• Title/Summary/Keyword: Viscoelastic Damping

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Frequency and instability responses in nanocomposite plate assuming different distribution of CNTs

  • Farokhian, Ahmad;Kolahchi, Reza
    • Structural Engineering and Mechanics
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    • v.73 no.5
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    • pp.555-563
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    • 2020
  • The objective of present paper is assessment of dynamic buckling behavior of an embedded sandwich microplates in thermal environment in which the layers are reinforced through functionally graded carbon nanotubes (FG-CNTs). Therefore, mixture rule is taken into consideration for obtaining effective material characteristics. In order to model this structure much more realistic, Kelvin-Voigt model is presumed and the sandwich structure is rested on visco-Pasternak medium. Exponential shear deformation theory (ESDT) in addition to Eringen's nonlocal theory are utilized to obtain motion equations. Further, differential cubature method (DCM) as well as Bolotin's procedure are used to solve governing equations and achieve dynamic instability region (DIR) related to sandwich structure. Different parameters focusing on volume percent of CNTs, dispersion kinds of CNTs, thermal environment, small scale effect and structural damping and their influences upon the dynamic behavior of sandwich structure are investigated. So as to indicate the accuracy of applied theories as well as methods, the results are collated with another paper. According to results, presence of CNTs and their dispersion kind can alter system's dynamic response as well.

Soil-structure interaction effect on active control of multi-story buildings under earthquake loads

  • Chen, Genda;Chen, Chaoqiang;Cheng, Franklin Y.
    • Structural Engineering and Mechanics
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    • v.10 no.6
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    • pp.517-532
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    • 2000
  • A direct output feedback control scheme was recently proposed by the authors for single-story building structures resting on flexible soil body. In this paper, the control scheme is extended to mitigate the seismic responses of multi-story buildings. Soil-structure interaction is taken into account in two parts: input at the soil-structure interface/foundation and control algorithm. The former reflects the effect on ground motions and is monitored in real time with accelerometers at foundation. The latter includes the effect on the dynamic characteristics of structures, which is formulated by modifying the classical linear quadratic regulator based on the fundamental mode shape of the soil-structure system. Numerical result on the study of a $\frac{1}{4}$-scale three-story structure, supported by a viscoelastic half-space of soil mass, have demonstrated that the proposed algorithm is robust and very effective in suppressing the earthquake-induced vibration in building structures even supported on a flexible soil mass. Parametric studies are performed to understand how soil damping and flexibility affect the effectiveness of active tendon control. The selection of weighting matrix and effect of soil property uncertainty are investigated in detail for practical applications.

Implementation of Semi-infinite Boundary Condition for Dynamic Finite Element Analysis (동적 유한요소해석에서의 반무한 경계조건의 실행)

  • Choi, Chang-Ho;Chung, Ha-Ik
    • Journal of the Korean Geotechnical Society
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    • v.22 no.9
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    • pp.37-43
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    • 2006
  • Dynamic numerical analysis of geotechnical problems requires a way to simulate the decrease of energy as the domain of interest gets larger. This phenomenon is usually referred to as radiation damping or geometric attenuation and it is distinguished from material damping in which elastic energy is actually dissipated by viscous, hysteretic, or other mechanism. The fact that the domain of analysis in numerical modeling must be chosen, however, causes a need for special attention at the boundary. This observation leads directly to the idea of determining the dynamic response of the interior region from a finite model consisting of the interior region subjected to a boundary condition which ensures that all energy arriving at the boundary is absorbed. This paper presents a simple methodology to simulate transmitting boundaries condition using viscoelastic infinite elements within the recently developed "OpenSees" finite element code. The methodology used here provides that the level of absorption for traveling waves is efficient enough for practical purposes, but unsatisfactory for the case of sharp incident angles. The effectiveness of the infinite elements for the absorption of incident waves at boundaries is evaluated via example analysis.

Quantification of the Effect of Medication and Deep Brain Stimulation on Parkinsonian Rigidity (파킨슨병 환자의 경직에 대한 약물과 DBS 의 효과의 정량화)

  • Kwon, Yu-Ri;Eom, Gwang-Moon;Park, Sang-Hun;Kim, Ji-Won;Kim, Min-Jik;Lee, Hye-Mi;Jang, Ji-Wan;Koh, Seong-Beom
    • Journal of the Korean Society for Precision Engineering
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    • v.30 no.5
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    • pp.559-563
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    • 2013
  • This study aims to quantify the effects of medication (Med) and deep brain stimulation (DBS) on resting rigidity in patients with Parkinson's disease. We tested 10 limbs of five patients under each of four treatment conditions: 1) baseline, 2) DBS, 3) Med, 4) DBS + Med. Rigidity at the wrist joint was assessed using the Unified Parkinson's Disease Rating Scale (UPDRS). The examiner randomly imposed flexion and extension movement on patient's wrist joint. Resistance to passive movement was quantified by viscoelastic properties. Not only rigidity score but also damping constant showed improvements in rigidity by DBS and Med treatments (p<0.05). This indicates that the viscosity can represent the change in rigidity due to DBS as well as Med, which was manifested by UPDRS score.

Stress analysis of a two-phase composite having a negative-stiffness inclusion in two dimensions

  • Wang, Yun-Che;Ko, Chi-Ching
    • Interaction and multiscale mechanics
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    • v.2 no.3
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    • pp.321-332
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    • 2009
  • Recent development in composites containing phase-transforming particles, such as vanadium dioxide or barium titanate, reveals the overall stiffness and viscoelastic damping of the composites may be unbounded (Lakes et al. 2001, Jaglinski et al. 2007). Negative stiffness is induced from phase transformation predicted by the Landau phase transformation theory. Although this unbounded phenomenon is theoretically supported with the composite homogenization theory, detailed stress analyses of the composites are still lacking. In this work, we analyze the stress distribution of the Hashin-Shtrikman (HS) composite and its two-dimensional variant, namely a circular inclusion in a square plate, under the assumption that the Young's modulus of the inclusion is negative. Assumption of negative stiffness is a priori in the present analysis. For stress analysis, a closed form solution for the HS model and finite element solutions for the 2D composite are presented. A static loading condition is adopted to estimate the effective modulus of the composites by the ratio of stress to average strain on the loading edges. It is found that the interfacial stresses between the circular inclusion and matrix increase dramatically when the negative stiffness is so tuned that overall stiffness is unbounded. Furthermore, it is found that stress distributions in the inclusion are not uniform, contrary to Eshelby's theorem, which states, for two-phase, infinite composites, the inclusion's stress distribution is uniform when the shape of the inclusion has higher symmetry than an ellipse. The stability of the composites is discussed from the viewpoint of deterioration of perfect interface conditions due to excessive interfacial stresses.

Experimental Study on the Vibration Control Capacity of Hybrid Buckling-Restrained Braces (하이브리드 비좌굴가새의 진동제어능력에 관한 실험적 연구)

  • Kim, Do Hyun;Ju, Young Kyu;Kim, Myung Han;Sung, Woo Gi;Kim, Sang Dae
    • Journal of Korean Society of Steel Construction
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    • v.21 no.1
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    • pp.83-91
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    • 2009
  • Buckling Restrained Braces (BRBs) show good seismic behavior. They do not dissipate energy, however, when they are subjected to minor earthquakes or wind. Hybrid Buckling Restrained Braces (H-BRBs), which can improve the wind performance of the BRB system, are a kind of hybrid damper system composed of a viscoelastic damper and BRBs. In this paper, two H-BRB specimens with different cores were experimentally investigated to ensure the structural behavior of the H-BRB system in an elastic range. The axial deformation of the primary resisting system was compared with that of the secondary resisting system, and the equivalent damping ratio of the H-BRBs was estimated. It was concluded that H-BRBs with double shear dampers show good structural behavior and are applicable to tall buildings, to improve the building performance at a comfortable level.

Parametric Study on Earthquake Responses of Soil-structure Interaction System by Substructure Method (부분구조법에 의한 지반-구조물상호작용시스템의 지진응답 매개변수 연구)

  • 박형기;조양희
    • Journal of the Earthquake Engineering Society of Korea
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    • v.2 no.1
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    • pp.1-10
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    • 1998
  • In the dynamic soil-structure interaction(SSI) analysis, numerous uncertain parameters are involved. They include the uncertainties in the definition of input motions, modeling of soil-structure interaction systems. analysis techniques, etc. This paper presents the results of parametric studies of the seismic responses of a reactor containment structure built on the viscoelastic layered soil. Among the numerous parameter, this study concentrates on the effects of definition point of the input motion, embedment of structure to the base soil, thickness of the top soil layer, and rigidity of the base soil. The substructure method using frequency independent impedances is adopted. The method is based on the mode superposition method in time domain using the composite modal damping values of th SSI system computed from the ratio of dissipated energy to the strain energy for each model. From the study results, the sensitivity of each parameter on the earthquake responses has been suggested for the practical application of the substructure method of SSI analysis.

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An Essay of the Reinforcing Effect of BNNT and CNT: A Perspective on Interfacial Properties (BNNT와 CNT의 강화효과에 대한 복합재 계면물성 관점의 고찰)

  • Seunghwa Yang
    • Composites Research
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    • v.37 no.3
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    • pp.155-161
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    • 2024
  • Boron nitride nanotubes and carbon nanotubes are the most representative one-dimensional nanostructures, and have received great attention as reinforcement for multifunctional composites for their excellent physical properties. The two nanotubes have similar excellent mechanical stiffness, strength, and heat conduction properties. Therefore, the reinforcing effect of these two nanotubes is greatly influenced by the properties of their interface with the polymer matrix. In this paper, recent comparative studies on the reinforcing effect of boron nitride nanotubes and carbon nanotubes through experimental pull-out test and in-silico simulation are summarized. In addition, the conflicting aspect of the two different nanotubes with structural defects in their side wall is discussed on the viscoelastic damping performance of nanocomposites.