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포텐셜함수 기반 초공동 수중운동체 플레이닝 회피 제어 연구
김선홍(Seonhong Kim),김낙완(Nakwan Kim),김민재(Minjae Kim),김종혁(Jonghoek Kim),이건철(Kurnchul Lee) 한국해양공학회 2018 韓國海洋工學會誌 Vol.32 No.3
In this paper, we focus on planing avoidance control for a supercavitating underwater vehicle based on the potential function method. The planing margin can be calculated using the relative position between the cavity center and vehicle center at the end of the vehicle. The planing margin was transformed into a limit variable such as the pitch angle and yaw angle limit. To prevent the vehicle attitude from exceeding the limit variable, a potential function based planing envelope protection method was proposed. The planing envelope protection system overrides commands from the tracking controller, and the vehicle attitude converges to a desired angle, in which the potential function is minimized. Numerical simulations were performed to analyze the physical feasibility and performance of the proposed method. The results showed that the proposed methods eliminated the planing, allowing the vehicle to follow tracking commands.
Control Strategy for a Ventilated Supercavitating Vehicle in Initial Phase
Kim, Seonhong,Kim, Nakwan International Society of Offshore and Polar Engine 2016 International journal of offshore and polar engine Vol.26 No.2
<P>Supercavitation reduces the resistance of an underwater vehicle by enveloping it in a bubble. When the velocity of the vehicle is low and the depth is significant, natural supercavitation is inhibited. Consequently, an artificial cavity to which gas is supplied, called a ventilated cavity, is used to maintain the supercavitating condition. This study models ventilated supercavity according to the cavity closure type and the design depth and proposes a ventilation control strategy that swiftly changes the closure type from the toroidal vortex regime to the twin vortex regime in the initial phase of flight. Numerical simulations verify the efficacy of the proposed strategy.</P>
Integrated dynamics modeling for supercavitating vehicle systems
Kim, Seonhong,Kim, Nakwan The Society of Naval Architects of Korea 2015 International Journal of Naval Architecture and Oc Vol.7 No.2
We have performed integrated dynamics modeling for a supercavitating vehicle. A 6-DOF equation of motion was constructed by defining the forces and moments acting on the supercavitating body surface that contacted water. The wetted area was obtained by calculating the cavity size and axis. Cavity dynamics were determined to obtain the cavity profile for calculating the wetted area. Subsequently, the forces and moments acting on each wetted part-the cavitator, fins, and vehicle body-were obtained by physical modeling. The planing force-the interaction force between the vehicle transom and cavity wall-was calculated using the apparent mass of the immersed vehicle transom. We integrated each model and constructed an equation of motion for the supercavitating system. We performed numerical simulations using the integrated dynamics model to analyze the characteristics of the supercavitating system and validate the modeling completeness. Our research enables the design of high-quality controllers and optimal supercavitating systems.
Joint Moments and Lumbar Lordosis during Symmetric Lifting
Seonhong Hwang,Sungjae Hwang,Youngeun Kim,Youngho Kim 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
In this study, contributions of lower extremity joints and lumbar lordotic angles were investigated for two different symmetrical lifting techniques using the three-dimensional motion analysis: squat and stoop. Joint angles and moments were determined when the lumbar curvature changed from kyphosis to lordosis. Thirteen male volunteers lifted boxes weighing 5, 10 and 15㎏ by both squat and stoop lifting techniques. Results showed that extension moments of hip and ankle joints contributed the most to support the body in squat lifting, and the knee flexion moment played an important role in stoop lifting. There were individual differences in lower extremity joint moments when the lumbar lordotic curve appeared. However, the correlations about angles and moments between lumbar and lower extremity joints could confirmed the results from the support moment analysis. In conclusion, there might be some strategy to minimize mechanical stress on the waist by the change of lordotic curvature in the lumbar spine for the safe lifting technique.