【作者】 曹正林；

【导师】 吴卫国；

【作者基本信息】 武汉理工大学 ， 船舶与海洋结构物设计制造， 2008， 博士

【摘要】 高速三体船的砰击强度研究是非常复杂和具有实际意义的课题。在国家863计划项目——高速三体船关键技术研究支持下,本文采用数值仿真与试验研究相结合的方法研究了高速三体船砰击强度问题,主要研究内容和结论如下:1、对国内外已有的结构入水砰击的基本理论进行消化、吸收和总结,重点介绍了楔形体入水砰击基本理论、数值计算方法和水弹性理论,平底结构入水的空气垫理论,考虑空气垫效应平底结构砰击压力峰值计算方法,三维钝体结构入水的线性理论及其“反问题”方法,分析总结了各理论的适用范围和存在的不足之处。2、对高速三体船砰击强度中运用的数值仿真方法的基本理论和关键技术进行了研究,明确了仿真中使用的流体材料和结构材料物理参数和力学行为,确定了使用无反射边界条件消除边界对砰击区域的影响,采用刚性墙对称边界条件减小运算量;研究了仿真计算模型的网格尺寸和精度控制的问题,得出了高速三体船结构入水砰击仿真计算较优的网格划分尺度,有效的解决了LS-DYNA通用软件在高速三体船砰击强度研究上的应用问题。3、在采用LS-DYNA仿真计算平板结构入水砰击问题与已有试验对比的基础上,证明用LS-DYNA仿真计算结构入水砰击问题的正确性和有效性。在此基础上,采用有限元流固耦合方法研究了高速三体船连接桥结构的入水砰击问题,得到了一些有意义的结论:(a)主船体溅射的浪花导致主船体和辅船体间空气的逃逸,削弱空气垫的缓冲作用,连接桥的砰击压力峰值比作为平板处理时的值大。(b)在系列仿真研究的基础上,回归了高速三体船入水砰击连接桥砰击压力峰值的公式,砰击压力峰值基本上与入水速度的平方成正比;空气垫、飞溅等非线性因素对连接桥砰击压力的影响随着砰击速度的增加成二次指数递减;砰击速度较低时影响随着速度的增加迅速减小,砰击速度较高时基本没有影响。(c)连接桥压力峰值在连接桥距主船体舷侧0.7b的距离形成最大值,在连接桥距主船体舷侧0.3b处形成次大值。(d)连接桥所受的砰击压力持续时间与速度成一次指数递减;在砰击速度较低时,压力峰值持续的时间随着砰击速度的增加迅速递减;在砰击速度较高时,压力峰值持续的时间递减速度十分缓慢。(e)空气层在高速三体船连接桥入水砰击中减小了压力峰值,起到缓冲垫作用,随着砰击速度的增加,空气层对压力峰值的影响减小;随着高速三体船结构质量增加,连接桥砰击压力峰值迅速增大,当结构质量超过一定的临界结构质量值时,砰击压力峰值基本保持不变;随着连接桥宽度的增加,连接桥压力峰值基本成线性增加;当高速三体船主船体舭部升高角度较小时,砰击压力峰值并不是很大,当角度到达第一临界角度时,连接桥的砰击压力峰值迅速增大,当角度到达第二临界角度时,随着角度的增大,砰击压力峰值增加速度减缓,在此基础上提出了砰击压力临界舭升高角的概念。4、采用数值仿真方法研究了高速三体船主船体砰击问题,得到一些有意义的结论:(a)在系列仿真研究的基础上,回归了高速三体船入水砰击主船体砰击压力峰值的公式,发现砰击压力峰值基本上与入水速度的平方成正比;空气垫、飞溅等因素对主船体砰击压力峰值的影响随着砰击速度的增加成二次指数递减;主船体砰击压力峰值在距主船体纵中剖面3/8B的距离处形成最大值;主船体砰击压力持续时间与速度成一次指数递减。(b)空气层在高速三体船主船体砰击中起到缓冲垫作用,有利于减小主船体砰击压力峰值;空气层对主船体砰击压力峰值的影响随着砰击速度的增加而减小,并且在低速时影响要比高速时显著;高速三体船结构质量和连接桥宽度对主船体砰击压力峰值的影响较小;随着高速三体船主船体舭部升高角度的增加,主船体的砰击压力峰值逐渐减小,并且与庄生仑博士试验结果具有相同的变化趋势。5、介绍了在水动力学冲击领域内试验研究一系列成果:庄生仑对平底结构和楔形体砰击的系列试验研究、MARINTEK实验室对楔形体和船艏外飘砰击的试验研究、楔形体入水冲击国际性比较研究、SWATH双体船入水砰击试验研究和VISBY隐身舰实船试验研究。在此基础上,试验研究了高速三体船砰击强度,自行设计了试验装置和试验模型,完成了试验装置和模型的加工,调试了整个试验系统,进行了高速三体船模型系列砰击试验。试验记录了高速三体船发生砰击时的完整过程,测试了高速三体船模型在不同高度下落入水砰击过程中主船体和连接桥受到的砰击压力峰值及分布、加速度响应值和变形响应值,并把压力峰值与入水速度值进行回归分析,提出了主船体和连接桥的砰击压力峰值预报公式,从公式中分析得知,压力峰值与入水砰击速度的平方成正比,空气垫、飞溅等非线性因素的影响随着速度的增加成二次指数递减趋势,验证了仿真研究高速三体船砰击强度相关规律的正确性。试验也证实了只有当高速三体船的相对速度超过砰击临界速度时才可能发生砰击。6、将试验取得的加速度响应值和变形响应值与三维仿真计算进行比较分析,验证了仿真方法计算高速三体船砰击强度的可行性和准确性,分析了两种方法误差的原因,指出了仿真方法的不足之处并提出改进方法,为仿真方法在高速三体船砰击强度问题上的进一步研究提供了参考。在此基础上计算分析了高速三体船发生砰击时结构的动力响应及相关规律。更多还原

【Abstract】 The study on slamming of high-speed trimaran is a very complicated and significative topic,it has boon supported by 863 program of China(Name:Key technique research of high-speed trimaran,No.2006AA11Z227).In this thesis, the topic has been studied with methods of simulation and experimentation,and the following efforts have been made and the conclusions are presented:1、Some existing water entry theories were introduced,including the theory of two-dimensional water entry of wedge bodies,the numerical method of two-dimensional water entry of wedge bodies,the air cushion theory of flat bottom structures and the inverse method of three-dimensional blunt bodies and so on.Finally,the shortage of these theories were analyzed.2、Some studies on the key techniques of LS-DYNA software simulation on the slamming of high-speed trimaran have been carried out,the solutions of non-reflection boundary condition,the symmetry boundary condition and fluid initial condition at simulation have boon brought forward.And also the mesh size and precision control has been studied in order to get optimal model scale of simulation calculation.3、The water entry of flat bottom structures has been simulated with LS-DYNA software.The results have been compared with the existent experimental study,and it has approved correctness and validity of simulation calculation on slamming by the LS-DYNA soft ware.Accordingly,the slamming of the trimaran cross-deck structure has been simulated.Some conclusions have been obtained:(a)The air between hulls was brought out by wave splashed by main hull, the effect of air cushion was weakened.So,the peak value of pressure on the cross-deck was increased comparing with flat bottom slamming.(b)The formula of peak value of slamming pressure on the cross-deck has been regressed.The peak value is directly proportional to quadratic in velocity of water entry.The effect of air cushion on the peak value decays in the form of second order exponential with increasing of velocity.When the velocity is lower,the effect decreases rapidly with increasing of velocity;when the velocity is higher,the effect changes inconspicuously.(c)The maximum peak value of slamming pressure on cross-deck locates 0.7b from the broadside of the main hull and the secondly locates 0.3b.(d)The continuance of slamming pressure peak value decays in the form of first order exponential with increasing of velocity.When the velocity is lower, the continuance decreases with increasing of velocity;when the velocity is higher,the continuance changes inconspicuously.(e)The air cushion can decrease the peak value of slamming pressure on cross-deck,the effect of air cushion on peak value decreases with increasing of velocity.The effect of trimaran mass on the peak value increases with increasing of mass.When the mass arrives at the threshold value,the peak value is kept inconspicuously.The peak value is directly proportional to cross-deck width,and increases with increasing deadrise angle.When the deadrise angle arrives at the first threshold value,the peak value increases rapidly.When the angle arrives at the second threshold value,the peak value is kept inconspicuously.4、The slamming of the trimaran main hull has been simulated with LS-DYNA software.Some conclusions have been obtained:(a)The formula of the peak value on the main hull has been regressed.As a result,the peak value is directly proportional to quadratic in velocity of water entry.The effect of air cushion on the peak value decays in the form of second order exponential with increasing of velocity.The maximum peak value locates 3/8B from the midship of main hull.The continuance of peak value decays in the form of first order exponential with increasing of velocity.(b)The air cushion can decrease the peak value of pressure on the main hull,the effect of air cushion on peak value decreases with increasing of velocity.The effect of trimaran mass and cross-deck width on the peak value is lessness.The slamming peak value increases with increasing of deadrise angle. 5、Experimental achivements in hydrodynamics impact were introduced, including Chuang’s slamming experimentations of flat bottom structure and wedge body,MARINTEK’s slamming experimentations of wedge body and bow flare,international comparative studies on slamming of wedge body, slamming experimentation of SWATH and VISBY’s experimentation with real situation.In this thesis,test equipment and trimaran model were designed and carried out.Slamming experimentation of high-speed trimaran has been processed.Salmming phenomenon of the high-speed trimaran was recorded. The peak value of slamming pressure,the responses of acceleration and deformation were obtained with different velocity.The formula of the peak value on the main hull and cross-deck has been regressed.The peak values is directly proportional to quadratic in velocity of water entry.The effect of air cushion on the peak value decays in the form of second order exponential with increasing of velocity.These have proved correctness of rules about slamming simulation of the high-speed trimaran.6、The veracity and creditability of simulation method has proved with comparing experimental conclusion with 3-D slamming simulation.The errors between experimental method and simulation method have been analyzed,and the slamming responses of the high-speed trimaran have been simulated.更多还原