The Optimization Design of the Nozzle Section for theWater Jet Propulsion System Applied in Jet Skis

The performance of a water jet propulsion system is related to the inlet duct,rotor,stator,and nozzle.Generally,the flow inlet design must fit the bottom line of the hull,and the design of the inlet duct is often limited by stern space.The entire section,from the rotor to the nozzle through the stator,must be designed based on system integration in that the individual performance of these three components will influence each other.Particularly,the section from the rotor to the nozzle significantly impacts the performance of a water jet propulsion system.This study focused on nozzle design and established referable analysis results to facilitate subsequent integrated studies on the design parameters regarding nozzle contour.Most existing studies concentrate on discussions on rotor design and the tip leakage flow of rotors or have replaced the existing complex computational domain with a simple flow field.However,research has yet to implement an integrated,optimal design of the section from the rotor to the nozzle.Given the above,our program conducted preliminary research on this system integration design issue,discussed the optimal nozzle for this section in-depth,and proposed design suggestions based on the findings.This program used an existing model as the design case.This study referred to the actual trial data as the design conditions for the proposed model.Unlike prior references’simple flow field form,this study added a jet ski geometry and free surface to the computational domain.After the linear hull shape was considered,the inflow in the inlet duct would be closer to the actual condition.Based on the numerical calculation result,this study recommends that the optimal nozzle outlet area should be 37%of the inlet area and that the nozzle contour should be linear.Furthermore,for the pump head,static pressure had a more significant impact than dynamic pressure.

Flow structures of gaseous jets injected into water for underwater propulsion

Gaseous jets injected into water are typically found in underwater propulsion, and the flow is essentially unsteady and turbulent. Additionally, the high water-to-gas density ratio can result in complicated flow structures; hence measuring the flow structures numerically and experimentally remains a challenge. To investigate the performance of the underwater propulsion, this paper uses detailed NavierStokes flow computations to elucidate the gas-water interactions under the framework of the volume of fluid （VOF） model. Furthermore, these computations take the fluid compressibility, viscosity, and energy transfer into consideration. This paper compares the numerical results and experimental data, showing that phenomena including expansion, bulge, necking/breaking, and back-attack are highlighted in the jet process. The resulting analysis indicates that the pressure difference on the rear and front surfaces of the propul- sion system can generate an additional thrust. The strong and oscillatory thrust of the underwater propulsion system is caused by the intermittent pulses of the back pressure and the nozzle exit pressure. As a result, the total thrust in underwater propulsion is not only determined by the nozzle geometry but also by the flow structures and associated pressure distri- butions.

On Prediction of Longitudinal Attitude of Planing Craft Based on Controllable Hydrofoils

The purpose of this research study was to examine the attitude response of a planing craft under the controllable hydrofoils.Firstly,a non-linear longitudinal attitude model was established.In the mathematical model,effects of wind loads were considered.Both the wetted length and windward area varied in different navigation conditions.Secondly,control strategies for hydrofoils were specified.Using the above strategies,the heave and trim of the planing craft was adjusted by controllable hydrofoils.Finally,a simulation program was developed to predict the longitudinal attitudes of the planing craft with wind loads.A series of simulations were performed and effects of control strategies on longitudinal attitudes were analyzed.The results show that under effects of wind loads,heave of fixed hydrofoils planing craft decreased by 6.3%,and pitch increased by 8.6% when the main engine power was constant.Heave decreased by less than 1% and trim angle decreased by 1.7% as a result of using variable attack angle hydrofoils;however,amplitude changes of heave and pitch were less than 1% under the control of changeable attack angle hydrofoils and longitudinal attitude.

Biologically-Inspired Water Propulsion System

Most propulsion systems of vehicles travelling in the aquatic environment are equipped with propellers. Observations of nature, however, show that the absolute majority of organisms travel through water using wave motion, paddling or using water jet power. Inspired by these observations of nature, an innovative propulsion system working in aquatic environment was developed. This paper presents the design of the water propulsion system. Particular attention was paid to the use of paddling techniques and water jet power. A group of organisms that use those mechanisms to travel through water was selected and analysed. The results of research were used in the design of a propulsion system modelled simultaneously on two methods of movement in the aquatic environment. A method for modelling a propulsion system using a combination of the two solutions and the result were described. A conceptual design and a prototype constructed based on the solution were presented. With respect to the solution developed, studies and analyses of selected parameters of the prototype were described.

基于最新数值行星历表的行星轨道仿真研究

为发展月球和行星探测,美国喷气推进实验室(Jet Propulsion Laboratory,JPL)、法国天体力学与历算研究所(Institut de Mécanique Céleste et de Calcul deséphémérides,IMCCE)、俄罗斯科学院应用天文研究所(Institute of Applied Astronomy of the Russian Academy of Sciences,IAA RAS)分别研制了各自的行星历表。就各个行星历表的发展历程进行概括,对最新版本的3个历表DE438、INPOP19a和EPM2017进行分析,并通过仿真计算比较了月球和行星在太阳质心参考系中的位置和速度的差异,评估了最新历表的相对精度,为中国深空探测和自主历表研制提供技术支撑。结果表明,历表间差异均较小,但月球历表的精度有待提高。