• Journal of Sensor Science and Technology
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• v.10 no.1
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• pp.1-8
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• 2001

Conventional microgyroscopes of vibrating type require resonant frequency tuning of the driving and sensing modes to achieve high sensitivity. These tuning conditions depend on each fabricated microgyroscopes, even though the microgyroscopes are identically designed. A new micromachined resonator, which is applicable to microgyroscopes with self-toning characteristics, is presented. Since the laterally driven two degrees of freedom (2DOF) resonator was designed as a symmetric structure with identical stiffness in two orthogonal axes, the resonator is applicable to vibrating microgyroscopes, which do not need mode tuning. A dynamic model of the resonator was derived considering gyroscopic application. The dynamic model was evaluated by experimental comparison with fabricated resonators. The microgyroscopes were fabricated using a simple 2-mask-process of a single polysilicon layer deposited on an insulator layer. The feasibility of the resonator as a vibrating microgyroscopes with self-tuning capability is discussed. The fabricated resonators of a particular design have process-induced non-uniformities that cause different resonant frequencies. For several resonators, the standard deviations of the driving and sensing frequencies were as high as 1232Hz and 1214Hz, whereas the experimental average detuning frequency was 91.75Hz. The minimum detuned frequency was 68Hz with $0.034mVsec/^{\circ}$ sensitivity. The sensitivity of the microgyroscopes was low due to process-induced non-uniformity; the angular rate bandwidth, however, was wide. This resonator could be successfully applicable to a vibrating microgyroscopes with high sensitivity, if improvements in uniformity of the fabrication process are achieved. Further developments in improved integrated circuits are expected to lower the noise level even more.

• Computational Structural Engineering
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• v.4 no.4
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• pp.14-23
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• 1991

T/G 가동중 발생한 Gear Box 파손원인을 조사하기 위하여 실시한 현장측정결과를 이용한 결과, 다음과 같은 사실을 알 수 있었다. 1) 현장 측정치와 구조해석 결과를 토대로 판단해 볼 때 본 연구대상 구조물의 구조상 문제는 없는 것으로 판단된다. 특히 측정된 진동변위를 여러기준과 비교해 볼 때 기계 가동시 구조물에 발생하는 진동은 사람이 감지할 정도에 속한다. 2) 본 연구대상 구조물과 기계의 진동수 차가 커 공진역을 벗어나므로 기계와 구조물이 공진을 일으킬 가능성은 없으며, 감쇠비에 따른 구조물의 동적응답에는 큰 변화가 없는 것으로 판단된다. 3) 구조물설계회사에서 사용한 구조해석 모델은 근사적 모델로서 구조해석 결과 안전한 값이 얻어졌다. 따라서 이 모델을 사용하여 기초설계를 실시할 경우 안전성 문제는 없는 것으로 판단되나, 다소 경제성이 문제가 되었을 것으로 사료된다. 4) 기계제작회사에서 제시한 해석자료의 불충분으로 기계제작회사의 구조해석 모형에 대해서는 충분한 검토를 실시할 수 없었으나 기계제작회사의 해석결과를 측정치와 비교해 볼 때 측정치를 훨씬 초과함을 알 수 있었다. 이는 해석모형 작성시 구조물과 하중의 실제 상황을 제대로 반영하지 못했기 때문으로 판단되며 따라서 해석결과는 타당성이 없어 보인다. 이상의 사실을 토대로 판단해 볼 때 Gear Box 파손의 주된 원인은 구조물의 결함이라기 보다는 기계 자체의 결함인 것으로 판단되나 기계에 대한 조사는 본 연구대상이 아니므로 이에 대한 검토는 실시하지 않았다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.4
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• pp.337-346
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• 2014

This study aimed to understand the mode characteristics of a droplet subject to periodic forced vibration and the detachment of a droplet placed on a plate surface. An surface was coated with Teflon to clearly observe the behavior of a droplet. The contact angle between the droplet and surface and the hysteresis were found to be approximately $115^{\circ}C$ and within $25^{\circ}C$, respectively. The coating process was performed in a clean room that had an environment with a low level of contaminants and impurities such as air dust, detergents, and particles. To predict the resonance frequency of a droplet, theoretical and experimental approaches were applied. Two high-speed cameras were configured to acquire side and top views and thus capture different characteristics of a droplet: the mode shape, the detachment, the separated secondary droplet, and the waggling motion. A comparison of the theoretical and experimental results shows no more than 18 discrepancies when predicting the resonance frequency. These differences seem to be caused by contact line friction, nonlinear wall adhesion, and the uncertainty of the experiment. For lower energy inputs, the contact line of the droplet was pinned and the oscillation pattern was axisymmetric. However, the contact line of the droplet was de-pinned as the oscillation became more vigorous with increased energy input. The size of each lobe at the resonance frequency is somewhat larger than that at the neighboring frequency. A droplet in mode 2, one of the primary mode frequencies, exhibits vertical periodic movement as well as detachment and secondary ejection from the main droplet.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.62-65
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• 2006

In this paper, nonlinear nonplanar vibration of a flexible rectangular cantilever beam is analyzed when one-to-one resonance occurs to the beam. The planar and nonplanar motions of the beam are analyzed in time and frequency domains. In frequency domain, FFT analyzer is used to perform autospectrum and cepstrum analyses for nonlinear response of the beam. In time domain, an oscilloscope is used to investigate the phase difference between the planar and nonplanar motions and to perform Torus analysis in the phase space. Through those analyzing process, the main frequencies of superharmonic, subharmonic, and super-subharmonic motions are investigated in the nonplanar motion due to one-to-one resonance. Analyzing the phase difference between the planar and nonplanar motions, it is observed that the phase difference varies in time.

• Geotechnical Engineering
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• v.11 no.1
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• pp.113-126
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• 1995

Both resonant column (RC) and torsional shear(TS) tests were performed at small to intermediate strain levels to investigate deformational characteristics of cohesive soils. The effects of variables such as strain amplitude, loading frequency, and number of loading cycles were studied. Plasticity index was found to be an important variables in evaluating these effects. Soils tested include undisturbed silts and clays and compacted subgrade soils. At small strains below the elastic threshold, shear modulus is independent of number of loading cycles and strain amplitude. Small strain material damping exists wi th ranges be tween 1.1% and 1.7% for 75 tests. The elastic threshold strain increases as confining pressure and plasticity index increases. Above the cyclic threshold strain, the modulus of cohesive soil decreases with increasing number of cycles while damping ratio is almost independent of number of load cycles. Moduli and damping ratios of cohesive soils obtanined by RC test are higher than those from 75 test because of the frequency effect. Shear modulus of cohesive soil increases linearly as a function of the logarithm of loading frequency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1994.04a
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• pp.76-81
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• 1994

승용차에 있어 엔진의 공회전시나 주행중에 발생하는 여러 형태의 진동 및 소음의 저감은 승차감 및 차량의 안정성에 있어 중요한 과제가 되고 있다. 이러한 소음, 진동은 주로 엔진에서 발생하는 토크의 비주기적인 변동성분이 클러치(clutch), 변속기(transmission), 구동축을 거쳐 바퀴로 전달되는 과정에서 발생한다. 셔플(shuffle)은 주행중 가속페달(accelerator)을 급조작(tip-in, tip-out)하였을 때 차량이 전후로 과도적으로 울렁거리는 종진동 현상을 말하며, 이것은 가속페달의 급조작으로 인해 엔진토크가 큰 변동을 일으키고, 동력전달계를 통해 타이어에 전달된 이 토오크는 타이어축에서 구동측으로 역토오크를 발생시키기 때문에 발생한다. 여기서 팁-인(tip-in)이란 승용차를 저속으로 운전하다가 갑자기 가속페달을 밟는 경우를 말하며, 팁-아웃(tip-out)은 반대로 고속상태에서 갑자기 가속페달을 떼는 경우를 말한다. 실험과 시뮬레이션을 사용한 자동차 동력전달계의 비틀림 진동에 대한 연구는 이미 여러 연구자들에 의해 보고되었다. H.Arai은 2자유도 비선형 모델을 사용하여 클러치 접속시 발생하는 외란과 계의 안정성을 고려하여 시뮬레이션을 수행하였고, M.Kataoka는 기어의 공차(clearance)를 고려한 변속기의 강제 비틀림 진동을 실험과 시뮬레이션을 통하여 해석하였다. 그리고, Wu Hui-Le는 자동차 동력전달계의 비틀림 진동 현상을 실험과 이론적인 계산을 통해 연구하였고, R.J.Comparin는 치타음의 발생구조와 특성을 고찰하고 비서형 비틀림 공진 저감에 의한 치타음 저감 기법에 대하여 연구하였다. 또한 G.J.Fudala는 다자유도 모델을 이용하여 클러치의 비틀림 특서엥 따라 주파수분석을 수행하여 치타음 저감 방법을 연구하였고, T.Sakai는 5자유도 모델을 이용하여 엔진 공회전시 발생하는 치타음에 대해 이론과 실험을 통해 해석하고, 엔진 회전수 변동, 클러치 특성, 변속기의 드래그(drag) 토크의 영향과 치타음 저감을 위한 개선된 클러치 특성을 제시하였다. 이 외에도 Thomas C.T.와 E.P.Petkus는 특정 차량에 대한 동력전달계의 비틀림 진동 현상에 대해 연구하였다. 이러한 연구들로 볼 때, 자동차 동력전달계에서 발생하는 진동은 이론과 실험을 통해 그 해석이 가능하며 설계에 매우 유용하게 이용되고 있음을 알 수 있다. 따라서, 본 연구는 4 실린더 4 싸이클 1.5 L 엔진을 장착한 경승용차의 실차 주행실험을 통해 가속 페달의 급조작에 따른 차체의 종진동 현상을 측정하고, 엔진-변속기-타이어-차체의 반환정계 4자유도 진동모델로 시뮬레이션을 수행하여 실차 주행실험의 결과치와 비교, 분석한 후 클러치 비틀림 특성을 비롯한 자동차 동력전달계의 각 설계인자들이 차체의 종진동에 어떠한 영향을 미치는가를 해석하고자 한다.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.913-915
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• 2001

본 논문에서는 유한 요소법을 압전체에 적용하여 계산한 임피던스 파형을 실험적으로 검증하였으며 이를 압전 변압기에 적용하여 압전 변압기의 공진 특성 즉 입력측에서의 전기적인 임피던스 및 출력측에서의 전기적인 임피던스를 해석하였다. 또한 압전 변압기의 공진 모드를 나타내는 어드미턴스 궤적을 이용한 압전 변압기의 등가 회로 정수의 계산을 통해 등가 회로를 구성하였으며 무 부하시의 승압비를 계산하였다. 등가 회로를 이용하여 계산된 승압비의 결과를 유한 요소법을 이용한 결과와 비교하여 손실을 나타내는 등가 회로 정수(R)를 계산하였으며 유한 요소법에 의한 기계적인 진동 손실의 결과와 비교하여 계산된 저항(R)값의 타당성을 검증하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.2 s.245
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• pp.171-178
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• 2006

Experimental and theoretical study of the non-planar response motions of a circular cantilever beam subject to base harmonic excitation has been presented in this paper work. Theoretical research is conducted using two non-linear coupled integral-differential equations of motion. These equations contain cubic linearities due do curvature term and inertial term. A combination of the Galerkin procedure and the method of multiple scales are used to construct a first-order uniform expansion for the case of one-to-one resonance. The results show that the non-linear geometric terms are very important for the low-frequency modes of the first and second mode. The non-linear inertia terms are also important for the high-frequency modes. We present the quantitative and qualitative results for non-planar motions of the dynamic behavior.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1613-1622
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• 2010

In this paper, the ultraprecision positioning control of an ultrasonic linear motor in a high-vacuum environment is presented. The bolt-clamped Langivin type transducer (BLT) with the 3rd longitudinal; and 6th lateral vibration modes was developed, which was excited by using the Eigen resonance frequency for two vibration modes in order to generate stable and high power. In practical applications, however, even if a geometrical design has an Eigen frequency, discordance between both mode frequencies can be generated by the contact mechanism and because of manufacturing errors as well as environmental factors. Both mode frequencies were precisely matched by adjusting the impedence. By using this method, the BLT can be driven under any environmental conditions. The nominal characteristic trajectory following(NCTF) control method was adopted to control the positioning of the system in vacuum. The developed linear motor stage show high positioning accuracy with 5 nm.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.4
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• pp.24-35
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• 2018

Impeller blades in the centrifugal compressor are subjected to periodic aerodynamic excitations by interactions between the impeller and the diffuser vanes (DV) in resonant conditions. This may cause high cycle fatigue (HCF) and eventually result in failure of the blades. In order to predict the structural response accurately, the aerodynamic excitation and the major resonant conditions were predicted using unsteady computational fluid dynamics (CFD) and structural analysis. Then, a forced vibration analysis was performed by going through one-way fluid-structure interaction (FSI). A numerical analysis procedure was established to evaluate the structural safety with respect to HCF. The numerical analysis procedure proposed in this paper is expected to contribute toward preventing HCF problems in the initial design stage of an impeller.