81 research outputs found
Isogeometric Analysis and Harmonic Stator-Rotor Coupling for Simulating Electric Machines
This work proposes Isogeometric Analysis as an alternative to classical
finite elements for simulating electric machines. Through the spline-based
Isogeometric discretization it is possible to parametrize the circular arcs
exactly, thereby avoiding any geometrical error in the representation of the
air gap where a high accuracy is mandatory. To increase the generality of the
method, and to allow rotation, the rotor and the stator computational domains
are constructed independently as multipatch entities. The two subdomains are
then coupled using harmonic basis functions at the interface which gives rise
to a saddle-point problem. The properties of Isogeometric Analysis combined
with harmonic stator-rotor coupling are presented. The results and performance
of the new approach are compared to the ones for a classical finite element
method using a permanent magnet synchronous machine as an example
Numerical Methods for the Estimation of the Impact of Geometric Uncertainties on the Performance of Electromagnetic Devices
This work addresses the application of Isogeometric Analysis to the simulation of particle accelerator cavities and other electromagnetic devices whose performance is mainly determined by their geometry. By exploiting the properties of B-Spline and Non-Uniform B-Spline basis functions, the Isogeometric approximation allows for the correct discretisation of the spaces arising from Maxwell's equations and for the exact representation of the computational domain. This choice leads to substantial improvements in both the overall accuracy and computational effort.
The suggested framework is applied to the evaluation of the sensitivity of these devices with respect to geometrical changes using Uncertainty Quantification methods and to shape optimisation processes. The particular choice of basis functions simplifies the construction of the geometry deformations significantly.
Finally, substructuring methods are proposed to further reduce the computational cost due to matrix assembly and to allow for hybrid coupling of Isogeometric Analysis and more classical Finite Element Methods. Considerations regarding the stability of such methods are addressed.
The methods are illustrated by simple numerical tests and real world device simulations with particular emphasis on particle accelerator cavities
Shape Optimization of Rotating Electric Machines using Isogeometric Analysis and Harmonic Stator-Rotor Coupling
This work deals with shape optimization of electric machines using
isogeometric analysis. Isogeometric analysis is particularly well suited for
shape optimization as it allows to easily modify the geometry without remeshing
the domain. A 6-pole permanent magnet synchronous machine is modeled using a
multipatch isogeometric approach and rotation of the machine is realized by
modeling the stator and rotor domain separately and coupling them at the
interface using harmonic basis functions. Shape optimization is applied to the
model minimizing the total harmonic distortion of the electromotive force as a
goal functional
Combined Parameter and Shape Optimization of Electric Machines with Isogeometric Analysis
In structural optimization, both parameters and shape are relevant for the
model performance. Yet, conventional optimization techniques usually consider
either parameters or the shape separately. This work addresses this problem by
proposing a simple yet powerful approach to combine parameter and shape
optimization in a framework using Isogeometric Analysis (IGA). The optimization
employs sensitivity analysis by determining the gradients of an objective
function with respect to parameters and control points that represent the
geometry. The gradients with respect to the control points are calculated in an
analytical way using the adjoint method, which enables straightforward shape
optimization by altering of these control points. Given that a change in a
single geometry parameter corresponds to modifications in multiple control
points, the chain rule is employed to obtain the gradient with respect to the
parameters in an efficient semi-analytical way. The presented method is
exemplarily applied to nonlinear 2D magnetostatic simulations featuring a
permanent magnet synchronous motor and compared to designs, which were
optimized using parameter and shape optimization separately. It is numerically
shown that the permanent magnet mass can be reduced and the torque ripple can
be eliminated almost completely by simultaneously adjusting rotor parameters
and shape. The approach allows for novel designs to be created with the
potential to reduce the optimization time substantially
Computational homogenization of soft matter friction: Isogeometric framework and elastic boundary layers
Cataloged from PDF version of article.A computational contact homogenization framework is established for the modeling and simulation of soft
matter friction. The main challenges toward the realization of the framework are (1) the establishment of
a frictional contact algorithm that displays an optimal combination of accuracy, efficiency, and robustness
and plays a central role in (2) the construction of a micromechanical contact test within which samples
of arbitrary size may be embedded and which is not restricted to a single deformable body. The former
challenge is addressed through the extension of mixed variational formulations of contact mechanics to
a mortar-based isogeometric setting where the augmented Lagrangian approach serves as the constraint
enforcement method. The latter challenge is addressed through the concept of periodic embedding, with
which a periodically replicated C1-continuous interface topography is realized across which not only pending
but also ensuing contact among simulation cells will be automatically captured. Two-dimensional
and three-dimensional investigations with unilateral/bilateral periodic/random roughness on two elastic
micromechanical samples demonstrate the overall framework and the nature of the macroscopic frictional
response. Copyright © 2014 John Wiley & Sons, Ltd
SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES
Crack propagation in thin shell structures due to cutting is conveniently simulated
using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell
elements are usually preferred for the discretization in the presence of complex material
behavior and degradation phenomena such as delamination, since they allow for a correct
representation of the thickness geometry. However, in solid-shell elements the small thickness
leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new
selective mass scaling technique is proposed to increase the time-step size without affecting
accuracy. New ”directional” cohesive interface elements are used in conjunction with selective
mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile
shells
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