[EN] In case of a severe accident in a NPP fission products are released from the degraded fuel and may reach the environment if their confinement is lost and/or bypassed. Given the high radio-toxic nature of nuclear aerosols for environment and population, their unrestricted release should be absolutely avoided. One particular situation is the core meltdown sequence with steam generator tube rupture (SGTR). The containment bypass turns this sequence into an indispensable scenario to model when assessing PWR risk. As a result, a significant database on the aerosol behavior in the secondary side of the steam generator (SG) has been developed within the international projects EU-SGTR, ARTIST and ARTIST-2. The role played by the break stage is particularly significant since it might be responsible for a good fraction of the total mass retained and for the shift of the particle size distribution towards smaller diameters. This awoke the interest in the effect of variables such as the particle nature, the breach type (size and shape) and the tubes vibration on the particle retention within the breach stage of a dry steam generator. Those aspects have been experimentally investigated in the first part of this thesis. Two experimental campaigns, CAAT2 and SET, were conducted in order to explore the potential influence of the particle nature on their retention. Moreover, the effect of the breach size and shape has been investigated in the CAAT2 campaign while the SET experiments were devoted to the tube vibration characterization and the effect of the vibration on the particle retention. The tests conducted highlighted several key insights: the strong effect of particle nature in the secondary side capability to scrub the particle-laden gas; the confirmation of the high retention efficiency when using compact particles and the significant one when using agglomerates; the similarities between guillotine and fish-mouth breaches in terms of efficiency, but their noticeable different deposition patterns; and the secondary effect of the breach size. Finally, the tube vibration is not as significant as the particle nature effect on the net deposition. The second part of the thesis is focused on the fraction of particles susceptible of leaving the containment in case of a severe accident regardless of the SGTR sequence. Accidents like Fukushima highlighted the importance of relying on efficient mitigation systems capable of reducing any release to the environment as much as possible. Although many reactors worldwide had installed filtered containment venting systems (FCVS) the interest in FCVS and even other mitigation systems has become of outstanding importance in nuclear safety. This is the frame of the PASSAM project in which an experimental sound database is being built to explore potential enhancement of existing source term mitigation devices and demonstrate the ability of innovative systems to achieve even larger source term attenuation. As a matter of fact, particle agglomeration processes via the propagation of acoustic vibrations through a gas could be applied for a better decontamination. High-intensity acoustic fields applied to an aerosol induce interaction effects among suspended particles, giving rise to successive collisions and agglomerations, resulting in larger particles that can be more easily removed or precipitated. The mitigative system acoustic agglomerator was built-up and tested in the AAA experimental campaign. The tests were conducted under a constant ultrasonic field with aerosols of different nature and size with different gas mass flow rates. The results pointed out two main insights: the small acoustic-agglomeration effect and the key effect of the gas mass flow rate and the aggregation state of the former particles in the agglomeration process. This research is the first approximation on the application of the ultrasonic chamber as an innovative system for the source term mitigation. / [ES] Durante un accidente severo en una central nuclear los productos de fisión liberados como consecuencia de la degradación del combustible podrían llegar a la atmósfera si se pierde la hermeticidad de la contención o si encuentran vías alternativas (bypass) para salir. Dada la radio-toxicidad del término fuente, las centrales nucleares deben contar con medios y medidas técnicas de seguridad para contener estos productos. En un reactor PWR, un caso particular de secuencia accidental donde los productos de fisión tienen acceso directo a la atmósfera, es aquella en el que además de la fusión de núcleo existe rotura de tubos del generador de vapor (secuencia SGTR). En este caso, es de vital importancia la evaluación del riesgo del suceso, objetivo de los proyectos internacionales EU-SGTR, ARTIST y ARTIST-2. Particularmente significativa es la "etapa de rotura" (break stage) del generador de vapor (SG), que es responsable de la retención de una fracción importante de partículas y de la evolución de su distribución a tamaños más pequeños. Estos motivos despertaron el interés hacia la propia retención de las partículas sobre los tubos y el efecto de variables como la naturaleza de la partícula, el tipo de rotura y la vibración de tubos sobre la retención en la etapa de rotura en condiciones secas; aspectos en los que se centra la primera parte de esta tesis. Con el objetivo de estudiar las cuestiones señaladas se han llevado a cabo dos campañas experimentales, CAAT2 y SET, con materiales enmarcados en el posible espectro de los aerosoles nucleares. La primera de ellas se centró en explorar la influencia potencial de la naturaleza de la partícula y el efecto del tipo de rotura de los tubos (forma y tamaño) sobre la retención de aerosoles. La segunda concierne la caracterización de la vibración de los tubos y el estudio de su efecto en la eficiencia de retención de partículas. Las pruebas realizadas resaltan varias ideas clave: el fuerte efecto de la naturaleza de la partícula sobre la retención en el lado secundario del SG; la alta eficiencia de retención cuando las partículas son compactas y la significativa retención cuando están aglomeradas; las pequeñas diferencias en eficiencia neta entre distintos tipos de rotura (guillotina vs. boca de pez) que resultan notables sobre los patrones de deposición, y el efecto secundario del tamaño de la rotura. Finalmente los resultados revelaron que frente a la naturaleza de la partícula, la vibración de tubos juega un papel secundario en la eficiencia de la retención. La segunda parte de este trabajo se centra en la fracción de partículas que es susceptible de alcanzar la contención en caso de accidente severo. Accidentes como el de Fukushima ponen de manifiesto la necesidad de tecnologías capaces de evitar las indeseadas consecuencias de la emisión de material radiactivo al medio ambiente. Esta es la dirección de investigación del proyecto PASSAM (7º Programa Marco de EURATOM) que está construyendo una base de datos experimental para el desarrollo de sistemas innovadores y la mejora de los sistemas de venteo filtrado de la contención que ya existen. Entre estos sistemas se encuentran las cámaras de ultrasonidos donde las ondas acústicas facilitan la aglomeración y el crecimiento de partículas, resultando sistemas potenciales para su mitigación. La campaña experimental AAA ha constituido una primera aproximación para la aplicación de las cámaras de ultrasonidos como sistemas innovadores para la mitigación del término fuente en la contención. El sistema de mitigación de aglomeración acústica (MSAA) se construyó y ha sido probado durante los experimentos AAA. Los resultados obtenidos ponen de manifiesto el leve efecto del campo acústico sobre el crecimiento de las partículas. Además, tanto el flujo másico de gas portador como la naturaleza de la partícula son claves en el proceso de aglomeración. / [CAT] En cas d'accident sever d'una central nuclear els productes de fissió resultants del combustible degradat podrien assolir l'atmosfera si es perd la hermeticitat de la contenció o si troben un camí alternatiu que l'evitin. Donada la naturalesa radio-tòxica dels aerosols nuclears ha d'evitar-se per tots els mitjans que surtin a l'exterior. En un reactor PWR, un cas particular d'accident és en el qual a més de la fusió de nucli existeix trencament de tubs del generador de vapor. En aquest cas, l'alliberament de material radioactiu cap al medi ambient fa que l'escenari sigui indispensable de modelar en l'avaluació del risc d'aquest reactor. Aquesta és la raó dels projectes internacionals EU-SGTR, ARTIST i ARTIST-2, gràcies als quals s'ha construït una extensa base de dades sobre el comportament dels aerosols en el circuit secundari del generador de vapor (Steam Generator, SG). Particularment significativa és l'etapa de trencament, que és responsable de la retenció d'una fracció important de partícules i de modificar la seva distribució cap a les mides més petites. Aquests motius van despertar l'interès vers l'efecte de variables com la naturalesa de la partícula, el tipus de trencament i la vibració de tubs sobre la retenció de partícules sobre els tubs en condicions seques a l'etapa de trencament del SG. Aquests són els aspectes en els quals es centra la primera part d'aquesta tesi. Dues campanyes experimentals, CAAT2 i SET, s'han dut a terme amb diferents materials, tots ells emmarcats dins del possible rang dels aerosols nuclears. La primera d'elles es va centrar a explorar la influència potencial de la naturalesa de la partícula i l'efecte del tipus de trencament (forma i grandària) sobre la retenció d'aerosols en els tubs. La segona va seguir per la caracterització en termes de vibració dels tubs i el seu efecte en l'eficiència de retenció de partícules. Les proves realitzades ressalten diverses idees clau: el fort efecte de la naturalesa de la partícula sobre la retenció en el costat secundari del SG; l'alta eficiència de retenció quan les partícules són compactes i la també significativa retenció quan són aglomerats; les petites diferències en eficiència entre diferents tipus de trencament (guillotina vs. boca de peix), però notables sobre els patrons de deposició, i l'efecte secundari de la grandària de trencament. Finalment van revelar que enfront de la naturalesa de la partícula, la vibració de tubs juga un paper secundari en l'eficiència de retenció del feix de tubs. La segona part d'aquesta tesi es centra en la fracció de partícules que en cas d'accident sever, amb o sense seqüència SGTR, és susceptible d'aconseguir la contenció. Accidents com Fukushima posen de manifest la necessitat de tecnologia capaç de cobrir les indesitjades conseqüències de l'emissió de material radioactiu al medi. Aquesta és la raó del projecte PASSAM (7é Programa Marc d'EURATOM) que està construint una base de dades experimental per al desenvolupament de sistemes innovadors i millorar els sistemes de venteig filtrat que ja existeixen de la contenció. Les ones d'ultrasons faciliten l'aglomeració de partícules i resulten sistemes potencials per a la seva mitigació. S'ha realitzat una primera aproximació per a l'aplicació de les càmeres d'ultrasons com a sistemes innovadors per a la mitigació del terme font en la contenció. El sistema de mitigació d'aglomeració acústica (MSAA) es va construir i ha estat provat durant la campanya experimental AAA. Els experiments duts a terme en la planta PECA-MSAA del LASS. Els resultats obtinguts posen de manifest dues idees: el sistema MSAA és efectiu en la reducció de la massa de partícules i tant el flux màssic de gas portador com la naturalesa de la partícula són claus en l'eficiència de retenció del sistema. / Delgado Tardáguila, R. (2016). Experimental investigations on nuclear aerosols in a severe accident [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/63243 / TESIS

No description available.

Hyperbole is the common response in the wake of any Supreme Court decision, but which cases have a lasting negative impression and why? This work seeks to clarify which rulings of the Court cause consternation among several different audiences. Through an experimental framework I conduct an examination of reactions to rulings in controversial cases among political scientists, legal scholars, and the public. I discover that there are some commonalities among the respondents, but also significant disagreement along issue areas, particularly cases decided based on economic property rights. Additionally I observe that partisan ideology has little impact on the perception of historic decisions, but in contemporary rulings the opposite is discovered. This finding suggests that time serves to mitigate partisan bias in evaluating the Supreme Court. Ultimately this work details information concerned with responses to previous Court decisions, but also provides context clues for predicting various reactions to future controversial rulings.

Corrosion of steel reinforcement has been identified as one of the major problems facing many existing reinforced concrete structures including bridges. The exposure to aggressive environmental conditions such as those with high concentrations of chloride ions due to the use of de-icing salt in cold regions or high concentrations of carbon dioxide due to increased greenhouse gas emissions, accelerate the initiation process of corrosion. As corrosion initiates, the structural performance in terms of load-carrying capacity, ductility, and service life deteriorate over time. Coupling the effect of reinforcement corrosion with service loads may further weaken the structural performance of reinforced concrete bridges due to the presence of transverse load-induced cracks. Accordingly, a research program was conducted to evaluate the structural performance of reinforced concrete beams subjected to coupled effects of service loads and reinforcement corrosion. The research project consisted of combined experimental and numerical investigations. The experimental phase consisted of tests of nine small-scale beams and six large-scale beams. The beams were designed, constructed, instrumented, and loaded under a four-point load test. The primary test variables were the applied corrosion current density, level of corrosion, and level of sustained loading as percentage of beam ultimate capacity (0% Pu, 40% Pu, and 60% Pu). The corrosion level of steel reinforcement was quantitatively assessed using gravimetric weight measurements and three-dimensional laser scanner technique. Test results indicated that failure of corroded RC beams was brittle due to premature rupture of corroded steel bars, which was attributed to the development of localized corrosion at the sections with flexural cracks in beams. Furthermore, it was found that beams subjected to higher levels of service loads, experienced further reductions in ultimate load capacity and ductility. In addition, tensile tests were used to evaluate the effect of corrosion on the mechanical performance of steel bars retrieved from the corroded beams. It was found that the tensile strength of corroded steel bars, based on nominal sectional area, was reduced with the increase of corrosion levels. In contrast, the tensile strength, based on minimum sectional area, was not influenced by the non-uniform distribution and localization of corrosion. In fact, there was a slight increase in strength with the increase of corrosion levels. The numerical phase consisted of finite element analyses of beams using DIANA FE analysis software. A simplified approach was implemented to introduce the damage induced by corrosion into two-dimensional nonlinear FE models, based on the experimental testing of corroded beams and corroded steel bars. The analyses were reasonably accurate in predicting cracking patterns, residual load capacity, residual ductility, and failure modes of corroded beams. Subsequently, the validated model was used to conduct a parametric study on the level of service loads, level of corrosion, strength of concrete, and tensile reinforcement ratio. It was found that the FE model of corroded beams was strongly influenced by the level of service loads, level of corrosion, and tensile reinforcement ratio.

No description available.

Ce travail de thèse s’appuie sur une étude expérimentale en tube à choc, plus précisément, c’est une approche expérimentale de l'étude de l'interaction fluide-structure. Considérons un solide indéformable auquel on laisse un degré de liberté en rotation autour d'un axe. Cette structure ferme un espace clos. Si le contenu de l'espace clos subit le passage d'une onde de choc, ce solide va être mis mouvement et tourner autour de son axe. Concrètement, l'onde de choc va augmenter les caractéristiques physiques, en particulier sa pression, du fluide en contact avec la face impactée de cette porte. La face opposée de la porte ne subissant pas ou que très peu l'influence de l'onde de choc, une seule de ses faces est soumise à la surpression. Au moment de l'impact, le déséquilibre ainsi créé impose une action mécanique sur la porte qui va la faire accélérer et tourner autour de son axe de rotation. Jusqu'à ce stade tout est relativement simple. La difficulté intervient à l'instant où la porte commence à s'ouvrir, car les frontières du volume dans lequel le fluide évolue sont modifiées. Des fuites apparaissent et le gaz qui était maintenu dans un volume clos peut maintenant s'écouler vers un milieu libre. Une communication entre les gaz agissant de chaque coté de la porte est créée modifiant leurs propriétés et par conséquent la pression agissant sur chaque côté de la porte. Les actions mécaniques qui s'appliquent sur la porte ne sont plus les mêmes, et par conséquent l'accélération que la porte subit aussi. Au fur et à mesure que la porte change de position, le problème fluide continue d'être modifié et change en retour son action sur la porte. Cette interaction perdure soit jusqu'à ce que les limites du problème cessent d'être modifiées, la porte ne peut plus bouger, ou bien lorsque les actions mécaniques agissant sur la porte s'équilibrent, les fluides de chaque côté de la porte étant dans le même état physique. Le travail présenté ici est une étude des paramètres du fluide ou du solide en mouvement qui sont les acteurs de la loi comportementale gérant ce système complexe. Pour ce faire, nous avons réalisé une maquette expérimentale mettant en action la physique que nous venons de décrire et nous l'avons adaptée à un tube à choc. En éprouvant de nombreuses configurations expérimentales, nous avons pu déterminer comment l'écoulement interne d'un tube à choc évolue lorsqu'il est plus ou moins ouvert à son extrémité. Comment une porte fermée réagit-elle à l'impact d'une onde de choc et quelles en sont les conséquences sur l'évolution des fluides mis en jeu? Quelles sont les conséquences d'une position différente de la porte au moment de l'impact avec l'onde de choc? Ou encore, quel rôle joue l'intensité de l'onde de choc incidente ou l'inertie de la porte sur toute cette dynamique? / This thesis is based on an experimental study carried out in shock tube; in particular, this is an experimental approach to the study of fluid-structure interaction. Consider a rigid body which is allowed to rotate only around an axis and which closes a confined space. If a shock wave crosses the content of the confined space, the body will accelerate and rotate around its axis. Specifically, the shock wave will increase the physical characteristics, especially its pressure, of the fluid acting on the impacted face of the door. The opposite side of the door is not influenced by the incident shock wave, only one of its faces is subjected to overpressure. Following the first impact, the resulting imbalance imposes a mechanical action on the door that will increase its speed and make it turn around its rotation axis. The difficulty comes when the door begins to open: the volume boundaries in which the fluid is contained are modified. Leaks occur and the gas kept in this closed volume can now flow to the atmosphere. Communication between the gas acting on each side of the door is created modifying their properties and consequently the pressure acting on each side of the door.The mechanical actions that apply to the door are no more the same with time, and therefore the acceleration of the door is changing. As the door moves, the fluid problem continues to be changed and in turn it changes its action on the door. This interaction process continues until either the limits of the problem ceases to be changed, the door cannot move, or when the mechanical actions acting on the door are in equilibrium, fluids on each side of the door are in the same physical state. The presented work is a study of the parameters of the fluid or the solid motion which are main actors in the behavioral law managing this complex system. In this aim, we designed an experimental device involving the physics that we have described and we have adapted it to a shock tube. Testing many experimental configurations, we could determine how the internal flow of a shock tube evolves when the end of this shock tube is more or less open.How a closed door reacts to the impact of a shock wave and what are the implications for the evolution of the involved fluids? What are the consequences of a different position of the door at the instant of the impact with the incident shock wave? What role plays the intensity of the incident shock wave or the inertia of the door on this dynamic?

Em experimentos com um cilindro flexível com rigidez a flexão ortotrópica, proporcionando razão entre frequências naturais longitudinal e transversal muito próximas a quatro (fx1fy1/=4,08), Fujarra et al (2001) [17] revelaram um ramo de resposta em VIV em alta velocidade. Tal ramo de respostas estável, excitado por perturbações a montante, era caracterizado por amplitudes transversais ao escoamento com ordem de 1 diâmetro e componentes de alta frequência no espectro de energia, estendendo-se por faixa de velocidade reduzida 12 < U* < 20 e esvaindo-se a partir da emergência de oscilações no segundo modo de vibração. Almejando aprofundar as investigações acerca deste intrigante achado experimental, uma nova campanha investigativa foi planejada e executada. Quatro cilindros flexíveis com distintas razões de rigidez ortotrópica foram construídos em resina polimérica, com enrijecedores internos de seções retangulares feitos de alumínio, resultando um conjunto com frequências naturais, correspondentes a modos longitudinais e transversais, com razões relativas: 4:1, 3:1, 2:1 e 1:1. Os cilindros foram verticalmente fixados a uma célula de carga 3D. Uma série de ensaios foi conduzida, sob velocidade de escoamento crescente e decrescente. As vibrações dos cilindros flexíveis foram capturadas através de um sistema óptico subaquático, posicionado a jusante, que rastreava a posição de alvos constituídos por fitas refletivas afixadas ao longo do comprimento do cilindro. Clássicas técnicas de análise espectral, decomposição modal no domínio do tempo e a Transformada de Hilbert-Huang foram utilizadas de modo encadeado e recursivo com o fim de determinar as respostas de vibração, em amplitude e frequências dominantes, em função da velocidade reduzida. O ramo de resposta em altas velocidades reduzidas foi recuperado nos experimentos com os quatro cilindros. Análise comparativa sistemática permitiu concluir que o ramo de resposta em tela se deve ao lock-in de modos longitudinais, que são excitados em velocidades reduzidas tão mais altas quanto maior for a razão de frequências considerada. Empregando-se, então, os deslocamentos e velocidades modais medidos em formulação de Mineto (2013) [23], foi realizada estimativa de potência elétrica a ser extraída pelo emprego de finos filmes de material piezelétrico depositados sobre as lâminas enrijecedoras internas aos cilindros. / A previous work by Fujarra et al. (2001) revealed a \"high speed mode branch\" in cantilevered flexible cylinders subjected to VIV. That work studied a flexible cylinder with orthotropic bending stiffness in a recirculating water channel, by setting the ratio between the first natural frequencies, in the in-line and cross-wise directions to the flow, very close to four (fx1fy1/=4,08). Such a new stable response branch, triggered by upstream hydrodynamic perturbations, was characterized by amplitudes, perpendicular to the flow, of order of one diameter and by high frequencies components in the energy spectrum. The branch extends from reduced velocity circa 12 up to 20, being extinguished by the onset of the second vibration mode lock-in. Aiming at investigating further this intriguing experimental finding, a new campaign has been planned and performed. Four flexible cylinders with distinct orthotropic bending ratios were built, by molding thin aluminum stiffeners, of rectangular cross section, inside the cylinders made of a flexible resin. The respective natural frequencies ratio, between in-line and cross-wise bending modes, was set to 4:1, 3:1, 2:1 and 1:1. The flexible cylinders were vertically clamped to a 3D load cell. A series of experimental runs were carried out, under ascending and descending flow speeds. The flexible cylinder vibration was captured trough an underwater optical system, placed downstream, by tracking 3D Cartesian coordinates of reflective strips placed all along the span, at equi-spaced cross sections. Besides standard spectral analysis techniques, modal decomposition in time domain and the Hilbert-Huang Transform have been recursively used together to determine amplitude and dominant response frequencies. The \"high speed mode branch\" revealed for all four cylinders tested. Systematic comparative analysis allowed us to conclude that such a response branch is caused by the lock-in of longitudinal modes, excited at reduced velocities ranges that increase with the frequency ratio considered. Finally, using measured modal responses in Mineto (2013) [23] formulation, the electric power that would be extracted by the use of thin piezoelectric layers deposited over the internal stiffeners blades was estimated.

The thesis comprises a collection of four papers with preceding summary and supplementary appendices. The core investigation solely is of experimental nature although reference and comparisons with numerical models will be addressed. The first admission stage in an industrial steam turbine is referred to as the control stage if partial admission is applied. In order to achieve high part load efficiency and a high control stage output it is routinely applied in industrial steam turbines used in combined heat and power plants which frequently operate at part load. The inlet flow is individually throttled into separate annular arcs leading to the first stator row. Furthermore, partial admission is sometimes used in small-scale turbine stages to avoid short vanes/blades in order to reduce the impact from the tip leakage and endwall losses. There are three main aspects regarding partial admission turbines that need to be addressed. Firstly, there are specific aerodynamic losses: pumping-, emptying- and filling losses attributed to the partial admission stage. Secondly, if it is a multistage turbine, the downstream stages experience non-periodic flow around the periphery and circumferential pressure gradients and flow angle variations that produce additional mixing losses. Thirdly, the aeromechanical condition is different compared to full admission turbines and the forcing on downstream components is also circumferentially non-periodic with transient load changes. Although general explanations for partial admission losses exist in open literature, details and loss mechanisms have not been addressed in the same extent as for other sources of losses in full admission turbines. Generally applicable loss correlations are still lacking. High cycle fatigue due to unforeseen excitation frequencies or due to under estimated force magnitudes, or a combination of both causes control stage breakdowns. The main objectives of this thesis are to experimentally explore and determine performance and losses for a wide range of partial admission configurations. And, to perform a forced response analysis from experimental data for the axial test turbine presented herein in order to establish the forced response environment and identify particularities important for the design of control stages. Performance measurements concerning the efficiency trends and principal circumferential and axial pressure distortions demonstrate the applicability of the partial admission setup employed in the test turbine. Findings reveal that the reaction degree around the circumference varies considerably and large flow angle deviations downstream of the first rotor are present, not only in conjunction to the sector ends but stretching far into the admission sector. Furthermore, it is found that the flow capacity coefficient increases with reduced admission degree and the filling process locally generates large rotor incidence variation associated with high loss. Moreover, the off design conditions and efficiency deficit of downstream stages are evaluated and shown to be important when considering the overall turbine efficiency. By going from one to two arcs at 52.4% admission nearly a 10% reduction in the second stage partial admission loss, at design operating point was deduced from measurements. Ensemble averaged results from rotating unsteady pressure measurements indicate roughly a doubling of the normalized relative dynamic pressure at rotor emptying compared to an undisturbed part of the admission jet for 76.2% admission. Forced response analysis reveals that a large number of low engine order force impulses are added or highly amplified due to partial admission because of the blockage, pumping, loading and unloading processes. For the test turbine investigated herein it is entirely a combination of number of rotor blades and low engine order excitations that cause forced response vibrations. One possible design approach in order to change the force spectrum is to alter the relationship between admitted and non-admitted arc lengths. / Denna sammanläggningsavhandling består av fyra artiklar och föregås av en sammanfattning med kompletterande bilagor. Kärnan av undersökningen är experimentell även om referenser och jämförelser med numeriska modeller förekommer där så bedöms lämpligt. Det första steget i en industriell ångturbin kallas reglersteg om partialpådrag tillämpas. Det används rutinmässigt i kraftvärmeanläggningar som ofta körs vid dellaster för att åstadkomma en hög dellastverkningsgrad och hög stegeffekt. Inloppsflödet delas in separata och individuellt strypreglerade pådragsbågar som leder till det första munstycksgittret. Ibland används partialpådrag i små turbiner för att undvika korta blad och på så sätt minska takläckage och ändväggsförlusternas inflytande på den totala förlusten. Det finns i huvudsak tre aerodynamiska/aeromekaniska egenheter som bör beaktas. Först det första är det speciella aerodynamiska förluster associerade till partialpådrag eller reglersteget: ventilations-, tömnings och fyllningsförluster. För det andra, om det är en flerstegsturbin påverkas också nedströms steg negativt av det asymmetriska flödet runt omkretsen som innefattar stora tryckvariationer och flödesvinkelvariationer. För det tredje är den aeromekaniska situationen speciell jämfört med ett fullpådraget steg. För partialpådrag existerar dynamiska krafter med snabba laständringar vid in och utpassering i pådragsbågen. Även om det existerar generella förklaringar i den öppna litteraturen angående förluster så har inte förlustmekanismerna utretts i samma omfattning jämfört med fullpådrag. Ingen generell förlustkorrelation finns. Utmattning på grund oförutsedda excitationsfrekvenser, underskattade kraftamplituder eller en kombination av båda orsakar reglerstegshaveri för ångturbinintressenter. De huvudsakliga målsättningarna med denna studie är att experimentellt utforska och bestämma prestanda och förluster för ett stort antal partialpådragskonfigurationer. Samt att genomföra en vibrationsanalys (relaterat till aerodynamiska kraftimpulser) utifrån mätdata från provturbinen avhandlad häri. Detta för att kartlägga de aeromekaniska förutsättningarna och om möjligt identifiera egenheter viktiga för konstruktion av reglersteg. Prestandamätningar rörande verkningsgradstrender och generella strömningsvariationer runt omkretsen bekräftar resultat från den öppna litteraturen och därmed demonstrerar dugligheten av den partialpådragskonfiguration som används i luftprovturbinen. Dessutom visar resultaten bland annat att reaktionsgraden varierar kraftigt runt omkretsen med stora variationer i rotorns utloppsvinkel inte enbart i anslutning till sektorändar utan långt in i pådragssektorn. Flödeskapacitetskoefficienten eller turbinkonstanten ökar med minskat pådrag och fyllningsprocessen genererar stora variationer i rotorns inloppsvinkel förknippade med höga förluster. Det är viktigt att beakta dellastförutsättningarna och verkningsgradsminskningen för nedströms steg. Genom att använda två pådragsbågar istället för en för ett givet pådrag av 52,4% minskar partialpådragsförlusterna för nedströmssteget med nästan 10 % vid designpunkten, härlett från mätningar. Samlade medelvärden från roterande instationära mätningar visar på en fördubbling av det relativa dynamiska trycket vid rotortömning jämfört med en opåverkad del av pådragsbågen. Vibrationsanalys (relaterat till aerodynamiska kraftimpulser) av mätdata avslöjar att partialpådrag orsakar en stor mängd kraftimpulser med låga varvtalsmultiplar, främst från ventilationen och påavlastningsprocesserna. För provturbinen så är det helt och hållet kombinationer mellan antalet rotorblad och dessa kraftimpulser som orsakar strömningspåverkade vibrationer. Ett möjligt tillvägagångssätt konstruktionsmässigt för att ändra kraftspektrumet är att ändra längförhållandet mellan pådragen och blockerad del. / QC 20120109

Sandwich panels comprise a thick, light-weight plastic foam such as polyurethane, polystyrene or mineral wool sandwiched between two relatively thin steel faces. One or both steel faces may be flat, lightly profiled or fully profiled. Until recently sandwich panel construction in Australia has been limited to cold-storage buildings due to the lack of design methods and data. However, in recent times, its use has increased significantly due to their widespread structural applications in building systems. Structural sandwich panels generally used in Australia comprise of polystyrene foam core and thinner (0.42 mm) and high strength (minimum yield stress of 550 MPa and reduced ductility) steel faces bonded together using separate adhesives. Sandwich panels exhibit various types of buckling behaviour depending on the types of faces used. Three types of buckling modes can be observed which are local buckling of plate elements of fully profiled faces, flexural wrinkling of flat and lightly profiled faces and mixed mode buckling of lightly profiled faces due to the interaction of local buckling and flexural wrinkling. To study the structural performance and develop appropriate design rules for sandwich panels, all these buckling failure modes have to be investigated thoroughly. A well established analytical solution exists for the design of flat faced sandwich panels, however, the design solutions for local buckling of fully profiled sandwich panels and mixed mode buckling of lightly profiled sandwich panels are not adequate. Therefore an extensive research program was undertaken to investigate the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. The first phase of this research was based on a series of laboratory experiments and numerical analyses of 50 foam-supported steel plate elements to study the local buckling behaviour of fully profiled sandwich panels made of thin steel faces and polystyrene foam core covering a wide range of b/t ratios. The current European design standard recommends the use of a modified effective width approach to include the local buckling effects in design. However, the experimental and numerical results revealed that this design method can predict reasonable strength for sandwich panels with low b/t ratios (< 100), but it predicts unconservative strengths for panels with slender plates (high b/t ratios). The use of sandwich panels with high b/t ratios is very common in practical design due to the increasing use of thinner and high strength steel plates. Therefore an improved design rule was developed based on the numerical results that can be used for fully profiled sandwich panels with any practical b/t ratio up to 600. The new improved design rule was validated using six full-scale experiments of profiled sandwich panels and hence can be used to develop safe and economical design solutions. The second phase of this research was based on a series of laboratory experiments and numerical analyses on lightly profiled sandwich panels to study the mixed mode buckling behaviour due to the interaction of local buckling and flexural wrinkling. The current wrinkling formula, which is a simple modification of the methods utilized for flat panels, does not consider the possible interaction between these two buckling modes. As the rib depth and width of flat plates between the ribs increase, flat plate buckling can occur leading to the failure of the entire panel due to the interaction between local buckling and wrinkling modes. Experimental and numerical results from this research confirmed that the current wrinkling formula for lightly profiled sandwich panels based on the elastic half-space method is inadequate in its present form. Hence an improved equation was developed based on validated finite element analysis results to take into account the interaction of the two buckling modes. This new interactive buckling formula can be used to determine the true value of interactive buckling stress for safe and economical design of lightly profiled sandwich panels. This thesis presents the details of experimental investigations and finite element analyses conducted to study the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. It includes development and validation of suitable numerical and experimental models, and the results. Current design rules are reviewed and new improved design rules are developed based on the results from this research.

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais / INCT-EIE - Instituto Nacional de Ciência e Tecnologia De Estruturas Inteligentes em Engenharia / UFU - Universidade Federal de Uberlândia / Este trabalho apresenta uma investigação numérica e experimental sobre o comportamento dinâmico de um sistema rotativo submetido a uma excitação pela base. Na área de aplicações aeronáuticas, o motor de uma aeronave é considerado um típico rotor embarcado, no qual seu comportamento dinâmico é afetado pela excitação da base. O modelo matemático do rotor é obtido a partir das equações de Lagrange e do método de elementos finitos, considerando as energias de deformação e cinética do eixo e as energias cinéticas do disco e da massa desbalanceada. A base do sistema rotativo é considerada rígida. As equações de movimento do sistema são utilizadas para determinar as respostas de vibração do rotor a partir das excitações devido ao desbalanceamento e ao movimento da base. Na análise numérica foi investigada uma máquina rotativa composta por um eixo horizontal flexível contendo dois discos e apoiada em suas extremidades. As diferenças entre o comportamento de rotores de base fixa e em movimento foram exploradas. Uma máquina rotativa composta por um eixo horizontal flexível apoiada em suas extremidades e um disco rígido foi utilizada na validação experimental do modelo adotado. As respostas de vibração do modelo matemático construído e medidas experimentalmente foram comparadas. Diferentes análises foram realizadas nos domínios de tempo e da frequência, onde foram obtidos funções de resposta em frequência, órbitas, respostas ao desbalanceamento e o diagrama de Campbell. Os resultados obtidos representam adequadamente o comportamento do sistema. / In the present work, a numerical and experimental investigation regarding the dynamic behavior of a rotating machine subjected to a base excitation is presented. Regarding the aeronautical applications, the aircraft engine is considered a typical onboard rotor which has its dynamic behavior influenced by base excitations. The mathematical model of the rotor is derived from the Lagrange’s equation and the finite element method, which is obtained by considering the strain and kinetic energies of the shaft, and the kinetic energy of the discs and mass unbalance. In this case, the base of the rotor system is considered as being rigid. The resulting differential equations are used to provide information about the vibration responses of the rotor under base and unbalance excitations simultaneously. In the numerical analysis a rotating machine composed by a horizontal flexible shaft containing two rigid discs and supported by two ball bearings was investigated. The differences between the dynamic behavior of a fixed base and onboard rotors were explored. A rotating machine is composed by a horizontal flexible shaft, one rigid disc, and two self-aligning ball bearings was used in the experimental validation of the adopted model. The vibration responses of the mathematical model and the experimental results were compared. Different analyses were performed both in the time and frequency domains, as generated by the orbits, unbalance response, and Campbell diagram. The obtained results adequately represent the behavior of the system. / Dissertação (Mestrado)