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المؤلفون: Rocha, Pedro Miguel Monteiro da
مصطلحات موضوعية: Ballistic impact, Lightweight armour, Layer optimisation, Finite element analysis, Wave propagation, Non-linear material behaviour, Abaqus python API, Particle swarm optimisation
الوصف: Technology advances continue to revolutionise military equipment. The development of new firepower induces an interest in the enhancement of protection gear, both for transportation vehicles and personnel. There has been a significant amount of research of methods to increase protection capabilities without increases in the weight of a given defence system. This dissertation seeks to develop an optimisation tool that results in light-weight armour plates without compromising protection capabilities. A thorough study on the propagation of elastic and plastic stress waves aims for a better understanding of how an armour system behaves upon ballistic impact. The first part of this dissertation focuses on the development of a Python script that provides an efficient approach to model generation in Abaqus. It enables the user to avoid time consuming actions when designing ballistic test models to later simulate through the software. This script is also used to validate the theory behind elastic and plastic stress wave propagation while also being able to access output databases and interpret obtained results. The importance of the script is relevant for the second part of the dissertation, which takes advantage of the Abaqus Python Application Programming interface (API) to perform optimisation procedures automatically. Focusing particularly on the application of the particle swarm optimisation algorithm, this work continuously improves the efficiency and accuracy of the mentioned algorithm by dividing three different optimisation problems into several experiments. Each one of the experiments is carefully defined to highlight the impact of a specific operating parameter of the algorithm. A validation of the stress wave propagation and how it is affected upon contact with layered media is carefully conducted through a series of different analysis approaches. It is shown that the plastic stress wave propagates slower than the elastic one and that plastic deformation affects the properties of the generated stress wave, such as wavelength. The implemented particle swarm optimisation algorithm proved to be an effective approach to problem solving, however, for complex problems the operational parameters must be carefully chosen.
الوصف (مترجم): Os avanços na tecnologia continuam a revolucionar equipamentos militares. O desenvolvimento de novas armas de fogo induz interesse no aprimoramento de equipamento de proteção, para veículos de transporte e pessoal. Tem havido uma quantidade significativa de investigação de métodos para aumentar as capacidades de proteção sem aumento de peso de um dado sistema de proteção. Esta dissertação tem como objetivo o desenvolvimento de uma ferramenta de otimização que resulta em placas de armadura de baixo peso sem comprometer capacidades de proteção. Um estudo cuidadoso acerca da propagação de ondas de tensão elásticas e plásticas procura compreender a forma como um sistema de armadura reage após um impacto balístico. A primeira parte desta dissertação foca-se no desenvolvimento de um código em Python que fornece uma abordagem eficiente à geração de modelos no Abaqus. Isto permite que o utilizador evite ações que consumam tempo ao criar modelos de teste balístico para simular mais tarde através do software. Este código é também usado para validar a teoria por detrás da propagação de ondas de tensão elásticas e plásticas e ao mesmo tempo habilitar o acesso a dados de saída do software e interpretar resultados obtidos. A importância do código é relevante para a segunda parte da dissertação, que tira vantagem da interface de aplicação e programação do Abaqus Python (API) para executar procedimentos de otimização de forma automática. Com foco em particular na aplicação do algoritmo de otimização por enxame de partículas, este trabalho melhora continuamente a eficácia e precisão do algoritmo mencionado através da divisão de três diferentes problemas de otimização em várias experiências. Cada uma das experiências é cuidadosamente definida para destacar o impacto de um parâmetro operacional específico do algoritmo. A validação da propagação da onda de tensão e como é afetada após contacto com um meio material de múltiplas camadas é cuidadosamente estudada através de séries de diferentes análises. É mostrado que a onda de tensão plástica se propaga mais lentamente que a elástica e que deformação plástica afeta as propriedades da onda de tensão gerada, tal como o comprimento de onda. O algoritmo de otimização por enxame de partículas implementado prova ser uma abordagem eficaz para a resolução de problemas, no entanto, para problemas complexos os parâmetros operacionais devem ser escolhidos com cuidado.
وصف الملف: application/pdf
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المؤلفون: Barbeiro, Sílvia, Serranho, Pedro
المساهمون: Repositório Aberto
مصطلحات موضوعية: Elastography, Method of fundamental solutions, Coupled acoustic wave propagation, Elastic displacement model
الوصف: This paper addresses the numerical simulation of the mechanical waves propagation and induced displacements in the human retina, for the elastography imaging modality. In this way, we use a model for the human eye and numerically approximate the propagation of time-harmonic acoustic waves through the different media of the eye and the respective elastic excitation in the retina, through a layered representation approach based on the method of fundamental solutions. We present numerical results showing the feasibility of the method.
الوصف (مترجم): FCT (Portugal) research project PTDC/EMD-EMD/32162/2017, COMPETE and Portugal2020. UIDB/00324/2020, by the Portuguese Government through FCT/MCTES. UID/NEU/04539/2019, funded by the Portuguese Government through FCT/MCTES.
وصف الملف: application/pdf
العلاقة: 978-3-030-52803-4 (Print); 2199-3041 (Print)
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المساهمون: Pinho, José L. S., Universidade do Minho
مصطلحات موضوعية: Maré, Agitação marítima, Modelo de propagação da agitação, Morfodinâmica costeira, Levantamento DGPS, Sensor de pressão TWR-2050, Delft3D, Tide, Wave propagation, Wave propagation model, Coastal morphodynamics, DGPS surveys, TWR-2050 pressure sensor, Engenharia e Tecnologia::Engenharia Civil
الوصف: Dissertação de mestrado integrado em Engenharia Civil
الوصف (مترجم): O fenómeno da erosão costeira afeta gravemente a costa portuguesa, sendo os seus principais agentes erosivos o vento, a maré e a agitação marítima. Não obstante, existem, ainda, outras causas de origem antropogénica que estão na origem de processos erosivos recentes. Com efeito, é fulcral a caracterização da hidrodinâmica, que constitui o primeiro passo em muitos estudos sobre a orla costeira, bem como a caracterização da agitação marítima da costa. O trabalho desenvolvido focou-se na praia de Ofir. Consistiu na realização de levantamentos topográficos de alta precisão com auxílio de equipamento DGPS e na medição de estados de agitação marítima, na zona em estudo, com o auxílio do sensor de pressão TWR-2050. O objetivo foi contribuir para a compreensão e avaliação de alterações morfológicas em diferentes estados de agitação e tipologia de maré, bem como realizar uma caracterização dos estados de agitação marítima da praia. Uma vez que só foram realizadas duas campanhas na praia, no dia 1 de maio e 28 de maio de 2018, recorreu-se aos levantamentos topográficos efetuados em 2017 Gomes (2017) para comparação com o levantamento efetuado a 1 e 28 de maio de 2018. Foram realizadas três sessões de trabalhos de campo na Praia de Ofir. A primeira campanha teve como finalidade adquirir experiência no manuseamento dos equipamentos (DGPS e sensor TWR-2050) e analisar posições estratégicas para instalação do sensor de pressão. A segunda visita ao terreno ocorreu no dia 1 de maio de 2018, onde foram realizados os levantamentos topográficos bem como a instalação do sensor TWR-2050 para medição da agitação no período de monitorização. E para finalizar, a terceira campanha ocorreu a 28 de maio e serviu para realizar um levantamento topográfico da praia que cobrisse na íntegra o areal compreendido entre o esporão norte e o sul. Após a fase de recolha e análise dos dados das medições em campo, foi criado um modelo de agitação no software Delft3D com vista a simular os estados verificados em campanha. Assim, a caracterização de estados de agitação marítima foi concebida através da comparação de dados registados no sensor de pressão (TWR-2050), e os resultados das simulações efetuadas pelo software Delft3D, bem como os registos cedidos pelo Instituto Hidrográfico registados pela boia do porto de Leixões. No final são apresentados todos os resultados e análises das medições e do modelo numérico de modo a avaliar as diferenças verificadas no período em análise.
The phenomenon of coastal erosion seriously affects the Portuguese coast, its main agents being erosion wind, tide and sea agitation. Nevertheless, there are still other causes of anthropogenic origin that are the origin of recent erosive processes. In fact, hydrodynamic characterization, which is the first step in many studies of the coastline, as well as the characterization of coastal sea agitation, is crucial. The work developed focused on the beach of Ofir. It consisted in the realization of topographic surveys of high precision with the aid of DGPS equipment and in the measurement of states of marine agitation, in the zone under study, with the aid of the pressure sensor TWR-2050. The objective was to contribute to the understanding and evaluation of morphological alterations in different states of tide agitation and typology, as well as to perform a characterization of the states of marine agitation of the beach. Since only two campaigns were carried out on the beach, on May 1st and on May 28th, 2018, topographic surveys were carried out in 2017 Gomes (2017) for comparison with the survey carried out on May 1st and on 28th, 2018. Three fieldwork sessions were carried out at Praia de Ofir. The first campaign was aimed at gaining experience in handling equipment (DGPS and TWR-2050 sensor) and analyzing strategic positions for pressure sensor installation. The second visit to the field, as already mentioned, took place on May 1st, 2018, where the topographic surveys were carried out, as well as the installation of the TWR-2050 sensor to measure the agitation during the monitoring period. To conclude, the third campaign took place on May 28th and served to carry out a topographic survey of the beach that covered in full the sand between the north and south spurs. After the phase of data collection and analysis of the field measurements, a model of agitation was created in the Delft3D software to simulate the states verified in the campaign. Thus, the characterization of maritime agitation states was conceived by comparing data recorded on the pressure sensor (TWR-2050), and the results of the simulations carried out by the Delft3D software, as well as the records provided by the Hydrographic Institute registered by the port buoy of Leixões. At the end, all the results and analyzes of the measurements and the numerical model are presented in order to evaluate the differences verified in the period under analysis.وصف الملف: application/pdf
العلاقة: 202641562
الإتاحة: http://hdl.handle.net/1822/71088Test
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المؤلفون: Carneiro, José João Fernandes
المساهمون: Pinho, José L. S., Granja, Helena Maria, Universidade do Minho
مصطلحات موضوعية: Maré, Agitação marítima, Registo de agitação marítima, Modelos de propagação da agitação, Tide, Wave propagation, Wave propagation registration, Shore, 556.465, 681.5, Engenharia e Tecnologia::Engenharia Civil
الوصف: Dissertação de mestrado integrado em Engenharia Civil
الوصف (مترجم): Na presente dissertação tem-se por objetivo recolher dados de medições de estados de agitação marinha na zona em estudo que é composta por elevado número de seixos, permitindo uma caracterização de estados de agitação marinha da praia, mais propriamente a praia de Belinho situada em Esposende É usual efectuar a caracterização da agitação com recurso a modelos numéricos complementados com registos de sensores de pressão instalados na zona em análise. Assim a caracterização de estados de agitação do trabalho aqui apresentado foi efectuada comparando os dados registados no sensor de pressão utilizado sendo ele o sensor TWR-2050, e os resultados das simulações efectuadas pelo software Coulwave, bem como os registos cedidos pelo Instituto Hidrográfico registados pela boia do porto de Leixões. O resultados apresentados são referentes as datas 24/04/2014, 28/04/2014, 13/05/2014 e 16/05/2014 e encontram-se em período de marés vivas. Relativamente as campanhas efectuadas in situ, o sensor foi instalado num local situado antes da rebentação, numa superfície plana, com fácil acesso a partir das rochas, sendo este colocado numa estrutura devidamente preparada para o efeito, com recurso a diversos materiais de fixação. Após a fase de recolha e análise dos dados das medições em campo, foi criado um modelo de agitação no software Coulwave, com base em registos da boia do porto de Leixões, com vista a simular os estados verificados em campanha, sendo que as condições de simulação introduzidas foram a altura significativa e o período significativo. São apresentados todos os resultados e analises das medições e do modelo numérico de modo a avaliar as diferenças verificadas nos períodos em análise. Da comparação efectuada em ambos os métodos, referentes à altura significativa e período significativo, conclui-se que em grande parte os valores se assemelham, de onde se deduz que os métodos tem uma eficácia satisfatória. Importante referir também que os valores registados em Leixões, no dia referente a primeira campanha possuem uma diferença significativa para com os registos in situ e os do modelo numérico. Do trabalho realizado é possível afirmar que a praia de Belinho não registou elevada agitação nas datas em analise e os dados de ondas registados são formadas ao largo.
The purpose of this work is to collect data from measurements of sea agitation in the study area which is composed of large number of pebbles, allowing a cause-effect analysis of the beach morphodynamics, allowing a characterization of sea agitation on the beach, more properly beach Belinho, located in Esposende, Braga. It is usual to perform the characterization of sea agitation using the numerical models supplemented with records of pressure sensors installed in the area os study. Thus the characterization agitation states here presented here was made by comparing the data recorded in the pressure sensor used (the TWR-2050 sensor), and the results of the simulations by Coulwave software, as well as records assigned by the Hydrographic Institute recorded by Leixões harbor buoy. The results presented refer to the following dates: 24/04/2014, 28/04/2014, 05/13/2014 and 16/05/2014. Regarding the campaigns carried out in situ, the sensor was installed at a location before the breaker point on a flat surface, with easy access from the rocks, which was placed in a structure properly prepared for this purpose, using various fastening materials. After the phase of gathering and analyzing data from field measurements, a model of agitation in Coulwave software was created, based on records of Leixões harbor buoy, in order to simulate the observed states during campaigns; the conditions introduced in the simulation were the significant height and period. All results and analysis of the measurements and the numerical model are presented in order to evaluate the differences in the periods under review. From the comparison made in both methods, related to the significant wave height and significant period, we concluded that the values largely resemble and thus the methods are satisfactory. It is also important to note that the values recorded in Leixoes on the day after the first campaign have a significant difference to the records in situ and the numerical model. From this work it is possible to affirm that the Belinho did not register a high agitation on the study dates and the analyzed and recorded data show us that the waves are formed offshore.وصف الملف: application/pdf
العلاقة: 201143453
الإتاحة: http://hdl.handle.net/1822/36255Test
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المؤلفون: Rios, Luís, Pereira, Cláudio, Correia, António Gomes, Parente, Manuel
المساهمون: Universidade do Minho
مصطلحات موضوعية: Wave propagation, Strain measurement, Stiffness, Anisotropy, Engenharia e Tecnologia::Engenharia Civil, Science & Technology
الوصف: This paper presents a study of a uniform dry sand compacted by the pluviation method and submitted to different isotropic and anisotropic stress paths. The stress states were performed in two distinct triaxial cells using specimens of 100 mm and 150 mm diameter in order to assess also the scale-effects. The small strain stiffness for each stress state was evaluated in both triaxial cells by bender elements which were assembled vertically and horizontally for the comparison of the shear wave velocity in the two directions. In the specimens of 100mm, additionally to the bender elements in the vertical direction, accelerometers were used for the improvement of the results accuracy. All tests results were analysed in order to assess the initial fabric (inherent) anisotropy and the induced anisotropy by the different anisotropic stress paths. - See more at: http://ascelibrary.org/doi/abs/10.1061/9780784480083.028#sthash.z0U2SnxA.dpufTest
الوصف (مترجم): Financial support provided by FCT (Portuguese Foundation for Science and Technology) in the form of the research project WaveSoil (PTDC/ECM/122751/2010).
وصف الملف: application/pdf
العلاقة: Rios, L., Pereira, C., Correia, A.G., Parente, M. Small Strain Stiffness of Sand under Different Isotropic and Anisotropic Stress Paths Measured by Seismic Wave-Based Testing Techniques (2016) Geotechnical Special Publication, 2016-January (265 GSP), pp. 224-231. doi: 10.1061/9780784480083.028; 0895-0563
الإتاحة: http://hdl.handle.net/1822/45136Test
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المؤلفون: Sousa, Fernando, Nunes, Fernando
المساهمون: RCIPL
مصطلحات موضوعية: Kalman Filters, Delay Lock Loops, Discriminators, Frequency Locked Loops, Ionospheric Electromagnetic Wave Propagation, Nonlinear Filters, Radio Receivers, Radiowave Propagation, Satellite Navigation
الوصف: A noncoherent vector delay/frequency-locked loop (VDFLL) architecture for GNSS receivers is proposed. A bank of code and frequency discriminators feeds a central extended Kalman filter that estimates the receiver's position and velocity, besides the clock error. The VDFLL architecture performance is compared with the one of the classic scalar receiver, both for scintillation and multipath scenarios, in terms of position errors. We show that the proposed solution is superior to the conventional scalar receivers, which tend to lose lock rapidly, due to the sudden drops of the received signal power.
وصف الملف: application/pdf
العلاقة: 978-147993320-4
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المؤلفون: Sousa, Fernando, Nunes, Fernando
المساهمون: RCIPL
مصطلحات موضوعية: Kalman Filters, Delay Lock Loops, Ionospheric Electromagnetic Wave Propagation, Radio Receivers, Radiowave Propagation, Satellite Navigation
الوصف: We analyze the advantages and drawbacks of a vector delay/frequency-locked loop (VDFLL) architecture regarding the conventional scalar and the vector delay-locked loop (VDLL) architectures for GNSS receivers in harsh scenarios that include ionospheric scintillation, multipath, and high dynamics motion. The VDFLL is constituted by a bank of code and frequency discriminators feeding a central extended Kaiman filter (EKF) that estimates the receiver's position, velocity, and clock bias. Both code and frequency loops are closed vectorially through the EKF. The VDLL closes the code loop vectorially and the phase loops through individual PLLs while the scalar receiver closes both loops by means of individual independent PLLs and DLLs.
وصف الملف: application/pdf
العلاقة: SOUSA, Fernando Manuel Gomes de; NUNES, Fernando D. – Performance analysis of a VDFLL GNSS receiver architecture under ionospheric scintillation and multipath conditions. In IEEE PLANS, Position Location and Navigation Symposium. New York : IEEE - Institute of Electrical and Electronics Engineers Inc., 2014. ISBN: 978-147993320-4. Art. nr. 6851421, p. 602-611.
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المؤلفون: Nunes, Fernando, Sousa, Fernando
المساهمون: RCIPL
مصطلحات موضوعية: Gaussian distribution, Nakagami channels, Ionospheric electromagnetic, Wave propagation, Radiowave propagation, Satellite navigation, Time series
الوصف: We propose a low complexity technique to generate amplitude correlated time-series with Nakagami-m distribution and phase correlated Gaussian-distributed time-series, which is useful in the simulation of ionospheric scintillation effects during the transmission of GNSS signals. The method requires only the knowledge of parameters S4 (scintillation index) and σΦ (phase standard deviation) besides the definition of models for the amplitude and phase power spectra. The Zhang algorithm is used to produce Nakagami-distributed signals from a set of Gaussian autoregressive processes.
وصف الملف: application/pdf
العلاقة: NUNES, Fernando D.; SOUSA, Fernando Manuel Gomes de – Practical simulation of GNSS signals in the presence of ionospheric scintillation. In IEEE PLANS, Position Location and Navigation Symposium. New York : IEEE - Institute of Electrical and Electronics Engineers Inc., 2014. ISBN: 978-147993320-4. Art. nr. 6851357, p. 50-58.; 978-147993320-4
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المؤلفون: Nunes, Fernando, Sousa, Fernando
المساهمون: RCIPL
مصطلحات موضوعية: Gaussian Distribution, Nakagami Channels, Autoregressive Processes, Ionospheric Electromagnetic Wave Propagation, Radiowave Propagation, Satellite Navigation, Time Series
الوصف: We propose a low complexity technique to generate amplitude correlated time-series with Nakagami-m distribution and phase correlated Gaussian-distributed time-series, which is useful for the simulation of ionospheric scintillation effects in GNSS signals. To generate a complex scintillation process, the technique requires solely the knowledge of parameters Sa (scintillation index) and σφ (phase standard deviation) besides the definition of models for the amplitude and phase power spectra. The concatenation of two nonlinear memoryless transformations is used to produce a Nakagami-distributed amplitude signal from a Gaussian autoregressive process.
وصف الملف: application/pdf
العلاقة: NUNES, Fernanco D.; SOUSA, Fernando Manuel Gomes de – Generation of Nakagami correlated fading in GNSS signals affected by ionospheric scintillation. In ESA Workshop on Satellite Navigation Technologies and European Workshop on GNSS Signals and Signal Processing. New York : IEEE - Institute of Electrical and Electronics Engineers Inc., 2014. p. 1-8.
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المؤلفون: Pinheiro, L., Fortes, C. J. E. M., Santos, J. A., Fernandes, J. L. M.
مصطلحات موضوعية: Wave propagation, Ship – wave interaction, Finite elements method, Panel method
الوصف: Sea waves inside harbors can affect scheduled port operations. Hence it is important to correctly predict and characterize the wave field inside ports and to describe the movements of the ship and forces acting upon it. A classical approach is to assume that shipwave interaction is linear, [1]. Then it is possible to decompose it in the so-called radiation and diffraction problems. Numerical models that solve such problems have been developed and used by the offshore industry for quite a while, [2], to study the interaction of sea-waves with floating objects. However, these models cannot be used to solve the diffraction problem of ships inside harbor basins where nearby reflecting boundaries and shallow depths create very complex nonlinear wave fields. A new set of procedures using coupled models is proposed in this work. First, a Boussinesqtype finite element wave propagation model is used to determine the wave field in the numerical domain containing the harbor. Then the velocity potentials are evaluated at the ship’s hull and finally, the Haskind relations [3] are used to determine the wave forces on the ship along the six modes of motion (heave, sway, surge, roll, pitch and yaw). This new methodology for the evaluation of diffraction forces on a ship inside a harbor basin is presented and tested in this paper. Movements of the moored ship and tensions on the mooring system are obtained using a numerical solver for the motion equations of a moored ship. An application to an open coast harbor is presented.
وصف الملف: application/pdf
