Modeling Simulation and Preliminary Experimentation on Towed Tether System

Abstract

Aero-dynamic drag forces and their effect on the path taken by a cable in a towed system are studied with the aid of an advanced computational software packages. A piece of rope (tether) is towed at the top end in a circular pattern and a body of known mass has been attached at the other end of the rope. Based on many computer simulations, observations have been made on the path traveled by the attached body at the lower end of the tether, for various angular velocities. The effect of certain factors such as internal damping, stiffness, mass-ratio and tow radii for increasing angular velocities, on the path traveled by the attached body have been studied, by modeling and simulations. Generally the tip radius and verticality of the lower end of the tether increases with increase in angular velocity, reaching a maximum value prior to a jump. The jump angular velocity range shifts towards higher velocities when parameters such as mass ratio, tow radius and bushings stiffness and damping are increased. Superposition plots have been obtained to visualize the envelope of space within which the tether can be found at any given angular velocity (within the range of angular velocities considered), showing the formation of a node for angular velocities higher than jump velocity. An experiment was performed to validate simulated results, using a 3.285E-5 lb/ft, 58--Y¡ long, Spider Wire as the tether. Based on drag coefficient parameter values that best fit the experimental data, simulated shapes matched experimental results, as did verticality, with maximum 33% error over a speed range of 12-25 radians/second. The use of material with unknown damping/stiffness and the use of inexpensive and imprecise equipment may have caused the variations between the simulated results and the experimental results, but nevertheless did bolster confidence in the simulated results.