ANSYS Mechanical APDL耦合场分析指南

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"ANSYS Mechanical APDL Coupled-Field Analysis Guide Release 15.0" 在工程领域，耦合场分析（Coupled-Field Analysis）是一种综合不同工程学科（物理学领域）的分析方法，用于解决涉及多物理现象的复杂问题，因此也常被称为多物理场分析。这种分析的核心在于各个领域的结果相互影响，共同解决全局问题。耦合场分析分为单向耦合和双向耦合。例如，在热应力问题中，温度场会导致结构产生热应变，但结构的应变通常不会反过来影响温度分布，这就是单向耦合的例子。在这个过程中，无需在两个物理场之间迭代求解。然而，更复杂的场景涉及到双向耦合。以压电分析为例，它处理结构场和电场之间的交互：根据施加的位移求解电压分布，或者相反。另一个例子是流体-结构相互作用（FSI）问题，流体压力导致结构变形，而结构的变形又会改变流体的解决方案。这类问题需要在两个物理场之间进行迭代，直到达到收敛状态。 ANSYS Mechanical APDL是一款强大的工具，支持耦合场分析。它允许用户结合不同的物理场，如结构力学、热力学、电磁学等，来模拟实际工程问题中的复杂交互。通过ANSYS Workbench平台，用户可以设置和管理这些耦合的分析，实现多物理场的集成建模和求解。在进行耦合场分析时，通常包括以下步骤： 1. 定义模型：创建包含所有相关物理场的几何模型。 2. 分离和定义物理域：将模型划分为不同的物理区域，每个区域对应一个特定的物理场。 3. 应用边界条件：设定各物理场的输入参数，如载荷、初始条件和约束。 4. 设定耦合关系：明确哪些物理场之间存在耦合作用，以及它们如何相互影响。 5. 求解：运行分析，可能需要迭代以达到各物理场之间的平衡和收敛。 6. 后处理：评估结果，分析解决方案，可能包括绘制结果图、计算关键参数等。耦合场分析对于理解和预测现实世界中的许多工程问题至关重要，比如在航空航天、汽车工程、生物医学和能源领域等。通过ANSYS软件，工程师能够准确预测和优化设计，减少实验成本，提高产品性能。请注意，使用ANSYS软件进行耦合场分析时，需要遵循软件许可协议，尊重其知识产权，并确保软件的合法使用。同时，用户应具备一定的工程背景知识和软件操作技能，以充分利用该工具进行高级的多物理场模拟。

– Load Transfer Coupled Physics Analysis (p. 171)

– Unidirectional Load Transfer (p. 195)

ANSYS also offers the following additional coupled-field methods:

• Coupled Physics Circuit Simulation (p. 205)

• Reduced Order Modeling (p. 229)

1.1.1. Direct Method

The direct method usually involves just one analysis that uses a coupled-field element type containing

all necessary degrees of freedom. Coupling is handled by calculating element matrices or element load

vectors that contain all necessary terms. An example of a direct method coupled-field analysis is a

piezoelectric analysis using the PLANE223, SOLID226, or SOLID227 elements. Another example is MEMS

analysis with the TRANS126 element.

1.1.2. Load Transfer Methods

The load transfer methods involve two or more analyses, each belonging to a different field. You couple

the two fields by applying results from one analysis as loads in another analysis. There are different

types of load transfer analyses, explained in the following sections.

1.1.2.1. Load Transfer Coupled Analysis - Workbench: System Coupling

You can perform coupled-field analyses using a System Coupling component system in Workbench.

Specifically, you can set up a one-way or two-way fluid-structure interaction (FSI) analysis or thermal-

structural analysis by connecting a System Coupling component system to Mechanical, Fluent, and Ex-

ternal Data systems.

Refer to System Coupling in the Mechanical User's Guide for more information on this load transfer

method. If you are new to Workbench, see the Overview in the Workbench User's Guide to get started.

Workbench offers the combination of the core product solvers with project management tools that

manage the project workflow.

This coupled-field analysis method supports the structural element types shown in Table 1.1: Structural

Elements (p. 2).

Table 1.1: Structural Elements

SHELLSOLID

SHELL181SOLID185

SOLSH190SOLID186

SHELL281SOLID187

SOLID226

SOLID227

All thermal element types are supported; however, for SHELL131 and SHELL132 thermal shell elements,

only the paint option (KEYOPT(6)=1, TEMP DOF on the bottom) is supported, and the temperatures or

heat flows at the bottom are used in the coupling.

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Coupled-Field Analyses

When coupling Mechanical and Fluent for a thermal-structural analysis, the coupled field elements

SOLID226 and SOLID227 (KEYOPT(1)=11) need to be used in Mechanical. See Thermal-Fluid-Structural

Analyses using System Coupling in the ANSYS Mechanical User's Guide for details about how to set up

this type of analysis.

A system coupling analysis can be run from the command line, rather than by using the Workbench

user interface. If the system coupling simulation involves Mechanical APDL, see Starting an ANSYS Session

from the Command Level in the Operations Guide for more information.

1.1.2.2. Load Transfer Coupled Analysis - ANSYS Multi-field solver

The ANSYS Multi-field solver, available for a large class of coupled analysis problems, is an automated

tool for solving load transfer coupled field problems. It supersedes the physics file-based procedure

and provides a robust, accurate, and easy to use tool for solving load transfer coupled physics problems.

Each physics is created as a field with an independent solid model and mesh. Surfaces or volumes are

identified for coupled load transfer. A multi-field solver command set configures the problem and

defines the solution sequencing. Coupled loads are automatically transferred across dissimilar meshes

by the solver. The solver is applicable to static, harmonic, and transient analysis, depending on the

physics requirements. Any number of fields may be solved in a sequential (or mixed sequential-simul-

taneous) manner.

Two versions of the ANSYS Multi-field solver, designed for different applications, offer their own benefits

and different procedures:

• MFS - Single code: The basic ANSYS Multi-field solver used if the simulation involves small models with

all physics field contained within a single product executable (e.g., ANSYS Multiphysics). The MFS - Single

code solver uses iterative coupling where each physics is solved sequentially, and each matrix equation

is solved separately. The solver iterates between each physics field until loads transferred across the

physics interfaces converge.

• MFX - Multiple code: The enhanced ANSYS Multi-field solver used for simulations with physics fields dis-

tributed between more than one product executable (e.g., between ANSYS Multiphysics and ANSYS CFX).

The MFX solver can accommodate much larger models than the MFS version. The MFX - Multiple code

solver uses iterative coupling where each physics is solved either simultaneously or sequentially, and each

matrix equation is solved separately. The solver iterates between each physics field until loads transferred

across the physics interfaces converge.

See Multi-field Analysis Using Code Coupling (p. 145) for detailed procedures.

1.1.2.3. Load Transfer Coupled Analysis - Physics File

With a physics file-based load transfer, you must explicitly transfer loads using the physics environment.

An example of this type of analysis is a sequential thermal-stress analysis where nodal temperatures

from the thermal analysis are applied as "body force" loads in the subsequent stress analysis. The

physics analysis is based on a single finite element mesh across physics. You create physics files that

define the physics environment; these files configure the database and prepare the single mesh for a

given physics simulation. The general process is to read in the first physics file and solve. Then read in

the next physics field, specify the loads to be transferred, and solve the second physics. Use the LDREAD

command to link the different physics environments and apply the specified results data from the first

physics environment as loads for the next environment's solution across a node-node similar mesh in-

terface. You can also use LDREAD to read results from one analysis as loads in a subsequent analysis,

without the use of physics files. See Load Transfer Coupled Physics Analysis (p. 171) for detailed proced-

ures.

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Types of Coupled-Field Analysis

1.1.2.4. Load Transfer Coupled Analysis - Unidirectional Load Transfer

You can also couple a fluid-solid interaction analysis by unidirectional load transfer. This method requires

that you know that the fluid analysis results do not affect the solid loads significantly, or vice-versa.

Loads from an ANSYS Multiphysics analysis can be unidirectionally transferred to a CFX fluid analysis,

or loads from a CFX fluid analysis can be transferred to an ANSYS Multiphysics analysis. The load

transfer occurs external to the analyses. See Unidirectional Load Transfer (p. 195) for detailed procedures

on both ANSYS-to-CFX and CFX-to-ANSYS unidirectional methods.

1.1.3.When to Use Direct vs. Load Transfer

Direct coupling is advantageous when the coupled-field interaction involves strongly-coupled physics

or is highly nonlinear and is best solved in a single solution using a coupled formulation. Examples of

direct coupling include piezoelectric analysis, conjugate heat transfer with fluid flow, and circuit-elec-

tromagnetic analysis. Elements are specifically formulated to solve these coupled-field interactions directly.

For coupling situations which do not exhibit a high degree of nonlinear interaction, the load transfer

method is more efficient and flexible because you can perform the two analyses independently of each

other. Coupling may be recursive, where iterations between the different physics are performed until

the desired level of convergence is achieved. In a load transfer thermal-stress analysis, for example, you

can perform a nonlinear transient thermal analysis followed by a linear static stress analysis. You can

then use nodal temperatures from any load step or time-point in the thermal analysis as loads for the

stress analysis.

Direct coupling typically requires less user-intervention because the coupled-field elements handle the

load transfer. Some analyses must be done using direct coupling (such as piezoelectric analyses). The

load transfer method requires that you define more details and manually specify the loads to be

transferred, but offers more flexibility in that you can transfer loads between dissimilar meshes and

between different analyses.

The following tables provides some general guidelines on using each method.

Table 1.2: Load-Transfer Method: Summary of Physics Coupled and Application

Physics ApplicationPhysics Coupled

Varied, such as gas turbines, MEMS resonatorsThermal-structural

Induction heating, RF heating, Peltier coolersElectromagnetic-thermal, electromagnetic-

thermal-structural

MEMSElectrostatic-structural, electrostatic-structural-

fluidic

Solenoids, electromagnetic machinesMagnetic-structural

Aerospace, automative fuel, hydraulic systems,

MEMS fluid damping, drug delivery pumps,

heart valves

FSI, using MFX (CFX based) or using System

Coupling

Fluid handling systems, EFI, hydraulic systemsElectromagnetic-solid-fluid

Electronics coolingThermal-CFD

Table 1.3: Direct Method: Summary of Physics Coupled and Application

Physics ApplicationPhysics Coupled

Varied, such as gas turbines, MEMS resonatorsThermal-structural

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Coupled-Field Analyses

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