• 호남수학학술지
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• 제28권1호
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• pp.23-29
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• 2006

Neutral subtraction algebras and neutral ideals are introduced, and related properties are investigated.

• Steel and Composite Structures
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• 제49권4호
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• pp.431-440
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• 2023

The functionally graded (FG) porous plates are usually characterized by the non-symmetric elastic modulus distribution through the thickness so that the plate neutral surface does not coincide with the mid-surface. Nevertheless, the conventional analysis models were mostly based on the plate mid-surface so that the accuracy of resulting numerical results is questionable. In this context, this paper presents the neutral surface-based static and free vibration analysis of FG porous plates and investigates the differences between the mid- and neutral surface-based analysis models. The neutral surface-based numerical method is formulated using the (3,3,2) hierarchical model and approximated by the last introduced natural element method (NEM). The volume fractions of metal and ceramic are expressed by the power-law function and the cosine-type porosity distributions are considered. The proposed numerical method is demonstrated through the benchmark experiment, and the differences between two analysis models are parametrically investigated with respect to the thickness-wise material and porosity distributions. It is found from the numerical results that the difference cannot be negligible when the material and porosity distributions are remarkably biased in the thickness direction.

• Computers and Concrete
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• 제26권1호
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• pp.95-106
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• 2020

Castellated beams fabricated from standard I-sections are being used for several structural applications such as commercial and industrial buildings, multistory buildings, warehouses and portal frames in view of numerous advantages. The advantages include enhanced moment of inertia, stiffness, flexural resistance, reduction in weight of structure, by passing the used plate girders, the passage of service through the web openings etc. In the present study, experimental and numerical investigations were carried out on concrete encased steel castellated beams with hexagonal openings under flexural loading. Various positions of openings such as along the neutral axis, above the neutral axis and below the neutral axis were considered for the study. From the experimental findings, it has been observed that the load-carrying capacity of the castellated beam with web opening above neutral axis is found to be higher compared to other configurations. Nonlinear finite element analysis was performed by using general purpose finite element software ABAQUS considering the material nonlinearities. Concrete damage plasticity model was employed to model the nonlinearity of concrete and elasto-plastic model for steel. It has been observed that FE model could able to capture the behaviour of concrete encased steel castellated beams and the predicted values are in good agreement with the corresponding experimental values.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2017년도 추계학술대회
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• pp.95-96
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• 2017

A three-level inverter is widely used thanks to its excellent performances, but the voltage may fluctuate at the neutral point of the split DC-Link. Neutral point voltage fluctuations cause inverter performance degradation and switching element damage, so the neutral point voltage control is essential. However, the neutral point control can be also limited by modulation index and power factor. This paper analyzes the limitation of the neutral point voltage control due to the limitation of zero-sequence voltage, and suggests a method to determine the region where the PWM has to be changed for a better neutral point control.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.2212-2213
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• 2008

In this paper, we studied the method for simultaneous quenching of a transformer type superconducting fault current limiter (SFCL) with two superconducting elements connected in series. Only an element between two elements of the transformer type SFCL was quenched like the case of the resistive type SFCL. By this quenching characteristics, the power burden of the superconducting element was increased. In order to solve this problem, we connected the neutral line between two superconducting elements and the center of secondary coils. The two elements were all quenched in the transformer type SFCL with a neutral line. As a result, the power burden of superconducting elements was decreased, so it was efficient for the increase of power capacity of the transformer type SFCL.

• Steel and Composite Structures
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• 제44권2호
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• pp.171-181
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• 2022

Functionally graded material (FGM) has been spotlighted as an advanced composite material due to its excellent thermo-mechanical performance. And the buckling of FGM resting on elastic foundations has been a challenging subject because its behavior is directly connected to the structural safety. In this context, this paper is concerned with a numerical buckling analysis of metal-ceramic FG plates resting on a two-parameter (Pasternak-type) elastic foundation. The buckling problem is formulated based on the neutral surface and the (1,1,0) hierarchical model, and it is numerically approximated by 2-D natural element method (NEM) which provides a high accuracy even for coarse grid. The derived eigenvalue equations are solved by employing Lanczos and Jacobi algorithms. The numerical results are compared with the reference solutions through the benchmark test, from which the reliability of present numerical method has been verified. Using the developed numerical method, the critical buckling loads of metal-ceramic FG plates are parametrically investigated with respect to the major design parameters.

• 대한기계학회논문집
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• 제15권1호
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• pp.145-153
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• 1991

본 연구에서는 Toh가 개발하여 stretchforming에 응용한 강소성 대변형 이론 을 압연문제에 적용하여 강소성 대변형 유한요소 프로그램을 개발하는데 있다.

• 한국가스학회지
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• 제28권2호
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• pp.32-37
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• 2024

최근 화석연료를 대체할 수 있는 수소에너지를 이용한 이동 수단에 대한 연구가 활발히 이루어지고 있다. 한편 이를 이용하기 위해서는 수소를 생산 저장 이송하는 과정이 필수적이다. 특히 수소를 90 MPa에 이르는 고압으로 저장 이송할 경우 기체 상태가 아닌 액체 상태이므로 부피가 감소하여, 상대적으로 비용을 절감 할 수 있다. 본 연구에서는 수소 액화에 필수적인 액화수소 펌프 개발을 위해 챔버 내의 유동을 유한요소해석 (Finite Element Methods (FEM)) 프로그램인 ANSYS를 이용하여 해석하였다. 그 결과, 1차 챔버에서 2차 챔버 사이에 밸브가 없는 경우, 2차 챔버 내의 최대 속도는 9.075 m/s, 밸브가 3 mm 열린 경우의 최대 속도는 8.111 m/s 로 10.6% 감소하였다. 또한 밸브가 없는 경우의 최대 압력은 0.62 MPa, 밸브가 3 mm 열린 경우의 최대 압력은 0.63 MPa 로 1.6% 증가하였다. 이 결과를 바탕으로 액화수소 펌프의 상세 설계에 활용할 경우, 좀 더 효율적인 펌프의 설계가 가능할 것으로 판단된다.

• Structural Engineering and Mechanics
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• 제85권1호
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• pp.105-118
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• 2023

The present work is an attempt to develop a simple and accurate finite element formulation for the assessment of thermal shock/thermally induced vibrations in pretwisted and tapered functionally graded material thin (FGM) blades obtained from Voigt and local representative volume elements (LRVE) homogenization models, based on neutral surface approach. The neutral surface of the FGM blade does not coincide with its mid-surface. A finite element model (FEM) is developed using first-order shear deformation theory (FSDT) and the FGM turbine blade is modelled according to the shallow shell theory. The top and the bottom layers of the FGM blade are made of pure ceramic and pure metal, respectively and temperature-dependent material properties are functionally graded in the thickness direction, the position of the neutral surface also depends on the temperature. The material properties are estimated according to two different homogenization models viz., Voigt or LRVE. The top layer of the FGM blade is subjected to high temperature and the bottom surface is either thermally insulated or kept at room temperature. The solution of the nonlinear profile of the temperature in the thickness direction is obtained from the Fourier law of heat conduction in the unsteady state. The results obtained from the present FEM are compared with the benchmark examples. Next, the effect of angle of twist, intensity of thermal shock, variable chord and span and volume fraction index on the transient response due to thermal shock obtained from the two homogenization models viz., Voigt and LRVE scheme is investigated. It is shown that there can be a significant difference in the transient response calculated by the two homogenization models for a particular set of material and geometric parameters.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 추계학술대회 논문집 전기설비전문위원
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• pp.37-39
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• 2004

To restrain abnormal voltage and effective operation in protect system, some of customer in Korea earth their own transformer in 154kV power system. The above ground system has some problems if ground fault occurs in other related area such as ground relay errors, under count register in two element register system. There for most huge customers opens the ground neutral and it causes errors in insulate and protection coordination and register system. In this paper presents the solution for above system.