Estimation of wave kinematics of nonlinear multidirectional waves using multiple surface elevation measurements

To correctly assess the wave loading on coastal and offshore structures in physical model testing, it is necessary to relate the wave forces to the wave kinematics. In the model, reflection may be present and, if neglected, could result in an incorrect evaluation of the load coefficients. Thus, measurement of the wave kinematics in physical model testing of such structures is needed to accurately estimate the load coefficients in the model. However, such measurements can be an expensive and cumbersome task, especially because measurement of the total acceleration, including the convective terms is difficult. Thus, the particle velocities and accelerations are often estimated by a mathematical model established from measurements of the surface elevation. The present work describes how the results from a NL-SORS wave decomposition of nonlinear, short-crested waves measured in physical models can be used for the estimation of the particle velocities and accelerations of such waves. The overall finding is that the wave particle velocities may be accurately estimated in the presence of nonlinear interactions, directional spreading and reflected waves, as opposed to existing methods that estimate the particle velocities assuming that all energy propagate in the same direction. The approach is demonstrated using data of increasing complexity, ranging from simple trichromatic synthetically generated wave fields to numerical, and finally, experimental data. • Results from a NL-SORS wave decomposition are used to estimate the wave kinematics. • The method applies to nonlinear, short-crested waves measured in physical models. • Estimated wave kinematics include the convective terms of the particle acceleration. • Accurate particle velocities are demonstrated on numerical and experimental data.