Energy performance evaluation of an innovative hydrostatic motor

The innovative motor uses seawater pressure energy, a green and renewable energy, to drive the underwater equipment. In this paper, the motor is employed in a seafloor sediment corer and drives the corer to operate as a pile-driver. The structure and working principles of the motor are briefly introduced together with its integration into a sediment corer. Then, the paper emphasizes the energy performance evaluation of the motor in driving the sediment corer. Because the output energy of the motor is the kinetic energy that is derived from the hammering action of the corer head, the analytical model of motor during the hammering stroke is constructed and used to calculate the hammering velocity and the hammering number. The model is validated through lab tests, and some important parameters are identified by the sea trial. Based on the validated model, it is found that the hammering velocity increases with the weight of the corer head, but the hammering number declines. The total output energy reaches the peak at a certain mass of the corer head and then declines sharply while the energy conversion efficiency continues to increase monotonically. Therefore, by adjusting the weight of the corer head, which is the payload of the motor, the energy performance of the motor can be optimized for specific applications. The analysis results demonstrate that the motor is capable of directly converting seawater pressure energy into the mechanical energy with high efficiency.