ANSYS System Coupling Users Guide

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System Coupling User's Guide

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About This Manual

This manual describes how to use the System Coupling component to control otherwise independent physics solvers or external data sources so that they work together in a coupled analysis such as Fluid-Structure Interaction (FSI).

This manual contains the following chapters:

• System Coupling Overview (p. 1) describes how System Coupling works and the types of simulations you can perform.

• System Coupling Workspace (p. 7) describes how to use the System Coupling views in ANSYS Workbench to control the analysis.

• Workflows for System Coupling (p. 33) describes common workflow topics such as using the command line, and restarting coupled analyses

• Understanding the System Coupling Service (p. 41) describes files used by the Coupling Service, the com-munication technology, the run time environment, and the mapping technologies.

• Best Practice Guidelines for Using System Coupling (p. 73) describes best practices for using System Coupling. • Tutorial: Oscillating Plate with Two-Way Fluid-Structure Interaction (p. 79) guides you through performing

an example of a coupled analysis.

• Tutorial: Heat Transfer from a Heating Coil (p. 111) demonstrates how to execute a sequence of one-way thermal transfers in a heat exchanger using System Coupling.

Document Conventions

This section describes the conventions used in this document to distinguish between text, file names, system messages, and input that you need to type.

File and Directory Names

File names and directory names appear in this font:/usr/lib.

User Input

Input you must type exactly is shown like this:

cd /usr

Input Substitution

Input that you must supply in a command is shown like this:

fluent 3d -schost="HostName"

That is, you should actually type fluent 3d -schost=" " and substitute a computer's name for HostName.

Optional Arguments

Optional arguments are shown using square brackets:

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Here the argument -verbose is optional, but you must specify a suitable file name.

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System Coupling Overview

The ANSYS suite of analysis software facilitates creation of a spectrum of single- and multidisciplinary simulations. Multidisciplinary simulations are offered within the context of a single piece of software (for example, within one solver) and using various dedicated mechanisms to couple a single piece of software with others. Examples of the latter include mechanisms to import external data from static sources, and the Multi-Field External (MFX) solver used for co-simulation between ANSYS Mechanical MAPDL and ANSYS CFX. These coupling mechanisms provide optimal solutions for the analyses that follow the single, specific workflow that they were built to solve.

The System Coupling infrastructure discussed in this manual should be considered for generic workflows involving any number of analysis types, static data source and co-simulation participants, and data transfer quantities and directions. The Workbench System Coupling component system is an easy-to-use, all-purpose infrastructure that facilitates comprehensive multidisciplinary simulations between coupling participants.

Coupling participants are systems that will provide and/or consume data in a coupled analysis. Example systems in Workbench include:

• Analysis Systems – Steady-State Thermal, Transient Thermal, Static Structural, Transient Structural, Fluid Flow (Fluent)

• Component Systems – Fluent, External Data

The execution of analyses involving couplings between any of these participants is managed by the System Coupling Service, which is the runtime component of the System Coupling system. During exe-cution, a variety of one- and two-way data transfers are performed between coupling participants. For example, when multiple participants are executing their parts of a coupled analysis together, which is often referred to as co-simulation, they may engage in both one- and two-way data transfers as either a source or target. Similarly, when participants are providing access to existing results or data, which shall be referred to as a static data source, they may engage in only one-way data transfers as a source. This documentation provides a detailed description of capabilities supported by the System Coupling component system. All of these capabilities may, however, not yet be supported in conjunction with other Workbench systems. For information about systems that may act as participants in system couplings, see the summary of Supported System Couplings (p. 3).

For information regarding product licensing details and interactions with System Couplings, see Product Licensing Considerations when using System Coupling (p. 4).

To set up and execute a system coupling simulation, perform the following steps: 1. Create the project.

2. Add the individual, participant systems to the project. 3. Add the System Coupling system to the project.

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4. Set up each individual, participating system (generally from top-to-bottom, until you have completed all the required steps for your analysis).

5. Connect the systems together as shown in Figure 1: Example of Connecting a System Coupling Component System with Various Types of Systems (p. 2). For co-simulation participants and the External Data static data participant, connections are drawn from the participants’ Setup cells.

6. Set up the System Coupling system (see System Coupling Workspace (p. 7)).

Figure 1: Example of Connecting a System Coupling Component System with Various Types of Systems

It is important to note that updates of co-simulation participant (for example, a solver) Solution cells are disabled for Workbench systems connected to the System Coupling system; these updates (and execution of the respective solvers) are automatically initiated when the System Coupling Solution cell

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is updated. Note, however, that these updates respect all settings (for example parallel, precision, and so on) already made for them.

Important

Using System Coupling in conjunction with the Remote Solver Manager (RSM) is not supported. In the isolated case of Mechanical, the use of RSM for runs on a single local host is, however, permitted.

After you have updated the System Coupling Solution cell, you can: • Pause the analysis by interrupting its progress.

• Restart the analysis as described in the Initialization Controls (p. 10).

• Debug your system coupling simulation by using the system coupling command line arguments (see System Coupling Command Line Options (p. 34)). You can also perform additional debugging of the connected systems as described in Troubleshooting Two-Way Coupled Analyses Problems (p. 73).

• Use CFD-Post to simultaneously analyze the results of the simulation by:

– Connecting other participant systems’ Solution cells to the Results cell of the Fluid Flow system, or – Connecting all participant systems’ Solution cells to a Results component system that you introduce in

the schematic.

Supported System Couplings

The following is the list of supported coupling participants: • Fluent • Static Structural • Transient Structural • Steady-State Thermal • Transient Thermal • External Data

Fluent can be connected with any of the other supported participants. In addition, the Steady-State Thermal system can be connected with external data. Note that Steady-State and Static systems cannot be coupled with Transient systems.

Note

Only two coupling participants can be connected to the System Coupling system at one time. However, more than one System Coupling system may be introduced within the same project schematic.

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For information about using System Coupling with the ANSYS Fluent system in Workbench, see Perform-ing System CouplPerform-ing Simulations UsPerform-ing Fluent in Workbench in the Fluent in Workbench User's Guide. For information about restarting a coupled analysis with Fluent, see Restarting Fluent Analyses as Part of System Couplings.

For information about using System Coupling with the ANSYS Mechanical system in Workbench, see

System Coupling in the ANSYS Mechanical User's Guide. For information about restarting a coupled analysis with Mechanical, see Restarting Structural Mechanical Analyses as Part of System Coupling. For information about using System Coupling with the External Data system in Workbench, see External Data.

Product Licensing Considerations when using System Coupling

The licenses needed for System Coupling analyses are listed in Table 1: Licenses Required for Participating Systems in System Coupling (p. 4). No additional licenses are required for the System Coupling infra-structure.

The simultaneous execution of coupling participants currently precludes the use of the license sharing feature that exists for some product licenses. The following specific requirements consequently exist: • Distinct licenses are required for each coupling participant.

• Licensing preferences should be set to ‘Use a separate license for each application’ rather than ‘Share a single license between applications when possible.’

The requirements listed above are particularly relevant for ANSYS Academic products.

Table 1: Licenses Required for Participating Systems in System Coupling

Academic License Required Commercial License

Required System

Fluent • ANSYS CFD, • ANSYS Academic Associate, • ANSYS Fluent, or • ANSYS Academic Associate CFD,

• ANSYS Academic Research, • ANSYS Fluent Solver

• ANSYS Academic Research CFD, • ANSYS Academic Teaching

Advanced,

• ANSYS Academic Teaching Introductory, or

• ANSYS Academic Teaching CFD Static

Structural or

• ANSYS Academic Associate, • ANSYS Structural,

• ANSYS Mechanical, • ANSYS Academic Research, Transient

Structural

•

• ANSYS Academic Research

Mechanical, ANSYS Mechanical CFD-Flo,

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Academic License Required Commercial License

Required System

• ANSYS Academic Teaching Advanced,

• ANSYS Multiphysics, • ANSYS Structural Solver,

• ANSYS Mechanical Solver, or

• ANSYS Academic Teaching Mechanical

• ANSYS Multiphysics Solver Steady-State

Thermal or

• ANSYS Academic Associate, • ANSYS Mechanical,

• ANSYS Mechanical CFD-Flo, • ANSYS Academic Research, Transient

Thermal

•

• ANSYS Academic Research

Mechanical, ANSYS Mechanical Emag,

• ANSYS Multiphysics,

• ANSYS Academic Teaching Advanced,

• ANSYS Structural Solver, • ANSYS Mechanical Solver,

or

• ANSYS Multiphysics Solver _{• ANSYS Academic Teaching} Mechanical

No license is needed to run External Data. External

Data

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System Coupling Workspace

This chapter discusses the following topics:

Setting Up a Simulation that Uses System Coupling Components of the System Coupling Workspace Settings for Completing a System Coupling Setup Settings for Running a System Coupling Solution

Setting Up a Simulation that Uses System Coupling

The general workflow for setting up a System Coupling simulation is presented in System Coupling Overview (p. 1).

Most participant systems with connections originating from their Setup cells will participate in the analysis in a co-simulation mode (visually indicated in the Project Schematic with connections between the Setup cells, and different icons and colors for the Solution cells). The exception to this is the External Data participant system, since a connection originates from its Setup cell, but it acts as a static data participant. The Update option is disabled from within the right-click menu of the co-simulation parti-cipant systems' Solution cells because the update (and solution execution) is now controlled by the System Coupling Solution cell.

Note that using System Coupling in conjunction with the Remote Solver Manager (RSM) is not supported for runs on multiple host machines. In the isolated case of Mechanical, the use of RSM for runs on a single local host is, however, permitted.

The System Coupling system in the Project Schematic has two cells:

• Setup: Use this cell to see participant, region, and variable information, and to define analysis settings and data transfer between participants. Double-click the Setup cell, or right-click and choose Edit from the context menu to display the System Coupling workspace.

• Solution: Use this cell to solve a coupled analysis and to see solution information and charts monitors. Double-click the Solution cell, or right-click and choose Edit from the context menu to display the System Coupling workspace.

Components of the System Coupling Workspace

When you edit the Setup or Solution cells of the System Coupling component system, the same System Coupling workspace is displayed in a tab within your workbench project. The Outline view, Properties view, System Coupling Chart view, and Solution Information view are displayed by default. For more information about the tabbed views in Workbench, see Workbench Tabs and Views in the Workbench User's Guide.

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Figure 2: The System Coupling Workspace

See the following sections for additional information:

Outline View Properties View

System Coupling Chart View Solution Information View

Outline View

The Outline view (in the upper left corner of Figure 2: The System Coupling Workspace (p. 8)) presents various fields related to the coupling participants and to the setup and solution of the coupled systems. The deepest fields can be edited in the Properties view. For additional information, see Settings for Completing a System Coupling Setup (p. 9) and Settings for Running a System Coupling Solution (p. 28).

Properties View

The Properties view (in the lower left corner of Figure 2: The System Coupling Workspace (p. 8)) presents the properties of an editable item selected in the Outline view. For additional information,

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see Settings for Completing a System Coupling Setup (p. 9) and Settings for Running a System Coupling Solution (p. 28).

System Coupling Chart View

The System Coupling Chart view (in the upper right corner of Figure 2: The System Coupling Work-space (p. 8)) presents chart monitors in the System Coupling workspace during the solution process. For additional information, see System Coupling Chart (p. 29) and Using the System Coupling Chart View (p. 31).

Solution Information View

The Solution Information view (in the lower right corner of Figure 2: The System Coupling Work-space (p. 8)) presents a text-based solution log of information output during the execution of the coupled analysis. For additional information, see Solution Information (p. 28).

Settings for Completing a System Coupling Setup

This section describes:

• All the settings that appear in the Outline and Properties views under the “Setup” branch. • Context menus (that is, the menus that appear with a right-click) for the Setup cell.

See the following sections for additional information:

Analysis Settings Participants Data Transfers Data Transfer Rules Execution Control

Validation and State of the System Coupling Setup Cell System Coupling Setup Cell Context Menus

Expert Settings

Analysis Settings

The Analysis Settings field has the following properties: • Analysis Type

• Initialization Controls • Duration Controls • Step Controls

Suggested best practices for analysis settings are discussed in Analysis Settings Best Practices (p. 12).

Analysis Type

This option is used to define the overall coupling type for the analysis. The available options are:

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• General

– This is the only available option when one or more of the coupling participants is executing steady or static analyses. Note that mixed steady/static and transient analyses are not currently possible.

• Transient

– This is the only available option when all of the coupling participants are executing transient analyses.

Initialization Controls

This option is used to define the initialization controls available for all coupling types.

Coupling Initialization

The available options are: • Program Controlled

– For initial runs (that is, not restart runs), the initial time and step are each set to 0.

– For restart runs, the initial time and step are set to the values obtained from the latest valid restart point. • Restart Points (indicated by Step and Time)

– The system coupling simulation can have multiple restart points when Intermediate Restart Data Out-put (p. 22) is selected for either all coupling steps or for a set of coupling step intervals. The next coupled analysis will be started based on the restart point that you have selected.

For more information regarding restarts, see Restarting a System Coupling Analysis (p. 35).

Important

Program controlled or explicitly specified restart points only affect the coupling step and/or time used to restart the coupling service. Appropriate restart points must also be specified for the co-simulation participants that are part of the coupled analysis. For more information about coupling participants, see Restarting a System Coupling Analysis.

Duration Controls

This option is used to define the duration for the analysis.

Duration Defined By

The options available to define the duration of a coupled analysis are: • End Time

– Available only when the Analysis Type is Transient

– When the End Time option is used, the coupling service will execute coupling steps until the specified end time is reached. In a transient analysis, each coupling step is a time step (with the time interval specified by the step size). Note that the final coupling step size is reduced automatically, if needed, so that the specified end time is respected.

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– Some of the participant systems, such as ANSYS Mechanical, require the end time specified in their setup to be respected. When a coupled analysis involves one or more participants that require their setup’s end time be respected, then the maximum allowable end time for the coupled analysis is the minimum of the end times reported by such participants. In this case, a validation error will be reported if the coupled analysis’ specified end time is greater than the minimum identified.

Other participant systems, such as Fluent, can run past the end time specified. These participant systems have no effect on the allowable end time of the coupled analysis.

• Number of Steps

– Available only when the Analysis Type is General.

– When this option is used, the coupling service will execute coupling steps until the specified number of steps is reached.

Step Controls

The duration of the coupled analysis is broken into a sequence of coupling steps. Data transfers between the coupled solvers occur at the beginning of each coupling iteration within a coupling step. Coupling steps are always indexed. During the analysis, each new coupling step is started when:

• The coupling analysis duration has not been reached, and

• Either the maximum number of coupling iterations has been reached or the coupling step is converged. The available options are:

• Step Size

– If the coupling is defined in terms of time (a transient analysis), then a coupling step is associated with a time interval. The Step Size option specifies the time interval associated with each coupling step (in seconds). The final coupling step size is reduced automatically, if needed, so that the specified end time is respected. This reduction does not occur if the analysis duration is set by the Number of Steps. – The coupling step size is fixed for the duration of the System Coupling analysis, but it can be changed

when restarting the analysis. • Minimum Iterations

– This option allows specification of the fewest number of coupling iterations (at least 1) that could be ex-ecuted per coupling step.

– The specified minimum number of coupling iterations will be executed even if all measures of convergence are realized in fewer iterations.

• Maximum Iterations

– This option allows specification of the greatest number of coupling iterations that could possibly be ex-ecuted per coupling step.

– The specified maximum number of coupling iterations may not be executed if the analysis converges prior to the maximum iteration step being reached.

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Analysis Settings Best Practices

This section provides information about best practices for the following analysis settings:

General Analysis Type Transient Analysis Type

General Analysis Type

With a General analysis type, accurate coupled solutions can be achieved using different combinations of coupling step and coupling iteration specifications. The two cases described below are: when an analysis is solved using one coupling step, and when an analysis is solved using many coupling steps. Your choice of the combination of coupling steps and coupling iterations will:

• determine when result and/or restart data is able to be written, as the restart points can only be written at the end of a coupling step,

• allow you to balance the required file storage space and your need for analysis restarts,

• determine how you can use system coupling’s under relaxation factor (see Under-Relaxation

Al-gorithm (p. 54)) and ramping (see Ramping Algorithm (p. 53)), as these only apply to coupling iterations and cannot be applied over coupling steps.

For more information about restarting your coupled analysis, see Restarting a System Coupling Analys-is (p. 35).

Coupled Analysis solved using only one Coupling Step

A coupled analysis can be solved using only one coupling step. In this case, the coupling step is made up of many coupling iterations, and the solution is complete at the end of this one step. The analysis will continue executing until either the solution converges, or the specified maximum number of coupling iterations is completed. Only the end of a coupling step can be used as a restart point. When only one coupling step is used, results and restart data is generated only at the end of the solution. The analysis can be terminated as usual, but because intermediate restart data is not generated, the coupled analysis cannot be restarted if it terminates abnormally (due to an error, power interruption, etc.) or if you terminate it before the coupling step is completed. Using only one coupling step within a coupled analysis minimizes file storage space at the expense of the ability to restart the analysis. In-terrupting the analysis will not affect the analysis, because System Coupling will complete the current coupling step (and so complete the solution) before stopping the analysis. Ramping and under-relaxation can be applied across coupling iterations within the single coupling step.

Coupled Analysis solved using many Coupling Steps

A coupled analysis can be solved using many coupling steps. In this case, the coupling steps are made up of one or more coupling iterations. The analysis will continue executing until the specified number of coupling steps is completed. The transition from one coupling step to the next will occur when either the solution converges or the specified maximum number of coupling iterations is completed. Only the end of a coupling step can be used as a restart point (you are able to specify which steps are used). Results and restart data is generated at the specified restart points. If the analysis should terminate abnormally within a coupling step, you can restart the analysis from the previous restart point. By using more coupling steps with fewer coupling iterations per step, as opposed to one coupling step with many coupling iterations, more points at which restarts can be done are created. For difficult or complex analyses, which might experience abnormal terminations, more restart points allow restarts of the analysis (saving time and computational effort) at the expense of file storage space. System Coupling’s ramping and under-relaxation can be used across coupling iterations, but cannot be used across

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coupling steps, so System Coupling always transfers the full data transfer value at the end of each coupling step. Participant solvers may ramp data received from System Coupling at the coupling steps.

Transient Analysis Type

In a transient analysis, a coupling step is associated with a time interval by specifying the coupling step size (in seconds). With a time specified, a coupling step is the same as a time step within the transient analysis. The coupling step size used should reflect the time scales of the physics being studied. Note that unless sub-stepping is supported by the co-simulation participants being coupled, the coupling step size will typically be limited by the finest/smallest time scale of the co-simulation participants. If the analysis duration is specified using an End Time, then care should be taken to ensure that an integral number of coupling steps can be executed between the (re)start time and the specified end time. If this is not done, then the final coupling step size will be reduced to respect the specified end time, and this may introduce temporal discretization error into the coupled analysis.

The minimum number of coupling iterations may be set to a value larger than one (one is the default). If the data transfers have been under relaxed, you want to ensure a minimum number of coupling iter-ations is performed so that you iterate out the effect of the under-relaxation. Note that the data transfer convergence criteria would usually make this unnecessary.

The maximum number of coupling iterations should be set to allow complete convergence within each coupling step. Failure to fully converge within a given coupling step will modify the transient behavior from that step onward.

Participants

You can connect a participant system's Setup cell to the System Coupling Setup cell in the project schematic. The system coupling workspace displays a read-only summary of the participant data after a refresh of the System Coupling Setup cell. The participant summary includes:

System name

The name of the participant as presented in the schematic.

Regions

The collection of regions from and to which data can be transferred. A region is most often a point, line, surface or volume that is part (or all) of the geometry or topology of a coupling participant. Note, however, that equations or probe (monitored) values may also be considered as point regions.

Note

System Coupling requires participants to use 3D meshes, with data transfer regions consisting of element faces from a 3D mesh. System Coupling data transfers cannot exist in 2D meshes.

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Variables

The collection of input and output variables available for data transfer for each region. A variable is a

physical quantity such as force, length, or temperature that can be transferred between regions of participant systems. Variables are defined as input or output variables for the specific region.

Note

For structural applications, data transfers are limited to force and displacement; for thermal heat transfer applications data transfers are limited to temperature, heat flow, heat transfer coefficient (also known as “convection coefficient”), and near wall temper-ature (also know as “bulk tempertemper-ature” or “ambient tempertemper-ature”).

Data Transfers

A data transfer is defined by one source and one target region, and is able to transfer one variable type in one direction between two participants.

Each data transfer is defined by a variety of properties such as Source, Target, and Data Transfer

Control. A one-way coupled analysis has data transfer(s) in only one direction between the coupled

participants. In this type of analysis, the source region(s) are defined on only the participant sending data, and the target regions(s) are defined on only the participant whose solver is receiving the data. A two-way coupled analysis has data transfers in both directions between the coupled participants. In this type of analysis, source and target regions are defined on both participants. For example, consider a coupled two-way fluid-structure interaction analysis where a Fluent system and a Static Structural system are the two participants. The Fluent system would have a region which is the source region for the transfer of force, and the target region for the transfer of incremental displacement. The Static Structural system would have a region that is the source region for the transfer of incremental displace-ment, and the target region for the transfer of force.

Source/Target

Both Source and Target are each defined by a coupling participant along with a region and a variable defined within the context of that participant. For a two-way data transfer on one region, you define two individual data transfers. When you set up your data transfers, a top-down approach should be followed when selecting Source and Target. Select in this order:

1. Source Participant 2. Source Region 3. Source Variable 4. Target Participant 5. Target Region 6. Target Variable

Data Transfer Control

Additional properties can be defined to control the way in which the specified data transfers are executed. For each data transfer you can specify controls that determine:

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• The under relaxation factor applied to the transfer. • The convergence target.

• If ramping is used when applying data from the source-side to the target-side of the data transfer.

Transfer At

The Transfer At property is used to control when the data transfer is executed by the solver. The only available option is:

Start of Iteration

Transfer data at the start of every coupling iteration within a coupling step.

Under Relaxation Factor

The factor multiplying the current data transfer values when under-relaxing them against the previous values. This is overridden with unity in the first coupling iteration of every coupling step only when the Analysis Type is Transient.

Note

When under-relaxation is used, there is no guarantee that the full value from the source side of the data transfer is applied to the target by the end of the coupling step.

RMS Convergence Target

The target value used when evaluating convergence of the data transfer within a coupling iteration. The default value is 1e-2. The convergence target is RMS-based. For information regarding how this target is applied, see Evaluating Convergence of Data Transfers (p. 43).

Ramping

The available options for ramping controlled by System Coupling are as follows:

None

The full data transfer value is applied to the target side of the interface for all coupling iterations. No ramping is the default option.

Linear to Minimum Iterations

Within each coupling step, the ramping factor is used to linearly increase the change in the data transfer value applied to the target side of the interface. The data transfer value is increased during each coupling iteration until the specified minimum number of coupling iterations, , is reached. The ramping factor is applied to the change in the data transfer value from the previous coupling step. If there is no change in this value from the last coupling step, the full data transfer value is applied to the target side of the interface for all coupling iterations of that coupling step. During the coupling iteration (for ), the ramping factor equals . The full data transfer value is applied for all coupling iterations that are equal to or greater than the minimum number of coupling iterations. As is always reached, the full data transfer value is always applied by the end of each coupling step. This ramping behavior is demon-strated in Figure 3: Schematic of the Linear to Minimum Iterations Ramping Concept (p. 16)

for the case where the minimum number of iterations specified is 5.

When ramping using Linear to Minimum Iterations, if the minimum number of iterations is the same as the maximum number of iterations, then it is unlikely that the data transfer will

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converge. It is a best practice for your maximum iterations to be larger than your minimum iterations.

Figure 3: Schematic of the Linear to Minimum Iterations Ramping Concept

Ramping and under-relaxation are independent operations. Ramping is applied before under-relaxation.

Note

System Coupling’s ramping will interact with ramping behaviors within the participant systems. To understand the full ramping behavior, verify ramping settings to see if your participant system is ramping loads received from System Coupling. For ramping behavior in Mechanical, see System Coupling Related Settings in Mechanical in the ANSYS Mechanical User's Guide. See Working with Data Transfers (p. 16) for details about how to create, modify data transfers and do other common operations.

Working with Data Transfers

After you connect a participant system's Setup cell to the System Coupling Setup cell in the project schematic, the System Coupling workspace displays the regions and variables available to create data transfers after a Refresh of the Setup cell:

Create Data Transfer

There are different ways to create single and multiple data transfers using the Create Data Transfer context menu option.

Create uninitialized data transfer

Select the "Data Transfers" tree node in Outline view, then select Create Data Transfer from the context menu. This creates a new data transfer without any source or target properties defined. You can later modify the data transfer definition in Properties view.

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Create data transfers for two regions from different participants

Select two regions from different participants in the Outline view, then select Create Data Transfer from the context menu. This creates multiple data transfers that vary based on the following criteria: • Whether the two regions have the same topology

• Whether the input variable from one region has the same properties (such as the physical type) as the output variable from the other region

Create data transfers for single region

Select a region from a participant in the Outline view, then select Create Data Transfer from the context menu. This creates data transfers for each variable associated with the region. If the variable is an output variable, then the source participant, source region, and source variable are defined for the new data transfer. If the variable is an input variable, then the target participant, target region, and target variable are defined for the new data transfer.

Create a data transfer for single variable

Select a region from a participant in Outline view, select a variable in the Properties view, then select

Create Data Transfer from the context menu. This creates a new data transfer. If the selected variable

is an output variable, then the source participant, source region, and source variable are defined for the new data transfer. If the selected variable is an input variable, then the target participant, target region, and target variable is defined for the new data transfer.

Modify Data Transfer

Select a data transfer in the Outline view. The Properties view displays all the properties for the data transfer. You can modify all the properties for the data transfers in the same view.

Rename Data Transfer

Select a data transfer in the Outline view. Double-click to rename the data transfer.

Duplicate Data Transfer

Select one or more data transfers in the Outline view. Right-click and select Duplicate. This operation creates new data transfers with the same Source, Target, and Data Transfer Control properties. Note that you can change these properties as needed for these new data transfers.

Suppress Data Transfer

Select one or more data transfers in the Outline view. Right-click and select Suppress to prevent the data transfer.

Delete Data Transfer

Select one or more data transfers in the Outline view. Right-click and select Delete to remove them.

Note

If the data transfer definition is not valid or the data is invalidated for any reason, the state of the node will show as a ? and the incorrect properties will need to be changed.

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Data Transfer Rules

When you create data transfers in System Coupling, certain rules must be observed in order to correctly define the analysis.

Note

Participant data transfer regions must consist of triangular or quadrilateral faces. Polyhedral faces as well as faces with hanging nodes (cut-cells) are not supported in System Coupling. Currently, the following three types of transfers are supported. Details of these three types of transfers are given in Table 2: Data Transfers available in System Coupling (p. 18).

• Force transfers • Motion transfers • Thermal transfers

Force and motion transfers are typical for fluid-structure interaction problems, where a load to the structure is transferred from a fluid solver, and the deformations to the fluid are transferred from the structural solver. There can only be one force transfer and one motion transfer for each data transfer region.

Thermal transfers can be transferred between ANSYS Fluent and ANSYS Mechanical directly through System Coupling, or through the coupling of the External Data system. Three thermal transfers are available, each transferring different thermal variables. The three thermal transfers are described in the table below.

For one-way thermal transfers, only one of the three options below for thermal transfers can be defined for a given pair of source and target regions.

For way thermal transfers, two data transfers are set up on the same data transfer region. In a two-way transfer:

• the two variables, heat transfer coefficient and near wall temperature, cannot be transferred on the same data transfer region as heat flow, and

• a participant’s data transfer region cannot provide and receive the same thermal variable(s); for example, Fluent cannot send and receive temperature data on the same data transfer region.

Table 2: Data Transfers available in System Coupling

Data Transfer Direction Variable(s) Transferred

Transfer Type

Force transfer • • from a fluid solver to

a structural solver Force (VectorXYZ*)

Motion transfer** • • from a structural

solver to a fluid solver Incremental displacement

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Data Transfer Direction Variable(s) Transferred Transfer Type 1. Temperature transfer Thermal Data Transfers • from a structural solver to a fluid solver, or • Temperature (Scalar)

• from a fluid solver to a structural solver 2. Heat flow transfer • from a structural solver to a fluid solver, or • Heat flow (also known as

heat rate) (Scalar)

• from a fluid solver to a structural solver 3. A pair of

variables***

• • Heat transfer coefficient

(also known as convection coefficient)** (Scalar)

from a fluid solver to a structural solver

• Near wall temperature (also known as bulk

temperature, or ambient temperature)** (Scalar)

* Represents the force vector ( , , ) and the incremental displacements vector ( , , ) respectively.

**In a general coupled analysis, when the solver receiving the motion (such as Fluent) solves before or simultaneously to the solver sending the motion (such as Mechanical), then the incremental displacement transferred during the first coupling iteration of each coupling step is identically zero. This behavior can be changed by using GeneralAnalysis_IncrDisp_InitIterationValue_Zero in the

Expert Settings (p. 24).

***You must correctly define both variables in the data transfer in order for this thermal transfer to be valid.

Note

For a given target region, there can only be one source region. However, a given source region can send data to multiple target regions. In other words, 1-to-M data transfers are supported, where M is an integer and is greater than or equal to 1. Note that M-to-1 data transfers are not supported.

Execution Control

Execution Control has the following capabilities:

Co-Simulation Participant Sequencing Debug Output Control

Intermediate Restart Data Output

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Co-Simulation Participant Sequencing

The System Coupling system offers comprehensive control over the sequencing of co-simulation parti-cipants, and specifically over the data transfers that are required to obtain a solution. This is controlled through the settings in the Co-Sim Sequence. The participants are sequenced by assigning a sequence value, which is an integer value between 1 and the number of participants in the analysis, to each participant. Each participant executes its solutions (that is, all required data transfers, followed by ob-taining the equation solution) in the order of its sequence value, where the participants with the lower sequence values execute first. The coupled analysis will use sequential solutions or simultaneous solutions, depending on the assigned sequence values. This is described in more detail below.

Note

To improve solution stability, sequential solutions are used by default. Note as well that, to facilitate synchronization of interface geometry, participants that consume geomet-rical or mesh deformations (for example, the Fluids solver in a Fluid Structure Interaction analysis) are automatically assigned larger sequence values by default.

Additional information can also be found in Best Practice Guidelines for Using System Coupling (p. 73).

Sequential Solutions

A sequential solution is done when all co-simulation participants are assigned different solution sequence values. In particular, participants perform their solutions (that is, all required data transfers, followed by obtaining the equation solution) in the order of the sequence values specified in the user interface. Sequential solutions are optimal for analyses that involve strong physical couplings, because the most recent information from one participant is always used by subsequent participants. This typically translates into requiring the fewest coupling iteration per coupling step to reach a converged solution. However, it may not yield the shortest (wall-clock) solution time if the participants are run on different CPUs.

Simultaneous Solutions

A simultaneous solution is done when one or more co-simulation participants are assigned identical solution sequence values. In particular, when the same sequence value is applied to multiple participants, then all those participants perform their respective data transfers, after which those same participants perform their equation solutions simultaneously.

Simultaneous solutions are optimal for analyses that involve weak physical couplings because the most recent information from one co-simulation participant is not required by other simultaneously executed participants in order to reach a converged solution. Additionally, the overall (wall-clock) solution time may be reduced if the simultaneously executed participants are run on different CPUs. However, if used with co-simulation participants that exhibit strong physical couplings, simultaneous solutions may ad-versely affect the rate of convergence, and possibly lead to divergence.

Debug Output Control

The Debug Output entity under Execution Control in the outline model controls the level of debug information written in the System Coupling Log (*.scl) file during the execution of the solution. The basic level of detail included is controlled using one of the following levels:

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• Level 1 • Level 2 • Level 3 • Level 4 • All Levels

By default, the value set for the Global Level is applied to all stages of solution execution listed below. To use a different value for one or more of the specific stages of solution execution, change the value from Use Global Level to the desired output level.

Note that stages of solution execution that are associated with Data Transfers are grouped together, and have their own default Data Transfers Level value. To use a different value for one or more of these stages of solution execution, change the value from Use Data Transfers Level to the desired output level.

The following properties control the debug level for different sections of the log:

Startup

Controls the level of output from the start of the coupling service until creation of the "Summary of SC Setup" banner in the SCL file.

Participant Connection

Controls the level of output from the end of the setup validation until the Initial Synchronization syn-chronization point (that is, between the Setup Validation and System Coupling Summary banners).

Analysis Initialization

Controls the level of output from the end of the setup validation until the Analysis Initialization synchron-ization point (that is, between the System Coupling Summary and Solution banners).

Solution Initialization

Controls the level of output during the setup of coupling steps and coupling iterations. This output does not include information related to the data transfers.

Data Transfers

Specifies the debug output generated for data transfers. Note that header information for mapping is generated whenever the mesh coordinate or mesh topology output is requested. Similarly, header inform-ation for the data transfers is generated whenever the transfer data output is requested.

Data Transfers Level

Provides the default level for the different debug output controls in the Data Transfers group. If the debug level of any property in the Data Transfers group is set to Default, then the debug level of that entry is governed by the level set here. If the Data Transfers Level itself is set to Use Global

Level, then it derives its value from the default level defined for all debug output controls. Source Mesh Coordinates

Controls the level of output for mesh coordinates of the source region in all data transfers.

Source Mesh Topology

Controls the level of output for mesh topology (elements and nodes) of the source region in all data transfers.

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Source Data

Controls the level of output for the source data in all data transfers.

Target Mesh Coordinates

Controls the level of output for mesh coordinates of the source region in all data transfers.

Target Mesh Topology

Controls the level of output for mesh topology (elements and nodes) of the source region in all data transfers.

Target Data

Controls the level of output for the target data in all data transfers.

Convergence Checks

Controls the level of output from the Check Convergence synchronization point until the next synchron-ization point, which may be either Shutdown or Solution.

Shutdown

Controls the level of output after the Shutdown synchronization point.

For information about synchronization points, see Process Synchronization and Analysis Evolution (p. 41).

Note

The debug level for all the properties, except Default, can be set at any level. For the Default property, the available levels are from None to All Levels. Increasing levels always generate more detailed output. Note, as well, that the output level settings for each of the mesh co-ordinates, topology, and transfer data, control the number of lines of output generated. Specifically, 10L lines of data will be written for an output level setting of L (for example, 100 lines will be written for an output level of 2, or Level 2).

Intermediate Restart Data Output

The Intermediate Restart Data Output entity under Execution Control in the outline model allows the selection of time points at which restart data should be generated during the execution of the solution. Depending on the participant, the restart data may or may not be the same as the results data. Writing of results data for post-processing should be set from within the participant setup cell.

Important

During execution of the coupled analysis, co-simulation participants will automatically be requested to generate intermediate restart data at the same frequency as the System

Coupling service. Note that this feature only affects the frequency at which data is generated; the content of data is determined by the participant. To see if this feature is supported, see

Supported System Couplings (p. 3).

Choose one of the following options to control when restart data is produced.

None

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All steps

Restart output files are generated at the end of each coupling step.

At Step Interval

Restart output files are generated at the end of the coupling steps corresponding to the interval specified in the Step Interval box below.

Note

If you specify a Step Interval that is above or below the allowed limit, an error is dis-played; change the Step Interval as required.

Validation and State of the System Coupling Setup Cell

Validation of the Setup cell depends upon the validation of the individual nodes in the Tree View (for example, Analysis Settings and Data Transfer). If any of these nodes is invalid, it would be marked by a ? (Attention Required) in front of the Setup cell. Details regarding why validation failed are presented when the mouse pointer is hovered over the ? symbol.

System Coupling Setup Cell Context Menus

The System Coupling Setup cell has several context menus:

• Start/Stop highlighting linked nodes: From the Setup cell, this option controls whether cells that are related to the selected cell are highlighted in the Outline view.

• Create Data Transfer: From Data Transfers you can create one or more data transfers using this context menu. See Working with Data Transfers (p. 16) for details.

• Auto Show/Hide • Toolbar Option

• Rename: From Data Transfers you can rename the selected data transfers using this context menu. See

Working with Data Transfers (p. 16) for details.

• Duplicate: From Data Transfers you can duplicate the selected data transfers using this context menu. See

Working with Data Transfers (p. 16) for details.

• Display Validation Failure: Select this to display error messages when System Coupling setup settings are found to be incorrect due to validation problems.

• Add Property: From Execution Control>Expert Settings, you can add specific expert settings. See Expert Settings (p. 24) for details about these settings.

• Remove Property: From Execution Control>Expert Settings, you can remove specific expert settings. See

Expert Settings (p. 24) for details about these settings.

• Read restart points: From Properties of Analysis Settings>Initialization Controls>Coupling Initialization, you can use this command to populate the list of restart points. This command is useful for abnormal situations such as a workbench crash. In such situations, the restart point list may be empty even though the interme-diate restart files exist on your disk. Read restart points is used to repopulate your list of restart points, so that you can restart from a previously saved restart point.

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See Understanding Cell States in the Workbench User’s Guide for detailed information on typical cell states.

Expert Settings

This subsection is used to specify the expert settings that are available. Expert settings provide you with additional advanced controls for many of the settings available in the Outline and Properties views under the Setup branch.

• General Expert Settings

– DumpInterfaceMeshes (string)

The only valid value for this setting is CFDPost. When this expert setting is used, files named <Name of Data Transfer>source.csv or <Name of Data Transfer>target.csv are generated during the mapping process. These files report values of 0 and 1 for unmapped and mapped nodes, respectively. These files are appropriate for import into CFD-Post as user defined surfaces for the visualization of mapping data.

– MeshSyncOption (integer)

Value is 0, 1, 2, or 3 (default: 0). This setting is only relevant for coupled analyses with a participant that consumes geometric data (for example, the Fluids solver in a Fluid Structure Interaction ana-lysis, which receives displacement data). This setting can be used when the solution of the participant consuming geometrical data is either sequenced identically as, or sequenced before, the solution of the participant that provides the geometric data. Available options are:

→ 0 (default): If the maximum number of coupling iterations per coupling step is 1, then the solution sequence is changed so that the participant that consumes geometrical data is solved last. If the maximum number of coupling iterations per coupling step is greater than 1, then one additional coupling iteration is performed at the end of the coupling step and only the participant that consumes geometrical data is re-solved.

→ 1: Regardless of the maximum number of coupling iterations per coupling step, the solution sequence is changed so that within each coupling iteration, the participant that consumes geo-metrical data is solved last.

→ 2: Regardless of the maximum number of coupling iterations per coupling step, one additional coupling iteration is performed at the end of the coupling step and only the participant that consumes geometrical data is re-solved.

→ 3: No setup modifications are applied, and the solution proceeds with the specified participant sequencing.

– GeneralAnalysis_IncrDisp_InitIterationValue_Zero (integer)

Value is 0 or 1 (default: 1). This setting is only relevant in a general coupled analysis, when displace-ment is transferred, and when the solver receiving the displacedisplace-ment (such as Fluent) solves before or simultaneously to the solver sending the displacement data (such as Mechanical).

→ 1: During the first coupling iteration of each coupling step the displacement transferred to the target is 0 [m] (irrespective of the value provided by the source). This override of the transfer value is to avoid possible double displacement, which could create folding of the mesh.

ANSYS System Coupling Users Guide

System Coupling User's Guide

Table of Contents

About This Manual

Document Conventions

Technical Support

System Coupling Overview

Important

Supported System Couplings

Note

Product Licensing Considerations when using System Coupling

System Coupling Workspace

Setting Up a Simulation that Uses System Coupling

Components of the System Coupling Workspace

Outline View

Properties View

System Coupling Chart View

Solution Information View

Settings for Completing a System Coupling Setup

Analysis Settings

Analysis Type

Initialization Controls

Coupling Initialization

Important

Duration Controls

Duration Defined By

Step Controls

Analysis Settings Best Practices

General Analysis Type

Coupled Analysis solved using only one Coupling Step

Coupled Analysis solved using many Coupling Steps

Transient Analysis Type

Participants

Note

Note

Data Transfers

Note

Note

Working with Data Transfers

Note

Data Transfer Rules

Note

Note

Execution Control

Co-Simulation Participant Sequencing

Note

Sequential Solutions

Simultaneous Solutions

Debug Output Control

Note

Intermediate Restart Data Output

Important

Note

Validation and State of the System Coupling Setup Cell

System Coupling Setup Cell Context Menus

Expert Settings