• Smart Structures and Systems
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• 제4권4호
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• pp.465-492
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• 2008

Proper pretest planning is a vital component of any successful vibration test on engineering structures. The most important issue in dynamic testing of many engineering structures is arriving at the number and optimal placement of sensors. The sensors must be placed on the structure in such a way that all the important dynamic behaviour of a structural system is captured during the course of the test with sufficient accuracy so that the information can be effectively utilised for structural parameter identification or health monitoring. Several optimal sensor placement (OSP) techniques are proposed in the literature and each of these methods have been evaluated with respect to a specific problem encountered in various engineering disciplines like aerospace, civil, mechanical engineering, etc. In the present work, we propose to perform a detailed characteristic evaluation of some selective popular OSP techniques with respect to their application to practical civil engineering problems. Numerical experiments carried out in the paper on various practical civil engineering structures indicate that effective independence (EFI) method is more consistent when compared to all other sensor placement techniques.

• Advances in aircraft and spacecraft science
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• 제6권6호
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• pp.463-478
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• 2019

The present work investigates the effect on the flow-induced vibrations of the lay-up sequence of composite laminated axisymmetric structures, using an hybrid approach based on a wave finite element and a transfer matrix method. The structural vibrations, under deterministic distributed pressure loads, diffuse acoustic field and turbulent boundary layer excitations, are analysed and compared. A multi-scale approach is used for the dynamic analysis of finite structures, using an elementary periodic subsystem. Different flow regimes and shell curvatures are analysed and the computational efficiency is also discussed.

• 한국공간구조학회논문집
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• 제3권2호
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• pp.101-107
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• 2003

There exists a structural problem for link structures in the unstable state. The primary characteristics of this problem are in the existence of rigid body displacements without strain, and in the possibility of the introduction of prestressing to change an unstable state into a stable state. When we make local linearized incremental equations in order to obtain knowledge about these unstable structures, the determinant of the coefficient matrices is zero, so that we face a numerically unstable situation. This is similar to the situation in the stability problem. To avoid such a difficult situation, in this paper a simple and straightforward method was presented by means of the generalized inverse for the numerical analysis of stability problem.

• Smart Structures and Systems
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• 제17권2호
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• pp.195-208
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• 2016

Seismic isolation systems are essentially designed to preserve structural safety, prevent occupants injury and properties damage. An active saturated LMI-based control design is proposed to attenuate seismic disturbances in base-isolated structures under saturation actuators. Using a mathematical model of an eight-storied building structure, an active control algorithm is designed. Performance evaluation of the controller is carried out in a simplified model version of a benchmark building system, which is recognized as a state-of-the-art model for numerical experiments of structures under seismic perturbations. Experimental results show that the proposed algorithm is robust with respect to model and seismic perturbations. Finally, the performance indices show that the proposed controller behaves satisfactorily and with a reasonable control effort.

• Smart Structures and Systems
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• 제13권2호
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• pp.257-280
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• 2014

In this paper, a novel PARAllel FACtor (PARAFAC) decomposition based Blind Source Separation (BSS) algorithm is proposed for modal identification of structures equipped with tuned mass dampers. Tuned mass dampers (TMDs) are extremely effective vibration absorbers in tall flexible structures, but prone to get de-tuned due to accidental changes in structural properties, alteration in operating conditions, and incorrect design forecasts. Presence of closely spaced modes in structures coupled with TMDs renders output-only modal identification difficult. Over the last decade, second-order BSS algorithms have shown significant promise in the area of ambient modal identification. These methods employ joint diagonalization of covariance matrices of measurements to estimate the mixing matrix (mode shape coefficients) and sources (modal responses). Recently, PARAFAC BSS model has evolved as a powerful multi-linear algebra tool for decomposing an $n^{th}$ order tensor into a number of rank-1 tensors. This method is utilized in the context of modal identification in the present study. Covariance matrices of measurements at several lags are used to form a $3^{rd}$ order tensor and then PARAFAC decomposition is employed to obtain the desired number of components, comprising of modal responses and the mixing matrix. The strong uniqueness properties of PARAFAC models enable direct source separation with fine spectral resolution even in cases where the number of sensor observations is less compared to the number of target modes, i.e., the underdetermined case. This capability is exploited to separate closely spaced modes of the TMDs using partial measurements, and subsequently to estimate modal parameters. The proposed method is validated using extensive numerical studies comprising of multi-degree-of-freedom simulation models equipped with TMDs, as well as with an experimental set-up.

• 한국공간구조학회논문집
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• 제3권1호
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• pp.87-97
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• 2003

The structural system that discreterized from continuous shells is frequently used to make a large space structures. As well these structures show the unstable phenomena when a load level over the limit load, and snap-through and bifurcation are most well known of it. For the collapse mechanism, rise-span ratio, element stiffness and load mode are main factor, which it give an effect to unstable behavior. In our real situation, most structures have semi-rigid joint that has middle characteristic between pin and rigid joint. So the knowledge of semi-rigid joint is very important problem of stable large space structure. And the instability phenemena of framed space structures show a strong non-linearity and very sensitive behavior according to the joint rigidity For this reason In this study, we are investigating to unstable problem of framed structure with semi-rigidity and to grasp the nonlinear instability behavior that make the fundamental collapse mechanism of the large space frame structures with semi-rigid joint, by proposed the numerical analysis method. Using the incremental stiffness matrix in chapter 2, we study instability of space structures.

• Corrosion Science and Technology
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• 제8권2호
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• pp.81-88
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• 2009

Chloride induced corrosion of steel reinforcement inside concrete is a major concern for concrete structures exposed to a marine environment. It is well known that transport of chloride ions in concrete occurs mainly through ionic/molecular diffusion, as a gradient of chloride concentration in the concrete pore solution is set. In the process of chloride transport, a portion of chlorides are bound in cement matrix then to be removed in the pore solution, and thus only the rest of chlorides which are not bound (i.e. free chlorides) leads the ingress of chlorides. However, since the measurement of free/bound chloride content is much susceptible to environmental conditions, chloride profiles expressed in total chlorides are evaluated to use in many studies In this study, the capacity of chloride binding in cement matrix was monitored for 150 days and then quantified using the Langmuir isotherm to determine the portions of free chlorides and bound chlorides at given total chlorides and the redistribution of free chlorides. Then, the diffusion of chloride ion in concrete was modeled by considering the binding capacity for the prediction of chloride profiles with the redistribution. The predicted chloride profiles were compared to those obtained from conventional model. It was found that the prediction of chloride profiles obtained by the model has shown slower diffusion than those by the conventional ones. This reflects that the prediction by total chloride may overestimate the ingress of chlorides by neglecting the redistribution of free chlorides caused by the binding capacity of cement matrix. From the evaluation, it is also shown that the service life prediction using the free chloride redistribution model needs different expression for the chloride threshold level which is expressed by the total chlorides in the conventional diffusion model.

• 항공우주산업기술동향
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• 제7권2호
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• pp.76-84
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• 2009

본 논문에서는 우주비행체에 사용하는 세라믹 복합재료의 기술개발에 대한 외국의 현황을 검토하였다. 우주선진국에서는 세라믹 복합재료의 경량 및 우수한 고온 특성을 이용하기 위해 최첨단 엔진구조물에 적용하여 우주비행체의 성능을 향상시키기 위하여 많이 사용해왔다. 특히 내열성, 내산화성 그리고 고온에서의 높은 강도가 요구되는 우주비행체에 적합하여, 로켓엔진챔버, 노즐, 태양판, 레이더안테나, 우주반사경 구조물, 초음속비행체 선단부, 재진입비행체의 노즈팁, 그리고 우주비행체의 방열판등에 사용하고 있다. 이러한 부품을 제작하기 위한 공정기술과 현재의 응용사례를 제시되어 향후 국내의 우주개발사업에 적용될 수 있도록 하였다.

• 대한토목학회논문집
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• 제3권2호
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• pp.137-144
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• 1983

고층건물에서의 전단벽(剪斷壁)은 횡하중을 지지(支持)하기 위해서 설치되는 구조물이다. 이 전단벽(剪斷壁)의 단면의 형태는 여러 가지 형태가 있을 수 있는데 개방단면을 갖게 되는 경우 이 부재는 비틀림에 약하기 때문에 이 점이 문제가 된다. 특히 그 구조물이 thin walled member인 경우는 더욱 그러하다. 최근에는 건물이 점점 고층화됨에 따라 이 문제는 더욱더 중요(重要)시 되어 보다 정확한 지식이 요구(要求)되고 있다. 본 논문(論文)에서는 고층건물에 설치되는 에리베이터 츄브가 전단벽 역할을 하는 경우로 단면의 형태는 channel형이고, 각 층마다 중방(中枋)(connecting beam)에 의해서 개방단면의 일부가 닫혀있게 되는 경우의 문제를 택하였다. 이를 해석(解析)하는데 복잡한 계산과 많은 계산량을 줄이고 적용에 대한 융통성을 부여하기 위해서 discrete 방법(方法)과 transfer matrix method을 사용(使用)하였다. 중방(中枋)의 영향을 고려함에 있어서는 중방(中枋)의 강도가 클 때나 적을 때나 합리적(合理的)으로 사용할 수 있는 식(式)을 적용하였다. 특히 이 방법(方法)은 불규칙한 변단면에도 쉽게 적용할 수 있을뿐만 아니라 여러 가지 하중조건에 대한 해를 일일이 구할 필요가 없으며, 형성되는 transfer matrix의 크기가 $4{\times}4$ 밖에 안되므로 쉽게 구할 수 있다.

• 센서학회지
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• 제7권2호
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• pp.97-102
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• 1998

PPV(poly(p-phenylenevinylene))를 발광체로 이용한 유기 박막 EL 소자를 다양한 구조와 조건으로 제작하였으며, 그 전기-광학적 특성을 평가하였다. 제작된 EL 소자는 단층구조(ITO(indium tin oxide)PPV/Mg), 이층구조 (ITO/PVK(poly(N-vinylcarbazole))/PPV)Mg와 ITO/PPV/Polymer matrix+PBD/Mg) 그리고 삼층구조 (ITO/PVK/PPV/PS(polystyrene)+PBD(butyl-2-(4-biphenyl)-5-(4-tert-butylphenyl-1,3,4-oxadiazole))/Mg)를 가지며, 그들의 전기광학적 특성을 상호 비교하였다. 이층구조(ITO/PPV)Polymer matrix+PBD/Mg)에서는 PMMA (poly(methyl methacrylate)), PC(polycarbonate) PS 와 MCH(side chain liquid crystalline homopolymer)를 고분자 메트릭스로 사용하였으며, 특히, PS 고분자 메트 릭스를 전자수송층으로 사용하는 경우에 전자수송제인 PBD의 농도에 따른 발광휘도 특성을 구하였다. 제작된 소자의 인가전압에 따른 전류, 휘도특성을 분석한 결과 터널링효과를 나타내었고 안정된 발광특성을 가진다는 것을 알 수 있었다.