ANSYS13.0理论参考手册 - 图文

Theory Reference

Release 13.0 - ? 2010 SAS IP, Inc. All rights reserved.

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Theory Reference

Table of Contents

1. Analyzing Thermal Phenomena

1.1. How ANSYS Treats Thermal Modeling

1.1.1. Convection 1.1.2. Radiation

1.1.3. Special Effects 1.1.4. Far-Field Elements 1.2. Types of Thermal Analysis 1.3. Coupled-Field Analyses

1.4. About GUI Paths and Command Syntax

2. Steady-State Thermal Analysis

2.1. Available Elements for Thermal Analysis 2.2. Commands Used in Thermal Analyses 2.3. Tasks in a Thermal Analysis 2.4. Building the Model

2.4.1. Using the Surface Effect Elements 2.4.2. Creating Model Geometry

2.5. Applying Loads and Obtaining the Solution

2.5.1. Defining the Analysis Type 2.5.2. Applying Loads

2.5.3. Using Table and Function Boundary Conditions 2.5.4. Specifying Load Step Options 2.5.5. General Options 2.5.6. Nonlinear Options 2.5.7. Output Controls

2.5.8. Defining Analysis Options 2.5.9. Saving the Model 2.5.10. Solving the Model 2.6. Reviewing Analysis Results

2.6.1. Primary data 2.6.2. Derived data

2.6.3. Reading In Results 2.6.4. Reviewing Results

2.7. Example of a Steady-State Thermal Analysis (Command or Batch Method)

2.7.1. The Example Described 2.7.2. The Analysis Approach

2.7.3. Commands for Building and Solving the Model

2.8. Performing a Steady-State Thermal Analysis (GUI Method)

2.9. Performing a Thermal Analysis Using Tabular Boundary Conditions

2.9.1. Running the Sample Problem via Commands 2.9.2. Running the Sample Problem Interactively 2.10. Where to Find Other Examples of Thermal Analysis

3. Transient Thermal Analysis

3.1. Elements and Commands Used in Transient Thermal Analysis 3.2. Tasks in a Transient Thermal Analysis 3.3. Building the Model

3.4. Applying Loads and Obtaining a Solution

3.4.1. Defining the Analysis Type

3.4.2. Establishing Initial Conditions for Your Analysis 3.4.3. Specifying Load Step Options

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Theory Reference 3.4.4. Nonlinear Options 3.4.5. Output Controls 3.5. Saving the Model

3.5.1. Solving the Model 3.6. Reviewing Analysis Results

3.6.1. How to Review Results

3.6.2. Reviewing Results with the General Postprocessor

3.6.3. Reviewing Results with the Time History Postprocessor 3.7. Reviewing Results as Graphics or Tables

3.7.1. Reviewing Contour Displays 3.7.2. Reviewing Vector Displays 3.7.3. Reviewing Table Listings 3.8. Phase Change

3.9. Example of a Transient Thermal Analysis

3.9.1. The Example Described

3.9.2. Example Material Property Values

3.9.3. Example of a Transient Thermal Analysis (GUI Method) 3.9.4. Commands for Building and Solving the Model

3.10. Where to Find Other Examples of Transient Thermal Analysis

4. Radiation

4.1. Analyzing Radiation Problems 4.2. Definitions

4.3. Using LINK31, the Radiation Link Element

4.4. Modeling Radiation Between a Surface and a Point 4.5. Using the AUX12 Radiation Matrix Method

4.5.1. Procedure

4.5.2. Recommendations for Using Space Nodes

4.5.3. General Guidelines for the AUX12 Radiation Matrix Method 4.6. Using the Radiosity Solver Method

4.6.1. Procedure

4.6.2. Further Options for Static Analysis 4.7. Advanced Radiosity Options

4.8. Example of a 2-D Radiation Analysis Using the Radiosity Method (Command Method)

4.8.1. The Example Described

4.8.2. Commands for Building and Solving the Model

4.9. Example of a 2-D Radiation Analysis Using the Radiosity Method with Decimation and Symmetry (Command Method)

4.9.1. The Example Described

4.9.2. Commands for Building and Solving the Model

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Theory Reference

Chapter 1: Analyzing Thermal Phenomena

A thermal analysis calculates the temperature distribution and related thermal quantities in a system or component. Typical thermal quantities of interest are:

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The temperature distributions The amount of heat lost or gained Thermal gradients Thermal fluxes.

Thermal simulations play an important role in the design of many engineering applications, including internal combustion engines, turbines, heat exchangers, piping systems, and electronic components. In many cases, engineers follow a thermal analysis with a stress analysis to calculate thermal stresses (that is, stresses caused by thermal expansions or contractions). The following thermal analysis topics are available:

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How ANSYS Treats Thermal Modeling Types of Thermal Analysis Coupled-Field Analyses

About GUI Paths and Command Syntax

1.1. How ANSYS Treats Thermal Modeling

Only the ANSYS Multiphysics, ANSYS Mechanical, ANSYS Professional, and ANSYS FLOTRAN programs support thermal analyses.

The basis for thermal analysis in ANSYS is a heat balance equation obtained from the principle of conservation of energy. (For details, consult the Theory Reference for the Mechanical APDL and Mechanical Applications.) The finite element solution you perform via ANSYS calculates nodal temperatures, then uses the nodal temperatures to obtain other thermal quantities.

The ANSYS program handles all three primary modes of heat transfer: conduction, convection, and radiation.

1.1.1. Convection

You specify convection as a surface load on conducting solid elements or shell elements. You specify the convection film coefficient and the bulk fluid temperature at a surface; ANSYS then calculates the appropriate heat transfer across that surface. If the film coefficient depends upon temperature, you specify a table of temperatures along with the corresponding values of film coefficient at each temperature.

For use in finite element models with conducting bar elements (which do not allow a convection surface load), or in cases where the bulk fluid temperature is not known in advance, ANSYS offers a convection element named LINK34. In addition, you can use the FLOTRAN CFD elements to simulate details of the convection process, such as fluid velocities, local values of film coefficient and heat flux, and temperature distributions in both fluid and solid regions. 1.1.2. Radiation

ANSYS can solve radiation problems, which are nonlinear, in four ways:

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By using the radiation link element, LINK31 By using surface effect elements with the radiation option (SURF151 in 2-D modeling or SURF152 in 3-D modeling) 第 4 页 共 79 页

Theory Reference

? ? By generating a radiation matrix in AUX12 and using it as a superelement in a thermal analysis. By using the Radiosity Solver method.

For detailed information on these methods, see Radiation. 1.1.3. Special Effects

In addition to the three modes of heat transfer, you can account for special effects such as change of phase (melting or freezing) and internal heat generation (due to Joule heating, for example). For instance, you can use the thermal mass element MASS71 to specify temperature-dependent heat generation rates.

1.1.4. Far-Field Elements

Far-field elements allow you to model the effects of far-field decay without having to specify assumed boundary conditions at the exterior of the model. A single layer of elements is used to represent an exterior sub-domain of semi-infinite extent. For more information, see Far-Field Elements in the Low-Frequency Electromagnetic Analysis Guide. 1.2. Types of Thermal Analysis

ANSYS supports two types of thermal analysis:

1. A steady-state thermal analysis determines the temperature distribution and other thermal

quantities under steady-state loading conditions. A steady-state loading condition is a situation where heat storage effects varying over a period of time can be ignored.

2. A transient thermal analysis determines the temperature distribution and other thermal quantities

under conditions that vary over a period of time. 1.3. Coupled-Field Analyses

Some types of coupled-field analyses, such as thermal-structural and magnetic-thermal analyses, can represent thermal effects coupled with other phenomena. A coupled-field analysis can use

matrix-coupled ANSYS elements, or sequential load-vector coupling between separate simulations of each phenomenon. For more information on coupled-field analysis, see the Coupled-Field Analysis Guide. 1.4. About GUI Paths and Command Syntax

Throughout this document, you will see references to ANSYS commands and their equivalent GUI paths. Such references use only the command name, because you do not always need to specify all of a command's arguments, and specific combinations of command arguments perform different functions. For complete syntax descriptions of ANSYS commands, consult the Command Reference. The GUI paths shown are as complete as possible. In many cases, choosing the GUI path as shown will perform the function you want. In other cases, choosing the GUI path given in this document takes you to a menu or dialog box; from there, you must choose additional options that are appropriate for the specific task being performed.

For all types of analyses described in this guide, specify the material you will be simulating using an intuitive material model interface. This interface uses a hierarchical tree structure of material categories, which is intended to assist you in choosing the appropriate model for your analysis. See Material Model Interface in the Basic Analysis Guide for details on the material model interface.

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