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The power performances of a point absorber wave energy converter (WEC) operating in a nonlinear multidirectional random sea are rigorously investigated. The absorbed power of the WEC Power-Take-Off system has been predicted by incorporating a second order random wave model into a nonlinear dynamic filter. This is a new approach, and, as the second order random wave model can be utilized to accurately simulate the nonlinear waves in an irregular sea, avoids the inaccuracies resulting from using a first order linear wave model in the simulation process. The predicted results have been systematically analyzed and compared, and the advantages of using this new approach have been convincingly substantiated.

In 2019 a Scientific Research & Demonstration Platform was deployed near islands and reefs in South China Sea by a joint research group of 7 institutes and universities in China. It is a simplified small model of a two-module semi-submersible-type VLFS. The test on site has continued for more than one and half years since then for long-term observations to validate the developed key technologies for design and behavior predictions of floating structures deployed near islands and reefs. An integrated information system was set up to continuously collect and inspect the data of the encountered waves, structure responses, connector forces, mooring line forces, anti-corrosion status of the platform, the performance efficiencies of a floating breakwater nearby and a wave energy converter attached on the breakwater. In this paper, the status of the on-site measurements and validations of the key technologies are briefly described.

This paper examines the response of a heaving plate wave energy converter integrated with a chambered breakwater system through experimental and numerical simulations. A porous seaside wall with 20% porosity and an impermeable back wall constitutes a chambered breakwater under investigation. The time-domain response of the wave energy converter before and after integration with the chambered breakwater is evaluated using an open-source code WEC-Sim implemented in MATLAB and Simulink. The performance of WEC subjected to regular wave conditions and the wave elevations measured from the experiments are examined in the present investigation. The reflection characteristics of the chambered breakwater system after integrating with the wave energy converter have been found to decrease. The heave RAO of the wave energy converter installed at a location toward the porous wall is observed to have improved by 22% after integrating with the chambered breakwater than the stand-alone wave energy converter. A similar increase in the power generation performance of the wave energy converter is also observed. The proposed system can improve the economic competitiveness of the wave energy converter by serving dual purposes.

The hydraulic power take-off (HPTO) is considered as the most promising method to convert wave power to electrical power. This paper presents an experimental assessment of the power conversion of a wave energy converter using HPTO. Based on the experimental results, a modification of accumulator pre-charged pressure and a control strategy were proposed to improve the system performance. System design, the working principle and mathematical model of all components were described. The proposed method was verified based on both simulation and experimental tests. The results showed that the system always works at an optimal condition under different input wave conditions.

In this study, power capture performance of a heaving wave energy converter has been optimized by investigating the effect of variation of power take-off damping. The wave energy converter model used in this study utilizes the sliding discrete Fourier transform technique to estimate the local wave frequency. The power take-off parameters are adjusted according to the estimated wave frequency. As a part of the study, two different cases are evaluated. In the first case, the conventional approach based on using power take-off damping equal to radiation damping which is a function of the estimated wave frequency is considered. In the second part of the study, as a proposed approach, the power take-off damping is calculated with a gain factor. This gain factor varies the hydrodynamic analysis-based frequency-dependent radiation damping by multiplying with it. The results show that the captured power results can be increased from 1.64 to 10.38%, while, in average, the power capture increase covering all datasets is 5.95%.

The information of the wave loads on a wave energy device in operational waves is required for designing an efficient wave energy system with high survivability. It is also required as a reference for numerical modeling. In this paper, a novel system, which integrates an oscillating wave energy converter with a pile-restrained floating breakwater, is experimentally investigated in a 2-D wave flume. The measurements of the wave pressure on the wet-surface of the device are made as the function of the power take-off (PTO) damping force. It is shown that the wave pressure is significantly affected by the PTO system, in particular, at the edges, and the wave pressure varies under different wave conditions. From the results, conclusions can be drawn on how the PTO damping force and wave conditions affect the loads on the device, which is of engineering concern for constructing safe and reliable devices.

Floating devices, such as a cavity resonance device, take advantage of both the water motion and the wave induced motions of the floating body itself. In the design of a wave energy converter (WEC), the most significant factor is that an optimum length of the internal water column should exists, that is, a length in which maximum power is converted near the heaving resonance. A theoretical analysis of this power generated by a pneumatic-type WEC is performed, and the results obtained from the analysis are used for a real WEC for a buoy. The length of the internal water column corresponds to that of the water mass in the water column. If designed properly, a WEC can take advantage not only of the cavity resonance but also of the heaving motion of the buoy. This paper presents the test results of the generation characteristic of a WEC and the harmful effect of fouling in the internal water column. The results are then applied to the design of a WEC for a buoy.

A conceptual scheme is proposed for a cylindrical thermionic energy converter with reduced radiation losses. The decrease in losses was achieved by using a perforated collector. The geometric dimensions of the thermionic energy converter with a perforated collector are optimized to obtain maximum efficiency by decreasing radiation losses with a small increase in losses in the plasma. Comparing the parameters of the converter with a perforated collector with the parameters of the conventional variant of a cylindrical thermionic energy converter showed that for the same power the former has a higher efficiency in almost the entire range of the electrode temperature and a more than two times greater power per unit total mass of the electrodes.

A method is proposed for electromagnetic regulation of the size and composition of the working substance vapor fed into the interelectrode gap of a TEC. It is been demonstrated that this method can be used to increase the output electrical parameters and operating efficiency of thermionic converters.

A unified thermodynamic theory of steady-state energy conversion is presented. A generalized energy converter is considered and its conversion efficiency determined. Two classes and types of energy converters are distinguished and their maximum conversion efficiency found to be given by the same expression. Illustrative examples are presented.

The authors explore the possibility of using a new form of magnetic expander that converts a cylindrical beam of charged particles into a tubular beam. The presented expander performs the following functions: when particles move along the adiabatically decreasing magnetic field the energy of rotational motion is converted into the energy of translational motion, the influence of the space charge decreases and the penetration of the electric field into the beam improves, and the heat removal from the collector system is improved. The operating principle of the expander in a reactor scheme is shown.