【作者】 任会礼；

【导师】 李成刚； 胡于进；

【作者基本信息】 华中科技大学 ， 机械设计及理论， 2008， 博士

【摘要】 起重船是海洋工程设施建设必不可少的工程船舶。起重船在海上作业或是航行由于受到海浪的作用,会引起船体运动。船体的运动不仅影响船上人员的舒适性,而且直接影响到起吊作业的效率和安全性。因此,分析起重船动态特性及其影响因素,并将之应用于起重船的设计和作业中是十分必要的。国内外学者对船舶在海浪上的运动响应进行了深入的研究,但因为起重船的船型、起吊机械的特殊性,对该系统的理论研究还较缺乏。随着海洋开发事业的发展,起重船为提高作业效率、降低环境对作业的影响,起重量越来越大,运行速度越来越快,其整体动态特性表现出一些新的特征,主要表现在:(1)吊臂柔性对系统的动力学特性有影响;(2)吊重与船舶之间存在双向耦合作用。本文在此背景下对该问题进行了深入的探讨,取得以下研究成果:(1)将锚泊起重船臂架和吊索看作弹性体,基于柔性多体动力学,针对锚泊起重船首次建立了系统刚柔混合动力学模型,分析了模型的影响因素,详细讨论了刚柔混合弹性模型与刚体模型、平面模型间的相互转换方法,模型具有良好的通用性。研究了吊物系统采用单摆及球摆模型造成的系统计算差异,确定吊物系统采用空间球摆模型更符合实际情况;探讨了船舶与吊重双向耦合作用的条件;(2)对吊物系统动力响应及吊索中的动张力响应进行了详细研究,发现单纯的面内激励会导致吊重面外的较大摆动;在特征频率附近,吊索中的动张力急剧增大;使用Melnikov函数确定了吊重混沌振动的参数阈值,根据相图、Poincare映射图和Lyapunov指数方法对吊物系统中出现的混沌现象进行了分析,确定了吊物系统发生混沌的影响因素是激励幅值、激励频率和吊索长度,提出了通过合理选择系统参数避开发生混沌的区域的方法。(3)依据有限单元法建立起锚泊系统非线性动力学方程,通过悬链线方程确定初始位置,通过静力分析求得静平衡位置,在此基础上对系统动态特性进行了分析,计算结果表明,采用多项式模拟锚泊力的作用是合理的。在此基础上设计了一套凸轮机构来模拟锚泊系统对船舶的作用,以便在进行实验时代替锚索来模拟锚泊系统作用。(4)采用自由度缩减的DC增益方法实现吊臂模态的选择,减小了系统动力学计算的规模,并对模态截断的精度进行了详细分析。在此基础上建立了起重船吊臂的弹性动力学模型,为刚柔耦合整体模型的建立及其动态特性分析奠定了基础。(5)建立了刚柔耦合锚泊起重船虚拟样机模型,为动态特性的研究提供了可靠的研究平台就设计参数(锚索刚度、吊臂质量、吊臂柔度)对系统特性的影响和典型工况(吊重跌落、起臂工况以及离地起升)下系统的响应特性进行了全面详细的分析。发现船舶运动幅值和吊重摆角并不总是随着锚索刚度的增加而减小;吊臂质量对船舶运动的影响与其绝对质量密切相关,与其相对于船的相对质量无关。最后,研制了船舶运动模拟实验平台,编制了相应的数据采集软件和平台运动控制程序,通过该平台可以模拟船舶的纵荡、垂荡运动,在该平台上进行了吊重振动试验,分析吊重摆振特性,验证了理论计算的正确性。更多还原

【Abstract】 Floating cranes play an important role in the operation of offshore engineering. During the operation or sail in the sea, wave-induced ship motions may cause the hoisted cargo to pendulate, so the crane payload pendulations became dangerous large and the operation had to be suspend. In order to avoid the loss during the operation, we should pay much attention to the dynamics of the floating crane. Although the issue of ship dynamics has been addressed extensively in a large number of recent researches, we still lack of full study on this problem because of the particularity of the floating crane.In order to save times during working in the sea, large ship-mounted crane appeared recently. The large crane ships are different from those small crane ships, the load is heavier and the operation speed is higher, so they have some new different features: (1) the flexibility of the boom can affect the dynamics of the crane-ship; (2) the dynamics of load and ship are coupled with each other. Aiming to the features in this dissertation, the whole crane-ship dynamics modeling theory and method are studied and the corresponding simulations are performed, and the main contributions of the research include:(1) The boom and rope are taken as elastic bodies, governing equations for the dynamic response of a crane-ship coupled with the pendulum motion of the payload are derived based on Lagrange’s equations. The presented flexible dynamics model has good versatility. The planar pendulum and sphere pendulum models are used to model the load system, and the difference of these two models are studied. The coupling of the ship and load are also studied.(2) A nonlinear three-dimensional lifting load system dynamic model was set up based on the general form of Lagrange’s equation, the dynamic response of the cargo was studied using numerical methods. The result demonstrates that the dynamic response of the cargo depends on the length of cable, reeling and unreeling speed and wave frequency, and the in-plane angle have coupling with the out-of-plane angle. Melnikov function are used to ascertain the key parameters that chaotic motions appeared in the system, and the chaotic vibration is studied using phase portraits, Poincare maps and maximum Lyapunov exponents. The method to avoid chaos is proposed.(3) Governing equations of mooring system are derived based on finite element method, the motion equation is solved by Wilson method to obtain the dynamic response of the mooring cable, the result demonstrate that the force of the mooring system can be approximated by a polynomial. A special mechanism has been developed to model the nonlinear behavior of real mooring systems, which can be used in experiment. The profile of the cam was defined and a solid model was designed in design software.(4) The boom is taken as flexible bodies and modeled based on finite element method, in order to avoid time consuming solution of equations in complex structures dynamics analysis, Dc gains of the individual modes of vibration were used as the criterion of modal truncation, the relative importance of the contributions of each of the individual modes was obtained and a small state space model was defined. The reduced model can accurately describe the pertinent dynamics of original system, and then the flexible model of the boom is established, which can be used for the rigid-flexible coupling model.5) A Virtual prototype model of the mooring crane-ship is established based on finite element method and flexible multi-body theory. Basic crane maneuvers, such as cable reeling and unreeling and load falling off, are taken into consideration, the analysis reveals how the dynamics of the crane-ship affected by those key parameters of the system. The influences of the flexibility of the boom are also taken into consideration.At last, we built an experimental setup, the platform used is capable of producting arbitrarily prescribed, independent surge and heave motions. The dynamic test of the load system is carried out. The comparison between test and simulation shows that the dynamics model presented in this dissertation is correct and feasible.更多还原