Second Order Directional Wave Kinematics in Shallow Waterby Jagat N. Sharma, Amoco Production Co, Tulsa, United States,
R. G. Dean, Amoco Production Co, Tulsa, United States,
Abstract: A theory numerical procedure were developed earlier to represent a real sea by the sum of many linear and second order directional wave components. Earlier publications showed that including short-crested nature of real seas could reduce design loads substantially (up to a factor of 3 for large four pile structures). Comparison of the theory with real sea data has been presented by the other investigators showing good agreement. Here, simulated second order directional wave velocities and accelerations for two directional spectra, which could be of interest to coastal and offshore engineers and scientists, are presented and their practical implications discussed. Simulations were carried out for a moderate sea state in 100 ft water depth. Directional wave kinematics (correct upto second order) at sea surface and seabed are presented and discussed, The maximum nonlinear correction is only 10% of wave height for a moderate seastate simulated here, but would be much higher for a design level seastate because the nonlinear correction is proportional to wave height squared. The second order corrections increase particle velocities under the wave crest and decrease them under the wave trough. With increasing directionality in wave spectrum, wave particle velocities and accelerations decrease in the inline direction but increase but increase in the transverse direction for a cosine-squared directional distribution are nearly equal to the maximum inline values.
Subject Headings: Wave velocity | Wave spectrum | Kinematic waves | Particle velocity | Seas and oceans | Wave height | Numerical methods
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