Browsing by Subject "wave"
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Item Analysis of WACSIS data using a directional hybrid wave model(Texas A&M University, 2007-04-25) Zhang, ShaosongThis study focuses on the analysis of measured directional seas using a nonlinear model, named Directional Hybrid Wave Model (DHWM). The model has the capability of decomposing the directional wave field into its free wave components with different frequency, amplitude, direction and initial phase based on three or more time series of measured wave properties. With the information of free waves, the DHWM can predict wave properties accurately up to the second order in wave steepness. In this study, the DHWM is applied to the analyses of the data of Wave Crest Sensor Inter-comparison Study (WACSIS). The consistency between the measurements collected by different sensors in the WACSIS project was examined to ensure the data quality. The wave characteristics at the locations of selected sensors were predicted in time domain and were compared with those recorded at the same location. The degree of agreement between the predictions and the related measurements is an indicator of the consistency among different sensors. To analyze the directional seas in the presence of strong current, the original DHWM was extended to consider the Doppler effects of steady and uniform currents on the directional wave field. The advantage of extended DHWM originates from the use of the intrinsic frequency instead of the apparent frequency to determine the corresponding wavenumber and transfer functions relating wave pressure and velocities to elevation. Furthermore, a new approach is proposed to render the accurate and consistent estimates of the energy spreading parameter and mean wave direction of directional seas based on a cosine-2s model. In this approach, a Maximum Likelihood Method (MLM) is employed. Because it is more tolerant of errors in the estimated cross spectrum than a Directional Fourier Transfer (DFT) used in the conventional approach, the proposed approach is able to estimate the directional spreading parameters more accurately and consistently, which is confirmed by applying the proposed and conventional approach, respectively, to the time series generated by numerical simulation and recorded during the WACSIS project.Item Dynamics of Wave Breaking at a Coastal Sea Wall(2010-07-14) Antoine, Arthur L.Structural designs barely consider the dynamic scenario of a well-developed impinging wave hitting the structure. The usual area of focus is on static and stability factors (e.g. drag, inertia, resistive forces related to weight, buoyancy, sliding etc). Even the "Factor of Safety" which is regularly used in designs to account for unknown and/or unforeseen situations which might occur implies a degree of uncertainty about the dynamic scenario of breaking waves in the coastal environment. In the present study the hydrodynamics of a coastal structure-turbulent bore interaction was studied by examination (two-dimensional) of the singular case of a plunging breaking wave forming a well developed turbulent bore which impacted on a model sea wall structure. The turbulent bore impact event was found to display similar characteristics to the impact event of other wave shapes, in particular that of a plunging breaker. Examination of the impact event confirmed the conversion of nearly all horizontal velocity to vertical velocity during the "flip through" event. In accordance with theoretical expectations the location of maximum pressure was found to occur just below the still water level (SWL). Resulting pressure data in the present study consisted of two blunt spikes as opposed to the "church-roof" (high spike) shape seen in other results. The shape of the pressure data was attributed to the following: firstly, to the initial impact of the protruding jet of the breaking wave which causes the first maxima, secondly, to the sensor encountering the bulk of the entrapped air hence causing the drop in pressure between the blunt spikes and lastly, to the inherent hydrostatic pressure combined with the compression of the entrapped air bubbles, by the subsequent forward motion of the water within the wave, which causes the second maxima. The point of maximum pressure was found to always be within the second maxima. Observation of the turbulent bore-structure interaction showed that the consequential maximum pressure was a direct result of the compression of entrapped air by the weight of the water in the wave as it continued forward onto the structure combined with the inherent hydrostatic pressure of the wave. The project was conducted in an attempt to contribute to the vast knowledge of coastal structure-wave interactions and to add to the understanding of the physics and characteristics of breaking waves. Whilst numerous studies and experiments have been carried out on the phenomenon of breaking waves by previous researchers the current project highlights the advent of new equipment and technological advances in existing methods.Item Evaluation of an approximate method for incorporating floating docks in harbor wave prediction models(Texas A&M University, 2005-11-01) Tang, ZhaoxiangComputer models are nowadays routinely used in harbor engineering applications. Models based on the two-dimensional elliptic mild-slope equation can simultaneously simulate refraction, diffraction, reflection, and dissipation in completely arbitrary coastal domains. However, floating structures such as floating breakwaters and docks are often encountered in the modeling domain. This makes the problem locally 3- dimensional. Hence it is problematic to incorporate a floating structure into the 2-d model. Tsay and Liu (1983) proposed a highly simplified but approximate approach to handle this problem practically. The validity of their approach is examined in detail and it is found that the actual solutions deviate considerably from the theoretical solutions, although their approximation provides results with the correct trend. Therefore, correction factors have been developed and may be used to produce more reliable results using the framework of Tsay and Liu (1983). The resulting method is applied to Douglas harbor in Alaska. The result shows that docks in the harbor distort the wave field considerably and create a reflective pattern that can affect navigation safety in some areas. Also plots are developed for the transmission coefficients for waves propagating past rectangular and cylindrical floating objects of infinite extent for a wide range of conditions encountered in practice.Item HURRICANE INDUCED WAVE AND SURGE FORCES ON BRIDGE DECKS(2010-01-16) McPherson, Ronald L.The damaging effects of hurricane landfall on US coastal bridges have been studied using physical model testing. Hurricane bridge damage and failure susceptibility has become very evident, especially during hurricane seasons 2004 and 2005 in the Gulf of Mexico. The combination of storm surge and high waves caused by a hurricane can produce substantial loads on bridge decks leading to complete bridge failure. Several theoretical methods have been developed to estimate these forces but have not been tested in a laboratory setting for a typical bridge section. Experiments were done using a large-scale 3-D wave basin located at the Haynes Coastal Engineering Laboratory at Texas A&M University to provide estimates of the horizontal and vertical forces for several conditions to compare with the forces predicted with the existing models. The wave force results show no strong correlation between the actual force measured and the predicted force of existing theoretical methods. A new method is derived from the existing theoretical methods. This model shows a strong correlation with both the measured horizontal and vertical forces.Item Numerical simulation of inviscid wave-current interaction with an FPSO(2009-05-15) Bae, Sang-YunThis study investigated Floating Production Storage and Offloading (FPSO) responses under wave and current interactions. A higher order boundary element method (HOBEM) was adopted to probe the behavior of an FPSO. Forces and moment of an FPSO were studied under wave and current interactions. The simulations of diffracted and radiated waves were performed in a time domain. Time marching schemes were used for this time domain calculation. The predictor-corrector(P-C) method was used. Boundary integral equations were used to solve each problem with Rankine sources and distributed over the entire calculation domain. For the far-field boundary condition, Orlanski?s truncated open boundary condition was used for an open truncated boundary condition to prevent reflected waves. The current effect was considered an explicit term due to being a moving coordinate. Various current heading angles were also studied. Truncated open boundary, maximum likelihood method, proper element size and shape, modulation function, and Chebyshev filtering were studied to avoid diverged solutions. From our findings, higher order elements fitted a complicated model such as an FPSO. We found that this method required considerably fewer elements than the constant panel method in order to obtain reasonable outcomes. Using our developed numerical method, we calculated wave forces and moment, mean drift forces, added mass, and damping coefficients. Conclusively, HOBEM was found to be more effective and more reliable in calculating and predicting wave and current influence on an FPSO. Future studies are needed to develop finer simulation tools for FPSO?s large horizontal behavior.