• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.5
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• pp.65-72
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• 2000

This paper presents the study of the tension control in a web transfer system. In this study the sliding mode controller is applied to a time-varying nonlinear mathematical model. The model was derived to consider the effects of changing the roll radius in tension variation during winding and unwinding. The uncertainty in modeling may be due to unmodelled dynamics, on variations in system model. Designed sliding mode controller made the system error always staying in the suggested surface from the beginning. Through this, system is maintained to be robust against a disturbance and uncertainty. To verify the designed controller has a good performance, various inputs such as desired velocity, step input, and trapezoidal input are applied. When the sliding mode controller was used, the system(the tension control) performance was improved comparing to the PID controller. The robustness of the controller with respect to an estimation error was verified through simulations.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1631-1635
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• 2006

본 연구에서는 레이놀즈응력모형(RSM: Reynolds Stress Model)을 이용하여 사다리꼴 개수로 흐름을 수치모의 하였다. 측벽 경사에 따른 사다리꼴 개수로 흐름을 수치모의 하였으며 계산된 평균유속 분포는 기존의 실험 결과와 비교하였다. 그 결과 개발된 레이놀즈응력이 사다리꼴 개수로 흐름을 비교적 잘 예측하는 것으로 나타났다. 또한 사다리꼴 수로에서는 직사각형 개수로 흐름과 달리 velocity dip 현상이 발생하지 않는 것으로 나타났다. 특히 측벽 경사가 32..인 사다리꼴 수로에서의 평균유속 및 바닥 전단응력 분포는 측벽 경사가 큰 경우와 다른 형태의 평균유속 및 전단응력 분포가 형성되는 것으로 나타났다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.206-211
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• 1996

Closed-die forging of external spine is analysed using an upper bound elemental technique. The kinematically admissible velocity field for three-dimensional deformation in forging of the external spine with trapezoidal teeth was obtained. The upper bound to the deforming load necessary and the the deformed configurations are predicted using integration of the formulation of energy expressions which were obtained from B(upset forging method) were considerd in the present analysis and the theoretical results compared with experimental ones Experiments were carried out on plasticine as model material at room temperature where talcum powder was used as a lubricant. The present investigation revealed that the analytical method B predicts a reducet forging load and improved configuration better than method A for the forged products.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.10a
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• pp.309-314
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• 2004

A flexible disk grinding system process has been introduced that utilized varying disk orientation with respect to workpiece along with the applied feed speed. Various process conditions including cutting speed, maximum feed speed and orientation angles could applied to observe process outcomes. Even though continuous and constant feed speed has been applied to the process, the results from the trapezoidal input velocity profiles would be observed and compared. Based on the control strategies including neural network methodologies, several output results were compared to find the optimum process condition. Two axis control results were displayed showing better performance with higher trajectory error for larger training epoch.

• Solar Energy
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• v.13 no.1
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• pp.31-38
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• 1993

A numerical study of natural convection heat transfer confined by circular parallel walls at different temperatures and flat adiabatic walls is investigated for Rayleigh numbers from $10^3$ to $10^5$and sectorial angles from $30^{\circ}$ to $180^{\circ}$. It is used by a finite difference method to solve the governing equations. The results show velocity and temperature distributions. Mean Nusselt numbers are shown by $\overline{Nu}=C(Ra_L)^m$.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.374-378
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• 2003

From linear motor feed system model, two axis control rules have been applied. As an application process, a flexible disk grinding system process has been also introduced that utilized varying disk orientation with respect to workpiece along with the applied feed speed. A known process model methodologies has been used to fomulate processed surface profiles. Various process conditions including cutting speed, maximum feed speed and orientation angles could applied to observe process results sensitivities. Even though continuous and constant feed speed has been applied to the process, the results from the trapezoidal input velocity profiles would be observed and compared.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.2
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• pp.40-47
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• 1993

To diversify the area of application of UBET to the analysis of ring rolling which produces rings having more complex cross-sectional configuration, an element of triangular cross-section has been introduced and the corresponding kinematically admissible velocity field has been derived while considering the material flow between neighboring elements. The theoretical perdictions in roll torque and profile formation show good agreement with the experiments. The effect of process parameters such as feed rate and taper angle of the roll groove has been discussed.

• Journal of Korea Water Resources Association
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• v.48 no.8
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• pp.635-645
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• 2015

The objective of this study is to examine the three-dimensional turbulent flows occurring in the meandering channel with presence of a groyne. A series of laboratory experiments are carried out in a meandering channel with trapezoidal cross sections. The channel is a 24.4 m long, 1.5 m wide, and the bottom slope in the longitudinal direction is 0.02. Two cases with and without the groyne are considered in the experiment. Three-dimensional velocity fields are measured using an acoustic Doppler velocimetry (ADV) at approximately sixty locations in each cross section. The measured velocity fields are averaged in time, and the time-averaged flow revealed that the mean velocity magnitude along the outer bank of the channel was reduced significantly and the direction of the primary flow was directed toward the center of the channel due to the presence of the groyne.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.3
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• pp.283-288
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• 2014

The use of robots is no longer limited to the field of industrial robots and is now expanding into the fields of service and medical robots. In this light, a trajectory generation method that can respond instantaneously to the external environment is strongly required. Toward this end, this study proposes a method that enables a robot to change its trajectory in real-time using a convolution operation. The proposed method generates a trajectory in real time and satisfies the physical limits of the robot system such as acceleration and velocity limit. Moreover, a new way to improve the previous method (11), which generates inefficient trajectories in some cases owing to the characteristics of the trapezoidal shape of trajectories, is proposed by introducing a triangle shape. The validity and effectiveness of the proposed method is shown through a numerical simulation and a comparison with the previous convolution method.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.4
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• pp.68-78
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• 1999

Heat transfer performance is studied for boiling and condensation of R-11 on integral-fin tubes. Nine tubes with trapezoidal integral-fins having fin densities from 748 to 1654fpm and 10,30 grooves and finned tubes with caves of 0.55 and 0.64 mm height respectively are tested. in case of condensation CFC-11 condensates at saturation stat of 32$^{\circ}C$ on the outside surface cooled by inside cooling water flows. And in case of boiling the refrigerant evaporates at a saturation state of 1 bar on the outside tube surface and heat is supplied by hot water which circulates inside of the tube,. The tube having fin transfer coefficient concerns fin tubes with caves show higher valve than low fin tube having find density of 1299fpm and 30grooves. The overall heat transfer coefficient of fin tube with caves is about 5155 W/mK at 2.8m/s of water velocity, The value is abuot 2.7 times higher than plain tube and 1.3 times higher than low fin tube having fin density of 1299fpm and 30 grooves.