Open-loop simulations for basic model checks

Open-loop simulation As an alternative to using signal sinks and sources as replacements for interface blocks to verify that your model runs correctly (or can at least be initialized) with its current configuration and resources (typically tables), you can temporarily change the interface type to Open-loop simulation in the Interface status display dialog box.

Figure 46: Interface status display

Note

You can open this dialog box in Sketch mode through the Interfaces menu.

This function allows you to perform minimal checks on the model by deactivating the connection with the companion tool without having to remove and replace the interface blocks.

Note

By default, the values of the model inputs (the interface block's outputs) are always zero when you perform an open-loop simulation. However, null inputs may not be suitable for some models (typically if absolute temperatures or absolute pressures are used as inputs). Before going to Simulation mode, you can define more meaningful (non-null) constant values in the Default start value column in the Interface Status window (which you can launch through the Interfaces

Interface status menu).

Figure 47: Example of non-null user-defined start value for a model input

Note

The values defined in the Interface status display window are stored in exported FMUs and are reused as default values during the initialization phase if the FMI importing tool does not assign start values for input variables. This can be useful when FMU end-users have no precise idea about suitable values for the initialization, or in the context of fully-automated processes to export, import and simulate FMUs. However, in most cases, and as specified in the FMI standard, it is the responsibility of the importing tool/user to initialize the FMUs with values consistent with the inputs sent to them.

Once you have verified that your model behaves correctly during open-loop simulations, you can switch back to your chosen interface type to reactivate it.