VLCC在波浪中弹性响应的理论与模型试验研究

Study of hydroelastic ship responses of a VLCC by theoretical and experimental methods

商船的大型化发展使得船长变得越来越长。这将导致大型船舶在大洋中航行时船体梁产生由于流固耦合作用引起的波激振动和砰击颤振。文章采用模型试验和理论预报方法研究了一艘VLCC在满载和压载条件下的低频和高频垂向波浪载荷响应特性。试验模型长度超过6 m,采用两根非均匀截面梁来连接模型分段,并在分段处测量模型横剖面处的垂向弯矩。理论计算采用二维非线性切片理论和三维线性水弹性理论,预报结果和模型试验结果进行了比较。分析发现船体梁的波激振动易在小波高和低波浪周期下发生,尤其是船体梁的两节点垂向湿谐振频率为遭遇波浪频率整数倍的时候。波幅增大后,船体梁还将发生砰击颤振。波浪持续激励时波激振动和砰击颤振往往会耦合发生,由于船体梁小结构阻尼的影响,目前的技术手段难以从船体梁总振动中把它们分离开来。船舶的装载条件会对船体梁的振动特性尤其是波激振动产生较大的影响,研究发现压载条件下的波激振动响应要比满载条件下的严重,在已有文献中提到这种影响的机理在文中得到了模型试验和理论计算的再验证。

With the large scale development trend of commercial ship, the length of ship becomes longer and longer. It will result in a ship sustaining both springing and slamming responses due to the fluid structure interaction in waves. In this paper, a VLCC is introduced to study its low and high frequency wave load responses in both full-loaded and ballast condition. Experimental and theoretical methods were employed to investigate the characteristic of this vessel＇s vertical wave loads. A segmented model with its length more than six meters being connected by two non-uniform beams was used to get the vertical bending moments at each measured cross-section. A 2D nonlinear theory and a 3D hydroelasticity theory were employed to predict the wave loads responses. The results were compared between experimental and theoretical methods.It was shown that springing was prone to happen when wave amplitude was low and its period was short,especially when the basic vibration frequency of ship hull girder was a multiple of wave encountering frequency. Slamming happened when wave amplitude was high. However, it was difficult to distinguish slamming or springing or their combination from the wave-induced vibration as its structural damping was very small. Loading condition has a great influence on wave loads responses especially on springing behavior. It was found that springing behavior will be more severe in ballast condition than in full-loaded condition.The mechanism of it which was mentioned in other references was reconfirmed from model test and theoretical calculations in this paper.