Efficient Identification of Naval High-Speed Craft Shock Mitigation Seat Modal Parameters From Drop-Test Data

Abstract

Naval high-speed craft (HSC) operating in moderate to high seas experiences high-g and repeated shock loading at the seat–deck interface. These conditions are known to pose a serious potential for injury to the occupants. While various shock-mitigating seats are commercially available; their designs are in many cases quite different, and quantifying their shock attenuation characteristics can be challenging. The need for a standard test platform and experimental analysis methodology to investigate HSC seat effectiveness is a major objective of research being conducted by Carleton University's Applied Dynamics Laboratory (ADL) in partnership with Defence Research and Development Canada-Atlantic (DRDC Atlantic). A drop tower was designed and manufactured for testing HSC seats in order to characterize their shock-mitigating effectiveness by simulating the severe conditions of a slam impact at sea. Further, in order to identify seat dynamic parameters from drop-test data, the eigensystem realization algorithm (ERA), a modal-analysis-based system identification method, was applied to efficiently extract the modal parameters. The technique was shown to successfully extract the damping ratio as well as the damped and undamped natural frequencies of the seats from impact test data. The evaluated dynamic properties of the seats can subsequently inform decisions related to the design and/or procurement of commercially available seats.