Optimization of Oscillation Dynamics in a VDS Deployment

Abstract Underwater detection is a fundamental capability for many vessels, especially for naval and research ships, where precise and reliable data is crucial. To achieve this capability ships can be equipped with a variable depth sonar (VDS) system, which is generally towed behind the vessel. When such a VDS system is launched into the water, it experiences excitation induced by the ship’s motion, causing the body to oscillate. These oscillations can result in amplitudes increases and uncontrolled behavior, which can damage the VDS and reduce the vessel’s operational effectiveness. If the oscillation of the VDS, while it’s launching, can effectively be predicted, and damping due to rope motion can be modeled the potential of underwater detection of the vessel can significantly be increased. In this paper, a method is presented to calculate the oscillation of the VDS system and to optimize the winch speed, while it’s launching, to reduce the oscillation. This approach relies on the differential equation of motion for the VDS system, taking into account a variable rope length and the ship induced excitations at the deployment point of the VDS. These excitations are calculated in the time domain using “E4-ROLLS”. To enable operations in conditions with higher significant wave heights, the method integrates the principle of swing damping along with a CHWARISMI optimizer to determine the optimal damping and winch speed for every situation. Initial results indicate that this optimized VDS system can be used effectively at significant wave heights up to one meter higher than previously feasible. This advancement enhances underwater detection capabilities and increases operational safety and efficiency for vessels in challenging sea conditions.