• 한국정보처리학회논문지
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• 제3권5호
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• pp.1329-1336
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• 1996

많은 영상 데이타 압축 응용분야에서 DCT는 높은 압축 성능으로 인하여 널리 잘 알려져 있다. 그러나 낮은 비트율에서는 인간의 시각에 거슬리는 블록 효과(block artifacls)가 생기는 문제점을 가지고 있다. 또한 실제적인 응용에 있어서, DCT계수의 빠른 계산과 간단한 VLSI 구현도 중요한 과제이다. 따라서 블록 효과의 제거와 빠른 CT 계산은 실제적인 연구의 대상이 된다. 본 논문에서는 수정된 DCT 계산 방법을 연구 하였고, 이것은 빠른 계산과 함께 블록 효과를 효과적으로 제거할 수 있었다. 이러한 새로운 접근 방법을 낮은 비트 율에서 영상의 부호화 및 복호화에 적용하였다. 실제 영상을 대상으로 실험한 결과, 제안된 방법을 통해 표준적인 방법에 비하여 성능을 개선할 수 있었다.

• 조명전기설비학회논문지
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• 제17권5호
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• pp.36-42
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• 2003

본 논문에서는 태양광 발전과 계통 연계를 위한 인터페이스 회로로서 Buck-Boost 형태에 기초한 전류형 PWM 인버터를 제안한다. 제안된 전류형 PU 인버터는 두 개의 Buck-Boost토폴로지를 조합하여 구성하였으며, 입력단의 인덕터 전류를 전류 불연속 모드로 동작시켜 별도의 입력 전류의 검출 없이도 출력단을 단위 역률화 할 수 있도록 구성하였다. 결과적으로 전체 시스템의 간략화가 가능하며, 특히, 부가적인 승압 장치 없이 태양전지 발전 전압 보다 높은 실효치의 교류 출력을 얻을 수 있는 장점을 가진다. 제안하는 인버터에 대한 동작을 이론적으로 분석하고 하드웨어 구현의 타당성을 검증하기 위하여 시제품을 제작하고 실험하였다.

• Computers and Concrete
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• 제20권1호
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• pp.39-47
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• 2017

In this paper, mode I fracture toughness of rock was determined by direct and indirect methods using Particle Flow Code simulation. Direct methods are compaction tension (CT) test and hollow centre cracked quadratic sample (HCCQS). Indirect methods are notched Brazilian disk (NBD) specimen, the semi-circular bend (SCB) specimen, hollow centre cracked disc (HCCD), the single edge-notched round bar in bending (SENRBB) specimen and edge notched disk (END). It was determined that which one of indirect fracture toughness values is close to direct one. For this purpose, initially calibration of PFC was undertaken with respect to data obtained from Brazilian laboratory tests to ensure the conformity of the simulated numerical models response. Furthermore, the simulated models in five introduced indirect tests were cross checked with the results from direct tests. By using numerical testing, the failure process was visually observed. Discrete element simulations demonstrated that the macro fractures in models are caused by microscopic tensile breakages on large numbers of bonded discs. Mode I fracture toughness of rock in direct test was less than other tests results. Fracture toughness resulted from semi-circular bend specimen test was close to direct test results. Therefore semi-circular bend specimen can be a proper test for determination of Mode I fracture toughness of rock in absence of direct test.

• Membrane and Water Treatment
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• 제9권3호
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• pp.173-179
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• 2018

Microcystin-LR, one of algal toxins induced by the eutrophication of a reservoir, is known to be harmful to human by adversely affecting our liver and brain. Hypochlorous acid is very efficient to remove Microcystin-LR in a clear well. The previous researches showed that CT, pH and temperature affected removal rate in batch tests. It was noted that hydrodynamic properties of clear well could also influence its removal rate. A mathematical model was built using an axial dispersion reactor model and software was used to simulate the removal rate. The model consisted of the second order differential equations including dispersion, convection, Microcystin-LR reaction with chlorine. Kinetic constants were obtained through batch tests with chlorine. They were $0.430{\times}10^{-3}L/mg/sec$ and $0.143{\times}10^{-3}L/mg/sec$ for pH 7.0 and 8.1, respectively. The axial dispersion reactor model was shown to be useful for the numerical model through conservative tracer tests. The numerical model successfully estimated the removal rate of Microcyctin-LR in a clear well. Numerical simulations showed that a small dispersion number, low pH and long hydraulic retention time were critical for higher removal rate with same chlorine dosage. This model could be used to optimize the operation of a clear well during an eutrophication season.

• 한국가시화정보학회지
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• 제9권3호
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• pp.65-70
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• 2011

Three major physiological functions of nose can be described as air-conditioning, filtering and smelling. Detailed knowledge of airflow characteristics in nasal cavities is essential to understanding of the physiological and pathological aspects of nasal breathing. In our laboratory, a series of experimental investigations have been conducted on the airflows in normal and abnormal nasal cavity models by means of PIV under both constant and periodic flow conditions. In this work, more specifically experimental and numerical results on the surgically modified inferior turbinate model were presented. With the high resolution CT data and a careful treatment of the model surface under the ENT doctor's advice yielded quite sophisticated cavity models for the PIV experiment. Physiological nature of the airflow was discussed in terms of velocity distribution and vortical structure for constant inspirational flow. Since the inferior and middle turbinate are key determinants of nasal airflow, the turbinectomy obviously altered the main stream direction. This phenomenon may cause local changes in physiological function and the flow resistance.

• Structural Engineering and Mechanics
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• 제66권3호
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• pp.379-386
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• 2018

The present study addresses the direct and indirect methods of determining the mode-I fracture toughness of concrete using experimental tests and particle flow code. The direct method used is compaction tensile test and the indirect methods are notched Brazilian disc test, semi-circular bend specimen test, and hollow center cracked disc. The experiments were carried out to determine which indirect method yields the fracture toughness closer to the one obtained by the direct method. In the numerical analysis, the PFC model was first calibrated with respect to the data obtained from the Brazilian laboratory test. The crack paths observed in the simulated tests were in reasonable accordance with experimental results. The discrete element simulations demonstrated that the macro fractures in the models are caused by microscopic tensile breakages on large numbers of bonded particles. The mode-I fracture toughness in the direct tensile test was smaller than the indirect testing results. The fracture toughness obtained from the SCB test was closer to the direct test results. Hence, the semi-circular bend test is recommended as a proper experiment for determination of mode-I fracture toughness of concrete in the absence of direct tests.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.60-65
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• 2004

Kim et al. described and compared other methods of measuring stress triaxiality using the displacements near the side necking, proved the validities of these models and explored the effect of location where the displacements are measured using three-dimensional finite element analysis for a standard CT specimen with 20% side-grooves. In this paper, the applicability of these models to various specimen and materials are examined in detail. To consider the effects of side groove, thickness of specimen, crack length, specimen geometry and strain hardening exponents, three-dimensional finite element simulation has been performed for various specimen geometries. For a case without a side groove, in the whole the difference between the stress triaxilaity analytically evaluated and directly determined is similar. For a case with a 20% side groove the stress triaxiality is measured at the area where ${\theta}$ is smaller than $60^{\circ}$, which excludes a side grooved area.

• Design & Manufacturing
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• 제11권3호
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• pp.29-34
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• 2017

Increased demand for parts with micro-pattern structure made of metals, ceramics, and composites in various fields such as medical ultrasonic sensors, CT collimators, and ultra-small actuator parts. Micro powder injection molding (PIM) is a technology for manufacturing micro size, high volume, complex, precision, net-shape components from either metal or ceramic powder. In the present study, a standard mold with a variable insert core capable of producing various micro patterns was investigated. An injection molding test was performed on a standard mold using a line type micro-pattern core having an aspect ratio of 2, a slenderness ratio of 70, a pattern size of $200{\mu}m$, and a pattern spacing of $150{\mu}m$. During the filling process, the deformation of the mold with large aspect ratio and slenderness ratio was analyzed by the experiment and the numerical simulation according to the position of the gate. We proposed a mold structure that minimizes mold deformation by gate modification and enables uniform pattern filling behavior.

• 전력전자학회논문지
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• 제4권6호
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• pp.608-615
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• 1999

본 논문에서는 초음파 모터의 위상차 구동원리에 관해서 명확히 하였고, 이를 이용하여 점·탄성 특성을 갖는 컴플라이언스 제어를 제시하였다. 제안된 컴플라이언스 제어는 인간의 근골격 시스템으로부터 유출하여 인간의 운동특성과 같이 매니퓰레이터의 관절 토크를 점성과 탄성계수의 조절에 의해 매니퓰레이터의 위치와 자세가 제어되도록 하였다. 초음파 모터의 위상차 구동원리에 대한 타당성을 모의실험을 통해 검증하였으며, 제시된 제어방법의 타당성을 검증하기 위하여 초음파모터를 이용하여 2축 수평형 직접구동 매니퓰레이터를 제작하여 점성과 탄성 특성에 대한 실험을 하였다.

• Structural Engineering and Mechanics
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• 제72권2호
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• pp.191-201
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• 2019

Finite element analysis is one of the most used tools for studying femoral neck fracture. Nerveless, consensus concerning either the choice of material characteristics, damage law and /or geometric models (linear on nonlinear) remains unreached. In this work, we propose a numerical quasi-brittle damage model to describe the behavior of the proximal femur associated with two methods to evaluate the Young modulus. Eight proximal femur finite elements models were constructed from CT scan data (4 donors: 3 women; 1 man). The numerical computations showed a good agreement between the numerical curves (load - displacement) and the experimental ones. A very encouraging result is obtained when a comparison is made between the computed fracture loads and the experimental ones ($R^2=0.825$, Relative error =6.49%). All specific numerical computation provided very fair qualitative matches with the fracture patterns for the sideway fall simulation. Finally, the comparative study based on 32 simulations adopting linear and nonlinear meshing led to the conclusion that the quantitatively results are improved when a nonlinear mesh is used.