Dynamic Responses of Plates With Viscoelastic Free Layer Damping Treatment
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Abstract:
Dynamic transient responses of plates with viscoelastic free damping layers are studied in order to evaluate free layer damping treatment performances. The effects of forcing frequencies and temperatures on free-layer viscoelastic damping treatment of plates are investigated analytically. Young’s modulus ratio of structures to viscoelastic damping materials and the damping layer thickness effects on the damping ability are also explored.Keywords:
Constrained-layer damping
Magnetic damping
Damping ratio
Thermoelastic damping
Transient (computer programming)
Based on a lot of dynamic tri-axial tests, dynamic properties of lime soils were thoroughly studied. Among many factors affecting dynamic modulus and damping ratio, dynamic strain was the most important one. Dynamic modulus E_d decreases and damping ratio increases very rapidly with the increase of dynamic strain. Both dynamic modulus and damping ratio increase with the increase of Lime dosage ratio. Dynamic modulus increases while damping ratio decreases as the confining pressure increases at the same strain level. It is found that the maximum dynamic modulus Edmax increases in the relation of exponential function to confining pressure. The maximum damping ratio varies from 7% to 40%; it decreases in the relation of exponential function to confining pressure, and the corresponding formula is put forward. 10figs., 4tabs., 14refs.
Damping ratio
Dynamic pressure
Overburden pressure
Strain (injury)
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It is becoming increasingly important to add damping to structures for vibration and noise control purposes. Most damping falls in two categories: passive damping and active damping. Recently, a new subset of damping was created by combining passive and active damping, thereby producing a hybrid damping treatment. This paper is a review of these damping treatments including the recent advances in the hybrid damping using active constrained layer damping (ACLD) treatment.
Constrained-layer damping
Damping torque
Magnetic damping
Damping off
Thermoelastic damping
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Based on amount of freeze-thaw tests and dynamic triaxial tests, the dynamic modulus and damping ratio properties of silty soil subjected to repeated freeze-thaw cycles were deeply researched and analyzed. The tests results are drawn as follows: At the same dynamic strain level, the relationships of dynamic stress and freeze-thaw cycles, water content present negative correlation, and the relationships of dynamic stress and confining pressure, frequency, compactness present positive correlation. The curves of dynamic stress vs. dynamic strain obviously present nonlinear relationship; and the dynamic modulus double decreases while the damping ratio double increases with the increasing of dynamic strain. The dynamic modulus sharply decreases while the damping ratio increases with the increasing of freeze-thaw cycles; and then the changes level off after 6 freeze-thaw cycles; while the mechanical properties after 6 freeze-thaw cycles are suggested for designing and calculating indexes. The soil particles contact area is improved by the increasing of confining pressure and compactness; and the dynamic modulus increases while the damping ratio decreases with the increasing of confining pressure and compactness. It is found that water content less affects damping ratio, but the dynamic modulus double decreases when the silty soil reaches saturation condition. The frequency is an important factor affecting on damping ratio, and damping ratio sharply decreases as the frequency increases.
Damping ratio
Overburden pressure
Shear modulus
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Based on a large amount of dynamic tri-axial tests, dynamic properties of cement treated soft soils are examined thoroughly. The results show that the dynamic strain ed is the most important factor affecting the dynamic modulus and the damping ratio λ. The dynamic modulus Ed decreases and the damping ratio λ increases very rapidly with the increase of the dynamic strain ed. Both the dynamic modulus Ed and the damping ratio λ increase with the increase in the cement dosage ratio. The dynamic modulus increases while the damping ratio decreases as the confining pressure σ3 increases, at the same strain level. It is further found that the maximum dynamic modulus Edmax increases as an exponential function of the confining pressure σ3. The maximum damping ratio λmax varies from 7% to 30% and decreases as an exponential function of the confining pressure σ3. The corresponding formulas are put forward.
Damping ratio
Overburden pressure
Dynamic pressure
Strain (injury)
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Significant improvement of damping characteristics can be achieved by using the new class of magnetic constrained layer damping treatment (MCLD). This paper presents the damping properties of the first and second torsional mode for a five-layer cantilever rectangular plate treated with partial MCLD. The Rayleigh-Ritz method and Hamilton’s principle are employed in the analysis. We have chosen both single and segmented patches with different sizes. It can be observed that for the two modes single-patched MCLD treatment induces less improvement of damping characteristics especially for the short patch. The effects of calculation of parameters like placement strategies of discrete patches, the length of patches are analyzed and discussed. The results obtained from analytical show that the optimum location of the patch, for the torsional mode, is at edge of the plate. Favorable comparisons with the conventional passive constrained layer damping treatment (PCLD) on various special cases of the problem are obtained. The results demonstrate MCLD treatment still improvements over PCLD in damping structural vibrations.
Constrained-layer damping
Magnetic damping
Damping torque
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Dynamic deformation behavior tests on dam materials are conducted using a large scale triaxial test apparatus.The effect of confining pressure and consolidated stress ratio on the maximum dynamic modulus,reduction of dynamic modulus and damping ratio is analyzed.It is shown that the maximum dynamic modulus increases with the increase of the confining pressure and consolidated stress ratio,and that the dynamic modulus decreases with the increase of the dynamic strain.The consolidated stress ratio has little effect on the maximum damping ratio.The modified formula of the maximum dynamic modulus and reduction of dynamic modulus with normalized dynamic strain is developed on the basis of the test results.This formula can describe the effect of the confining pressure and consolidated stress ratio on the dynamic modulus.The effect on dynamic deformation of reduced scale is discussed using particles finer than 5 mm.Compared with the field soil,the maximum dynamic modulus of the soil from laboratory tests is smaller,and the maximum damping ratio of the soil from laboratory tests is larger.
Damping ratio
Overburden pressure
Triaxial shear test
Aggregate modulus
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Previous studies have centred on the long-term permanent deformation behaviour of soil under traffic loading while neglecting the dynamic parameters as it is affected by cycle number. In this study, forty tri-axial dynamic tests were conducted to assess the effects of cycle number, confining pressure, and dynamic stress on the dynamic modulus and damping ratio of compacted loess. Empirical models of both parameters were established and examined, from which emerged a nearly linear relationship between the dynamic stress-strain points when dynamic stress fell below a given threshold value. The representative dynamic modulus in the linear range initially increased and then decreased. The maximum representative dynamic modulus linearly increased as confining pressure increased, while confining pressure had no clear effect on the damping ratio. As the dynamic stress increased, the damping ratio was initially stable and then gradually increased until becoming stable again at a higher level.
Damping ratio
Overburden pressure
Dynamic stress
Dynamic pressure
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Dynamic modulus and damping ratio of dredger fill in Tianjin Binhai New Area were tested while the seismic loading was simulated through dynamic triaxial testing equipment.The impact of frequency and confining pressure on dynamic modulus and damping ratio was explored.Studying results show that the dynamic modulus and damping ratio of dredger fill in Tianjin Binhai New Area improved with the increment of frequency and confining pressure.The maximum dynamic shear modulus of this kind of dredger fill was obtained which can give reference on seismic safety evaluation in geotechnical and other civil engineering project.
Damping ratio
Shear modulus
Overburden pressure
Dynamic testing
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Constrained-layer damping
Magnetic damping
Smart material
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Abstract A new class of structural damping treatments is introduced. This class is the Electro-Magnetic Damping Treatment (EMDT) which relies in its operation on a viscoelastic damping layer sandwiched between two magnetic layers. Interaction between the magnets generates magnetic forces that enhance the compressional damping mechanism of the viscoelastic layer. With proper tuning of the magnetic forces, in response to the structural vibration, undesirable resonances and catastrophic failures can be avoided. The fundamentals and the underlying phenomena associated with the EMDT are investigated theoretically and experimentally. A finite element model is developed to describe the interaction between the dynamics of flexible beams, the viscoelastic damping layer and the magnetic layers. The validity of the developed finite element model is checked experimentally using aluminum beams treated with EMDT patches. The beam/EMDT system is subjected to sinusoidal excitations and its multi-mode response is monitored when the magnetic layers are activated or not. Several control strategies are considered to activate the magnetic layers including simple PD controllers. The performance of the uncontrolled and controlled system is determined at various operating conditions. Comparisons with conventional Passive Constrained Layer Damping (PCLD) treatments emphasize the potential of the EMDT treatment as an effective means for controlling structural vibrations.
Magnetic damping
Constrained-layer damping
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