Hydraulic cylinders play a vital role in the energy output (PTO) system of an oscillating float-type wave energy converter, whose function is to convert the mechanical energy captured by the float from the waves into hydraulic energy. The performance of the hydraulic cylinder determines the conversion efficiency of mechanical energy to hydraulic energy in the system; therefore, it is necessary to study the working mechanism of the hydraulic cylinder. This paper takes a self-developed oscillating float-type wave energy converter as the research object, and studies the working mechanism of its hydraulic cylinder, and uses the linear analysis method to derive the critical self-excited vibration curve of the hydraulic cylinder. In addition, the effects of the external load, hydraulic cylinder load mass, stroke length, spring stiffness and piston area on the performance of the hydraulic cylinder were studied by AMESim simulation software. According to the simulation results, a physical model of the hydraulic cylinder is established. Finally, the physical model is tested in a hydrodynamic pool. The test results show that the hydraulic cylinder can stably and efficiently convert mechanical energy into hydraulic energy even under small waves, thus verifying the rationality of the hydraulic cylinder design.

In order to solve the problem of energy shortage and focus on the development of wave energy, a jack-up platform is used as the carrier, and a new type of wave energy power generation device is designed. Compared with other power generation devices, this new type of jack-up wave energy power generation device owns the advantage of wind and wave resistance, is continuous, highly efficient, stable, and strongly adaptable. By means of combination of theoretical analysis and physical test, the feasibility of the device implementation of wave power is explored. The results showed that the jack-up wave energy power generation device can normally work in the sea state, which verified the feasibility of the device. This device has achieved wave power efficiency by more than 15% of the technical indicators of the project and the desired effect. In general, the jack-up wave energy power generation device has achieved breakthrough in many aspects, and the overall technology has reached the leading domestic level.

The wave energy converter captures the wave power by buoy’s heaving motion, transfers it by hydraulic system, and converts it into the electric power by generator. The hydraulic conversion system plays an important role that can realize the effective regulation of the output power. In order to develop the working characteristics of the hydraulic transmission system, a new wave energy experimental platform was devised. The platform adopts the matching design mode of the driving oil cylinder and the driven oil cylinder. The active hydraulic cylinder and the clump weight can simulate the movement of the oscillating float under certain sea conditions, and the driven oil cylinder realizes the conversion and the output of wave energy. In order to improve the operation accuracy of the active hydraulic cylinder, the control strategy of the active hydraulic cylinder was studied. An adaptive sliding mode control strategy based on the back-stepping method was proposed to overcome the influence of the parameter uncertainty in state equation. The adaptive law was designed by Lyapunov criterion to ensure the stability and the convergence of the closed-loop system. The proposed control strategy was verified and compared with proportional integral derivative control strategy through the concrete experiment, which shows the rapidity and the stability of it. The hydraulic transmission system of wave energy converter was developed; at the same time, the characteristics of hydraulic regulation under different working conditions were summarized through experiments. The results of the research could be the guidance for the power control design.

Among renewable energy sources derived from the ocean, wind power has developed rapidly. This article proposes an optimization algorithm framework that integrates two objectives: aerodynamic shape optimization and structural optimization. For practical reasons, the 5−MW wind turbine blade was selected as the research object, and the sea conditions near the East China Sea were chosen as the environmental parameters for its service environment. The FAST simulation software was employed for verification purposes. The results indicated that the optimized blade not only meets the target power output but also possesses unique economic advantages, such as being lightweight and exhibiting low aerodynamic force.

In order to ensure that the robot has good mechanical properties, stability and hydrodynamic characteristics in underwater motion, and to protect the ROV core control module, battery compartment and other internal precision systems, this paper develops and designs a streamlined underwater robot shell, operating at a depth of 50m, with an overall theoretical linear design, regular shape using strength theory calculations and stress simulation analysis methods, and irregular shape using Solidworks Simutian numerical simulation method, based on Fluent for the overall shell in the fluid stress analysis. The results show that the stress σ₁= 9.33MPa and yield pressure pCR₁ = 13.368MPa for the large spherical shell; the stress σ₂ = 6.67MPa and yield pressure pCR₂ = 13.44MPa for the small spherical shell, both of which are less than the theoretical stress of 42.5MPa and yield pressure P_j=0.8MPa to meet the design requirements for strength and stability; the circular table shape and parabolic The maximum equivalent stress is 0.728MPa ≤ σ_s=50MPa, which meets the physical properties of ABS material; by simulating the stress changes in the three degrees of freedom of the ROV shell in and out, lift and rudder, 527.202Pa, 535.1Pa and 529.1Pa respectively, The yield strength of ABS material is 50MPa, which is much higher than the stresses in the three degrees of freedom of the ROV shell inlet and outlet, dive and rudder, indicating that the ROV meets the stress design requirements in the water.

Based on the land-based self-elevating marine simulation platform developed in advance, this paper uses AMESim and SolidWorks to model the operation of the marine platform pile insertion process and uses hydraulic servo cylinders to simulate the work of pile insertion, which integrates the lifting power, pile legs, and the seabed in a complete way. By changing the pile damping input signal of the hydraulic servo control system, the operating conditions of the jack-up marine platform under the ‘eggshell’ stratum are effectively simulated. Through the simulation experiment and result analysis, it can be seen that: the influence of different valve opening sizes on the system can be simulated visually by the simulation analysis to show the pile leg inserting phenomenon in different soils. The paper has a certain reference value for the pile insertion operation system of the offshore platform, and also has some significance for the safety of the offshore platform.