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Rubber isolator is commonly used as vibration isolation device for piston pump, and the vibration of piston pump can be effectively reduced by adjusting the dynamic stiffness of rubber isolator. In this paper, in order to study the effect of rubber isolator's dynamic stiffness on the dynamic of seawater hydraulic piston pump (SWHPP), four kinds of rubber isolators with different dynamic stiffness were selected. An experimental modal analysis (EMA) experiment was conducted to study the influence of rubber isolator's dynamic stiffness on the natural frequency of SWHPP. The experimental results indicated that the natural frequency of the pump structure decreased as the dynamic stiffness of rubber isolator increased. Then, the influence of the rubber isolator's dynamic stiffness on the vibration of SWHPP was further studied, and conclusions can be obtained that: the vibration level of the pump decreases with the dynamic stiffness of rubber isolator increases. For the four kinds of rubber isolators, when the dynamic stiffness of rubber isolator is 5800N/cm, the vibration reduction effect of the isolator is the best, which reaching 38%. In addition, the dynamic stiffness of rubber isolator mainly affects the vibration of the pump in the frequency of 0–20 Hz.

An investigation into the dynamic behavior of the piston pump is an important method to reduce its vibration and noise. In this paper, an approach to predict the dynamics of a seawater hydraulic piston pump (SWHPP) from output-only transmissibility measurements is introduced. In order to eliminate the harmonic interference generated by spindle rotation, the excitation in this method is the pressure which caused by the SWHPP operating at a constant speed and under different loading conditions. The first four modes of the SWHPP were estimated utilizing the method proposed in this paper, and the influence of the pressure on the dynamics of the SWHPP structure was further studied. The experimental results indicated that peak occurred around the frequency of 20 Hz, and the reason is that the estimated second-order natural frequency (19.8 Hz) is near to the frequency of 20 Hz which is the excitation frequency of the swash plate and the flat valve of the SWHPP. In addition, this method can identify modal parameters of the piston pump structure in the working state, so it can effectively predict the dynamic behaviors of the piston pump.

Maneuverability is one of the most important performances of underwater vehicles. To improve the maneuverability of underwater vehicles, a high-pressure waterjet propulsion system combined with a Thrust Vector Control System (TVCS) was presented, which controlled the sailing trajectory through adjusting the waterjet deflection angle and thrust vector instead of rudders and sterns. The TVCS was established in the form of 3RPS Parallel Manipulator and the position feedback was provided by measuring the displacements of three actuator cylinders. The relationship between the thrust direction and the displacements of the actuator cylinders was established through the procedure of solving an inverse kinematics problem. Simultaneously, the motion transformation function of the system was derived, and the Fuzzy-PID strategy was adopted. Accordingly, the Simulink model was built, and the simulation indicated that the system had good performance. In addition, the sailing trajectory was obtained, and the results showed that the turning diameter was 78 m, and it was independent of thrust and sailing speed. The underwater vehicle utilizing high-pressure water jet propulsion with TVCS had good maneuverability at either high or low speed conditions.

Water jet propulsion is a crucial technology for ships and underwater vehicles. A high-pressure water jet propulsion system was proposed in this paper. The fundamental thrust theory of this system was studied and the influence of cavitation on the thrust was investigated. First, the mathematical model of thrust based on momentum equation coupled with cavitation theory was established. Then, the performance of cavitation two-phase flow field was simulated through computational fluid dynamics (CFD), and the thrust was calculated according to these simulation results. Finally, experiments were conducted on a test rig to study its force performance. The experimental results showed that the maximum thrust reached 4000 N with a 16-mm nozzle at the flow rate of 1200 L/min. The experimental results were both higher than the simulation and the calculation results. The theoretical force model coupled with the cavitation model was better matched with the experimental results.

Rubber isolator commonly used as support of piston pump, and the stiffness and damping nonlinearity of rubber isolator will significantly affect the vibration characteristics of piston pump. In this paper, two kinds of rubber isolators were selected, and the effect of pressure excitation amplitude on the vibration isolation effect of rubber isolator under different pressure conditions is studied. The vibration of piston pump and the base with different rubber isolators are further measured, and the vibration isolation effect of rubber isolators under different discharge pressure of piston pump is calculated. Experimental results show that: with the increase of pressure, the vibration of the piston pump and the base increases, on the contrary, the vibration isolation effect decreases. The vibration of the pump and the base with rubber isolator BE400 is lower than that of BH400. This study can contribute to the vibration and noise control of piston pump in engineering.