1,506 research outputs found
Proper conformal symmetries in SD Einstein spaces
Proper conformal symmetries in self-dual (SD) Einstein spaces are considered.
It is shown, that such symmetries are admitted only by the Einstein spaces of
the type [N]x[N]. Spaces of the type [N]x[-] are considered in details.
Existence of the proper conformal Killing vector implies existence of the
isometric, covariantly constant and null Killing vector. It is shown, that
there are two classes of [N]x[-]-metrics admitting proper conformal symmetry.
They can be distinguished by analysis of the associated anti-self-dual (ASD)
null strings. Both classes are analyzed in details. The problem is reduced to
single linear PDE. Some general and special solutions of this PDE are
presented
Local bisection for conformal refinement of unstructured 4D simplicial meshes
We present a conformal bisection procedure for
local refinement of 4D unstructured simplicial meshes with
bounded minimum shape quality. Specifically, we propose a
recursive refine-to-conformity procedure in two stages, based on
marking bisection edges on different priority levels and defining
specific refinement templates. Two successive applications
of the first stage ensure that any 4D unstructured mesh can
be conformingly refined. In the second stage, the successive
refinements lead to a cycle in the number of generated similarity
classes and thus, we can ensure a bound over the minimum
shape quality. In the examples, we check that after successive
refinement the mesh quality does not degenerate. Moreover, we
refine a 4D unstructured mesh and a space-time mesh (3D + 1D)
representation of a moving object
Compliance error compensation technique for parallel robots composed of non-perfect serial chains
The paper presents the compliance errors compensation technique for
over-constrained parallel manipulators under external and internal loadings.
This technique is based on the non-linear stiffness modeling which is able to
take into account the influence of non-perfect geometry of serial chains caused
by manufacturing errors. Within the developed technique, the deviation
compensation reduces to an adjustment of a target trajectory that is modified
in the off-line mode. The advantages and practical significance of the proposed
technique are illustrated by an example that deals with groove milling by the
Orthoglide manipulator that considers different locations of the workpiece. It
is also demonstrated that the impact of the compliance errors and the errors
caused by inaccuracy in serial chains cannot be taken into account using the
superposition principle.Comment: arXiv admin note: text overlap with arXiv:1204.175
Möbius Geometry and Cyclidic Nets: A Framework for Complex Shape Generation
International audienceFree-form architecture challenges architects, engineers and builders. The geometrical rationalization of complex structures requires sophisticated tools. To this day, two frameworks are commonly used: NURBS modeling and mesh-based approaches. The authors propose an alternative modeling framework called generalized cyclidic nets that automatically yields optimal geometrical properties for the façade and the structure. This framework uses a base circular mesh and Dupin cyclides, which are natural objects of the geometry of circles in space, also known as Möbius geometry. This paper illustrates how new shapes can be generated from generalized cyclidic nets. Finally, it is demonstrated that this framework gives a simple method to generate curved-creases on free-forms. These findings open new perspectives for structural design of complex shells
Euclidean distance geometry and applications
Euclidean distance geometry is the study of Euclidean geometry based on the
concept of distance. This is useful in several applications where the input
data consists of an incomplete set of distances, and the output is a set of
points in Euclidean space that realizes the given distances. We survey some of
the theory of Euclidean distance geometry and some of the most important
applications: molecular conformation, localization of sensor networks and
statics.Comment: 64 pages, 21 figure
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