• Transactions of Materials Processing
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• v.7 no.4
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• pp.340-346
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• 1998

A kinematically admissible velocity field is developed for the analysis of twisting of the extruded products with elliptical shapes from round billet. The twisting of extruded product is caused by the lin-early increased rotational velocity from the center on the cross-section of the workpiece at the die exit. In the analysis the rotational velocity in angular direction is assumed by the multiplication of radial distance and angular velocity. The angular velocity is zero at the die entrance. The increase rate of angular velocity is determined by the minimization of plastic work. The results of the analysis show that the angular velocity of the extruded product in creases with the die twisting angle, the aspect ratio of product the friction condition, the reduction of area, and decreases with the die length.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1853-1857
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• 2005

In most of motor-driven motion control systems, an encoder is used to measure a position of the motor and the velocity information is obtained by measuring the position increment over a sampling period. The quantization effect due to limited resolution of the encoder induces some measurement errors, and consequently causes deterioration of the motion performance especially in low velocity. In this paper, we propose a gain-scheduled acceleration estimator which works in wider velocity range than the original acceleration estimator. We investigate and analyze characteristics of the velocity measurement mechanism which takes into account the quantization effect of the encoder. Next, we introduce the acceleration estimator and propose a gain-scheduled acceleration estimator. The bandwidth of the gain-scheduled acceleration estimator is automatically adjusted by the velocity command. Finally, its performance is evaluated by simulation and experiment, and the results are compared with those of a conventional method and the original acceleration estimator.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.122-123
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• 2014

Measurement of the strength of concrete is an important indicator of the safety of the fresh as well as old concrete structures. It is possible to evaluate the strength of the concrete by means of an ultrasonic velocity method which is a kind of non-destructive inspection method for safety diagnostic evaluation of the building structures with aging. Steel embedded in the concrete and age of the concrete may affect ultrasonic pulse velocity. In order to accurately assess the strength of the concrete, it is necessary to understand rebar embedded in the concrete, steel shapes in various forms which effect ultrasonic pulse velocity. In this study, by measuring the velocity of ultrasonic waves generated when the waves pass through the ultrasonic pulse in a direction perpendicular to the reinforcing bars embedded in concrete, the effect of reinforcing bars on ultrasonic velocity accurately was verified and used to estimate the strength of the concrete.

• Journal of Ocean Engineering and Technology
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• v.12 no.2 s.28
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• pp.111-120
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• 1998

Laboratory settling experiments (column, recirculating flume) were conducted for further understanding of the physical processes of cohesive sediment transport. \In still water experiments, the growth rate of flocculation is dependent upon the initial suspended concentration. Consequently, the settling velocity increases with concentration of flees. In flocculation settling regime, the exponent n in the settling velocity, $w_s=kC^n$, for Nakdong estuary mud was obtained empirically. The exponents were found to be 1.33, and 1.06 for the initial suspended concentrations of 1 g/i and 3 g/t, respectively. In flowing water, experiments for the median settling velocity with Nakdong mud in a recirculating flume were conducted. Settling velocity was found to depend much more strongly on the current velocity than initial concentrations. The temporal variation of suspended concentration increases as current velocity decreases.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.51.4-52
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• 2017

We present the derived kinematic characteristics of low-${\alpha}$ thin-disk and high-${\alpha}$ thick-disk stars in the Milky Way, investigated with a sample of about 33,900 G- and K-type dwarfs from the Sloan Extension for Galactic Understanding and Exploration (SEGUE). Based on the level of ${\alpha}$-element enhancement as a function of [Fe/H], we separate our sample into thin- and thick-disk stars and then derive mean velocity, velocity dispersion, and velocity gradients for the U, V and W velocity components, respectively, as well as the orbital eccentricity distribution. There are notable gradients in the V velocity over [Fe/H] in both populations: -23 km s-1 dex-1 for the thin disk and +44 km s-1 dex-1 for the thick disk. The velocity dispersion of the thick disk decrease with increasing [Fe/H], while the velocity.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.3
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• pp.441-450
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• 2004

The velocity distribution of gas molecules from the experimental results was confirmed as the same with the Maxwell-Boltzmann's theoretical results within the experimental error. This study is on the realization of the Maxwell-Boltzmann's velocity distribution of gas molecules by the molecular dynamics(MD) method. The Maxwell-Boltzmann's velocity distribution of gas molecules is extremely important to confirm the equilibrium state because the properties of a thermodynamic system shall be obtained from the system's equilibrium configuration in the MD method. This study is the first trial in the successive researches to calculate the properties of a thermodynamic system by the computer simulations. We confirmed that the maxwell-boltzmann's velocity distribution is developed in some transient time after starting a simulation and dependent on the size of a system. Also it is found that the velocity distribution has no relation with an initial configuration of gas molecules.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.1089-1092
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• 2001

In the stereolithography process, build parameters are laser power, scan velocity, scan width, bean diameter, layer thickness and so on. These values are determined according to product accuracy and build time. Build time can be reduced by improving of scan velocity, laser power, layer thickness, hatching space and so on. But variation of these parameters influence part accuracy, surface roughness, strength. This paper observed cure properties in various beam diameter. In order to examine these, relationships of scan velocity and cure depth, scan velocity and cure width according to various beam diameter in one scan line are measured. And cure thickness is measured according to beam diameter and scan velocity in scan surface of one layer. For reduction of build time, beam diameter and scan velocity is proposed in stereolithography process.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.6
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• pp.477-483
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• 2002

This paper deals with a workspace analysis of multi-legged walking robots in velocity domain(velocity workspace analysis). Noting that when robots are holding the same object in multiple cooperating robotic arm system the kinematic structure of the system is basically the same with that of a multi-legged walking robot standing on the ground, we invented a way ot applying the technique for multiple arm system to multi-legged walking robot. An important definition of reaction velocity is made and the bounds of velocities achievable by the moving body with multi-legs is derived from the given bounds on the capabilities of actuators of each legs through Jacobian matrix for given robot configuration. After some assumption of hard-foot-condition is adopted as a contact model between feet of robot and the ground, visualization process for the velocity workspace is proposed. Also, a series of application examples will be presented including continuous walking gaits as well as several different stationary posture of legged walking robots, which validate the usefulness of the proposed technique.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.250-253
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• 1998

The kinematically admissible velocity field is developed for the shapes of dead metal zone and the curving velocity distribution in the eccentric plane dies extrusion. The shape of dead metal zone is defined as the boundary surface with the maximum friction constant between the deformable zone and the rigid zone. The curving phenomenon in the eccentric plane dies is caused by the eccentricity of plane dies. The axial velocity distribution in the plane dies is divided in to the uniform velocity and the deviated velocity. The deviated velocity is linearly changed with the distance from the center of cross-section of the workpiece. The results show that the curvature of products and the shapes of the dead metal zone are determined by the minimization of the plastic work and that the curvature of the extruded products increases with the eccentricity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.10a
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• pp.136-142
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• 1995

The kinematically admissible velocity field is developed for the analysis of extruded products. The curving of product in extrusion is caused by the linearly distributed longitudinal velocity on the cross-section of the workpiece at the die exit. In the analysis, the longitudinal velocity in extrusion direction is divided into the uniform velocity and the deviated velocity. In order to satify the requirement of the kinematically admissible velocity field, the average value of the deviated velocity should be zero. At the same time, it should Iinearly change with the destance from the center of gravity of the cross-section of the workpiece. The results of the analysis show that the curvature of product incresses with increses in eccentricity of gravity center of the cross-section of workpiece at die entrance from that of the cross-sectio at the die exit.