Fractional Dynamics in the Rayleigh's Piston

This paper studies the dynamics of the Rayleigh piston using the modeling tools of Fractional Calculus. Several numerical experiments examine the effect of distinct values of the parameters. The time responses are transformed into the Fourier domain and approximated by means of power law approximations. The description reveals characteristics usual in Fractional Brownian phenomena.

A framework for using real data with distributed low cost sensors

Currently, due to the widespread use of computers and the internet, students are trading libraries for the World Wide Web and laboratories with simulation programs. In most courses, simulators are made available to students and can be used to proof theoretical results or to test a developing hardware/product. Although this is an interesting solution: low cost, easy and fast way to perform some courses work, it has indeed major disadvantages. As everything is currently being done with/in a computer, the students are loosing the “feel” of the real values of the magnitudes. For instance in engineering studies, and mainly in the first years, students need to learn electronics, algorithmic, mathematics and physics. All of these areas can use numerical analysis software, simulation software or spreadsheets and in the majority of the cases data used is either simulated or random numbers, but real data could be used instead. For example, if a course uses numerical analysis software and needs a dataset, the students can learn to manipulate arrays. Also, when using the spreadsheets to build graphics, instead of using a random table, students could use a real dataset based, for instance, in the room temperature and its variation across the day. In this work we present a framework which uses a simple interface allowing it to be used by different courses where the computers are the teaching/learning process in order to give a more realistic feeling to students by using real data. A framework is proposed based on a set of low cost sensors for different physical magnitudes, e.g. temperature, light, wind speed, which are connected to a central server, that the students have access with an Ethernet protocol or are connected directly to the student computer/laptop. These sensors use the communication ports available such as: serial ports, parallel ports, Ethernet or Universal Serial Bus (USB). Since a central server is used, the students are encouraged to use sensor values results in their different courses and consequently in different types of software such as: numerical analysis tools, spreadsheets or simply inside any programming language when a dataset is needed. In order to do this, small pieces of hardware were developed containing at least one sensor using different types of computer communication. As long as the sensors are attached in a server connected to the internet, these tools can also be shared between different schools. This allows sensors that aren't available in a determined school to be used by getting the values from other places that are sharing them. Another remark is that students in the more advanced years and (theoretically) more know how, can use the courses that have some affinities with electronic development to build new sensor pieces and expand the framework further. The final solution provided is very interesting, low cost, simple to develop, allowing flexibility of resources by using the same materials in several courses bringing real world data into the students computer works.

Introducing numerical analysis tools in engineering: a Scilab user case in electronics course

Software tools in education became popular since the widespread of personal computers. Engineering courses lead the way in this development and these tools became almost a standard. Engineering graduates are familiar with numerical analysis tools but also with simulators (e.g. electronic circuits), computer assisted design tools and others, depending on the degree. One of the main problems with these tools is when and how to start use them so that they can be beneficial to students and not mere substitutes for potentially difficult calculations or design. In this paper a software tool to be used by first year students in electronics/electricity courses is presented. The growing acknowledgement and acceptance of open source software lead to the choice of an open source software tool – Scilab, which is a numerical analysis tool – to develop a toolbox. The toolbox was developed to be used as standalone or integrated in an e-learning platform. The e-learning platform used was Moodle. The first approach was to assess the mathematical skills necessary to solve all the problems related to electronics and electricity courses. Analysing the existing circuit simulators software tools, it is clear that even though they are very helpful by showing the end result they are not so effective in the process of the students studying and self learning since they show results but not intermediate steps which are crucial in problems that involve derivatives or integrals. Also, they are not very effective in obtaining graphical results that could be used to elaborate reports and for an overall better comprehension of the results. The developed tool was based on the numerical analysis software Scilab and is a toolbox that gives their users the opportunity to obtain the end results of a circuit analysis but also the expressions obtained when derivative and integrals calculations, plot signals, obtain vector diagrams, etc. The toolbox runs entirely in the Moodle web platform and provides the same results as the standalone application. The students can use the toolbox through the web platform (in computers where they don't have installation privileges) or in their personal computers by installing both the Scilab software and the toolbox. This approach was designed for first year students from all engineering degrees that have electronics/electricity courses in their curricula.

A learning environment for robotic production line simulation

This paper presents a framework for a robotic production line simulation learning environment using Autonomous Ground Vehicles (AGV). An eLearning platform is used as interface with the simulator. The objective is to introduce students to the production robotics area using a familiar tool, an eLearning platform, and a framework that simulates a production line using AGVs. This framework allows students to learn about robotics but also about several areas of industrial management engineering without requiring an extensive prior knowledge on the robotics area. The robotic production line simulation learning environment simulates a production environment using AGVs to transport materials to and from the production line. The simulator allows students to validate the AGV dynamics and provides information about the whole materials supplying system which includes: supply times, route optimization and inventory management. The students are required to address several topics such as: sensors, actuators, controllers and an high level management and optimization software. This simulator was developed with a known open source tool from robotics community: Player/Stage. This tool was extended with several add-ons so that students can be able to interact with a complex simulation environment. These add-ons include an abstraction communication layer that performs events provided by the database server which is programmed by the students. An eLearning platform is used as interface between the students and the simulator. The students can visualize the effects of their instructions/programming in the simulator that they can access via the eLearning platform. The proposed framework aims to allow students from different backgrounds to fully experience robotics in practice by suppressing the huge gap between theory and practice that exists in robotics. Using an eLearning platform eliminates installation problems that can occur from different computers software distribution and makes the simulator accessible by all students at school and at home.

Teaching accounting and management through business simulation

Everyday accounting and management teachers face the challenge of creating learning environments that motivate students. This chapter describes the Business Simulation (BS) experience that has taken place at the Polytechnic Institute of Porto, Institute of Accounting and Administration (IPP/ISCAP). The chapter presents students’ perceptions about the course and the teaching/learning approach. The results show that pedagogical methods used (competency-oriented), generic competencies (cooperation and group work), and interpersonal skills (organisational and communication skills) are relevant for future accounting professionals. In addition, positive remarks and possible constraints based on observation, staff meetings, and past research are reported. The chapter concludes with some recommendations from the project implementation

Simulation Environment for Multi-Robot Cooperative 3D Target Perception

4th International Conference, SIMPAR 2014, Bergamo, Italy, October 20-23, 2014

Multi-agent simulation of competitive electricity markets: Autonomous systems cooperation for European market modeling

The electricity market restructuring, and its worldwide evolution into regional and even continental scales, along with the increasing necessity for an adequate integration of renewable energy sources, is resulting in a rising complexity in power systems operation. Several power system simulators have been developed in recent years with the purpose of helping operators, regulators, and involved players to understand and deal with this complex and constantly changing environment. The main contribution of this paper is given by the integration of several electricity market and power system models, respecting to the reality of different countries. This integration is done through the development of an upper ontology which integrates the essential concepts necessary to interpret all the available information. The continuous development of Multi-Agent System for Competitive Electricity Markets platform provides the means for the exemplification of the usefulness of this ontology. A case study using the proposed multi-agent platform is presented, considering a scenario based on real data that simulates the European Electricity Market environment, and comparing its performance using different market mechanisms. The main goal is to demonstrate the advantages that the integration of various market models and simulation platforms have for the study of the electricity markets’ evolution.

Strength improvement of adhesively-bonded scarf repairs in aluminium structures with external reinforcements

Adhesively bonded techniques are an attractive option to repair aluminium structures, compared to more traditional methods. Actually, as a result of the improvement in the mechanical characteristics of adhesives, adhesive bonding has progressively replaced the traditional joining methods. There are several bonded repair configurations, as single-strap, double-strap and scarf. Compared with strap repairs, scarf repairs have the advantages of a higher efficiency and the absence of aerodynamic disturbance. The higher efficiency is caused by the elimination of the significant joint eccentricities of strap repairs. Moreover, stress distributions along the bond length are more uniform, due to tapering of the scarf edges. The main disadvantages of this technique are the difficult machining of the surfaces, associated costs and requirement of specialised labour. This work reports on an experimental and numerical study of the tensile behaviour of two-dimensional (2D) scarf repairs of aluminium structures bonded with the ductile epoxy adhesive Araldite® 2015. The numerical analysis, by Finite Elements (FE), was performed in Abaqus® and used cohesive zone models (CZM) for the simulation of damage onset and growth in the adhesive layer, thus enabling the strength prediction of the repairs. A parametric study was performed on the scarf angle (α) and different configurations of external reinforcement (applied on one or two sides of the repair, and also different reinforcement lengths). The obtained results allowed the establishment of design guidelines for repairing, showing that the use of external reinforcements enables increasing α for equal strength recovery, which makes the repair procedure easier. The numerical technique was accurate in predicting the repairs’ strength, enabling its use for design and optimisation purposes.

Matrix fractional systems

This paper addresses the matrix representation of dynamical systems in the perspective of fractional calculus. Fractional elements and fractional systems are interpreted under the light of the classical Cole–Cole, Davidson–Cole, and Havriliak–Negami heuristic models. Numerical simulations for an electrical circuit enlighten the results for matrix based models and high fractional orders. The conclusions clarify the distinction between fractional elements and fractional systems.

Visualization and interaction in a simulation system for flood emergencies

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Engenharia Informática

Stochastic simulation of the morphology of fluvial sand channels reservoirs

Dissertação para obtenção do Grau de Mestre em Engenharia Geológica (Georrecursos)

Estudo de Ferramentas FEA Comerciais na Simulação Numérica de Processos de Conformação de Chapas Metálicas. Aplicação à Indústria Automóvel.

Os componentes obtidos através da conformação plástica de chapas têm uma grande importância, tanto na etapa de concepção do produto como na etapa de produção na indústria automóvel. Isto comprova-se pelo facto de, em média, cada automóvel integrar cerca de 500 componentes estampados para construir o chassis e a carroçaria [Alves 2003]. Deste total de componentes, 50 são de grandes dimensões (portas, tejadilho, painéis inferior e laterais, entre outros) e necessitam, em média, de cinco ferramentas para o seu fabrico, sendo o custo estimado para cada ferramenta de 230 000 € [Col 2000, Alves 2003]. Para além da indústria automóvel, a conformação plástica de chapas metálicas é um processo tecnológico presente nas indústrias relativas à aeroespacial, petrolífera, decoração, alimentar, entre outras. Do ponto de vista do enquadramento económico, cerca de 20% do custo total de um automóvel novo é devido à incorporação de componentes metálicos estampados. [Alves 2003]. A pressão do “Mercado Global” faz com que os custos relativos à matéria-prima, energia e mão-de-obra sejam uma constante em termos de redução do seu impacte no orçamento das empresas fornecedoras destes produtos. É neste contexto que surge a necessidade da realização deste estudo de Benchmark de Softwares, tornando-se bastante importante, quer ao nível da competitividade industrial, quer ao nível da inovação para novos produtos. A análise por elementos finitos desempenha um papel primordial no tryout virtual e otimização das ferramentas e processos de conformação plástica. Os objetivos principais deste estudo de simulação numérica são a identificação e comparação dos resultados obtidos pelo AUTOFORM e pelo PAMSTAMP, para cada uma das variáveis identificadas como as mais influentes na robustez dos processos de estampagem de chapa metálica. Estas variáveis identificadas são: consumo de material (Draw-in) após conformação; forças de conformação; valores de variação de espessura e dos valores de extensão e resultados de Springback. Os resultados obtidos são comparados com os resultados experimentais e, desta forma, avalia-se a capacidade inovadora e a eficácia de cada um dos softwares, obtendo-se assim, uma orientação mais real para o software mais indicado aos objetivos impostos pela indústria automóvel. Para este efeito, a indústria automóvel, como maior impulsionador e motor da investigação na área da simulação numérica aplicada aos processos de estampagem, tem aderido em peso ao Benchmarking. Um exemplo disto, é o que acontece nas conferências Numisheet. O Benchmark #2 da conferência Numisheet 2008 é analisado pormenorizadamente e os resultados numéricos e experimentais são comparados e apresentados. Dois materiais distintos (aço HC260LAD e liga de alumínio AC170), assim como três modelos com geometrias diferentes (com e sem freios) são apresentados neste relatório. Com vista à redução dos ciclos tentativa-erro, tem-se adotado ciclos virtuais ou numéricos e tem-se incrementado a interatividade entre as fases de concepção e projeto, num conceito muito próprio, mas cada vez mais abrangente, denominado “produção virtual”. É nesta filosofia que se insere a simulação numérica dos processos de conformação de chapa.

Avaliação numérica e experimental da carga admissível de vigas compostas para monocarris de sistemas de elevação

Este trabalho foi realizado com o apoio, e em colaboração da empresa Flexcrane, que constrói e comercializa soluções flexíveis de pontes rolantes para cargas ligeiras. Com cargas máximas de 2 toneladas estas pontes e seus caminhos de rolamento são construídas essencialmente enformados a frio. O objetivo deste trabalho é a verificação numérica e experimental das cargas que este tipo de estrutura suporta, nas suas diferentes configurações. Numa aproximação por engenharia inversa, com a realização deste trabalho, foi possível determinar a carga admissível das vigas compostas utilizadas, assim como o seu comportamento quando em carga. Para obtenção destes resultados foram realizadas simulações computacionais recorrendo ao método de elementos finitos, utilizando para isso o software Ansys Workbench e ainda ensaios experimentais que permitiram validar os resultados obtidos numericamente e consolidar o conhecimento sobre o comportamento desta solução comercial. Por ser de construção modular, são possíveis diferentes combinações para o produto final, por esta razão foram estudados numericamente diferentes configurações possíveis, com e sem reforços. Foi realizada a validação experimental para a configuração mais usual, fazendo recurso a um dispositivo para ensaio de estruturas e componentes, pertencente ao Isep. Foi ainda utilizada a técnica extensométrica para avaliar as tensões em pontos selecionados e compara-los com os obtidos numericamente. Concluiu-se pelo ótimo desempenho dos produtos Flexcrane.

Heat recovery from wastewater: numerical modelling of sewer systems

Dissertação para obtenção do Grau de Mestre em Engenharia do Ambiente, perfil Engenharia Sanitária