• 소음진동
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• 제7권3호
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• pp.439-447
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• 1997

In this study, the dynamic instabilities of a nonlinear elastic system subjected to follower forces are investigated. The two-degree-of-freedom double pendulum model with nonlinear geometry, cubic spring, and linear viscous damping is used for the study. The constant, the initial impact forces acting at the end of the model are considered. The chaotic nature of the system is identified using the standard methods, such as time histories, power density spectrum, and Poincare maps. The responses are chaotic and unpredictable due to the sensitivity to initial conditions. The sensitivities to parameters, such as geometric initial imperfections, magnitude of follower force, direction control constant, and viscous damping, etc., are analysed. Dynamic buckling loads are computed for various parameters, where the loads are changed drastically for the small change of parameters.

• 한국정밀공학회지
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• 제23권7호
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• pp.122-129
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• 2006

The linear compressor has lately attracted considerable attention because of its low power consumption and excellent efficiency. For an efficient design, it is necessary to develop an analytical model of the linear compressor. The effective flow and force areas are important parameters to describe the behavior of the linear compressor, which are used to determine the mass flow rates through the valving systems and the forces on the valves, respectively. It is not easy to estimate these parameters because shapes of the valve systems of the linear compressor are so different from those of tile conventional valve systems. In this paper, we suggest method to measure experimentally the effective discharge flow and force areas of the linear compressor and analyze valve characteristic to apply the experimental results to their theoretical model.

• Macromolecular Research
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• 제15권7호
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• pp.610-616
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• 2007

We developed a coarse-grained force field and have extended it to polystyrene with longer chain length. A systematic method was introduced and was utilized to explain how the coarse-grained force field for polystyrene could be developed from the atomistic simulation in the paper. We elected to use polystyrene with different chain lengths of 20, 40 and 80 monomers in this study. In three cases, we utilized the same new mapping scheme. The coarse-grained force field does reproduce the bond, angle, and radial distribution of the atomistic model. The coarse-grained model proved successful, as shown by analyses of the static and dynamic properties of different chain lengths.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.723-732
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• 2020

A theoretical calculation model for ship stern bearings with large hull deformation is established and validated theoretically and experimentally. A hull simulation model is established to calculate hull deformations corresponding to the reaction force of stern bearings under multi-factor and multi-operating conditions. The results show that in the condition of wave load, hull deformation shows randomness; the aft stern tube bearing load obeys the Gaussian distribution and its value increases significantly compared with the load under static, and the probability of aft stern tube bearing load greater than 1 is 65.7%. The influence laws and levels between hull deformation and bearing reaction force are revealed, and suggestions for ship stern bearing specifications are proffered accordingly.

• 대한기계학회논문집A
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• 제20권7호
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• pp.2257-2265
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• 1996

In the cold rolling mill, it is very important that a constrained static flow stress of rolled strip and rolling force calculation model be exactly considered to improve an prediction accuracy for rolling forces. Therefore, in this study, the values of the constrained static flow stress are used by deriving the regression equation which is a function of rolling conditions(FDT, CT) and chemical compositions(C, Si, Mn), previously applied by making the tables of yield strength for hot coils with size. And with the consideration that an elastic deformation part of an rolled strip appears at the entry and delivery side of the contacting area between the work roll and rolled strip is calculated. By applying these methods, the more accurate prediction for rolling force is obtained. As a results, the deviation of thickness is significantly reduced in the rolling direction.

• 한국항공우주학회지
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• 제30권7호
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• pp.11-19
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• 2002

낙하산 축소모형으로부터 캐노피의 전개시간과 최대 전개력을 측정하기 위하여 낙하산 캐노피의 전개특성에 관한 실험연구를 수행하였다. 시험에는 낙하산 모형을 풍동 유동장 내부로 사출하고 모형에 작용하는 항력을 측정하도록 하기 위한 장치가 사용되었다. 시간에 따른 전개력 변화특성과 최대 전개력이 획득되었으며, 전방체로 인한 후류효과를 비롯한 이들 공력특성에 대한 비교평가를 실시하였다. 링슬롯형 낙하산의 경우 기존의 시험자료들에 비해 약 10~40% 가량 빠른 전개특성을 보였으며, reefing 형상의 리본형은 기존의 결과들과 잘 일치하였다.

• 대한기계학회논문집
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• 제16권11호
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• pp.2049-2058
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• 1992

본 연구에서는 OHC형 캠-밸브 기구의 6자유도 집중 질량계 모델을 기본으로 하고, 밸브변위와 선회종동자(oscillating-follower or finger-follower)의 동적 스트 레인을 측정하여 모델의 타당성을 검증하고, 또 최적화 기법을 도입하여 밸브 개폐시 기, 밸브변위 그리고 최소 접촉력 등을 구속조건으로 주고 캠과 종동자 사이의 최대 접촉력을 최소화 시키도록 최적 캠 형상을 설계하였다. 그리고 설계된 캠을 정밀 가 공하여 최적화 설계의 타당성 및 접촉력을 실험을 통하여 검증하였다.

• 한국전자통신학회논문지
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• 제10권7호
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• pp.845-850
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• 2015

사람의 감정 중의 하나인 사랑은 사회학과 심리학에서 주된 관심사로 연구되어 왔다. 기본적인 사랑 모델에서 비선형 특성을 찾기는 어렵다. 따라서 본 논문에서는 기본적인 사랑모델에서 비선형 거동을 찾기 위하여 기본적인 사랑 방정식에 외력을 주고 이때의 시계열과 위상 공간을 통하여 비선형 거동이 있음을 확인한다. 또한 이 비선형거동이 일반 카오스 발생현상인 주기배증과정, 카오스, 주기과정의 현상과 유사하게 유사한 주기 배증 과정, 카오스, 주기과정이 있음을 확인한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.261-267
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• 2000

A mathematical model was developed to calculate the muscle force of lower extremity during the gait. We constructed a model of human locomotion, which includes a muscle-skeletal system with 7 segments and 16 lower limb muscles. Using a optimization technique, muscle forces variation of the lower extremity during the gait were generated and its result was verified by comparing a experimental results of EMG analysis. Moreover. the walking movement of the model could be compared quantitatively with those of experimental studies in human by inverse dynamics.

• Coupled systems mechanics
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• 제7권4호
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• pp.421-440
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• 2018

In this study, a computational method for wall shear stress combined with an implicit direct-forcing immersed boundary method is presented. Near the immersed boundaries, the sub-grid stress is determined by a wall model in which the wall shear stress is directly calculated from the Lagrangian force on the immersed boundary. A coupling mathematical model of the transition process for a model Francis turbine comprising turbulent flow and rotating rigid guide vanes is established. The spatiotemporal distributions of pressure, velocity, vorticity and turbulent quantity are gained with the transient process; the drag and lift coefficients as well as other forces (moments) are also obtained as functions of the attack angle. At the same time, analysis is conducted of the characteristics of pressure pulsation, velocity stripes and vortex structure at some key parts of flowing passage. The coupling relations among the turbulent flow, the dynamical force (moment) response of blade and the rotating of guide vane are also obtained.