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다자유도 곡선맞춤법을 이용한 감쇠보 모델의 실험 진동해석
민천홍(CHEON-HONG MIN),박한일(HAN-IL PARK),배수룡(SOO-RYONG BAE) 한국해양공학회 2008 韓國海洋工學會誌 Vol.22 No.1
It is important to reduce the vibration and noise of submarines and ships. For the purpose of noise reduction, various researches are actively being conducted on the employment of complex structures. However, in the case of numerical analysis for complex structures with damping materials, substantial errors can be generated by the absence of an exact damping model. Thus experimental model analysis is necessary for the verification of a numerical analysis for complex structures. In this research, vibration experiments are conducted in order to ascertain the vibration properties of cantilever beam attached damping materials. First, an initial value is obtained by using a direct linear method. Next, based on this intial value, the exact modal parameters of the cantilever beam are obtained by using the Newton-Raphson method.
민천홍(Cheon-Hong Min),박한일(Han-Il Park) 한국마린엔지니어링학회 2009 한국마린엔지니어링학회 학술대회 논문집 Vol.2009 No.-
The viscoelastic materials and composite structures currently have a wide range of engineering applications, especially in ship, submarine and marine structures. The increasing use of composite materials in engineering structures has cause many new problems for structural maintenance, inspection and vibration control. Vibration damping becomes increasingly important for improvement of vibration and noise control, and fatigue and impact resistance in advanced engineering systems. The examination of environmental factors on structural vibration properties is important in order to reliably apply the vibration control techniques to engineering structures. Environmental conditions affect structural vibration properties in a complicated manner, so in this paper the variations of frequencies, mode shapes and damping with respect to temperature changes from 5 to 45 degrees Celsius are investigated. The modal properties are identified from vibration tests of cantilever beams using a Non-Linear Least Squares (NLLS) method.
민천홍(Cheon-Hong Min),김형우(Hyung-Woo Kim),이창호(Chang-Ho Lee),홍섭(Sup Hong),최종수(Jong-Su Choi),여태경(Tae-Kyeong Yeu) 한국해양공학회 2012 韓國海洋工學會誌 Vol.26 No.4
A new identification method for a nonproportional damping matrix using the finite element (FE) model updating technique is proposed. Mass and stiffness matrices of the undamped system are identifed by FE model updating method. Sensitivity analysis is used to update the FE model, and zero frequencies are considered as design parameters to supplement the information of vibration characteristics. The nonproportional damping matrix is identified through the proposed method. A numericl example is considered to verify the performance of the proposed method. As a result, the damping matrix of the nonproportional system is estimated accurately.
다자유도 곡선 맞춤법과 PKU 기법을 이용한 점탄성 감쇠재의 탄성 및 손실계수 추정방법 연구
민천홍(Cheon-Hong Min),박한일(Han-Il Park),배수룡(Soo-Ryong Bae),전재진(Jae-Jin Jeon) 한국해양공학회 2011 韓國海洋工學會誌 Vol.25 No.1
Offshore structures, such as a platform, a buoy, or a floating vessel, are exposed to several dynamic loads, and viscoelastic damping material is used to reduce the vibration of offshore structures. It is important to know the properties of viscoelastic materials because loss factor and Young's modulus of the viscoelastic damping material are dependent on frequency and temperature. In this study, an advanced technique for obtaining accurate loss factor and Young's modulus of the viscoelastic damping material is introduced based on a multi degree of freedom curve-fitting method and the RKU (Ross-Kenwin-Ungar) equations. The technique is based on a modified experimental procedure from ASTM E 756-04. Loss factor and Young's modulus of the viscoelastic damping material are measured for different temperatures by performing the test in a temperature-controlled vibration measurement room where temperature varies from 5 to 45 degrees Celsius.
비선형 최소제곱법을 이용한 점탄성 감쇠를 갖는 원통셸의 실험진동해석
민천홍(CHEON-HONG MIN),박한일(HAN-IL PARK),배수룡(SOO-RYONG BAE) 한국해양공학회 2008 韓國海洋工學會誌 Vol.22 No.3
It is a recent trend for advanced ships and submarines to incorporate composite structureswith viscoelastically damping material. Much research has been done on curve-fitting techniquesto identify vibration characteristic parameters such as natural frequencies, modal damping ratios, and mode shapes of the composite structure. In this study, an advanced technique for accurately determining vibration characteristic of a circular cylindrical shell-attached viscoelastically damping material is used, based on a multi-degree of freedom (MDOF) curve-fitting method. First, an initial value is obtained by using a linear least square method. Next,sung the initial value, the exact model parameters of the composite circular cylindrical shell are obtained by using a nonlinear least square method. Results show computation time is greatly decreased and accurate results are obtained by the MDOF curve-fitting method.
모바일 보안 서비스에 대한 인식 정도가 모바일 결제 시스템 범용성에 미치는 영향에 관한 연구
민천홍 ( Cheon Hong Min ),고완석 ( Wan Suk Ko ) 한국인터넷비즈니스학회 2005 인터넷비지니스연구 Vol.6 No.2
모바일 상거래의 확산에 따라 모바일 서비스의 사용이 증가되고 있는데, 모바일 서비스 중에서 모바일 결제서비스는 매우 중요하다. 특히 모바일 결제 시스템의 범용성은 모바일의 편재성(ubiquity) 특성을 잘 반영하므로 모바일 서비스에 가장 많은 영향을 미치고 있다(도진환, 2002). 모바일 결제 서비스가 활성화되기 위해서는 사용자가 모바일 보안문제에 대해서 안심할 수 있어야 하므로 이와 관련하여 각종 보안 서비스 특성들이 제공되고 있다. 본 연구는 이와 같은 모바일 보안 서비스에 관한 사용자 인식의 정도가 모바일 결제시스템의 범용성 특성에 미치는 영향을 알아보고자 한다. 이와 같은 연구를 통하여 모바일 결제시스템에 보안의 중요성을 제시하고자 한다. The commonplace characteristics of mobile payment would influence mobile services because they well reflect ubiquity of mobile commerce. In order to widen mobile payment use, user must be safe with security problem. In relation to this purpose, today, mobile operators provide kinds of security services with user. In conclusion, our paper suggests the importance of security in mobile payment system.
민천홍(Cheon-Hong Min),최종수(Jong-Su Choi),홍섭(Sup Hong),김형우(Hyung-Woo Kim),여태경(Tae-Kyeong Yeu) 한국해양공학회 2012 韓國海洋工學會誌 Vol.26 No.5
In this study, a damage detection method that uses sensitivity-based finite (FE) element model updating with the natural frequency and zero frequency was proposed. The stiffness matrix for a structure was modified using the sensitivity-based FE model updating method. A sensitivity analysis was used to update the FE model, and the natural frequencies and zero frequencies were considered as target parameters to supplement the information on the vibration characteristics. The locations and values of the damages were estimated from the modified stiffness matrix. Several numerical examples were considered to verify the performance of the proposed method.