Export/interface Julia code to FMI/FMU standard .fmu

Specific Domains Modelling & Simulations
1

Hi everyone,

I will start to build a modeling framework.
I have simulation models which are built with Modelica, some others with Simulink/Simscape Toolbox and finally I have a control system designs with Julia and package JuMP. The control system aims to regulates the behavior of systems models (the master piece of my case study).

I have seen the FMI standard [1] and .fmu which is suitable to co-simulate from different tools and I would like to use it. I haved uploaded a figure to illustrate it.

My question is :

Does a julia package exist to export julia code to .fmu standard ? Or does a FMU interface to my julia code exist?

Thanks for all your answers.
julialangpost|554x392

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

2

I haven’t run across anything. This post suggests interest in doing that, but I don’t see an followup work at Modelon. Julia is good at wrapping C code. You might have a look at wrapping FMILibrary. You could also try using PyFMI through Julia’s Python interface.

Maybe you could convert your Modelica models to Modia. You might also have a look at OMJulia, a Julia interface to OpenModelica.

3

Thank for your answer and your links.

First of all, I have also a look here, where FMI import and export tools are listed. However according to the webpage, SimulatorToFMU is able to export pyhton script.

Second, I can convert the Modelica models to Modia, however I have also some models which are based on Simscape toolbox from Simulink. My constraint is to export julia script to .fmu, where the .fmu can be reutilised.

Third, I tried a different way. According to Dymola User Manuel page 407, external functions in orther languages is possible (C, C++, fortran and Java), and also link to DLL in this web page and of course Dymola user manuel page 412.

I tried to build a share library from my julia function with PackageCompiler.jl which it can be a external library in modelica/Dymola and, finaly export this modelica model with the external function in .fmu. It can be summarise as:

  1. Julia function : MyFunction.jl
  2. Build a share library from the julia function with build_shared_lib(“.jl”): Myfunction.dll
  3. External functions linking with DLL inside one Modelica model: ModelicaModelWithExternalFunction.mo
  4. Export the modelica model with the linking DLL to .FMU: MyFMU.fmu

I have implemented the 4 steps. My trial julia function return the cab number:

Base.@ccallable function julia_main()::Cint
return 1729
end

Then, with REPL : build_shared_lib(“TaxiCabNumber.jl”). REPL wrote “All done”. The builddir is created, with the TaxiCabNumber.dll, however a large amount of other .dll are also there.

builddir
builddir584Ă—860 60.4 KB

Then, I did my modelica.mo with external function. The modelica function is called add2bis (please note the julia_main) (I did like here case B):

function add2bis
output Real sum;
external “C” sum=julia_main() annotation (
LibraryDirectory=“modelica://TestFunctionExt2/Ressources/Library”,
Library=“TaxiCabNumber”);
end add2bis;

Then, I exported my modelica model (with add2bis call) to .fmu. My fmu is called TestfunctionsExt2.fmu. Dymola built the .fmu and I imported with simulink:
simulinkFMU

Then, I have run the simulation, and there was an error and simulation failed. I logged the FMU debug and I’ve got the following log:

Log From FMU: [category:, status:fmierror] Problem with loading TaxiCabNumber.dll

The .fmu is equiavalent to .zip, I have modified .fmu to .zip in order to have a look inside, and the two dll files are presents: TaxeCabNumber.dll and TestFunctionsExt2.dll.

I have the following questions:

  • Did I do some mistakes with the julia function according to PackageCompiler usage?
  • According to build_shared_lib, the generated library is called : buildir/libhello.{so,dylib,dll}. I do not understand the others files.dll from the buildir, what are their purpose? Also, what is the TaxiCabNumber.a?
  • Are there some limitations with the TaxiCabNumber.dll generated from build_shared_lib(“TaxiCabNumber.jl”)?

Thanks for all your answers. Warmest regards.

4

Hi,

Faced with a similar problem (coupling a Python or Julia optimization-based control algorithm with a Modelica model), I’ve started exploring an alternative way: call the Python/Julia code from Modelica.
Since embedding the Python interpreter is complicated, I’ve used a client-server approach with a messaging between the two. The code is available at:

This code is certainly not finished, by I’ve a running demo of a simple Python thermal controller with a simple Modelica thermal model. In an ideal world, I would have finished this along with a nice descriptive article for Modelica 2019 conf, but this didn’t happen :frowning:…

The Julia part is not started, but at least ZMQ.jl does exist (which is why I selected this messaging lib), while I had to do the low-level C code for the Modelica side (it would probably have been easy for somebody proficient in C, but this is not my case).

5

Hello Pierre,

Thanks a lot for NumRPC.

I tried a different way from my last post. Instead of building a .dll file from my julia code, I used the build_executable(“–.jl”, “–”) from PackageCompiler.jl to build an exe file. The .exe file is called inside the Modelica external C function with: system(“–.exe arg”);

I did the same steps as discribed in last post with the exe file. It works, dymola allows external C function wich run the exe, and I can export my Modelica package to fmu. I simulated the fmu with Simulink and it works too.

Regards

6

I wish a package for dealing with FMI/FMU for both import and import gets implemented someday also.

I think it would be a good selling point for Julia (in particular in industry -iaw fmi-standard.org it is supported by over 100 tools including Dymola, Modelica, Matlab and many others engineering tools-).

I have taken a look myself, but I feel I am not smart enough. :frowning:

At the end of the day, it looks like a zip file with a XML description file and the DLLs embedded. There seems to be C libraries for both import and export. So it looks like the blocks are nearly there.

Then just a stupid question just in case somebody knows (despite this is probably the wrong forum). Would it be a good idea to perform what fmi-standard tries to do in WebAssembly? I understand it is more “cross-platform” that FMU’s DLLs. Besides those “TaxicabNumber.a” and “TaxiCabNumber.dll” seem to be huge (>130Mb each) while exports to webassembly from julia seem to be tiny. Now even more when it looks like you don’t need to run it in a browser with things like life.

7

I also have a need for FMI/FMU support as I have to interface my Julia control systems algorithms with a fast physics model written in C++. The FMI/FMU standard is the only way I wish to go as that will also provide access to other code that supports the same standards. I will start using JuliaFMI soon but it would be good to know who else is using this.
Roger.

8

Hi all,
I just came across this topic and wanted to let you know that we recently published a FMI-Library for Julia called fmi.jl. We support full FMI 2.0 including CS and ME (with event handling). Windows and Linux, but Linux is currently not completely tested. FMI Cross Checks coming soon :wink:

1 Like
10

Hi, Have you seen GitHub - AnHeuermann/JuliaFMI: Simulator for FMUs in Julia (WIP) ?

11

My AnHeuermann/JuliaFMI was a first try on getting a FMU simulator to run with just Julia. I started the project to teach myself Julia and did most of it during my free time. As I don’t have much time to actually finish the simulator and stumbled across some fundamental difficulties, the current state is not satisfying.

@ThummeTo and I are in contact and I will probably archive the AnHeuermann/JuliaFMI repo soon. The fmi.jl project is actively developed, so it has the potential to become the default FMI tool for Julia based FMU import.

I guess FMU export on the other side would be best implemented in the available packages that deal with ODE/DAE simulation. According to this issue about FMI support it looks like ModelingToolkit.jl will add something in that direction.

12

@AnHeuermann I am using the fruits of your labours and I know you’ve been in contact with @jcook with whom I work. It’s great to know this really important work is convergent. I wish I were clever enough to contribute. However, as my colleague will tell you, I am an expert at breaking things and/or failing to get things to work. So I can lend a hindrance if required. :yum: