scholarly journals Simulation and Analysis with Wavelet Transform Technique and the Vibration Characteristics for Early Revealing of Cracks in Structures

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Nidal H. Abu-Hamdeh ◽  
Khaled Daqrouq ◽  
Fateh Mebarek-Oudina
Keyword(s):  
Wavelet Packet ◽  
Crack Depth ◽  
Element Model ◽  
Absolute Error ◽  
Crack Size ◽  
Maximum Absolute Error ◽  
Vibration Technique ◽  
Aluminum Beam ◽  
Crack Position ◽  
Response Feature

Implementation of improved instruments is used to detect damage in an accurate manner and fully analyze its characteristics. An aluminum beam has been used in this work to identify cracks by using a vibration technique. The simulation of frequency response feature was conducted using a finite element model to provide average measures of intensities of vibration. Two forms of wavelet packet transform (WPT) entropies Shannon and log energy were applied to identify the position, width, and size of the crack. The results showed that with an increase in crack depth, the amplitude also increased at certain crack sizes and for all crack positions. For two crack depths of 1.6 mm and 0.16 mm having the same crack size and position 12 mm and 60 mm, respectively, a 4.5% increase in amplitude was observed at a crack depth of 1.6 mm. Moreover, the amplitude varied inversely with the position. A 12.6% increase in amplitude was observed at a crack depth of 1.6 mm rather than 0.16 mm, while both depths occurred at the same crack position (75 mm) and size (20 mm). Experimental validation was performed on a cantilever beam with one crack. The maximum absolute error found was 7.5% for the crack position and 9.1% for the crack size. With the increase in crack depth, the obtained results decrease the stiffness of a beam in a single crack case.

scholarly journals https://marz.kau.edu.sa/Files/320/Researches/70650_43625.pdf

2017 ◽  
Vol 28 (1) ◽  
pp. 67-90
Author(s):  
Khalid H. Almitani Khalid H. Almitani
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Frequency Response ◽  
Dynamic Stiffness ◽  
Crack Depth ◽  
Element Model ◽  
Spectral Element ◽  
Crack Size ◽  
Aluminum Beam ◽  
Crack Position

A crack is a type of damage that can lead to catastrophic failure when it grows in a structure. Thus prediction of cracks is a very important problem that has to be addressed. Some studies have been done on non-destructive techniques to identify cracks. Research interest in this area has been growing up quickly. In this study, a beam made of aluminum was used for detecting cracks using vibration characteristics. A method to identify cracks in an aluminum beam was derived from the equation of the dynamic stiffness. Rotational springs were used to model the cracks in the beam and the frequency response function was calculated using a spectral element model using Finite Element Model (FEM). This procedure provides a relationship between the frequency response and crack structure. The inverse problem was solved repetitively for crack positions and sizes using the Newton-Raphson method. The finite element model was formulated to simulate the results and to provide vibration overall amplitude measurements. The results showed at certain crack size, the amplitude increases with increasing crack depth for all crack positions. At crack size of 12 mm, an increase of 4.5% in amplitude was obtained for 60 mm crack position at a depth of 1.6 mm compared to its value at a depth of 0.16 mm. Similarly, it was 8.4% at crack size of 16 mm. Also, the amplitude varies inversely with position. Furthermore, at certain crack position, the amplitude increases with increasing crack depth for all crack sizes. At crack position of 75 mm, an increase of 12.6% in amplitude was obtained for 20 mm crack size at a depth of 1.6 mm compared to its value at a depth of 0.16 mm. Similarly, it was 5.4% at crack position of 150 mm. Finally, the amplitude increases as crack size increases at a certain depth.

Error Compensation Techniques for Fixed-Width Array Multiplier Design — A Technical Survey

2016 ◽  
Vol 26 (03) ◽  
pp. 1730003 ◽  
Author(s):  
S. Balamurugan ◽  
P. S. Mallick
Keyword(s):  
Error Compensation ◽  
Absolute Error ◽  
Mean Square ◽  
Maximum Absolute Error ◽  
Comprehensive Review ◽  
Related Research ◽  
Error Formula ◽  
Error Metrics ◽  
Array Multiplier ◽  
Future Work

This paper provides a comprehensive review of various error compensation techniques for fixed-width multiplier design along with its applications. In this paper, we have studied different error compensation circuits and their complexities in the fixed-width multipliers. Further, we present the experimental results of error metrics, including normalized maximum absolute error [Formula: see text], normalized mean error [Formula: see text] and normalized mean-square error [Formula: see text] to evaluate the accuracy of fixed-width multipliers. This survey is intended to serve as a suitable guideline and reference for future work in fixed-width multiplier design and its related research.

Quantitative acoustic emission investigation on the crack evolution in concrete prisms by frequency analysis based on wavelet packet transform

2021 ◽  
pp. 147592172110188
Author(s):  
Zonglian Wang ◽  
Keqin Ding ◽  
Huilan Ren ◽  
Jianguo Ning
Keyword(s):  
Acoustic Emission ◽  
Frequency Band ◽  
Wavelet Packet ◽  
Strain Energy Release ◽  
Crack Size ◽  
Frequency Bands ◽  
Emission Signal ◽  
Damage Process ◽  
Concrete Materials ◽  
Stage 1

To gain an insight into the evolution of micro-cracks in concrete materials, a quantitative acoustic emission investigation on the damage process of concrete prisms subjected to three-point bending loading was performed. Each of the monitored acoustic emission signals was processed by a two-level wavelet packet decomposition into four different frequency bands (AA2, DA2, AD2, and DD2), and the energy coefficients R1, R2, R3, and R4 that parameterize their characteristic frequency bands were calculated. By analyzing variations in energy coefficients of the lowest frequency band (AA2), R1, and the energy coefficients of the highest frequency band (DD2), R4, the whole damage process was divided into three stages: crack initiation, crack growth, and crack coalescence. An inverse relationship between the frequency of the acoustic emission signal emitted by the propagating crack and the crack size in concrete materials was acquired based on the damage theory of brittle materials and the strain energy release theory. The statistical analysis results of the experimental data indicated that the average of R1 increased in turn, and the average of R4 correspondingly decreased in turn from Stage 1 to Stage 3. It revealed that the frequencies of acoustic emission signals decreased gradually with the evolution of the damage of concrete prisms, which is in a good agreement with the theoretical analysis result.

scholarly journals Vehicle speed measurement by on-board acoustic signal processing

2018 ◽  
Vol 51 (5-6) ◽  
pp. 138-149 ◽  
Author(s):  
Hüseyin Göksu
Keyword(s):  
Relative Motion ◽  
Wavelet Packet ◽  
Absolute Error ◽  
Frequency Resolution ◽  
Vehicle Speed ◽  
Air Conditioner ◽  
Wavelet Packet Analysis ◽  
Time Frequency ◽  
Speed Sensor ◽  
Frequency Domain Methods

Estimation of vehicle speed by analysis of drive-by noise is a known technique. The methods used in this kind of practice generally estimate the velocity of the vehicle with respect to the microphone(s), so they rely on the relative motion of the vehicle to the microphone(s). There are also other methods that do not rely on this technique. For example, recent research has shown that there is a statistical correlation between vehicle speed and drive-by noise emissions spectra. This does not rely on the relative motion of the vehicle with respect to the microphone(s) so it inspires us to consider the possibility of predicting velocity of the vehicle using an on-board microphone. This has the potential for the development of a new kind of speed sensor. For this purpose we record sound signal from a vehicle under speed variation using an on-board microphone. Sound emissions from a vehicle are very complex, which is from the engine, the exhaust, the air conditioner, other mechanical parts, tires, and air resistance. These emissions carry both stationary and non-stationary information. We propose to make the analysis by wavelet packet analysis, rather than traditional time or frequency domain methods. Wavelet packet analysis, by providing arbitrary time-frequency resolution, enables analyzing signals of stationary and non-stationary nature. It has better time representation than Fourier analysis and better high-frequency resolution than Wavelet analysis. Subsignals from the wavelet packet analysis are analyzed further by Norm Entropy, Log Energy Entropy, and Energy. These features are evaluated by feeding them into a multilayer perceptron. Norm entropy achieves the best prediction with 97.89% average accuracy with 1.11 km/h mean absolute error which corresponds to 2.11% relative error. Time sensitivity is ±0.453 s and is open to improvement by varying the window width. The results indicate that, with further tests at other speed ranges, with other vehicles and under dynamic conditions, this method can be extended to the design of a new kind of vehicle speed sensor.

scholarly journals Crack Detection through the Change in the Normalized Frequency Shape

Vibration ◽  
2018 ◽  
Vol 1 (1) ◽  
pp. 56-68
Author(s):  
Mustapha Dahak ◽  
Noureddine Touat ◽  
Tarak Benkedjouh
Keyword(s):  
Stiffness Matrix ◽  
Electrical Discharge ◽  
Inverse Method ◽  
Crack Detection ◽  
Natural Frequencies ◽  
Electrical Discharge Machining ◽  
Element Model ◽  
Experimental Application ◽  
Flexibility Matrix ◽  
Crack Position

The objective of this work is to use natural frequencies for the localization and quantification of cracks in beams. First, to study the effect of the crack on natural frequencies, a finite element model of Euler–Bernoulli is presented. Concerning the damaged element, the stiffness matrix is calculated by the theory of fracture mechanics, by inverting the flexibility matrix. Then, in order to detect damage, we are going to show that the shape given by the change in the natural frequencies is as function of the damage position only. Thus, the crack is located by the correlation between the shape of the measured frequencies and those obtained by the finite elements, where the position that gives the calculated shape which is the most similar to the measured one, indicates the crack position. After the localization, an inverse method will be applied to quantify the damage. Finally, an experimental application is presented to show the real applicability of the method, in which the crack is introduced by using an Electrical Discharge Machining. The results confirm the applicability of the method for the localization and the quantification of cracks.

Spatial Dynamic Analysis of a Mangeove Patch Based on Unmanned Aerial Vehicle: A Case Study in Pear Bay in Guangxi, China

2021 ◽  
Author(s):  
Xin Lin ◽  
Chungan Li ◽  
Mei Zhou ◽  
Wenhai Liang ◽  
Biao Li
Keyword(s):  
Unmanned Aerial Vehicle ◽  
Spatial Dynamics ◽  
Absolute Error ◽  
Maximum Error ◽  
Canopy Height ◽  
Accurate Information ◽  
Maximum Absolute Error ◽  
Patch Area ◽  
Maximum Increase ◽  
Aerial Vehicle

Abstract This study investigated the short-term spatial variability of an mangrove patch, located in the Pearl Bay in Guangxi, China. Unmanned aerial vehicle (UAV) imagery covering the period from March 2015 to October 2017 were used and the following models were developed: two annual ultra-high resolution spatial resolution digital orthophoto maps (DOMs), two digital elevation models (DEMs), two digital surface models (DSMs), two canopy height models (CHMs), and a canopy height difference model (d-CHM). Using these models, the spatial dynamics of the extent and canopy height of the patch were analyzed. The resolution of the DOMs was 0.1 m, with an average geometrical error of 0.17 m and a maximum error of 0.44 m. The resolutions of DEMs, DSMs, CHMs, d-CHM were all 1 m. The average elevation errors of CHM in 2015 and 2017 were 0.002 m and -0.001 m, respectively, with maximum absolute errors of 0.034 m and 0.030 m, respectively. The average elevation error of d-CHM was -0.003 m and the maximum absolute error was 0.036 m, and the data quality were rated as good. From 2015 to 2017, the area of the mangrove patch increased from 8.16 ha to 8.79 ha, with an average annual increase of 3.7%. Specifically, the areas of expansion, shrinkage, and maximum seaward expansion were 6356 m2, 19 m2, and 24 m, respectively. The driving factor for the variability was natural processes. Stand canopy height exhibited a particular trend of decrease from northwest to southeast (horizontal; parallel to the seawall) and from the land to the sea (vertically; perpendicular to the seawall). From 2015 to 2017, 88.2% of the patch area showed increased canopy height, with an average increase of 0.78 m and a maximum increase of 3.2 m. In contrast, 11.8% of the patch area showed decreased canopy height with a maximum decrease of 3.1 m. The main reason for the decrease in canopy height was the death of trees caused by serious insect plagues. On the other hand, the reason for the increase in height could be attributed to the natural growth of mangrove trees, but further studies are required to verify the cause. UAV remote sensing has an incomparable advantage over traditional methods in that it provides extremely detailed and highly accurate information for in-depth study of the spatial evolution of mangrove patches, which would significantly contribute towards the protection and management of mangroves.

scholarly journals Fatigue Life Appraisal and Its Corrected Stress Intensity Factor for Repaired Off-CentrallyCracked Aluminum Plates

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4014
Author(s):  
Xiang You ◽  
Zhiyu Wang ◽  
Xiafang Zhou ◽  
Zifeng Liu ◽  
Ruijuan Jiang ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Element Model ◽  
Crack Size ◽  
Plate Edge ◽  
Life Estimation ◽  
Fatigue Life Estimation ◽  
Life Improvement ◽  
Edge Cracks ◽  
Aluminum Plates ◽  
Sensitive Parameters

This paper presents an experimental study on the fatigue life estimation of off-centrally cracked aluminum plates. Typical theoretical equations for off-central, central and edge cracks were reviewed and compared in terms of their sensitive parameters and applicability. A finite element model has been validated in its capacity in modelling the influences of eccentricity and crack size on the boundary correction coefficients. The Forman equation has been employed along with numerical results for the prediction of fatigue lives. Based on the test data, the fatigue life results of aluminum plates with and without patched laminate repair have been compared with codified fatigue classes. It is demonstrated that the repair at the crack tip close to the plate edge is effective in the fatigue life improvement for off-centrally crackedaluminum plates.

scholarly journals Advanced interpretation of subsidence in Murcia (SE Spain) using A-DInSAR data – modelling and validation

2009 ◽  
Vol 9 (3) ◽  
pp. 647-661 ◽  
Author(s):  
G. Herrera ◽  
J. A. Fernández ◽  
R. Tomás ◽  
G. Cooksley ◽  
J. Mulas
Keyword(s):  
Time Series ◽  
Metropolitan Area ◽  
Prediction Models ◽  
Time History ◽  
Element Model ◽  
Absolute Error ◽  
Sar Interferometry ◽  
Se Spain ◽  
Drought Period ◽  
Aquifer System

Abstract. Subsidence is a natural hazard that affects wide areas in the world causing important economic costs annually. This phenomenon has occurred in the metropolitan area of Murcia City (SE Spain) as a result of groundwater overexploitation. In this work aquifer system subsidence is investigated using an advanced differential SAR interferometry remote sensing technique (A-DInSAR) called Stable Point Network (SPN). The SPN derived displacement results, mainly the velocity displacement maps and the time series of the displacement, reveal that in the period 2004–2008 the rate of subsidence in Murcia metropolitan area doubled with respect to the previous period from 1995 to 2005. The acceleration of the deformation phenomenon is explained by the drought period started in 2006. The comparison of the temporal evolution of the displacements measured with the extensometers and the SPN technique shows an average absolute error of 3.9±3.8 mm. Finally, results from a finite element model developed to simulate the recorded time history subsidence from known water table height changes compares well with the SPN displacement time series estimations. This result demonstrates the potential of A-DInSAR techniques to validate subsidence prediction models as an alternative to using instrumental ground based techniques for validation.

scholarly journals Method of Measuring Liquid Water Mass Fraction of Snow by Alcohol Solution

1986 ◽  
Vol 32 (112) ◽  
pp. 538-539 ◽  
Author(s):  
D. Fisk
Keyword(s):  
Liquid Water ◽  
Water Mass ◽  
Field Measurements ◽  
Absolute Error ◽  
Liquid Water Content ◽  
Snow Sample ◽  
Maximum Absolute Error ◽  
Water Fraction ◽  
Single Operator ◽  
Temperature Depression

Abstracta method of making field measurements of the liquid water fraction of snow has been developed in which a snow sample is dissolved in methanol to produce a temperature depression. The depression is linearly related to the liquid water content of the snow sample. a single operator can perform four to five measurements per hour with a maximum absolute error of 1.0%.

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