Papers
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Railway track support condition assessment
AbstractA novel methodology to evaluate railway track support conditions is currently being developed. This methodology is based on modal analysis of the multi-element system composed by the railway infrastructure and an instrumented railway vehicle. It belongs to the group of vibration-based structural damage identification methods and is focused on observing the characteristic frequencies of this multi-element system, which can be related with changes in the physical properties of the railway infrastructure. As opposed to other vehicle-based track monitoring methods, the proposed methodology should enable condition assessment of the railway infrastructure subgrade, an element that is often neglected during railway monitoring operations. Since this methodology is vehicle-based, it can be used to assess the entire extension of a railway infrastructure to gather data regarding the support conditions of the track. It can also assess the evolution of track support conditions over time by comparing different rides over the same railway stretch. An important aspect of this methodology that still lacks validation is the topic of characterizing track support conditions of a railway infrastructure through its natural frequencies. The suitability of the theoretical model behind this methodology is another aspect that needs to be assessed. Numerical simulations tests using the multibody simulation software Simpack® are currently being performed to address both topics. This paper describes some of the simulations performed in this context, including a description of the numerical models used. The obtained results support the selected theoretical model and the overall validity of the proposed methodology.
Year: 2023
Author(s): Mendes, J.; Calçada, R.; Ribeiro, D.; Fortunato, E.; Morais, J.
: Engineering Failure Analysis
Editor: ELSEVIER
Volume:
Volume 152, October 2023, 107483.
Keywords: Early detection; Natural degradation; Degradation; Physical properties analysis; Natural materials; Railway track; Mechanical engineering
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Double bridge circuit for self-validated structural health monitoring strain measurements
N/A
Year: 2018
Number Pages:
12p.
Author(s): Reis, J. P.; Oliveira Costa, C.; Costa , J.
: Strain (the Journal)
Editor: 2018 John Wiley & Sons, Ltd
Keywords: Strain measurement; Strain gauge debonding; Self-diagnosis sensor; Measuring bridges; Loop current step response (LCSR) method
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Local validation of structural health monitoring strain measurements
N/A
Year: 2018
Number Pages:
143-153pp.
Author(s): Reis, J. P.; Oliveira Costa, C.; Costa , J.
: 0263-2241/ 2018 Elsevier Ltd. All rights reserved
Editor: ELSEVIER
Keywords: Structural health monitoring; Fault detection; Non-stationary time series; Strain measurement; Sensor validation
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Strain gauges debonding fault detection for structural health monitoring
N/A
Year: 2018
Number Pages:
14p.
Author(s): Reis, J. P.; Oliveira Costa, C.; Costa , J.
: Strain (the Journal)
Editor: 2018 John Wiley & Sons, Ltd
Keywords: Strain measurement; Thermal sensors; Temperature measurement; Self-diagnosis sensor; Loop current step response (LCSR) method
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Linear and Sliding-Mode Control Design for Matrix Converter-Based Unified Power Flow Controllers
This paper presents the design and compares the performance of linear, decoupled and direct power controllers for three-phase matrix converters operating as Unified Power Flow Controllers (lIPFC). A simplified steady-state model of the matrix converter based UPFC (MC-UPFC) fitted with a modified Venturini high frequency PWI\I modulator is first used to design the linear controllers for the transmission line active (P) and reactive (Q) power. ln order to minimize the resulting cross-coupling between P and Q power control, decoupled linear controllers (DLC) are synthesized using inverse dynamics linearization. Direct power controllers (DPC) are then developed using sliding mode control techniques, in order to guarantee both robustness and decoupled control. The designed P and Q power controllers are compared using simulations and experimental results. Linear controllers show acceptable steady-state behavior but still exhibit coupling between P and Q powers in transient operation. DLC are free from cross-coupling but are parameter sensitive. Results obtained by DPC show decoupled power control with zero error tracking and guarantee faster responses with no overshoot and no steady-state error. Ali the designed controllers were implemented using the sarne digital signal processing (DSP) hardware.
Year: 2014
Number Pages:
3357-3367pp.
Author(s): Monteiro, J.; Silva, J. F.; Pinto, S. F.; Palma, J.
: Revista IEEE Transactions on Power Electronics
Editor: IEEE
Volume:
Volume 29 / N.º 7.
Keywords: Unified power flow controllers (upfc); Matrix converter; Linear controllers; Direct power controllers (dpc)
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Medição não-intrusiva da densidade superficial de depósitos de sedimentos em camada fina
O processo de medição de espessuras e de densidades superficiais de sedimentos depositados em modelos físicos tem sido motivo de investigação, conhecendo-se alguns métodos para o efeito, mas todos eles exibindo limitações sérias, em especial quando se pretendem medir depósitos em camada fina, isto é, com poucos milímetros de espessura. O presente estudo refere-se a um método para realizar este tipo de medição, baseado na variação de resistência elétrica entre elétrodos que fiquem cobertos com a camada de sedimentos. Pretende-se aplicar um método de medição que não perturbe o processo de sedimentação, com sensibilidade para medição de camadas finas (até 1cm) de sedimento, que permita a medição ao longo do tempo, robusto aos efeitos eletroquímicos da água e robusto às perturbações do meio (variação de temperatura, salinidade e nível da água). Inicialmente é feito um resumo sucinto do estado de arte dos métodos de medição de sedimentos, com a descrição das vantagens e limitações de cada um e salientando a sua aplicabilidade à medição de sedimentos em camadas finas. Segue-se uma descrição do princípio de medição adoptado, identificam-se diversos fatores de influência que, na abordagem convencional, perturbam ou dificultam a medição pretendida, propondo-se soluções para os compensar ou os retirar da cadeia de transdução. É feita uma descrição do circuito eletrónico desenvolvido que permite implementar o método de medição proposto. Finalmente são apresentados os resultados de um estudo experimental feito em protótipo que mostram a viabilidade do método com as inovações introduzidas para superar as limitações do princípio de medição.
Year: 2014
Number Pages:
27-42pp.
Author(s): Coelho, G.; Palma, J.; Alves, E.
: Revista Medições e Ensaios
Editor: SPMet - Sociedade Portuguesa de Metrologia
Volume:
N.º 7.
Info
Predictive Control for Earthquake Response Mitigation of Buildings Using Semiactive Fluid Dampers
N/A
Year: 2014
Number Pages:
14pp.
Author(s): Oliveira, F. S. B. F.; Gil de Morais, P.; Suleman, A.
: Revista Shock and Vibration
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A new control strategy with saturation effect compensation for an autonomous induction generator driven by wide speed range turbines
This paper presents a variable speed autonomous squirrel cage generator excited by a current-controlled voltage source inverter to be used in stand-alone micro-hydro power plants. The paper proposes a system control strategy aiming to properly excite the machine as well as to achieve the load voltage control. A feed-forward control sets the appropriate generator flux by taking into account the actual speed and the desired load voltage. A load voltage control loop is used to adjust the generated active power in order to sustain the load voltage at a reference value. The control system is based on a rotor flux oriented vector control technique which takes into account the machine saturation effect. The proposed control strategy and the adopted system models were validated both by numerical simulation and by experimental results obtained from a laboratory prototype. Results covering the prototype start-up, as well as its steady-state and dynamical behavior are presented.
Year: 2011
Number Pages:
2142-2152pp.
Author(s): Margato, E.; Faria, J.; Resende, M. J.; Palma, J.
: Energy Conversion and Management
Editor: ELSEVIER
Volume:
52.
Keywords: Static var excitation; Rotor flux oriented control; Micro-hydro power plants; Magnetic saturation effect; Autonomous induction generator
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Calibration methodology of a vision system for measuring the displacements of long-deck suspension bridges
SUMMARY Structural health monitoring is an emergent powerful diagnostic tool that can be used to identify and to prevent possible failures of the various components that comprise an infrastructure. In a suspension bridge, the measurement of the vertical and transversal displacements plays an important role for its safety evaluation. Considering the restrictions usually found on these structures, an enhanced solution comprises a non-contact vision-based measurement system with dynamic response, accuracy and amplitude range well suited to the physical phenomenon to measure. A methodology to perform the vision system calibration is described, which can be carried out in situ, while the deck is moving, requiring little effort and a minimum set of information. The key idea is to use the factorization method to get an initial estimation of the object shape and cameras parameters, and to incorporate the knowledge about the distances between the calibration targets in a non-linear optimization process to achieve a metric shape reconstruction and optimize the cameras parameters estimation. Results obtained by numerical simulation experiments are reported, showing the negligible influence of noisy calibration data in the calibration performance and also the robustness of the calibration process on the cameras parameters estimation. Tests carried out to assess the calibration and tracking of the bridge deck motion showed that, even in an environmental severely affected by noise, it is possible to measure the vertical and transversal displacements of the bridge deck with excellent levels of accuracy.
Year: 2011
Number Pages:
20.
Author(s): Santos, C.; Oliveira Costa, C.; Batista, J.
: Structural Control and Health Mnitoring
Editor: Structural Control and Health Monitoring
Keywords: Affine camera; Displacements; Structural health monitoring; Long-range photogrammetry; Non-contact measuring system; Suspension bridge; Vision metrology
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Long Deck Suspension Bridge Monitoring: The Vision System Calibration
ABSTRACT: Structural Health Monitoring is an emergent powerful diagnostic tool that can be used to identify and to prevent possible failures of the various components that comprise an infrastructure. In the particular case of a suspension bridge, the measurement of the vertical and transversal displacements plays an important role for its safety evaluation. Taking into account the restrictions usually found on these structures, an enhanced solution comprises a non-contact vision-based measurement system with dynamic response, accuracy and amplitude range well suited to the physical phenomenon to measure. The paper describes a methodology to perform the vision system calibration that can be carried out in-situ, while the deck is moving, requiring little effort and a minimum set of information. Specifically, only a set of active targets fixed on the deck and the knowledge about the distances between them is required. Results related to the performance evaluation, obtained by numerical simulation and by real experiments with a reduced structure model, are presented and they show that, even in an environment severely affected by disturbance noise, it is possible to measure the vertical and transversal displacements with a standard accuracy better than 10 mm.
Year: 2011
Number Pages:
16.
Author(s): Santos, C.; Oliveira Costa, C.; Batista, J.
: Strain An International Journal for Experimental Mechanics
Editor: Blackwell Publishing Ltd
Keywords: Structural health mnitoring; Non-contact measurement system; Long-range ptotogrammetry; Vision metrology; Suspension bridge
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Comunicação
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Orthodynamometer for Measurement of Longitudinal and Transverse Loads in Wind Tunnel Testing
N/A
Year: 2014
Number Pages:
7pp.
Author(s): Freitas, A.; Gil de Morais, P.
Keywords: Wind tunnel testing; Bi-axial balance; Orthodynamometer
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Semi-Active Control of Base-isolated Structures Using a Nonlinear Feedback Strategy
Base isolation systems have been proposed for reducing the transmission of seismic forces and energy to buildings when subjected to earthquake loads. Passive devices are ofien prescribed to reduce displacements at the isolation levei but in certain circumstances structural interstorey drifis and absolute accelerations can increase. This work explores the use of semi-active devices whose input is obtained from an output nonlinear control law resulting from the transformation of the nonlinear system into a linear one which is then controlled bya proportional controller. Within this nonlinear feedback control strategy the whole system formulation is considered for deriving the control law. A two degree of freedom experimental model representative of a typical base isolated building, currently under development at LNEC, is used as an example to evaluate the ( performance of the proposed strategy when subjected to accelerograms for the Portuguese territory. The results of the experimental characterization of the model components and for a magneto-rheological damper are presented. Numerical simulation results show that the proposed strategy to command the damper in real time can reduce the base relative displacement with better performance at the superstructure leveI (interstorey and accelerations) than the damper working in the passive mode. Although a small incre ase in the base acceleration for one type of seismic action is observed when compared to the original structure, it is always lower than the one resulting with the passive case.
Year: 2014
Number Pages:
8pp.
Author(s): Oliveira, F. S. B. F.; Gil de Morais, P.; Suleman, A.
Keywords: Mr dampers; Nonlinear feedback control; Semi-active control; Seismic protection; Hybrid base isolation
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Predictive Control for Earthquake Response Mitigation of Building With Semi-Active Fluid Dampers
ln this paper a predictive control strategy in conjunction with sem i-active control algorithms are proposed for damping control of base isolation systems employing semi-active fluid dampers when subjected to earthquakes. Twenty artificial accelerograms for the Portuguese territory were considered in the numerical simulations of the base isolation system representative model. The results of a parametric study give some hints for controller design in this type of problems. It will be shown that a well tuned controller could outperform the original structure and the structural system with a passive device (optimized) in terms of performance: relative displacement and absolute acceleration reductions.
Year: 2013
Number Pages:
9pp.
Author(s): Oliveira, F. S. B. F.; Gil de Morais, P.; Suleman, A.
Keywords: Vibration mitigation; Seismic protection; Semi-active control systems; Predictive control
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A travelling sand pluviator to reconstruct large soil specimens
N/A
Year: 2012
Number Pages:
16.
Author(s): Oliveira, F. S. B. F.; Freitas, A.; Gil de Morais, P.; Mendes, B.; Carvalho, A. T.; Bilé Serra, J.
Keywords: Relative density; Terminal falling height; Terminal velocity; Sand specimen preparation; Stationary pluviator; Travelling sand pluviator
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A Vision-based IEKF full-motion estimation on Long Deck suspension bridges
N/A
Year: 2012
Number Pages:
12.
Author(s): Santos, C.; Oliveira Costa, C.; Batista, J.
Info
Integrated safety functions in the automatic transport system of Oeiras
N/A
Year: 2012
Number Pages:
8.
Author(s): Lourenço, F.; Vicente, L.; Palma, J.; Emílio, F. T.; Oliveira Costa, C.
Keywords: Hmi - human-machine interface; Electromagnetic cable control; Cable traction; Atp - automatc train protection; Lnec; Satu
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Laboratory tests of compressive creep in concrete samples: development of solutions for problems of actuation, measurement, data acquisition and load balancing
N/A
Year: 2012
Number Pages:
7.
Author(s): Palma, J.; Gil de Morais, P.; Coelho, G.; Ribeiro, A. C.
Info
Mathematical Model for 400mm Extensometer: Construction, Validation and Parameterization
N/A
Year: 2012
Number Pages:
16.
Author(s): Freitas, A.; Oliveira, F. S. B. F.; Gil de Morais, P.; Ribeiro, A.
Keywords: Mathematical model; Strain gauge; Extensometer; Structure monitoring
Info
Semi-active control of a fluid viscous damper for vibration mitigation
N/A
Year: 2012
Number Pages:
10p.
Author(s): Oliveira, F. S. B. F.; Gil de Morais, P.; Suleman, A.
Keywords: Vibration mitigation; Seismic protection; Semi-active control
Info
Semi-active viscous damper for controlling civil engineering structures subjected to earthquakes
N/A
Year: 2012
Number Pages:
6p.
Author(s): Oliveira, F. S. B. F.; Botto, M.; Suleman, A.; Gil de Morais, P.
Keywords: Control applications; Seismic protection; Vibration mitigation; Linear quadratic regulator; Sky-hook damper; Semi-active viscous dampers
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Books
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Unified Power Flow Controllers Without Energy Storage: Designing Power Controllers for the Matrix Converter Solution
N/A
Year: 2011
Number Pages:
425-438.
Author(s): Monteiro, J.; Silva, J. F.; Pinto, S. F.; Palma, J.
Editor: INTECH
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Capítulo de Livro
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Positioning systems for bed profiling in hydraulics physical models
N/A
Year: 2010
Number Pages:
512-532 pp.
Author(s): Palma, J.; Gil de Morais, P.; Guilherme, L.; Alves, E.
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Relatório Científico
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FO-SINC - Sistema de transmissão por fibra óptica dos sinais de sincronismo de módulos de aquisição de dados
FO-Sinc sistema de transmissão por fibra óptica dos sinais de sincronismo de módulos de aquisição de dados
Year: 2010
Number Pages:
31pp.
Author(s): Almeida Garrett, J.; Reis, J. P.
Editor: LNEC
Info
CABRILAQUIS - Manual do utilizador
Apresenta-se o Manual do Utilizador do programa CabrilAquis, parte integrante do sistema de monitorização do comportamento dinâmico da Barragem do Cabril. Este programa controla uma rede de dispositivos e.Pacs (Programmable Automation Controller) que mantém sincronizados, recuperando automaticamente de situações anómalas. Procede ainda à leitura contínua dos conteúdo dos buffers circulares dos equipamentos que se encontrem activos, gerando ficheiros horários para cada um deles. O acesso do utilizador ao painel de controlo do programa CabrilAquis pode ser feito no local onde se encontra o servidor ou, remotamente, a partir de qualquer computador que disponha de ligação à internet e esteja devidamente autorizado a estabelecer essa ligação.
Year: 2009
Number Pages:
40pp.
Author(s): Reis, J. P.; Oliveira Costa, C.
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Outro
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Segurança funcional em domínios de engenharia civil
A ciência e a tecnologia estão na base da realização de grandes empreendimentos, mas trazem muitas vezes riscos tecnológicos para os indivíduos ou o ambiente. Por outro lado, é inevitável que se recorra à própria ciência e à tecnologia para antecipar, prevenir e mitigar as consequências do seu impacto na sociedade e no ambiente. O presente programa de investigação é dirigido para o estudo da utilização de sistemas automáticos com vista à redução de risco (segurança funcional), bem como de sistemas de aviso e de planos de mobilização de pessoas e de recursos para a mitigação de riscos em cenários consumados. Os alvos de estudo circunscrevem-se essencialmente a certos empreendimentos de engenharia civil, nomeadamente: edifícios importantes, túneis rodoviários e barragens; mas, nos estudos referentes a sistemas de aviso e planos de emergência, estendem-se ainda a outros contextos e a fenómenos de origem natural. Após a alusão a alguns factos históricos e dados estatísticos sobre acidentes tecnológicos e à evolução das abordagens à segurança, são identificadas as perspetivas de investigação e de aplicação da segurança funcional no contexto do LNEC. Seguidamente são apresentados os fundamentos da segurança funcional, é empreendida uma revisão do estado da arte das suas principais ferramentas de análise e de síntese, nomeadamente, a análise sistémica da fiabilidade, os processos de Markov, a simulação estocástica, o fator humano e a problemática do risco. São propostos três planos de estudos de investigação, a saber: (i) desenvolvimento e avaliação de soluções de segurança funcional para edifícios; (ii) métodos e critérios de segurança funcional para túneis rodoviários; (iii) desenvolvimento de bases para a avaliação da confiabilidade de planos de emergência e de sistemas de aviso de catástrofes. Finalmente apresenta-se um programa de formação pós-graduada onde são propostos planos de teses de doutoramento e de dissertações de mestrado relacionados com os planos de estudo anteriormente apresentados.
Year: 2018
Author(s): Palma, J.
Keywords: Fator humano; Sistemas automáticos; Sistema de segurança; Sistema de alarme; Segurança contra incêndios; Segurança de edifícios; Segurança de estruturas; Automação; Túnel rodoviário; Plano de emergência; Análise de risco
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