ABSTRACT

The Naval Coastal Systems Center performed a series of cable tests in the high speed tow basin at the David Taylor Naval Ship Research and Development Center. The test program was intended to provide data to aid in the design of marine cable systems and the development of predictive methods. Lift and drag characteristics and strum responses were measured for five stranded cables. Cable samples 14 feet long were tensioned between two struts and towed over a velocity range of 2 to 10 knots with yaw angles varying from 20 to 90 degrees. Lift and drag loading functions were developed from the mean steady force data. The force and strum characteristics of the cables were compared with results from previous tests of yawed cables.

INTRODUCTION

A wide variety of marine systems use stranded cables, also referred to as wire ropes. Moored platforms and oceanographic buoys are examples of stationary systems using cables. Ship and helicopter towed systems consist of cables and hydrodynamic bodies. Such systems are used for naval defense purposes, underwater environmental tests, and seabed mapping. The performance of stationary and towed cable systems can be significantly affected by the lift, drag, and strum properties of the cables. Yet the stranding geometry of a cable is rarely chosen to optimize the system's performance. This is due to the lack of analytic methods for arbitrary cablegeometries and to the relatively small data base available for cable hydrodynamic properties.

The placement of a mine sweep device is one technology issue illustrating the need for improved understanding of cable hydrodynamics. The capability to position accurately a mine sweep device requires the design of a sweep wire that produces a specific lift component allowing it to remain in the horizontal plane while under tow.

Analytic methods to predict the force and strum characteristics of arbitrary cable geometries have not been developed. Therefore, experimental measurements are relied upon for the design of cable systems. Various tests have been conducted on stranded cables to characterize their hydrodynamic properties. The three-dimensional forces developed by several cables at yaw angles were measured in a wind tunnel at the David Taylor Model Basin in 1945 and 1962. Other wind tunnel measurements of cable forces have been performed at Imperial College of Science and Technology in the United Kingdom. 3 The strum properties of stranded cables have been measured by several investigators.

The unique aspect of the present test program is that both the hydrodynamic forces and the strum properties have been measured for several stranded cables over a range of incidence angles and towspeeds. This wide range of test parameters allows the cables to be well characterized.

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