• 대한기계학회논문집A
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• 제20권7호
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• pp.2108-2117
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• 1996

The purpose of this paper is to investigate the influence of the exciter attached for the measurement of natural frequencies when extracting the frequency response functions of the test structure in experimental modal analysis. The procedure is first to model the attached exciter as an additional degree of freedom system and next to verify the suggested model by experimentally extracting the natural frequencies of the test structure with various values of exciter mass, stinger stiffness and attachment position of the exciter on the test structure. It is concluded that as additional degree of freedom system which includes the natural frequency of the exciter itself and axial stiffness of stinger should be considered to quantatively define the coupling effects of structure-exciter interaction on the measured natural frequencies. It is not the mass of the exciter itself but the coupling effect of the additional degree of freedom mass-spring system consisting of exciter body and armature coil that characterizes the natural frequency deviation. Therefore, when the natural frequency of this additional mass-spring system is outside of the test frequency range, the coupling effect of structure-exciter interaction can be minimized.

• 융합신호처리학회논문지
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• 제16권2호
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• pp.63-68
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• 2015

본 논문에서는 신호의 파워에 따라 적응적 스텝 사이즈를 갖는 개선된 QIM(Quantization index modulation)과 SVM(Support vector machine) 디코딩 모델을 이용한 다중 오디오 워터마킹 알고리즘을 제안한다. 워터마크는 주파수 크기 응답과 주파수 위상 응답에 QIM을 이용하여 삽입한다. 이는 주파수 크기 응답과 위상 응답에 강인한 공격이 다르기 때문에 양쪽 모두 삽입하여 강인성을 보완하기 위해서이다. 검출시에는 SVM 디코딩 모델을 사용하여 검출된 워터마크가 워터마크로서의 기능이 애매모호한 경우를 개선하여 검출 비율을 향상시킨다. 강인성 검증을 위해 11개의 공격을 사용하였고 그 결과 SVM 디코딩 모델을 사용하지 않은 기존의 다중 오디오 워터마킹 방법보다 훨씬 우수한 성능을 보였다. 특히 PSNR은 최대 7dB의 개선 효과를, BER은 10%의 개선 효과를 보인 것은 주목할 만한 결과이다.

• Earthquakes and Structures
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• 제7권6호
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• pp.1025-1044
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• 2014

In this paper, a systematic technique is proposed for the optimal placement and design of nonlinear dampers for building structures. The concept of Output Frequency Response Function (OFRF) is applied to analytically represent the output frequency response of a building frame where nonlinear viscous dampers are fitted for suppression of vibration during earthquakes. An effective algorithm is derived using the analytical representation to optimally determine the locations and parameters of the nonlinear dampers. Various numerical examples are provided to verify the effectiveness of the optimal designs. A comparison of the vibration suppression performance with that of the frame structure under a random or uniform damping allocation is also made to demonstrate the advantages of the new designs over traditional solutions.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1987년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 16-17 Oct. 1987
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• pp.370-375
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• 1987

Damping piston with an orifice in the piston head is utilized to improve the damping characteristics of a pneumatic push-push type rotary actuator. Through linearized analysis, the optimum size of orifice, which gives maximum damping effect at the frequency where damping is desired. most, is predicted. The frequency response test of teal system were carried out to see the effects of damping piston and to obtain true optimum size of orifice by trying orifices of various size near the predicted value. During the tests, both air and helium were tried as working fluid, and a lag-lead compensation circuit was incorporated to improve system dynamics. The finally chosen orifice size is a little bigger than that predicted from analysis, however it gives high damping effects for the finally designed pneumatic system enough to have wide frequency response bandwidth.

• 한국소음진동공학회논문집
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• 제15권2호
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• pp.123-128
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• 2005

Forced vibration of a thin circular ring with a concentrated harmonic force is analyzed when the ring is free and has only the in-plane motion. Using the unit doublet function for external force, the governing equation is obtained and is solved by the use of Laplace transform. The exact solutions of displacement components and bending moment are obtained. In order to verify the solutions of analysis, finite element analysis is performed and the results shows good agreement. Then, frequency response curves for displacement and bending moment are obtained. In deriving the governing equations and the solutions, nondimensional parameter of the exciting frequency and the magnitude of exciting force are extracted. As the displacement components are obtained, the remaining bending strain, slope, curvature, shear force, etc. can also be derived. With the results of this work, the responses of a free ring excited on multiple points with different frequencies can also be obtained easily by superposition.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 E
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• pp.2444-2446
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• 1999

In this paper, a fiber-optic voltage sensor for measurement of impulse voltage is implemented. A BSO single crystal is used as a Pockels cell. A new signal processing technique is adopted not only to avoid the influences of external perturbations of transmitting optical fiber, but to improve the frequency response characteristics of the optical voltage sensor. Experimental results show that proposed sensor has maximum ${\pm}$2.5% error rate, and has good frequency response.

• 대한기계학회논문집A
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• 제28권4호
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• pp.325-332
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• 2004

Tire vibration modes are known to play a key role in vehicle ride and comfort characteristics. Inputs to the tire such as impacts, rough road surface, tire nonuniformities, and tread patterns can potentially excite tire vibration. In this study, experimental modal analysis on the tire with ground contact are performed by impacting the tire in the radial direction at the center of contact patch. To investigate which modes of tire influence the vibration of wheel and axle when the tire is in contact with ground, the vibration characteristics such as frequency response functions, natural frequencies and their mode shapes from tire to wheel/axle are examined.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1997년도 춘계학술대회 논문집
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• pp.198-201
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• 1997

The new system for identification of organic vapours and analysis method of mechanism between organic vapours and sensitive materials were attempted using the resonant resistance and resonant frequency of Quartz Crystal Analyzer (Q. C. A.). The resonant resistance shift means rheological changes in sensitive LB films occurred by the adsorption of organic vapours, while the resonant frequency shift represent the mass of organic vapour loaded in or on the sensitive LB films. It is thought that we can obtain more accurate response mechanism of organic vapour using the resonant frequency and resonant resistance diagram. The polymeric sensitive material were quantitively depositied using the LB method. In the experimental results, the adsorption behavior of organic vapour response can be decided by two type ; surface adsorption and penetration into sensitive material. Organic vapours had different positions in the Frequency-Resistance (F-R) diagram as to the kinds and concentrations of organic vapours. Thus F-R diagram can be applied to the development of one channel gas sensing system using the Quartz Crystal Analyzer.

• 한국소음진동공학회논문집
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• 제26권1호
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• pp.104-109
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• 2016

The noncontact vibration exciter system using the electro-magnet for a thin plate is studied in this paper. Based on the Euler-Bernoulli beam theory, the equation of motion of thin plate is derived. The main purpose of this experiment is to match the input-frequency and response frequency of thin plate. The test equipment is configured to vibrate on both sides of the thin plate using the electro-magnet. Two frequencies(input frequency and response frequency) in our experiments show very good agreement. This study results will contribute to basic investigate of an alternative air-knife system for the steel industry.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.298-302
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• 2002

Equivalent volume estimation of the coupler and two coupled microphones has a key role in standard microphone pressure calibration. The equivalent volume of the microphone is determined by the dynamic characteristics of the diaphragm system and front cavity. Therefore the modal parameters of diaphragm system - natural frequency and damping fatter - should be measured explicitly for the estimation of the equivalent volume. The diaphragm system is composed of the vibrating diaphragm, back slit behind diaphragm, pressure equalization vent, and front cavity which are acoustically coupled. In the measurement, the electrostatic actuator was used to excite the system with the swept sine, and the frequency response was obtained. The close actuator in front of the diaphragm must influence the radiation impedance of the system, and then the modal parameters. From the measured frequency response, the natural frequency and the damping factor could be estimated with the Complex exponential method based on the Prony model and the zero crossing real and imaginary plot.