• Title/Summary/Keyword: Structural mode

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MODE CONTROL OF GUIDED WAVE IN MAGNETIC HOLLOW CYLINDER USING ELECTROMAGNETIC ACOUSTIC TRANSDUCER ARRAY

  • FURUSAWA, AKINORI;KOJIMA, FUMIO;MORIKAWA, ATSUSHI
    • Nuclear Engineering and Technology
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    • v.47 no.2
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    • pp.196-203
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    • 2015
  • The aim of this work is to demonstrate a method for exciting and receiving torsional and longitudinal mode guided waves with an electromagnetic acoustic transducer (EMAT) ring array. First of all, a three-dimensional guided wave simulator is developed in order to numerically analyze the propagation of the guided wave. The finite difference time domain method is used for the simulator. Second, two guided wave testing systems using an EMAT ring array are provided: one is for torsional mode (T-mode) guided wave and the other is for longitudinal mode (L-mode). The EMATs used in the both systems are the same in design. A method to generate and receive the T- and L-mode guided waves with the same EMAT is proposed. Finally, experimental and numerical results are compared and discussed. The results of experiments and simulation agree well, showing the potential of the EMAT ring array as a mode controllable guided wave transmitter and receiver.

Assessment for Failure Probability of Landing Gear Structural Fuse and Improvement Measure (착륙장치용 Structural Fuse 파손확률 계산 및 개선 방안)

  • Lee, Seung-Gyu;Kim, Tae-Uk;Hwang, In-Hee;Lee, Jeong-Sun;Jo, Jeong-Jun;Park, Chong-Yeong
    • Proceedings of the KSME Conference
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    • 2008.11a
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    • pp.469-474
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    • 2008
  • The reason for crashworthy landing gear is to contribute to the overall aircraft design goals in the event of a crash. One of crashworthy landing gear design approaches is inclusion of structural fuse. Structural fuse is used to control the mode of failure of landing gear. If structural fuse doesn't work at desired condition, other unexpected accidents can occur. In this paper, failure probability is calculated for landing gear structural fuse and improvement measure is introduced to improve failure probability of structural fuse.

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Experimental Verification of a Structural Damage Identification Method for Beam Structures (보 구조물에 대한 손상검출기법의 실험적 검증)

  • 조국래;이우식
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.10a
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    • pp.837-840
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    • 1997
  • This paper provides an experimental verification of an FRF-based structural damage identification method (SDIM) developed by the authors for beam structures. The FRF-based SDIM requires the following data : (1) natural frequencies and mode shapes measured at the intact state and (2) the FRF-data measured at the damaged state. Experiments are conducted for the cantilevered beam with one slot and three slots. It is shown that the FRF-based SDIM developed by the authors provide very successful damage identification results which agree well with true damage state.

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Determination of Vibration Parameters Using The Improved Time Domain Modal Identification Algorithm (개선된 시간영역 해석기법에 의한 동특성 추정)

  • Jung, Beom-Seok
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.3 no.2
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    • pp.147-154
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    • 1999
  • A new approach to conducting the vibration parameters identification algorithm is proposed. The approach employs the concept of modal amplitude ratio implemented in a mode shape estimation. The accuracy of the improved Ibrahim Time Domain identification algorithm in extracting structural modal parameters from free response functions has been studied using computer simulated data for 9 stations on the two-span continuous beam. Simulated responses from the lumped and distributed parameter system demonstrate that this algorithm produces excellent results, even in the 300% noise response.

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Structural System Parameter Estimation using Strain Output Feedback (스트레인 출력 되먹임을 이용한 구조 시스템 계수 추정)

  • Ha, Jae-Hoon;Park, Youn-Sik;Park, Young-Jin
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.05a
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    • pp.124-127
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    • 2005
  • As computer capability and test skill become more and more advanced, finite element method and modal test are being widely applied in engineering design. In order to correlate and reconcile the inevitable discrepancies between the analytical and experimental models, many techniques have been developed. Among these methods, multiple-system methods are known as the effective tools in that they can supply the rich modal data available which are experimentally obtained. These abundant modal data can help structural system parameters estimated well. Multiple-system methods can be classified into the structural modification methods and feedback controller methods. The structural modification methods need the physical attachment of structures and their concept may limit the application of them. To overcome this drawback, the feedback controller methods are addressed which enable us to get more modal data without the structural change. Mode decoupling controller(MDC), one of them, is to use acceleration out)ut feedback to perturb an open-loop system. The output feedback controller generally cannot guarantee the stability of a closed-loop system. However, MDC can solve this problem under the certain constraints. So far, MDC utilizes accelerations as the sensor signals. In this research, strain sensors are going to be picked up to apply to the MDC. Strain output is recently used for structural system identification due to the drastically improved and miniaturized strain sensor. In this paper, we show that the MDC using strain output has differences compared with acceleration output in estimating the structural system parameters. The associated simulation is performed to demonstrate the above mentioned characteristics.

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An efficient method for structural damage localization based on the concepts of flexibility matrix and strain energy of a structure

  • Nobahari, Mehdi;Seyedpoor, Seyed Mohammad
    • Structural Engineering and Mechanics
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    • v.46 no.2
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    • pp.231-244
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    • 2013
  • An efficient method is proposed here to identify multiple damage cases in structural systems using the concepts of flexibility matrix and strain energy of a structure. The flexibility matrix of the structure is accurately estimated from the first few mode shapes and natural frequencies. Then, the change of strain energy of a structural element, due to damage, evaluated by the columnar coefficients of the flexibility matrix is used to construct a damage indicator. This new indicator is named here as flexibility strain energy based index (FSEBI). In order to assess the performance of the proposed method for structural damage detection, two benchmark structures having a number of damage scenarios are considered. Numerical results demonstrate that the method can accurately locate the structural damage induced. It is also revealed that the magnitudes of the FSEBI depend on the damage severity.

Designing a Hydro-Structural Ship Model to Experimentally Measure its Vertical Bending and Torsional Vibrations

  • Houtani, Hidetaka;Komoriyama, Yusuke;Matsui, Sadaoki;Oka, Masayoshi;Sawada, Hiroshi;Tanaka, Yoshiteru;Tanizawa, Katsuji
    • Journal of Advanced Research in Ocean Engineering
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    • v.4 no.4
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    • pp.174-184
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    • 2018
  • We herein propose a new design procedure of a flexible container ship model where the vertical bending and torsional vibration modes are similar to its prototype. To achieve similarity in torsional vibration mode shapes, the height of the shear center of the model must be located below the bottom hull, similar to an actual container ship with large opening decks. Therefore, we designed a ship model by imparting appropriate stiffness to the hull, using urethane foam without a backbone. We built a container ship model according to this design strategy and validated its dynamic elastic properties using a decay test. We measured wave-induced structural vibrations and present the results of tank experiments in regular and freak waves.

Effect of Power Mode of Plasma Anodization on the Properties of formed Oxide Films on AZ91D Magnesium Alloy

  • Lee, Sung-Hyung;Yashiro, Hitoshi;Kure-Chu, Song-Zhu
    • Korean Journal of Materials Research
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    • v.28 no.10
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    • pp.544-550
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    • 2018
  • The passivation of AZ91D Mg alloys by plasma anodization requires deliberate choice of process parameters due to the presence of large amounts of structural defects. We study the dependence of pore formation, surface roughness and corrosion resistance on voltage by comparing the direct current (DC) mode and the pulse wave (pulse) mode in which anodization is performed. In the DC plasma anodization mode, the thickness of the electrolytic oxide film of the AZ91D alloy is uneven. In the pulse mode, the thickness is relatively uniform and the formed thin film has a three-layer structure. The pulse mode creates less roughness, uniform thickness and improved corrosion resistance. Thus, the change of power mode from DC to pulse at 150 V decreases the surface roughness (Ra) from $0.9{\mu}m$ to $0.1{\mu}m$ and increases the corrosion resistance in rating number (RN) from 5 to 9.5. Our study shows that an optimal oxide film can be obtained with a pulse voltage of 150 V, which produces an excellent coating on the AZ91D casting alloy.

Study of central buckle effects on flutter of long-span suspension bridges

  • Han, Yan;Li, Kai;Cai, C.S.
    • Wind and Structures
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    • v.31 no.5
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    • pp.403-418
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    • 2020
  • To investigate the effects of central buckles on the dynamic behavior and flutter stability of long-span suspension bridges, four different connection options between the main cable and the girder near the mid-span position of the Aizhai Bridge were studied. Based on the flutter derivatives obtained from wind tunnel tests, formulations of self-excited forces in the time domain were obtained using a nonlinear least square fitting method and a time-domain flutter analysis was realized. Subsequently, the influences of the central buckles on the critical flutter velocity, flutter frequency, and three-dimensional flutter states of the bridge were investigated. The results show that the central buckles can significantly increase the frequency of the longitudinal floating mode of the bridge and have greater influence on the frequencies of the asymmetric lateral bending mode and asymmetric torsion mode than on that of the symmetric ones. As such, the central buckles have small impact on the critical flutter velocity due to that the flutter mode of the Aizhai Bridge was essentially the symmetric torsion mode coupled with the symmetric vertical mode. However, the central buckles have certain impact on the flutter mode and the three-dimensional flutter states of the bridge. In addition, it is found that the phenomenon of complex beat vibrations (called intermittent flutter phenomenon) appeared in the flutter state of the bridge when the structural damping is 0 or very low.

A Study on Evaluation Method for Piping Shell Mode Vibration (배관 Shell Mode 진동 평가방법에 대한 연구)

  • Chun, Chang-Bin;Park, Soo-Il;Chun, Hyong-Sik
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2006.05a
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    • pp.1285-1289
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    • 2006
  • In a large diameter piping system, high frequency energy can produce excessive noise, high vibration, and failures of thermo-well, instrumentation, and attached small-bore piping. High frequency energy is generated by flow induced vibration like vortex shedding in orifices and valves. Once this energy is generated, amplification may occur from acoustical and/or structural resonances, resulting in high amplitude vibration and noise. At low frequencies, pipe vibration occurs laterally along the pipe's length, but at higher frequencies, the pipe shell wall vibrates radially across its cross-section. The simple beam analogy which is based on the beam mode vibration can not be applied to evaluate shell mode vibration. ASME OM3 recommends that the stress be measured directly by strain gauge and be evaluated according to the fatigue curves of the piping material. This Paper discusses the excitation and amplification mechanism relevant to high frequency energy generation in piping system, the monitoring method of the shell mode vibration in ASME OM3, the evaluation method generally used in the industry. Finally this paper presents the stress evaluation of the cavitating venturi down stream piping, where high frequency shell mode vibrations were observed during the operation.

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