150 research outputs found
Finite Element Analysis of an Arbitrary Lagrangian–Eulerian Method for Stokes/Parabolic Moving Interface Problem With Jump Coefficients
In this paper, a type of arbitrary Lagrangian–Eulerian (ALE) finite element method in the monolithic frame is developed for a linearized fluid–structure interaction (FSI) problem — an unsteady Stokes/parabolic interface problem with jump coefficients and moving interface, where, the corresponding mixed finite element approximation in both semi- and fully discrete scheme are developed and analyzed based upon one type of ALE formulation and a novel H1- projection technique associated with a moving interface problem, and the stability and optimal convergence properties in the energy norm are obtained for both discretizations to approximate the solution of a transient Stokes/parabolic interface problem that is equipped with a low regularity. Numerical experiments further validate all theoretical results. The developed analytical approaches and numerical implementations can be similarly extended to a realistic FSI problem in the future
Distributed Lagrange Multiplier/Fictitious Domain Finite Element Method for a Transient Stokes Interface Problem with Jump Coefficients
The distributed Lagrange multiplier/fictitious domain (DLM/FD)-mixed finite element method is developed and analyzed in this paper for a transient Stokes interface problem with jump coefficients. The semi- and fully discrete DLM/FD-mixed finite element scheme are developed for the first time for this problem with a moving interface, where the arbitrary Lagrangian-Eulerian (ALE) technique is employed to deal with the moving and immersed subdomain. Stability and optimal convergence properties are obtained for both schemes. Numerical experiments are carried out for different scenarios of jump coefficients, and all theoretical results are validated
Numerical Analysis of Finite Element Method for a Transient Two-phase Transport Model of Polymer Electrolyte Fuel Cell
AbstractIn this paper, we study a 2D transient two-phase transport model for water species in the cathode gas diffusion layer of hydrogen polymer electrolyte fuel cell (PEFC), the reformulation of water concentration equation is described by using Kirchhoff transformation, and its numerical efficiency is demonstrated by successfully dealing with the discontinuous and degenerate water diffusivity. The semi-discrete and fully discrete finite element approximations with Crank-Nicolson scheme are developed for the present model and the optimal error estimate in H1 norm and the sub-optimal error estimate in L2 norm are established for both finite element schemes
An Efficient Two-grid Method for a Two-phase Mixed-domain Model of Polymer Exchange Membrane Fuel Cell
AbstractIn this paper, an efficientandfast numerical methodis studiedand implementedfora simplifiedtwo-phasemixed domain model of polymer exchange membrane fuel cell (PEMFC), which fully incorporates both the anode and cathode sides, including the conservation equations of mass, momentum, water vapor concentration, liquid water saturationandwater content.Theproposed numericalalgorithmisbasedonthetwo-grid discretization technique,the combined finite element-upwind finitevolume method and some other appropriate linearization schemes. The original nonlinear partial differential equations are only solved on the coarse grid while the fine grid approximation solution is obtained linearly. Therefore the computational time can be reduced tremendously compared with the traditional one-grid method. Numerical experiments of the two-grid method and conventional method for a two-phase mixed domain fuel cell model are carried out, showing that the presented method is effective and accurate for the numerical simulation of PEMFC
A Deep Neural Network/Meshfree Method for Solving Dynamic Two-phase Interface Problems
In this paper, a meshfree method using the deep neural network (DNN) approach
is developed for solving two kinds of dynamic two-phase interface problems
governed by different dynamic partial differential equations on either side of
the stationary interface with the jump and high-contrast coefficients. The
first type of two-phase interface problem to be studied is the fluid-fluid
(two-phase flow) interface problem modeled by Navier-Stokes equations with
high-contrast physical parameters across the interface. The second one belongs
to fluid-structure interaction (FSI) problems modeled by Navier-Stokes
equations on one side of the interface and the structural equation on the other
side of the interface, both the fluid and the structure interact with each
other via the kinematic- and the dynamic interface conditions across the
interface. The DNN/meshfree method is respectively developed for the above
two-phase interface problems by representing solutions of PDEs using the DNNs'
structure and reformulating the dynamic interface problem as a least-squares
minimization problem based upon a space-time sampling point set. Approximation
error analyses are also carried out for each kind of interface problem, which
reveals an intrinsic strategy about how to efficiently build a sampling-point
training dataset to obtain a more accurate DNNs' approximation. In addition,
compared with traditional discretization approaches, the proposed DNN/meshfree
method and its error analysis technique can be smoothly extended to many other
dynamic interface problems with fixed interfaces. Numerical experiments are
conducted to illustrate the accuracies of the proposed DNN/meshfree method for
the presented two-phase interface problems. Theoretical results are validated
to some extent through three numerical examples
A Projection-Based Time-Segmented Reduced Order Model for Fluid-Structure Interactions
In this paper, a type of novel projection-based, time-segmented reduced order
model (ROM) is proposed for dynamic fluid-structure interaction (FSI) problems
based upon the arbitrary Lagrangian--Eulerian (ALE)-finite element method (FEM)
in a monolithic frame, where spatially, each variable is separated from others
in terms of their attribution (fluid/structure), category (velocity/pressure)
and component (horizontal/vertical) while temporally, the proper orthogonal
decomposition (POD) bases are constructed in some deliberately partitioned time
segments tailored through extensive numerical trials. By the combination of
spatial and temporal decompositions, the developed ROM approach enables
prolonged simulations under prescribed accuracy thresholds. Numerical
experiments are carried out to compare numerical performances of the proposed
ROM with corresponding full-order model (FOM) by solving a two-dimensional FSI
benchmark problem that involves a vibrating elastic beam in the fluid, where
the performance of offline ROM on perturbed physical parameters in the online
phase is investigated as well. Extensive numerical results demonstrate that the
proposed ROM has a comparable accuracy to while much higher efficiency than the
FOM. The developed ROM approach is dimension-independent and can be seamlessly
extended to solve high dimensional FSI problems
ANALYSIS OF A VIBRATING-BEAM-BASED MICROMIXER
ABSTRACT The mixing of two or more streams in microscale devices is a slowly molecular diffusion process due to the unique laminar flows, and some 'turbulence' based mixing technologies which are effective in macroscales become hard to implement in such small dimensions. The chaotic advection based mixing, depending on the stretching and folding of interface, has been proved to be effective for low Reynolds numbers (Re) and is a very promising technology for micro mixing. We propose a new mixing concept based on a vibrating micro-beam in microfluidic channels to generate chaotic advection to achieve an efficient mixing. The simplicity of the proposed mixer design makes microfabrication process easy for practical applications. The feasibility of the concept is evaluated computationally and moving mesh technique (ALE) is utilized to trace the beam movement. The simulation shows that the mixing quality is determined by parameters such as flow velocities, amplitudes and frequencies of vibrating beam. The Reynolds number (Re) is less than 2.0, Pelect number (Pe) ranges from 5 to 1000, and Strohal number (St) 0.3 to 3.0. It was found that vortex type of flows were generated in microchannel due to the interaction between beam and channel wall. The mixing efficiency with this design is well improved comparing with the flows without beam vibration
A Unified-Field Monolithic Fictitious Domain-Finite Element Method for Fluid-Structure-Contact Interactions and Applications to Deterministic Lateral Displacement Problems
Based upon two overlapped, body-unfitted meshes, a type of unified-field
monolithic fictitious domain-finite element method (UFMFD-FEM) is developed in
this paper for moving interface problems of dynamic fluid-structure
interactions (FSI) accompanying with high-contrast physical coefficients across
the interface and contacting collisions between the structure and fluidic
channel wall when the structure is immersed in the fluid. In particular, the
proposed novel numerical method consists of a monolithic, stabilized mixed
finite element method within the frame of fictitious domain/immersed boundary
method (IBM) for generic fluid-structure-contact interaction (FSCI) problems in
the Eulerian-updated Lagrangian description, while involving the no-slip type
of interface conditions on the fluid-structure interface, and the repulsive
contact force on the structural surface when the immersed structure contacts
the fluidic channel wall. The developed UFMFD-FEM for FSI or FSCI problems can
deal with the structural motion with large rotational and translational
displacements and/or large deformation in an accurate and efficient fashion,
which are first validated by two benchmark FSI problems and one FSCI model
problem, then by experimental results of a realistic FSCI scenario -- the
microfluidic deterministic lateral displacement (DLD) problem that is applied
to isolate circulating tumor cells (CTCs) from blood cells in the blood fluid
through a cascaded filter DLD microchip in practice, where a particulate fluid
with the pillar obstacles effect in the fluidic channel, i.e., the effects of
fluid-structure interaction and structure collision, play significant roles to
sort particles (cells) of different sizes with tilted pillar arrays.Comment: 32 pages, 42 figures, 5 tables, 66 reference
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