• 한국CDE학회논문집
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• 제11권4호
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• pp.289-302
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• 2006

It is becoming a common trend that many designers work on a very complex assembly together in a collaborative environment. In this environment, every designer should be able to see the whole assembly in a full detail or in a rough shape at least. Even though the hardware technology is being improved very rapidly, it is very difficult to display a very complex assembly at a speed to allow smooth interactions for designers. This problem could be solved if a designer could manipulate his portion of the assembly in a full resolution while the remaining portion of the assembly is displayed in a rough resolution. It is also desired that the remaining portion is converted to the full resolution when needed. To realize this environment, the capabilities to simplify the portions of an assembly and to reset to the original resolution should be added to the current CAD systems. Thus operators realizing multi-resolution on B-rep are proposed in this paper. They are: wrap-around, smooth-out, and thinning operator. Through appropriately applying these operators sequentially, an assembly model of any desired resolution can be easily generated. Of course, the assembly can go back to the finer resolution. In this paper, the data structures and the processes to realize these operators are described and a prototype modeling system with these operators is also demonstrated.

• Journal of Power Electronics
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• 제15권1호
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• pp.190-201
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• 2015

This paper uses the switching function approach to present a simple state model of the Vienna-type rectifier. The approach introduces the relationship between the DC-link neutral point voltage and the AC side phase currents. A novel direct power control (DPC) strategy, which is based on the sliding mode control (SMC) for Vienna I rectifiers, is developed using the proposed power model in the stationary ${\alpha}-{\beta}$ reference frames. The SMC-based DPC methodology directly regulates instantaneous active and reactive powers without transforming to a synchronous rotating coordinate reference frame or a tracking phase angle of grid voltage. Moreover, the required rectifier control voltages are directly calculated by utilizing the non-linear SMC scheme. Theoretically, active and reactive power flows are controlled without ripple or cross coupling. Furthermore, the fixed-switching frequency is obtained by employing the simplified space vector modulation (SVM). SVM solves the complicated designing problem of the AC harmonic filter. The simplified SVM is based on the simplification of the space vector diagram of a three-level converter into that of a two-level converter. The dwelling time calculation and switching sequence selection are easily implemented like those in the conventional two-level rectifier. Replacing the current control loops with power control loops simplifies the system design and enhances the transient performance. The simulation models in MATLAB/Simulink and the digital signal processor-controlled 1.5 kW Vienna-type rectifier are used to verify the fast responses and robustness of the proposed control scheme.

• Coupled systems mechanics
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• 제8권4호
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• pp.299-313
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• 2019

The paper represents computer modeling of the deformed state of physically nonlinear transversally isotropic bodies with hole. In order to describe the anisotropy of the mechanical properties of transversally-isotropic materials a structurally phenomenological model has been used. This model allows representing the initial material in the form of the coupled isotropic materials: the basic material (binder) considered from the positions of continuum mechanics and the fiber material oriented along the anisotropy direction of the original material. It is assumed that the fibers perceive only the axial tensile-compression forces and are deformed together with the base material. To solve the problems of the theory of plasticity, simplified theories of small elastoplastic deformation have been used for a transversely-isotropic body, developed by B.E. Pobedrya. A simplified theory allows applying the theory of small elastoplastic deformations to solve specific applied problems, since in this case the fibrous medium is replaced by an equivalent transversely isotropic medium with effective mechanical parameters. The essence of simplification is that with simple stretching of composite in direction of the transversal isotropy axis and in direction perpendicular to it, plastic deformations do not arise. As a result, the intensity of stresses and deformations both along the principal axis of the transversal isotropy and along the perpendicular plane of isotropy is determined separately. The representation of the fibrous composite in the form of a homogeneous anisotropic material with effective mechanical parameters allows for a sufficiently accurate calculation of stresses and strains. The calculation is carried out under different loading conditions, keeping in mind that both sizes characterizing the fibrous material fiber thickness and the gap between the fibers-are several orders smaller than the radius of the hole. Based on the simplified theory and the finite element method, a computer model of nonlinear deformation of fibrous composites is constructed. For carrying out computational experiments, a specialized software package was developed. The effect of hole configuration on the distribution of deformation and stress fields in the vicinity of concentrators was investigated.

• 대한화학회지
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• 제67권5호
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• pp.378-392
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• 2023

본 연구의 목적은 테크놀로지를 활용한 모델의 설계와 개발 과정에서 나타난 모델의 본성에 대한 예비화학교사의 인식을 분석하는 것이다. 이를 위하여 중부 지역에 있는 사범대학 3학년에 재학 중인 예비화학교사 19명을 대상으로 중학교 1학년 과학 교과서에 제시된 보일 법칙에 관련된 실험 현상을 관찰하고, 테크놀로지를 활용하여 관찰된 실험 결과와 관련된 모델을 설계하고 개발하도록 요구하였다. 선행연구를 바탕으로 모델의 본성을 표상적 측면과 설명적 측면으로 분류하고, 표상적 측면은 표상화, 함축화, 간단화로, 설명적 측면은 분석, 해석, 추론, 설명, 정량화로 분류하였다. 그리고 이 분류를 기준으로 하여 예비화학교사들의 인식을 분석하였다. 연구 결과, 표상적 측면의 표상화에서는 부피가 변하는 공간을 표현한 형태로 획일화되어 있었으며, 함축화에서는 압력을 실린더 내부의 밝기나 입자의 색 변화 빈도로 표현하였다. 간단화의 경우에는 입자 충돌을 완전탄성충돌로 표상화하였으나, 입자의 종류를 간단히 표상화하지 못하는 그룹들이 있었다. 설명적 측면에서는 분석의 경우 부피를 조작 변인으로 구분하였으며, 해석의 경우 대부분 그룹이 기체 입자의 충돌로 압력의 변화를 해석하였다. 그러나 추론에 관련된 인식은 많이 관찰되지 않았다. 설명의 경우 입자가 충돌하는 면적을 설정하지 않거나 잘못 설정하여 설명에 성공하지 못한 그룹들이 있었으며, 정량화에서는 단위시간 당 충돌 횟수를 수식화한 그룹들과 이와는 반대로 충돌 횟수를 수치화하지 못하여 정량화하지 못한 그룹들이 있었다.

• 조명전기설비학회논문지
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• 제24권7호
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• pp.41-46
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• 2010

With the improvement of industrial society, high quality electrical energy, simplification of operation and maintenance, and ensuring reliability are being required. Also we request an urgent change from $SF_6$ gas to an environment-friendly gas insulation material. In this paper, the experiments of breakdown characteristics by pressure and gap change of $N_2/O_2$ mixture gas through a GIS (Gas Insulated Switchgear) model were described. This paper reviews basic data of the surface discharge characteristics for Teflon resin in not only pure $N_2$, $N_2:O_2$ mixture gas as being focused on environmentally-friendly insulating gas, but also $SF_6$. Also, insulation characteristics by breakdown voltage and surface discharge voltage of $N_2:O_2$ mixture gas in the experimental chamber were studied.

• Spatial Information Research
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• 제11권1호
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• pp.23-32
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• 2003

GIS분야에서 불규칙삼각망은 저수량계산, 지형분석 등에 활용되며 표고, 경사, 방향 정보를 가지고 있기 때문에 처리시간과 용량이 많이 소요된다. 등고선을 활용하여 TIN을 구축하는 과정에서, 선의 단순화를 위해 사용하는 weed tolerance는 등고선상의 샘플 간격에 영향을 미치게 된다. 본 연구에서는 다양한 크기의 weed tolerance에 따른 TIN의 처리시간과 용량을 계산하였으며, 적절한 weed tolerance를 제시하기 위해 TIN으로부터 생성된 수치표고모형의 표준오차를 평가하여 허용오차 범위를 만족하는 weed tolerance를 결정하였다. 평가결과, DEM 표준오차 5m를 만족하는 TIN의 weed tolerance 는 70m였으며, DEM의 해상도는 20m로 나타났다.

• Computers and Concrete
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• 제15권6호
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• pp.903-919
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• 2015

The flow of freshly mixed cement-based material shows thixotropy, which implies some difficulties on robust measurement of its rheological properties: The flow curve of thixotropic materials depends on the used protocol. For examples, higher viscosity is obtained when the rate of shear strain is more quickly increased. Even though precise measurement and modelling of the concrete rheology needs to consider the thixotropic effect, engineers in the concrete field prefer considering as a non-thixotropic Herschel-Bulkley fluid, even more simply Bingham fluid. That is due to robustness of the measurement and application in casting process. In the aspect of simplification, this papers attempts to mimic the thixoropic flow by the non-thixotropic Herschel-Bulkley model. Disregarding the thixotropy of cement based materials allows us to adopt the rheological concept in the field. An optimized protocol to measure the Bingham parameters was finally found based on the accuracy and reproducibility test of cement paste samples, which minimizes the error of simulation stemming from the assumption of non-thixotropy.

• 한국자동차공학회논문집
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• 제18권5호
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• pp.68-75
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• 2010

The one of the major problems in the development of PEMFC was regarding to the assurance of sealing on stack. The failure on the sealing creates the problems of fuel leakage, mixing, internal combustion, damage on parts and can be a direct reason for the degrading the efficiency of fuel cell. This paper studies on the analytical approach for improving the contacting pressure distribution on the gasket at the evaluation on the sealing of fuel cell stack. So, the assembly analysis on multi layered fuel cell stack was performed. The research on the simplification of finite element model was performed for three dimensional analysis at the multi layered state. The improved contact pressure distribution was obtained through the case studies on gasket for better sealing. In addition, the number of the cell was determined for the effective analysis and the structural characteristics were evaluated based on this research.

• Journal of Electrical Engineering and Technology
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• 제12권6호
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• pp.2187-2195
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• 2017

In order to solve the AC optimal power flow (OPF) problem considering the generators' on/off status, it is necessary to model the problem as mixed-integer nonlinear programming (MINLP). Because the computation time to find the optimal solution to the mixed-integer AC OPF problem increases significantly as the system becomes larger, most of the existing solutions simplify the problem either by deciding the on/off status of generators using a separate unit commitment algorithm or by ignoring the minimum output of the generators. Even though this kind of simplification may make the overall computation time tractable, the results can be significantly erroneous. This paper proposes a novel algorithm for the mixed-integer AC OPF problem, which can provide a near-optimal solution quickly and efficiently. The proposed method is based on a combination of the outer approximation method and the relaxed AC OPF theory. The method is applied to a real-scale power system that has 457 generators and 2132 buses, and the result is compared to the branch-and-bound (B&B) method and the genetic algorithm. The results of the proposed method are almost identical to those of the compared methods, but computation time is significantly shorter.

• Steel and Composite Structures
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• 제28권5호
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• pp.573-588
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• 2018

The objective of this paper is to investigate the mechanical performances of polygonal concrete-filled circular steel tubular (CFT) stub columns under axial loading through combined experimental and numerical study. A total of 32 specimens were designed to investigate the effect of the concrete strength and steel ratio on the compressive behavior of polygonal CFT stub columns. The ultimate bearing capacity, ductility and confinement effect were analyzed based on the experimental results and the failure modes were discussed in detail. Besides, ABAQUS was adopted to establish the three dimensional FE model. The composite action between the core concrete and steel tube was further discussed and clarified. It was found that the behavior of CFT stub column changes with the change of the cross-section, and the change is continuous. Finally, based on both experimental and numerical results, a unified formula was developed to estimate the ultimate bearing capacity of polygonal CFT stub columns according to the superposition principle with rational simplification. The predicted results showed satisfactory agreement with both experimental and FE results.