What is difference between FMU and FMI?

The main difference between FMU (Functional Mock-up Unit) and FMI (Functional Mock-up Interface) lies in their roles and definitions within the context of model-based engineering and simulation:FMU (Functional Mock-up Unit): File format encapsulating dynamic system models, including inputs, outputs, parameters, and simulation algorithms.FMI (Functional Mock-up Interface): Standard interface specification defining interactions between FMUs and simulation environments, including importing, querying, exchanging data, and analyzing results.

How does Functional Mockup Interface work?

The Functional Mock-up Interface (FMI) is a standard for exchange and simulation of dynamic system model code.Model Export: Dynamic system model saved as an FMU, encapsulating inputs, outputs, parameters, and simulation code.Model Import: FMUs imported into simulation environment supporting FMI standard, querying for model information and code.Co-simulation: Multiple FMUs representing system components, each using its own numerical solver, exchanging data during simulation.Model Exchange: Simulation environment can simulate FMU, using a common numerical solver and error checking.Simulation Execution: Simulation time advances, with FMUs computing outputs based on inputs and updating internal states.Results Analysis: Results from each FMU analyzed post-simulation to evaluate system performance and make design decisions.

What is the FMI method?

The FMI method is a standardized protocol for integrating and interacting with Functional Mock-up Units (FMUs) in simulation environments. It covers importing FMUs, data exchange, model exchange, co-simulation, integration into workflows, and result analysis.

What is FMU used for?

FMU stands for Functional Mock-up Unit. It is used in the context of Model-Based System Engineering (MBSE) and refers to a standardized unit or encapsulation of a dynamic system model. FMUs are employed for model exchange and co-simulation across different simulation environments and tools. They enable interoperability between various modeling and simulation tools by encapsulating a model along with its inputs, outputs, parameters, and simulation algorithms. FMUs are used for tasks such as model integration, co-simulation, and model exchange in engineering and scientific domains, allowing users to combine models from different sources and perform comprehensive system-level simulations.

Modelica Functional Mockup Interface

Integration and Model Export Capabilities in Dymola

Dymola offers excellent capabilities to interface to other software tools and simulation environments. Along with this Dymola supports model export options such as Real time simulation, Binary model export, Source Code Generation.

FMI: Industry Standard for Simulation Code Exchange

Functional Mockup Interface (FMI) is a vendor-independent standard, developed by the Modelica Association, for combining simulation code modules (FMUs) from various tools. FMI offers two exchange formats: model exchange with a central solver for consistency, and co-simulation allowing embedded solvers for application-specific flexibility. It fosters a versatile simulation infrastructure.

The Advantage of FMI
FMI Support in Dymola

FA non-proprietary standard for exchange of simulation code

The Functional Mockup Interface (FMI) is an industry standard for combining simulation code modules (FMUs) from multiple tools and vendors. Developed under the auspices of the Modelica Association, the specification provides a well-defined and vendor-independent exchange format for code (binary or source) as well as associated data and documentation.

FMI is supported by many authoring tools, including tools which are not Modelica based, making it the ideal foundation for a vendor independent simulation infrastructure.
Choice of exchange formats

The FMI specification defines two exchange formats. FMI for model exchange defines the interface for simulation code modules that must be combined with a common, central, solver. This ensures a uniform numeric solution and reliable centralized simulation error control.

FMI for co-simulation defines the interface for code modules with embedded numeric solvers, as used by the generating tool. This approach gives the opportunity to embed dedicated solvers for the modeled application, and facilitates compatibility with simulation in the authoring tool.

Export Capabilities

Dymola has support for exporting models and model source code. Three export alternatives with different functionality are provided.

Real-time simulation
Binary model export
Source code generation

Real-time Simulation enables the model to be used in environments not supporting the Microsoft C compilers. It is specifically designed for real-time platforms, such as the dSPACE and xPC platforms that are supported by Dymola for Hardware-In-the-Loop (HIL) simulation. Real-time simulation is part of the standard Dymola product. The following restrictions apply

Real-time Simulation only allows export of models that use inline integration, i.e., that have embedded fixed-step integrators. The run-time routines exported using Real-time Simulation does not include the most advanced library routines.

Interfacing Other Software

DYMOLA can be easily integrated with other software.

FMI enables seamless integration of dynamic system models from various tools in Dymola. Importing FMUs allows easy inclusion of controllers or sub-systems, enhancing Modelica models with advanced capabilities.

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