Numerical Modeling and Field Investigation of Nearshore Nonlinear Wave Propagation

First, a phase-resolving frequency-domain wave model that solves nonlinear wave-wave interactions is improved to account for wave dissipation and modulations over viscoelastic mud layer. Model results show satisfactory agreement with laboratory measurements. The model is then used to investigate the combined effect of mud viscoelasticity and nonlinear wave-wave interactions on surface wave evolution using cnoidal and random wave simulations. In general, qualitative measures such as shape of cnoidal waves or pattern of variation in Hrms of random waves are dictated by direct mud-induced damping which, due to resonance effects, has a substantially different structure over viscoelastic mud compared to viscous mud. Nonlinear interactions affect spectral shape and distribution of energy loss across the spectrum. Subharmonic interactions cause indirect damping of high frequencies but ameliorate damping of harmonics around mud’s resonance frequency. Therefore, neglecting mud elasticity can result in significant errors in estimation of bulk wave characteristics and spectral shape. Next, a phase-resolving frequency-domain model for wave-current interaction is improved to account for wave modulations due to viscoelastic mud. Results indicates that copropagating currents decrease frequency-dependent damping at low frequencies while they increase it at higher frequencies. The opposite is true for counterpropagating currents. The impact of currents at high frequency increases with increase in mud shear modulus and it is observed in both monochromatic and random wave simulations. The Performance of two mud-induced wave evolution models are compared. One model assumes that the mud layer is thin and the other is applicable to mud of arbitrary depth. It is found that a model based on thin-mud assumption overestimates damping over viscous mud in both monochromatic and random wave scenarios. However, for viscoelastic muds, this model slightly underestimates and overestimates damping for monochromatic and random wave scenarios, respectively. Finally, a preliminary field measurement and data analysis of wave and flow over a seagrass meadow is conducted. In addition, a computational model for hydrodynamics of wave-vegetation interaction is linked to a computational biophysical model for seagrass growth. As a result of this integration, the wave-vegetation model provides improved information on leaf orientation to the seagrass growth model

Nonlinear Wave Evolution in Interaction With Currents and Viscoleastic Muds

A numerical model is extended to investigate the nonlinear dynamics of surface wave propagation over mud in the presence of currents. A phase-resolving frequency-domain model for wave-current interaction is improved to account for wave modulations due to viscoelastic mud of arbitrary thickness. The model compares well with published laboratory data and performs slightly better than the model with viscous mud-induced wave damping mechanism. Monochromatic and random wave simulations are conducted to examine the combined effect of currents, mud-induced wave dissipation and modulation, and nonlinear wave-wave interactions on surface wave spectra. Results indicate that current effects on wave damping over viscoelastic mud is not as straightforward as that over viscous mud. For example, while opposing currents consistently increase damping of random waves over viscous mud, they can decrease damping over viscoelastic mud due to high variations in frequency-dependent damping stemming from mud’s elasticity. It is shown that a model that assumes the mud layer to be thin for simplification can overestimate wave damping over thick mud layers