11 research outputs found
The effects of a counter-current interstitial flow on a discharging hourglass
This work experimentally investigates the effects of an interstitial fluid on the discharge of granular material within an hourglass. The experiments include observations of the flow patterns, measurements of the discharge rates, and pressure variations for a range of different fluid viscosities, particle densities and diameters, and hourglass geometries. The results are classified into three regimes: (i) granular flows with negligible interstitial fluid effects; (ii) flows affected by the presence of the interstitial fluid; and (iii) a no-flow region in which particles arch across the orifice and do not discharge. Within the fluid-affected region, the flows were visually classified as lubricated and air-coupled flows, oscillatory flows, channeling flows in which the flow preferentially rises along the sidewalls, and fluidized flows in which the upward flow suspends the particles. The discharge rates depends on the Archimedes number, the ratio of the effective hopper diameter to the particle diameter, and hourglass geometry. The hopper-discharge experiments, as well as experiments found in the literature, demonstrate that the presence of the interstitial fluid is important when the nondimensional ratio (N) of the single-particle terminal velocity to the hopper discharge velocity is less than 10. Flow ceased in all experiments in which the particle diameter was greater than 25% of the effective hopper diameter regardless of the interstitial fluid
Origin of stabilization of macrotwin boundaries in martensites
The origin of stabilization of complex microstructures along macrotwin
boundaries in martensites is explained by comparing two models based on
Ginzburg-Landau theory. The first model incorporates a geometrically nonlinear
strain tensor to ensure that the Landau energy is invariant under rigid body
rotations, while the second model uses a linearized strain tensor under the
assumption that deformations and rotations are small. We show that the
approximation in the second model does not always hold for martensites and that
the experimental observations along macrotwin boundaries can only be reproduced
by the geometrically nonlinear (exact) theory
Solving the Klein-Gordon equation using Fourier spectral methods: A benchmark test for computer performance
The cubic Klein-Gordon equation is a simple but non-trivial partial
differential equation whose numerical solution has the main building blocks
required for the solution of many other partial differential equations. In this
study, the library 2DECOMP&FFT is used in a Fourier spectral scheme to solve
the Klein-Gordon equation and strong scaling of the code is examined on
thirteen different machines for a problem size of 512^3. The results are useful
in assessing likely performance of other parallel fast Fourier transform based
programs for solving partial differential equations. The problem is chosen to
be large enough to solve on a workstation, yet also of interest to solve
quickly on a supercomputer, in particular for parametric studies. Unlike other
high performance computing benchmarks, for this problem size, the time to
solution will not be improved by simply building a bigger supercomputer.Comment: 10 page
Strong linear scaling for spectral simulations of time dependent semilinear partial differential equations on Marenostrum
ABSTRACT We solve a time dependent semilinear partial differential equation using a spectral collocation method on a distributed memory supercomputer. Previous attempts to use spectral methods to solve evolutionary partial differential equations have scaled poorly on distributed memory machines because typical time stepping algorithms require fast global all-to-all communications. Consequently, primarily expensive supercomputers with very fast interprocessor communications are used to do large scale spectral simulations -see for exampl