浅水中航行船舶的水动力系数

本文利用切片理论数值研究了浅水中前进船舶的水动力系数.为计及水深的影响,采用简单格林函数方法求解剖面水动力系数,提出了满足辐射条件的一种较方便的数值方法.计算了一数学船型的水动力系数,并与有关文献结果比较验证了数值方法的可行性.数值结果显示了水底效应对航行船舶水动力的影响,为进一步研究浅水航行船舶的耐波性提供了基础.     

能量耗散效应的多域边界元法(英文)

The wave diffraction and radiation around a floating body is considered within the framework of the linear potential theory in a fairly perfect fluid.The fluid domain extended infinitely in the horizontal directions but is limited by the sea bed,the body hull,and the part of the free surface excluding the body waterplane,and is subdivided into two subdomains according to the body geometry.The two subdomains are connected by a control surface in fluid.In each subdomain,the velocity potential is described by using the usual boundary integral representation involving Green functions.The boundary integral equations are then established by satisfying the boundary conditions and the continuous condition of the potential and the normal derivation across the control surface.This multi-domain boundary element method(MDBEM) is particularly interesting for bodies with a hull form including moonpools to which the usual BEM presents singularities and slow convergence of numerical results.The application of the MDBEM to study the resonant motion of a water column in moonpools shows that the MDBEM provides an efficient and reliable prediction method.     

军船雷达目标有效截面预报和缩减研究(英文)

Radar cross section(RCS) is the measurement of the reflective strength of a target.Reducing the RCS of a naval ship enables its late detection,which is useful for capitalizing on elements of surprise and initiative.Thus,the RCS of a naval ship has become a very important design factor for achieving surprise,initiative,and survivability.Consequently,accurate RCS determination and RCS reduction are of extreme importance for a naval ship.The purpose of this paper is to provide an understanding of the theoretical background and engineering approach to deal with RCS prediction and reduction for naval ships.The importance of RCS,radar fundamentals,RCS basics,RCS prediction methods,and RCS reduction methods for naval ships is also discussed.     

液舱晃荡与浮体非线性耦合运动分析(英文)

Nonlinear interactions among incident wave, tank-sloshing and floating body coupling motion are investigated. The fully nonlinear sloshing and body-surface nonlinear free surface hydrodynamics is simulated using a Non-Uniform Rational B-Spline (NURBS) higher-order panel method in time domain based on the potential theory. A robust and stable improved iterative procedure (Yan and Ma, 2007) for floating bodies is used for calculating the time derivative of velocity potential and floating body motion. An energy dissipation condition based on linear theory adopted by Huang (2011) is developed to consider flow viscosity effects of sloshing flow in nonlinear model. A two-dimensional tank model test was performed to identify its validity. The present nonlinear coupling sway motion results are subsequently compared with the corresponding Rognebakke and Faltinsen (2003)’s experimental results, showing fair agreement. Thus, the numerical approach presented in this paper is expected to be very efficient and realistic in evaluating the coupling effects of nonlinear sloshing and body motion.     

载人深潜器接近海底结构物时水动力变化特性研究

采用数值模拟和试验相结合的方法对某型载人深潜器水下接近海底结构物时的水动力变化规律进行了研究,验证了数值方法的可靠性,通过数值模拟对物理试验的外延,得到了许多重要的水动力的变化规律,对载人深潜器操纵性能预报具有参考价值,对水下物体间的协同工作具有一定的指导意义。     

考虑流动分离的有限宽楔形剖面匀速入水受力分析

文章基于MLM砰击模型（Modified Logvinovich Model）研究有限宽度楔形剖面匀速入水受力问题。当流动在折角处分离后,通过引入虚拟物面扩展MLM计算方法适用范围,使其可以考虑流动分离对剖面受力的影响。并计算了垂向水动力在流动分离前、后随时间的变化。将结果与非线性数值解、试验值进行比较表明：这是一种相对简单且计算快速的有效方法,易于工程实际应用。     

不规则波中二阶辐射问题时域数值模拟

能够有效地模拟不规则波中非线性的波物相互作用是深海工程领域一直关心的热点问题,因此有必要采用时域理论对不规则波中非线性的波物相互作用进行研究和分析。对自由面和物面条件进行Taylor 级数和Stokes摄动展开得到一阶和二阶边值问题。使用基于Rankine源的边界元法计算每一时刻的流场,并在自由面上采用积分格式的自由面条件;在远方控制面上采用多次透射边界条件以及其耦合阻尼区的边界条件;对做不规则垂荡运动的截断圆柱所受到的水动力进行了时域数值模拟。结果表明：文中方法可以用于时域研究不规则波中的二阶问题,在人工边界处达到无反射的效果。     

Time-domain simulation for water wave radiation by floating structures （Part A）

Direct time-domain simulation of floating structures has advantages： it can calculate wave pressure fields and forces directly; and it is useful for coupled analysis of floating structures with a mooring system. A time-domain boundary integral equation method is presented to simulate three-dimensional water wave radiation problems. A stable form of the integration free-surface boundary condition （IFBC） is used to update velocity potentials on the free surface. A multi-transmitting formula （MTF） method with an artificial speed is introduced to the artificial radiation boundary （ARB）. The method was applied to simulate a semi-spherical liquefied natural gas （LNG） carrier and a semi-submersible undergoing specified harmonic motion. Numerical parameters such as the form of the ARB, and the time and space discretization related to this method are discussed. It was found that a good agreement can be obtained when artificial speed is between 0.6 and 1.6 times the phase velocity of water waves in the MTF method. A simulation can be done for a long period of time by this method without problems of instability, and the method is also accurate and computationally efficient.     

粘性和航行姿态对高速船运动预报的影响

发展了基于二维半理论的预报排水型单体船在波浪上的水动力特征及运动性能的方法。采用横向流方法对常规高速排水型单体船所受的粘性影响进行修正。在考虑粘性影响和航行姿态的条件下,对NPL系列单体船和SER IES64单体船型的运动性能作了理论预报,并与船模试验结果和势流理论预报结果作了比较。结果表明:考虑粘性影响能够在一定程度上降低高速常规排水型船舶运动预报的峰值,而航行姿态对其影响不大。     

船体在波浪中的非线性水动压力

本文提出了一个预报船体在波浪中大幅运动时非线性水动压力场的二维时域理论。船体扰动势用时域自由面格林函数和在入射波下的瞬时湿表面上的分布源求解;与非线性水动压力场相匹配的船体运动用差分法求得。为提高计算效率和避免数值过程发散,采用了改进的数值模型和方案。通过线性理论计算与模型试验结果的比较,指出了线性切片理论在预报水动压力场时的不足,水动压力与波高的非线性关系及正负水动压力沿船体表面的分布在Wigley船的计算比较中得到了说明。初步计算表明,该理论的实用化发展前景是令有鼓舞的。相应的计算机程序可在PC机上运行。