Experimental Study Of Multi-directional Focused Wave Interaction With A Vertical Cylinder

Wave effect is one of the main loads which impact on the ocean engineering structures nd must be concerned in the designing of structures. Extreme wave which also usually called ague wave can lead to extreme loads is one of the main factors of ocean structures estruction, and often becomes the control factor of structures design. There is great nportant significance studying extreme wave impact on ocean structures for structures esign and safety assessment.In the paper, wave focusing method was used to generate the multi-directional focused yave in order to simulate extreme wave, and acted on fixed vertical cylinder. We study the rave run-up around the cylinder, wave forces and pressure distributions around the cylinder if different wave parameters, such as peak frequencies, directional spreading indexes, requency bandwidths and wave crests.Through the analysis of characteristics of the multi-directional focused wave, the results how that wave parameters have great effect on the water surface of the focused wave. The>eak frequencies, frequency bandwidths and wave crests are larger, the wave groups are wider, nd the wave steepnesses are larger. The directional spreading indexes are larger, the wave ends to be unidirectional wave, the wave groups are narrower, and the wave steepnesses are arger.Through the analysis of wave run-up, the results show that the focused wave parameters, ncluding wave steepness, frequency bandwidth, and directional spreading index, have ignificant impact on the wave run-up on the cylinder. More specifically, the focused wave un-up increases as these parameters increasing, and the maximum value of the measured vave run-up ratio can be as high as1.68. The variations of the multi-directional focused wave un-up around the cylinder are also analyzed. The wave run-up at the front of the cylinder are;reater than that at the other positions around the cylinder. The wave run-up reaches the owest values at135°. The associated focused wave parameters also impact the wave run-up listribution around the cylinder.Through the analysis of wave forces, the results show that the non-dimensional wave brces of the cylinder decrease with wave steepnesses increasing. The non-dimensional wave brces of the cylinder increase with directional spreading indexes increasing when relative limensions of the cylinder are smaller, and decrease with directional spreading indexes increasing while relative dimensions of the cylinder are larger. The ringing phenomenon is also observed in the experiment. When kiA>0.36, the ringing will happen and this will not happen when kiA<0.36.Through the analysis of pressure distribution around the cylinder, the results show that the dimensionless pressures at the SWL increase with directional spreading indexes while relative dimension of the cylinder and wave steepnesses have non-obvious effect at the weather side of the cylinder. The dimensionless pressures under the SWL decrease with relative dimension of the cylinder, wave steepnesses and directional spreading indexes increasing. At the SWL, the maximum dimensionless pressures around the cylinder are at the position of45°of the cylinder and the minimum values are at the135°position at the weather side of the cylinder; under the SWL, the maximum dimensionless pressures are at the weather side of the cylinder while the minimum values are at the position of90°.