• Title, Summary, Keyword: Mode Shape

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A new damage detection indicator for beams based on mode shape data

  • Yazdanpanah, O.;Seyedpoor, S.M.;Bengar, H. Akbarzadeh
    • Structural Engineering and Mechanics
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    • v.53 no.4
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    • pp.725-744
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    • 2015
  • In this paper, a new damage indicator based on mode shape data is introduced to identify damage in beam structures. In order to construct the indicator proposed, the mode shape, mode shape slope and mode shape curvature of a beam before and after damage are utilized. Mode shape data of the beam are first obtained here using a finite element modeling and then the slope and curvature of mode shape are evaluated via the central finite difference method. In order to assess the robustness of the proposed indicator, two test examples including a simply supported beam and a two-span beam are considered. Numerical results demonstrate that using the proposed indicator, the location of single and multiple damage cases having different characteristics can be accurately determined. Moreover, the indicator shows a better performance when compared with a well-known indicator found in the literature.

Damage Detection of a Steel Member Using Modal Testing (강부재의 손상발견을 위한 모달실험 기법)

  • Jang, Jeong Hwan;Lee, Jung Whee;Kim, Sung Kon;Chang, Sung Pil
    • Journal of Korean Society of Steel Construction
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    • v.9 no.4
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    • pp.467-477
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    • 1997
  • A series of experimental tests have been performed on a tube beam in which artificial damage is applied in order to address damage detectability using modal analysis. Modal parameters considered are frequency, displacement mode shape and strain mode shape CoMAC(Coordinate Modal Assurance Criterion) and Modal Vector Error have been adopted for presenting the change of displacement mode shape and strain mode shape. It is revealed strain mode shape is the most sensitive to damage.

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Delamination identification of laminated composite plates using measured mode shapes

  • Xu, Yongfeng;Chen, Da-Ming;Zhu, Weidong;Li, Guoyi;Chattopadhyay, Aditi
    • Smart Structures and Systems
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    • v.23 no.2
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    • pp.195-205
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    • 2019
  • An accurate non-model-based method for delamination identification of laminated composite plates is proposed in this work. A weighted mode shape damage index is formulated using squared weighted difference between a measured mode shape of a composite plate with delamination and one from a polynomial that fits the measured mode shape of the composite plate with a proper order. Weighted mode shape damage indices associated with at least two measured mode shapes of the same mode are synthesized to formulate a synthetic mode shape damage index to exclude some false positive identification results due to measurement noise and error. An auxiliary mode shape damage index is proposed to further assist delamination identification, by which some false negative identification results can be excluded and edges of a delamination area can be accurately and completely identified. Both numerical and experimental examples are presented to investigate effectiveness of the proposed method, and it is shown that edges of a delamination area in composite plates can be accurately and completely identified when measured mode shapes are contaminated by measurement noise and error. In the experimental example, identification results of a composite plate with delamination from the proposed method are validated by its C-scan image.

Assessment of Lateral Deformation Shape for High-rise Building Structures (고층건물의 수평변형형상에 대한 평가)

  • 서현주
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • pp.36-43
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    • 1998
  • The purpose of study is to propose numerical assessment methods of lateral deformation shape under lateral loads for regular high-rise buildings. The normalized 1st mode shape is used to assess lateral deformation shape. The assessment method are mass participation factor, representative value by RMS, the mean value, median of the nomalized 1st mode shape. These methods are able to know a fundamental lateral deformation shape of the building and effects of interactive systems numerically. Generally the characteristics of normalized 1st mode shape for various models coincide with numerical assessment results.

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Shape Optimization of Structures with a Crack (균열이 있는 구조물의 형상 최적화)

  • 한석영;송시엽;백춘호
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • pp.298-303
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    • 2001
  • Most of mechanical failures are caused by repeated loadings and therefore they are strongly related to fatigue. To avoid the failures caused by fatigue, determination of an optimal shape of a structure is one of the very important factors in the initial design stage. Shape optimization for a compact tension specimen in opening mode in fracture mechanics, was accomplished by the linear elastic fracture mechanics and the growth-strain method in this study. Also shape optimization for a cantilever beam in mixed mode was carried out by the same techniques. The linear elastic fracture mechanics was used to estimate stress intensity factors and fatigue lives. And the growth-strain method was used to optimize the shape of the initial shape of the specimens. From the results of the shape optimization, it was found that shapes of two types of specimens and a cantilever beam optimized by the growth-strain method prolong their fatigue lives very much. Therefore, it was verified that the growth-strain method is an appropriate technique for shape optimization of a structure having a crack.

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Vibration Mode Shape Changed by Phase Angle in Vibration Testing Using Phase-Shifting ESPI (위상이동 ESPI를 이용한 진동실험에서 위상각에 따른 진동모드 형상의 변화)

  • 정현철;김경석;양승필;장호섭;박찬주;조영학;김종수
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.443-446
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    • 2003
  • The vibration mode shape changed by the phase angle that can be controlled by phase-shifting ESPI system is discussed. For the phase-shifting ESPI experiment the stroboscopic illumination by using AOM(Acousto-Optic Modulator) is needed, and the initial phase angle can be adjusted by the program. The vibration mode shape is changed when the initial phase angle is changed. We examined the vibration mode shape change due to the initial phase angle change at each resonance frequency. Through this study, we found that in the vibration testing using phase-shilling ESPI the vibration mode shape is improved in the quality by adjusting exact phase angle and the error of the quantitative vibration analysis can be reduced.

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Visualization of Delamination Region in Concrete Structures using Mode Shapes of Delaminated Concrete Section (II) : Impact-Echo Test (박리된 콘크리트의 진동 모드 형상을 이용한 콘크리트 구조물 박리 손상 영역 가시화 (II) : 충격-반향 시험)

  • Oh, Taekeun;Shin, Sung Woo
    • Journal of the Korean Society of Safety
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    • v.28 no.6
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    • pp.36-41
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    • 2013
  • Previous study showed that delamination region in concrete structures can be successfully visualized using mode shapes of delaminated concrete section. However, modal tests for this purpose to obtain mode shapes of the delaminated concrete section may not be applicable in practice since, to correctly obtain the mode shapes of the section, the location and the shape of the delamination region in a structure should be known in advance. Unfortunately those are normally unknown in a real structure. Therefore, a moving forward test method may be useful to obtain the mode shapes of the concrete section when the location and the shape of the delamination region are not known. In this study, impact-echo testing based mode shape estimation technique is proposed and experimentally validated for visualization of delamination region.

Evaluation of mode-shape linearization for HFBB analysis of real tall buildings

  • Tse, K.T.;Yu, X.J.;Hitchcock, P.A.
    • Wind and Structures
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    • v.18 no.4
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    • pp.423-441
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    • 2014
  • The high frequency base balance (HFBB) technique is a convenient and relatively fast wind tunnel testing technique for predicting wind-induced forces for tall building design. While modern tall building design has seen a number architecturally remarkable buildings constructed recently, the characteristics of those buildings are significantly different to those that were common when the HFBB technique was originally developed. In particular, the prediction of generalized forces for buildings with 3-dimensional mode shapes has a number of inherent uncertainties and challenges that need to be overcome to accurately predict building loads and responses. As an alternative to the more conventional application of general mode shape correction factors, an analysis methodology, referred to as the linear-mode-shape (LMS) method, has been recently developed to allow better estimates of the generalized forces by establishing a new set of centers at which the translational mode shapes are linear. The LMS method was initially evaluated and compared with the methods using mode shape correction factors for a rectangular building, which was wind tunnel tested in isolation in an open terrain for five incident wind angles at $22.5^{\circ}$ increments from $0^{\circ}$ to $90^{\circ}$. The results demonstrated that the LMS method provides more accurate predictions of the wind-induced loads and building responses than the application of mode shape correction factors. The LMS method was subsequently applied to a tall building project in Hong Kong. The building considered in the current study is located in a heavily developed business district and surrounded by tall buildings and mixed terrain. The HFBB results validated the versatility of the LMS method for the structural design of an actual tall building subjected to the varied wind characteristics caused by the surroundings. In comparison, the application of mode shape correction factors in the HFBB analysis did not directly take into account the influence of the site specific characteristics on the actual wind loads, hence their estimates of the building responses have a higher variability.

Failure-Proof Design of the PCB of a Monitor Using Deformed Mode Shape (변형 모드를 이용한 모니터용 회로 기판의 파손 저감 설계에 관한 연구)

  • Park, Sang-Hu;Lee, Bu-Yun
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.1
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    • pp.111-116
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    • 2001
  • A practical scheme to reduce failure of the PCB(Printed Circuit Board) of a monitor is introduced using deformed mode shape under mechanical shock. When the monitor is given critical shock loads, cracks are commonly initiated at the tip of a hole on the PCB. Accordingly, a deformed mode shape of the PCB is obtained using a FEM code to define a weak point on the PCB under mechanical shock, and then the position and direction of the hole is determined to prevent the failure at the critical mode shape. Also, the stress intensity factor around the weak point on the PCB is calculated to check the possibility of fracture by normal tensile stress. In conclusion, present research is useful to assist the practical design of components-layout on the PCB.

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Mode Shape Variation of Disc Brake with Respect to Contact Stiffness Variation (마찰재 접촉강성에 따른 디스크 브레이크 진동모드 형상화)

  • Kang, Jae-Young
    • Transactions of the Korean Society of Automotive Engineers
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    • v.18 no.3
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    • pp.127-132
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    • 2010
  • Eigensolutions associated with self-excited vibration of disc brake system can be obtained by complex eigenvalue analysis. The eigenvalue sensitivity to change in contact stiffness can be used to demonstrate stability criteria and eigenvalue veering. Dynamic instability on eigenvalue loci with respect to the variation of contact stiffness is found to be related to mode interaction between two adjacent modes. This modal interaction can be effectively shown by mode shape visualization. This paper presents the methodology to construct the mode shape of disc brake system where a disc and two brake pads are coupled with contact stiffness.