The discussion in this paper focuses on how boundary based smooth shape design can be carried out. For this we treat surface generation as a mathematical boundary-value problem. In particular, we utilize elliptic Partial Differential Equations (PDEs) of arbitrary order. Using the methodology outlined here a designer can therefore generate the geometry of shapes satisfying an arbitrary set of boundary conditions. The boundary conditions for the chosen PDE can be specified as curves in 3-space defining the profile geometry of the shape. We show how a compact analytic solution for the chosen arbitrary order PDE can be formulated enabling complex shapes to be designed and manipulated in real time. This solution scheme, although analytic, satisfies exactly, even in the case of general boundary conditions, where the resulting surface has a closed form representation allowing real time shape manipulation. In order to enable users to appreciate the powerful shape design and manipulation capability of the method, we present a set of practical examples

Aggregate shape and texture are important parameters that have a direct influence on the strength and durability of the asphalt and concrete products made from these materials. Shape is characterized in terms of elongated and flat particles. Typically, a given batch of material is rejected if more than a specific percentage of particles have elongation and flatness ratios which exceed some limiting value. Present procedures for determining these ratios rely heavily on manual measurements which are time consuming and limit the sample size. A recently developed rapid shape analysis system can significantly reduce the time required for this procedure. The new system can determine elongation and flatness for a standard batch of 100 particles in under 10 minutes. The system consists of a PC-based image analyzer. Samples of crushed stone are imaged by two video cameras and the images are processed by the computer to determine the flatness and elongation distributions within the sample. Validation procedures indicate an excellent agreement between the rapid analysis system and standard manual techniques. Additionally, the system can provide two quantitative measures of particle roughness which are not measurable by current manual techniques. Preliminary analysis of shape distributions from a sampling campaign indicate that it is possible to determine the effects of crusher type and material type on shape by examining the feed and product shape distributions. Introductory work with manufactured sands indicates that the analyzer can effectively measure all four shape attributes, none of which can currently be measured by manual techniques. / Master of Science

Shape memory alloys (SMA) have the unique ability to recover large strains and generate large recovery stresses via a repeatable martensitic transformation. Stress-strain and shape memory effect characteristics are needed in order to develop SMA force actuator design methods. Moreover, constitutive models able to quantitatively predict these characteristics and thus be useful as engineering design tools are also needed. An experimental apparatus designed to characterize the mechanical behavior of SMA was built and utilized. The apparatus is used specifically to gather stress-strain and shape memory effect characteristics from nitinol wire whereby mechanical properties associated with the material are determined. Phenomena such as the R-phase and stress induced martensite serration are investigated. A one-dimensional constitutive model is presented that quantitatively predicts stress-strain and shape memory effect behavior and was developed with the intention of being an engineering design tool for SMA force actuators. Experimental stress-strain and shape memory effect results are compared against that predicted by the model with the intention of verifying the model. The model displays the ability to predict stress-strain behavior that is in good quantitative agreement with experiment. The model also displays the ability to predict hysteric shape memory effect behavior for free, controlled, and restrained recovery cases of selected prestrains that is in good quantitative agreement with experiment. The model is unable to predict shape memory effect behavior such as the R-phase. Demonstrating the ability to experimentally investigate a constitutive model will hopefully inspire further combined experimental and theoretical SMA research. / Master of Science

The design of unmanned underwater vehicle (UUV) was inspired by the form and functionality of Jellyfish. These natural organisms were chosen as bio-inspiration for a multitude of reasons including: efficiency, good room for payload, and a wide range of sizes and morphology. Shape memory alloy (SMA) actuators were selected as the primary source of actuation for the propulsion of the artificial jellyfish node. These actuators offer high power density which enables a compact system size and silent operation which is preferred for surveillance.  SMA wires mimic the form and function of natural muscles; allowing for a wider range of applications than conventional actuators. Commercial SMA wires (100 um in diameter) can exhibit a 4% deformation of the initial actuator length with a blocking stress of over 200 MPa. The deformation of SMA wire is not enough to mimic the bell contraction of jellyfish. In order to resolve this problem, a beam-shape composite actuator using SMA wires as the active component, termed as BISMAC, was designed to provide large curvature. The BISMAC design was inspired by rowing jellyfish bell contraction. Characterization of maximum deformation in underwater conditions was performed for different actuator configurations to analyze the effect of design parameters that include silicone thickness, flexible steel thickness and distance between SMA and flexible steel. A constant cross-section (CC) BISMAC of 16 cm in length was found to achieve deformation with a radius of curvature of 3.5 cm. Under equilibrium conditions, the CC-BISMAC was found to achieve 80% of maximum deformation consuming 7.9 J per cycle driven at 16.2 V/0.98 A and frequency of 0.25 Hz. Using the a developed analytical model, an actuator design was fabricated mimicking the maximum deformation profile of the A. aurita. The optimized AA-BISMAC achieved a maximum curvature of 0.428 1/cm as compared to 0.438 1/cm for the A. aurita with an average squared root error of 0.043 (1/cm), 10.2% of maximum A. aurita curvature.   BISMAC actuators are unidirectional flexible actuators capable of exhibiting high curvature. To extend the application range of these actuators, they were modified to achieve bidirectional deformation. The new bidirectional actuators termed as "BiFlex" actuators had the capability to achieve large deformation in two directions. The FlexLegs consist of six segments which can be actuated individually. Two different sets of legs were constructed to determine the effect of size. The small legs measured 35.8 mm in height and 63.2 mm in width and the large legs were 97.4 mm in height and 165.4 mm in width. The small FlexLegs achieved a maximum deformation of 12 % and 4 % in the x- and y-direction respectively using a power of 0.7 W while producing a maximum force of 0.023 N. They were also able to withstand a load of 1.18 N. The large FlexLegs had a maximum deformation of 57 % and 39 % in the x- and y-direction respectively using a power of 3 W while producing a force of 0.045 N. They were able to withstand a load of 0.25 N. The legs were also able to perform several walking algorithms consisting of stepping, crabbing and yawing. In order to reduce the power consumption and contraction time of SMA wires, a feedback control scheme using wire resistance was developed. The controller required the knowledge of threshold resistance and safe current inputs which were determined experimentally. The overheating effect of SMA wires was analyzed for BioMetal Fiber (BMF) and Flexinol 100 "m diameter wires revealing an increase in resistance as the wires overheated. The controller was first characterized on a SMA wire with bias spring system for a BMF 100 using I_hi=0.5 A and I_low=0.2 A, where hi corresponds to peak current for fast actuation and low corresponds to the safe current which prevents overheating and maintains desired deformation. A contraction of 4.59% was achieved in 0.06 s using the controller and the deformation was maintained for 2 s at low current. The BISMAC actuator was operated using the controller with I_hi=1.1 A and I_low=0.65 A achieving a 67% decrease in contraction time compared to using a constant driving current of I_low=0.2 A and a 60% decrease in energy consumption compared to using constant I_hi=0.5 A while still exceeding the contraction requirements of the Aurelia aurita. Two fundamental parameters at the composition level were associated with the power consumption of SMA: i) martensite to austentite phase transition temperature and ii) thermal hysteresis. Ideally, one would like to reduce both these quantities and for this purpose an equiatomic Ni-Ti alloy was modified with Cu. Replacing nickel with 10 at% copper reduces the thermal hysteresis by 50% or more. For Ni-Ti alloys with nickel content greater than 50 at%, transition temperature decreases linearly at a rate of 100 "C/Ni at%. Given these two power reducing factors, an alloy with composition of Ni40+xTi50-xCu10 was synthesized with x = 0, ±1, ±2, ±3, ±4, ±5. Metal powders were melted in an argon atmosphere using an RF induction furnace to produce ingots. All the synthesized samples were characterized by differential scanning calorimetric (DSC) analysis to reveal martensite to austenite and austenite to martensite transition temperatures during heating and cooling cycles respectively. Scanning electron microscopy (SEM) was conducted to identify the density and microstructure of the fractured samples. The results show the possibility of achieving low power consuming high performance SMAs. Using the BISMAC actuator and feedback control system, a robotic jellyfish called Robojelly that mimics the morphology and kinematics of the Aurelia aurita species was created. A systematic fabrication technique was developed to replicate the essential structural features of A. aurita. Robojelly's body was fabricated from RTV silicone having a total mass of 242 g and bell diameter of 16.4 cm. Robojelly was able to generate enough thrust in static water conditions to propel itself and achieve a proficiency of 0.19 s-1 while the A. aurita achieves a proficiency of around 0.25 s-1. A thrust analysis based on empirical measurements for natural jellyfish was used to compare the performance of the different robotic configurations. The configuration with best performance was a Robojelly with segmented bell and a passive flap structure. Robojelly was found to consume an average power on the order of 17 W with the actuators not having fully reached thermal steady state. A comparative kinematics analysis was conducted between a natural Aurelia aurita and Robojelly. The resistance feedback controller was implemented to tailor the deformation profile of BISMAC actuators embedded in Robojelly. Robojelly's performance was quantified in terms of thrust production and power consumption during vertical swimming experiments. A maximum average instantaneous thrust production of 0.006 N was achieved at a driving current (Ihi) of 1.5 A with 35% duty cycle. Rapid heating of SMA wires was found to reduce power consumption and increase thrust. The bell kinematic analysis revealed resemblance and differences in bell deformation trajectories of the biomimetic and natural jellyfish. The inflexion point of the A. aurita was found to convert an inner bell trajectory into an outer one during contraction which assists the thrust production. A biomimetic robot inspired by Cyanea capillata, termed as "Cyro", was developed to meet the functional demands of underwater surveillance in defense and civilian applications. The design of Cyro required kinematics of large C. capillata which are elusive creatures. Obtaining accurate kinematic data of animals is essential for many biological studies and bio-inspired engineering applications. Many animals such as the C. capillata however, are either too large or too delicate to transport to controlled environments where accurate kinematic data can easily be obtained. Often, in situ recordings are the only means available but are often subject to multi-axis motion and relative magnification changes with time, which lead to large discrepancies in animal kinematics. In Chapter 5, techniques to compensate for magnification and body rotation of animal footage were developed. A background reference point and animal dimensions were used to account for magnification. A linear fit of body points were used to measure body rotation. These techniques help resolve animal kinematics from in situ video footage. The techniques were applied to a large jellyfish, Cyanea capillata, swimming in ocean waters. The bell kinematics were captured by digitizing exumbrella profiles for two full swimming cycles. Magnification was accounted for by tracking a reference point on the ocean floor and by tracking the C. capillata exumbrella arclength in order to have a constant scale through the swimming cycles. A linear fit of the top bell portion was used to find the body angle with respect to the camera coordinate system. Bell margin trajectories over two swimming cycles confirm the accuracy of the correction techniques. The corrected profiles were filtered and interpolated to provide a set of time-dependent points along the bell. The ability to use in situ footage with significant multi-axis motion provides an opportunity to analyze previously impractical footage for gaining a better understanding of large or delicate organisms. The swimming kinematics of the C. capillata were analyzed after extracting the required kinematics from the in situ video. A discrete model of the exumbrella was developed and used to analyze the kinematics. The exumbrella discretization was done using three different methods. The first method consists of analyzing the animal anatomy for structural and mechanical features. The second method consists of analyzing the bell kinematics for areas of highest deformation over time. The third method consists of optimizing node locations that can provide minimal error with comparison to the digitized profiles. Two kinematic models of the C. capillata swimming motion were developed by fitting Fourier series to the discretized segments and angles formed by each segment. The four-segment anatomical kinematic model was used to analyze the bell kinematics of the C. capillata. It was found that the bell does not deform uniformly over time with segments lagging behind others. Hysteresis between contraction and relaxation was also present through most of the exumbrella. The bell margin had the largest hysteresis with an outer path during contraction and inner path during relaxation. The subumbrella volume was approximated based on the exumbrella kinematics and was found to increase during contraction. Cyro was designed to mimic the morphology and swimming mechanism of the natural counterpart. The body of the vehicle consists of a rigid support structure with linear DC motors which actuate eight mechanical arms. The mechanical arms in conjunction with artificial mesoglea create the hydrodynamic force required for propulsion. The full vehicle measures 170 cm in diameter and has a total mass of 76 kg. An analytical model of the mechanical arm kinematics was developed. The analytical and experimental bell kinematics were analyzed and compared to the C. capillata. Cyro reached the water surface untethered and autonomously from a depth of 182 cm in five actuation cycles. It achieved an average velocity of 8.47 cm/s while consuming an average power of 70 W. A thrust stand was developed to calculate the thrust directly from a single bell segment yielding an average thrust of 27.9 N for the whole vehicle. Steady state velocity during Cyro's swimming test was not reached but the measured performance during its last swim cycle resulted in a cost of transport of 10.9 J/kg m and total efficiency of 3%. It was observed that a passive flexible margin or flap, drastically increases the performance of the Robojelly. The effects of flap length and geometry on Robojelly were analyzed using PIV. The flap was defined as the bell section which is located between the flexion point and bell margin. The flexion point was established as the location where the bell undergoes a significant change compliance and therefore in slope. The flap was analyzed in terms of its kinematics and hydrodynamic contribution. An outer trajectory is achieved by the flap margin during contraction while an inner trajectory is achieved during relaxation. The flap kinematics was found to be replicable using a passive flexible structure. Flaps of constant cross section and varying lengths were put on the robotic vehicle to conduct a systematic parametric study. Robojelly's swimming performance was tested with and without a flap. This revealed a thrust increase 1340% with the addition of a flap.  Velocity field measurements were performed using planar Time Resolved Digital Particle Image Velocimetry (TRDPIV) to analyze the change in vortex structures as a function of flap length.  The robot input parameters stayed constant over the different configurations tested thus maintaining a near constant power consumption. Non-dimensional circulation results show a dependence on flap kinematics and geometry. The robot was approximated as a series of pitching panels circularly oriented around its apex. The first circulation peak of the pitching panel approximation revealed a normalized standard deviation of 0.23. A piston apparatus was designed and built to test different flexible margin configurations. This apparatus allow the isolation of the flap parameters and remove the uncertainties coming from the robotic vehicle. / Ph. D.

The invention of shape memory alloys spurred a period of intense interest in the area of heat engines in the late 70's and early 80's. It was believed that these engines could use heat from low temperature sources such as solar heated water, geothermal hot water and rejected heat from conventional engines as a significant source of power. The interest has since dwindled, largely because small prototype devices developed in the laboratory could not be scaled up to produce significant power. It is believed that the scaled-up designs failed because they were dependent on friction as the driving mechanism, which led to large energy losses and slip. This thesis proposes a new chain and sprocket driving mechanism that is independent of friction and should therefore allow for large-scale power generation. This thesis begins by presenting properties and applications of shape memory alloys. The proposed design is then described in detail, followed by a review of the evolution that led to the final design. A brief chapter on thermodynamic modeling and a summary chapter suggesting improvements on the current design follow. / Master of Science

Numerical noise is a prevalent concern in many practical optimization problems. Convergence of gradient based optimization algorithms in the presence of numerical noise is not always assured. One way to improve optimization algorithm performance in the presence of numerical noise is to adjust the method of gradient computation. This study investigates the use of Continuous Sensitivity Equation (CSE) gradient approximations in the context of numerical noise and optimization. Three problems are considered: a problem with a system of ODE constraints, a single parameter flow problem constrained by the Navier-Stokes equations, and a multiple parameter flow problem constrained by the Navier-Stokes equations. All three problems use adaptive methods in the simulation of the constraint and are numerically noisy. Gradients for each problem are computed with both CSE and finite difference methods. The gradients are analyzed and compared. The two flow problems are optimized with a trust region optimization algorithm using both sets of gradient calculations. Optimization results are also compared, and the CSE gradient approximation yields impressive results for these examples. / Master of Science

Tesis por compendio / Sus1 is a conserved protein involved in chromatin remodeling and mRNA biogenesis. The SUS1 gene of Saccharomyces cerevisiae is unusual, as it contains two introns and is alternatively spliced, retaining one or both introns in response to changes in environmental conditions. SUS1 splicing may allow the cell to control Sus1 expression, but the mechanisms that regulate this process remain unknown. In this thesis project, we have investigated whether the structure adopted by SUS1 RNA sequences contributes to regulate the splicing of this gene. Using in silico analyses together with NMR spectroscopy, gel electrophoresis and UV thermal denaturation experiments, we first show that the downstream intron (I2) of SUS1 forms a weakly-stable, 37-nucleotide stem-loop structure containing the branch site near its apical loop and the 3' splice site after the stem terminus. A cellular assay revealed that two of four mutants containing altered I2 structures had significantly impaired SUS1 expression. Semi-quantitative RT-PCR experiments indicated that all mutants accumulated unspliced SUS1 pre-mRNA and/or induced distorted levels of fully spliced mRNA relative to wild-type. Concomitantly, Sus1 cellular functions in histone H2B deubiquitination and mRNA export were affected in I2 hairpin mutants that inhibited splicing. The second part of the thesis project focuses on the exon located between the two introns of the SUS1 gene. This middle exon (E2) can be skipped during splicing, is generated in circular form, and has been found to influence the splicing of the flanking introns, an unusual situation in budding yeast where splicing mainly relies on intron recognition. Using NMR spectroscopy, gel electrophoresis, UV thermal denaturation and ribose 2'-OH modification experiments combined with computational predictions, we show that E2 of SUS1 comprises a conserved double-helical stem topped by a three-way junction. One of the hairpins emerging from the junction exhibited significant thermal stability and was closed by an unusually structured purine-rich loop. This loop contained two consecutive sheared G:A base pairs and was structurally related to the substrate loop of the VS ribozyme. Cellular assays revealed that three mutants containing altered E2 structures had impaired SUS1 expression and that a compensatory mutation restoring the conserved stem recovered expression to wild-type levels. Semi-quantitative RT-PCR experiments indicated that all mutants were capable of altering the quantities of unspliced and/or fully-spliced SUS1 RNA transcripts relative to wildtype. Overall, the results gathered in this thesis project indicate that RNA structures formed by the middle exon and the second intron of the S. cerevisiae SUS1 gene are relevant for splicing and also influence other processes of SUS1 mRNA biogenesis. / Sus1 es una proteína conservada implicada en remodelación de cromatina y biogénesis de moléculas de ARNm. El gen SUS1 de Saccharomyces cerevisiae es peculiar, ya que contiene dos intrones y sufre un proceso de ayuste (corte y empalme) alternativo, reteniendo uno o ambos intrones en respuesta a cambios en las condiciones ambientales. El ayuste del ARNpre-m de SUS1 puede permitir a la célula controlar la expresión de la proteína Sus1, pero los mecanismos que regulan este proceso son poco conocidos. En este proyecto de tesis hemos investigado si la estructura adoptada por secuencias de ARN de SUS1 contribuye a regular el proceso de ayuste de este gen. Utilizando análisis in silico junto con espectroscopia de RMN, electroforesis en gel y experimentos de desnaturalización térmica monitorizados por UV, primero demostramos que el ARN del segundo intrón (I2) del gen SUS1 forma una horquilla débilmente estable de 37 nucleótidos. Esta horquilla contiene nucleótidos del sitio de ramificación (branch site) en su bucle apical y nucleótidos del sitio 3' de empalme adyacentes al extremo inferior del tallo. A través de ensayos funcionales descubrimos que dos de cuatro mutantes que alteran la estructura de la horquilla I2 exhibían peor expresión de SUS1. Experimentos de RT-PCR semicuantitativos indicaron que todos los mutantes acumularon ARNpre-m SUS1 no ayustado y/o indujeron cambios en los niveles de ARNm maduro con respecto a la secuencia silvestre. Además, las funciones celulares de Sus1 relativas a desubicuitinación de histona H2B y transporte de ARNm se vieron afectadas en los mutantes de la horquilla I2 que inhibían el proceso de ayuste. La segunda parte de la memoria de tesis se centra en el análisis del exón central (E2) situado entre los dos intrones del gen SUS1. Este exón puede eliminarse durante el proceso de ayuste, se genera en forma circular, e influye en el procesamiento de los intrones adyacentes, una situación inusual para las regiones exónicas de S. cerevisiae, donde el ayuste se basa principalmente en el reconocimiento de intrones. Utilizando experimentos de espectroscopía de RMN, electroforesis en gel, desnaturalización térmica y modificación química combinados con predicciones computacionales, demostramos que el ARN del exón E2 de SUS1 forma un tallo conservado de doble hélice coronado por una intersección de tres hélices. Una de las horquillas que emergen de esta intersección presentó una estabilidad térmica significativa, así como un bucle apical rico en purinas inusualmente estructurado. Este bucle contiene dos pares de bases G:A consecutivos y está estructuralmente relacionado con el bucle de substrato de la ribozima VS. Ensayos celulares revelaron que tres mutantes con estructuras modificadas de E2 exhibían peor expresión de SUS1, y que una mutación compensatoria que restauraba el tallo conservado recuperaba la expresión a los niveles de la secuencia silvestre. Experimentos de RT-PCR semicuantitativos indicaron que todos los mutantes de E2 eran capaces de alterar las cantidades de transcritos ayustados y no ayustados de SUS1 con respecto a la secuencia silvestre. En general, los resultados obtenidos en este proyecto de tesis indican que las estructuras de ARN formadas por el exón central y el segundo intrón del gen SUS1 de S. cerevisiae son relevantes para el ayuste y otros procesos implicados en la biogénesis del ARNm del gen SUS1. / Sus1 és una proteïna conservada implicada a la remodelació de la cromatina i la biogènesi de l'ARNm. El gen SUS1 de Saccharomyces cerevisiae és inusual, ja que conté dos introns i s'empalma de manera alternativa, retenint un o ambdós introns en resposta a canvis en les condicions ambientals. L'empalmament de SUS1 pot permetre a la cèl·lula controlar l'expressió de Sus1, però els mecanismes que regulen aquest procés són segueixen sent desconeguts. En aquest projecte de tesi investiguem si l'estructura adoptada per seqüències d'ARN de SUS1 contribueix a regular l'empalmament d'aquest gen. Emprant anàlisi in silico juntament amb espectrometria de RMN, electroforesi en gel i experiments de desnaturalització tèrmica d'UV, es mostra primer que l'intró aigües a baix (I2) de SUS1 forma una estructura de forqueta de 37 nucleòtids feblement estable que conté el lloc de la branca a prop del seu bucle apical; i el lloc d'empalmamnet 3¿ després de l'extrem de la forqueta. Un assaig cel·lular va revelar que dos de quatre mutants que contenien estructures alterades de l'I2 havien modificat significativament l'expressió de SUS1. Els experiments semi-quantitatius de RT-PCR van indicar que tots els mutants acumulaven el pre-ARNm madur respecte al tipus salvatge. Concomitantment, les funcions cel·lulars de Sus1 a la desubiqüitinació de la histona H2B i l'exportació d'ARNm es van veure afectats als mutants de la forqueta d'I2 que inhibeixen l'empalmament. La segona part del projecte de tesi se centra a l'exó situat entre els dos introns del gen SUS1. Aquest exó (E2) es pot ometre durant l'empalmament, es genera amb forma circular, i s'ha trobat que influeix a l'empalmamet dels introns que flanquegen, una situació inusual al llevat on l'empalmament està basat principalment al reconeixement d'introns. Emprant espectroscòpia de RMN, electroforesi en gel, desnaturalització tèrmica d'UV i experiments de modificació de ribosa 2¿-OH combinats amb prediccions computacionals, mostrem que E2 de SUS1 comprén un tall conservat de doble hèlix corornat per una unió de tres vies. Una de les forquetes que emergeixen de la unió, va mostrar una estabilitat tèrmica significativa i va ser tapada per un bucle ric en purina inusualment estructurat. Aquest bucle contenia dos pars de bases G:A tallats consecutivament i estava estructuralment relacionat amb el bucle de substrat del ribozim VS. Els assajos cel·lulars van revelar que tres mutants que contenien estructures alterades de E2 havien alterat l'expressió de SUS1 i que una mutació compensatòria que restaurava el tall conservat recuperava l'expressió a nivells del tipus salvatge. Els assajos cel·lulars van revelat que tres mutants que contenien estructures alterades d'E2 havien alterat l'expressió de SUS1 i que una mutació compensatòria que restaurava el tall conservat recuperava l'expressió a nivell d'un tipus salvatge. Els experiments semi-quantitatius de RT-PCR van indicar que tots els mutants eren capaços d'alterar les quantitats de transcrits d'ARN de SUS1 no empalmats i/o empalmats en relació amb el tipus salvatge. En general, els resultats obtinguts en aquesta investigació indiquen que les estructures d'ARN formades per l'exó mitjà i el segon intró de SUS1 de S. cerevisiae són rellevants per l'empalmament i també influeixen a altres processos de biogènesi de l'ARN de SUS1 / Abuqattam, AN. (2017). IDENTIFICATION OF RNA STRUCTURES MODULATING THE EXPRESSION OF THE mRNA BIOGENESIS FACTOR SUS1 [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90524 / Compendio

While computational fluid dynamics (CFD) simulations are an indispensable tool in modern aerospace engineering design, they bear a severe computational burden in applications where simulation results must be found quickly or repeatedly. Therefore, creating computationally inexpensive models that can capture complex fluid behaviors is a long-sought-after goal. As a result, methods to construct these reduced order models (ROMs) have seen increasing research interest. Still, parameter dependent high-speed flows that contain shock waves are a particularly challenging class of problems that introduces many complications in ROM frameworks. To make approximations in a linear space, ROM techniques for these problems require that basis functions are transformed such that discontinuities are aligned into a consistent reference frame. Techniques to construct these transformations, however, fail when the topology of shocks is not consistent between data snapshots. In this work, we first identify key features of these topology changes, and how that constrains transformations of this kind. We then construct a new modeling framework that can effectively deal with shockwave interactions that are known to cause failures. The capabilities of the resulting model were evaluated by analyzing supersonic flows over a wedge and a forward-facing step. In the case of the forward-facing step, when shock topology changes with Mach number, our method exhibits significant accuracy improvements. Suggestions for further developments and improvements to our methodology are also identified and discussed / Master of Science / While computational fluid dynamics (CFD) simulations are an indispensable tool in modern aerospace engineering design, they bear a severe computational burden in applications where simulation results must be found quickly or repeatedly. Therefore, creating computationally inexpensive models that can capture complex fluid behaviors is a long-sought-after goal. As a result, methods to construct these reduced order models (ROMs) have seen increasing research interest. Still, high-speed flows that contain shock waves are a particularly challenging class of problems that introduces many complications in ROM frameworks. First, we identify some of the common failure modes in previous ROM methodologies. We then construct a new modeling framework that can effectively deal with shockwave interactions that are known to cause these failures. The capabilities of the resulting model were evaluated by analyzing supersonic flows over a wedge and a forward-facing step. In cases where previous modeling frameworks are known to fail, our method exhibits significant accuracy improvements. Suggestions for further developments and improvements to our methodology are also identified and discussed.

Yes / Individual radial frequency (RF) patterns are generated by modulating a circle's radius as a sinusoidal function of polar angle and have been shown to tap into global shape processing mechanisms. Composite RF patterns can reproduce the complex outlines of natural shapes and examining these stimuli may allow us to interrogate global shape mechanisms that are recruited in biologically relevant tasks. We present evidence for a global shape aftereffect in a composite RF pattern stimulus comprising two RF components. Manipulations of the shape, location, size and spatial frequency of the stimuli revealed that this aftereffect could only be explained by the attenuation of intermediate-level global shape mechanisms. The tuning of the aftereffect to test stimulus size also revealed two mechanisms underlying the aftereffect; one that was tuned to size and one that was invariant. Finally, we show that these shape mechanisms may encode some RF information. However, the RF encoding we found was not capable of explaining the full extent of the aftereffect, indicating that encoding of other shape features such as curvature are also important in global shape processing. / This research was supported by a Biotechnology and Biological Sciences Research Council (BBSRC) grant #BB/L007770/1.

There are often discrepancies in how a product is perceived in different representation media employed in typical product development processes. The first goal of this research project was to determine how visual illusions influence a designer's perception of a product across three representations: industrial design sketches, computer aided design (CAD) models, and physical prototypes (FDM rapid prototyping). A visualization experiment was conducted in which participants were asked to report how they perceived the shape and size of certain features, representing two types of illusions across the three model representations. Their statements were analyzed to identify the trends of how these two illusions affect overall appearance, categorized by representation type and the users' backgrounds (i.e., specialization and years of experience). The participants included students and professionals with various levels of engineering and industrial design experience. The analysis shows that there are differences in how designers see models depending on the representation media, and to some degree depending on the participants' professional background. The second goal was to explore the process of identifying such illusions automatically during the design process. In this regard, a discussion on how to implement the results from the visualization experiment is presented. Emphasis is on the potential development of a tool in CAD systems that would identify illusory effects and subsequently suggest potential design solutions. The possibility of using spectral analysis (fast Fourier transform) for an automated shape recognition capability in CAD systems is discussed. / Master of Science