Elasticity (physics)

Summary

In physics and materials science, elasticity is the ability of a body to resist a distorting influence and to return to its original size and shape when that influence or force is removed. Solid objects will deform when adequate loads are applied to them; if the material is elastic, the object will return to its initial shape and size after removal. This is in contrast to plasticity, in which the object fails to do so and instead remains in its deformed state. The physical reasons for elastic behavior can be quite different for different materials. In metals, the atomic lattice changes size and shape when forces are applied (energy is added to the system). When forces are removed, the lattice goes back to the original lower energy state. For rubbers and other polymers, elasticity is caused by the stretching of polymer chains when forces are applied. Hooke's law states that the force required to deform elastic objects should be directly proportional to the distance of deformation, r

Official source

https://en.wikipedia.org/wiki/Elasticity_(physics)

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Experiments on grid turbulence are reported for pure water and dilute Polyox WSR 301 solutions. A novel passive grid, which consists of a square mesh grid with tethered spheres, has been developed to enhance the turbulence properties. In pure water the new grid produces higher turbulence intensities per unit Cp (pressure drop coefficient) than the classic plain grid, and the turbulence Reynolds number Reλ is increased by a factor of roughly two. In polymer solutions turbulence dissipation rates and energy spectra were measured using PIV with a high spatial resolution. The energy spectra reveal a characteristic length scale at which the polymers begin to affect the energy cascade. Above this scale the turbulence is essentially Newtonian, whereas below this scale the energy flux from large to small scales is reduced proportional to the length scale squared. Consequently, the energy in this new self-regulating spectral region scales according to a power-law with an exponent of -3 instead of the -5/3 for Newtonian turbulence, and the excess energy is dissipated by the polymers.

EPFL2010

The virtual frame technique: ultrafast imaging with any camera

John Martin Kolinski

Many phenomena of interest in nature and industry occur rapidly and are difficult and cost-prohibitive to visualize properly without specialized cameras. Here we describe in detail the virtual frame technique (VFT), a simple, useful, and accessible mode of imaging that increases the frame acquisition rate of any camera by several orders of magnitude by leveraging its dynamic range. The VFT is a powerful tool for capturing rapid phenomena where the dynamics facilitate a transition between two states, and are thus binary. The advantages of the VFT are demonstrated by examining such dynamics in five physical processes at unprecedented rates and spatial resolution: fracture of an elastic solid, wetting of a solid surface, rapid fingerprint reading, peeling of adhesive tape, and impact of an elastic hemisphere on a hard surface. We show that the performance of the VFT exceeds that of any commercial high-speed camera not only in rate of imaging but also in field of view, achieving a 65MHz frame rate at 4MPx resolution. Finally, we discuss the performance of the VFT with several commercially available conventional and high-speed cameras. In principle, modern cell phones can achieve imaging rates of over a million frames per second using the VFT.

2019

We elaborate in this thesis the numerical simulation of the fluid-structure interaction by the spectral element method. To this end we consider the Navier-Stokes equations for a viscous Newtonian incompressible fluid with an elastic solid the movement of which being described by the equations of the dynamics. The arbitrary Lagrangian Eulerian (ALE) formulation is introduced in the fluid governing equations to deal with the structure movement that is described in Lagrangian representation. The geometrical motion in each domain is built up by the mesh deformation. The space-time discretization of the full mathematical model rests upon the spectral element method. The solid is discretized in the space of polynomials of degree N, PN, while the fluid uses the PN - PN-2 approach. The efficiency of the ALE formulation is tested and validated through various applications. The full algorithm is based on a particular case of the staggered method. The simplified case of a solid immersed in a plane channel closes the thesis. It is then possible to draw the conclusions about the pros and cons of the proposed methodology.

EPFL2006