Sound generation mechanism of compressible vortex reconnection

2021 ◽  
Vol 933 ◽  
Author(s):  
Hamid Daryan ◽  
Fazle Hussain ◽  
Jean-Pierre Hickey
Keyword(s):  
Sound Pressure ◽  
Source Term ◽  
Near Field ◽  
Generation Mechanism ◽  
Sound Generation ◽  
Source Terms ◽  
Acoustic Source ◽  
Spatial Gradients ◽  
Delayed Onset ◽  
Vortex Reconnection

We study the sound generation mechanism of initially subsonic viscous vortex reconnection at vortex Reynolds number $Re~(\equiv \text {circulation}/\text {kinematic viscosity})=1500$ through decomposition of Lighthill's acoustic source term. The Laplacian of the kinetic energy, flexion product, enstrophy and deviation from the isentropic condition provide the dominant contributions to the acoustic source term. The overall (all time) extrema of the total source term and its dominant hydrodynamic components scale linearly with the reference Mach number $M_o$ ; the deviation from the isentropic condition shows a quadratic scaling. The significant sound arising from the flexion product occurs due to the coiling and uncoiling of the twisted vortex filaments wrapping around the bridges, when a rapid strain is induced on the filaments by the repulsion of the bridges. The spatial distributions of the various acoustic source terms reveal the importance of mutual cancellations among most of the terms; this also highlights the importance of symmetry breaking in the sound generation during reconnection. Compressibility acts to delay the start of the sequence of reconnection events, as long as shocklets, if formed, are sufficiently weak to not affect the reconnection. The delayed onset has direct ramifications for the sound generation by enhancing the velocity of the entrained jet between the vortices and increasing the spatial gradients of the acoustic source terms. Consistent with the near-field pressure, the overall maximum instantaneous sound pressure level in the far field has a quadratic dependence on $M_o$ . Thus, reconnection becomes an even more dominant sound-generating event at higher $M_o$ .

Hydrodynamic Noise and Radiated Mechanism of 3D Cavity

2012 ◽  
Vol 217-219 ◽  
pp. 2590-2593 ◽  
Author(s):  
Yu Wang ◽  
Bai Zhou Li
Keyword(s):  
Sound Pressure ◽  
Near Field ◽  
Low Frequency ◽  
Dipole Source ◽  
Fluctuating Pressure ◽  
Common Structure ◽  
Hydrodynamic Noise ◽  
Near Field Sound ◽  
Equivalent Sources ◽  
Field Sound

The flow past 3D rigid cavity is a common structure on the surface of the underwater vehicle. The hydrodynamic noise generated by the structure has attracted considerable attention in recent years. Based on LES-Lighthill equivalent sources method, a 3D cavity is analyzed in this paper, when the Mach number is 0.0048. The hydrodynamic noise and the radiated mechanism of 3D cavity are investigated from the correlation between fluctuating pressure and frequency, the near-field sound pressure intensity, and the propagation directivity. It is found that the hydrodynamic noise is supported by the low frequency range, and fluctuating pressure of the trailing-edge is the largest, which is the main dipole source.

scholarly journals CP-violating transport theory for electroweak baryogenesis with thermal corrections

2021 ◽  
Vol 2021 (11) ◽  
pp. 042
Author(s):  
Kimmo Kainulainen
Keyword(s):  
Source Term ◽  
Transport Theory ◽  
Finite Width ◽  
Source Terms ◽  
Boltzmann Equations ◽  
Current Divergence ◽  
The One ◽  
Infrared Divergences ◽  
Correct Implementation ◽  
Divergence Equations

Abstract We derive CP-violating transport equations for fermions for electroweak baryogenesis from the CTP-formalism including thermal corrections at the one-loop level. We consider both the VEV-insertion approximation (VIA) and the semiclassical (SC) formalism. We show that the VIA-method is based on an assumption that leads to an ill-defined source term containing a pinch singularity, whose regularisation by thermal effects leads to ambiguities including spurious ultraviolet and infrared divergences. We then carefully review the derivation of the semiclassical formalism and extend it to include thermal corrections. We present the semiclassical Boltzmann equations for thermal WKB-quasiparticles with source terms up to the second order in gradients that contain both dispersive and finite width corrections. We also show that the SC-method reproduces the current divergence equations and that a correct implementation of the Fick's law captures the semiclassical source term even with conserved total current ∂μ j μ = 0. Our results show that the VIA-source term is not just ambiguous, but that it does not exist. Finally, we show that the collisional source terms reported earlier in the semiclassical literature are also spurious, and vanish in a consistent calculation.

scholarly journals Development of Direct-Vibration Actuator for Bezel-Less Display Panels on Mobile Phones

2020 ◽  
Vol 10 (14) ◽  
pp. 4975 ◽  
Author(s):  
Ki-Hong Park ◽  
Zhi-Xiong Jiang ◽  
Yuan-Wu Jiang ◽  
Sang-Moon Hwang
Keyword(s):  
Mobile Phones ◽  
Sound Pressure ◽  
Wearable Devices ◽  
Pressure Level ◽  
Sound Generation ◽  
Force Factor ◽  
Display Design ◽  
3D Finite Element ◽  
3D Finite Element Method ◽  
Direct Vibration

With the development of technology, multimedia devices such as smartphones, tablets, and wearable devices have become necessities in our lives, and many new products are introduced every year. Companies are expanding smartphone displays and are developing bezel-less display panel designs. The enlarged display limits the space available for a speaker, and a new actuator must therefore be developed. Indirect-vibration actuators were developed for full-wide display designs. Using the same sound-generation principle as that of the indirect-vibration actuator, the mechanism and design of the direct-vibrating actuator is proposed in this paper. Using 3D finite element method (FEM), the force factor is obtained and used for design optimization. A sample is produced, and an experiment is conducted for sound pressure level (SPL) comparison. The experiment results show that the newly designed direct-vibration actuator can replace the dynamic receiver in mobile devices and enable the application of the bezel-less display design.

scholarly journals Verification of SpacePy's radial diffusion radiation belt model

2011 ◽  
Vol 4 (3) ◽  
pp. 2165-2197 ◽  
Author(s):  
D. T. Welling ◽  
J. Koller ◽  
E. Camporeale
Keyword(s):  
Radiation Belt ◽  
Source Term ◽  
Model Verification ◽  
Radiation Environment ◽  
Source Terms ◽  
Time Step ◽  
Manufactured Solutions ◽  
Quantitative Verification ◽  
Numerical Solver ◽  
Selection Of

Abstract. Model verification, or the process of ensuring that the prescribed equations are properly solved, is a necessary step in code development. Careful, quantitative verification guides users when selecting grid resolution and time step and gives confidence to code developers that existing code is properly instituted. This work introduces the RadBelt radiation belt model, a new, open-source version of the Dynamic Radiation Environment Assimilation Model (DREAM) and uses the Method of Manufactured Solutions (MMS) to quantitatively verify it. Order of convergence is investigated for a plethora of code configurations and source terms. The ability to apply many different diffusion coefficients, including time constant and time varying, is thoroughly investigated. The model passes all of the tests, demonstrating correct implementation of the numerical solver. The importance of DLL and source term dynamics on the selection of time step and grid size is also explored. Finally, an alternative method to apply the source term is examined to illustrate additional considerations required when non-linear source terms are used.

scholarly journals Higher-order dissipation in the theory of homogeneous isotropic turbulence

2016 ◽  
Vol 803 ◽  
pp. 250-274 ◽  
Author(s):  
Norbert Peters ◽  
Jonas Boschung ◽  
Michael Gauding ◽  
Jens Henrik Goebbert ◽  
Reginald J. Hill ◽  
...  
Keyword(s):  
Source Term ◽  
Isotropic Turbulence ◽  
Stokes Equations ◽  
Higher Order ◽  
Distribution Functions ◽  
Order Structure ◽  
Source Terms ◽  
Homogeneous Isotropic Turbulence ◽  
Higher Order Moments ◽  
Even Order

The two-point theory of homogeneous isotropic turbulence is extended to source terms appearing in the equations for higher-order structure functions. For this, transport equations for these source terms are derived. We focus on the trace of the resulting equations, which is of particular interest because it is invariant and therefore independent of the coordinate system. In the trace of the even-order source term equation, we discover the higher-order moments of the dissipation distribution, and the individual even-order source term equations contain the higher-order moments of the longitudinal, transverse and mixed dissipation distribution functions. This shows for the first time that dissipation fluctuations, on which most of the phenomenological intermittency models are based, are contained in the Navier–Stokes equations. Noticeably, we also find the volume-averaged dissipation $\unicode[STIX]{x1D700}_{r}$ used by Kolmogorov (J. Fluid Mech., vol. 13, 1962, pp. 82–85) in the resulting system of equations, because it is related to dissipation correlations.

Effects of Quay Wall and Seabed Reflection on the AUV Acoustic Radiation Test Analysis

2014 ◽  
Vol 599-601 ◽  
pp. 922-926
Author(s):  
Guo Liang Xu ◽  
Qi Wei He ◽  
Shao Chun Ding ◽  
Hai Bo Wan
Keyword(s):  
Acoustic Field ◽  
Field Test ◽  
Sound Pressure ◽  
Acoustic Radiation ◽  
Near Field ◽  
Test Analysis ◽  
Complex Sound ◽  
Quay Wall ◽  
Radiation Test ◽  
Acoustical Holography

To analyze effects of quay environment on the AUV radiated acoustic field test, the PNAH (PNAH: planar near-field acoustical holography) was used to simulate acoustic field. By simulating the free and non-free acoustic field and comparing amplitudes and angles of complex sound pressure, Analyze effects of quay wall and seabed reflection on the AUV radiated acoustic field test to determine the standard of quay wall and seabed environment which meets testing. The work would provide a certain reference for the AUV radiated acoustic field test.

scholarly journals The overlapping roles of the inner ear and lateral line: the active space of dipole source detection

2000 ◽  
Vol 355 (1401) ◽  
pp. 1115-1119 ◽  
Author(s):  
Christopher B. Braun ◽  
Sheryl Coombs
Keyword(s):  
Inner Ear ◽  
Lateral Line ◽  
Near Field ◽  
Dipole Source ◽  
Source Detection ◽  
Sound Sources ◽  
Distance Range ◽  
Spatial Gradients ◽  
Theoretical Predictions ◽  
Benthic Fishes

The problems associated with the detection of sounds and other mechanical disturbances in the aquatic environment differ greatly from those associated with airborne sounds. The differences are primarily due to the incompressibility of water and the corresponding increase in importance of the acoustic near field. The near field, or hydrodynamic field, is characterized by steep spatial gradients in pressure, and detection of the accelerations associated with these gradients is performed by both the inner ear and the lateral line systems of fishes. Acceleration–sensitive otolithic organs are present in all fishes and provide these animals with a form of inertial audition. The detection of pressure gradients, by both the lateral line and inner ear, is the taxonomically most widespread mechanism of sound–source detection amongst vertebrates, and is thus the most likely primitive mode of detecting sound sources. Surprisingly, little is known about the capabilities of either the lateral line or the otolithic endorgan in the detection of vibratory dipole sources. Theoretical considerations for the overlapping roles of the inner ear and lateral line systems in midwater predict that the lateral line will operate over a shorter distance range than the inner ear, although with a much greater spatial resolution. Our empirical results of dipole detection by mottled sculpin, a benthic fish, do not agree with theoretical predictions based on midwater fishes, in that the distance ranges of the two systems appear to be approximately equal. This is almost certainly as a result of physical coupling between the fishes and the substrate. Thus, rather than having a greater active range, the inner ear appears to have a reduced distance range in benthic fishes, and the lateral line distance range may be concomitantly extended.

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