174 research outputs found
Embedding Schemes for Interconnection Networks.
Graph embeddings play an important role in interconnection network and VLSI design. Designing efficient embedding strategies for simulating one network by another and determining the number of layers required to build a VLSI chip are just two of the many areas in which graph embeddings are used. In the area of network simulation we develop efficient, small dilation embeddings of a butterfly network into a different size and/or type of butterfly network. The genus of a graph gives an indication of how many layers are required to build a circuit. We have determined the exact genus for the permutation network called the star graph, and have given a lower bound for the genus of the permutation network called the pancake graph. The star graph has been proposed as an alternative to the binary hypercube and, therefore, we compare the genus of the star graph with that of the binary hypercube. Another type of embedding that is helpful in determining the number of layers is a book embedding. We develop upper and lower bounds on the pagenumber of a book embedding of the k-ary hypercube along with an upper bound on the cumulative pagewidth
Approximation Methods for Non-linear Gravitational Clustering
We discuss various analytical approximation methods for following the
evolution of cosmological density perturbations into the strong (i.e.
nonlinear) clustering regime. These methods can be classified into five types:
(i) simple extrapolations from linear theory, such as the high--peak model and
the lognormal model; (ii) {\em dynamical} approximations, including the
Zel'dovich approximation and its extensions; (iii) non--linear models based on
purely geometric considerations, of which the main example is the Voronoi
model; (iv) statistical solutions involving scaling arguments, such as the
hierarchical closure {\em ansatz} for BBGKY, fractal models and the
thermodynamic model of Saslaw; (v) numerical techniques based on particles
and/or hydrodynamics. We compare the results of full dynamical evolution using
particle codes and the various other approximation schemes. To put the models
we discuss into perspective, we give a brief review of the observed properties
of galaxy clustering and the statistical methods used to quantify it, such as
correlation functions, power spectra, topology and spanning trees.Comment: 175 pages, 20 figures. To appear in Phys. Rep. 1995. Hard copies of
figures/Manuscript available upon request from: [email protected]
Application of HPC in eddy current electromagnetic problem solution
As engineering problems are becoming more and more advanced, the size of an average model solved by partial differential equations is rapidly growing and, in order to keep simulation times within reasonable bounds, both faster computers and more efficient software implementations are needed.
In the first part of this thesis, the full potential of simulation software has been exploited through high performance parallel computing techniques. In particular, the simulation of induction heating processes is accomplished within reasonable solution times, by implementing different parallel direct solvers for large sparse linear system, in the solution process of a commercial software. The performance of such library on shared memory systems has been remarkably improved by implementing a multithreaded version of MUMPS (MUltifrontal Massively Parallel Solver) library, which have been tested on benchmark matrices arising from typical induction heating process simulations.
A new multithreading approach and a low rank approximation technique have been implemented and developed by MUMPS team in Lyon and Toulouse. In the context of a collaboration between MUMPS team and DII-University of Padova, a preliminary version of such functionalities could be tested on induction heating benchmark problems, and a substantial reduction of the computational cost and memory requirements could be achieved.
In the second part of this thesis, some examples of design methodology by virtual prototyping have been described. Complex multiphysics simulations involving electromagnetic, circuital, thermal and mechanical problems have been performed by exploiting parallel solvers, as developed in the first part of this thesis. Finally, multiobjective stochastic optimization algorithms have been applied to multiphysics 3D model simulations in search of a set of improved induction heating device configurations
Linearly polarised photon beams at the BGO-OD experiment at ELSA
The BGO-OD experiment, located at the electron stretcher facility ELSA in Bonn, is constructed for the study of meson photo-production reactions off the nucleon. The two main detector parts of the experimental setup are a central electromagnetic BGO calorimeter covering most of the solid angle and a magnetic spectrometer enclosing the most forward angles. This combination allows the detection of complicated mixed, charged and neutral, final states over almost the full solid angle and is optimised for the investigation of low momentum transfer processes at extreme forward angles. Physics proposals for the BGO-OD experiment include the measurement of the photon beam asymmetry Σ in different decay channels. The highly energetic photon beam is produced from the electron beam of ELSA via the process of bremsstrahlung. Due to the continuous energy spectrum, the energy of the produced bremsstrahlung photon is a priori unknown. The energy Eγ corresponds to the difference between the energy E0 of the incoming electron beam and the energy Ee- of the post-bremsstrahlung electron. With a detector setup known as a photon tagger, consisting of a dipole magnet and a scintillator hodoscope, it is possible to measure the momentum of the post-bremsstrahlung electron and therefore to determine the energy of the produced bremsstrahlung photon. The hodoscope of the BGO-OD photon tagger is designed, assembled and commissioned within this thesis. An energy range from 10%E0 to 90%E0 is covered with 120 plastic scintillators. The energy width of two adjacent scintillators ranges between 0.55%E0 and 2.28%E0. Since the post-bremsstrahlung electrons are detected with a time resolution of better than 210 ps, the tagger system also provides the time reference for the BGO-OD experiment. Using a linearly polarised photon beam allows the measurement of the photon beam asymmetry. A linearly polarised photon beam can be achieved through coherent bremsstrahlung off a diamond crystal properly aligned with respect to the incoming electron beam. For the alignment of the crystal, the Stonehenge technique performed with a goniometer system is made operational at the BGO-OD experiment within this thesis and has been successfully used since November 2014. Additionally, the C++ based program called COBRIS used to determine the degree of polarisation of the produced bremsstrahlung photon beam is further improved. A more precise calculation of the degree of polarisation and the determination of its error based on the uncertainty of the input parameters is now possible. A cross check on the determination of the degree of linear polarisation is performed through the measurement of the photon beam asymmetry in π0 photo-production off the proton. The results are compared to calculations of the Bonn-Gatchina partial wave analysis, which is a representation of existing accurate measurements. The energy range from 1100 MeV to 1500 MeV was studied, in which the expected degree of linear polarisation amounts to at least ~10%. From the comparison of the extracted photon beam asymmetries with the BnGn calculations it can be concluded, that the determination of the degree of linear polarisation is accurate at least within the errors of the extracted beam asymmetry. The relative error on the degree of polarisation derived from the error of the photon beam asymmetry is in the order of 10%. A more likely relative error of the degree of polarisation of 1% - 2% is determined from COBRIS
A comprehensive electromagnetic analysis of AC losses in large superconducting cables
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (p. 173-176).by Yu Ju Chen.Ph.D
Simulation of Early C. elegans Embryogenesis
Simulations are powerful tools that can be utilized to understand complex mechanisms within a system. Our project focuses on simulating the first several cell divisions of C. elegans embryogenesis. C. elegans is used as biological model for development, aging, and cell biology and is an ideal simulation candidate. Our four-dimensional simulation contains known information and hypotheses about molecular interactions within cells. Using rules to represent biological functions, our project visually and computationally shows the effects of several different mutations
The application of pole mounted amorphous core transformers to the electrical distribution network.
Master of Science in Electrical Engineering. University of KwaZulu-Natal, Durban 2016.With the drive to save money when supplying electricity to customers, utilities are looking
for solutions to decrease losses on distribution lines while maintaining good quality of
supply. Amorphous core transformers are known for having the lower no-load losses
compared to cold rolled grain orientated transformers and hence may be an important
technology to decrease losses on the distribution network. The amorphous material is easily
magnetised, however this comes at the expense of a lower saturation point and the
transformer may need to be designed at a lower peak flux density.
Inrush currents are a phenomenon that occurs when a transformer is switched on. The
combination of the voltage switching angle and the remnant flux lead to an overflux and
subsequent saturation of the core material, this leads to a high current.
The purpose of this dissertation is to investigate the performance of amorphous core
transformers installed on distribution lines, where they are switched onto the network from
the high voltage side, and conclude if they are a suitable replacement for cold rolled grain
oriented steel core.
Inrush currents have been investigated through a circuit model developed in Alternative
Transients Program/Electromagnetic Transients Program (ATP/EMTP) to determine the
currents for various designs of transformers. The model consists of the non-linear component
related to the core used as well as the air core of the high voltage winding. The circuit model
has been validated through an experiment.
A study was undertaken to understand the difference in the forces between amorphous core
transformers and cold rolled grain orientated, this was investigated in Finite Element Method
Magnetics (FEMM) by determining the distribution of magnetic flux. Additionally, as the
inrush current is only seen on the high voltage winding and not the low voltage winding, the
models were compared to the forces due to short-circuit currents, where there is current on
both high voltage and low voltage windings and a different magnetic flux distribution. The
position of the tap winding was of interest as it results in an unsymmetrical force
distribution
Development and prototyping of a Point Coupled Linear Transformer (PCLT) displacement sensor
Includes bibliographical references (leaves 78-80).The main aims of this project were to develop and prototype a Point Coupled Linear Transformer (PCLT) displacement sensor, and to perform a general exploration of the PCLT technology. The PCLT is a recent invention that has planar PCB windings and a non-contacting movable core, and relies on variable induction to detect displacement. Different core materials and shapes are investigated. The transformer windings layout is optimized for symmetrical response and high primary to secondary voltage coupling
Magnetic Actuators and Suspension for Space Vibration Control
The research on microgravity vibration isolation performed at the University of Virginia is summarized. This research on microgravity vibration isolation was focused in three areas: (1) the development of new actuators for use in microgravity isolation; (2) the design of controllers for multiple-degree-of-freedom active isolation; and (3) the construction of a single-degree-of-freedom test rig with umbilicals. Described are the design and testing of a large stroke linear actuator; the conceptual design and analysis of a redundant coarse-fine six-degree-of-freedom actuator; an investigation of the control issues of active microgravity isolation; a methodology for the design of multiple-degree-of-freedom isolation control systems using modern control theory; and the design and testing of a single-degree-of-freedom test rig with umbilicals
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