# ANSYS order flow, the secondary development of documentation and HELP - understanding of mesh

Print View , by: **iSee** ,Total views: **22** ,Word Count: **1254** ,Date: Fri, 14 Aug 2009 Time: 4:05 PM

1 Introduction

There are two types of ANSYS finite element model-building approach: solid modeling and direct generation. The use of solid modeling, the first generation model to describe the geometry of the geometric model, and then by the ANSYS program modules in accordance with the specified size and shape of the geometry mesh to generate nodes and modules. For the direct generation of law, the need for manual definition of the location of each node and cell connections.

In general for smaller problems for the direct generation of law, frequently asked questions will need to pass to generate the geometric model of solid modeling, and then divided into its mesh generation finite element model. With the improvement of computer performance, model complexity and size are increasing, but also because of the direct generation of the limitations of their own gradually be eliminated, so divided the correct understanding of the purpose of the grid into the grid and master regardless of the method is a learning ANSYS or secondary **development** have an important role, especially when the model complexity, and some parts of the model grid the need for special treatment, this division of the grid on the depth of understanding of the role of become more pronounced.

2 commonly used methods of high-level grid

With more and more powerful functionality ANSYS computer performance and the rapid increase toward large-scale finite element analysis, and complex development, and the delineation of the concept of Grid also needs to shift from two-dimensional model of three-dimensional model to change. Described here mainly divided into three common high-level grid method, the correct understanding and grasp of these ideas into the grid for the second development is very important persons.

1) an extension of grid

Grid extension refers to an extension of a two-dimensional grid to generate a three-dimensional grid; three-dimensional mesh generation removed after the two-dimensional grid, grid extension steps generally include: cross-section of Mr. Cheng, the designated mesh density and carried out across the grid, drag the grid surface mesh generation, the designated unit properties, drag to complete the body mesh, the release of the plane has been chosen unit.

Here through an extension of a simple mesh examples to deepen their understanding of this understanding of mesh.

Figure 1, for example an extension of grid

The establishment as shown in Figure 1 and divided into the three-dimensional model grid, we can create end-z direction, and then divided into grids, through drag-and-drop method in the z direction shown in accordance with the plans and three-dimensional model of the size required, just a operation will be able to complete the transition from two-dimensional finite element model to the three-dimensional finite element model of transformation.

2) freedom of the grid mesh and the mapping

Mapped mesh grid and freedoms is the most commonly used ANSYS mesh of the two methods.

Free surface and the grid is a grid separated from the default settings, to generate the grid is easier to free the main steps:

a, Export MeshTool tool set free classified division;

b, recommend the use of smart grid mesh free, activate it and specify a size level. storage database.

c, divided by Mesh Grid button to start, according to pick-up devices in the [Pick All] to select all entities (recommended). Or use the command VMESH, ALL or AMESH, ALL.

Mapped mesh face and body due to certain requirements must be met to generate a grid map grid than to generate a free easy to generate more rules but the finite element model. When mapped mesh model must meet the following conditions:

a, surface must contain 3 or 4 lines (triangle or quadrilateral);

b, body must include the 4, 5, or 6 face (tetrahedron, prism, or hexahedron);

c, cell-to-edge partition must match;

d, side of the triangle or tetrahedron, the number of units must be an even split.

Free mesh grid mapping

Figure 2 Grid and free mapping grid

3) layered mesh

Layered mesh is mainly used to generate 2D linear analysis of the freedom of the transition grid, this method is widely used in the model has the following characteristics: parallel to the direction of the cell line a considerable size, the direction perpendicular to the line of unit size and the number of sharp change, when the boundary element analysis of high-precision requirements. Effect diagram in Figure 3.

Figure 3 Layered Grid View

3 mesh error estimates

ANSYS general-purpose post-processing contains discrete grid error estimates. Error estimation is based along the border unit of stress or lack of continuity of heat flow is the average node and not the average difference between the stress. Error estimation methods are mainly the following:

• the percentage of error energy sepc

• unit sdsg stress deviation

• unit of energy deviation serr

• stress, the lower limit of smnb smxb

Energy percentage of error is the choice of unit of displacement, stress, temperature or heat flux of a rough estimate. It can be used to compare similar load bearing structure is similar to the similar model. This value should normally be below 10%. If you do not choose other units, but only on the imposed choice in the node load or stress concentration points of the unit Department error values can sometimes reach 50% or more.

A bias unit is the unit stress on the stress of all the six sub-node to this node money the average stress difference between the maximum value.

Each unit is an alternative energy error error. Node with the unit on the margin of stress-related, used to calculate the energy unit chosen percentage of error.

Stress is not the estimated upper and lower limits of the maximum or minimum stress. Convinced that it defines a range. If there are no other verification of the evidence, we can not believe that the maximum stress is lower than the actual SMXB. **display** or list the maximum and minimum levels of stress include:

• estimate the upper limit - SMXB;

• estimate the lower limit - SMNB.

4 This summary

This paper describes the meshing of several common high-level methods and the ANSYS mesh error estimation methods, only a brief description, to understand the more detailed information is available through the ANSYS the help-Modeling and Meshing Guide section.

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