Ocean Testing of Motion Compensating Crane and Kevlar Tether Cable Dynamics for an Unmanned Deep Submersible Using Real Time Spectral Analysis

This is a description of the RUWS (Remote Unmanned Work System) ocean testing of the MCDHS (Motion Compensating Deck Handling System) crane and Kevlar electro-mechanical tether cable. The RUWS is an unmanned, tethered, deep submersible capable of working in depths to 20,000 ft (6096m). The MCDHS uses a feedback control system to minimize accelerations at the boom tip. A real time, FFT cross-spectral analyzer was used to determine the dynamic frequency characteristics of the MCDHS and the tether cable. The transfer function between ship heave and boom tip accelerometers indicates the motion compensation performance of the MCDHS. The best performance was 94% compensation. The transfer function between accelerometers at the top and bottom of the cable indicates its longitudinal vibration characteristics (response ratio and phase lag). Theoretical and measured fundamental, first and second harmonics of vibration were comparable.