scholarly journals Estimation of Cavities beneath Plate Structures Using a Microphone: Laboratory Model Tests

Sensors ◽  
2021 ◽  
Vol 21 (9) ◽  
pp. 2941
Author(s):  
Seonghun Kang ◽  
Jung-Doung Yu ◽  
Won-Taek Hong ◽  
Jong-Sub Lee
Keyword(s):  
Wavelet Transform ◽  
Plate Thickness ◽  
Laboratory Model ◽  
Sound Waves ◽  
Cavity Size ◽  
Plate Structures ◽  
Cavity Detection ◽  
Peak Magnitude ◽  
Acrylic Plate ◽  
Model Chamber

The objective of this study is to detect a cavity and estimate its size using sound waves in a laboratory model chamber filled with dry sand. One side of the chamber is covered with an acrylic plate, and a cavity is placed between the plate and sand. Sound waves are generated by impacting the plate with an instrumented hammer, and are measured using a microphone. The measured sound waves are analyzed with four comprehensive analyses including the measured area under the rectified signal envelope (MARSE) energy, flexibility, peak magnitude of wavelet transform, and frequency corresponding to the peak magnitude. The test results show that the accuracy of cavity detection using the MARSE energy is higher for thicker plates, whereas that using flexibility is higher for thinner plates. The accuracies of cavity detection using the peak magnitude of wavelet transform, and frequency corresponding to the peak magnitude are consistently high regardless of the plate thickness. Moreover, the cavity size may be under- or overestimated depending on the plate thickness and the selected analysis method. The average of the cavity sizes estimated by these methods, however, is slightly larger than the actual cavity size regardless of the plate thickness. This study demonstrates that microphones may be effectively used for the identification of a cavity and the estimation of its size.

scholarly journals Detection of Cavities Beneath Plate Structure using a Microphone

2020 ◽  
Vol 20 (6) ◽  
pp. 229-237
Author(s):  
Seonghun Kang ◽  
Jong-Sub Lee ◽  
Jung-Doung Yu ◽  
Sang Yeob Kim
Keyword(s):  
Flexural Vibration ◽  
Signal Amplitude ◽  
Laboratory Model ◽  
Sound Waves ◽  
Plate Structures ◽  
Plate Structure ◽  
Acrylic Plate ◽  
Model Chamber ◽  
Dry Soil ◽  
Measurement Location

Failure of plate structures such as pavements can be caused by the occurrence of cavities beneath the structure. In this study, a cavity beneath the plate structure were detected in a laboratory model chamber using a hammer and microphone. Specifically, a chamber was constructed using an acrylic plate and dry soil to simulate the pavement and the subgrade, respectively. A plastic box was placed between the acrylic plate and dry soil to simulate a cavity beneath the pavement. The sound waves generated by impacting the acrylic plate with a hammer were measured using a microphone. The measured area under the rectified signal envelope (MARSE) energy was calculated for the measured sound waves, and the variation in it were analyzed according to the measurement location. The test results show that the signal attenuation was low at the cavity section owing to the conservation of impact energy and that the signal amplitude becomes lower at the soil section owing to the weakened flexural vibration. Therefore, the estimated MARSE energy at the cavity section was larger than that at the soil section. This study demonstrates the effective utilization of microphones for detecting cavities beneath the plate structures.

Full-Scale Measurements of Welding-Induced Initial Deflections and Residual Stresses in Steel-Stiffened Plate Structures

2018 ◽  
Vol Vol 160 (A4) ◽  
Author(s):  
M S Yi ◽  
C M Hyun ◽  
J K Paik
Keyword(s):  
Residual Stresses ◽  
Ultimate Strength ◽  
Computational Models ◽  
Plate Thickness ◽  
Offshore Structures ◽  
Full Scale ◽  
Stiffened Plate ◽  
Plate Structures ◽  
Initial Imperfections ◽  
Numerical Predictions

Plated structures such as ships and offshore structures are constructed using welding techniques that attach support members (or stiffeners) to the plating. During this process, initial imperfections develop in the form of initial deformations (deflections or distortions) and residual stresses. These initial imperfections significantly affect the buckling and ultimate strength of these structures. Therefore, to assess the strength of welded plate structures, it is very important to predict the magnitude and pattern of welding-induced initial imperfections and their effects on buckling and ultimate strength. To determine the reliability of the prediction methods, it is desirable to validate the theoretical or numerical predictions of welding-induced initial imperfections through comparison with full-scale actual measurements. However, full-scale measurement databases are lacking, as they are costly to obtain. This study contributes to the development of a full-scale measurement database of welding-induced initial imperfections in steel-stiffened plate structures. The target structures are parts of real (full-scale) deckhouses in very large crude oil carrier class floating, production, storage and offloading unit structures. For parametric study purposes, four test structures by varying plate thickness are measured while the stiffener types and weld bead length are fixed. Modern technologies for measuring initial deformations and residual stresses are applied. The details of the measurement methods are documented for the use of other researchers and practicing engineers who want to validate their computational models for predicting welding-induced initial imperfections.

scholarly journals Stiffness and Cavity Test of Concrete Face Based on Non-Destructive Elastic Investigation

2018 ◽  
Vol 10 (12) ◽  
pp. 4389 ◽  
Author(s):  
Jinpyo Hong ◽  
Seokhoon Oh ◽  
Eunsang Im
Keyword(s):  
Electrical Resistivity ◽  
Dynamic Stiffness ◽  
Poor Quality ◽  
High Resistivity ◽  
Destructive Testing ◽  
Plate Structures ◽  
Cavity Detection ◽  
Concrete Face ◽  
Concrete Face Rockfill Dam ◽  
Non Destructive

A non-destructive testing (NDT) method was used in a concrete face rockfill dam (CFRD) to identify the condition of the concrete face slab and detect any existing cavities between the concrete face slab and the underlying support layer. The NDT for the concrete face slab was conducted using the impulse response (IR) method and the electrical resistivity tomography (ERT) method with the application of non-destructive electrodes. Information regarding the dynamic stiffness and average mobility of the concrete was obtained based on the mobility-frequency of the IR method, and cavity detection under the plate structures was analyzed using the two-dimensional (2D) electrical resistivity section of the ERT method. The results of the IR method showed that zones with low dynamic stiffness and high average mobility were expected to be found in concrete of poor quality and in cavities beneath the concrete face slab. The results of the ERT method showed that zones with high resistivity were expected to be cavities between the concrete face slab and the underlying support layer. As a result, the tendency toward low dynamic stiffness, high average mobility, and high resistivity in both methods implies unstable concrete conditions and the possible occurrence of a cavity. The results of the two methods also showed a good correlation, and it was confirmed that the NDT method was reliable in terms of cavity estimation.

Time-Resolved Analysis of SF6 Arc Plasmas in a Laboratory Model Chamber for Circuit Breaker

2020 ◽  
Vol 48 (11) ◽  
pp. 3968-3974
Author(s):  
Sungbin Park ◽  
Donghee Kim ◽  
Yoosung Kim ◽  
Seunggi Ham ◽  
Jonghyeon Ryu ◽  
...  
Keyword(s):  
Circuit Breaker ◽  
Laboratory Model ◽  
Time Resolved ◽  
Model Chamber ◽  
Arc Plasmas

Paper 11: Variation of Hydraulic Pressure in Annular Space between Guide Vanes and Impeller of a Francis Turbine

1966 ◽  
Vol 181 (1) ◽  
pp. 109-118
Author(s):  
E. Lund
Keyword(s):  
Wave Propagation ◽  
Sound Wave ◽  
Pressure Wave ◽  
Resonance Phenomenon ◽  
Francis Turbine ◽  
Laboratory Model ◽  
Hydraulic Pressure ◽  
Sound Waves ◽  
Annular Space ◽  
Guide Vanes

One of the main sources of vibration in Francis turbines is thought to be pressure-wave disturbances generated from the impeller and interference impulses between impeller vanes and guide vanes. A theory is developed which explains the occurrence of severe vibrations caused by the elasticity of the water as a resonance phenomenon between the disturbing impulses and normal modes of vibration in the space between the impeller and the guide wheel. The wave propagation in the fluid, which is assumed to be uniform with no steady flow, is thought to satisfy the well-known sound-wave differential equation without any damping effects. The natural frequencies for one- and two-dimensional pressure-wave oscillations are calculated. The calculations, based on prior knowledge of the velocity of sound-wave propagation, show that a simple theory of one-dimensional oscillations interpreted as rotating sound waves in the annular space is sufficient to predict critical speeds of the turbine. Measurements carried out on a laboratory model Francis turbine for a head of 4.5 m and a capacity of about 1.0 m3/s confirmed the presence of free oscillations and indicated the occurrence of a resonance phenomenon in the annular space.

scholarly journals Experimental damage assessment of support condition for plate structures using wavelet transform

2019 ◽  
Vol 57 (2) ◽  
pp. 501-518 ◽  
Author(s):  
Muyideen Abdulkareem ◽  
Norhisham Bakhary ◽  
Mohammadreza Vafaei ◽  
Norhazilan Md Noor ◽  
Roslida Samat
Keyword(s):  
Wavelet Transform ◽  
Damage Assessment ◽  
Support Condition ◽  
Plate Structures

Application of Wavelets in Detection of Cavities Under Pavements by Surface Waves

2003 ◽  
Vol 1860 (1) ◽  
pp. 57-65 ◽  
Author(s):  
Parisa Shokouhi ◽  
Nenad Gucunski ◽  
Ali Maher
Keyword(s):  
Wavelet Transform ◽  
Wavelet Transforms ◽  
Element Model ◽  
Energy Concentration ◽  
Response Analysis ◽  
Analysis Tool ◽  
Cavity Detection ◽  
Time Frequency ◽  
Homogeneous Half Space ◽  
Power Spectral

Application of wavelet transforms in the detection of underground shallow cavities is investigated. Wave propagation is simulated through a transient response analysis on an axisymmetric finite element model. Cavities in a homogeneous half-space and a pavement system of a variety of shapes and embedment depths are considered. The continuous wavelet transform is introduced as a new tool for cavity detection. Effects of different types of cavities on power spectral surfaces (power spectral amplitudes versus frequency and receiver location) and Gaussian wavelet time-frequency maps (wavelet transform coefficients versus time and frequency) are studied. Results show strong energy concentration in power spectral surfaces right in front of a cavity in certain frequency bands. Time and frequency signatures of waves reflected from near and far faces of the cavity can be clearly observed in the wavelet time-frequency maps. These observations are used to locate and estimate the size of the cavity. It is demonstrated that the wavelet transform is a promising analysis tool for cavity detection and characterization.

Application of two-dimensional wavelet transform to detect damage in steel plate structures

Measurement ◽  
2019 ◽  
Vol 146 ◽  
pp. 912-923 ◽  
Author(s):  
Muyideen Abdulkareem ◽  
Norhisham Bakhary ◽  
Mohammadreza Vafaei ◽  
Norhazilan Md Noor ◽  
Roslli Noor Mohamed
Keyword(s):  
Wavelet Transform ◽  
Steel Plate ◽  
Two Dimensional ◽  
Plate Structures

Comparisons of wavelets and contourlets for vibration-based damage identification in the plate structures

2019 ◽  
Vol 22 (7) ◽  
pp. 1672-1684
Author(s):  
Sepideh Vafaie ◽  
Eysa Salajegheh
Keyword(s):  
Wavelet Transform ◽  
Traditional Method ◽  
Damage Identification ◽  
Poor Performance ◽  
Contourlet Transform ◽  
Two Dimensional ◽  
Plate Structures ◽  
New Approach ◽  
Fixed Boundary ◽  
Efficient Performance

The objective of the present study is to compare a new approach based on contourlet transform and a traditional method based on wavelet transform to demonstrate curve damages in plate structures. The contourlet transform approach, as a novel two-dimensional development of wavelet transform, was extended to deal with inherent restrictions of wavelets. According to previous studies, wavelets have indicated poor performance to detect curve damages due to its basic elements. Therefore, this study utilized contourlet transform as a new method having an efficient performance to display this kind of discontinuities. In this research, contourlet transform and wavelet transform have been applied to a plate using four fixed boundary conditions including circle damages with arbitrary specifications and location in order to demonstrate their performance in damage identification. Comparing damage shape attained from contourlet transform and wavelet transform, it was revealed that contourlet transform could be utilized as an accessible and useful technique to detect damage with curvature.

FULL-SCALE MEASUREMENTS OF WELDING-INDUCED INITIAL DEFLECTIONS AND RESIDUAL STRESSES IN STEEL-STIFFENED PLATE STRUCTURES

2021 ◽  
Vol 160 (A4) ◽  
Author(s):  
M S Yi ◽  
C M Hyun ◽  
J K Paik
Keyword(s):  
Residual Stresses ◽  
Ultimate Strength ◽  
Plate Thickness ◽  
Offshore Structures ◽  
Full Scale ◽  
Stiffened Plate ◽  
Plate Structures ◽  
Initial Imperfections ◽  
Numerical Predictions ◽  
Modern Technologies

Plated structures such as ships and offshore structures are constructed using welding techniques that attach support members (or stiffeners) to the plating. During this process, initial imperfections develop in the form of initial deformations (deflections or distortions) and residual stresses. These initial imperfections significantly affect the buckling and ultimate strength of these structures. Therefore, to assess the strength of welded plate structures, it is very important to predict the magnitude and pattern of welding-induced initial imperfections and their effects on buckling and ultimate strength. To determine the reliability of the prediction methods, it is desirable to validate the theoretical or numerical predictions of welding-induced initial imperfections through comparison with full-scale actual measurements. However, full-scale measurement databases are lacking, as they are costly to obtain. This study contributes to the development of a full-scale measurement database of welding-induced initial imperfections in steel-stiffened plate structures. The target structures are parts of real (full-scale) deckhouses in very large crude oil carrier class floating, production, storage and offloading unit structures. For parametric study purposes, four test structures by varying plate thickness are measured while the stiffener types and weld bead length are fixed. Modern technologies for measuring initial deformations and residual stresses are applied. The details of the measurement methods are documented for the use of other researchers and practicing engineers who welding-induced initial imperfections.

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