The Experts below are selected from a list of 52557 Experts worldwide ranked by ideXlab platform
E. Joseph Metzger - One of the best experts on this subject based on the ideXlab platform.
-
The impact of ocean surface currents on global eddy kinetic energy via the wind Stress Formulation
Ocean Modelling, 2019Co-Authors: E. Joseph MetzgerAbstract:Abstract A pair of 12.5-year (July 2002–December 2014) HYbrid Coordinate Ocean Model (HYCOM) simulations that only differ in the wind Stress Formulation are used to investigate the effect of ocean surface currents on global monthly eddy kinetic energy (EKE) variation. The model results (2004–2014) show that the global monthly mean EKE is reduced by 37%, from 1.76 EJ (1018 J) to 1.10 EJ after ocean surface currents are included in the wind Stress Formulation. The monthly EKE budget indicates that the shear production and buoyancy work are positive (energy source) and the eddy wind work on the geostrophic currents is negative (energy sink) in the steady state (2004–2014) for both simulations. All of these three terms are reduced in the steady state when the ocean currents are included in the wind Stress Formulation. The global integral of the EKE difference budget suggests that the EKE reduction is primarily due to the reduction of the buoyancy work, followed by the reduction of the wind work on the geostrophic currents and the shear production. To our knowledge this is the first study to separate the eddy wind work into the geostrophic and ageostrophic components to investigate the impact of ocean surface currents on global and depth integrated EKE via the wind Stress Formulation using HYCOM simulations.
-
The Impact of Ocean Surface Currents on Sverdrup Transport in the Midlatitude North Pacific via the Wind Stress Formulation
Journal of Physical Oceanography, 2017Co-Authors: E. Joseph Metzger, Yalin FanAbstract:AbstractA more complete wind Stress τn Formulation takes into account the ocean surface currents Vo, while the conventional wind Stress τc popularly used in ocean circulation models is only a function of 10-m winds V10. An analytical solution is derived for the difference of Sverdrup transport induced by using τn instead of τc. A scaling analysis of the analytical solution indicates a 6% reduction of the Sverdrup transport in the North Pacific (i.e., the Kuroshio transport in the East China Sea) when Ekman velocity dominates the ocean surface currents. Because of the quadratic nature of wind Stress, four nonlinear terms contribute equally to this difference: two vorticity torque terms and two speed gradient torque terms. A pair of 12.5-yr (July 2002–14) Hybrid Coordinate Ocean Model simulations that only differ in the wind Stress Formulation are used to test the analytical solution. The model results (2004–14) confirm that using τn instead of τc reduces the Sverdrup transport in the North Pacific by 8%–17...
Heiner Dietze - One of the best experts on this subject based on the ideXlab platform.
-
Effects of mesoscale eddy/wind interactions on biological new production and eddy kinetic energy
Journal of Geophysical Research, 2009Co-Authors: Carsten Eden, Heiner DietzeAbstract:Accounting for ocean currents in the bulk parameterization of the wind Stress might represent a physically more plausible way to force an ocean model than ignoring their effect. We show in this study that using the air-sea velocity difference instead of the atmospheric wind in the wind Stress Formulation dampens both the near-surface eddy activity and the biotic carbon assimilation in a high-resolution model of the North Atlantic. The former is significant, corresponding to a reduction down to 50% in the tropical Atlantic, while in higher latitudes (in agreement with previous results) the reduction of eddy activity is only around 10%. The effect on biotically mediated new production and air-sea carbon fluxes is, on the other hand, minor. New production is reduced by less than 5% on a basin average, while simulated air-sea CO2 fluxes are barely affected at all. The model results imply that eddy/wind interaction introduced by accounting for ocean currents in the wind Stress Formulation does not drive any additional (and hitherto unaccounted) nutrient fluxes to the sunlit surface of the subtropical gyre, as was recently proposed in the literature.
-
effects of mesoscale eddy wind interactions on biological new production and eddy kinetic energy
Journal of Geophysical Research, 2009Co-Authors: Carsten Eden, Heiner DietzeAbstract:Accounting for ocean currents in the bulk parameterization of the wind Stress might represent a physically more plausible way to force an ocean model than ignoring their effect. We show in this study that using the air-sea velocity difference instead of the atmospheric wind in the wind Stress Formulation dampens both the near-surface eddy activity and the biotic carbon assimilation in a high-resolution model of the North Atlantic. The former is significant, corresponding to a reduction down to 50% in the tropical Atlantic, while in higher latitudes (in agreement with previous results) the reduction of eddy activity is only around 10%. The effect on biotically mediated new production and air-sea carbon fluxes is, on the other hand, minor. New production is reduced by less than 5% on a basin average, while simulated air-sea CO2 fluxes are barely affected at all. The model results imply that eddy/wind interaction introduced by accounting for ocean currents in the wind Stress Formulation does not drive any additional (and hitherto unaccounted) nutrient fluxes to the sunlit surface of the subtropical gyre, as was recently proposed in the literature.
Sun Chen-yan - One of the best experts on this subject based on the ideXlab platform.
-
Least-squares Finite Element Method for Unsteady Stress Formulation of Navier-Stokes Equations
Chinese Journal of Computational Physics, 2015Co-Authors: Sun Chen-yanAbstract:To solve unsteady laminar flow problems,a method of velocity-Stress-pressure Formulation instead of velocity-vorticitypressure Formulation is developed. With Newton's linearized method to linearize convective terms and preconditioned conjugate gradient method to solve equations,unsteady Stress Formulation of Navier-Stokes equations is solved. Comparison between numerical and experimental results of cavity laminar flow shows that result of Stress Formulation fits experiment better and has higher accuracy than vorticity Formulation. The Stress Formulation can deal with subgrid Stress with least squares finite element method. Comparison with experimental results of cavity turbulent flow reveals feasibility of the method. It lays a firm foundation for large eddy simulation computation.
-
Solving Stress Formulation of Equations with Least Squares Finite Element Method
Computer Simulation, 2014Co-Authors: Sun Chen-yanAbstract:In order to solve laminar and turbulent flow problems efficiently with least squares finite element method and get more accurate results,this paper used a new Formulation of velocity-Stress-pressure instead of traditional Formulation of velocity-vorticity-pressure.With the Newton's linearized method and preconditioned conjugate gradient method,the Stress Formulation of Navier-Stokes equations was solved.The correspondence between the numerical results and experimental results of backward facing step flow and circular cylinder flow shows that,the least squares finite element method can get more accurate results than finite volume method.Also,the results of Stress Formulation fit better to the experiment results than those of vorticity Formulation.The solution for Stress Formulation can cope with the subgrid-scale model well,which is very difficult for vorticity Formulation.This lays a solid foundation for large eddy simulation to solve turbulent problems.
Cassio M. Oishi - One of the best experts on this subject based on the ideXlab platform.
-
Numerical study of the Stress singularity in stick-slip flow of the Phan-Thien Tanner and Giesekus fluids
Physics of Fluids, 2019Co-Authors: Jonathan D. Evans, J. A. Cuminato, I. L. Palhares Junior, Cassio M. OishiAbstract:Stick-slip flow is a challenging viscoelastic benchmark problem due to the presence of a separation or transition point at the die exit where a sudden change in flow boundary conditions occurs. We present numerical simulations of transient planar stick-slip flow of the Phan-Thien–Tanner (PTT) and Giesekus fluids, investigating the polymer Stress behavior around the Stress singularity at the stick-slip point, confirming the asymptotic results presented by Evans et al. [“Stresses of the Oldroyd-B, PTT and Giesekus fluids in a Newtonian velocity field near the stick-slip singularity,” Phys. Fluids 29, 1–33 (2017)]. In order to improve the numerical knowledge about this viscoelastic benchmark problem, two distinct mathematical methodologies are used for comparison in the computational simulations: the Cartesian and natural Stress Formulations. The former is widely applied in computational rheology, while the latter is used for the first time in the context of this problem. The natural Stress Formulation gives improved convergence results both temporally and spatially near to the singularity while maintaining the same global flow characteristics as the Cartesian.Stick-slip flow is a challenging viscoelastic benchmark problem due to the presence of a separation or transition point at the die exit where a sudden change in flow boundary conditions occurs. We present numerical simulations of transient planar stick-slip flow of the Phan-Thien–Tanner (PTT) and Giesekus fluids, investigating the polymer Stress behavior around the Stress singularity at the stick-slip point, confirming the asymptotic results presented by Evans et al. [“Stresses of the Oldroyd-B, PTT and Giesekus fluids in a Newtonian velocity field near the stick-slip singularity,” Phys. Fluids 29, 1–33 (2017)]. In order to improve the numerical knowledge about this viscoelastic benchmark problem, two distinct mathematical methodologies are used for comparison in the computational simulations: the Cartesian and natural Stress Formulations. The former is widely applied in computational rheology, while the latter is used for the first time in the context of this problem. The natural Stress Formulation gives...
-
Application of the natural Stress Formulation for solving unsteady viscoelastic contraction flows
Journal of Computational Physics, 2019Co-Authors: Jonathan D. Evans, Hugo L. França, Cassio M. OishiAbstract:Abstract We present a numerical scheme for a previously unexploited Formulation of the equations for unsteady viscoelastic flow. The Formulation aligns the polymer Stress along particle paths/streamlines, utilising the characteristic curves associated with the hyperbolic part of the constitutive equations. We illustrate the approach for the Oldroyd-B model in the benchmark 4:1 contraction for moderate elasticity numbers. We show that the scheme is able to accurately capture the re-entrant corner singularity for the polymer Stresses and the pressure, the latter variable being inaccurately determined by schemes using the traditional Formulation in terms of Cartesian polymer Stresses. A space-step restriction for stability is derived, which can be numerically limiting in certain recirculation regions. This contrasts with the equivalent space-step restriction for the Formulation in Cartesian Stresses, which is limiting in flow regions of high velocity gradients, for example, at sharp corners in contraction flows.
-
Transient computations using the natural Stress Formulation for solving sharp corner flows
Journal of Non-Newtonian Fluid Mechanics, 2017Co-Authors: Jonathan D. Evans, Cassio M. OishiAbstract:Abstract In this short communication, we analyse the potential of the natural Stress Formulation (NSF) (i.e. aligning the Stress basis along streamlines) for computing planar flows of an Oldroyd-B fluid around sharp corners. This is the first attempt to combine the NSF into a numerical strategy for solving a transient fluid flow problem considering the momentum equation in Navier–Stokes form (the elastic Stress entering as a source term) and using the constitutive equations for natural Stress variables. Preliminary results of the NSF are motivating in the sense that accuracy of the numerical solution for the extra Stress tensor is improved near to the sharp corner. Comparison studies among the NSF and the Cartesian Stress Formulation (CSF) (i.e. using a fixed Cartesian Stress basis) are conducted in a typical benchmark viscoelastic fluid flow involving a sharp corner: the 4 : 1 contraction. The CSF needs a mesh approximately 10 times smaller to capture similar near singularity results to the NSF.
-
Testing viscoelastic numerical schemes using the Oldroyd-B fluid in Newtonian kinematics
Applied Mathematics and Computation, 1Co-Authors: Jonathan D. Evans, I. L. Palhares Junior, H.l. França, Cassio M. OishiAbstract:Abstract We focus here on using a Newtonian velocity field to evaluate numerical schemes for two different Formulations of viscoelastic flow. The two distinct Formulations we consider, correspond to either using a fixed basis for the elastic Stress or one that uses the flow directions or streamlines. The former is the traditional Cartesian Stress Formulation, whilst the later may be referred to as the natural Stress Formulation of the equations. We choose the Oldroyd-B fluid and three benchmarks in computational rheology: the 4:1 contraction flow, the stick-slip and cross-slot problems. In the context of the contraction flow, fixing the kinematics as Newtonian, actually gives a larger Stress singularity at the re-entrant corner, the matched asymptotics of which are presented here. Numerical results for temporal and spatial convergence of the two Formulations are compared first in this decoupled velocity and elastic Stress situation, to assess the performance of the two approaches. This may be regarded as an intermediate test case before proceeding to the far more difficult fully coupled velocity and Stress situation. We also present comparison results between numerics and asymptotics for the stick-slip problem. Finally, the natural Stress Formulation is used to investigate the cross-slot problem, again in a Newtonian velocity field.
Lucia Pineau-guillou - One of the best experts on this subject based on the ideXlab platform.
-
Impact of wave-dependent Stress on storm surge simulations in the North Sea: Ocean model evaluation against in situ and satellite observations
Ocean Modelling, 2020Co-Authors: Lucia Pineau-guillou, Marie-noëlle Bouin, Fabrice Ardhuin, Florent Lyard, Jean-raymond Bidlot, Bertrand ChapronAbstract:Abstract We investigate the impact of wave-dependent Stress on surge modelling, from case studies in the North Sea, using a global ocean model forced with a wave-atmosphere coupled model. We select the storms with the largest surges and a range of sea state development from young to mature seas. The modelled surges are compared to tide gauges and altimeter data. The ocean model is able to accurately predict storm surges in coastal areas. The consistency of the model outputs, the altimeter, and the tide gauge data confirms the accuracy of altimeters for storm surge measurements. We show that using a wave-dependent rather than a wind-dependent only Stress Formulation gives more accurate surge simulations when the sea state is young and the sea rougher. Taking into account the waves in the Stress Formulation has a significant impact on the surges (up to 20 cm).
-
Ocean-atmosphere interaction : improvement of wind Stress for coastal physical modelling
2018Co-Authors: Lucia Pineau-guillouAbstract:Storm surges may be underestimated in hydrodynamic models, as well as large wave heights in wave models. This could come from an underestimation of strong winds in atmospheric models and/or an inappropriate wind Stress Formulation. The objectives of the present work are (1) to estimate how strong are the biases for high winds in atmospheric models (2) to develop a new drag parameterization that could reduce this bias (3) to investigate the impact of the waves on the wind Stress. The method consists of studying the response of the atmosphere and the ocean to the wind Stress.In a first part, we use the coupled wave-atmosphere model from ECMWF. We show that strong winds may be underestimated, as much as -7 m/s at 30 m/s.Significant differences also exist between observations, with buoys and ASCAT-KNMI generally showing lower wind speeds than the platforms and other remote-sensing data used in this study(AMSR2, ASCAT-RSS, WindSat, SMOS and JASON-2).The newly empirically adjusted Charnock parameterization leads to higher winds compared to the default ECMWF parameterization. In a second part, we use the global ocean model TUGO fromLEGOS forced with ECMWF coupled wave-atmopshere model. We show that a wave-dependent rather than wind-dependent Stress Formulation is more appropriate, when the sea state is young and the sea rougher. It yields to simulated surges closer to observations (i.e. tide gauges and JASON-2 altimeter tracks). The wave impact on the surges is significant, and may reach 20 cm.