• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.808-815
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• 2001

The three-phase diode rectifier with a capacitive filter is highly sensitive to line voltage unbalance, and may cause significantly unbalanced line currents even under slightly unbalanced voltage condition. This paper presents an analysis of this 'unbalance amplification' effect for an ideal rectifier circuit without ac-and dc-side inductors. The voltage unbalance is modeled by introducing a deviation voltage superimposed on balanced three-phase line voltages. With proper approximations, closed-form expressions for symmetrical components of the line current and current unbalance factor are derived in terms of the voltage unbalance factor, filter reactance, and load current. The validity of analytical predictions is confirmed by simulation.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.7
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• pp.758-768
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• 2005

The ball screw actuated by the electric motor is widely used as an essential actuator for driving the mechanical system by virtue of accuracy and force transmission capability. In this paper, a design of the global sliding mode control is presented to drive the ball screw actuator along the minimum time trajectory, In the proposed control scheme, if the ranges of parametric uncertainties and torque limits of the system are specified, the arrival time of the load along the minimum time trajectory can be estimated. Also, the arriving time at the reference input and the maximum acceleration are expressed in a closed form solution. Conversely, the capacity of a ball screw actuator including the motor can be easily designed if the external load and its transportation time are specified. The superior performance of the proposed control scheme and analysis is validated by the computer simulation and experiments comparing with other sliding mode controllers.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.8
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• pp.1547-1554
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• 2011

As process parameters scale, interconnect width are reduced rapidly while the current flowing through interconnects does not decrease in a proportional manner. This effect increases current density in metal interconnects which may result in poor reliability. Since RMS(root-mean-square) current limits are used to evaluate self-heating and short-time stress failures caused by high-current pluses, RMS current estimation is very important to guarantee the reliability of semiconductor systems. Hence, it is critical to estimate the current limits through interconnects earlier in semiconductor design stages. The purpose of this paper is to propose a fast, yet accurate RMS current estimation technique that can offer a relatively precise estimate by using closed-form equations. The efficiency and accuracy of the proposed method have been verified through simulations using HSPICE for a vast range of interconnect parameters.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.288-291
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• 2005

This paper is aimed at presenting a proton exchange membrane (PEM) fuel cell stack. The fuel cell electrical output voltage and current (V-I) characteristic is described for the first time by a simplified closed form suitable. The characteristics obtained from the simulation are compared with the experimental results on a Ballard commercial fuel cell stack as well as to the manufacturer given data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.3 no.4
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• pp.158-163
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• 1979

An approximate theory of circular chlindrical shells under arbitrary load is derived on the basis of Vlasov's semimembrane theory. With this approximate theory concrete cylindrical shells subjected to wind loading is analized and its accuracy is investigated with the results of Donnell's equation. In this study the foollowing results are abtained : (1) The expression of .kappa.$\_$2/=.part.$\^$2/.omega./.part. s$\^$2/ for the change of curvature gives much simplicated closed form colution. (2) This approximate theory is to be applicable with sufficient accuracy in the stress analysis of concrete cylindreical shells which the ratio L/D is equal or greater than three.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1766-1771
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• 2007

This paper presents plastic limit loads and approximate J-integral estimates for circumferential part-through surface crack at the interface between elbows and pipes. Based on finite element limit analyses using elastic-perfectly plastic materials, plastic limit moments under in-plane bending are obtained and it is found that they are similar those for circumferential part-through surface cracks in the center of elbow. Based on present FE results, closed-form limit load solutions are proposed. Welds are not explicitly considered and all materials are assumed to be homogeneous. And the method to estimate the elastic-plastic J-integral for circumferential part-through surface cracks at the interface between elbows and straight pipes is proposed based on the reference stress approach, which was compared with corresponding solutions for straight pipes.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1836-1841
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• 2007

Based on three-dimensional (3-D) FE limit analyses, this paper provides plastic limit and TES(Twice-Elastic-Slope) loads for pipe bends under combined pressure and out-of-plane bending. The plastic limit loads are determined from FE limit analyses based on elastic-perfectly-plastic materials using the small geometry change option, and the FE limit analyses using the large geometry change option provide TES plastic loads. A wide range of parameters related to the bend geometry is considered. Based on the FE results, closed-form approximations of plastic limit and TES plastic load solutions for pipe bends under out-of-plane bending are proposed.

• The Journal of Korea Robotics Society
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• v.12 no.2
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• pp.161-172
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• 2017

Foot mechanisms play the role of interface between the main body of robotic systems and the ground. Biomimetic design of the foot mechanism is proposed in the paper. Specifically, multi-chained and multiple contact characteristics of general foot mechanisms are analyzed and their advantages are highlighted in terms of impulse. Using Newton-Euler based closed-form external and internal impulse models, characteristics of multiple contact cases are investigated through landing simulation of an articulated leg model with three kinds of foot. It is shown that in comparison to single chain and less articulated linkage system, multi-chain and articulated linkage system has superior characteristic in terms of impulse absorption as well as stability after collision. The effectiveness of the simulation result is verified through comparison to the simulation result of a commercialized software.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.1
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• pp.58-78
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• 2016

Compressed sensing (CS) possesses the potential benefits for spectrum sensing of wideband signal in cognitive radio. The sparsity of signal in frequency domain denotes the number of occupied channels for spectrum sensing. This paper presents a scheme of adaptively adjusting the number of compressed measurements to reduce the unnecessary computational complexity when priori information about the sparsity of signal cannot be acquired. Firstly, a method of sparsity estimation is introduced because the sparsity of signal is not available in some cognitive radio environments, and the relationship between the amount of used data and estimation accuracy is discussed. Then the SNR of the compressed signal is derived in the closed form. Based on the SNR of the compressed signal and estimated sparsity, an adaptive algorithm of adjusting the number of compressed measurements is proposed. Finally, some simulations are performed, and the results illustrate that the simulations agree with theoretical analysis, which prove the effectiveness of the proposed adaptive adjusting of compressed measurements.

• Computers and Concrete
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• v.10 no.5
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• pp.541-555
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• 2012

This paper presents an algorithm for the evaluation of stresses in reinforced concrete sections under service loads. The algorithm is applicable to any section defined by polygonal contours and is based on an analytical integration of the stresses. The nonlinear behaviour of concrete is represented by the parabola-rectangle law used in the Eurocode-2 for the ultimate concrete design. An integrated definition of the strains in concrete and steel is possible by the use of Heaviside functions, similarly to what is done for ultimate section design in Barros et al. (2004). Other constitutive equations for the definition of the stresses in the concrete or steel can be easily incorporated into the code. The examples presented consist in the evaluation of resulting axial load and bending moment in an irregular section and in a section in L shape. The results, for service stresses, can also be plotted in terms of design abacus; a rectangular doubly reinforced section is presented as example.