• 한국전자파학회논문지
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• 제11권6호
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• pp.946-951
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• 2000

본 논문은 접지면에 형성된 디펙트를 갖는 전송선로 구조인 DGS의 특성 및 등가회로를 구하고 디펙트의 크기에 따른 등가 집중소자 값을 추출하였으며, DGS에 집중소자를 달아주어 그 영향을 살펴보았다. 제시된 DGS는 아령 모양의 디펙트로 아였으며, 병렬 단락 공진기에 적용하였다. 침 형태의 집중소자인 저항, 인덕터, 커패시터를 각각 달아주어 주파수 특성을 살펴보았다. 또한 실험결과 Q factor와 공진 주파수가 DGS에 달아준 외부소자에 의해 제어됨을 보였다.

• 한국입자에어로졸학회지
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• 제8권2호
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• pp.75-81
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• 2012

The strength of lumped cokes can be represented by some index numbers. Although some indexes are suggested, these indexes are not enough to enlighten fracture mechanism. To find essential mechanism, a computational way, discrete element method, is applied to the uniaxial compression test for cylindrical specimen. The cylindrical specimen is a kind of lumped particle mass with parallel bonding that will be broken when the normal stress and shear stress is over a critical value. It is revealed that the primary factors for cokes fracture are parallel spring constant, parallel bond strength, bonding radius and packing ratio the parallel bond strength and radius of the parallel combination the packing density. Especially, parallel spring constant is directly related with elastic constant and yield strength.

• 한국전산구조공학회논문집
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• 제31권6호
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• pp.381-388
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• 2018

본 논문은 고전적인 오일러-베르누이 보의 집중소성힌지 모델링을 위한 일반유한요소법을 제안한다. 이 기법에서 소성힌지는 해의 약불연속을 묘사하는 적절한 확장함수에 의해 모델링되며, 요소간의 연결성을 변화시키지 않으면서 임의의 위치에 소성힌지를 삽입하는 것이 가능하다. 대신 소성힌지는 이미 존재하는 요소에 위계적으로 자유도를 추가함으로써 형성된다. 제안된 기법의 유효성을 검증하기 위해 수치해석 예제에 대해 h-, p-확장과 같은 수렴성 해석을 수행하였다. 수렴성 해석의 결과가 제안된 기법이 소성힌지가 절점 및 요소 내의 임의의 위치에 존재하는 두 가지 경우 모두에 대하여 유한요소이론에 의한 수렴속도를 얻을 수 있음을 보여주어 기법의 정확성을 입증하였다.

• Structural Engineering and Mechanics
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• 제22권6호
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• pp.701-717
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• 2006

In the existing reports regarding free transverse vibrations of the Euler-Bernoulli beams, most of them studied a uniform beam carrying various concentrated elements (such as point masses, rotary inertias, linear springs, rotational springs, spring-mass systems, ${\ldots}$, etc.) or a stepped beam with one to three step changes in cross-sections but without any attachments. The purpose of this paper is to utilize the numerical assembly method (NAM) to determine the exact natural frequencies and mode shapes of the multiple-step Euler-Bernoulli beams carrying a number of lumped masses and rotary inertias. First, the coefficient matrices for an intermediate lumped mass (and rotary inertia), left-end support and right-end support of a multiple-step beam are derived. Next, the overall coefficient matrix for the whole vibrating system is obtained using the numerical assembly technique of the conventional finite element method (FEM). Finally, the exact natural frequencies and the associated mode shapes of the vibrating system are determined by equating the determinant of the last overall coefficient matrix to zero and substituting the corresponding values of integration constants into the associated eigenfunctions, respectively. The effects of distribution of lumped masses and rotary inertias on the dynamic characteristics of the multiple-step beam are also studied.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제20권3호
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• pp.243-259
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• 2016

The Richards equation for water movement in unsaturated soil is highly nonlinear partial differential equations which are not solvable analytically unless unrealistic and oversimplifying assumptions are made regarding the attributes, dynamics, and properties of the physical systems. Therefore, conventionally, numerical solutions are the only feasible procedures to model flow in partially saturated porous media. The standard Finite element numerical technique is usually coupled with an Euler time discretizations scheme. Except for the fully explicit forward method, any other Euler time-marching algorithm generates nonlinear algebraic equations which should be solved using iterative procedures such as Newton and Picard iterations. In this study, lumped mass and distributed mass in the frame of Picard and Newton iterative techniques were evaluated to determine the most efficient method to solve the Richards equation with finite element model. The accuracy and computational efficiency of the scheme and of the Picard and Newton models are assessed for three test problems simulating one-dimensional flow processes in unsaturated porous media. Results demonstrated that, the conventional mass distributed finite element method suffers from numerical oscillations at the wetting front, especially for very dry initial conditions. Even though small mesh sizes are applied for all the test problems, it is shown that the traditional mass-distributed scheme can still generate an incorrect response due to the highly nonlinear properties of water flow in unsaturated soil and cause numerical oscillation. On the other hand, non oscillatory solutions are obtained and non-physics solutions for these problems are evaded by using the mass-lumped finite element method.

• 한국생산제조학회지
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• 제5권2호
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• pp.29-37
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• 1996

High speed engines with high power are increasingly on demands and almost engines employ crankshafts Such problems as bending and torsional vibrations become the point at issue in crankshaft analysis and design. In this study to overcome the diffiiculty with the large amount of computation in finite element vibration analysis of a crankshaft, a reduction method based on influence coefficient and lumped parameter is presented. which reduces the computation amount effectively and can be used in vibrational analysis and design of any types of crankshafts Crank journal and pinparts are meodelled as elements with 6degrees of freedom per node. Crank web part is modelled using equivalent mass and stiffness matices . based up on lumped parameter and influence coefficient respectively to reduce total degrees of freedom considerablely. To confirm the scheme of the study the results are compared with the known data and they are coincident. Also a simple crankshaft is designed and manufactured for experiments. The calculated results using reduction method and the experimental results agree well The scheme of this study can be utilized in evaluation results agree well. The calculated result are compared with the known data and they are coincident. Also a simple crankshaft is designed and manufactured for experiments. The calculated results using reduction method and the experimental results agree well. The scheme of this study can be utilized in evaluation and development of high speed engine.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.88-93
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• 1995

The ball screw preloaded for high nigidity and accuracy increases frictional resistance, therefore, its temperature and positioning error rise. In this paper, 2 diamensional temperature distributions of a ball screw with preload are analyzed according to the rotational speeds and stop times by a finite element method. The theremal behaviors of a ball screw are measured to examine the analyzed datum. The examined results show that the trends of temperature rising and axial distributions in steady state are nearly extimate but the temperature low. The differences of temperature ate seems to be caused by not exact heat transfer coefficients. More than an hour is consumed for calculation by FEM. So the modified lumped method for the real-time estimation of the thermal distribution is proposed. The estimated temperature of a ball serw by the modified lumped method is more exactly estimated than by FEM, nd that method takes less than several millisec. Moreover it can be used to estimate heat transfer coefficients.

• 전자공학회논문지B
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• 제32B권10호
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• pp.1286-1293
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• 1995

Modified equivalent lumped element model for square spiral inductors have been derived. This model shows more accurate analysis performance than conventional models, and gives reliable design parameters. And this model is made through comparison among distributed multiple coupled line, numerical analysis and experimental data.

• Journal of Electrical Engineering and Technology
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• 제10권5호
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• pp.2040-2045
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• 2015

This paper deals with the electromagnetic and thermal analysis of high speed induction motor. The induction motor is analyzed by time-varying magnetic finite element method and its thermal analysis is carried out by using analytical lumped-circuit method. Analysis results are compared with the experiment of 29kW high speed motor prototype at 12,000rpm.

• 대한전자공학회논문지
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• 제13권6호
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• pp.12-15
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• 1976

본논문은 현재 AF주파수변역에서 90° 정위상기를 실현하고 있는 방법과는 전혀 다른 착상으로 VHF 고파수대에서 90° 정위상기를 실현하는 새로운 방법을 제시하였다. 이 90° 정위상기의 구조는 간단하며 분포정수소자인 전송선과 집중정수소자인 R.L.C로 용이하게 실현된다. This paper presents the realization method of 90° constant phase shifter in the VHF band, constructed by the entirely differens idea from the conventional method of the realization of constant phase shifter in the audio frequency range. The construction of 90° constant phase shifter is. simple and can be easily realized by using the distributed constant element, transmission line, and the lumped constant elements, R,C,L.