• Steel and Composite Structures
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• 제36권1호
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• pp.31-45
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• 2020

The purpose of this study is to develop an effective iterative two-stage method (ITSM) for structural damage identification of offshore platform structures. In each iteration, a new damage index, Modal Energy-Based Damage Index (MEBI), is proposed to help effectively locate the potential damage elements in the first stage. Then, in the second stage, the beetle antenna search (BAS) algorithm is used to estimate the damage severity of these elements. Compared with the well-known particle swarm optimization (PSO) algorithm and genetic algorithm (GA), this algorithm has lower computational cost. A modal energy based objective function for the optimization process is proposed. Using numerical and experimental data, the efficiency and accuracy of the ITSM are studied. The effects of measurement noise and spatial incompleteness of mode shape are both considered. All the obtained results show that under these influences, the ITSM can accurately identify the true location and severity of damage. The results also show that the objective function based on modal energy is most suitable for the ITSM compared with that based on flexibility and weighted natural frequency-mode shape.

• Structural Engineering and Mechanics
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• 제35권4호
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• pp.387-407
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• 2010

In this paper, using perturbation and Galerkin method, the response of a resonant viscoelastic microbeam to an electric actuation is obtained. The microbeam is under axial load and electrical load. It is assumed that midplane is stretched, when the beam is deflected. The equation of motion is derived using the Newton's second law. The viscoelastic model is taken to be the Kelvin-Voigt model. In the first section, the static deflection is obtained using the Galerkin method. Exact linear symmetric mode shape of a straight beam and its deflection function under constant transverse load are used as admissible functions. So, an analytical expression that describes the static deflection at all points is obtained. Comparing the result with previous research show that using deflection function as admissible function decreases the computation errors and previous calculations volume. In the second section, the response of a microbeam resonator system under primary and secondary resonance excitation has been obtained by analytical multiple scale perturbation method combined with the Galerkin method. It is shown, that a small amount of viscoelastic damping has an important effect and causes to decrease the maximum amplitude of response, and to shift the resonance frequency. Also, it shown, that an increase of the DC voltage, ratio of the air gap to the microbeam thickness, tensile axial load, would increase the effect of viscoelastic damping, and an increase of the compressive axial load would decrease the effect of viscoelastic damping.

• Structural Engineering and Mechanics
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• 제34권6호
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• pp.719-738
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• 2010

The aim of this paper concerns with the nonlinear analysis of cable-stayed bridges including the vibration effect of cable stays. Two models for the cable stay system are built up in the study. One is the OECS (one element cable system) model in which one single element per cable stay is used and the other is MECS (multi-elements cable system) model, where multi-elements per cable stay are used. A finite element computation procedure has been set up for the nonlinear analysis of such kind of structures. For shape finding of the cable-stayed bridge with MECS model, an efficient computation procedure is presented by using the two-loop iteration method (equilibrium iteration and shape iteration) with help of the catenary function method to discretize each single cable stay. After the convergent initial shape of the bridge is found, further analysis can then be performed. The structural behaviors of cable-stayed bridges influenced by the cable lateral motion will be examined here detailedly, such as the static deflection, the natural frequencies and modes, and the dynamic responses induced by seismic loading. The results show that the MECS model offers the real shape of cable stays in the initial shape, and all the natural frequencies and modes of the bridge including global modes and local modes. The global mode of the bridge consists of coupled girder, tower and cable stays motion and is a coupled mode, while the local mode exhibits only the motion of cable stays and is uncoupled with girder and tower. The OECS model can only offers global mode of tower and girder without any motion of cable stays, because each cable stay is represented by a single straight cable (or truss) element. In the nonlinear seismic analysis, only the MECS model can offer the lateral displacement response of cable stays and the axial force variation in cable stays. The responses of towers and girders of the bridge determined by both OECS- and MECS-models have no great difference.

• 한국기계가공학회지
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• 제9권3호
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• pp.28-34
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• 2010

The suggested coupled system was analyzed using FRF and mode analysis. The eigen-mode of FRF analysis is consistent with that of conventional FFT in spectrum. Also, three numerical responses of second order system, which are coupled, was obtained using the Runge-Kutta Gill method. The displacement, velocity and acceleration response were calculated for the numerical analysis of coupled system and the displacement response was used for the calculation of FRF of this system. Using the mixed response of 1st and 2nd mode in example, the FRF was analysed for the analysis of mixed mode coupled system. Also, its mode shape was acquired by solving the eigen problem of coupled system.

• 대한기계학회논문집A
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• 제25권10호
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• pp.1671-1677
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• 2001

Cracks at mechanical fastener holes usually nucleate as elliptical comer cracks at the faying surface of the mechanical joints and grow as elliptical arc through cracks. The weight function method for elliptical arc through cracks at mechanical fastener holes has been developed and verified in the part I of this study. In part H, applying the weight function method, the effects of the amount of clearance on the mixed-mode stress intensity (actors are investigated and the change of crack shape is predicted from the analysis for various crack shapes. The stress intensity factors leer inclined crack are analyzed and critical angle at which mode I stress intensity factor becomes maximum is determined.

• 한국기계가공학회지
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• 제9권3호
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• pp.35-41
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• 2010

In this study, a mode analysis of uncoupled system was discussed using FRF. The eigen-mode range of FRF analysis is consistent with conventional FFT in spectrum. Also, the numerical response of second order uncoupled system was obtained using the Runge-Kutta Gill method. The displacement, velocity and acceleration response were calculated after numerical analysis and its response was used for the calculation of FRF for uncoupled system. Using the separated and mixed response of 1st and 2nd mode in example, its FRF was analysed for the prediction of the uncoupled systems and its mode shape was calculated by solving the eigen problem.

• Proceedings of the National Institute of Ecology of the Republic of Korea
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• 제3권1호
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• pp.32-40
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• 2022

The trade-off between morphology and physical function may vary according to ecological traits. Taking a quantitative approach, we attempted to analyze the differences in the skeletal shape of the lower body and limbs in relation to the ecological traits of four anuran species (Dryophytes japonicus, Glandirana rugosa, Pelophylax nigromaculatus, and Lithobates catesbeianus) occurring in South Korea. Body size, locomotor mode, microhabitat, trophic positions, and predator defense mechanisms were selected for the ecological traits of the anurans. The pelvis, ilium, and urostyle, which are associated with locomotor performance, were selected for the skeletal shape of the lower body. The ratio of limbs, which is related to locomotor mode and microhabitat, was confirmed by analyzing the skeletons of the forelimbs (radio-ulnar and humerus) and hindlimbs (femur and tibiofibular). Both landmark-based geometric morphometrics and traditional methods were used for skeletal shape comparison. The skeletal shape of the lower body was completely different among the four species, whereas the ratio of the limbs was only different in D. japonicus. The skeletal shape of the lower body may be related to body mass and predator defense mechanisms, whereas the ratio of the limbs was related to the locomotor mode and microhabitat. Quantifying these morphological differences among various species can help elucidate the mechanisms of behavioral and morphological changes in response to ecological effects.

• 한국자동차공학회논문집
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• 제10권3호
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• pp.227-236
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• 2002

We have performed two kinds of experimental modal analyses fur a radial tire for passenger car under free-suspension. One is the modal analysis to obtain three-dimensional modes of tire using accelerometers and the other is the one to identify cavity resonance frequency using a pressure sensor. From the first analysis, we have obtained the three-dimensional natural modes, which makes it possible to grasp the features of the modes and to classify the vibrational modes into symmetric, non-symmetric, and antisymmetric modes in a simple way by using the experimental results. From the first and the second experimental analyses we have identified the cavity resonance frequency and its three-dimensional mode shape.

• 한국통신학회논문지
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• 제17권8호
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• pp.816-822
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• 1992

본 논문에서는 중심코어가 사다리꼴분포를 갖는 segmented core 단일모드 광섬유의 전파특성을 \ulcorner=1.55um에서 영분산을 만족하는 조건하에서 상대 굴절율차비의 변화에 대해 이론적으로 조사하였다. 기존의 광섬유(삼각형 굴정율, 이중형 코어)와 곡률손실을 비교한 결과 크게 감소함을 확인하였다. 그리고 코어내의 모드필드의 집속효과가 기존의 사다리꼴 굴절율 광섬유보다 28% 더 향상되었다. 기존의 삼각형 분포를 갖는 segmented core 광섬유와 비교하여 여러 장점들을 제시 하였다.

• 대한기계학회논문집
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• 제16권5호
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• pp.849-863
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• 1992

본 연구에서는 훨씬 간단하고 직교 다항식이 아니더라도 단지 기하학적 경계 조건만을 만족하는 단순 급수함수(simplified series function)와 Rayleigh-Ritz met- hod를 이용하여 동방성 및 복합재료 직각삼각형에 대하여 수렴성을 검토하고, 경계조 건의 변화와 직교이방성 재료의 물성치 E$_{1}$, E$_{2}$, G, .nu.$_{12}$의 변화와 기 하학적 형상비 .alpha.=b/a의 변화가 무차원 고유진동수에 대해 얼마나 영향을 미치는지를 조사하고, 각 mode 별 nodal patterns과 mode shapes의 변화를 시각적으로 제시하여 보이므로써, 유사한 문제를 단순화시켜 효율적으로 해석 할수 있음을 보이고자 한다. 따라서 본 연구에서는 두개의 직각좌표가 경계에서 동시에 변하는 가장 간단하면서도 대표적인 직각 삼각형에 대해서 논하고, 앞으로 모든 임의의 형상에 대해서도 확장할 수 있는 가능성을 제시하고자 한다.다.