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권대규,최병용,임숙정,방두열,이성철 전북대학교 공업기술연구소 2001 工學硏究 Vol.32 No.-
This paper presents the active control of a flexible intelligent beam with added mass. The two types of different materials which are the glass fiber reinforced(GFR) thermoplastic composite and the carbon fabric/epoxy(CFE) theromosetting composite, are employed to achieve vibration characteristics according to added mass induced end of composite beam with a distributed PVDF sensor and piezo-ceramic actuator. The PID controllers are employed to achieve vibration suppression in tranisent vibration situations. Simulations and experiments were carried out with the designed controllers in order to demonstrate the suppression efficiency of each controller.
부분적으로 유체가 채워진 원통형 관내의 외팔보 진동특성에 관한 실험적 연구
권대규,유계형,소순선,이성철 전북대학교 공학연구원 ( 구 전북대학교 공업기술연구소 ) 2003 工學硏究 Vol.34 No.-
This paper presents the vibration characteristics of an intelligent cantilever beam in contact with fluid using PZT actuator and PVDF film. The effect of liquid level on free vibration of composite beam in a partially liquid-filled circular cylinder is investigated. The dynamic behaviors of a flexible beam-water interaction system are examined. The coupled system is subject to an undisturbed boundary condition in the fluid domain. In the vibration analysis of wetted beam, the decoupled analyses between beam and fluid have been conventionally employed by considering firstly the composite beam vibration in air and secondly performing the correction taking account for surrounding fluid effects. That is, this investigation was to look at how natural frequencies, mode shapes, and damping are affected by liquid level variations. Using the coupled modal reanalysis method employing the governing equations and the clamped-free and free-free boundary conditions, the vibration analysis of beam in contact with fluid is performed. We also carried out the experimental verification about reliability of theoretical methods to inclusive vibration analysis of the fluid-structure system with PZT actuator and PVDF film. It was found that the coupled natural frequencies decrease with the fluid level for the identical composite beam due to added mass effect.
권대규,Gwon, Dae-Gyu 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.4
This paper presents the synchronous vibration control of a rotor system using an active air bearing(AAB). In order to suppress the synchronous vibration, it is necessary to actively control the air film pressure or the air film thickness. In this study, active pads are used to control the air film thickness. Active pads are supported by pivots containing piezoelectric actuators and their radial position can be actively controlled by applying voltage to the actuators. Thus, disturbances, i. e. various kinds of external force can cause shaft vibration as well as change of the air film thickness. The dynamic behavior of a rotary system supported by two tilting-pad gas bearings and its active stabilization using the tilting-pads as actuators are investigated numerically. The $\mu$ synthesis are applied to the AAB system with three pads, two of which contain piezoelectric actuators. To test the validity of the theoretical method, the performance of this control method is evaluated through experiments. The experimental results also show the effectiveness of the control system for suppressing the unbalanced response of the rigid modes.
권대규,강승철,정진엽,이상형,이경민,최인호,조태준,유원준,Young Jin Park,박문석 대한정형외과학회 2011 Clinics in Orthopedic Surgery Vol.3 No.3
Background: There is a worldwide tendency of an increasing prevalence of obesity. Therefore, this study aimed at determiningwhether such a trend exists among cerebral palsy (CP) patients. We also tried to compare this trend with the trend in the generalpopulation. We also discuss the importance of obesity trends in CP patients. Methods: This retrospective study was performed on 766 ambulatory patients who were diagnosed with CP since 1996 in our institution. The associations among the prevalence of obesity and the body mass index, age, gender, the type of CP, the gross motorfunction classifi cation system and the time of survey were investigated. Results: The overall prevalence of obesity was 5.7%, and the overall prevalence of obesity together with being overweight was14.6% for the ambulatory patients with CP. The prevalence of obesity and of obesity together with being overweight did not showa statistically signifi cant temporal increase. On the other hand, age and gender were found to affect the body mass index of theambulatory CP patients (p < 0.001 and 0.003, respectively). Conclusions: The extent of obesity and being overweight in the ambulatory patients with CP in this study was far less than thatreported in the United States (US). In addition, it appears that the differences of the prevalence of obesity in children and adolescentsbetween those with and without CP are disappearing in the US, whereas the differences of the prevalence of obesity in childrenand adolescents between those with and without CP seem to be becoming more obvious in Korea. Accordingly, care shouldbe taken when adopting the data originating from the US because this data might be affected by the greater prevalence of obesityand the generally higher body mass indices of the US.