Improvement of FEM's dynamic property

The discretization size is limited by the sampling theorem, and the limit is one half of the wavelength of the highest frequency of the problem. However, one half of the wavelength is an ideal value. In general, the discretization size that can ensure the accuracy of the simulation is much smaller than this value in the traditional finite element method. The possible reason of this phenomenon is analyzed in this paper, and an efficient method is given to improve the simulation accuracy.

Shape-optimized mesh partitioning and load balancing for parallel adaptive FEM

We present a dynamic distributed load balancing algorithm for parallel, adaptive Finite Element simulations in which we use preconditioned Conjugate Gradient solvers based on domain-decomposition. The load balancing is designed to maintain good partition aspect ratio and we show that cut size is not always the appropriate measure in load balancing. Furthermore, we attempt to answer the question why the aspect ratio of partitions plays an important role for certain solvers. We define and rate different kinds of aspect ratio and present a new center-based partitioning method of calculating the initial distribution which implicitly optimizes this measure. During the adaptive simulation, the load balancer calculates a balancing flow using different versions of the diffusion algorithm and a variant of breadth first search. Elements to be migrated are chosen according to a cost function aiming at the optimization of subdomain shapes. Experimental results for Bramble's preconditioner and comparisons to state-of-the-art load balancers show the benefits of the construction.

3D FEM simulation of helical milling hole process for titanium alloy Ti-6Al-4V

As an emerging hole-machining methodology, helical milling process has become increasingly popular in aeromaterials manufacturing research, especially in areas of aircraft structural parts, dies, and molds manufacturing. Helical milling process is highly demanding due to its complex tool geometry and the progressive material failure on the workpiece. This paper outlines the development of a 3D finite element model for helical milling hole of titanium alloy Ti-6Al-4V using commercial FE code ABAQUS/Explicit. The proposed model simulates the helical milling hole process by taking into account the damage initiation and evolution in the workpiece material. A contact model at the interface between end-mill bit and workpiece has been established and the process parameters specified. Furthermore, a simulation procedure is proposed to simulate different cutting processes with the same failure parameters. With this finite element model, a series of FEAs for machined titanium alloy have been carried out and results compared with laboratory experimental data. The effects of machining parameters on helical milling have been elucidated, and the capability and advantage of FE simulation on helical milling process have been well presented.

Litteracitet i fem högstadieungdomars en-till-en-datorpraktiker

The study focuses on five lower secondary school pupils’ daily use of their one-toone computers, the overall aim being to investigate literacy in this form of computing. Theoretically, the study is rooted in the New Literacy tradition with an ecological perspective, in combination with socio-semiotic theory in a multimodal perspective. New Literacy in the ecological perspective focuses on literacy practices and place/space and on the links between them. Literacy is viewed as socially based, in specific situations and in recurring social practices. Socio-semiotic theory embodying the multimodal perspective is used for the text analysis. The methodology is known as socio-semiotic ethnography. The ethnographic methods encompass just over two years of fieldwork with participating observations of the five participants’ computing activities at home, at school and elsewhere. The participants, one boy and two girls from the Blue (Anemone) School and two girls from the White (Anemone) School, were chosen to reflect a broad spectrum in terms of sociocultural and socioeconomic background. The study shows the existence of a both broad and deep variation in the way digital literacy features in the participants’ one-to-one computing. These variations are associated with experience in relation to the home, the living environment, place, personal qualities and school. The more varied computer usage of the Blue School participants is connected with the interests they developed in their homes and living environments and in the computing practices undertaken in school. Their more varied usage of the computer is reflected in their broader digital literacy repertoires and their greater number and variety of digital literacy abilities. The Blue School participants’ text production is more multifaceted, covers a wider range of subjects and displays a broader palette of semiotic resources. It also combines more text types and the texts are generally longer than those of the White School participants. The Blue School girls have developed a text culture that is close to that of the school. In their case, there is clear linkage between school-initiated and self-initiated computing activities, while other participants do not have the same opportunities to link and integrate self-initiated computing activities into the school context. It also becomes clear that the Blue School girls can relate and adapt their texts to different communicative practices and recipients. In addition, the study shows that the Blue School girls have some degree of scope in their school practice as a result of incorporating into it certain communicative practices that they have developed in nonschool contexts. Quite contrary to the hopes expressed that one-to-one computing would reduce digital inequality, it has increased between these participants. Whether the same or similar results apply in a larger perspective, on a more structural level, is a question that this study cannot answer. It can only draw attention to the need to investigate the matter. The study shows in a variety of ways that the White School participants do not have the same opportunity to develop their digital literacy as the Blue School participants. In an equivalence perspective, schools have a compensational task to perform. It is abundantly clear from the study that investing in one-to-one projects is not enough to combat digital inequality and achieve the digitisation goals established for school education. Alongside their investments in technology, schools need to develop a didactic that legitimises and compensates for the different circumstances of different pupils. The compensational role of schools in this connection is important not only for the present participants but also for the community at large, in that it can help to secure a cohesive, open and democratic society.

FEM based Virtual Prototyping and Design of Third Harmonic Excitation System for Low Voltage Brushless Alternators

Salient pole brushless alternators coupled to IC engines are extensively used as stand-by power supply units for meeting in- dustrial power demands. Design of such generators demands high power to weight ratio, high e ciency and low cost per KVA out- put. Moreover, the performance characteristics of such machines like voltage regulation and short circuit ratio (SCR) are critical when these machines are put into parallel operation and alterna- tors for critical applications like defence and aerospace demand very low harmonic content in the output voltage. While designing such alternators, accurate prediction of machine characteristics, including total harmonic distortion (THD) is essential to mini- mize development cost and time. Total harmonic distortion in the output voltage of alternators should be as low as possible especially when powering very sophis- ticated and critical applications. The output voltage waveform of a practical AC generator is replica of the space distribution of the ux density in the air gap and several factors such as shape of the rotor pole face, core saturation, slotting and style of coil disposition make the realization of a sinusoidal air gap ux wave impossible. These ux harmonics introduce undesirable e ects on the alternator performance like high neutral current due to triplen harmonics, voltage distortion, noise, vibration, excessive heating and also extra losses resulting in poor e ciency, which in turn necessitate de-rating of the machine especially when connected to non-linear loads. As an important control unit of brushless alternator, the excitation system and its dynamic performance has a direct impact on alternator's stability and reliability. The thesis explores design and implementation of an excitation i system utilizing third harmonic ux in the air gap of brushless al- ternators, using an additional auxiliary winding, wound for 1=3rd pole pitch, embedded into the stator slots and electrically iso- lated from the main winding. In the third harmonic excitation system, the combined e ect of two auxiliary windings, one with 2=3rd pitch and another third harmonic winding with 1=3rd pitch, are used to ensure good voltage regulation without an electronic automatic voltage regulator (AVR) and also reduces the total harmonic content in the output voltage, cost e ectively. The design of the third harmonic winding by analytic methods demands accurate calculation of third harmonic ux density in the air gap of the machine. However, precise estimation of the amplitude of third harmonic ux in the air gap of a machine by conventional design procedures is di cult due to complex geome- try of the machine and non-linear characteristics of the magnetic materials. As such, prediction of the eld parameters by conven- tional design methods is unreliable and hence virtual prototyping of the machine is done to enable accurate design of the third har- monic excitation system. In the design and development cycle of electrical machines, it is recognized that the use of analytical and experimental methods followed by expensive and in exible prototyping is time consum- ing and no longer cost e ective. Due to advancements in com- putational capabilities over recent years, nite element method (FEM) based virtual prototyping has become an attractive al- ternative to well established semi-analytical and empirical design methods as well as to the still popular trial and error approach followed by the costly and time consuming prototyping. Hence, by virtually prototyping the alternator using FEM, the important performance characteristics of the machine are predicted. Design of third harmonic excitation system is done with the help of results obtained from virtual prototype of the machine. Third harmonic excitation (THE) system is implemented in a 45 KVA ii experimental machine and experiments are conducted to validate the simulation results. Simulation and experimental results show that by utilizing third harmonic ux in the air gap of the ma- chine for excitation purposes during loaded conditions, triplen harmonic content in the output phase voltage is signi cantly re- duced. The prototype machine with third harmonic excitation system designed and developed based on FEM analysis proved to be economical due to its simplicity and has the added advan- tage of reduced harmonics in the output phase voltage.

Matemàtiques a l'educació infantil : fem comparacions.'Matemáticas en Educación Infantil : hacemos comparaciones'.

Se expone una actividad de matemáticas realizada por la escuela de Sineu, Mallorca. Se trata de medir el campanario del pueblo para obtener información real y adaptar las medidas a las necesidades de aprendizaje de los niños des de una visión global tomada de la vida cotidiana. Finalmente, se llevan a cabo una serie de actividades relacionadas con las medidas.

I què fem a casa nostra? Reflexions i experiències sobre esport i immigració.

Se muestran fotografías. Contiene anexo al final del artículo. Resumen tomado del autor

CEIP Santa Gertrudis : aquesta escola la fem tots. 'CEIP Santa Gertrudis : esta escuela la hacemos todos'.

Resumen tomado del autor

Programa d'ajut a la docència universitària : fem camí cap a Europa. 'Programa de ayuda a la docencia universitaria : hacemos camino hacia Europa'.

Se presenta un programa cuyo objetivo es la mejora de la calidad de la docencia universitaria y facilitar su adaptación al nuevo espacio europeo de educación superior. Para ello se presentan cuatro cursos dirigidos al profesorado universitario para adaptarse a los futuros planes de estudio.

Fem quart en dos cursos? : adaptació curricular duta a terme per l'IES Celestí Ballera de Granollers. '¿Hacemos cuarto en dos cursos? : adaptación curricular llevada a cabo por el IES Celestí Ballera de Granollers'.

Teniendo en cuenta que hay alumnado que al acabar tercero de secundaria no está preparado para alcanzar los objetivos finales de etapa, pero sí que es suficientemente maduro para darse cuenta de su realidad y tomar una decisión juntamente con su familia, esta escuela realizó una adaptación curricular para estos estudiantes. Los autores exponen la experiencia de adaptación a la diversidad en la ESO, mencionando aspectos como los recursos que disponían, el marco legal, y como se organiza una adaptación.

Fer memoria a aprendre a escriure sobre allò que fem a l'aula. 'Hacer memoria sobre eso que hacemos en el aula'.

Resumen de las autoras en catalán

Com fem El matí de Catalunya Ràdio. '¿Cómo hacemos El matí de Catalunya Ràdio?'.

Resumen basado en el de los autores en catalán

Fem de periodistes a l'escola : una experiència d'escriptura de notícies a primer de primària. 'Hacemos de periodistas en la escuela : una experiencia de escritura de noticias en primero de primaria'.

Resumen de la autora en catalán

Els joves fem recerca. 'Los jóvenes hacemos investigación'.

Resumen de la revista en catalán