Computer game simulation technology for wave energy

Alex Chow, PhD student at the University of Manchester
Alex Chow, PhD student at the University of Manchester
2-D simulation of a propagating focused wave overtopping a rectangular box
2-D simulation of a propagating focused wave overtopping a rectangular box
3-D simulation of a focused breaking-wave impacting a vertical cylinder
3-D simulation of a focused breaking-wave impacting a vertical cylinder

A PhD student at the University of Manchester has unveiled an innovative new method and software for using computer game technology to carry out complex scientific simulations in the wave energy sector.

As the method's creator, Alex Chow, explains, the traditional simulation methods used within the realm of computational fluid dynamics (CFD) all use a mesh, and are typically very good for a wide range of applications.  However, they do not perform so well when it comes to simulating violent free-surface fluid flows where the water 'exhibits large deformations and can become fragmented.'

In order to overcome these limitations, Chow's team use a method called 'Incompressible Smoothed Particle Hydrodynamics' (ISPH), which does not use a mesh and is more suitable for simulating the characteristics of violent fluid flows.  In ISPH, instead of using a fixed mesh, the fluid is represented as a set of points that can move about according to the governing physical equations.

GRAPHICS CARDS
However, the problem with ISPH is that for large simulations of millions of particles it can be very time consuming because it requires solving millions of simultaneous equations with millions of variables, which constantly change throughout the simulation. To help in accelerating this process, the Manchester team uses widely available graphics processing units, or cards, found in computers.

"I have used DualSPHysics, an open-source weakly-compressible smoothed particle hydrodynamics (WCSPH) code on the GPU, to develop the new software - which I have converted to run ISPH instead," says Chow.

"Although WCSPH can also represent violent free-surface fluid flows, they cannot give a pressure field as accurate as ISPH, which is important for calculating forces in fluid-structure interaction as seen in offshore and marine applications.  ISPH is a much more complex method to implement on the GPU and has not been done until now," he adds.

CHEAP AND PORTABLE
Within the DualSPHysics package there is dedicated pre-processing software which allows users to easily setup simulation test cases, and post-processing software to allow for visualisation of processing of simulation results.

According to Chow, these simulations will allow engineers to predict the forces imposed by the fluid onto structures, and also see how fluid flow behaviour changes around the structure, allowing engineers to 'better design their structures and mitigate structure failure or any other consequences of the fluid-structure interaction.'

At this stage, key applications include the investigation of flow around and beneath ships and the impact of waves on ships and other structures like turbines, wave energy devices, as well as prediction of the energy yield of new devices.  It can even be used to help design new sophisticated laboratory wave basins to see how they might behave before construction and testing.

Chow reveals that the current plan is for the new ISPH version of DualSPHysics to be released 'sometime in 2019' - a date that 'may change due to the other developers' commitments and the fact that 'there is still work to be done for the release to be made public.'  Ultimately, though, he is confident that the approach will prove useful, particularly since GPUs 'have a very unique computing architecture, are very good for parallel computations and are a very cheap and efficient alternative to common massive CPU supercomputers.'

"You can buy a good GPU device for about a £1,000 or even less, put it on your laptop or PC and use it whenever.  Supercomputers on the other hand cost hundreds of thousands, or even millions, and not everyone will have access to one all the time.  There are also maintenance costs associated with supercomputers and their dedicated facilities," he says.

"In addition to using only open-source software, once it is released then anyone can use it. So the combination of cheap, portable GPUs and open-source software means that it can even be used by most small research groups and industrial users," he adds.

By Andrew Williams

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