Research on flow loss of inlet duct of marine waterjets

In the process of performance prediction of waterjet system,the flow loss of inlet duct is usually reckoned by the rule of thumb. But its value is often overestimated to some extent,resulting in error of prediction accuracy. This paper introduces a new method to determine the flow loss by means of computational fluid dynamic (CFD). Firstly,the fluid field around waterjet system is simulated by solving the Reynolds Averaged Navier-Stokes (RANS) equations using commercial CFD code Fluent. Then an additional U...     

Coupled analysis of multi-body motions in offshore connecting process

The coupled dynamic responses of two pontoons while connecting with each other in irregular waves are calculated by means of 3D potential flow theory. The computation is used to find the optimal status for connecting at certain sea state. On the basis of the relative motion of two pontoons in irregular waves,visual FORTRAN programming language,as well as open graphics library (OpenGL),is used to develop a set of virtual reality system,which is fully interactive and with realistic effect. The transfinite int...     

Development of a twin-accumulator hydro-pneumatic suspension

A twin-accumulator hydro-pneumatic suspension has been developed based on the off-road vehicle in order to meet the requirements of ride comfort. The working principle and elements construct of the developed suspension are studied. And then,a mathematical model of the developed suspension is built. The influence of twin-accumulator hydro-pneumatic suspension parameters on the vehicle body vertical acceleration,suspension travel and dynamic tyre load is studied by simulation based on a quarter off-road vehic...     

Low cost and reliable anonymity protocols in P2P reputation systems

In peer-to-peer (P2P) reputation systems,each peer's trustworthiness is evaluated based on its pseudonym's rating values given by other peers. Since it is assumed that each peer has a long lived pseudonym,all the transactions conducted by the same peer may be linked by its pseudonym. Therefore,one of the fundamental challenges in P2P reputation systems is to protect peers' identity privacy. In this paper,we present two independent anonymity protocols to achieve all the peers' anonymity by changing pseudonym...     

Numerical study of the forming process of high frequency welded pipe

The roll forming process is applied to the manufacturing of high frequency welded (HFW) pipes,section steels,etc. In this paper,the roll forming process of the HFW pipe is simulated with the finite element method (FEM). A user-defined material routine of the commercial finite element code ABAQUS/Explicit is developed,and the mixed hardening constitution model is realized through the user-defined material routine. Based on the mixed hardening constitutive equation,the numerical simulation of roll forming pro...     

Performance research of a micro-CCHP system with adsorption chiller

This paper describes a new micro-combined cooling,heating and power(CCHP) system,which is especially suitable for domestic and light commercial applications. It mainly consists of a natural gas-fired internal combustion engine,a silica gel-water adsorption chiller and other heat recovery units. In order to study the energy effciency and economic feasibility,an experimental investigation has been carried out. The experimental system has a rated electricity power of 12 kW,a rated cooling capacity of 9 kW and a rated heating capacity of 28 kW. Evaluation and analysis of the system are discussed in detail. The testing results show that the energy effciency of the overall system depends on different modes. The overall thermal and electrical effciency is over 70%. Higher heat load supplied causes higher effciency of the system. Economic evaluation shows that the micro-CCHP system enjoys a small capital cost and short payback period,which is easily accepted by customers. At current natural gas price of 1.9 RMB/m3(nominal condition) and electric price of 0.754 RMB/(kW·h) ,the total capital cost is only 90 000 RMB with a payback period of 3.21 years.     

Effect of absorption layer on interior sound field of sonar dome

Using the finite element method (FEM) and boundary element method (BEM) and considering the sound absorption layer which is covered on the backing of the sonar dome, the interior field in the dome which is excited by the incident plane wave has been studied. This method is validated by comparing numerical results with that of classic elastic theory. Then the effect of parameters of the sound absorption layer on interior sound field has been analyzed. The numerical calculation results show that uniformity of interior sound pressure is improved when the backing is covered with a sound absorption layer. The thicker the layer is, or the higher the loss factor of layer is, the more uniform the sound field is.     

Analysis and enhancement of a watermarking protocol suitable for web context

AbstractA buyer-seller watermarking protocol is a combination of traditional watermarking and fingerprinting techniques. Recently, Frattolillo proposed such a watermarking protocol suitable for web context. Frattolillo’s scheme has two problems which would make it hard to implement practically. Several possible solutions to the two problems are presented in this paper.     

Opportunistic preventive maintenance optimization for multi-unit series systems with combing multi-preventive maintenance techniques

This paper proposes a dynamic opportunistic preventive maintenance (PM) optimization policy for multi-unit series systems by integrating multi PM techniques. Two PM techniques, periodic PM and sequential PM, are considered. Whenever one of the units reaches its reliability threshold, a PM action has to be performed on that unit. At that time the whole system has to be stopped and PM opportunities arise for the other units of the system. An optimal PM practice is determined by maximizing the short-term cumulative opportunistic maintenance (OM) cost savings for the whole system. Numerical examples are given to show how this approach works. Finally, a comparison between the proposed PM policy and the other policies is given.     

On the algorithms of adaptive neural network-based speed control of switched reluctance machines

AbstractA switched reluctance machine(SRM)drive is a time-varying,strongly nonlinear system.High performance control can no longer be achieved by using linear techniques.This paper describes the back-propagation (BP)neural network-based proportional-integral-derivative(PID)speed control of the SRM.It’s the interest of this paper to explore the utilization of the prior empirical knowledge as guidance in the initializing and training of the neural networks.The purpose is to make the networks less sensitive on the initial weights.Two modified algorithms are presented and simulation experiments show some interesting findings about their control effects and their corresponding sensitivity on the initial weights of the networks.