4,107 research outputs found
Correlation between surface topography and slippage: a Molecular Dynamics study
Using Molecular Dynamics simulations of a polymer liquid flowing past flat
and patterned surfaces, we investigate the influence of corrugation,
wettability and pressure on slippage and friction at the solid-liquid
interface. For one-dimensional, rectangular grooves, we observe a gradual
crossover between the Wenzel state, where the liquid fills the grooves, and the
Cassie state, where the corrugation supports the liquid and the grooves are
filled with vapor. Using two independent flow set-ups, we characterize the
near-surface flow by the slip length, , and the position,
, at which viscous and frictional stresses are balanced according
to Navier's partial slip boundary condition. This hydrodynamic boundary
position depends on the pressure inside the channel and may be located above
the corrugated surface. In the Cassie state, we observe that the edges of the
corrugation contribute to the friction.Comment: 13 pages, 13 figure
Multi-Architecture Monte-Carlo (MC) Simulation of Soft Coarse-Grained Polymeric Materials: SOft coarse grained Monte-carlo Acceleration (SOMA)
Multi-component polymer systems are important for the development of new
materials because of their ability to phase-separate or self-assemble into
nano-structures. The Single-Chain-in-Mean-Field (SCMF) algorithm in conjunction
with a soft, coarse-grained polymer model is an established technique to
investigate these soft-matter systems. Here we present an im- plementation of
this method: SOft coarse grained Monte-carlo Accelera- tion (SOMA). It is
suitable to simulate large system sizes with up to billions of particles, yet
versatile enough to study properties of different kinds of molecular
architectures and interactions. We achieve efficiency of the simulations
commissioning accelerators like GPUs on both workstations as well as
supercomputers. The implementa- tion remains flexible and maintainable because
of the implementation of the scientific programming language enhanced by
OpenACC pragmas for the accelerators. We present implementation details and
features of the program package, investigate the scalability of our
implementation SOMA, and discuss two applications, which cover system sizes
that are difficult to reach with other, common particle-based simulation
methods
Directed transport of polymer drops on vibrating superhydrophobic substrates: A Molecular Dynamics study
Using Molecular Dynamics simulations of a coarse-grained polymer liquid we
investigate the transport of droplets on asymmetrically structured (saw-tooth
shaped), vibrating substrates. Due to a continuous supply of power by substrate
vibrations and the asymmetry of its topography, the droplets are driven in a
preferred direction. We study this directed motion as a function of the size of
the droplets, the linear dimensions of the substrate corrugation, and the
period of vibrations.
Two mechanisms of driven transport are identified: (i) one that relies on the
droplet's contact lines and (ii), in a range of vibration periods, the entire
contact area contributes to the driving. In this latter regime, the set-up may
be used in experiments for sorting droplets according to their size.
Additionally, we show that the linear dimension of the substrate corrugation
affects the flux inside the droplet. While on a substrate with a fine
corrugation droplets mostly slide, on a more coarsely corrugated substrate the
flux may exhibit an additional rotation pattern.Comment: 24 pages, 17 figures, 2 table
Grid Integration Costs of Fluctuating Renewable Energy Sources
The grid integration of intermittent Renewable Energy Sources (RES) causes
costs for grid operators due to forecast uncertainty and the resulting
production schedule mismatches. These so-called profile service costs are
marginal cost components and can be understood as an insurance fee against RES
production schedule uncertainty that the system operator incurs due to the
obligation to always provide sufficient control reserve capacity for power
imbalance mitigation. This paper studies the situation for the German power
system and the existing German RES support schemes. The profile service costs
incurred by German Transmission System Operators (TSOs) are quantified and
means for cost reduction are discussed. In general, profile service costs are
dependent on the RES prediction error and the specific workings of the power
markets via which the prediction error is balanced. This paper shows both how
the prediction error can be reduced in daily operation as well as how profile
service costs can be reduced via optimization against power markets and/or
active curtailment of RES generation.Comment: Accepted for SUSTECH 2014, Portland, Oregon, USA, July 201
Interface repulsion and lamellar structures in thin films of homopolymer blends due to thermal oscillations
In equilibrium the interface potential that describes the interaction between
two AB interfaces in a binary blend of A and B homopolymers is attractive at
all distances, resulting in coarsening of the blend morphology even in the
absence of interface curvature. We demonstrate that the dissipative assembly in
response to a time-periodic variation of the blend incompatibility
qualitatively alters this behavior, i.e., for suitable parameters the interface
potential exhibits a periodic spatial modulation and AB interfaces adopt a
well-defined distance. We explore for which oscillation periods and amplitudes
an interface repulsion occurs and demonstrate that we can control the preferred
interface distance over a wide range by varying the oscillation period. Using
particle-based simulations we explicitly demonstrate that this dissipative
assembly of a homopolymer blend results in a lamellar structure with multiple
planar interfaces in a thin film geometry
- …