249 research outputs found
Cauer ladder network representation of eddy-current fields using the partial element equivalent circuit method
No full textLAUREA MAGISTRALELe correnti parassite indotte all'interno dei conduttori da un campo magnetico variabile nel tempo (legge di Faraday) causano, soprattutto alle alte frequenze, perdite addizionali non trascurabili. La tesi presenta un nuovo approccio per la modellazione dei fenomeni di correnti parassite nei materiali conduttivi.
Applicando il metodo PEEC (Partial Element Equivalent Circuit) al caso di studio, dopo aver definito una mesh adeguata, si ottiene una funzione di trasferimento simmetrica. Il metodo PEEC consente di modellare correttamente i fenomeni di correnti parassite, ma per rappresentare accuratamente il comportamento elettromagnetico anche alle alte frequenze, il numero di celle della mesh – e quindi il tempo di calcolo dell’analisi – può risultare molto elevato.
Per questo motivo viene applicato alla formulazione PEEC il metodo Cauer Ladder Network (CLN), che agisce come una Model Order Reduction (MOR). A partire dalla funzione di trasferimento simmetrica ottenuta dalla formulazione PEEC, il metodo CLN permette di rappresentare i campi di correnti parassite attraverso una rete a scala di Cauer, consentendo una riduzione del tempo di calcolo senza perdita di accuratezza nel modello risultante. Il metodo viene applicato a due casi di studio: un sistema composto da due conduttori rettangolari paralleli e un altro sistema composto da conduttori circolari trifase. I risultati vengono infine confrontati con quelli ottenuti dal modello COMSOL per i due casi analizzati, evidenziando l’efficienza e l’accuratezza del metodo sia nel dominio del tempo che in quello della frequenza.Eddy currents induced within conductors through a time-varying magnetic field (Faraday's law) cause, especially at high frequencies, additional non-negligible losses. The thesis presents a new approach for modeling eddy current phenomena in conductive materials.
Applying the Partial Element Equivalent Circuit (PEEC) method to the study case, after defining a proper meshing, a symmetric transfer function for the system is obtained. The PEEC method allows for modeling the eddy current phenomena correctly, but to model the electromagnetic behaviour also at high frequencies, the number of cells of the mesh and hence the time computation of the analysis could be very high.
For this reason Cauer Ladder Network (CLN) method is applied to the PEEC formulation, acting as Model Order Reduction (MOR). CLN allows, starting from the symmetric transfer function obtained from the PEEC formulation, to represent eddy-current fields through a Cauer ladder network, reducing time computation without any loss in the accuracy of the resulting model. The method is applied to two test cases: one system composed of two parallel rectangular conductors and another system composed of three-phase circular conductors. The results are then compared with those obtained from the COMSOL model of the two test cases under analysis, showing the efficiency and accuracy of the results, both in the time and frequency domains
Fast computation of copper and iron losses using model order reduction
No full textThis paper introduces a new method for fast computing of the iron and copper losses in electromagnetic systems. In the method, the finite element equation is reduced to the equivalent Cauer circuit via model order reduction. The nonlinear property due to core saturation is pre-computed and included in the Cauer circuit. While the copper loss is computed as the Jule loss in the circuit, the iron loss is computed in the post process by restoring the field distribution from the solution to the circuit equation with aid of the proper orthogonal decomposition
Fast 3-D Analysis of Eddy Current in Litz Wire Using Integral Equation
No full textEddy current loss in a litz wire which has 3-D structure is analyzed using the integral equation method considering the proximity effect. In the present method, each wire is modeled as a polygonal line. 1-D integral equation is solved for the dipole magnetization generated by the anti-parallel eddy currents in the wire. The discretized integral equation can effectively be solved using an iterative method solver to compute the eddy current distribution in the wire due to the proximity effect
Time-Domain Analysis of Homogenized Finite-Element Method for Eddy Current Analysis With Reduced Unknown Variables
No full textThis article presents a new method for time-domain analysis based on the homogenized finite-element method (FEM). The permeability in the homogenized domain is expressed by the Cauer-equivalent circuit. The auxiliary unknowns relevant to the Cauer circuit are then eliminated using the finite-difference method. The homogenized finite-element (FE) equation without the auxiliary unknowns can be effectively solved
Homogenization Method Based on Cauer Circuit via Unit Cell Approach
No full textThis article proposes a novel homogenization method based on the unit cell approach which provides the continued fraction and, equivalently, the Cauer circuit representation of the complex permeability of fine structure materials. The proposed method makes it possible to perform the homogenization analysis in time domain. It is shown that the proposed method provides a more accurate resistance factor in comparison to the Dowell method and other classical methods
Model Order Reduction for Linear Time-Invariant System With Symmetric Positive-Definite Matrices: Synthesis of Cauer-Equivalent Circuit
No full textThis article introduces a new model order reduction method for a linear time-invariant system with symmetric positive-definite matrices. The proposed method allows the construction of a reduced model, represented by a Cauer-equivalent circuit, from the original system. The method is developed by extending the Cauer ladder network method for the quasi-static Maxwell's equations, which is shown to be regarded as the Lanczos algorithm with respect to a self-adjoint matrix. As a numerical example, a Cauer-equivalent circuit is generated from a simple mathematical model as well as the finite-element (FE) model of a magnetic reactor that is driven by a pulsewidth modulation voltage wave. The instantaneous power obtained from the circuit analysis is shown to be in good agreement with that obtained from the original FE model
Evaluation of Post-license Advanced Driver Training in Italy
No full textAbstractPost-license advanced driver training addresses different categories of road users such as: novice drivers, professional drivers, company employers and recidivists. These training courses can be carried out on-track or on the road. On-track courses allow participants to gain knowledge on driving physics and experience limits in a safe road environment. On-road courses are more focused on hazard perception and situation awareness.Although extensive research has been done in this field, knowledge of the effects of these courses on road accident risk remains unclear. Previous evaluation of on-track courses did not always show a positive effect on crash rate. For example, post-license training focused on mastery of driving skills can lead to an increase of accident risk, especially on young males.However, research identified several factors that may enhance the effectiveness of driving training. In Europe a new framework for driver education and training has been proposed based on a safe driver hierarchical model (the GADGET model) and the development of a strategy for continuous learning.According to this framework, an evaluation study of on-track post-license advanced driver training has been undertaken in Italy with the main goal of assessing the safety effects of these courses and identifying training aspects to be improved. Besides crash rate, the study aims at assessing also driver behavior, knowledge of risks, self-evaluation and training quality.This paper presents the results of the possible effects of advanced driver training on driving behavior, considering in particular the number and type of violations. For each driver, data on age, gender and driving violations history were extracted from the platform and the national violations database.Three cases were addressed through a before-after analysis with control group. Case 1 considers all drivers who attended an ADT course. Case 2 aimed at understanding the effects of the courses on a specific target group: the traffic violators. Case 3 is similar to Case 2, however the control group was selected in a way that drivers characteristics and the violation rate was similar to the violation rate of the treatment group in the before period.The significance of the differences highlighted was assessed through appropriate statistical tests (i.e. paired t-test and the Wilcoxon signed-rank test).The study showed in general a higher propensity to commit traffic violations after attending an ADT course. These results are in contrast to what expected and show the necessity to diversify the training classes according to the different needs of participants
動的モード関数のStieltjes連分数およびCauer回路表示について (諸科学分野を結ぶ基礎学問としての数値解析学)
No full text電磁界・流体などを対象とした場の3次元解析や大規模系の制御においては, システムを記述する行列が大規模となる. このため精度を維持したままで計算コストを削減することが求められる. 近年, 大規模行列で記述される系を少数の変数で近似表現するモデル縮約法が注目されている. モデル縮約法には固有直交分解(POD)を用い, 変数を少数の基底の線形結合で表現する方法[1]-[3]や, ダイナミックモード分解(DMD)を用いてシステムの時間挙動を予測するモデルを構築する方法などがある[4], [5]. さらに, システムが線形な方程式で記述される場合にはLanczos法を用いたモデル縮約法が有効であることが知られている[6], [7]. 近年, 著者らはLanczos法を用いて準静(quasi-static)Maxwell方程式をCauer等価回路で表現する方法を提案した[8]. Cauer等価回路の低次側は直流・低周波特性, 高次側は高周波特性を表す. また電気機器の鉄心に磁気飽和がある場合には, Cauer回路の最低次のインダクタンスに, 飽和特性を反映させることができる. このようにCauer回路表示は, 大規模システムの縮約モデルとして工学的に有用である. 本報告では上記のような準静Maxwell方程式の縮約法を, 低励起状態の量子多体模型に拡張する方法について述べる
Eddy Current Analysis of Litz Wire Using Homogenization-Based FEM in Conjunction With Integral Equation
No full textA new method is introduced to evaluate the macroscopic permeability of a litz wire which is composed of stranded conductors. In this method, an integral equation is solved for the complex magnetization in the litz wire generated due to the proximity effect. The macroscopic permeability computed from the magnetization is used in the homogenization-based finite-element analysis of eddy currents in a litz-wire coil. It is shown that the wire twist has a little effect on the complex permeability
A methodology to assess pedestrian crossing safety
No full textPurpose: The safety level of a pedestrian crossing is affected by infrastructure characteristics and vehicular and pedestrian traffic level. This paper presents a methodology that allows assessing the safety level of a pedestrian crossing, regulated or not by traffic light, in an urban area according to the features of the crossing. Methods: A hierarchical structure representing factors influencing crossing safety has been developed and the relative contributions of each factor were calculated using AHP method. A composite index for crossing safety and specific indexes for main aspects included in the assessment have been developed. Results: Main assessment aspects are: Spatial and Temporal Design, Day-time and Night-time Visibility and Accessibility. Night-time Visibility resulted to have the higher weight (about 41%). Conclusion: Developed indexes allow ranking of pedestrian crossings and assigning intervention priorities, highlighting the aspects which are to be enhanced. The methodology has been used for the evaluation of 215 pedestrian crossings in 17 European cities for the Pedestrian Crossing Assessment Project co-financed by FIA Foundation. © 2010 The Author(s)
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