• Journal of the Society of Naval Architects of Korea
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• v.47 no.3
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• pp.291-305
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• 2010

A three-dimensional time-domain calculation method is of crucial importance in prediction of the motions and wave loads of a ship advancing in a severe irregular sea. The exact solution of the free surface wave-ship interaction problem is very complicated because of the essentially nonlinear boundary conditions. In this paper, an approximate body nonlinear approach based on the three-dimensional time-domain forward-speed free-surface Green function has been presented. The Froude-Krylov force and the hydrostatic restoring force are calculated over the instantaneous wetted surface of the ship while the forces due to the radiation and scattering potentials over the mean wetted surface. The time-domain radiation and scattering potentials have been obtained from a time invariant kernel of integral equations for the potentials which are discretized according to the second-order boundary element method (Hong and Hong 2008). The diffraction impulse-response functions of the Wigley seakeeping model advancing in transient head waves at various Froude numbers have been presented. A simulation of coupled heave-pitch motion of a long rectangular barge advancing in regular head waves of large amplitude has been carried out. Comparisons between the linear and the approximate body nonlinear numerical results of motions and wave loads of the barge at a nonzero Froude number have been made.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.11
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• pp.18-25
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• 2006

Unsteady aerodynamic force measurements were carried out in order to investigate the effects of phase difference of a dragonfly-type model with two pairs of wing. A load-cell was employed to measure the aerodynamic force generated by a plunging motion of the dragonfly-type model. The dragonfly-type model has a dynamic similarity with real one, and incidence angles of fore- and hind-wing are 0° and 10°, respectively. Other experimental conditions are as follows: The freestream velocity was 1.6 m/sec and corresponding chord Reynolds number was 2.88×103, and phase differences of fore- and hind-wing were 0°, 90°, 180° and 270°. The variation of aerodynamic coefficients during one cycle of the wing motion is presented. Results show that the lift is generated during the downstroke motion and the drag generated during the hind-wing‘s downstroke motion with the lift generation.

• The Journal of Korean Institute for Practical Engineering Education
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• v.3 no.2
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• pp.53-62
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• 2011

The elliptical trainers(ET) can be a good tool for educating engineers by analyzing physical responses in terms of Respiratory Exchange Ratio (RER, epm) and Heart Rate (HR, bpm). For the various energy expenditure, exercise speed, and weight loss both RER and HR are studied in order to study the blood circulations based on the health training cardiorespiratory. As the results, (1) RER increases gradually as the energy expenditure, however, HR increases gradually up to a critical value and then increases rapidly. The critical value of the energy expenditure in our studies was 275 Cal. (2) RER increases gradually as the ET speed increases, however, HR increases gradually up to a critical value and then increases rapidly. The critical value of the ET speed in our studies was about 6.7km/h. (3) RER increases gradually as the weight loss increases (or, the metabolic cost increases), however, HR is almost nothing to do with the increase of the weight loss.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1033-1042
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• 1994

Dynamic behavior of flexible rectangular liquid containers is analyzed by a two-dimensional coupled boundary element-finite element method. The irrotational motion of inviscid and incompressible ideal fluid is modeled by boundary elements and the motion of structure by finite elements. A singularity free integral formulation is employed for the implementation of boundary element method. Coupling is performed by using compatibility and equilibrium conditions along the interface between the fluid and structure. The fluid-structure interaction effects are reflected into the coupled equation of motion as added fluid mass matrix and sloshing stiffness matrix. By solving the eigen-problem for the coupled equation of motion, natural frequencies and mode shapes of coupled system are obtained. The free surface sloshing motion and hydrodynamic pressure developed in a flexible rectangular container due to horizontal and vertical ground motions are computed in time domain.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.2
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• pp.95-101
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• 2017

In this study, we derived theoretical equations for the zigzag movement of a leading vehicle, which is the most frequent behavior in train accidents, by using a simplified spring-mass model for the rolling stock. In order to solve the equations of motion, we applied the Runge-Kutta method, which is the typical numerical analysis method used for differential equations. Furthermore, the lateral displacement of the wheel-set at the wheel-rail interface was estimated using kinetic energy. In order to verify the derived equations, we compared the theoretical and simulated results under various collision conditions. The maximum relative deviations of the lateral displacements were 0.8 [%] ~ 4.7 [%] in light collisions and 0.6 [%] ~ 5.1 [%] under derailment conditions. When an accident is simulated, these theoretical equations can be used to predict the overall behavior and obtain the offset of the body-to-body link as the initial perturbation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.2
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• pp.185-196
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• 1988

In this study, a method of nonlinear dynamic analysis of suspension bridges subjected to random wind loads is pre.sented. The nonlinearity considered is the one due to the interaction between the motion of the bridge girder and the tertsion variation of the main cables. The equation of motion is formulated using a continuum approach. The coupling between the vertical and torsional motions are included in the analysis. The equation of motion is solved by using the mode superposition method. The analysis is carried out in the frequency domain utilizing the stochastic linearization technique on to the modal equations. In the linearization procedure, the nonlinear terms are approximated as linear ones with constant terms. The verification of the method has been performed on a case with four modal degrees of freedom. Example analyses are carried out on two suspension bridges for various wind speeds and wind force parameters. Numerical results indicate that, by including the nonlinearity into the analysis, the dynamic responses of the bridges, particularly in the vertical direction, change considerably.

• Proceedings of the Korean Society of Computer Information Conference
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• 2014.07a
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• pp.21-24
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• 2014

본 연구는 뇌손상(뇌졸중, 외상성 뇌손상, 뇌성마비 등)으로 인하여 손의 능동적 움직임이 결여되어 발생하는 관절의 구축, 근육의 단축, 근육의 탄력성 저하 등의 문제점을 분석하여 인체 역학적 모델에 따른 과학적 설계를 기반으로 환자의 손 기능 회복을 위하여 로봇 기술과 스마트폰의 융합을 통한 재활 로봇 보조 치료기를 설계하고 구현하였다. 제안된 시스템은 일반적인 근 경직을 치료하는 방법을 응용하여 IT 기술과 로봇기술을 융합하여 치료사들의 부담을 덜어 주고, 환자들에게 오랫동안 정확한 운동을 반복적으로 할 수 있도록 하는데 목적이 있다. 하나의 구동기로 2자유도의 움직임을 조절 할 수 있는 링크 매커니즘과 링크의 길이를 조절하여 신전(extension)과 과신전(Hyperextension)의 범위 조절이 가능하도록 로봇 플랫폼을 설계하였다. 또한 환자의 재활정도 및 상태에 적합한 운동속도, 운동반복횟수 등을 손쉽게 조작할 수 있는 등의 개인 맞춤형 재활훈련이 가능한 사용자 인터페이스를 설계 및 구현하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.11
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• pp.2751-2757
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• 2015

To obtain the system requirement specification in the beginning of the precision guidance and control system development, the effectiveness and reliability analysis for the system are necessary. The main purpose of this research is to obtain the system requirement specification by carrying out the effectiveness analysis using the modeling and simulation(M&S) scheme. M&S model is constructed using 6-DOF dynamic model, environment model, guidanc -navigation & control model. Assume that the navigation sensor is consist of inertial navigation sensor(INS) and doppler velocity log(DVL), and the speed and direction of current is environment parameter. The effectiveness analysis is carried out using circular error probability(CEP) and variance analyze scheme. Also, the effectiveness analysis is utilized for cost-performance analysis considering the cost of commercial INS and DVL sensor. This paper shows the high-level INS and the low-level DVL configure a high price-performance integrated navigation system.

• Journal of the Korean Society for Library and Information Science
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• v.49 no.3
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• pp.185-208
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• 2015

The purpose of this study is to understand the value of Fahrenheit 451 by Ray Bradbury as the second most favored 'One Book', and the goals of the communities which selected this particular book. A total of 53 'One Book' programs from 2001 through 2014 and 136 TBR programs from 2007 through 2015 selected this book as 'One Book' to read. In this study, 270 programs in TBR 2008/09, and more than 240 programs in TBR 2014/15 and several 'One Book' projects were analyzed. The results confirm the significance of book discussions and movie showing, the focus on such subjects as censorship, banned books, and freedom of expression, etc., and a close relationship between the diversity of programs and cooperation with community members.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.2
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• pp.97-104
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• 2005

A simple but efficient grid generation technique by using the modified compressible form of stream function has been formulated. Transformation of a physical plane to a streamline plane, the Von Mises Transformation, has been widely used to solve the differential equations governing flow phenomena, however, limitation arises in low velocity region of boundary layer, mixing layer and wake region where the relatively large grid spacing is inevitable. Modified Von Mises Transformation with simple mathematical adjustment for the stream function is suggested and applied to solve the confined coaxial turbulent jet mixing with simple $\kappa-\epsilon$ turbulence model. Comparison with several experimental data of axial mean velocity, turbulent kinetic energy, and Reynolds shear stress distribution shows quite good agreement in the mixing layer except in the centerline where the turbulent kinetic energy distributions were somewhat under estimated. This formulation is strongly suggested to be utilized specially for free turbulent mixing layers in axisymmetric flow conditions such as the investigation of mixing behavior, jet noise production and reduction for Turbofan engines.