船舶甲板上浪的非线性横摇响应

考虑甲板上浪引起的横倾力矩、非线性阻尼和非线性恢复力矩,建立了规则横浪中船舶横摇运动方程;基于伯努利方程,推导了船舶甲板上浪水质量的计算公式.以66.01米长的拖网渔船为例,计算了不同波浪扰动力矩作用下的横摇响应,并构造了响应的分岔图和庞加莱截面.结果表明:甲板上浪后船舶横摇运动包括混沌运动和周期二、周期三、周期四等多周期运动;随着波浪扰动力矩幅值的增大,横摇响应发生从周期运动到混沌运动或从混沌运动到周期运动的阵发性分岔、正向及反向倍周期分岔.     

潮流能发电平台的水动力特性及动力响应分析

运用水动力学软件AQWA对潮流能发电平台进行了频域分析,得到不同重心高度、不同水深、遭遇不同浪向角条件下平台各自由度幅值响应算子随波浪圆频率的变化曲线。再对平台进行了风浪流联合作用下的时域耦合分析,研究不同系泊角度对平台运动响应和系泊缆张力的影响。计算结果表明:纵荡幅值响应算子峰值随浪向角的增大而逐渐减小,横荡幅值响应算子峰值随浪向角的增大而增大,纵荡、横荡上主要表现为与波浪的低频共振,浪向角较小会产生较大的垂荡运动、纵荡运动、纵摇运动,浪向角较大会导致较大的横摇运动;水深小于10m时,海底对波浪的反射作用对平台纵荡和艏摇运动影响比较明显;小范围内的重心高度变化对平台各自由度幅值响应算子影响较小。当系泊角度为45°时,系泊系统对平台运动响应的控制更好,且此时系泊系统的安全系数最大,主要系泊缆受力更加合理,平台更安全。     

关于舰船横摇中的若干非线性问题

对船舶横摇运动中的一些非线性问题的若干研究现状进行了总结,讨论了所存在的一些问题及其发展趋势。对横摇非线性问题的产生以及导致非线性的因素作了简述,从大幅非线性横摇运动、横摇-垂荡耦合运动、和横摇-纵摇耦合运动三方面,详细综述了国内外关于舰船在波浪中的力学研究的发展趋势,提出了几个有待深入加强研究的问题。     

耦合船体横摇的减摇水舱流体运动和减摇效果预测

减摇水舱用于减小船体的横摇运动。由于水舱内部结构复杂,导致流体晃荡呈非线性。为了降低预测水舱特性和减摇效果的难度,采用计算流体力学VOF模型来分析水舱中流体的晃荡,在时域内,运用数值方法完成船体非线性横摇运动的实时仿真,其中耦合了水舱中流体和船体的运动。船体随机横摇时,进行水舱流体流量和力矩的功率谱分析,得到减摇频率范围及减摇前后的效果。结果表明,在其减摇频率范围内,减摇水舱具有良好的减摇能力,验证了此方法的可行性。     

耦合船体横摇的减摇水舱流体运动和减摇效果预测Fluid motion and stabilization effect prediction of anti-rolling tank coupled ship rolling

减摇水舱用于减小船体的横摇运动。由于水舱内部结构复杂,导致流体晃荡呈非线性。为了降低预测水舱特性和减摇效果的难度,采用计算流体力学VOF模型来分析水舱中流体的晃荡,在时域内,运用数值方法完成船体非线性横摇运动的实时仿真,其中耦合了水舱中流体和船体的运动。船体随机横摇时,进行水舱流体流量和力矩的功率谱分析,得到减摇频率范围及减摇前后的效果。结果表明,在其减摇频率范围内,减摇水舱具有良好的减摇能力,验证了此方法的可行性。     

海洋平台损伤诊断研究

结合动力学和有限元方面的知识,以杭州湾跨海大桥海洋平台为背景,分别从固有频率和应变能损伤因子两个方面对损伤进行评估和定位.然后基于平台的工作环境,考虑了波浪力、水流力和阻尼等作用因素,进行了非线性动力响应分析,根据位移和截面应变变化率的变化情况进行损伤诊断.同时从概率论的角度上考虑了随机波浪力荷载,通过对所测波浪力荷载的统计,算出功率谱密度函数,然后计算了此荷载下结构的动力响应,并用应变均方根的变化值来检测结构的损伤和损伤程度,最后为今后大型海洋平台的损伤诊断提出建议和方法.     

传统Spar平台垂荡主共振时非线性耦合响应的研究

考虑瞬时波面影响,建立了Spar平台垂荡-纵摇运动的参数激励耦合运动方程,应用多尺度法导出了波浪频率接近垂荡固有频率时响应方程的一阶摄动解并做数值验证。计算结果显示:当波浪高度达到一定值时,纵摇运动中出现大量的亚谐频率成分;随着波浪高度进一步增大,纵摇运动将出现明显的幅值跳跃现象。研究结果表明,能量渗透现象是纵摇运动失稳的主要原因,波浪激励力矩对于纵摇本身的贡献很小。由于垂荡模态存在能量饱和现象,多余的垂荡能量将会向纵摇模态转移,导致出现大幅值的纵摇运动。     

热环境中功能梯度圆形薄板的混沌运动

针对陶瓷-金属功能梯度圆板,同时考虑几何非线性、材料物性参数随温度变化且材料组分沿厚度方向按幂律分布的情况,应用虚功原理给出了热载荷与横向简谐载荷共同作用下的非线性振动偏微分方程。在固支无滑动的边界条件下,通过引入位移函数,利用伽辽金方法得到了达芬型非线性动力学方程。利用Melnikov方法,给出了热环境中功能梯度圆板可能发生混沌运动的临界条件。通过数值算例,给出了不同体积分数指数和温度的同宿分岔曲线,平面相图和庞加莱映射图,讨论其对临界条件的影响,证实了系统混沌运动的存在。通过分岔图和与其相对应的最大李雅普诺夫指数图,分析了激励频率和激励幅值对倍周期分岔的影响及变化规律,发现系统可出现周期、倍周期和混沌等复杂动力学响应。     

考虑胎路多点接触的电动汽车?路面耦合系统振动分析

轮毂电机驱动电动汽车的簧下质量大, 使得轮胎动载荷增加, 且电机激励进一步加剧车轮振动. 同时, 轮胎与路面单点接触的简化模型, 其动力学计算结果与实际存在差别. 鉴于此, 考虑电机的电磁激励、胎路多点接触和非线性地基, 建立了电动汽车?路面系统机电耦合动力学模型, 通过Galerkin法推导了非线性地基梁的垂向振动, 利用积化和公式推导了非线性地基梁中非线性项积分的精确表达式, 提出了路面截断阶数选取的简易方法, 并通过路面位移响应的收敛性进行了验证. 在此基础上, 研究了胎路多点接触、非线性地基、电机激励、车速、路面不平顺幅值等对路面及车辆响应的影响. 结果表明, 非线性地基及多点接触对车辆响应的影响中, 轮胎动载荷的影响最大, 车身加速度和悬架动挠度的影响较小, 且考虑电机激励时, 二者对车辆响应的影响显著增大. 从对路面响应的影响看, 电机激励的影响最大, 非线性地基的影响次之, 多点接触的影响较小. 所建模型及研究方法可为电动汽车的垂向动力学分析提供一种新思路.      

浮台多向运动对水下锚索共振响应影响研究

在复杂的海洋环境中,上部浮式结构受到波、浪、流共同作用,会产生多个方向的运动,进而诱发水下锚索产生复杂的动力学行为,影响海洋工程结构的安全性和稳定性．本文考虑水下锚索垂度效应所带来的二次非线性效应,探究上部浮台纵荡和垂荡运动对水下锚索振动响应的影响．建立上部浮台多方向运动影响下水下锚索的动力学模型,推导其运动微分方程,并采用多尺度法对运动微分方程开展近似分析以及稳定性分析．研究结果表明：系统的共振响应随着垂荡位移的增加而增加,随着垂跨比的增加而减小;随着垂荡位移的增加,系统越发容易失去稳定性;随着倾角和初始张力的变化,系统的不稳定区域也会发生定性和定量的改变;与仅考虑参激作用的情况相比,参强联合作用时水下锚索的振动响应幅值会增加．     

SYNCHRONOUS EFFECT OF SLIPPING HEAVY LOADS ON RO-RO SHIP ROLLING IN WAVES

Common effect of wave and slip of internal vehicles will make rolling of the roll-on ship serious. This is one of the important reasons for overturn of ro-ro ships. The multibody system with a floating base is composed of ro-ro ship and slipping vehicles. Takes the rolling angle of the ship and the transverse displacements of the slipping vehicles on desk as freedoms. Making use of the analysis of apparent gravitation and apparent buoyancy, the wave rolling moment is derived. By means of dynamic method of multibody system, dynamic equations of the system are established. Taking a certain channel ferry as an example, a set of numerical calculation have been carried out for rolling response of the multibody system with a floating base of a ro-ro ship and displacements response of the slipping vehicles under common effect of free slipping vehicles and wave, and a conclusion has been drawn that the motion of the numerous free slipping heavy loads will trend to be synchronous under restraining of the side-wall bulkhead with time because of repeated collision.     

浮动冲击平台冲击环境对设备响应的影响

对浮动冲击平台提供给设备的冲击环境及舰载设备在不同冲击环境下的响应进行了数值模拟和理论分析。以美国中型浮动冲击平台为计算模型,将设备基座的冲击环境与德国规范BV 043-85进行了比较,为分析两个体系在设备抗冲击要求中谱加速度的差异,对不同舰载设备进行数值模拟计算,并通过虚拟约束边界模态方法,提出不同冲击环境下基础激励的多自由度系统响应的计算方法。数值分析及理论计算结果表明:冲击谱中谱加速度对舰载设备响应影响较小,而谱位移和谱速度对设备响应有较大影响,理论计算得到的多自由度系统响应与数值模拟结果较一致,同时在进行浮动冲击平台设计时可不考虑谱加速度对设备响应的影响。     

Shear deformable bars of doubly symmetrical cross section under nonlinear nonuniform torsional vibrations—application to torsional postbuckling configurations and primary resonance excitations

In this paper a boundary element method is developed for the nonuniform torsional vibration problem of bars of arbitrary doubly symmetric constant cross section, taking into account the effects of geometrical nonlinearity (finite displacement—small strain theory) and secondary twisting moment deformation. The bar is subjected to arbitrarily distributed or concentrated conservative dynamic twisting and warping moments along its length, while its edges are subjected to the most general axial and torsional (twisting and warping) boundary conditions. The resulting coupling effect between twisting and axial displacement components is also considered and a constant along the bar compressive axial load is induced so as to investigate the dynamic response at the (torsional) postbuckled state. The bar is assumed to be adequately laterally supported so that it does not exhibit any flexural or flexural–torsional behavior. A coupled nonlinear initial boundary value problem with respect to the variable along the bar angle of twist and to an independent warping parameter is formulated. The resulting equations are further combined to yield a single partial differential equation with respect to the angle of twist. The problem is numerically solved employing the Analog Equation Method (AEM), a BEM based method, leading to a system of nonlinear Differential–Algebraic Equations (DAE). The main purpose of the present contribution is twofold: (i) comparison of both the governing differential equations and the numerical results of linear or nonlinear free or forced vibrations of bars ignoring or taking into account the secondary twisting moment deformation effect (STMDE) and (ii) numerical investigation of linear or nonlinear free vibrations of bars at torsional postbuckling configurations. Numerical results are worked out to illustrate the method, demonstrate its efficiency and wherever possible its accuracy.

     

Comparison of linear spring and nonlinear FEM methods in dynamic coupled analysis of floating structure and mooring system

This paper compares the dynamic coupled behavior of floating structure and mooring system in time domain using two numerical methods for the mooring lines such as the linear spring method and the nonlinear FEM (Finite Element Method). In the linear spring method, hydrodynamic coefficients and forces on the floating body are calculated using BEM (Boundary Element Method) and the time domain equation is derived using convolution. The coupled solution is obtained by simply adding the pre-determined spring constants of the mooring lines into the floating body equation. In FEM, the minimum energy principle is applied to formulate the nonlinear dynamic equation of the mooring system with a discrete numerical model. The ground contact model and Morison formula for drag forces are also included in the formulation. The coupled solution is obtained by iteratively solving the floating body equation and the FEM equation of the mooring system. Two example structures such as weathervane ship and semi-submersible structure are analyzed using linear spring and nonlinear FEM methods and the difference of those two methods are presented. By analyzing the cases with or without surge-pitch or sway-roll coupling stiffness of mooring lines in the linear spring method, the effect of coupling stiffness of the mooring system is also discussed.     

轨下支承失效对直线轨道动态响应的影响

建立了基于Timoshenko梁模型的车辆/轨道耦合动力学模型,分析轨下支承失效对直线轨道动态响应的影响. 钢轨被视为连续弹性离散点支承上的无限长Timoshenko梁,通过假设轨道系统刚度沿纵向分布发生突变来模拟轨下支承失效状态. 推导了考虑钢轨横向、垂向和扭转运动的轮轨滚动接触蠕滑率计算公式. 利用Hertz法向接触理论和沈氏蠕滑理论计算轮轨法向力及轮轨滚动接触蠕滑力. 采用移动轨下支承模型的车辆/轨道耦合系统激振模式,考虑轨枕离散支承对系统动力响应的影响. 通过新型显式积分法求解车辆/轨道耦合动力学系统运动方程,由数值分析计算得到不同轨下支承失效状态下直线轨道的动态响应. 结果表明,轨下支承失效对直线轨道变形及加速度有显著的影响,随着失效轨下支承个数的增加,轮轨相互作用力和轨道部件的位移、加速度将会急剧增大,将加速失效区段线路状况的恶化.      

Fluid–structure interaction between a two-dimensional mat-type VLFS and solitary waves by the Green–Naghdi theory

The two-dimensional, nonlinear hydroelasticity of a mat-type very large floating structure (VLFS) is studied within the scope of linear beam theory for the structure and the nonlinear, Level I Green–Naghdi (GN) theory for the fluid. The beam equation and the GN equations are coupled through the kinematic and dynamic boundary conditions to obtain a new set of modified GN equations. These equations represent long-wave motion beneath an elastic plate. A set of jump conditions that are necessary for the continuity (or the matching) of the solutions in the open water region and that under the structure is derived through the use of the postulated conservation laws of mass, momentum, and mechanical energy. The resulting governing equations, subjected to the boundary and jump conditions, are solved by the finite-difference method in the time domain. The present model is applicable, for example, to the study of the hydroelastic response of a mat-type VLFS under the action of a solitary wave, or a frontal tsunami wave. Good agreement is observed between the model results and other published theoretical and numerical predictions, as well as experimental data. The results show that consideration of nonlinearity is important for accurate predictions of the bending moment of the floating elastic plate. It is found that the rigidity of the structure greatly affects the bending moment and displacement of the structure in this nonlinear theory.     

Geometric nonlinear formulation for thermal-rigid-flexible coupling system

This paper develops geometric nonlinear hybrid formulation for flexible multibody system with large deformation considering thermal efect. Diferent from the conventional formulation, the heat flux is the function of the rotational angle and the elastic deformation, therefore, the coupling among the temperature, the large overall motion and the elastic deformation should be taken into account. Firstly,based on nonlinear strain–displacement relationship, variational dynamic equations and heat conduction equations for a flexible beam are derived by using virtual work approach,and then, Lagrange dynamics equations and heat conduction equations of the first kind of the flexible multibody system are obtained by leading into the vectors of Lagrange multiplier associated with kinematic and temperature constraint equations. This formulation is used to simulate the thermal included hub-beam system. Comparison of the response between the coupled system and the uncoupled system has revealed the thermal chattering phenomenon. Then, the key parameters for stability, including the moment of inertia of the central body, the incident angle, the damping ratio and the response time ratio, are analyzed. This formulation is also used to simulate a three-link system applied with heat flux. Comparison of the results obtained by the proposed formulation with those obtained by the approximate nonlinear model and the linear model shows the significance of considering all the nonlinear terms in the strain in case of large deformation. At last, applicability of the approximate nonlinear model and the linear model are clarified in detail.     

Developments of numerical methods for linear and nonlinear fluid-solid interaction dynamics with applications

本文综述了线性与非线性流固耦合问题数值方法的进展及工程应用. 讨论了四种数值分析方法: (1) 混合有限元-子结构-子区域数值模型, 以求解有限域线性流固耦合问题, 如流体晃动, 声腔-结构耦合, 流体中的压力波, 化工容器的地震响应,坝水耦合等; (2) 混合有限元-边界元数值模型, 以求解涉及无限域的线性流固耦合问题, 如大型浮体承受飞机降落冲击, 船舰的炮击回应等; (3) 混合有限元-有限差分(体积) 数值模型, 以求解不涉及破浪和两相分离的非线性流固耦合问题; (4) 混合有限元-光滑粒子数值模型, 以求解涉及破浪和两相分离的非线性流固耦合问题. 文中推荐分区迭代求解过程, 以便应用现有的固体及流体求解器, 于毎一时间步长分别求解固体及流体的方程, 通过耦合迭代收敛, 向前推进以达问题求解. 文中选用的工程应用例子包含气-液-壳三相耦合, 液化天然气船水晃动, 人体步行冲击引起的声腔-建筑结构耦合, 大型浮体承受飞机降落冲击的瞬态动力回应, 涉及破浪和两相分离的气-翼耦合及结构于水上降落的冲击. 数值分析结果与可用的实验或计算结果作了比较, 以说明所述方法的精度及工程应用价值. 文中列出了基于流固耦合的波能采积装置模型, 以应用线性系统的共振及非线性系统的周期解原理, 有效地采积波能. 本文列出了231 篇参考文献, 以便读者进一步研讨所感兴趣方法.     

考虑海底接触的钢悬链式立管触地点动力响应以及疲劳损伤分析

基于考虑接触的钢悬链式立管SCR(Steel Catenary Riser)触地点处的结构特性,分别采用了考虑管土分离的线性截断模型以及包含土体吸力效应的帽盖模型来描述P-y曲线。通过改变上端浮体的垂荡运动幅度、土体吸力系数以及海床刚度,对SCR触地点处的动力响应以及疲劳损伤特性进行了分析。分析结果表明,SCR触地点的垂向位移、弯矩、等效应力以及疲劳损伤均随着浮体垂荡运动幅度的增加而呈上升趋势。SCR触地点的垂向位移随着土体吸力系数的增大由高幅低频响应转变为低幅高频响应。SCR触地点的疲劳损伤随着海床刚度的增加呈现先稳定再增加再稳定的趋势。