scholarly journals Parametric Analysis for Underwater Flapping Foil Propulsor

Water ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2103
Author(s):  
Lei Mei ◽  
Junwei Zhou ◽  
Dong Yu Weichao Shi ◽  
Xiaoyun Pan ◽  
Mingyang Li
Keyword(s):  
Phase Difference ◽  
Amplitude Ratio ◽  
Angle Of Attack ◽  
Systematic Investigation ◽  
Influential Factor ◽  
Maximum Efficiency ◽  
Propulsion Efficiency ◽  
Flapping Foil ◽  
Maximum Angle ◽  
Flow Field Characteristics

This paper researched into the harmonic and anharmonic underwater flapping foil propulsion systems to improve the efficiency of these bioinspired propulsors. The angle of attack, the pitching angle, the heaving amplitude, and the phase difference are parametrically investigated in this paper. A rigid two-dimensional NACA (National Advisory Committee for Aeronautics) 0012 airfoil is modeled with the aid of a commercial computational fluid dynamics software, FINE™/Marine. Unsteady Reynolds Average Navier-Stokes (URANS) equation is solved together with dynamic mesh to simulate the foil motion. The investigation first verifies the reliability of the developed modeling method against the benchmark data. Then, the systematic investigation is conducted and identifies that the heaving amplitude is most influential factor for the propulsion efficiency. Secondly, phase difference also has a significant influence on efficiency, but this effect is related to the reference working condition, which needs further study. Then, the pitching amplitude has little effect on the maximum efficiency value of flapping foil, while it will affect its optimal speed range. When the heaving amplitude ratio reaches 3 and the corresponding maximum angle of attack is about 9°, the maximum efficiency can reach 87%. The effect of anharmonic motion on the efficiency is very small and varies with the St number, but in summary, it can maintain the peak efficiency over a wider range of operations. In addition, the force and flow field characteristics of different efficiency points are compared and analyzed to distinguish their corresponding relationship with the propulsion efficiency.

scholarly journals Performance Degradation in Cross-Eye Jamming Due to Amplitude/Phase Instability between Jammer Antennas

Sensors ◽  
2021 ◽  
Vol 21 (15) ◽  
pp. 5027
Author(s):  
Je-An Kim ◽  
Joon-Ho Lee
Keyword(s):  
Performance Analysis ◽  
Phase Difference ◽  
Taylor Expansion ◽  
Amplitude Ratio ◽  
Random Variables ◽  
Performance Degradation ◽  
Analytical Performance ◽  
Phase Instability ◽  
Gaussian Random Variables ◽  
First Order

Cross-eye gain in cross-eye jamming systems is highly dependent on amplitude ratio and the phase difference between jammer antennas. It is well known that cross-eye jamming is most effective for the amplitude ratio of unity and phase difference of 180 degrees. It is assumed that the instabilities in the amplitude ratio and phase difference can be modeled as zero-mean Gaussian random variables. In this paper, we not only quantitatively analyze the effect of amplitude ratio instability and phase difference instability on performance degradation in terms of reduction in cross-eye gain but also proceed with analytical performance analysis based on the first order and second-order Taylor expansion.

scholarly journals Comparative investigations in the effect of angle of attack profile on hydrodynamic performance of bio-inspired foil, (corrected)

2013 ◽  
Vol 10 (2) ◽  
pp. 99-108 ◽  
Author(s):  
J. A. Esfahani ◽  
E. Barati ◽  
Hamid Reza Karbasian
Keyword(s):  
Angle Of Attack ◽  
Underwater Vehicles ◽  
Hydrodynamic Performance ◽  
Profile Function ◽  
Flapping Foil ◽  
Propulsive Performance ◽  
Wide Range ◽  
Effective Angle ◽  
Thrust Production ◽  
Optimum Profile

In flapping underwater vehicles the propulsive performance of harmonically sinusoidal heaving and pitching foil will be degraded by some awkward changes in effective angle of attack profile, as the Strouhal number increases. This paper surveys different angle of attack profiles (Sinusoidal, Square, Sawtooth and Cosine) and considers their thrust production ability. In the wide range of Strouhal numbers, thrust production of Square profile is considerable but it has a discontinuity in heave velocity profile, in which an infinite acceleration exists. This problem poses a significant defect in control of flapping foil. A novel profile function is proposed to omit sharp changes in heave velocity and acceleration. Furthermore, an optimum profile is found for different Strouhal numbers with respect to Square angle of attack profile.DOI: http://dx.doi.org/10.3329/jname.v10i2.14229

scholarly journals A Numerical Study of Metachronal Propulsion at Low to Intermediate Reynolds Numbers

Fluids ◽  
2020 ◽  
Vol 5 (2) ◽  
pp. 86 ◽  
Author(s):  
Shawtaroh Granzier-Nakajima ◽  
Robert D. Guy ◽  
Calvin Zhang-Molina
Keyword(s):  
Phase Difference ◽  
Nearest Neighbor ◽  
Numerical Study ◽  
Full Range ◽  
Reynolds Numbers ◽  
Maximum Efficiency ◽  
Immersed Boundary ◽  
Dynamics Model ◽  
Underwater Propulsion ◽  
Average Flux

Inspired by the forward swimming of long-tailed crustaceans, we study an underwater propulsion mechanism for a swimming body with multiple rigid paddles attached underneath undergoing cycles of power and return strokes with a constant phase-difference between neighboring paddles, a phenomenon known as metachronal propulsion. To study how inter-paddle phase-difference affects flux production, we develop a computational fluid dynamics model and a numerical algorithm based on the immersed boundary method, which allows us to simulate metachronal propulsion at Reynolds numbers (RE) ranging from close to 0 to about 100. Our main finding is that the highest average flux is generated when nearest-neighbor paddles maintain an approximate 20%–25% phase-difference with the more posterior paddle leading the cycle; this result is independent of stroke frequency across the full range of RE considered here. We also find that the optimal paddle spacing and the number of paddles depend on RE; we see a qualitative transition in the dynamics of flow generated by metachronal propulsion as RE rises above 80. Roughly speaking, in terms of average flux generation, a tight paddle spacing is preferred when RE is less than 10, but a wider spacing becomes clearly favored when RE is close to or above 100. In terms of efficiency of flux generation, at RE 0.1 the maximum efficiency occurs at two paddles, and the efficiency decreases as the number of paddles increases. At RE 100 the efficiency increases as the number of paddles increases, and it appears to saturate by eight paddles, whereas using four paddles is a good tradeoff for both low and intermediate RE.

scholarly journals Mode Discrimination in Nonradially Oscillating Stars From Light, Colour and Velocity Observations

1980 ◽  
Vol 58 ◽  
pp. 371-376
Author(s):  
L.A. Balona ◽  
R.S. Stobie
Keyword(s):  
Radial Velocity ◽  
Phase Difference ◽  
Spherical Harmonic ◽  
Amplitude Ratio ◽  
Harmonic Mode ◽  
Instability Strip ◽  
Nonradial Oscillation ◽  
Mode Discrimination ◽  
Velocity Variations

AbstractExpressions for the amplitudes and phases of the light, colour and radial velocity variations are derived for a star in nonradial oscillation. For stars in the cepheid instability strip the spherical harmonic mode of the oscillation can be obtained from the phase difference between the light and colour variations. For 3 Cep stars the mode can be estimated from the amplitude ratio of the light and colour variations.

Investigation of aerodynamic coefficients at Mach 6 over conical, hemispherical and flat-face spiked body

2017 ◽  
Vol 121 (1245) ◽  
pp. 1711-1732 ◽  
Author(s):  
R. Kalimuthu ◽  
R. C. Mehta ◽  
E. Rathakrishnan
Keyword(s):  
Flow Field ◽  
Blunt Body ◽  
Angle Of Attack ◽  
Separated Flow ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Geometrical Parameters ◽  
Aerodynamic Coefficients ◽  
Aerodynamic Forces ◽  
Flow Field Characteristics

ABSTRACTA forward spike attached to a blunt body significantly alters its flow field characteristics and influences aerodynamic characteristics at hypersonic flow due to formation of separated flow and re-circulation region around the spiked body. An experimental investigation was performed to measure aerodynamic forces for spikes blunt bodies with a conical, hemispherical and flat-face spike at Mach 6 and at an angle-of-attack range from 0° to 8° and length-to-diameterL/Dratio of spike varies from 0.5 to 2.0, whereLis the length of the spike andDis diameter of blunt body. The shape of the leading edge of the spiked blunt body reveals different types of flow field features in the formation of a shock wave, shear layer, flow separation, re-circulation region and re-attachment shock. They are analysed with the help of schlieren pictures. The shock distance ahead of the hemisphere and the flat-face spike is compared with the analytical solution and is showing satisfactory agreement with the schlieren pictures. The influence of geometrical parameters of the spike, the shape of the spike tip and angle-of-attack on the aerodynamic coefficients are investigated by measuring aerodynamic forces in a hypersonic wind tunnel. It is found that a maximum reduction of drag of about 77% was found for hemisphere spike ofL/D= 2.0 at zero angle-of-attack. Consideration for compensation of increased pitching moment is required to stabilise the aerodynamic forces.

scholarly journals Effect of angle of attack profiles in flapping foil propulsion

2004 ◽  
Vol 19 (1) ◽  
pp. 37-47 ◽  
Author(s):  
F.S. Hover ◽  
Ø. Haugsdal ◽  
M.S. Triantafyllou
Keyword(s):  
Angle Of Attack ◽  
Flapping Foil

Vibration Parameter Analysis of Non-Harmonic Vibration Conveyor

2013 ◽  
Vol 694-697 ◽  
pp. 61-64
Author(s):  
Zhi Ying Qin ◽  
Yao Liu
Keyword(s):  
Phase Difference ◽  
Amplitude Ratio ◽  
Parameter Analysis ◽  
Harmonic Vibration ◽  
Dynamics Model ◽  
Bulk Materials ◽  
Optimum Frequency ◽  
Single Degree Of Freedom ◽  
Harmonic Components ◽  
Vibration Parameters

For the non-harmonic vibration conveyor, a single-degree-of-freedom dynamics model is built for the horizontal motion of bulk materials, in which the dry friction force is piecewise nonsmooth. The effect on conveying velocity is studied for six vibration parameters in the excitation force with two harmonic components. The conveying velocity increases with the increase of frequency and amplitude, but the optimum frequency ratio is 2, and the optimum amplitude ratio approaches 1/3. The initial phase has no effect on conveying velocity, and the effect of phase difference is periodic, i.e. the forward conveying is best on phase difference π/2, and the backward conveying is best on phase difference -π/2.

The upper frequency limit for the binaural localization of a pure tone by phase difference

1940 ◽  
Vol 128 (852) ◽  
pp. 293-305 ◽  
Keyword(s):  
Phase Difference ◽  
Pure Tone ◽  
Amplitude Ratio ◽  
Median Plane ◽  
Rapid Onset ◽  
Continuous Phase ◽  
Phase Changes ◽  
Considerable Difficulty ◽  
Intensity Changes ◽  
Binaural Localization

It is well known that if a pure tone is presented binaurally so that its intensity is the same in each ear, and there is no phase difference between the notes at the ears, the resulting sensation is that of a source of sound located in the median plane and situated is that of a source of sound located in the median plane and situated either within the skull or outside it. If a difference of phase between the notes is gradually introduced without altering their intensities, and the frequency of the tone is, say, 800 cyc. /sec., then the source appears to move laterally towards the side of the ear in which the phase is made to lead. According to some observers, the movement is on a horizontal circular arc centred between the ears, while others consider it to be along a line joining the ears. There is general agreement among workers on localization that considerable difficulty exists in the detection of such movements at frequencies above 800 cyc. /sec., and that their extent is more limited, but they disagree as to the frequency above which the lateral motion ceases to be noted. Stewart (1920) obtained movement at 1280 cyc. /sec., but not 1536 cyc. /sec.; Banister (1925) found movements at 1040 and 1345 cyc. /sec., but anomalous in character. On the other hand, von Hornbostel and Wertheimer (1920) state that at about 800 cyc. /sec., the lateral movement no longer extends 90° left and right, but decreases as the frequency increases, and should reach zero at 17,000 cyc. /sec. Halverson (1927) found that observable right and left effects appear to be present up to the upper auditory limit. Below 1400 cyc. /sec. judgments of direction are fairly consistent, between 1400 and 3000 cyc. /sec. there is no particular difficulty if allowance is made for the more rapid onset of fatigue at these frequencies. Above 3000 cyc. /sec. lateral effects are still observable, though median localization is extremely difficult to achieve. Hartley (1919) gave theoretical curves showing the phase difference produced at the ears by sources of various frequencies at different distances from the head. According to these, above 650 cyc. /sec. the maximum movement of the apparent source would be less than 90°, though at 1860 cyc. /sec. there should still be about 27° of movement on either side of the median plane. These curves have been checked experimentally by Firestone (1930), who found for three frequencies the phase difference and amplitude ratio of the sounds entering the ears of a man-shaped wax dummy from a source at varying azimuths around the head and at different distances from it. The phase differences found were in good agreement with the values calculated by Hartley. Various methods have been used to present the notes to the ears and to vary the phase difference between them. In the experiments of Halverson the sounds were produced by a tuning fork and led to the ears through tubes, in one of which was incorporated a sliding section to vary its length and thus the phase difference at the ears. An objection to this is the possibility of resonances in the tubes, different on both sides on account of their different lengths, so that intensity changes might occur as well as changes oh phase. Stewart, and Banister, used notes generated electrically and presented to the ears by telephones. Continuous phase changes could be made with their generators, but the purity of the resulting notes was doubtful.

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