The crew of small, high-speed marine craft (HSC) is exposed to high levels of vibrations and shocks that can imply risks for adverse health effects. The working environment needs to be improved by appropriately isolating the crew from the severe, non-linear accelerations that characterise the motions of small HSCs. This thesis presents a brief overview of the vibration mitigation techniques flexible hull design, active vibration control and suspension seats. The suspension seat is analysed further. A boat-seat interaction model describing the seat motions when excited by non-linear, vertical accelerations is established. The seat model is used to investigate how the seat characteristics influence the seat response motion, that is, the crew vibration exposure. Published experiment data in terms of accelerations at the seat base measured on a 10 meters HSC unit of the Swedish Coast Guard is used as exciting motion of the seat. By systematically varying the spring stiffness and damping coefficients of the seat, the response motion for 10 different seats are calculated and evaluated according to existing standards regarding whole body vibration exposure, ISO 2631-1 and ISO 2631-5. The thesis concludes that the mitigating effect of the seat can be improved radically by reducing the spring stiffness coefficients and increasing the damping coefficients of the seat. The spring stiffness is however limited downwards by the seat motion stroke, since bottoming out events have to be avoided and the motion stroke for practical reasons cannot be too large. Further, the relation between crew weight and resulting vibration exposure is investigated by varying the crew weight for two different seats. Slightly higher vibration levels are found for the lower crew weigths, although the distinction between the seat reponse motions is small compared to the variations found when comparing different seats. However, it is concluded that the crew weight is an important parameter when studying the vibration exposure, since it influence the motion stroke of the seat.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kth-118798 |
| Date | January 2012 |
| Creators | Olausson, Katrin |
| Publisher | KTH, Marina system |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | Trita-AVE, 1651-7660 ; 2012:65 |
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