• Journal of the Korean Society for Precision Engineering
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• v.17 no.7
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• pp.162-169
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• 2000

In this paper, we develop a parallel inverted pendulum system that has the characteristics of the strongly coupled dynamics of motion by an elastic spring, the time-variant system parameters, and inherent instability, and so on. Hence, it is possible to approximate some kinds of a physical system into this representative system and to apply the various control theories to this system in order to verie their fidelity and efficiency. For this purpose, an experimental system of the parallel inverted pendulum has been implemented, and a control scheme using the eigenstructure assignment for decoupling control is presented in comparison with the conventional LQR optimal control method. Furthermore, this system can be utilized as a testbed to develop and evaluate new control algorithms through various setups. Finally, in this paper, the results of the experiment are compared with those of numerical simulations for validation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.2
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• pp.1019-1031
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• 2017

In this study, we propose a new method for simulating water responding to human motion. Motion data obtained from motion-capture devices are represented as a jointed skeleton, which interacts with the velocity field in the water simulation. To integrate the motion data into the water simulation space, it is necessary to establish a mapping relationship between two fields with different properties. However, there can be severe numerical instability if the mapping breaks down, with the realism of the human-water interaction being adversely affected. To address this problem, our method extends the joint velocity mapped to each grid point to neighboring nodes. We refine these extended velocities to enable increased robustness in the water solver. Our experimental results demonstrate that water animation can be made to respond to human motions such as walking and jumping.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.631-636
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• 2014

본 연구는 전산 유체 해석 프로그램인 EDISON_CFD 해석 결과 산출 된 정적공기력계수(양력계수, 항력계수)를 이용하여 교량 단면의 갤로핑(Galloping)에 대한 안정성 평가를 실시하는데 그 목적이 있다. 특히 해상 교량은 장대 교량인데다 높은 풍속까지 견뎌 내야 하므로 내풍 안정성 검토의 중요성이 부각되고 있다. 전산 해석에 사용된 교량은 이순신 대교와 거가 대교의 표준 단면을 사용하였으며, 받음각과 풍속의 변화를 주어 높은 레이놀즈수 영역에서 공기력계수의 변화에 대해 검토하였다.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.1
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• pp.69-78
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• 1997

Main sources of the vibration in gear driving system are transmission error and backlash. Transmission error is the difference of the rotation between driving and driven gear due to tooth deformation and profile error. Vibro-impacts induced by backlash between meshing gears lead to excessive vibration and noise in many geared rotation systems. Nonlinear dynamic characteristics of the gear driving system due to transmi- ssion error and backlash are investigated. Transmission error is calculated for spur gear. Nonlinear equation of motion for the gear driving system is developed with the calculated transmission error and backlash. Numerical analysis of the equation and the experimental results show the existence of meshing frequency, superharmonic compon- ents. Instability of the gear driving motion is found on the basis of Mathieu equation. Rattle vibration due to backlash is also discussed on the basis if nonlinear jump phenomenon.

• International Journal of Aeronautical and Space Sciences
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• v.14 no.3
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• pp.210-214
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• 2013

The sensitivity of transonic flow past a Whitcomb airfoil to deflections of an aileron is studied at free-stream Mach numbers from 0.81 to 0.86 and vanishing or negative angles of attack. Solutions of the Reynolds-averaged Navier-Stokes equations are obtained with a finite-volume solver using the $k-{\omega}$ SST turbulence model. The numerical study demonstrates the existence of narrow bands of the Mach number and aileron deflection angles that admit abrupt changes of the lift coefficient at small perturbations. In addition, computations reveal free-stream conditions in which the lift coefficient is independent of aileron deflections of up to 5 degrees. The anomalous behavior of the lift is explained by interplay of local supersonic regions on the airfoil. Both stationary and impulse changes of the aileron position are considered.

• Journal of The Korean Astronomical Society
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• v.39 no.4
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• pp.95-105
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• 2006

We have calculated the cosmic ray(CR) acceleration at young remnants from Type Ia supernovae expanding into a uniform interstellar medium(ISM). Adopting quasi-parallel magnetic fields, gasdynamic equations and the diffusion convection equation for the particle distribution function are solved in a comoving spherical grid which expands with the shock. Bohm-type diffusion due to self-excited $Alfv\acute{e}n$ waves, drift and dissipation of these waves in the precursor and thermal leakage injection were included. With magnetic fields amplified by the CR streaming instability, the particle energy can reach up to $10^{16}Z$ eV at young supernova remnants(SNRs) of several thousand years old. The fraction of the explosion energy transferred to the CR component asymptotes to 40-50 % by that time. For a typical SNR in a warm ISM, the accelerated CR energy spectrum should exhibit a concave curvature with the power-law slope flattening from 2 to 1.6 at $E{\gtrsim}0.1$ TeV.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.84.2-84.2
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• 2011

A numerical simulation study of the solar coronal plasma reveals that a ballooning instability can develop in the course of flux rope merging. When magnetic field lines from different flux ropes reconnect, a new field line connecting farther footpoints is generated. Since the field line length abruptly increases, the field line expands outward. If the plasma beta is low, this expansion takes place more or less evenly over the whole field line. If, on the other hand, the plasma beta is high enough somewhere in this field line, the outward expansion is not even, but is localized as in a bulging balloon. This ballooning section of the magnetic field penetrates out of the overlying field, and eventually the originally underlying field and the overlying field come to interchange their apex positions. This process may explain how a field structure that has stably been confined by an overlying field can occasionally show a localized eruptive behavior.

• Structural Engineering and Mechanics
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• v.10 no.5
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• pp.479-489
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• 2000

Based on the stiffness equation of the tapered beam element involving the effects of axial force and shear deformation, numerical investigations are carried out on elastic instability for web-linearly tapered columns with I-section of steel portal frames. Effects of shear deformation on the effective length of the tapered columns with I-section are studied. An efficient approach for determining the effective length of the tapered portal frame columns considering effects of shear deformation is proposed.

• Coupled systems mechanics
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• v.4 no.3
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• pp.251-262
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• 2015

The current paper aims at investigating the nonlinear dynamical behaviour of an electrically actuated microcantilever. The microcantilever is excited by a combination of AC and DC voltages. The nonlinear equation of motion of the microcantilever is obtained by means of force and moment balances. A high-dimensional Galerkin scheme is then applied to reduce the equation of motion to a discrete model. A numerical technique, based on the pseudo-arclength continuation method, is used to solve the discretized model. The electrostatic deflection of the microcantilever and static pull-in instabilities, due to the DC voltage, are analyzed by plotting the so-called DC voltage-deflection curves. At the simultaneous presence of the DC and AC voltages, the nonlinear dynamical behaviour of the microcantilever is analyzed by plotting frequency-response and force-response curves.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.10a
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• pp.133-140
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• 1998

Material nonlinear analyses of RC(Reinforced Concrete) beams considering the tension stiffening effect and plastic hinge length have been conducted. Instead of taking the sophisticated layer approach which has some limitations in application to the large structures with many degrees of freedom. the moment-curvature relationships of RC sections previously constructed through the section analysis have been used. To reduce the numerical instability in nonlinear analysis and to remove the imprecision in calculation of ultimate resisting capacity, according to the used finite element mesh size, the tension stiffening effect and plastic hinge length have been taken into consideration. Finally, correlation studies between analytical and experimental results have been conducted with the objective to establish the validity of the proposed algorithms.