9,174 research outputs found
Identification of inelastic parameters of the 304 stainless steel using multi-objective techniques
This work addresses identification of inelastic parameters based on an optimization method using a multi-objective technique. The problem consists in determining the best set of parameters which approximate three different tensile tests. The tensile tests use cylindrical specimens of different dimensions manufactured according to the American ASTM E 8M and Brazilian ABNT NBR ISO 6892 technical standards. A tensile load is applied up to macroscopic failure. The objective functions for each tensile test/specimen is computed and a global error measure is determined within the optimization scheme. The Nelder-Mead simplex algorithm is used as the optimization tool. The proposed identification strategy was able to determine the best set of material parameters which approximate all tensile tests up to macroscopic failure
Further studies on identification of inelastic parameters for damaged materials
A proper set of material parameters is one of the most important aspects for a successful simulation of metal forming processes. Several issues must be observed when choosing the constitutive relation and corresponding material parameters, amongst which the most important are: (i) the magnitude of the plastic deformation of the target forming operation must be contemplated by the parameters of the constitutive model, (ii) possibility of failure prediction in fracture-free materials, and (iii) accurate prediction of geometrical changes caused by plastic deformation. Within this framework, the present article discusses techniques to obtain constitutive parameters of a Lemaitre-type material model. The strategy requires compliance of multiple tensile tests with specimens prepared according to different technical standards. Parameter identification is regarded as an inverse problem and solved using optimization methods
Divide and conquer: resonance induced by competitive interactions
We study an Ising model in a network with disorder induced by the presence of
both attractive and repulsive links. This system is subjected to a subthreshold
signal, and the goal is to see how the response is enhanced for a given
fraction of repulsive links. This can model a network of spin-like neurons with
excitatory and inhibitory couplings. By means of numerical simulations and
analytical calculations we find that there is an optimal probability, such that
the coherent response is maximal
Non-Markovian Dynamics of Charge Carriers in Quantum Dots
We have investigated the dynamics of bound particles in multilevel
current-carrying quantum dots. We look specifically in the regime of resonant
tunnelling transport, where several channels are available for transport.
Through a non-Markovian formalism under the Born approximation, we investigate
the real-time evolution of the confined particles including transport-induced
decoherence and relaxation. In the case of a coherent superposition between
states with different particle number, we find that a Fock-space coherence may
be preserved even in the presence of tunneling into and out of the dot.
Real-time results are presented for various asymmetries of tunneling rates into
different orbitals.Comment: 9 pages, 3 figures, International Workshop on Physics-Based
Mathematical Models for Low-Dimensional Semiconductor Nanostructures. BIRS,
November 18-23, 200
Are You Gonna Eat That?: A New Wave of Mandatory Recycling has Massachussetts and Other New England States Paving the Way Towards Feasible Food Waste Diversion and a New Player in Alternative Energy
A benchmark study on identification of inelastic parameters based on deep drawing processes using pso – nelder mead hybrid approach
Optimization techniques have been increasingly used to identification of inelastic material parameters owing to their generality. Development of robust techniques to solving this class of inverse problems has been a challenge to researchers mainly due to the nonlinear character of the problem and behaviour of the objective function. Within this framework, this work discusses application of Particle Swarm Optimization (PSO) and a PSO – Nelder Mead hybrid approach to identification of inelastic parameters based on a benchmark solution of the deep drawing process
The partial cavity on a 2D foil revisited
The partial cavity on a 2D NACA0015 foil at 6 degrees angle-of-attack is studied numerically. Assuming the fluid to be a continuum of variable density, we solve the RANS equations, complemented with turbulence and cavitation models. Some important details of the mathematical model are pointed out first. We study then carefully what occurs in the numerical simulations in and near the cavity from the inception phase to the stage well before serious unsteadiness (cavity shedding) starts. By making the computations on grids of different densities we get an impression of numerical uncertainties. This is important for the interpretation and the subsequent comparison with what experimental investigations have learned us about the physics of these almost steady partial cavities on foils. The results show that close to inception a cavity exists while the boundary layer is nonseparating. The liquid-vapour interface turns out not to be a material surface, neither at the front end nor at the tail of the cavity. It also appears that the widely accepted re-entrant jet model as conceived from free-streamline theory is not a good description of the flow at the tail. The confrontation of the numerical results with information from experiments indicates that there is agreement and corroboration in several respects, but also intriguing discrepancies are found which require further elucidation.http://deepblue.lib.umich.edu/bitstream/2027.42/84243/1/CAV2009-final43.pd
Reflection and Transmission at the Apparent Horizon during Gravitational Collapse
We examine the wave-functionals describing the collapse of a self-gravitating
dust ball in an exact quantization of the gravity-dust system. We show that
ingoing (collapsing) dust shell modes outside the apparent horizon must
necessarily be accompanied by outgoing modes inside the apparent horizon, whose
amplitude is suppressed by the square root of the Boltzmann factor at the
Hawking temperature. Likewise, ingoing modes in the interior must be
accompanied by outgoing modes in the exterior, again with an amplitude
suppressed by the same factor. A suitable superposition of the two solutions is
necessary to conserve the dust probability flux across the apparent horizon,
thus each region contains both ingoing and outgoing dust modes. If one
restricts oneself to considering only the modes outside the apparent horizon
then one should think of the apparent horizon as a partial reflector, the
probability for a shell to reflect being given by the Boltzmann factor at the
Hawking temperature determined by the mass contained within it. However, if one
considers the entire wave function, the outgoing wave in the exterior is seen
to be the transmission through the horizon of the interior outgoing wave that
accompanies the collapsing shells. This transmission could allow information
from the interior to be transferred to the exterior.Comment: 19 pages, no figures. To appear in Phys. Rev.
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