• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.109-117
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• 2008

In this study, a method predicting the displacement responseof structures from the measured dynamic strain signal is proposed by using a mode decomposition technique. Dynamic loadings including wind and seismic loadings could be exerted to the bridge. In order to examine the bridge stability against these dynamic loadings, the prediction of displacement response is very important to evaluate bridge stability. Because it may be not easy for the displacement response to be acquired directly on site, an indirect method to predict the displacement response is needed. Thus, as an alternative for predicting the displacement response indirectly, the conversion of the measured strain signal into the displacement response is suggested, while the measured strain signal can be obtained using fiber optic Bragg-grating (FBG) sensors. To overcome such a problem, a mode decomposition technique was used in this study. The measured strain signal is decomposed into each modal component by using the empirical mode decomposition(EMD) as one of mode decomposition techniques. Then, the decomposed strain signals on each modal component are transformed into the modal displacement components. And the corresponding mode shapes can be also estimated by using the proper orthogonal decomposition(POD) from the measured strain signal. Thus, total displacement response could be predicted from combining the modal displacement components.

• 한국지반공학회지:지반
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• 제11권3호
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• pp.69-80
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• 1995

초기간극비가 큰 연약점토의 일차원 압밀특성을 조사하기 위하여 수치해석 연구슬 실시하였다. 유한변형률 압밀지배방정식을 바탕으로 양해차분의 수치해석기법을 사용하여 점토 토립자의 자중에 의한 압밀침하량의 산정을 실시하였다.

• 한국생산제조학회지
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• 제22권1호
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• pp.50-55
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• 2013

In order to understand the biomaterial like the blood vessel of artery, there is a need to quantify the biomechanical behavior of the vessel. However, theoretical framework to describe and quantify the behaviour of blood vessel was not well established so far. For studying the biomechanical behavior of artery, Rubber-liked material which is similar to passive artery is selected since conventional theoretical interpretation is very limited to understand and predict the behavior of biomaterial. Rubber-like material is assumed to be very similar to artery and has properties of isotropy, homogeneity and is undergoing large deformation. Based on this assumption, stress developed on Rubber-like material is described by strain energy function and strain invariants which are required to understand the nonlinear elastic behavior of biomaterial. The descriptor which would be used for understanding the biomechanical behavior of artery is studied in this work.

• 비파괴검사학회지
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• 제32권6호
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• pp.669-677
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• 2012

This study presents a method to monitor cable force using wireless sensor nodes and piezoelectric sensors. The following approaches are carried out to achieve the objective. Firstly, the principle of piezoelectric materials (e.g., PZT) as strain sensors is reviewed. A cable force estimation method using dynamic features of cables measured by piezoelectric materials is presented. Secondly, the design of an automated cable force monitoring system using the data acquisition sensor-node Imote2/SHM-DAQ is described. The sensor node is originally developed by University of Illinois at Urbana-Champaign and is adopted in this study to monitor strain-induced voltage from PZT sensors. The advantages of the system are cheap, and eligible for wireless communication and automated operation. Finally, the feasibility of the proposed monitoring system is evaluated on a lab-scaled cable.

• Journal of Mechanical Science and Technology
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• 제16권3호
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• pp.310-319
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• 2002

This paper deals with the analytical modeling, and the experimental verification of the strain rate self-sensing method using a hybrid adaptive filter for a cantilevered piezoelectric beam. The piezoelectric beam consists of two laminated lead zirconium titanates (PZT) on a metal shim. A mathematical model of the beam dynamics is derived by Hamilton's principle and the accuracy of the modeling is verified through the comparison with experimental results. For the strain rate estimation of the cantilevered piezoelectric beam, a self-sensing mechanism using a hybrid adaptive filter is considered. The discrete parts of this mechanism are realized by the DS1103 DSP board manufactured by dSPACE$\^$TM/. The efficacy of this method is investigated through the comparison of experimental results with the predictions from the derived analytical model.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.49-55
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• 2008

Strip bending test has been frequently utilized to measure the mechanical properties of freestanding thin films in substitute for the micro-tensile test. However, in spite of its simplicity and reliability, strip bending test has a few problems, for example, the measurement of strain and the calculation of stress at zero strain. In this study, these problems are precisely reviewed and proved. Upon this review, strip bending tester has been developed, which uses the confocal laser displacement meter to measure the deformed configuration of the specimen and the possibility and limitation of this testing system is carefully investigated including the estimation of uncertainty of the measurement of strain. Finally, to prevent errors and to improve the accuracy of this testing system, the shape of the specimen has been carefully studied and is proposed.

• Journal of Ship and Ocean Technology
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• 제7권3호
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• pp.56-65
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• 2003

The hull monitoring systems of container ships with four long-base gages give enough information for identifying the hull girder loads such as bending and torsional moments. But such a load-identification for container ships has not been known. In this paper, a load-identification method is suggested in terms of a linear matrix equation that the measured strain vector equals to the multiplication of the transformation matrix and the desired strain component vector. The equation is proved to be mathematically complete by the property of positive-definite determinant of the transformation matrix. The method is applied to a hull stress monitoring system for 8100TED container ship during sea trial, and the estimated external loads illustrate reasonable results in comparison with the pre-estimated results. This moment decomposition concept has also been tested in real operation conditions. The typical phenomena over the Suez Canal illustrated very suitable results comparing with the physical understandings. Henceforth, one can effectively use the proposed concept to monitor the hull girder loads such as bending and torsional moments.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 봄 학술발표회 논문집
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• pp.41-48
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• 2002

The fact that nonlinearity and anisotropy of soil should be considered for the proper estimation of soil deformation has been recongnized for a long time. In this study, a new stiffness model which can reflect both nonlinearity and anisotropy is proposed. Nonlinearity is simulated by Ramberg-Osgood model and anisotropy is modeled with the cross-anisotropic elasticity. Analysis results with the developed model compared with those from analyses using linear isotropic model, linear anisotropic model, and nonlinear isotropic model. In the triaxial compression like condition, the effects of nonlinearity on the vertical strain are significant, but soil anisotropy does not affect the vertical strain. In 1-dimensional deformation condition, however, both nonlinearity and anisotropy of soil influence the final magnitude of the vertical strain. Also the increase of poisson's ratio magnifies the effect of anisotropy on the vertical strain in this condition.

• Smart Structures and Systems
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• 제12권3_4호
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• pp.381-397
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• 2013

In this paper, wireless health monitoring of stay cables using piezoelectric strain sensors and a smart skin technique is presented. For the cables, tension forces are estimated to examine their health status from vibration features with consideration of temperature effects. The following approaches are implemented to achieve the objective. Firstly, the tension force estimation utilizing the piezoelectric sensor-embedded smart skin is presented. A temperature correlation model to recalculate the tension force at a temperature of interest is designed by correlating the change in cable's dynamic features and temperature variation. Secondly, the wireless health monitoring system for stay cables is described. A piezoelectric strain sensor node and a tension force monitoring software which is embedded in the sensor are designed. Finally, the feasibility of the proposed monitoring technique is evaluated on stay cables of the Hwamyung Grand Bridge in Busan, Korea.

• 대한토목학회논문집
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• 제30권3A호
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• pp.257-264
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• 2010

일반적으로 대형구조물의 건전성평가에 있어 중요한 인자인 변위를 추정함으로써 구조물의 성능 저하 및 노후도를 판단하는 근거가 된다. 그러나 변위응답의 계측이 중요함에도 불구하고 계측 방법의 부재로 말미암아 현수교와 같은 대형구조물의 변위응답을 측정하는 방법이 용이치 않은 것이 현실이다. 본 논문에서는 변형률신호로부터 변위응답을 추정하는 방법인 모드분해기법을 제시하였다. 모드분해기법은 등가정적 변위응답과 구조물의 주요거동을 나타내는 저차모드의 변위응답을 합하여 최종변위응답을 추정하는 방법이다. 변형률신호의 계측시 전기저항식 변형률센서를 사용할 경우 전기적 노이즈 문제가 발생할 소지가 크며, 측점이 많아질수록 경제적 부담감이 커진다. 이런 문제점을 극복하기 위하여 전기적 노이즈의 영향이 없고 다중측정이 가능한 광섬유 브래그 격자 센서를 사용하였다. 현수교와 플레이트거더교의 동재하실험을 통하여 모드분해기법의 사용성을 검토하였다.