Browsing by Author "Van Eeden, Frans"
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- ItemSWASH: A robust numerical model for shallow water coastal engineering applications(Stellenbosch : Stellenbosch University, 2017-03) Van Eeden, Frans; Schoonees, J. S.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Integral to coastal engineering design is the understanding and analysis of the wave climate at an arbitrary site under consideration. In most cases, these wave climate and extreme conditions are simulated by means of numerical computer models. These models a ord the coastal engineer the tools to test a wide range of climatic and extreme conditions applicable to the design. The output from these models is used as input into the design formulas for the various structural elements. However, in order for these numerical models to be reliable, some form of calibration is needed. The surf zone is an area of coastal engineering that is generally di cult to simulate numerically, as this is a highly dynamic zone with numerous interactive processes. The nature of the surf zone makes collecting calibration data to use in numerical models fairly di cult to nearly impossible. Researchers and coastal engineers turn to laboratory measurements to quantify surf zone processes and to calibrate numerical models. A non-hydrostatic numerical model SWASH (SimulatingWAves till SHore) is analysed in terms of its numerical capability to simulate wave breaking, in particular, spilling and plunging waves. Laboratory data were made available for calibration purposes. The data describe regular spilling and plunging breakers on plane slopes of 1:20 and 1:35. Water levels and instantaneous horizontal and vertical velocities at various positions pre- and post-wave breaking were measured using particle image velocimetry and laser-Doppler velocimetry. The laboratory data are used to test the sensitivity of the SWASH model in terms of numerical parameters; i.e. the explicit conservation of momentum, bed friction and various discretisation and interpolation schemes that in uence the stability and accuracy of the numerical model. The sensitivities are compared to the laboratory measured data sets in terms of the incipient breaking point, phase averaged water levels and the phase averaged horizontal and vertical particle velocities. The results of the sensitivity analysis are subsequently used to test the robustness of the SWASH model by comparing three modes of the SWASH model: a calibrated wave model, an uncalibrated model (using default or recommended parameters) and the hydrostatic front approximation. The three modes are compared to the measured data and to each other in terms of breaker depth index, wave setup, phase averaged water levels and the phase averaged horizontal and vertical particle velocities and modelled turbulence. The root mean squared error is calculated between the model data and the measured data in order to gauge the accuracy of the three modes. It can be concluded that the SWASH model is capable of numerically representing surf zone processes that can assist the engineer in his designs. In addition, the model performs very well in most areas when an uncalibrated SWASH model is employed with accuracy limited to that of the preliminary design stage. The SWASH model offers a vivid array of numerical schemes and parameters that can be used for calibration purposes. However, the exibility of the model does not overshadow the robustness and simplicity with which the model can be set up. Regardless, the model does live up to its claim of robustness and accuracy without specifying external parameters to a preliminary design level. Beyond this design level, proper calibration of the model is necessary before the model results can be utilised in detailed design.