Zonal jets in the Southern Ocean: a semi-analytical model based on scale separation

A reduced-order semi-analytic model of multiple zonal jets in the Southern Ocean is proposed based on the statistical approach and scale decomposition. By introducing two dominant scales in the vorticity equation, the model describes the large-scale and mesoscale dynamics using the explicit momentum dissipation in the horizontal and vertical directions. For validation and physical insights, the results of the reduced-order model are compared with solutions of two eddy-resolving ocean models: i) a realistic primitive-equation HYCOM (HYbrid Coordinate Ocean Model) simulation of the Southern Ocean and ii) an idealized quasi-geostrophic model of a shear-driven channel flow

Flux-corrected dispersion-improved CABARET schemes for linear and nonlinear wave propagation problems

The new two-time-level dispersion improved CABARET scheme is developed as an upgrade of the original CABARET for improved wave propagation modelling in multiple dimensions and for nonlinear conservation laws including gas dynamics. The new upgrade retains many attractive features of the original CABARET scheme such as shock-capturing and low dissipation. It is simple for implementation in the existing CABARET codes and leads to a greater accuracy for solving linear wave propagation problems. A non-linear version of the dispersion-improved CABARET scheme is introduced to efficiently deal with contact discontinuities and shocks. The properties of the new linear and nonlinear CABARET schemes are analysed for numerical dissipation and dispersion error based on Von Neumann analysis and Pirrozolli's method. Numerical examples for one-dimensional and two-dimensional linear advection, the one-dimensional inviscid Burger's equation, and the isothermal gas dynamics problems in one and two dimensions are presented

Aerofoil broadband and tonal noise modelling using stochastic sound sources and incorporated large scale fluctuations

The work has been supported by BAE Systems Ltd and the Engineering and Physical Sciences Research Council (EPSRC) (1357499). One of the authors is grateful to the Royal Society of London for their continuing support. Computations were performed on the QM cluster ‘Apocrita’. The authors are grateful to Dr Mark Allan for the initial introduction to the BAE Altus solver and fruitful discussions

An investigation of the mechanisms of sound generation in initially laminar subsonic jets using the Goldstein acoustic analogy

This version has been accepted for publication.Published in Journal of Fluid Mechanics / Volume 714 / January 2013, pp 24 - 57 Copyright © Cambridge University Press 2013 DOI: http://dx.doi.org/10.1017/jfm.2012.448, Published online: 02 January 201

The Effect of Particle Gas Composition and Boundary Conditions on Triboplasma Generation: A Computational Study Using the Particle-in-Cell Method

Two dimensional particle in cell simulations of free charge creation by collisional ionization of C12 and C60 molecules immersed in plasma for the parameters of relevance to plasma gasification are presented. Our main findings are that (i) in uniform plasmas with smooth walls two optimal values which emerge for free electron production by collisional ionization (i.e. a most efficient discharge condition creation) are $C60:C12$ fractions of $10:90$ and $80:20$, (ii) in plasmas with rough walls, modelled by comb-like electric field at the boundary, the case of tangential electric field creates significant charge localization in C12+ and C60+ species, again creating most favorable discharge condition for tribo-electrically generated plasma. The numerical simulation results are discussed with reference to recent triboelectric plasma experiments and are corroborated by suitable analytical models.Comment: The final version accepted for publication in IEEE Trans. Plasm. Sc

Excitation of the Earth's Chandler wobble by a turbulent oceanic double-gyre

We develop a layer-averaged, multiple-scale spectral ocean model and show how an oceanic double-gyre can communicate with the Earth's Chandler wobble. The overall transfers of energy and angular momentum from the double-gyre to the Chandler wobble are used to calibrate the turbulence parameters of the layer-averaged model. Our model is tested against a multilayer quasi-geostrophic ocean model in turbulent regime, and base states used in parameter identification are obtained from mesoscale eddy resolving numerical simulations. The Chandler wobble excitation function obtained from the model predicts a small role of North Atlantic ocean region on the wobble dynamics as compared to all oceans, in agreement with the existing observations

A Thermostat-Consistent Fully Coupled Molecular Dynamics-Generalized Fluctuating Hydrodynamics Model

The previously developed multiscale method for concurrently coupling atomistic and continuum hydrodynamic representations of the same chemical substance is extended to consistently incorporate the Langevin‐type thermostat equations in the model. This allows not only to preserve the mass and momentum conservation laws based on the two‐phase flow analogy modeling framework but also to capture the correct local fluctuations and temperature in the pure atomistic region of the hybrid model. Numerical results for the test problem of equilibrium isothermal fluctuations of SPC/E water are presented. Advantages of using local thermostat equations adjusted for the multiresolution model for accurately capturing of the local water density in the atomistic part of the hybrid simulation domain are discussed. Comparisons with the reference pure all‐atom molecular dynamics simulations in GROMACS show that the suggested hybrid models are by a factor of 5–20 faster depending on the simulation domain size

On latency of multiple zonal jets in the oceans

Author Posting. © Cambridge University Press, 2011. This article is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Journal of Fluid Mechanics 686 (2011): 534-567, doi:10.1017/jfm.2011.345.Most of the nearly zonal, multiple, alternating jets observed in the oceans are latent, that is, their amplitudes are weak relative to the ambient mesoscale eddies. Yet, relatively strong jets are often observed in dynamical simulations. To explore mechanisms controlling the degree of latency, we analyse solutions of an idealized, eddy-resolving and flat-bottom quasigeostrophic model, in which dynamically generated mesoscale eddies maintain and interact with a set of multiple zonal jets. We find that the degree of the latency is controlled primarily by the bottom friction: the larger the friction parameter, the more latent are the jets; and the degree of the latency is substantial for a realistic range of the oceanic bottom friction coefficient. This result not only provides a plausible explanation for the latency of the oceanic jets, but it may also be relevant to the prominent atmospheric multiple jets observed on giant gas planets, such as Jupiter. We hypothesize that these jets can be so strong because of the relative absence of the bottom friction. The mechanism controlling the latency in our solutions is understood in terms of the changes induced in the linear eigenmodes of the time–mean flow by varying the bottom friction coefficient; these changes, in turn, affect and modify the jets. Effects of large Reynolds numbers on the eddies, jets, and the latency are also discussed.Funding was provided: for P.B. by NSF grants OCE 0725796 and OCE 0845150, for J.T.F. by NSF grant OCE 0845150, for I.K. by NSF grant OCE 0842834, and for S.K. by the University Research Fellowship from the Royal Society. S.K. also acknowledges support from the Mary Sears Grant from the Woods Hole Oceanographic Institution.2012-09-2

Fast spectral solutions of the double-gyre problem in a turbulent flow regime

Several semi-analytical models are considered for a double-gyre problem in a turbulent flow regime for which a reference fully numerical eddy-resolving solution is obtained. The semi-analytical models correspond to solving the depth-averaged Navier–Stokes equations using the spectral Galerkin approach. The robustness of the linear and Smagorinsky eddy-viscosity models for turbulent diffusion approximation is investigated. To capture essential properties of the double-gyre configuration, such as the integral kinetic energy, the integral angular momentum, and the jet mean-flow distribution, an improved semi-analytical model is suggested that is inspired by the idea of scale decomposition between the jet and the surrounding flow