FORCES FROM FLUID FLOW AROUND OBJECTS

Abstract

All hydrodynamic forces on submerged objects are shown to be due to the acceleration effects of the fluid flow. However, it is useful to consider separately the influence from the various ambient flow and local flow conditions. At times certain aspects of the flow can be ignored, which simplifies the analysis. Examples are developed for circular cylinders near a plane boundary with a flow direction parallel to the boundary and perpendicular to the cylinder. Potential flow theory predicts that large vertical forces exist away from the boundary when the cylinder is against the boundary and that large negative forces exist toward the boundary when the cylinder is positioned a small distance from the boundary, when the viscous effects are small. When the cylinder is near the boundary, the added mass coefficient is the same regardless of the direction of the flow, providing the flow is perpendicular to the cylinder. In addition, the added mass coefficient is much larger for cylinders near the boundary than when they are in a free stream. Good agreement between theory and laboratory experimentation was obtained for various coefficients with waves on horizontal cylinders near a plane boundary.