Heterogeneous Objects are engineered with multiple materials to achieve multiple functionalities like high hardness, high toughness and low structural weight. Heterogeneous objects are increasingly used to achieve multiple and often conflicting behaviour within a single object. Developing heterogeneous objects needs computational model for design, analysis and manufacturing. The computational model should map the geometry of the object with the material composition. The most general model is the volume based model that decomposes the geometry exhaustively into simple elements and defines the material distribution over these elements. This approach can model a wide range of objects. However, defining material distribution needs manual intervention to select these elements for material continuity, and to segment or subdivide them for better material approximation. Volume based representation is quite large in size and is cumbersome to edit, query or reuse. Feature based approaches have been proposed to address some of these issues. However, current art can model only limited class of Heterogeneous Objects that includes simple material distribution over complex geometry or complex material distribution over simple geometry. The thesis presents a new method to overcome these limitations. The method, a hybrid of volume based and feature based approaches, allows the user to define the complex material distribution over complex geometries intuitively and represent the same. The complex material distribution is modelled using material reference entities that may be mixed-dimensional, inclusive of non-manifold entities. It uses Medial Axis Transform for automated segmentation of these entities into independent regions, where the material distribution can be intuitively prescribed starting from the entity and terminating at the medial axis. The spatial variation of the material is captured by a parameterized distance field from the material reference entities. It develops new constructive operators to build a complex heterogeneous object model that allows the reuse of the existing heterogeneous object models, automates handling of material continuity, and controls the gradation of the material in the interface of the constituent heterogeneous objects. Constructions using these operators can be geometry driven or material driven i.e. the geometric form controls the material distribution or the material distribution is independent of the geometric form. The proposed representation can be adaptively meshed for generation of mesh in the direction of gradation of the material for finite element analysis and process planning for additive manufacturing. An iso-material contour representation has been proposed for process planning of Heterogeneous Object Models. This avoids the stair case effect by depositing material in the direction of material gradation, and avoids over-deposition or under-deposition due to frequent start and stop of the nozzles. The proposed method has been implemented to show that it can model wide range of heterogeneous objects and can be integrated with additive manufacturing.

Prior to radiation therapy planning, tumours and organs at risk need to be delineated. In recent years, deep learning models have opened the possibility of automating the contouring process, speeding up the procedures and helping clinicians. However, deep learning models, trained using ground truth labels from different clinicians, inevitably incorporate the human-based inter-observer variability as well as other machine-based uncertainties and biases. Consequently, this affects the accuracy of segmentation, representing the primary source of error in contouring tasks. Therefore, clinicians still need to check and manually correct the segmentation and still do not have a measure of reliability. To tackle these issues, researchers have shifted their focus to the topic of probabilistic neural networks and uncertainties in deep learning models. Hence, the main research question of the project is whether a 3D U-Net neural network trained on CT lung cancer images can enhance clinical contouring practice by implementing a probabilistic auto-contouring system. The Monte Carlo dropout technique was employed to generate probabilistic and uncertainty maps. The model calibration was assessed using reliability diagrams, and subsequently, a clinical experiment with a radiation oncologist was conducted. To assess the clinical validity of the uncertainty maps two novel metrics were identified, namely mean uncertainty (MU) and relative uncertainty volume (RUV). The results of this study demonstrated that probability and uncertainty mapping effectively identify cases of under or over-contouring. Although the reliability analysis indicated that the model tends to be overconfident, the outcomes from the clinical experiment showed a strong correlation between the model results and the clinician’s opinion. The two metrics exhibited promising potential as indicators for clinicians to determine whether correction of the predictions is necessary. Hence, probabilistic models revealed to be valuable in clinical practice, supporting clinicians in their contouring and potentially reducing clinical errors.

<p>In rotating detonation engines the turbine inlet conditions may be transonic with unprecedented unsteady fluctuations, very different from those in conventional high-pressure turbines. To ensure an acceptable engine performance, the turbine passages must be unchoked at subsonic and started at supersonic conditions. Additionally, to maximize the aerodynamic performance potential, ad-hoc designs are required, suited for the oscillations in Mach number and flow angle. This manuscript focuses on designing and characterizing diffusive turbine vanes that can operate downstream of a transonic rotating detonation combustor.  </p> <p><br></p> <p>First, the phenomenon of unstarting is presented, concentrating on the effect of pressure loss on the accurate prediction of the starting limit. Afterward, a multi-objective optimization with steady Reynolds Averaged Navier Stokes simulations, including the endwall and 3D vane design, is performed. The results are discussed, highlighting the impact of the throat-to-inlet area ratio on the pressure loss and the geometric features of the top-performing designs. Compared to previous  research on stator passages with contoured endwalls, considerable reductions in pressure loss and stator-induced rotor forcing are obtained, with an extended operating range and preserving high turning.  </p> <p><br></p> <p>Subsequently, the influence of the inlet boundary layer thickness on the vane performance is evaluated, inducing remarkable increases in pressure loss and downstream pressure distortion. Employing an optimization with a thicker inlet boundary layer, specific endwall design recommendations are found, providing a notable improvement in both objective functions. The impact of the geometry variations on flow detachment is assessed as well.</p> <p><br></p> <p>Finally, the impact of the inlet flow angle on the vane design is studied through a multi-point, multi-objective optimization with different inlet angles. The effect of incidence on the flow field and vane performance is evaluated first. Then, by comparing the optimized geometries with those optimized for axial inflows, several design guidelines are identified </p>

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We present an implicit approach for constructing smooth isolated or interconnected 3-D inscribed volumes which can be employed for volumetric modeling of various kinds of spongy or porous structures, such as volcanic rocks, pumice stones, Cancellus bones *, liquid or dry foam, radiolarians, cheese, and other similar materials. The inscribed volumes can be represented in their normal or positive forms to model natural pebbles or pearls, or in their inverted or negative forms to be used in porous structures, but regardless of their types, their smoothness and sizes are controlled by the user without losing the consistency of the shapes. We introduce two techniques for blending and creating interconnections between these inscribed volumes to achieve a great flexibility to adapt our approach to different types of porous structures, whether they are regular or irregular. We begin with a set of convex polytopes such as 3-D Voronoi diagram cells and compute inscribed volumes bounded by the cells. The cells can be irregular in shape, scale, and topology, and this irregularity transfers to the inscribed volumes, producing natural-looking spongy structures. Describing the inscribed volumes with implicit functions gives us a freedom to exploit volumetric surface combinations and deformations operations effortlessly / Graduate

Efficiency improvement is an important aspect to reduce the use of fossil-based fuel in order to achieve a sustainable future. Gas turbines are mainly fossil-fuel based turbomachines, and, therefore, efficiency improvement is still the subject of many on-going research activities in the gas turbine community. This study is incorporated into a research project that investigates design possibilities of efficiency improvement at the high pressure turbine (HPT) stage. In the search for HPT-stage efficiency gains, leading edge (LE) contouring near the endwall is one of the methods found in the published literature that has shown a potential to increase the efficiency by decreasing the amount of secondary losses. The overall objective of the thesis is to contribute to the development of gas turbine efficiency improvements in relation to the HPT stage. Particularly, the influence of the LE fillet on losses and flow structure is investigated concentrating on the secondary flow. The core investigation is of an experimental nature. Detailed investigations of the flow field in an annular sector cascade (ASC) are presented with and without the LE fillet, using a geometric replica of a modern gas turbine nozzle guide vane (NGV) with a contoured tip endwall. Furthermore, a separate investigation is performed on a hub-cooled NGV, which focuses on endwalls, specifically the interaction between the hub film cooling and the mainstream (MS). The experimental investigations indicate that the LE fillet has no significant effect on the flow and energy losses of the investigated NGV. The reason why the LE fillet does not affect the losses might be due to the use of a three-dimensional vane with an existing typical fillet over the full hub and tip profile. Findings also reveal that the complex secondary flow depends heavily on the incoming boundary layer. Oil flow visualisation for the baseline case displays a clear saddle point, with a separation line where the horseshoe (HS) vortex separates into the suction side (SS) and the pressure side (PS), whereas for the filleted case, the saddle point is not noticeable. The investigation of a cooled vane, using a tracer gas carbon dioxide (CO2), reveals that the upstream platform film coolant is concentrated along the SS surfaces and does not reach the PS of the hub surface, leaving it less protected from the hot gas. / För att åstadkomma en uthållig kraftproduktion i framtiden och en minskning i användandet av fossila bränslen är effektivitetsförbättringar av central betydelse. Gasturbiner är i grund och botten fossilbaserade turbomaskiner och därför bedrivs forsknings- och utvecklingsarbete kring verkningsgradsförbättringar. Den här studien ingår i ett forskningsprojekt som undersöker designmodifieringar med målet att höja verkningsgraden för ett högtrycksturbinsteg. Förändringar av bladets eller ledskenans framkantsgeometri nära ändväggarna har i den öppna litteraturen funnits vara en lovande metod för att minska ändväggsförlusterna. Det övergripande målet med denna studie är att bidra till utvecklingen av effektiva högtrycksturbinsteg för gasturbiner. Kärnan i undersökningen är experimentell. Särskilt påverkan från förändring av framkanten på förluster och flödesstruktur undersöks, med fokus på det sekundära flödet. Detaljerade strömningsundersökningar i ett bågformat statorgitter bestående av en geometrisk replika av en stator från en modern gasturbin presenteras, med och utan geometrisk förändring av framkanten. Vidare så genomförs en separat undersökning av en filmkyld ledskena utan framkantsförändring med fokus på interaktionen mellan filmkylningen vid inre ändväggen och huvudflödet. De experimentella undersökningarna visar att den undersökta geometriska förändringen av framkanten inte är av signifikant betydelse för strömningsförlusterna med den studerade ledskenan. Anledningen till att designförändringen inte påverkar förlusterna kan bero på användandet av en tredimensionell ledskena med en existerande typisk kärlradie mellan ledskenan och ändväggarna. Observationerna visar också att den komplexa ändväggsströmningen är starkt beroende av det inkommande gränsskiktets egenskaper. Oljevisualisering för referensledskenan visar en tydlig stagnationspunkt på ändväggen där gränsskiktet delas upp likt en hästskoformation i virvlar på sug- respektive trycksidan av ledskenan. För den modifierade framkanten har ingen tydlig stagnationspunkt på ändväggen observerats. Spårgasundersökningar med den filmkylda ledskenan visar att filmkylningen på den inre plattformen är koncentrerad längs sugsidan och når inte trycksidan på plattformen som därmed är mindre skyddad mot den varma gasströmningen. / QC 20120330