scholarly journals 3D simulations of internal gravity waves in solar-like stars

2013 ◽  
Vol 9 (S301) ◽  
pp. 375-376
Author(s):  
Lucie Alvan ◽  
Allan Sacha Brun ◽  
Stéphane Mathis
Keyword(s):  
Numerical Simulations ◽  
Gravity Waves ◽  
Rotation Rate ◽  
Spherical Harmonic ◽  
Internal Gravity Waves ◽  
3D Simulations ◽  
Frequency Splitting ◽  
Theoretical Predictions ◽  
First Time ◽  
Good Agreement

AbstractWe perform numerical simulations of the whole Sun using the 3D anelastic spherical harmonic (ASH) code. In such models, the radiative and convective zones are non-linearly coupled and in the radiative interior a wave-like pattern is observed. For the first time, we are thus able to model in 3D the excitation and propagation of internal gravity waves (IGWs) in a solar-like star's radiative zone. We compare the properties of our waves to theoretical predictions and results of oscillation calculations. The obtained good agreement allows us to validate the consistency of our approach and to study the characteristics of IGWs. We find that a wave's spectrum is excited up to radial order n=58. This spectrum evolves with depth and time; we show that the lifetime of the highest-frequency modes must be greater than 550 days. We also test the sensitivity of waves to rotation and are able to retrieve the rotation rate to within 5% error by measuring the frequency splitting.

scholarly journals THE NUCLEAR SPIN RESONANCE SPECTRUM OF Al27 IN SPODUMENE

1958 ◽  
Vol 36 (10) ◽  
pp. 1295-1307 ◽  
Author(s):  
L. B. Robinson
Keyword(s):  
Nuclear Spin ◽  
Resonance Spectrum ◽  
Companion Paper ◽  
Quadrupole Interactions ◽  
Resonance Frequencies ◽  
Spin Resonance ◽  
Theoretical Predictions ◽  
Induction Type ◽  
First Time ◽  
Good Agreement

An experimental study has been made of the nuclear spin resonance spectrum of Al27 in a single crystal of spodumene (LiAl(SiO3)2) over a range of external magnetic field H0 wide enough [Formula: see text] to bridge for the first time the gap between pure quadrupole spectra (R = 0) and Zeeman spectra slightly perturbed by quadrupole interactions [Formula: see text]. Experimental results on the resonance frequencies and relative signal amplitudes obtained with an induction type of nuclear resonance spectrometer are described, and are found to be in good agreement with the theoretical predictions given in the preceding companion paper.

scholarly journals A theoretical analysis of the semileptonic decays $$\eta ^{(\prime )}\rightarrow \pi ^0l^+l^-$$ and $$\eta ^\prime \rightarrow \eta l^+l^-$$

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
Rafel Escribano ◽  
Emilio Royo
Keyword(s):  
Theoretical Analysis ◽  
Semileptonic Decays ◽  
Coupling Constants ◽  
Energy Spectra ◽  
Radiative Decays ◽  
Vector Meson Dominance ◽  
Decay Widths ◽  
Theoretical Predictions ◽  
First Time ◽  
Good Agreement

AbstractA complete theoretical analysis of the C- conserving semileptonic decays $$\eta ^{(\prime )}\rightarrow \pi ^0l^+l^-$$ η ( ′ ) → π 0 l + l - and $$\eta ^\prime \rightarrow \eta l^+l^-$$ η ′ → η l + l - ($$l=e$$ l = e or $$\mu $$ μ ) is carried out within the framework of the Vector Meson Dominance (VMD) model. An existing phenomenological model is used to parametrise the VMD coupling constants and the associated numerical values are obtained from an optimisation fit to $$V\rightarrow P\gamma $$ V → P γ and $$P\rightarrow V\gamma $$ P → V γ radiative decays ($$V=\rho ^0$$ V = ρ 0 , $$\omega $$ ω , $$\phi $$ ϕ and $$P=\pi ^0$$ P = π 0 , $$\eta $$ η , $$\eta ^{\prime }$$ η ′ ). The decay widths and dilepton energy spectra for the two $$\eta \rightarrow \pi ^0l^+l^-$$ η → π 0 l + l - processes obtained using this approach are compared and found to be in good agreement with other results available in the published literature. Theoretical predictions for the four $$\eta ^{\prime }\rightarrow \pi ^0l^+l^-$$ η ′ → π 0 l + l - and $$\eta ^\prime \rightarrow \eta l^+l^-$$ η ′ → η l + l - decay widths and dilepton energy spectra are calculated and presented for the first time in this work.

scholarly journals Direct numerical simulations of an inertial wave attractor in linear and nonlinear regimes

2014 ◽  
Vol 745 ◽  
pp. 223-250 ◽  
Author(s):  
Laurène Jouve ◽  
Gordon I. Ogilvie
Keyword(s):  
Numerical Simulations ◽  
Gravity Waves ◽  
Dissipation Rate ◽  
Laboratory Experiments ◽  
Rotation Axis ◽  
Internal Gravity Waves ◽  
Direct Numerical Simulations ◽  
Inertial Wave ◽  
Linear And Nonlinear ◽  
Nonlinear Regimes

AbstractIn a uniformly rotating fluid, inertial waves propagate along rays that are inclined to the rotation axis by an angle that depends on the wave frequency. In closed domains, multiple reflections from the boundaries may cause inertial waves to focus onto particular structures known as wave attractors. These attractors are likely to appear in fluid containers with at least one boundary that is neither parallel nor normal to the rotation axis. A closely related process also applies to internal gravity waves in a stably stratified fluid. Such structures have previously been studied from a theoretical point of view, in laboratory experiments, in linear numerical calculations and in some recent numerical simulations. In the present paper, two-dimensional direct numerical simulations of an inertial wave attractor are presented. By varying the amplitude at which the system is forced periodically, we are able to describe the transition between the linear and nonlinear regimes as well as the characteristic properties of the two situations. In the linear regime, we first recover the results of the linear calculations and asymptotic theory of Ogilvie (J. Fluid Mech., vol. 543, 2005, pp. 19–44) who considered a prototypical problem involving the focusing of linear internal waves into a narrow beam centred on a wave attractor in a steady state. The velocity profile of the beam and its scalings with the Ekman number, as well as the asymptotic value of the dissipation rate, are found to be in agreement with the linear theory. We also find that, as the beam builds up around the wave attractor, the power input by the applied force reaches its limiting value more rapidly than the dissipation rate, which saturates only when the beam has reached its final thickness. In the nonlinear regime, the beam is strongly affected and becomes unstable to a subharmonic instability. This instability transfers energy to secondary waves possessing shorter wavelengths and lower frequencies. The onset of the instability of a narrow inertial wave beam is investigated by means of a separate linear analysis and the results, such as the onset of the instability, are found to be consistent with the global simulations of the wave attractor. The excitation of such secondary waves described theoretically in this work has also been seen in recent laboratory experiments on internal gravity waves.

Ratchet mechanism of drops climbing a vibrated oblique plate

2017 ◽  
Vol 835 ◽  
Author(s):  
Hang Ding ◽  
Xi Zhu ◽  
Peng Gao ◽  
Xi-Yun Lu
Keyword(s):  
Contact Angle ◽  
Theoretical Analysis ◽  
Numerical Simulations ◽  
Contact Angle Hysteresis ◽  
Three Dimensional ◽  
Direct Numerical Simulations ◽  
Ratchet Mechanism ◽  
Wetted Area ◽  
First Time ◽  
Good Agreement

In this paper, we investigate the ratchet mechanism of drops climbing a vibrated oblique plate based on three-dimensional direct numerical simulations, which for the first time reproduce the existing experiment (Brunet et al., Phys. Rev. Lett., vol. 99, 2007, 144501). With the help of numerical simulations, we identify an interesting and important wetting behaviour of the climbing drop; that is, the breaking of symmetry due to the inclination of the plate with respect to the acceleration leads to a hysteresis of the wetted area in one period of harmonic vibration. In particular, the average wetted area in the downhill stage is larger than that in the uphill stage, which is found to be responsible for the uphill net motion of the drop. A new hydrodynamic model is proposed to interpret the ratchet mechanism, taking account of the effects of the acceleration and contact angle hysteresis. The predictions of the theoretical analysis are in good agreement with the numerical results.

On the role of density jumps in the reflexion and breaking of internal gravity waves

1975 ◽  
Vol 69 (3) ◽  
pp. 445-464 ◽  
Author(s):  
Donald P. Delisi ◽  
Isidoro Orlanski
Keyword(s):  
Gravity Waves ◽  
Gravitational Instability ◽  
Internal Gravity Waves ◽  
Basic Flow ◽  
Density Jump ◽  
Critical Amplitude ◽  
Horizontal Advection ◽  
Reflected Wave ◽  
Good Agreement

A laboratory experiment is presented which examines the role of density jumps in the reflexion and breaking of internal gravity waves. It is found that the measured phase shift of the reflected wave and the measured amplitude of the density jump are in good agreement with linear theory. Local overturning occurs when wave amplitude becomes large, and there appears to be a critical amplitude above which overturning will occur and below which it will not. The overturning seems to be due to local gravitational instability, caused by the horizontal advection of density. Overturning changes the basic flow field in the region of interaction; and it results in smaller-scale motions.

scholarly journals THE INFLUENCE OF THE MASS DISTRIBUTION OF STELLAR OBJECTS ON THEIR GRAVITATIONAL FIELDS

2020 ◽  
Vol 56 (2) ◽  
pp. 201-216
Author(s):  
V. A. Stephanovich ◽  
W. Godłowski ◽  
M. Biernacka ◽  
B. Mrzygłód
Keyword(s):  
Numerical Simulations ◽  
Mass Distribution ◽  
Stellar Objects ◽  
Gravitational Fields ◽  
Mass Distributions ◽  
Angular Momenta ◽  
Cluster Morphology ◽  
Theoretical Predictions ◽  
Non Gaussian ◽  
Good Agreement

We study the influence of the mass randomness of astronomical objects on the distribution function of their gravitational fields. Based on purely theoretical arguments and on a comparison with extensive data collected from observations and numerical simulations, we show that while mass randomness does not alter the non-Gaussian character of the gravitational field distribution, it does changes the dependencies of mean angular momenta of galaxies and clusters on their richness. The specific form of such dependencies is determined by the interplay of the character of the mass distributions and different assumptions about cluster morphology. We trace the influence of the mass distribution on the time evolution of the angular momenta of stellar objects in CDM and ΛCDM models. Our theoretical predictions are in very good agreement with the statistical results derived both from observational data and numerical simulations.

On the shape of progressive internal waves

1968 ◽  
Vol 263 (1145) ◽  
pp. 563-614 ◽  
Keyword(s):  
Experimental Evidence ◽  
Internal Waves ◽  
Gravity Waves ◽  
Boussinesq Approximation ◽  
Internal Gravity Waves ◽  
Finite Amplitude ◽  
Fluid System ◽  
Expansion Technique ◽  
Theoretical Predictions ◽  
Two Fluid

An expansion technique, analogous to that of Stokes in the study of surface waves, is used to investigate the effects of finite amplitude on a progressive train of internal gravity waves. The paper is divided into two main parts, a study of interfacial waves in a two-fluid system and an examination of internal waves in a continuously stratified fluid. Experimental evidence is presented which confirms some of the theoretical predictions. The validity of the Boussinesq approximation is examined and particular examples are taken to illustrate the general results.

scholarly journals Photometric detection of internal gravity waves in upper main-sequence stars

2019 ◽  
Vol 621 ◽  
pp. A135 ◽  
Author(s):  
D. M. Bowman ◽  
C. Aerts ◽  
C. Johnston ◽  
M. G. Pedersen ◽  
T. M. Rogers ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Gravity Waves ◽  
Main Sequence ◽  
Low Frequency ◽  
Internal Gravity Waves ◽  
Main Sequence Stars ◽  
Photometric Detection ◽  
F Stars ◽  
Low Frequency Power ◽  
Frequency Power

Context. Main sequence stars with a convective core are predicted to stochastically excite internal gravity waves (IGWs), which effectively transport angular momentum throughout the stellar interior and explain the observed near-uniform interior rotation rates of intermediate-mass stars. However, there are few detections of IGWs, and fewer still made using photometry, with more detections needed to constrain numerical simulations. Aims. We aim to formalise the detection and characterisation of IGWs in photometric observations of stars born with convective cores (M ≳ 1.5 M⊙) and parameterise the low-frequency power excess caused by IGWs. Methods. Using the most recent CoRoT light curves for a sample of O, B, A and F stars, we parameterised the morphology of the flux contribution of IGWs in Fourier space using an MCMC numerical scheme within a Bayesian framework. We compared this to predictions from IGW numerical simulations and investigated how the observed morphology changes as a function of stellar parameters. Results. We demonstrate that a common morphology for the low-frequency power excess is observed in early-type stars observed by CoRoT. Our study shows that a background frequency-dependent source of astrophysical signal is common, which we interpret as IGWs. We provide constraints on the amplitudes of IGWs and the shape of their detected frequency spectrum across a range of mass, which is the first ensemble study of stochastic variability in such a diverse sample of stars. Conclusions. The evidence of a low-frequency power excess across a wide mass range supports the interpretation of IGWs in photometry of O, B, A and F stars. We also discuss the prospects of observing hundreds of massive stars with the Transiting Exoplanet Survey Satellite (TESS) in the near future.

scholarly journals Cutoff periods of magnetoacoustic waves in the solar atmosphere

2019 ◽  
Vol 623 ◽  
pp. A62 ◽  
Author(s):  
J. Kraśkiewicz ◽  
K. Murawski ◽  
Z. E. Musielak
Keyword(s):  
Numerical Simulations ◽  
Solar Atmosphere ◽  
Realistic Model ◽  
Evanescent Waves ◽  
Wave Period ◽  
Atmospheric Parameters ◽  
Magnetoacoustic Waves ◽  
Theoretical Predictions ◽  
The Waves ◽  
Good Agreement

We perform numerical simulations of magnetoacoustic waves (MAWs) in the solar atmosphere, which is gravitationally stratified and structured by either vertical or horizontal uniform magnetic fields. These waves are excited by a monochromatic driver that operates in the photosphere. We show that the gradients of the atmospheric parameters lead to filtering of the waves through the solar atmosphere and to variations of the dominant wave period with height. We use these variations to determine a local cutoff period, which shows a good agreement with the previously obtained analytical and numerical results in an isothermal solar atmosphere. In our numerical simulations, the propagation of MAWs in a more realistic model of the solar atmosphere is considered, and the obtained results demonstrate that the waves with periods higher than a local cutoff wave period are strongly reflected and become evanescent with height, while the waves with shorter wave periods are propagating, and may even reach the solar corona. Some of the evanescent waves may also tunnel and reach the atmospheric heights that would not be otherwise accessible to them. An important result of our study is excitation of chromospheric oscillations with periods equal to the period that is comparable to the observed solar chromospheric oscillations. Implications of our theoretical predictions are discussed.

Gravity waves on a rough bottom: experimental evidence of one-dimensional localization

1988 ◽  
Vol 186 ◽  
pp. 539-558 ◽  
Author(s):  
Max Belzons ◽  
Elisabeth Guazzelli ◽  
Olivier Parodi
Keyword(s):  
Experimental Evidence ◽  
Gravity Waves ◽  
Finite Size ◽  
Finite Size Effects ◽  
One Dimensional ◽  
Localization Phenomenon ◽  
Resonant Modes ◽  
Theoretical Predictions ◽  
Rough Bed ◽  
First Time

We present experimental evidence of the localization of linear gravity waves on a rough (i.e. random) bottom in a one-dimensional channel. The localization phenomenon is observed through very precise measurements in a wave tank. Viscous dissipation and rough-bed finite-size effects are examined. The experimental estimation of the localization lengths are compared with the theoretical predictions of Devillard, Dunlop & Souillard (1988). Finally, the resonant modes due to the disorder are directly observed for the first time.

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