21,488 research outputs found
Adaptive FE-BE coupling for strongly nonlinear transmission problems with friction II
This article discusses the well-posedness and error analysis of the coupling
of finite and boundary elements for transmission or contact problems in
nonlinear elasticity. It concerns W^{1,p}-monotone Hencky materials with an
unbounded stress-strain relation, as they arise in the modelling of ice sheets,
non-Newtonian fluids or porous media. For 1<p<2 the bilinear form of the
boundary element method fails to be continuous in natural function spaces
associated to the nonlinear operator. We propose a functional analytic
framework for the numerical analysis and obtain a priori and a posteriori error
estimates for Galerkin approximations to the resulting boundary/domain
variational inequality. The a posteriori estimate complements recent estimates
obtained for mixed finite element formulations of friction problems in linear
elasticity.Comment: 20 pages, corrected typos and improved expositio
Vibrational transfer functions for base excited systems
Computer program GD203 develops transfer functions to compute governing vibration environment for complex structures subjected to a base motion
A Nash-Hormander iteration and boundary elements for the Molodensky problem
We investigate the numerical approximation of the nonlinear Molodensky
problem, which reconstructs the surface of the earth from the gravitational
potential and the gravity vector. The method, based on a smoothed
Nash-Hormander iteration, solves a sequence of exterior oblique Robin problems
and uses a regularization based on a higher-order heat equation to overcome the
loss of derivatives in the surface update. In particular, we obtain a
quantitative a priori estimate for the error after m steps, justify the use of
smoothing operators based on the heat equation, and comment on the accurate
evaluation of the Hessian of the gravitational potential on the surface, using
a representation in terms of a hypersingular integral. A boundary element
method is used to solve the exterior problem. Numerical results compare the
error between the approximation and the exact solution in a model problem.Comment: 32 pages, 14 figures, to appear in Numerische Mathemati
Chaos properties and localization in Lorentz lattice gases
The thermodynamic formalism of Ruelle, Sinai, and Bowen, in which chaotic
properties of dynamical systems are expressed in terms of a free energy-type
function - called the topological pressure - is applied to a Lorentz Lattice
Gas, as typical for diffusive systems with static disorder. In the limit of
large system sizes, the mechanism and effects of localization on large clusters
of scatterers in the calculation of the topological pressure are elucidated and
supported by strong numerical evidence. Moreover it clarifies and illustrates a
previous theoretical analysis [Appert et al. J. Stat. Phys. 87,
chao-dyn/9607019] of this localization phenomenon.Comment: 32 pages, 19 Postscript figures, submitted to PR
Long titanium heat pipes for high-temperature space radiators
Titanium heat pipes are being developed to provide light weight, reliable heat rejection devices as an alternate radiator design for the Space Reactor Power System (SP-100). The radiator design includes 360 heat pipes, each of which is 5.2 m long and dissipates 3 kW of power at 775 K. The radiator heat pipes use potassium as the working fluid, have two screen arteries for fluid return, a roughened surface distributive wicking system, and a D shaped cross section container configuration. A prototype titanium heat pipe, 5.5 m long, was fabricated and tested in space simulating conditions. Results from startup and isothermal operation tests are presented. These results are also compared to theoretical performance predictions that were used to design the heat pipe initially
- …