1,323 research outputs found
TVD differencing on three-dimensional unstructured meshes with monotonicity-preserving correction of mesh skewness
This data set contains the data accompanying the article F. Denner and B. van Wachem, TVD differencing on three-dimensional unstructured meshes with monotonicity-preserving correction of mesh skewness, Journal of Computational Physics (2015), http://dx.doi.org/10.1016/j.jcp.2015.06.008.This data set contains the data accompanying the article F. Denner and B. van Wachem, TVD differencing on three-dimensional unstructured meshes with monotonicity-preserving correction of mesh skewness, Journal of Computational Physics (2015), http://dx.doi.org/10.1016/j.jcp.2015.06.008
Artificial viscosity model to mitigate numerical artefacts at fluid interfaces with surface tension
The numerical onset of parasitic and spurious artefacts in the vicinity of uid interfaces with surface tension is an important and well-recognised problem with respect to the accuracy and numerical stability of interfacial ow simulations. Issues of particular interest are spurious capillary waves, which are spatially underresolved by the computational mesh yet impose very restrictive time-step requirements, as well as parasitic currents, typically the result of a numerically unbalanced curvature evaluation. We present an arti cial viscosity model to mitigate numerical artefacts at surface-tension-dominated interfaces without adversely a ecting the accuracy of the physical solution. The proposed methodology computes an additional interfacial shear stress term, including an interface viscosity, based on the local ow data and uid properties that reduces the impact of numerical artefacts and dissipates underresolved small scale interface movements. Furthermore, the presented methodology can be readily applied to model surface shear viscosity, for instance to simulate the dissipative e ect of surface-active substances adsorbed at the interface. The presented analysis of numerical test cases demonstrates the e cacy of the proposed methodology in diminishing the adverse impact of parasitic and spurious interfacial artefacts on the convergence and stability of the numerical solution algorithm as well as on the overall accuracy of the simulation results
Two-loop electroweak next-to-leading logarithmic corrections to massless fermionic processes
We consider two-loop leading and next-to-leading logarithmic virtual
corrections to arbitrary processes with external massless fermions in the
electroweak Standard Model at energies well above the electroweak scale. Using
the sector-decomposition method and alternatively the strategy of regions we
calculate the mass singularities that arise as logarithms of Q^2/MW^2, where Q
is the energy scale of the considered process, and 1/\epsilon poles in
D=4-2\epsilon dimensions, to one- and two-loop next-to-leading logarithmic
accuracy. The derivations are performed within the complete electroweak theory
with spontaneous symmetry breaking. Our results indicate a close analogy
between the form of two-loop electroweak logarithmic corrections and the
singular structure of scattering amplitudes in massless QCD. We find agreement
with the resummation prescriptions that have been proposed in the literature
based on a symmetric SU(2) \times U(1) theory matched with QED at the
electroweak scale and provide new next-to-leading contributions proportional to
ln(MZ^2/MW^2).Comment: 63 pages, LaTeX, references updated, some typos corrected, version to
appear in Nucl. Phys.
Self-similarity of solitary waves on inertia-dominated falling liquid films
We propose consistent scaling of solitary waves on inertia-dominated falling liquid films, which accurately accounts for the driving physical mechanisms and leads to a self-similar characterization of solitary waves. Direct numerical simulations of the entire two-phase system are conducted using a state-of-the-art finite volume framework for interfacial flows in an open domain that was previously validated against experimental film-flow data with excellent agreement. We present a detailed analysis of the wave shape and the dispersion of solitary waves on 34 different water films with Reynolds numbers Re=20–120 and surface tension coefficients σ=0.0512–0.072Nm−1 on substrates with inclination angles β=19◦ − 90◦. Following a detailed analysis of these cases we formulate a consistent characterization of the shape and dispersion of solitary waves, based on a newly proposed scaling derived from the Nusselt flat film solution, that unveils a self-similarity as well as the driving mechanism of solitary waves on gravity-driven liquid films. Our results demonstrate that the shape of solitary waves, i.e., height and asymmetry of the wave, is predominantly influenced by the balance of inertia and surface tension. Furthermore, we find that the dispersion of solitary waves on the inertia-dominated falling liquid films considered in this study is governed by nonlinear effects and only driven by inertia, with surface tension and gravity having a negligible influence
Fermionic and Scalar Corrections for the Abelian Form Factor at Two Loops
Two-loop corrections for the form factor in a massive Abelian theory are
evaluated, which result from the insertion of massless fermion or scalar loops
into the massive gauge boson propagator. The result is valid for arbitrary
energies and gauge boson mass. Power-suppressed terms vanish rapidly in the
high energy region where the result is well approximated by a polynomial of
third order in ln(s/M^2). The relative importance of subleading logarithms is
emphasised.Comment: Latex, 10 pages, 5 figures. B. Feucht is B. Jantzen in later
publications. (The contents of the paper is unchanged.
A closed expression for the UV-divergent parts of one-loop tensor integrals in dimensional regularization
Starting from the general definition of a one-loop tensor N-point function,
we use its Feynman parametrization to calculate the UV-divergent part of an
arbitrary tensor coefficient in the framework of dimensional regularization. In
contrast to existing recursion schemes, we are able to present a general
analytic result in closed form that enables direct determination of the
UV-divergent part of any one-loop tensor N-point coefficient independent from
UV-divergent parts of other one-loop tensor N-point coefficients. Simplified
formulas and explicit expressions are presented for A-, B-, C-, D-, E-, and
F-functions.Comment: 19 pages (single column), the result of previous versions is further
evaluated leading to a closed analytic expression for the UV-divergent part
of an arbitrary one-loop tensor coefficient, title is modified accordingly, a
sign error in the appendix (C_{00000000}) has been corrected, a mathematica
notebook containing an implementation of the newly derived formula is
attache
Weak Boson Emission in Hadron Collider Processes
The O(alpha) virtual weak radiative corrections to many hadron collider
processes are known to become large and negative at high energies, due to the
appearance of Sudakov-like logarithms. At the same order in perturbation
theory, weak boson emission diagrams contribute. Since the W and Z bosons are
massive, the O(alpha) virtual weak radiative corrections and the contributions
from weak boson emission are separately finite. Thus, unlike in QED or QCD
calculations, there is no technical reason for including gauge boson emission
diagrams in calculations of electroweak radiative corrections. In most
calculations of the O(alpha) electroweak radiative corrections, weak boson
emission diagrams are therefore not taken into account. Another reason for not
including these diagrams is that they lead to final states which differ from
that of the original process. However, in experiment, one usually considers
partially inclusive final states. Weak boson emission diagrams thus should be
included in calculations of electroweak radiative corrections. In this paper, I
examine the role of weak boson emission in those processes at the Fermilab
Tevatron and the CERN LHC for which the one-loop electroweak radiative
corrections are known to become large at high energies (inclusive jet, isolated
photon, Z+1 jet, Drell-Yan, di-boson, t-bar t, and single top production). In
general, I find that the cross section for weak boson emission is substantial
at high energies and that weak boson emission and the O(alpha) virtual weak
radiative corrections partially cancel.Comment: revtex3, 41 pages, 16 figures, 3 table
Supersymmetric Corrections to the Threshold Production of Top Quark Pairs
In this paper we investigate supersymmetric effects to the threshold
production cross section of top quark pairs in electron positron annihilation.
In particular, we consider the complete one-loop corrections from the strong
and weak sector of the Minimal Supersymmetric Standard Model.Comment: 18 pages, 7 figure
Estimation of curvature from volume fractions using parabolic reconstruction on two-dimensional unstructured meshes
This paper proposes a method to estimate the curvature of an interface represented implicitly by discrete volume fractions on an unstructured two-dimensional mesh. The method relies on the computation of local parabolic reconstructions of the interface. The parabolic reconstruction of the interface in a given computational cell is obtained by solving a local non-linear minimisation problem, and only requires additional information from two neighbouring cells. This compactness ensures a robust behaviour on poorly-resolved interfaces. The proposed method is proven to be analogous to the height-function method for Cartesian configurations with consistent heights, and can be interpreted as a generalisation of the height-function method to meshes of any type. Tests are conducted on a range of interfaces with known curvature. The method is shown to converge with mesh refinement with the same order of accuracy as the height-function method for all three types of meshes tested, i.e. Cartesian, triangular, and polygonal
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