Abstract : Deterioration of concrete structures reinforced with steel bars can be seen daily in regions with aggressive weather as steel-corrosion problems worsen. Fiber-reinforced-polymers (FRP) reinforcement has proven its feasibility through different civil structural elements. Present guidelines for FRP structures in North-America and Europe have not yet handled axially loaded members, due to the lack of research and experiments. This research takes charge of providing experimental database as well as extensive analyses and design recommendations of circular concrete columns reinforced totally with different FRP bars and spirals/hoops (FRP-RC columns). Full-scale columns were tested under monotonic loading with different levels of eccentricity. Test variables included the eccentricity-to-diameter ratio (e/D); reinforcement type (GFRP and CFRP vs. steel); concrete strength; longitudinal and transverse reinforcement ratio; and confinement configuration. All specimens measured 305 mm diameter and 1500 mm height. Test results indicated that specimens reinforced with glass-FRP (GFRP) or carbon-FRP (CFRP) reached their peak strengths with no damages to GFRP or CFRP rebar on either side of specimens. Specimens with CFRP reinforcement (CFRP-RC) behaved very similarly to their steel counterparts, and achieved almost the same nominal axial forces. Specimens with GFRP reinforcement (GFRP-RC) exhibited, however, reduced stiffness and achieved lower nominal axial forces than their steel or CFRP counterparts. Failure of GFRP-RC and CFRP-RC specimens was dominated by concrete crushing at low levels of eccentricity (e/D ratios of 8.2% and 16.4%). Experimental strain results revealed that GFRP bars developed high levels of strains and stresses on the compression and tension sides and hence the GFRP-RC specimens could sustain constant axial load after peak for some time up to the limit of concrete crushing at higher levels of eccentricity (e/D ratios of 8.2% and 16.4%), which help to delay the full damage. At these levels, flexural–tension failure initiated in the GFRP-RC specimens resulting from large axial and lateral deformations and cracks on the tension side until secondary compression failure occurred due to strain limitations in concrete and degradation of the concrete compressive block. The failure of CFRP-RC specimens at higher levels of eccentricity (e/D ratios of 8.2% and 16.4%) was characterized as flexural–compression in which it took place in a less brittle manner. On the other hand, this research also included different studies to analyze the test results, evaluate rebar efficiency, and provide recommendations for analysis and design. It was, therefore, indicated that the axial and flexural capacities of the tested FRP-RC specimens could be reasonably predicted using plane sectional analysis, utilizing the equivalent rectangular stress block (ERSB) parameters given by the ACI 440.1R-15 or CSA S806-12. All predictions underestimated the actual strength with variable levels of conservatism ranged between 1.05 to 1.25 for the GFRP-RC specimens and between 1.20 to 1.40 for the CFRP-RC specimens. These levels were noticeably reduced to critical limits in specimens with high-strength concretes. An elaborate review was made to the available ERSB parameters in the present steel and FRP design standards and guidelines. Modified expressions of the ERSB given in ACI 440.1R-15 and CSA S806-12 were developed. The results indicated good correlation of predicted and measured strength values with enhanced levels of conservatism. Additionally, sets of axial force–bending moment (P-M) interaction diagrams and indicative bar charts are introduced, and recommendations drawn. The compressive-strength contribution of FRP reinforcement was thoroughly reviewed and discussed. The minimum GFRP and CFRP reinforcement ratios to avoid rebar rupturing were broadly examined. Finally, the flexure stiffness (EI) of the tested specimens was analytically determined and compared with the available expressions using experimental and analytical M-ψ responses. Proposed equations are developed and validated against the experimental results to represent the stiffness of GFRP-RC and CFRP-RC columns at service and ultimate levels. / La détérioration des structures en béton armé avec des barres d’armature d’acier peut être observée quotidiennement dans les régions à climat agressif. Le renforcement interne en polymères renforcés de fibres (PRF) a démontré sa faisabilité grâce à différents éléments structuraux en génie civil. Les lignes directrices actuelles pour les structures en béton armé de PRF en Amérique du Nord et en Europe n'ont pas encore gérées les sections soumises à des efforts axiaux excentrique, en raison du manque de recherches et d'expériences. Cette recherche permet d’augmenter la base de données expérimentales ainsi établir des analyses approfondies et des recommandations de conception pour les colonnes circulaires en béton armé complètement renforcées de PRF (barres et spirales). Des grandeur-nature colonnes ont été testées sous charge monotone avec différents niveaux d'excentricité. Les variables de test comprenaient le rapport excentricité / diamètre (e/D) ; le type de renfort (PRFV et PRFC comparativement à l’acier); la résistance du béton en compression; le taux d’armature longitudinal et transversal; et la configuration de l’armature de confinement. Tous les échantillons mesuraient 305 mm de diamètre et 1500 mm de hauteur. Les résultats des tests ont indiqué que les spécimens renforcés avec des PRF de verre ou des PRF de carbone atteignaient leur résistance maximale sans endommager les barres d’armature. Des deux types de renforcement, les spécimens de PRFCCFRP se comportaient de manière très similaire à leurs homologues en acier et atteignaient presque les mêmes résistances axiales. Cependant, les spécimens avec renforcement en PRFV ont présenté une rigidité réduite et des forces axiales nominales inférieures à celles de leurs homologues en acier ou en PRFC. Le mode de rupture des spécimens de PRFC et de PRFV a été dominé par l’écrasement du béton à de faibles niveaux d'excentricité (rapports e/D de 8,2% et 16,4%). Les résultats ont révélé que les barres de PRFV ont développé des niveaux élevés de déformations et de contraintes sur les faces en compression et en tension et, par conséquent, les spécimens de PRFVC pourraient supporter une charge axiale constante après la résistance ultime pendant un certain temps jusqu'à la limite de la rupture en compression du béton du noyau à des niveaux supérieurs d'excentricité (rapport e/D de 8,2% et 16,4%), ce qui contribue à retarder la dégradation. À ces niveaux, une rupture en tension a été initiée dans les spécimens de PRFV résultant à de grandes déformations axiales et latérales et des fissures du côté de la face en tension jusqu'à ce que la rupture en compression du béton. La rupture des spécimens de PRFC à des niveaux supérieurs d'excentricité (rapport e/D de 8,2% et 16,4%) a été caractérisé comme étant en compression du béton dans laquelle il s'est déroulé de manière moins fragile. D'autre part, cette recherche comprenait également différentes études pour analyser les résultats des tests, évaluer l'efficacité des barres d'armature et fournir des recommandations pour l'analyse et la conception. Il a donc été indiqué que les capacités axiales et de flexion des spécimens en PRF testées pourraient être raisonnablement prédites en utilisant une analyse en section plane, en utilisant les paramètres du bloc de contrainte rectangulaire équivalent (BCRE) donnés par l'ACI 440.1R-15 ou la CSA S806- 12. Toutes les prédictions ont sous-estimé la résistance réelle avec des niveaux de variabilité conservateur entre 1,05 et 1,25 pour les spécimens de PRFC et entre 1,20 et 1,40 pour les spécimens de PRFC. Ces niveaux ont été nettement réduits à des limites critiques dans les spécimens avec des bétons à haute résistance. Un examen approfondi a été effectué sur les paramètres du BCRE disponibles dans les normes et les directives de conception actuelles en acier et en PRF. Les expressions modifiées du BCRE fournies dans ACI 440.1R-15 et CSA S806-12 ont été développées. Les résultats indiquent une bonne corrélation entre les valeurs de résistance prédites et mesurées avec des niveaux accrus de conservatisme. La contribution de la résistance à la compression du renforcement en PRF a été soigneusement examinée et discutée. Le taux d’armature minimum de PRFV et de PRFC pour éviter la rupture de l'armature ont été largement examinés. Enfin, la rigidité en flexion (EI) des spécimens testés a été déterminée de manière analytique et comparée aux expressions disponibles dans la littérature en utilisant les réponses expérimentales et analytiques M-ψ. Les expressions modifiées de la rigidité en flexion EI apportées dans l’ACI 440.1R ont été développées et validées.

Bien que constitué anatomiquement et physiologiquement pour la course d’endurance, l’Homme est considérablement exposés à diverses blessures musculo-squelettiques liées à la répétition de contraintes mécaniques. Le coureur de trail running par exemple est soumis à de nombreux impacts ainsi qu’à une fatigue et des dommages musculaires sévères. Ces chocs répétitifs et dommages musculaires réduiraient la tolérance du coureur face aux contraintes mécaniques le poussant ainsi à altérer sa cinématique de course. Par conséquent, minimiser les dommages musculo-squelettiques serait déterminant pour la performance en trail running. Des évidences montrent que la pose de pied altère la localisation et l’intensité des contraintes appliquées au système musculo-squelettique. L’objectif de ce travail de thèse a été d’étudier l’influence du pattern de pose de pied sur l’impact et la fatigue neuromusculaire en trail running. Les phases de descente ont été tout particulièrement étudiées du fait qu’elles sont les plus traumatisantes. En effet, ce travail de thèse a mis en évidence qu’en situation de trail running, l’intensité de l’impact augmente lorsque la pente diminue, et que la fatigue neuromusculaire périphérique est aussi sévère à la suite d’une descente isolée qu’après un ultra-trail de plusieurs heures. En étudiant l’influence de la pose de pied adoptée au cours d’une descente en situation de trail running, il a été observé qu’attaquer le sol par l’avant du pied augmentait la fatigue neuromusculaire aux extenseurs du genou. Cependant, une importante variabilité dans les patterns de pose de pied adoptés au cours de la descente a été associée à une baisse de la fatigue neuromusculaire aux extenseurs du genou et fléchisseurs plantaires. L’influence de la pose de pied sur l’intensité du choc et le contenu vibratoire le long des axes axial et transversal a également été démontrée : adopter une attaque talon diminue la sévérité du choc axial mais réduit l’intensité du choc transversal. La principale conclusion est qu’aucun pattern de course ne saurait être universellement recommandé du fait que « changer de pose de pied » est synonyme de « changer la localisation et la magnitude des contraintes appliquées au système musculo-squelettique ». En ce sens, alterner entre différents patterns de course serait une stratégie efficiente en trail running / Although Humans are “born” anatomically and physiologically adapted to long distances run, they are substantially exposed to various musculoskeletal overuse injuries. Trail runners sustain a high number of foot-to-ground contacts and develop severe muscle fatigue and damages. Repetitive shocks and muscle damages would reduce the runners’ tolerance to mechanical strains leading to changes in running kinematics. Minimizing musculoskeletal damages is therefore considered paramount for performance in trail running. Numerous studies highlighted that the foot strike pattern alters the localization and magnitude of the mechanical strains applied on the musculoskeletal system. The main purpose of this thesis was to study the influence of the foot strike pattern on impact and neuromuscular fatigue in trail running. Downhill sections were mainly investigated since they are the most mechanically stressful. Indeed, it was observed from this thesis’ work that, in real trail running practice, the impact intensity increases as the slope decreases, and that the neuromuscular fatigue induced by a single downhill run is as severe as the one induced by an ultratrail race that lasts several hours. Investigating the effect of the foot strike pattern adopted during a downhill trail run on fatigue, it was observed that forefoot striking increases the neuromuscular fatigue at knee extensors. However, a high variability in foot strike patterns adopted was associated to a lower neuromuscular fatigue at both knee extensors and plantar flexors. The effect of the foot strike pattern on axial and transversal shock and vibration content was also demonstrated: heel striking was correlated to a lower impact severity along the axial axis of the skeleton but a greater one along its transversal axis. The main conclusion of this thesis is that no single foot strike pattern should be universally advised due to “changing of foot strike” means “changing the localization and magnitude of the mechanical stress applied on the musculoskeletal system”. Switching between different running patterns might be an efficient strategy in trail running

La chromatographie membranaire est une alternative à la chromatographie classique sur résine basée sur le transport convectif des solutés à travers une membrane microporeuse plutôt que par le transport diffusif des solutés dans les particules de résines. Cette technique présente les avantages de diminuer les phénomènes de diffusion, de réduire les temps de séjour et les pertes de charge, et de permettre la purification rapide de quantités importantes de molécules. La chromatographie membranaire connaît un fort succès commercial. Une gamme importante de membranes chromatographiques mettant en jeu différents mécanismes de rétention (échange d’ions, affinité, etc.) et différentes géométries (feuille, spirale, etc.) est actuellement commercialisée. Malgré ce succès, différents aspects relatifs à la chromatographie membranaire restent mal connus. Cette thèse de doctorat se propose de répondre à certaines questions relatives à cette technique / Membrane chromatography (MC) is an alternative to traditional resin packed columns chromatography. The solute mass transport in the membrane occurs in convective through-pores rather than in stagnant fluid inside the pores of the resins particles, which is limited by the slow diffusive transport. MC offers the main advantage of reducing diffusion phenomena, shorter residence time and lowered pressures drops, and thus, facilitates rapid purification of large quantities of molecules. A wide range of chromatographic membranes involving different molecules retention mechanisms (ion exchange, affinity, etc...) is now commercialized. Despite their success, the influence of the geometry of the membrane chromatography devices remains relatively unexplored from a theoretical point of view. This doctoral thesis is aimed to clarify some ambiguous points related to this technique

Evaluation of the performance of a product and its components under impact loading is one of the key considerations in design. In order to assess resistance to damage or ability to absorb energy through plastic deformation of a structural component, impact testing is often carried out to obtain the 'Force - Displacement' response of the deformed component. In this context, it may be noted that load cells and accelerometers are commonly used as sensors for capturing impact responses. A drop-weight impact testing set-up consisting of a moving impactor head with a lightweight piezoresistive accelerometer and a strain gage based compression load cell mounted on it is used to carry out the impact tests. The basic objective of the present study is to assess the accuracy of responses recorded by the said transducers, when these are mounted on a moving impactor head. In the present work, a novel approach of theoretically evaluating the responses obtained from this drop-weight impact testing set-up for different axially loaded specimen has been executed with the formulation of an equivalent lumped parameter model (LPM) of the test set-up. For the most common configuration of a moving impactor head mounted load cell system in which dynamic load is transferred from the impactor head to the load cell, a quantitative assessment is made of the possible discrepancy that can result in load cell response. Initially, a 3-DOF (degrees-of-freedom) LPM is considered to represent a given impact testing set-up with the test specimen represented with a nonlinear spring. Both the load cell and the accelerometer are represented with linear springs, while the impacting unit comprising an impactor head (hammer) and a main body with the load cell in between are modelled as rigid masses. An experimentally obtained force-displacement response is assumed to be a nearly true behaviour of a specimen. By specifying an impact velocity to the rigid masses as an initial condition, numerical solution of the governing differential equations is obtained using Implicit (Newmark-beta) and Explicit (Central difference) time integration techniques. It can be seen that the model accurately reproduces the input load-displacement behaviour of the nonlinear spring corresponding to the tested component, ensuring the accuracy of these numerical methods. The nonlinear spring representing the test specimen is approximated in a piecewise linear manner and the solution strategy adopted and implemented in the form of a MATLAB script is shown to yield excellent reproduction of the assumed load-displacement behaviour of the test specimen. This prediction also establishes the accuracy of the numerical approach employed in solving the LPM system. However, the spring representing the load cell yields a response that qualitatively matches the assumed input load-displacement response of the test specimen with a lower magnitude of peak load. The accelerometer, it appears, may be capable of predicting more closely the load experienced by a specimen provided an appropriate mass of the impactor system i.e. impacting unit, is chosen as the multiplier for the acceleration response. Error between input and computed (simulated) responses is quantified in terms of root mean square error (RMSE). The present study additionally throws light on the dependence of time step of integration on numerical results. For obtaining consistent results, estimation of critical time step (increment) is crucial in conditionally stable central difference method. The effect of the parameters of the impact testing set-up on the accuracy of the predicted responses has been studied for different combinations of main impactor mass and load cell stiffness. It has been found that the load cell response is oscillatory in nature which points out to the need for suitable filtering for obtaining the necessary smooth variation of axial impact load with respect to time as well as deformation. Accelerometer response also shows undulations which can similarly be observed in the experimental results as well. An appropriate standard SAE-J211 filter which is a low-pass Butterworth filter has been used to remove oscillations from the computed responses. A load cell is quite capable of predicting the nature of transient response of an impacted specimen when it is part of the impacting unit, but it may substantially under-predict the magnitudes of peak loads. All the above mentioned analysis for a 3 DOF model have been performed for thin-walled tubular specimens made of mild steel (hat-section), an aluminium alloy (square cross-section) and a glass fibre-reinforced composite (circular cross-section), thus confirming the generality of the inferences drawn on the computed responses. Further, results obtained using explicit and implicit methodologies are compared for three specimens, to find the effect, if any, on numerical solution procedure on the conclusions drawn. The present study has been further used for investigating the effects of input parameters (i.e. stiffness and mass of the system components, and impact velocity) on the computed results of transducers. Such an investigation can be beneficial in designing an impact testing set-up as well as transducers for recording impact responses. Next, the previous 3 DOF model representing the impact testing set-up has been extended to a 5 DOF model to show that additional refinement of the original 3 DOF model does not substantially alter the inferences drawn based on it. In the end, oscillations observed in computed load cell responses are analysed by computing natural frequencies for the 3 DOF lumped parameter model. To conclude the present study, a 2 DOF LPM of the given impact testing set-up with no load cell has been investigated and the frequency of oscillations in the accelerometer response is seen to increase corresponding to the mounting resonance frequency of the accelerometer. In order to explore the merits of alternative impact testing set-ups, LPMs have been formulated to idealize test configurations in which the load cell is arranged to come into direct contact with the specimen under impact, although the accelerometer is still mounted on the moving impactor head. One such arrangement is to have the load cell mounted stationary on the base under the specimen and another is to mount the load cell on the moving impactor head such that the load cell directly impacts the specimen. It is once again observed that both these models accurately reproduce the input load-displacement behaviour of the nonlinear spring corresponding to the tested component confirming the validity of the model. In contrast to the previous set-up which included a moving load cell not coming into contact with the specimen, the spring representing the load cell in these present cases yields a response that more closely matches the assumed input load-displacement response of a test specimen suggesting that the load cell coming into direct contact with the specimen can result in a more reliable measurement of the actual dynamic response. However, in practice, direct contact of the load cell with the specimen under impact loading is likely to damage the transducer, and hence needs to be mounted on the moving head, resulting in a loss of accuracy, which can be theoretically estimated and corrected by the methodology investigated in this work.

The Master`s Thesis deals with design and construction of a valve block for a hydrostatic recuperative module of a vehicle with a direct application on pneu tyred roller AP 240H produced by the AMMANN company. The thesis aims to analyze recovery functions of the valve block in several operating modes of the roller, followed by a selection of the right hydraulic components from the perspective of predefined parameters and pressure differences. Design specifications are based on measurements and mathematical simulations on the experimental stand. The experimental stand for this application has been developed at 1:4 scale as compared to a real vehicle. The thesis includes also design of the supporting console for the module on the frame of the vehicle. The Master`s Thesis is a part of project EUREKA with cooperation Bosch Rexroth.

Background: Axial spondyloarthritis (axSpA) is a chronic inflammatory rheumatic disease affecting primarily the spine and its adjacent structures. The disease is characterized not only by destructive joint changes but also by excessive osteoproduction, which can lead to gradual ankylosis of the spine and thus significantly reduce the mobility and quality of life. The pathogenesis of the disease is not yet fully understood, but a strong genetic background is suggested, along with dysregulation of tissue metabolism resulting from an imbalance of pro- and anti-inflammatory immune mechanisms. We are still lacking biomarker with sufficient sensitivity and specificity which could help to identify early diagnosis, to monitor subchondral damage, and to differentiate rapidly progressing patients. The aim of this work was to determine the levels of potential biomarkers of connective tissue metabolism, fat metabolism and new promising biomarkers for both disease subtypes, their relationship to disease activity and progressive structural changes. Results: We have shown increased serum/plasma levels of connective tissue metabolism biomarkers (especially matrix metalloproteinase mediated metabolites), which were able to differentiate patients with early and late forms of axSpA from healthy individuals (HC), were...

Title: Axial system straining during martial arts and after care compensation of injuries Objective: The main goal of this diploma thesis is to bring complex view on injuries of axial system, which happend during martial arts. This thesis is going to define the ijuries and offer an alternative compensation of these injuries. Furthermore, the focus is on summarizing current knowledge about this issue Methods: The thesis is based on literary research and has an analytical-descriptive character. The studies used meet predetermined criteria. The work is divided into several parts. The first part, called the theoretical background, focuses on the description of combat, further analyzes the axial system of man and also the biomechanics of the components of the axial system. The next part discusses the load of the axial system in the fights. After that, the work deals with injuries in combat. Results: Based on the findings of individual studies, it can be said that the vast majority of all injuries incurred during judo and Brazilian jiu jitsu are orthopedic. Large joints were most affected by the injury. Injuries within the axial system occurred rather sporadically and were mostly head and cervical spine injuries. Keywords: axial system, axial system injuries, fights, judo, Brazilian jiu jitsu, combat in...

<p>Positive displacement machines (PDMs) operate based on the principle of positive displacement, which necessitates a periodic alteration of volume. This volume variation is accomplished through relative motion between machine components. PDMs find extensive applications in diverse domains, encompassing fluid power systems, lubrication systems, fluid transport systems, fuel injection systems, and more. The primary distinction among PDMs lies in the geometric mechanisms employed for fluid displacement, as well as the flow distribution mechanisms they employ. PDMs can be broadly classified into piston machines, vane machines, screw machines, and gear machines. In fluid power systems, the most commonly used PDMs are the piston and gear machines. Piston machines can be further classified into radial piston machines, in-line piston machines, and axial piston machines. The most commonly used piston machines are the axial piston machine owing to their superior efficiency and compactness. Gear machines can be further classified into external gear machines, internal gear machines, and annular gear machines. The most commonly used gear machine is the external gear machine owing to its price.</p> <p><br></p> <p>PDMs typically involve multiple solid bodies in relative motion, with micron-level gaps between them. These gaps, known as lubricating interfaces, present a significant design challenge during the machine development process. They are a primary source of power losses and play a crucial role in determining the efficiency and durability of the machine. The lubricating interfaces must effectively balance loads and maintain a high-pressure fluid seal. Achieving this delicate balance necessitates a comprehensive understanding of the underlying physical phenomena. Lubricating interfaces generate substantial heat due to viscous dissipation, which directly impacts the operation of the entire machine. The viscosity of the working fluid rapidly decays with temperature, causing the warmer fluid within the lubricating interface to possess lower viscosity. Consequently, it can support lesser loads and is more prone to leakage. Moreover, as the solid bodies enclosing the warmer fluid heat up, they undergo thermal expansion, further changing the clearance and leading to a decline in performance. Additionally, the elevated temperature of the fluid within the lubricating interface affects the compressibility of the displacement chamber fluid, thereby influencing the pressurization characteristics of the entire unit. Thus, thermal effects play a critical role in the performance of PDMs.</p> <p><br></p> <p>  The ever-increasing market demand for more compact, efficient, and reliable designs requires a continuous process of design improvements over previous designs, and sometimes completely new designs. Sophisticated simulation tools are a necessity for such a design process. Additionally, these simulation tools also prove to be valuable in formulating design modifications in case of underperforming designs. Due to the complexity associated with the operation of such units, the simulation tools need to capture a wide variety of physical phenomena. Over the past few decades, owing to the increasing computing power of the desktop computer, several simulation tools have been proposed across the literature to aid the design process of such machines with each having limitations of their own.</p> <p><br></p> <p>  The objective of the present thesis is to propose a modeling approach that assists in the design process of positive displacement machines, addressing various limitations identified in the existing literature. The approach is intentionally designed to be generic, enabling its application across a diverse range of positive displacement machines. The modeling approach encompasses three distinct domains: the displacement chamber fluid domain, the lubricating interface fluid domain, and the solid domain. A novel thermal model that integrates all three domains is introduced. </p> <p><br></p> <p>  To validate the effectiveness of the proposed modeling approach, two separate validation studies are conducted. The first study focuses on a model for an isolated piston/cylinder interface of an axial piston machine, operating under the mixed lubrication regime. The model demonstrates a strong agreement with the measured data. The second study involves steady-state measurements of an entire axial piston machine. The model is validated by comparing the steady-state flow characteristics and temperature distribution on the valveplate, both of which are accurately captured by a single fully coupled model. The modeling approach developed in this study, specifically, the energy conservation in the lubricating interface, heat transfer in the solid bodies, and thermal deformation in the solid bodies are all generalized for applicability in different types of PDMs. However, the results presented in this thesis pertain to an axial piston machine.</p>

Master of Science / Department of Mechanical and Nuclear Engineering / Donald L. Fenton / Increase in demand for energy necessitates nuclear power units to increase their peak power limits. This increase implies significant changes in the design of the nuclear power unit core in order to provide better economy and safety in operations. A major hindrance to the increase of nuclear reactor performance especially in Pressurized Water Reactors (PWR) is the so called ‘Axial Offset Anomaly (AOA)’. An Axial Offset Anomaly (AOA) is the unexpected change in the core axial power distribution during the operation of a PWR from the predicted distribution. This problem is thought to be occurring because of precipitation and deposition of lithiated compounds such as lithium metaborate (LiBO[subscript]2) on the fuel rod. Due to its intrinsic property, the deposited boron absorbs neutrons thereby affecting the total power distribution in the reactor. AOA is thought to occur when there is sufficient build up of crud deposits on the cladding during subcooled nucleate boiling. Predicting AOA is difficult because there is little information regarding the heat and mass transfer during subcooled nucleate boiling. This thesis describes the experimental investigation that was conducted to study the heat transfer characteristics during subcooled nucleate boiling at prototypical PWR conditions. Pool boiling tests were conducted with varying concentrations of LiBO[subscript]2 and boric acid (H[subscript]2BO[subscript]3) solutions along with deionized water. The experimental data collected includes the effect of coolant concentration, degree of subcooling, system pressure and heat flux on pool boiling heat transfer coefficients. An analysis of deposits formed on the fuel rod during subcooled nucleate boiling is also included in the thesis. The experimental results reveal that the pool boiling heat transfer coefficient is degraded by the presence of boric acid and lithium metaborate in water. At concentration of 5000 ppm in water, the boric acid solution reduced the heat transfer coefficient by 23% and lithium metaborate solution reduced the heat transfer coefficient by 26%.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Axial flow fans used in large-scale air-cooled steam condensers (ACSCs) may operate under distorted inflow conditions. These conditions occur due to the prevailing wind conditions, the presence of buildings, and the location of the fan within the ACSC. Fans located on the periphery of the ACSC are affected the most due to their exposure to strong winds and the inner fans drawing in air past them. Distorted inflow conditions cause varying fan blade and gearbox loading conditions. The purpose of the investigation was to simultaneously measure the inlet air flow and the resultant blade and gearbox loading conditions of a single fan located on the periphery of a large-scale ACSC. Inlet and heat exchanger bundle outlet air flow velocities were measured using a combination of ultrasonic and propeller anemometers while blade loading was measured with strain gauges attached at the neck of the specific blade being monitored. Strain gauges were also attached to the low-speed fan shaft to measure gearbox loading. Measurements were recorded over a period of 8 days where it was found that increased wind resulted in increased air flow in the axial direction of the fan, which then caused a reduction in average blade loading. This was due to a decreased static pressure rise over the fan. The fan blade was found to vibrate at its own natural frequency of 6 Hz when excited by the variable aerodynamic loading. The aerodynamic loading was extracted from the measured data and was found to correlate well with previous experimental work performed by Bredell et al. (2006a). Shaft bending stresses and torque were found to oscillate at the fan’s rotational frequency of 2Hz with a large torque exerted on the shaft during fan start-up. / AFRIKAANSE OPSOMMING: Aksiaalvloeiwaaiers wat by groot lugverkoelde stoomkondensors gebruik word, werk dikwels onder verwronge inlaat lugvloei toestande wat geskied as gevolg van heersende winde, die teenwoordigheid van geboue en die posisie van die waaier in die kondensor. Waaiers wat geleë is op die rand van die kondensor word die meeste beïnvloed as gevolg van blootstelling aan die sterk winde en dwarsvloei wat deur die binneste waaiers geïnduseer word. Verwronge inlaat lugvloei veroorsaak gevolglik variërende waaierlem en ratkas belastingstoestande. Die doel van hierdie ondersoek was om terselfdetyd die inlaat lugvloei asook waaierlem en ratkas belastingstoestande van ’n enkele waaier wat op die rand van ’n grootskaalse lugverkoelde stoomkondensor geleë is, te meet. Waaier inlaat en warmteruiler uitlaat lugvloei snelhede is gemeet met ’n kombinasie van ultrasoniese- en skroefwindsnelheidsmeters terwyl die lem en ratkas belastings gemeet is met rekstrokies. Metings is oor ’n tydperk van 8 dae geneem. Die bevindinge toon dat ’n toename in windsnelheid ’n toename in aksiale lugvloei tempo, deur die waaier veroorsaak. ’n Afname in die gemiddelde lembelasting is waargeneem as gevolg van ’n afname in die waaier statiese druk. Daar is ontdek dat die waaierlem teen ’n natuurlike frekwensie van 6 Hz vibreer wanneer dit opgewek word deur die wisselende aerodinamiese belasting. Die aerodinamiese belasting is verkry uit die gemete data en vergelyk goed met die numeriese werk van Bredell et al. (2006a). Daar is ook bevind dat waaier-as buigspannings en wringkragte ossileer teen die waaier se rotasiefrekwensie van 2Hz met ’n groot wringkrag wat op die as uitgeoefen word wanneer die waaier aangeskakel word. iii