• Advances in concrete construction
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• v.13 no.6
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• pp.423-431
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• 2022

Although the influence of moisture content on the mechanical properties of concrete has been studied for a long time, research related to its influence on the damping and energy dissipation property of concrete structure is still very limited. In this paper, the relationship between damping property and moisture content of concrete using cyclic uniaxial compression is firstly presented, and the mechanism of the influence of moisture content on concrete damping and energy dissipation capacity is analyzed. Based on the experimental research, moisture-related damping and energy dissipation model is proposed. Results show that the dissipated energy of concrete and loss factor increase as the moisture content increasing. The energy dissipation coefficient reflecting the influence of stress level of concrete under cyclic load, decreases first and then increases as the moisture content increasing. The mechanism of moisture-related energy dissipation behavior can be divided into the reactive force of water, the development of the internal micro cracks and the pore water pressure. Finally, the proposed moisture-related damping and energy dissipation model are verified.

• Steel and Composite Structures
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• v.13 no.6
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• pp.501-519
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• 2012

As an alternative to current conventional force-based assessment methods, the energy-based seismic performance of a code-designed 20-storey high-rise steel building is evaluated in this paper. Using 3D nonlinear dynamic time-history method with consideration of additional material damping effect, the influences of different restoring force models and P-${\Delta}/{\delta}$ effects on energy components are investigated. By combining equivalent viscous damping and hysteretic damping ratios of the structure subjected to strong ground motions, a new damping model, which is amplitude-dependent, is discussed in detail. According to the analytical results, all energy components are affected to various extents by P-${\Delta}/{\delta}$ effects and a difference of less than 10% is observed; the energy values of the structure without consideration of P-${\Delta}/{\delta}$ effects are larger, while the restoring force models have a minor effect on seismic input energy with a difference of less than 5%, but they have a certain effect on both viscous damping energy and hysteretic energy with a difference of about 5~15%. The paper shows that the use of the hysteretic energy at its ultimate state as a seismic design parameter has more advantages than seismic input energy since it presents a more stable value. The total damping ratio of a structure consists of viscous damping ratio and hysteretic damping ratio and it is found that the equivalent viscous damping ratio is a constant for the structure, while the equivalent hysteretic damping ratio approximately increases linearly with structural response in elasto-plastic stage.

• Earthquakes and Structures
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• v.26 no.3
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• pp.219-228
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• 2024

This study examines damping modification factors (DMFs) of elastic input energy spectra corresponding to a set of 116 earthquake ground motions. Mean input energy per mass spectra and mean DMFs are presented for both considered ground motion components. Damping ratios of 3%, 5%, 10%, 20%, and 30% are used and the 5% damping ratio is considered the benchmark for DMF computations. The geometric mean DMFs of the two horizontal components of each ground motion are computed and coefficients of variation are presented graphically. The results show that the input energy spectra-based DMFs exhibit a dependence on the damping ratio at very short periods and they tend to be nearly constant for larger periods. In addition, mean DMF variation is obtained graphically for also the damping ratio, and mathematical functions are fitted as a result of statistical analyses. A strong correlation between the computed DMFs and the ones from predicted equations is observed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.6
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• pp.406-413
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• 2015

The piezoelectric coupling in piezoelectric vibration energy harvesters with load resistance induces electrical damping as well as increase in the system stiffness. Starting from analytically deriving the explicit relations through governing equations in the frequency domain, this work identifies the characteristics of the electrically induced damping mechanism and shows that the electrically induced damping serves as a structural hysteretic damping on condition that a piezoelectric vibration energy harvester is excited at its short-circuit resonant frequency and its load resistor is optimally impedance- matched at the same time. Finally, it is analytically verified that the equivalence of a mechanical and an electrically induced damping ratio is required for the maximum power generation at a load resistor, which was claimed in some literature.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.280-286
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• 2018

A sensorless active damping scheme for LCL filters in grid-connected parallel inverters for battery energy storage systems is proposed. This damping method is superior to the conventional notch filter and virtual damping methods with respect to robustness against the variation of the resonance of the filter and unnecessary additional current sensors. The theoretical analysis of the proposed damping method is explained in detail, along with the characteristic comparison to the conventional active damping methods. The performance verification of the proposed sensorless active damping method shows that its performance is comparable to that of the conventional virtual damping method, even without additional current sensors. Finally, simulation and experimental results are provided to examine the overall characteristics of the proposed method.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.11
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• pp.1199-1205
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• 2008

The vehicle design engineers have studied the method of applying damping materials to the vehicle bodies by computer simulations and experimental methods in order to improve the vibration and noise characteristics of the vehicles. The unconstrained layer damping, being concerned with this study, has two layers(base layer and damping layer) and proyides vibration control of the base layer through extensional damping. Generally this kind of surface damping method is effectively used in reducing structural vibration at frequencies beyond 150Hz. The most important thing is how to apply damping treatment with respect to location and size of the damping material. To solve these problems, the current experimental methods have technical limits which are cumbersome, time consuming, and expensive. This Paper proposes a method based on finite element method and it employes averaged ESE(element strain energy) percent of total of dash panel assembly for 1/1 octave band frequency range by MSC/NASTRAN. The regions of high ESE percent of total are selected as proposed location of damping treatment. The effect of damping treatment is analyzed by comparing the frequency response function of the SPCC bare Panel and the damping treated panels.

• The Journal of Korea Robotics Society
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• v.1 no.2
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• pp.135-141
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• 2006

This paper presents offline estimation of equivalent physical damping parameter in haptic interaction systems where damping is the most important parameter for stability. Based on the previous energy bounding algorithm, an offline procedure is developed in order to estimate the physical damping parameter of a haptic device by measuring energy flow-in to the haptic device. The proposed method does not use force/torque sensor at the handgrip. Numerical simulation and experiments verified effectiveness of the proposed method.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.6
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• pp.31-37
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• 2005

This paper presents an experimental study on vibration characteristics of an automotive roof with damping material. The goal of the study is to extract modal parameters(natural frequency, loss factor, and mode shape) of automotive roof with damping materials treatment. To determine the effective positions and thickness of the damping material on a roof, vibration tests have been carried out for six cases; an aluminum plate with damping material on maximum strain energy positions, and an aluminum plate with damping material on nodal lines. From the result of aluminum plate, it is found that the damping material should be placed on the location with maximum strain energy part. For the automotive roof, patches of constrained damping material, which has two different density, have been attached to the positions of the maximum strain energy with four kinds of thicknesses. This paper shows that the proper positioning of the damping material is very important and the effective thickness is about twice that of the roof panel.

• Structural Engineering and Mechanics
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• v.9 no.3
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• pp.241-256
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• 2000

The major sources of energy dissipation in steel frames with partially restrained (PR) connections are evaluated. Available experimental results are used to verify the mathematical model used in this study. The verified model is then used to quantify the energy dissipation in PR connections due to hysteretic behavior, due to viscous damping and at plastic hinges if they are formed. Observations are made for two load conditions: a sinusoidal load applied at the top of the frame, and a sinusoidal ground acceleration applied at the base of the frame representing a seismic loading condition. This analytical study confirms the general behavior, observed during experimental investigations, that PR connections reduce the overall stiffness of frames, but add a major source of energy dissipation. As the connections become stiffer, the contribution of PR connections in dissipating energy becomes less significant. A connection with a T ratio (representing its stiffness) of at least 0.9 should not be considered as fully restrained as is commonly assumed, since the energy dissipation characteristics are different. The flexibility of PR connections alters the fundamental frequency of the frame. Depending on the situation, it may bring the frame closer to or further from the resonance condition. If the frame approaches the resonance condition, the effect of damping is expected to be very important. However, if the frame moves away from the resonance condition, the energy dissipation at the PR connections is expected to be significant with an increase in the deformation of the frame, particularly for low damping values. For low damping values, the dissipation of energy at plastic hinges is comparable to that due to viscous damping, and increases as the frame approaches failure. For the range of parameters considered in this study, the energy dissipations at the PR connections and at the plastic hinges are of the same order of magnitude. The study quantitatively confirms the general observations made in experimental investigations for steel frames with PR connections; however, proper consideration of the stiffness of PR connections and other dynamic properties is essential in predicting the dynamic behavior.

• Progress in Superconductivity
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• v.14 no.1
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• pp.66-70
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• 2012

Superconductor flywheel energy storage system (SFESs) is an electro-mechanical battery with high energy storage density, long life, and good environmental affinity. SFESs have been developed for application to a regenerative power of train, the storage of distributed power sources such as solar and wind power, and a power quality improvement. As superconductor bearing is completely passive, it is not necessary to control a system elaborately but accurate analysis in mechanical properties of the HTS bearing is very important for application to SFESs. Stiffness and damping properties are the main index for evaluation the capacity of HTS bearings and make it possible to adjust rotordynamic properties while operating the rotor-bearing system. The superconductor bearing consists of a stator containing single grain YBCO bulks, a ring-type permanent magnet rotor with a strong magnetic field that can reach the bulk surface, and a bearing support for assembly to SFESs frame. In this study, we investigated the stiffness and damping properties of superconductor bearings in 35 kWh SFESs. Finally, we found that 35 kWh superconductor bearing has uniform stiffness properties depend on the various orientations of rotor vibration. We discovered total damping coefficient of superconductor bearing is affected by not only magnetic damping in superconductor bulk but also external damping in bearing support. From the results, it is confirmed that the conducted evaluation can considerably improve energy storage efficiency of the SFESs, and these results can be used for the optimal capacity of superconductor bearings of the SFESs.