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Investigation of a simplified open boundary condition for coastal and shelf sea hydrodynamic models
Thesis (MSc)--Stellenbosch University, 2015.
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| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2015
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| _version_ | 1867613852788588544 |
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| access_status_str | Open Access |
| author | Shabangu, Patrick Eminet |
| author2 | Smit, G. J. F. |
| author_browse | Shabangu, Patrick Eminet Smit, G. J. F. |
| author_facet | Smit, G. J. F. Shabangu, Patrick Eminet |
| author_sort | Shabangu, Patrick Eminet |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2015. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/96839 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:42:44.343Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2015 |
| publishDateRange | 2015 |
| publishDateSort | 2015 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/96839 Investigation of a simplified open boundary condition for coastal and shelf sea hydrodynamic models Shabangu, Patrick Eminet Smit, G. J. F. Diedericks, G. P. J. Van Ballegooyen, R. C. Stellenbosch University. Faculty of Science. Department of Applied Mathematics. Ocean -- Coast boundary condition Mathematical models -- Computer Programmes Mathematical models -- Computer software UCTD Oceanography -- Mathematical models Hydrodynamics -- Mathematical models Hydrodynamics -- Computer programs Thesis (MSc)--Stellenbosch University, 2015. ENGLISH ABSTRACT : In general, coastal and shelf hydrodynamic modelling is undertaken with limited area numerical models such as Delft3D or Mike 21. To conduct successful numerical simulations these programmes require appropriate boundary conditions. Various options exist to obtain boundary conditions such as Neumann conditions, specifying water levels, specifying velocities and combination of these, amongst others. In this study one specific method is investigated, namely the specification of water levels on all the open boundaries using a "reduced physics" approach. This method may be more appropriate than Neumann conditions when the domain is fairly large and is also of particular interest as it allows measured data to be incorporated in the boundary conditions, although the latter was not considered in this study. The boundary conditions of interest are determined by separating the crossshore and alongshore components of the momentum equations. To justify the separation, the equations of motion are firstly non-dimensionalised to determine the relative importance of various terms and then scaled to determine under which conditions the cross-shore and alongshore components can be solved independently. The efficacy of a computer program, Tilt, to calculate the open boundary conditions have been investigated for a number of idealised cases. Based on an understanding of the underlying physics and scaling assumptions, situations where these open boundary conditions underperformed have been analysed and reasons given for their underperformance. When applied to "real-life" situations it is likely that one or more of the scaling assumptions will be violated. Comment is provided on the likely errors in model simulations should this occur. The main conclusions are that the "reduced physics" approach used in Tilt restricts fairly significantly the range of flow that can be simulated. Should the scaling assumptions underlying Tilt be satisfied, Tilt performs adequately for limited area model simulations of coastal and shelf regions, however there remain some concerns: • The no flux condition at the coast and clamped water level offshore AFRIKAANSE OPSOMMING : Oor die algemeen word kus en kontinentale bank hidrodinamiese modellering met beperkte area numeriese modelle soos Delft3D of Mike 21 gedoen. Om suksesvolle simulasies te doen, benodig hierdie programme geskikte randwaardes. Daar bestaan verskeie opsies om randwaardes te verkry soon byvoorbeeld Neuman kondisies, spesifisering van watervlakke, spesifisering van snelheid en kombinasies van hierdie. In hierdie studie word een spesifieke metode ondersoek, naamlik om watervlakke op al die oop rande te spesifiseer deur ’n "gereduseerde fisika" benadering te gebruik. Hierdie metode is meer van toepassing as Neuman randwaardes wanneer die modelleringsgebied redelik groot is en ook van spesifieke belang aangesien dit die inkorporering van gemete data in die randwaardes moontlik maak, alhoewel laasgenoemde nie in hierdie studie ondersoek is nie. Die randwaardes wat van belang is, word bepaal vanaf die momentumvergelykings wat in komponente loodreg op die kus en parallel aan die kus geskei word. Om die skeiding te regverdig, word die bewegingsvergelykings eerstens nie-dimensionaliseer om die relatiewe belangrikheid van terme te bepaal en daarna word die vergelykings geskaal om te bepaal onder watter kondisies mag die komponente loodreg op die kus en parallel aan die kus onafhanklik opgelos word. Die doeltreffendheid van ’n bestaande rekenaarprogram, Tilt, wat gebruik word om die randwaardes te bepaal, word getoets vir ’n aantal ge-idialiseerde toetsgevalle. Gebasseer op die verstaan van die onderliggende fisika en aannames in die skaling, is situasies waar die randwaardes onderpresteer analiseer en redes vir die onderprestering word gegee. Tydens toepassings in werklike situasies is dit heel moontlik dat daar nie voldoen sal word aan al die aannames wat in die skaling gebruik is nie. Kommentaar word oor die moontlike foute wat in die simulasies kan voorkom gelewer indien daar nie aan die aannames voldoen word nie. Die belangrikste gevolgtrekkings is dat die "gereduseerde fisika" benadering in Tilt, Tilt die bereik van die skaal van die vloei wat gesimuleer kan word tot ’n redelike mate beperk. Indien voldoen word aan die aannames in die skaling wat onderliggend is aan Tilt, dan presteer Tilt goed vir beperkte area model simulasies van die kus en kontinentale bank gebiede. Daar is egter wel kommer: • Die geen-vloed kondisie teen die kus en geklampde watervlakke aflandig, beperk die vloei dwars op die kus en dwing vloei parallel aan die kus af. Gevolglik bevredig die oop randwaardes vanaf Tilt vloei tot parallel aan die kus van barotropiese vloei wanneer die simulasies getoets is met winde wat vloei na die kus toe deflekteer as gelog van die Coriolis krag. Waar die wind vloei in ’n aflandige rigting deflekteer, kan redelike groot foute voorkom langs die aflandige rand. Dit is waarskynlik omdat dit ’n lang tyd neem vir die rand langs die kus om sy invloed te laat geld. • Waar nie aan die aannames in die skaling wat onderliggend is aan Tilt voldoen word nie, kan beduidende foute in die oop rande van die model gebied voorkom. Die voorkoms van die foute hang af van die mate waarin daar nie aan die aannames voldoen word nie. Praktiese oplossings vir sommige van hierdie situasies word verskaf. 2015-05-20T09:27:51Z 2015-05-20T09:27:51Z 2015-03 Thesis http://hdl.handle.net/10019.1/96839 en_ZA Stellenbosch University xvi, 117 pages, illustrations (mainly colour) application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Ocean -- Coast boundary condition Mathematical models -- Computer Programmes Mathematical models -- Computer software UCTD Oceanography -- Mathematical models Hydrodynamics -- Mathematical models Hydrodynamics -- Computer programs Shabangu, Patrick Eminet Investigation of a simplified open boundary condition for coastal and shelf sea hydrodynamic models |
| title | Investigation of a simplified open boundary condition for coastal and shelf sea hydrodynamic models |
| title_full | Investigation of a simplified open boundary condition for coastal and shelf sea hydrodynamic models |
| title_fullStr | Investigation of a simplified open boundary condition for coastal and shelf sea hydrodynamic models |
| title_full_unstemmed | Investigation of a simplified open boundary condition for coastal and shelf sea hydrodynamic models |
| title_short | Investigation of a simplified open boundary condition for coastal and shelf sea hydrodynamic models |
| title_sort | investigation of a simplified open boundary condition for coastal and shelf sea hydrodynamic models |
| topic | Ocean -- Coast boundary condition Mathematical models -- Computer Programmes Mathematical models -- Computer software UCTD Oceanography -- Mathematical models Hydrodynamics -- Mathematical models Hydrodynamics -- Computer programs |
| url | http://hdl.handle.net/10019.1/96839 |
| work_keys_str_mv | AT shabangupatrickeminet investigationofasimplifiedopenboundaryconditionforcoastalandshelfseahydrodynamicmodels |