133,623 research outputs found
Torque ripple reduction of a direct-drive permanent-magnet synchronous machine by material-efficient axial pole pairing
No full textThis paper investigates a material-efficient axial pole pairing method for torque ripple reduction in a direct-drive outer-rotor surface-mounted permanent-magnet synchronous machine. The effects of the magnet pole arc width on the torque ripple characteristics of the machine are first established by both analytical and 2-D finite element approaches. Furthermore, the effectiveness of the axial pole pairing technique in mitigating the machine cogging torque, back electromotive force harmonics, and overall torque quality is comprehensively examined. Finally, 3-D finite element analysis and experiments are carried out to validate the proposed approach, and the results show that axial pole pairing can be cost efficiently implemented in terms of magnet material usage and assemblyIEEE Transactions on Industrial Electronic
A ripple-spreading genetic algorithm for the aircraft sequencing problem
No full textWhen genetic algorithms (GAs) are applied to combinatorial problems, permutation
representations are usually adopted. Asa result, suchGAsare often confronted with feasibility
and memory-efficiency problems. With the aircraft sequencing problem (ASP)
as a study case, this paper reports on a novel binary-representation-based GA scheme
for combinatorial problems. Unlike existing GAs for the ASP, which typically use
permutation representations based on aircraft landing order, the new GA introduces
a novel ripple-spreading model which transforms the original landing-order-based
ASP solutions into value-based ones. In the new scheme, arriving aircraft are projected
as points into an artificial space. A deterministic method inspired by the natural
phenomenon of ripple-spreading on liquid surfaces is developed, which uses a few
parameters as input to connect points on this space to form a landing sequence. A
traditional GA, free of feasibility and memory-efficiency problems, can then be used to
evolve the ripple-spreading related parameters in order to find an optimal sequence.
Since the ripple-spreadingmodel is the centerpiece of the new algorithm, it is called the
ripple-spreading GA (RSGA). The advantages of the proposed RSGA are illustrated by
extensive comparative studies for the case of the ASP
A Self-Learning Solution for Torque Ripple Reduction for Non-Sinusoidal Permanent Magnet Motor Drives Based on Artificial Neural Networks
No full textThis paper presents an original method, based on artificial neural networks, to reduce the torque ripple in a permanent-magnet non-sinusoidal synchronous motor. Solutions for calculating optimal currents are deduced from geometrical considerations and without a calculation step which is generally based on the Lagrange optimization. These optimal currents are obtained from two hyperplanes. The study takes into account the presence of harmonics in the back-EMF and the cogging torque. New control schemes are thus proposed to derive the optimal stator currents giving exactly the desired electromagnetic torque (or speed) and minimizing the ohmic losses. Either the torque or the speed control scheme, both integrate two neural blocks, one dedicated for optimal currents calculation and the other to ensure the generation of these currents via a voltage source inverter. Simulation and experimental results from a laboratory prototype are shown to confirm the validity of the proposed neural approach.CPER Région Alsace 2007-201
Multi-objective new product development by complete Pareto front and ripple-spreading algorithm
No full textGiven several different new product development projects and limited resources, this paper is concerned with the optimal allocation of resources among the projects. This is clearly a multi-objective optimization problem (MOOP), because each new product development project has both a profit expectation and a loss expectation, and such expectations vary according to allocated resources. In such a case, the goal of multi-objective new product development (MONPD) is to maximize the profit expectation while minimizing the loss expectation. As is well known, Pareto optimality and the Pareto front are extremely important to resolve MOOPs. Unlike many other MOOP methods which provide only a single Pareto optimal solution or an approximation of the Pareto front, this paper reports a novel method to calculate the complete Pareto front for the MONPD. Some theoretical conditions and a ripple-spreading algorithm together play a crucial role in finding the complete Pareto front for the MONPD. Simulation results illustrate that the reported method, by calculating the complete Pareto front, can provide the best support to decision makers in the MONPD
Early detection of ripple propagation in evolving software systems
No full textRipple effect analysis is the analysis of the consequential knock on effects of a change to a software system. In the first part of this study, ripple effect analysis methods are classified into several categories based on the types of information the methods analyse and produce. A comparative and analytical study of methods from these categories was performed in an attempt to assist maintainers in the selection of ripple effect analysis methods for use in different phases of the software maintenance process. It was observed that existing methods are most usable in the later stages of the software maintenance process and not at an early stage when strategic decisions concerning project scheduling are made. The second part of the work, addresses itself to the problem of tracing the ripple effect of a change, at a stage earlier in the maintenance process than existing ripple effect analysis methods allow. Particular emphasis is placed upon the development of ripple effect analysis methods for analysing system documentation. The ripple effect analysis methods described in this thesis involve manipulating a novel graph theory model called a Ripple Propagation Graph. The model is based on the thematic structure of documentation, previous release information and expert judgement concerning potential ripple effects. In the third part of the study the Ripple Propagation Graph model and the analysis methods are applied and evaluated, using examples of documentation structure and a major case study
Mandated Wage Floors and the Wage Structure: New Estimates of the Ripple Effects of Minimum Wage Laws
No full textMinimum wage laws have become a key political issue, following on the heels of over 130 successful living wage campaigns around the country. In the debates surrounding these mandated wage floors, one recurring issue has been whether the legislation has wider-ranging impacts on wages than the legally-required raises alone. Advocates on both sides of the debate dispute the potential magnitude of 'ripple effects'- the non-mandated raises given by employers to maintain a similar wage hierarchy before and after a change in the wage floor. These ripple effects have the potential to greatly expand the overall impact of mandated wage floors. This study uses data from twenty years of the Current Population Survey to assess the magnitude of ripple effects in the context of variations in minimum wage laws, and looks specifically at the retail trade sector to model the potential magnitude of ripple effects under living wage ordinances, where the 'bite' of the legislation would encompass a larger share of the workforce.ripple effect, wage spillover, wage norms, minimum wage, living wage, wage distribution, retail trade, low wage
Estratégias para redução de ruído em bomba hidráulica automotiva
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2012O presente trabalho analisa o funcionamento de uma bomba hidráulica automotiva e apresenta o estudo de três propostas para redução de ruído gerado pelo escoamento. A análise é realizada a partir da simulação de um modelo numérico da bomba desenvolvido para plataforma MatLab/Simulink. Os resultados da simulação são, então, validados experimentalmente em bancada de testes apropriada que utiliza o Método da Segunda Fonte (SSM) para calcular a flutuação do escoamento (flow ripple) da bomba. Após a análise detalhada dos mecanismos de geração de escoamento da bomba, é realizado o estudo de três propostas de alterações no desenho dos componentes do conjunto rotativo da bomba de modo a proporcionar um escoamento de saída mais plano possível, isto é, isento de flutuações. Duas dessas propostas, chamadas de 3P e 9P, apresentaram ótima redução de amplitude de flutuação. Entretanto, como efeito colateral, ambas deram origem a um desbalanceamento no eixo da bomba que pode provocar vibração e desgaste excessivo. A última proposta (8P) utiliza um rotor de oito palhetas e um novo perfil interno de anel came na tentativa minimizar o caráter pulsátil da bomba. Os resultados simulados mostram uma boa redução do ruído, principalmente nas frequências de interesse características do ruído tipo moan e whine. A partir destes resultados são fabricadas bombas-protótipos que são testadas experimentalmente em bancada e avaliadas em veiculo. Estas, por sua vez, não apresentaram o desempenho acústico esperado. Discussões sobre estes resultados, assim como sugestões para trabalhos futuros, são apresentados no final do trabalho.Abstract : This paper analyses the operation of an automotive hydraulic pump and presents three proposals to reduce flow ripple noise. The analysis is carried numerically using a Matlab / Simulink based pump model. The simulation results are validated experimentally on a test rig using the Second Source Method (SSM) that calculates the pump flow ripple. After detailed analysis of the pump flow generation mechanisms, three proposals considering rotating group components design changes are presented in order to make the pump outlet flow as flat as possible, i.e., free of ripple. Two of those proposals, called 3P and 9P, have showed great flow ripple reduction. However, as a side effect, both gave rise to unbalanced forces on pump shaft which can cause excessive vibration and wear. The last proposal (8P) uses an eight vanes rotor and a new internal profile cam ring in order to minimize the pulsatile pump flow characteristics. The simulated results show good noise reduction, especially in the frequencies of interest related with moan and whine noise. From this new rotating group design, new pumps are manufactured and tested on vehicle as well as on a bench test. However, the evaluations results have not presented the acoustical performance expected. Discussions about these results, as well as suggestions for future work are presented in the work
Platinum versus palladium thermocouples: an emf-temperature reference function for the range 0 °C to 1500 °C
No full text
Ripple elimination for DC/AC DAB converter with phase shift and duty cycle control
No full textActive ripple current reduction method is proposed for isolated DC/AC dual active bridge (DAB) converter to reduce the double grid frequency ripple in the DC current. Unlike those active methods that require extra switches to construct separate ripple reduction circuit, in this method, one or two branches of LC ripple steering circuits are used along with existing full bridge switches in a multiplexing manner. For the purpose of the ripple elimination, unsymmetrical phase shift modulation and duty cycle regulation methods are proposed and applied to both legs of the converter on the primary side of DAB converter. Also a current sharing (CS) scheme is presented to balance the current on both LC ripple steering circuits
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