Supporting coastal flow modelling

The Smith Institute designed algorithms to overcome numerical instability in fluid flow models and improve HR Wallingford's consultancy service.

The problem

HR Wallingford makes extensive use of the TELEMAC modelling system as part of its consultancy activities. TELEMAC is an open-source, finite-element software package designed for simulating free-surface fluid flow, and is particularly suited to modelling coastal flows.

In recent consultancy work, HR Wallingford discovered that TELEMAC exhibited numerical instability when modelling sediment transport in shallow or intertidal areas. This instability, which was observed to grow and affect the entire model domain, brought the physical relevance of the results into question. Elimination of this instability was crucial to the success of the numerical models under construction.

The solution

The Smith Institute was able to combine its expertise in scientific programming and algorithm design with particular specialist knowledge of the TELEMAC system to quickly diagnose and understand the cause of the numerical instability, which transpired to be related to the way in which particle settling was handled numerically.

Having identified the root cause, the Smith Institute proposed an explicit, flux-limiting implementation of particle settling that overcame the limitations of the existing implicit scheme.  This new approach not only eliminated the numerical instability, but also ensured that the mass of sediment was conserved throughout the simulation. The new scheme was tested in close collaboration with HR Wallingford staff, and will be included in a future release of the open source TELEMAC code.

The benefit

Having eliminated numerical instability from the sediment transport models in question, HR Wallingford are now able to construct numerical models of coastal processes with greater confidence and accuracy than before.

Furthermore, regular discussions between the Smith Institute and key HR Wallingford staff have cemented the understanding of the TELEMAC code, giving them greater ability to modify the code to accommodate future needs.

Working with the Smith Institute we quickly reproduced the code instabilities and were then able to identify the cause, correct the code, debug and test, so that updated model could then be applied in consultancy studies.

Tim ChesherGroup Manager at HR Wallingford
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