• 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.23 no.1
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• pp.39-48
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• 2004

In terms of women engaged in clerical job. working time of the workers who mainly keep standing with their high-heeled shoes on has been increasing. According]y. they are exposed to many kinds of foot deformation caused by loads of lower back and lower extremities due to high-heeled shoes. The type of heels they usually wear are diverse though the hight is same. In this study. we investigated most women's favorite styles of shoes concerned with heights. types and contact areas of the heels. Hence. we designed three kinds of shoes for an experiment: their contact areas with ground are 1 cm2. 2-4 cm2 and over 9 cm2 according to the heel heights. respectively. To investigate the biomechanical effects. analysis of motion and EMG were applied to the experiments. In addition. foot pressure distribution was measured for more detailed analysis. Six healthy young women were participated in this experiments. The result showed the heel becoming higher and narrower increased not only fluctuation of CBM(Center of Body Mass). but also the load of low back muscle and lower extremities. Accordingly. there was significant difference among types of the heel in terms of the role supporting load of the body. though the height is same. Especially. the difference among the pressures on a foot was most significant. In conclusion. we verified biomechanical effects are related with the contact area of a heel with ground as well as the hight.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.103-108
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• 2004

In this study, examined heavy-weight floor impact sound to structure that have slab thickness of 4 form at a standard laboratory through noise and vibration measured. The results show that the nature Natural frequency increased according to change of thickness of each slab by finite element analysis, and acceleration value decreased. Results of measurements of noise and vibration at a standard laboratory, the slab 210, 240mm structures was construed result such as finite element analysis but the slab 150, 180mm structures is construed that influence in vibration acceleration level because edge condition has condition that contact to ground. Therefore, in modelling process for analysis, is thought that need that condition analyzes examining element influencing about structure that contact to ground.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.3
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• pp.226-232
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• 2002

In this work, the quasi-static crawling of the four-bar mechanism is investigated. Since the crawling of the mechanism is based on sliding of contact points of the mechanism with the ground, interaction forces and friction forces at contact points of the mechanism with the ground should be computed. For this purpose, we introduce the concept of imaginary joints to find these forces and treat the closed mechanism as a serial one. Lastly, the required torques for the mechanism to crawl with respect to various configurations of the mechanism on a flat ground with uniform friction coefficient, based on sliding conditions of the mechanism in quasi-static equilibrium, are investigated.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.2
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• pp.121-128
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• 2020

The purpose of this study is to investigate the distribution patterns of displacement and acceleration fields in a nonlinear soil ground based on the interaction of high-speed train, wheel, rail, and ground. For this purpose, a high-speed train in motion was modeled as the actual wheel, and the vertical contact of wheel and rail and the lateral contact, caused by meandering motion, were simulated; this simulation was based on the moving mass analysis. The soil ground part was given the nonlinear behavior of the upper ground part by using the modified the Drucker-Prager model, and the changes in displacement and acceleration were compared with the behavior of the elastic and inelastic grounds. Using this analysis, the displacement and acceleration ranges close to the actual ground behavior were addressed. Additionally, the von-Mises stress and equivalent plastic strain at the ground were examined. Further, the equivalent plastic and total volumetric strains at each failure surface were examined. The variation in stresses, such as vertical stress, transverse pressure, and longitudinal restraint pressure of wheel-rail contact, with the time history was investigated using moving mass. In the case of nonlinear ground model, the displacement difference obtained based on the train travel is not large when compared to that of the elastic ground model, while the acceleration is caused to generate a large decrease.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.566-569
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• 2000

This hybrid position/force control for the dynamic walking of the biped robot is performed in this paper. After the biped robot was modeled with 14 degrees of freedom of the multibody dynamics, the equations of motion are constructed using velocity transformation technique. Then the inverse dynamic analysis is performed for determining the driving torques and the ground reaction forces. From this analysis, obtains the maximum ground contact force at the moment of contacting which act on the rear of the sole of swing leg and the distribution curve of the ground reaction. Because these maximum force and distribution type acts an important role to the stability of the whole dynamic walking, they are reduced and distributed smoothly by means of the trajectory of the modified ground reaction force. This new trajectory is used to the reference input for more stable dynamic walking of the whole walking region.

• International Journal of Highway Engineering
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• v.17 no.4
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• pp.25-31
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• 2015

PURPOSES: Implementation and verification of the simple linear cohesive viscoelastic contact model that can be used to simulate dynamic behavior of sticky aggregates. METHODS: The differential equations were derived and the initial conditions were determined to simulate a free falling ball with a sticky surface from a ground. To describe this behavior, a combination of linear contact model and a cohesive contact model was used. The general solution for the differential equation was used to verify the implemented linear cohesive viscoelastic API model in the DEM. Sensitivity analysis was also performed using the derived analytical solutions for several combinations of damping coefficients and cohesive coefficients. RESULTS : The numerical solution obtained using the DEM showed good agreement with the analytical solution for two extreme conditions. It was observed that the linear cohesive model can be successfully implemented with a linear spring in the DEM API for dynamic analysis of the aggregates. CONCLUSIONS: It can be concluded that the derived closed form solutions are applicable for the analysis of the rebounding behavior of sticky particles, and for verification of the implemented API model in the DEM. The assumption of underdamped condition for the viscous behavior of the particles seems to be reasonable. Several factors have to be additionally identified in order to develop an enhanced contact model for an asphalt mixture.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.2
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• pp.217-223
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• 2020

As construction work on soft ground increases, many researchers have studied to secure the stability of trafficability with interest in construction safety accidents due to reinforcement work. Although the stability of soft ground is evaluated based on the allowable bearing capacity of theoretical equations proposed in the literature such as Yamanouchi and Meyerhof formulas, further numerical verification also requires comparison of the stress increase (Δσ_z) and deformation of the distributed contact pressure on the soft ground. In this study, the deformation of the soft ground is compared with the increasing the seam tensile strength of geotextile using the finite element analysis program, and the stress increase is investigated by variation of the distributed contact pressure by appling input data of case study.

• Korean Journal of Applied Biomechanics
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• v.19 no.1
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• pp.87-98
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• 2009

This study was conducted to compare biomechanical differences in throwing movement between skilled and unskilled high school students using three-dimensional analysis system with a force platform. The findings indicated that skilled students showed shorter throwing time, faster horizontal speed of (1) the center of mass at heel contact of left foot, (2) the forearm throughout swing phase, (3) the hand after heel contact while unskilled students showed faster horizontal speed of, (1) the center of mass after heel contact and (2) the hand at heel contact of left foot. Skilled students showed greater (1) shoulder angle during throwing, (2) elbow angle after take off of foot, (3) peak vertical ground reaction force during throwing and (4) peak anterior-posterior ground reaction force at heel contact of right foot. While skilled students showed leaning backward of the trunk during throwing, unskilled students showed leaning forward during release phase with leaning backward before release.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 2004.11a
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• pp.169-175
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• 2004

Considering the present development situation of domestic apartment complexes, the environment and its landscape is monotonous and dull, so the diversity is very important socially and visually. The ground floor dwellings can influence the richness and diversity of ground landscape in the apartment housing. Because they are set on the ground and directly contact with people's sight line. In this context, this study aims to identify the elements of design diversity in the ground floor dwellings, to analysis the architectural characteristics of them and to propose the improvement of diversity.