FMU

Description

According to the Functional Mock-up Interface standard (https://fmi-standard.org), “The Functional Mock-up Interface is a free standard that defines a container and an interface to exchange dynamic simulation models using a combination of XML files, binaries and C code, distributed as a ZIP file. It is supported by 170+ tools and maintained as a Modelica Association Project.”

The Functional Mock-up Interface (FMI) is an open standard for the interface that facilitates model coupling between many simulation tools. It defines a ZIP archive and an application programming interface (API) to exchange dynamic models using a combination of XML files, binaries, and C code: the Functional Mock-up Unit (FMU).

The Functional Mock-up Unit (FMU) is created following the FMI 2.0.4 standard specification. The chart below shows the different components included in an FMU:
Figure 1.


Co-Simulation and Model Exchange

FMI 2.0.4 supports two interface types:
Co-Simulation
  • Coupling of simulation tools.
  • Coupling of subsystem models, exported by a modeling environment, together with their solvers, as runnable code.
Figure 2.


Model Exchange
  • Models are described by differential, algebraic, and discrete equations with time, state, and step events.
  • Usually, an ODE/DAE solver.
Figure 3.


FMU in Flow Simulator

  • Flow Simulator supports "exporting" an FMU. “Import” of an FMU is not supported.
  • Only a co-simulation interface is supported.
  • File-based coupling has been implemented.
  • FMU supports both steady and transient cases.
  • The FMU file structure in the ZIP file:
    Figure 4.


FMU Creation in the GUI

FMUs work like components in Flow Simulator; an FMU does not have a chamber association. You can drag-and-drop an FMU from the Element Library.
Figure 5.


Figure 6.


Define Inputs and Outputs
Defining input and output variables using the Define Inputs and Define Outputs options are similar.
Figure 7.


Use the Select Entity or Add Properties menu to add entities.
  1. Click Select from View to select objects from the Flow Simulator model window. Select objects until the Select from View icon is clicked again, or the Define Inputs or Define Outputs window is closed.
  2. If you select Add Properties, empty Inputs or Outputs columns are created. Define each item.
  3. If you select Select Entity, then the Object Selection window is displayed. From here, enter the object ID in the Selection Range section.
    1. You can select more than one object. Use “,” to select the item ID, or use “-“ to define a range.
    2. Objects are selected based on the selected Object Type.
    Figure 8.


Gauge and manipulated variables contain the following fields:
Entity
Chamber, Element, Component, and Thermal Component.
ID
The ID of the object for flow objects, or thermal network ID for thermal components.
Name
The Input/Output Variable name. When using Select from View, the name depends on the “Entity” selected. The naming convention is:
name: {Property}_{Type(1st 2 chars)}_{id}_{idx1}_{idx2}.
Property
Input or Output property of the object.
IDX1
Specific property types. For example, the station number for some Tube element properties, or Combination Flow Element flow fraction table row numbers, or the Thermal Component type: Tnode, Conductor, Convector, Radiator, or Heat Flow.
IDX2
Specific property types. For example, circumferential wall side ID for some Incompressible Tube properties, or the Thermal Component ID.
IDX3
Specific property types. For example, the left or right emissivity value of a two-surface radiator.
Unit
Selectable unit of each property, used to define inputs in the selected unit.

Additional options include Remove Selected Properties and Remove All Properties.

Define File Names
File Name Option: Name of the FMU. For example, in this case, once the FMU is created, it is named “FMUFile.fmu”. This name is different from the name of the Flow Simulator model.
Log File Name: Name of the log file created by the FMU. By default, “FS_FMU_log.dat” is created in the resources folder of the unpacked FMU.
Exporting FMU
Export Option: Once all the parameters are set, the Flow Simulator model needs to be saved before exporting. Export creates an FMU by the name provided in the "File Name".
If any changes are made to the Flow Simulator model, you must save the model and export the FMU to get the latest changes into the FMU.
Zipping FMU (if the exported FMU is modified)
If the exported FMU must be extracted and modified, you must zip it manually. The following specification for zipping must be followed:
FMI specification 2.0.4, page 69 – Section 2.3: FMU Distribution
  • The extension of the ZIP file must be “.fmu”
  • The compression method for all files stored in the ZIP archive must be either 8 (“deflate”), or 0 (“store”).
  • Only files stored using compression method 8 (“deflate”) may be stored, with general purpose bit 3 set.
  • The field version needed to extract of the archive must not be higher than 2.0, and encryption must not be employed.
  • The archive must not be a split or spanned ZIP archive.
  • Links must not be used inside the ZIP archive.

These restrictions ensure broad compatibility of the archive with common ZIP processing tools and libraries.

Special Note for Transient Cases
While setting up a transient case for FMU creation, verify that Initial Conditions Options in the Run Control Parameters is set to Steady State Solution at Start Time.
Figure 9.


FMU .flo Entries

Index UI Name (.flo label) Description
1 Type (CPTYPE) Component Type. 5=Controller.
2 (SUBTYPE) FMU = 6.
3 Active (ACTIVE) Active or Inactive option for the FMU.
4 Debug (DEBUG) Not used for FMU.
5 Relation Type 1 (RELATION1) NONE: Always for FMU (Not used for FMU).
6 Relation Type 2 (RELATION2) NONE: Always for FMU (Not used for FMU).
7 Name (VARNAME) The Input/Output Variable name. When using Select from View, the name is determined by the Entity selected. The naming convention is:

name: {Property}_{Type(1st 2 chars)}_{id}_{idx1}_{idx2}.
8 (VARTYPE) “GAUGE”: Input

“MANIP”: Output
9 (ACT) Active or Inactive option for the Input or Output variable.
10 Entity (ITEMTYPE) Flow or thermal component that is defined as an input or output variable in the FMU to be considered or affected during the run time.

Input and Output: “ELEMENT”, “CHAMBER”, “COMPONENT”, “THERMAL”.

Output only: “MISSION”.
11 ID Chamber/Element/Component ID or Thermal Network ID.
12 IDX1 List of Flow Component specific properties. For example, the station number for some properties of the Tube element.

Thermal Component type: Tnode, Conductor, Convector, Radiator, or Heat Flow.
13 IDX2 List of Flow Component specific properties. For example, circumferential wall side ID for some Incompressible Tube properties.

Thermal Component ID.
14 IDX3 List of specific properties. For example, the left or right emissivity value of a two-surface radiator.
15 Property (PROPERTY) Selected entity property that is counted (as GAUGE) or altered (as MANIP) during the simulation.

See the full list of available items in this file:

<installation_directory>\Resources\misc_solver_files\controller_working_get_set.dat
16 Unit (UNIT_SET) Selectable unit of each property, used to define inputs in the selected unit.

References

  1. https://fmi-standard.org/