Gyrostat dynamics on a circular orbit

The attitude control of a modern satellite is a crucial condition for its operation. In this work, is investigated the dynamics of an asymmetrical inertial distribution gyrostat satellite, subjected to gravitational torque, moving along a circular orbit in a central Newtonian gravitational field. To solve the problem it is proposed a symbolic-numerical method for determining all equilibrium orientations of an asymmetrical gyrostat satellite in the orbital coordinate system with a given gyrostatic torque and given principal central moments of inertia. The conditions of equilibria are obtained depending on four dimensionless parameters of the system. The evolution of the domains in the study of equilibria and stability is carried out in great detail. All bifurcation values of parameters at which there is a change of numbers of equilibrium orientations are determined with great accuracy. For each equilibrium orientation the sufficient conditions of stability are obtained as a result of analysis of the generalized integral of energy used as a Lyapunov’s function. It is shown that the number of equilibria of a gyrostat satellite in the general case must be between 8 and 24, and that the number of stable equilibria changes from 4 to 2

Gyrostat dynamics on a circular orbit

This work deals with a general gyrostat moving along a circular orbit in a central Newtonian force field. The main purpose is to determine all equilibria positions for our spacecraft in the case when internal angular momentum of the gyrostat satellite is collinear to its principal axis of inertia, when the gyrostatic moment vector lies in one of the satellite’s principal central plane of inertia and for a general position where the gyrostatic moment doesn’t coincide with any of the principal axis of inertia

The impact of blended learning on the value perceived of higher education

In this paper, the impact of blended learning on the value perceived of higher education is studied. Focusing on Nova SBE Master’s programs, the methodology consists of measuring the dichotomy of benefits and sacrifices. A statistical hypothesis testing is used to attest the significance of the difference between blended learning and the face-to-face approach. The three main results of the study are: (i) student’s unfavourable overall perception of blended learning, (ii) the extremely adverse impact on conditional and epistemic value and (iii) the contribution of campus and the lack of social interaction with fellow students as major points of concern

On the utilization of simplified methodologies for the wheel-rail contact

First Online: 14 October 2021The utilization of multibody systems formulation allows to study the railway vehicle dynamics, as well study local damaging phenomena that occur in the wheel-rail interaction. However, the analysis of these phenomena requires long simulations to perform a significant prediction of their evolution. Having that in mind, the utilization of simplified approaches for the different steps of calculation of wheel-rail contact interaction are addressed. Two parametric surfaces are used to describe both wheel and rail geometries, namely a revolution and an extruded body, respectively. Regarding the normal and tangential contact forces, an elastic approach is considered, therefore, these forces are treated as external forces acting on the multibody system and an Hertzian model with damping is employed for their evaluation. Finally, a trailer vehicle is considered as example of application to study different modeling strategies.This work has been supported by FCT with the reference project POCI-01-0145-FEDER-028424, by FEDER funds through the COMPETE 2020 - Programa Operacional Competitividade e Internacionalização. This work has been also sup ported by Portuguese Foundation for Science and Technology, under the national support to R&D units grant, with the reference project UIDB/04436/2020 and UIDP/04436/2020

Scaling Spatial Multiplexing with Principal Modes

We assess the robustness of a principal modes approach to scalable space-division multiplexing transceivers in the presence of mode-dependent loss. Results show resilience to several mode-dependent loss regimes

Dynamic study of railway vehicles considering a variable coefficient of friction in the wheel-rail interface

The continuous improvement of the railway field constitutes a major contribution for the existence of a more sustainable and environmentally friendly transportation network. Thus, the development of reliable computational multibody models to reproduce the dynamic behavior of vehicles, tracks and their mutual interaction is key to design suspension, traction and braking systems, prevent derailments, perform virtual homologation, or even to use the virtual twin of the system to perform condition monitoring of both the vehicle and the track and schedule maintenance operations. Moreover, the wheel-rail contact plays a role in those models, since the contact forces are responsible for supporting and guiding the vehicle, as well as promoting traction and braking actions. The accurate modeling of the wheel-rail contact is also important to consider several tribological phenomena that damage the surfaces, as the wear, plastic deformation or rolling contact fatigue. A significant part of the rolling stock and railway infrastructure maintenance costs is related to these damage phenomena, namely the inspection operations, track downtime, reprofiling and replacement of parts. In particular, the surface wear is highly linked with the magnitude of existing creepages and creep forces, which are dependent on the friction level between wheel and rail. Although the coefficient of friction is usually taken as constant value for railway dynamics analyses, due to the introduction of local lubrication or friction modifiers on the wheel flange and/or rail gauge, or even due to the presence of contaminating substances, friction can vary along the contacting surfaces. This work aims to study the influence of considering a variable friction coefficient along the wheel profile on the dynamic response of a railway vehicle and wear index calculation. For this purpose, a vehicle negotiating a curved track under different operating conditions is used to verify the results of the application of the developed methodology

On the advantages of principal modes for multimode SDM transmission systems

MISO array size is shown to scale sub-linearly with an increasing number of tributaries under modal dynamics and mode-dependent loss with up to 330 principal modes over a fibre optimised for low modal dispersion

A Reconfigurable OADM Architecture for High-Order Regular- and Offset- QAM based OFDM Super-Channels

We investigate the performance of a Reconfigurable All-Optical Add Drop Multiplexer (ROADM) architecture, that is suitable of supporting high-order regular and offset based QAM signals. The design is based on a highly modular interferometric, structure, in which OFDMA sub-channels remain in the optical domain. Sub-channel extraction is achieved via waveform splitting and coherent subtraction. Numerical studies have been carried out to validate performance and optimize critical parameters of the add/drop process. Particularly, input parameters like the signal extinction ratio, pulse rise time, switching window and input power levels have been optimized for single sub-carrier add/drop operation, from an OFDM super-channel comprising seven optical sub-carriers with 10 GHz spacing. Results have shown that the proposed ROADM architecture can accommodate and process both regular and offset based high-order QAM signals

DESIGNA 2015 - 2016

Este projeto identifica todos os pontos durante o estágio, realçando os processos, os resultados obtidos na elaboração do Logo e do Inventario do DESIGNA – Conferencia Internacional de Investigação em Design. Esta Conferencia é anual e tem como intuito criar um ponto de ligação entre os variados conhecimentos de Design nas variadas áreas sendo estas: Multimédia, Industrial, Moda, Comunicação, Gráfico e Teórico. O projeto apresentado é de conteúdo prático, com uma breve vertente teórica de introdução ao que é o Design Gráfico, foca-se prioritariamente no desenvolvimento do Logotipo a ser usado no DESIGNA e na criação do inventário com as várias componentes gráficas criadas e utilizadas desde a primeira edição desta conferência em questão. Todos os resultados obtidos neste projeto resolveram de uma aplicação de vários conhecimentos adquiridos ao longo do meu percurso como aluno.This project identifies all points during the internship, highlighting all processes, the obtained results during the elaboration of the Logo and the invetory of DESIGNA – International Conference in Design Research. This Conference is yearly and has the intuit to create a connection point between the varied knowledge in design in the varied areas being: Multimedia, Industrial, Fashion, Comunication, Graphic and Theoric. The presented project is of pratical content, with a brief theoric introduction to what is Graphic Design, it focus mainly in the development of the Logo being used in DESIGNA and in the creation of the Inventory with the multiple graphic components created and used since the frist DESIGNA edition. All results obtained in this project resolved from the aplication of multiple knowledge aquired during my course as student

My Business Consultores Financeiros e Informáticos, Lda.

O presente relatório visa descrever as atividades desenvolvidas ao longo do estágio curricular realizado na My Business Consultores Financeiros e Informáticos, Lda., que presta serviços nas áreas da contabilidade e da fiscalidade. O estágio teve a duração de seis meses e tinha como objetivo o desenvolvimento no mestrando de um conhecimento profissional nas áreas da contabilidade, da fiscalidade e do controlo interno, para facilitar a futura integração do mestrando no mercado laboral. O trabalho desenvolvido foi muito enriquecedor, pois permitiu o contacto direto com as atividades efetuadas e desta forma ter algum conhecimento da vida profissional esperada no futuro