1,946 research outputs found
Large droplet impact on water layers
The impact of large droplets onto an otherwise undisturbed layer of water is considered. The work, which is motivated primarily with regard to aircraft icing, is to try and help understand the role of splashing on the formation of ice on a wing, in particular for large droplets where splash appears, to have a significant effect. Analytical and numerical approaches are used to investigate a single droplet impact onto a water layer. The flow for small times after impact is determined analytically, for both direct and oblique impacts. The impact is also examined numerically using the volume of fluid (VOF) method. At small times there are promising comparisons between the numerical results, the analytical solution and experimental work capturing the ejector sheet. At larger times there is qualitative agreement with experiments and related simulations. Various cases are considered, varying the droplet size to layer depth ratio, including surface roughness, droplet distortion and air effects. The amount of fluid splashed by such an impact is examined and is found to increase with droplet size and to be significantly influenced by surface roughness. The makeup of the splash is also considered, tracking the incoming fluid, and the splash is found to consist mostly of fluid originating in the layer
Recommended from our members
Spall And Dynamic Yielding Of Aluminum And Aluminum Alloys At Strain Rates Of 3X10(6) S(-1)
We have explored the role that grain size, impurity particles and alloying in aluminum play in dynamic yielding and spall fracture at tensile strain rates of similar to 3x10(6) We achieved these strain rates shocking the aluminum specimens via laser ablation using the Z-Beamlet Laser at Sandia National Laboratories. The high purity aluminum and 1100 series aluminum alloy produced very different spall strengths and nearly the same yield strengths. In contrast, various grain-sized Al + 3 wt. % Mg specimens presented the lowest spall strength, but the greatest dynamic yield strength. Fracture morphology results and particle analysis are presented along with hydrodynamic simulations to put these results in context. Impurity particles appeared to play a vital role in spall fracture at these fast strain rates. Alloying elements such as Mg seem to be the dominant factor in the dynamic yield results.Mechanical Engineerin
Evolutionary Roots of Property Rights; The Natural and Cultural Nature of Human Cooperation
Debates about the role of natural and cultural selection in the development of prosocial, antisocial and socially neutral mechanisms and behavior raise questions that touch property rights, cooperation, and conflict. For example, some researchers suggest that cooperation and prosociality evolved by natural selection (Hamilton 1964, Trivers 1971, Axelrod and Hamilton 1981, De Waal 2013, 2014), while others claim that natural selection is insufficient for the evolution of cooperation, which required in addition cultural selection (Sterelny 2013, Bowles and Gintis 2003, Seabright 2013, Norenzayan 2013). Some scholars focus on the complexity and hierarchical nature of the evolution of cooperation as involving different tools associated with lower and the higher levels of competition (Nowak 2006, Okasha 2006); others suggest that humans genetically inherited heuristics that favor prosocial behavior such as generosity, forgiveness or altruistic punishment (Ridley 1996, Bowles and Gintis 2004, Rolls 2005). We argue these mechanisms are not genetically inherited; rather, they are features inherited through cultural selection. To support this view we invoke inclusive fitness theory, which states that individuals tend to maximize their inclusive fitness, rather than maximizing group fitness. We further reject the older notion of natural group selection - as well as more recent versions (West, Mouden, Gardner 2011) – which hold that natural selection favors cooperators within a group (Wynne-Edwards 1962). For Wynne-Edwards, group selection leads to group adaptations; the survival of individuals therefore depends on the survival of the group and a sharing of resources. Individuals who do not cooperate, who are selfish, face extinction due to rapid and over-exploitation of resources
Numerical study of the strongly screened vortex glass model in an external field
The vortex glass model for a disordered high-T_c superconductor in an
external magnetic field is studied in the strong screening limit. With exact
ground state (i.e. T=0) calculations we show that 1) the ground state of the
vortex configuration varies drastically with infinitesimal variations of the
strength of the external field, 2) the minimum energy of global excitation
loops of length scale L do not depend on the strength of the external field,
however 3) the excitation loops themself depend sensibly on the field. From 2)
we infer the absence of a true superconducting state at any finite temperature
independent of the external field.Comment: 6 pages RevTeX, 5 eps-figures include
Effects of point defects on the phase diagram of vortex states in high-Tc superconductors in B//c axis
The phase diagram for the vortex states of high- superconductors
with point defects in axis is drawn by large-scale Monte
Carlo simulations. The vortex slush (VS) phase is found between the vortex
glass (VG) and vortex liquid (VL) phases. The first-order transition between
this novel normal phase and the VL phase is characterized by a sharp jump of
the density of dislocations. The first-order transition between the Bragg glass
(BG) and VG or VS phases is also clarified. These two transitions are compared
with the melting transition between the BG and VL phases.Comment: 4 pages, 9 eps figures (included in text), uses revtex.sty, overall
changes with several additional data points, though conclusion is unchange
Energy cost associated with vortex crossing in superconductors
Starting from the Ginzburg-Landau free energy of a type II superconductor in
a magnetic field we estimate the energy associated with two vortices crossing.
The calculations are performed by assuming that we are in a part of the phase
diagram where the lowest Landau level approximation is valid. We consider only
two vortices but with two markedly different sets of boundary conditions: on a
sphere and on a plane with quasi-periodic boundary conditions. We find that the
answers are very similar suggesting that the energy is localised to the
crossing point. The crossing energy is found to be field and temperature
dependent -- with a value at the experimentally measured melting line of
, where is the Lindemann
melting criterion parameter. The crossing energy is then used with an extension
of the Marchetti, Nelson and Cates hydrodynamic theory to suggest an
explanation of the recent transport experiments of Safar {{\em et al.}\ }.Comment: 15 pages, RevTex v3.0, followed by 5 postscript figure
GINZBURG-LANDAU THEORY OF VORTICES IN -WAVE SUPERCONDUCTORS
Ginzburg-Landau theory is used to study the properties of single vortices and
of the Abrikosov vortex lattice in a superconductor. For a single
vortex, the -wave order parameter has the expected four-lobe structure in a
ring around the core and falls off like at large distances. The
topological structure of the -wave order parameter consists of one
counter-rotating unit vortex, centered at the core, surrounded by four
symmetrically placed positive unit vortices. The Abrikosov lattice is shown to
have a triangular structure close to and an oblique structure at lower
temperatures. Comparison is made to recent neutron scattering data.Comment: 4 pages, REVTeX, 3 figures available upon reques
Vortex Matter Transition in BiSrCaCuO under Tilted Fields
Vortex phase diagram under tilted fields from the axis in
BiSrCaCuO is studied by local magnetization
hysteresis measurements using Hall probes. When the field is applied at large
angles from the axis, an anomaly () other than the well-known
peak effect () are found at fields below . The angular dependence of
the field is nonmonotonic and clearly different from that of
and depends on the oxygen content of the crystal. The results suggest existence
of a vortex matter transition under tilted fields. Possible mechanisms of the
transition are discussed.Comment: Revtex, 4 pages, some corrections are adde
- …