• Journal of the Korean Society for Railway
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• v.9 no.5 s.36
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• pp.618-623
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• 2006

Understanding the contact between wheel and rail is a starting point in railway vehicle dynamic research area and especially analysis for the contact geometry between wheel and rail is important. On the one hand, the critical speed as the natural characteristics of rolling-stock is generally tested on the roller rig. The geometrical characteristics of the wheel/roller contact on the roller rig are different from these of the general wheel/rail contact because the longitudinal radius of roller is not infinite compared with rail. Thus, in this paper we developed the algorithm to analyze the wheel/roller contact geometry of our roller rig which is constructed now and analyzed the difference between whee/roller contact and wheel/rail contact. In conclusion, we found that the yaw motion of wheelset and the roller radius influence the geometrical contact parameters in wheel flange contact area.

• Journal of the Korean Society for Railway
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• v.13 no.1
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• pp.16-22
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• 2010

Various programs for dynamic simulation of the railway vehicle have advantages and disadvantages. These programs have limitation that cannot express a large deformable body for an wire of the railway vehicle. In this study, a program for dynamic simulation of the railway vehicle is developed. And the rigid, flexible and large deformable body can be simulated using this program. Its reliability is verified by comparison with a commercial program. Also, a wire is considered as the large deformable body and a sliding joint which connects the rigid body to the large deformable body is included. Moreover, as the wheel-rail contact module is added, the dynamic simulation of the railway vehicle can be analyzed using the developed program.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.11
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• pp.1146-1154
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• 2008

This paper presents a method for the acceleration analysis of multi-legged walking robots in consideration of the frictional ground contact. This method is based on both unified dynamic equation for finding the acceleration of a robot's body and constraint equation for satisfying no-slip condition. After the dynamic equation representing relationship between actuator torques and body acceleration, is derived from the force and acceleration relationship between foot and body's gravity center, the constraint equation is formulated to reconfigure the maximum torque boundaries satisfying no-slip condition from given original actuator torque boundaries. From application of the reconfigured torques to the dynamic equation, interested acceleration boundaries are obtained. The approach based on above two equations, is adapted to the changes of degree-of-freedoms of legs as well as friction of ground. And the method provides the maximum translational and rotational acceleration boundaries of body's center that are achievable in every direction without occurring slipping at the contact points or saturating all actuators. Given the torque limits in infinite normsense, the resultant accelerations are derived as a polytope. From the proposed method, we obtained achievable acceleration boundaries of 4-legged and 6-legged walking robot system successfully.

• Journal of the Ergonomics Society of Korea
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• v.32 no.6
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• pp.489-494
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• 2013

Objective: This study compared the effects of streamlined shoes on dynamic gait and foot plantar pressure in healthy young adults. Background: With the importance of ankle and lower extremity mechanism, streamlined shoes are contributing to a static gait factors. However, the study of dynamic gait factor is still insufficient. Method: Sixty subjects were randomly allocated to two groups: experimental group(n=30) and control(n=30), respectively. The experimental group performed streamlined shoes, whereas the control group applied usual shoes. Main outcome measurements were assessed contact time, step length and foot plantar pressure using gait analysis with the treadmill. Independent t-test was used to compare the both groups. Results: Compared with control group, contact time of forefoot, midfoot and hindfoot decreased significantly in experimental group(p<.05), Step length increased significantly in experimental group(p<.05). Foot plantar pressure of midfoot and hindfoot increased significantly in experimental group(p<.05), whereas that of forefoot did not show significantly in experimental group(p>.05). Conclusion: Our findings suggest that streamlined shoes was more effective than usual shoes in dynamic gait change including contact time and step length and foot plantar pressure in healthy young adults. Application: The results of streamlined shoes might help to control for the gait of industrial workers.

• Proceedings of the KIEE Conference
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• 2003.04a
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• pp.82-84
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• 2003

In case contact between point of contacts is not achieved well, contact resistance is grown, and by current concentration at current conducting contacts can weld. In order to decrease contact resistance between contacts in case of busbar, installing spring between fixed contact and moving contact. and then force on faying surface of contacts increase and contact resistance decrease. But, in case increase force of spring to widen contact area, operating force moving contact can grow, on the contrary force of spring is small, contact resistance becomes low. Therefore, need to optimize force and number of spring. position, and also need to examine force change on contact surface at point of contact moving. In this paper, dynamic kinetics analysis for force on faying surface of contacts is performed at unsteady state. It is showed to not uniform force on surface between contacts, and we can got more uniform force by means of change spring position.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.842-846
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• 1996

Leaf springs are widely used as a major suspension component in many commercial vehicles, such as buses, trucks, etc. They have a complex dynamic behavior due to the geometric nonlinear and the contact mechanism between the leaves. The interface conditions between the leaves play a significant role in the global behavior of the comfort and ride of the vehicle system. The paper concentrates on modeling leaf springs and contact frictions between the leaves using a nonlinear finite element approach. A nonlinear load-displacement hysteresis curve for the leaf spring is simulated and its results are compared with test results.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.314-319
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• 2005

The rubber tire type AGT vehicles had been developed in a few years. And testing are finished on the test track. The extremely differ from heavy train with iron wheels are current collect type and wheel's characteristic. Analysis the current collect gear dynamic with vehicle dynamic and reduce the exchange rate shoes of current collect gear's.

• Journal of the Korean Society of Visualization
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• v.22 no.1
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• pp.28-33
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• 2024

We visualized the rupturing of liquid films flowing over a disk rotating with large angular velocity. A setup of high speed imaging for liquid flows on dark and reflective surfaces are suggested. From the result, rivulet structures are revealed to be strongly governed by three-dimensional surface structures developed in the film flow. Additionally, unique flow structures including the rivulet sliding and internal meandering are investigated. Generation mechanism of such structures are discussed in terms of the dynamic contact angle theory.

• Geomechanics and Engineering
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• v.34 no.5
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• pp.577-595
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• 2023

A dynamic triaxial discrete element numerical model of lightweight soil was established using the discrete element method to study the microscopic mechanism of expanded polystyrene (EPS) particles in the soil under cyclic loading. The microscopic parameters of the discrete element model of the lightweight soil were calibrated depending on the dynamic triaxial test hysteresis curves. Based on the calibration results, the effects of the EPS particles volume ratio and amplitude on the contact force, displacement field, and velocity field of the lightweight soil under different accumulated strains were studied. The results showed that the hysteresis curves of lightweight soil exhibit nonlinearity, hysteresis, and strain accumulation. The strain accumulated in remolded soil is mainly tensile strain, and that in lightweight soil is mainly compressive strain. As the volume ratio of EPS particles increased, the contact force first increased and then decreased, and the displacement and velocity of the particles increased accordingly. With an increase in amplitude, the dynamic stress of the particle system increased, and the accumulation rate of the dynamic strain of the samples also increased. At 5% compressive strain, the contact force of the particles changed significantly and the number of particles deflected in the direction of velocity also increased considerably. These results indicated that the cemented structure of the lightweight soil began to fail at a compressive strain of 5%. Thus, a compressive strain of 5% is more reasonable than the dynamic strength failure standard of lightweight soil.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.924-929
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• 2001

The flying height of contact slider is determined by vertical and pitching motions of slider. This paper performed the computer simulation for flying height change of contact slider. It is changed by many parameters, contact stiffness, contact damping, air bearing stiffness ratio, a location of mass center, and so on. Computer simulation is performed for knowing for what change of these parameters influences in flying height of contact slider. Disk surface is modeled in harmonic wave with from 10㎑ to 600㎑. Tri-pad slider is modeled in that contact slider has 2-DOF motion (vertical motion, pitching motion). Tri-pad contact slider is analyzed by numerical analysis method in computer simulation.