 10.16 above. The more stable graduation of element size has produced more elements overall, resulting in an improved mesh which is most obvious around the large centre circle.
Note
It is valid to enter a Maximum Increase value of zero. Such a value means that the increase in edge length between neighbouring elements is zero. Therefore the entire mesh will be composed of elements of a size dictated by the smallest edge length in the model.
Edges Per Circle
The Edges per Circle setting determines the minimum number of elements to be placed around a circle and effectively any curved edges. For this example, with no closely spaced vertices defining the geometry, the Edges per Circle setting is the one factor that forces some elements down to a size that approaches the Length Ratio setting.
If a circle is too small, placing the minimum number of elements specified could mean the edge length of those elements would be smaller than that defined by the Length Ratio. If that is so, the number of elements created around the small circle will be less than the minimum specified, as the governing control is the minimum edge length
specified by the length ratio. The minimum value that can be assigned to the Edges per Circle setting is 8. Again this is overridden if the length ratio is too large.
1. Undo the previous mesh.
2. Enter 8 In the Edges per Circle box.
3. Click Mesh.
4. Click Close.
5. Repeat these steps with Edges per Circle value of 34.
Figure 10.18 and Figure 10.19 below shows the Edges per Circle set to 8 and 34 respectively.
Figure 10.18 - Resultant Mesh with Edges per Circle set to 8
Figure 10.19 - Resultant Mesh with Edges per Circle set to 34
... on edges longer than
This parameter determines on which edges the Edges per Circle setting should be applied. By default this value is set to 0.0, meaning that the Edges per Circle setting is applicable to all edges. However, if this value is set such that it is greater than the circumference of a particular circle, that circle will not be assigned the specified minimum number of edges.
1. Undo the previous mesh.
2. Enter 10 In the ...on edges longer than box (this value is larger than the circumference of the two smaller circles).
3. Click Mesh.
4. Click Close.
Figure 10.20 below shows the result.
Figure 10.20 - Resultant Mesh with ...on edges longer than set to 10
The Edges per Circle and ...on edges longer than settings are not limited in their application to circles only, the settings apply to any edge with curvature. An edge with curvature has a radius of curvature, and based on this radius, a
circumference is derived.
This circumference is compared to the ...on edges longer than setting. If it is greater than that value, the edge is assigned a portion of the elements defined by the Edges per Circle value. The number of elements defined corresponds to the ratio of the edge length and the circumference of a circle with the same curvature. For example, if an edge has a length of 10mm and is shaped as a quarter arc of a circle, it is considered as a circle of length (circumference) 40mm.
An ...on edges longer than setting of less than 40mm will assign the minimum number of elements to that edge.