• 한국소음진동공학회논문집
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• 제19권4호
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• pp.400-408
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• 2009

이 논문에서는 제어 가능한 ER 마운트를 이용한 유연 구조물의 진동제어 성능을 실험적으로 고찰하였다. 압착 모드형 ER 마운트를 설계하고, 전기장 인가에 따른 댐핑력 특성을 실험적으로 평가하였다. 제작된 ER 마운트를 빔과 프레임 형태의 유연 구조물에 적용하였고, 최적 제어기를 사용하여 시간 영역과 주파수 영역에서 진동제어 성능을 평가하였다.

• 소음진동
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• 제9권6호
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• pp.1247-1258
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• 1999

This paper presents vibration control of a CD-ROM(compact disc-read only memory) drive feeding system consisting of a new type of CD-ROM mount using an electro-rheologocal(ER) fluid. Chemically treated starch particles and silicon oil are used for EF fluid, and its field-dependent yield stresses are experimentally distilled under both the shear and the flow modes. On the basis of the yield stress, an appropriate size of ER CD-ROM mount adapted to conventional feeding system is designed and manufactured. Vibration isolation performance of the proposed mount is evaluated in the frequency domain and compared with that of conventional rubber mount. The ER CD-ROM mount is then installed to the drive feeding system and the system equation of motion is derived. The skyhook controller is then incorporated with the fuzzy technique to improve the performance of ER CD-ROM mount. A set of fuzzy parameters and control rules are obtained from a relation between vertical displacement and pitching motion of the feedng system. Followingthe formulation of the fuzzy-skyhook controller, computer simulation is undertaken in order to evaluate vibration suppression of the CD-ROM drive feeding system subjected to various excitations.

• 한국소음진동공학회논문집
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• 제25권10호
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• pp.707-713
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• 2015

This paper proposes experimental results for control performance deterioration of a piezoelectric actuator under high temperature conditions due to external heat environment. In this work, a heat environment from 30 ℃ to 190 ℃ is established by a heat chamber which is capable of high temperature of heat environment. Inside the heat chamber, an experimental apparatus consisting of the stack type of piezoelectric actuator, laser sensor, gap sensor and temperature sensor is established. After evaluating temperature dependent blocking force, displacement and time response of a piezoelectric actuator inside the heat chamber, tracking control performances are evaluated under various temperature conditions via proportional-integral-derivative(PID) feedback controller. The desired position trajectory has a sinusoidal wave form with a fixed frequency. Control performances are experimentally evaluated at both room temperature and high temperature and presented in time domain.

• 한국정보통신학회논문지
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• 제18권5호
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• pp.1051-1060
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• 2014

본 논문에서는 충격성 잡음 환경에서 직교 주파수분할다중화 시스템의 성능에 대하여 분석한다. 여기서는 충격성 잡음 완화알고리즘 가운데 윈도우 비선형성 방법이 적용된 직교 주파수분할다중화 시스템의 오류 성능이 과표본화율과 윈도우 크기에 의존적임을 모의실험을 통하여 확인한다. 그리고 과표본화율과 윈도우 크기의 변화에 따라 표본화된 신호의 진폭을 제어하는 문턱치의 적절한 영역을 제시한다. 그 결과, 이전의 연구에서 보고된 인자 조합보다 직교 주파수분할다중화 시스템의 심볼 오류 성능 면에서 더욱 우수한 성능을 가지는 인자 조합을 제시한다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
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• pp.34-39
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• 1998

In order to compute the forces which are transmitted through rubber bushings with a commercial multibody dynamic analysis (MBDA) program, a rubber bushing model is needed. The rubber bushing model of MBDA programs such as DADS or ADAMS is the Voigt model which is simply a parallel spring-viscous damper system, meaning that the damping force of the Voigt model is proportional to the frequency. However, experiments do not necessarily support this proportionality. Alternatively, the viscoelastic characteristics of rubber bushings can be better represented by the complex stiffness. The purpose of this paper is to develop a viscoelastic rubber bushing model for the MBDA programs. Firstly, a methodology is proposed to calculate the complex stiffness of rubber bushings considering static and dynamic load conditions. Secondly, a viscoelastic rubber bushing model developed which uses standard elements provided by DADS. The proposed methods are applied to the rubber bushings of the lower control arms of a rear suspension of a 1994 Ford Taurus model. Then, the forces computed for the rubber bushing model are analyzed and compared with the Voigt model in time and frequency domains.

• 대한기계학회논문집A
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• 제32권10호
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• pp.866-872
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• 2008

Torsional oscillations of the mechanical drivetrain in electric vehicles are generated under rapid driving conditions. These lead to an uncomfortable jerking of the vehicle and to an increased stress of the mechanical components. To analyze this phenomenon, a drivetrain model is constructed with lumped parameters. The model parameters are identified by geometrical design data and experimental tests. The proposed model is validated by simulation and experimental tests in the time and the frequency domains. As a result, the torsional oscillations are observed at 7Hz of a low damped natural frequency. Also, the analysis of the effect of the parameter variations on the oscillations shows that the oscillation characteristic is mainly dependent on the rotor inertia, and the stiffness of the mounting of the drive aggregate and the driveshaft. The results will be utilized on the basis of the design of an electric drivetrain and an active control of drivetrain oscillations.

• Food Science and Biotechnology
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• 제16권1호
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• pp.146-149
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• 2007

Dynamic rheological properties of hot pepper-soybean paste (HPSP) mixed with xanthan gum were evaluated at different gum concentrations (0.3, 0.6, and 0.9%) and fermentation times (12 and 24 week). Magnitudes of storage (G') and loss moduli (G") in the HPSP-xanthan gum mixture systems increased with an increase in frequency ($\omega$), while complex viscosity (${\eta}^*$) decreased. G' values were higher than the G" values over most of the frequency range (0.63-63 rad/sec), and were frequency-dependent. The dynamic moduli (G', G", and ${\eta}^*$) of the HPSP-xathan mixtures were lower than those of the control (0% gum). The differences between the dynamic moduli values at 12-week and 24-week fermentation decreased with increasing gum concentration, showing that xanthan gum can be used to stabilize and improve the viscoelastic rheological properties of HPSP. The G' value of the HPSP-xathan mixtures increased with an increase in gum concentration from 0.3 to 0.9%, whereas the G" decreased. The ability of xanthan gum to increase the elastic properties in the HPSP-xanthan mixture systems seemed to be the result of the incompatibility phenomena existing between xanthan gum and glutinous rice starch.

• Computers and Concrete
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• 제27권2호
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• pp.85-97
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• 2021

In this study, the effect of steel fiber utilization, boundary conditions, different beam cross-section, and length parameter are investigated on the free vibration behavior of fiber reinforced self-compacting concrete beam on elastic foundation. In the analysis of the beam model recommended by Euler-Bernoulli, a method utilizing Stokes transformations and Fourier Sine series were used. For this purpose, in addition to the control beam containing no fiber, three SCC beam elements were prepared by utilization of steel fiber as 0.6% by volume. The time-dependent fresh properties and some mechanical properties of self-compacting concrete mixtures were investigated. In the modelled beam, four different beam specimens produced with 0.6% by volume of steel fiber reinforced and pure (containing no fiber) SCC were analyzed depending on different boundary conditions, different beam cross-sections, and lengths. For this aim, the effect of elasticity of the foundation, cross-sectional dimensions, beam length, boundary conditions, and steel fiber on natural frequency and frequency parameters were investigated. As a result, it was observed that there is a noticeable effect of fiber reinforcement on the dynamic behavior of the modelled beam.

• Steel and Composite Structures
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• 제45권1호
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• pp.119-131
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• 2022

Due to the complexity of the structure and the limits of classical SEA, a combined SEA approach is employed, with angle-dependent SEA in the low- and mid-frequency ranges and advanced SEA (ASEA) considering indirect coupling in the high-frequency range. As an important component of the steel box girder, the dynamic response of an L-junction periodic ribbed plate is calculated first by the combined SEA and validated by the impact hammer test and finite element method (FEM). Results show that the indirect coupling due to the periodicity of stiffened plate is significant at high frequencies and may cause the error to reach 38.4 dB. Hence, the incident bending wave angle cannot be ignored in comparison to classical SEA. The combined SEA is then extended to investigate the vibration properties of the steel box girder. The bending wave transmission study is likewise carried out to gain further physical insight into indirect coupling. By comparison with FEM and classical SEA, this approach yields good accuracy for calculating the dynamic responses of the steel box girder made of periodic ribbed plates in a wide frequency range. Furthermore, the influences of some important parameters are discussed, and suggestions for vibration and noise control are provided.

• 보건교육건강증진학회지
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• 제28권4호
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• pp.51-61
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• 2011

Objectives: The main purpose of this study was to examine factors associated with depression of middle school students in relation to self-esteem, type A behavior pattern, and locus of control. Methods: A survey was administered to a convenience sample of 309 middle school students. The data analysis procedure included frequency distribution, t-test, ANOVA, Pearson correlation coefficients, and stepwise multiple regression using depression as the dependent variable. Results: The prevalence of depression was 27.2%. Stepwise multiple regression revealed that the factors such as self-esteem(${\beta}$=0.422, p<0.001), type A behavior pattern(${\beta}$=0.166, p<0.001), and locus of control(${\beta}$=-0.165, p<0.001) turned out to be significant affecting factors. Forty nine percent of variance in depression was explained by these factors(40% of variance by self-esteem). Conclusions: The findings suggest that personal internalizing variables should be considered when developing mental health education program to prevent the occurrence of depression for middle school students.