2,268 research outputs found
LES of the turbulent compressible flow spatially developing in a plane channel
Large eddy simulation of the turbulent flow
which spatially develops in a plane channel with a length of 88h will be presented for
Re=4880 and M=0.7. The effect of realistic inflow conditions and low reflective outflow
conditions will be analysed and discussed. Supersonic channel flow case and distorsion
of the flow by mean of adverse pressure gradient will be further considered
Hydrodynamics of steep streams with planar coarse-grained beds: Turbulence, flow resistance, and implications for sediment transport
The hydraulics of steep mountain streams differ from lower gradient rivers due to shallow and rough flows, energetic subsurface flow, and macro-scale form drag from immobile boulders and channel- and bed-forms. Heightened flow resistance and reduced sediment transport rates in steep streams are commonly attributed to macro-scale form drag; however, little work has explored steep river hydrodynamics in the absence of complex bed geometries. Here we present theory for the vertical structure of flow velocity in steep streams with planar, rough beds that couples surface and subsurface flow. We test it against flume experiments using a bed of fixed cobbles over a wide range of bed slopes (0.4 – 30%). Experimental flows have a nearly logarithmic velocity profile far above the bed; flow velocity decreases less than logarithmically towards the bed and is non-zero at the bed surface. Velocity profiles match theory derived using a hybrid eddy-viscosity model, in which the mixing length is a function of height above the bed and bed roughness. Subsurface flow velocities are large (> 1 m/s) and follow a modified Darcy-Brinkman-Forchheimer relation that accounts for channel slope and shear from overlying surface flow. Near-bed turbulent fluctuations decrease for shallow, rough flows and scale with the depth-averaged flow velocity rather than bed shear velocity. Flow resistance for rough, planar beds closely matches observations in natural steep streams despite the lack of bed- or channel-forms in the experiments, suggesting that macro-scale form drag is smaller than commonly assumed in stress partitioning models for sediment transport
A PROBABILISTIC APPROACH FOR COMPRESSOR SIZING AND PLANT DESIGN
LectureEquipment sizing decisions in the Oil and Gas Industry often
have to be made based on incomplete data. Often, the exact
process conditions are based on numerous assumptions about
well performance, market conditions, environmental
conditions and others. Since the ultimate goal is to meet
production commitments, the traditional way of addressing
this is, to use worst case conditions, and often adding margins
onto these. This will invariably lead to plants that are
oversized, in some instances by large margins. In reality, the
operating conditions are very rarely the assumed worst case
conditions, but they are usually more benign most of the time.
Plants designed based on worst case conditions, once in
operation, will therefore usually not operate under optimum
conditions, have reduced flexibility, and therefore cause both
higher capital expenses and operating expenses.
The authors outline a new probabilistic methodology that
provides a framework for more intelligent process-machine
designs . A standardized framework using Monte Carlo
simulation and risk analysis is presented that more accurately
defines process uncertainty and its impact on machine
performance .
This paper describes a new method for the design of efficient
plants. The use of statistical and probabilistic tools allows to
better account for the unpredictability of component
performance, as well as for ambient conditions and demand.
Using the methodology allows to design plants that perform
best under the most likely scenarios, as opposed to traditional
designs that tend to work best under unlikely worst case
scenarios. A study was performed for a relatively simple
scenario, but the method is not limited, and can easily be
adapted to scenarios involving entire pipeline systems,
complete plants, or platform operations. Based on these
considerations, significant cost reductions are possible in
many cases
Finite element modeling of dynamic frictional rupture with rate and state friction
Numerous laboratory experiments have demonstrated the dependence of the
friction coefficient on the interfacial slip rate and the contact history, a
behavior generically called rate and state friction. Although numerical models
have been widely used for analyzing rate and state friction, in general they
consider infinite elastic domains surrounding the sliding interface and rely on
boundary integral formulations. Much less work has been dedicated to modeling
finite size systems to account for interactions with boundaries. This paper
investigates rate and state frictional interfaces in the context of finite size
systems with the finite element method in explicit dynamics. We investigate the
long term behavior of the sliding interface for two different friction laws: a
velocity weakening law, for which the friction monotonously decreases with
increasing sliding velocity, and a velocity weakening-strengthening law, for
which the friction coefficient first decreases but then increases above a
critical velocity. We show that for both friction laws at finite times, that is
before wave reflections from the boundaries come back to the sliding interface,
a temporary steady state sliding is reached, with a well-defined stress drop at
the interface. This stress drop gives rise to a stress concentration and leads
to an analogy between friction and fracture. However, at longer times, that is
after multiple wave reflections, the stress drop is essentially zero, resulting
in losing the analogy with fracture mechanics. Finally, the simulations reveal
that velocity weakening is unstable at long time scales, as it results in an
acceleration of the sliding blocks. On the other hand, velocity
weakening-strengthening reaches a steady state sliding configuration
Antiplasmodial activity of a series of 1,3,5-triazine-substituted polyamines
Polyamine biosynthesis and function has been shown to be a good drug target in some parasitic protozoa and it is proposed that the pathway might also represent a target in the malaria parasite Plasmodium falciparum. A series of 1,3,5-triazine-substituted polyamine analogues were tested for activity against Plasmodium falciparum in vitro. The series showed activity against the parasites and were generally more active against the chloroquine-resistant line K1 than the chloroquine-susceptible line NF54. Simple unbranched analogues had better activity than analogues carrying branched or cyclic central chains. Addition of multiple triazine units in general led to increased activity of the compound
Socioeconomic agents as active matter in nonequilibrium Sakoda-Schelling models
How robust are socioeconomic agent-based models with respect to the details
of the agents' decision rule? We tackle this question by considering an
occupation model in the spirit of the Sakoda-Schelling model, historically
introduced to shed light on segregation dynamics among human groups. For a
large class of utility functions and decision rules, we pinpoint the
nonequilibrium nature of the agent dynamics, while recovering the
equilibrium-like phase separation phenomenology. Within the mean field
approximation we show how the model can be mapped, to some extent, onto an
active matter field description (Active Model B). Finally, we consider
non-reciprocal interactions between two populations, and show how they can lead
to non-steady macroscopic behavior. We believe our approach provides a unifying
framework to further study geography-dependent agent-based models, notably
paving the way for joint consideration of population and price dynamics within
a field theoretic approach.Comment: 12 pages, 7 figure
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