273 research outputs found
An Energetic Variational Approach for ion transport
The transport and distribution of charged particles are crucial in the study
of many physical and biological problems. In this paper, we employ an Energy
Variational Approach to derive the coupled Poisson-Nernst-Planck-Navier-Stokes
system. All physics is included in the choices of corresponding energy law and
kinematic transport of particles. The variational derivations give the coupled
force balance equations in a unique and deterministic fashion. We also discuss
the situations with different types of boundary conditions. Finally, we show
that the Onsager's relation holds for the electrokinetics, near the initial
time of a step function applied field
Behavior of different numerical schemes for population genetic drift problems
In this paper, we focus on numerical methods for the genetic drift problems,
which is governed by a degenerated convection-dominated parabolic equation. Due
to the degeneration and convection, Dirac singularities will always be
developed at boundary points as time evolves. In order to find a \emph{complete
solution} which should keep the conservation of total probability and
expectation, three different schemes based on finite volume methods are used to
solve the equation numerically: one is a upwind scheme, the other two are
different central schemes. We observed that all the methods are stable and can
keep the total probability, but have totally different long-time behaviors
concerning with the conservation of expectation. We prove that any extra
infinitesimal diffusion leads to a same artificial steady state. So upwind
scheme does not work due to its intrinsic numerical viscosity. We find one of
the central schemes introduces a numerical viscosity term too, which is beyond
the common understanding in the convection-diffusion community. Careful
analysis is presented to prove that the other central scheme does work. Our
study shows that the numerical methods should be carefully chosen and any
method with intrinsic numerical viscosity must be avoided.Comment: 17 pages, 8 figure
A Scatter Search Approach for Multiobjective Selective Disassembly Sequence Problem
Disassembly sequence has received much attention in recent years. This work proposes a multiobjective optimization of model for selective disassembly sequences and maximizing disassembly profit and minimizing disassembly time. An improved scatter search (ISS) is adapted to solve proposed multiobjective optimization model, which embodies diversification generation of initial solutions, crossover combination operator, the local search strategy to improve the quality of new solutions, and reference set update method. To analyze the effect on the performance of ISS, simulation experiments are conducted on different products. The validity of ISS is verified by comparing the optimization effects of ISS and nondominated sorting genetic algorithm (NSGA-II)
A phase field model for mass transport with semi-permeable interfaces
In this paper, a thermal-dynamical consistent model for mass transfer across
permeable moving interfaces is proposed by using the energy variation method.
We consider a restricted diffusion problem where the flux across the interface
depends on its conductance and the difference of the concentration on each
side. The diffusive interface phase-field framework used here has several
advantages over the sharp interface method. First of all, explicit tracking of
the interface is no longer necessary. Secondly, the interfacial condition can
be incorporated with a variable diffusion coefficient. A detailed asymptotic
analysis confirms the diffusive interface model converges to the existing sharp
interface model as the interface thickness goes to zero. A decoupled energy
stable numerical scheme is developed to solve this system efficiently.
Numerical simulations first illustrate the consistency of theoretical results
on the sharp interface limit. Then a convergence study and energy decay test
are conducted to ensure the efficiency and stability of the numerical scheme.
To illustrate the effectiveness of our phase-field approach, several examples
are provided, including a study of a two-phase mass transfer problem where
drops with deformable interfaces are suspended in a moving fluid.Comment: 20 pages, 15 figure
Using Shallow Platform Drilling Technology to Tap the Reserves of the Below Constructed Area of Fuyu Oilfield: Taking Chengping Block 12 as an Example
The special geographical conditions in the below constructed area of the surface have caused the poor oil-water well condition, incomplete well patterns, difficult measures for tapping potential, and no effective development of reserves, which have affected the comprehensive adjustment of Fuyu oilfield. In order to solve this problem, the shallow large platform horizontal well technology was studied in Fuyu oilfield by taking Chengping 12 reservoir as an example. This technology has been successfully applied under limited ground conditions, and underground reserves have been fully utilized. This study has laid a solid foundation for fuyu oilfield to increase recoverable reserves and achieve stable production during the 12th Five-year plan
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