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Keywords: ESMF, DBuilder, model coupling, high performance computing, ADCIRC, pWASH123D.

Summary

This paper describes the development of a parallel, coupled ocean-watershed model, COSM, designed for high resolution modelling within a high performance computing environment. The COSM model couples pWASH123D for the simulation of water flow on the land with ADCIRC for storm induced ocean circulation and surge. The pWASH123D model simulates water flow in watershed systems that can be conceptualized as combinations of one-dimensional stream-river networks, two-dimensional overland regimes, and three-dimensional subsurface media. ADCIRC is a coastal circulation and storm surge model widely used for hurricane simulation modelling. These two models are coupled in a concurrent mode with time lagging using the Earth System Modelling Framework, ESMF and the DBuilder toolkits. ESMF and DBuilder provide the software architecture and parallel data management to support run-time coupling, including all data exchanges between the two unstructured finite element models. New techniques developed in this research include the coupling methodology and element searching algorithms used to combine the models.

A simplified simulation of Biloxi Bay is used to demonstrate the capabilities of COSM. A number of aspects of the coupled model are investigated, including scalability performance, accuracy performance, coupling scheme effect, time lagging effect, and hydraulic conductivity effect. The following were observed:

COSM provides consistent computational results in stand-alone, one-way coupling, and two-way coupling simulations when the number of processors varies.
Two-way coupling is necessary to account for watershed-nearshore interaction accurately during storm events.
The most significant impact from coupling ADCIRC to pWASH123D was on the areas around the coastal line near shallow water areas and the channels.
The most significant impact from coupling pWASH123D to ADCIRC was on the bay area and around the coastal line.
The time lagging effect became significant during storm events, suggesting that higher coupling frequency should be used during these periods of time.
Large hydraulic conductivity promotes water exchange between the watershed and nearshore models.

COSM is the first coupled unstructured-mesh model using ESMF. Features and capabilities developed for this coupled model can also be applied to the coupling of structured- and unstructured-mesh models. When compared to stand-alone models, the coupled model exhibits more accurate boundary conditions applied to the interface boundary between the watershed and the coastal models. As a result, the hydro-system in the nearshore area has been modelled better, and an improved understanding of the complex interactions can be obtained. The future improvement/development may include the following.

Incorporate temporal interpolation to reduce the time lagging effect.
Implement the coupling through overlapped wetting-drying areas and extend the subsurface domain to some distances off the coastal line.
Make the watershed-nearshore coupling time-step a factor, rather than a multiple, of the subsurface time-step.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 94 PROCEEDINGS OF THE SEVENTH INTERNATIONAL CONFERENCE ON ENGINEERING COMPUTATIONAL TECHNOLOGY Edited by: Paper 13 COSM: A Parallel Coupled Ocean Watershed Model H.-P. Cheng¹, J.-R.C. Cheng¹, R.M. Hunter¹, T. Campbell² and H.-C. Lin¹ ¹U.S. Army Engineer Research and Development Centre, Vicksburg MS, United States of America ²The Naval Research Laboratory, Stennis Space Centre, Bay St. Louis MS, United States of America doi:10.4203/ccp.94.13 purchase the full-text of this paper Full Bibliographic Reference for this paper H.-P. Cheng, J.-R.C. Cheng, R.M. Hunter, T. Campbell, H.-C. Lin, "COSM: A Parallel Coupled Ocean Watershed Model", in , (Editors), "Proceedings of the Seventh International Conference on Engineering Computational Technology", Civil-Comp Press, Stirlingshire, UK, Paper 13, 2010. doi:10.4203/ccp.94.13 Keywords: ESMF, DBuilder, model coupling, high performance computing, ADCIRC, pWASH123D. Summary This paper describes the development of a parallel, coupled ocean-watershed model, COSM, designed for high resolution modelling within a high performance computing environment. The COSM model couples pWASH123D for the simulation of water flow on the land with ADCIRC for storm induced ocean circulation and surge. The pWASH123D model simulates water flow in watershed systems that can be conceptualized as combinations of one-dimensional stream-river networks, two-dimensional overland regimes, and three-dimensional subsurface media. ADCIRC is a coastal circulation and storm surge model widely used for hurricane simulation modelling. These two models are coupled in a concurrent mode with time lagging using the Earth System Modelling Framework, ESMF and the DBuilder toolkits. ESMF and DBuilder provide the software architecture and parallel data management to support run-time coupling, including all data exchanges between the two unstructured finite element models. New techniques developed in this research include the coupling methodology and element searching algorithms used to combine the models. A simplified simulation of Biloxi Bay is used to demonstrate the capabilities of COSM. A number of aspects of the coupled model are investigated, including scalability performance, accuracy performance, coupling scheme effect, time lagging effect, and hydraulic conductivity effect. The following were observed: COSM provides consistent computational results in stand-alone, one-way coupling, and two-way coupling simulations when the number of processors varies. Two-way coupling is necessary to account for watershed-nearshore interaction accurately during storm events. The most significant impact from coupling ADCIRC to pWASH123D was on the areas around the coastal line near shallow water areas and the channels. The most significant impact from coupling pWASH123D to ADCIRC was on the bay area and around the coastal line. The time lagging effect became significant during storm events, suggesting that higher coupling frequency should be used during these periods of time. Large hydraulic conductivity promotes water exchange between the watershed and nearshore models. COSM is the first coupled unstructured-mesh model using ESMF. Features and capabilities developed for this coupled model can also be applied to the coupling of structured- and unstructured-mesh models. When compared to stand-alone models, the coupled model exhibits more accurate boundary conditions applied to the interface boundary between the watershed and the coastal models. As a result, the hydro-system in the nearshore area has been modelled better, and an improved understanding of the complex interactions can be obtained. The future improvement/development may include the following. Incorporate temporal interpolation to reduce the time lagging effect. Implement the coupling through overlapped wetting-drying areas and extend the subsurface domain to some distances off the coastal line. Make the watershed-nearshore coupling time-step a factor, rather than a multiple, of the subsurface time-step. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £125 +P&P)
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