160 research outputs found
Some basic formulations of the virtual element method (VEM) for finite deformations
Abstract We present a general virtual element method (VEM) framework for finite elasticity, which emphasizes two issues: element-level volume change (volume average of the determinant of the deformation gradient) and stabilization. To address the former issue, we provide exact evaluation of the average volume change in both 2D and 3D on properly constructed local displacement spaces. For the later issue, we provide a new stabilization scheme that is based on the trace of the material tangent modulus tensor, which captures highly heterogeneous and localized deformations. Two VEM formulations are presented: a two-field mixed and an equivalent displacement-based, which is free of volumetric locking. Convergence and accuracy of the VEM formulations are verified by means of numerical examples, and engineering applications are demonstrated
On the regularity up to the boundary for certain nonlinear elliptic systems
We consider a class of nonlinear elliptic systems and we prove regularity up to the boundary for second order derivatives. In the proof we trace carefully the dependence on the various parameters of the problem, in order to establish, in a further work, results for more general systems
A posteriori error estimates for the virtual element method
An a posteriori error analysis for the virtual element method (VEM) applied to general elliptic problems is presented. The resulting error estimator is of residual-type and applies on very general polygonal/polyhedral meshes. The estimator is fully computable as it relies only on quantities available from the VEM solution, namely its degrees of freedom and element-wise polynomial projection. Upper and lower bounds of the error estimator with respect to the VEM approximation error are proven. The error estimator is used to drive adaptive mesh refinement in a number of test problems. Mesh adaptation is particularly simple to implement since elements with consecutive co-planar edges/faces are allowed and, therefore, locally adapted meshes do not require any local mesh post-processing
Vanishing Viscous Limits for 3D Navier-Stokes Equations with A Navier-Slip Boundary Condition
In this paper, we investigate the vanishing viscosity limit for solutions to
the Navier-Stokes equations with a Navier slip boundary condition on general
compact and smooth domains in . We first obtain the higher order
regularity estimates for the solutions to Prandtl's equation boundary layers.
Furthermore, we prove that the strong solution to Navier-Stokes equations
converges to the Eulerian one in and
L^\infty((0,T)\times\o), where is independent of the viscosity, provided
that initial velocity is regular enough. Furthermore, rates of convergence are
obtained also.Comment: 45page
Weak in Space, Log in Time Improvement of the Lady{\v{z}}enskaja-Prodi-Serrin Criteria
In this article we present a Lady{\v{z}}enskaja-Prodi-Serrin Criteria for
regularity of solutions for the Navier-Stokes equation in three dimensions
which incorporates weak norms in the space variables and log improvement
in the time variable.Comment: 14 pages, to appea
Viscous-Inviscid Interactions in a Boundary-Layer Flow Induced by a Vortex Array
In this paper we investigate the asymptotic validity of boundary layer
theory. For a flow induced by a periodic row of point-vortices, we compare
Prandtl's solution to Navier-Stokes solutions at different numbers. We
show how Prandtl's solution develops a finite time separation singularity. On
the other hand Navier-Stokes solution is characterized by the presence of two
kinds of viscous-inviscid interactions between the boundary layer and the outer
flow. These interactions can be detected by the analysis of the enstrophy and
of the pressure gradient on the wall. Moreover we apply the complex singularity
tracking method to Prandtl and Navier-Stokes solutions and analyze the previous
interactions from a different perspective
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