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Simulation Accuracy Setting (Mesh/Element)

For the proper finite element analysis, a model should be divided into smaller meshes, or elements, such as triangular, tetrahedral, or hexahedral ones.

Set the mesh size to control the division.

Also, set the element type and order, which influence the simulation accuracy.

1. How to Optimize the Simulation Accuracy

Generally, a smaller mesh size increases the number of meshes, which results in better accuracy and longer calculation time.

And 2nd-order elements result in better accuracy and longer calculation time than 1st-order elements.

It is ideal for Femtet users to perform their analysis with optimal simulation accuracy.

Here, "Optimal simulation accuracy" means

the accuracy achieved within allowable errors

in the allowable calculation time,

according to each user's individual situation.

You may substitute "optimal" with "preferable for the user case" herein.

The simulation error is explained here.

To achieve this optimal simulation accuracy, set the mesh size as well as element type and order.

2. Mesh Size Setting

There are two types of mesh sizes: general mesh size and specific mesh size.

The mesh size determines how finely the model is divided into meshes.

The general mesh size applies to the whole model. Unless individual bodies are set with mesh sizes, the model will be meshed using the general mesh size.

A specific mesh size can be set for a specific body or topology. For instance, the finer mesh size can be set on the area where higher analysis accuracy is required.

Using the specific mesh can achieve fast calculations while maintaining simulation accuracy. -> [Optimizing the Mesh Size]

Type	Note
General Mesh Size	This mesh size is applied to the whole model unless otherwise specified partially. A Large mesh size may be used to check the modeling, analysis condition, and attribute settings. For more accurate calculations, a smaller mesh size should be used. The results from the different general mesh size are shown in [General Mesh Size]. How to Set General Mesh Size On the [Model] tab, go to , click [Analysis Condition] . The [Analysis Condition Setting] dialog box will appear. On the [Mesh] tab, deselect [Calculate the general mesh size] and enter a value at [General mesh size]. See [Mesh Tab] for the detail.
Specific Mesh Size	It is not adequate to apply the general mesh size to the whole model that has an area where drastic field changes are expected. That may prevent proper calculations. By applying a smaller specific mesh size to areas with large field changes, and a larger specific mesh size to areas with small changes, high simulation accuracy can be achieved with fewer meshes. See [Specific Mesh Size] for examples. There are two methods. How to specify the mesh size of the body and topology. See [How to Set Specific Mesh Size for a Part of Model (Body and Topology)] for the detail. How to specify the mesh size of the specific domain. See [How to Set Specific Mesh Size for a Part of Model (Specific Domain)] for the detail. To analyze a thin plate with higher simulation accuracy, the mesh size only in the thickness direction can be set finely. See [How to Set Number of Mesh Divisions in Thickness].
Adaptive Mesh	Adaptive meshing automatically sets an appropriate mesh size for the area mentioned above. See [Adaptive Meshing] for examples. Also see [Mesh Tab] for setting. Technical details are explained on Technical Note [Adaptive Meshing].

3. Element Type Setting

Specifies element types (triangle or tetrahedron and rectangle or hexahedron) for meshing.

Set the element type on the [Mesh] tab in the analysis condition dialog box. See [Mesh Tab] for the detail.

It is not needed to change the default setting of triangle or tetrahedron.
For simple shapes that can be created using sweep meshing, using rectangular or hexahedral elements tends to improve the quality of mesh and simulation accuracy. -> [Sweep Mesh and Free Mesh]
- Using 1st-order triangular or tetrahedral elements can significantly reduce accuracy in stress analysis.
- Using 1st-order rectangular or hexahedral elements involves processes that prevent a decrease in accuracy in stress analysis. ->[Enhanced Assumed Strain Method]

4. Element Order Setting

Specifies element orders.

Set the element order on the [Mesh] tab in the analysis condition dialog box.

There are two element types.

Order of Element

Feature

Recommended cases

2nd-order Element

- More accurate than the 1st-order element.

- Calculation time is longer and uses more memory than the 1st-order element.

- When the better accuracy is required

1st-order Element

- Less accurate than the 2nd-order element.

- Calculation time is shorter than the 2nd-order element.

- Using 1st-order triangular or tetrahedral elements can significantly reduce accuracy in stress analysis.

- Using 1st-order rectangular or hexahedral elements involves processes that prevent a decrease in accuracy in stress analysis. ->[Enhanced Assumed Strain Method]

- When the model is complicated and the memory is short for 2nd-order element.

- When the shorter calculation time is required.

See also [Unknown Variables of Elements] for the difference between 1st- and 2nd-order elements.