• Journal of the Earthquake Engineering Society of Korea
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• v.2 no.3
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• pp.27-35
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• 1998

Steel structures with added viscoelastic dampers are analysed to investigat their behavior under earthquake excitation. The direct integration method, which produces exact solution for the non-proportional or non-classical damping system, is used throughout the analysis. The results from modal strain energy method are also provided for comparison. Then a new analytical a, pp.oach, based on the rigid floor diaphragm assumption and matrix condensation technique, is introduced, and the results are compared with those obtained from direct integration method and modal strain energy method. The well known phenomenon, that the effectiveness of the viscoelastic dampers depends greatly on the location of the dampers, is once again confirmed in the analysis. It is also found that the modal strain energy method generaly underestimates the responses obtained from the direct integration method, especially when the dampers are placed in only a part of the building. The proposed method turns out to be very efficient with considerable saving in computation this and reasonably accurate considering the reduced degrees of freedom.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.09a
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• pp.239-246
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• 2002

Viscoelastic dampers are known effective devices for response reduction under earthquakes and winds. This study addresses how to design the optimum viscoelastic dampers installed at the full scale five-story steel building and novel approach to carry out the experimental work to verify the damper performance. First, an exciter of hybrid mass-type actuator is designed, which can move the building and its mathematical model is derived. The integrated system of building-actuator is experimentally analyzed for mathematical model. Second, convex model is applied for the prediction of required additional damping ratios to reduce responses below a specified target level. Chevron-type viscoelastic dampers are manufactured and installed at the first and second inter-stories, which are optimum places for response reduction. Sine-sweep and white noise excitations, which are generated by the hybrid mass-type actuator, are applied to the full scale building without and with dampers for performance verification. The transfer function of the building with four dampers, two of them installed at each first and second inter-story, are found to be lower than that of the building with two dampers installed at the first inter-story

• Steel and Composite Structures
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• v.24 no.4
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• pp.499-512
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• 2017

This paper deals with nonlinear dynamic stability of embedded piezoelectric nano-composite separators conveying pulsating fluid. For presenting a realistic model, the material properties of structure are assumed viscoelastic based on Kelvin-Voigt model. The separator is reinforced with single-walled carbon nanotubes (SWCNTs) which the equivalent material properties are obtained by mixture rule. The separator is surrounded by elastic medium modeled by nonlinear orthotropic visco Pasternak foundation. The separator is subjected to 3D electric and 2D magnetic fields. For mathematical modeling of structure, three theories of classical shell theory (CST), first order shear deformation theory (FSDT) and sinusoidal shear deformation theory (SSDT) are applied. The differential quadrature method (DQM) in conjunction with Bolotin method is employed for calculating the dynamic instability region (DIR). 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 dynamic instability of structure. The numerical results are validated with other published works as well as comparing results obtained by three theories. Numerical results indicate that the magnetic and electric fields as well as SWCNTs as reinforcer are very important in dynamic instability analysis of structure.

• Journal of KSNVE
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• v.5 no.2
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• pp.225-234
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• 1995

In this study, first, transformation process of damping ratios, whose are evaluated in active control analysis, into damping matrix resulting from installed viscous dampers is illustrated. Then, a method is followed to maximize the effect of response reduction, which leads to optimum locations and size of viscous dampers using sensitivity analysis. Highly coupled nonlinearity between damping ratios and dampers makes it hard to find the optimal size of dampers. Therefore, the nonlinearity is transformed to linear problem with small increments of damping ratios and the size of dampers can be found. However, there are many cases for the size of dampers satisfying the small increment of damping ratios, so it is necessary to select minimum size using optimization technique. To determine optimum locations of dampers, dampers are assumed to be installed between the different stories and their locations are selected corresponding corresponding to the degree of damping size. Numerical examples for the frame structure and the shear wall structure show that optimum locations and size of dampers are different form each other depending on the characteristics of modal responses of the structures. The proposed method in this study can be applied to get optimum locations of active controller in the active control.

• Structural Engineering and Mechanics
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• v.60 no.3
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• pp.489-505
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• 2016

Sinusoidal shear deformation theory (SSDT) is developed here for dynamic buckling of functionally graded (FG) nano-plates. The material properties of plate are assumed to vary according to power law distribution of the volume fraction of the constituents. In order to present a realistic model, the structural damping of nano-structure is considered using Kelvin-Voigt model. The surrounding elastic medium is modeled with a novel foundation namely as orthotropic visco-Pasternak medium. Size effects are incorporated based on Eringen'n nonlocal theory. Equations of motion are derived from the Hamilton's principle. The differential quadrature method (DQM) in conjunction with Bolotin method is applied for obtaining the dynamic instability region (DIR). The detailed parametric study is conducted, focusing on the combined effects of the nonlocal parameter, orthotropic visco-Pasternak foundation, power index of FG plate, structural damping and boundary conditions on the dynamic instability of system. The results are compared with those of first order shear deformation theory and higher-order shear deformation theory. It can be concluded that the proposed theory is accurate and efficient in predicting the dynamic buckling responses of system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.1
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• pp.53-60
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• 2012

To reduce the vibration in industrial settings, the viscous fluid dampers have been widely used. Since the damper shows a viscoelastic behavior, many methods to predict the behavior have been investigated. But the methods did not consider a change of damper size that is important factor for practical design engineer. In this study, to predict a change of damper ability with respect to a change of damper size, the dynamic experiment were conducted with fixed aspect ratio and gap. The damping coefficient at zero frequency was computed through theoretical and experiment approach in order to fit the experimental results using fractional derivative Maxwell model.

• Journal of KSNVE
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• v.8 no.1
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• pp.157-170
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• 1998

This paper proposes a new technique to formulate the finite element model of a sandwich beam by using GHM (Golla-Hughes-McTavish) internal auxiliary coordinates to account for frequency dependence. Through the use of auxiliary coordinates, the equation of motion of undamped mass and stiffness matrix form is extended to encompass viscoelastic damping matrix. However, this methods all suffer from an increase in order of the final finite element model which is undesirable in many applications. Here we propose to combine the GHM method with model reduction techniques to remove the objection of increased model order.

• Journal of Mechanical Science and Technology
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• v.20 no.5
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• pp.658-667
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• 2006

Fractional derivative models, which are used to describe the viscoelastic behavior of material, have received considerable attention. Thus it is necessary to put forward the analysis solutions of dynamic systems containing a fractional derivative. Although previously reported such kind of fractional calculus-based constitutive models, it only handles the particularity of rational number in part, has great limitation by reason of only handling with particular rational number field. Simultaneously, the former study has great unreliability by reason of using the complementary error function which can't ensure uniform real number. In this paper, a new approach is proposed for an analytical scheme for dynamic system of a spring-mass-damper system of single-degree of freedom under general forcing conditions, whose damping is described by a fractional derivative of the order $0<{\alpha}<1$ which can be both irrational number and rational number. The new approach combines the fractional Green's function and Laplace transform of fractional derivative. Analytical examples of dynamic system under general forcing conditions obtained by means of this approach verify the feasibility very well with much higher reliability and universality.

• Steel and Composite Structures
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• v.37 no.2
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• pp.229-251
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• 2020

In this paper, dynamic buckling of a smart sandwich nanotube is studied. The nanostructure is composed of a carbon-nanotube with inner and outer surfaces coated with ZnO piezoelectric layers, which play the role of sensor and actuator. Nanotube is under magnetic field and ZnO layers are under electric field. The nanostructure is located in a viscoelastic environment, which is assumed to obey Visco-Pasternak model. Non-local piezo-elasticity theory is used to consider the small-scale effect, and Kelvin model is used to describe the structural damping effects. Surface stresses are taken into account based on Gurtin-Murdoch theory. Hamilton principle in conjunction with zigzag shear-deformation theory is used to obtain the governing equations. The governing equations are then solved using the differential quadrature method, to determine dynamic stability region of the nanostructure. To validate the analysis, the results for simpler case studies are compared with others reported in the literature. Then, the effect of various parameters such as small-scale, surface stresses, Visco-Pasternak environment and electric and magnetic fields on the dynamic stability region is investigated. The results show that considering the surface stresses leads to an increase in the excitation frequency and the dynamic stability region happens at higher frequencies.

• Advances in nano research
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• v.13 no.4
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• pp.369-378
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• 2022

Dynamic study of concrete plates under impact load is presented in this article. The main objective of this work is presenting a mathematical model for the concrete plates under the impact load. The concrete plate is reinforced by carbon nanoparticles which the effective material proprieties are obtained by mixture's rule. Impacts are assumed to occur normally over the top layer of the plate and the interaction between the impactor and the structure is simulated using a new equivalent three-degree-of-freedom (TDOF) spring-mass-damper (SMD) model. The structure is assumed viscoelastic based on Kelvin-Voigt model. Based on the classical plate theory (CPT), energy method and Hamilton's principle, the motion equations are derived. Applying DQM, the dynamic deflection and contact force of the structure are calculated numerically so that the effects of mass, velocity and height of the impactor, volume percent of nanoparticles, structural damping and geometrical parameters of structure are shown on the dynamic deflection and contact force. Results show that considering structural damping leads to lower dynamic deflection and contact force. In addition, increasing the volume percent of nanoparticles yields to decreases in the deflection.