AcuSim 1.7

09 October 2008

Al Dean takes a look at the new kid on the computational fluid dynamics block and finds a system that uses technology from the FEA world to great effect in pushing the boundaries of what can be realistically simulated.

Product AcuSim 1.7
Company name Acusim + SSA
Price From £16,000 per year

It’s not often that you get to look at brand new technology, and it’s certainly not every day (or indeed every year) that you get to see a brand new CFD solver code. But this is exactly what I was presented with on a recent visit to SSA, which has just signed up as UK reseller for a new product from AcuSim.

As you might guess, you don’t start developing a new computational fluid dynamics software product willy-nilly, so it’s good to know that the team behind the product was formerly at Centric, developer of Spectrum, which was acquired by Ansys some time ago. Centric was one of the first companies to try its hand at fluid structure interaction simulation. If you’re not up to speed with this, it’s the ability to have both CFD and FEA working in concert to accurately simulate how fluids have an effect on the structure of a product and vice versa, to gain a true, real world understanding.

The AcuSim interface is well thought out, leads you through the process of setting up a CFD analysisand guides you to where you need to add information and set variables

Unlike many initial release simulation codes, I’m pleased to say that the AcuSim user interface, AcuConsole, is pretty well developed. It’s not all whizz bang and Windows ribbon based, but it’s clearly laid out, and the operations you need are arranged in a way that makes perfect sense.

The graphics display window takes up the vast majority of the user interface, for viewing, interrogating the mesh, boundary conditions and, ultimately, the results. File and view operations are in toolbars around that window, but the majority of the action is found in the tried and tested panel to the left, which contains an extensive list of all the inputs for each simulation run.

While this is a very long list, it provides you with a fantastic guide to setting up a CFD simulation, following industry standard workflows, where you begin by defining volumes with fluid properties (or movement or structure), then surfaces, then walls, inlets and outlets and so on. As you work through the list, it’s pretty clear where you need to add information. The system has a good number of presets libraries, such as material models for air, metals and fluids.

Unlike many other standalone CFD applications, AcuConsole is not supplied with any tools for creating geometry from scratch, so you need to import data from your CAD system. The system reads in data from Pro/Engineer (both parts and assemblies), Parasolid and ACIS, as well as Catia readers. It also reads in decks from other FEA systems, such as Nastran. Once your data is read in, then comes the fun bit – meshing. And in the case of AcuSim, all is not as you might expect.

Finite elements and CFD

What’s interesting about AcuSim is that the system doesn’t use the traditional CFD finite volume method of creating meshes, but instead uses one that’s more akin to finite element analysis, where highly ordered meshing is far less critical and models run quickly and accurately without the upfront effort typically associated with CFD. This also gives you huge benefits when you’re looking at more advanced simulation tasks, such as moving frames and complex geometric forms. The system also includes a pretty nifty set of mesh refinement tools for getting the exact mesh you require on wall boundaries without a great deal of input.

AcuSim is ideal for anyone interested in higher-level simulation tools at a more affordable price. In specifics, it’s ideal for those looking at fluid structure interaction at a high level and anyone with hyper accurate solution requirements

Another area in which this aspect of the system gives you huge benefits is fluid structure interaction (see the box for a brief guide). One of the challenges of fluid structure interaction is that the foundation meshing used in CFD (the fluid part) is dramatically different to that used in FEA (the structure part) and the interaction between the two needs to overcome this difference.
Of course, the reason a system like AcuSim is so interesting to those conducting that type of work (and it’s not alone in this approach – it may well be because there aren’t may FEA-based CFD codes out there), is that similar solution processes are used, so the process becomes more connected. AcuSolve is excellent for tying up to Abaqus in particular, so AcuSolve takes over control of both the fluid based calculations done in AcuSolve and the structural simulation done within Abaqus, so you have a single point of access for set-up and solving.

Solving and calculation

Once you have your simulation study set-up, the system lets you crack on with it quickly. AcuSolve is highly parallel and it scales nicely across multiple cores and mutiple processors. The really interesting thing is that AcuSim does not charge for multiple processors.

While it’s not a well known fact, those involved with higher-end, more traditional simulation technology will be aware that many vendors charge per CPU, or even worse, per core. So, if you want to run your simulation solver across multiple processors, you get charged. The good news is that AcuSim doesn’t believe this is the way forward and charges for the software, rather than penalising you for having more advanced hardware.

If there’s a failing with AcuSolve as it stands, it’s the fact that the system doesn’t have fully integrated results visualisation tools. At present the system is supplied with ParaView, a cross platform application for reading and presenting simulation results data, and it gives you all the tools to slice up models, create the plots and extract the data you need to create your reports and document results.

In conclusion

We haven’t delved deeply into the technicalities of AcuSim for a couple of reasons. Firstly, the system has a great deal of functionality and as such, its use is going to vary widely depending on the industry you work in. Use of the system would be different if you’re working in oil and gas, compared to aerospace, compared to petrochemical. So who is the target market? The answer, in general terms, is that AcuSim is ideal for anyone interested in higher-level simulation tools at a more affordable price. In specifics, it’s ideal for those looking at fluid structure interaction at a high level and anyone with hyper accurate solution requirements. That said, it’s also ideal for the general purpose CAD market as the FE based meshing is so much more tolerant of messy meshes than many CFD codes. The bottom line is that AcuSim is fast, accurate and easy to use – which sounds like a marketing message from a vendor, so let’s put it this way: it provides high level functionality not compromised by ease of use, and has the potential to take you further than more mainstream solvers.

Go with the flow

According to that source of mildly accurate information, Wikipedia, fluid structure interaction occurs when “a fluid interacts with a solid structure, exerting pressure on it which may cause deformation in the structure and thus alter the flow of the fluid itself”. Essentially, what this means is that when a fluid (that can be liquid or air) passes over a more rigid object, that fluid can deform the solid. In turn, the deformation of the solid causes a change in the fluid flow, so its characteristics change, which effect the deformation again. The best analogy I’ve ever heard is to consider one of those nasty little plastic stirrers you get in service stations. When you stir your tea, the stirrer swirls in your tea and it bends because of the resistance from the tea.

In turn, the bending changes how the tea resists the stirrer. Computationally speaking the simulation of this effect is incredibly complex and is only now starting to be solved. You need both computational fluid dynamics (for fluid flow) working alongside finite element analysis (for deformation and such), and the process is highly iterative in nature. Because the two fields are quite different in approach, in addition to the computing power required to achieve something feasible in terms of accuracy, this could be the next big thing in simulation.


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