Unstructured meshes and adaptivity for 3D multi-scale ocean modelling

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• Matthew Piggott, Imperial College London
• Tuesday 22 January 2008, 11:00-12:00
• British Antarctic Survey, Room 307.

If you have a question about this talk, please contact Deb Shoosmith.

Open to non-BAS; please contact Deb Shoosmith (drsho@bas.ac.uk or 221702) if you would like to attend.

Over the past decade there has been growing interest in the use of unstructured mesh based methods in ocean modelling. Moving from structured to unstructured meshes offers many potential benefits. In particular it allows for an excellent representation of complex coastlines and bathymetry, and the ability to use wildly different resolutions in different parts of the domain. For example enhanced resolution may be employed to better resolve important localised phenomena such as boundary layer separations and overflows, and also regions of particular socio-economic or scientific importance. Importantly, unstructured meshes allow for the efficient representation of any interaction between a range of coupled spatial scales. Due to their geometric flexibility this can be achieved with unstructured meshes without resorting to the unsatisfactory approach of nesting due to the fact that smooth variations in mesh resolution are easily achieved.

Unstructured meshes are also the natural framework within which to formulate robust adaptive mesh capabilities. Extending the above multi-scale ability of the mesh, adaptive methods can be used to optimally resolve and track the formation and evolution of localised features in a priori unknown and/or evolving locations. This would be impossible with any fixed mesh, whether unstructured or not.

When utilising adaptive algorithms a model is able to automatically allocate computational resources in an optimal and dynamic manner, as dictated by evolving solution fields and estimates of model and discretisation errors. The aim is that this will lead to more efficient calculations, i.e. overall less mesh nodes would be required to yield a particular solution to a given accuracy; also for a given computational resource problems can be solved which are more complex than is currently feasible.

In this presentation we will describe some of our experiences with constructing a three-dimensional non-hydrostatic finite element ocean model using fully unstructured adaptive mesh techniques. The model is being developed as an open source community project with the aim of maximising flexibility in terms of what it can simulate without compromising on computational power and novelty.

Of particular importance and focus will be mesh generation; mesh optimisation operations and mesh anisotropy; error measures; techniques for accurately describing model states close to hydrostatic and geostrophic balance on arbitrary irregular meshes; sharp interface representation; arbitrary mesh movement; and load-balanced parallelisation.

With any new modelling approach validation is crucial. Here a range of standard benchmarks will be presented where comparisons with laboratory and other well-validated numerical codes are possible. Applications and validation against overflow problems, internal waves, flow past bathymetry, western boundary currents, basin and global scale tides, tsunami, wetting and drying in estuaries, and baroclinic circulation in the North Atlantic will also be presented.

We will conclude by highlighting future plans for the model.

This talk is part of the British Antarctic Survey series.

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