Дисертації з теми "Radiating elements"
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1
McColl, Iain. "Radiating and coupling elements in waveguide planar array antennas." Thesis, Heriot-Watt University, 1992. http://hdl.handle.net/10399/788.
2
Foster, Adam. "On the behaviour and radiating properties of heavy elements in fusion plasmas." Thesis, University of Strathclyde, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501815.
Анотація:
Radiation from Impurities in magnetically confined fusion devices is regularly utilised on existing tokamaks for both diagnostic purposes (to reveal plasma conditions) and to estimate the impurity content itself to detect any detrimentally high radiation power losses. For the light elements (Z <8) commonly found in tokamaks the atomic physics infrastructure to allow such observations and model the results is well developed. The proposed design for ITER calls for a partially tungsten divertor. This has led to a resurgence of interest in the behaviour of heavy impurities in plasma. Many codes for generating fundamental atomic data and for modelling plasma behaviour encounter significant difficulties when dealing with heavy elements. This work addresses some of these issues.
3
Tang, Ming-Chun, Ting Shi, and Richard W. Ziolkowski. "Electrically Small, Broadside Radiating Huygens Source Antenna Augmented With Internal Non-Foster Elements to Increase Its Bandwidth." IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2017. http://hdl.handle.net/10150/623616.
Анотація:
A broadside radiating, linearly polarized, electrically small Huygens source antenna system that has a large impedance bandwidth is reported. The bandwidth performance is facilitated by embedding non-Foster components into the near-field resonant parasitic elements of this metamaterial-inspired antenna. High-quality and stable radiation performance characteristics are achieved over the entire operational bandwidth. When the ideal non-Foster components are introduced, the simulated impedance bandwidth witnesses approximately a 17-fold enhancement over the passive case. Within this -10-dB bandwidth, its maximum realized gain, radiation efficiency, and front-to-back ratio (FTBR) are, respectively, 4.00 dB, 88%, and 26.95 dB. When the anticipated actual negative impedance convertor circuits are incorporated, the impedance bandwidth still sustains more than a 10-fold enhancement. The peak realized gain, radiation efficiency, and FTBR values are, respectively, 3.74 dB, 80%, and 28.01 dB, which are very comparable to the ideal values.
4
LaPean, James William. "Analysis of infinite arrays of arbitrarily shaped planar radiating elements using a Floquet mode based Method of Moments approach." Diss., This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-06062008-152047/.
5
ʿUs̲mān, Muḥammad. "Investigation, design and implementation of MIMO antennas for mobile phones : simulation and measurement of MIMO antennas for mobile handsets and investigations of channel capacity of the radiating elements using spatial and polarisation diversity strategies." Thesis, University of Bradford, 2009. http://hdl.handle.net/10454/4279.
Анотація:
The objectives of this work were to investigate, design and implement Multiple-Input Multiple-Output (MIMO) antenna arrays for mobile phones. Several MIMO antennas were developed and tested over various wireless-communication frequency bands. The radiation performance and channel capacity of these antennas were computed and measured: the results are discussed in the context of the frequency bands of interest. A comprehensive study of MIMO antenna configurations such as 2 × 1, 3 × 1, 2 × 2 and 3 × 3, using polarisation diversity as proposed for future mobile handsets, is presented. The channel capacity is investigated and discussed, as applying to Rayleigh fading channels with different power spectrum distributions with respect to azimuth and zenith angles. The channel capacity of 2 × 2 and 3 × 3 MIMO systems using spatial polarisation diversity is presented for different antenna designs. The presented results show that the maximum channel capacity for an antenna contained within a small volume can be reached with careful selection of the orthogonal spatial fields. The results are also compared against planar array MIMO antenna systems, in which the antenna size considered was much larger. A 50% antenna size reduction method is explored by applying magnetic wall concept on the symmetry reference of the antenna structure. Using this method, a triple dual-band inverted-F antenna system is presented and considered for MIMO application. Means of achieving minimum coupling between the three antennas are investigated over the 2.45 GHz and 5.2 GHz bands. A new 2 2 MIMO dual-band balanced antenna handset, intended to minimise the coupling with the handset and human body was proposed, developed and tested. The antenna coupling with the handset and human hand is reported in terms the radiation performance and the available channel capacity. In addition, a dual-polarisation dipole antenna is proposed, intended for use as one of three collocated orthogonal antennas in a polarisation-diversity MIMO communication system. The antenna actually consists of two overlaid electric and magnetic dipoles, such that their radiation patterns are nominally identical but they are cross-polarised and hence only interact minimally.
6
Usman, Muhammad. "Investigation, Design and Implementation of MIMO Antennas for Mobile Phones. Simulation and Measurement of MIMO Antennas for Mobile Handsets and Investigations of Channel Capacity of the Radiating Elements Using Spatial and Polarisation Diversity Strategies." Thesis, University of Bradford, 2009. http://hdl.handle.net/10454/4279.
Анотація:
The objectives of this work were to investigate, design and implement Multiple-Input Multiple-Output (MIMO) antenna arrays for mobile phones. Several MIMO antennas were developed and tested over various wireless-communication frequency bands. The radiation performance and channel capacity of these antennas were computed and measured: the results are discussed in the context of the frequency bands of interest.
A comprehensive study of MIMO antenna configurations such as 2 × 1, 3 × 1, 2 × 2 and 3 × 3, using polarisation diversity as proposed for future mobile handsets, is presented. The channel capacity is investigated and discussed, as applying to Rayleigh fading channels with different power spectrum distributions with respect to azimuth and zenith angles. The channel capacity of 2 × 2 and 3 × 3 MIMO systems using spatial polarisation diversity is presented for different antenna designs. The presented results show that the maximum channel capacity for an antenna contained within a small volume can be reached with careful selection of the orthogonal spatial fields. The results are also compared against planar array MIMO antenna systems, in which the antenna size considered was much larger.
A 50% antenna size reduction method is explored by applying magnetic wall concept on the symmetry reference of the antenna structure. Using this method, a triple dual-band inverted-F antenna system is presented and considered for MIMO application. Means of achieving minimum coupling between the three antennas are investigated over the 2.45 GHz and 5.2 GHz bands.
A new 2 2 MIMO dual-band balanced antenna handset, intended to minimise the coupling with the handset and human body was proposed, developed and tested. The antenna coupling with the handset and human hand is reported in terms the radiation performance and the available channel capacity.
In addition, a dual-polarisation dipole antenna is proposed, intended for use as one of three collocated orthogonal antennas in a polarisation-diversity MIMO communication system. The antenna actually consists of two overlaid electric and magnetic dipoles, such that their radiation patterns are nominally identical but they are cross-polarised and hence only interact minimally.
7
Abidin, Zuhairiah Zainal. "Design, modelling and implementation of antennas using electromagnetic bandgap material and defected ground planes : surface meshing analysis and genetic algorithm optimisation on EBG and defected ground structures for reducing the mutual coupling between radiating elements of antenna array MIMO systems." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5385.
Анотація:
The main objective of this research is to design, model and implement several antenna geometries using electromagnetic band gap (EBG) material and a defected ground plane. Several antenna applications are addressed with the aim of improving performance, particularly the mutual coupling between the elements. The EBG structures have the unique capability to prevent or assist the propagation of electromagnetic waves in a specific band of frequencies, and have been incorporated here in antenna structures to improve patterns and reduce mutual coupling in multielement arrays. A neutralization technique and defected ground plane structures have also been investigated as alternative approaches, and may be more practical in real applications. A new Uni-planar Compact EBG (UC-EBG) formed from a compact unit cell was presented, giving a stop band in the 2.4 GHz WLAN range. Dual band forms of the neutralization and defected ground plane techniques have also been developed and measured. The recorded results for all antenna configurations show good improvement in terms of the mutual coupling effect. The MIMO antenna performance with EBG, neutralization and defected ground of several wireless communication applications were analysed and evaluated. The correlation coefficient, total active reflection coefficient (TARC), channel capacity and capacity loss of the array antenna were computed and the results compared to measurements with good agreement. In addition, a computational method combining Genetic Algorithm (GA) with surface meshing code for the analysis of a 2×2 antenna arrays on EBG was developed. Here the impedance matrix resulting from the meshing analysis is manipulated by the GA process in order to find the optimal antenna and EBG operated at 2.4 GHz with the goal of targeting a specific fitness function. Furthermore, an investigation of GA on 2×2 printed slot on DGS was also done.
8
Abidin, Z. Z. "Design, modelling and implementation of antennas using electromagnetic bandgap material and defected ground planes. Surface Meshing Analysis and Genetic Algorithm Optimisation on EBG and Defected Ground Structures for Reducing the Mutual Coupling between Radiating Elements of Antenna Array and MIMO Systems." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5385.
Анотація:
The main objective of this research is to design, model and implement several antenna
geometries using electromagnetic band gap (EBG) material and a defected ground
plane. Several antenna applications are addressed with the aim of improving
performance, particularly the mutual coupling between the elements.
The EBG structures have the unique capability to prevent or assist the propagation of
electromagnetic waves in a specific band of frequencies, and have been incorporated
here in antenna structures to improve patterns and reduce mutual coupling in multielement
arrays. A neutralization technique and defected ground plane structures have
also been investigated as alternative approaches, and may be more practical in real
applications.
A new Uni-planar Compact EBG (UC-EBG) formed from a compact unit cell was
presented, giving a stop band in the 2.4 GHz WLAN range. Dual band forms of the
neutralization and defected ground plane techniques have also been developed and
measured. The recorded results for all antenna configurations show good improvement
in terms of the mutual coupling effect.
The MIMO antenna performance with EBG, neutralization and defected ground of
several wireless communication applications were analysed and evaluated. The
correlation coefficient, total active reflection coefficient (TARC), channel capacity and
capacity loss of the array antenna were computed and the results compared to
measurements with good agreement.
In addition, a computational method combining Genetic Algorithm (GA) with surface
meshing code for the analysis of a 2×2 antenna arrays on EBG was developed. Here the
impedance matrix resulting from the meshing analysis is manipulated by the GA
process in order to find the optimal antenna and EBG operated at 2.4 GHz with the goal
of targeting a specific fitness function. Furthermore, an investigation of GA on 2×2
printed slot on DGS was also done.Ministry of Higher Education Malaysia and Universiti Tun Hussein Onn Malaysia (UTHM)
9
Sinanoglou, Panagiotis A. "Quantitative evaluation of the limitations of the radiation boundary elements in the finite element code ATILA." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA313103.
Анотація:
Thesis (M.S. in Applied Physics) Naval Postgraduate School, June 1996.Thesis advisor(s): Steven R. Baker, Clyde L. Scandrett. "June 1996." Includes bibliographical references. Also available online.
10
Dillon, Bernice Mary. "Finite element analysis of radiating waveguide discontinuities." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357770.
11
Coquillas, Benjamin. "Nouvelles topologies d’amplificateurs de puissance SiGe en bande Ku, optimisées en puissance, rendement et robustes au TOS actif." Thesis, Bordeaux, 2022. http://www.theses.fr/2022BORD0173.
Анотація:
L’amélioration des systèmes RADAR des aéronefs actuels est confrontée aux deux défis majeurs que sont la réduction des surfaces occupées et la maîtrise du coût. Ces défis s’ajoutent aux contraintes matérielles spécifiques des missiles autodirecteurs concernant la tenue en puissance à forte température et la robustesse aux variations de charge extérieure causées par le dépointage des éléments rayonnants environnants (apparentées au phénomène de TOS actif). Un enjeu majeur réside dans la réponse de l’amplificateur de puissance, identifié comme brique élémentaire, à ces défis actuels. La technologie Silicium Germanium (SiGe) est mise en avant par de nombreux travaux académiques sur les nouvelles générations de télécommunication (5G, 6G). Des travaux récents sur des amplificateurs de puissance publiés entre 2016 et 2020 apportent des résultats proches des caractéristiques souhaitées sur des bandes de fréquence bande X et la partie basse de la bande Ku. Ce double contexte industriel et académique justifie une étude originale sur les caractéristiques et les limites de la technologie SiGe en haut de la bande Ku au regard de la puissance de sortie, du rendement, de la robustesse au TOS actif et de la tenue des performances en température. Au cours de ces travaux, avec à l’appui une étude bibliographique documentée et un cahier des charges précis, cinq motifs de puissance et trois types de coupleur sont réalisés, simulés, envoyés en fabrication et mesurés. La topologie d’architecture équilibrée, mise en exergue sur de nombreuses études relatives au self-contained, constitue notamment un pilier central de cette étude. Les choix de conception et les performances obtenues sont détaillés. Ces dernières sont comparées à l’état de l’art. Elles démontrent des avancées significatrices valorisées dans trois conférences majeures du domaine scientifique et apportent des réponses originales aux défis contemporains de conception d’amplificateurs de puissance pour une application RADAR au sein de missiles autodirecteursThe improvement of the RADAR systems of the current aircraft is confronted with the two major challenges of the reduction of the areas occupied and the control of the cost. These challenges are added to the specific material constraints of self-guided missiles concerning power handling at high temperature and robustness to external load variations caused by the misalignment of surrounding radiating elements (related to the active SWR phenomenon). A major challenge is based on the response of the power amplifier, identified as an elementary building block, to these current challenges. The Silicon Germanium (SiGe) technology is highlighted by many academic works on new generations of telecommunications (5G, 6G). Several recent works on power amplifiers published between 2016 and 2020 bring results close to the desired characteristics on X-band and low Ku-band. This dual industrial and academic context justifies an original study on the characteristics and limits of the SiGe technology at the top of the Ku band with regard to the output power, efficiency, robustness to active SWR and the power handling to temperature variations. During this work, with the support of a documented bibliographical study and acurrate specifications, five power patterns and three types of coupler are designed, simulated, sent to manufacturing and measured. The balanced architecture topology, highlighted in several self contained studies, is a central pillar of this study. The design choices and the performances obtained are detailed. These are compared to the state of the art. They demonstrate significant advances valued in three major conferences in the scientific field and provide original answers to the contemporary challenges of designing power amplifiers for a RADAR application within self-guided missiles
12
Ali, Hassan O. "Finite-element time-domain analysis of axisymmetrical radiating structures." Thesis, University of Ottawa (Canada), 1992. http://hdl.handle.net/10393/7897.
Анотація:
A method of computation based on the finite element method was used to solve axisymmetrical electromagnetic wave propagation problems directly in the time-domain. The finite element method, employing first order triangular elements, was used to generate a system of second order linear differential equations. The system of differential equations was solved for the magnetic field using a suitable differential equation solving algorithm written in the course of this work. The method was used to model several situations involving axisymmetrical radiating structures directly in the time domain and the results compared well with the published data. Situations involving pulses, which are of particular interest to EMI/EMC field, were successfully studied. Conclusions were drawn on the suitability of the method in modeling radiated emissions from printed circuit board configurations, under the influence of transient exciting fields.
13
Buxton, Carey G. "Design of a Broadband Array Using the Foursquare Radiating Element." Diss., Virginia Tech, 2001. http://hdl.handle.net/10919/28363.
Анотація:
Broadband scanning arrays require small element spacing over a broad frequency band to achieve the desired scan capabilities. Previous research has concentrated on the development of small broadband elements to meet the demands of broadband arrays. However, mutual coupling between elements in a tightly spaced array can change the operating frequency and bandwidth from that of the single isolated element. Several research efforts have focused on minimizing the mutual coupling to maintain the frequency response of the single isolated element. This dissertation focuses on using the strong coupling between Foursquare antennas to obtain the broadband frequency response while maintaining a small element spacing.
The isolated Foursquare antenna was modeled using an in-house FDTD code. The modeled current distribution over the frequency band of operation revealed how the antenna achieved a broadband frequency response. Because of this understanding of the single element, the downward shift in the frequency response of the Foursquare antenna in a fully active array could be anticipated. Furthermore, the infinite array models of the Foursquare revealed an increase in bandwidth. Both are desirable characteristics for a broadband scanning array. Therefore, through this research using the Foursquare element, it has been shown that the strong mutual coupling in a tightly spaced array can have advantages if initially taken into consideration when designing the array.Ph. D.
14
Masani, Deekshitha. "Analysis of radiation induced errors in transistors in memory elements." OpenSIUC, 2020. https://opensiuc.lib.siu.edu/theses/2791.
Анотація:
From the first integrated circuit which has 16-transistor chip built by Heiman and Steven Hofstein in 1962 to the latest 39.54 billion MOSFET’s using 7nm FinFET technology as of 2019 the scaling of transistors is still challenging. The scaling always needs to satisfy the minimal power constraint, minimal area constraint and high speed as possible. As of 2020, the worlds smallest transistor is 1nm long build by a team at Lawrence Berkeley National Laboratory. Looking at the latest trends of 14nm, 7nm technologies present where a single die holds more than a billion transistors on it. Thinking of it, it is more challenging for dyeing a 1nm technology. The scaling keeps going on and if silicon does not satisfy the requirement, they switch to carbon nanotubes and molybdenum disulfide or some newer materials. The transistor sizing is reducing but the pressure of radiation effects on transistor is in quench of more and more efficient circuits to tolerate errors. The radiation errors which are of higher voltage are capable of hitting a node and flipping its value. However, it is not possible to have a perfect material to satisfy no error requirement for a circuit. But it is possible to maintain the value before causing the error and retain the value even after occurrence of the error. In the advanced technologies due to transistor scaling multiple simultaneous radiation induced errors are the issue. Different latch designs are proposed to fix this problem. Using the CMOS 90nm technology different latch designs are proposed which will recover the value even after the error strikes the latch. Initially the errors are generally Single event upsets (SEUs) which when the high radiation particle strikes only one transistor. Since the era of scaling, the multiple simultaneous radiation errors are common. The general errors are Double Node Upset (DNU) which occurs when the high radiation particle strikes the two transistors due to replacing one transistor by more than one after scaling. Existing designs of SEUs and DNUs accurately determine the error rates in a circuit. However, with reference to the dissertation of Dr. Adam Watkins, proposed HRDNUT latch in the paper “Analysis and mitigation of multiple radiation induced errors in modern circuits”, the circuits can retain its error value in 2.13ps. Two circuits are introduced to increase the speed in retaining the error value after the high energy particle strikes the node. Upon the evaluation of the past designs how the error is introduced inside the circuit is not clear. Some designs used a pass gate to actually introduce the error logic value but not in terms of voltage. The current thesis introduces a method to introduce error with reduced power and delay overhead compared to the previous circuits. Introducing the error in the circuits from the literature survey and comparing the delay and power with and without introducing the error is shown. Introducing the errors in the two new circuits are also shown and compared with when no errors are injected.
15
Pattnaik, Aliva. "Parallel Performance Analysis of The Finite Element-Spherical Harmonics Radiation Transport Method." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14069.
Анотація:
In this thesis, the parallel performance of the finite element-spherical harmonics (FE-PN) method implemented in the general-purpose radiation transport code EVENT is studied both analytically and empirically. EVENT solves the coupled set of space-angle discretized FE-PN equations using a parallel block-Jacobi domain decomposition method. As part of the analytical study, the thesis presents complexity results for EVENT when solving for a 3D criticality benchmark radiation transport problem in parallel. The empirical analysis is concerned with the impact of the main algorithmic factors affecting performance. Firstly, EVENT supports two solution strategies, namely MOD (Moments Over Domains) and DOM (Domains Over Moments), to solve the transport equation in parallel. The two strategies differ in the way they solve the multi-level space-angle coupled systems of equations. The thesis presents empirical evidence of which of the two solution strategies is more efficient. Secondly, different preconditioners are used in the Preconditioned Conjugate Gradient (PCG) inside EVENT. Performance of EVENT is compared when using three preconditioners, namely diagonal, SSOR(Symmetric Successive Over-Relaxation) and ILU. The other two factors, angular and spatial resolutions of the problem affect both the performance and precision of EVENT. The thesis presents comparative results on EVENTs performance as these two resolutions are increased.
From the empirical performance study of EVENT, a bottleneck is identified that limits the improvement in performance as number of processors used by EVENT is increased. In some experiments, it is observed that uneven assignment of computational load among processors causes a significant portion of the total time being spent in synchronization among processors. The thesis presents two indicators that identify when such inefficiency occur; and in such a case, a load rebalancing strategy is applied that computes a new partition of the problem so that each partition corresponds to equal amount of computational load.
16
Rega, Silva Jose Jererson do. "Boundary element formulations for radiation and scattering problems." Thesis, University of Portsmouth, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357222.
17
Demetrescu, Cristian. "Elements of diffraction theory for urban radiowave propagation modelling." Thesis, University of Birmingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340005.
18
Lester, Martin Richard. "Selective intensimetry for the measurement of sound radiation from building elements." Thesis, Liverpool John Moores University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294022.
19
Scott, H. M. "Near field modification techniques for pattern shaping in antenna elements and arrays." Thesis, Queen's University Belfast, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269176.
20
Sousa, Wellington Viana de. "InvestigaÃÃo de Novas EstratÃgias de Preparo de Amostras OrgÃnicas Auxiliado por RadiaÃÃo Infravermelha." Universidade Federal do CearÃ, 2013. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=12056.
Анотація:
CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorEste trabalho investiga a utilizaÃÃo da radiaÃÃo infravermelha como fonte de aquecimento no preparo de amostras orgÃnicas por via Ãmida visando à determinaÃÃo de elementos traÃos por ICP OES. As estratÃgias foram elaboradas com o objetivo de solubilizar e/ou digerir maiores massas de amostras. Assim, foram estudadas trÃs estratÃgias: 1) sistema IR-MW que combina o uso da radiaÃÃo infravermelha e micro-ondas, por meio de uma digestÃo prÃvia com radiaÃÃo infravermelha e posterior digestÃo no forno de micro-ondas com cavidade; 2) digestÃo parcial utilizando somente radiaÃÃo infravermelha (IR); 3) digestÃo parcial utilizando radiaÃÃo infravermelha e pentÃxido de vanÃdio (IR com V2O5) como reagente oxidante auxiliar. Diferentes procedimentos foram estudados sendo avaliados atravÃs da determinaÃÃo por ICP OES de macro e microelementos (Al, Fe, Cu, Mn, Zn, Se, Cd, Ni, Pb, Ca, K, Mg, Na e P) em diferentes tipos de leite em pÃ. O sistema IR-MW permitiu a digestÃo de massas de amostra de atà 1 g, obtendo-se boas precisÃes para a maioria dos elementos determinados. Para o procedimento IRMW A, a exatidÃo foi confirmada com material certificado Whole Milk Powder NIST 8435. Para os procedimentos IR-MW B e C foram obtidas percentagens de recuperaÃÃo variadas dependendo do elemento e da amostra. As estratÃgias IR e IR com V2O5 possibilitaram a digestÃo parcial de 2 g de amostra. A precisÃo e a exatidÃo desses procedimentos variaram de acordo com o elemento e a amostra. Todavia, a quantificaÃÃo de alguns elementos sà foi possÃvel por meio destas estratÃgias como, por exemplo, a detecÃÃo de Mn (0,30  0,01 Âg g-1 por IR; 0,35  0,01 Âg g-1 por IR com V2O5) na amostra de leite de cabra em pà integral e de Mn (1,63  0,02 Âg g-1 por IR; 1,78  0,06 Âg g-1 por IR com V2O5) na amostra de leite em pà desnatado nÃo enriquecido. O uso do V2O5 foi essencial na quantificaÃÃo de Fe (0,54  0,13 Âg g-1) no leite de cabra em pà integral. De uma maneira geral, dependendo do elemento e de seu teor na amostra, sua determinaÃÃo por ICP OES sà à possÃvel quando se usa maiores quantidades de massa de amostra. O emprego da radiaÃÃo infravermelha no auxilio de digestÃo de maiores massas de amostra à uma alternativa para laboratÃrios que utilizam apenas forno de micro-ondas com cavidade.
In this work it was investigated the use of infrared radiation as heating source in the preparation of organic samples aiming the determination of trace elements by ICP OES. The strategies were developed in order to solubilize and / or digest larger masses of samples. Thus, three strategies were studied: 1) IR-MW system which combines the use of infrared radiation and microwave through a previous digestion with infrared radiation and subsequent digestion in the oven microwave cavity; 2) partial digestion using only infrared radiation (IR); 3) partial digestion using infrared radiation and vanadium pentoxide (IR with V2O5) as auxiliary oxidizing reagent. Various procedures were studied and the efficiencies were evaluated by the determination of macro-and microelements (Al, Fe, Cu, Mn, Zn, Se, Cd, Ni, Pb, Ca, K, Mg, Na, and P) in milk samples by ICP OES. The IR-MW system allowed the digestion of sample masses of up to 1 g, to obtain good precision for most of the elements determined. For the IR-MW A procedure the accuracy was confirmed with certified material of whole milk powder NIST 8435. For the IR-MW B and C procedures were obtained recovery rates varied depending upon the element and the sample. Strategies IR and IR with V2O5 allowed the partial digestion of 2 g of sample. The precision and accuracy of these procedures varied according to the element and the sample. However, the determination of some elements was only possible using these strategies, for instance, the detection of Mn (0.30 Â 0.01 Âg g-1 by IR; 0.35 Â 0.01 Âg g-1 by IR with V2O5) in the goat whole milk powder sample of and Mn (1.63 Â 0.02 Âg g-1 by IR; 1.78 Â 0.06 Âg g-1 by IR with V2O5) in the non-fat milk powder not enriched sample. The use of V2O5 was essential in the quantification of some elements such as Fe (0.54 Â 0.13 Âg g-1) in goat milk powder samples. In general, the determination of trace elements by ICP OES is only possible using larger amounts of sample, depending on the element and its content in the sample. The use of infrared radiation to accomplish the digestion of larger masses of samples is an alternative to using only laboratory microwave oven cavity.
21
AVEGLIANO, ROSEANE P. "Estudo de dieta total no estado de Sao Paulo: estimativa de ingestao dietetica de elementos toxicos (arsenico e cadmio) e essenciais (calcio, cromo, ferro, selenio, sodio, potassio e zinco)." reponame:Repositório Institucional do IPEN, 2009. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11523.
Анотація:
Made available in DSpace on 2014-10-09T12:52:50Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:02:47Z (GMT). No. of bitstreams: 0
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
22
Moslemi, Parisa. "Design, fabrication, and test of a radiating element for a KU-BAND smart antenna." Mémoire, École de technologie supérieure, 2012. http://espace.etsmtl.ca/1107/7/MOSLEMI_Parisa.pdf.
Анотація:
Les antennes planaires multiéléments ont fait l'objet de nombreuses recherches ces dernières années en tant que candidates pour diverses applications telles que les communications par satellite. Parmi les nombreux avantages de ce type d'antenne on compte la capacité de diriger le faisceau de façon électrique, sa haute fiabilité, ainsi que son moindre coût à long terme; cela motive de pousser encore plus loin la recherche dans ce domaine.
Les antennes microrubans sont largement utilisées dans les réseaux d’antennes en raison de leur faible coût et de leur légèreté. De plus, elles peuvent facilement être imprimées sur un substrat diélectrique avec des techniques de photolithographie.
L'objectif de ce mémoire est la conception et la fabrication d'une antenne patch large bande, afin qu’elle soit utilisée dans un réseau d’antennes dans le contexte d’application de la communication par satellite. Ce patch est conçu pour fonctionner dans le domaine fréquentiel entre 10.7 GHz et 12.7 GHz. Dans ce projet, nous avons utilisé la technologie de la céramique cocuite à basse température à côté du circuit imprimé, ce qui n'a jamais encore été appliqué auparavant. En outre, nous proposons une nouvelle structure de l'antenne patch qui augmente la bande passante jusqu'à 19%. Les correctifs proposés sont fabriqués avec les matériaux 591 et 9K7 Green Tape et Rogers RT5870. Les dessins ont été effectuées en utilisant le simulateur de champ électromagnétique planaire Momentum, faisant partie de Advanced Design System (ADS) de Agilent technologies.
23
Zolfaghari-Daaryaani, Ahmed Reza. "Multidimensional finite element modelling of thermal radiation in participating media." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299974.
24
Vujičić, Mile R. "Finite element modelling and experimental validation in radiative heat transfer." Thesis, Swansea University, 2006. https://cronfa.swan.ac.uk/Record/cronfa42640.
Анотація:
The work presented in this thesis can be divided into two parts: numerical modelling and experimental validation. The first part considers a finite element computer code called Pharo which has been developed to simulates heat transfer exchanged in an enclosure via thermal radiation and conduction. This finite element heat transfer code has been written for the Defence, Science and Technology Laboratory (DSTL). Face to face (zonal) thermal radiation which operates with diffuse surface properties of materials without a participating media is analyzed and included in Pharo. To analyze the net heat exchanged within an enclosure several methods for view factor calculation, such as the Monte Carlo and Hemi-cube methods were included in Pharo. During heat transfer simulations a better accuracy of results has been demonstrated using a new approach called the Multiple Reflection of View Factors 'MRV' method. Transient heat flow is solved using both finite difference and finite element time stepping. Also, an analysis of transient heat flow using different solvers (direct and iterative) to find the most appropriate one was carried out. The second part of the work considers experimental validation of numerical results obtained using Pharo. Special attention was given to the analysis of the relationship between view factors and measured heat transfer. To make the experimental data complete the measurements of surface properties including emissivity, reflectivity for different wavelengths as well as roughness of materials is presented. These experimental results can be used as experimental benchmark data for model users and developers.
25
Badri, Mohd Afeef. "Efficient finite element strategies for solving the radiative transfer equation." Thesis, Nantes, 2018. http://www.theses.fr/2018NANT4050/document.
Анотація:
La méthode des ordonnées discrètes couplée à la méthode des éléments finis est souvent utilisée pour résoudre numériquement l’équation de transfert radiatif. L’objectif principal de cette thèse est d’améliorer cette technique numérique. Au lieu d’utiliser des éléments finis standards, cette thèse reformule l’équation de transfert radiatif en utilisant des éléments finis vectoriels. Par rapport aux éléments finis standards, cette reformulation donne des temps plus courts pour la phase d’assemblage des systèmes linéaires, et surtout pour la phase de résolution. Des méthodes itératives de sous-espaces de Krylov préconditionnées, comme le GMRES et le BiCGSTAB, sont employées pour résoudre les systèmes linéaires résultant de la discrétisation par éléments finis. La méthode développée a été validée par rapport à des problèmes de référence. Pour résoudre de gros problèmes de rayonnement sur des calculateurs parallèles, la méthode des éléments finis vectoriels est parallélisée en utilisant des approches de décomposition de domaine et de décomposition angulaire. Les méthodes parallèles proposées possèdent des capacités de mise à l’échelle quasi-linéaires sur un grand nombre de processeurs. Les solveurs parallèles développés sont utilisés pour effectuer des simulations numériques à grande échelle avec des milliards d’inconnues. Dans l’ensemble, il est montré comment effectuer des simulations numériques complexes de rayonnement à des échelles auparavant inaccessibles pour les solveurs de transfert radiatif standardThe discrete ordinate method coupled with the finite element method is often used for numerically solving the radiative transfer equation. The main goal of this thesis is to improve upon such numerical technique. Instead of using standard finite elements, this thesis reformulates the radiative transfer equation using vectorial finite elements. In comparison to standard finite elements, this reformulation yields faster timings for the linear system assemblies, as well as for the solution phase when solving scattering media problems. Preconditioned Krylov subspace methods like the GMRES and the BiCGSTAB are employed for solving the linear systems arising from the proposed vectorial finite element discretization. The developed methods are validated against benchmark problems available in literature. In addition, the method of manufactured solutions is used for verifying the proposed method. For solving large problems of radiation on parallel computers, the vectorial finite element method is parallelized using domain decomposition and angular decomposition approaches. The proposed parallel methods possess quasi-linear scaling capabilities on a large number of processes. The developed parallel solvers are used to perform large scale numerical simulations with billions of unknowns. Overall it is shown how to perform complex numerical simulations of radiation at scales that were previously unattainable by standard radiative transfer equation solvers
26
Kirkup, Stephen Martin. "Solution of exterior acoustic problems by the boundary element method." Thesis, University of Brighton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327859.
27
Ozgun, Ozlem. "Finite Element Modeling Of Electromagnetic Radiation/scattering Problems By Domain Decomposition." Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/3/12608290/index.pdf.
Анотація:
The Finite Element Method (FEM) is a powerful numerical method to solve wave propagation problems for open-region electromagnetic radiation/scattering problems involving objects with arbitrary geometry and constitutive parameters. In high-frequency applications, the FEM requires an electrically large computational domain, implying a large number of unknowns, such that the numerical solution of the problem is not feasible even on state-of-the-art computers. An appealing way to solve a large FEM problem is to employ a Domain Decomposition Method (DDM) that allows the decomposition of a large problem into several coupled subproblems which can be solved independently, thus reducing considerably the memory storage requirements. In this thesis, two new domain decomposition algorithms (FB-DDM and ILF-DDM) are implemented for the finite element solution of electromagnetic radiation/scattering problems. For this purpose, a nodal FEM code (FEMS2D) employing triangular elements and a vector FEM code (FEMS3D) employing
tetrahedral edge elements have been developed for 2D and 3D problems, respectively. The unbounded domain of the radiation/scattering problem, as well as the boundaries of the subdomains in the DDMs, are truncated by the Perfectly Matched Layer (PML) absorber. The PML is implemented using two new approaches: Locally-conformal PML and Multi-center PML. These approaches are based on a locally-defined complex coordinate transformation which makes possible to handle challenging PML geometries, especially with curvature discontinuities. In order to implement these PML methods, we also introduce the concept of complex space FEM using elements with complex nodal coordinates. The performances of the DDMs and the PML methods are investigated numerically in several applications.
28
Bain, James Gregory. "A boundary element scheme for three-dimensional acoustic radiation with flow." Thesis, University of Canterbury. Mechanical Engineering, 1985. http://hdl.handle.net/10092/6407.
Анотація:
A boundary element approach is proposed for acoustical radiation in non-uniform, low Mach number flows. The formulation utilizes a transformation, valid at low Mach number for short wavelength disturbances, which converts this problem into an analogous no-flow problem for the same geometry. Two distinct boundary integral schemes are considered. An overdetermined combined surface-interior formulation and a combined surface-surface derivative formulation are both used to calculate the velocity potential due to the vibration of an arbitrary body in a uniform mean flow. Results are presented for the test cases of pulsating and juddering spheres in low Mach number flows. Good agreement is established between the results produced by the present boundary element formulations and those obtained from an analytic solution and an alternative numerical (finite element) scheme.
29
Brooke, Matthew. "Numerical simulation of guitar radiation fields using the boundary element method." Thesis, Cardiff University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311465.
30
Nagpal, Charu. "A delay-efficient radiation-hard digital design approach using code word state preserving (cwsp) elements." Texas A&M University, 2008. http://hdl.handle.net/1969.1/85906.
Анотація:
With the relentless shrinking of the minimum feature size of VLSI Integrated
Circuits (ICs), reduction in operating voltages and increase in operating frequencies,
VLSI circuits are becoming more vulnerable to radiation strikes. As a result, this
problem is now important not only for space and military electronics but also for
consumer ICs. Thus, the design of radiation-hardened circuits has received significant
attention in recent times.
This thesis addresses the radiation hardening issue for VLSI ICs. In particular,
circuit techniques are presented to protect against Single Event Transients (SETs).
Radiation hardening has long been an area of research for memories for space and
military ICs. In a memory, the stored state can ip as a result of a radiation strike.
Such bit reversals in case of memories are known as Single Event Upsets (SEUs).
With the feature sizes of VLSI ICs becoming smaller, radiation-induced glitches have
become a source of concern in combinational circuits also. In combinational circuits,
if a glitch due to a radiation event occurs at the time the circuit outputs are being
sampled, it could lead to the propagation of a faulty value. The current or voltage
glitches on the nodes of a combinational circuit are known as SETs. When an SET
occurring on a node of a logic network is propagated through the gates of the network
and is captured by a latch as a logic error, it is transformed to an SEU.
The approach presented in this thesis makes use of Code Word State Preserving
(CWSP) elements at each ip-op of the design, along with additional logic to trigger
a recomputation in case a SET induced error is detected. The combinational part of
the design is left unaltered. The CWSP element provides 100% SET protection for
glitch widths up to min{(Dmin-D1)/2, (Dmax-D2)/2}, where Dmin and Dmax are
the minimum and maximum circuit delay respectively. D1 and D2 are extra delays
associated with the proposed SET protection circuit. The CWSP circuit has two
inputs - the flip flop output signal and the same signal delayed by a quantity 6. In
case an SET error is detected at the end of a clock period i, then the computation is
repeated in clock period i+1, using the correct output value, which was captured by
the CWSP element in the ith clock period. Unlike previous approaches, the CWSP
element is i) in a secondary computational path and ii) the CWSP logic is designed to
minimally impact the critical delay path of the design. It was found through SPICE
simulations that the delay penalty of the proposed approach (averaged over several
designs) is less than 1%. Thus, the proposed technique is applicable for high-speed
designs, where the additional delay associated with the SET protection must be kept
at a minimum.
31
Carter, Ki-Jana. "Radiation damage quantification in elemental copper using Wigner energy storage." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112482.
Анотація:
Thesis: S.B., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 55-58).
Radiation damage in materials can cause critical components in fission and fusion reactors to fail with potentially catastrophic consequences. Radiation damage quantification is essential for understanding, predicting, and preventing such failures. The current unit of radiation damage, displacements per atom (DPA), is not a measurable quantity, and it is known to be an inaccurate measure of radiation damage. This project aims to quantify radiation damage accurately and measurably by characterizing the storage of energy in radiation-induced material defects, known as Wigner energy storage. In order to gain an atomistic understanding of radiation damage, the irradiation and calorimetry of elemental copper were simulated using molecular dynamics code. A custom defect analysis script was used to determine the energy stored as a function of irradiation energy and defect type. Wigner energy peaks were clearly visible in the calorimetry data, indicating that Wigner energy measurement is a plausible technique for quantifying radiation damage. Future work should focus on achieving more realistic heating rates and measuring Wigner energy storage experimentally using fast scanning calorimetry.
by Ki-Jana Carter.
S.B.
32
Vales, Luiz Fernando. "Análise numérica da influência de parâmetros estruturais no desempenho vibroacústico de placas flexíveis." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/18/18149/tde-22042018-155437/.
Анотація:
Vibrações estruturais constituem uma das principais fontes de ruído e de desconforto em diversas aplicações, tais como nos produtos das indústrias automotiva, aeroespacial e naval, que, em grande parte, são compostos por estruturas flexíveis semelhantes a placas. Ao mesmo tempo, a demanda crescente por aumento de eficiência energética e por redução de emissão de gases nocivos ao meio ambiente tem levado os fabricantes de todos os segmentos para a utilização de materiais cada vez mais leves. Um desafio importante relacionado ao uso dessas soluções diz respeito ao seu comportamento vibroacústico, já que estruturas leves tendem a transmitir e emitir ruídos de forma mais intensa, particularmente em baixas frequências. Em decorrência disso, a obtenção de uma boa relação entre peso e desempenho vibroacústico usualmente demanda algumas iterações de projeto. Nesse contexto, este trabalho tem por objetivo estabelecer um procedimento numérico para avaliar as propriedades vibroacústicas de placas flexíveis excitadas por um campo gerado no interior de uma cavidade acústica, bem como investigar a influência de parâmetros estruturais que definem a placa sobre o seu desempenho vibroacústico. O escopo aqui é a faixa de baixas frequências, na qual o comportamento do sistema é descrito de forma determinística através de características modais. Foi desenvolvido um modelo numérico em elementos finitos de uma cavidade acústica retangular de paredes rígidas acoplada a uma placa flexível. Uma fonte acústica posicionada no interior da cavidade produz um campo de pressão sonora que induz a placa à vibração e, consequentemente, a irradiar potência sonora para o campo livre exterior. Para realização das análises de sensibilidade, desenvolveu-se um conjunto de rotinas de modo a permitir o gerenciamento automatizado de simulações. Resultados numéricos são apresentados para avaliar a influência de diversos parâmetros estruturais sobre o desempenho vibroacústico da superfície estrutural. O procedimento proposto pode ser aplicado de forma eficiente para a análise de sensibilidade da transmissão de ruído em sistemas vibroacústicos sujeitos à variação de parâmetros estruturais e pode também ser utilizado para avaliar diversos tipos de materiais, como isotrópicos, ortotrópicos e até metamateriais.Structural vibrations are the major causes of noise and people discomforts in several applications, such as in the products of the automotive, aerospace and naval industries, which are mainly composed of flexible plate-like structures. At the same time, the ever-increasing demands for energy efficiency and for reduced emissions of harmful gases into the environment lead product manufacturers of all industrial sectors towards an increased use of lighter materials. However, these solutions are most sensitive to issues related to vibroacoustic behavior, since the lightweight structures tend to present a high sound transmission, particularly at low frequencies. Consequently, the optimal design of lightweight and noise insulation properties of a structure usually require some design trade-offs. In this context, this dissertation aims to propose a numerical procedure to analyze the vibroacoustic performance of flexible plates subject to an interior acoustic field, as well as to investigate the influence of structural parameters on the sound insulation properties of the plate. The scope here is the low frequency range, in which the response of the coupled system is described in a deterministic way in terms of a mode set. A finite element model of a rigid rectangular acoustic cavity coupled to a flexible plate was developed. An acoustic source inside the cavity produces an interior sound pressure field that forces the flexible plate to vibrate and, consequently, to radiate sound power to the external free field. In order to enable the automatic management of the variability simulations, a set of routines was also developed. Numerical results are presented in order to evaluate the influence of several structural parameters on the vibroacoustic properties of the plate. The proposed methodology can be largely used in sensitivity analysis of noise transmission in vibroacoustic systems subject to the variation of structural parameters and can be used to evaluate many material types, as isotropic, orthotropic and even metamaterials.
33
Castro, Douglas de Aquino. "Projeto de estruturas sujeitas à radiação térmica no interior de confinamentos utilizando o método da otimização topológica." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/3/3152/tde-16102014-153615/.
Анотація:
Estruturas que estão sujeitas a altas temperaturas absolutas, à convecção natural, ou ainda, estruturas que trocam calor na ausência de um meio físico, apresentam relevante transferência de calor por radiação térmica. Este fenômeno é importante para diversas aplicações e processos, como, por exemplo, no funcionamento de coletores solares, satélites, fornos industriais, motores a combustão e usinas nucleares. O presente trabalho de mestrado apresenta a aplicação do método da otimização topológica (MOT) no projeto de estruturas que trocam calor substancialmente por radiação térmica no interior de confinamentos, através da distribuição de material refletor ou de aquecedores. Por meio do MOT, cuja principal característica é a liberdade de distribuição do material dentro de um domínio inicial, é possível adicionar ou remover material de uma determinada região do domínio, criando ou desfazendo fronteiras, de forma livre, visando à obtenção de um projeto otimizado. O algoritmo de otimização é baseado no Método das Assíntotas Móveis (MMA) e é complementado pelo Método dos Elementos Finitos (MEF), para a análise do fenômeno de radiação em confinamentos. Ambos são implementados através do software Matlab. Os casos considerados são o da distribuição de material refletor de radiação térmica ou de aquecedores, sujeitos a uma eventual restrição nas quantidades destes materiais, sobre uma superfície plana, de forma a extremizar-se a irradiação ou a minimizar-se a temperatura em determinada área específica do domínio de projeto. Este problema depende, dentre outros fatores, da geometria da superfície e dos ângulos dos raios incidentes sobre ela.Structures subjected to high absolute temperatures or to natural convection, as well structures that exchange heat in the absence of a physical medium present significant heat transfer through thermal radiation. This phenomenon is important for several applications and processes, such as in the operation of solar collectors, satellites, industrial furnaces, combustion engines and nuclear plants. The present work shows the application of topology optimization to the design of structures that exchange heat substantially by thermal radiation within an enclosure, through the distribution of reflective material or heaters. However, the design of such radiant enclosures is not trivial and it is necessary to use robust and systematic design tools, such as optimization techniques. Topology optimization is a numerical method which allows finding the layout, or topology, of a structure such that a prescribed objective is maximized or minimized subjected to design constraints. The optimization algorithm, based on the method of moving asymptotes (MMA), and the finite element method for analysis of the phenomenon of radiation in enclosures, are implemented using $Matlab^\\circledR$. The cases considered are the distribution of thermal radiation reflective material or heaters, subjected to a volume fraction constraint of these materials on a flat surface, in order to extremize the irradiation or to minimize the temperature in a specified region of the design domain. This problem depends, among other factors, on the geometry of the surfaces that exchange heat through thermal radiation.
34
Kumar, Gaurav. "Structual-acoustic properties of automotive panels with shell elements." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/13950.
Анотація:
The automotive industry has witnessed a trend in the recent years of reducing the bulk weight of the vehicle in order to achieve improved ride dynamics and economical fuel consumption. Unfortunately, reducing the bulk weight often compromises the noise, vibra- tion, and harshness (NVH) characteristics of the vehicle. In general, the automotive body panels are made out of thin sheet metals (steel and aluminium) that have a very low bend- ing stiffness. Hence, it becomes important to find countermeasures that will increase the structural stiffness of these thin body panels without affecting their bulk weight. One such countermeasure is to introduce the geometrical indentations on various body panels. The geometrical indentation explained in this thesis is in the shape of elliptical dome, which supports the increase of the structural stiffness whilst keeping the bulk weight constant. The primary reason to choose elliptical domes as the applied geometrical indentation is due to a significant amount of interest shown by Jaguar Land Rover. Moreover, the elliptical domes, because of the nature of its design, can cover a larger surface area with minimal depth, thereby, eliminating the possibility of sharp and pointy indentations. This thesis presents a comprehensive study of the structural-acoustic behaviour of the automotive-type panels with dome-shaped indentations. The ultimate aim of this research is to establish a set of design guidelines in order to produce automotive-type panels with optimised dome-shaped indentations. In order to do so, a new design optimisation strategy is proposed that results in the optimal placement of the required dome-shaped indenta- tions. The optimisation problem addressed in this thesis is unlike a general mathematical problem, and requires specific methodologies for its solution. Therefore, the use of genetic algorithm is observed as the most suitable method in order to tackle this type of design optimisation problem. During the development of the optimisation procedure, the preliminary results show a consistency in the design patterns. This led to the motivation to investigate a few intuitively designed panels, which are inspired by the initial, trial, optimisation results. Therefore, four intuitively designed panels are investigated for their structural-acoustic characteristics. The study of the intuitively designed panels provided essential physical insight into the design optimisation problem, which ultimately defined the guidelines in order to develop the proposed optimisation procedure. This type of optimisation procedure is completely new in the domain of structural-acoustic optimisation. The efficiency of the underlying work lies in the separate investigation of both the structural and the acoustic properties of the panels with various dome-shaped indentations, and then utilising the insights gained in order to develop a specific optimisation algorithm to stream-line the dome-shaped panel design procedure.
35
Cutshall, Ryan Thomas. "Achieving Wide Bandwidth Electrically Small Antennas Using Internal Non-Foster Elements." Thesis, The University of Arizona, 2013. http://hdl.handle.net/10150/305873.
Анотація:
Electromagnetic equations pertaining to electrically small dipole antennas and electrically small monopole antennas with small circular ground planes are reviewed. Two electrically small antenna designs are analyzed numerically and the results are compared. The first is a frequency agile version of the two-dimensional (2D) planar Egyptian axe dipole (EAD) antenna. The second is its three-dimensional (3D) counterpart. The frequency agile performance characteristics of both the 2D and 3D EAD designs are studied and compared. The potential for non-Foster augmentation to achieve large instantaneous fractional impedance bandwidths is detailed for each antenna. In addition, details are given on how to run frequency agile simulations in both ANSYS HFSS and Agilent's ADS. Details are also provided on how to generate an antenna's non-Foster |S₁₁| and radiation efficiency curves using HFSS, and how to generate an antenna's non-Foster |S₁₁| curve using ADS.
36
Nezhi, Zouhair [Verfasser]. "Adaptive time domain boundary element method for sound radiation of tyres / Zouhair Nezhi." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2014. http://d-nb.info/1058237659/34.
37
Trasi, Natasha Shanta. "A finite element-spherical harmonics model applied to radiative transfer in inhomogeneous clouds." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404477.
38
Durak, R., A. Ates, M. F. Turhan, and M. Saglam. "Measurements of Radiative Vacancy Transfer Probabilities for Some Elements Irradiated with Photons of 0.0208 Nanometer Wavelengths." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35440.
Анотація:
The radiative vacancy transfer probabilities of K to L2, L3, M2, M3 sub-shells were calculated using the
experimental K level widths and theoretical partial radiative transitions. The targets were irradiated with
photons of 0.0208 nm wavelength. It has been observed that the obtained values in the present study agree
with theoretical results, theoretical predictions and the other available experimental values.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35440
39
Giroux, Matthieu. "Patient-specific biomechanical model of the respiratory system for radiation therapy." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1205.
Анотація:
La Radio/Hadron-thérapie consiste à déposer une dose létale de rayonnement dans la tumeur tout en réduisant l'impact de cette dose sur les tissus sains. Les mouvements internes, en particulier ceux engendrés par la respiration modifient la forme, la position et la densité des organes, source d'erreur et d'incertitude sur la position du dépôt de dose. Lorsque la tumeur se trouve sur un organe en mouvement, la dificulté majeure est de cibler la tumeur pendant le traitement. Cette incertitude sur la position rend indispensable la mise en place d'une stratégie permettant la prédiction du mouvement tumoral. Ceci permet en eet de guider le faisceau de rayons ionisants de sorte qu'il suive les mouvements tumoraux. De plus, le traitement par hadronthérapie nécessite également l'accès à une description précise de la densité de l'ensemble des organes traversés par le faisceau, car la position du dépôt maximal de l'énergie véhiculée par les ions (le pic de Bragg) en dépend. Malheureusement, le mouvement respiratoire est complexe et sa prédiction n'est pas une tâche simple – en particulier, la respiration est commandée par l'action indépendante des muscles de la cage thoracique et du diaphragme. Les techniques actuelles basées sur l'imagerie, telles que le Cone-Beam ou le recalage dé- formable d'images, tentent de prédire la position des tumeurs pulmonaires. Ces méthodes font l'hypothèse d'un mouvement reproductible de l'appareil respiratoire dans le temps. D'autres techniques basées sur l'emploi de deux caméras à rayons X (cyberknife, tracking mis au point par l'équipe du Centre carbone d'Heildelberg [HIT]) peuvent permettre la pré- diction de la position des tumeurs, quand leur segmentation et leur contourage automatique en temps réel est possible. Cependant, ces méthodes sont, si ce n'est risquées, invasives, et elles ne permettent pas de calculer l'évolution des organes environnants, une information indispensable pour déterminer la position du pic de Bragg. Ainsi déduire le mouvement de la tumeur à partir de seules séries d'images médicales apparaît comme insuffisant. Une solution peut alors résider dans le développement d'un modèle biomécanique patient-spécifique du système respiratoire intégrant la variabilité du mouvement respiratoire. Pour que ce modèle soit précis, il doit comprendre la modélisation de la cage thoracique, du diaphragme et des poumons. Il est tout aussi important que ce modèle puisse être piloté par des paramètres mesurés en externe (capteurs 3D, spiromètre, etc.) an de préserver un caractère non-invasif et de corréler le mouvement externe du thorax et de l'abdomen, ainsi que le ux d'air échangé avec les mouvements internes. Les changements de propriétés mécaniques des milieux traversés par le faisceau doivent également être modélisés an de satisfaire les besoins de l'hadronthérapieThe 4D computational patient specic of the respiratory system could be potentially used in various medical contexts; for diagnosis, treatment planning, laparoscopic, dose computation or the registration between online imaging systems such as positron emission tomography (PET), computed-tomography (CT) as well as high delity and precise computer-based training simulators. The main novelty of this PhD project lies in the context of radiation therapy; we have developed a patient-specic biomechanical model of the respiratory system enabling the correlation of the internal organs motion with respiratory surrogate signal(s) during the treatment. This permits to take into account the respiratory motion variabilities. The deformation of the dierent structures is controlled and driven by simulated rib cage (mimic the external intercostal muscles) and diaphragm actions. For the diaphragm, we have applied the radial direction of muscle forces, and simple homogeneous dirichlet boundary condition is applied to the lower part of the diaphragm, which is attached to the rib cage. For each rib a rigid transformation is calculated automatically by nite helical axis method (rigid translation and rotation) and used to dene displacement boundary conditions. The resulting widening of the thoracic cavity forces the lungs to expand due to an applied negative pressure in the pleural cavity. Other novelty of the PhD project, that the amplitude of the lung pressure and diaphragm force are patient-specic, and determined at dierent respiratory states by an optimization framework based on inverse FE analysis methodology, by minimizing the volume lungs errors, between the respiratory volume (calculated from CT scan images at each state) and the simulated volume (calculated by biomechanical simulation). All other structures are linked to each other, but feature dierent deformation behavior due to the assigned material properties. Our results are quite realistic compared to the 4D CT scan images and the proposed physically-based FE model is able to predict correctly the respiratory motion
40
Cui, Xiaoming. "Discontinuous finite/boundary element method for radiative heat transfer with application in laser cancer therapy." Online access for everyone, 2005. http://www.dissertations.wsu.edu/Dissertations/Fall2005/x%5Fcui%5F121805.pdf.
41
Wu, Shu-Wei. "A fast, robust and accurate procedure for radiation and scattering analyses of submerged elastic axisymmetric bodies." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46618.
42
Jones, C. J. C. "Finite element analysis of loudspeaker diaphragm vibration and prediction of the resulting sound radiation." Thesis, University of Brighton, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370173.
43
DiMarco, John Stephen. "Finite element implementation of a new variational principle for acoustic radiation from a circular disk." Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/17649.
44
Dolven, Eric T. "Seaquake waves - standing wave dynamics with Faraday excitation and radiative loss /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/6785.
45
Tehrani, Mehran. "Next Generation Multifunctional Composites for Impact, Vibration and Electromagnetic Radiation Hazard Mitigation." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/49547.
Анотація:
For many decades, fiber reinforced polymers (FRPs) have been extensively utilized in load-bearing structures. Their formability and superior in-plane mechanical properties have made them a viable replacement for conventional structural materials. A major drawback to FRPs is their weak interlaminar properties (e.g., interlaminar fracture toughness). The need for lightweight multifunctional structures has become vital for many applications and hence alleviating the out-of-plane mechanical (i.e., quasi-static, vibration, and impact) and electrical properties of FRPs while retaining minimal weight is the subject of many ongoing studies. The primary objective of this dissertation is to investigate the fundamental processes for developing hybrid, multifunctional composites based on surface grown carbon nanotubes (CNTs) on carbon fibers\' yarns. This study embraces the development of a novel low temperature synthesis technique to grow CNTs on virtually any substrate. The developed method graphitic structures by design (GSD) offers the opportunity to place CNTs in advantageous areas of the composite (e.g., at the ply interface) where conventional fiber architectures are inadequate. The relatively low temperature of the GSD (i.e. 550 C) suppresses the undesired damage to the substrate fibers. GSD carries the advantage of growing uniform and almost aligned CNTs at pre-designated locations and thus eliminates the agglomeration and dispersion problems associated with incorporating CNTs in polymeric composites. The temperature regime utilized in GSD is less than those utilized by other synthesis techniques such as catalytic chemical vapor deposition (CCVD) where growing CNTs requires temperature not less than 700 C.It is of great importance to comprehend the reasons for and against using the methods involving mixing of the CNTs directly with the polymer matrix, to either fabricate nanocomposites or three-phase FRPs. Hence, chapter 2 is devoted to the characterization of CNTs-epoxy nanocomposites at different thermo-mechanical environments via the nanoindentation technique. Improvements in hardness and stiffness of the CNTs-reinforced epoxy are reported. Long duration (45 mins) nanocreep tests were conducted to study the viscoelastic behavior of the CNT-nanocomposites. Finally, the energy absorption of these nanocomposites is measured via novel nanoimpact testing module.
Chapter 3 elucidates a study on the fabrication and characterization of a three phase CNT-epoxy system reinforced with woven carbon fibers. Tensile test, high velocity impact (~100 ms-1), and dynamic mechanical analysis (DMA) were employed to examine the response of the hybrid composite and compare it with the reference CFRP with no CNTs. Quasi-static shear punch tests (QSSPTs) were also performed to determine the toughening and damage mechanisms of both the CNTs-modified and the reference CFRP composites during transverse impact loading.
The synthesis of CNTs at 550 C via GSD is the focus of chapter 4. The GSD technique was adjusted to grow Palladium-catalyzed carbon filaments over carbon fibers. However, these filaments were revealed to be amorphous (turbostratic) carbon. Plasma sputtering was utilized to sputter nickel nano-films on the surface of the substrate carbon fibers. These films were later fragmented into nano-sized nickel islands from which CNTs were grown utilizing the GSD technique. The structure and morphology of the CNTs are evaluated and compared to CNTs grown via catalytic chemical vapor deposition (CCVD) over the same carbon fibers.
Chapter 5 embodies the mechanical characterization of composites based on carbon fibers with various surface treatments including, but not limited to, surface grown CNTs. Fibers with and without sizing were subjected to different treatments such as heat treatment similar to those encountered during the GSD process, growing CNTs on fabrics via GSD and CCVD techniques, sputtering of the fibers with a thin thermal shield film of SiO2 prior to CNT growth, selective growth of CNTs following checkerboard patterns, etc.
The effects of the various surface treatments (at the ply interfaces) on the on-axis and off-axis tensile properties of the corresponding composites are discussed in this chapter. In addition, the DMA and impact resistance of the hybrid CNT-CFRP composites are measured and compared to the values obtained for the reference CFRP samples. While the GSD grown CNTs accounted for only 0.05 wt% of the composites, the results of this chapter contrasts the advantages of the GSD technique over other methods that incorporate CNTs into a CFRP (i.e. direct growth via CCVD and mixing of CNTs with the matrix).
Understanding the behavior of the thin CFRPs under impact loadings and the ability to model their response under ballistic impact is essential for designing CFRP structures. A precise simulation of impact phenomenon should account for progressive damage and strain rate dependent behavior of the CFRPs. In chapter 6, a novel procedure to calibrate the state-of-the-art MAT162 material model of the LS-DYNA finite element simulation package is proposed. Quasi-static tensile, compression, through thickness tension, and in-plane Isopescu shear tests along with quasi-static shear punch tests (QSSPTs) employing flat cylindrical and spherical punches were performed on the composite samples to find 28 input parameters of MAT162. Finally, the capability of this material model to simulate a transverse ballistic impact of a spherical impactor with the thin 5-layers CFRP is demonstrated.
It is hypothesized that the high electrical conductivities of CNTs will span the multifunctionality of the hybrid composites by facilitating electromagnetic interference (EMI) shielding. Chapter 6 is devoted to characterizing the electrical properties of hybrid CNT-fiberglass FRPs modified via GSD method. Using a slightly modified version of the GSD, denser and longer CNTs were grown on fiberglass fabrics. The EMI shielding performance of the composites based on these fabrics was shown to be superior to that for reference composites based on fiberglass and epoxy. To better apprehend the effect of the surface grown CNTs on the electrical properties of the resulting composites, the electrical resistivities of the hybrid and the reference composites were measured along different directions and some interesting results are highlighted herein.
The work outlined in this dissertation will enable significant advancement in protection methods against different hazards including impact, vibrations and EMI events.
Ph. D.
46
Zulkifli, Ediansjah. "Consistent description of radiation damping in transient soil-structure interaction." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1217499921691-59045.
Анотація:
Dynamic soil-structure interaction problems are characterized by an unbounded soil-domain and thus by radiation damping. This radiation damping arises due to wave propagation from the excited structure into the subsoil and may lead to a reduction of the structural response. A consistent description of this radiation damping has been carried out by means of different concepts. A widely used approach truncates the unbounded medium by a special kind of absorbing boundaries which are free of artificial reflection. The resulting finite domain can be treated as usually by finite elements. In this report, an alternative method to represent an unbounded medium in a dynamic analysis is presented. In principle, it is a conjunction of the boundary element method (BEM) in the frequency domain to reproduce the far-field and the finite element method (FEM) in the time domain to analyze the near-field. This alternative procedure avoids the introduction of any artificial boundaries. The procedure is based on a rational approximation of the dynamic stiffness of the unbounded domain in the frequency-domain. In this report, the dynamic stiffness of the unbounded domain is obtained from the BEM. The matrix-valued coefficients of the rational approximation function are determined by means of a least-square procedure. The time-domain representation is achieved by splitting the rational force-displacement relation into a series of linear functions in the frequency-domain corresponding with first order differential equations in the time-domain. This splitting process has been demonstrated as numerically effective and in addition, no Fourier transformation is necessary. In this thesis, dynamic soil-structure interaction problems with a relatively large number of degrees of freedom have been examined. These degrees of freedom arise from the discretization of the coupling interface, internal variables from the splitting procedure and from modeling the structure. The new method is especially suitable for systems with transient excitations as arising from rotating machines at startup and shutdown. The theoretical part of the thesis contains elements of system theory and discusses particularly stability problems arising from the rational approximation. The practical part presents a large amount of convergence studies and numerical results for layered soil and finally represents the propagation damping as a kind of damping ratio which is typically used in elementary structural dynamicsIn der Dynamik der Boden-Bauwerk-Interaktion wird der Boden in vielen Fällen durch ein unbegrenztes elastisches Medium beschrieben, wodurch das Phänomen der Abstrahldämpfung begründet wird. Diese Dämpfung entsteht durch Energietransfer von der erregten Struktur in den Boden durch Wellenausbreitung und reduziert somit die Strukturschwingungen. Um das infinite Bodengebiet dennoch durch finite Elemente beschreiben zu können, werden üblicherweise als Hilfsmaßnahme künstliche sogenannte absorbierende Ränder eingeführt. In dieser Arbeit wird eine alternative Methode zur Darstellung des unbegrenzten Mediums in der Dynamik vorgelegt. Im Prinzip handelt es sich um eine Kopplung der Rand-Element-Methode (REM) für den unendlichen Boden (das sogenannte Fernfeld) im Frequenzbereich und der Finite-Element-Methode (FEM) für das Nahfeld im Zeitbereich. Dieses alternative Verfahren vermeidet die Einführung künstlicher Ränder. Das Verfahren basiert auf einer rationalen Beschreibung der dynamischen Steifigkeit des Fernfeldes im Frequenzbereich. Diese Steifigkeit wird in der vorliegenden Arbeit durch die Rand-Element-Methode erzeugt. Die Matrix-wertigen Koeffizienten der rationalen Frequenzfunktion werden durch Minimierung des Fehlerquadrates berechnet. Die Transformation dieser Frequenzdarstellung in den Zeitbereich gelingt durch algebraische Überführung der rationalen Funktion in ein in der Frequenz lineares Hypersystem mit einer zugeordneten Zustandsgleichung erste Ordnung im Zeitbereich. Dieser Prozess hat sich als numerisch effektiv erwiesen und erfordert darüberhinaus keine Fourier-Transformation. Das entwickelte Vorgehen wird in dieser Arbeit an Problemen der dynamischen Boden-Bauwerk-Interaktion mit einer großen Anzahl von Freiheitsgraden erprobt. Diese Freiheitsgrade folgen aus der Diskretisierung in der Koppelfuge zwischen Boden und Struktur, der Diskretisierung der Struktur selbst und aus der Überführung in das Hypersystem mittels interner Variablen. Das neue Verfahren eignet sich insbesondere für Systeme mit transienter Erregung, wie sie beim An- und Auslaufen von Rotationsmaschinen ensteht. Der theoretische Teil der Arbeit wird geprägt durch Elemente der Systemtheorie und setzt sich zudem mit typischen Stabilitätsproblemen auseinander, die aus der rationalen Beschreibung entstehen. Der praktische Teil präsentiert Konvergenzstudien und numerische Ergebnisse für Boden-Bauwerk- Interaktionsprobleme mit geschichtetem Boden bei transienter Erregung mit Resonanzdurchlauf. Zudem gelingt eine Darstellung der Abstrahldämpfung in Form des Dämpfungsgrades D, wie er in der klassischen Strukturdynamik verwendet wird
47
Koroliov, Anton. "Semiconductor characterization by terahertz radiation pulses." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20140922_141151-18493.
Анотація:
The goal of this dissertation work was to develop pulsed terahertz radiation techniques and use them to study different properties of the semiconductor materials and semiconductor devices. Three groups of materials were investigated: GaAsBi, GaAs nanowires, copper-indium chalcogenide. The used techniques are THz-TDS, optical pump – THZ probe, optical pump – optical probe and THz excitation spectral measurements. The main results that were presented in this dissertation are the following: thermal annealing has resulted in the shortening of electron lifetime in GaAsBi to picosecond values, which is important achievement for the application of this material in THz range components. In GaAsBi layers with larger than 10% Bi content absorption bleaching recovering on the picosecond time scale and its saturation can be realized when the wavelengths of the optical signals are as long as 1600 nm. The results of these studies can be applied in the production of SESAM with bismide absorption layer. The samples with GaAs nanowires emit THz radiation several times better than the bulk GaAs substrates due to enhanced light absorption because of localized surface plasmon resonances in GaAs nanowires. THz emission efficiency from thin copper-indium chalcogenide layers strongly depends on their stoichiometry and on the parameters of the top transparent contact layers, thus it can be used for the mapping of built-in electric fields in solar cells made from these layers.Šio darbo tikslas buvo susipažinti su terahercinių impulsų generavimo ir detektavimo būdais, įsisavinti įvairias terahercinių impulsų panaudojimo metodikas bei pritaikyti jas puslaidininkių medžiagų ir puslaidininkinių prietaisų tyrimui. Buvo tirtos trys medžiagų grupės: GaAsBi, GaAs nanovielutės ir Cu – In chalkogenidai. Tyrimui buvo naudojamos: THz – TDS, optinio žadinimo – THz zondavimo, optinio žadinimo – optinio zondavimo bei THz sužadinimo spektroskopijos metodikos. Pagrindiniai rezultatai aprašyti disertacijoje yra šie: GaAsBi bandinių atkaitinimas stipriai sumažino krūvininkų gyvavimo trukmes, kas yra naudinga THz komponentų gamyboj. Optinio praskaidrėjimo efektas ir pikosekundžių eilės krūvininkų gyvavimo trukmės GaAsBi epitaksiniuose sluoksniuose su 10% ir daugiau Bi atomų stebimas žadinant juos optine spinduliuote, kurios bangos ilgiai siekia iki 1600 nm. Šios GaAsBi bandinių savybės leidžia juos priakyti įsisotinančių sugėriklių veidrodžių gamyboje. Bandiniai su GaAs nanovielutėmis emituoja THz spinduliuotę kelis kartus geriau nei GaAs padėklas, dėl padidėjusios sugerties, kurią skatina paviršinių optinių plazmonų rezonansai GaAs nanovielutėse. THz emisijos efektyvumas iš Cu-In chalkogenidų sluoksnių stipriai priklauso nuo jų stechiometrijos ir viršutinio skaidraus kontakto parametrų, ir gali būti naudojamas saulės elementų, pagamintų šių sluoksnių pagrindu, vidinių elektrinių laukų tyrimui.
48
Mohapatra, Debabrata. "Observation of b to d gamma and determination of |Vtd/Vts|." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/28129.
Анотація:
The flavor changing neutral current process
b -> dγ is a sensitive probe to the Standard Model of elementary particle physics. Using a sample of
386 Ã 106 B meson pairs accumulated by the Belle detector at the KEKB e+e− collider, we measure the branching fractions for the exclusive modes
B −> ρ−γ, B0 -> ρ0γ and B0 -> ωγ as follows:
B(B −> ρ−γ) = 0.55 +0.42−0.36 +0.09−0.08
B(B0 -> ρ0γ) = 1.25 +0.37−0.33 +0.07−0.06
B(B0 -> ωγ) = 0.56 +0.34−0.27 +0.05−0.10
where the first error on each value is statistical and the second is systematic. Assuming that these three modes are related by isospin conservation
rules, we find the combined branching fraction
B(B -> (ρ, ω)γ) = 1.32 +0.34−0.31 +0.10−0.09 .
This result is used to determine the ratio of CKM matrix elements,
|Vtd/Vts| = 0.199 +0.026−0.025 +0.018−0.015 .Ph. D.
49
Avila, Matías. "Nonlinear subgrid finite element models for low Mach number flows coupled with radiative heat transfer." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/285809.
Анотація:
The general description of a fluid flow involves the solution of the compressible Navier-Stokes equations, a very complex problem whose mathematical structure is not well understood. It is widely accepted that these equations provide an accurate description of any problem in fluid mechanics which may present many different nonlinear physical mechanisms. Depending on the physics of the problem under consideration, different simplified models neglecting some physical mechanisms can be derived from asymptotic analysis. On the other hand, radiative heat transfer can strongly interact with convection in high temperature flows, and neglecting its effects may have significant consequences in the overall predictions. Problems as fire scenarios emphasized the need for an evaluation of the effect of radiative heat transfer. This work is directed to strongly thermally coupled low Mach number flows with radiative heat transfer.
The complexity of these mathematical problem makes their numerical solution very difficult. Despite the important difference in the treatment of the incompressibility, the low Mach number equations present the same mathematical structure as the incompressible Navier-Stokes equations, in the sense that the mechanical pressure is determined from the mass conservation constraint. Consequently the same type of numerical instabilities can be found, namely, the problem of compatibility conditions between the velocity and pressure finite element spaces, and the instabilities due to convection dominated flows. These instabilities can be avoided by the use of stabilization techniques. Many stabilization techniques used nowadays are based on the variational multiscale method, in which a decomposition of the approximating space into a coarse scale resolvable part and a fine scale subgrid part is performed. The modeling of the subgrid scale and its influence leads to a modified coarse scale problem providing stability. The quality of the final approximation (accuracy, efficiency) depends on the particular model.
The extension of these techniques to nonlinear and coupled problems is presented. The distinctive features of our approach are to consider the subscales as transient and to keep the scale splitting in all the nonlinear terms appearing in the finite element equations and in the subgrid scale model. The first ingredient permits to obtain an improved time discretization scheme(higher accuracy, better stability). The second ingredient permits to prove global conservation properties, being also responsible of the higher accuracy of the method. This ingredient is intimately related to the problem of thermal turbulence modeling from a strictly numerical point of view. The capability for the simulation of turbulent flows is a measure of the ability of modeling the effect of the subgrid flow structures over the coarser ones. The performance of the model in predicting the behavior of turbulent flows is demonstrated.
The radiation transport equation has been also approximated within the variational multiscale framework, the design and analysis of stabilized finite element methods is presented.La descripción general del movimiento de un flujo implica la solución de las ecuaciones de Navier-Stokes compresibles, un problema de muy compleja estructura matemática. Estas ecuaciones proporcinan una descripción detallada de cualquier problema en mecánica de fluidos, que puede presentar distintos mecanismos no lineales que interactúan entre si. En función de la física del problema que se esté considerando, pueden derivarse modelos simplificados de las ecuaciones de Navier-Stokes mediante analisis dimensional, que ignoran algunos fenómenos físicos. Por otro lado, la transferencia de calor por radiación puede interactuar con el movimiento de un fluido, e ignorar sus efectos puede tener consecuencias importantes en las predicciones del flujo. Problemas donde hay fuego implican la evaluacion del efecto del calor por radiación. El presente trabajo está dirigido a flujos a bajo número de Mach térmicamente acoplados, donde el calor por radiación afecta al flujo. Debido a la complejidad del problema matemático, la solución numérica es muy complicada. A pesar de las diferencia en el tratamiento de la incompresibilidad, las ecuaciones de flujo a bajo número de Mach poseen una estructura matemática similar a la de flujo incompresible, en el sentido que la presión mecánica se determina a partir de la ecuación de conservación de la masa. En consecuencia poseen el mismo tipo de inestabilidades numéricas, que son el problema de condiciones de compatibilidad entre los espacios de elementos finitos de velocidad y presión, y las inestabilidades debidas a flujos con convección dominante. Estas inestabilidades pueden evitarse mediante técnicas de estabilización numérica. Muchos métodos de estabilización utilizados hoy día se basan en el método de multiscalas variacionales, donde el espacio funcional de la solucion se divide en un espacio discreto y resolubre y un espacio infinito de subscalas. El modelado de las subescalas y su influencia modifican el problema discreto proporcionando estabilidad. La calidad de la aproximación numérica final (precisión, eficiencia) depende del modelo particular de subescalas. En este trabajo se extienden estas técnicas de estabilización a problemas no lineales y acoplados. Las características que distinguen a nuestra aproximación son considerar las subsecalas como transitorias y mantener la división de escalas en todos los términos no lineales que aparecen en las ecuaciones de elementros finitos y en las del modelo de subescalas. La primera característica permite obtener mayor precisión y mejor estabilidad en la solución, la segunda característica permite obtener esquemas donde las propiedades se conservan globalmente, y mayor precisión del método. El hecho de mantener la división de escalas en todos los términos no lineales está intimamemte relacionado con el modelado de turbulencia en flujos térmicamente acoplados desde un punto de vista estrictamente numérico. La capacidad de simulación de flujo turbulento es una medida de la habilidad de modelar el efecto de las estructuras de escala fina sobre las estructuras de escala gruesa. Se muestra en esta tesis el desempeño del método para de predecir flujo turbulento. La ecuación de transporte de radiación también se aproxima numéricamente en el marco de multiscala variacional. El diseño y análisis de este método se presenta en detalle en esta tesis
50
Pourzand, Mehran. "Application of new variational principles in finite element method solutions of the radiation transport equation." Thesis, Imperial College London, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393263.