Ripple Depth Research Articles

Flow and heat transfer mechanism and optimization design of spirally corrugated tubes

Abstract Spirally corrugated tubes are widely used as high-efficiency heat transfer tubes in various industrial production fields due to their simple manufacturing, low cost, and bi-directional enhanced heat transfer ability. In this study, numerical simulations were conducted on the flow in multi-start spirally corrugated tubes with an equivalent inner diameter of Di=20 mm. The effects of starts value of 1-8, pitch ratio p/Di of 1.5-3.0, ripple depth ratio e/Di of 0.05-0.20, and Reynolds number Re of 5000-3000 on the heat transfer and resistance characteristics of the multi-start spirally corrugated tubes were studied, and the mechanism of heat transfer enhancement was demonstrated by field synergy theory. In addition, through the performance evaluation standard PEC, the optimization design of the multi-start spirally corrugated tube was achieved. The research results indicate that increasing the start value and ripple depth improves heat transfer performance, despite higher flow resistance. As the pitch increases, the heat transfer performance decreases, and the flow resistance correspondingly decreases. When the start value is 8, p/Di=1.5, e/Di=0.20, and Re=20000, it is the optimal performance evaluation criteria (PEC) value, equal to 1.764. This will be of great significance for the design, manufacturing, and practical application of spirally corrugated tubes.

Spectrotemporal Modulation Discrimination in Infants With Normal Hearing.

Spectral resolution correlates with speech understanding in post-lingually deafened adults with cochlear implants (CIs) and is proposed as a non-linguistic measure of device efficacy in implanted infants. However, spectral resolution develops gradually through adolescence regardless of hearing status. Spectral resolution relies on two different factors that mature at markedly different rates: Resolution of ripple peaks (frequency resolution) matures during infancy whereas sensitivity to across-spectrum intensity modulation (spectral modulation sensitivity) matures by age 12. Investigation of spectral resolution as a clinical measure for implanted infants requires understanding how each factor develops and constrains speech understanding with a CI. This study addresses the limitations of the present literature. First, the paucity of relevant data requires replication and generalization across measures of spectral resolution. Second, criticism that previously used measures of spectral resolution may reflect non-spectral cues needs to be addressed. Third, rigorous behavioral measurement of spectral resolution in individual infants is limited by attrition. To address these limitations, we measured discrimination of spectrally modulated, or rippled, sounds at two modulation depths in normal hearing (NH) infants and adults. Non-spectral cues were limited by constructing stimuli with spectral envelopes that change in phase across time. Pilot testing suggested that dynamic spectral envelope stimuli appeared to hold infants' attention and lengthen habituation time relative to previously used static ripple stimuli. A post-hoc condition was added to ensure that the stimulus noise carrier was not obscuring age differences in spectral resolution. The degree of improvement in discrimination at higher ripple depth represents spectral frequency resolution independent of the overall threshold. It was hypothesized that adults would have better thresholds than infants but both groups would show similar effects of modulation depth. Participants were 53 6- to 7-month-old infants and 23 adults with NH with no risk factors for hearing loss who passed bilateral otoacoustic emissions screening. Stimuli were created from complexes with 33- or 100-tones per octave, amplitude-modulated across frequency and time with constant 5 Hz envelope phase-drift and spectral ripple density from 1 to 20 ripples per octave (RPO). An observer-based, single-interval procedure measured the highest RPO (1 to 19) a listener could discriminate from a 20 RPO stimulus. Age-group and stimulus pure-tone complex were between-subjects variables whereas modulation depth (10 or 20 dB) was within-subjects. Linear-mixed model analysis was used to test for the significance of the main effects and interactions. All adults and 94% of infants provided ripple density thresholds at both modulation depths. The upper range of threshold approached 17 RPO with the 100-tones/octave carrier and 20 dB depth condition. As expected, mean threshold was significantly better with the 100-tones/octave compared with the 33-tones/octave complex, better in adults than in infants, and better at 20 dB than 10 dB modulation depth. None of the interactions reached significance, suggesting that the effect of modulation depth on the threshold was not different for infants or adults. Spectral ripple discrimination can be measured in infants with minimal listener attrition using dynamic ripple stimuli. Results are consistent with previous findings that spectral resolution is immature in infancy due to immature spectral modulation sensitivity rather than frequency resolution.

Ripple density resolution dependence on ripple width.

The goal of the study was to investigate how variations in ripple width influence the ripple density resolution. The influence of the ripple width was investigated with two experimental paradigms: (i) discrimination between a rippled test signal and a rippled reference signal with opposite ripple phases and (ii) discrimination between a rippled test signal and a flat reference signal. The ripple density resolution depended on the ripple width: the narrower the width, the higher the resolution. For distinguishing between two rippled signals, the resolution varied from 15.1 ripples/oct at a ripple width of 9% of the ripple frequency spacing to 8.1 ripples/oct at 64%. For distinguishing between a rippled test signal and a non-rippled reference signal, the resolution varied from 85 ripples/oct at a ripple width of 9% to 9.3 ripples/oct at a ripple width of 64%. For distinguishing between two rippled signals, the result can be explained by the increased ripple depth in the excitation pattern due to the widening of the inter-ripple gaps. For distinguishing between a rippled test signal and a non-rippled reference signal, the result can be explained by the increased ratio between the autocorrelated and uncorrelated components of the input signal.

AC corrosion analysis of the buffer layer in HV corrugated-aluminum sheathed power cables

Here we examine the AC corrosion characteristics of the buffer layer in high voltage corrugated-aluminum sheathed power cables, and analyze the relationship between corrosion and cable failure. Penetration of moisture into the buffer layer, including dampness introduced during manufacture and direct water entry through mechanical damage to the cable sheath, results in AC corrosion and formation of hydrogen and Al(OH)3. On the basis of AC current density spectroscopy, the influences of voltage, moisture content, and pressure on the threshold current density are investigated. The cable structure is considered, and a relationship between the AC corrosion and cable failure is determined. A large ripple depth of the corrugated aluminum promotes a non-uniform circular current distribution. The combination of high moisture content and non-uniform current density results in local high temperatures in the buffer layer that ultimately cause the failure of the power cables.

Effects of ripple width on ripple density resolution

Effects of ripple width in rippled-spectrum signals on ripple density resolution was investigated. Two measurement paradigms were tested: (i) ripple density resolution for discrimination between two rippled signals and (ii) discrimination between a rippled test signal and non-rippled reference signal. The ripple widths varied from 9% to 64% of the ripple frequency spacing. For both paradigms, the ripple density resolution increased with deceasing the ripple width. For discrimination between two rippled signals, the resolution was 8.1 ripples/oct for a ripple width of 64% and increased to 15.1 ripples/oct at the ripple width of 9%. For discrimination between a rippled test and non-rippled reference signal, the resolution was 9.3 ripples/oct at a ripple width of 64% and increased to 85 ripples/oct at a ripple width of 9%. Discrimination between two rippled signals is hypothesized to depend on ripple depth in the excitation pattern; the depth increases with narrowing the ripple width. Discrimination between a rippled test and non-rippled reference signal is hypothesized to depend on temporal processing; the effect of the ripple width appears due to increasing the ratio of the autocorrelated to uncorrelated components of the input signal with narrowing the ripples.

Mathematical modeling and stability analysis for laser cutting via asymptotic expansion

A new model for laser cutting is presented. It is derived by an asymptotic expansion of a free boundary problem for the arising melt and describes the coupled movements of the melt boundaries by a system of two nonlinear partial differential equations. The paper extends former models by presenting a complete first-order expansion allowing to include arbitrary higher-order terms. A stationary solution is derived and investigated for stability since damped perturbations do not disturb the solidification process whereas growing perturbations lead to unwanted ripple structures at the cutting front. New higher order terms in the model are identified with physical phenomena which are shown to provide stabilization of the process. The stability analysis is evaluated in a parameter study with varying cutting velocities for 1µm fiber laser cuttings and validated with published experimental and simulated data for the same study. Increasing the cutting speed provides larger stability areas leading to smoother cutting fronts. As a novelty, published ripple depth tendencies are shown to be met qualitatively by our model and typical ripple wavelengths are predicted in the order of magnitude. Hence, our model provides a purely analytical method to investigate the cutting quality.

Ripple density resolution in the presence of an additional rippled pattern

Rippled-spectrum signals are known for measurements of ripple density resolution. Such signals used previously had uniform ripple patterns across the entire signal’s frequency band. In the present study, signals consisted of two overlapping test and additional patterns with different ripple densities. Ripple density resolution in the test signal was measured as a function of ripple density in the additional pattern. Two discrimination tasks were conducted: either discrimination between a rippled test signal and rippled reference signal or a non-rippled reference signal. The additional pattern reduced the resolution of the test signal in general. For a rippled reference signal, the effect of the additional pattern could be explained by decreased ripple depth in the test signal. For a non-rippled reference signal, the resolution of the test signal was lower for a rippled than for a non-rippled additional pattern. In such a case, there was no dependence on the density of ripples in the additional pattern. The last cannot be explained by a decrease of the ripple depth and was interpreted as a manifestation of temporal processing equivalent to the reveal of a delayed segment of the autocorrelation function of the test signal. [This study was supported by Russian Foundation for Basic research, Grant No. 20-015-00054.]

Transient otoacoustic emissions and audiogram fine structure in the extended high-frequency region

Objective Previous studies at conventional audiometric frequencies found associations between the ripple depth seen in audiogram fine structure (AFS) and amplitudes of both transient evoked otoacoustic emissions (TEOAEs) and overall hearing threshold levels (HTLs). These associations are explained by the cochlear mechanical theory of multiple coherent reflections of the travelling wave apically by reflections sites on the basilar membrane and basally by the stapes. Design The aim was to investigate whether a similar relationship is seen in the extended high-frequency (EHF) range from 8–16 kHz. Measurements from 8–16 kHz were obtained in normal-hearing subjects comprising EHF HTLs, EHF TEOAEs using a double evoked paradigm, and Bekesy audiometry to assess AFS ripple depth and spectral periodicity. Study Sample Twenty eight normal-hearing subjects participated. Results Results showed no significant correlation between AFS ripple depth and either frequency-averaged EHF HTLs or EHF TEOAE amplitudes. The amplitude of AFS ripple depth was also lower than that seen in the conventional frequency region and spectral periodicity in the ripple more difficult to discern. Conclusion The results suggest a weaker interference pattern between forward and reverse cochlear travelling waves in the most basal region compared to more apical regions, or a difference in cochlear mechanical properties.

Effect of wavy trachea walls on the oscillation onset pressure of silicone vocal folds.

The influence of non-smooth trachea walls on phonation onset and offset pressures and the fundamental frequency of oscillation were experimentally investigated for three different synthetic vocal fold models. Three models of the trachea were compared: a cylindrical tube (smooth walls) and wavy-walled tubes with ripple depths of 1 and 2 mm. Threshold pressures for the onset and offset of phonation were measured at the lower and upper ends of each trachea tube. All measurements were performed both with and without a supraglottal resonator. While the fundamental frequency was not affected by non-smooth trachea walls, the phonation onset and offset pressures measured right below the glottis decreased with an increasing ripple depth of the trachea walls (up to 20% for 2 mm ripples). This effect was independent from the type of glottis model and the presence of a supraglottal resonator. The pressures at the lower end of the trachea and the average volume velocities showed a tendency to decrease with an increasing ripple depth of the trachea walls but to a much smaller extent. These results indicate that the subglottal geometry and the flow conditions in the trachea can substantially affect the oscillation of synthetic vocal folds.

Rippled Depth Thresholds: Estimates Obtained by Discrimination From Rippled and Nonrippled Reference Signals

The objective of the study was to better understand of contribution of excitation-pattern and temporal-processing mechanisms of frequency analysis to discrimination of complex-spectrum signals in various discrimination tasks. Using rippled-spectrum signals, the ripple depth thresholds were measured as functions of ripple density under conditions of rippled or non-rippled reference signals. With rippled reference signals, the ripple depth thresholds were as low as 0.11 at low ripple densities (2–3 cycles/oct) and rose to 1.0 at a ripple density of 8.9 cycles/oct. For non-rippled reference signals, ripple depth thresholds were nearly the same as for rippled reference signals at ripple densities of up to 7 cycles/oct; at ripple densities of 10 cycles/oct and higher, ripple depth thresholds rose slowly and reached 1.0 at a ripple density of 26 cycles/oct. The results hypothetically suggest contributions of the excitation-pattern processing and temporal-processing mechanisms of frequency analysis to discrimination of rippled signals. The excitation-pattern mechanism featured low depth thresholds at low ripple densities but could not function at ripple densities above 10 cycles/oct. The temporal-processing mechanism manifested at higher ripple densities and non-rippled reference stimuli.

Ripple depth and density thresholds: Estimate dependence on the measurement paradigm

Rippled-spectrum signals are a convenient test to measure spectro-temporal resolution of auditory stimuli. There is no commonly adopted paradigm for measurements of rippled-spectrum resolution. Test stimuli may be either rippled-spectrum signals with ripple phase changes during the signal or constant-phase rippled-spectrum signals. Reference stimuli may have either rippled or non-rippled spectra. In the present study, a direct comparison revealed that for rippled reference signals, the ripple depth thresholds were as low as 0.1 at low ripple densities; for a maximum ripple depth of 1.0, the ripple density resolution was 8 to 9 ripple/oct. For nonrippled reference stimuli, the ripple density resolution was as high as 25–30 ripple/oct; however, ripple depth thresholds were not less than 0.5 at ripple densities above 7 ripples/oct. It is hypothesized that the differences between resolution estimates obtained with different reference stimuli appear due to exploiting different cues for discrimination between test and reference stimuli, specifically, the cues provided by the excitation-pattern and temporal-processing mechanisms of frequency analysis. Discrimination between rippled test and rippled reference signals agrees with an excitation-pattern model, whereas discrimination between rippled test and non-rippled reference stimuli agrees with a temporal-processing model. [Work supported by Russian Science Foundation, Grant No. 16-15-10046.]

Spectral Ripple Discrimination in Normal-Hearing Infants.

Spectral resolution is a correlate of open-set speech understanding in postlingually deaf adults and prelingually deaf children who use cochlear implants (CIs). To apply measures of spectral resolution to assess device efficacy in younger CI users, it is necessary to understand how spectral resolution develops in normal-hearing children. In this study, spectral ripple discrimination (SRD) was used to measure listeners' sensitivity to a shift in phase of the spectral envelope of a broadband noise. Both resolution of peak to peak location (frequency resolution) and peak to trough intensity (across-channel intensity resolution) are required for SRD. SRD was measured as the highest ripple density (in ripples per octave) for which a listener could discriminate a 90° shift in phase of the sinusoidally-modulated amplitude spectrum. A 2 × 3 between-subjects design was used to assess the effects of age (7-month-old infants versus adults) and ripple peak/trough "depth" (10, 13, and 20 dB) on SRD in normal-hearing listeners (experiment 1). In experiment 2, SRD thresholds in the same age groups were compared using a task in which ripple starting phases were randomized across trials to obscure within-channel intensity cues. In experiment 3, the randomized starting phase method was used to measure SRD as a function of age (3-month-old infants, 7-month-old infants, and young adults) and ripple depth (10 and 20 dB in repeated measures design). In experiment 1, there was a significant interaction between age and ripple depth. The infant SRDs were significantly poorer than the adult SRDs at 10 and 13 dB ripple depths but adult-like at 20 dB depth. This result is consistent with immature across-channel intensity resolution. In contrast, the trajectory of SRD as a function of depth was steeper for infants than adults suggesting that frequency resolution was better in infants than adults. However, in experiment 2 infant performance was significantly poorer than adults at 20 dB depth suggesting that variability of infants' use of within-channel intensity cues, rather than better frequency resolution, explained the results of experiment 1. In experiment 3, age effects were seen with both groups of infants showing poorer SRD than adults but, unlike experiment 1, no significant interaction between age and depth was seen. Measurement of SRD thresholds in individual 3 to 7-month-old infants is feasible. Performance of normal-hearing infants on SRD may be limited by across-channel intensity resolution despite mature frequency resolution. These findings have significant implications for design and stimulus choice for applying SRD for testing infants with CIs. The high degree of variability in infant SRD can be somewhat reduced by obscuring within-channel cues.

Influence of TiO2(110) surface roughness on growth and stability of thin organic films.

We have investigated the growth and stability of molecular ultra-thin films, consisting of rod-like semiconducting para-hexaphenyl (6P) molecules vapor deposited on ion beam modified TiO2(110) surfaces. The ion bombarded TiO2(110) surfaces served as growth templates exhibiting nm-scale anisotropic ripple patterns with controllable parameters, like ripple depth and length. In turn, by varying the ripple depth one can tailor the average local slope angle and the local step density/terrace width of the stepped surface. Here, we distinguish three types of substrates: shallow, medium, and deep rippled surfaces. On these substrates, 6P sub-monolayer deposition was carried out in ultra-high vacuum by organic molecular beam evaporation (OMBE) at room temperature leading to the formation of islands consisting of upright standing 6P molecules, which could be imaged by scanning electron microscopy and atomic force microscopy (AFM). It has been found that the local slope and terrace width of the TiO2 template strongly influences the stability of OMBE deposited 6P islands formed on the differently rippled substrates. This effect is demonstrated by means of tapping mode AFM, where an oscillating tip was used as a probe for testing the stability of the organic structures. We conclude that by increasing the local slope of the TiO2(110) surface the bonding strength between the nearest neighbor standing molecules is weakened due to the presence of vertical displacement in the molecular layer in correspondence to the TiO2 atomic step height.

Discrimination of rippled spectra in background of maskers of different frequencies

Discrimination of rippled-spectrum signals in masking noise was investigated in normal listeners. The rippled-spectrum signal was 0.5-oct wide centered at 2 kHz. Simultaneous masker was a 0.5-oct wide noise centered below, on, or above the signal band (low-, on-, and high-frequency maskers, respectively). Discrimination of the signals was assessed by (i) threshold for discrimination of ripple spacing; (ii) threshold for discrimination of spectrum-pattern shift. The threshold dependence on the masker level was qualitatively different for the low- and on-frequency maskers. For the on-frequency masker, the masking effect primarily depended on the masker/signal ratio: the thresholds steeply increased at a ratio of 5 dB; no ripple pattern was discriminated at a ratio of 10 dB or higher. Alternatively, for the low-frequency masker, the masking effect primarily depended on the masker SPL: the threshold increased at a masker SPL of 70–80 dB; no ripple pattern was discriminated at a masker SPL of 100 dB. The high-frequency masker produced little effect. Hypothetically, the effect of the on-frequency masker appeared due to a decrease of ripple depth when the masker overlapped the signal, whereas the effect of the low-frequency masker appeared due to widening of the auditory filters at high sound levels.

Hearing Sensitivity to Shifts of Rippled-Spectrum Sound Signals in Masking Noise.

The goal of the study was to enlarge knowledge of discrimination of complex sound signals by the auditory system in masking noise. For that, influence of masking noise on detection of shift of rippled spectrum was studied in normal listeners. The signal was a shift of ripple phase within a 0.5-oct wide rippled spectrum centered at 2 kHz. The ripples were frequency-proportional (throughout the band, ripple spacing was a constant proportion of the ripple center frequency). Simultaneous masker was a 0.5-oct noise below-, on-, or above the signal band. Both the low-frequency (center frequency 1 kHz) and on-frequency (the same center frequency as for the signal) maskers increased the thresholds for detecting ripple phase shift. However, the threshold dependence on the masker level was different for these two maskers. For the on-frequency masker, the masking effect primarily depended on the masker/signal ratio: the threshold steeply increased at a ratio of 5 dB, and no shift was detectable at a ratio of 10 dB. For the low-frequency masker, the masking effect primarily depended on the masker level: the threshold increased at a masker level of 80 dB SPL, and no shift was detectable at a masker level of 90 dB (for a signal level of 50 dB) or 100 dB (for a signal level of 80 dB). The high-frequency masker had little effect. The data were successfully simulated using an excitation-pattern model. In this model, the effect of the on-frequency masker appeared to be primarily due to a decrease of ripple depth. The effect of the low-frequency masker appeared due to widening of the auditory filters at high sound levels.

Laser induced periodic surface structure formation in germanium by strong field mid IR laser solid interaction at oblique incidence.

Laser induced periodic surface structures (LIPSS or ripples) were generated on single crystal germanium after irradiation with multiple 3 µm femtosecond laser pulses at a 45° angle of incidence. High and low spatial frequency LIPSS (HSFL and LSFL, respectively) were observed for both s- and p-polarized light. The measured LSFL period for p-polarized light was consistent with the currently established LIPSS origination model of coupling between surface plasmon polaritons (SPP) and the incident laser pulses. A vector model of SPP coupling is introduced to explain the formation of s-polarized LSFL away from the center of the damage spot. Additionally, a new method is proposed to determine the SPP propagation length from the decay in ripple depth. This is used along with the measured LSFL period to estimate the average electron density and Drude collision time of the laser-excited surface. Finally, full-wave electromagnetic simulations are used to corroborate these results while simultaneously offering insight into the nature of LSFL formation.

Femtosecond laser fabrication of large-area periodic surface ripple structure on Si substrate

In this paper, we report the fabrication of a large area uniformly distributed periodic nano-ripple structure on silicon substrate through the proper scanning of a line-shaped femtosecond laser beam. The fabricated nano-ripple structure has a periodicity of ∼600nm and a ripple depth of ∼300nm. The modulation depth is much deeper than the one previously reported. The developed structure is demonstrated to be able to substantially reduce light reflection due to the effective optical coupling between the incident sunlight with the nano-ripple structure and exhibit an absorption enhancement of ∼41% compared with planar silicon wafer. The physics underlying the formation of the nano-ripple structure is also discussed.

Creation of periodic subwavelength ripples on tungsten surface by ultra-short laser pulses

Formation of periodic subwavelength ripples on a metallic tungsten surface is investigated through a line-scribing method under the irradiation of 800 nm, 50 fs to 8 ps ultra-short laser pulses. The distinctive features of the induced ripple structures are described in detail with different laser parameters. Experimental measurements reveal that with gradual decrease of the laser fluence, the pulse duration or the scanning speed, the ripple period is inclined to reduce but the ripple depth tends to become pronounced. Theoretical analyses suggest that the transient dielectric function change of the tungsten surface mainly originates from the nonequilibrium distribution of electrons due to the d-band transitions. A sandwich-like physical model of air–plasma–target is proposed and the excitation of a surface plasmon polaritonic (SPP) wave is supposed to occur on the interface between the metallic target and the electron plasma layer. Formation of ripples can be eventually attributed to the laser–SPP interference. Theoretical interpretations are consistent with the experimental observations.

Thresholds for Perception of Ripple Depth in the Passband of a Low-Pass Filter

Filters are often used in research related to speech and tone perception. Idealized filters with flat pass-bands, flat stop-bands, and infinitely steep rolloff are impossible to implement, thus practical filters often have a frequency response curve that has a certain degree of ripple, and always have finite rolloff. Despite this, there is a dearth of literature concerning the sensitivity of the ear to such artifacts. In the current study we examined the threshold of sensitivity to ripple depth in the pass-band of a digital low pass finite impulse response (FIR) filter. FIR filters are often used due to their lack of phase distortion, and due to the fact that their ripple depth can be closely controlled. Using an adaptive threshold detection paradigm, we found the threshold of noticeable ripple depth to be 2.7 dB (SD = 1.45) for filtered noise, and 4.89 dB (SD = 2.09) for a filtered chirp signal. This is significantly larger than the difference limen in intensity (DLI) for noise or pure tones. Notably, the threshold for filtered noise is significantly lower and more uniform across subjects, compared to the threshold for a filtered chirp signal. We conclude that these issues must be addressed when the necessity for filtering arises, though they cannot be considered independently of the signals themselves.

Rippled-spectrum resolution dependence on level

Rippled-density resolution of a rippled sound spectrum (probe band) in both the presence and absence of another band (masker) was studied as a function of sound level in normal listeners. The resolvable ripple density in the probe band was measured by finding the highest ripple density at which an interchange of ripple peak and valley positions was detectable (the phase-reversal test). Probe bands were 0.5 oct wide with center frequencies of 1, 2, and 4 kHz. In the control condition (no masker), the ripple-density resolution was almost independent of sound level within a range of 40–90 dB SPL. When an on-frequency masker coincided with the probe band (that resulted in reduced ripple depth), resolution decreased slightly relative to the control condition but remained little dependent on level. With an off-frequency low-side masker, the ripple-density resolution was a little less than in the control but almost independent of level within a range of 40–60 dB SPL and progressively decreased with level increase from 70 to 90 dB SPL. The dependence on level was qualitatively similar at all probe frequencies and at various widths and positions of the low-side off-frequency masker band.