Specifying Co-Simulation Settings in Simcenter STAR-CCM+

Specify the general settings for co-simulation with Abaqus in the Simcenter STAR-CCM+ simulation.

For co-simulation with Abaqus, you require two physics continua—one continuum for the physics that are solved in Simcenter STAR-CCM+ (the internal continuum) and one continuum that represents the physics in Abaqus (the external continuum).

To enable co-simulation, add the following physics models to the continuum that represents the physics that are solved in Simcenter STAR-CCM+:


Group	Physics Model
Optional Models	Co-Simulation
Co-Simulation Models	Abaqus
Abaqus Coupling Models	Select one of the following: Abaqus Explicit Coupling Abaqus Implicit Coupling For weakly coupled applications, where the effect of the structure on the fluid is much larger than the effect of the fluid on the structure, choose the explicit scheme. This method allows the simulations to exchange data not more than once per time-step. To maintain stability with this scheme, choose a sufficiently small coupling step. For strongly coupled applications, choose the implicit scheme, which allows the simulations to exchange data more than once per time-step, and therefore allows you to use larger time-steps than the explicit scheme.

To represent the physics in Abaqus, create an additional physics continuum.

For this continuum, select the following models in order:


Group box	Model
Optional Models	External Continuum
External Continuum	External Application (selected automatically)
External Application	Abaqus
Space	Surface Three Dimensional
Time	Implicit Unsteady or PISO Unsteady

Select the External Links > [Link 1] > Conditions > External Continua node and set Continua to the external physics continuum that you created.

In addition to the external continuum, you require a region that represents the external coupled parts:

Right-click the External Links > [Link 1] node and select Update.
Simcenter STAR-CCM+ adds a region under the Regions node, representing the external parts defined in the Abaqus simulation.
Specify an appropriate simulation time-step. The time-step size determines the time that it takes to solve a case, the stability of the solution, and its ability to capture all physical effects in the case.
- For steady-state cases with static loads, such as a deformed wing under fluid loads, the effect of time-step on accuracy is minimal. Use time-steps larger than the fluid or structural time scale for the best results.
- For cases with impact loading, such as fluid loads from sloshing, choose a time-step to resolve the peak load.
- For cases with oscillations or vibrations, such as releasing a pre-stressed cantilever, set a time-step of one hundredth (1/100) of the expected period of oscillations to capture the behavior of the system adequately.
To test if the time-step is sufficiently small for accuracy, run a simulation with a time-step of half the original value, and observe if there is a change in results.

Specify the options for launching and running the Abaqus job:

Expand the External Links > [Link 1] > Conditions node.
Select the Abaqus Release node and set Release to the Abaqus version that you are using.
You are advised to use one of the recommended versions, which appear as menu options. However, you can specify a different version by selecting the Custom option and using the corresponding [Link 1] > Values > Custom Code Version node.

In order to communicate with Abaqus, Simcenter STAR-CCM+ requires the location of the Abaqus co-simulation library file. On Linux, the required library file is libABQSMACseModules.so; on Windows, ABQSMACseModules.dll. The location of the library file depends on your Abaqus installation. Currently, Simcenter STAR-CCM+ allows you to save the path to the required library file using the $SIMULIA_CSE_LIBPATH environment variable.

Select the Load Partner Library Option node and set Option to one of the following:
- If you saved the path to the required library file using the $SIMULIA_CSE_LIBPATH environment variable, select Use Environment Variable.
- Otherwise, select Specify Library File. Then, select the [Link 1] > Values > Abaqus Library node and specify the absolute path to the Abaqus library file.

To specify how Simcenter STAR-CCM+ and Abaqus are connected, select the External Links > [Link 1] > Conditions > Launch Partner Option node and set Option as follows:


Launch Partner Option	Workflow
Launch Application	Select the External Links > [Link 1] > Values > Abaqus Execution node and set the Input File and Executable Name properties. Select the Values > Partner Job Name node and set Partner Job Name.
Do Not Launch	Select the External Links > [Link 1] > Values > Partner Job Name and set Partner Job Name. Select the Values > Partner Host:Port and set Partner Host:Port.

Note	Ensure that the Partner Job Name is different to the simulation file name.

For more information, see Abaqus Link Reference.

Define whether Simcenter STAR-CCM+ and Abaqus run simultaneously or sequentially. For implicit coupling, only sequential runs are possible.

Select the [Link 1] > Conditions > Time-Marching Sequence node.
- To run both codes simultaneously, set Option to Concurrent. This option is the least stable option. However, if the computation time per time-step is equal and the partition of processors is balanced, then running the codes simultaneously is faster than running sequentially—assuming that resources are available to run each code on separate hosts.
- To run the codes sequentially during the co-simulation, set Option to either Abaqus Leads or STAR-CCM+ Leads. The stability and computational costs for both these options are identical. Choose the leading code based on the physics that is being solved.
  The leading code should be solving the physics which is least sensitive to the initial prediction of the state at the end of the time-step. In mechanical co-simulation analyses, the guidelines is for the solid mechanics to lead. In this case, the solid uses the data from the previous time-step as initial prediction of the fluid loads at the end of the current time-step. It is not recommended to set the fluid mechanics to lead, as this requires a prediction of the displacement of the solid, which can be accelerating. It is also preferable for the solid to lead because the fluid mesh will be in sync with the solid mesh instead of lagging by an iteration. This is particularly important for explicit coupling.
  
  In thermal co-simulation analyses, it is best for the fluid mechanics to lead. In this case, the fluid uses the data from the previous time-step as initial prediction for the surface temperature at the end of the current time-step. It is not recommended to set the solid mechanics to lead, as this requires a prediction of the fluid heat transfer coefficient and ambient temperature, and the fluid may require several interactions before it is sufficiently converged to provide a reasonable estimate.
For more information, see Abaqus Link Reference.

Optionally, if you wish Simcenter STAR-CCM+ to automatically add co-simulation definitions to the Abaqus *.inp file, follow the respective steps below:


Launch Partner Option	Workflow
Launch Application	Select the [Link 1] > Conditions > Write Abaqus Keywords node and set Option to Yes. Use the [Link 1] > Values > Abaqus Keywords Step Number node to specify the step in the Abaqus input file where the co-simulation keywords are inserted.
Do Not Launch	Right-click the External Links > Link 1 node and select Write Abaqus Keywords... In the Open dialogue select the Abaqus *.inp file and select Open.

Optionally, if you wish to specify the maximum time Simcenter STAR-CCM+ waits for the partner operation:

Select the [Link 1] > Values > Partner Timeout node and set the Partner Timeout to the desired value.

Specify the method by which the transfer interval is determined:

Select the [Link 1] > Conditions > Coupling Negotiation Method and set Option to the desired method.
In some co-simulation cases, it can be expensive to run Simcenter STAR-CCM+ and Abaqus at the smallest time scale of the two codes. The user-defined coupling negotiation method allows you to specify different time intervals for each code. This coupling negotiation method is useful for loosely coupled problems. For more information, see Abaqus Link Reference.

When using the Abaqus Implicit Coupling model, specify the number of inner iterations between data exchanges:

Select the [Link 1] > Values > Inner Iterations per Exchange and set Number of Inner Iterations to the desired number of iterations.

For implicit coupling, you can also modify the stabilization option, tolerance, and the minimum number of exchanges for the imported fields. For more information, see Co-Simulation Zones Reference.

To specify the units for data that is imported from and exported to Abaqus:

Expand the [Link 1] > Values > External Code Units Manager node and set the units as required.

Specify whether the mapping of data at the fluid-structure interface is performed by Abaqus or Simcenter STAR-CCM+:

Select the [Link 1] > Conditions > Mapping Option node and choose the desired mapper code.
For more information, see Abaqus Link Reference.
Complete the simulation set-up by specifying the coupled boundaries and the fields that are exchanged with Abaqus. See Specifying the Coupled Boundaries and Specifying Exported and Imported Fields.