• Journal of Institute of Control, Robotics and Systems
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• v.14 no.7
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• pp.663-671
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• 2008

This paper presents a real-time haptic rendering method for multi-contact interaction with virtual environments. Haptic systems often employ physics-based deformation models such as finite-element models and mass-spring models which demand heavy computational overhead. The haptic system can be designed to have two sampling times, T and JT, for the haptic loop and the graphic loop, respectively. A multi-rate output-estimation with an exponential forgetting factor is proposed to implement real-time haptic rendering for the haptic systems with two sampling rates. The computational burden of the output-estimation increases rapidly as the number of contact points increases. To reduce the computation of the estimation, the multi-rate output-estimation with reduced parameters is developed in this paper. Performance of the new output-estimation with reduced parameters is compared with the original output-estimation with full parameters and an exponential forgetting factor. Estimated outputs are computed from the estimated input-output model at a high rate, and trace the analytical outputs computed from the deformation model. The performance is demonstrated by simulation with a linear tensor-mass model.

• Journal of Ocean Engineering and Technology
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• v.24 no.1
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• pp.10-19
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• 2010

ANSYS multi-physics software was applied to solve the coupled dynamic problem related to a full-scale TLP foundation for floating wind turbines. In this coupled dynamics simulation, the forced oscillation imposed on the tethers' top resulting from the sway of the wind turbine platform and the self-excited vortex-induced vibration (VIV) along the tether span have been taken into account. The stability of this tensioned tether system has been validated in the form of separate static and dynamic analyses. The dynamic characteristics of the tensioned tether linked to the floating wind turbine were analyzed by the resultant modal form and its corresponding vortex shedding pattern. The calculated result shows that even a slight forced oscillation imposed on the tethers' top leads to the VIV amplification and enhances the risk of instability in the case of low pretension. It is also found that the "synchronization" would be aggravated when the top tension decreases and the "2P" vortex shedding mode takes place. The increased top tension imposed on the tethers contributes to the stability of the tensioned legs by diminishing the oscillation amplitude markedly.

• Journal of Korea Game Society
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• v.9 no.5
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• pp.95-104
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• 2009

Recently, increasing numbers of games and simulators are being implemented by employing the physically-based modeling techniques for better realism. In this paper, we propose the implementation techniques for overhead crane simulator based on ODE, the well-known open source dynamic engine. By comparing the dynamic behavior of the proposed system with a commercial engine based simulator, the physical plausibility and the effectiveness of the ODE based OHC simulator are verified. We expect the proposed the OHC simulator can be successfully utilized for virtual training in various educational institutes.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.6
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• pp.252-257
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• 2016

Dust-collecting behavior of tonpilz transducer was simulated with finite-element-method (FEM) software. In order to optimize the performance of tonpilz transducer, the shape factors including the thickness of head mass, the diameter of tail mass and the depth of bolt were analyzed as variables. As a vibrating energy source, the piezoelectric materials was also tested with PZT-4 and two kinds of piezoelectric single crystals. The output power of the transducer was maximized with the shape factors and then the behavior of the dust-collection was demonstrated with the multi-physics software, COMSOL.

• Journal of Power System Engineering
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• v.15 no.6
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• pp.27-34
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• 2011

The increasing capabilities of the computers enable us to utilize various numerical schemes for the time-domain simulations concerned with 3-dimensional free-surface wave problems. There are still difficulties to solve such kind of problems, however. That's because long time simulations with large computational domain are needed in time-domain analysis. So, we need faster and more efficient numerical schemes to get the solutions practically for these problems. In this paper, a high-order spectral/boundary-element method is used for the numerical investigation of physics involved in wave-body interaction. This method is one of the most efficient numerical methods by which the nonlinear gravity waves can be simulated and hydrodynamic forces also can be calculated in time-domain. To get the robust study in these topics, various numerical tests are performed and compared with others' works.

• Journal of the Optical Society of Korea
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• v.17 no.3
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• pp.262-268
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• 2013

We study the focusing properties of a two-dimensional square-lattice photonic crystal (PC) comprising silica and germanium partitioned cylinders in air background. The finite difference time domain (FDTD) method with periodic boundary condition is utilized to calculate the dispersion band diagram and the FDTD method incorporating the perfectly matched layer boundary condition is employed to simulate the image formation. In contrast to the common square PCs in which the negative refraction effect occurs in the first photonic band without negative phase propagation, in our suggested model system, the frequency with negative refraction exists in the second band and in near-infrared region. In this case, the wave propagates with a negative phase velocity and the evanescent waves can be supported. We also discuss the dependency of the image resolution and its location on surface termination, source location, and slab thickness. According to the simulation results, spatial resolution of the proposed PC lens is below the radiation wavelength.

• Applied Microscopy
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• v.35 no.4
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• pp.1-9
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• 2005

In this paper it is reported that a comprehensive study of the crystal structure of the fine size S-phase ($Al_2CuMg$) precipitate in Al-Cu-Mg alloy by electron diffraction experiments. The experiments involve taking the selected area diffraction pattern for a S-phase particle, simulations of the pattern based on the kinematical diffraction theory and quantitative data collection from the zone axis diffraction patterns for the comparison with calculated diffraction intensity using both the kinematical and the dynamical diffraction theory. As a result, a good fitting model of the S-phase structure turns out to be the model reported early by X-ray methods (Perlitz & Westgren, 1943), not the new model determined by HRTEM methods (Radmilovic et al., 1999).

• Applied Microscopy
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• v.37 no.4
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• pp.259-269
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• 2007

In this paper we explored a possibility of observation for effects of higher-order Laue zone(HOLZ) reflections on high resolution transmission electron microscope(HRTEM) images for illumination along an off-zone axis of a crystal. The analysis of the observation could give useful three dimensional crystal structure information. For the image simulation the Howie-Whelan equation was used with modification of including HOLZ reflections. This study clearly indicates that HRTEM images for a very thin crystal tilted by a few degrees from a zone axis show the effects of HOLZ reflections and contain some information of atomic arrangements along the zone axis.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.7
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• pp.43-50
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• 2002

This paper presents the new gait implementation of a biped robot with smooth walking using 3-dimensional continuous trunk motion and kick action of ankle joints. Trajectory generation ova trunk is performed not on a unit gait but on a whole walking interval. In applying kick action such as heel-touch or toe-off, varying coordinate system was employed for the simplification of the kinematic analysis. Desired ZMP (zero moment point) is also changed to implement the efficient kick action. As a result, balancing motion of the proposed gait was much more decreased than that of conventional one. Moreover, robot\\`s walking behavior is very smooth, natural and similar to the pace of a human. The walking experiment system is composed of eight AC servo motors and a DSP controller. The walking simulation and the experimental results are shown using the proposed new walking algorithm.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.26.2-26.2
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• 2010

It has been a puzzle in solar physics how a low-lying magnetic structure such as a solar prominence surrounded by a strongly line-tied overlying field sometimes intrudes through the latter and goes into eruption. A numerical simulation study of the solar coronal plasma reveals that a ballooning instability can explain this type of eruptive process. We consider an idealized situation with two flux ropes 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.