An overview of what enables 1D/3D CFD co-simulation in Simcenter Amesim

In Simcenter Amesim, only external variables (and not internal variables) are exchanged with the CFD code CFD code , via interface blocks, sensors and actuator blocks. The variables sent to the CFD package are usually applied as boundary conditions, or as geometrical parameter settings. The variables are exchanged at specific intervals, called co-simulation time steps. These can be fixed in length, or scheduled by the co-simulation master.

Particular care must be given to the co-simulation time step, as it is a crucial factor in terms of the co-simulation’s stability stability . A correct balance must be struck between stability and performance. Indeed, high dynamics within the coupling can lead to instabilities – users must be aware of these dynamics, and take them into account while defining the co-simulation time step – failing to do this will, at best, cause the co-simulation to produce unrealistic results, possibly for it to fail due to the solution diverging.

Figure 29: The interactions between the 2 solvers present in a co-simulation scenario

Simcenter Amesim offers a number of different co-simulation configurations, namely:

• Co-simulation with Simcenter Amesim as Master, imposing the co-simulation time step and exchanging data with the companion software, of which an instance is running.

• Co-simulation with the third-party tool as Master, imposing the co-simulation time step and exchanging data with the Simcenter Amesim GUI, of which an instance is running.

• Co-simulation with the third-party tool as Master, running in a single process, and piloting the Simcenter Amesim model, which is present as a DLL (or shared library).

The third category of co-simulation is the UserCosim approach in Simcenter Amesim, and is the one you should use if you wish to co-simulate your Simcenter Amesim model with a third-party software package.

In this scenario, Simcenter Amesim does not need to be launched – indeed, when a user compiles a model in which a UserCosim interface block is present, a DLL (Dynamic Linked Library) is created, which the third-party software package can then load and pilot  using a specific API (Application Programming Interface) in order to carry out the co-simulation.

The strength of this API is that it enables the user not only to load the DLL and initialize the Simcenter Amesim model for simulation, but also to exchange variables with the CFD code, and define how these 1D variables should be associated with the 3D code. This affords you the flexibility (in terms of setting up the interface) that you need when co-simulating 1D models with 3D CFD.

Note

For more information about the API used in UserCosim, refer to Simple examples and Simcenter Amesim "UserCosim" API functions and parameters.