Meshing Tools in ANSYS and CFD Calculations

Have you flown in an aeroplane? I am sure you have.

Oh wait, what about using a computer? No, I am not crazy. You have used it as well, right?

And you have also crossed bridges at least once in your life, haven’t you? Did you know that ANSYS played a significant role in all these? What? Are you shocked?

In modern technology, ANSYS has played a role so crucial that it is being used right from something as complex as launching a rocket into space to designing a mobile phone. Yes. You know why is that? It is because ANSYS is an engineering simulation software.

[caption id="attachment_4311" align="aligncenter" width="3000"] The Delta II rocket carrying the GLAST spacecraft lifts off from Launch Complex 17-B.[/caption]

Meshing Tools In ANSYS

Meshing is an important part of any computer-aided engineering simulation. The mesh is directly involved with the accuracy and speed of the solution. The mesh creation takes time and so does generating results from CAE.

Hence, ANSYS gives the availability of a number of meshing tools which makes the solution better.

The ANSYS uses automation capabilities so that a mesh can be generated at the first try. This is done with the help of keying off physics preferences and using default settings. You, the user, can also update the information in the parameter change.

The mesh generated are complex pure hex to a highly detailed hybrid. The mesh is flexible in the ANSYS software and the right mesh can be put in the right place after a little practice.

The meshing tools in ANSYS are useful in –

• Solid models
• Fluid models
• Electromagnetic models
• Shell models
• 2-D models
• Beam models

Structures Modeling

This is used for the modeling of solids. The ANSYS is able to provide a quadratic tetrahedral meshing on even the most complex geometries. Despite the availability of an automatic contact detection and setup, to perform complex analysis, you need to have a little training or the guidance of an ANSYS help provider.

The meshing technology in ANSYS allows a physics preference that enables the meshing process to be automated. In an initial design, the mesh is generally created in a batch with a solution run. This identifies the points of interest in the design.

The physics features in structural dynamics are –

• Automated contact handling
• Automated beam and shell meshing
• CAD instance modeling
• Rigid body contact meshing
• Solver based refinement
• Gasket element meshing
• Periodic mesh matching

Fluid Modeling

The fluid models’ meshing offers an unstructured tri-surface and a quad-surface meshing. This meshing is driven by the curvature, proximity, quality and smoothness with a help of automatic feature that removes irrelevant features.

The automated surface modeling, a boundary layer technology (that includes an automatic proximity handling) and a front tet mesh algorithm; they all ascertain a high-quality meshing for fluid analysis.

Additional flexibility is achieved by –

• Extended sizing
• Matching
• Mapping
• Sweep controls

Just like a solid mesh, the user can create hex meshes in the fluid analysis as well. To capture the boundary layers, inflation can be added to the hex-meshing methods.

There are detailed tools as well that are used for hybrid meshing with hexahedral and tetrahedral regions. This is another way apart from tet and hex meshing. Moreover, these meshes can also mesh with a conformal or nonconformal mesh. When you are working with a large change in mesh size or an interface between different physics, this merging of meshes is really useful.

But I understand if you need total control of every step. This will allow you to create a highly crafted brick mesh or to mesh directly on scan data.

The electromagnetics models have narrow gaps between their parts. For example, the gap between a rotor and a stator. These gaps need to have a refined mesh. For that, you can use the ANSYS Emag meshing for this air gap meshing.

Shell and 2D Modeling

The shell modeling and meshing in ANSYS has a number of approaches that provide mesh to meet the physics involved.

For this, there are two approaches –

• One is the use of 2D axisymmetric or planar models. They are used to simplify a 3D physics in a 2D fashion.
• The other is the use of a 2D model which can be meshed with quad meshes, a quad-dominant mesh or all-triangle mesh.

The shell models are used when a 3D model has to be simplified to look like a set of thick sheets. This is useful when a sheet metal or thin structural parts are to mesh. The shell parts also mesh with quad meshes, quad-dominant meshes or all-triangle meshes.

Beam Modeling

In an ANSYS meshing, a geometry can be easily simplified to beam models or to create beam models that help users to easily construct simplified models for a quick analysis.

Computational Fluid Dynamics or CFD Calculations

The CFD uses numerical analysis and data structures to analyse and solve problems of fluid flow. To solve a CFD problem, several methods are available –

Discretisation Methods

The discretisation is transforming models, variable and equations into discrete counterparts. So, these methods are helpful for the numeric linear problems.

Finite Volume Method

The governing partial differential equations are presented in a conservative form and are solved for a discrete control volume.

Where, Q = vector of conserved variables

F = vector of fluxes

V = volume of control element

A = surface area of the control volume element

Finite Element Method

A weighted residual is formed in this method.

R_i = equation residual at an element vertex i

Q = conversation equation

W_i = weight factor

V^e = volume of element

Finite Difference Method

It is used in codes which have a complex geometry with high accuracy and efficiency.

Q = vector of conserved variables

F, G and H = flux in x, y and z-direction

Spectral Element Method

In this, the differential equation is multiplied by an arbitrary test function and then integrating the same over the whole domain.

Boundary Element Method

In this, the boundary is divided by the fluid into the surface mesh.

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