• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.3
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• pp.78-87
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• 1998

A dynamic model of direct-acting OHC valve train system has been used to determine the load conditions in the system. The modified equations for calculating the friction forces between cam and HLA, and at a camshaft bearing have been defined considering the lubrication conditions. Then, to understand the frictional characteristics in the system, a parameter study has been performed. As the results of the analysis, valve spring stiffness and preload have great effects on the friction in the system, but the effects of other parameters are negligible. So, how to design the valve train system with respect to the reduction of friction is to minimize the valve spring stiffness and preload in the limit of satisfying the dynamic constraints.

• Korean Journal of Optics and Photonics
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• v.14 no.4
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• pp.423-428
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• 2003

In a direct modulated semiconductor laser diode. the structural dependence of current blocking layers was studied in view of the leakage current reduction and the bandwidth expansion. To analyze the leakage current and the parasitic effects, the current-voltage derivation characteristics and the subtraction method were used, respectively. It was shown that the‘inin’type current blocking structure might be the best choice for the purpose of the static and dynamic characteristics.

• 전기의세계
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• v.23 no.3
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• pp.43-52
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• 1974

The matrix inversion is very inefficient for computing direct solutions of the large spare systems of linear equations that arise in many network problems as a large electrical power system. Optimally ordered triangular factorization of sparse matrices is more efficient and offers the other important computational advantages in some applications with this method. The direct solutions are computed from sparse matrix factors instead of a full inverse matrix, thereby gaining a significant advantage is speed and computer memory requirements. In this paper, it is shown that the sparse matrix method is superior to the inverse matrix method to solve the linear equations of large sparse networks. In addition, it is shown that the sparse matrix method is superior to the inverse matrix method to solve the linear equations of large sparse networks. In addition, it is shown that the solutions may be applied directly to sove the load flow in an electrical power system. The result of this study should lead to many aplications including short circuit, transient stability, network reduction, reactive optimization and others.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.494-497
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• 2005

Direct velocity feedback (DVFB) control with a collocated distributed actuator and point sensor pair is known that it offers a good stability with high performance when the control strategy is applied at the suppression of structural vibration. Also decentralized control method introduced to offer to reduce implementaion effort and malfunction due to failure in sensors and actuators of control system has become an important position in DVFB. In this paper, the decentralized control is compared with centralized control in terms of vibrational velocity reduction in a clamped-clamped beam.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1455-1458
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• 2005

This paper presents the method of reducing torque ripple of Blushless Direct Current(BLDC) motor. In the BLDC motor, the torque is decided by the back-EMF and current waveform. If the back-EMF is constant, the torque ripple depends on the current ripple during commutation period. The current in commutation period is acquired by circuit analysis and then the torque ripple simply can be reduced by varying input voltage to flow the current continuously. And suggested method is confirmed by dynamic with parameters of 500W BLDC motor.

• Korean Journal of Construction Engineering and Management
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• v.7 no.6
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• pp.202-211
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• 2006

Rework in the construction industry can adversely affect project cost and schedule performance. Based on direct rework costs recorded on 359 construction projects, this paper presents an assessment of the magnitude of rework by various types of projects and sources of rework. The results from this paper establish that on average 4.5% and 2.5% of actual construction costs were spent on rework for owner and contractor projects, respectively. Furthermore, this paper determines that the direct rework costs differ by project types and sources of rework. Finally, it permits the development of rework reduction initiatives. By quantifying and recognizing the different magnitude of rework, the industry can be aware of the waste from rework and develop effective plans for managing rework, ultimately improving project cost performance.

• Proceedings of the KIEE Conference
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• 2007.10c
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• pp.135-137
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• 2007

In this paper, an advanced torque control scheme of SRM using DITC(Direct Instantaneous Torque Control) and PWM(pulse width modulation) is presented. Different from conventional DITC method, proposed method uses one or two switching modes at every sampling time, instead of only one switching mode. The duty ratio of the phase switch is regulated according to the torque error and simple control rules of DITC. Moreover the sampling time of control can be extended, which allows implementation on low cost microcontrollers. The proposed control method is verified by the simulations and experimental results.

• International Journal of Control, Automation, and Systems
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• v.4 no.1
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• pp.113-123
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• 2006

In this paper, an improved direct torque control (DTC) method for sensorless matrix converter drives is proposed which enables to minimize torque ripple, to obtain unity input power factor, and to achieve good sensorless speed-control performance in the low speed operation, while maintaining constant switching frequency and fast torque dynamics. It is possible to combine the advantages of matrix converters with the advantages of the DTC strategy using space vector modulation and a flux deadbeat controller. To overcome the phase current distortion by the non-linearity of a matrix converter drive, the simple non-linearity compensation method using PQR power theory are presented in the proposed scheme. Experimental results are shown to illustrate the feasibility of the proposed strategy.

• The Research Journal of the Costume Culture
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• v.11 no.3
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• pp.423-430
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• 2003

Cotton fabric md nylon fabric were chosen as base fabric specimens for dyeing using Japanese pagoda tree colorants through chitosan, treatment. With the chitosan treatment, the dye-uptake of the treated fabric increased. This treatment is also expected to be effective in terms of environment-friendliness. The effect of the dyeing methods, mordanting or non-mordanting, and chitosan treatment on the dye-uptake and air permeability of the treated fabrics was investigated. In case of cotton fabric, Al mordanted dyeing resulted in higher dye-uptake through the chitosan treatment. Therefore, the chitosan treatment is effective in this case. Japanese pagoda tree seems to have direct affinity for nylon fabric without the mordanting treatment. In case of cotton fabric, it seems that the cellulose molecules, colorants, and the chitosan make a complex, thereby reducing the air permeability. In case of nylon fabric, due to the fact the Japanese pagoda tree colorant molecules form direct physical bonding with the nylon molecules, it seems that there is not much of air permeability reduction.

• Journal of the Korean Institute of Telematics and Electronics
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• v.11 no.2
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• pp.1-4
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• 1974

Matrix inversion is very inefficient for computing direct solutions of the large sparse systems of linear equations that arise in many network problems. This paper describes some computer programming techniques for taking advantage of the sparsity of the admittance matrix. with this method, direct solutions are computed from sparse matrix. It is Possible to gain a significant reduction in computing time, memory and round-off emir[r. Retails of the method, numerical examples and programming are given.