Transient Distortion Research Articles

Development of Predicted Stress and Strain during Conventional and after Mitigation of Welded Aluminium-Manganese Alloy

The trend in automotive, aircraft, and marine industries is the increasing use of sheet materials to reduce weight in components and optimize materials performance. Welding is the main fabrication and assembly process in many of these industrial applications. However, in using thin-shell structures in such applications, welding may results in significant residual stresses and out-of-plane distortion. Transient thermal stresses, residual stresses, and distortion sometimes cause cracking and mismatching of joints. High tensile residual stresses are undesirable since they can contribute to fatigue failure. The analysis and measurement of temperature and stresses in component are often too complex to conduct in practise, and thus finite element models provide feasible approach to examine these matters. In this paper, finite element analysis has been performed using the ANSYS package to study the behaviour of longitudinal residual stress and strain in a welded thin aluminium-manganese alloy. The model presented simulates conventional welding and welding with the introduction of welding mitigation technique for enhancement of heat transfer, in which a trailing heat sink was applied. The thermal profiles obtained using the mitigation technique is completely different from those obtained in the conventional cooling. The localized transient residual stress and through-thickness strain after applying a cooling sink are discussed. The transient residual stress behaviour was highly affected by the modified temperature distribution and magnitude due to introducing the heat transfer enhancement.

Transient lattice distortion induced by ultrashort heat pulse propagation through thin film metal/metal interface

Phonon propagation across the Cu/Ag(111) interface and transient structural disorder in Ag(111) crystal, after excitation of 18 nm copper layer with UV femtosecond pulses has been studied by means of picosecond time resolved X-ray diffraction. The lattice disorder was measured by the changes in peak shift and broadening of the XRD rocking curve. A blast force was formed within 2 ps after fs UV irradiation. After fast initial expansion and contraction, a sharp oscillation is observed, while the subsequent oscillations were found to be broader due to out-of phase relationship between the sound waves in the copper and silver layers.

Effects of noise and distortion in measurement of room impulse response by swept sine technique

Swept sine technique is one of the most used techniques for measurement of the impulse response of acoustical systems including rooms. During its application, some common disturbances, such as noise and distortion, could reduce the quality of the measurement results. Two different noise categories can be distinguished - background noise always present in room acoustic measurements and transient noise that appears suddenly and has a short duration. Distortion typically occurs in the transducer. The effects of these disturbances (especially transient noise and distortion) are investigated here with an emphasis on reduction of negative effects of transient noise. For that purpose, several procedures for noise effects reduction are proposed and analysed. The results show that noise and distortion cause certain artefacts disturbing the measured response. Some of these artefacts can be reduced by applying adequate procedures.

Visual disruption using the thermal lensing effect in the human eye: pilot study

At select wavelengths, near infrared (IR) light is absorbed in the preretinal media of the eye. This produces small transient increases in temperature that temporarily alter the local index of refraction. If the IR exposure is sufficiently high, a momentary reduction in the focusing power of the eye can be induced through an effect known as thermal lensing. Fundamental optical interaction and safety aspects of this phenomenon have been demonstrated previously in animal and artificial eye models. However, whether the effect will induce an observable visual change in human subjects has not been explored. Here, results of a pilot study are shown where eight human subjects were exposed to an IR laser at levels that were below the safe exposure limit. The exposures did induce a transient visual distortion if sufficiently high levels were used. While the description of the visual change varied between subjects, this experiment was able to determine a general guideline for power needed to induce significant effects in human subjects.

Onset- and offset-specific effects in interaural level difference discrimination

The relative sensitivity of human listeners to interaural level differences (ILDs) carried by the onsets, offsets, and interior portions of brief sounds was examined. Stimuli consisted of single 4000-Hz Gabor clicks (Gaussian-windowed tone bursts) or trains of 16 such clicks repeating at an interclick interval (ICI) of 2 or 5 ms. In separate conditions, ILDs favored the right ear by a constant amount for all clicks (condition RRRR) or a changing amount that was maximal at sound onset (condition R000), offset (condition 000R), both onset and offset (condition R00R), or at the temporal midpoint of the stimulus (condition 0RR0). ILD increases and decreases were implemented as linear decibel sweeps across four clicks to minimize transient distortion. Threshold ILDs were determined adaptively for each of these conditions and for single clicks. Thresholds were similar for ILDs presented near sound onset or offset (condition R000 vs 000R) but lower when ILDs were carried by both onset and offset clicks (condition R00R) than for ILDs carried by interior clicks alone (condition 0RR0). The results suggest that similar sensitivity to onset and offset ILD does not reflect uniform temporal weighting; instead, ILD sensitivity favors onsets and offsets over the interior portions of sounds.

Otoacustic Emission Test Abnormalities among Teenagers

Objective: To investigate the prevalence of injury of outer hair cells by means of transient evoked otoacoustic emission and distortion product evoked otoacoustic emission tests among teenagers of a private high school in Brazil. Method: Survey study. We performed transient evoced otoacoustic emission and distortion product evoced otoacoustic emission tests in 134 young individuals from January to December 2011. We analyzed the results according to the “pass/fail” criterion for the parameters amplitude of the signal and signal/noise ratio. Results: A total of 80.6% of 134 participants had abnormal transient otoacoustic emissions and most were men (92.9%; P < .05). In all, 97.8% showed abnormal distortion product otoacoustic emissions and no difference regarding the gender ( P = .2). A total of 79.9% showed abnormalities in both transient and distortion product in at least 1 ear, most were men ( P < .05). In sum, 94.0% reported the use of headphones, and 82.8% reported attending some type of place with amplified music. Conclusion: The high prevalence of abnormal tests could early indicate a cochlear dysfunction, and the high number of participants who reported being exposed to loud music leads to suspicion that this habit might be causing these cochlear changes.

A Method to Determine the Existence of Genuine Interharmonics

Interharmonic components can often be seen from the discrete Fourier transform (DFT) results of measured voltage or current waveforms. These components may be caused by various factors, such as transient waveform distortions or noises. They are not necessarily related to the real interharmonics. This letter presents a simple method to verify the existence of a genuine interharmonic component contained in the DFT results. The method can also reveal the characteristics of the component. The method has been demonstrated on various field measurement data that contain genuine and false interharmonic components.

Mitigating the Impacts of CCVT Subsidence Transients on the Distance Relay

This paper presents a comprehensive time-domain model of the coupling capacitor voltage transformer (CCVT) to investigate the effect of CCVT subsidence transients on the distance relay. The studies show that voltage-zero subsidence transients can adversely impact the performance of the distance relay and result in the overreach problem. This paper also introduces a new approach to mitigate the effect of CCVT voltage-zero subsidence transients on the distance relay. The method is based on improving the degree of accuracy of the voltage phasor estimation during the CCVT subsidence transients. The proposed method is not affected by harmonics and high-frequency transient distortions of the voltage, and prevents the relay overreach problem even under high source impedance ratio (SIR). Moreover, the proposed method noticeably decreases the close-in fault clearance time under low SIR conditions, based on a fast current phasor estimation approach. The reported studies are conducted in the PSCAD/EMTDC software environment.

Cortical processing of degraded speech sounds: Effects of distortion type and continuity

Human speech perception is highly resilient to acoustic distortions. In addition to distortions from external sound sources, degradation of the acoustic structure of the sound itself can substantially reduce the intelligibility of speech. The degradation of the internal structure of speech happens, for example, when the digital representation of the signal is impoverished by reducing its amplitude resolution. Further, the perception of speech is also influenced by whether the distortion is transient, coinciding with speech, or is heard continuously in the background. However, the complex effects of the acoustic structure and continuity of the distortion on the cortical processing of degraded speech are unclear. In the present magnetoencephalography study, we investigated how the cortical processing of degraded speech sounds as measured through the auditory N1m response is affected by variation of both the distortion type (internal, external) and the continuity of distortion (transient, continuous). We found that when the distortion was continuous, the N1m was significantly delayed, regardless of the type of distortion. The N1m amplitude, in turn, was affected only when speech sounds were degraded with transient internal distortion, which resulted in larger response amplitudes. The results suggest that external and internal distortions of speech result in divergent patterns of activity in the auditory cortex, and that the effects are modulated by the temporal continuity of the distortion.

CREATING DIGITAL SIGNAL PROCESSING (DSP) FILTERS TO IMPROVE LOUDSPEAKER TRANSIENT RESPONSE

A method is provided for creating a series of digital signal processing (DSP) filters to improve the transient response of a loudspeaker, wherein the loudspeaker is formed of multiple components. The method includes generally six steps. The first step involves identifying a substantially linear, time-invariant, and spatially-consistent loudspeaker mechanism causing transient response distortion. The second step involves characterizing the identified mechanism. The third step involves determining the characterized mechanism's two-port response. The fourth step involves establishing a target response for the characterized mechanism. The fifth step involves calculating an ideal filter to achieve the target response. The sixth step involves designing a cost-reduced filter based on the ideal filter.

Finite Element Analysis of Transient Welding Stress and Strain during Ti-6Al-4V Thin Plate Welding with Impact Rotation

The internal thermal transient stress and strain is difficult to be real time measured by experimental methods during welding, but the stress and strain is vital to understand the mechanism of the control on the wave-like deformation. Large nonlinear finite element software of MSC.Mrac is used to illustrate decrease of the wave-like deformation of the Ti-6Al-4V thin plate weldment by a new technique called welding with impacting rotation. Some simulation results such as temperature field, thermal transient stress evolution, elastic strain, plastic strain and distortion of thin plate are shown. By the help of the finite element analysis, the mechanism of control on the wave-like deformation was put forward, i.e. the residual stress was decreased by the certain amount plastic extensive deformation generated by the impacting revolution. Keywords: finite element analysis (FEA), Ti-6Al-4V, thin plate weldment, wave-like deformation, residual stress

Case Study for Welding Simulation in the Automotive Industry

Welding is one of the most widely used joining processes in structural applications, like in car body production in the automotive industry. It is well-known that distortions and residual stresses occur during and after the welding process. Many procedures exist to decrease these negative heat effects of welding, but are often coupled with highly cost intensive experiments. For several decades, simulation models have been developed to understand and predict the heat effects of welding and to reduce experimental effort. In the production planning of various Original Equipment Manufacturers (OEM), some simulation tools are already well established, e. g. for crash test, forming or casting simulations. For welding, the demand is high but the implementation of welding simulation software is still not yet established. Welding is a complex process and the development of a flexible simulation tool, which produces good simulation results without expert knowledge in simulation, is not an easy task. In this paper, a welded assembly from the automotive industry has been simulated and compared to experimental data. Temperature fields and transient distortion distributions have been measured with thermocouples and with an optical 3D deformations analysis tool, respectively. The simulation has been run with a commercially available welding simulation software. The simulated temperature fields match the numerical ones perfectly. The simulated distortions are also qualitatively in best agreement with the experimental ones. Quantitatively, a difference of approximately 20 % between the simulated and the measured distortions is visible; this is acceptable considering the simplifications and assumptions of the simulation model. The global time to solution to get these results without expert knowledge in welding simulation was between 4 and 6 weeks, which is a reasonable time frame for an industrial application of welding simulation.

Experimental and Numerical Study of Transient Distortion in Titanium Alloy Tig Welding

In this paper, the convex distortion and transient distortion characteristics of TIG welding for a titanium alloy with finite dimensional thin plate were investigated experimentally and numerically. A three dimensional thermal-mechanical finite element method (FEM) was adopted to predict the characteristics of Transient distortion by taking the initial shape, gravity loading and restriction conditions into account. The simulation results were validated by the experimental results. The results show that the numerical simulations could provide accurate prediction on the Transient temperature and distortion processing. The temperature gradient through thickness, the dimension of plate and the clamping were main factors governing the distortion during welding.

You are only as old as you sound: Auditory aftereffects in vocal age perception

High-level adaptation not only biases the perception of faces, but also causes transient distortions in auditory perception of non-linguistic voice information about gender, identity, and emotional intonation. Here we report a novel auditory aftereffect in perceiving vocal age: age estimates were elevated in age-morphed test voices when preceded by adaptor voices of young speakers (∼20 yrs), compared to old adaptor voices (∼70 yrs). This vocal age aftereffect (VAAE) complements a recently reported face aftereffect ( Schweinberger et al., 2010) and points to selective neuronal coding of vocal age. Intriguingly, post-adaptation assessment revealed that VAAEs could persist for minutes after adaptation, although reduced in magnitude. As an important qualification, VAAEs during post-adaptation were modulated by gender congruency between speaker and listener. For both male and female listeners, VAAEs were much reduced for test voices of opposite gender. Overall, this study establishes a new auditory aftereffect in the perception of vocal age. We offer a tentative sociobiological explanation for the differential, gender-dependent recovery from vocal age adaptation.

Settling Behavior of the Bridge Voltage in Resistance Ratio Measurements With Cryogenic Current Comparators

A long settling time of the bridge voltage in resistance comparison setups with cryogenic current comparators might become crucial with respect to the type-A uncertainty, because it effectively limits the frequency of current reversals. Using a new bridge voltage detector with considerably increased bandwidth, we were able to trace the transient distortions caused by current reversal. Significant influence of the cabling is observed. Comparing a 12.9-kΩ quantum Hall resistor and a 100-Ω standard resistor, we achieved an expanded type-A uncertainty of about three parts in 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> after 24 min of measurement for current reversal frequencies down to 100 mHz.

Improvement of Time and Frequency Domain Performance of Antipodal Vivaldi Antenna Using Multi-Objective Particle Swarm Optimization

The design of an antipodal Vivaldi antenna for ultra wideband (UWB) applications is presented. The main purpose of this design is the reduction of three parameters of transient distortion, reflection coefficient and cross polarization level. Multi-objective particle swarm optimization (MOPSO) is applied to handle these objectives simultaneously. All antenna simulations are performed using the CST MWS software. Several design cases of the resultant Pareto fronts are compared, and finally, a sample of the Pareto front is fabricated. To assess the time domain performance of the antenna, two identical antennas are placed in an end-to-end orientation. The simulated correlation factor in this scenario is more than 93%. Measurement results show that the |S11| of the developed antenna is less than -10 dB, the cross polarization level is below -11.5 dB and the gain is between 4.5 dBi and 9 dBi over the whole UWB frequency band.

Thermal-Structure Coupling Numerical Simulation of a Special-Type Plug Nozzle

Two-dimensional transient heat transfer model of the plug of regenerative cooling plug nozzle is built. Based on the convective heat-transfer coefficient and the radiation heat flux obtained using analytic method and axisymmetric unstructured Delaunay grid applied to mesh the simplified physical model, numerical simulations of transient temperature field and thermal distortion are carried out by finite element method combined with thermal-structure coupling theory. Not only the results of numerical calculation under working conditions with and without regenerative cooling, but the results under low and high working conditions are compared. The results shows that thermal distortion can be reduced effectively when regenerative cooling method is adopted in the throat and combustion chamber that have the most serious thermal condition.

UWB Monopole Antenna With Stable Radiation Pattern and Low Transient Distortion

In this letter, an ultrawideband (UWB) microstrip-fed planar monopole antenna with stable radiation pattern is presented. Although compact and simple structure of the planar antennas made them a good candidate in UWB applications, due to unwanted current distribution on the ground section, they suffer from transient distortion and radiation pattern rotation in different frequencies. To alleviate this effect, a metallic staircase plane is placed in the bottom of the substrate. In addition, a mushroom-like electromagnetic band-gap (EBG) structure is embedded on the top layer of the substrate to increase the gain in higher frequencies. Measurement results show 2.2-6 dB gain in broadside direction in 3-10-GHz frequency. A new definition of pattern stability factor (PSFII) is proposed, which is proper for both directional and omnidirectional radiation patterns. Calculated PSFII for the proposed antenna is higher than 95%, which shows a stable radiation pattern. Furthermore, it shows a low distortion manner where the fidelity factor in the main beam direction is more than 95%. In comparison to similar antennas presented in literature, PSFII and gain have been improved noticeably.

Underestimation of perceived number at the time of saccades

Saccadic eye movements produce transient distortions in both space and time. Mounting evidence suggests that space and time perception are linked, and associated with the perception of another important perceptual attribute, numerosity. Here we investigate the effect of saccades on the perceived numerosity of briefly presented arrays of visual elements. We report a systematic underestimation of numerosity for stimuli flashed just before or during saccades, of about 35% of the reference numerosity. The bias is observed only for relatively large arrays of visual elements, in line with the notion that a distinct perceptual mechanism is involved with enumeration of small numerosities in the ‘subitizing’ range. This study provides further evidence for the notion that space, time and number share common neural representations, all affected by saccades.

Absolute measurement of surface and bulk absorption in DUV optics from temperature induced wavefront deformation

A measurement system for quantitative determination of both surface and bulk contributions to the photo-thermal absorption in DUV optics was developed. It is based upon a Hartmann-Shack wavefront sensor with a sensitivity of ~λ/10000 rms, accomplishing precise on-line monitoring of wavefront deformations of a collimated test laser beam transmitted perpendicular through the excimer laser-irradiated site of a cuboid sample. Caused by the temperature dependence of the refractive index as well as thermal expansion, the initially plane wavefront of the test laser is distorted into a cylindrical shape, with bending ends towards the surface. Sign and magnitude depend on index change and expansion. By comparison with thermal theory, this transient wavefront distortion yields a quantitative absolute measure of bulk and surface absorption losses in the sample. First rresults for fused silica are presented.