• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.383-386
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• 2006

In this study, we propose a new fast algorithm for calculating short range forces in molecular dynamics, This algorithm uses a new hierarchical tree data structure which has a high adaptiveness to the particle distribution. It can divide a parent cell into k daughter cells and the tree structure is independent of the coordinate system and particle distribution. We investigated the characteristics and the performance of the tree structure according to k. For parallel computation, we used orthogonal recursive bisection method for domain decomposition to distribute particles to each processor, and the numerical experiments were performed on a 32-node Linux cluster. We compared the performance of the oct-tree and developed new algorithm according to the particle distributions, problem sizes and the number of processors. The comparison was performed sing tree-independent method and the results are independent of computing platform, parallelization, or programming language. It was found that the new algorithm can reduce computing cost for a large problem which has a short search range compared to the computational domain. But there are only small differences in wall-clock time because the proposed algorithm requires much time to construct tree structure than the oct-tree and he performance gain is small compared to the time for single time step calculation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.4 no.4
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• pp.171-180
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• 2000

This study aims to present a more reasonable control value than the exiting one by comparing and analyzing control values and field instrumentation values of the whole excavation depth of the four case sites using geometric averaging as a statistical method. The range of the study is confined to three things: (1) the axial force of the braced excavation walls among a variety of items prescribed in the control values by stress deformation of walls and adjacent structures; (2) by approximation of the allowable and design value; (3) and by safety factor. As a res it is desirable to revise "(Long term allowable stress + Short term allowable stress)/2 ~ Short term allowable stress," presented in the present control values by stress deformation of walls and adjacent structures, to "(Long term allowable stress + Short term allowable stress)/5 ~ (Short term allowable stress)/3." The result also shows that since there is a difference of about 3.5%, it is not necessary to revise 70, 90, and 100 percent of LEVEL I, II, and III, prescribed in the control values by the allowable and design value approximation. In addition, modifying the control value by the safety factor, now 1.07, is unnecessary, although it varies little difference from the present value.

• Geomechanics and Engineering
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• v.36 no.2
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• pp.157-166
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• 2024

Generally, the rubble mound installed on the slope embankment of the open-type wharf is designed based on the impact of wave force, with no consideration for the impact of seismic force. Therefore, in this study, dynamic centrifuge model test results were analyzed to examine the acceleration amplification of embankment reinforced with rubble mound under seismic conditions. The experimental results show that when rubble mounds were installed on the ground surface of the embankment, acceleration response of embankment decreased by approximately 22%, and imbalance in ground settlement decreased significantly from eight to two times. Furthermore, based on the experimental results, one-dimensional site response (1DSR) analyses were conducted. The analysis results indicated that reinforcing the embankment with rubble mound can decrease the peak ground acceleration (PGA) and short period response (below 0.6 seconds) of the ground surface by approximately 28%. However, no significant impact on the long period response (above 0.6 seconds) was observed. Additionally, in ground with lower relative density, a significant decrease in response and wide range of reduced periods were observed. Considering that the reduced short period range corresponds to the critical periods in the design response spectrum, reinforcing the loose ground with rubble mound can effectively decrease the acceleration response of the ground surface.

• Korean Journal of Applied Biomechanics
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• v.14 no.3
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• pp.191-202
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• 2004

The batting performance in baseball is a repetitive movement. In order to make the stabilization of posture and the efficient shift of body weight, both the range of stance and stride are important. The previous studies explained that the consistent stride which included the amount of time, stance, and direction were needed. However, the batting performance is frequently changed according to the several speed of ball. Therefore, this study was to analyze the reaction time, the range of stance, the change of stride, and the change of GRF during the batting movement in three kinds of ball speed (120km/h, 130km/h, & 140km/h). Seven elite players are participated in this study. 1. The reaction time of the stride phase was short whereas the time of the swing phase was long according to the increasing ball speed. 2. The range of the stance was wide and the mediolateral direction of the stride was decreased according to the increasing ball speed. 3. In the three kinds of ball speed, the change of body weight was transferred to the center, the rear foot, and the front foot directions. The ball speed of 130km/h showed the high frequency of the suitable batting. At this ball speed, the movement of the body weight was shifted smoothly and the value of the Ground Reaction Force was large enough.

• Korean Journal of Applied Biomechanics
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• v.19 no.3
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• pp.529-538
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• 2009

The purpose of this study was to investigate correlation between BBS(Berg balance scale), SPPB(short physical performance battery,) TUG(timed up and go) and COP(center of pressure) during quiet standing in elderly women. Ten elderly women aged 65 to 75 years participated in this study. Subjects were measured physical functional test and they were stood in quiet stance on force platform positioned in one of three different fixed positions(flat, downward, upward). The COP range and mean velocity data were calculated using an experimental setup with the ground reaction force system. COP range and mean velocity of AP direction showed significant more expanded than ML direction of all slope types. Physical performance scores were significant correlated between COP range and mean velocity according to surface slopes. After all elderly women get high score of physical performance that brought decreased on one's COP range and mean velocity. This study suggests that clinical therapist have application to COP parameters as well as BBS, SPPB, TUG of balance assessment in elderly women.

• Macromolecular Research
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• v.16 no.4
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• pp.320-328
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• 2008

We established a thermodynamic framework of group contribution method based on modified double lattice (MDL) model. The proposed model included the long-range interaction contribution caused by the Coulomb electrostatic forces, the middle-range interaction contribution from the indirect effects of the charge interactions and the short-range interaction from modified double lattice model. The group contribution method explained the combinatorial energy contribution responsible for the revised Flory-Huggins entropy of mixing, the van der Waals energy contribution from dispersion, the polar force, and the specific energy contribution from hydrogen bonding. We showed the solvent activities of various polymer solution systems in comparison with theoretical predictions based on experimental data. The proposed model gave a very good agreement with the experimental data.

• Journal of the Korea Society for Simulation
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• v.29 no.4
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• pp.47-54
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• 2020

North Korea has recently developed and deployed missiles with various ranges as asymmetrical forces. Among them, short-range ballistic missiles with improved accuracy are expected to aim at achieving tactical goals by hitting important military facilities in Korea with a small number of missiles. Damage to the air force airfields, one of North Korea's main targets of missiles attack, could limit the operation of air force fighters essential to gaining air superiority. Based on the attack by the short range ballistic missiles, the damage probability of military airfields was simulated. And as the one of the concepts of passive defense, the way to reduce the loss of combat power was studied through the changes of the air force squadrons deployment. As a result, the effective deployment plan could be obtained to reduce the amount of power loss compared to the current deployment.

• Atmosphere
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• v.21 no.2
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• pp.197-208
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• 2011

The objective of this study is to describe the short-range forecast system of the Korea Air Force (KAF) and to verificate its performace in 2009 summer. The KAF weather prediction model system, based on the Weather Research and Forecasting (WRF) model (i.e., the KAF-WRF), is configured with a parent domain overs East Asia and two nested domains with the finest horizontal grid size of 2 km. Each domain covers the Korean peninsula and South Korea, respectively. The model is integrated for 84 hour 4 times a day with the initial and boundary conditions from National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) data. A quantitative verification system is constructed for the East Asia and Korean peninsula domains. Verification variables for the East Asia domain are 500 hPa temperature, wind and geopotential height fields, and the skill score is calculated using the difference between the analysis data from the NCEP GFS model and the forecast data of the KAF-WRF model results. Accuracy of precipitation for the Korean penisula domain is examined using the contingency table that is made of the KAF-WRF model results and the KMA (Korea Meteorological Administraion) AWS (Automatic Weather Station) data. Using the verification system, the operational model and parallel model with updated version of the WRF model and improved physics process are quantitatively evaluated for the 2009 summer. Over the East Aisa region, the parallel experimental model shows the better performance than the operation model. Errors of the experimental model in 500 hPa geopotential height near the Tibetan plateau are smaller than errors in the operational model. Over the Korean peninsula, verification of precipitation prediction skills shows that the performance of the operational model is better than that of the experimental one in simulating light precipitation. However, performance of experimental one is generally better than that of operational one, in prediction.

• Korean Journal of Applied Biomechanics
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• v.13 no.1
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• pp.173-184
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• 2003

The purpose of this study was to investigate the batting characteristics in elite baseball players. Seven skilled collegiate players hit the ball which was thrown by a pitching machine linearly and strongly to the center of the field. Time, velocity, angle and pound reaction force variables were measured by using high-speed video cameras and pound reaction force analyzer. The results were as follows: 1. The elite players finished their stride performance in a short time and they stayed longer in a swing phase. The increases in the range of trunk rotation were associated with the delay of the swing phase. 2. The 'take-back' phenomenon in the trunk was showed after the stride phase. 3. The down swing demonstrated powerful line drives. 4. Equivalent body weights were placed on both feet during the ready phase. 95% of the body weights were moved to the rear foot during the stride phase, whereas the body weights were driven to the front foot during the swing phase. 95% of the body weights were placed on the front foot at impact.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.511-518
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• 2006

In this study, seismic response mitigation effect of an MR damper generating response-dependent frictional force is investigated. It has been reported in previous studies that passively operated MR damper with constant input current doesn't show better control performance than semi-active MR damper with varying input current calculated by control algorithms such as linear quadratic regulator and sliding mode control. However, in order to operate the MR damper semi-actively, other control systems besides the damper itself such as sensors for measuring structural responses and controller for calculating optimal input current are necessary, which deteriorate the economical efficiency. This study presents a MR damper generating frictional force of which magnitude is controlled in accordance to the displacement and velocity transferred to the damper. Numerical analyses results indicate that the performance of the response dependent MR damper is closely related with the range of the friction force and it can be designed to short better control performance than the passive MR damper.