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Chhabra R.,MacDonald, Dettwiler and Associates | Emami M.R.,University of Toronto | Emami M.R.,LuleaUniversity of Technology
Journal of Geometry and Physics | Year: 2015

This paper presents a two-step symplectic geometric approach to the reduction of Hamilton's equation for open-chain, multi-body systems with multi-degree-of-freedom holonomic joints and constant momentum. First, symplectic reduction theorem is revisited for Hamiltonian systems on cotangent bundles. Then, we recall the notion of displacement subgroups, which is the class of multi-degree-of-freedom joints considered in this paper. We briefly study the kinematics of open-chain multi-body systems consisting of such joints. And, we show that the relative configuration manifold corresponding to the first joint is indeed a symmetry group for an open-chain multi-body system with multi-degree-of-freedom holonomic joints. Subsequently using symplectic reduction theorem at a non-zero momentum, we express Hamilton's equation of such a system in the symplectic reduced manifold, which is identified by the cotangent bundle of a quotient manifold. The kinetic energy metric of multi-body systems is further studied, and some sufficient conditions are introduced, under which the kinetic energy metric is invariant under the action of a subgroup of the configuration manifold. As a result, the symplectic reduction procedure for open-chain, multi-body systems is extended to a two-step reduction process for the dynamical equations of such systems. Finally, we explicitly derive the reduced dynamical equations in the local coordinates for an example of a six-degree-of-freedom manipulator mounted on a spacecraft, to demonstrate the results of this paper. © 2014 Elsevier B.V. Source

Hansson J.,LuleaUniversity of Technology
Electronic Journal of Theoretical Physics | Year: 2014

In contemporary particle physics, the masses of fundamental particles are incalculable constants, being supplied by experimental values. Inspired by observation of the empirical particle mass spectrum, and their corresponding physical interaction couplings, we propose that the masses of elementary particles arise solely due to the self-interaction of the fields associated with the charges of a particle. A first application of this idea is seen to yield correct order of magnitude predictions for neutrinos, charged leptons and quarks. We then discuss more ambitious models, where also different generations may arise from e.g. self-organizing bifurcations due to the underlying non-linear dynamics, with the coupling strength acting as "non-linearity" parameter. If the model is extended to include gauge bosons, the photon is automatically the only fundamental particle to remain massless as it has no charges. It results that gluons have an effective range ~ 1fm, physically explaining why QCD has finite reach. © Electronic Journal of Theoretical Physics. Source

Poppe A.R.,University of California at Berkeley | Poppe A.R.,NASA | Fatemi S.,Swedish Institute of Space Physics | Fatemi S.,LuleaUniversity of Technology | And 5 more authors.
Geophysical Research Letters | Year: 2014

We present two Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) observations of diamagnetic fields in the lunar wake at strengths exceeding twice the ambient magnetic field during high plasma beta conditions. The first observation was 350 km from the lunar surface while the Moon was located in the terrestrial magnetosheath with elevated particle temperatures. The second observation was in the solar wind ranging from 500 to 2000 km downstream, with a relatively low magnetic field strength of approximately 1.6 nT. In both cases, the plasma beta exceeded 10. We discuss the observations and compare the data to hybrid plasma simulations in order to validate the model under such extreme conditions and to elucidate the global structure of the lunar wake during these observations. The extreme nature of the diamagnetic field in the lunar wake provides an important end-member test case for theoretical and modeling studies of the various plasma processes operating in the lunar wake. © 2014. American Geophysical Union. All Rights Reserved. Source

Karlsson L.,Lulea University of Technology | Pahkamaa A.,LuleaUniversity of Technology | Karlberg M.,Lulea University of Technology | Lofstrand M.,Lulea University of Technology | And 2 more authors.
Journal of Mechanics of Materials and Structures | Year: 2011

Engineering product development has developed considerably over the past decade. In order for industry to keep up with continuously changing requirements, it is necessary to develop new and innovative simulation methods. However, few tools and methods for simulation-driven design have been applied in industrial settings and proven to actually drive the development and selection of the ideal solution. Such tools, based on fundamental equations, are the focus of this paper. In this paper the work is based on two cases of mechanics of materials and structures: welding and rotor dynamical simulations. These two examples of simulation-driven design indicate that a larger design space can be explored and that more possible solutions can be evaluated. Therefore, the approach improves the probability of innovations and finding optimal solutions. A calibrated block dumping approach can be used to increase the efficiency of welding simulations when many simulations are required. Source

Pupurs A.,LuleaUniversity of Technology | Varna J.,LuleaUniversity of Technology
Plastics, Rubber and Composites | Year: 2010

The aim of this paper is to analyse fibre/matrix debond crack growth during high stress cyclic tension-tension loading of unidirectional composites. The debond crack evolution analysis is based on fracture mechanics concepts that mode II energy release rate calculations are performed analytically for long debonds, where crack growth is self-similar, and numerically for short debonds by finite element method in combination with virtual crack closure technique. From the calculation results simple expressions are derived for an arbitrary mechanical and thermal loading case. Finally, the obtained expressions are applied in Paris law for debond growth simulations in cyclic tension-tension loading. © 2010 Maney Publishing. Source

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