2,046 research outputs found
Constitutive Modelling of Soils and Computation of Earthquake Damage and Liquefaction
For realistic modelling oi deformation and collapse of soil structures, an accurate constitutive model for the soil materials is necessary. In this paper we shall show i) how such very successful models can be obtained by the use of generalized plasticity theory; ii) the modification of such models for semi-saturated behavior; and finally iii) How incorporation of such models into a two phase computer program allows the solution of complex problems. A possible mode of failure of the San Fernando dam is included. This paper is divided into three parts according to the above
Monocular, Real-Time Surface Reconstruction using Dynamic Level of Detail
We present a scalable, real-time capable method for robust surface reconstruction that explicitly handles multiple scales. As a monocular camera browses a scene, our algorithm processes images as they arrive and incrementally builds a detailed surface model. While most of the existing reconstruction approaches rely on volumetric or point-cloud representations of the environment, we perform depth-map and colour fusion directly into a multi-resolution triangular mesh that can be adaptively tessellated using the concept of Dynamic Level of Detail. Our method relies on least-squares optimisation, which enables a probabilistically sound and principled formulation of the fusion algorithm. We demonstrate that our method is capable of obtaining high quality, close-up reconstruction, as well as capturing overall scene geometry, while being memory and computationally efficient
Generalized Berreman's model of the elastic surface free energy of a nematic liquid crystal on a sawtoothed substrate
In this paper we present a generalization of Berreman's model for the elastic
contribution to the surface free-energy density of a nematic liquid crystal in
presence of a sawtooth substrate which favours homeotropic anchoring, as a
function of the wavenumber of the surface structure , the tilt angle
and the surface anchoring strength . In addition to the previously
reported non-analytic contribution proportional to , due to the
nucleation of disclination lines at the wedge bottoms and apexes of the
substrate, the next-to-leading contribution is proportional to for a given
substrate roughness, in agreement with Berreman's predictions. We characterise
this term, finding that it has two contributions: the deviations of the nematic
director field with respect to the corresponding to the isolated disclination
lines, and their associated core free energies. Comparison with the results
obtained from the Landau-de Gennes model shows that our model is quite accurate
in the limit , when strong anchoring conditions are effectively achieved.Comment: 13 pages, 9 figures; revised version submitted to Phys. Rev.
Maximizing the hyperpolarizability of one-dimensional systems
Previous studies have used numerical methods to optimize the
hyperpolarizability of a one-dimensional quantum system. These studies were
used to suggest properties of one-dimensional organic molecules, such as the
degree of modulation of conjugation, that could potentially be adjusted to
improve the nonlinear-optical response. However, there were no conditions set
on the optimized potential energy function to ensure that the resulting
energies were consistent with what is observed in real molecules. Furthermore,
the system was placed into a one-dimensional box with infinite walls, forcing
the wavefunctions to vanish at the ends of the molecule. In the present work,
the walls are separated by a distance much larger than the molecule's length;
and, the variations of the potential energy function are restricted to levels
that are more typical of a real molecule. In addition to being a more
physically-reasonable model, our present approach better approximates the bound
states and approximates the continuum states - which are usually ignored. We
find that the same universal properties continue to be important for optimizing
the nonlinear-optical response, though the details of the wavefunctions differ
from previous result.Comment: 10 pages, 5 figure
Recommended from our members
Finite-Element Model for Pretensioned Prestressed Concrete Girders
This paper presents a nonlinear model for pretensioned prestressed concrete girders. The model consists of three main components: a beam-column element that describes the behavior of concrete, a truss element that describes the behavior of prestressing tendons, and a bond element that describes the transfer of stresses between the prestressing tendons and the concrete. The model is based on a two-field mixed formulation, where forces and deformations are both approximated within the element. The nonlinear response of the concrete and tendon components is based on the section discretization into fibers with uniaxial hysteretic material models. The stress transfer mechanism is modeled with a distributed interface element with special bond stress-slip relation. A method for accurately simulating the prestressing operation is presented. Accordingly, a complete nonlinear analysis is performed at the different stages of prestressing. Correlation studies of the proposed model with experimental results of pretensioned specimens are conducted. These studies confirmed the accuracy and efficiency of the model
A stabilized finite point method for analysis of fluid mechanics problems
flow type problems is presented. The method is based on the use of a weighted
least square interpolation procedure together with point collocation for evaluating the
approximation integrals. Some examples of application to convective trasport and
compressible flow problems are presented
Modelling Heat Transfer of Carbon Nanotubes
Modelling heat transfer of carbon nanotubes is important for the thermal
management of nanotube-based composites and nanoelectronic device. By using a
finite element method for three-dimensional anisotropic heat transfer, we have
simulated the heat conduction and temperature variations of a single nanotube,
a nanotube array and a part of nanotube-based composite surface with heat
generation. The thermal conductivity used is obtained from the upscaled value
from the molecular simulations or experiments. Simulations show that nanotube
arrays have unique cooling characteristics due to its anisotropic thermal
conductivity.Comment: 10 pages, 4 figure
A node-based smoothed conforming point interpolation method (NS-CPIM) for elasticity problems
This paper formulates a node-based smoothed conforming point interpolation method (NS-CPIM) for solid mechanics. In the proposed NS-CPIM, the higher order conforming PIM shape functions (CPIM) have been constructed to produce a continuous and piecewise quadratic displacement field over the whole problem domain, whereby the smoothed strain field was obtained through smoothing operation over each smoothing domain associated with domain nodes. The smoothed Galerkin weak form was then developed to create the discretized system equations. Numerical studies have demonstrated the following good properties: NS-CPIM (1) can pass both standard and quadratic patch test; (2) provides an upper bound of strain energy; (3) avoid the volumetric locking; (4) provides the higher accuracy than those in the node-based smoothed schemes of the original PIMs
Control-volume representation of molecular dynamics
A Molecular Dynamics (MD) parallel to the Control Volume (CV) formulation of
fluid mechanics is developed by integrating the formulas of Irving and
Kirkwood, J. Chem. Phys. 18, 817 (1950) over a finite cubic volume of molecular
dimensions. The Lagrangian molecular system is expressed in terms of an
Eulerian CV, which yields an equivalent to Reynolds' Transport Theorem for the
discrete system. This approach casts the dynamics of the molecular system into
a form that can be readily compared to the continuum equations. The MD
equations of motion are reinterpreted in terms of a
Lagrangian-to-Control-Volume (\CV) conversion function , for
each molecule . The \CV function and its spatial derivatives are used to
express fluxes and relevant forces across the control surfaces. The
relationship between the local pressures computed using the Volume Average (VA,
Lutsko, J. Appl. Phys 64, 1152 (1988)) techniques and the Method of Planes
(MOP, Todd et al, Phys. Rev. E 52, 1627 (1995)) emerges naturally from the
treatment. Numerical experiments using the MD CV method are reported for
equilibrium and non-equilibrium (start-up Couette flow) model liquids, which
demonstrate the advantages of the formulation. The CV formulation of the MD is
shown to be exactly conservative, and is therefore ideally suited to obtain
macroscopic properties from a discrete system.Comment: 19 pages, 15 figure
- …