• Geotechnical Engineering
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• v.11 no.3
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• pp.43-54
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• 1995

The aim of the work described in this paper is to develope a constitutive model for the prediction of an unsaturated soil and to confirm the application'of the model, which is composed of the elastic and plastic part in consideration of the matric suction and the net mean stress. From test results, volume changes and deviator stresses are analyzed at each state and their relationships are formulated. The application of the model to silty sands is confirmed by the comparison between test and predicted results. During drying -wetting and loading -unloading processes for isotropic states, the agreement between predicted and test results are satisfactory. Predicted deviator stresses are well agreed with test results in shearing process. Overall acceptable predictions are reproduced in high confining pressure. Usefulness of the model is confirmed for the unsaturated soil except volumetric strain, which is not well agreed with the test results due to deficiency of dilatancy of the model in low confining pressure. It is, therefore. recommended to study the behavior of dilatancy for an unsaturated soil.

• Magazine of the Korean Society of Agricultural Engineers
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• v.40 no.5
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• pp.37-42
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• 1998

This study was performed to evaluate the characteristics of volume change is unsaturated clayed soil. The medium-plastic clay was selected and compacted by 50% of Proctor standard compaction energy at 6% higher moisture content than its OMC. A series of isotropic compression tests and triaxial shear tests were performed. The results of the study are summarized as follows. At each matric suction, when the matric suction was increased, the yield stress was increased and slope of volume change was decreased. The more net mean stress was, the less the quantity of volume change was. In shear test, the volumetric strain was much rapidly changed in large matric than in low matric suctions. But the effect of matric suction to volume change disappeared under high net mean stress. At lower deviator stress the more matric suction was, the higher volume change was. But As the matric suction was increasing, the behavior of the unsaturated clayey soil was similar to that of saturated clayey soil. Volume change in the unsaturated clayey soil can be represented as a unique plane in three-dimensional space, which is the axes of net mean stress, matric suction and void ratio.

• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.3
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• pp.101-110
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• 1996

The aim of the work described in this paper is to develope a constitutive model for the prediction of an unsaturated clayey soil and to confirm the application of the model. To this end a series of suction controlled isotropic and triaxial compression tests are conducted on clayey soils. Matric suction is controlled by the axis translation technique using high air entry ceramic disk. Total volume change, air and water volume changes are measured by the device made for the experiment. The specimens are compacted by dynamic compaction using a half of Proctor compaction energy with the water contents of 5% drier than the optimum moisture contents. From test results, volume changes and deviator stresses are analyzed at each state and their relationships are formulated. And the application of the model to clayey soils is confirmed by the comparison between test and predicted results. During drying-wetting and loading-unloading processes for isotropic states, the agreement between predicted and test results are satisfactory. And predicted deviator stresses are well agreed with the test results in shearing process, but volumetric strain is not well agreed with the test results in high suctions.

• Proceedings of the KIPE Conference
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• 2010.11a
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• pp.302-303
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• 2010

본 논문은 계통연계형 인버터의 성능 개선을 위한 슬라이딩 모드 기반의 직접전력제어기법을 제안한다. 제안하는 제어기법은 전류의 축변환 없이 시스템의 유, 무효 전력을 직접 제어함으로써 계통사고 시 빠른 응답특성을 가지고, 불평형 사고 시 계통주파수의 2배에 해당하는 전력 리플이 발생하지 않으므로 계통연계형 인버터 제어에 적합하다. 시뮬레이션 결과를 통해 제안하는 제어기법의 타당성과 강인성을 확인한다.

• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.2
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• pp.152-162
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• 2008

This paper presents a sliding mode controller (SMC) to directly control the active and reactive powers of a doubly ffd induction generator (DFIG) for wind turbines. Sliding-mode control (SMC) and space-vector modulation (SVM) are combined to ensure high-performance operation. SMC scheme is designed to provide robust and fast power controls without frame transformation and current controller used in the conventional FOC drive. Simulation results and experimental results demonstrate that proposed methods preserve the effectiveness and robustness during variations of active and reactive power.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.6
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• pp.515-521
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• 2014

In this paper, we designed axis-displaced Gregorian antenna by using Ray-tracing method. This antenna improves gain, VSWR by rotating the axis of the sub-reflector to get rid of E-field wave returned from sub-reflector to feed horn. Therefore it reduce the sub-reflector size and the volume of antenna. This method is used to track the propagation path for radiation pattern of feed horn from feed horn to sub-reflector, main-reflector and air. We get E-field distribution of this antenna aperture and calculate antenna radiation pattern and optimize the antenna performance. The Ray-tracing Method was verified because the gain, radiation patterns, side lobe level, beam width and return loss of the designed antenna are very similar to CST simulation result and a measured result of the fabricated antenna.