• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.6 s.52
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• pp.57-65
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• 2006

This paper presents hybrid structural damage monitoring system which performs both global damage assessment of structure and damage detection of local structural joints. Hybrid damage monitoring system is composed of vibration-based technique and electro/mechanic impedance technique. Vibration-based technique detects global characteristic change ot structure using modal characteristic change of structure, and electro/mechanical impedance technique detects damage existence of local structural joints using impedance change of PZT sensor. For the verification of the proposed hybrid monitoring system, a series of damage scenarios are designed to loosened bolts situations of the structural joints, and acceleration response and impedance response signatures are measured. The proposed hybrid monitoring system is implemented to monitor global damage-state and local damages in structural joints.

• Korean Journal of Optics and Photonics
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• v.13 no.4
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• pp.308-313
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• 2002

One of the nonclassical effects in two-photon interference experiments, spatial quantum beating, is observed in fourth-order interference with pairs of photons produced by a spontaneous parametric down-conversion process. When photon pairs in different frequencies $\omega1$ and $\omega2$ are mixed together, and directed to two detectors, the coincidence counts exhibit a cosine modulation with difference frequency | $\omega1$- $\omega2$|. The measured coincidence counts turned out to have an interference pattern with periodicity of 10.45 ㎛ in position or 34.82fs in time delay, which corresponds to the period 2$\pi$/| $\omega1$- $\omega2$| for the beat frequency of 0.29${\times}10^{14}$Hz.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.3
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• pp.232-241
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• 2011

The hybrid rocket shows interesting characteristics of complicated mixing layer developed by the interaction between turbulent oxidizer flow and injected surface mass flow from fuel vaporization. In this study, the compressible LES was conducted to explore the physical phenomena of surface oscillatory flow induced by the flow interferences in a duct domain. From the numerical results, the wall injection generates the stronger streamwise vorticites and the negative components of axial velocity accompanied with the azimuthal vorticity near the surface. And the vortex shedding with a certain time scale was found to be developed by hydrodynamic instability in the mixing layer. The pressure fluctuations in this calculation exhibit a peculiar peak at a specific angular frequency($\omega$=8.8) representing intrinsic oscillation due to the injection.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.5
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• pp.50-57
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• 2004

For the application of structural health monitoring such as AE detection, a stabilized FBG sensor system with wide dynamic range was proposed. A tunable Fabry-Perot filter with narrow free spectral range(FSR) was used to simplify the multiplexing demodulator for FBG vibration sensors. Stabilization controlling system was also developed for the maintenance of maximum sensitivity of the sensors. In order to verify the performance of the proposed FBG vibration sensor system, we measured sensitivity, and the system showed the average sensitivity of 256 $n{\in}_{mas}/{\sqrt{Hz}}$. Finally, multi-points vibration tests using in-line FBG sensors were conducted to validate the multiplexing performance of the FBG system.

• Journal of KIISE
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• v.44 no.4
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• pp.374-382
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• 2017

As the walking exercise is emphasized in personalized healthcare, numerous services demand walking information. Along with the propagation of smartphones nowadays, many step-counter applications have been released. But these applications are error-prone to abnormal movements such as simple shaking or vibrations; also, different step counts are shown when the phone is positioned in different locations of the body. In this paper, the proposed method accurately counts the steps regardless of the smartphone position by using an accelerometer and a proximity sensor. A threshold is set on each of the six positions to minimize the error of undetection and over-detection, and the cut-off section is set to eliminate any noise. The test results show that the six position type were successfully identified, and through a comparison experiment with the existing application, the proposed technique was verified as superior in terms of accuracy.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.12
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• pp.1040-1047
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• 2012

This paper presents a fault diagnosis algorithm of control surfaces of small fixed-wing aircraft to reduce maintenance cost or to improve repair efficiency by estimation of fault occurrence or part replacement periods. The proposed fault diagnosis algorithm consists of ANPSD (Averaged Normalized Power Spectral Density), PCA (Principle Component Analysis), and GC (Geometric Classifier). ANPSD is used for frequency-domain vibration testing. PCA has advantage to extract compressed information from ANPSD. GC has good properties to minimize errors of the fault detection and isolation. The algorithm was verified by the accelerometer measurements of the scaled normal and faulty ailerons and the test results show that the algorithm is suitable for the detection and isolation of the control surface faults. This paper also proposes solutions for some kind of implementation problems.

• Journal of Navigation and Port Research
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• v.33 no.1
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• pp.57-63
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• 2009

In order to effectively isolate the marine wastes with an effluent standard, the pretreatment process is required to isolate solid materials from the liquid-solid mixed wastes. The more effective the pretreatment becomes, the more processing capacity of posttreatment will be improved and process facilities will be downsized. In this paper, we suggested the vibrating reverse-slant screen, investigated the optimal vibration frequency and vibrator installation angle for the separation of the liquid solid mixed wastes. Several experiments for separation efficiency were conducted under the condition of various vibration frequency($35{\sim}60Hz$, 5Hz interval) and vibrator angle($0^{\circ}$, $30^{\circ}$, $45^{\circ}$, $90^{\circ}$) considering the crack of screen. The screen inclination angle is set up the gradient as $3^{\circ}{\sim}5^{\circ}$ through the preliminary experiments. Also, we made two types of screen(respectively rectangle and square screen). The separation device has shown the optimum efficiency at vibrator angle $0^{\circ}$ and vibration frequency 60Hz, and has no relation with the shape of screen. And the proposed technology is verified by comparing with quantity of suspended solids before and after filtration.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.997-999
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• 2008

In this paper, viologen derivative is used as charge transfer material to develop sensors for detecting the organic pollutants which are the main reason of harbor pollution. We fabricated self-assembled monolayers of viologen derivative on gold electrode of QCM and investigated an electrochemical behavior property. We also determined electrochemical sensing property about environmental pollution materials such as bezene, phosphate and surfactant through quantitative and qualitative analysis of charge transfer using intrinsic property of viologen derivative by temperature and concentration change. From the achieved results, we can apply and develope the detecting sensors for harbor pollutants.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.6
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• pp.429-436
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• 2014

Most mechanical systems are now operating consistently and getting faster due to the development of automation systems. Peoples' dependence on machines have increased as when problems occur within the mechanical system, personal injury and production loss may come as a result, as most of the mechanical system's malfunctions are caused by the failure of the rotational bearing. What we need now is a maintenance system that can warn us when it detects abnormal conditions before significant damage occurs to the bearing. In this study, we have developed an acoustic emissions sensor that can figure if the bearing works under the normal condition. With this acoustic emissions sensor, we can inspect the bearing for defects by using the Heterodyne technique, which converts the ultrasound signal into audio, as a signal conditioning process.

• Korean Journal of Materials Research
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• v.7 no.8
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• pp.694-700
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• 1997

TiC(001) 면위에 Mg 금속을 단원자층으로 증착시킨 후 산화 및 열처리 과정을 거쳐서 MgO 초박막을 성장시키고, 성장된 MgO 막의 전자상태 및 표면포논을 UPS, XPS 및 HREELS를 사용하여 측정하였다. 전도성 기판위에 epitaxial 산화물막을 성장시킨 후 성장된 막의 전자구조 및 표면포논을 측정함으로써 벌크에서 분리된 2차원적 특성을 갖는 '표면 모델'의 물성을 연구하고자 하였는데, 이러한 '표면모델'은 잘 배열된 원자구조를 얻을 수 있고 두께가 충분히 얇아서 전하축적을 피할 수 있기 때문이다. 기판으로는 MgO와 같은 암염형 결정구조를 갖고 있고, 격자상수 차이가 2.6% 로서 매우 작으며, 비저항이 매우 낮은 전이 금속 탄화물 중의 하나인 TiC(001) 면을 사용하였다. TiC(001)면에 증착된 MgO층의 UPS He-l 스펙트럼을 측정한 결과 O2p및 XPS스펙트럼은 열처리를 전후로 하여 변하지 않았으며, 이로부터 상온에서 산소의 확산만으로 MgO 상이 형성됨을 알 수 있었다. MgO초박막의 표면 포논을 HREELS를 사용하여 검출하였다. 거시적 포논중에서 F-K 파 및 Rayleigh 모드가 관찰되었는데, F-k파는 MgO막의 2차원성으로 인하여 벌크의 경우보다 높은 진동 에너지를 갖고 있었고 Rayleigh모드는 벌크 MgO와 유사한 분산관계를 보였다. 미시적 포논중에서 Wallis(S/sub 2/)모드가 측정되었는데, 그 진동에너지는 벌크에서와 같고 off-specular방향에서도 소멸되지 않았다.