scholarly journals An Experimental Study on the Defect Detectability of Time- and Frequency-Domain Analyses for Flash Thermography

2020 ◽  
Vol 10 (22) ◽  
pp. 8051
Author(s):  
Gaétan Poelman ◽  
Saeid Hedayatrasa ◽  
Joost Segers ◽  
Wim Van Paepegem ◽  
Mathias Kersemans
Keyword(s):  
Frequency Domain ◽  
Spectral Band ◽  
Frequency Domain Analysis ◽  
Post Processing ◽  
Analysis Techniques ◽  
Thermal Signal ◽  
Evaluation Procedures ◽  
Flash Thermography ◽  
The Time Domain ◽  
Defect Detectability

A defect’s detectability in flash thermography is highly dependent on the applied post-processing methodology. The majority of the existing analysis techniques operate either on the time-temperature data or on the frequency-phase data. In this paper, we compare the efficiency of time- and frequency-domain analysis techniques in flash thermography for obtaining good defect detectability. Both single-bin and integrated-bin evaluation procedures are considered: dynamic thermal tomography and thermal signal area for the time-domain approach, and frequency domain tomography and adaptive spectral band integration for the frequency-domain approach. The techniques are applied on various carbon fiber reinforced polymer samples having a range of defect sizes and defect types. The advantages and drawbacks of the different post-processing techniques are evaluated and discussed. The best defect detectability is achieved using the integrated procedure in frequency domain.

A Frequency Domain Analysis of Learning Control

1994 ◽  
Vol 116 (4) ◽  
pp. 781-786 ◽  
Author(s):  
C. J. Goh
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Linear Time ◽  
Planning Horizon ◽  
Time Domain Analysis ◽  
Learning Control ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Convergence Criterion ◽  
The Time Domain

The convergence of learning control is traditionally analyzed in the time domain. This is because a finite planning horizon is often assumed and the analysis in time domain can be extended to time-varying and nonlinear systems. For linear time-invariant (LTI) systems with infinite planning horizon, however, we show that simple frequency domain techniques can be used to quickly derive several interesting results not amenable to time-domain analysis, such as predicting the rate of convergence or the design of optimum learning control law. We explain a paradox arising from applying the finite time convergence criterion to the infinite time learning control problem, and propose the use of current error feedback for controlling possibly unstable systems.

Hydrodynamic Interactions and Relative Motions Analysis for Installation of an Extendable Draft Platform

2009 ◽  
Author(s):  
Bonjun Koo ◽  
Jang Whan Kim
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Hydrodynamic Interactions ◽  
Coupled Analysis ◽  
Heave Plate ◽  
The Time Domain ◽  
Stabilized Platform ◽  
Relative Motions

The Extendable Draft Platform (EDP) is a deep draft, column stabilized platform with a deck box support for topsides and a single, deep draft heave plate that provides suitable motion characteristics to enable the use of dry tree top tensioned risers. The EDP can be fabricated with topsides installed on the deck box and commissioned quayside in a typical construction yard. With the columns in the retracted position, the EDP floats on its deck box and can be towed, in this configuration, to the location of interest. Once the EDP is transported to its final site, the columns and heave plate are lowered to their final operating draft. During the lowering sequence, the deck box and the lower hull become two relatively independent bodies, mechanically connected by chains that control the lowering of the columns and heave plate, and the guides between the deck box and the columns. This multi-body system is hydrodynamically coupled because of radiated and diffracted waves. The global performance analyses of the installation process (lowering of the lower hull) are carried out by three different methods. The first method is frequency-domain analysis by WAMIT and a frequency domain motion solver. In the frequency domain analysis, all the mechanical connections are modeled as linear springs. The second method is time-domain, partially coupled analysis using HARP/WINPOST. In this analysis, the off diagonal 6×6 hydrodynamic interactions are ignored. The last method is a time domain, fully coupled analysis using HARP/WINPOST. In this analysis, full 12×12 hydrodynamic interactions are considered. In the time domain analyses, the mechanical couplings between each column and deck box are modeled with linear springs and the chain connections are modeled with slender rods by using the nonlinear finite element method. This paper presents and compares analysis results based on the three methods for relative motions and loads between the deck box and the lower hull during the lowering of the columns and heave plate.

Children Display Adult-Like Kinetic Patterns in the Time Domain, But Not in the Frequency Domain, While Walking With Ankle Load

2015 ◽  
Vol 31 (5) ◽  
pp. 292-308 ◽  
Author(s):  
Jianhua Wu ◽  
Toyin Ajisafe ◽  
Matthew Beerse
Keyword(s):  
Young Adults ◽  
Frequency Domain ◽  
Body Mass ◽  
Time Domain ◽  
Second Harmonic ◽  
Reaction Force ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Spatiotemporal Parameters ◽  
The Time Domain

This study used both time and frequency domain analyses to investigate walking patterns with ankle load in children and adults. Twenty-two children aged 7–10 years and 20 young adults participated in this study. Three levels of ankle load were manipulated: no load, low load (2% of body mass on each side), and high load (4% of body mass on each side). An instrumented treadmill was used to register vertical ground reaction force (GRF) and spatiotemporal parameters, and peak vertical GRFs were determined. A frequency domain analysis was conducted on the vertical GRF data. Results demonstrate that, in the time domain, children showed adult-like spatiotemporal parameters and adult-like timing and magnitude of the 2 peak vertical GRFs under each load. In the frequency domain, children produced a lower power from the second harmonic than young adults, although both groups showed the highest power from this harmonic and increased this power with ankle load. It was concluded that children aged 7–10 years may start showing adult-like neuromuscular adaptations to increasing ankle load and display similar spatiotemporal control of foot falls and foot–floor kinetic interaction; however, a frequency domain analysis is effective in revealing different kinetic and neuromuscular characteristics between children and adults.

scholarly journals Time-resolving the COVID-19 outbreak using frequency domain analysis

2020 ◽  
Author(s):  
Keno L. Krewer ◽  
Mischa Bonn
Keyword(s):  
Steady State ◽  
Severe Acute Respiratory Syndrome ◽  
Spectral Density ◽  
Frequency Domain ◽  
Time Domain ◽  
Case Fatality ◽  
Frequency Domain Analysis ◽  
Time Domain Data ◽  
Current Outbreak ◽  
The Time Domain

AbstractDifficulties assessing and predicting the current outbreak of the severe acute respiratory syndrome coronavirus 2 can be traced, in part, to the limitations of a static description of a dynamic system. Fourier transforming the time-domain data of infections and fatalities into the frequency domain makes the dynamics easily accessible. Defining a quantity like the “case fatality” as a spectral density allows a more sensible comparison between different countries and demographics during an ongoing outbreak. Such a case fatality informs not only how many of the confirmed cases end up as fatalities, but also when. For COVID-19, knowing this time and using the entire case fatality spectrum allows determining that an outbreak had entered a steady-state (most likely its end) about 14 days before this is obvious from time-domain data. The lag between confirmations and deaths also helps to estimate the effectiveness of contact management: The larger the lag, the less time the average confirmed person had to infect people before quarantine.

The Interrelated Mechanics of Poroelastic Gels in Time- and Frequency-Domain Detected by Indentation

2020 ◽  
Vol 12 (09) ◽  
pp. 2050103
Author(s):  
Alvin Maningding ◽  
Mojtaba Azadi
Keyword(s):  
Elastic Modulus ◽  
Stress Relaxation ◽  
Frequency Domain ◽  
Time Domain ◽  
Poisson Ratio ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Master Curves ◽  
The Time Domain ◽  
First Time

The force response of poroelastic materials including poroelastic gels to indentation is known to be time- and space-dependent (i.e., a function of indenter shape and size). Despite the complexity of the poroelastic response and in contrast to viscoelastic mechanics, poroelastic mechanics can be captured in terms of several intrinsic mechanical properties, such as elasticity, permeability, and Poisson ratio. While these intrinsic properties can be found from time-domain or frequency-domain master curves, indentation is usually conducted and analyzed only in the time domain using stress-relaxation or creep experiments. This paper advocates using frequency-domain analysis of poroelastic gels by reviewing and analyzing the relevant works of the literature. The analysis and methods, proposed here, enable researchers to characterize dynamic moduli of poroelastic gels in frequency domain using only a few experimental defining parameters. The authors have intentionally provided extensive details and background, to make this work useful for researchers who consider using frequency-domain analysis for the first time. This work reviews and explains the instantaneous elastic modulus, depicted over normalized time as a unifying and understandable set of master curves for time-domain stress relaxation tests on poroelastic gels for cylindrical, conical, and spherical indenters. The dynamic elastic modulus, depicted over normalized frequency, are derived symbolically and numerically and explained for the first time as master curves with simple transfer function in the frequency domain for presenting poroelastic mechanics of gels.

scholarly journals Frequency-Domain Evidence for Climate Change

Econometrics ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 28
Author(s):  
Manveer Kaur Mangat ◽  
Erhard Reschenhofer
Keyword(s):  
Climate Change ◽  
Frequency Domain ◽  
Long Range ◽  
Low Frequency ◽  
Frequency Domain Analysis ◽  
Conclusive Evidence ◽  
Small Sample ◽  
Sample Test ◽  
The Time Domain ◽  
Memory Parameter

The goal of this paper is to search for conclusive evidence against the stationarity of the global air surface temperature, which is one of the most important indicators of climate change. For this purpose, possible long-range dependencies are investigated in the frequency-domain. Since conventional tests of hypotheses about the memory parameter, which measures the degree of long-range dependence, are typically based on asymptotic arguments and are therefore of limited practical value in case of small or medium sample sizes, we employ a new small-sample test as well as a related estimator for the memory parameter. To safeguard against false positive findings, simulation studies are carried out to examine the suitability of the employed methods and hemispheric datasets are used to check the robustness of the empirical findings against low-frequency natural variability caused by oceanic cycles. Overall, our frequency-domain analysis provides strong evidence of non-stationarity, which is consistent with previous results obtained in the time domain with models allowing for stochastic or deterministic trends.

Vehicle Vibration Analysis Using Frequency Domain Techniques

1969 ◽  
Vol 91 (4) ◽  
pp. 1075-1080 ◽  
Author(s):  
W. F. Lins
Keyword(s):  
Frequency Domain ◽  
Transfer Functions ◽  
Frequency Domain Analysis ◽  
Test Case ◽  
Response Functions ◽  
Vehicle Simulation ◽  
Absorbed Power ◽  
The Time Domain ◽  
Comparison Of The Results ◽  
Frequency Domain Techniques

This paper describes a method of determining and evaluating vehicle vibration through frequency-response functions. Human transfer functions and absorbed power are used to investigate the effects of vibration on the human being. The advantages and limitations of frequency domain analysis in contrast to vehicle simulation in the time domain are discussed. A test case showing a series of computer simulations using both techniques is presented, and a comparison of the results is made.

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