• Title/Summary/Keyword: mode coupling

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An Experimental Study of Radiated So from Elastic Thin Plate in a Turbulent Boundary Layer (난류 유동장 내에 놓인 탄성을 갖는 박판의 방사소음에 대한 실험적 연구)

  • Lee, Seung-Bae;Gwon, O-Seop;Lee, Chang-Jun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.10
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    • pp.1327-1336
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    • 2001
  • The structural modes driven by the low wave-number components of smooth elastic wall pressure provide a relatively weak coupling between the flow and the wall motion. If the elastic thin plate has any resonant mode whose wave-number of resonance coincides with $\omega$/U$\sub$c/, the power will be transmitted to those modes of vibration by the flows. We examine the problem in which the elastic thin plate is subject to pressure fluctuations under turbulent boundary layer. Measurements are presented of the frequency spectra of the near- and far-field pressures and radiated sound contributed by the various wave modes of the thin elastic plate. Dispersion equation for wave motions of elastic plate is used to investigate the effect of bending waves of relatively low wave number on radiated sound. The low wave-number motion of elastic plate is observed to have much less influence on the low-frequency energy of wall pressure fluctuations than that of the rediated sound. High amplitude events of the wall pressure are observed to weakly couple with high-frequency energy of radiated sound for case of low tension applied to the plate. The sound source localization is applied to the measurement of radiated sound by using acoustic mirror system.

Dynamic Analysis of Geometric Nonlinear Behavior of Suspension Bridges under Random Wind Loads (랜덤풍하중에 대한 현수교의 기하학적 비선형 거동의 동적해석)

  • Yun, Chung Bang;Hyun, Chang Hun;Yoo, Je Nam
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.8 no.2
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    • pp.185-196
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    • 1988
  • In this study, a method of nonlinear dynamic analysis of suspension bridges subjected to random wind loads is pre.sented. The nonlinearity considered is the one due to the interaction between the motion of the bridge girder and the tertsion variation of the main cables. The equation of motion is formulated using a continuum approach. The coupling between the vertical and torsional motions are included in the analysis. The equation of motion is solved by using the mode superposition method. The analysis is carried out in the frequency domain utilizing the stochastic linearization technique on to the modal equations. In the linearization procedure, the nonlinear terms are approximated as linear ones with constant terms. The verification of the method has been performed on a case with four modal degrees of freedom. Example analyses are carried out on two suspension bridges for various wind speeds and wind force parameters. Numerical results indicate that, by including the nonlinearity into the analysis, the dynamic responses of the bridges, particularly in the vertical direction, change considerably.

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The Effect of Zirconate Addition on the Joint Properties of Epoxy Adhesive for Car Body Assembly (차체 구조용 에폭시 접착제의 접합부 특성에 미치는 Zirconate 첨가효과)

  • Jeung, Eun-Taek;Lee, Hye-Rim;Lee, So-Jeong;Lim, Chang-Young;Seo, Jong-Dock;Kim, Mok-Soon;Kim, Jun-Ki
    • Journal of Welding and Joining
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    • v.31 no.5
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    • pp.71-76
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    • 2013
  • The effect of zirconate having - NH functional group on the T-peel and lap shear strength of $CaCO_3$ containing structural epoxy adhesive for car body assembly was investigated. Curing behavior of epoxy adhesive samples were investigated by differential scanning calorimeter (DSC) techniques. The addition of zirconate up to 7.5 phr did not affect the curing mechanism of epoxy adhesive. While the small amount of zirconate addition less than 1.1 phr increased the cross-linking density, the excess addition of zirconate resulted in the increase of uncross-linked impurity. From the increase of T-peel and lap shear strength and the change of fracture mode from the adhesive failure to the mixed one, it was considered that the small addition of zirconate was effective in improving the adhesion strength of epoxy adhesive to the adherend and inorganic filler surfaces. The formation of uncross-linked impurity with the excess addition of zirconate was considered to decrease the joint strength by decreasing the cohesive strength of the cured epoxy.

An Analysis of the Transition Time between Dry and Wet Period in the Han River Basin (한경유역에서의 건기와 우기의 변이기간 분석)

  • Lee, Jae-Su
    • Journal of Korea Water Resources Association
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    • v.33 no.3
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    • pp.375-382
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    • 2000
  • The surface hydrology of large watershed is susceptible to several preferred stable states with transitions between stable states induced by stochastic fluctuations. This comes about due to the close coupling of land surface and atmospheric interaction. An interesting and important issue is the duration of residence in each mode. In this study, mean transition tunes between the stable modes are analyzed for the Han River Basin. On the basis of historical data, the nonlinear water balance model is calibrated for the Han River Basin. The transition times between the stable modes in the model are studied based on the stochastic representation of the physical processes and on the calibrated model parameters. This study has implications for prediction of the transition time between stable modes or residence times, that is, the time the system spends in a given stable modes, since this would be equivalent to predicting the duration of drought or wet conditions.

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Different Analysis of b2 Peaks in SERS Spectra of 4-aminobenzenethiol

  • Choe, Han-Gyu;Son, Hyeon-Gyeong;Yu, Hyeon-Ung;Lee, Tae-Geol;Kim, Ji-Hwan
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.02a
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    • pp.257-258
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    • 2012
  • The SERS spectra of 4-aminobenzenethiol (ABT) have served as the "probe" molecule, which have helped spectroscopists to build up the electromagnetic (EM) and chemical (CHEM) enhancement mechanisms. In particular, the b2-peaks (9b, 3, and 19b) of the SERS spectra of ABT have been attributed to arise from the vibronic charge-transfer (CT) between Au or Ag surface and the ABT. Quite recently, however, Tian and co-workers [1] claimed that the b2-peaks are not the CT-enhanced spectra of ABT. Instead, these peaks arise from the 4,4'-dimercaptoazobenzenes (DMABs) that are produced by the oxidative coupling of two ABTs. Their claim is under intense debate currently. Herein, we studied spatially and temporally resolved SERS spectra of ABTs on Ag thin film (thickness of 10 nm), to investigate such claim. Herein, we present a series of additional evidences that strongly support that the b2 intensities of ABTs do not arise from the CT-enhancement: (1) the b2-peaks can be locally "activated" (i. e. turned on) irreversibly with focused laser radiation; (2) the TOF-SIM spectrometry on the activated region show depletion of ABT-Ag+ ions; and finally (3) the spatially resolved FT-IR spectra of the activated region show two pronounced peaks at 1377 cm-1 and 1460 cm-1, both of which can be assigned to the stretching mode of N=N bond. While the result does not disprove the existence of CT or CHEM enhancement in general, the results do show that previous interpretations of the spectra of ABTs should be re-interpreted.

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Flow Visualization by Light Emission in the Post-chamber of Hybrid Rocket (광도측정에 의한 하이브리드 로켓 후연소실의 유동 가시화)

  • Park, Kyung-su;Choi, Go Eun;Lee, Changjin
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.43 no.8
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    • pp.677-683
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    • 2015
  • Hybrid rocket combustion displays low frequency instability(LFI, 10~30Hz) at a certain condition. Vortex shedding in the post-chamber is suspected to cause the occurrence of LFI. This study focused on the visualization of flow image using light emissions from high temperature combustion gas. Results shows that combustion pressure oscillates at a frequency of about 18 Hz, which is in phase with oscillations of light emission. Since LFI is not a property of thermo-acoustic instability, this result suggested there exists a physical coupling of pressure fluctuations with light emissions proportional to chemical reaction. Also POD analysis shows that dominant symmetric spatial modes in the stable combustion shift suddenly into asymmetric spatial pattern with the appearance of LFI. Especially, the appearance of mode 3 is a typical change of flow dynamics in unstable combustion representing a rotational fluid motions associated with vortex shedding.

Fiber optic temperature sensor using evanescent field coupling of the thermo-optic polymer planar waveguide (열광학 폴리머 평면도파로의 소산장결합을 이용한 광섬유형 온도센서)

  • Kim, Si-Hong;Jung, Woong-Gyu;Kim, Kwang-Tack;Song, Jae-Won;Kang, Shin-Won
    • Journal of Sensor Science and Technology
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    • v.9 no.1
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    • pp.15-21
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    • 2000
  • Optical fiber temperature sensor, using resonance wavelength shifting of single mode fiber-to-planar waveguide coupler by heat, was fabricated. Thermo-optic polymers, have large change of refractive index due to heat, were used for planar waveguide. The device fabrication procedure including fiber polishing steps was illustrated and the device structure with independent polarization was demonstrated experimentally. The resonance wavelength difference of fabricated device was less than 2nm. The resonance wavelength shifting owing to temperature variation, from room temperature($24^{\circ}C$) to $90^{\circ}C$, was showed $-0.54nm/^{\circ}C$, $-3nm/^{\circ}C$.

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Analysis of a preliminary configuration for a floating wind turbine

  • Wang, H.F.;Fan, Y.H.;Moreno, Inigo
    • Structural Engineering and Mechanics
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    • v.59 no.3
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    • pp.559-577
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    • 2016
  • There are many theoretical analyses and experimental studies of the hydrodynamics for the tension leg platform (TLP) of a floating wind turbine. However, there has been little research on the arrangement of the TLP's internal structure. In this study, a TLP model and a 5-MW wind turbine model as proposed by the Minstitute of Technology and the National Renewable Energy Laboratory have been adopted, respectively, to comprehensively analyze wind effects and wave and current combinations. The external additional coupling loads on the TLP and the effects of the loads on variables of the internal structure have been calculated. The study investigates preliminary layout parameters-namely, the thickness of the tension leg body, the contact mode of the top tower on the tension leg, the internal stiffening arrangement, and the formation of the spoke structure-and conducts sensitivity analyses of the TLP internal structure. Stress is found to be at a maximum at the top of the tension leg structure and the maximum stress has low sensitivity to the load application point. Different methods of reducing maximum stress have been researched and analyzed, and the effectiveness of these methods is analyzed. Filling of the spoke structure with concrete is discussed. Since the TLP structure for offshore wind power is still under early exploration, arrangements and the configuration of the internal structure, exploration and improvements are ongoing. With regard to its research and analysis process, this paper aims to guide future applications of tension leg structures for floating wind turbine.

FLUID-STRUCTURE INTERACTION IN A U-TUBE WITH SURFACE ROUGHNESS AND PRESSURE DROP

  • Gim, Gyun-Ho;Chang, Se-Myoung;Lee, Sinyoung;Jang, Gangwon
    • Nuclear Engineering and Technology
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    • v.46 no.5
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    • pp.633-640
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    • 2014
  • In this research, the surface roughness affecting the pressure drop in a pipe used as the steam generator of a PWR was studied. Based on the CFD (Computational Fluid Dynamics) technique using a commercial code named ANSYS-FLUENT, a straight pipe was modeled to obtain the Darcy frictional coefficient, changed with a range of various surface roughness ratios as well as Reynolds numbers. The result is validated by the comparison with a Moody chart to set the appropriate size of grids at the wall for the correct consideration of surface roughness. The pressure drop in a full-scale U-shaped pipe is measured with the same code, correlated with the surface roughness ratio. In the next stage, we studied a reduced scale model of a U-shaped heat pipe with experiment and analysis of the investigation into fluid-structure interaction (FSI). The material of the pipe was cut from the real heat pipe of a material named Inconel 690 alloy, now used in steam generators. The accelerations at the fixed stations on the outer surface of the pipe model are measured in the series of time history, and Fourier transformed to the frequency domain. The natural frequency of three leading modes were traced from the FFT data, and compared with the result of a numerical analysis for unsteady, incompressible flow. The corresponding mode shapes and maximum displacement are obtained numerically from the FSI simulation with the coupling of the commercial codes, ANSYS-FLUENT and TRANSIENT_STRUCTURAL. The primary frequencies for the model system consist of three parts: structural vibration, BPF(blade pass frequency) of pump, and fluid-structure interaction.

Outcoupling Enhancement of OLED using Microlens Array and Diffractive Grating (마이크로 렌즈 어레이와 회절격자 레지스트 패턴을 이용한 유기광원(OLED)의 광 추출 효율 향상)

  • Jang, Ji-Hyang;Kim, Kyung-Jo;Kim, Jin-Hun;Oh, Min-Cheol
    • Korean Journal of Optics and Photonics
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    • v.18 no.6
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    • pp.441-446
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    • 2007
  • Outcoupling efficiency of the OLED device is improved by incorporating both a microlens array and a diffractive grating pattern. The microlens array improves the light transmission at the interface of glass and air, and the diffractive grating outcouples the guided mode propagating at the waveguide, which consists of ITO and organic layers. By using the PDMS soft mold imprinting method, the microlens array is fabricated on the glass substrate. The diffractive grating pattern is directly fabricated on the ITO surface by using laser interferometry. A microlens array with a diameter of $10{\mu}m$ improves the light coupling efficiency by 22%. The diffractive grating made of TSMR photoresist enhances the luminance power efficiency by 41% at a current density of $20mA/cm^2$.