The work-class remotely-operated-underwater-vehicles (ROVs) are mainly driven by hydraulic propulsion system, and the effeciency of hydraulic propulsion system is an important performance index of ROVs. However, the efficiency of traditional hydraulic propulsion system controlled by throttle valves is too low. Therefore, in this paper, for small and medium ROVs, a novel propulsion system with higher efficiency based on high speed on/off valve control hydraulic propeller is proposed. To solve the conflict between large flow rate and high frequency response performance, a two-stage high speed on/off valve-motor unit with large flow rate and high response speed simultaneously is developed. Through theoretical analysis, an effective fluctuation control method and a novel pulse-width-pulse-frequency-modulation (PWPFM) are introduced to solve the conflict among inherently fluctuation, valve dynamic performance and system efficiency. A simulation model is established to evaluate the system performance. To prove the advantage of system in energy saving, and test the dynamic control performance of high speed on/off valve control propeller, a test setup is developed and a series of comparative experiments is completed. The smimulation and experiment results show that the two-stage high speed on/off valve has an excellent dynamic response performance, and can be used to realize high accuracy speed control. The experiment results prove that the new propulsion system has much more advantages than the traditional throttle speed regulation system in energy saving. The lowest efficiency is more than 40%. The application results on a ROV indicate that the high speed on/off valve control propeller system has good dynamic and steady-state control performances. Its transient time is only about 1 s–1.5 s, and steady-state error is less than 5%. Meanwhile, the speed fluctuation is small, and the smooth propeller speed control effect is obtained. On the premise of good propeller speed control performance, the proposed high speed on/off valve control propeller can improve the effeciency of ROV propulsion system significantly, and provides another attractive ROV propulsion system choice for engineers.

The oscillating flow field of the double nozzle flapper servo valve pre-stage is numerically analyzed through Large Eddy Simulation (LES) turbulent modeling with the previous grid independence verification. The vortex street flow phenomenon can be observed when the flow passes through the nozzle flapper channel, the vortex alternating in each side produces the periodical flow oscillation. The structural and flow parameter effects on the oscillating flow are emphasized, and it could be determined that the pressure on the flapper is nearly proportional to the flow velocity and inversely proportional to the actual distance between the flapper and the nozzle. On the other hand, the main frequency of oscillation decreases with the velocity and increases with the distance between the nozzle flapper. The main stage movement is further considered with a User Defined Function (UDF), and it could be determined that the influences of the structural and flow parameters on the flow oscillation are rarely changed, but the main frequencies drop, generally.

The throttling characteristics of the diaphragm valve are numerically studied in this paper. Firstly, the diaphragm deformation performance is analyzed by a finite element method, while the upper boundary morphology of the internal flow field under different valve openings was obtained. Then the two-dimensional simulation of the weir diaphragm valve flow field is carried out in order to explore the optimal design of flow path profile. The study shows that the throttling characteristics can be improved by flatting the ridge side wall, widening the top of the ridge and gently flatting the internal protruding of the flow path. In addition, using the local grid encryption techniques based on velocity gradient adaptive and y⁺ adaptive can improve the accuracy of simulation results. Finally, a cavitation two-phase flow simulation is carried out. The results show that cavitation may occur below 50% opening of diaphragm valve in ultra-pure water system, which becomes more intense with the increase of inlet pressure and even leading to flow saturation on the micro-orifice state.

Hydrothermal liquefaction (HTL) has been widely investigated as a suitable process method for the preparation of alternative fuels from algae, due to its mild reaction conditions and environmentally benign reaction medium. HTL requires heat input to a large amount of aqueous phase medium, which accounts for most of the heat consumption in the bio-crude preparation stage; in addition, co-processing requires bio-crude as a feedstock for the fuel refinery system. Therefore, energy consumption in the preparation stage of bio-crude is important for industrial cost control. In this paper, HTL from different types of algae and process methods is evaluated from the perspective of energy consumption. One-step HTL, two-step HTL, and co-solvent system HTL were modelled and calculated using the chemical simulation software Aspen Plus. Five algal species with lipid contents ranging from 6.15 wt% to 47.80 wt% were evaluated. The results showed that both process method and algal species had a significant effect on the energy consumption of the HTL process. The co-solvent system HTL using a methanol:water ratio of 1:19 (v/v) and an ethanol:water ratio of 3:97 (v/v) consumed less heat (based on fatty acids and fatty acid esters (FAFEs)) than one-step HTL while obtaining high quality bio-crude. Two-step HTL has about 20% higher process heat consumption, although there are advantages in bio-crude quality and by-products over one-step HTL.