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Journal articles on the topic 'Low Mach assumption'

Author: Grafiati

Published: 20 February 2024

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1

Fu, Jian-Ming, Hai-Min Tang, and Hong-Quan Chen. "Rapid computation of rotary derivatives for subsonic and low transonic flows." Engineering Computations 36, no. 9 (2019): 3108–21. http://dx.doi.org/10.1108/ec-09-2018-0399.

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Purpose The purpose of this paper is to develop a new approach for rapid computation of subsonic and low-transonic rotary derivatives with the available steady solutions obtained by Euler computational fluid dynamics (CFD) codes. Design/methodology/approach The approach is achieved by the perturbation on the steady-state pressure of Euler CFD codes. The resulting perturbation relation is established at a reference Mach number between rotary derivatives and normal velocity on surface due to angular velocity. The solution of the reference Mach number is generated technically by Prandtl–Glauert c

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2

Zhang, Zhicheng, Yuhong Li, Étienne Spieser, Peng Zhou, and Xin Zhang. "An improved artificial compressibility method for aeroacoustics at low Mach numbers." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 268, no. 5 (2023): 3025–33. http://dx.doi.org/10.3397/in_2023_0437.

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This work presents an improved artificial compressibility method that enables correct sound propagation behaviour in low Mach number flows. As an extension of incompressible approaches, it offers the advantage of low computational costs since compressible flow equations are simplified under the isentropic assumption, and the coupling of flow and sound is preserved. The non-uniform speed of sound is considered in this method, and eigenvalue analysis of the modified governing equations reveals that the propagation speed of pseudo waves restores to that of physical acoustic waves. The effect of M

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HULSHOFF, S. J., A. HIRSCHBERG, and G. C. J. HOFMANS. "Sound production of vortex–nozzle interactions." Journal of Fluid Mechanics 439 (July 23, 2001): 335–52. http://dx.doi.org/10.1017/s0022112001004554.

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The factors which affect the sound production of a vortex as it passes through a nozzle are investigated at both low and high Mach numbers using time-accurate inviscid-flow computations. Vortex circulation, initial position, and mean-flow Mach number are shown to be the primary factors which influence the amplitude and phase of the sound produced. Nozzle geometry and distribution of vorticity are also shown to play significant roles in determining the detailed form of the signal. Additionally, it is shown that solution bifurcations are possible at sufficiently large values of vortex circulatio

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4

Donzis, Diego A., and Shriram Jagannathan. "Fluctuations of thermodynamic variables in stationary compressible turbulence." Journal of Fluid Mechanics 733 (September 23, 2013): 221–44. http://dx.doi.org/10.1017/jfm.2013.445.

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AbstractA large database of new direct numerical simulations of forced compressible turbulence on up to $204{8}^{3} $ grids, and a range of Reynolds (${R}_{\lambda } $) and turbulent Mach (${M}_{t} $) numbers, is analysed to study the scaling of pressure, density and temperature fluctuations. Small-perturbation analysis is used to study the scaling of variances, and different cross-correlations as well as spectra. Qualitative differences are observed between low and high ${M}_{t} $. The probability density functions (p.d.f.s) of pressure and density are negatively skewed at low ${M}_{t} $ (con

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Freitas Rachid, Felipe B., and Heraldo S. Costa Mattos. "On the Suitability of the Low Mach Number Assumption in the Modeling of the Damage Induced by Pressure Transients in Piping Systems." Journal of Fluids Engineering 121, no. 1 (1999): 112–17. http://dx.doi.org/10.1115/1.2821990.

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One-dimensional models for predicting the damage induced by pressure transients in piping systems conveying liquids have been proposed and analysed recently. However, such works have been concerned mainly with the adequacy of the constitutive equations adopted for different pipe materials and with the numerical techniques used for approximating the solution of the resulting mathematical problems. In the present paper the suitability of the simplifying low Mach number assumption adopted in the modeling is investigated. The analysis is carried out based on the eigenvalue problem associated to th

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6

FREUND, JONATHAN B. "Noise sources in a low-Reynolds-number turbulent jet at Mach 0.9." Journal of Fluid Mechanics 438 (July 5, 2001): 277–305. http://dx.doi.org/10.1017/s0022112001004414.

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The mechanisms of sound generation in a Mach 0.9, Reynolds number 3600 turbulent jet are investigated by direct numerical simulation. Details of the numerical method are briefly outlined and results are validated against an experiment at the same flow conditions (Stromberg, McLaughlin & Troutt 1980). Lighthill's theory is used to define a nominal acoustic source in the jet, and a numerical solution of Lighthill's equation is compared to the simulation to verify the computational procedures. The acoustic source is Fourier transformed in the axial coordinate and time and then filtered in ord

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7

Skalidis, R., J. Sternberg, J. R. Beattie, V. Pavlidou, and K. Tassis. "Why take the square root? An assessment of interstellar magnetic field strength estimation methods." Astronomy & Astrophysics 656 (December 2021): A118. http://dx.doi.org/10.1051/0004-6361/202142045.

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Context. The magnetic field strength in interstellar clouds can be estimated indirectly from measurements of dust polarization by assuming that turbulent kinetic energy is comparable to the fluctuating magnetic energy, and using the spread of polarization angles to estimate the latter. The method developed by Davis (1951, Phys. Rev., 81, 890) and by Chandrasekhar and Fermi (1953, ApJ, 118, 1137) (DCF) assumes that incompressible magnetohydrodynamic (MHD) fluctuations induce the observed dispersion of polarization angles, deriving B ∝ 1∕δθ (or, equivalently, δθ ∝ MA, in terms of the Alfvénic Ma

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8

Lee, Incheol, and Duck Joo Lee. "Investigation on the Source Locations of Axisymmetric Screech Tones Utilizing Data from Numerical Simulation." Journal of Theoretical and Computational Acoustics 27, no. 04 (2019): 1850058. http://dx.doi.org/10.1142/s2591728518500585.

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The source locations of axisymmetric modes of screech tones are numerically investigated. Fourth-order optimized compact scheme and fourth-order Runge–Kutta method are used to solve the 2-D axisymmetric Euler equations. The screech tone is successfully reproduced, and the change in wavelength with respect to jet Mach number shows good agreement with the experimental data. At various low supersonic jet Mach numbers, the time-averaged contours of Mach number and root-mean-square pressure are investigated to identify the location of maximum interaction between shock cell structures and vortices.

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9

Ouajdi, Sanae, Fayçal Moufekkir, Ahmed Mezrhab, and Jean Pierre Fontaine. "Numerical Method of Weakly Compressible Poiseuille Flow Using Lattice Boltzmann Method." Defect and Diffusion Forum 384 (May 2018): 99–116. http://dx.doi.org/10.4028/www.scientific.net/ddf.384.99.

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The present work focuses on the numerical simulation of isothermal and weakly compressible Poiseuille flow in a planar channel using the Lattice Boltzmann method with multiple times of relaxation (MRT-LBE) coupled to the Finite Difference method (FDM). The active fluid considered is the air under low Mach number assumption. The flow is two-dimensional, laminar and all the physical properties are constants except the density which varies in the sense of the Boussinesq approximation. The effects of the compressibility, the inclination angle and the Reynolds number on the dynamical and thermal fi

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10

Almagro, Antonio, Manuel García-Villalba, and Oscar Flores. "A numerical study of a variable-density low-speed turbulent mixing layer." Journal of Fluid Mechanics 830 (October 2, 2017): 569–601. http://dx.doi.org/10.1017/jfm.2017.583.

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Direct numerical simulations of a temporally developing, low-speed, variable-density, turbulent, plane mixing layer are performed. The Navier–Stokes equations in the low-Mach-number approximation are solved using a novel algorithm based on an extended version of the velocity–vorticity formulation used by Kim et al. (J. Fluid Mech., vol 177, 1987, 133–166) for incompressible flows. Four cases with density ratios $s=1,2,4$ and 8 are considered. The simulations are run with a Prandtl number of 0.7, and achieve a $Re_{\unicode[STIX]{x1D706}}$ up to 150 during the self-similar evolution of the mixi

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11

Blair, Dane. "Seismic radiation from an explosive column." GEOPHYSICS 75, no. 1 (2010): E55—E65. http://dx.doi.org/10.1190/1.3294860.

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A scale-independent analytic model of seismic radiation from a column of explosive is derived in terms of the blast hole radius [Formula: see text], charge length, explosive velocity of detonation (VoD), and distance [Formula: see text] to a monitoring station. The treatment is based on linear viscoelasticity in which the nonlinear response of rock close to the blast hole is modeled as a sufficiently low-[Formula: see text] material having an exponential increase in [Formula: see text] with distance from the source. Although limited by this assumption, the present analytic model avoids the mor

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12

Sommer, T. P., R. M. C. So, and H. S. Zhang. "Supersonic Flow Calculations Using a Reynolds-Stress and a Thermal Eddy Diffusivity Turbulence Model." Journal of Fluids Engineering 116, no. 3 (1994): 469–76. http://dx.doi.org/10.1115/1.2910300.

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A second-order model for the velocity field and a two-equation model for the temperature field are used to calculate supersonic boundary layers assuming negligible real gas effects. The modeled equations are formulated on the basis of an incompressible assumption and then extended to supersonic flows by invoking Morkovin’s hypothesis, which proposes that compressibility effects are completely accounted for by mean density variations alone. In order to calculate the near-wall flow accurately, correcting functions are proposed to render the modeled equations asymptotically consistent with the be

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13

Fulat, Karol, Artem Bohdan, Gabriel Torralba Paz, and Martin Pohl. "Kinetic Simulations of Nonrelativistic High-mach-number Perpendicular Shocks Propagating in a Turbulent Medium." Astrophysical Journal 959, no. 2 (2023): 119. http://dx.doi.org/10.3847/1538-4357/ad04dc.

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Abstract Strong nonrelativistic shocks are known to accelerate particles up to relativistic energies. However, for diffusive shock acceleration, electrons must have a highly suprathermal energy, implying the need for very efficient preacceleration. Most published studies consider shocks propagating through homogeneous plasma, which is an unrealistic assumption for astrophysical environments. Using 2D3V particle-in-cell simulations, we investigate electron acceleration and heating processes at nonrelativistic high-Mach-number shocks in electron-ion plasma with a turbulent upstream medium. For t

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14

Tabrizi, Amir Bashirzadeh, and Binxin Wu. "The role of compressibility in computing noise generated at a cavitating orifice." International Journal of Aeroacoustics 18, no. 1 (2018): 73–91. http://dx.doi.org/10.1177/1475472x18812801.

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The computational fluid dynamics calculation can be accomplished by solving either compressible or incompressible Navier–Stokes equations to determine the flow-field variables of the noise source. The proper assumption depends on both the physical situation and the Mach number. Although in cavitating devices usually we are dealing with low Mach number flow, cavitation is an acoustic phenomenon that can be affected by compressibility. Cavitation behaves acoustically as a monopole and it is mentioned by some researchers that incompressible solution is sufficient to study the dipole sources. Howe

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15

Josserand, M. A., and G. C. Lauchle. "Modeling the Wavevector-Frequency Spectrum of Boundary-Layer Wall Pressure During Transition on a Flat Plate." Journal of Vibration and Acoustics 112, no. 4 (1990): 523–34. http://dx.doi.org/10.1115/1.2930138.

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A spectral model for the wall-pressure fluctuations induced on a zero pressure gradient, flat, rigid surface by a transitioning boundary layer at low Mach number is developed in this paper. The central assumption used in this modeling is that the space-time statistics associated with the formation, convection, and interaction of turbulent spots in a naturally occurring boundary-layer transition are independent of the space-time statistics of the wall-pressure fluctuations that are induced by the turbulence in the individual spots. Space-time correlations for the spots were determined experimen

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16

Sundermeier, Stephan, Maximilian Passmann, Stefan aus der aus der Wiesche, and Eugeny Y. Kenig. "Flow in Pillow-Plate Channels for High-Speed Turbomachinery Heat Exchangers." International Journal of Turbomachinery, Propulsion and Power 7, no. 2 (2022): 12. http://dx.doi.org/10.3390/ijtpp7020012.

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In numerous turbomachinery applications, e.g., in aero-engines with regenerators for improving specific fuel consumption (SFC), heat exchangers with low-pressure loss are required. Pil low-plate heat exchangers (PPHE) are a novel exchanger type and promising candidates for high-speed flow applications due to their smooth profiles avoiding blunt obstacles in the flow path. This work deals with the overall system behavior and gas dynamics of pillow-plate channels. A pillow-plate channel was placed in the test section of a blow-down wind tunnel working with dry air, and compressible flow phenomen

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17

Wu, Zhaoyu, Mingsong Ding, Weizhong Dong, Tiesuo Gao, and Tao Jiang. "Effect of MHD Control on Turbulent Boundary Layer Separation Flow in Scramjet Inlet." Journal of Physics: Conference Series 2381, no. 1 (2022): 012015. http://dx.doi.org/10.1088/1742-6596/2381/1/012015.

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Abstract In order to study the effect of MHD control on the separation flow of turbulent boundary layer in the scramjet inlet based on the assumption of low magnetic Reynolds number, considering the source term of turbulent electromagnetic dissipation, the numerical simulation method is developed for electromagnetic field coupled with flow field. A Mach 4 plate is adopted as the basic configuration to assess the accuracy of the solver’s source term of turbulent electromagnetic dissipation. On this basis, numerical simulation of MHD control on the separation flow of boundary layer in scramjet i

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18

Barrios-Piña, Hector, Stéphane Viazzo, and Claude Rey. "Total energy balance in a natural convection flow." International Journal of Numerical Methods for Heat & Fluid Flow 27, no. 8 (2017): 1735–47. http://dx.doi.org/10.1108/hff-03-2016-0093.

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Purpose The purpose of this paper is to show a thermodynamic analysis to determine the contribution of each term of the total energy balance. Design/methodology/approach The thermodynamic analysis comprises a number of numerical simulations where some terms, typically ignored by the commonly used approximations, are removed from the total energy equation to quantify the effects in the flow and heat transfer fields. The case study is the differentially heated square cavity flow, in which the effects of work done by the pressure forces contribute significantly to the energy balance. Because loca

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19

Chen, Kang Ping, and Di Shen. "Drainage flow of a viscous compressible fluid from a small capillary with a sealed end." Journal of Fluid Mechanics 839 (February 2, 2018): 621–43. http://dx.doi.org/10.1017/jfm.2018.56.

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Volumetric expansion driven drainage flow of a viscous compressible fluid from a small capillary with a sealed end is studied in the low Mach number limit using the linearized compressible Navier–Stokes equations with no-slip condition. Density relaxation, oscillation and decay as well as the velocity field are investigated in detail. It is shown that fluid drainage is controlled by the slow decay of the standing acoustic wave inside the capillary; and the acoustic wave retards the density diffusion by reducing the diffusion coefficient of the density envelope equation by one half. Remarkably

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20

Polifke, W., A. Fischer, and T. Sattelmayer. "Instability of a Premix Burner With Nonmonotonic Pressure Drop Characteristic." Journal of Engineering for Gas Turbines and Power 125, no. 1 (2002): 20–27. http://dx.doi.org/10.1115/1.1519267.

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Instabilities in combustion systems have frequently been reported to occur when slight changes in operating conditions lead to significant and abrupt changes in flame shape or flame position, i.e., changes in the mode of flame stabilization. The present paper offers an explanation and mathematical model of this observation. The analysis rests on the assumption that changes in the mode of flame stabilization are accompanied by a significant variation of the pressure drop across burner and flame, such that the pressure drop-flow rate characteristic locally displays a negative slope. In the limit

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21

Guicking, L., K. H. Glassmeier, H. U. Auster, et al. "Low-frequency magnetic field fluctuations in Venus' solar wind interaction region: Venus Express observations." Annales Geophysicae 28, no. 4 (2010): 951–67. http://dx.doi.org/10.5194/angeo-28-951-2010.

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Abstract. We investigate wave properties of low-frequency magnetic field fluctuations in Venus' solar wind interaction region based on the measurements made on board the Venus Express spacecraft. The orbit geometry is very suitable to investigate the fluctuations in Venus' low-altitude magnetosheath and mid-magnetotail and provides an opportunity for a comparative study of low-frequency waves at Venus and Mars. The spatial distributions of the wave properties, in particular in the dayside and nightside magnetosheath as well as in the tail and mantle region, are similar to observations at Mars.

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22

Oliveira, T. F., R. B. Miserda, and F. R. Cunha. "Dynamical Simulation and Statistical Analysis of Velocity Fluctuations of a Turbulent Flow behind a Cube." Mathematical Problems in Engineering 2007 (2007): 1–28. http://dx.doi.org/10.1155/2007/24627.

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A statistical approach for the treatment of turbulence data generated by computer simulations is presented. A model for compressible flows at large Reynolds numbers and low Mach numbers is used for simulating a backward-facing step airflow. A scaling analysis has justified the commonly used assumption that the internal energy transport due to turbulent velocity fluctuations and the work done by the pressure field are the only relevant mechanisms needed to model subgrid-scale flows. From the numerical simulations, the temporal series of velocities are collected for ten different positions in th

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23

Gao, Yuan, Liuming Yang, Yang Yu, Guoxiang Hou, and Zhongbao Hou. "Improved simplified and highly stable lattice Boltzmann methods for incompressible flows." International Journal of Modern Physics C 32, no. 06 (2021): 2150077. http://dx.doi.org/10.1142/s0129183121500777.

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In this work, improved simplified and highly stable lattice Boltzmann methods (SHSLBMs) are developed for incompressible flows. The SHSLBM is a newly developed scheme within the lattice Boltzmann method (LBM) framework, which utilizes the fractional step technology to resolve the governing equations recovered from lattice Boltzmann equation (LBE) and reconstructs the equations in the Lattice Boltzmann frame. By this treatment, the SHSLBM directly tracks the macroscopic variables in the evolution process rather than the distribution functions of each grid node, which greatly saves virtual memor

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24

Bra¨unling, W., and F. Lehthaus. "Investigations of the Effect of Annulus Taper on Transonic Turbine Cascade Flow." Journal of Engineering for Gas Turbines and Power 108, no. 2 (1986): 285–92. http://dx.doi.org/10.1115/1.3239901.

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In a test facility for rotating annular cascades with three conical test sections of different taper angles (0, 30, 45 deg), experiments are conducted for two geometrically different turbine cascade configurations, a hub section cascade with high deflection and a tip section cascade with low deflection. The evaluation of time-averaged data derived from conventional probe measurements upstream and downstream of the test wheel in the machine-fixed absolute system is based on the assumption of axisymmetric stream surfaces. The cascade characteristics, i.e., mass flow, deflection, and losses, for

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25

Fossi, Alain, and Alain DeChamplain. "Large eddy simulation of spark ignition of a bluff-body stabilized burner using a subgrid-ignition model coupled with FGM-based combustion models." International Journal of Numerical Methods for Heat & Fluid Flow 27, no. 2 (2017): 400–427. http://dx.doi.org/10.1108/hff-07-2015-0299.

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Purpose Safety improvement and pollutant reduction in many practical combustion systems and especially in aero-gas turbine engines require an adequate understanding of flame ignition and stabilization mechanisms. Improved software and hardware have opened up greater possibilities for translating basic knowledge and the results of experiments into better designs. The present study deals with the large eddy simulation (LES) of an ignition sequence in a conical shaped bluff-body stabilized burner involving a turbulent non-premixed flame. The purpose of this paper is to investigate the impact of s

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26

van Limbeek, Michiel A. J., Martin H. Klein Schaarsberg, Benjamin Sobac, et al. "Leidenfrost drops cooling surfaces: theory and interferometric measurement." Journal of Fluid Mechanics 827 (August 29, 2017): 614–39. http://dx.doi.org/10.1017/jfm.2017.425.

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When a liquid drop is placed on a highly superheated surface, it can be levitated by its own vapour. This remarkable phenomenon is referred to as the Leidenfrost effect. The thermally insulating vapour film results in a severe reduction of the heat transfer rate compared to experiments at lower surface temperatures, where the drop is in direct contact with the solid surface. A commonly made assumption is that this solid surface is isothermal, which is at least questionable for materials of low thermal conductivity, resulting in an overestimation of the surface temperature and heat transfer for

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27

Stevens, Robin, Andrei Ryjkov, Mahtab Majdzadeh, and Ashu Dastoor. "An improved representation of aerosol mixing state for air quality–weather interactions." Atmospheric Chemistry and Physics 22, no. 20 (2022): 13527–49. http://dx.doi.org/10.5194/acp-22-13527-2022.

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Abstract. We implement a detailed representation of aerosol mixing state in the Global Environmental Multiscale – Modelling Air quality and CHemistry (GEM-MACH) air quality and weather forecast model. Our mixing-state representation includes three categories: one for more hygroscopic aerosol, one for less hygroscopic aerosol with a high black carbon (BC) mass fraction, and one for less hygroscopic aerosol with a low BC mass fraction. The more detailed representation allows us to better resolve two different aspects of aerosol mixing state: differences in hygroscopicity due to aerosol compositi

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28

Bradley, M. T., and K. I. Klohn. "Machiavellianism, the Control Question Test and the Detection of Deception." Perceptual and Motor Skills 64, no. 3 (1987): 747–57. http://dx.doi.org/10.2466/pms.1987.64.3.747.

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Individuals, differing in levels of Machiavellianism, were involved in a mock crime psychophysiological detection of deception study. It was hypothesized that those scoring high on Machiavellianism would perceive detection results as more accurately reflecting their actual guilt or innocence, especially under conditions of high arousal, than those with low scores. The hypothesis was based on assumptions that subjects must appropriately discriminate amongst crime-relevant and irrelevant questions, that this discrimination is moderately difficult with Control Question Tests, and that high-Mach s

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29

GEDALIN, M., and M. BALIKHIN. "Rankine–Hugoniot relations for shocks with demagnetized ions." Journal of Plasma Physics 74, no. 2 (2008): 207–14. http://dx.doi.org/10.1017/s0022377807006708.

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AbstractThe width of a quasi-perpendicular collisionless shock front is smaller than the convective ion gyroradius so that ions become demagnetized in the ramp. An approach is proposed for derivation of approximate expressions for the magnetic compression ratio and cross-shock potential from the analysis of the ion motion across the ramp and pressure balance condition, without making assumptions about the ion equation of state. The cross-shock potential and magnetic compression ratio are found as functions of the Mach number for low-Mach-number perpendicular shocks.

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Hientzsch, Lars Eric. "On the low Mach number limit for 2D Navier–Stokes–Korteweg systems." Mathematics in Engineering 5, no. 2 (2022): 1–26. http://dx.doi.org/10.3934/mine.2023023.

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<abstract><p>This paper addresses the low Mach number limit for two-dimensional Navier–Stokes–Korteweg systems. The primary purpose is to investigate the relevance of the capillarity tensor for the analysis. For the sake of a concise exposition, our considerations focus on the case of the quantum Navier-Stokes (QNS) equations. An outline for a subsequent generalization to general viscosity and capillarity tensors is provided. Our main result proves the convergence of finite energy weak solutions of QNS to the unique Leray-Hopf weak solutions of the incompressible Navier-Stokes equa

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31

Farhad, Abu Baker Mohammad, and Abul Kalam Azad. "Power law inflation with a varying condstant of gravitation and Brans-Dicke cosmology." GANIT: Journal of Bangladesh Mathematical Society 31 (April 9, 2012): 23–32. http://dx.doi.org/10.3329/ganit.v31i0.10305.

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The homogeneous and isotropic Brans-Dicke cosmological solutions satisfying Whitrow Randalls[18] relation which have been discussed recently by Berman and Som[2] are re-examined. We extend their results and present the most general solution by solving a differential equation completely. We show that Machs assumption leads to power-law solutions in the Euclidean case.DOI: http://dx.doi.org/10.3329/ganit.v31i0.10305GANIT J. Bangladesh Math. Soc. (ISSN 1606-3694) 31 (2011) 23-32

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Luo, Zhengyan, Lintao Ma, and Yinghui Zhang. "Optimal decay rates of higher–order derivatives of solutions for the compressible nematic liquid crystal flows in $ \mathbb R^3 $." AIMS Mathematics 7, no. 4 (2022): 6234–58. http://dx.doi.org/10.3934/math.2022347.

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<abstract><p>In this paper, we are concerned with optimal decay rates of higher–order derivatives of the smooth solutions to the $ 3D $ compressible nematic liquid crystal flows. The main novelty of this paper is three–fold: First, under the assumptions that the initial perturbation is small in $ H^N $–norm $ (N\geq3) $ and bounded in $ L^1 $–norm, we show that the highest–order spatial derivatives of density and velocity converge to zero at the $ L^2 $–rates is $ (1+t)^{-\frac{3}{4}-\frac{N }{2 }} $, which are the same as ones of the heat equation, and particularly faster than the

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GRAZIOSI, PAOLO, and GARRY L. BROWN. "Experiments on stability and transition at Mach 3." Journal of Fluid Mechanics 472 (November 30, 2002): 83–124. http://dx.doi.org/10.1017/s0022112002002094.

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The results of an experimental study of stability, receptivity and transition of the flat-plate laminar boundary layer at Mach 3 are discussed. With a relatively low free-stream disturbance level (∼0.1%), spectra, growth rates and amplitude distributions of naturally occurring boundary layer waves were measured using hot wires. Physical (mass-flux) amplitudes in the boundary layer and free stream are reported and provide stability and receptivity results against which predictions can be directly compared. Comparisons are made between measurements of growth rates of unstable high-frequency wave

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34

Chirinko, Robert S., and Debdulal Mallick. "The Substitution Elasticity, Factor Shares, and the Low-Frequency Panel Model." American Economic Journal: Macroeconomics 9, no. 4 (2017): 225–53. http://dx.doi.org/10.1257/mac.20140302.

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The value of the elasticity of substitution between labor and capital (σ) is a crucial assumption in understanding the secular decline in the labor share of income. This paper develops and implements a new strategy for estimating this crucial parameter by combining a low-pass filter with panel data to identify the low-frequency/long-run relations appropriate to production function estimation. Standard estimation methods, which do not filter out transitory variation, generate downwardly biased estimates of 40 percent to 70 percent relative to the benchmark value. Despite correcting for this bia

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HALLERÖD, BJÖRN. "Sour Grapes: Relative Deprivation, Adaptive Preferences and the Measurement of Poverty." Journal of Social Policy 35, no. 3 (2006): 371–90. http://dx.doi.org/10.1017/s0047279406009834.

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One frequently used direct measure of deprivation and poverty is the objective relative deprivation index (O-RDindex), developed by Mack and Lansley (1985). One assumption underlying the O-RDindex is that respondents can distinguish between what that they cannot afford and what they do not want. This assumption contradicts the subjective usage of the concept relative deprivation (S-RD), which suggests a connection between economic circumstances, choice of reference group and consumption preferences.The present analysis supports the S-RD assumptions. People with limited access to economic resou

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Sansica, A., J. Ch Robinet, F. Alizard, and E. Goncalves. "Three-dimensional instability of a flow past a sphere: Mach evolution of the regular and Hopf bifurcations." Journal of Fluid Mechanics 855 (September 24, 2018): 1088–115. http://dx.doi.org/10.1017/jfm.2018.664.

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A fully three-dimensional linear stability analysis is carried out to investigate the unstable bifurcations of a compressible viscous fluid past a sphere. A time-stepper technique is used to compute both equilibrium states and leading eigenmodes. In agreement with previous studies, the numerical results reveal a regular bifurcation under the action of a steady mode and a supercritical Hopf bifurcation that causes the onset of unsteadiness but also illustrate the limitations of previous linear approaches, based on parallel and axisymmetric base flow assumptions, or weakly nonlinear theories. Th

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Zhou, Zhiteng, Yi Liu, Hongping Wang, and Shizhao Wang. "Mass-Conserved Solution to the Ffowcs-Williams and Hawkings Equation for Compact Source Regions." Aerospace 10, no. 2 (2023): 148. http://dx.doi.org/10.3390/aerospace10020148.

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A mass-conserved formulation for the Ffowcs-Williams–Hawkings (FW–H) integral is proposed to suppress contributions of spurious mass flux to the far-field sound at very low Mach numbers. The far-field condition and compact-source region assumptions are employed. By using higher-order derivatives of Green’s function, an expansion of the integrand in the monopole term is performed. This expansion transforms the mass-flux like monopole term into a series including different orders of velocity moment. At very low Mach numbers, the zero-order term is exactly the contribution from the spurious mass

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Ganguli, Swetava, and Sanjiva K. Lele. "Drag of a heated sphere at low Reynolds numbers in the absence of buoyancy." Journal of Fluid Mechanics 869 (April 23, 2019): 264–91. http://dx.doi.org/10.1017/jfm.2019.187.

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Fully resolved simulations are used to quantify the effects of heat transfer in the absence of buoyancy on the drag of a spatially fixed heated spherical particle at low Reynolds numbers ($Re$) in the range $10^{-3}\leqslant Re\leqslant 10$ in a variable-property fluid. The case where buoyancy is present is analysed in a subsequent paper. This analysis is carried out without making any assumptions on the amount of heat addition from the sphere and thus encompasses both the heating regime where the Boussinesq approximation holds and the regime where it breaks down. The particle is assumed to ha

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Peña Balderrama, Jenny, Thomas Alfstad, Constantinos Taliotis, Mohammad Hesamzadeh, and Mark Howells. "A Sketch of Bolivia’s Potential Low-Carbon Power System Configurations. The Case of Applying Carbon Taxation and Lowering Financing Costs." Energies 11, no. 10 (2018): 2738. http://dx.doi.org/10.3390/en11102738.

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This paper considers hypothetical options for the transformation of the Bolivian power generation system to one that emits less carbon dioxide. Specifically, it evaluates the influence of the weighted average cost of capital (WACC) on marginal abatement cost curves (MACC) when applying carbon taxation to the power sector. The study is illustrated with a bottom-up least-cost optimization model. Projections of key parameters influence the shape of MACCs and the underlying technology configurations. These are reported. Results from our study (and the set of assumptions on which they are based) ar

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Steinke, Robert. "Walther, Reinmar, and Biographism in the Second Degree: A Text-Centered Interpretation of Walther von der Vogelweide's Obituary of Reinmar Walther, Reinmar und der Biographismus auf zweiter Stufe: Eine textfokussierte Interpretation des Reinmar-Nachrufs Walthers von der Vogelweide." Zeitschrift fuer deutsches Altertum und Literatur 149, no. 1 (2020): 22–42. http://dx.doi.org/10.3813/zfda-2020-0002.

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Most critics have seen the remarks of Walther von der Vogelweide on the death of his colleague Reinmar as an expression of a private quarrel between both singers. The contrast between the obituary's emphatic praise of Reinmar's singing on the one hand and apparent personal disparagement on the other is usually regarded either as a result of interpersonal conflicts or, alternatively, as a rhetorical means to even intensify the praise of Reinmar's art. This article wants to demonstrate that the assumption of a personal struggle between Walther and Reinmar is based on a biographistic circular arg

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Xu, Mingzhou. "Complete convergence and complete moment convergence for maximal weighted sums of extended negatively dependent random variables under sub-linear expectations." AIMS Mathematics 8, no. 8 (2023): 19442–60. http://dx.doi.org/10.3934/math.2023992.

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<abstract><p>In this article, we study the complete convergence and complete moment convergence for maximal weighted sums of extended negatively dependent random variables under sub-linear expectations. We also give some sufficient assumptions for the convergence. Moreover, we get the Marcinkiewicz-Zygmund type strong law of large numbers for weighted sums of extended negatively dependent random variables. The results obtained in this paper generalize the relevant ones in probability space.</p></abstract>

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Huang, Haiwu, Yuan Yuan, and Hongguo Zeng. "An extension on the rate of complete moment convergence for weighted sums of weakly dependent random variables." AIMS Mathematics 8, no. 1 (2022): 622–32. http://dx.doi.org/10.3934/math.2023029.

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<abstract><p>The authors study the convergence rate of complete moment convergence for weighted sums of weakly dependent random variables without assumptions of identical distribution. Under the moment condition of $ E{{{\left| X \right|}^{\alpha }}}/{{{\left(\log \left(1+\left| X \right| \right) \right)}^{\alpha /\gamma -1}}}\; &lt; \infty $ for $ 0 &lt; \gamma &lt; \alpha $ with $ 1 &lt; \alpha \le 2 $, we establish the complete $ \alpha $-th moment convergence theorem for weighted sums of weakly dependent cases, which improves and extends the related known result

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Tang, Shuqi, and Chunhua Li. "Decay estimates for Schrödinger systems with time-dependent potentials in 2D." AIMS Mathematics 8, no. 8 (2023): 19656–76. http://dx.doi.org/10.3934/math.20231002.

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<abstract><p>We consider the Cauchy problem for systems of nonlinear Schrödinger equations with time-dependent potentials in 2D. Under assumptions about mass resonances and potentials, we prove the global existence of the nonlinear Schrödinger systems with small initial data. In particular, by analyzing the operator $ \Delta $ and time-dependent potentials $ {V_{j}} $ separately, we show that the small global solutions satisfy time decay estimates of order $ O((t\log{t})^{-1}) $ when $ p = 2 $, and the small global solutions satisfy time decay estimates of order $ O({t}^{-1}) $ whe

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Amiet, R. K. "Airfoil leading-edge suction and energy conservation for compressible flow." Journal of Fluid Mechanics 289 (April 25, 1995): 227–42. http://dx.doi.org/10.1017/s0022112095001315.

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When a flat-plate airfoil at zero angle of attack encounters a vertical gust in an otherwise uniform flow, it experiences a force along the chord. This leading-edge suction force is examined for compressible flow with a time-dependent gust. A simple derivation of the thrust force is based on the fact that the leading edge is a singular point so that the flow here is dominated by the leading-edge dipole strength. From the viewpoint of a fluid-fixed observer the fluid does work on the airfoil, and this energy must come from the incident gust. Demonstrating energy conservation is not surprising,

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Commault, Jeanne. "Does Consumption Respond to Transitory Shocks? Reconciling Natural Experiments and Semistructural Methods." American Economic Journal: Macroeconomics 14, no. 2 (2022): 96–122. http://dx.doi.org/10.1257/mac.20190296.

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Studies based on natural experiments find that consumption responds strongly and significantly to a transitory variation in income, while semistructural estimations find no pass-through of transitory shocks to consumption. I develop a more robust semistructural estimator that relaxes the assumption that log consumption is a random walk. The robust pass-through estimate is significant and large, implying a yearly marginal propensity to consume of 0.32, close to the natural experiment findings. The robust estimator performs well in numerical simulations of a life cycle model, while nonrobust est

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Nan, Jiaqi, Jingxuan Li, and Lijun Yang. "Three-Dimensional Analytical Solutions for Acoustic Transverse Modes in a Cylindrical Duct with Axial Temperature Gradient and Non-Zero Mach Number." Aerospace 9, no. 10 (2022): 588. http://dx.doi.org/10.3390/aerospace9100588.

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Cylindrical ducts with axial mean temperature gradient and mean flows are typical elements in rocket engines, can combustors, and afterburners. Accurate analytical solutions for the acoustic waves of the longitudinal and transverse modes within these ducts can significantly improve the performance of low order acoustic network models for analyses of acoustic behaviours and combustion instabilities in these kinds of ducts. Here, we derive an acoustic wave equation as a function of pressure perturbation based on the linearised Euler equations (LEEs), and the modified WKB approximation method is

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Cheng, Yuanyuan, and Yuan Li. "A novel event-triggered constrained control for nonlinear discrete-time systems." AIMS Mathematics 8, no. 9 (2023): 20530–45. http://dx.doi.org/10.3934/math.20231046.

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<abstract><p>In this paper, a novel event-triggered optimal control method is developed for nonlinear discrete-time systems with constrained inputs. First, a non-quadratic utility function is constructed to overcome the challenge caused by saturating actuators. Second, a novel triggering condition is designed to reduce computational burden. Difference from other triggering conditions, fewer assumptions are required to guarantee asymptotic stability. Then, the optimal cost function and control law are obtained by constructing the action-critic network. Convergence analysis of the sy

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Kafkas, Angelos, and George Lampeas. "Static Aeroelasticity Using High Fidelity Aerodynamics in a Staggered Coupled and ROM Scheme." Aerospace 7, no. 11 (2020): 164. http://dx.doi.org/10.3390/aerospace7110164.

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Current technology in evaluating the aeroelastic behavior of aerospace structures is based on the staggered coupling between structural and low fidelity linearized aerodynamic solvers, which has inherent limitations, although tried and trusted outside the transonic region. These limitations arise from the assumptions in the formulation of linearized aerodynamics and the lower fidelity in the description of the flowfield surrounding the structure. The validity of low fidelity aerodynamics also degrades fast with the deviation from a typical aerodynamic shape due to the inclusion of various cont

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Lu, Guanghui, та Shuangping Tao. "Commutators of Littlewood-Paley gκ∗ $g_{\kappa}^{*} $-functions on non-homogeneous metric measure spaces". Open Mathematics 15, № 1 (2017): 1283–99. http://dx.doi.org/10.1515/math-2017-0110.

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Abstract The main purpose of this paper is to prove that the boundedness of the commutator $\mathcal{M}_{\kappa,b}^{*} $ generated by the Littlewood-Paley operator $\mathcal{M}_{\kappa}^{*} $ and RBMO (μ) function on non-homogeneous metric measure spaces satisfying the upper doubling and the geometrically doubling conditions. Under the assumption that the kernel of $\mathcal{M}_{\kappa}^{*} $ satisfies a certain Hörmander-type condition, the authors prove that $\mathcal{M}_{\kappa,b}^{*} $ is bounded on Lebesgue spaces Lp(μ) for 1 < p < ∞, bounded from the space L log L(μ) to the weak Le

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Grubin, S. E., and V. N. Trigub. "The asymptotic theory of hypersonic boundary-layer stability." Journal of Fluid Mechanics 246 (January 1993): 361–80. http://dx.doi.org/10.1017/s0022112093000175.

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In this paper the linear stability of the hypersonic boundary layer is considered in the local-parallel approximation. It is assumed that the Prandtl-number ½ < σ < 1 and the viscosity-temperature law is a power function: μ/μ∞ = (T/T∞)ω. The asymptotic theory in the limit M∞ → ∞ is developed.Smith & Brown found for the Blasius base flow and Balsa & Goldstein for the mixing layer that, in this limit, the disturbances of the vorticity mode are located in the thin region between the boundary layer and the external flow. The gas model with σ = 1, ω = 1 was exploited in these studies.

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