253,687 research outputs found
Dynamical modelling of the motorised momentum exchange tether incorporating axial elastic effects
A discretised planar tether model is proposed for the Motorised Momentum Exchange Tether (MMET) in which axial elasticity is accommodated. The model uses a generalised co-ordinate defining angular motion of the tether
about its centre of mass, as it travels at constant velocity on a circular orbit in the Earth’s equatorial plane and a generalised coordinate depicting the
elastic part of the tether length. The system comprises a symmetrical double payload configuration, with outrigger counter inertia, and it is shown that including axial elasticity permits an enhanced level of modelling accuracy for the tether both in librating and spinning modes. A simulation has been devised in MATLAB and SIMULINK for different data cases. This work will be used later within a spin-up control system and will act as a precursor for
an in-depth study into the multi-scale dynamics of MMET tethers and space webs, on more complicated orbits. This, in turn, will be assimilated within new mission architectures
Hybrid fuzzy sliding mode control for motorised space tether spin-up when coupled with axial and torsional oscillation
A specialised hybrid controller is applied to the control of a motorised space tether spin-up space coupled with an axial and a torsional oscillation phenomenon. A seven-degree-of-freedom (7-DOF) dynamic model of a motorised momentum exchange tether is used as the basis for interplanetary payload exchange in the context of control. The tether comprises a symmetrical double payload configuration, with an outrigger counter inertia and massive central facility. It is shown that including axial and torsional elasticity permits an enhanced level of performance prediction accuracy and a useful departure from the usual rigid body representations, particularly for accurate payload positioning at strategic points. A simulation with given initial condition data has been devised in a connecting programme between control code written in MATLAB and dynamics simulation code constructed within MATHEMATICA. It is shown that there is an enhanced level of spin-up control for the 7-DOF motorised momentum exchange tether system using the specialised hybrid controller.
hybrid controller
Prandtl number of lattice Bhatnagar-Gross-Krook fluid
The lattice Bhatnagar-Gross-Krook modeled fluid has an unchangeable unit
Prandtl number. A simple method is introduced in this letter to formulate a
flexible Prandtl number for the modeled fluid. The effectiveness was
demonstrated by numerical simulations of the Couette flow.Comment: 4 pages, uuencoded postscript fil
Characterization of the 4-canonical birationality of algebraic threefolds
In this article we present a 3-dimensional analogue of a well-known theorem
of E. Bombieri (in 1973) which characterizes the bi-canonical birationality of
surfaces of general type. Let be a projective minimal 3-fold of general
type with -factorial terminal singularities and the geometric genus
. We show that the 4-canonical map is {\it not}
birational onto its image if and only if is birationally fibred by a family
of irreducible curves of geometric genus 2 with
where is a general irreducible member in .Comment: 25 pages, to appear in Mathematische Zeitschrif
Semi-Finite Forms of Bilateral Basic Hypergeometric Series
We show that several classical bilateral summation and transformation
formulas have semi-finite forms. We obtain these semi-finite forms from
unilateral summation and transformation formulas. Our method can be applied to
derive Ramanujan's summation, Bailey's transformations,
and Bailey's summation.Comment: 8 pages. accepted by Proc. Amer. Math. So
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