• Structural Engineering and Mechanics
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• v.85 no.6
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• pp.743-753
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• 2023

Piezoelectricity is defined as the ability of certain materials to produce electric signals when mechanically stressed or to deform when an electrical potential is applied. Piezo technology is becoming increasingly crucial as intelligent devices use vibration sensors to detect vibrations in consumer electronics, the automotive industry, architectural design, and other applications. A wide range of applications is now possible with piezoelectric sensors, such as skin-attachable devices that monitor health and detect diseases. In this article, copper nanoparticles are used in the piezoelectric sensor as the driving agent of the magnetic field. Magnetic nanocatalysts containing copper nanoparticles are used due to their cheapness and availability. Considering that the increase of the electric field acting on the piezoelectric increases the damping (As a result, damping materials reduce radiation noise and increase material transfer losses by altering the natural vibration frequency of the vibrating surface). Among the advantages of this method are depreciating a significant amount of input energy using high energy absorption capacity and controlling slight vibrations in the sensors.

• Journal of Mechanical Science and Technology
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• v.17 no.3
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• pp.457-466
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• 2003

In this paper, the numerical finite element formulations were derived for the linearized Navier-Stokes' equations with assumptions of two-dimensional incompressible, homogeneous viscous fluid field, and small oscillation and the FAMD (Fluid Added Mass and Damping) code was developed for practical applications calculating the fluid added mass and damping. In formulations, a fluid domain is discretized with C$\^$0/-type quadratic quadrilateral elements containing eight nodes using a mixed interpolation method, i.e., the interpolation function for the velocity variable is approximated by a quadratic function based on all eight nodal points and the interpolation function for the pressure variable is approximated by a linear function based on the four nodal points at vertices. Using the developed code, the various characteristics of the fluid added mass and damping are investigated for the concentric cylindrical shell and the actual hexagon arrays of the liquid metal reactor cores.

• Earthquakes and Structures
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• v.4 no.5
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• pp.489-508
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• 2013

Design spectra for damping ratios higher than 5% have several important applications in the design of earthquake-resistant structures. These highly damped spectra are usually derived from a 5%-damped reference pseudo-acceleration spectrum by using a damping modification factor. In cases of high damping, the absolute acceleration and the relative velocity spectra instead of the pseudo-acceleration and the pseudo-velocity spectra should be used. This paper elaborates on the recovery of spectral absolute acceleration and spectral relative velocity from their pseudo-spectral counterparts. This is accomplished with the aid of correction factors obtained through extensive parametric studies, which come out to be functions of period and damping ratio.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.6
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• pp.460-470
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• 2015

In general ships and FPSOs, roll damping is very small and consequently roll motion is very large at the roll resonance frequency. Proper evaluation of the roll damping coefficient at the resonance frequency is an important task in the study of roll motion and usually it is done by the analysis of free roll decay tests. The relative decrement method based on energy relation has been used mainly for the evaluation of roll damping coefficient from the roll decay test so far. As another method, the logarithmic decrement method based on equivalent linear decay assumption can be used for the same purpose and it is relatively simple. In this paper, both of the relative decrement method and the logarithmic decrement method are used for the evaluation of roll damping coefficient including quadratic damping from the free roll decay tests, and their results are cross-checked for verifying the obtained damping coefficients. Through applications to a box-type floating body equiped with bilge keels, it is shown that the two methods give almost the same damping coefficients in a practical view point and the cross-check of their results is to be a good tool to prevent a possible error. And also the quantitative effects of the bilge keels on the roll damping of box-type floating body are shown and discussed.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.2
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• pp.116-121
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• 2009

Distributed power systems (DPSs) has been widely used various industrial/military applications due to their various advantages. Furthermore, the "All electric" concept, in conjunction with DC DPS, appears to be more advanced and mature in the AEV(All-Electric Vehicular) industry. Generally, AEV carry many loads with varied functions. However, there may be large pulsed loads with short duty ratios which can affect the normal operation of other loads. In this paper, a converter with spilt capacitors and a simple adaptive controller is proposed as a active damping device to mitigate the voltage transients on the bus. The proposed converter allows the smaller capacitive storage. In addition, the proposed control approach has the advantage of requiring only one sensor and performing both the functions of mitigating the voltage bus transients and maintaining the level of energy stored. The control algorithm has been implemented on a TMS320F2812 Digital Signal Processor (DSP). Simulation and experimental results are presented which verify the proposed control principle and demonstrate the practicality of the circuit topology.

• Structural Engineering and Mechanics
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• v.51 no.6
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• pp.1047-1065
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• 2014

The article presents the methodology for finding material damping capacity at higher frequency and at relatively lower amplitudes. The Lamb wave dispersion theory and loss less finite element model is used to find the damping capacity of composite materials. The research has been focused on high frequency applications materials. The method was implemented on carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) plates. The Lamb waves were generated using ultrasonic pulse generator setup. The hybrid method has been explored in this article and the results have been compared with bandwidth methods available in the literature.

• Structural Engineering and Mechanics
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• v.65 no.1
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• pp.91-98
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• 2018

Three structure-dependent integration methods with no numerical dissipation have been successfully developed for time integration. Although these three integration methods generally have the same numerical properties, such as unconditional stability, second-order accuracy, explicit formulation, no overshoot and no numerical damping, there still exist some different numerical properties. It is found that TLM can only have unconditional stability for linear elastic and stiffness softening systems for zero viscous damping while for nonzero viscous damping it only has unconditional stability for linear elastic systems. Whereas, both CEM and CRM can have unconditional stability for linear elastic and stiffness softening systems for both zero and nonzero viscous damping. However, the most significantly different property among the three integration methods is a weak instability. In fact, both CRM and TLM have a weak instability, which will lead to an adverse overshoot or even a numerical instability in the high frequency responses to nonzero initial conditions. Whereas, CEM possesses no such an adverse weak instability. As a result, the performance of CEM is much better than for CRM and TLM. Notice that a weak instability property of CRM and TLM might severely limit its practical applications.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.581-586
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• 2004

This paper presents Newtonian formulation of the dynamics of plates treated fully with Active Constrained Layer Damping (ACLD). The developed equations of the plate/ACLD system provide analytical models far predicting the dynamic of laminated plates subjected to passive and active vibration damping controls. Numerical solutions of the analytical models are presented fir simply-supported plates in order to study the performance of the plate/ACLD system for different control strategies. The developed models present invaluable means for designing and predicting the performance of the smart laminated plates that can be used in many critical engineering applications.

• Wind and Structures
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• v.2 no.3
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• pp.201-251
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• 1999

Flexible structures may experience excessive levels of vibration under the action of wind, adversely affecting serviceability and occupant comfort. To ensure the functional performance of a structure, various design modifications are possible, ranging from alternative structural systems to the utilization of passive and active control devices. This paper presents an overview of state-of-the-art measures that reduce the structural response of buildings, including a summary of recent work in aerodynamic tailoring and a discussion of auxiliary damping devices for mitigating the wind-induced motion of structures. In addition, some discussion of the application of such devices to improve structural resistance to seismic events is also presented, concluding with detailed examples of the application of auxiliary damping devices in Australia, Canada, China, Japan, and the United States.

• International Journal of High-Rise Buildings
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• v.8 no.4
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• pp.275-281
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• 2019

The paper presents a generalization of existing analytical approaches to determine the across-wind aerodynamic damping of tall structures through the quasi-steady theory. The theory takes into account the nature of non-uniform wind, structural mode shapes and the variation of structural parameters. Numerical applications on a prototype high-rise building and a real sculptural tower point out that the common approach may be over simplified, giving rise to inappropriate predictions of the aerodynamic damping. The role of the structural mode shapes, usually being neglected for uniform structures, is then highlighted.