Chen Jiawang

Research progress in artificial upwelling and its potential environmental effects

Artificial upwelling, as a geoengineering tool, has received worldwide attention because it may actualize ocean fertilization in a sustainable way, which could potentially alleviate the pressures on the fish stocks and human-driven climate change in the ocean. We reviewed the current knowledge on the development of an artificial upwelling system and its potential environmental effects. Special attention was given to the research progress on the air-lift concept artificial upwelling by Zhejiang University. The research on artificial upwelling over the past few decades has generated a range of devices that have been successfully applied in the field for months. Based on field experiments and the associated modeling results, part of them reported positive effects on increasing primary production and enhancing CO2 sequestration. However, as a significant disturbance to the environment, especially for large-scale applications, the uncertainties related to the potential effects on ecosystem remain unsolved. Zhejiang University has overcome the technical challenges in designing and fabricating a robust and high efficiency artificial upwelling device which has been examined in two field experiments in Qiandao Lake and one sea trial in the East China Sea. It was investigated that cold and hypoxic deep ocean water (DOW) could be uplifted to the euphotic layer, which could potentially change the nutrient distribution and adjust the N/P ratio. Both simulation and field experiments results confirmed that utilizing self-powered energy to inject compressed air to uplift DOW was a valid and efficient method. Therefore, further field-based research on artificial upwelling, especially for long-term field research is required to test the scientific hypothesis.

Simulation research on the variable displacement hydraulic motor with variable effective piston stroke for hydraulic propulsion system

Variable displacement speed regulation is a good method for hydraulic propulsion system compared with throttle speed regulation and high speed on/off valve speed regulation, however the minimum variable displacement motor we can get is about 28cc/r, which is too large for a light or medium weight ROV. The variable effective piston stroke (VEPS) motor is a kind of virtual variable displacement (WD) motor which is suitable for hydraulic propulsion system. The VEPS motor have hydro-mechanically controlled poppet control valves on every cylinder of the piston motor, and have a completely symmetrical port plate instead of a kidney plate as in a conventional motor, creating a hydraulic motor capable of producing variable power. It is based on the conventional axial piston motor but with hydraulic operated poppet valves as distributor for each cylinder. All the poppet control valves are set to execute at the same setpoint(an angle position on the portplate), each cylinder works as a independent WD motor and drives the shaft with the other cylinder. The VEPS motor adjust its displacement by changing the duty ratio of the effective piston stroke. The VEPS motor can change its rotate direction, adjust its displacement just by changing the setpoint of the poppet control valves. A computer model of the VEPS motor based on AMEsim is built to check the novel variable piston motor, and the simulation results show that VEPS motor can achieve the functions mentioned above with proper parameters. The functional test of the prototype also shows that the VEPS pump-motor is feasible.