• Title/Summary/Keyword: 진동 응답 스펙트럼

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Evaluation of Structural Robustness of External Fuel Tank and Pylon for Military Aircraft under Random Vibration (랜덤진동에서 군용 항공기 외부연료탱크 및 파일런 구조 강건성 평가)

  • Kim, Hyun-Gi;Kim, Sungchan
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.22 no.3
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    • pp.777-783
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    • 2021
  • Aircraft are affected by various vibrations during maneuvering. These vibrations may have a fatal effect on the survival of aircraft in some cases, so the safety of components applied to the aircraft should be proven against various vibrations through random vibration analysis. In this study, the structural robustness of an external fuel tank and pylon for military aircraft was evaluated under random vibration conditions using commercial software, MSC Random. In the random vibration analysis, a frequency response analysis was performed by imposing a unit load on the boundary condition point, and then excitation was performed with a PSD profile. In this process, the required mode data was extracted through a modal analysis method. In addition, the random vibration profile specified in the US Defense Environment Standard was applied as random vibration conditions, and the PSD profile given in units of G's was converted into units of gravitational acceleration. As a result of the numerical analysis, we evaluated the structural robustness of the external fuel tank and pylon by identifying the safety margins of beam elements, shell elements, and solid elements in a numerical model for random vibration in the x, y, and z directions.

Finite Element Dynamic Analysis of a Vertical Pile by Wave and Tidal Current (파도와 조류에 의한 수직 파일의 유한요소 동적거동 해석)

  • 박문식
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.17 no.2
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    • pp.183-192
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    • 2004
  • New dynamic analysis procedures lot the vertically drilled sea water pile are suggested and demonstrated by the typical design Problem. Pile structure submerged in the sea water as well as forces by the ocean waves and tidal currents are modeled and formulated by finite element method. To obtain wave forces for the finite element equation, Airy's wave theory is tested and selected among others. Lateral lifting forces induced by the vortex shedding of current flow is simply based on the harmonic function with the Strouhal frequency and lifting coefficient. Natural frequencies and frequency responses for the pile are calculated by NASTRAN using the results of the formulation. Dynamic displacement and stress results obtained by these procedures are shown to be applicable to predict the dynamic behaviors of the ocean pile by the wave and lifting forces as a preliminary design analysis.

Wind Tunnel Test Study on the Characteristics of Wind-Induced Responses of Tall Buildings with Openings (중공부(中空部)를 가진 고층건축물(高層建築物)의 풍응답(風應答) 특성(特性)에 관한 풍동실험(風洞實驗) 연구(硏究))

  • Kim, Dong Woo;Kil, Yong Sik;Ha, Young Cheol
    • Journal of Korean Society of Steel Construction
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    • v.17 no.4 s.77
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    • pp.499-509
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    • 2005
  • The excessive wind-induced motion of tall buildings most frequently result from vortex-shedding-induced across-wind oscillations. This form of excitation is most pronounced for relatively flexible, lightweight, and lightly damped high-rise buildings with constant cross-sections. This paper discusses the aerodynamic means ofmitigating the across-wind vortex shedding induced in such situations. Openings are added in both the drag and lift directions in the buildings to provide pressure equalization. Theytend to reduce the effectiveness of across-wind forces by reducing their magnitudes and disrupting their spatial correlation. The effects of buildings with several geometries of openings on aerodynamic excitations and displacement responses have been studied for high-rise buildings with square cross-sections and an aspect ratio of 8:1 in a wind tunnel. High-frequency force balance testshave been carried out at the Kumoh National University of Technology using rigid models with 24 kinds of opening shapes. The measured model's aerodynamic excitations and displacement were compared withthose of a square cylinder with no openings to estimate the effectiveness of openings for wind-induced oscillations. From these results, theopening shape, size, and location of buildings to reduce wind-induced vortex shedding and responses were pointed out.

A New Methodology for Seismic Capacity Evaluation of Low-rise R/C Buildings (비선형요구내력스펙트럼을 이용한 저층 R/C 건물의 내진성능 평가법)

  • Lee, Kang Seok
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.15 no.3
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    • pp.106-115
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    • 2011
  • This study proposed a new methodology for seismic capacity evaluation of low-rise reinforced concrete (RC) buildings based on non-linear required spectrum. In order to verify the reliability of the proposed method, relationships between results obtained using the proposed method and the non-linear dynamic analyses were investigated. Compared with the seismic protection index (Es=0.6) defined in the Japanese Standard, the applicability of the method was also estimated. Research results indicate that the method proposed in this study compares reasonably well with the detailed evaluation methods. Using the seismic evaluation method developed in this study, the seismic capacity category and earthquake damage degree of low-rise RC buildings corresponding to a specific earthquake level can be effectively estimated.

Measurement of natural frequency of aluminum honeycomb sandwich beams using high speed digital cameras (고속 디지털 카메라를 이용한 알루미늄 하니콤 샌드위치 보의 고유 진동수 계측)

  • Goo, Nam Seo;Vang, Hoang My;Le, Vinh Tung;Jin, Tailie
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.45 no.1
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    • pp.30-35
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    • 2017
  • In this study, we measured the natural frequencies of aluminum honeycomb sandwich beams using digital image correlation technique. The vibration images were captured using two high speed digital cameras and the images were converted to displacements by the digital image correlation technique. Displacement data in time domain were tranformed to frequency domain data by fast Fourier transform software. To reduce noise invoked by random exitation, a spectrum averaging technique and Savitsky-Golay digital filter were adopted. A conventional vibration measurement using an accelerometer and a finite element analysis were performed to compare the results by high speed digital camera measurement method. In conclusion, new method using high speed digital cameras and digital image correlation technique can measure the vibration of beam structures and can be applied to bio-structures where sensors cannot be attached.

A study of Kem County earthquake (Kern County 지진에 대한 연구)

  • 김준경
    • The Journal of Engineering Geology
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    • v.2 no.2
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    • pp.155-165
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    • 1992
  • The purpose of this study is to evaluate compatability of seismic source characteristics of the Kern County earthquake to those of Korean Peninsula seismotectonics. The compatability could be used to make Korean type response spectrum from the strong ground motions observed from the assingned earthquake. The July 21, 1952, Kern County, California, earthquake is the largest earthquake to occur in the western U.S. since 1906, and the repeat of this event poses a significant seismic hazard. The Kern County event was a complex thrusting event, with a surface rupture pattern that varied from pure leftlateral strike-slip to pure dip-slip. A time dependent moment tensor inversion was applied to ten observed teleseismic long-period body waves to investigate the source complexity. Since a conventional moment tensor inversion(constant geometry through time) returns a non-double-couple source when the seismic source changes(fault orientation and direction of slip) with time, we are required to use the time dependent moment tensor which allows a first-order mapping of the geometric and temporal complexity. From the moment tensor inversion, a two-point seismic source model with significant overlap for the White Wolf fault, which propagates upward(20 km to 5 km) from SW to NE, fits most of the observed seismic waveforms in the least squares sense. Comparison of P, T and B axes of focal mechanisms and focal depths suggests that seismic source characteristics of the Kern County earthquake is consistant with those of Korean Peninsula Seismotectonics.

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Comparison of Approximate Nonlinear Methods for Incremental Dynamic Analysis of Seismic Performance (내진성능의 증분동적해석을 위한 비선형 약산법의 비교 검토)

  • Bae, Kyeong-Geun;Yu, Myeong-Hwa;Kang, Pyeong-Doo;Kim, Jae-Ung
    • Journal of the Earthquake Engineering Society of Korea
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    • v.12 no.1
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    • pp.79-87
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    • 2008
  • Seismic performance evaluation of structure requires an estimation of the structural performance in terms of displacement demand imposed by earthquakes on the structure. Incremental Dynamic Analysis(IDA) is a analysis method that has recently emerged to estimate structural performance under earthquakes. This method can obtained the entire range of structural performance from the linear elastic stage to yielding and finally collapse by subjecting the structure to increasing levels of ground acceleration. Most structures are expected to deform beyond the limit of linearly elastic behavior when subjected to strong ground motion. The nonlinear response history analysis(NRHA) among various nonlinear analysis methods is the most accurate to compute seismic performance of structures, but it is time-consuming and necessitate more efforts. The nonlinear approximate methods, which is more practical and reliable tools for predicting seismic behavior of structures, are extensively studied. The uncoupled modal response history analysis(UMRHA) is a method which can find the nonlinear reponse of the structures for ESDF from the pushover curve using NRHA or response spectrum. The direct spectrum analysis(DSA) is approximate nonlinear method to evaluate nonlinear response of structures, without iterative computations, given by the structural linear vibration period and yield strength from the pushover analysis. In this study, the practicality and the reliability of seismic performance of approximate nonlinear methods for incremental dynamic analysis of mixed building structures are to be compared.

A Shaking Table Test for an Re-evaluation of Seismic Fragility of Electrical Cabinet in NPP (원전 전기캐비넷의 지진취약도 재평가를 위한 진동대 실험)

  • Kim, Min-Kyu;Choi, In-Kil
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.24 no.3
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    • pp.295-305
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    • 2011
  • In this study, a seismic behavior of electrical cabinet system in Nuclear Power Plants(NPPs) was evaluated by the shaking table test. A 480V Motor Control Centers(MCCs) was selected for the shaking table test, and a real MCC cabinet for the Korea Nuclear Power Plant site was rented by manufactured company. For the shaking table tests, three kinds of seismic input motions were used, which were a US NRC Reg. guide 1.60 design spectrum, a UHS spectrum and PAB 165' floor response spectrum(FRS). Especially, the UHS input motion was selected for an evaluation of structural seismic amplification effects, three directional accelerations were measured at three points outside on the cabinet system and also that of the incabinet response amplification, accelerations were measure at two points which were mounted in electrical equipment such as relay. Seismic amplification effect is determined at the outside and inside of a cabinet as input seismic motion, and compared to the results which are calculated by analytical method based on NUREG/CR-5203.

A Development of Real-time Vibration Monitoring and Analysis System Linked to the Integrated Management System of Ministry of Public Safety and Security (국민안전처 통합관리시스템 연계 가능한 시설물 진동 감지 및 분석 시스템 개발)

  • Lim, Ji-Hoon;Jung, Jin-Woo;Moon, Dae-Joong;Choi, Dong-Ho
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.20 no.3
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    • pp.130-139
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    • 2016
  • A frequency of earthquake occurrence in the Republic of Korea is increasing over the past few decades. In this situation, an importance of earthquake prevention comes to the fore because the earthquake does damage to structures and causes severe damage of human life. For the earthquake prevention, a real-time vibration measurement for structures is important. As an example, the United States of America and Japan have already been monitoring real-time earthquake acceleration for the important structures and the measured acceleration data has been managed by forming database. This database could be used for revising the seismic design specifications or predicting the damage caused by earthquake. In Korea, Earthquake Recovery Plans Act and Enforcement Regulations are revised and declared lately. Ministry of Public Safety and Security is constructing a integrated management system for the measured earthquake acceleration data. The purpose of this research is to develop a real-time vibration monitoring and analysis system for structures which links to the integrated management system. The developed system contains not only a monitoring function to show real-time acceleration data but also an analysis system to perform fast fourier transform, to obtain natural frequency and earthquake magnitude, to show response spectrum and power spectrum, and to evaluate structural health. Additionally, this system is designed to be able to link to the integrated management system of Ministry of Public Safety and Security. It is concluded that the developed system can be useful to build a safety management network, minimize maintenance cost of structures, and prevention of the structural damage due to earthquake.

A Study on the Seismic Response of Arch Structures Using Artificial Earthquake Ground Motions (아치구조물의 모의지진파 입력에 따른 지진응답특성에 관한 연구)

  • Jung, Chan-Woo;Park, Sung-Moo;Kang, Joo-Won
    • Journal of Korean Association for Spatial Structures
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    • v.8 no.6
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    • pp.59-66
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    • 2008
  • Seismic safety is more important for large spatial structure such as theaters, stadiums, gymnasiums since these structure are public goods. It is, however, difficult to understand behavior taking place when large spatial structure which has variety of structural system and shape receives seismic load. On this study, the natural vibration mode of arch structure which is main structural element of the large spatial structure, is checked. And then, when the artificial earthquake ground motion is applied to arch structure, it is more affective by long period component than magnitude of design acceleration spectrum.

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