Active Suspension Seat for High Speed Craft

Abstract: Master of Science thesis in Naval Architecture presents a study and the performance of an active seat suspension with the purpose to suppress shocks, caused by slamming in High Speed Crafts (HSCs). The system is modelled and simulated with the aid of the Mathworks software Simulink, with the main objective to evaluate if the active suspension seat has the potential to mitigate slamming impact loads to a larger extent compared to a passive suspension seat. The active suspension model is developed by adding a PD-controlled actuator in parallel with the spring and damper of a passive seat’s suspension. This paper presents the performance study of an active suspension seat where the seat is given a single impact load as input. The results are then compared to a comparable passive seat. The most promising results show that the active system can reduce the passenger seat’s acceleration response by roughly 30 %. This is achieved on the expense of an increased stroke length, from 30 mm for a comparable passive system, to 34 mm for the active system. To achieve this the actuator need to provide up to 900 N of force with a rise-time of 15 ms. During the assessment of the suspension seat performance four key performance indicators(KPI) were found to be of significance. Those are the seat response acceleration, seat displacement relative to the seat base, settling time and the zero crossing time. The seat acceleration is directly proportional to the load that the passenger is being subjected to. Hence, the acceleration is the property that needs to be reduced in order to decrease risk of injuries. The stroke length of the seat in relation to the seat base should be kept to a minimum for several reasons. One being the risk of bottoming out the suspension if the stroke length is too high, risking damage on equipment as well as injuries on passenger. Since the conditions on sea entail series of impact loads on the hull, the settling time need to be as short as possible to avoid accumulating the displacement. This is caused when the seat has not yet returned to its neutral position before next impact occurs. To define the response time of the system, the zero-crossing performance indicator was defined. Zero-crossing time is defined as the time from when the displacement of the seat starts (the suspension being compressed) until it returns and crosses the neutral position, regardless if the suspension stops at the neutral position or continue extending. A correlation was found between the zero-crossing time and the settling time. Both KPIs are dependent on the