Trigno River Mouth Evolution via Littoral Drift Rose

A mid-term analysis of shoreline evolution was carried out in the present paper for the Trigno river mouth area (5.2 km), located in the northern part of the Molise coast region (southeast Italy). The littoral drift rose (LDR) concept was employed, coupled to the GENESIS one-line model, to produce numerical simulations. The LDR graph was used to define a single, time-invariant, “equivalent wave” component (EW), which was supposed to entirely rule the shoreline changes. Given the inherent bimodality affecting the Molise wave climate, EW could result not significant in forecasting shoreline evolution, since both a climate inversion and a time-varying diffusion extra effect are expected. These aspects, never investigated in the literature, are deepened in the present paper, with the main aims of firstly assessing the explanatory power of the LDR equivalent wave and its significance within a bimodal climate, and secondly checking the role of a time-varying diffusivity. Results confirmed the reliability of the EW concept, even within a bimodal climate. Moreover, the possible effect of a time-varying diffusion, which is expected with a large directional variability, produced insignificant results with respect to the EW.

Analytical and Numerical Results on Global Dynamics of the Generalized Boussinesq Equation with Cubic Nonlinearity and External Excitation

This paper analytically and numerically presents global dynamics of the generalized Boussinesq equation (GBE) with cubic nonlinearity and harmonic excitation. The effect of the damping coefficient on the dynamical responses of the generalized Boussinesq equation is clearly revealed. Using the reductive perturbation method, an equivalent wave equation is then derived from the complex nonlinear equation of the GBE. The persistent homoclinic orbit for the perturbed equation is located through the first and second measurements, and the breaking of the homoclinic structure will generate chaos in a Smale horseshoe sense for the GBE. Numerical examples are used to test the validity of the theoretical prediction. Both theoretical prediction and numerical simulations demonstrate the homoclinic chaos for the GBE.

A Medium-Term Study of Molise Coast Evolution Based on the One-Line Equation and “Equivalent Wave” Concept

The Molise region (southern Italy) fronts the Adriatic Sea for nearly 36 km and has been suffering from erosion since the mid-20th century. In this article, an in-depth analysis has been conducted in the time-frame 2004–2016, with the purpose of discussing the most recent shoreline evolution trends and individuating the climate forcings that best correlate with them. The results of the study show that an intense erosion process took place between 2011 and 2016, both at the northern and southern parts of the coast. This shoreline retreat is at a large extent a downdrift effect of hard protection systems. Both the direct observation of the coast and numerical simulations, performed with the software GENESIS, indicate that the shoreline response is significantly influenced by wave attacks from approximately 10° N; however, the bimodality that characterizes the Molise coast wave climate may have played an important role in the beach dynamics, especially where structural systems alternate to unprotected shore segments.

Development and Validation of Passive Yaw in the Open-Source WEC-Sim Code

A passive yaw implementation is developed, validated, and explored for the WEC-Sim, an open-source wave energy converter modeling tool that works within MATLAB/Simulink. The Reference Model 5 (RM5) is selected for this investigation, and a WEC-Sim model of the device is modified to allow yaw motion. A boundary element method (BEM) code was used to calculate the excitation force coefficients for a range of wave headings. An algorithm was implemented in WEC-Sim to determine the equivalent wave heading from a body’s instantaneous yaw angle and interpolate the appropriate excitation coefficients to ensure the correct time-domain excitation force. This approach is able to determine excitation force for a body undergoing large yaw displacement. For the mathematically simple case of regular wave excitation, the dynamic equation was integrated numerically and found to closely approximate the results from this implementation in WEC-Sim. A case study is presented for the same device in irregular waves. In this case, computation time is increased by 32x when this interpolation is performed at every time step. To reduce this expense, a threshold yaw displacement can be set to reduce the number of interpolations performed. A threshold of 0.01° was found to increase computation time by only 22x without significantly affecting time domain results. Similar amplitude spectra for yaw force and displacements are observed for all threshold values less than 1°, for which computation time is only increased by 2.2x.

Tidal Turbine Load Variability in Following and Opposing Irregular Wave Conditions

Waves induce large loads on tidal turbines, yet the effect of irregular waves, particularly those which oppose the current direction, have received little attention. Here we experimentally assess the loading resulting from 24 irregular combined wave-current cases, statistically presenting the load variability acting on a 1:15 scale tidal turbine. Comparisons are made between following and opposing conditions of equivalent wave parameters, and the effect of varying frequency and amplitude is assessed. Example load distributions are also shown, along with streamwise variation of significant wave height around the turbine. It is concluded that both opposing and following conditions must be assessed to effectively de-risk tidal turbine design: large differences are observed both in terms of the nature & magnitude of the resulting loads and the wave interaction with the surrounding flow field.