• Tribology and Lubricants
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• v.36 no.1
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• pp.39-46
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• 2020

Air stages are usually applied to precision engineering in sectors such as the semiconductor industry owing to their excellent performance and extremely low friction. Since the productivity of a semiconductor depends on the acceleration and deceleration performance of the air stage, many attempts have been made to improve the speed of the stage. Even during sudden start or stop sequences, the stage should maintain an air film to avoid direct contact between pad and the rail. The purpose of this study is to quantitatively predict the dynamic behavior of the air stage when acceleration and deceleration occur. The air stage is composed of two parts; the stage and the guide-way. The stage transports objects to the guideway, which is supported by an externally pressurized gas bearing. In this study, we use COMSOL Multiphysics to calculate the pressure of the air film between the stage and the guide-way and solve the two-degree-of-freedom equations of motion of the stage. Based on the specified velocity conditions such as the acceleration time and the maximum velocity of stage, we calculate the eccentricity and tilting angle of the stage. The result shows that the stiffness and damping of the gas bearing have non-linear characteristics. Hence, we should consider the operating conditions in the design process of an air stage system because the dynamic behavior of the stage becomes unstable depending on the maximum velocity and the acceleration time.

• Journal of Korea Game Society
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• v.18 no.5
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• pp.123-132
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• 2018

Various methods have been proposed to efficiently animate the motion of soft objects in realtime. In order to maintain the topology between the elements of the objects, it is required to employ constraint forces, which limit the size of the time steps for the numerical integration and reduce the efficiency. To tackle this, an implicit method with larger steps was proposed. However, the method is, in essence, a linear system with a large matrix, of which solution requires heavy computations. Several approximate methods have been proposed, but the approximation is obtained with an increased damping and the loss of accuracy. In this paper, new integration method based on harmonic oscillation with better stability was proposed, and it was further stabilized with the hybridization with approximate implicit method. GPU parallelism can be easily implemented for the method, and large-scale soft objects can be simulated in realtime.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.5
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• pp.375-387
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• 2023

The subsea power cables are increasingly important for harvesting renewable energies as we develop offshore wind farms located at a long distance from shore. Particularly, the continuous flexural motion of inter-array dynamic power cable of floating offshore wind turbine causes tremendous fatigue damages on the cable. As the subsea power cable consists of the helical structures with various components unlike a mooring line and a steel pipe riser, the fatigue analysis of the cables should be performed using special procedures that consider stick/slip phenomenon. This phenomenon occurs between inner helically wound components when they are tensioned or compressed by environmental loads and the floater motions. In particular, Vortex-induced vibration (VIV) can be generated by currents and have significant impacts on the fatigue life of the cable. In this study, the procedure for VIV fatigue analysis of the dynamic power cable has been established. Additionally, the respective roles of programs employed and required inputs and outputs are explained in detail. Demonstrations of case studies are provided under severely sheared currents to investigate the influences on amplitude variations of dynamic power cables caused by the excitation of high mode numbers. Finally, sensitivity studies have been performed to compare dynamic cable design parameters, specifically, structural damping ratio, higher order harmonics, and lift coefficients tables. In the future, one of the fundamental assumptions to assess the VIV response will be examined in detail, namely a narrow-banded Gaussian process derived from the VIV amplitudes. Although this approach is consistent with current industry standards, the level of consistency and the potential errors between the Gaussian process and the fatigue damage generated from deterministic time-domain results are to be confirmed to verify VIV fatigue analysis procedure for slender marine structures.

• Journal of Korean Society of Steel Construction
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• v.24 no.3
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• pp.289-299
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• 2012

The goal of this paper is to apply the multi-step Taylor method to a space truss, a non-linear discrete dynamic system, and analyze the non-linear dynamic response and unstable behavior of the structures. The accurate solution based on an analytical approach is needed to deal with the inverse problem, or the dynamic instability of a space truss, because the governing equation has geometrical non-linearity. Therefore, the governing motion equations of the space truss were formulated by considering non-linearity, where an accurate analytical solution could be obtained using the Taylor method. To verify the accuracy of the applied method, an SDOF model was adopted, and the analysis using the Taylor method was compared with the result of the 4th order Runge-Kutta method. Moreover, the dynamic instability and buckling characteristics of the adopted model under step excitation was investigated. The result of the comparison between the two methods of analysis was well matched, and the investigation shows that the dynamic response and the attractors in the phase space can also delineate dynamic snapping under step excitation, and damping affects the displacement of the truss. The analysis shows that dynamic buckling occurs at approximately 77% and 83% of the static buckling in the undamped and damped systems, respectively.

• Journal of the Korean Geotechnical Society
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• v.27 no.5
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• pp.85-92
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• 2011

The dynamic behavior of piles becomes very complex due to soil-pile dynamic interaction, soil non-linearity, resonance phenomena of soil-pile system and so on. Therefore, the proper numerical simulation of the pile behavior needs much effort and calculation time. In this research, a new modeling method, which can be applied to the conventional finite difference analysis program FLAC 3D, was developed to reduce the calculation time. The soil domain in this method is divided into a near-field region and a far-field region, which is not influenced by the soil-pile dynamic interaction. Then, the ground motion of the far-field is applied to the boundaries of the near-field instead of modeling the far-field region as finite meshes. In addition, the soil non-linearity behavior is modeled by using the hysteretic damping model, which determines the soil tangent modulus as a function of shear strain and the interface element was applied to simulate the separation and slip between the soil and pile. The proposed method reduced the calculation time by as much as one third compared with a usual modeling method and maintained the accuracy of the calculated results. The calculated results by the proposed method showed a good agreement with the prototype pile behavior, which was obtained by applying a similitude law to the 1-g shaking table test results.