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。     

Comparison of numerical and experimental results of nonlinear wave-induced vertical ship motions and loads

 A nonlinear time-domain procedure is presented which is used to calculate the vertical responses of a container ship advancing in head waves. The method assumes linear radiation forces represented by time convolution of memory functions, infinite frequency added masses, and radiation restoring coefficients. The nonlinear hydrostatic restoring and Froude–Krilov forces are computed exactly over the instantaneous wetted surface of the ship's hull. Forces due to green water on deck are calculated using the momentum method. Nonlinear effects are identified on different vertical ship responses, namely on the heave and pitch motions, the vertical accelerations, and the vertical bending moment. These non-linear effects are expressed by the variation of the transfer function with the wave amplitude, the higher-order harmonics of the time signals, the offset of the time series, and the asymmetry of the peaks. The numerical results and the quantified nonlinear effects are compared with experimental results showing an ability to reproduce the main nonlinear effects. Received: December 17, 2001 / Accepted: January 31, 2002     

波激振动和砰击颤振对大型油船疲劳强度影响研究

文章给出线性波激振动和砰击颤振引起的大型油船结构疲劳贡献度的计算方法。基于三维线性水弹性理论可计算得到包括刚体和2节点的振动模态下的垂向弯矩的传递函数,采用谱分析法对某30万吨油船进行结构疲劳强度计算,分析波激振动对船体结构疲劳损伤影响;基于二维非线性波浪载荷程序（含砰击颤振的波浪载荷）,采用时域方法对该油船进行船体梁弯矩计算,分析砰击颤振对船体梁弯矩及疲劳载荷的影响;结果表明对于该类大型油船波激振动和砰击颤振对船体的结构疲劳损伤的影响不可忽略。     

水下爆炸二次脉动压力下舰船抗爆性能研究

将船体梁视为两端自由的Timoshenko梁,在借用二维切片法和水弹性方法的基础上,计算船体染在水下爆炸二次脉动压力下的响应特性。同时,还建立了在考虑水面效应和气泡运动时舰船受到二次脉动压力的计算模型。最后,分析了浮筏式减振装置在水下爆炸二次脉动压力下船用设备的减振抗冲性能。     

船体湿表面脉动压力预报的三维非线性方法

本文给出了一种预报船体湿表面脉动压力响应的三维非线性时历模拟方法.计及瞬时物面变化引起的各种非线性因素,在时域内建立船体非线性运动方程.在每一时刻,认为船体以其瞬时平均湿表面为平衡位置做简谐振荡运动,利用三维线性频域解来简化运算.在此基础上,进一步将绕射和辐射问题在静平衡位置求解,仅考虑占主导地位的入射波和静恢复力变化的非线性,作为一种兼顾工程需要的计算精度和计算效率的简化方法.以此方法为基础编制了计算机程序,对实船进行了计算,并与模型试验进行了对比.分析比较表明,该方法能够给出令人满意的船体湿表面脉动压力响应预报结果.     

一种船舶运动和载荷响应的非线性预报方法

首先采用半解析的方法得到时域水动力系数,并给出一些数值计算时实用性的建议,然后计及瞬时湿表面变化引起的非线性恢复力和入射波力并在时间域内计算运动方程,最后对实船进行了运动和载荷预报,数值结果与模型试验数据对比表明,载荷非线性要比运动非线性明显;采用的计及非线性影响的预报方法是切实可行的。     

An approach to estimating the hull girder response of a ship due to springing

This article describes an estimation method for the hull girder response of a ship due to springing. The linear and nonlinear springing effects on the hull girder are evaluated. Previous studies on the springing response focused mainly on the symmetric response, or vertical response. In this article, however, the springing analysis is extended to asymmetric responses, or horizontal and torsional responses. The Timoshenko beam model was used to calculate the hull girder response and the quadratic strip method was employed to calculate hydrodynamic forces and moments on the hull. To remove irregular frequencies, a rigid lid was adopted on the hull free surface level and hydrodynamic coefficients were interpolated for asymptotic values. Applications to two ships for the symmetric and asymmetric responses were carried out and the effect of springing responses is also discussed.     

弹性船体波激响应时域过程的数值模拟

本文从入射波的波浪现实出发，用非线性水弹性积分─微分法进行船体运动和结构动响应的时间历程模拟，直接将试验测量结果与理论计算在时域内作比较，这有利于揭示砰击和上浪等非线性瞬态作用导致冲荡响应的力学机理。这种模拟及其验证方法避免了对理论和试验结果的统计特性进行比较时，因子样长度的限制和数据处理过程所带来的不确定性，比峰值比较更能说明波激响应数学模型的精确性和可靠性。     

水下爆炸气泡激起的船体鞭状运动

本文揭示了水下非接触爆炸产生的气泡脉冲缴起细长形船体鞭状响应运动的现象。考虑到了水下爆炸气泡的脉冲多次性,迁移和水面效应,计算结果与弹性船模试验结果进行了对比,符合程度令人满意。     

Green water loading on a floating structure with degree of freedom effects

The aim of the present work is to investigate whether the degree of freedom (DOF) of a floating body has a notable effect on the maximum impact pressure due to green water on deck. The analysis is carried out for a box-shaped floating structure with a deckhouse, using experimental and numerical means to model the green water load. Green water on deck and impact on the deckhouse is generated by the impingement of a focusing wave group on a floating structure. Computations are performed using a two-dimensional constrained interpolation profile-based model solving the Navier–Stokes (N–S) equations with free surface boundary condition to deal with nonlinear water–structure interactions. The free surface is captured by a volume of fluid (VOF)-type tangent of hyperbola for interface capturing/slope weighting (THINC/SW), which is more accurate than the original THINC scheme. The verifications of the simulation through a series of model-to-model comparisons are performed in a two-dimensional glass-wall wave tank. Experimental water surface elevations, body motions and impact pressure are compared satisfactorily with the computed results for different DOFs cases. As a result, the peak impact pressure due to green water decreases rapidly with the increasing DOF.     

浮体升沉和纵摇运动对甲板上浪载荷影响数值研究（英文）

In this paper, the influence of heave and pitch motions on green water impact on the deck is numerically investigated. The vessel motions are determined using a potential theory based method and provided as input to finite volume based CFD computations of green water phenomenon. A dynamic mesh approach is adopted to determine instantaneous body positioning in the fluid domain.Detailed validation studies with published experimental results for 2D and 3D fixed vessel cases are initially performed to validate the present numerical approach before studying the moving vessel problem. The results show that inclusion of heave and pitch motion changes the disturbed wave field near the bow which influences the free surface as well as the impact loading due to green water. The effect of wave steepness on green water impact is also investigated and it is seen that the present numerical method is capable of capturing green water load. It is observed that the effects of vessel motions on green water load are not negligible and one should consider this effect too. The incorporation of vessel motions in the vertical plane affects the green water loading on the deck.     

规则迎浪中船舶参数横摇的三维时域预报方法研究

参数横摇是船舶因复原特性改变而引起的典型非线性现象。文章采用三维时域方法预报规则迎浪中船舶的参数横摇运动。该方法引入匹配面将流域分为内域和外域,内域中采用Rankine源来满足物面条件和线性自由面条件,而外域中应用时域格林函数来满足线性自由面条件和远场辐射条件。数值方法中,Froude-Krylov力和恢复力是通过对船舶瞬时湿表面积积分获得,同时考虑了横摇、垂荡和纵摇三自由度之间的耦合作用,以及非线性横摇阻尼的影响。数值结果与试验结果吻合很好,说明该方法可以有效地预报参数横摇。     

舰船波浪弯矩响应的频率特性

非直壁式舰船在高浪级和高航速下的弯矩响应中,除了含有低频遭遇频率成分外,还存在着一定数量的遭遇频率的倍频成分及船体各谐调的垂向总振动频率成份,它们都会对舰船波浪弯矩的非线性响应产生相应的影响。如果舰船的第一谐调垂向总振动频率正好是遭遇频率的整数倍,这时弯矩的非线性响应将达到极值。本文从模型试验及理论计算两方面分析了舰船波浪弯矩的频率特性,对船体载荷响应理论的发展及设计载荷的确定具有指导意义。     

弹体出水附加质量计算及对阻尼系数的影响分析

给出了水下结构刚体运动、弹性振动引起的附加质量的计算方法;考虑水下结构运动产生的附加质量是随时间变化的量,给出了计及这种变化的结构运动方程,由此得出变化的附加质量所引起的阻尼系数的改变项。在此基础上以弹体出水过程为研究对象,计算了出水过程中结构附加质量随时间的变化情况,同时得出弹体附加质量的变化所引起的阻尼系数的改变量。计算结果表明：附加质量在水深和自由液面附近变化平缓,结构在二者之间运动时变化显著,且由此引起的阻尼系数的改变量不可忽略。     

不同海况下艏部砰击及鞭状效应的试验与数值分析

为了更深入地研究船舶的鞭状效应,在拖曳水池中对某船进行了艏部砰击及鞭状效应分段模型试验研究。提出了一种可以考虑砰击力的非线性水弹性计算方法。并改进了传统的分段模型,采用变截面梁对船体刚度进行模拟以更好地接近实船。在规则波迎浪下观察到了严重的艏部砰击现象。试验数据表明,当波高从5.6m增大到21m时,由于鞭状效应原因,总弯矩相比低频波浪弯矩的增大值从24.64%增长到92.02%。最后,将不同海况下的测量结果与基于线性与非线性水弹性理论的计算结果进行了比较分析,初步验证了文中方法和程序在预报船体波浪载荷中的适用性。     

系泊浮体运动响应分析的非线性水动力学方法（英文）

Nonlinear wave loads can induce low-frequency and high-frequency resonance motions of a moored platform in deep water. For the analysis of the nonlinear response of an offshore platform under the action of irregular waves, the most widely used method in practice is the Cummins method, in which the second-order exciting forces in the time domain are computed by a two-term Volterra series model based on incident waves, first-order body motion response, and quadratic transfer functions(QTFs). QTFs are bichromatic waves acting on a body and are computed in the frequency domain in advance. For moving bodies, QTFs are related to the first-order body response, which is to be determined in the simulation process of body motion response but is unknown in the computation procedure of QTFs. In solving this problem, Teng and Cong(2017) proposed a method to divide the QTFs into different components,which are unrelated to the body response. With the application of the new QTF components, a modified Cummins method can be developed for the simulation of the nonlinear response of a moored floating platform. This paper presents a review of the theory.     

Numerical computation of motions and structural loads for large containership using 3D Rankine panel method

In this paper, we present the results of our numerical seakeeping analyses of a 6750-TEU containership, which were subjected to the benchmark test of the 2 nd ITTC–ISSC Joint Workshop held in 2014. We performed the seakeeping analyses using three different methods based on a 3D Rankine panel method, including 1) a rigid-body solver, 2) a flexible-body solver using a beam model, and 3) a flexible-body solver using the eigenvectors of a 3D Finite Element Model(FEM). The flexible-body solvers adopt a fully coupled approach between the fluid and structure. We consider the nonlinear Froude–Krylov and restoring forces using a weakly nonlinear approach. In addition, we calculate the slamming loads on the bow flare and stern using a 2D generalized Wagner model. We compare the numerical and experimental results in terms of the linear response, the time series of the nonlinear response, and the longitudinal distribution of the sagging and hogging moments. The flexible-body solvers show good agreement with the experimental model with respect to both the linear and nonlinear results, including the high-frequency oscillations due to springing and whipping vibrations. The rigid-body solver gives similar results except for the springing and whipping.     

Oblique wave trapping by vertical permeable membrane barriers located near a wall

The effectiveness of a vertical partial flexible porous membrane wave barrier located near a rigid vertical impermeable seawall for trapping obliquely incident surface gravity waves are analyzed in water of uniform depth under the assumption of linear water wave theory and small amplitude membrane barrier response. From the general formulation of the submerged membrane barrier, results for bottom-standing and surface-piercing barriers are computed and analyzed in special cases. Using the eigenfunction expansion method, the boundary-value problems are converted into series relations and then the required unknowns are obtained using the least squares approximation method. Various physical quantities of interests like reflection coefficient, wave energy dissipation, wave forces acting on the membrane barrier and the seawall are computed and analyzed for different values of the wave and structural parameters. The study will be useful in the design of the membrane wave barrier for the creation of tranquility zone in the lee side of the barrier to protect the seawall.     

基于不同试验方法和非线性水弹性时域理论的鞭振弹振响应研究

船体主尺度增大会导致严重的鞭振和弹振现象,这会增大船体结构的极限载荷和疲劳损伤.为了深入探究船体的振动响应,文中在拖曳水池对某万箱集装箱船分别进行了分段模型的自航和拖航试验.分析了不同海况下自航和拖航这两种试验方式对鞭振和弹振响应的影响.为计及不同振动频率成分对载荷响应的影响,提出一种考虑波浪记忆效应的非线性水弹性方法.文中提出了一种求解延时函数的方法,能够解决高频区域的阻尼系数的计算限制.最后,船舯弯矩试验结果分别和线性与非线性理论结果进行了比较,发现文中提出的非线性方法能够更好地预报弹性船体的振动响应.     

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.