Stardis - The Monte-Carlo solver for coupled thermal problems
Stardis computes the propagator (aka the Green function) of coupled thermal systems under the linear assumption. Here coupled refers to conductive, convective and radiative transfers, and linear means that each modeled phenomena is represented using a model that is linear with temperature. Stardis can deal with complex geometries as well as high-frequency external solicitations over a very long period of time, relative to the characteristic time of the system.
Stardis does not compute temperature fields as a whole. It is designed to compute specific observables such as temperatures at probe points / dates or the mean temperature in a specific volume / period of time. In addition to temperature values, Stardis gives access to an evaluation of the propagator. The propagator is of great value for thermicist engineers as it gives some crucial information to analyse heat transfers in the system. It helps engineers answer questions like "Where from does the heat come at this location?". Propagators seamlessly agregate all the provided geometrical and physical information on the system in an unbiased and very-fast statistical model.
Stardis' algorithms are based on state-of-the-art Monte-Carlo method applied to radiative transfer physics (Delatorre [1]) combined with conduction's statistical formulation (Kac [2] and Muller [3]). Thanks to recent advances in computer graphics technology which has already been a game changer in the cinema industry (FX and animated movies), this theoretical framework can now be practically used on the most geometrically complex models. While this capability is part of the StarEngine Star3D library, it is internally powered by Intel® Rendering Framework: Embree.
Everytime the linear assumption is relevant, this theoretical framework allows to encompass all the heat transfer mecanisms (conductive-convective-radiative) in an unified statistical model. Such models can be solved by a Monte-Carlo approach just by sampling thermal paths. This can be seen as an extension of Monte-Carlo algorithms that solve radiative transfer by sampling optical paths. A main property of this approach is that the resulting algorithms does not rely on a volume mesh of the system.
An example of propagator use
Here is an example of practical use of a propagator (Green function), obtained by using the Stardis solver on a basic IGBT (a power semiconductor device):
- the object of interest is an IGBT,
- in this simple setting, the limit conditions of the system are fully defined by the bottom face tempature, and the environment temperature (exchange by convection),
- the value of interest is the core temperature (semiconductor junction) in the red-colored region of the IGBT which is also the source of dissipated power (see figure below),
- an estimate of the propagator has been precomputed using the Stardis Monte-Carlo solver from the 3D description of the model and the materials' properties (see figure below); the estimate is based on 10,000 paths and the resulting statistical uncertainty could be reduced by just sampling additional paths,
- on request, the propagator is applied to the user-provided temperatures and dissipated power; it acts as a super-fast direct model to compute the value of the core temperature together with its statistical uncertainty (standard error),
- as it carries temporal information, the propagator could be used in transient computations; in this case the input temperatures and dissipated power would be temporal data.
Dissipated power (in W/mm^{3}) | |
Air environment temperature (in K) | |
Bottom temperature (in K) | |
Core temperature | +/- |
Getting Stardis
Stardis is not a monolithic software, but a solver which can be integrated in various thermal engineering simulation toolchain for designing and optimizing. It is available on GNU/Linux and Microsoft Windows 7 or later. It is licensed under the GPLv3+ license and is thus distributed with its source code without additional fees. Refer to the license for details. A commercial license is also available to users for who the conditions of the GPLv3+ are too restrictive.
Stardis is closely developed with the physics laboratories behind its theoretical advances. Both physicists and programmers working on and with Stardis also do its theoretical and technical support. When you need help, you are always going to talk to someone that knows what they are doing.
Our commercial offer is versatile:
- we provide software developers with a Stardis SDK,
- we assist users in integrating Stardis in their workflow,
- we propose both theoretical and technical training and support,
- we develop custom software from / on top of Stardis,
- we have a study service based on the method implemented in Stardis.
To get access to Stardis and for more informations on our offer, please contact us.
Examples of integration and development
EDF R&D - SYRTHES
Mainly to address its own numerical simulation needs on thermal transfer, EDF R&D has been developing and maintaining the SYRTHES software for years. SYRTHES is dedicated to solve the conductive and radiative transfers in complex geometries and was designed to be integrated in the EDF software toolchain (SALOME). Inside SYRTHES, the conductive heat transfer solver is a finite elements solver and the radiative solver is based on radiosity.
Meso-Star staff and SYRTHES developers collaborate since 2015 to incorporate new features into SYRTHES, based on Stardis and its statistical point of view of the thermal transfers. The purpose is not to substitude new solvers to the existing ones, but rather to add some complementary features to help analysing numerical simulations results.
PROMES-CNRS - Star-Therm
Based on the Stardis solver which solves coupled conductive and radiative thermal problems, Meso-Star has developped the Star-Therm code for the PROMES-CNRS laboratory. Star-Therm is designed to deal with the geometric complexity of metallic or SiC foams. This type of foam is used in the design of heat exchangers in concentrated solar processes to transfer the energy of the incoming sunlight radiation to a working fluid.
The physical model in Star-Therm considers the incoming thermal radiation in vacuum and its coupling with conduction in an opaque solid. The incoming solar energy (radiation) is deposited at the surface of the metallic foam, which allows to determine a boundary temperature. Knowing boundary conditions and initial conditions, Star-Therm can compute the temperature at any position within the solid.