楔形物体の水面衝撃における限界速度の模型実験

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Water impact loads on a hull induced by slamming sometimes cause heavy damages to hull structures. Therefore estimation and evaluation of slamming loads are important and inevitable for the design of ships. This paper deals with threshold velocity of water impact of wedges and its validation by model experiments. At first, threshold velocity of water impact is deduced for wedges in the form of Froude's scaling law, according to the mechanism of water impact suggested by Sellars. Next, model experiments are carried out with wedges whose deadrise angles are 30, 45, 60 degrees. Water pile up phenomena are observed using a high-speed video recorder. Vertical displacements and acceleration of the model and pressures at the bottom of the model are measured at the same time. Threshold velocities are determined by the changes of water pile up and the changes of dynamic pressures. The threshold velocities obtained from the experiments by the authors together with one by Arai show very good agreements with ones computed by the afore mentioned Froude's scaling law. It was found that while the drop velocity is greater than the threshold velocity, water pile up around the model agrees very well with theoretical ones by Wagner or Ferdinande, which were deduced with an assumption of gravity-free condition. Furthermore, water pile up by drop tests of wedges partially immersed in water initially at rest also showed the almost same property. This property is very interesting, but can not be accounted for theoretically. These results concerning the threshold velocity and water pile up are effective to assemble Wagner type impact model, by which non-linear simulation method for hull response in waves is expected to work much more effectively.
社団法人日本船舶海洋工学会の論文
2000-09-04

楔形物体の水面衝撃における限界速度の模型実験

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