Industry is heavily dependent on the process of combustion and with a projected rapid increase for the demand of combustion-derived energy it is imperative to expose a new age of engineering professionals to the discipline of combustion engineering. One purpose of this study was to modify an existing scaled-down industrial furnace and to retrofit it with the ability to interchange burners for academic application and combustion testing. A number of available industrial burners are presented and their qualities and drawbacks discussed. The modification of an existing scaled-down industrial tunnel furnace is proposed in this work with the objective of providing users with exposure to the control and safe operating strategies associated with industrial combustion. The furnace system simulates a square-shaped tunnel geometry commonly found in industrial applications. A single nozzle mix burner is mounted along the furnace axis and operated with supporting equipment such as a burner control safeguard, a gas train, and an air supply. Details of the furnace are provided in this work. The concept of radiative heat transfer within a combustion enclosure is demonstrated through furnace simulation with Hottel’s Zone Method. / Thesis (Master, Chemical Engineering) -- Queen's University, 2010-07-19 09:50:22.797

Finite element analysis using Cohesive Zone Method (CZM) is a commonly used method to investigate delamination in laminated composites. In this study, two plane strain, zero-thickness six-node quadratic (6-NQ) and four-node linear (4-NL) interface elements are developed to implement CZM. Two main approaches for CZM formulation are categorized as Unified Mode Approach (UMA) and Separated Mode Approach (SMA), and implemented into 6-NQ interface elements to model a double cantilever beam (DCB) test of a unidirectional laminated composite. The results of the approaches are nearly identical. However, it is theoretically shown that SMA spawns non-symmetric tangent stiffness matrices, which may lower convergence and/or overall performance, for mixed-mode loading cases. Next, a UMA constitutive relationship is rederived. The artificial modifications for improving convergence rates such as lowering penalty stiffness, weakening interfacial strength and using 6-NQ instead of 4-NL interface elements are investigated by using the derived UMA and the DCB test model. The modifications in interfacial strength and penalty stiffness indicate that the convergence may be improved by lowering either parameter. However, over-softening is found to occur if lowering is performed excessively. The morphological differences between the meshes of the models using 6-NQ and 4-NL interface elements are shown. As a consequence, it is highlighted that the impact to convergence performance and overall performance might be in opposite. Additionally, benefits of selecting CZM over other methods are discussed, in particular by theoretical comparisons with the popular Virtual Crack Closure Technique. Finally, the numerical solution scheme and the Arc-Length Method are discussed.

Baigiamajame magistro darbe nagrinėjamas gaisro temperatūrų poveikio vertinimas gelžbetoninėms konstrukcijoms. Aptariami standartinio ir natūralaus gaisro parametrai, skaičiavimo pagrindai, vertinimo kriterijai, bendrieji priešgaisrinio projektavimo reikalavimai, tikslai ir metodai. Analizuojamas gaisro poveikis betono ir armatūros mechaninėms, fizikinėms – cheminėms ir šiluminėms savybėms, temperatūros pokyčio įtaka bendram gelžbetonio darbui. Detaliai išnagrinėtas paprastasis skaičiavimo modelis standartinio gaisro veikiamų gelžbetoninių konstrukcijų laikomajai galiai vertinti, aptartos jo prielaidos. Pateikti 500 °C izotermės ir zonų skaičiavimo metodų principai, vertinimai. Išnagrinėti du analitiniai temperatūros pasiskirstymo betoniniame skerspjūvyje metodai, pateikti jų pavyzdžiai. Parodytas gelžbetoninių konstrukcijų projektavimo metodas pagal lentelių duomenis. Tyrimui sumodeliuotas dviaukštis pastatas, kurio pirmame aukšte nagrinėjamas standartinio gaisro temperatūros poveikis ekscentri����kai gniuždomoms gelžbetoninėms kolonoms. Pastatas sumodeliuotas skaičiavimo programa STAAD Pro 2007 tam, kad gautume realias veikiančias apkrovas nagrinėjamiems konstrukciniams elementams. Skaičiavimai atlikti trims kolonoms, kurių paviršius yra skirtingai veikiamas gaisro temperatūros. Skaičiavimai atlikti pagal analitinio temperatūros sklidimo skerspjūvyje modelį bei pagal temperatūrinius laukus pagal EN 1992-1-2. Analogiškai įvertinamas gaisro poveikis gelžbetoniniu... [toliau žr. visą tekstą] / This master thesis considers effect of fire temperatures on reinforced concrete structures. Parameters and mathematical characteristics of standard and natural fire, also objectives and methods of fire engineering is given. Mechanical, physical – chemical properties and behaviour of concrete and reinforcement separately and as composite structure analysed. Details and assumptions of simple calculation model stated. Principles of zone method (method of slices) and 500 °C izotherm (reduced section method) discussed. Two empirical methods examined for calculation of temperatures and heat rise in concrete element, presentation and examples is given. Design of reinforced concrete elements using tabulated data showned. Two – storey building designed using structural design and analysis software STAAD Pro. Building model is portrayed to obtain realistic loads on estimated elements. Calculations of fire resistance performed with three columns differently affected by temperature load. Fire design and analysis performed applying and comparing temperature fields received by calculation using empirical methods and charts given in EN 1992-1-2. Parallel analysis aplied on reinforced concrete columns strengthened with casing. Structure: introduction, literature review, research part, conclusions and suggestions, references. Thesis consist of: 96 p. text without appendixes, 84 pictures, 14 tables, 28 bibliographical entries.

A mathematical model of a steam-methane reformer (SMR) was developed for use in process performance simulations and on-line monitoring of tube-wall temperatures. The model calculates temperature profiles for the outer-tube wall, inner-tube wall, furnace gas and process gas. Reformer performance ratios and composition profiles are also computed. The model inputs are the reformer inlet-stream conditions, the geometry and material properties of the furnace and catalyst-bed. The model divides the furnace and process sides of the reformer into zones of uniform temperature and composition. Radiative-heat transfer on the furnace side is modeled using the Hottel Zone method. Energy and material balances are performed on the zones to produce non-linear algebraic equations, which are solved using the Newton-Raphson method with a numerical Jacobian. Model parameters were ranked from most-estimable to least estimable using a sensitivity-based estimability analysis tool, and model outputs were fitted to limited data from an industrial SMR. The process-gas outlet temperatures were matched within 4 ºC, the upper and lower peep-hole temperatures within 12 ºC and the furnace-gas outlet temperature within 4 ºC. The process-gas outlet pressure, composition and flow rate are also accurately matched by the model. The values of the parameter estimates are physically realistic. The model developed in this thesis has the capacity to be developed into more specialized versions. Some suggestions for more specialized models include modeling of separate classes of tubes that are in different radiative environments, and detailed modeling of burner configurations, furnace-gas flow patterns and combustion heat-release patterns. / Thesis (Master, Chemical Engineering) -- Queen's University, 2009-01-06 21:50:35.04

Les solutions solides appartenant au système quasi-ternaire BaTiO3-CaTiO3-BaZrO3 (BCTZ) sont des candidates prometteuses pour les piézoélectriques sans plomb. Ce travail de thèse expérimental est consacré à la cristallogenèse et à la caractérisation de différents monocristaux dans le système BCTZ : BaZrO3, CaTiO3 ainsi que les solutions solides Ba1-xCaxTi1-yZryO3 présentant des teneurs en zirconium (Zr) et en calcium (Ca) proches de celles de la composition Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 (BZT-50BCT) où les performances piézoélectriques sont exacerbées.Les monocristaux de CaTiO3 et de BaZrO3 ont été obtenus à la fois depuis une solution à haute température par la méthode du flux et à partir de leur phase fondue par la technique de la zone flottante optique. Dans le cas de CaTiO3 obtenu dans un four à image à 1975°C, l'aluminium (Al), le magnésium (Mg) et le baryum (Ba) ont été détectés comme étant les principales impuretés. Les spectres Raman de CaTiO3 sont en bon accord avec les spectres référencés dans la littérature. La croissance cristalline de BaZrO3 est beaucoup plus difficile à cause de son point de fusion très élevé (2700°C). Le flux BaB2O4 a été utilisé avec succès pour faire croitre des cristaux d’environ 150-200μm à 1350°C, soit à la moitié de son point de fusion. Des boules de BaZrO3 de taille centimétrique ont également été obtenues à partir de la phase fondue en four à image. Les impuretés majoritaires telles le strontium (Sr), l’hafnium (Hf), le calcium (Ca) et le titane (Ti) ont été détectées par GDMS et SIMS dans une gamme de concertation atomique de 0.3-0.5%. L’énergie de gap optique est d'environ 4,8 eV et souligne la grande qualité des cristaux de BaZrO3 obtenus en four à image. Les propriétés diélectriques à basse température de BaZrO3 confirment l'absence de transition de phase structurelle. Les études de Raman révèlent que même si BaZrO3 n'a pas de transition de phase à basse température, il présente une transition de phase cubique-quadratique sous haute pression à 11GPa à température ambiante.Dans la deuxième partie de cette thèse, des monocristaux centimétriques de BCTZ ont été obtenus avec succès par la croissance en flux. Les profils de concentrations en Ca et Zr le long des boules indiquent que leurs coefficients effectifs de ségrégation dépendent fortement de leur concentration initiale dans la solution liquide. Ceux-ci évoluent considérablement au cours du processus de cristallogenèse, rendant ainsi la croissance de BCTZ très délicate en vue d’obtenir des compositions constantes et proches de celles de la région de convergence de phases. De plus, une décomposition spinodale a été mise en évidence, indiquant la coexistence de deux solutions solides de compositions proches au sein des cristaux de BCTZ. Les propriétés diélectriques et piézoélectriques des cristaux obtenus ont été déterminées et présentent des caractéristiques allant du ferroélectrique classique au relaxeur. Les mesures diélectriques montrent notamment une double boucle d'hystérésis (PE) anormale qui disparaît après polarisation. / Solid solutions belonging to BaZrO3–BaTiO3–CaTiO3 (BCTZ) pseudo-ternary system are promising candidates for lead-free piezoelectrics. This thesis aims at growing and characterizing various single crystals of the BCTZ system: the end members BaZrO3 and CaTiO3 as well as Ba1-xCaxTi1-yZryO3 solid solution compounds with zirconium (Zr) and calcium (Ca) contents close to Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 composition (BZT-50BCT) where high piezoelectric performances are expected.CaTiO3 and BaZrO3 single crystals were both grown from high temperature solution by the flux method and from the melt by the optical floating zone technique. In the case of CaTiO3 grown with a mirror furnace at 1975°C, aluminum (Al), magnesium (Mg) and barium (Ba) as main impurities were detected. The Raman spectra of CaTiO3 are in good agreement with the spectra referenced in the literature. The growth of BaZrO3 was more challenging because of its very high melting point (2700°C). BaB2O4 flux was successfully used to produce 150-200 μm-sized BaZrO3 crystals at half its melting point (1350°C) and bulk centimeter-sized BaZrO3 boules were grown from the melt. Sr, Hf, Ca and Ti were detected by GDMS and SIMS as main impurities in the range of 0.3-0.5 at.%. The optical band gap is found to be ~4.8 eV and indicates the high quality of the BaZrO3 crystals grown with mirror furnace. Low temperature dielectric properties of BaZrO3 are displayed and confirmed the absence of structural phase transition. Raman investigations reveal that even though BaZrO3 does not have any phase transition at low temperatures, it exhibits a high-pressure phase transition from cubic to tetragonal at 11GPa at room temperature.In the second part, BCTZ centimeter-sized single crystals have been successfully grown by the top seeded solution growth technique. Ca and Zr content profiles throughout the as-grown boules indicate that their effective segregation coefficients are highly dependent on their initial concentration in the liquid solution. Concentrations evolve substantially during the crystal growth, making the BCTZ crystal growth a tricky issue when a narrow compositions range is targeted, as in the vicinity of the phase convergence region. Furthermore, spinodal decomposition was observed, indicating the coexistence of two solid solutions with close compositions in BCTZ crystals. Dielectric and piezoelectric properties were measured for some crystals, which were found to display a variety of behavior form relaxor to pure ferroelectric. In addition, an abnormal double-like PE hysteresis loop was observed, that was associated to an irreversible effect disappearing upon poling.

The diploma thesis deals with the analysis of internal forces and the design of the reinforcement of a reinforced concrete monolithic slab, a reinforcing wall and a column in the 1st floor of a dairy hall building. The fire resistance of selected structures was taken into account during dimensioning. The calculation of the internal forces was performed by the finite element method in Dlubal RFEM 5.24.

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<p dir="ltr">This work focuses on the fracture behavior and failure mechanisms of Prepreg Platelet Molded Composites (PPMCs), which are characterized by meso-structural variability. The study investigates the interlaminar fracture toughness of PPMCs using both experimental and computational approaches, with a particular focus on Mode-I fracture testing. Cohesive zone models are developed to simulate interfacial behavior in composite laminates. The research introduces the concept of the platelet critical length problem and explores how platelet geometry, arrangement, and meso-structural features affect fracture toughness and energy absorption. Findings indicate that smaller platelets enhance fracture toughness through mechanisms like platelet bridging and crack deflection, while larger platelets provide more consistent fracture properties but exhibit greater variability in stiffness. This work offers valuable insights for optimizing PPMC performance in high-performance applications.</p>

The main goal of our thesis is to understand qualitative properties of solutions to the Cauchy problem for the semi-linear wave model with time-dependent speed and dissipation. We greatly benefited from very precise estimates for the corresponding linear problem in order to obtain the global existence (in time) of small data solutions. This reason motivated us to introduce very carefully a complete description for classification of our models: scattering, non-effective, effective, over-damping. We have considered those separately.