743 research outputs found
Revitalizing the WTO: Settling Trade Disputes in a Turbulent Multipolar World
Despite growing consensus on the need to update the trade rules and strengthen the World Trade Organization, there is little agreement on which reforms are necessary. While some place priority on resolving the impasse over appointments to the Appellate Body, other reforms to the dispute settlement mechanism may be more important to respond to the challenges facing judicialized dispute settlement of trade disputes in the WTO. The changing balance of economic power, ageing trade rules and a backlash against globalization make it difficult to achieve legitimate outcomes through win-lose adjudication. Increasing demand, a potential for a chill on ongoing negotiations and an imbalance between the political and adjudicative functions of the WTO exacerbate these challenges. Resolving the impasse over the Appellate Body will not, on its own, resolve the more profound legitimacy crisis facing the trading system. Members should instead focus on pursuing broader improvements to the dispute settlement mechanism to ensure that it remains fit-for-purpose in the service of trade cooperation in a turbulent multipolar world
Dissipation and enstrophy statistics in turbulence : are the simulations and mathematics converging?
Since the advent of cluster computing over 10 years ago there has been a steady output of new and better direct numerical simulation of homogeneous, isotropic turbulence with spectra and lower-order statistics converging to experiments and many phenomenological models. The next step is to directly compare these simulations to new models and new mathematics, employing the simulated data sets in novel ways, especially when experimental results do not exist or are poorly converged. For example, many of the higher-order moments predicted by the models converge slowly in experiments. The solution with a simulation is to do what an experiment cannot. The calculation and analysis of Yeung, Donzis & Sreenivasan (J. Fluid Mech., this issue, vol. 700, 2012, pp. 5–15) represents the vanguard of new simulations and new numerical analysis that will fill this gap. Where individual higher-order moments of the vorticity squared (the enstrophy) and kinetic energy dissipation might be converging slowly, they have focused upon ratios between different moments that have better convergence properties. This allows them to more fully explore the statistical distributions that eventually must be modelled. This approach is consistent with recent mathematics that focuses upon temporal intermittency rather than spatial intermittency. The principle is that when the flow is nearly singular, during ‘bad’ phases, when global properties can go up and down by many orders of magnitude, if appropriate ratios are taken, convergence rates should improve. Furthermore, in future analysis it might be possible to use these ratios to gain new insights into the intermittency and regularity properties of the underlying equations
Bounds for Euler from vorticity moments and line divergence
The inviscid growth of a range of vorticity moments is compared using Euler
calculations of anti-parallel vortices with a new initial condition. The primary goal
is to understand the role of nonlinearity in the generation of a new hierarchy of
rescaled vorticity moments in Navier–Stokes calculations where the rescaled moments
obey Dm ≥ Dm+1, the reverse of the usual
Ωm+1 ≥ Ωm Hölder ordering of the original
moments. Two temporal phases have been identified for the Euler calculations. In the
first phase the 1 < m < ∞ vorticity moments are ordered in a manner consistent with
the new Navier–Stokes hierarchy and grow in a manner that skirts the lower edge of
possible singular growth with D2
m → � sup ӏωӏ ~ Am(Tc-t)-1 where the Am are nearly
independent of m. In the second phase, the new Dm ordering breaks down as the Ωm
converge towards the same super-exponential growth for all m. The transition is
identified using new inequalities for the upper bounds for the -dD-2m/dt that are based
solely upon the ratios Dm+1/Dm, and the convergent super-exponential growth is shown
by plotting log(d log Ωm/dt). Three-dimensional graphics show significant divergence
of the vortex lines during the second phase, which could be what inhibits the initial
power-law growth
A Northern Snowmelt Model
In early 1968, a large petroleum discovery was made in the Prudhoe
Bay area of Alaska's Arctic Coastal Plain. This discovery has led Alaska
into a period of development of unprecedented speed and magnitude. This
development will require the construction of many engineering facilities
which are affected by the water resources. The design of each of these
requires an understanding of the hydrologic system, a system which is
dominated in Alaska by low temperatures, high latitudes, large elevation
differences and sparse data. The latter factor is unique to Alaska and
makes application of common design techniques virtually impossible
The application of network modelling techniques to steady-and-unsteady-state multiphase flow in porous media
Vorticity moments in four numerical simulations of the 3D Navier–Stokes equations
The issue of intermittency in numerical solutions of the 3D Navier–Stokes equations on a periodic box [0,L]3 is addressed through four sets of numerical simulations that calculate a new set of variables defined by Dm(t)=(ϖ−10Ωm)αm for 1≤m≤∞ where αm=2m/(4m−3) and [Ωm(t)]2m=L−3∫V|ω|2mdV with ϖ0=νL−2. All four simulations unexpectedly show that the Dm are ordered for m=1,…,9 such that Dm+1<Dm. Moreover, the Dm squeeze together such that Dm+1/Dm↗1 as m increases. The values of D1 lie far above the values of the rest of the Dm, giving rise to a suggestion that a depletion of nonlinearity is occurring which could be the cause of Navier–Stokes regularity. The first simulation is of very anisotropic decaying turbulence; the second and third are of decaying isotropic turbulence from random initial conditions and forced isotropic turbulence at fixed Grashof number respectively; the fourth is of very-high-Reynolds-number forced, stationary, isotropic turbulence at up to resolutions of 40963
Network modelling analysis of a depressurization experiment on a North Sea reservoir core sample
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