FhSim is a software tool and API for describing and simulating dynamic systems in the time domain. Systems are formulated as ordinary differential equations (ODEs), and FhSim provides multiple integration routines, optional 3D visualisation, and a plugin architecture for reusable simulation models called SimObjects.

A simulation is defined in terms of SimObjects, their parameters and interconnections. SimObjects are compiled into shared libraries and loaded at runtime. The simulation scenario — which objects to use, how they connect, and how the integrator runs — is described in an XML input file.

Which path is mine?

I want to…	Start here
Install FhSim and see it produce a result	Quick start — five minutes, self-contained
Run a model somebody else wrote	Running simulations, then Available model libraries
Write my own scenario XML against an existing model library	The FhSim input file
Know what units a number in the XML is in	Units and coordinate conventions
Write a new SimObject in C++	Setup developer environment, then Create a new SimObject
Call FhSim from my own program	Running FhSim from your own software
Fix an error message	Troubleshooting and Runtime errors and diagnostics
Upgrade a model from FhSim 2.x	Migrating to FhSim 3.0

Note: Writing a SimObject, and all but one of the Tutorials, require a C++ developer toolchain and a source build — an installer-only installation cannot follow them. Screenshots, videos and camera control is the exception: it needs only FhVis and an installed model library. Everything under Getting started, Running simulations and The FhSim input file works from an installer installation alone.

Getting started — Get installed and run your first simulation.
Running simulations — Run simulations with existing model libraries.
The FhSim input file — The FhSim XML input file format.
Running FhSim from your own software — Drive a simulation from code you write yourself: the shared library, an exported FMU, or the standalone executable.
Model development — Develop SimObjects and model libraries.
Tutorials — Hands-on tutorials.
Reference and appendix — Cheat sheet, troubleshooting, and migration notes.