• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.15 no.3
• /
• pp.6-14
• /
• 2007

In this research, vibration reduction and aeroelastic stability of a composite hingeless rotor hub flexure with viscoelastic constrained layer damping treatment(CLDT) were investigated. The composite flexures with viscoelastic CLDT were applied to hingeless rotor system to improve the in-plane stability of the lead-lag motion causing resonance. The modal test was performed and dynamic properties(natural frequency and loss factor) were acquired. Also, complex eigenvalue analysis(SOLlO7) in the NASTRAN structural analysis module was performed and compared with results of the modal test. To insure aeroelastic stability, damping ratio analyses of the hingeless rotor system with CLDT were accomplished at hovering condition due to collective pitch angle changes. Satisfactory results of increasing structural damping and stability were obtained.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 1998.04a
• /
• pp.196-203
• /
• 1998

Viscoelastic dampers have been successfully applied to building structures for reduction of vibration induced by wind or earthquakes. But accurate estimation of responses of building structures with viscoelastic dampers is very difficult, because the properties of viscoelastic damper is dependent on temperature and frequency of vibration. For efficient control of building vibration, required damping of viscoelastic damping device need be estimated and dynamic analysis method which can estimate the response of building structure with viscoelastic damper system is indispensable. In this paper, an efficient dynamic analysis method of a building structure with viscoelastic dampers is proposed. Efficiency and accuracy of the proposed method are verified comparing analytic results with shaking table test results using reduced building models.

• Structural Engineering and Mechanics
• /
• v.33 no.4
• /
• pp.391-406
• /
• 2009

Viscoelastic materials store as well as dissipate energy to the thermal domain under deformation. Two efficient modelling techniques reported in literature use coupled (thermo-mechanical) ATF (Augmenting Thermodynamic Fields) displacements and ADF (Anelastic Displacement Fields) displacements, to represent the constitutive relationship in time domain by using certain viscoelastic parameters. Viscoelastic parameters are first extracted from the storage modulus and loss factor normally reported in hand books with the help of Genetic Algorithm and then constitutive relationships are used to obtain the equations of motion of the continuum after discretizing it with finite beam elements. The equations of motion are solved to get the frequency response function and modal damping ratio. The process may be applied to study the dynamic behaviour of composite beams and rotors comprising of several viscoelastic layers. Dynamic behaviour of a composite beam, formed by concentric layers of steel and aluminium is studied as an example.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.15 no.2
• /
• pp.329-339
• /
• 2002

This research presents a systematic design procedure for supplemental viscoelastic dampers required to satisfy the given performance objectives using capacity spectrum method. To obtain required damper size, the amount of supplemental damping was computed from effective damping minus equivalent damping and inherent damping of structure. In the case of viscoelastic damper, iterative procedure is required because of the inherent stiffness of the damper. To verify the design method proposed in this study, parametric studies were performed for single degree of freedom systems with design variables. The method was also applied to a 10-story steel framed structure and the earthquake responses were obtained. According to time history analysis result the controlled displacements turned out to be close to the target displacement regardless of the design parameters.

• Computational Structural Engineering
• /
• v.7 no.1
• /
• pp.99-107
• /
• 1994

Viscoelastic materials are widely used to solve the vibration and noise problems. To apply the well-known damping technologies successfully to the vibration and noise problems, the damping characteristics of the viscoelastic materials applied to the base structures must be thoroughly understood. The objectives of the present study are : 1) to establish the damping measurement technique via modal testing by which the damping characteristics of viscoelastic materials can be measured in the university laboratory environment, and 2) to develop a computer program to draw the reduced-frequency-nomogram by use of restricted number of experimental data, which can be used efficiently for the damping analysis and application.

• Journal of Mechanical Science and Technology
• /
• v.20 no.8
• /
• pp.1139-1148
• /
• 2006

This paper addresses the analytical modeling and dynamic response of the advanced composite rotating blade modeled as thin-walled beams and incorporating viscoelastic material. The blade model incorporates non-classical features such as anisotropy, transverse shear, rotary inertia and includes the centrifugal and coriolis force fields. The dual technology including structural tailoring and passive damping technology is implemented in order to enhance the vibrational characteristics of the blade. Whereas structural tailoring methodology uses the directionality properties of advanced composite materials, the passive material technology exploits the damping capabilities of viscoelastic material (VEM) embedded into the host structure. The VEM layer damping treatment is modeled by using the Golla-Hughes-McTavish (GHM) method, which is employed to account for the frequency-dependent characteristics of the VEM. The case of VEM spread over the entire span of the structure is considered. The displayed numerical results provide a comprehensive picture of the synergistic implications of both techniques, namely, the tailoring and damping technology on the dynamic response of a rotating thin-walled b ε am exposed to external time-dependent excitations.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.15 no.3
• /
• pp.421-432
• /
• 2002

In this study the modal characteristics and responses of an asymmetric structure with added viscoelastic dampers were investigated for design parameters such as eccentricity of stiffness and added dampers, the loss factor of the damping materials used. For modal characteristics, variation of the quantities such as natural frequencies, modal damping ratios, modal participation factors, and dynamic amplification factors were observed, and displacements at flexible and stiff edges, and at center of mass were obtained. Based on the results, the problem of the optimum damper distribution to minimize the torsional effects was addressed, and the proposed method for optimum damper distribution was applied to a multi-story structure to verify the applicability Finally the effect of viscous and viscoelastic dampers were compared by varying the loss factor of the viscoelastic material.

• International Journal of Automotive Technology
• /
• v.5 no.3
• /
• pp.189-194
• /
• 2004

The viscoelastic layer material is widely used to control the noise and vibration characteristics of the panel structure. This paper describes the design technology of the effective vibration damping treatment using the concept of the equivalent parameter of viscoelastic layer materials. Applying the equivalent parameter concepts based on theories of shell, it is possible to simulate the finite element analysis of damping layer panel treatments on the vibration characteristics of the structure. And it is achieved the reduced computational cost and the optimal design of topological distribution for the reduction of vibration effect.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2000.11a
• /
• pp.224-227
• /
• 2000

Modal damping characteristics of the flexural vibration of a sandwich beam with paaially inserted viscoelastic layer have been quantitatively studied using the finite element analysis in combination with an experiment. Antisymmetric mode shapes of the flexural vibration were visualized by the holographic interferometry and agreed with those calculated by the finite element simulation. Effects of the length and thickness of partial viscoelastic layers on the system loss factor($\mu$) and resonant frequency($\omega$) were considerably latge at both symmetric and antisymmetric modes of the sandwich beam.

• Journal of KSNVE
• /
• v.10 no.1
• /
• pp.64-73
• /
• 2000

We present finite element equations in the Laplace-domain for linear viscoelastic and viscoelstically damped structures governed by a constitutive equation involving factional order derivative opeartors. These equations yield a nonstandard eigenproblem consisted of frequency dependent stiffness matrix. To solve this nonstandard eigenproblem we suggest an eigenvalue iteration procedure in the Laplace-domain. Improved Zenor and GHM material function type constitutive equations in the Laplace-domain are also available for this procedure. From above equations, complex eigenvalues and complex eigenvectors are obtained. Using obtained eigenvalues and eigenvectors, time domain analysis is performed by means of mode superposition. Finally, finite element solutions of viscoelastic and viscoeleastically damped sandwich beam are presented as an example.