Fracture mechanics of a verticel-wall struetuve and the predicting wodel

本文通过一系列的实验研究了弹性直墙在破碎波冲击力作用下的动力特性。本文在试验的基础上，讨论了直墙式结构的严重局部破坏问题，提出了一个计算波浪冲击力的模型，并根据波浪对直墙式结构的碰撞或加载情况，提出了弹性墙的不同破坏行为。该壁在短时间内不会对高冲击压力作出响应，因为这种高压产生在静水水位附近的非常有限的区域。通常，较低的冲击压力与较低的压力脉冲相关联。因此，与阻尼力振荡相关的较长持续时间的低冲击力比单峰冲击更有效地产生更大的壁偏转。此外，当冲击波上升时间与壁面振动的固有周期基本相同时，壁面的最大挠度出现。插入式破碎机的碰撞通常在冲击波作用下形成一个大的气穴，冲击波作用后产生阻尼力振荡。这种冲击力的加载条件导致结构的壁构件疲劳断裂的更高可能性。另一方面，一个很大的冲击压力和短的持续时间发生在墙上的静水水位附近的剪切断裂。由此产生的损害会发展，并可能导致突然的结构failure.To开发的冲击压力模型，在破碎波对墙壁的冲击过程中的可变性进行检查相对于每单位宽度的墙壁的力脉冲，截留的空气体积，等等。采用有限元方法进行了数值分析，以证实实验结果和冲击力模型。

A series of experimental programs has been performed to study the physics of dynamic behaviors of an elastic vertical wall to impulsive forces due to breaking waves. On basis of the experiments, the author discussed severe local fractures of the vertical-wall type structure, and intended to develop a model for evaluating the wave impact force which brings about the failure.The elastic wall exhibits different behaviors according to the colliding or loading condition of breaking waves on the wall. The wall does not respond to the high impact pressure with short duration, because such high pressure generated at a very limited area in the vicinity of the still water level. In general, a lower impact pressure is associated with a lagerpressure impulse. Consequently, the longer-lasting low impact force associated with damping force oscillations is more effective in producing the larger wall deflection than the single-peaked impact. In addition, the largest wall deflection occurs when the rise time of the impact is almost the same to the natural period of wall oscillations.Collisions of plunging breakers usually entrap a large air pocket at impact and produce damped force oscillations after impact. Such loading condition of the impact force brings about a higher probability of fatigue fracture to the wall member of the structure. On the other hand, a sharp impact pressure with very high magnitude and short duration occurs a shear fracture around the still water level on the wall. The resulting damage would develop and may cause a sudden failure of the structure.To develop the impact pressure model, variability in the impact processes of breaking waves on the wall is examined with respect to the force impulse per unit width of the wall, the entrapped air volume, and so forth. Numerical analyzes using an finite element method were made to substantiate the experimental results and the impact force model.