Influence of Cathode Materials on Opening Performance of Plasma Opening Switch

Experiments have been conducted on a plasma opening switch (POS) test-bed to investigate the influence of cathode materials made of aluminum, stainless steel, molybdenum and tungsten on opening performance for conduction time up to 3 microseconds, conduction current up to 100 kA. Remarkaly different opening characteristics have been shown for these materials,with tungsten being of the best opening performance.

Effect of Time Step Size and Turbulence Model on the Open Water Hydrodynamic Performance Prediction of Contra-Rotating Propellers

A growing interest has been devoted to the contra-rotating propellers （CRPs） due to their high propulsive efficiency, torque balance, low fuel consumption, low cavitations, low noise performance and low hull vibration. Compared with the single-screw system, it is more difficult for the open water performance prediction because forward and aft propellers interact with each other and generate a more complicated flow field around the CRPs system. The current work focuses on the open water performance prediction of contra-rotating propellers by RANS and sliding mesh method considering the effect of computational time step size and turbulence model. The validation study has been performed on two sets of contra-rotating propellers developed by David W Taylor Naval Ship R ＆ D center. Compared with the experimental data, it shows that RANS with sliding mesh method and SST k-ω turbulence model has a good precision in the open water performance prediction of contra-rotating propellers, and small time step size can improve the level of accuracy for CRPs with the same blade number of forward and aft propellers, while a relatively large time step size is a better choice for CRPs with different blade numbers.

Kappel型叶梢纵斜螺旋桨的尺度效应研究

In this paper,the scale effect of Kappel tip-rake propellers with different end plate designs was studied using computational fluid dynamics.Given the base size of the mesh and the appropriate numerical model for the determined simulation,the open-water performance of three Kappel propellers with different bending degrees of the end plate at different scales was calculated.Comparing the scale effect of these propellers,the scale effect of the torque coefficient of a Kappel propeller is more intense than that of the conventional propeller.In addition,the scale effect of the torque coefficient is strong when the bending degree of the end plate increases,dwarfing the scale effect on the thrust coefficient.Following the research on the scale effect of the wake field for the Kappel propeller,the laws that reveal the influence of the scale on the wake field were summarized;that is,the high-speed zone in the wake relatively expands with the increase of the scale in company with a trend of tip cross flow.The research reveals the basic variation trend and rule of the open-water performance and wake distribution for the Kappel propeller under different scales within the Reynolds number range of 4.665×10^(5)-8.666×10^(7)consideringγtransition,as well as the characteristic differences between the Kappel propellers with different end plate designs,which will be of great significance to its optimization design and application to marine vehicles of different scales.

船用螺旋桨叶片应力的数值分析

In this study,a series of numerical calculations are carried out in ANSYS Workbench based on the unidirectional fluid–solid coupling theory.Using the DTMB 4119 propeller as the research object,a numerical simulation is set up to analyze the open water performance of the propeller,and the equivalent stress distribution of the propeller acting in the flow field and the axial strain of the blade are analyzed.The results show that FLUENT calculations can provide accurate and reliable calculations of the hydrodynamic load for the propeller structure.The maximum equivalent stress was observed in the blade near the hub,and the tip position of the blade had the largest stress.With the increase in speed,the stress and deformation showed a decreasing trend.

Single-shot incoherent optical processing of microwave signals： opening the path to low cost high performance analog photonics

Incoherent optical processing of microwave signals,where low-coherence broadband light sources are employed instead of costly mode locked lasers,has attracted great interest thanks to its wide applications in microwave photonics filtering[1–3],arbitrary generation[4–6]and analog to digital conversion[7]。

A Study on Performance and Reliability of Urethral Valve Driven by Ultrasonic-vaporized Steam

The aim of this study is to investigate the performance and reliability of urethral valve driven by ultrasonic-vaporized steam.The performance model of urethral valve is established to analyze the driving and opening/closing performances of urethral valve.The reliability model of urethral valve is obtained,and the reliability simulation algorithm is proposed to calculate the reliability index of urethral valve.The numerical simulation and experimental results show that urethral valve has a good opening/closing performance,the driving performance can be improved by increasing ultrasonic intensity,radiation area and ultrasonic frequency,and the corrosion and aging of driving bags are the weak links of urethral valve.

NUMERICAL RESEARCHES ON INTERACTION BETWEEN PROPELLERS IN UNIFORM FLOW

Numerical simulations of the flow around two bidirectional staggered propellers are conducted in uniform flow. The computed open water performance of the fore-propeller is compared with the corresponding experimental results, and the influence of the fore-propeller on the aft one is carefully investigated. It is found that the inflow around the aft propeller close to the side of the fore is especially affected by the fore one, leading to abnormal circumferential distribution of force on the blade in the shade region. For either forces or velocity distributions, the abnormal changes behave contrarily for cases with the rotating speed larger or smaller than the idle. Moreover, the more the rotating speed of the fore differs from the idle, the larger the abnormal values become.