Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
Results
ABSTRACT Field tests were carried out over a two-year period to obtain the drag and inertia coefficients of a surface piercing vertical cylinder fixed in irregular waves using an ocean research platform. The wave forces were measured with two 2-component dynamometers set at either end of the test cylinder: data on waves were recorded using a wave height meter array, and orbital velocity was also measured with a 3-component electromagnetic current meter to confirm the accuracy of estimated values of orbital velocity calculated from wave data and linear wave theory. The following was found.the values of CD and CM obtained from least squares fit of the complete force time series of a random wave record were well ordered as a function of KeuleganCarpenter number Kc defined by significant orbital displacement and the diameter of the cylinder, but those determined by the least squares fit on a wave-by-wave basis were widely scattered. ocean wave force exerted on the cylinder was well represented by Morison's formula; the ratio of predicted wave force by this formula to the directly measured force was 90%, and the ratio was very stable throughout the experiments. 1. INTRODUCTION The hydrodymamic forces acting on a cylinder in a harmonically oscillating flow (Keulegan and Carpenter, 1958) or in regular waves (Koterayama, 1979) have been investigated in detail and accurately in various laboratories. But for the design of an ocean structure it is difficult to use these results directly because of the many unknown factors such as the effects of scale, roughness (Sarpkaya, 1976), current (Moe and Verley, 1980; Koterayama, 1984), random waves (Bostrom and Overvik, 1986), wave spreading (Sarpkaya and Isaacson, 1981) and three dimensional effects (Nakamura et at., 1991) on the wave force coefficients.
A Study On Cable Fairing
Nakamura, Masahiko (Kyushu University) | Koterayama, Wataru (Kyushu University)
ABSTRACT Cable vibration caused by vortex shedding is an undesirable phenomenon in the design of a towed vehicle system or the mooring system of an ocean structure. Severe vibrations cause fatigue failure or a great increase in the drag coefficient of the cable. A series of experimental studies was carried out on airfoil and several other types of fairings. Normal and tangent drag coefficients were obtained for inclined faired cables, and effects on submerged depth and towing tension of the towing vehicle were calculated for the faired towing cable. 1. INTRODUCTION Fairing can reduce the drag force acting on a cable, and several studies have been done on airfoil fairing of a towing cable for a towed vehicle (Eames, 1968; Wingham et al., 1978; and Kato et aI., 1980), while other types of fairing (Myers et al., 1969) have been scarcely treated. In this paper, the effects of six cable fairings including two airfoil fairings on the reduction of drag force are studied. The advantages of a cable fairing are reduction of the normal drag force and prevention of cable vibration; an airfoil fairing, however, reportedly increases the tangent drag force (Eames, 1968). This phenomenon suggests that a towuig cable with airfoil fairing causes an increase in the towing tension is well as the submerged depth of the towed vehicle. We measured tangent drag coefficients with normal drag coefficients of cables can which various fairings had been used to determine what kind of fitting is superior. Computation was made of the effects of faired cables on the towing tension and the submerged depth Of the towed vehicle" DRAKE., which was developed by our research institute (Koterayama et al., 1990), and synthetic performances of the fairings were evaluated.
- Research Report > New Finding (0.54)
- Research Report > Experimental Study (0.54)