• Smart Structures and Systems
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• 제5권3호
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• pp.209-221
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• 2009

A control algorithm for seismic protection of building structures based on the theory of variable structural control or sliding mode control is presented. The paper focus in the design of sliding surface. A method for determining the sliding surface by pole assignment algorithm where the poles of the system in the sliding surface are obtained on-line, based on the frequency content of the incoming earthquake signal applied to the structure, is proposed. The proposed algorithm consists of the following steps: (i) On-line FFT process is applied to the incoming part of the signal and its frequency content is recognized. (ii) A transformation of the frequency content to the complex plane is performed and the desired location of poles of the controlled structure on the sliding surface is estimated. (iii) Based on the estimated poles the sliding surface is obtained. (iv) Then, the control force which will drive the response trajectory into the estimated sliding surface and force it to stay there all the subsequent time is obtained using Lyapunov stability theory. The above steps are repeated continuously for the entire duration of the incoming earthquake. The potential applications and the effectiveness of the improved control algorithm are demonstrated by numerical examples. The simulation results indicate that the response of a structure is reduced significantly compared to the response of the uncontrolled structure, while the required control demand is achievable.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.1169-1176
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• 2002

Analytical model of beat response is derived on a slightly asymmetric ring and is veryfied by experiment. The asymmetric ring is a simplified model used to explain the beat property of a Korean bell. The asymmetric ring has mode pair having slight frequency difference in each radial mode. Each mode pair produces beat phenomenon by the interaction of the two close frequency components. Based on the analytical model, beat maps are first proposed and characteristics of beat on the circumference are detaily explained.

• 소음진동
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• 제5권1호
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• pp.117-122
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• 1995

The transfer matrix method is proposed to compensate the attachment effect of a piezo-electric impedance head. To validate the proposed method, an experiment is carried out for axial vibration of a uniform rod for which an analytical solution is known. The impedance head is attached to the test rod by a stud and is connected to the exciter. The frequency response function is mesured by applying random excitation from the electro-magnetic exciter. The frequency response function compensated by the method proposed in this research shows good agreement with the analytical solution.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 춘계학술대회 논문집
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• pp.496-497
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• 2009

In this paper the power flow finite element method (PFFEM) has been used to analyze the vibration of a plate partially covered with a damping sheet. Experiments have been performed to measure the loss factor and frequency response functions of the plate partially covered with the damping sheet. The data for the loss factor has been used as the input data to predict the vibration of the coupled plates with PFFEM. The comparison between the experimental results and the predicted PFFEM results for the frequency response functions has been performed. It showed that PFFEM can be effectively used to predict structural vibration in medium-to-high frequency ranges.

• 산업기술연구
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• 제27권A호
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• pp.47-53
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• 2007

A theoretical model based on Rayleigh-Ritz method is proposed to predict the resonance frequency of a W/T(Wind Turbine) tower structure supported by guy cables. In order to verify the validity of the theoretical model, a reduced W/T tower system is manufactured and tested. Frequency response and mode data are determined by modal testing and finite element analysis is performed to calculate the natural frequency of the tower model. Numerical and experimental results are compared with those by the theoretical analysis. Parametric study by the theoretical model shows how the cable tension and cable elasticity influence the resonance frequency of the W/T tower structure. Finally, vibration response under various rotating speed is investigated to examine the possibility of severe resonance.

• Advanced Composite Materials
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• 제17권2호
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• pp.111-124
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• 2008

The effect of temperature on natural frequency and damping is investigated in two different composite materials, Kevlar 29 fiber woven and polyethylene cloth, used especially to design ballistic armor. A damping monitoring method is used experimentally to measure the frequency response curve and it is also modeled numerically using a finite element program. The natural frequencies of a material, or a system, are a function of its elastic properties, dimensions and mass. This concept is used to calculate theoretical vibration modes of the composites. The damping properties in terms of the damping factor are determined by the half-power bandwidth technique. Numerically analyzed and experimentally measured time response curves are compared. It is seen that polymer matrix composites have temperature dependent mechanical properties. This relationship is functional and they have different effects against temperature.

• Structural Engineering and Mechanics
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• 제68권1호
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• pp.103-119
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• 2018

In the present research, an attempt is made to obtain a semi analytical solution for both nonlinear natural frequency and forced vibration of embedded functionally graded double layered nanoplates with all edges simply supported based on nonlocal strain gradient elasticity theory. The interaction of van der Waals forces between adjacent layers is included. For modeling surrounding elastic medium, the nonlinear Winkler-Pasternak foundation model is employed. The governing partial differential equations have been derived based on the Mindlin plate theory utilizing the von Karman strain-displacement relations. Subsequently, using the Galerkin method, the governing equations sets are reduced to nonlinear ordinary differential equations. The semi analytical solution of the nonlinear natural frequencies using the homotopy analysis method and the exact solution of the nonlinear forced vibration through the Harmonic Balance method are then established. The results show that the length scale parameters give nonlinearity of the hardening type in frequency response curve and the increase in material length scale parameter causes to increase in maximum response amplitude, whereas the increase in nonlocal parameter causes to decrease in maximum response amplitude. Increasing the material length scale parameter increases the width of unstable region in the frequency response curve.

• Journal of Acupuncture Research
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• 제20권1호
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• pp.177-190
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• 2003

Objective : This study was intended to investigate the analgesic effects of electroacupuncture(EA) on mechanical allodynia according to the frequency and intensity of EA. Also to know if mechanical allodynia and the analgesic effects of EA is related to the sympathetci nervous system and/or the purinergic system. Methods : mechanical allodynia-induced rats were produced by resecting S1-S2 nerve. The zusanli(ST36) was used for acupoint and the rats were divided into 4 groups. Each group was given different stimuli[low frequency low intensity-EA(LFLI-EA), low frequency high intensity-EA(LFHI-EA), high frequency low intensity-EA(LFHI-EA), high frequency high intensity-EA(HFHI-EA)]. Futhermore, to make sympathectomy6-OHDA and phentolamine were administered intraperitonially and the concentration of norepinephrine(NE) were measured. As a ATP blocker, suramin was applied for this study. Results : Comparing to control group, each of the 4 groups(LFLI-EA, LFHI-EA, HFLI-EA, HFHI-EA) showed a significant reduction of response frequency of mechanical allodynia. LFHI-EA was more effective than that of LFLI-EA. The LFHI-EA group also had longer lasting effects from the stimulation than the other groups. Sympathectomy didn't show any reduction of response frequency of mechanical allodynia.(Each n=6, n=4). Nor did both sympathectomy and ATP block. The response frequency wasn't reduced by sympathectomy or by sympathectomy and ATP block, but was significantly reduced with LFHI-EA Conclusions : These results suggest that EA has a significant analgesic effect on mechanical allodynia which has no connection with NE and/or ATP.

• Tribology and Lubricants
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• 제14권1호
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• pp.14-22
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• 1998

This paper describes the effects of exciting frequency on the stiffness and damping coefticients of a 5-pad tilting pad journal bearing, LOP (load on pad) type. The stiffness and damping coefficients are investigated experimentally under the different values of exciting frequency, bearing load and shaft speed. These coefficients are estimated by measuring the response of the relative displacement between the bearing and the shaft and acceleration of the bearing due to the known exciting loads acting on the bearing. In order to analysis the response of exciting load, displacement and acceleration, a FFT analyzer is used. It is shown that the variation of exciting frequency has a little effect on both the stiffness and damping coefficients. Both the stiffness and damping coefficients in the loading direction are decreased by the increase of shaft speed but increased by the increase of bearing load.

• Asian-Australasian Journal of Animal Sciences
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• 제8권5호
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• pp.471-476
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• 1995

The relationship between udder maximum capacity (36-h accumulated milk yield) and the response of dairy cows (average producers) to thrice-daily milking was studied in 25 Friesian and 15 Jersey cows using the technique of half-udder study. Maximum half-udder capacity (acual yield) as well as whole udder capacity (estimated by udder measurements) was not altered significantly after 12-day thrice-daily milking period compared with a similar twice-daily period, although there was a positive response to increased milking frequency on secretion rate during this period. No effect of breed, season of the year or stage of lactation was observed on the above relationship. Hours-worth of capacity was higher with increased milking frequency, with Jersey than Friesian. These results suggest that udder capacity is not a limiting factor in increased milk production.