An experimental study and a three-dimensional numerical wave basin model of solitary wave impact on a vertical cylinder

Graduation date: 2009An experiment on solitary wave impact on a vertical cylinder was conducted in\ud the three-dimensional wave basin at the Oregon State University Hinsdale Wave\ud Research Laboratory. The cylinder was designed using mechanic principles and finite element analysis techniques to enable accurate measurement of horizontal force and overturning moment. Video data of wave motions was collected during the experiment along with wave-gauge, ADV, pressure-sensor and strain-gauge data for post processing. It is observed that the measured surface profile and water particle velocity of the solitary waves generated by the piston wavemaker closely match theoretical predictions and the waves propagate from the wave generator to the cylindrical structure 22.1m downstream with little decay. From the measured data, an averaged percentage of the volume under the effective solitary wave profile is estimated based on the first detection time of the wave gauges. An associated analytical expression of the effective wave length is proposed.\ud The wave impact on the cylindrical structure results in an increase in the wave\ud height on both the front (impact) side as well as the back (lee) side. As expected, the wave run-up on the cylindrical structure is depending on the incident wave amplitude and water depth. On the other hand, a shielding effect due to the presence of two front cylinders at upstream is observed with the maximum of center-to-center distance between the two cylinders equal to twice the cylinder diameter. Two methods of the predictions of horizontal force and overturning moment are discussed – regression analysis and the Morison formulation. Regression analysis shows the predicted force and moment are functions of wave-amplitude to water-depth H/h and focal angel θ. Based on least squared method, the calculated CD and CM are obtained for the Morison formulation. The predicted force and moment match the measured data very well.\ud The experimental results are used to evaluate the predictive capability of a\ud multi-physics finite-element based nonlinear numerical code -- LS-DYNA. The code contains both fluid and structural modules. The focus of this study is to evaluate the predictive capability of the explicit finite-element arbitrary Lagrangian-Eulerian (ALE) option for the fluid to model full-scale fluid-structure interaction laboratory experiments in a three-dimensional (3-D) wave basin. Specifically, a 3-D numerical wave basin model is developed using LS-DYNA corresponding to the experiment with\ud two wave excitation conditions (plane and focused solitary waves) and two cylinder\ud arrangements. It is used to simulate tsunami impact on a structure. Numerical\ud predictions of water surface elevation and water particle velocity for the fluid domain, and wave horizontal force, overturning moment and pressure on the cylindrical structure are obtained and calibrated against experimental results. It is observed that the numerical wave basin model can predict well the wave motion characteristics (elevation and horizontal velocity) as well as integrated structural responses (horizontal force and overturning moment) for the given wave conditions. A half-basin model is developed to take advantage of symmetry to reduce the computation time. As the nonlinear nature of fluid structure interaction problem becomes more significant, the computation time increases, while the predictive accuracy decreases. A number of computational settings were examined but found to have little effect on the\ud computational performance of LS-DYNA. It is observed that further improvement on\ud LS-DYNA by better modeling of the basic physics including compressibility and\ud turbulent behavior need to be made to include highly nonlinear effects due to wave\ud breaking