• Steel and Composite Structures
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• 제23권6호
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• pp.691-714
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• 2017

Rotating fluid induced vibration and instability of embedded piezoelectric nano-composite separators subjected to magnetic and electric fields is the main contribution of present work. The separator is modeled with cylindrical shell element and the structural damping effects are considered by Kelvin-Voigt model. Single-walled carbon nanotubes (SWCNTs) are used as reinforcement and effective material properties are obtained by mixture rule. The perturbation velocity potential in conjunction with the linearized Bernoulli formula is used for describing the rotating fluid motion. The orthotropic surrounding elastic medium is considered by spring, damper and shear constants. The governing equations are derived on the bases of classical shell theory (CST), first order shear deformation theory (FSDT) and sinusoidal shear deformation theory (SSDT). The nonlinear frequency and critical angular fluid velocity are calculated by differential quadrature method (DQM). The detailed parametric study is conducted, focusing on the combined effects of the external voltage, magnetic field, visco-Pasternak foundation, structural damping and volume percent of SWCNTs on the stability of structure. The numerical results are validated with other published works as well as comparing results obtained by three theories. Numerical results indicate that with increasing volume fraction of SWCNTs, the frequency and critical angular fluid velocity are increased.

• Smart Structures and Systems
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• 제5권6호
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• pp.613-632
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• 2009

The present paper is concerned with the design of a proper patch actuator network in order to track a desired displacement of the sidewalls of a one-storey frame structure; both, for the static and the dynamic case. Weights for each patch of the actuator network found in our previous work were based on beam theory; in the present paper a refinement of these weights by modeling the sidewalls of the frame structure as thin plates is presented. For the sake of calculating the refined weights approximate solutions of the plate equations are calculated by an extended Galerkin method. The solutions based on the analytical plate model are compared with three-dimensional Finite Element results computed in the commercially available code ANSYS. The patch actuator network is put into practice by means of four piezoelectric patches attached to each of the two sidewalls of the frame structures, to which electric voltages proportional to the analytically refined patch weights are applied. Analytical and numerical results coincide very well over a broad frequency range.

• Steel and Composite Structures
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• 제31권4호
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• pp.341-359
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• 2019

Non-monolithic concrete structural connections are commonly used both in new constructions and retrofitted structures where anchors are used for connections. Often, flaws are present in anchor system due to poor workmanship and deterioration; and methods available to check the quality of the composite system afterward are very limited. In case of presence of flaw, load transfer mechanism inside the anchor system is severely disturbed, and the load carrying capacity drops drastically. This raises the question of safety of the entire structural system. The present study proposes a wave propagation technique to assess the integrity of the anchor system. A chemical anchor (embedded in concrete) composite system comprising of three materials viz., steel (anchor), polymer (adhesive) and concrete (base) is considered for carrying out the wave propagation studies. Piezoelectric transducers (PZTs) affixed to the anchor head is used for actuation and the PZTs affixed to the surrounding concrete surface of the concrete-anchor system are used for sensing the propagated wave through the anchor interface to concrete. Experimentally validated finite element model is used to investigate three types of composite chemical anchor systems. Studies on the influence of geometry, material properties of the medium and their distribution, and the flaw types on the wave signals are carried out. Temporal energy of through time domain differentiation is found as a promising technique for identifying the flaws in the multi-layered composite system. The present study shows a unique procedure for monitoring of inaccessible but crucial locations of structures by using wave signals without baseline information.

• Smart Structures and Systems
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• 제28권6호
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• pp.761-777
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• 2021

This study presents a numerical investigation on the sensitivity of electromechanical (EM) impedance responses to inner damaged concrete of a prestressed anchorage zone. Firstly, the Ottosen yield criterion is selected to simulate the plasticity behavior of the concrete anchorage zone under the compressive loading. Secondly, several overloading cases are selected to analyze inner damage formations in the concrete of the anchorage zone. Using a finite element (FE) model of the anchorage zone, the relationship between applied forces and stresses is analyzed to illustrate inner plasticity regions in concrete induced by the overloading. Thirdly, EM impedance responses of surface-mounted PZT (lead-zirconate-titanate) sensors are numerically acquired before and after concrete damage occurrence in the anchorage zone. The variation of impedance responses is estimated using the RMSD (root-mean-square-deviation) damage metric to quantify the sensitivity of the signals to inner damaged concrete. Lastly, a novel PZT skin, which can measure impedance signatures in predetermined frequency ranges, is designed for the anchorage zone to sensitively monitor the EM impedance signals of the inner damaged concrete. The feasibility of the proposed method is numerically evaluated for a series of damage cases of the anchorage zone. The results reveal that the proposed impedance-based method is promising for monitoring inner damaged concrete in anchorage zones.

• 한국소음진동공학회논문집
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• 제17권7호
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• pp.617-623
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• 2007

This paper presents an active vibration control of a dynamic system using hybrid mount which consists of elastic rubber-piezostack actuator and elastic rubber-electromagnetic actuator, respectively. After identifying stiffness, damping properties of the elastic rubber, PZT actuator and electromagnetic element, a mathematical model of the hybrid mount is established. The mount model is then incorporated into the dynamic system and the governing equation of motion is obtained in a state space. A sliding mode controller is designed in order to actively attenuate the vibration of the system. Control responses such as acceleration and transmitted force of the dynamic system are experimentally evaluated and presented in time and frequency domains.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.1131-1136
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• 2007

This paper presents an active vibration control of a 1-DOF system using hybrid mount which consists of elastic rubber and PZT(piezostack) actuator and elastic rubber and electromagnetic actuator, respectively After identifying stiffness, damping properties of the elastic rubber, PZT actuator and electromagnetic element, a mathematical model of the hybrid mount is established. The mount model is then incorporated into the 1-DOF system and the governing equation of motion is obtained in a state space. A sliding mode controller is designed in order to actively attenuate the vibration of the system. Control responses such as acceleration and transmitted force of the 1-DOF system are experimentally evaluated and presented in time and frequency domains.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.228-231
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• 2000

The active vibration control of laminated composite shell has been performed with the optimized sensor/actuator system. PVDF film is used fur the material of sensor/actuator. Finite element method is utilized to model the whole structure including the piezoelectric sensor/actuator system, The distributed selective modal sensor/actuator system is established to prevent the adverse effect of spillover. In the finite element discretization process, the nine-node shell element with five nodal degrees of freedoms is used. Electrode patterns and lamination angles of sensor/actuator are optimized using genetic algorithm. Sensor is designed to minimize the observation spillover, and actuator is designed to minimize the system energy of the control modes under a given initial condition. Modal sensor/actuator profiles are optimized for the first and the second modes suppression of singly curved cantilevered composite shell structure. Discrete LQG method is used as a control law. The real time vibration control with profile optimized sensor/actuator system has been performed. Experimental result shows successful performance of the integrated structure for the active vibration control.

• 한국전산구조공학회논문집
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• 제24권5호
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• pp.553-567
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• 2011

최근 3년간 판 구조물 건전성 감시분야에서 시간반전램파(Time reversal Lamb waves)의 가능성이 주목받고 있다. 이 연구에서는 직사각형 평판에서 시간반전램파의 공간모임을 적은 연산비용으로 효과적으로 모사할 수 있는 수치기법을 제안한다. 제안된 기법에서는 파 반사에 의해 발생하는 실제 탐지자의 거울상 효과와 등가를 이루는 활성 가상탐지자를 이용하여 시간반전과정을 주파수 영역에서 정식화한다. 시간반전램파의 공간모임 모사에서 필요한 순방향 및 역방향 파 전달은 스칼라 형태의 함수로 표현한다. 제안된 방법을 웨이퍼 형태의 압전소자가 병치된 직사각형 평판에서 시간반전램파의 공간 모임 문제에 적용하고 유한요소해석 결과와 비교하여 타당성을 검증한다.

• 대한토목학회논문집
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• 제32권6A호
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• pp.379-387
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• 2012

본 연구에서는 새로운 에너지 수확용 Multi-layer 블록 구조를 제시하고 고체 및 Shell 유한 요소를 사용하여 다양한 기하학적 형상 변화에 대한 자유진동 특성을 분석하고 압전 성능을 실험적으로 평가한다. 본 연구에서 제시하는 블록 구조에 대한 2차원 및 3차원 유한요소 모델은 해석의 정확성 뿐 만 아니라 전체 진동 모드를 정확히 보여준다는 점에서 장점을 갖는다. ABAQUS가 적용된 유한요소 모델은 다양한 Tip mass 및 PZT 변화에 따른 Multi-layer 블록 구조의 자유진동을 분석하기 위하여 사용되었다. 특히, 본 연구에서 제시한 결과는 블록구조 전체의 기하학적 형상, Tip mass 및 Hole의 유무, Tip mass 및 PZT의 위치변화 등에 대하여 국부 및 전체 진동 모드에 미치는 중요한 영향들에 대하여 초점을 둔다. 또한, 실험실 규모의 실제 모형 실험을 수행하여 개발한 에너지 블록구조의 발전성능을 평가하였다.

• The Journal of the Acoustical Society of Korea
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• 제14권2E호
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• pp.73-86
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• 1995

전향 초음파 영상 캐서터의 트랜스듀스 (FLUIC) 부분은 진동자인 원형 전기음향 소자와 원뿔꼴 반사체인 음향 반사체로 구성된다. 소형의 전기음향 소자는 캐서터의 회전자 축 측면에 탑재된다. 전향 초음파 영상 캐서터의 특징은 기존의 IVUS 트랜스듀서가 제공할 수 없는 캐서터 전단에서 혈관의 단층 2-D 영상과 종래의 측면 영상을 동시에 제공하는 것이다. FLUIC의 트랜스듀서에 사용된 음향 반사체를 설계하기 위해 근사화된 레이 추적 기법을 이용하였다. 음향 반사체로부터 2차 외절 특성을 예측하기 위해 회절전달함수방식에[1] 의한 1차 음원으로 부터의 장 예측모델을 확장하여 일반화 하였다. 확장된 모델은 단순한 평판 반사체에 적용하여 시뮬레이션과 실험에 의해 검증되었으며 FLUIC의 잘 특성을 해석하는데 사용되었다.