• 대한조선학회지
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• 제23권3호
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• pp.39-44
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• 1986

The basic BFGS procedure for the nonlinear finite element analysis is reviewed. Through a simple numerical example, promising characteristics of the method evaluated discussed. Based on the discussion of computational performance, a modified BFGS algorithm with substructuring is derived and proposed for the quasi-static analysis of large-scale nonlinear structures.

• 연구논문집
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• 통권27호
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• pp.57-73
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• 1997

The bogie between the track and the railway vehicle body, is one of the most important component in railroad vehicle. Its effects on the safety of both passengers and vehicle itself, and on the overall performance of the vehicle such as riding quality, noise and vibration are critical. The bogie is mainly consisted of the bogie frame, suspensions, wheels and axles, braking system, and transmission system. The complex shapes of the bogie frame and the complicate loading condition (both static and dynamic) induced in real operation make it difficult to design the bogie frame fulfilling all the requirements. The complicated loads applied to the bogie frame are i) static load due to the weight of the vehicle and passengers, ii) quasi-static load due to the rolling in curves iii) dynamic load due to the relative motion between the track, bogie, and vehicle body. In designing the real bogie frame, fatigue analysis based on the above complicated loading conditions is a must. In this study, stress analysis of the bogie frame has been performed for the various loading conditions according to the UIC Code 6 15-4. Magnitudes of the stress amplitude and mean stress were estimated based on the stress analysis results to simulate the operating loads encountered in service. Fatigue strength of the bogie frame was evaluated by using the constant life diagram of the material. 3-D surface modelling, finite element meshing, and finite element analysis were performed by Pro-Engineer, MSC/PATRAN, and MSC/NASTRAN, respectively.

• 한국음향학회지
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• 제22권6호
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• pp.512-518
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• 2003

본 논문에서는 차량시스템의 진동효과를 고려하는 내구평가를 위한 공진내구해석이 수행된다. 공진내구해석을 수행하는데 있어서 주파수응답과 주파수영역의 동하중이 사용된다. 다물체 동역학해석, 유한요소해석 및 피로수명예측기법이 가상내구 평가를 위해 적용된다. 주파수응답과 동하중이력을 얻기 위해 차량 다물체 모델을 이용하여 전형적인 파트홀과 벨지안로를 통과하는 컴퓨터 시뮬레이션을 수행한다. 공진내구해석기법을 사용하여 승용차의 후방 현가장치에 대한 내구평가를 수행하고 그 결과를 준정적내구해석결과와 비교한다. 본 연구를 통하여 차량 시스템의 공진주파수를 고려한 피로수명을 초기설계 단계에서 효과적으로 평가할 수 있다는 것을 알 수 있다.

• Wind and Structures
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• 제8권6호
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• pp.443-454
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• 2005

Wind loading is very important, even dominant in some cases, to large-span single-layer reticulated shells. At present, usually equivalent static methods based on quasi-steady assumption, as the same as the wind-resistant design of low-rise buildings, are used in the structural design. However, it is not easy to estimate a suitable equivalent static wind load so that the effects of fluctuating component of wind on the structural behaviors, especially on structural stability, can be well considered. In this paper, the effects of fluctuating component of wind load on the stability of a single-layer reticulated spherical shell model are investigated based on wind pressure distribution measured simultaneously in the wind tunnel. Several methods used to estimate the equivalent static wind load distribution for equivalent static wind-resistant design are reviewed. A new simple method from the stability point of view is presented to estimate the most unfavorable wind load distribution considering the effects of fluctuating component on the stability of shells. Finally, with comparisive analyses using different methods, the efficiency of the presented method for wind-resistant analysis of single-layer reticulated shells is established.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 추계학술대회
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• pp.390-395
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• 2003

Moving flexible structures such as transfer systems in press machine, crane, working table of machine tools have vibration problems because of starting, feeding and stopping. An analysis method is suggested and experimentally studied in order to solve a vibration problem of a moving flexible structure. In this method, the concepts of substructure synthesis method and semi-static displacement including rigid body mode were used. Total deformation of a structure was assumed to be composed of quasi-static and dynamic components. Experimental results from an elementary model of a transfer feeder showed good agreements with computational results.

• 대한기계학회논문집A
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• 제39권10호
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• pp.1039-1044
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• 2015

차량의 개발단계에서 내구성 평가는 많은 시간과 비용이 소요된다. 최근 완성차 업체들은 자사만의 내구성 평가방법을 개발하고 수정 보완하는데 많은 노력을 기울이고 있다. 본 연구는 토션빔 액슬의 내구성 평가를 위한 통합 CAE 기법을 개발함에 있어 세계적인 자동차 업체의 정형화된 CAE 기법과의 비교를 통해 경제성을 평가하고 실험적 방법을 통해 얻은 데이터와의 비교를 통해 신뢰성을 확보하는 것을 목표로 하였다. 이를 위해 현재까지 널리 사용되어 온 준정적 내구해석의 과정 및 결과에서 보완점과 문제점을 분석하였고, 업계의 요구사항을 면밀히 검토하여 정규모드해석을 통해 다물체 동역학 모델을 구성하고 이를 이용한 동역학 해석을 진행한 후 그 결과를 이용하여 내구해석인 공진 내구해석 기법을 제안하였다.

• 한국철도학회논문집
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• 제8권5호
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• pp.444-453
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• 2005

The safety evaluations of railway wheelsets make use of the static fracture toughness obtained in ingot materials. The static fracture toughness of wheelset materials has been extensively studied by experiments, but the dynamic fracture toughness with respect to wheelset materials has not been studied enough yet. It is necessary to evaluate the characteristics of the fracture mechanics depending on each location for a full-scale wheelset for high-speed trains, because the load state for each location of the wheelset while running is different the contact load between the wheel and rail, cyclic stress in the wheel plate, etc. This paper deals with the fracture toughness depend on load rates. The fracture toughness depending on load rate data shows that once the downward curve from quasi-static values was reached, subsequent values showed a slow increase with respect to the impact velocity. This means that dynamic fracture toughness should be considered in the design code of the wheelset material.

• Wind and Structures
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• 제7권6호
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• pp.359-372
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• 2004

Wind tunnel model studies were carried out to determine the wind load distribution on tributary areas near the gable-end of large, low-rise buildings with high pitch planar and curved roof shapes. Background pressure fluctuations on each tributary area are described by a series of uncorrelated modes given by the eigenvectors of the force covariance matrix. Analysis of eigenvalues shows that the dominant first mode contributes around 40% to the fluctuating pressures, and the eigenvector mode-shape generally follows the mean pressure distribution. The first mode contributes significantly to the fluctuating load effect, when its influence line is similar to the mode-shape. For such cases, the effective static pressure distribution closely follows the mean pressure distribution on the tributary area, and the quasi-static method would provide a good estimate of peak load effects.

• 한국자동차공학회논문집
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• 제9권4호
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• pp.148-156
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• 2001

Brake judder, one of low Sequency vibrations in brake system is determined by the excitation of Brake Torque Variation (BTV). The largest contributor to BTV is disc thickness variation. In this study, the static loads of brake torque at Suspension Mounting Points (SW) are obtained by the quasi-static analysis using DADS. The dynamic loads with frequency of BTV at SW are derived from correlation between forced vibration analysis with static loads and brake test results. And the accelerations at steering wheel were analyzed by forced vibration analysis with dynamic loads using commercial finite element program MSC/NASTRAN so that vibration characteristics of vehicle due to brake judder were investigated. Reliability of analysis results was verified through comparing the brake test results. Also, a parametric study with natural frequencies of frame, such as the 1st torsional mode and 1st bending mode, was conducted to reduce vibration amplitudes. As a result we could detect frame natural frequency conditions to improve vibration characteristics and obtained the frame model to reduce vibration amplitude.

• 대한전자공학회논문지TC
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• 제40권11호
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• pp.17-26
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• 2003

시간영역 확산을 하는 순방향 링크 OFCDM 시스템에서 고출력 증폭기의 비선형 왜곡을 경감시키고자 IFFT단 부반송파의 다중레벨 입력신호를 clipping을 한 후 MPSK(Multilevel-PSK) 신호로 전송하는 기술을 적용한다. AWGN 채널에서 고출력 증폭기의 비선형 왜곡이 고려된 경우 extended m 부호열을 사용한 clipping OFCDM 시스템이 extended m 부호열을 사용한 OFCDM 시스템에 비해 N이 8, 16명인 경우 2.2㏈ 이상 성능이 우수하였다. Quasi-static 채널에서 고출력 증폭기의 비선형 왜곡이 고려된 경우 extended m 부호열을 사용한 clipping OFCDM 시스템이 extended m 부호열을 사용한 OFCDM 시스템에 비해 N이 8, 16명인 경우는 2㏈ 이상 우수하였다.