590 research outputs found
Fully-implicit log-conformation formulation of constitutive laws
Subject of this paper is the derivation of a new constitutive law in terms of
the logarithm of the conformation tensor that can be used as a full substitute
for the 2D governing equations of the Oldroyd-B, Giesekus and other models. One
of the key features of these new equations is that - in contrast to the
original log-conf equations given by Fattal and Kupferman (2004) - these
constitutive equations combined with the Navier-Stokes equations constitute a
self-contained, non-iterative system of partial differential equations. In
addition to its potential as a fruitful source for understanding the
mathematical subtleties of the models from a new perspective, this analytical
description also allows us to fully utilize the Newton-Raphson algorithm in
numerical simulations, which by design should lead to reduced computational
effort. By means of the confined cylinder benchmark we will show that a finite
element discretization of these new equations delivers results of comparable
accuracy to known methods.Comment: 21 pages, 5 figure
Boundary-Conforming Finite Element Methods for Twin-Screw Extruders: Unsteady - Temperature-Dependent - Non-Newtonian Simulations
We present a boundary-conforming space-time finite element method to compute
the flow inside co-rotating, self-wiping twin-screw extruders. The mesh update
is carried out using the newly developed Snapping Reference Mesh Update Method
(SRMUM). It allows to compute time-dependent flow solutions inside twin-screw
extruders equipped with conveying screw elements without any need for
re-meshing and projections of solutions - making it a very efficient method. We
provide cases for Newtonian and non-Newtonian fluids in 2D and 3D, that show
mesh convergence of the solution as well as agreement to experimental results.
Furthermore, a complex, unsteady and temperature-dependent 3D test case with
multiple screw elements illustrates the potential of the method also for
industrial applications
Automatic implementation of material laws: Jacobian calculation in a finite element code with TAPENADE
In an effort to increase the versatility of finite element codes, we explore
the possibility of automatically creating the Jacobian matrix necessary for the
gradient-based solution of nonlinear systems of equations. Particularly, we aim
to assess the feasibility of employing the automatic differentiation tool
TAPENADE for this purpose on a large Fortran codebase that is the result of
many years of continuous development. As a starting point we will describe the
special structure of finite element codes and the implications that this code
design carries for an efficient calculation of the Jacobian matrix. We will
also propose a first approach towards improving the efficiency of such a
method. Finally, we will present a functioning method for the automatic
implementation of the Jacobian calculation in a finite element software, but
will also point out important shortcomings that will have to be addressed in
the future.Comment: 17 pages, 9 figure
Combining Boundary-Conforming Finite Element Meshes on Moving Domains Using a Sliding Mesh Approach
For most finite element simulations, boundary-conforming meshes have
significant advantages in terms of accuracy or efficiency. This is particularly
true for complex domains. However, with increased complexity of the domain,
generating a boundary-conforming mesh becomes more difficult and time
consuming. One might therefore decide to resort to an approach where individual
boundary-conforming meshes are pieced together in a modular fashion to form a
larger domain. This paper presents a stabilized finite element formulation for
fluid and temperature equations on sliding meshes. It couples the solution
fields of multiple subdomains whose boundaries slide along each other on common
interfaces. Thus, the method allows to use highly tuned boundary-conforming
meshes for each subdomain that are only coupled at the overlapping boundary
interfaces. In contrast to standard overlapping or fictitious domain methods
the coupling is broken down to few interfaces with reduced geometric dimension.
The formulation consists of the following key ingredients: the coupling of the
solution fields on the overlapping surfaces is imposed weakly using a
stabilized version of Nitsche's method. It ensures mass and energy conservation
at the common interfaces. Additionally, we allow to impose weak Dirichlet
boundary conditions at the non-overlapping parts of the interfaces. We present
a detailed numerical study for the resulting stabilized formulation. It shows
optimal convergence behavior for both Newtonian and generalized Newtonian
material models. Simulations of flow of plastic melt inside single-screw as
well as twin-screw extruders demonstrate the applicability of the method to
complex and relevant industrial applications
ВИПУСКНИК КАТЕРИНОСЛАВСЬКОГО ГІРНИЧОГО ІНСТИТУТУ – БУДІВНИЧИЙ ВИЩОЇ ГІРНИЧОЇ ОСВІТИ У КРИВОМУ РОЗІ
У статті досліджено життєвий і трудовий шлях засновника і першого керівника Криворізького вечірнього робітничого технікуму В.І. ЖигаловськогоThe article studied the life and career of the founder and first director of Krivoy Rog evening working college V.I. Zhigalovskiy
Simplex space-time meshes in thermally coupled two-phase flow simulations of mold filling
The quality of plastic parts produced through injection molding depends on
many factors. Especially during the filling stage, defects such as weld lines,
burrs, or insufficient filling can occur. Numerical methods need to be employed
to improve product quality by means of predicting and simulating the injection
molding process. In the current work, a highly viscous incompressible
non-isothermal two-phase flow is simulated, which takes place during the cavity
filling. The injected melt exhibits a shear-thinning behavior, which is
described by the Carreau-WLF model. Besides that, a novel discretization method
is used in the context of 4D simplex space-time grids [2]. This method allows
for local temporal refinement in the vicinity of, e.g., the evolving front of
the melt [10]. Utilizing such an adaptive refinement can lead to locally
improved numerical accuracy while maintaining the highest possible
computational efficiency in the remaining of the domain. For demonstration
purposes, a set of 2D and 3D benchmark cases, that involve the filling of
various cavities with a distributor, are presented.Comment: 14 pages, 11 Figures, 4 Table
Wavelet-based Adaptive Techniques Applied to Turbulent Hypersonic Scramjet Intake Flows
The simulation of hypersonic flows is computationally demanding due to large
gradients of the flow variables caused by strong shock waves and thick boundary
or shear layers. The resolution of those gradients imposes the use of extremely
small cells in the respective regions. Taking turbulence into account
intensives the variation in scales even more. Furthermore, hypersonic flows
have been shown to be extremely grid sensitive. For the simulation of
three-dimensional configurations of engineering applications, this results in a
huge amount of cells and prohibitive computational time. Therefore, modern
adaptive techniques can provide a gain with respect to computational costs and
accuracy, allowing the generation of locally highly resolved flow regions where
they are needed and retaining an otherwise smooth distribution. An h-adaptive
technique based on wavelets is employed for the solution of hypersonic flows.
The compressible Reynolds averaged Navier-Stokes equations are solved using a
differential Reynolds stress turbulence model, well suited to predict
shock-wave-boundary-layer interactions in high enthalpy flows. Two test cases
are considered: a compression corner and a scramjet intake. The compression
corner is a classical test case in hypersonic flow investigations because it
poses a shock-wave-turbulent-boundary-layer interaction problem. The adaptive
procedure is applied to a two-dimensional confguration as validation. The
scramjet intake is firstly computed in two dimensions. Subsequently a
three-dimensional geometry is considered. Both test cases are validated with
experimental data and compared to non-adaptive computations. The results show
that the use of an adaptive technique for hypersonic turbulent flows at high
enthalpy conditions can strongly improve the performance in terms of memory and
CPU time while at the same time maintaining the required accuracy of the
results.Comment: 26 pages, 29 Figures, submitted to AIAA Journa
ОЦЕНКА ОСНОВНЫХ СОСТАВЛЯЮЩИХ ПОГРЕШНОСТИ КАНАЛА ИЗМЕРЕНИЯ СИСТЕМЫ ЭЛЕКТРОМАГНИТНОГО КОНТРОЛЯ СТРУКТУРООБРАЗОВАНИЯ В ПРОКАТЕ
Кратко рассмотрены структура и принцип
действия системы электромагнитного контроля
структурообразования в прокате. Проведена
оценка величины основных составляющих
погрешности канала измерения системы.
Предложены пути уменьшения результирующей
погрешности
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