• Title/Summary/Keyword: mode shape

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Analytical Study on Seismic Performance Assesment of Reinforced Concrete Shear Wall using High-Strength Reinforcing Bar (고강도 철근을 적용한 철근콘크리트 전단벽체의 내진성능평가를 위한 해석적 연구)

  • Cheon, Ju-Hyun;Kim, Kyung-Min;Park, Kwang-Min;Shin, Hyun-Mock
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.21 no.2
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    • pp.138-145
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    • 2017
  • The purpose of this study is to establish a reasonable analytical method for the estimation of overall behavior characteristic from cracking to yielding of rebar and crushing of concrete and seismic performance of reinforced concrete shear wall with high-strength reinforcing bar. A total of 8 specimens of reinforced concrete walls which have constant aspect ratio and a variety of variables such as reinforcement ratio, reinforcement yielding strength, reinforcement details, concrete design strength, section shape and whether lateral restraint hoop were selected and the analysis was performed by using a non-linear finite element analysis program (RCAHEST) applying the proposed constitutive equation by the authors. The mean and coefficient of variation for maximum load from the experiment and analysis results was predicted 1.04 and 8%. The mean and coefficient of variation for displacement corresponding maximum load from the experiment and analysis results was predicted 1.17 and 19% respectively. The analytical results were predicted relatively well the fracture mode and the overall behavior until fracture for all specimens. These results are expected to be used as basic data for application of high-strength reinforcing bar to design codes in the future.

The Active Noise Control in Harmonic Enclosed Sound Fields (I) Computer Simulation (조화가진된 밀폐계 음장에서의 능동소음제어 (I) 컴퓨터 시물레이션)

  • Oh, Jae-Eung;Lee, Tae-Yeon;Kim, Heung-Seob;Shin, Joon
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.5
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    • pp.1054-1065
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    • 1993
  • A computer simulation is performed on the effectiveness of the active minimization of harmonically excited enclosed sound fields for producing global reduction in the amplitude of the pressure fluctuations. In this study for the appreciable reductions in total time averaged acoustic potential energy, $E_{pp}$, the transducer location strategies for three dimensional active noise control is presented based on a state space modal which approximates the closed acoustic field.In this study, the above theoretical basis is used to investigate the application of active control to sound fields of low modal density. By the used of room-like 3-dimensional rectangular enclosure it is demonstrated that the reductions in $E_{pp}$ can be achieved by using a single secondary source, provided that the source is placed within the half a wavelength from the primary source and placed away from nodal line of the sound field. Concerning the reductions in $E_{pp}$ by minimzing the pressure in sound fields by the use of 3-dimensional rectangular enclosure, the effects of the number of sensors and the locations of these sensors are investigated. When a few modes dominate the response it is found that if only a limited number of sensors are located away from nodal line and located at the pressure maxima of the sound field such as at each corner of a rectangular enclosure.

A Study on the Seismic Response of a Non-earthquake Resistant RC Frame Using Inelastic Dynamic Analyses (비선형 동적 해석을 이용한 비내진 상세 RC 골조의 지진거동 특성 분석)

  • Jeong, Seong-Hoon;Lee, Kwang-Ho;Lee, Soo-Kueon
    • Journal of the Korea Concrete Institute
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    • v.22 no.3
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    • pp.381-388
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    • 2010
  • In this study, characteristics of the seismic response of the non-earthquake resistant reinforced concrete (RC) frame were identified. The test building is designed to withstand only gravity loads and not in compliance with modern seismic codes. Smooth bars were utilized for the reinforcement. Members are provided with minimal amount of stirrups to withstand low levels of shear forces and the core concrete is virtually not confined. Columns are slender and more flexible than beams, and beam-column connections were built without stirrups. Through the modeling of an example RC frame, the feasibility of the fiber elementbased 3D nonlinear analysis method was investigated. Since the torsion is governed by the fundamental mode shape of the structure under dynamic loading, pushover analysis cannot predict torsional response accurately. Hence, dynamic response history analysis is a more appropriate analysis method to estimate the response of an asymmetric building. The latter method was shown to be accurate in representing global responses by the comparison of the analytical and experimental results. Analytical models without rigid links provided a good estimation of reduced stiffness and strength of the test structure due to bond-slip, by forming plastic hinges closer to the column ends. However, the absence of a proper model to represent the bond-slip poased the limitations on the current inelastic analysis schemes for the seismic analysis of buildings especially for those with round steel reinforcements. Thus, development of the appropriate bond-slip model is in need to achieve more accurate analysis.

Experimental Analysis on Vibration of Composite Plate by Using FBG Sensor System (브래그 격자 센서 시스템을 이용한 복합재 평판 진동의 실험적 해석)

  • Kim, Dae-Hyun
    • Journal of the Korean Society for Nondestructive Testing
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    • v.29 no.5
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    • pp.436-441
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    • 2009
  • A fiber optic sensor is prospective to be applied to structural health monitoring. Especially, a fiber Bragg grating(FBG) sensor is one of the most popular sensors for the structural health monitoring. The FBG sensor has several demodulation systems for tracking the shift of the Bragg wavelength. The dynamic bandwidth is dependent on the demodulation system. In this paper, the sensing mechanism is that the slope of the optical spectrum of FBG could be used as its sensitivity when the tunable laser shot the monochromatic laser wavelength at the highest slope point. In this technique, the high sensitivity is guaranteed even though the sensing range is limited. In an example of the application, the composite plate embedding a FBG sensor was manufactured by using an autoclave method and the above sensing mechanism was applied to the composite plate. Firstly, the natural frequencies of the plate were successfully measured by the FBG sensor during the impact hammer test. Secondly, a high-power speaker was used to force the plate to be vibrated at the specific frequency that was one of the natural frequencies. During the shaking, the FBG sensor measures the dynamic characteristics and ESPI was also used to measure the mode shape. From the two dynamic tests, the availability of the FBG sensor system and the ESPI was proven as a technique for measuring the dynamic characteristics of composite structure.

Implementation of AC Direct Driver Circuit for Ultra-slim LED Flat Light System (초슬림 LED 면조명 기구용 교류 직결형 구동 회로 구현)

  • Cho, Myeon-Gyun;Choi, Hyo-Sun;Yoon, Dal-Hwan
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.13 no.9
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    • pp.4177-4185
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    • 2012
  • LEDs are becoming the most suitable candidate replacing traditional fluorescent lamps because of its eco-friendly characteristics. LEDs are also actively used to design green building system and to make outdoor billboard as a back-light system due to its high energy efficiency. In this paper, we have developed AC direct driver for $12{\times}12$ FLB(flexible LED board) and LED flat light without SMPS. It has LID-PC-R101B driver IC that can support the high power factor and be composed of LED switching circuit in group. Also, an elaborate system designs can guarantee a high luminous efficiency, a high reliability and a low power consumption. The proposed FLB has the ultra slim shape of $450{\times}450$ mm, width of 4 mm and weight of 280 g. In the end, we have developed a prototype of FLB for billboard and flat light for room lighting with AC direct driver iposrder to verify the performance of the proposed system.

Study on Modal Test Method for Vibration Characteristics of the Cylindrical Structure Filled with Liquid (액체가 채워진 원통형 구조물의 진동 특성 규명을 위한 모달 시험 방법 연구)

  • Kim, Gen-Sang;Kim, Mun-Guk;Kim, In-Gul;Park, Jae-Sang;Park, Soon-Hong
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.46 no.8
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    • pp.621-630
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    • 2018
  • In the case of launch vehicles using liquid fuel, natural frequency changes due to fuel consumption after launch, and a modal test is essential to investigate its effect. However, when relying on modal test to characterize the free vibration characteristics, the testing time is excessively increased and accuracy is reduced. Therefore, this paper suggests a modal test method with finite element analysis to overcome these drawbacks. A cylindrical structure filled with liquid are considered as a study model, and modal tests and finite element analyses are performed. The modal tests are conducted by an impulsive method using an impact hammer and accelerometers. Through the comparison of the modal test and the finite element analysis results, the validity of the proposed modal test method is verified. In addition, the free vibration characteristics and the tendency for the cylindrical structure according to the liquid filled ratio were investigated.

Resonant Characteristics in Rectangular Harbor with Narrow Entrance (1.Field Measurements and Data Analyses) (개구부가 좁은 직사각형 항만의 공진특성(1.현장관측과 자료 분석))

  • 정원무;박우선;서경덕;채장원;정신택
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.11 no.4
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    • pp.201-215
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    • 1999
  • Field measurements were made for long- and short-period waves and current velocities at the harbor mouth using pressure-type wave gauges and a current meter, respectively, at the Gamcheon Harbor which has a rectangular shape with a narrow entrance. The measured pressure data were subjected to spectral analyses after removing tidal effects by applying trend removal and high-pass filtering. For the band averaging of the raw spectra, in order to obtain good resolution over the entire frequency, instead of a constant band width, variable band widths were used, which gradually increase as marching from the lowest frequency towards higher frequencies. The Helmholtz resonance mode at the Gamcheon Harbor shows the relative amplification ratio of 9.2 at the wave period of 31.7 minutes, which is quite large compared with those at the harbors located on the east coast of Korea. The second and the third resonance period was 10.3 and 5.4 minute, respectively. On the other hand, the analysis of every 24 hours data shows that during storms the spectral densities are very large compared to those during calm seas and also the second and third resonances are predominant.

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The suggestion of Steel Plate-Concrete Composite Beam Shape with Bolts (볼트 체결형 강판-콘크리트 합성보의 형상 제안)

  • Cho, Tae-Gu;Choi, Byong-Jeong
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.19 no.7
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    • pp.305-314
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    • 2018
  • The steel-plate concrete composite beam is composed of a steel plate, concrete and a shear connector to combine the two inhomogeneous materials. In general, the steel plate is assembled by welding an existing composite beam. In this study, a new steel-plate concrete composite (SPCC) beam was developed to reduce the size of the shear connector and improve its workability. The SPCC beam was composed of folded steel plates and concrete, without any shear connector. The folded steel plate was assembled with high strength bolts instead of welding. To improve the workability in field construction, a hat-shaped cap was attached in the junction with the slab. Monotonic two-point load testing was conducted under displacement control mode. The flexural strength of the SPCC beam specimen was calculated to be 76% of that of the complete composite beam by using the plastic stress distribution method and strain compatibility method. The cap acted as the stud and accessory. The synthesis rate could be increased by controlling the gap of the cap, and the bending performance could be evaluated by using the strain fitting method considering the synthesis rate of the SPCC beam.

Embryology of Jeffersonia dubia Baker et S. Moore (Berberidaceae) and comparison with allied genera (깽깽이풀의 발생과 근연속간 비교)

  • Ghimire, Balkrishna;Heo, Kweon
    • Korean Journal of Plant Taxonomy
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    • v.42 no.4
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    • pp.260-266
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    • 2012
  • Because the embryological features of Jeffersonia dubia are poorly understood, we conducted the first embryological study comparing it to other related genera of Berberidaceae. Important embryological features of J. dubia are as follows: the anther is tetrasporangiate, anther wall formation confirms basic type, glandular tapetum cells are two nucleate, the epidermis persistent, and the endothecium develops fibrous thickenings, anther dehiscence by two valves, meiosis in a microspore mother cell is accompanied by simultaneous cytokinesis, microspore tetrads are usually tetrahedral, pollen grains two cells at the time of anthesis. The ovule is bitegmic, anatropous and crassinucellate, archesporium single celled, development of the embryo sac Polygonum type, a mature embryo sac is ellipsoidal in shape. Endosperm formation is of Nuclear type and embryogeny Onagrad type. Seeds are arillate and seed coat exotestal type. Embryological comparisons showed that Jeffersonia resemble to Epimedium and Vancouveria rather than Berberis and Mahonia in some features, like as number of tapetal cells, cytokinesis in meiosis, and thickness of exotesta. It also resembles to Gymnospermium in mode of anther wall formation, number of tapetal cells, formation of nucellar cap, and nature of antipodal cells. Nevertheless, Jeffersonia and Gymnospermium differ from several other embryological features and molecular data too. Therefore, embryological evidences support that Jeffersonia is closely related with Epimedium and Vancouveria.

Optical thyristor operating at 1.55 μm (장파장에서 동작하는 Optical Thyristor)

  • Kim, Doo-Gun;Kim, Hyung-Soo;Jung, Sung-Jae;Choi, Young-Wan;Lee, Seok;Woo, Deok-Ha;Jhon, Young-Min;Yu, Byung-Geel
    • Korean Journal of Optics and Photonics
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    • v.13 no.2
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    • pp.146-150
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    • 2002
  • 1.55${\mu}{\textrm}{m}$ PnpN optical thyristor as a smart optical switch has potential applications in advanced optical communication systems. PnpP optical thyristors operating at 1.55${\mu}{\textrm}{m}$ are proposed and fabricated for the first time. In the optical thyristors, we employ InGaAs/InP multiple quantum well (MQW) for the active n- and p-layers. The thyristors show sufficiently nonlinear s-shape I-V characteristics and spontaneous emission. In the OFF-state, the device has a high-impedance up to switching voltage of 4.03(V). On the other hand, it has low-impedance and emits spontaneous light as a light-emitting diode in the ON-state voltage of 1.77(V), and switching voltage is changed under several light input conditions. It can be used as a header processor in optical asynchronous transfer mode (ATM), as a hard limiter in optical code division multiple access (CDMA) and as a wavelength converter in optical WDM systems.