ABSTRACT

In a multiple array of vertical cylinders, flow patterns are very complex and very interactive between cylinders. The patterns are turbulent and non-linear depending on various factors. The gap and flow incoming velocity of upstream can affect on the downstream cylinder. In this study, the flow characteristics around two vertical cylinders are investigated numerically and experimentally. As the gap between cylinders is changed at fixed coming velocity, the pressure distributions around cylinders are observed and compared by experimental and numerical approaches. The F.D.M and multi-block method are applied in the study. The pressures at 12 points around the cylinder are measured in the experiment. The results can be applied in the understanding and design of multiple pile array structures.

INTRODUCTION

Generally the offshore structures are constructed with number of vertical cylinders. In a multiple array of vertical cylinders, flow patterns are very complex and interactive between them. The patterns are turbulent and non-linear affected by various factors. The space and flow velocity of upstream can affect on the downstream cylinder. Multiple arrays of cylindrical bodies create a complex flow behavior in turbulent form. In past studies, several investigations on the linear interaction between arrays of identical cylinders have been undertaken. Sumer (1997) has issued a book covering widely about the flow patterns around cylindrical bodies. A study considering unequal diameters was presented by Spring and Monkmeyer (1974). Their results were obtained by a method of multiple scattering and restricted to the diffraction force on uniform vertical cylinders in intermediate or deep water. Kaemoto and Yue (1986) used an algebraic method to calculate added mass and damping for a two or four equalsized circular cylinder array using diffraction solution of a single isolated cylinder, but for having different geometries their solution is likely to become very inefficient.

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