• Title/Summary/Keyword: Sine Sweep

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Sine sweep effect on specimen modal parameters characterization

  • Roy, Nicolas;Violin, Maxime;Cavro, Etienne
    • Advances in aircraft and spacecraft science
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    • v.5 no.2
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    • pp.187-204
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    • 2018
  • The sine sweep base excitation test campaign is a major milestone in the process of mechanical qualification of space structures. The objectives of these vibration tests are to qualify the specimen with respect to the dynamic environment induced by the launcher and to demonstrate that the spacecraft FE model is sufficiently well correlated with the test specimen. Dynamic qualification constraints lead to performing base excitation sine tests using a sine sweep over a prescribed frequency range such that at each frequency the response levels at all accelerometers, load cells and strain gages is the same as the steady state response. However, in practice steady state conditions are not always satisfied. If the sweep rate is too high the response levels will be affected by the presence of transients which in turn will have a direct effect on the estimation of modal parameters. A study funded by ESA and AIRBUS D&S was recently carried out in order to investigate the influence of sine sweep rates in actual test conditions. This paper presents the results of this study along with recommendations concerning the choice of methods.

Beating phenomena in spacecraft sine testing and an attempt to include the sine sweep rate effect in the test-prediction

  • Nali, Pietro;Bettacchioli, Alain
    • Advances in aircraft and spacecraft science
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    • v.3 no.2
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    • pp.197-209
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    • 2016
  • The Spacecraft (S/C) numerical sine test-predictions are usually performed through Finite Element Method (FEM) Frequency Response Analysis (FRA), that is the hypothesis of steady-state responses to harmonic excitation to the S/C base is made. In the test practice, the responses are transient and may be significantly different from those predicted through FRA. One of the most significant causes of discrepancy between prediction and test consists in the beating phenomena. After a brief overview of the topic, the typical causes of beating are described in the first part of the paper. Subsequently, focus is made on the sine sweep rate effect, which often leads to have beatings after the resonance of weakly damped modes. In this work, the approach illustrated in the literature for calculating the sine sweep rate effect in the case of Single-Degree-Of-Freedom (SDOF) oscillators is extended to Multi-Degrees-Of-Freedom (MDOF) systems, with the aim of increasing the accuracy of the numerical sine test-predictions. Assumptions and limitations of the proposed methodology are detailed along the paper. Several assessments with test results are discussed and commented.

Room acoustic measurement and analysis (실내 음향 측정 및 분석 기법 연구)

  • Hong Seung-Wook;Jeon Jin-Ho;Lee Sin-Lyul
    • Proceedings of the Acoustical Society of Korea Conference
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    • autumn
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    • pp.557-560
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    • 2004
  • 본 논문에서는 실내음향을 측정하기 위해 사용되는 음향 측정 신호인 blank pistol, maximum length sequence, sine sweep 을 이용한 충격응답 특성을 분석한다. 각 충격응답의 실내음향 인자들을 먼저 비교 분석하고 sine sweep 속도에 따른 충격응답 특성을 분석하여 최적의 실내음향 인자를 찾기 위한 sine sweep 속도를 결정한다.

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Investigation of the BSR Noise characteristics in Seat Cushion-frame with respect to Vibration Durability Test Using Multi-simulator (다축 가진기를 이용한 시트 쿠션 프레임의 내구 전후 BSR 진동특성 연구)

  • Choi, Ho-Il;Nam, Jae-Hyun;Kang, Jae-Young;Park, Jung-Hee
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.15 no.8
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    • pp.4776-4783
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    • 2014
  • Many studies have examined the reduction of primary noise sources, but quality-related noise, such as BSR, is rarely studied. This study describes the quantitative BSR test method using a multi-axial simulator. The sine sweep test was conducted to detect the system resonance and its relation to BSR noise with high frequency. This method is applied to the seat frame with/without the vibration durability test. The results showed that the $1^{st}$ lateral resonance leads to higher BSR frequency noise. In addition, the reduction of the lateral mode system stiffness after the durability test results in a decrease in the BSR noise in sine sweep test mode.

Lateral torsional buckling of steel I-beams: Effect of initial geometric imperfection

  • Bas, Selcuk
    • Steel and Composite Structures
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    • v.30 no.5
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    • pp.483-492
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    • 2019
  • In the current study, the influence of the initial lateral (sweep) shape and the cross-sectional twist imperfection on the lateral torsional buckling (LTB) response of doubly-symmetric steel I-beams was investigated. The material imperfection (residual stress) was not considered. For this objective, standard European IPN 300 beam with different unbraced span was numerically analyzed for three imperfection cases: (i) no sweep and no twist (perfect); (ii) three different shapes of global sweep (half-sine, full-sine and full-parabola between the end supports); and (iii) the combination of three different sweeps with initial sinusoidal twist along the beam. The first comparison was done between the results of numerical analyses (FEM) and both a theoretical solution and the code lateral torsional buckling formulations (EC3 and AISC-LRFD). These results with no imperfection effects were then separately compared with three different shapes of global sweep and the presence of initial twist in these sweep shapes. Besides, the effects of the shapes of initial global sweep and the inclusion of sinusoidal twist on the critical buckling load of the beams were investigated to unveil which parameter was considerably effective on LTB response. The most compatible outcomes for the perfect beams was obtained from the AISC-LRFD formulation; however, the EC-3 formulation estimated the $P_{cr}$ load conservatively. The high difference from the EC-3 formulation was predicted to directly originate from the initial imperfection reduction factor and high safety factor in its formulation. Due to no consideration of geometric imperfection in the AISC-LFRD code solution and the theoretical formulation, the need to develop a practical imperfection reduction factor for AISC-LRFD and theoretical formulation was underlined. Initial imperfections were obtained to be more influential on the buckling load, as the unbraced length of a beam approached to the elastic limit unbraced length ($L_r$). Mode-compatible initial imperfection shapes should be taken into account in the design and analysis stages of the I-beam to properly estimate the geometric imperfection influence on the $P_{cr}$ load. Sweep and sweep-twist imperfections led to 10% and 15% decrease in the $P_{cr}$ load, respectively, thus; well-estimated sweep and twist imperfections should considered in the LTB of doubly-symmetric steel I-beams.

Transient testing from LV / SC coupled analysis by new shock synthesis

  • Girard, Alain;Cavro, Etienne;Dupuis, Paul-Eric
    • Advances in aircraft and spacecraft science
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    • v.5 no.2
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    • pp.177-186
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    • 2018
  • This paper deals with the idea to replace the usual high-level sine sweep test on shaker at system level, very severe, by a low level one completed by a transient test in the same configuration, in order to be more representative of the real environment, thus limiting over testing and improving the payload comfort. The problem of the transient test specification is first discussed. The proposed solution is to derive from LV/SC coupled analyses a shock response spectrum corresponding to two damping ratios. Then, the question of adequate shock synthesis is tackled. A new method with a given spectrum is considered for better potential and accuracy than the usual wavelets. A campaign on the Intespace bi-shaker devoted to system level showed its capability to perform the resulting test with one spectrum. First investigations to extend this approach to two spectra are in progress.

A Study on the Vibrational Environment Test of KSLV-1 Demonstration Satellite (한국형 위성 발사체 성능 검증위성의 진동환경에 관한 연구)

  • Seo, Hyun-Suk;Kim, Hong-Bae;Woo, Sung-Hyun;Chae, Jang-Soo;Oh, Tae-Sik
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.05a
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    • pp.966-970
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    • 2005
  • On the basis of the development of KSLV-1, KoDSat was designed and manufactured to demonstrate the performance of KSLV-1. KoDSat is exposed to a severe vibrational environment at launch. The structural reliability of KoDSat has to be verified using vibrational test. The structural compatibility and verification of components between analysis and test can be proved using environmental vibration test. In this paper, we review the structural characteristic of thruster control unit for a space launch vehicle and design TCU housing using mathematical model. In order to verify the structural compatibility and reliability, half-sine shock, random and sing sweep vibration test was performed. Especially, sing sweep vibration test result is compared with analysis result and mathematical model is verified.

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Flexural Vibration Analysis of a Sandwich Beam Specimen with a Partially Inserted Viscoelastic Layer

  • Park, Jin-Tack;Park, Nak-Sam
    • Journal of Mechanical Science and Technology
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    • v.18 no.3
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    • pp.347-356
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    • 2004
  • The flexural vibration characteristics of a sandwich beam system with a partially inserted viscoelastic layer were quantitatively studied using the finite element analysis in combination with the sine-sweep experiment. Asymmetric mode shapes of the flexural vibration were visualized by holographic interferometry, which agreed with those obtained by the finite element simulation. Effects of the length and the thickness of the partial viscoelastic layer on the system loss factor (η$\_$s/) and resonant frequency (f$\_$r/) were significantly large for both the symmetric and asymmetric modes of the beam system.

A study of commercial vehicle cab vibration on the driving conditions (상용 차량의 주행 중 발생하는 캡의 진동에 관한 연구)

  • Choi, Byungjae;Han, In-kyu;Cho, Jeong-wook
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2014.10a
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    • pp.472-475
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    • 2014
  • Abnormal cab vibrations in the Y direction in commercial vehicles during driving(70~90kph) are not common vibrations that happen to vehicles during driving and can be an obstacle to normal driving. This study conducted Operation Deflection Shape(ODS) testing to identify the causes of those abnormal cab vibrations and find solutions for them and also a sine sweep test to find resonance and frequency in the cab suspension system and set directions for improvement. The study also altered the shape of the bush inner part for changes to the rigidity features of the cab bush in the Y direction and revised the design with optimal rigidity in the Y direction, thus improving abnormal cab vibrations in the Y direction during driving.

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A Study on the Correlation between the Prestress Force and the Effective Rigidity of the Bonded Tendon (부착식 텐던의 긴장력과 유효 강성의 상관성 연구)

  • Jang, Jung-Bum;Lee, Hong-Pyo;Hwang, Kyeong-Min;Song, Young-Chul
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2010.04a
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    • pp.641-644
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    • 2010
  • 프리스트레싱 시스템이 도입된 구조물의 사용수명이 오래됨에 따라, 이들 구조물의 잔존수명 평가와 보수 및 보강 등의 유지관리 차원에서 프리스트레싱 시스템의 현재 긴장력에 대한 평가는 매우 중요한 현안이 되어왔다. 따라서, 본 논문에서는 프리스트레싱 시스템의 현재 긴장력을 평가하기 위한 첫 단계로서 프리스트레싱 시스템의 긴장력이 구조계의 강성에 미치는 영향을 평가하였다. 이를 위하여 부착식 텐던 형식의 프리스트레싱 시스템이 도입된 시험체를 대상으로 SIMO sine sweep test를 수행하고 긴장력과 시험체의 유효 강성에 대한 상관성을 규명하였다. 그 결과, 프리스트레싱 시스템의 긴장력은 시험체의 유효강성을 증가시키며, 저차 고유진동수가 긴장력과 높은 상관성을 지니는 것으로 나타났다.

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