9,909 research outputs found
Sustainability of small reservoirs and large scale water availability under current conditions and climate change
Semi-arid river basins often rely on reservoirs for water supply. Small reservoirs may impact on large-scale water availability both by enhancing availability in a distributed sense and by subtracting water for large downstream user communities, e.g. served by large reservoirs. Both of these impacts of small reservoirs are subject to climate change. Using a case-study on North-East Brazil, this paper shows that climate change impacts on water availability may be severe, and impacts on distributed water availability from small reservoirs may exceed impacts on centralised water availability from large reservoirs. Next, the paper shows that the effect of small reservoirs on water availability from large reservoirs may be significant, and increase both in relative and absolute sense under unfavourable climate change
Finding the optimal nets for self-folding Kirigami
Three-dimensional shells can be synthesized from the spontaneous self-folding
of two-dimensional templates of interconnected panels, called nets. However,
some nets are more likely to self-fold into the desired shell under random
movements. The optimal nets are the ones that maximize the number of vertex
connections, i.e., vertices that have only two of its faces cut away from each
other in the net. Previous methods for finding such nets are based on random
search and thus do not guarantee the optimal solution. Here, we propose a
deterministic procedure. We map the connectivity of the shell into a shell
graph, where the nodes and links of the graph represent the vertices and edges
of the shell, respectively. Identifying the nets that maximize the number of
vertex connections corresponds to finding the set of maximum leaf spanning
trees of the shell graph. This method allows not only to design the
self-assembly of much larger shell structures but also to apply additional
design criteria, as a complete catalog of the maximum leaf spanning trees is
obtained.Comment: 6 pages, 5 figures, Supplemental Material, Source Cod
Numerical modeling of the wind flow over a transverse dune
Transverse dunes, which form under unidirectional winds and have fixed
profile in the direction perpendicular to the wind, occur on all celestial
objects of our solar system where dunes have been detected. Here we perform a
numerical study of the average turbulent wind flow over a transverse dune by
means of computational fluid dynamics simulations. We find that the length of
the zone of recirculating flow at the dune lee --- the {\em{separation bubble}}
--- displays a surprisingly strong dependence on the wind shear velocity,
: it is nearly independent of for shear velocities within
the range between ms and $0.8\,$ms but increases linearly with
for larger shear velocities. Our calculations show that transport in
the direction opposite to dune migration within the separation bubble can be
sustained if is larger than approximately ms, whereas a
larger value of $u_{\ast}$ (about $0.49\,$ms) is required to initiate this
reverse transport.Comment: 11 pages, 8 figure
Screening effects in flow through rough channels
A surprising similarity is found between the distribution of hydrodynamic
stress on the wall of an irregular channel and the distribution of flux from a
purely Laplacian field on the same geometry. This finding is a direct outcome
from numerical simulations of the Navier-Stokes equations for flow at low
Reynolds numbers in two-dimensional channels with rough walls presenting either
deterministic or random self-similar geometries. For high Reynolds numbers,
when inertial effects become relevant, the distribution of wall stresses on
deterministic and random fractal rough channels becomes substantially dependent
on the microscopic details of the walls geometry. In addition, we find that,
while the permeability of the random channel follows the usual decrease with
Reynolds, our results indicate an unexpected permeability increase for the
deterministic case, i.e., ``the rougher the better''. We show that this complex
behavior is closely related with the presence and relative intensity of
recirculation zones in the reentrant regions of the rough channel.Comment: 4 pages, 5 figure
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