• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2000년도 추계학술대회 논문집
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• pp.53-56
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• 2000

This paper discusses the horizontally rotaling wind power generator. Quasi static analysis are applied to performance. Translational velocity. which varies on the distance from the rotating wind power generator is effective in speed. In high rotation. the reverse torque reduces the total effective troque. It is recommended to giver efforts to redutorque for the acceptavle performance of the horizontallv rogatting tvpe generator.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.768-771
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• 2002

A method to derive the constitutive relations of a piezoelectric bender actuator is developed here. The constitutive relations are derived from the geometry, material properties of the actuator. The very complicated constitutive relations can be easily calculated by use of symbolic function in Mathematica. The developed program can calculate the constitutive relations for the unimorph bender made by attaching a short piezoelectric beam on a longer metal beam. The program can also calculate the constitutive relations of a piezoelectric bender with spring at its end.

• 전산구조공학
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• 제7권3호
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• pp.167-176
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• 1994

균열전파 현상은 항상 형상이 변화하는 대표적인 문제중의 하나이다. 본 연구는 준-정적 균열전파 현상을 해석하기 위하여 들로네이 특성을 이용한 국지 요소재편 알고리즘을 제시하였다. 이 알고리즘은 요소 재편성과 세분화를 모두 수행할 수 있도록 준비되었다. 적용예로 M 적분법을 사용하여 주로 혼합 모우드로 균열이 전파되는 스폴링 현상을 해석하였다.

• Nuclear Engineering and Technology
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• 제50권6호
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• pp.971-980
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• 2018

Using the concept of quasi-static decomposition and using three-noded isoparametric locking-free element, this article presents a formulation of the finite element method for Timoshenko beam subjected to spatially different time-dependent motions at supports. To verify the validity of the formulation, three fixed-hinged beams excited by the real seismic motions are examined; one is a slender beam, another is a stocky one, and the other is an intermediate one. The numerical results of time histories of motions of the three beams are compared with corresponding analytical solutions. The internal loads such as bending moment and shearing force at a specific time are also compared with analytic solutions. These comparisons show good agreements. The comparisons between static components of the internal loads and the corresponding total internal loads show that the static components predominate in the stocky beam, whereas the dynamic components predominate in the slender one. Thus, the total internal loads of the stocky beam, which is governed by static components, can be predicted simply by static analysis. Careful numerical experiments indicate that the fundamental frequency of a beam can be used as a parameter identifying such a stocky beam.

• 한국구조물진단유지관리공학회 논문집
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• 제9권2호
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• pp.129-136
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• 2005

교량의 안전진단 과정에서 안전성 평가를 위해 전면교통통제 하에 차량재하시험이 일반적으로 실시된다. 교통통제의 단점을 개선시킨 최근에 제안된 의사정적재하시험에서는 계측된 시간이력 데이터 중 자유진동 부분을 퓨리에변환시켜 고유진동수를 구한다. 이렇게 구해진 고유진동수에는 분석기법에 따른 오차가 포함되며, 자유진동 데이터의 획득에도 다소 애로사항이 따른다. 이 연구에서는 Morlet wavelet를 모웨이블렛으로 하는 웨이블렛변환을 의사정적재하시험으로 계측한 데이터에 적용하여 구한 고유진동수와 감쇠율이 신뢰성을 가지며, 이 분석기법이 의사정적재하시험에 의한 차량재하시험의 자료 분석에 적용 가능하고 타당성이 있음을 보인다.

• 한국전산구조공학회논문집
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• 제31권2호
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• pp.105-114
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• 2018

본 연구에서 페리다이나믹 이론 모델을 이용하여 준정적하중과 동적 하중, 균열전파와 분기균열 패턴 그리고 등방성재료, 직교 이방성 재료의 균열 진전 해석 등 다양한 조건을 고려한 전산 시뮬레이션을 수행하여 그 적합성을 검토하였다. 초기 균열은 없지만 중심에 홀이 있는 등방성 재료, 초기 균열이 존재하는 등방성 및 이방성 재료에 대한 전산 시뮬레이션이 수행되었다. 조정 동적 완화 기법이 사용되어 준정적 하중을 모사하였고, 이방성 재료 해석에서는 고전 연속체 역학과 페리다이나믹의 변형률 에너지를 고려한 균질화 방법이 사용되었다. 균열 전파와 분기 균열이 성공적으로 확인되었으며 파괴 거동의 시작과 그 방향 역시 페리다이나믹 이론으로 확인되었다. 페리다이나믹을 균질화 방법을 사용하여 비교적 복잡한 이방성 재료에 적용한 경우 역시 실험 결과 값과 비교하여 검증하였다.

• 대한금속재료학회지
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• 제48권1호
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• pp.8-18
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• 2010

This study aimed at investigating quasi-static and dynamic torsional deformation behavior of three API X70 and X80 linepipe steels. Quasi-static and dynamic torsional tests were conducted on these steels. having different grain sizes and volume fractions of acicular ferrite and polygonal ferrite, using a torsional Kolsky bar. The test data were then compared via microstructures and adiabatic shear band formation,. The dynamic torsional test results indicated that the steels rolled in the single phase region had higher maximum shear stress than the steel rolled in the two phase region, because the microstructures of the steel rolled in the single phase region were composed mainly of acicular ferrites. In the X80 steel rolled in the single phase region, the increased dynamic torsional properties could be explained by a decrease in the overall effective grain size due to the presence of acicular ferrite having smaller effective grain size. The possibility of adiabatic shear band formation was analyzed from the energy required for void initiation and variation in effective grain size.

• Structural Engineering and Mechanics
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• 제81권4호
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• pp.411-428
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• 2022

This paper presents the Campbell diagram analysis of the rotordynamic system using the full order model (FOM) and the reduced order model (ROM) techniques to determine the critical speeds, identify the stability and reduce the computational time. Due to the spin-speed-dependent matrices (e.g., centrifugal stiffening matrix), several model order reduction (MOR) techniques may be considered, such as the modal superposition (MS) method and the Krylov subspace-based MOR techniques (e.g., Ritz vector (RV), quasi-static Ritz vector (QSRV), multifrequency quasi-static Ritz vector (MQSRV), multifrequency/ multi-spin-speed quasi-static Ritz vector (MMQSRV) and the combined Ritz vector & modal superposition (RV+MS) methods). The proposed MMQSRV method in this study is extended from the MQSRV method by incorporating the rotational-speed-dependent stiffness matrices into the Krylov subspace during the MOR process. Thus, the objective of this note is to respond to the question of whether to use the MS method or the Krylov subspace-based MOR technique in establishing the Campbell diagram of the shaft-disc-blade assembly systems in three-dimensional (3D) finite element analysis (FEA). The Campbell diagrams produced by the FOM and various MOR methods are presented and discussed thoroughly by computing the norm of relative errors (ER). It is found that the RV and the MS methods are dominant at low and high rotating speeds, respectively. More precisely, as the spinning velocity becomes large, the calculated ER produced by the RV method is significantly increased; in contrast, the ER produced by the MS method is smaller and more consistent. From a computational point of view, the MORs have substantially reduced the time computing considerably compared to the FOM. Additionally, the verification of the 3D FE rotordynamic model is also provided and found to be in close agreement with the existing solutions.

• 소성∙가공
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• 제16권5호통권95호
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• pp.348-353
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• 2007

The propagation of a macro-scale crack and the accompanying transformation zone around it was visualized in an Y-TZP ceramic using a mechano-luminescence (ML) technique. The technique allows realistic fractures that take place catastrophically in actual applications to be realistically stimulated. Unlike conventional quasi-static R-curves, the ML technique on a relatively fast time frame permitted a so-called quasi-dynamic R-curve in the crack speed range from 50 to 140 m/sec. to be measured. Effective toughening then commenced and the applied stress intensity factor increased to 27 $MPa{\sqrt{m}}$. The transformation zone height obtained from the ML observations was in good agreement with that predicted by the Marshall model, and coincided with previously observed results for quasi-static conditions by Raman spectorscopy and x-ray analysis.

• Smart Structures and Systems
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• 제26권1호
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• pp.77-87
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• 2020

By employing a quasi-3D plate formulation, the present research studies static stability of magneto-electro-thermo-elastic functional grading (METE-FG) nano-sized plates. Accordingly, influences of shear deformations as well as thickness stretching have been incorporated. The gradation of piezo-magnetic and elastic properties of the nano-sized plate have been described based on power-law functions. The size-dependent formulation for the nano-sized plate is provided in the context of nonlocal elasticity theory. The governing equations are established with the usage of Hamilton's rule and then analytically solved for diverse magnetic-electric intensities. Obtained findings demonstrate that buckling behavior of considered nanoplate relies on the variation of material exponent, electro-magnetic field, nonlocal coefficient and boundary conditions.