scholarly journals The relevance of non-stationarities and non-Gaussianities in vibration fatigue

2018 ◽  
Vol 165 ◽  
pp. 10011 ◽  
Author(s):  
Martin Česnik ◽  
Janko Slavič ◽  
Lorenzo Capponi ◽  
Massimiliano Palmieri ◽  
Filippo Cianetti ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Dynamic Loading ◽  
Amplitude Modulation ◽  
Time History ◽  
Power Density Spectrum ◽  
Time To Failure ◽  
Density Spectrum ◽  
Frequency Domain Methods ◽  
Vibration Fatigue ◽  
Non Gaussian

In classical fatigue of materials, the frequency contents of dynamic loading are well below the natural frequencies of the observed structure or test specimen. However, when dealing with vibration fatigue the frequency contents of dynamic loading and structure's dynamic response overlap, resulting in amplified stress loads of the structure. For such cases, frequency counting methods are especially convenient. Gaussianity and stationarity assumptions are applied in frequency-domain methods for obtaining dynamic structure's response and frequency-domain methods for calculating damage accumulation rate. Since it is common in real environments for the structure to be excited with non-Gaussian and non-stationary loads, this study addresses the effects of such dynamic excitation to experimental time-to-failure of a structure. Initially, the influence of non-Gaussian stationary excitation is experimentally studied via excitation signals with equal power density spectrum and different values of kurtosis. Since no relevant changes of structure's time-to-failure were observed, the study focused on non-stationary excitation signals that are also inherently non-Gaussian. The non-stationarity of excitation was achieved by amplitude modulation and significantly shorter times-to-failure were observed when compared to experiments with stationary non-Gaussian excitation. Additionally, the structure's time-to-failure varied with the rate of the amplitude modulation. To oversee this phenomenon the presented study proposes a non-stationarity index which can be obtained from the excitation time history. The non-stationarity index was experimentally confirmed as a reliable estimator for severity of non-stationary excitation. The non-stationarity index is used to determine if the frequencydomain methods can safely be applied for time-to-failure calculation.

scholarly journals Artificial neural network for Gaussian and non-Gaussian random fatigue loading analysis

2019 ◽  
Vol 233 (23-24) ◽  
pp. 7525-7544
Author(s):  
JF Durodola
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Frequency Domain ◽  
Fatigue Loading ◽  
Neural Network Approach ◽  
Frequency Domain Methods ◽  
Artificial Neural ◽  
Non Gaussian ◽  
Random Fatigue ◽  
Loading Analysis

There has been a lot of work done on the analysis of Gaussian loading analysis perhaps because its occurrence is more common than non-Gaussian loading problems. It is nevertheless known that non-Gaussian load occurs in many instances especially in various forms of transport, land, sea and space. Part of the challenge with non-Gaussian loading analysis is the increased number of variables that are needed to model the loading adequately. Artificial neural network approach provides a versatile means to develop models that may require many input variables in order to achieve applicable predictive generalisation capabilities. Artificial neural network has been shown to perform much better than existing frequency domain methods for random fatigue loading under stationary Gaussian load forms especially when mean stress effects are included. This paper presents an artificial neural network model with greater predictive capability than existing frequency domain methods for both Gaussian and non-Gaussian loading analysis. Both platykurtic and leptokurtic non-Gaussian loading cases were considered to demonstrate the scope of application. The model was also validated with available SAE experimental data, even though the skewness and kurtosis of the signal in this case were mild.

scholarly journals Dirlik and Tovo-Benasciutti Spectral Methods in Vibration Fatigue: A Review with a Historical Perspective

Metals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1333
Author(s):  
Turan Dirlik ◽  
Denis Benasciutti
Keyword(s):  
Frequency Domain ◽  
Spectral Methods ◽  
Historical Background ◽  
Random Loading ◽  
Element Analysis ◽  
Frequency Domain Methods ◽  
Vibration Fatigue ◽  
The Time Domain ◽  
Frequency Domain Techniques ◽  
Future Work

The frequency domain techniques (also known as “spectral methods”) prove significantly more efficient than the time domain fatigue life calculations, especially when they are used in conjunction with finite element analysis. Frequency domain methods are now well established, and suitable commercial software is commonly available. Among the existing techniques, the methods by Dirlik and by Tovo–Benasciutti (TB) have become the most used. This study presents the historical background and the motivation behind the development of these two spectral methods, by also emphasizing their application and possible limitations. It further presents a brief review of the other spectral methods available for cycle counting directly from the power spectral density of the random loading. Finally, some ideas for future work are suggested.

Short Term Prediction of Hydroelastic Dynamic Response in Random Waves for an 1100 TEU Container Ship

2013 ◽  
Vol 837 ◽  
pp. 464-470
Author(s):  
Ionica Rubanenco ◽  
Leonard Domnisoru
Keyword(s):  
Dynamic Response ◽  
Frequency Domain ◽  
Time Domain ◽  
Power Density Spectrum ◽  
Container Ship ◽  
Short Term ◽  
Density Spectrum ◽  
Non Linear ◽  
The Waves ◽  
Ship Speed

This paper is focused on a short term statistical analysis of the ship dynamic response in random head waves. The waves and the ship responses are considered to be homogenous random processes, being described by a short term Rayleigh first order probability density function. The waves are described in the frequency domain by ITTC power density spectrum function, with time domain formulation by Airy-Faltinsen and Longuet-Higgins models. The numerical analysis are carried out with own program codes package DYN, based on the hydroelasticity theory, with oscillation and vibration components, taking into account the ship speed influence on the dynamic response. The dynamic analysis is based on frequency domain procedures, for linear steady state response, and direct time domain integration procedures, for non-linear and transitory response, resulting power and amplitude density spectrum functions by Fast Fourier Transformation method. The numerical analyses are applied for an optimized 1100 TEU container ship structure, considering six different ship speeds, from 0 to 20 knots, for the full containers loading case. The short term statistical numerical results are pointing out that the ship speed has higher influence on the global vibrations response in compare to the oscillations response, with better accuracy on the non-linear model.

scholarly journals Behaviour of selected table fats at the dynamic loading

2009 ◽  
Vol 57 (4) ◽  
pp. 43-54
Author(s):  
Šárka Nedomová
Keyword(s):  
Frequency Domain ◽  
Dynamic Loading ◽  
Response Function ◽  
Mechanical Behaviour ◽  
Time History ◽  
Surface Displacement ◽  
Fat Content ◽  
Impact Response ◽  
Two Factors ◽  
History Of

The new method of the evaluation of the mechanical behaviour of fats has been designed. This method is based on the evaluation of the fat response to dynamic loading. Dynamic loading has been rea­li­zed by fall of bar impact. Response function has been represented by the time history of the fat surface displacement. Response of the tested table fats have been evaluated both in the time and frequency domain. Two factors affected rheology of the examined fat products: temperature of the measurement and product origin. The influence of fat content can be described namely in the frequency domain. The results obtained between 14 and 20 °C showed significant differences in the fat rigidity.

scholarly journals Properties of Faint X-ray Activity of XTE J1908+094 in 2019

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 25
Author(s):  
Debjit Chatterjee ◽  
Arghajit Jana ◽  
Kaushik Chatterjee ◽  
Riya Bhowmick ◽  
Sujoy Kumar Nath ◽  
...  
Keyword(s):  
Black Hole ◽  
Temporal Analysis ◽  
Power Density Spectrum ◽  
Periodic Oscillations ◽  
Telescope Array ◽  
Density Spectrum ◽  
X Ray ◽  
Black Hole Candidate ◽  
Short Period ◽  
Spectral State

We study the properties of the faint X-ray activity of Galactic transient black hole candidate XTE J1908+094 during its 2019 outburst. Here, we report the results of detailed spectral and temporal analysis during this outburst using observations from Nuclear Spectroscopic Telescope Array (NuSTAR). We have not observed any quasi-periodic-oscillations (QPOs) in the power density spectrum (PDS). The spectral study suggests that the source remained in the softer (more precisely, in the soft–intermediate) spectral state during this short period of X-ray activity. We notice a faint but broad Fe Kα emission line at around 6.5 keV. We also estimate the probable mass of the black hole to be 6.5−0.7+0.5M⊙, with 90% confidence.

scholarly journals Experimental Design and Validation of an Accelerated Random Vibration Fatigue Testing Methodology

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Yu Jiang ◽  
Gun Jin Yun ◽  
Li Zhao ◽  
Junyong Tao
Keyword(s):  
Fatigue Life ◽  
Stress Responses ◽  
Life Prediction ◽  
Random Vibration ◽  
Fatigue Testing ◽  
Fatigue Tests ◽  
Fatigue Life Prediction ◽  
Power Spectral ◽  
Vibration Fatigue ◽  
Non Gaussian

Novel accelerated random vibration fatigue test methodology and strategy are proposed, which can generate a design of the experimental test plan significantly reducing the test time and the sample size. Based on theoretical analysis and fatigue damage model, several groups of random vibration fatigue tests were designed and conducted with the aim of investigating effects of both Gaussian and non-Gaussian random excitation on the vibration fatigue. First, stress responses at a weak point of a notched specimen structure were measured under different base random excitations. According to the measured stress responses, the structural fatigue lives corresponding to the different vibrational excitations were predicted by using the WAFO simulation technique. Second, a couple of destructive vibration fatigue tests were carried out to validate the accuracy of the WAFO fatigue life prediction method. After applying the proposed experimental and numerical simulation methods, various factors that affect the vibration fatigue life of structures were systematically studied, including root mean squares of acceleration, power spectral density, power spectral bandwidth, and kurtosis. The feasibility of WAFO for non-Gaussian vibration fatigue life prediction and the use of non-Gaussian vibration excitation for accelerated fatigue testing were experimentally verified.

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