基于摇板式造波机的无反射造波仿真

在海洋工程水池试验中,造波机与模型之间的二次波浪反射严重影响试验结果的准确性和可靠性。在势流理论的基础上,采用边界元法建立了二维线性数值波浪水池。通过数值模拟结果与解析解的比较,证实该数值波浪水池的适用性。采用全相位频谱分析方法作为水动力反馈,对入射和反射波进行分离,以分离的反射波信号控制摇板运动以达到吸收二次反射波浪的目的。在此基础上,对摇板式造波机在数值波浪水池中进行了无反射造波仿真试验。仿真结果表明,采用无反射造波后,能有效减弱波浪的二次反射。     

平推式造波板运动的数值模拟

平推式推板造波机是近岸及海洋工程波浪物理模型试验中非常重要的试验设备.文章通过垂向二维数学模型,利用线性造波理论来模拟造波板运动,分析了造波板前后水体动力过程,以及当造波板后不设消波设施时,造波板至后墙距离对水体动力过程的影响.该数学模型以包含水气二相流系统的Navier-Stokes方程为基本控制方程,应用粒子Lev...     

具有ARC功能的摇板式造波机的应用研究

船舶试验科学的发展促进了水池试验水平的提高,采用具有ARC(主动式消波)技术的造波系统会有效地吸收各种反射波,明显提高水池的波浪模拟质量.本文针对摇板式造波机,对主动反射吸收造波原理进行推导,提出了适用于规则波和不规则波的摇板式造波机的主动消波方法,并在水槽中设计出一套用于ARC造波的计算机控制单元板造波装置,最后通过试验结果对这种方法进行了主动消波的验证.     

堤心石级配变化对不规则波传播影响的试验研究

通过物理模型试验的方法,研究深水斜坡堤的不同质量级配堤心石对不规则波传播的影响。对不规则波的外在规律进行了统计分析,且研究入射波周期、入射波高、堤心石质量级配等因素对防波堤透浪系数的影响,拟合得到考虑无因次参数H_i/d、gT~2/d及堤心石结构B/D_(50)等因素的不规则波透浪系数的计算经验公式,为防波堤工程建设和研究提供参考依据。     

初稳性高时变特性对横摇运动的影响

研究纵浪中船舶初稳性高时变特性对横摇运动的影响。假设升沉和纵摇是准静力平衡,建立纵浪中船舶横摇参数激励运动方程,提出了稳性高波动项与瞬时波浪高度及波面升高加速度之间的函数关系式,提供了稳性高波动项的计算方法。以一艘渔政船为例,在不同航速下,分别计算规则波和非规则波中船舶参数激励横摇运动。得到稳性高波动项的时间历程及功率谱,并模拟由初稳性高随机波动引起的参数激励横摇。结果表明：在船遭遇一系列高波情况下,当特征波长接近船长,且参数激励频率集中在二倍横摇固有频率时,船舶发生参数激励大幅横摇。     

参数横摇对集装箱船设计和运营的影响

<正>纯稳性丧失、参数横摇、骑浪(横甩)是船舶在波浪中的3种典型倾覆现象,其中,参数横摇是目前国际海事组织(IMO)正在研究的船舶第二代完整稳性衡准技术中5种失效模式之一。研究人员普遍认为,参数横摇是由船舶在波浪中的复原力周期性变化而导致的非线性现象,其主要特点是:船舶在顶浪状态下产生垂荡、纵摇运动的同时伴随着大幅度横摇运动。大量研究表明,当船舶的横摇固有频率等于其在波浪中遭遇频率的50%时,船舶可能产生显著的横摇运动,即参数横摇。大型集装箱船的艏     

阻振质量对板平面弯曲波传播的阻抑

研究了无限板上受点激励时阻振质量对结构声传递的阻抑,采用基于能量观点的隔振度来定义阻振质量的阻抑作用.通过理论分析验证了隔振度简化公式的可行性.发现板平面弯曲波分别和阻振质量的弯曲波和扭转波达到最佳耦合时,平面弯曲波发生最大透射.算例分析和试验研究论证了理论分析的正确性,为阻振质量应用于结构声传递途径的控制提供了理论和试验基础.     

船舶板材几何尺寸的变化对高频感应弯板成形的影响

采用ANSYS软件对低碳钢平板的高频感应线状加热弯板成形过程进行热弹塑性有限元分析.利用相关数值结果定性分析了板材几何尺寸对温度场、最终面内收缩变形和角变形的影响,比较了3个不同尺寸平板以及单一变化板宽或板长的各类变形、应力场及塑性应变.研究结果表明,加热条件完全相同时,平板尺寸的变化对最终温度场的变化影响不大;平板长度及宽度方向的尺寸变化对平板的变形均有较大影响.     

漂移运动对横浪中船体横摇的影响

实验论述船体在激烈规则横浪中漂移运动对横摇的影响。船体运动测量结果表明，用线性切片法预估的有无舭龙骨船体的横摇运动，即使通过实验获得精确的横摇阻尼，在高波下也估计得过高。这说明，由于高频高波造成的高速漂移运动导致了横摇阻尼的增加和作用于船体上的波浪扰动力矩的减少，以及遭遇频率的变化，为精确估算高波横浪下的横摇运动，应求出波浪-频率-横摇运动和稳定漂移运动耦合方程。     

Numerical analysis of the hydroelastic behavior of a vertical plate due to solitary waves

Interactions of a vertical elastic plate with fully nonlinear water waves were simulated. Utilizing the mixed Eulerian Lagrangian method for the free-surface flow and the finite element method for the deflection of an elastic plate, a fully coupled scheme for accurately determining fluid–plate motions was developed. Using this scheme, some modifications to the solvers for both fluid and plate were made. A hybrid wave-absorbing beach was installed to prevent wave reflection from the end of the wave tank. A fourth-order Runge–Kutta time-marching scheme with a uniform time step was applied to achieve numerical stability. The method was validated by simulating the wave generated by the initial deformation of a vertical plate and comparing the result with the corresponding analytical solution. For further validation, the hydroelastic behavior of a vertical plate induced by a pulse-type wave (where the initial pulse-type elevation of the free surface is specified) was computed, and the result was compared with another numerical result from a mode-expansion method. The interaction of a surface-piercing plate with nonzero initial free surface was then simulated, and the result was compared with the corresponding linear analytical solution. Finally, the hydroelastic response of a surface-piercing vertical plate due to a solitary wave (generated by actuating the vertical plate at the right end of the tank only at the beginning) was computed and investigated systematically.     

经过海峡的双层流体由底部波动产生的斜向波散射问题研究(英文)

The problem of oblique wave(internal wave) propagation over a small deformation in a channel flow consisting of two layers was considered.The upper fluid was assumed to be bounded above by a rigid lid,which is an approximation for the free surface,and the lower one was bounded below by an impermeable bottom surface having a small deformation;the channel was unbounded in the horizontal directions.Assuming irrotational motion,the perturbation technique was employed to calculate the first-order corrections of the velocity potential in the two fluids by using Green’s integral theorem suitably with the introduction of appropriate Green’s functions.Those functions help in calculating the reflection and transmission coefficients in terms of integrals involving the shape function representing the bottom deformation.Three-dimensional linear water wave theory was utilized for formulating the relevant boundary value problem.Two special examples of bottom deformation were considered to validate the results.Consideration of a patch of sinusoidal ripples(having the same wave number) shows that the reflection coefficient is an oscillatory function of the ratio of twice the x-component of the wave number to the ripple wave number.When this ratio approaches one,the theory predicts a resonant interaction between the bed and the interface,and the reflection coefficient becomes a multiple of the number of ripples.High reflection of incident wave energy occurs if this number is large.Similar results were observed for a patch of sinusoidal ripples having different wave numbers.It was also observed that for small angles of incidence,the reflected energy is greater compared to other angles of incidence up to.These theoretical observations are supported by graphical results.     

Scattering of surface waves by the edge of a small undulation on a porous bed in an ocean with ice-cover

Scattering of surface waves by the edge of a small undulation on a porous bed in an ocean of finite depth, where the free surface has an ice-cover being modelled as an elastic plate of very small thickness, is investigated within the framework of linearized water wave theory. The effect of surface tension at the surface below the ice-cover is neglected. There exists only one wave number propagating at just below the ice-cover. A perturbation analysis is employed to solve the boundary value problem governed by Laplace＇s equation by a method based on Green＇s integral theorem with the introduction of appropriate Green＇s function and thereby evaluating the reflection and transmission coefficients approximately up to first order. A patch of sinusoidal ripples is considered as an example and the related coefficients are determined.     

迎浪船舶的参数横摇分析

  目的  参数横摇是船舶在波浪中的特殊失稳现象,现有研究认为,波浪经过船体时稳性参数的变化是激发船体横摇的主要原因,但其力学机理并不明确。  方法  首先,基于惯性坐标下的垂荡和纵摇耦合运动方程,以及船体坐标下的横摇运动方程,建立垂荡、纵摇和横摇的混合动力学模型;然后采用所提出的摇荡耦合切片计算方法,数值计算船舶参数横摇运动,分析数值计算的横摇运动规律,并基于能量原理提出发生参数横摇的衡准。  结果  研究结果表明,船舶发生参数横摇的力学机理是,在横摇角增大过程中回复力矩系数吸收的能量小于横摇角减小过程中回复力矩释放的能量;发生参数横摇的衡准是,回复力矩系数一阶谐波分量的相位角位于[0,π]内。  结论  明确参数横摇力学机理有助于深入认识参数横摇失稳模式的物理本质,提出的参数横摇衡准对于船舶第2代完整稳性衡准的制定具有参考意义。     

水下非接触爆炸载荷下双层底结构单元抗冲击性能研究

舰船结构水下非接触爆炸的动态响应研究是舰船生命力评估的基础。基于普通双底结构,设计了3种新式的X型、Y型双底单元和Ⅰ型双层底结构单元,分析了4种结构在200 kg TNT炸药不同爆距冲击波载荷作用下的损伤变形特征,运动响应以及结构的吸能特性。结果表明,X型、Y型单元吸收较少能量,尤其内底板吸收能量少,应变、冲击速度和加速度响应值也小,内底板更安全。Ⅰ型单元外底板的变形和应变小,其安全半径约为15 m,其余3种单元安全半径都约为20 m。4种结构临界半径都小于10 m。     

低频波浪在常水深地形中传播的数值研究

利用基于Boussinesq方程的波浪辐射应力计算模型,模拟常水深地形中传播的低频波浪,研究其形态变化,以及低频波浪与波浪辐射应力之间的关系。结果发现约束长波的波幅和波群的辐射应力值基本保持在某一均值不变;主频的波幅、约束长波的波幅都会做一定周期的震荡,同时波群的辐射应力也随之而震荡,三者之间的变化关系是波群非线性能量传递的表现。     

舵速对船舶波浪中回转及横摇的影响

基于经典MMG模型和统一理论建立操纵性和横摇四自由度耦合模型,利用耦合模型叠加波浪力的方式来预报船舶波浪中的回转和横摇特性。波浪力采用三维面元法计算,并根据船舶实时速度和遭遇浪向进行二维插值。通过自航模试验进行模型验证,预报了不同操舵速度对船舶回转和横摇的影响。研究表明耦合模型能够有效地仿真船舶的回转及横摇,回转过程中操舵速度越大船舶改变航向和航迹的能力越强,纵距越小,但会给船舶造成较大的横摇。     

On the dispersion relation of hydroelastic waves in a plate

This paper deals with the dispersion relation of hydroelastic waves in pontoon-type very large floating structures (VLFS) using a simple beam modeling, where the term hydroelastic waves means propagation of deflection vibrations in VLFS. The purpose of this paper is to show the properties of the hydroelastic waves. The dispersion relation of hydroelastic waves propagating in an infinite plate floating on the water is derived based on the linear water wave theory. The effects of the water depth and of the bending rigidity of the floating plate on the wavelength, phase velocity, and group velocity of the hydroelastic waves are shown theoretically or numerically. Then, the dispersion relation of hydroelastic waves in a finite plate floating on shallow water is investigated. It is shown that the wavelength or the phase velocity of the hydroelastic waves varies with the location in the plate. Received for publication on April 7, 1999; accepted on Aug. 20, 1999     

随机波中船舶参数横摇研究

针对随机波中船舶参数横摇,提出一种数值预报方法。采用新的随机波成形方法,求解出船舶无横倾时在随机波中时间序列垂荡和纵摇运动,确定出船-波相对位置。利用3个坐标系之间的转换关系确定船体各横剖面左右舷与波面瞬时交点,然后对波浪压力沿船长湿表面积分,得出船舶复原力的Froude-Krylov部分。提出复原力之辐射力和绕射力部分和横摇角的非线性假定。确定一个参数横摇数学模型,实现随机波中参数横摇计算;通过试验和数值模拟对一艘巴拿马型集装箱船进行了参数横摇预报,研究了随机波中参数横摇的实际非各态历经的特点。     

水下运动物体产生内波的研究进展

水下运动物体产生内波是内波动力学研究的一项重要内容,具有重要的军事应用价值。依据水下运动物体对周围层化流体扰动方式的不同,将水下运动物体产生的内波分为两类：Lee波和尾流内波。文章首先在综合Lee波产生机制的基础上,对Lee波的理论、实验和数值研究工作进行了归纳,并给出了通过这三种手段对Lee波进行研究所取得的成果。同时,对尾流塌陷内波和尾流随机内波的研究状况和研究成果进行了介绍和总结。最后,提出在推进水下运动物体产生内波的研究过程中需要关注的几个问题和相应的研究思路。