An investigation of free surface effects on drag and lift coefficients of an autonomous underwater vehicle (AUV) using computational and experimental fluid dynamics methods

In the present paper, in order to investigate the effect of free surface on drag and lift coefficients of an Autonomous Underwater vehicle,¹ two phase flow Reynolds Averaged Navier–Stokes (RANS) equations were solved using computational fluid dynamics. The numerical results were compared with those obtained from both numerical single phase flow simulations and the experiments conducted in the towing tank of the Subsea R&D Center at Isfahan University of Technology, using a 1:1 scale model of AUV developed in this center. The study was conducted at various submergence depths ranging from 0.87 to 5.22 of the AUV diameter and at the speeds of 1.5 and 2.5 m/s (corresponding to Reynolds numbers of 1.9 and 3.17 million, respectively). The variation of drag and lift coefficients of the AUV with the submergence depth were shown to be very sensitive to the AUV speed.     

复合式循环养殖系统——"藻塘"与"食藻动物塘"研究进展

近年来随着海水养殖业的发展,因海水养殖而对环境造成的污染得到人们的重视,联合养殖系统作为一种环境友好的养殖方法,成为目前海水养殖的研究热点.本文综述了联合养殖系统中"藻塘"和"食藻动物塘"的研究进展,并对其未来发展方向进行了预测.     

贮箱漏率正压检测方法

氦质谱检漏技术是目前国内外应用较多的一种先进的检漏技术。"贮箱漏率正压检测方法"是为适应航天贮箱结构复杂、漏率要求严格等特点而开发的一种氦质谱检漏方法。被检容器充正压,外部集气容器保持常压或抽成真空,实现正压差累积法检漏和压力真空检漏,消除了人为及环境因素影响,具有检测效率高、结果精确、安全可靠等优点。经测算该检测方法较传统方法可降低成本30%。     

低温容器绝热真空丧失后的绝热夹层漏热量计算分析

真空丧失对低温容器的安全性是一大威胁,可能会造成严重后果。文中通过实验,利用氮气为破空介质,测得了高真空多层绝热低温容器在真空丧失情况下的排放率,根据测得的排放率计算了热流密度。结果表明,根据测得的排放率,不考虑液体温度变化计算得到的热流密度与考虑液体温度变化计算得到的热流密度之间存在差异。     

坦克用光电系统的发展现状及趋势

综述了坦克用光电系统的发展过程，现状及发展趋势。     

An efficient numerical tank for non-linear water waves,based on the multi-subdomain approach with BEM

An efficient 2D non-linear numerical wave tank called LONGTANK has been developed based on a multi-subdomain (MSD) approach combined with the conventional boundary element method (BEM). The multi-subdomain approach aims at optimized matrix diagonalization, thus minimizing the computing time and reserved storage. The CPU per time step in LONGTANK simulation is found to increase only linearly with the number of surface nodes, which makes LONGTANK highly efficient especially when simulating long-time wave evolutions in space. Appropriate treatment of special points on the boundary ensures high resolution in LONGTANK simulation beyond initial deformation and breaking, which allows detailed study of breaking criterion, breaker morphology, breaking dissipation, vorticity generation, etc. Detailed numerical implementation has been given with demonstration of LONGTANK simulations.     

Influence of skirt radius on performance of circular clarifier with density stratification

A numerical model for predicting the velocity field and suspended solids distribution in a secondary circular clarifier with density difference is evaluated. The density effects are characterized by the inlet densimetric Froude number. This study focuses on the role of the reaction baffle position in the performance of the clarifiers. For a large-radius baffle and low densimetric Froude number an important phenomenon known as the density waterfall occurs in the inlet zone of the clarifiers. This was predicted by the numerical model and confirmed by the physical model tests. This model consists of a series of conservation equations for fluid mass and momentum and sediment concentration. The turbulent stresses are calculated by use of the eddy viscosity concept and the κ–?. turbulence model. The study showed that the density waterfall results in high entrainment and high recirculation. A comparison of the solids concentration distribution for a tank with a small skirt radius to that with a large skirt radius shows that small skirt radius reduces the density waterfall effect and significantly improves the clarifier performance at low densimetric Froude numbers.     

A new parameterization of temperature structure parameter in entraining convective boundary layer

Temperature structure parameter () controls the propagation of electromagnetic and acoustic waves in the atmospheric boundary layer (ABL), but it is difficult to be measured, especially in the upper part of the ABL. In this paper, optical turbulence is simulated in a laboratory convective tank, and profiles in the tank are measured by using laser beam patterns. Simulation results show that the Wyngaard’s scaling relationship for in the entrainment layer is only valid for large convective Richardson number (Ri > 40) cases. When Ri < 40, a new scaling relationship is proposed based on the laboratory and field measurements. The application of these relationships in estimating optical turbulence in the entrainment layer is discussed.