• 한국기계가공학회지
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• 제15권2호
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• pp.125-130
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• 2016

In this paper, we deal with the dynamic walking of a humanoid robot. In our method, the inverted pendulum model is used as a dynamic model for a humanoid robot in which the Zero Moment Point (ZMP) and COG constraints of the robot are analyzed by considering the motion of the robot as that of an inverted pendulum. The motion of a humanoid robot should be generated by considering the dynamics of the robot, which commonly requires a large amount of computation. If a robot walks from one position to another while keeping the ZMP in the stable region, then the robot remains dynamically stable. The linear inverted pendulum model regards the whole robot as a point mass. It is simple, and relatively less computation is needed; however, it cannot model the whole dynamics of a humanoid robot. We propose a method for modeling a humanoid robot as an inverted pendulum system having 14 point masses. We also show that the dynamic stability of a humanoid robot can be determined more precisely by our method.

• 소음진동
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• 제8권4호
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• pp.616-622
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• 1998

An analytical method has been developed to estimate the dynamic contact force between wheel and rail when trains are running on rail with vertical irregularities. In this method, the effect of Hertzian deformation at the contact point is considered as a linearized spring and the wheel is considered as an sprung mass. The rail is modelled as a discretely-supported Timoshenko beam, and the periodic structure theory was adopted to obtain the driving-point receptance. As an example, the dynamic contact force for a typical wheel/rail system was analysed by the method developed in this research and the dynamic characteristics of the system was also discussed. It is revealed that discretely-supported Timoshenko beam model should be used instead of the previously used continuously-supported model or discretelysupported Euler beam model, for the frequency range above several hundred hertz.

• 지구물리
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• 제7권2호
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• pp.121-134
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• 2004

This study has tried to develop the modified DRASTIC Model by supplying the parameters, such as structural lineament density and land-use, into conventional DRASTIC model, and to predict the potential of groundwater contamination using GIS in Hwanam 2 District, Gyeonggi Province, Korea. Since the aquifers in Korea is generally through the joints of rock-mass in hydrogeological environment, lineament density affects to the behavior of groundwater and contaminated plumes directly, and land-use reflect the effect of point or non-point source of contamination indirectly. For the statistical analysis, lattice-layers of each parameter were generated, and then level of confidence was assessed by analyzing each correlation coefficient. Groundwater contamination potential map was achieved as a final result by comparing modified DRASTIC potential and the amount of pollutant load logically. The result suggest the predictability of contamination potential in a specified area in the respects of hydrogeological aspect and water quality.

• Environmental Engineering Research
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• 제12권4호
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• pp.176-193
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• 2007

The ability to measure groundwater contaminant flux is increasingly being recognized as crucial in order to prioritize contaminated site cleanups, estimate the efficiency of remediation technologies, measure rates of natural attenuation, and apply proper source terms to model groundwater contaminant transport. Recently, a number of methods have been developed and subsequently applied to measure contaminant mass flux in groundwater in the field. Flux measurement methods can be categorized as either point methods or integral methods. As the name suggests, point methods measure flux at a specific point or points in the subsurface. To increase confidence in the accuracy of the measurement, it is necessary to increase the number of points (and therefore, the cost) of the sampling network. Integral methods avoid this disadvantage by using pumping wells to interrogate large volumes of the subsurface. Unfortunately, integral methods are expensive because they require that large volumes of contaminated water be extracted and managed. Recent work has investigated the development of an integral method that does not require extraction of contaminated water from the subsurface. We begin with a review of the significance and importance of measuring groundwater contaminant mass flux. We then review groundwater contaminant flux measurement methods that are either currently in use or under development. Finally, we conclude with a qualitative comparison of the various flux measurement methods.

• Structural Engineering and Mechanics
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• 제57권6호
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• pp.989-1014
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• 2016

This paper deals with the analysis of the natural frequencies, mode shapes of an axially loaded beam system carrying ends consisting of non-concentrated tip masses and three spring-two mass sub-systems. The influence of system design and sub-system parameters on the combined system characteristics is the major part of this investigation. The effect of material properties, rotary inertia and shear deformation of the beam system is included. The end masses are elastically supported against rotation and translation at an offset point from the point of attachment. Sub-systems are attached to center of gravity eccentric points out of the beam span. The boundary conditions of the ordinary differential equation governing the lateral deflections and slope due to bending of the beam system including developed shear force frequency dependent terms, due to the sub.system suspension, have been formulated. Exact formulae for the modal frequencies and the modal shapes have been derived. Based on these formulae, detailed parametric studies are carried out. The geometrical and mechanical parameters of the system under study have been presented in non-dimensional analysis. The applied mathematical model is presented to cover wide range of mechanical, naval and structural engineering applications.

• 에너지공학
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• 제18권3호
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• pp.203-211
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• 2009

기존의 CFC 계열 및 HCFC 계열 냉매들이 오존층 붕괴와 지구온난화의 원인들 중의 한가지로 밝혀지면서 이것을 대체할 수 있는 냉매의 개발은 주요한 연구과제였다. 이제 몇 가지 대체 냉매들이 개발되면서 이것들 이 냉동시스템에 사용될 때 발생하는 상용성 (Compatibility)이 연구될 필요가 있다. 본 연구에서는 대체냉매의 상용성 연구의 일환으로 1,1,1,2-Tetrafluoroethane(HFC-134a) +1,1,1-Trifluoroetane(HFC-143a) + Pentafluoroethane (HFC-125)의 혼합대체냉매 HFC-404a 와 냉매 윤활유의 하나인 POE 오일 혼합물의 증기압을 측정하였다. 측정온도범위는 냉매 시스템의 운전온도를 고려하여, 263.15K 에서 323.15 K로 하였으며 오일농도범위는 0 mass% 에서 90 mass% 까지로 하였다. 측정결과 273.15K 이하의 온도에서 오일 농도 30 mass%까지 증기압에 대한 오일의 영향은 미미하였으며 50 mass% 이상에서는 증기압이 급격히 떨어지는 것이 밝혀졌다. 측정자료를 이용하여 HFC-404a와 POE 오일 혼합물의 증기압을 예측할 수 있는 모형을 개발 하기 위하여 Rault 모델과 Flory-Huggins 모델을 사용하여 측정치와 비교하였다. 그리고 보다 정확하고 실용적으로 증기압을 예측할 수 있는 경험식을 도출하였다.

• 한국감성과학회:학술대회논문집
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• 한국감성과학회 2002년도 추계학술대회 논문집
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• pp.85-96
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• 2002

본 연구에서는 ‘대량 맞춤화(Mass Customization)' 트렌드의 부상과 그 맥락을 같이 하여, 텍스타일 분야의 혁명이라 일컬어지는 디지털 텍스타일 프린팅 기술을 기반으로 한 소비자 참여형 의류 디자인 프로세스 모형 두 가지를 제안하고, 기존의 고전적인 디자인 프로세스와 이 모형들 사이의 효율성, 적합성을 비교 고찰함으로써, 대량 맞춤화 시대를 위한 새로운 의류 디자인 프로세스의 가능성을 모색하였다. 20대∼30대 여성을 대상으로 설문조사를 실시한 결과, 전체 응답자들은 선택의 기회를 가장 많이 가질 수 있는 대량 맞춤화형 디자인 프로세스를 가장 선호하였으며, 응답자들은 의류 소재의 디자인 요소 중에서 문양보다는 색채의 영향을 더 많이 받는 것으로 나타났다. 본 연구의 결과를 통하여 획일화되고 대량화된 상품보다는 보다 차별화되고 자신의 요구를 반영한 상품을 선호하는 소비자들의 수요를 발견하였으며 이에 부응하는 디자인 프로세스로의 패러다임 변화에 관한 지표를 얻을 수 있었다.

• 한국지진공학회논문집
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• 제22권7호
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• pp.379-390
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• 2018

In this study, a numerical approach based on mid-point integrated finite elements and a viscous boundary is proposed for time-domain wave-propagation analyses in infinite poroelastic media. The proposed approach is accurate, efficient, and easy to implement in time-domain analyses. In the approach, an infinite domain is truncated at some distance. The truncated domain is represented by mid-point integrated finite elements with real element-lengths and a viscous boundary is attached to the end of the domain. Given that the dynamic behaviors of the proposed model can be expressed in terms of mass, damping, and stiffness matrices only, it can be implemented easily in the displacement-based finite-element formulation. No convolutional operations are required for time-domain calculations because the coefficient matrices are constant. The proposed numerical approach is applied to typical wave-propagation and soil-structure interaction problems. The model is verified to produce accurate and stable results. It is demonstrated that the numerical approach can be applied successfully to nonlinear soil-structure interaction problems.

• 한국항공우주학회지
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• 제37권7호
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• pp.661-668
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• 2009

본 논문에서는 시간영역에서 최소자승법을 이용하여 실린더 용기의 슬로시 주파수와 댐핑 계수와 함께 슬로시 모드 질량 및 슬로시 힘 작용점 높이를 시험을 통해 추정하였다. 추정한 결과가 해석 결과와 비교적 잘 일치함을 확인 할 수 있었으며 추정기법의 정확성을 파악할 수 있었다. 향후 이 기법을 이용해 액체 연료 용기의 슬로시 모델 파라미터를 추정하는데 적용할 예정이다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.33-36
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• 2008

The transient behavior of a passive air breathing direct methanol fuel cell (DMFC) operated on vapor-feeding mode is studied in this paper. It generally takes 30 minutes after starting for the cell response to come to its steady-state and the response is sometimes unstable. A mathematical dynamic one-dimensional model for simulating transient response of the DMFC is presented. In this model a DMFC is decomposed into its subsystems using lumped model and divided into five layers, namely the anodic diffusion layer, the anodic catalyst layer, the proton exchange membrane (PEM), the cathodic catalyst layer and the cathodic diffusion layer. All layers are considered to have finite thickness, and within every one of them a set of differential-algebraic governing equations are given to represent multi-components mass balance, such as methanol, water, oxygen and carbon dioxide, charge balance, the electrochemical reaction and mass transport phenomena. A one-dimensional, isothermal and mass transport model is developed that captures the coupling between water generation and transport, oxygen consumption and natural convection. The single cell is supplied by pure methanol vapor from a methanol reservoir at the anode, and the oxygen is supplied via natural air-breathing at the cathode. The water is not supplied from external source because the cell uses the water created at the cathode using water back diffusion through nafion membrane. As a result of simulation strong effects of water transport were found out. The model analysis provides several conclusions. The performance drop after peak point is caused by insufficiency of water at the anode. The excess water at the cathode makes performance recovery impossible. The undesired crossover of the reactant methanol through the PEM causes overpotential at the cathode and limits the feeding methanol concentration.