Comsol Multiphysics 4.0
11 March 2011
While the heavy simulation tools used for FEA or CFD have been widely adopted, systems simulation is still a relatively niche technology. Al Dean takes a look at Comsol Multiphysics, which aims to change just that
|Product||Comsol Multiphysics 4.0|
Comsol is a name I’ve been aware of for some time but I only recently got to sit down with the team to look at what the system does. If you’re not familiar with the name, the company’s product was formerly known as FEMLAB and has been around in one guise or another since the 1990s.
The product suite is comprised of a base level multiphysics platform. This means that it allows the definition and solving of all manner of complex engineering and physics-based problems and isn’t restricted to a specific domain.
The base level system provides everything needed to define and build meshes and FEA/CFD style problems, but also something more fundamental. Comsol also allows problems to be defined from fundamental physics - whether that’s using an extensive library of materials with physics definitions or down to the level of forming custom partial differential equations from scratch.
This means that users can develop their own applications if they wish.
The majority of the UI is then devoted to definition of those tree items (think material, physics definition, results) and visualisation of results. Perhaps a good place to start is to give you an idea of how the system works.
As with many systems today, there are wizard-based tools available to help set-up and define a study. This is not the stripped back ‘guide you by the hand’ type of affair found in many systems. Instead, it is designed to allow the efficient creation of your study within a system that has a lot of options - and as such it excels.
The starting point is to create the space in which your study occurs - whether that’s 1D, 2D or 3D (with options for axisymmetric conditions). The next stage is to define the physics required within your study.
Here, Comsol’s extensive support for the physical world stands out. Those familiar with more traditional FEA systems will be used to a few options at this point, but within Comsol there’s support for all the basics (such as linear and non-linear structural analysis, and fluid flow) plus a number of more specialised options that we’ll explore later.
The next stage is to define each with its own parameters and variables. Now that the basics are in place, the Model Builder is populated with a list of the physics within the project as well as more common aspects, such as materials and geometry that require further work.
Geometry is an interesting one as Comsol has links with the majority of mainstream design or engineering software. These ‘LiveLink’ tools allow integration with data, not only from SolidWorks, Pro/Engineer and Inventor but other common engineering tools such as Matlab.
The CAD tools links allow linking to geometric parameters in the native CAD data and this offers great potential for optimisation routines to be built. In terms of Matlab support, these seem to be pretty unique, allowing the user to combine Matlab with Comsol’s FEA tools.
Comsol decks can be saved out directly to Matlab’s native format as well as allowing the user to call on Matlab functionality to solve specific problems.
Materials definition is pretty standard for anyone involved in simulation. Comsol is supplied with an extensive library of pre-set materials and these can be adapted, if needs be, and applied to the geometry.
What’s interesting is how the subject of materials is handled considering the more open nature of the system. Comsol is much more free in terms of the types of physics and conditions that can be simulated compared to many simulation tools.
As a result, it may be the case that the materials used don’t necessarily have the values required for a specific study. To get over this, Comsol includes material checks to ensure that your material is suitable for the physics in use - if you get a green tick, you’re ready, if not, then you’ll need to add additional data. That data may come from a textbook or a supplier.
Alternatively, test data can be read and used to derive the required value by interpolating the data. The next steps depend entirely on the nature of your study, but follow a pretty familiar flow for anyone with simulation experience.
Meshing is of particular interest. There are automatic meshing tools that will define the mesh based on the physics being solved since each has its own requirements - but there’s a lot of control available too if you need it. Presets are available for the basics, such as tetrahedral meshing, but as with every aspect of the system, it’s possible to dive in and define everything from scratch.
When it comes to results visualisation, openness and flexibility are again key. Results are automatically created as per your set-up. It’s then a case of defining the specific images and reporting tools to show exactly what you want .
This is done by pulling in the results visualisation techniques from the mix of physics contained within your study. If you’re conducting a study that combines fluid flow with heat characteristics, then you have access to results display techniques appropriate to both and these can be combined to show exactly what you want.
Many designers and engineers are being turned on to the benefits of simulation - but there’s something of an issue with many of the highly CAD integrated tools.
Looking at the FEA and CFD tools out there, while they are all-encompassing and powerful, problems can arise when working on complex problems that can’t be easily categorised as structural mechanics or fluid/heat flow.
CFD and FEA tools are essentially black box/closed systems and you can only work on their terms. It’s hard to gain insight into how fluid flow/heat transfer affects structural performance and vice versa. And they don’t stand a chance if you’re looking to simulate a product like a fuel cell which not only combines these two disciplines but also adds electro magnetic and chemical reaction into the mix.
This is where a system such as Comsol steps in and excels. Within an environment like Comsol, there are no real constraints on the number of individual problems that can be combined as long as you can couple the equations together to achieve a realistic result.
The provision of preset templates and additional modules can save you much of the hard graft but even if there’s not a module available for your specific application you can dive in and build it yourself with access to the variables, equations and inputs at a core, fundamental level.
The most impressive thing about Comsol is that all of this is done within an environment that’s not overly complex and supports that experimentation process without too much of a learning overhead.
If you’re engaging in simulation, find yourself struggling with the black box nature of your existing simulation tools, then Comsol is worth investigation.
Comsol Multiphysics Specialist Modules
In the main body of this review we’ve discussed Comsol in general terms, but it should be clear that the system is incredibly flexible in terms of what can be set-up and solved.
All manner of physics can be pulled together to define your studies as and when required. Alongside this, the developers also offer a range of more specialised pre-defined physics models that couple together fundamental physics to solve specific problems.
The development of these new modules is driven by customer demand and they essentially collect together previously manual processes and add in tools to solve a specific task. If you’re working on highly complex simulation tasks, for example, then it’s worth exploring whether there are modules already available than can save you coupling together physics manually.
There are a couple of examples worth exploring starting with the wonderfully named AC/DC module.
The AC/DC module provides pre-sets for the simulation and modelling of resistors, capacitors, inductors, coils, motors, and sensors. While on the surface of things, simulation of these types of products is an electromagnetic problem, the important thing to note is that results are also influenced by other physics, such as thermal effects which can change the electrical properties.
There’s another module for the simulation of batteries and fuel cells. This is designed to study primary, secondary and tertiary current density distributions in electrochemical cells.
It also has specialised interfaces for lithium-ion, nickelmetal hydride and lead-acid battery chemistries - all of which can reduce simulation set-up times for those working in a rapidly advancing field that takes in structural mechanics, electromagnetics, chemical reactions, fluid flow, acoustics and heat transfer.
Multicore and Clusters
Comsol Multiphysics has been designed to run on standard PCs and supports Windows, Linux and Mac.
Its solver code is parallelised to take advantage of multicore processors, but for those with compute intensive problems it can also work with distributed clusters.
Unlike many of the leading simulation software providers, however, Comsol does not charge more based on the number of computers and processors that are used.