• 한국연소학회:학술대회논문집
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• 한국연소학회 1997년도 제15회 KOSCO SYMPOSIUM 논문집
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• pp.113-122
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• 1997

The conditional moment closure formulation considering the molecular and turbulent diffusion is derived. A simplified solution procedure is proposed to reduce the computational burden due to the increased dimensionality of the conditionally averaged variables. A conditionally averaged variable is expressed as a linear weighted average of the two extremes, 'no reaction' and 'equilibrium' states. The modified elliptic-type conditional moment closure formulation is implemented to simulate a two dimensional nonpremixed mixing layer reacting flow. Results show good agreement for the conditional averages of the species concentration in Bilger et al.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.1186-1190
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• 1995

This paper is focused on the formulation of explicit closed-form functions describing the performance measures of the general flexible manufacturing system (FMS)according to the strategy of material handling system(MHS). the performance measures such as the production rate, the production lead-time and the utilization rate of the general FMS are expressed, respectively, as the explicit closed-form functions of the part processing time, the service rate of the material handling system (MHS) and the number of machine tools in the FMS. For this, the gensral FMS is presented as a generalized stochastic Petri net model, then, the moment generating function (MGF) based approach is applied to obtain the steady-state probabity formulation. Based on the steady-state formulation, the explicit closed-form functions for performance measures of the probability FMS can be obtained. Finally, the analytical results are compared with the Petri net simulation results to verify the validity of the suggested method. The paper is of significance in the sense that it provides a comprehensive formula for performance measures of the FMS even to the industry engineers and academic reademic resuarchers who have no background on Markov chain analysis method or Petrinet modeling

• Steel and Composite Structures
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• 제39권5호
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• pp.599-614
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• 2021

This study deals with the Lateral-Torsional Buckling (LTB) of a mono-symmetric tapered I-beam, in which the cross-section is varying longitudinally. To obtain the buckling moment, two concentrated bending moments should be applied at the two ends of the structure. This structure is made of Functionally Graded Material (FGM). The Young's and shear modules change linearly along the longitudinal direction of the beam. It is considered that this tapered beam is laterally restrained continuously, by using torsional springs. Furthermore, two rotational bending springs are employed at the two structural ends. To achieve the buckling moment, Ritz solution method is utilized. The response of critical buckling moment of the beam is obtained by minimizing the total potential energy relation. The lateral and torsional displacement fields of the beam are interpolated by harmonic functions. These functions satisfy the boundary conditions. Two different support conditions are considered in this study. The obtained formulation is validated by solving benchmark problems. Moreover, some numerical studies are implemented to show the accuracy, efficiency and high performance of the proposed formulation.

• Structural Engineering and Mechanics
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• 제28권5호
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• pp.495-514
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• 2008

In this paper, experimental and theoretical investigations of the effect of the mean moment on the response and collapse of circular thin-walled tubes subjected to cyclic bending are discussed. To highlight the influence of the mean moment effect, three different moment ratios r (minimum moment/ maximum moment) of -1, -0.5 and 0, respectively, were experimentally investigated. It has been found that the moment-curvature loop gradually shrinks with the number of cycles, and becomes stable after a few cycles for symmetric cyclic bending (r = -1). However, the moment-curvature loop exhibits ratcheting and increases with the number of cycles for unsymmetric cyclic bending (r = -0.5 or 0). In addition, although the three groups of tested specimens had three different moment ratios, when plotted in a log-log scale, three parallel straight lines describe the relationship between the controlled moment range and the number of cycles necessary to produce buckling. Finally, the endochronic theory combined with the principle of virtual work was used to simulate the relationship among the moment, curvature and ovalization of thin-walled tubes under cyclic bending. An empirical formulation was proposed for simulating the relationship between the moment range and the number of cycles necessary to produce buckling for thin-walled tubes subjected to cyclic bending with different moment ratios. The results of the experimental investigation and the simulation are in good agreement with each other.

• 대한기계학회논문집
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• 제18권7호
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• pp.1654-1663
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• 1994

Even if the ball bearing was conservatively designed considering the dynamic capacity and the rating life, sometimes the bearing was early failed on account of the misalignment and the lubricant contaminations etc. Misalignment was generated when bearing-shaft system transmitted large power and when the bearing was inadequately mounted. It was possible to predict the fatigue life of ball bearing under the misalignment considering the motions of ball, cage and raceway, and the factors of the effect on fatigue life. Misalignment affected on ball bearing as radial and moment load and the relationships between misalignment and moment were obtained. In this paper, the analysis of the load distributions between ball and raceway, and the prediction of fatigue life of deep groove ball bearing under radial and moment loads were carried out. And, the new formulation of equivalent dynamic load considering the effects of moment load was proposed.

• 대한전기학회논문지:전력기술부문A
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• 제48권8호
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• pp.1022-1030
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• 1999

This paper is concerned with the balancing motion formulation and the control of ZMP (zero moment point) for a biped walking robot with balancing joints. The balancing equation of a biped robot can be modeled as the second order non-homogeneous differential equation, which makes it possible to plan the desired trajectories for various gaits or motions. Also, the balancing motion can be defined easily by solving the differential equation without pre-processing or heuristic procedures. The actual experiments are performed on biped walking robot system IWR-III, developed in our Automatic Control Lab. The system has the structure of three pitches in each leg, and one roll and one prismatic type in balancing joints. The walking simulations and the experimental results on IWR-III are shown using the proposed formula and control algorithm.

• Structural Engineering and Mechanics
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• 제69권4호
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• pp.427-437
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• 2019

In this study, an alternative solution procedure presented by using variational methods for analysis of shear deformable functionally graded material (FGM) beams with mixed formulation. By using the advantages of $G{\hat{a}}teaux$ differential approaches, a refined complex general functional and boundary conditions which comprises seven independent variables such as displacement, rotation, bending moment and higher-order bending moment, shear force and higher-order shear force, is derived for general thick-thin FGM beams via shear deformation beam theories. The mixed-finite element method (FEM) is employed to obtain a beam element which have a 2-nodes and total fourteen degrees-of-freedoms. A computer program is written to execute the analyses for the present study. The numerical results of analyses obtained for different boundary conditions are presented and compared with results available in the literature.

• 대한기계학회논문집A
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• 제35권2호
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• pp.163-168
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• 2011

설계단계에서 시스템의 불확실성을 반영하려는 노력이 다양하게 이루어지고 있으며, 강건 최적설계 혹은 신뢰도 기반 최적설계는 이에 대한 대표적인 설계 방법론이다. 실제 문제에 이러한 방법론을 적용하기 위해서는 성능함수의 통계적 모멘트와 손상확률에 대한 정확하고 효율적인 추정 방법이 필요하고, 더불어 최적화를 위한 방향탐색과정에서 요구되는 민감도 해석의 정확성 및 효율성이 확보되어야 한다. 본 연구에서는 함수근사모멘트 방법을 기존에 유도된 적분 형태의 민감도 해석 식에 적용하여 그 민감도 해석 결과의 정확성을 확인하고, 이를 대표적인 신뢰도 기반 최적설계 문제에 적용하고자 한다. 민감도 해석 결과 및 신뢰도 기반 최적설계 결과를 타방법의 결과와 비교하여 함수근사모멘트 방법의 타당성을 입증하고자 한다. 활용된 적분 형태의 민감도 해석은 손상확률 혹은 통계적 모멘트가 계산된 경우 추가적인 함수 계산 없이 민감도를 얻을 수 있는 효율적인 방법이다.

• Steel and Composite Structures
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• 제24권5호
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• pp.523-536
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• 2017

A layerwise (LW) formulation based on the Galerkin method is presented to investigate the three-dimensional stress state in long sandwich plate which is subjected to tension force and pure bending moment. Based on the Galerkin method and the LW discretization approach, the equilibrium equations of elasticity for the long plate are written in the weak form and discretized through the thickness of the plate. The discretized equations are written in terms of displacement components of the numerical layers. The governing equations of the plate are solved analytically for the free edge boundary conditions. The distribution of stress state especially the 3D stress state in the vicinity of the edges of the sandwich plate which is subjected to tension and pure bending is studied. In order to increase the accuracy, the out of plane stresses are obtained by integrating the equilibrium equations of elasticity. The convergence and accuracy of the predictions are studied and various numerical results are presented for distribution of the in-plane and out of plane stresses in symmetric and un-symmetric sandwich plates.

• Structural Engineering and Mechanics
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• 제15권2호
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• pp.199-223
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• 2003

The formulation of a non-linear shear deformable shell element is presented for the solution of stability problems of stiffened plates and shells. The formulation of the geometrical stiffness presented here is exactly defined on the midsurface and is efficient for analyzing stability problems of thick plates and shells by incorporating bending moment and transverse shear resultant force. As a result of the explicit integration of the tangent stiffness matrix, this formulation is computationally very efficient in incremental nonlinear analysis. The element is free of both membrane and shear locking behaviour by using the assumed strain method such that the element performs very well in the thin shells. By using six degrees of freedom per node, the present element can model stiffened plate and shell structures. The formulation includes large displacement effects and elasto-plastic material behaviour. The material is assumed to be isotropic and elasto-plastic obeying Von Mises's yield condition and its associated flow rules. The results showed good agreement with references and computational efficiency.