On the Importance of High–Fidelity Numerical Modelling of Ocean Wave Energy Converters under Controlled Conditions

Numerical modelling tools are commonly applied during the development and optimisation of ocean wave energy converters (WECs). Models are available for the hydrodynamic wave structure interaction, as well as the WEC sub–systems, such as the power take–off (PTO) model. Based on the implemented equations, different levels of fidelity are available for the numerical models. Specifically under controlled conditions, with enhance WEC motion, it is assumed that non-linearities are more prominent, re- quiring the use of high–fidelity modelling tools. Based on two different test cases for two different WECs, this paper highlights the importance of high–fidelity numerical modelling of WECs under controlled conditions.

Wind speed and direction estimation from wave spectra using deep learning

High-frequency parts of ocean wave spectra are strongly coupled to the local wind. Measurements of ocean wave spectra can be used to estimate sea surface winds. In this study, two deep neural networks (DNNs) were used to estimate the wind speed and direction from the first five Fourier coefficients from buoys. The DNNs were trained by wind and wave measurements from more than 100 meteorological buoys during 2014–2018. It is found that the wave measurements can best represent the wind information about 40 min previously because the high-frequency portion of the wave spectrum integrates preceding wind conditions. The overall root-mean-square error (RMSE) of estimated wind speed is ∼1.1 m s−1, and the RMSE of the wind direction is ∼ 14∘ when wind speed is 7–25 m s−1. This model can be used not only for the wind estimation for compact wave buoys but also for the quality control of wind and wave measurements from meteorological buoys.

Modelling Ocean Waves and an Investigation of Ocean Wave Spectra for the Wave-to-Wire Model of Energy Harvesting

Ocean wave energy is an abundant and clean source of energy; however, its potential is largely untapped. Although the concept of energy harvesting from ocean waves is antiquated, the advances in wave energy conversion technologies are embryonic. In many major studies related to wave-to-wire technologies, ocean waves are considered to be regular waves with a fixed amplitude and frequency. However, the actual ocean waves are the sum of multiple frequencies that exhibit a particular sea state with a significant wave height and peak period. Therefore, in this paper, detailed modelling of the ocean waves is presented and different wave spectra are analyzed. The wave spectra will eventually be used for the generation of wave elevation time series. Those time series can be used for the wave-to-wire model-based studies for improved investigations into wave energy conversion mechanisms, mimicking the real ocean conditions.

A Review of the Optimization Design and Control for Ocean Wave Power Generation Systems

Ocean wave power generation techniques (converting wave energy into electrical energy) have been in use for many years. The objective of this paper is to review the design, control, efficiency, and safety of ocean wave power generation systems. Several topics are discussed: the current situation of ocean wave power generation system tests in real ocean waves; the optimization design of linear generator for converting ocean wave energy into electrical energy; some optimization control methods to improve the operational efficiency of ocean wave power generation systems; and the current policy and financial support of ocean wave power generation in some countries. Due to the harsh ocean environment, safety is another factor that ocean wave power generation systems will face. Therefore, before the conclusion of this review, a damping coefficient optimization control method based on the domain partition is proposed to improve the efficiency and safety of ocean wave power generation systems.

Rolling Spherical Triboelectric Nanogenerators (RS-TENG) under Low-Frequency Ocean Wave Action

Triboelectric nanogenerators (TENG), which convert mechanical energy (such as ocean waves) from the surrounding environment into electrical energy, have been identified as a green energy alternative for addressing the environmental issues resulting from the use of traditional energy resources. In this experimental design, we propose rolling spherical triboelectric nanogenerators (RS-TENG) for collecting energy from low-frequency ocean wave action. Copper and aluminum were used to create a spherical frame which functions as the electrode. In addition, different sizes of spherical dielectric (SD1, SD2, SD3, and SD4) were developed in order to compare the dielectric effect on output performance. This design places several electrodes on each side of the spherical structure such that the dielectric layers are able to move with the slightest oscillation and generate electrical energy. The performance of the RS-TENG was experimentally investigated, with the results indicating that the spherical dielectrics significantly impact energy harvesting performance. On the other hand, the triboelectric materials (i.e., copper and aluminum) play a less important role. The copper RS-TENG with the largest spherical dielectrics is the most efficient structure, with a maximum output of 12.75 V in open-circuit and a peak power of approximately 455 nW.

Effects of wave loads on the strength of semisubmersible drilling platform

In order to reduce the failure risk of the structures of semisubmersible drilling platform during its service life, this research studies the effects of ocean wave loads on the strength of the platform’s structures. The response spectra of the platform obtained from model test in wave tank were used to verify the accuracy of the numerical model employed in this research. Eight wave load cases, which may affect the strength of the platform but not involved in the classification societies such as ABS and DNV, were newly considered in this research. The results of the research indicate that a) four of the eight newly added wave load cases are found to be greatly affecting the strength of the platform and need to be considered in designing the structures; b) torsional moment and shearing force caused by the ocean wave would cause the stress of the structures of platform at a high level and need to be carefully evaluated.