Semi-active suspension seats in High speed crafts

Sammanfattning: The working environment of a high-speed-craft (HSC) can be uncomfortable and hazardous for the crew and passengers on board. This due to the repeated exposure to high levels of vibration and shocks, that can lead to reduced performance and severe injuries to the back and neck. The most common method to reduce the vibration and shock exposure (to the crew) has been to install passive suspension seats. The passive suspension seats have proved to reduce the vibration and shock exposure to the crew aboard HSC’s, by the measures presented in the international standards SS-ISO 2631-5 and SS-ISO 2631-1. The applicability of these measures towards HSC has been debated for a long time, especially the limit values presented in them for maximum vibration and shock exposure. Also, the limit values that are set are often quickly exceeded despite the use of passive suspension seats. The purpose of this thesis is to investigate the possible improvement of reduction of vibrations and shocks by the use of some sort of actively controlled suspension, and to identify what measures are best suited for comparing passive suspension seats with actively controlled suspension seats. A study is conducted where several different measures are evaluated. The measures aim at capturing vibrations and shock aboard HSC’s, the effect they have on the human body from long time exposure and immediate exposure. A semi-active suspension system is chosen as the most suitable suspension system and is compared to a passive system by using several measures that are best suited for evaluating the risks of injuries associated with shocks and vibrations. The semi-active suspension is simulated using Matlab Simulink, where the control method of continuous skyhook control is used for achieving the most efficient damping. Different mechanical set ups for semi-active damping is investigated in order to obtain limitations for the simulation program. The simulation program has seat base acceleration data as the input, and the seat acceleration, that migrate to the human body, as the output. The seat acceleration data of the semi-active seat is compared to recorded and simulated seat acceleration data of passive seats. The result of the comparison is evaluated with the measures presented in ISO 2631-1, ISO 2631-5, BS 1987, and measures that are currently under development. The results show that a semi-active system is more superior than a passive system, but at the cost of a higher travelling distance.