In year 2016 CDH AG acquired marketing, sales and support rights from scapos AG to distribute MpCCI products in Japan and USA. The MpCCI interface software is a vendor neutral solution for co-simulation and file-based data transfer. MpCCI supports a growing number of commercial as well as research simulation tools in different engineering disciplines.
The MpCCI CouplingEnvironment has been developed in order to provide an application independent interface for the direct coupling of different simulation codes. MpCCI CouplingEnvironment has been accepted as a ‘de facto’ neutral standard for simulation code coupling and provides a multi-physics framework. Within the MpCCI CouplingEnvironment the engineer can combine several ready to use models, define the application field and choose for the best-fit coupling method.
MpCCI CouplingEnvironment has already successfully been used in various application domains:
- Fluid-Structure-Interaction for Aero-Elasticity and flexible Components in Machinery Design
- Thermal Stress and Vibrations in Turbomachinery Applications
- Combined System and 3D Continuum Models for Vehicle and Machine Dynamics
- Coupled Fluid and Radiation for Automotive Thermal Management
- Thermal and Magneto-Hydrodynamic Effects in Electrical Components
- Fluid-Structure-Interactions in Bio-Medical Applications
MpCCI Coupling Environment employs a staggered approach for all co-simulation problems which can be defined as
- A globally explicit coupling method: the coupled fields are exchanged only once per coupling step. This solution is applicable to problems with weak physics coupling.
- An implicit iterative coupling method: the coupled fields are exchanged several times per coupling step until an overall stabilized solution is achieved and before advancing to the next coupling step. This approach is applicable to problems with strong physics coupling.
MpCCI Coupling Environment offers standard coupling algorithms to implement the above coupling approaches - e.g. Gauss-Seidel and Jacobi.
Gauss-Seidel coupling scheme is also known as serial or "Ping-Pong" algorithm where one code waits while the partner code proceeds.
© Photo Fraunhofer SCAI
Jacobi coupling scheme is also known as parallel algorithm where both analysis codes run concurrently.
In addition to these coupling algorithms different transfer options are provided to control the data exchange of the quantities:
- The data exchange can be defined as an optional or forced synchronization point. The optional synchronization point provides the alternative to activate the data exchange on request. This request can be triggered by the availability of the quantities or by a physical quantity criterion. This provides an adaptive coupling scheme where bi-directional and uni-directional data transfer can be mixed.
- The synchronization point can be defined at different coupling iteration step for a steady state solution, or at different coupling time step sizes for a transient solution. The coupling iteration step, resp. coupling time step size may differ from the solver iteration step, resp. time step size. By this way a sub-cycling has been added to the coupling algorithm.
Coupling analysis of steady state solutions
For stationary problems, it is assumed that there is exactly one solution of the coupled problem, which shall be found. The coupling algorithm does not have a big influence on the solution in this case.
Coupling analysis of transient solutions
Typical applications focus on the transient effect of the coupled solution, e.g. pressure oscillation, heat dissipation, etc. The fully transient analysis provides an accurate solution. As the solution is dominated by the time component several co-simulation approaches are supported by MpCCI CouplingEnvironment:
- Fixed coupling time step size: in this configuration both simulations are constrained to use the same coupling time step size during the complete co-simulation. The time step size is equally defined in each application in this case and there is no need to exchange this time information.
- Exchange of time step size: instead of using a fixed coupling time step size it is also possible to use adaptive time stepping. In this case the time step size is determined by one code and sent to the partner code, which changes its own time step to the received value.
- Non-matching time step size: codes may run at different local time stepping and also exchange data at non-matching points in time. MpCCI CouplingEnvironment takes care of a proper ‘interpolation in time’ for the coupled physical quantities. MpCCI CouplingEnvironment offers three different methods for the data time-interpolation: constant, linear, and cubic.
Coupling analysis of mixed solutions steady state and transient
A fully transient coupling is challenging because of the great disparities of the physical models between the coupled domains (e.g. fluid-structure, fluid-electromagnetics, FEM structural analysis and discrete element models for particles) and the high computational time. The main difficulty is due to the significant discrepancy of characteristic times since the transient phenomena in the fluid usually take place at a much smaller time scale than those in the solid. The fully transient coupling method describing the transient effects in both coupled domains leads to a highly accurate solution but might be too expensive for some applications. As a computationally cheaper mode you can couple transient models with a sequence of steady state models:
- Full-vehicle thermal management of driving cycles: In this coupling procedure you should adopt a coupling interval which is at least equal to the solid time step. The flow solution is considered as a sequence of steady state solutions and in the solid the fields evolve in a fully transient manner. This co-simulation provides a flexible solution approach to consider driving cycles. A good compromise between a high computational time and modeling of transient physics is provided by a co-simulation of the transient thermal model with steady-state fluid models in a pseudo-transient approach.
- Magnetohydrodynamic analysis for electric arcs: In this application you may assume a steady state computation of the electromagnetic phenomena because the electromagnetic phenomena are faster than the gas dynamic. The Maxwell equations will be solves as a sequence of steady state solutions whereas in the fluid the Navier-Stockes equations evolve in fully transient manner.
High performant coupling server
The MpCCI CouplingEnvironment offers a high performant exchange of data between the coupled codes. In a very simple but FSI-like benchmark two basic codes running on a standard workstation and exchange pseudo-physical data at high speed. For surface meshes of ~4K nodes on each side the internal server engine of the MpCCI CouplingEnvironment can execute
- up to ~400 exchanges per second if the mesh definitions in the coupled codes are incompatible and fixed (identical) coupling time steps are used on both sides
- if conformal mesh definitions and non-matching-time steps with a ratio of 1/10 are used the code with the coarser time step can send ~200 data sets per second while the ‘fine’ code can receive up to ~2,000 (interpolated-in-time) data sets per second
MpCCI CouplingEnvironment will automatically exchange the data between the meshes of two or more simulation codes by using the best-fit interpolation method and considering the nature of the quantities exchanged. The co-simulation application can exchange nearly any kind of data between the coupled codes; e.g. energy and momentum sources, material properties, boundary condition values, mesh definitions, or global quantities. To ensure best interoperability between different simulation codes the coupling procedures are independent from the utilized codes and coupling quantities definition: energy sources, e.g. joule heat; momentum sources, e.g. Lorentz forces; boundary conditions values, e.g. temperature, pressure. All details of the data exchange are automatically handled by a coupling manager behind the concise interface of MpCCI CouplingEnvironment.
Standard interfaces for commercial codes - MpCCI v4.4.2 (October 2015)
The MpCCI CouplingEnvironment supports most of the leading commercial codes for fluid-dynamics, structural analysis, electro-magnetic, and other disciplines:
The MpCCI CouplingEnvironment has an open Programming Interface (API) which can be used to adapt inhouse or further commercial codes. This API is designed as a general and discipline independent toolkit and can be used for different levels of co-simulation:
- Surface-2-Surface interface suitable for all simulation methods which provide a discretised surface definition, support for deformable walls, and physical quantities located on surface elements or nodes (e.g. for modelling methods like FEM/CSD, FEM/Radiation, FVM/CFD, DEM/Particles, SPH or FPM/fluid models, etc.)
- Volume-2-Volume coupling suitable for all simulation methods which provide a discretised volume definition and physical quantities located per volume element or per node (e.g. modelling methods like FVM/CFD, FEM/EMAG, etc.)
- Point-2-Surface coupling suitable for all system simulation tools using ‘control nodes’ and physical quantities related to these nodes (e.g. modelling methods MBS, 1D-CFD pipeline models, general control models, FMI-for-co-simulation, etc.)
FMI for Co-Simulation
Functional Mock-up Interface (FMI) is a tool independent standard to support both model exchange and co-simulation of dynamic models using a combination of xml-files and compiled C-code. The first version, FMI 1.0, was published in 2010, followed by FMI 2.0 in July 2014. The FMI development was initiated by Daimler AG with the goal to improve the exchange of simulation models between suppliers and OEMs. As of today, development of the standard continues through the participation of 16 companies and research institutes.
FMI is currently supported by 87 tools and is used by automotive and non-automotive organizations throughout Europe, Asia and North America.
3D simulations – e.g. Finite Element Methods (FEM), Multibody Systems (MBS) and Computational Fluid Dynamics (CFD) – focus on the behavior of single components and are usually very specialized to depict a small selection of physical phenomena in a very detailed manner. Systems simulations, on the other hand, focus on the overall nonlinear dynamic behavior of complex systems consisting of many components. With today’s computational power it is not farfetched to depict the behavior of single components in a complex system via coupling to a full 3D simulation tool.
To bring the two worlds together, a MpCCI code adapter to the “Fraunhofer EAS Master” has been implemented. With this new feature it becomes easy to couple a system of FMUs, simulated with the EAS Master, to a full 3D simulation (or co-simulation) using any of the CAE tools supported by MpCCI.