• Title/Summary/Keyword: modal energy

Search Result 399, Processing Time 0.026 seconds

A Study on the Contribution of Each Mode in Vibration Response (진동응답에 나타난 모드의 기여도 평가에 관한 연구)

  • Jung, Soon-Chul;Lee, Jae-Eung
    • Transactions of the Korean Society for Noise and Vibration Engineering
    • /
    • v.16 no.4 s.109
    • /
    • pp.339-345
    • /
    • 2006
  • In this paper, a physically meaningful methodology which can assess the contribution of each vibration mode to various vibration response signals (displacement, velocity, acceleration) is developed. Based on these results, the problem of quantitative assessment of the relative importance of a structural system's vibrational modes is discussed. In addition, a direct method which ran assess the relative importance of each mode from uniformly sampled experimental data is also proposed.

Random Vibration of Coupled Beams (연결된 보의 랜덤진동해석)

  • 김현실;강현주;김재승
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.17 no.10
    • /
    • pp.2491-2497
    • /
    • 1993
  • Random vibration of the coupled identical beams subject to band-limted white noise is studied. The mean-square displacements average dspatially over each beam are derived analytically using two different modal analysis techniques and compared to the results by SEA(Statistical Energy Analysis). It is shown that when frequency is high and a large number of modes are included in the frequency band, the modal analysis methods and the SEA yield the same results provided that the loss factors are very small and the modal separation is much larger than the half-power bandwidth.

Large deformations of a flexural frame under nonlinear P-delta effects

  • Afshar, Dana;Afshar, Majid Amin
    • Earthquakes and Structures
    • /
    • v.22 no.5
    • /
    • pp.517-526
    • /
    • 2022
  • In this paper, nonlinear P-delta effects are studied on the seismic performance, and the modal responses of a flexural frame, considering large deformations. Using multiple scales method, the nonlinear differential equations of motion are estimated, and the nonlinear interactions between the frame's degrees of freedom are outcropped. The results of time and frequency domain analyzes of a dynamic model are examined under internal resonance cases, and the linear and nonlinear responses are investigated in each modal cases. Also, changing the modal responses with respect to the amplitude and frequency of the harmonic forces is evaluated. It is shown that the dominant absorption of energy is in the first natural frequency of the frame, in the case of earthquake excitation, and when a harmonic force is applied to the frame, the peaks of the frequency domain responses depending on the frequency of harmonic force are in the first, and second or third natural frequency of the structure.

Damage Detection in Beam Structures using Harmony Search Method and Frequency Response (보 구조물의 주파수응답을 이용한 화음탐색법 기반 손상검색)

  • Lee, So-Young;Park, Jae-Hyung;Yi, Jin-Hak;Ryu, Yeon-Sun;Kim, Jeong-Tae
    • Proceedings of the Computational Structural Engineering Institute Conference
    • /
    • 2008.04a
    • /
    • pp.139-144
    • /
    • 2008
  • In this study, damage detection method using harmony search method and frequency response is proposed. In order to verify this method, the following approaches are implemented. Firstly, damage detection method using harmony search is developed. To detect damage, objective function that minimize difference with natural frequency and modal strain energy from undamaged and damaged model is used. Secondly, finite element model for beam structure is created. And damage scenario is determined. Lastly, damage detection is performed by proposed method and utility of proposed method is verified.

  • PDF

A wave model of two identical beams coupled by a plate for a mid-frequency analysis (중주파수 해석을 위한 웨이브 모형 연구: 두개의 보와 판 연성계)

  • Thompson, D.J.;Ferguson, N.S.;Yoo, Ji-Woo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
    • /
    • 2006.11a
    • /
    • pp.771-775
    • /
    • 2006
  • There has been much effort to find suitable methods for structural analysis in the mid-frequency region where traditional low frequency methods have increasing uncertainties whilst statistical energy analysis is not strictly applicable. Systems consisting of relatively stiff beams coupled to flexible plates have a particularly broad mid-frequency region where the beams support only a few modes whilst the plate has a high modal density and modal overlap. A system of two parallel beams coupled to a plate is investigated based on the wave method, which is an approximate method. The wave model is extended from a single-beam-plate system, to a plate with two identical beams which is modelled using a symmetric-anti symmetric technique. Experimental results such as powers and energy ratios show the validity of the analytical wave models.

  • PDF

Three-dimensional Topology Optimization using the CATO Algorithm

  • LEE, Sang Jin;BAE, Jung Eun
    • Architectural research
    • /
    • v.11 no.1
    • /
    • pp.15-23
    • /
    • 2009
  • An application of the constrained adaptive topology optimization (CATO) algorithm is described for three-dimensional topology optimization of engineering structures. The enhanced assumed strain lower order solid finite element (FE) is used to evaluate the values of objective and constraint functions required in optimization process. The strain energy (SE) terms such as elastic and modal SEs are employed as the objective function to be minimized and the initial volume of structures is introduced as the constraint function. The SIMP model is adopted to facilitate the material redistribution and also to produce clearer and more distinct structural topologies. The linearly weighted objective function is introduced to consider both static and dynamic characteristics of structures. Several numerical tests are tackled and it is used to investigate the performance of the proposed three-dimensional topology optimization process. From numerical results, it is found to be that the CATO algorithm is easy to implement and extremely applicable to produce the reasonable optimum topologies for three dimensional optimization problems.

Adaptive-scale damage detection strategy for plate structures based on wavelet finite element model

  • He, Wen-Yu;Zhu, Songye
    • Structural Engineering and Mechanics
    • /
    • v.54 no.2
    • /
    • pp.239-256
    • /
    • 2015
  • An adaptive-scale damage detection strategy based on a wavelet finite element model (WFEM) for thin plate structures is established in this study. Equations of motion and corresponding lifting schemes for thin plate structures are derived with the tensor products of cubic Hermite multi-wavelets as the elemental interpolation functions. Sub-element damages are localized by using of the change ratio of modal strain energy. Subsequently, such damages are adaptively quantified by a damage quantification equation deduced from differential equations of plate structure motion. WFEM scales vary spatially and change dynamically according to actual needs. Numerical examples clearly demonstrate that the proposed strategy can progressively locate and quantify plate damages. The strategy can operate efficiently in terms of the degrees-of-freedom in WFEM and sensors in the vibration test.

Evaluation on the Floor Vibration Characteristics for the Vibration Control of Vibration Sensitive Equipments (정밀 혐진기기 방.제진을 위한 바닥 진동성능평가에 관한 연구)

  • Lee, Ho-Beom;Lho, Byeong-Cheol;Cho, Dong-Jin
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
    • /
    • 2000.06a
    • /
    • pp.933-939
    • /
    • 2000
  • In this paper we present an overview of the factors and techniques that must be considered in vibration measurements in the floor structures for microelectronics facilities. Normally narrowband vibration spectrum or equivalent signals are suggested as the guide indexes of site vibration phenomina. But it cannot support perfect informations in designing vibration control systems for the vibration sensitive equipment even though the spectrum serves to illustrate the fact that most real vibration environments are dominated by broadband energy as opposed to tonal energy. The major topics cover stiffness in frequency and time domain, acceleration level and modal characteristics from experimental modal analysis as well as narrowband spectrum. The combined signal analysis through the items mentioned above can give better solutions and would be positively recomended to solve the vibration problems on a sort of limited field.

  • PDF

Active Noise Control In a Cylindrical Cavity (원통형 밀폐공간 내부의 능동소음제어)

  • Lee, Ho-Jun;Park, Hyeon-Cheol;Hwang, Un-Bong
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.24 no.9 s.180
    • /
    • pp.2302-2312
    • /
    • 2000
  • An active control of the transmission of noise through an aircraft fuselage is investigated numerically. A cylinder-cavity system was used as a model for this study. The fuselage is modeled as a fi nite, thin shel cylinder with constant thickness. The sound field generated by an exterior monopole source is transmitted into the cavity through the cylinder. Point force actuators on the cylinder are driven by error sensor that is placed in 3D cavity. Modal coupling theory is used to formulate the numerical models and describe the system behavior. Minimization of the acoustic potential energy in the fuselage is carried out as a performance index. Continuous parameter genetic algorithm is used to search the optimal actuator position and both results are compared.

Two-step approaches for effective bridge health monitoring

  • Lee, Jong Jae;Yun, Chung Bang
    • Structural Engineering and Mechanics
    • /
    • v.23 no.1
    • /
    • pp.75-95
    • /
    • 2006
  • Two-step identification approaches for effective bridge health monitoring are proposed to alleviate the issues associated with many unknown parameters faced in real structures and to improve the accuracy in the estimate results. It is suitable for on-line monitoring scheme, since the damage assessment is not always needed to be carried out whereas the alarming for damages is to be continuously monitored. In the first step for screening potentially damaged members, a damage indicator method based on modal strain energy, probabilistic neural networks and the conventional neural networks using grouping technique are utilized and then the conventional neural networks technique is utilized for damage assessment on the screened members in the second step. The effectiveness of the proposed methods is investigated through a field test on the northern-most span of the old Hannam Grand Bridge over the Han River in Seoul, Korea.