A novel wave propagation method for measuring viscoelastic properties of pre-strained materials

2021 ◽  
pp. 1-19
Author(s):  
Pierre Lemerle
Keyword(s):  
Wave Propagation ◽  
Viscoelastic Properties ◽  
Time History ◽  
Main Concept ◽  
Frequency Dependent ◽  
Damping Characteristics ◽  
History Of ◽  
Propagation Methods ◽  
The Time Domain ◽  
Waveform Pattern

Abstract Viscoelastic materials are widely used for vibroacoustic solutions due to their ability to mitigate vibration and sound. Wave propagation methods are based on the measurement of the waveform pattern of a transitory pulse in one-dimensional structures. The time evolution of the pattern can be used to deduce the material elasticity and damping characteristics. The most popular propagation methods, namely Hopkinson bar methods, assume no dispersion, i.e. the complex elasticity modulus is not frequency-dependent. This is not significant for resilient materials such as elastomers. More recent approaches have been developed to measure frequency-dependent properties from a pulse propagating in a slender bar. We showed in previous works how to adapt these techniques for shorter samples of materials, representing a real advance, as extrusion is a cumbersome process for many materials. The main concept was to reconstruct the time history of the wave propagating in a composite structure composed of a long incident bar made of a known material and extended by a shorter sample bar. Then the viscoelastic properties of the sample material were determined in the frequency domain within an inverse method held in the time domain. In industry, most isolation solutions using mounts or bushings must support structural weights. This is why it is particularly interesting to know the viscoelastic properties of the material in stressed state. Here, we show how to overcome this challenging issue. The theoretical framework of the computational approach is detailed and the method is experimentally verified.

scholarly journals Transient Response of an Impacted Beam and Indirect Impact Force Identification Using Strain Measurements

1994 ◽  
Vol 1 (3) ◽  
pp. 267-278 ◽  
Author(s):  
Hyungsoon Park ◽  
Youn-sik Park
Keyword(s):  
Impulse Response ◽  
Impact Force ◽  
Impulse Response Function ◽  
Time History ◽  
Impulse Response Functions ◽  
Transverse Impact ◽  
History Of ◽  
Convolution Approach ◽  
The Time Domain ◽  
The Impact

The impulse response functions (force-strain relations) for Euler–Bernoulli and Timoshenko beams are considered. The response of a beam to a transverse impact force, including reflection at the boundary, is obtained with the convolution approach using the impulse response function obtained by a Laplace transform and a numerical scheme. Using this relation, the impact force history is determined in the time domain and results are compared with those of Hertz's contact law. In the case of an arbitrary impact, the location of the impact force and the time history of the impact force can be found. In order to verify the proposed algorithm, measurements were taken using an impact hammer and a drop test of a steel ball. These results are compared with simulated ones.

A non-linear model for elastic hysteresis in the time domain: Computational procedure

2020 ◽  
pp. 095440622098202
Author(s):  
MMS Dwaikat ◽  
C Spitas ◽  
V Spitas
Keyword(s):  
Time Domain ◽  
Mechanical Energy ◽  
Numerical Procedure ◽  
Time History ◽  
Computational Procedure ◽  
Continuous Systems ◽  
Full Time ◽  
Proposed Model ◽  
History Of ◽  
The Time Domain

Hysteretic damping of a material or structure loaded within its elastic region is the dissipation of mechanical energy at a rate independent of the frequency of vibration while at the same time directly proportional to the square of the displacement. Generally, reproducing this frequency-independent damping can be computationally complex and requires prior knowledge of the system’s natural frequencies or the full time history of the system’s response. In this paper, a new model and numerical procedure are proposed whereby hysteretic material damping is achieved in the time domain. The proposed procedure is developed based on modifying the viscous model through a correction factor calculated exclusively using the local response. The superiority of the proposed approach lies in its ability to capture material hysteresis without any knowledge of the eigen- or modal frequencies of the system and without knowledge of the past time history of the system’s response or the characteristics of any excitation forces. A numerical procedure is also presented for implementing the proposed model in vibration analysis. The simplicity of the approach enables its generalisation to continuous systems and to systems of multi-degrees of freedom as demonstrated herein. The proposed model is presented as a correction to the viscous damping model which makes it attractive to implement into commercial finite element package using user-defined element subroutines as demonstrated in this study.

Transient Simulation of the Aerodynamic Response of a Double-Deck Bus in Gusty Winds

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Hassan Hemida ◽  
Siniša Krajnović
Keyword(s):  
Time History ◽  
Flow Structures ◽  
Detached Eddy Simulation ◽  
Aerodynamic Coefficients ◽  
Eddy Simulation ◽  
Reference Length ◽  
History Of ◽  
The Time Domain ◽  
Natural Wind ◽  
Good Agreement

The purpose of the research reported in this paper was to investigate the aerodynamic response of a double-deck bus in gusty winds using a detached-eddy simulation (DES). The bus was subjected to three different scenarios of wind gusts: gust in a wind tunnel, gust in a natural wind, and gust behind the exit of a tunnel. The proposed scenarios of gusts are in the time domain and take into account the dynamic behavior of natural winds. The Reynolds number of the flow, based on the time-averaged speed of the side wind and a reference length of 0.1 m, was 1.3×106. Detailed transient responses of the aerodynamic coefficients and flow structures were investigated. Good agreement was found between the DES results and the available experimental data. A comparison between the influence of the different gust scenarios on the aerodynamic coefficients shows that the gust behind the exit from a tunnel has a stronger influence on the aerodynamics than the other gust scenarios. Moreover, the influence of the gusts on the time history of aerodynamic coefficients is found to be limited to the period of the gust.

A Time-Domain Method for Hydroelasticity of a Curved Floating Bridge in Inhomogeneous Waves

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Wei Wei ◽  
Shixiao Fu ◽  
Torgeir Moan ◽  
Chunhui Song ◽  
Shi Deng ◽  
...  
Keyword(s):  
Time Domain ◽  
Time History ◽  
Dynamic Responses ◽  
Irregular Waves ◽  
Inhomogeneous Wave ◽  
Inhomogeneous Waves ◽  
Hydroelastic Analysis ◽  
History Of ◽  
Floating Bridge ◽  
The Time Domain

This paper presents a time-domain hydroelastic analysis method for bridges supported by floating pontoons in inhomogeneous wave conditions. The inhomogeneous wave effect is accounted for by adopting different wave spectra over different regions along the structure, then the time history of inhomogeneous first-order wave excitation forces on the floating pontoons can be obtained. The frequency-domain hydrodynamic coefficients are transformed into the time-domain hydroelastic model using Cummins' equations. The linear hydroelastic responses of a curved floating bridge with end supports, subjected to irregular waves with spatially varying significant wave heights and peak periods, are investigated. Moreover, sensitive analyses are performed to study the effects of the inhomogeneity on the hydroelastic responses. The primary results indicate that the inhomogeneity of the waves has a significant effect on the dynamic responses of the floating bridge.

Acoustic Impact Technique for Characterization of Defects in Laminated Composites

1993 ◽  
Author(s):  
A. Haque ◽  
Pollapragada K. Raju
Keyword(s):  
Time Domain ◽  
Laminated Composites ◽  
Time History ◽  
Region Of Interest ◽  
Experimental Configuration ◽  
History Of ◽  
Acoustic Impact ◽  
The Time Domain ◽  
Laminated Structures

Abstract The Acoustic Impact Technique (AIT) of nondestructive testing (NDT) has been investigated in detecting gross defects such as delamination in laminated composites. The use of Acoustic Impact Technique has shown encouraging results by previous investigators in identifying defects like delamination and disbonds in honeycomb structures. Very limited work has been reported in the literature about the utility of AIT as a NDT tool for testing in laminated structures. The present work investigates the sensitiveness of the AIT method in detecting delamination in laminated composites in terms of size, shape, position and degree of concentration. The significant advantage of AIT is that this technique is attractive for field applications. The method involves striking the structure with an instrumented impacter in the region of interest and recording the time history of the impulse. The response of the signals received from both good and defective zones of a specimen were analyzed in the time domain. The experimental configuration used by previous investigators was very restrictive. In this study a different approach to AIT is developed. The effectiveness of AIT was evaluated by making a comparative study with ultrasonic C-scan in detecting similar types of defects. The results indicate the sensitiveness of AIT in detecting delamination in laminated composites in terms of size, depth and degree of concentration.

PROGRAM OF PREDICTION AND MANAGEMENT OF COINTEGED DYNAMIC ECONOMIC PROCESSES BASED ON THE CYBERNETIC APPROACH

2019 ◽  
Author(s):  
Olena Bundak ◽  
Nataliia Zubovetska
Keyword(s):  
Computer Program ◽  
Pair Correlation ◽  
Time History ◽  
Critical Area ◽  
Concrete Object ◽  
Graphic Arts ◽  
Ex Post ◽  
History Of ◽  
Successive Change ◽  
Rms Errors

A method and computer program ConRow, which prognostication of development of the dynamically CPLD economic transients is executed by, is described in the article. Such prognostication of economic processes is very important in the cases when their development can result in undesirable consequences, that to go out in the so-called critical area. Extrapolation in a critical area with the use of information about the conduct of the system at an area, near to it, allows to estimate to the lead through of experiment in the critical area of his consequence. For the imitation of conduct of object the function of review is set on entrance influence. For a concrete object this function can express, for example, dependence of change of level sale from time-history of charges on advertising and set as a numeral row. Statistics as a result of analysis of row are represented in a table, where the level of meaningfulness is set statistician, and also parameters of the handed over criteria. The graphic reflection of information is intended for visualization of analysis. Here represented on the points of graphic arts, the crooked smoothing which are calculated as полиномиальные regressions is added. The best approaching is controlled by sight on the proper graph, and also by minimization of their rms errors. Models of prognostication by sight and as formulas represented on graphic arts, the middle is here determined tailings and their chance is checked up on statistics of signs. After the got models determined also and prognosis values of influences and reviews. Establishing an order models of Сr(p) of co integrate regression is carried out separate custom controls. The coefficient of clay correlation of ruФ shows by itself pair correlation between lines with a successive change in relation to each other on a size to лагу of l = 1, 2, 3 . The program was tested on the example of ex-post prognosis at establishing an integration connection and possibility of prognostication of growth of nominal average monthly settlings on the basis of these statistical indexes of consumer inflation in Ukraine.

scholarly journals Comparison of Novel Seismic Protection Devices to Attenuate the Earthquake Induced Energy

Actuators ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 73
Author(s):  
Osman Hansu ◽  
Esra Mete Güneyisi
Keyword(s):  
Lateral Displacement ◽  
Time History ◽  
Seismic Protection ◽  
Base Shear ◽  
Seismic Demands ◽  
Nonlinear Time History Analyses ◽  
History Of ◽  
Protection Devices ◽  
Nonlinear Time History ◽  
Better Than

This study addresses an alternative use of viscous dampers (VDs) associated with buckling restrained braces (BRBs) as innovative seismic protection devices. For this purpose, 4-, 8- and 12-story steel bare frames were designed with 6.5 m equal span length and 4 m story height. Thereafter, they were seismically improved by mounting the VDs and BRBs in three patterns, namely outer bays, inner bays, and all bays over the frame heights. The structures were modeled using SAP 2000 software and evaluated by the nonlinear time history analyses subjected to the six natural ground motions. The seismic responses of the structures were investigated for the lateral displacement, interstory drift, absolute acceleration, maximum base shear, and time history of roof displacement. The results clearly indicated that the VDs and BRBs reduced seismic demands significantly compared to the bare frame. Moreover, the all-bay pattern performed better than the others.

scholarly journals Comparison of Diesel Engine Vibroacoustic Properties Powered by Bio and Standard Fuel

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1478
Author(s):  
Radoslaw Wrobel ◽  
Gustaw Sierzputowski ◽  
Zbigniew Sroka ◽  
Radostin Dimitrov
Keyword(s):  
Alternative Fuels ◽  
Internal Combustion Engines ◽  
Combustion Process ◽  
Significant Other ◽  
Engine Torque ◽  
Engine Model ◽  
Vehicle Operation ◽  
History Of ◽  
Profile Changes ◽  
The Time Domain

Alternative fuels appeared soon after the first internal combustion engines were designed. The history of alternative fuels is basically as long as the history of the automotive industry. Initially, fuels whose physicochemical properties allowed for a change in parameters of the combustion process in order to achieve greater efficiency and reliability were searched for. Nowadays, there are significantly more variables; in addition to the above mentioned parameters, alternative fuels are being sought that will ensure environmental protection during vehicle operation and improve the ergonomics of use. This article outlines the results of the authors’ own comparative tests of vibrations of a vibroacoustic character. Based on a popular engine model, the vibration–acoustic responses of a system powered by two types of fuel, namely, diesel and biodiesel (B10), are compared. The research consists of comparing vibrations in both time and frequency domains. In the case of the time domain, the evaluation was performed with vibrations as a function of engine torque and speed. In the case of frequency analysis, the focus was on changes in the frequency response for the tested fuels. The research shows that the profile of vibroacoustic vibrations changes in the case of biodiesel power supply in relation to standard fuel. The vibration profile changes significantly as a function of speed and only slightly in relation to the engine load. The results presented in this article show different vibroacoustic responses of an engine powered by diesel and biodiesel; the change is minor for lower speeds but significant (other harmonics are dominant) for higher speeds (changes in the dominant harmonic magnitude of up to 10% at a crankshaft speed of 3000 rpm).

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