scholarly journals Non-model-based damage identification of plates using principal, mean and Gaussian curvature mode shapes

2017 ◽  
Vol 400 ◽  
pp. 626-659 ◽  
Author(s):  
Y.F. Xu ◽  
W.D. Zhu ◽  
S.A. Smith
Keyword(s):  
Gaussian Curvature ◽  
Damage Identification ◽  
Mode Shapes ◽  
Model Based

Non-model-based damage identification of plates using measured mode shapes

2016 ◽  
Vol 16 (1) ◽  
pp. 3-23 ◽  
Author(s):  
Yongfeng Xu ◽  
Weidong Zhu
Keyword(s):  
Structural Damage ◽  
Damage Identification ◽  
Damage Index ◽  
Thickness Reduction ◽  
Aluminum Plate ◽  
Mode Shapes ◽  
Identification Method ◽  
Model Based

Mode shapes (MSs) have been extensively used to detect structural damage. This paper presents a new non-model-based damage identification method that uses measured MSs to identify damage in plates. A MS damage index (MSDI) is proposed to identify damage near regions with consistently high values of MSDIs associated with MSs of different modes. A MS of a pseudo-undamaged plate can be constructed for damage identification using a polynomial of a properly determined order that fits the corresponding MS of a damaged plate, if the associated undamaged plate is geometrically smooth and made of materials that have no stiffness and mass discontinuities. It is shown that comparing a MS of a damaged plate with that of a pseudo-undamaged plate is better for damage identification than with that of an undamaged plate. Effectiveness and robustness of the proposed method for identifying damage of different positions and areas are numerically investigated using different MSs; effects of crucial factors that determine effectiveness of the proposed method are also numerically investigated. Damage in the form of a machined thickness reduction area was introduced to an aluminum plate; it was successfully identified by the proposed method using measured MSs of the damaged plate.

Motion planning of a fish-like piezoelectric actuated robot using model-based predictive control

2021 ◽  
pp. 107754632110482
Author(s):  
Arthur S Barbosa ◽  
Lucas Z Tahara ◽  
Maíra M da Silva
Keyword(s):  
Motion Planning ◽  
Predictive Control ◽  
Fiber Composite ◽  
Beam Theory ◽  
Mode Shapes ◽  
Design Strategies ◽  
Mechanical Coupling ◽  
Model Based ◽  
Input Signals ◽  
Bounded Input

This work proposes a novel methodology for planning the motion of fish-like soft robots actuated by macro-fiber composite (MFC) pairs. These structures should mimic oscillatory and undulation movements, which can be accomplished if the amplitude of the tail motion is larger than that of the head motion. Design strategies, such as the use of concentrated and distributed masses, are addressed to mimic fish-like motion since they guarantee suitable mode shapes for the structure. The motion planning proposal explores a model-based predictive control (MPC) strategy for deriving the input signals for the MFC actuators. This model-based control strategy requires the use of reasonably small-sized models. This is accomplished by extracting modal state-space models based on the free–free Euler–Bernoulli beam theory considering the electro-mechanical coupling of the MFC actuator pairs. Numerical results demonstrate the capability of the proposal for deriving bounded input signals that generate oscillatory and undulation movements even in the presence of disturbances. This general approach can be further extended for other applications.

Free Vibration of Damaged Beam Structure with a Notch Defect

2012 ◽  
Vol 226-228 ◽  
pp. 44-47 ◽  
Author(s):  
Jiang Yi Chen ◽  
Li Ge Fan ◽  
Dong Chen Qin
Keyword(s):  
Damage Identification ◽  
Delta Function ◽  
Theoretical Background ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Beam Structure ◽  
Arbitrary Boundary ◽  
Numerical Examples ◽  
Elastically Supported ◽  
Universal Expression

In this paper, we derive the universal expression of the modal parameters for a damaged beam under arbitrary boundary conditions. The delta function is first employed to describe a notch damage in the beam and consequently to derive the governing equation for the damaged beam. Second, by virtue of the perturbation method, the eigenvalues and the corresponding mode shapes are obtained for the damaged beam. Finally, numerical examples are given for an elastically supported beam. It is believed that the proposed approach could provide the necessary theoretical background for damage identification in beam structures.

scholarly journals Damage Identification by Using a Self-Synchronizing Multipoint Laser Doppler Vibrometer

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Chong Yang ◽  
Yu Fu ◽  
Jianmin Yuan ◽  
Min Guo ◽  
Keyu Yan ◽  
...  
Keyword(s):  
Mode Shape ◽  
Natural Frequencies ◽  
Damage Identification ◽  
Reference Beam ◽  
Laser Doppler Vibrometer ◽  
Laser Doppler ◽  
Vibration Measurement ◽  
Mode Shapes ◽  
Interference Signal ◽  
Short Period

The vibration-based damage identification method extracts the damage location and severity information from the change of modal properties, such as natural frequency and mode shape. Its performance and accuracy depends on the measurement precision. Laser Doppler vibrometer (LDV) provides a noncontact vibration measurement of high quality, but usually it can only do sampling on a single point. Scanning LDV is normally used to obtain the mode shape with a longer scanning time. In this paper, a damage detection technique is proposed using a self-synchronizing multipoint LDV. Multiple laser beams with various frequency shifts are projected on different points of the object, reflected and interfered with a common reference beam. The interference signal containing synchronized temporal vibration information of multiple spatial points is captured by a single photodetector and can be retrieved in a very short period. Experiments are conducted to measure the natural frequencies and mode shapes of pre- and postcrack cantilever beams. Mode shape curvature is calculated by numerical interpolation and windowed Fourier analysis. The results show that the artificial crack can be identified precisely from the change of natural frequencies and the difference of mode shape curvature squares.

A Flexibility-Based Method for Structural Damage Identification Using Ambient Modal Data

2009 ◽  
Vol 24 (3) ◽  
pp. 153-159 ◽  
Author(s):  
Q. W. Yang
Keyword(s):  
Structural Damage ◽  
Damage Identification ◽  
Simulated Data ◽  
Least Square ◽  
Ambient Vibration ◽  
Mode Shapes ◽  
Vibration Modes ◽  
Sensitivity Equation ◽  
Structural Damage Identification ◽  
Normalization Factors

Structural damage identification using ambient vibration modes has become a very important research area in recent years. The main issue surrounding the use of ambient vibration modes is the mass normalization of the measured mode shapes. This paper presents a promising approach that extends the flexibility sensitivity technique to tackle the ambient vibration case. By introducing the mass normalization factors, manipulating the flexibility sensitivity equation, the unknown damage parameters and mass normalization factors can be computed simultaneously by the least-square technique. The effectiveness of the proposed method is illustrated using simulated data with measurement noise on three examples. It has been shown that the proposed procedure is simple to implement and may be useful for structural damage identification under ambient vibration case.

Damage Identification in Collocated Structural Systems Using Structural Markov Parameters

2013 ◽  
Author(s):  
Ramin Bighamian ◽  
Hamid Reza Mirdamadi ◽  
Jin-Oh Hahn
Keyword(s):  
Structural Damage ◽  
Damage Identification ◽  
Mode Shapes ◽  
Structural Systems ◽  
Structural System ◽  
Computationally Efficient ◽  
Markov Parameters ◽  
Novel Approach ◽  
Stiffness Matrices ◽  
Stiffness Characteristics

This paper presents a novel approach to damage identification in a class of collocated multi-input multi-output structural systems. In the proposed approach, damage is identified via the structural Markov parameters obtained from a system identification procedure, which is in turn exploited to localize and quantify damage by evaluating relative changes occurring in the mass and stiffness matrices associated with the structural system. To this aim, an explicit relationship between structural Markov parameters versus mass and stiffness matrices is developed. The main strengths of the proposed approach are that it is capable of quantitatively identifying the occurrence of multiple damages associated with both mass and stiffness characteristics in the structural system, and it is computationally efficient in that it is solely based on the structural Markov parameters but does not necessitate costly calculations related to natural frequencies and mode shapes, making it highly attractive for structural damage detection and health monitoring applications. Numerical examples are provided to demonstrate the validity and effectiveness of the proposed approach.

A Damage Identification Method Using Vibration Modal Parameters Through Finite Element Discretization

2003 ◽  
Author(s):  
Xiaoping Zhou ◽  
Abhijit Gupta
Keyword(s):  
Finite Element ◽  
Natural Frequencies ◽  
Damage Identification ◽  
Least Squares Method ◽  
Modal Testing ◽  
Mode Shapes ◽  
Element Formulation ◽  
Element Discretization ◽  
Damage Indices ◽  
Actual Damage

Natural frequencies and mode shapes of a structure will change whenever the structure has any kind of damage. This paper introduces a technique to quantify and locate the damage when the natural frequencies and mode shapes of undamaged and damaged structure are known. Aluminum beams (with and without damage) are used for numerical simulation and experimental verification. To establish the theoretical basis of this method, finite element formulation is used. A set of undetermined equations involving damage indices and natural frequencies and mode shapes of undamaged and damaged structures are obtained. The damage indices are computed using non-negative least squares method. Impact modal testing was conducted with three aluminum beams and damage indices based on experimental data are compared with actual damage cases to establish the effectiveness of this method to identify the damage.

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