• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.7
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• pp.595-600
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• 2014

The characteristics of kinetic energy transfer during a collision between a rigid target particle on a surface and a fragile bullet particle moving at a high velocity were analyzed using molecular dynamics simulation. Bullet particles made of $CO_2$ were considered and their size, temperature, and velocity were varied over a wide range. The fraction of kinetic energy transferred from the bullet particle to the target particle was almost independent of the former's size or velocity; however, it was sensitively dependent on its temperature, which can be attributed to the change in the bullet rigidity with temperature. This fraction was nearly twice as high for $CO_2$ bullets as for Ar bullets. This result explains the reason for the more superior cleaning performance of $CO_2$ bullets than Ar bullets with regard to contaminants in the 10 nm size range.

• Journal of the Korean Vacuum Society
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• v.12 no.1
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• pp.25-34
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• 2003

Deposition behavior of hard amorphous carbon film was investigated by molecular dynamic simulation using Tersoff potential which was suggested for the interaction potential between carbon atoms. When high energy carbon atoms were collided on diamond (100) surface, dense amorphous carbon film could be obtained. Physical properties of the simulated carbon film were compared with those of the film deposited by filtered cathodic arc process. As in the experimental result, the most diamond-like film was obtained at an optimum kinetic energy of the incident carbon atoms. The optimum kinetic energy was 50 eV, which is comparable to the experimental observation. The simulated film was amorphous with short range order of diamond lattice. At the optimum kinetic energy condition, we found that significant amount of carbon atom were placed at a metastable site of distance 2.1 $\AA$. By melting and quenching simulation of diamond lattice, it was shown that this metastatic peak is Proportional to the quenching rate. These results show that the hard and dense diamond-like film could be obtained when the localized thermal spike due to the collision of high energy carbon atom can be effectively dissipated to the lattice.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.6
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• pp.743-751
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• 2017

To evaluate the structural integrity of the helicopter radome, we performed bird strike analysis using SPH (Smoothed Particle Hydrodynamics) technique. Since the SPH method is a meshfree method, there is no phenomenon such as mesh tangling and it is suitable to predict the dispersion behavior of debris and debris cloud generated by high-speed impact. In order to observe the scattering direction of fractured bolts, the analysis were performed under the condition that the fracture occurs at the proof load. As a result of bird strike analysis, there is no secondary damage as well as the damage due to, the dispersion behavior of the bird model, and the scattering of the fractured bolts and radome. From the additional analysis that were performed to determine the actual bolt fracture, only plastic deformation is predicted since the maximum stress of the bolt does not exceed the ultimate stress.

• Journal of Biomedical Engineering Research
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• v.20 no.1
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• pp.21-27
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• 1999

In order to increase our understanding of the injury mechanism in the child occupant, three year old child model was developed using commercial dynamic package DADS. Total 14 segments and 12 joints were used to compose a model in three points belted condition with booster seat. HYGE sled test case was simulated to validate the developed model. Based on the comparison of the model and published test results, the developed model appears to be a resonable representation of the three year old dummy.

• Journal of the Korean Society for Railway
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• v.14 no.3
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• pp.203-210
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• 2011

This study formulates the theoretical wheel-set model to evaluate wheel-climbing derailments of rolling stock due to collision, and verifies this theory with dynamic simulations. The impact forces occurring during collision are transmitted from a car body to axles through suspensions. As a result of combinations of horizontal and vertical forces applied to axles, rolling stock may lead to derailment. The derailment type will depend on the combinations of the horizontal and vertical forces, flange angle and friction coefficient. According to collision conditions, the wheel-lift, wheel-climbing or roll-over derailments can occur between wheel and rail. In this theoretical derailment model of wheelset, the wheel-climbing derailment types are classified into Climb-over, Climb/roll-over, and pure Roll-over according to derailment mechanism between wheel and rail, and we proposed the theoretical conditions to generate each derailment mechanism. The theoretical wheel-set model was verified by dynamic simulations.

• Journal of the Korea Society for Simulation
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• v.20 no.1
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• pp.79-85
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• 2011

The problem of evacuating pedestrians from a room or channel under panic conditions is of obvious importance in daily life. In recent years, several computer models have been developed to simulate pedestrian dynamics. Understanding evacuation dynamics can allow for the design of more comfortable and safe pedestrian facilities. However, these models do not take into account the type and state of mind of pedestrians. They deal with pedestrians as particles and the state of mind as a social force, which is represented by conservative and long-range interactions between individuals. In this study, I used the lattice model proposed in my previous study to explore the evacuation behavior of pedestrians with morality. In this model, three types of pedestrians are considered: adults, children, and injured people. Collisions between adults and children result in injured people. When the number of injured people continuously in contact with each other reaches a given value k, the injured people are removed from the lattice space. This situation is the same as that in which pedestrians start stepping over injured people. This behavior was interpreted as the morality of pedestrians. Simulations showed that the evacuation showed down and eventually became jammed owing to the injured people acting as "obstacles" in relation to the morality k.

• Proceedings of the KIEE Conference
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• 2004.10a
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• pp.73-76
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• 2004

자동 부하 전환 개폐기는 일반적으로 주 전원의 전압 상태를 감시하여 주 전원의 정전이나, 저 전압 이 감지 될 때 주 전원을 개방시키고, 예비 전원으로 신속하게 전환 시킬 수 있는 구동 메커니즘이 필요하며, 주 전원이 정상 상태로 복구되면 다시 예비 전원에서 주 전원으로의 신속한 전환이 요구 되어진다. 본 논문에서 연구되는 자동 부하 전환 개폐기의 구동부는 1개의 구동력으로 2개 선로의 스위치를 동시에 조작하게 할 수 있는 링크 구조와 동작 원리를 간지고 있으며, 이 동작을 안정적이고 신뢰도 높게 조작하기 위해서 개폐기 구동부의 동특성을 구현할 수 있는 동적 모델로 검증하여 재작하였다. 보다 정확한 모델 수립을 위하여 기구 동작 시에 발생하는 부품들 사이의 충돌, 마찰, 유연성 등의 많은 동적특성들을 정밀하게 모사 할 수 있는 유연 다물체 동역학을 적용하였으며, 검증하였다.

• Geophysics and Geophysical Exploration
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• v.8 no.1
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• pp.1-6
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• 2005

Analogue physical modelling using granular materials (i.e., sandbox experiments) has been applied with great success to a number of geological problems at various scales. Such physical experiments can also be simulated numerically with the Discrete Element Method (DEM). In this study, we apply the DEM simulation to the collision between the Indian subcontinent and the Eurasian Plate, one of the most significant current tectonic processes in the Earth. DEM simulation has been applied to various kinds of dynamic modelling, not only in structural geology but also in soil mechanics, rock mechanics, and the like. As the target of the investigation is assumed to be an assembly of many tiny particles, DEM simulation makes it possible to treat an object with large and discontinuous deformations. However, in DEM simulations, we often encounter difficulties when we examine the validity of the input parameters, since little is known about the relationship between the input parameters for each particle and the properties of the whole assembly. Therefore, in our previous studies (Yamada et al.,2002a,2002b,2002c), we were obliged to tune the input parameters by trial and error. To overcome these difficulties, we introduce a numerical biaxial test with the DEM simulation. Using the results of this numerical test, we examine the validity of the input parameters used in the collision model. The resulting collision model is quite similar to the real deformation observed in eastern Asia, and compares well with GPS data and in-situ stress data in eastern Asia.

• Journal of the Korea Computer Industry Society
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• v.2 no.6
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• pp.853-858
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• 2001

When an absolute elastic collision occurs between a motion body and the another body inside a closed space, according to the current physical law and thus a computer graphical expression, it is defined that the center of mass of the closed space is not moved. This paper defines a physical law which includes a minor facts of the center of mass of a closed space moves during an absolute elastic collision occurs between a motion body and another body inside a closed space. The law defined in this paper has been verified using approximate lab equipments, and using this, graphical expression models and mathematical expressions for an absolute elastic collision between two bodies inside a closed space are del ed. When the minor effects of the center of mass moves is applied to the multi-body dynamic simulation program or haptic program, more accurate motion could be expressed. This definition can also be applied to an animation movie or other graphical motion expression for more realistic expression.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.12
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• pp.829-838
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• 2022

This study conducts Hypervelocity Impact(HVI) simulations considering space objects with various shapes and different impact angles. A commercial nonlinear structural dynamics analysis code, LS-DYNA, is used for the present simulation study. The Smoothed Particle Hydrodynamic(SPH) method is applied to represent the impact phenomena with hypervelocity. Mie-Grüneisen Equation of State and Johnson-Cook material model are used to consider nonlinear structural behaviors of metallic materials. The space objects with various shapes are modeled as a sphere, cube, cylinder, and cone, respectively. The space structure is modeled as a thin plate(200 mm×200 mm×2 mm). HVI simulations are conducted when space objects with various shapes with 4.119 km/s collide with the space structures, and the impact phenomena such as a debris cloud are analyzed considering the space objects with various shapes having the same mass at the different impact angles of 0°, 30° and 45° between the space object and space structure. Although space objects have the same kinetic energy, different debris clouds are generated due to different shapes. In addition, it is investigated that the size of the debris cloud is decreased by impact angles.