Simcenter STAR-CCM+ Link Reference

Simcenter STAR-CCM+ creates a link node when you activate the External continuum model. A link node represents a connection to an external application and allows you to specify co-simulation settings.

Under a link, you can define global settings, such as the connection method and concurrency mode, and co-simulation zones. Zones define sets of boundaries, or regions, where fields are exchanged with the partner simulation.

For details on the co-simulation zone settings, see Co-Simulation Zones Reference.

[Link 1] Properties

Link Type: Describes the type of connection. Read-only.

Link Priority: Specifies the order in which the links are executed.

Link Models

In a Simcenter STAR-CCM+ simulation, you access the co-simulation framework by activating co-simulation models in the physics continua. These models determine the physics of the coupling, including the fields that can be exchanged with the partner simulation.

Link models configure the connection to a partner application or file. The link icon changes based on the application, or file, that Simcenter STAR-CCM+ connects to through the link. The link model must be appropriate for the co-simulation or file export model selected in the physics continuum.

[Link 1] Conditions and Values

You specify the general settings of the co-simulation under the [Link 1] > Conditions and [Link 1] > Values nodes.

Launch Partner Option

Allows you to specify which method Simcenter STAR-CCM+ uses to launch the partner simulation. You only need to set this option in the simulation where you click Run, as Simcenter STAR-CCM+ automatically specifies consistent settings in the partner simulation.

Method	Corresponding Value Nodes
Do Not Launch Requires you to manually launch the partner simulation. Choose this option when the partner simulation (either a Simcenter STAR-CCM+ server or a Simcenter STAR-CCM+ API server) is already launched.	None
Launch Application Automatically launches a specified partner simulation on co-simulation run.	Launch Simcenter STAR-CCM+ Allows you to specify the options for launching the partner simulation in a new Simcenter STAR-CCM+ session. You can type the launch command directly, or click (Custom Editor) to select the simulation file and run mode in the Load Simulation dialog.
Launch Application via Command Line Automatically launches a specified partner program on co-simulation run. Selecting this option when coupling partner code to Simcenter STAR-CCM+ through the Co-Simulation API allows you to use a single shared license for both the Simcenter STAR-CCM+ and the Simcenter STAR-CCM+ API server. For more information, see Running a Co-Simulation with Partner Code.	Launch Command Line Allows you to type the command to launch the partner program.
Launch Application via Resource Manager Enables launching of the Co-Simulation via the Resource Manager Command Line. For more information see Resource Manager.	Simcenter STAR-CCM+ Simulation File Allows you to specify the simulation file to be launched using resource manager.

Connect Option

Allows you to specify which method the simulation uses to connect to the partner simulation. The available options depend on the selected Launch Partner Option method.

Method	Corresponding Value Nodes
Host:Port Allows you to specify the host and port where the partner simulation is running. You only need to set this option in the simulation where you click Run. When you click Run, the simulation connects to the partner simulation (either a Simcenter STAR-CCM+ simulation or a Simcenter STAR-CCM+ API server) that is running on the host and port that you specified. This option is available when you launch the simulations separately, that is, when `Launch Partner Option` is set to Do Not Launch.	Simcenter STAR-CCM+ Partner Host:Port Specifies the host and port where the partner simulation is running. Click (Custom Editor) to select the partner simulation from a list of running Simcenter STAR-CCM+ servers.
Connection Settings via File Allows you to connect simulations that are located in the same directory without specifying the connection details manually. When you select this option, Simcenter STAR-CCM+ automatically writes the host and port details of the simulation to a file with extension .cosim. The connection file is saved to the simulation directory and has the unique name, <Link>.<UUID>.cosim, where <Link> is the name of the co-simulation link and <UUID> is a unique identifier. If a simulation is new and has not been saved to a directory, Simcenter STAR-CCM+ saves the connection file to a temporary directory and then moves it to the relevant directory when you save the simulation. As this connection mode requires co-located connection files for both simulations, make sure that the simulations are in the same folder and that you activate this option in both simulations. When you click Run in either simulation, the simulation automatically connects to the partner simulation based on the host and port details that are contained in the partner connection file. This option is available when you launch the simulations separately, that is, when `Launch Partner Option` is set to Do Not Launch. Simcenter STAR-CCM+ automatically removes a connection file when you close the corresponding simulation. You can manually delete all connection files or regenerate a connection file using the co-simulation link right-click options. See Link Right-Click Actions.	Partner File (read only) Displays the name of the connection file containing the host and port details of the partner simulation. As Simcenter STAR-CCM+ identifies the partner connection file by link name, make sure that the co-simulation links associations are uniquely defined. That is, make sure that the directory does not contain more than two simulations with the same co-simulation link name.
Determined Automatically Available when the current simulation automatically launches the partner simulation, that is, when `Launch Partner Option` is set to either Launch Application or Launch Application via Command Line. The current simulation automatically connects to the partner simulation based on the partner launching details. You only need to set this option in the simulation where you click Run.	Assigned Partner Host:Port Displays the host and port where the partner simulation is running.

Concurrency Option

Allows you to specify which simulation runs first when the co-simulation starts. The available options are Lead and Lag. The leading simulation runs first and, when the exchange criteria are met, it sends initial data to the partner simulation. The lagging simulation waits for initial data from the leading simulation before running. When the exchange criteria are met, it sends data back to the leading simulation. The exchange process continues until the stopping criteria are satisfied.

Coupling Negotiation Option (Only for Explicit Coupling)

In unsteady simulations (explicit coupling), specifies the method to determine the time interval between data exchanges. The following methods are available:

Method	Corresponding Value Nodes
Matched Coupling Time The simulations exchange data at a specified time interval. The time interval between exchanges is the same in both simulations. Select this option in both simulations.	Transfer Interval Specifies the time interval at which the simulations exchange data. Make sure that you enter a value that is consistent with the simulations time-step (that is, the time-step that you set for the Implicit or Explicit Unsteady solvers).
Independent Coupling Time The simulations exchange data at a specified time interval. You set the time interval between exchanges independently in each simulation. This method is particularly useful when the simulations have different time scales, as the simulations can transfer data at convenient, independent frequencies. Select this option in both simulations.	Transfer Interval Specifies the time interval at which the current simulation exchanges data. Make sure that you enter a value that is consistent with the simulation time-step.
Time-Step The simulations exchange data at a time interval equal to the current simulation time-step. The time interval between exchanges is the same in both simulations. When using this option, set the partner simulation to use the Partner Time-Step option.	Transfer Interval Displays the time interval at which data is exchanged. Read only.
Partner Time-Step The simulations exchange data at a time interval equal to the partner simulation time-step. The time interval between exchanges is the same in both simulations. When using this option, set the partner simulation to use the Time-Step option.	Transfer Interval Displays the time interval at which data is exchanged. Read only.
Maximum Time-Step The simulations exchange data at a time interval equal to the largest of the time-steps (either the current simulation time-step or the partner simulation time-step). The time interval between exchanges is the same in both simulations.	Transfer Interval Displays the time interval at which data is exchanged. Read only.

Note	To prevent conflict, the simulation where you click Run dictates the method that is used in the partner simulation.

Time-Step Adjustment Option (Only for Explicit Coupling)

When using the explicit coupling scheme, the time interval between data exchanges cannot be less than the solution time-step. The time interval between exchanges is determined by the Coupling Negotiation Option (see Coupling Negotiation Option). Simcenter STAR-CCM+

If the transfer interval is greater than the simulation time-step, the Time-Step Adjustment Option allows you to choose the strategy for adjusting the time-step to reach the coupling time. The available options are:
- Adjust All Time-Steps—At each time-step, if the time to the next exchange is not an exact multiple of the simulation time-step, Simcenter STAR-CCM+ automatically reduces the size of the subsequent time-steps to meet the coupling time exactly.
- Adjust Last Time-Step—During the last time-step, if the time to the next exchange is not an exact multiple of the simulation time-step, Simcenter STAR-CCM+ automatically reduces the time-step to meet the coupling time exactly. The previous time-steps are not adjusted and coupling occurs when the coupling time is exactly met or exceeded.
- Do Not Adjust—Simcenter STAR-CCM+ does not adjust the simulation time-step. Coupling occurs when the coupling time is exactly met or exceeded.
If the transfer interval is equal to the simulation time-step or is an exact multiple of the simulation time-step, Simcenter STAR-CCM+ ignores the settings for this option, as the time-step always meets the coupling time exactly.
If the transfer interval is less than the simulation time-step, Simcenter STAR-CCM+ automatically reduces the simulation time-step to match the coupling time.

Mapping Option

Determines which simulation controls mapping of the exchanged fields. Corresponding mapper controls are added to the relevant [STAR-CCM+ Co-Simulation] > Zones > [Zone] > Values nodes. The available options are:

Map Before Export: After the solver runs, the simulation maps the solution data (that you specified for export) to the partner simulation mesh. To have consistent settings, select this option in both simulations, so that each simulation is responsible for mapping the fields that are sent to the partner. As both simulations are mapping data, each simulation has a copy of both meshes. This option is typically optimal when the solver is run in parallel.
Map After Import: Before the solver runs, the simulation maps the solution data (that you specified for import) from the partner simulation mesh. To have consistent settings, select this option in both simulations, so that each simulation is responsible for mapping the fields that are imported from the partner. As both simulations are mapping data, each simulation has a copy of both meshes.
Map Both Directions: Before the solver runs, the simulation maps the solution data (that you specified for import) from the partner simulation mesh. After the solver runs, the simulation maps the solution data (that you specified for export) to the partner simulation mesh. To have consistent settings, set the partner simulation to use Partner maps both directions. Only the simulation that is doing the mapping has a copy of both meshes. You can use this option when one of the simulations has many more CPUs than the other, that is, allow the simulation with the most processors to do the mapping.
Partner Maps Both Directions: The partner simulation maps both imported and exported data. To have consistent settings, set the partner simulation to use Map Both Directions.

Note	To prevent conflict, the simulation where you click Run enforces the correct mapping option in the partner simulation.

Disconnect Option

Allows you to specify whether the simulation disconnects or stays connected to the partner simulation when the co-simulation is complete.

Verbosity Level

Allows you to choose the solver verbosity, that is, the amount of information that is printed to the Output window.

Co-Simulation Progression

Displays the current stage in the co-simulation.

Connection to Partner Simulation

Displays the state of connection between the simulations.

External Continua

Allows you to select the physics continua that represent the partner simulation in the current simulation.

Field Exchange Controls (Only for Steady or Implicit Coupling)

Allows you to set the number of iterations between data exchanges:

When using the Steady Coupling model, specify the number of iterations to run before transferring data.
When using the Implicit Coupling model, which allows for data exchange at a frequency smaller than a simulation time-step, specify the number of inner iterations (within a simulation time-step) between exchanges.

Link Right-Click Actions

Simcenter STAR-CCM+ initiates several actions automatically based on the specified settings. For example, when you click Run in one of the simulations, the simulation automatically launches (if instructed to do so) and connects to its partner based on the specified launch and connect settings. Simcenter STAR-CCM+ also provides right-click options, to allow you to manually initiate the following actions:

Create New Zone: Allows you to create a new zone within an existing link.
Launch: The simulation launches the partner simulation based on the specified launching details (see Launch Partner Option), without connecting to it.
Connect: The simulation connects to the partner simulation, based on the specified connection settings (see Connect Option). This action does not modify the settings in the partner simulation, as consistency checks are performed during initialization.
Update: When you execute this action in either simulation, both simulations exchange metadata on the partner mesh, but no meshes or fields are transferred.
Import Meshes: The simulation imports the mesh from the partner simulation.
Map Export Fields: The simulation maps the solution data that are set for export from its mesh to the mesh imported from the partner simulation. This option is available only when you set Mapping Option to Map Before Export. See Mapping Option.
Import Fields: The simulation imports solution data from the partner.
Map Import Fields: The simulation maps the solution data that are set for import from the imported mesh to its mesh. This option is available only when you set Mapping Option to Map After Import. See Mapping Option.
Disconnect: Terminates the connection between the simulations.
Delete Connection Files: Deletes all connection files from the directory where the current simulation is located (see Connection Settings via File).
Create Connection File: Generates a connection file containing the host port details of the current simulation (see Connection Settings via File). This option does not generate a connection file for the partner simulation.
Show Status: Displays the co-simulation status in the Output window, provided that the Simcenter STAR-CCM+ Co-Simulation solver Verbosity is set to either Low or High.