【作者】 张文鹏；

【导师】 宗智；

【作者基本信息】 大连理工大学 ， 船舶与海洋结构物设计制造， 2013， 博士

【摘要】 船舶在其整个的运营航行周期中,会受到各种外载荷的作用。按照载荷随时间变化快慢程度,可以分为静载荷和动载荷。对于同样幅值的两种载荷,动载荷的作用效果更为强烈,因此船舶在动载荷作用下的响应更需要对其关注和开展研究。本文对船舶所遭遇的典型动载——水下爆炸载荷和波浪载荷具有不同时间尺度的特点,对在这些载荷作用下船舶的弹性以及刚体响应进行研究。具体研究内容如下：1.对水中三维结构的自由振动特性进行了研究。与传统方法将船体横剖面作为刚性平面计算其附加质量不同,考虑横剖而变形对流体附加质量的影响,采用边界元方法计算水中结构的三维附加质量矩阵,对水中三维结构的自由振动进行了计算。结果表明,三维的结构在水中的固有频率要比在空气中低20～25%,并且水中振型与空气中振型不同。随后,采用三维附加质量矩阵的方法对水中结构的尺度效应进行计算,结果表明水中结构的比例尺度效应与空气中一样符合弹性力相似规律。2.对水下爆炸冲击波作用下船体弹性及刚体响应进行研究。首先采用在水下爆炸领域广泛应用的DAA方法,编制程序计算船体结构在水下爆炸载荷作用下的弹性响应。计算表明,船体迎爆面响应最大,但是最大响应并不出现在距爆点最近的位置,而是以距爆点最近的位置为中心,在距其一定距离处呈球面分布。然后,对水下爆炸冲击波作用下,船体刚体运动响应进行研究。推导出冲击波作用下船体刚体运动的理论计算方法,该方法可以在设计初期,船体参数较少的情况下,对船体响应进行计算评估。应用该方法计算一条小艇的运动响应,计算结果与实验结果比较吻合,验证了该方法的有效性。在此基础上,对船体剖面参数——宽度、吃水以及剖面形状对响应的影响进行了计算比较。结果表明对于冲击载荷不太大的情况,船体剖而B/T值越大,响应越大,但是当冲击载荷比较大时,增大剖面B/T值有可能使响应有所下降。剖面的形状对刚体运动响应的影响是钝角三角形剖面响应最大,半圆型剖面响应最小。3.对水下爆炸气泡作用下船体的弹性及刚体响应进行了研究。将船体简化为船体梁,采用Vernon模型描述气泡,并考虑了气泡上浮效应、上浮阻力效应、水面效应和能量损失。求解气泡作用下船体梁的运动响应。计算表明,船体梁在气泡作用下,既有刚体位移,又有弹性变形。另外,如果不考虑气泡能量损失,可能会导致计算的船体梁的响应过高。在此基础上,对船体的细长程度即长宽比和刚体响应和弹性响应比例的关系进行了计算研究,计算结果表明,船体长宽比在10～11之间,船体所产生的鞭状运动的幅值最大,比较危险。4.对波浪载荷作用下船舶的刚体运动响应情况,尤其是三体新船型给船舶在波浪中的运动响应计算带来了新的问题。三体船航速很高,其航行状态属于半滑行状态。高航速使得三体船航行姿态变化较大,另外,三体船主侧体之间存在自由面,会出现数值水动力扰动,在较高频段,出现实际不存在的异常峰值。为解决上述问题,首先在计算中以三体船航行姿态作为平衡位置,来解决高速航行姿态变化大问题；而对于数值水动力扰动,首先对其产生的机理进行分析,通过研究指出数值水动力扰动是由于脉动源方法计算三体船时产生“伪驻波”共振而产生的。通过在主船体与侧体之间的水面加入粘性项,来解决高频异常峰值问题。通过二维剖面的计算,表明该方法可以较好的解决高频异常峰值的问题。最后,对一个三体船模型的运动响应进行计算,并与实验结果进行比较。比较表明,计算与实验结果比较一致,较好的解决了数值水动力扰动与高航速运动预报误差大的问题。更多还原

【Abstract】 During the whole period of operation and navigation, ship should be affected by various forces. According to the rate of change, the forces can be classified into static and dynamic loads. By comparing with each other, the effect of dynamic load should be stronger. Thus, the response of ship under dynamic load should be more paid attention to and studied. The evaluation standard on dynamic load includes force magnitude and acting time. Therein the loads with high impulse, which include not only small amplitude and long time but also big amplitude and short time, are usually considered to be relative stronger. Under these high loads, the characteristic and rules of ship responses should be studied in this paper.1. The free vibration of3D submerge structure is studied. In the traditional method, by assuming the cross section to be rigid plane, the added mass is computed. In the present method of this paper, by considering the interaction of fluid and elastic structure, added mass matrix of submerge structure is calculated by3D BEM method. Then the results show that the natural frequency of submerge structure is lower than structure in air by20-25%, and the vibration modes of each other are different. Finally, the scale effect of submerged structure are calculated by3D added mass matrix, and the results show that the scale effects of structure in water and air satisfy the similarity law of elastic force simultaneously.2. The ship elastic and rigid responses under shock wave have been studied. Here the popular DAA method is studied and programmed to compute the resonance of vessel structure by underwater explosion. Then the results show that the response on ship side towards explosion wave is max, and the peak of acceleration response isn’t the nearest position but spherical distribution on ship structure. Furthermore, a theory method about rigid motion of ship under shock wave is deduced to evaluate the ship response, which can be used in the initial phase of design and validated to be efficient and feasible. On this basis, by comparing the influence of ship section parameters (width, draft and section shape) on ship response, for the small impulse load, the bigger the B/T, the higher ship response. However, while the impulse load is relative big, the response may decrease with the B/T increase. Furthermore the section shape of obtuse triangle has max effect on motion performance, and semi-circular section has min influence.3. The elastic and rigid ship responses under the effect of Bubble arc discussed. In this method, the ship is simplified into a hull girder under the Bubble which can be described by Vemon model. Meanwhile the bubble floating effect, floating drag effect, water surface effect and energy loss are considered. The results show that the hull girder has not only rigid displacement but also elastic deformation. Moreover, the response of hull girder should be over-evaluated by neglecting energy loss of bubble. On this basis, the elongated degree of vessel is calculated and analyzed, the results show that the amplitude of whipping motion should be max with the10-11length-width ratio, and this situation is very dangerous.4. The rigid motion of ship in wave is studied, and new special problems about high speed vessels (such as trimaran) are further analyzed, which include the large change of navigation attitude and abnormal peak due to numerical hydrodynamic disturbances of free surface. Therein for the large error of high-speed motion response, the navigation attitude is considered in the relative calculation. On the other hand, by theoretical analysis, the reason of numerical hydrodynamic disturbances should be the resonance of false stationary wave due to pulsating source method. Thus the artificial viscous is introduced into the free surface between main and side hulls to solve the problem of abnormal peak. By the calculation of2D cross section, it can be found that the abnormal crest value can be successfully solved. Finally, the motion responses of a trimaran model are calculated and compared with experiment, which shows that the results are in good agreement with experimental data and this method has good ability to accurately and effectively solve the "numerical hydrodynamic disturbances" and the large error of high-speed motion problems.更多还原