新型高效活鱼起捕系统设计与试验

针对当前发展迅速的双罐式真空活鱼起捕装置采用的抽吸同步和零压排鱼方式会在一定程度上制约活鱼起捕系统初始吸力和排鱼动力的问题,设计出一套具有预抽真空和加压排鱼功能的双罐式真空起捕系统。对该系统的组成和原理进行阐述,并给出真空罐和真空泵等主要设备相关参数的计算方法,形成完整的系统设计流程。在此基础上研制活鱼起捕样机,并对其进行鱼水比、真空度、吸程和临界压力试验,验证该设计的合理性,获取系统运行的最佳参数。试验结果表明：当鱼水比约为1∶1时,系统的起捕效率最高;当罐体内的负压值维持在-65 kPa～0时,鱼体的损伤率相对较小;3 m、4 m、5 m和6 m吸程对应的临界压力分别为-15 kPa、-18 kPa、-22 kPa和-27 kPa;当维持压力为-65 kPa时,该起捕样机能满足吸程3m～6m的工作需求,且鱼损率较小,可认定其为系统工程运用中最佳的真空度设定值。     

Numerical Simulation of Focused Wave and Its Uncertainty Analysis

On the basis of the transient water wave (TWW) theory, focused wave is generated in the circulating water channel. Numerical simulation of the focused wave is carried out by solving the Reynolds averaged Navier-Stokes (RANS) equations. The dynamic grid technique is adopted to simulate the motion of the wave maker, and the volume of fluid (VOF) method is used to capture the free surface of the wave. The simulation results are compared with the measured data, and good agreement is obtained. For quantitative estimation of the numerical simulation error and uncertainty, the uncertainty analysis method recommended by the International Towing Tank Conference (ITTC) procedure is performed for the simulation results of the surface elevations at different positions. Both grid-convergence and time-step-size convergence studies are conducted using three types of grids and time step sizes. The simulation results are all monotonously convergent in the verification procedure, and the validations of the simulated surface elevations with the positions at 3.5, 4.0 and 4.5m are all achieved by comparing with the validation uncertainty. It is found that the numerical simulation errors caused by the grid and time-step-size in the convergence studies have the same order of magnitude. In addition, the numerical errors and uncertainties for the surface elevations at different positions are compared and discussed in detail. This paper presents the first attempt to carry out the uncertainty analysis of the simulation of focused wave, and the effectiveness of the proposed verification and validation procedures in the uncertainty analysis is demonstrated.