scholarly journals Clarifying the relationship between efficiency and resonance for flexible inertial swimmers

2018 ◽  
Vol 853 ◽  
pp. 271-300 ◽  
Author(s):  
Daniel Floryan ◽  
Clarence W. Rowley
Keyword(s):  
Travelling Wave ◽  
Power Coefficient ◽  
Mass Ratio ◽  
Eigenvalues And Eigenfunctions ◽  
Trailing Edge ◽  
Thrust Coefficient ◽  
Low Frequencies ◽  
High Frequencies ◽  
Wave Kinematics ◽  
The Relationship

We study a linear inviscid model of a passively flexible swimmer, calculating its propulsive performance, eigenvalues and eigenfunctions with an eye towards clarifying the relationship between efficiency and resonance. The frequencies of actuation and stiffness ratios we consider span a large range, while the mass ratio is mostly fixed to a low value representative of swimmers. We present results showing how the trailing edge deflection, thrust coefficient, power coefficient and efficiency vary in the stiffness–frequency plane. The trailing edge deflection, thrust coefficient and power coefficient show sharp ridges of resonant behaviour for mid-to-high frequencies and stiffnesses, whereas the efficiency does not show resonant behaviour anywhere. For low frequencies and stiffnesses, the resonant peaks smear together and the efficiency is high. In this region, flutter modes emerge, inducing travelling wave kinematics which make the swimmer more efficient. We also consider the effects of a finite Reynolds number in the form of streamwise drag. The drag adds an offset to the net thrust produced by the swimmer, causing resonant peaks to appear in the efficiency (as observed in experiments in the literature).

Hearing loss in diabetics

1993 ◽  
Vol 107 (3) ◽  
pp. 179-182 ◽  
Author(s):  
J. R. Cullen ◽  
M. J. Cinnamond
Keyword(s):  
Hearing Loss ◽  
Sensorineural Deafness ◽  
Insulin Dosage ◽  
Speech Discrimination ◽  
Low Frequencies ◽  
High Frequencies ◽  
History Of ◽  
Insulin Dependent ◽  
Stapedial Reflex ◽  
The Relationship

The relationship between diabetes and senbsorineural hearing loss has been disputed. This study compares 44 insulin-dependent diabetics with 38 age and sex matched controls. All had pure tone and speech audiometry performed, with any diabetics showing sensorineural deafness undergoing stapedial reflecx decat tests. In 14 diabetics stapedial reflex tests showed no tone decay in any patient, but seven showed evidence of recruitment. Analysis of vaiance showed the diabetics to be significantly deafer than the control population.The hearing loss affected high frequencies in both sexes, but also low frequencies in the male. Speech discrimination scores showed no differences. Further analysis by sex showed the males to account for most of the differences. Analysys of the audiograms showered mostly a high tone loss. Finally duration of disbetes, insulin dosage and family history of diabtes were not found to have a significant effect on threshold.

Relations among Nightmare Frequency and Ego Strength, Death Anxiety, and Sex of College Students

1989 ◽  
Vol 69 (3-2) ◽  
pp. 1107-1113 ◽  
Author(s):  
Ross Levin
Keyword(s):  
Death Anxiety ◽  
Significant Negative Correlation ◽  
Anxiety Scale ◽  
Ego Strength ◽  
Low Frequencies ◽  
Men And Women ◽  
High Frequencies ◽  
Self Reports ◽  
Mediating Factor ◽  
The Relationship

The present study was designed to investigate empirically the relationship between self-reports of nightmare frequency and ego strength and death anxiety in both men and women. In addition, the interrelations among these variables were assessed. 20 undergraduates with high frequencies of nightmares and 20 with low frequencies (10 men and 10 women per group) were administered the Barron Ego Strength Scale and a death anxiety scale. Significant differences were found between nightmare groups on the Barron scale for men and women but none on the death anxiety scale either by nightmare frequency or sex. A significant negative correlation of -.47 between death anxiety and ego strength was found for women and in one high frequency group. Women with high frequencies of nightmares showed the highest correlation, -.83. These data suggest that nightmare frequency may be a mediating factor in the relationship between ego strength, death anxiety, and sex of subject.

Relations among Nightmare Frequency and Ego Strength, Death Anxiety, and Sex of College Students

1989 ◽  
Vol 69 (3_suppl) ◽  
pp. 1107-1113 ◽  
Author(s):  
Ross Levin
Keyword(s):  
Death Anxiety ◽  
Significant Negative Correlation ◽  
Anxiety Scale ◽  
Ego Strength ◽  
Low Frequencies ◽  
Men And Women ◽  
High Frequencies ◽  
Self Reports ◽  
Mediating Factor ◽  
The Relationship

The present study was designed to investigate empirically the relationship between self-reports of nightmare frequency and ego strength and death anxiety in both men and women. In addition, the interrelations among these variables were assessed. 20 undergraduates with high frequencies of nightmares and 20 with low frequencies (10 men and 10 women per group) were administered the Barron Ego Strength Scale and a death anxiety scale. Significant differences were found between nightmare groups on the Barron scale for men and women but none on the death anxiety scale either by nightmare frequency or sex. A significant negative correlation of −.47 between death anxiety and ego strength was found for women and in one high frequency group. Women with high frequencies of nightmares showed the highest correlation, −.83. These data suggest that nightmare frequency may be a mediating factor in the relationship between ego strength, death anxiety, and sex of subject.

Development and Testing of a Kilohertz Solar-to-Acoustic Energy Converter

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Kuan Chen ◽  
Mohammed Albonaeem ◽  
Yeongmin Kim ◽  
Nam Jin Kim ◽  
Sang Hoon Lim ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Fresnel Lens ◽  
Pulse Frequency ◽  
Acoustic Energy ◽  
Sound Waves ◽  
Energy Converter ◽  
Low Frequencies ◽  
High Frequencies ◽  
The Relationship ◽  
Acoustical Energy

A thermal-to-acoustic energy converter (TAC) was developed and tested to produce sound waves in the kilohertz range directly from solar energy. The converter consisted of a glass window and a small amount of steel wool in the shape of a disk sealed in an aluminum housing. A Fresnel lens and a chopper wheel with 60 holes in it were employed to generate a pulsed sunbeam of approximately 200 sun intensity as the heat source of the TAC. Various designs and techniques were tested to improve the sound amplitude and signal-to-noise ratio of the converter at high frequencies. Reduction in air volume, better cooling, and improvement in air tightness were found to be effective in enhancing the sound amplitude. A shockproof mount commonly used in radio studios to reduce microphone vibration was essential in noise reduction for the TAC at high chopper wheel rotations. The sound amplitude was found to rapidly decrease with the increase in pulse frequency of the sunbeam at low frequencies. The relationship between the decibel value and frequency of the generated sound waves was changed to linear for sunbeam frequencies above 1 kHz. This is the frequency at which the penetration of surface temperature fluctuations into the aluminum housing becomes comparable with the aluminum housing thickness. At a given frequency, the sound amplitude increased almost exponentially with the increase in solar flux intensity. To the best of our knowledge, the 3 kHz sound frequency measured in our experiments is by far the highest frequency produced by a solar-to-acoustical energy converter.

Effects of Damping on Flow-Mediated Interaction Between Two Cylinders

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Zhonglu Lin ◽  
Dongfang Liang ◽  
Ming Zhao
Keyword(s):  
Vibration Amplitude ◽  
Amplitude Ratio ◽  
Damping Factor ◽  
Structural Damping ◽  
Mass Ratio ◽  
Low Frequencies ◽  
Master Cylinder ◽  
High Frequencies ◽  
Gap Ratio ◽  
Highly Sensitive

This study investigates the flow-mediated interaction between two vibrating cylinders of the same size immersed in an otherwise still fluid. The master cylinder carries out forced vibration, while the slave cylinder is elastically mounted with one degree-of-freedom along the centerline between the two cylinders. We examined the stabilized vibration of the slave cylinder. In total, 6269 two-dimensional (2D) cases were simulated to cover the parameter space, with a fixed Reynolds number of 100, the structural damping factor of the slave cylinder ranging from 0 to 1.4, the mass ratio of the slave cylinder ranging from 1.5 to 2.5, the initial gap ratio ranging from 0.2 to 1.0, the vibration amplitude ratio of the master cylinder ranging from 0.025 to 0.1, and the vibration frequency ratio ranging from 0.05 to 2.4. We found that the vibration amplitude of the slave cylinder is highly sensitive to damping when the damping coefficient is small. The two cylinders' vibration is in antiphase at low frequencies but in phase at high frequencies. The phase of the slave cylinder changes abruptly at resonance when it has little damping, but the phase change with the frequency becomes increasingly gradual with increasing damping. With a nonzero damping factor, the maximum vibration amplitude of the slave cylinder is inversely correlated with its mass ratio. The response of the slave cylinder is explained by examining the pressure distribution and velocity field adjacent to it.

SOUND PULSE SIMULATION IN DEEP OCEAN

1995 ◽  
Vol 03 (01) ◽  
pp. 57-68 ◽  
Author(s):  
A. G. ALENITSYN ◽  
V. S. BULDYREV ◽  
V. E. GRIKUROV ◽  
A. A. FEDOTOV
Keyword(s):  
Deep Ocean ◽  
Wide Band ◽  
Sound Pulse ◽  
Asymptotic Approach ◽  
Ray Method ◽  
Eigenvalues And Eigenfunctions ◽  
Low Frequencies ◽  
High Frequencies ◽  
Mode Method ◽  
Stratified Ocean

In this paper, the computer sound pulse simulation in deep stratified ocean is embodied. The restrictions on sound speed profiles are minimal. Pulse spectra are assumed to be wide band. Reasonable combination of numerical and asymptotic techniques is applied to construct an effective algorithm. The principle points of discussion here are the normal mode method for low frequencies, the numerical asymptotic approach to calculate the eigenvalues and eigenfunctions, the ray method for high frequencies, and the numerical results.

scholarly journals A Bootstrap Method to Test Granger-Causality in the Frequency Domain

2021 ◽  
Author(s):  
Matteo Farnè ◽  
Angela Montanari
Keyword(s):  
Stochastic Process ◽  
Frequency Domain ◽  
Granger Causality ◽  
Bootstrap Method ◽  
Money Stock ◽  
Bootstrap Test ◽  
Low Frequencies ◽  
Economic Output ◽  
Stationary Bootstrap ◽  
The Relationship

AbstractWe propose a bootstrap test for unconditional and conditional Granger-causality spectra in the frequency domain. Our test aims to detect if the causality at a particular frequency is systematically different from zero. In particular, we consider a stochastic process derived applying independently the stationary bootstrap to the original series. At each frequency, we test the sample causality against the distribution of the median causality across frequencies estimated for that process. Via our procedure, we infer about the relationship between money stock and GDP in the Euro Area during the period 1999–2017. We point out that the money stock aggregate M1 had a significant impact on economic output at all frequencies, while the opposite relationship is significant only at low frequencies.

Effect of Blowing Agent on Cell Morphology and Acoustic Absorption of Natural Rubber Foam

2015 ◽  
Vol 804 ◽  
pp. 25-29 ◽  
Author(s):  
Wanlop Harnnarongchai ◽  
Kantima Chaochanchaikul
Keyword(s):  
Natural Rubber ◽  
Cell Size ◽  
Cell Morphology ◽  
Foam Cell ◽  
Adsorption Coefficient ◽  
Low Frequencies ◽  
Potassium Oleate ◽  
High Frequencies ◽  
Blowing Agent ◽  
Open Cell Foam

The sound absorbing efficiency of natural rubber (NR) foam is affected by the cell morphology of foam. Potassium oleate (K-oleate) and sodium bicarbonate (NaHCO3) were used as blowing agents to create open-cell foam. Amounts of the blowing agent were varied from 0.5 to 8.0 part per hundred of rubber (phr) to evaluate cell size and number of foam cell as well as sound adsorption coefficient of NR foam. The NR foam specimens were prepared using mould and air-circulating oven for vulcanizing and foaming processes. The results indicated that K-oleate at 2.0 phr and NaHCO3 at 0.5 phr led to form NR foam with the smallest cell size and the largest number of foam cell. At low frequencies, the optimum sound adsorption coefficient of NR foam was caused by filling K-oleate 2 phr. However, that of NR foam at high frequencies was provided by 0.5 phr-NaHCO3 addition.

Use of Measured Mobility to Improve SEA Predictions in the Mid-Frequency Range

1999 ◽  
Author(s):  
Jerome E. Manning
Keyword(s):  
Dynamic Systems ◽  
Broad Band ◽  
Measured Data ◽  
Hybrid Technique ◽  
Complex Dynamic ◽  
Low Frequencies ◽  
Large Variability ◽  
High Frequencies ◽  
Complex Dynamic Systems ◽  
Light Coupling

Abstract Statistical energy analysis provides a technique to predict acoustic and vibration levels in complex dynamic systems. The technique is most useful for broad-band excitation at high frequencies where many modes contribute to the response in any given frequency band. At mid and low frequencies, the number of modes contributing to the response may be quite small. In this case SEA predictions show large variability from measured data and may not be useful for vibroacoustic design. This paper focuses on the use of measured data to improve the accuracy of the predictions. Past work to measure the SEA coupling and damping loss factors has not been successful for a broad range of systems that do not have light coupling. This paper introduces a new hybrid SEA technique that combines measured mobility functions with analytical SEA predictions. The accuracy of the hybrid technique is shown to be greatly improved at mid and low frequencies.

Frequency-Weighted Variable-Length Controllers Using Anytime Control Strategies

2011 ◽  
Author(s):  
Gundula B. Runge ◽  
Al Ferri ◽  
Bonnie Ferri
Keyword(s):  
Time Scale ◽  
Weighting Function ◽  
Control Strategies ◽  
Low Frequency ◽  
Low Frequencies ◽  
High Frequencies ◽  
Frequency Components ◽  
Computational Resources ◽  
Weighted Variable ◽  
Selection Of

This paper considers an anytime strategy to implement controllers that react to changing computational resources. The anytime controllers developed in this paper are suitable for cases when the time scale of switching is in the order of the task execution time, that is, on the time scale found commonly with sporadically missed deadlines. This paper extends the prior work by developing frequency-weighted anytime controllers. The selection of the weighting function is driven by the expectation of the situations that would require anytime operation. For example, if the anytime operation is due to occasional and isolated missed deadlines, then the weighting on high frequencies should be larger than that for low frequencies. Low frequency components will have a smaller change over one sample time, so failing to update these components for one sample period will have less effect than with the high frequency components. An example will be included that applies the anytime control strategy to a model of a DC motor with deadzone and saturation nonlinearities.

Sign in / Sign up

Export Citation Format

Share Document