جستجوی مقالات مرتبط با کلیدواژه "پایش سلامت" در نشریات گروه "مکانیک"

Health monitoring and damage detection in structures is important for maintaining the safety and health of individuals as well as for dealing with economic losses. This article compares primary and secondary modal information, including the frequency values and vibration mode shapes, for health monitoring and damage detection in beams. The impact of the damage is observed as a difference between primary and secondary frequency values, as well as a difference between the coefficients of the polynomial curves. Also, the Pearson's Correlation Coefficient (PCC) between the primary and secondary modes is calculated as values other than 1 and -1 that indicate the impact of damage on the relative displacement of degrees of freedom. However, damage locations cannot be identified by curve fitting, correlation, and comparison of natural frequencies; thus, comparison of primary and secondary shapes of vibration modes was made based on determination of central curvature. It was shown that the difference between the primary and secondary curvature graphs occurs as fractures created in damaged positions and in the curvature graph of the secondary situation; hence, the damaged locations are identifiable.

Identifying piezoelectric defects and ultrasonic transducers failure based on electromechanical impedance is one of the methods to assess their health. In a healthy piezoelectric, the electromechanical impedance is determined based on the piezoelectric properties, shape and size. In order to identify and predict the failure of piezoelectric, in this paper, a practical and effective method for evaluating the quality and health of piezoelectric used in high power ultrasonic transducers is presented. The basis of this procedure is to study the change in electric impedance characteristics of the piezoelectric disc, which can be measured according to the standard. This method can be used by researchers and manufacturers of piezoelectric. The results of experimental tests have shown that by analyzing the impedance diagram of piezoelectric, it is possible to identify faults and defects in them; even before they are visible to the naked eye. It is also possible to compare the quality of different piezoelectric manufacturers and to evaluate the performance of a healthy worked piezoceramic compared to a new component.

Structures suffer local damages due to various reasons. If these damages are not identified, they could be aggravated by natural disasters such as earthquakes or artificial factors such as unprincipled excavations, leading to total destruction of the structure. As a result, health monitoring in structures and their elements is regarded as one of the most significant research topics in civil, mechanical, and aerospace engineering. A damage detection method is to process the time or frequency domain of structural responses. In this context, wavelet transform is one of the processing methods for both time and frequency domains, and many studies have utilized it to investigate structural health monitoring. In this paper, a comprehensive review was conducted on the published studies. Besides, damage detection was performed by considering the vibration mode shapes of a defective cantilever, which were used as wavelet-transform input signals. The diagram of the detail coefficients resulting from the wavelet analysis of the input signal presented the maximum and minimum values in the defective positions. These findings support the efficiency of using wavelet transform in damage detection. Further, the sensitivity of damage detection based on wavelet transform to the severity of damages showed that with the rise in damage severity in a location, a larger relative jump occurs in the output signal of all modes.

This paper deals with active vibration control (AVC) and structural health monitoring of a maneuvering flexible spacecraft with a cracked panel using piezoelectric (PZT) sensor/actuator patches and strain rate feedback (SRF) method. The cracked panel is modeled using the Euler-Bernoulli beam theory and the finite element method (FEM). The nonlinear equations of motion of the fully coupled rigid-flexible system are extracted using the Lagrangian formulation and solved with Newmark-β algorithm. Two approaches of structural health monitoring; first, trial and error, and second, maximum strain rates (online measurement) along with AVC (applying control signals based on the maximum values of strain rates to the predefined number, but unknown locations of PZT actuators), are performed. The strain rates change directly with mission conditions and crack locations, and the corresponding actuators are activated simultaneously. Moreover, to identify the dynamic behavior of the whole, cracked system, an energy function with different weighting coefficients is introduced to propose a suitable criterion for the performance evaluation of the second approach. Simulations for different crack numbers and locations and external disturbances as a comparative study (in MATLAB/Simulink) demonstrate suitable criteria to determine the number and locations of actuators and reduce the power costs in modern spacecraft in high-precision missions.

The use of structural vibration is one of the bridge health monitoring approaches which is often costly, time-consuming. The response of a passing vehicle includes the bridge response so that it is used for extracting the bridge modal parameters. In this paper, the transmissibility measurement of a passing vehicle is employed in order to identify the bridge mode shape indirectly. As the sensor is embedded on the axle of the vehicle, recording the signal is fulfilled during the vehicle passage and there is no need to stop the vehicle. On the other hand, there is white noise assumption in most other techniques, but excitation characteristics are not considered in the proposed method which is another advantage. In the numerical simulation, the bridge is assumed to be Euler Bernoulli and the vehicle is modeled as a 4DOF system. Solving the vehicle-bridge interaction equations, the acceleration of all degrees of freedom are obtained. Afterwards, the mode shape is identified by applying the short time transmissibility measurement on the acceleration. Since the performance of the indirect methods in real cases is associated with many obstacles and challenges, a setup for experimental verification of the proposed method has been designed and constructed in a laboratory. Numerical simulations and experimental results indicate the capability of the proposed method for indirect identification of bridge mode shape.