The objective of this thesis is to develop and validate a computational framework based on mathematical models for the motion prediction and dynamic stability quantification of human walking, which can differentiate the dynamic stability of human walking with different mechanical properties of the leg. Firstly, a large measurement database of human walking motion was created. It contains walking measurement data of 8 subjects on 3 self-selected walking speeds, which 10 trials were recorded at each walking speed. The motion of whole-body centre of mass and the leg were calculated from the kinetic-kinematic measurement data. The fundamentals of leg property have been presented, and the parameters of leg property were extracted from the measurement data of human walking where the effects of walking speed and condition of foot-ground contact were investigated. Three different leg property definitions comprising linear axial elastic leg property, nonlinear axial elastic leg property and linear axial-tangential elastic leg property were used to extracted leg property parameters. The concept of posture-dependent leg property has been proposed, and the leg property parameters were extracted from the measurement data of human walking motion where the effects of walking speed and condition of foot-ground contact were also investigated. The compliant leg model with axial elastic property (CAE) was used for the dynamic stability analysis of human walking with linear and nonlinear axial elastic leg property. The compliant leg model with axial and tangential elastic property (CATE) was used for that with linear axial-tangential elastic leg property. The posture - dependent elastic leg model (PDE) was used for that with posture-dependent leg property. It was found that, with linear axial elastic leg property, the global stability of human walking improves with the bigger touchdown contact angle. The average leg property obtained from the measurement data of all participants allows the maximum global stability of human walking. With nonlinear axial elastic leg property, the global stability decreases with the stronger nonlinearity of leg stiffness. The incorporation of the tangential elasticity improves the global stability and shifts the stable walking velocity close to that of human walking at self-selected low speed (1.1-1.25 m/s).By the PDE model, the human walking motions were better predicted than by the CATE model. The effective range of walking prediction was enlarged to 1.12 – 1.8 m/s. However, represented by PDE model, only 1-2 walking steps can be achieved. In addition, the profiles of mechanical energies represented by the PDE model are different from that of the orbital stable walking represented by CATE model. Finally, the minimal requirements of the human walking measurements and the flexibility of simple walking models with deliberate leg property definitions allow the computational framework to be applicable in the dynamic stability analysis of the walking motion with a wide variety of mechanical property of the leg.

Motions and stability of a typical B.C. fishing vessel were experimentally and numerically investigated in a longitudinal seaway condition. The experimental model was self-propelled, radio-controlled and equipped with an on-board data acquisition system. Pitch, roll, yaw, surge, and heave responses to regular waves of predetermined frequencies and amplitudes generated along a 220-ft model basin were obtained. Different displacement conditions and GM configurations were tested. The numerical model for the dynamic analysis of the fishing vessel motions has been implemented using strip theory. A computer program was developed to study the nonlinear motions of the vessel. The velocity dependent coupling terms, responsible for a major part of the nonlinear behavior, were included. A time dependent component analysis of the roll damping has been performed. Regular linear and nonlinear waves were used. A parametric study of the fishing vessel stability has been carried out by considering its dynamic response in waves of varying characteristics. Unstable behaviour was found to be closely related to waves of length of similar magnitude to the ship length. The effects of wave amplitude and rudder usage were found to be of capital importance in the capsizing process. Experimental and numerical results showed good agreement. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The evolutionarily persistent and widespread use of carotenoid pigments in animal coloration contrasts with their biochemical instability. Consequently, evolution of carotenoid-based displays should include mechanisms to accommodate or limit pigment degradation. In birds, this could involve two strategies: (i) evolution of a moult immediately prior to the mating season, enabling the use of particularly fast-degrading carotenoids and (ii) evolution of the ability to stabilize dietary carotenoids through metabolic modification or association with feather keratins. Here, we examine evolutionary lability and transitions between the two strategies across 126 species of birds. We report that species that express mostly unmodified, fast-degrading, carotenoids have pre-breeding moults, and a particularly short time between carotenoid deposition and the subsequent breeding season. Species that expressed mostly slow-degrading carotenoids in their plumage accomplished this through increased metabolic modification of dietary carotenoids, and the selective expression of these slow-degrading compounds. In these species, the timing of moult was not associated with carotenoid composition of plumage displays. Using repeated samples from individuals of one species, we found that metabolic modification of dietary carotenoids significantly slowed their degradation between moult and breeding season. Thus, the most complex and colourful ornamentation is likely the most biochemically stable in birds, and depends less on ecological factors, such as moult timing and migration tendency. We suggest that coevolution of metabolic modification, selective expression and biochemical stability of plumage carotenoids enables the use of unstable pigments in long-term evolutionary trends in plumage coloration.

The detection of damage in structures through the use of vibrational methods offers particular advantages, which makes it an attractive method to use in specific applications. In this work the advantages and some of the possible applications of vibrational damage detection methods will be discussed. A study of the field of damage detection using vibration techniques is undertaken. Available methods are categorised in general groups according to the underlying principles. The principle, on which each group functions, as well as the advantages and disadvantages of each, concerning the practical application thereof, is explained. The goal of this work, which entails developing a damage detection method using large amounts of raw data directly and combining some of the most favourable properties of the different groups to detect damage, are set. The new method is developed and compared both numerically as well as experimentally to two methods, chosen from the literature because of similar methodology and their reputation for effective damage detection. The methods will be tested numerically with respect to accuracy, sensitivity and multiple damage detection ability. Finally experimental data is gathered and used to verify the methods damage detection ability. The new method provides a different approach to damage detection, by combining an available vibration detection method with the maximum available amount of data in order to increase the damage detection ability. / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted

Orientador: Flavia Maria Netto / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-03T15:38:40Z (GMT). No. of bitstreams: 1 Righetto_AndreaMara_D.pdf: 10238421 bytes, checksum: 93662e77f53fe2e459fa3a0a3895a2b7 (MD5) Previous issue date: 2003 / Resumo: A acerola é uma fruta tropical, cujo principal atrativo é o alto teor de vitamina C que apresenta. O teor de vitamina C da fluta decresce com a maturação, mas não há estudos na literatura que explorem o potencial da acerola verde como matéria prima de produtos com alta concentração desta vitamina. O presente trabalho objetivou a produção, a caracterização físico-química e a verificação da estabilidade do suco de acerola verde microencapsulado por atomização e liofílização utilizando diferentes proporções de goma arábica e maltodextrina DE 20 como agentes encapsulantes. No início dos estudos caracterizou-se o suco de acerola verde concentrado, comparando-o ao suco de acerola verde e da acerola madura e verificou-se o potencial antioxidante dos três sucos. O suco de acerola verde concentrado apresentou a maior concentração de vitamina C, 4,9%, e compostos fenólicos, 9,2 mglg de suco. Os três sucos estudados apresentaram atividade antioxidante. O suco concentrado apresentou a maior atividade antioxidante, reduzindo em 57,2%.a oxidação do metillinolato.O suco de acerola madura diminuiu em 44,7% a oxidação do metil linolato, uma redução maior que a apresentada pelo suco de acerola verde, 28,1%. Não houve correlação entre o teor de fenóis totais nos sucos estudados e a atividade antioxidante. O alto teor de vitamina C bem como a alta atividade antioxidante do suco concentrado de acerola verde indicam que este produto pode ser uma matéria-prima interesante ara a elaboração de produtos com características de alimento funcional, , onde o sabor e o aroma característicos da fluta madura são dispensáveis. Com o objetivo de aumentar a estabilidade deste produto ao armazenamento, em especial da vitamina C, o suco da acerola verde foi microencapsulado utilizando-se dois processsos, liofilização e atomização. Maltodextrina DE 20 (M), goma arábica (G) e a mistura destes em diferentes proporções foram utilizadas como agentes encapsulantes. As diferentes formulações do material encapsulante resultaram em diferentes retenções de vitamina C, sendo que a formulação com maior proporção de maltodextrina apresentou a melhor retenção (37,5%M+12,5%G), 80%, e a menor retenção foi apresentada pela formulação com igual proporção de goma arábica e maltodextrina (25%M+25%G), 65%. A maior retenção de vitamina C, foi obtida no processo de atomização. As partículas produzidas por liofílização mostraram formas complexas e tamanhos variados devido à moagem a que os produtos foram submetidos. O processo de atomização produziu microcápsulas globosas com predomínio de superfícies rugosas e com paredes formadas por uma matriz sólida sem poros. As isotermas de sorção dos encapsulados obtidos por atomização e liofilização, nas temperaturas de 25°, 35° e 45°C mostraram uma faixa crítica de atividade de água, entre 0,33 e 0,43, onde todos os encapsulados, independente da formulação utilizada apresentaram modifícações físicas. Um maior escurecimento foi observado nos microencapsulados produzidos por liofilização e também nas formulações com predomínio de goma arábica. Os agentes encapsulantes estudados apresentaram temperaturas de transição vítrea (Tg) similares nas mesmas atividades de água (Aa), resultando em microencapsulados com temperaturas de transição vítrea também similares. Em Aa 0,43 a Tg dos microencapsulados foi próxima a temperatura ambiente. A formulação contendo L50%G apresentou a maior Tg, 34°C, enquanto as formulações 25%M+25%G e 50%M encapsulados por liofilização apresentaram as menores Tg, 26 e 25°C, respectivamente. O colapso dos microencapsulados foi observado em temperaturas 20° C acima da Tg. Os microencapsulados produzidos por atomização, que reuniram as melhores características fisico-químicas, 37,5%M+ 12,5%G, 37,5%G+ 12,5%M e 50%M, foram avaliados quanto à estabilidade ecomparados com ácido ascórbico sintético microencapsulado nas mesmas condições e com o suco de acerola liofilizado sem a adição de encapsulantes. Os encapsulados de ácido ascórbico sintético (AA) apresentaram retenção inicial de vitamina C entre 8 e 15% menor que os encapsulados do suco de acerola. A cinética de degradação da vitamina C nos encapsulados seguiu o modelo cinético de primeira ordem, enquanto o escurecimento não enzimático seguiu um modelo cinético de ordem zero.Ambas apresentaram um período lento, seguido por um período com reação com constante de velocidade maior. As constantes de velocidade, tanto para a reação de degradação da vitamina C quanto para o escurecimento enzimático, foram similares para todas as formulações dos agentes encapsulantes. As três formulações estudadas apresentaram comportamentos similares, proporcionando proteção ao ácido ascórbico sintético e também à vitamina C do suco de acerola verde. Em temperaturas mais elevadas, 35° e 45° C, no entanto, os microencapsulados de suco de acerola verde foram mais estáveis que os microencapsulados de ácido ascórbico sintético, sugerindo assim um efeito protetor dos compostos fenólicos presentes no suco à vitamina C. O estudo realizado demonstrou que o suco de acerola verde microencapsulado é uma produto interessante para ser utilizado como fonte natural de vitamina C e de compostos fenólicos / Abstract: During the maturation process, the vitamin C content decreases significantly, but there are no studies in which the unripe West Indian cherry was investigated as potential raw material for products with high content of vitamin C. The purpose of this research was to characterize the unripe West Indian cherry juice, and to produce and characterize microencapsulated unripe West Indian cherry juice produced out of spray and freeze drying, as well the use of different proportions of arabic gum and maltodextrin DE 20 as encapsulating agents. Unripe West 1ndian cherry concentrated juice, unripe West 1ndian cherry, and ripe West 1ndian cherry juice, were characterized and the antioxidant activity was studied. The unripe West 1ndian cherry concentrated juice presented the higher vitamin C concentration, 4,9%, and phenolics content, 9,2 mg/g of juice. The three juices studied presented antioxidant activity. The concentrated juice presented the highest antioxidant activity, reducing to 57,2% the methyl linoleate oxidation. No correlation was observed between the content of total phenolics the antioxidant activity. The unripe West 1ndian cherry concentrated juice showed characteristics, which are interesting for the elaboration of products with functional food characteristics. In order to improve the storage stability and protect the vitamin C, the unripe West 1ndian cherry juice was microencapsulated by freeze and spray drying, using maltodextrin DE 20 (M), arabic gum (G) and the mixture of both in different proportions, as coating material. Different coating material formulations resulted in different vitamin C retention for the both processes studied. The formulation with higher proportion of maltodextrin presented the best retention (37,5%M+ 12,5%G), 80%, and the lowest was presented by formulation with equal proportion of arabic gum and maltodextrin (25%M+25%G), 65%. The spray and freeze drying led to products with different morphological characteristics, as well with different vitamin C retention, the spray drying showed higher values than the freeze drying process. The spray drying process produced spherical microcapsules which have displayed dented surface and walls as solid matrix without voids. The moisture sorption isotherms determined at 25°, 35° and 45°C showed a critical water activity, between 0,33 and 0,43, where all the encapsulates presented physical modification. Browning was more intense in powders produced out of freeze drying and in formulations with prevalence of arabic gum. The both core material studied presented similar glass transition temperature (Tg), at the same water activity (Aw), hence the microencapsulated juice, independently of the core composition, showed a similar Tg. At Aw 0,43, all the microencapsulated studied showed Tg elose to ambient temperature. The formulation containing 50%G, presented the highest Tg, 34°C, while the 25%M+25%G formulation and 50%M encapsulated by freeze drying presented the lowest Tg, 26 and 25° C, respectively. The collapse of microencapsulates was observed at temperature 20°C above the Tg. The stability of the microencapsulated juice produced out of spray drying, which presented the best physical-chemical characteristics, 37,5%M+ 12,5%G, 37,5%G+ 12,5%M and 50%M, were evaluated and compared to synthetic microncapsulated ascorbic acid and with freeze dried West lndian cherry juice, at the same storage condition. The encapsulated synthetic acid ascorbic (AA) presented initial vitamin C retention between 8 and 15%, lower than the encapsulated unripe West lndian cherry juice. The kinetic of degradation of vitamin C in encapsulates followed first-order model, while the nonenzymatic browning a zero-order model. The different proportions of arabic gum and maltodextrin used as coating material resulted in similar rate constant, for the vitamin C degradation and for nonenzymatic browning. The three fonnulation tested, provided similar protection for the encapsulated synthetic ascorbic acid and also for the vitamin C of encapsulated unripe West lndian cherry juice At higher temperatures, 35° and 45° C, the encapsulated unripe West lndian cherry juice was more stable than the encapsulated synthetic ascorbic acid, suggesting a protective effect of phenolic compounds on vitamin C. The results indicated that microencapsulated unripe West Indian cherry juice is an interesting product to be used as natural source of vitamin C and phenolic compounds / Doutorado / Doutor em Ciência da Nutrição

Shock waves in reactive media possess very rich dynamics: from formation of cells in multiple dimensions to oscillating shock fronts in one-dimension. Because of the extreme complexity of the equations of combustion theory, most of the current understanding of unstable detonation waves relies on extensive numerical simulations of the reactive compressible Euler/Navier-Stokes equations. Attempts at a simplified theory have been made in the past, most of which are very successful in describing steady detonation waves. In this work we focus on obtaining simplified theories capable of capturing not only the steady, but also the unsteady behavior of detonation waves. The first part of this thesis is focused on qualitative theories of detonation, where ad hoc models are proposed and analyzed. We show that equations as simple as a forced Burgers equation can capture most of the complex phenomena observed in detonations. In the second part of this thesis we focus on rational theories, and derive a weakly nonlinear model of multi-dimensional detonations. We also show, by analysis and numerical simulations, that the asymptotic equations provide good quantitative predictions.

Phase-field models are emerging as a promising strategy to simulate interfacial phenomena. Rather than tracking interfaces explicitly as done in sharp interface descriptions, these models use a diffuse order parameter to monitor interfaces implicitly. This implicit description, as well as solid physical and mathematical footings, allow phase-field models to overcome problems found by predecessors. Nonetheless, the method has significant drawbacks. The phase-field framework relies on the solution of high-order, nonlinear partial differential equations. Solving these equations entails a considerable computational cost, so finding efficient strategies to handle them is important. Also, standard discretization strategies can many times lead to incorrect solutions. This happens because, for numerical solutions to phase-field equations to be valid, physical conditions such as mass conservation and free energy monotonicity need to be guaranteed. In this work, we focus on the development of thermodynamically consistent algorithms for time integration of phase-field models. The first part of this thesis focuses on an energy-stable numerical strategy developed for the phase-field crystal equation. This model was put forward to model microstructure evolution. The algorithm developed conserves, guarantees energy stability and is second order accurate in time. The second part of the thesis presents two numerical schemes that generalize literature regarding energy-stable methods for conserved and non-conserved phase-field models. The time discretization strategies can conserve mass if needed, are energy-stable, and second order accurate in time. We also develop an adaptive time-stepping strategy, which can be applied to any second-order accurate scheme. This time-adaptive strategy relies on a backward approximation to give an accurate error estimator. The spatial discretization, in both parts, relies on a mixed finite element formulation and isogeometric analysis. The codes are available online and implemented in PetIGA, a high-performance isogeometric analysis framework.

This diploma thesis deals with the description of selected statistical process control tools, applied to Proxima frame cab tractor made by Zetor company. There is also a statistical evaluation of measured data and determination of significant correlations.

abstract: Materials have been the backbone of every major invention in the history of mankind, e.g. satellites and space shuttles would not exist without advancement in materials development. Integral to this, is the development of nanocrystalline (NC) materials that promise multitude of properties for advanced applications. However, they do not tend to preserve structural integrity under intense cyclic loading or long-term temperature exposures. Therefore, it is imperative to understand factors that alter the sub-features controlling both structural and functional properties under extreme conditions, particularly fatigue and creep. Thus, this dissertation systematically studies the tensile creep and fatigue behaviour of a chemically optimized and microstructurally stable bulk NC copper (Cu)-3at.% tantalum (Ta) alloy. Strategic engineering of nanometer sized clusters of Ta into the alloy’s microstructure were found to suppress the microstructure instability and render remarkable improvement in the high temperature tensile creep resistance up to 0.64 times the melting temperature of Cu. Primary creep in this alloy was found to be governed by the relaxation of the microstructure under the applied stress. Further, during the secondary creep, short circuit diffusion of grain boundary atoms resulted in the negligible steady-state creep rate in the alloy. Under fatigue loading, the alloy showed higher resistance for crack nucleation owing to the inherent microstructural stability, and the interaction of the dislocations with the Ta nanoclusters. The underlying mechanism was found to be related to the diffused damage accumulation, i.e., during cyclic loading many grains participate in the plasticity process (nucleation of discrete grain boundary dislocations) resulting in homogenous accumulation rather than localized one as typically observed in coarse-grained materials. Overall, the engineered Ta nanoclusters were responsible for governing the underlying anomalous high temperature creep and fatigue deformation mechanisms in the alloy. Finally, this study presents a design approach that involves alloying of pure metals in order to impart stability in NC materials and significantly enhance their structural properties, especially those at higher temperatures. Moreover, this design approach can be easily translated to other multicomponent systems for developing advanced high-performance structural materials. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2019

Hydrotalcite (HTC) was intercalated with different aromatic carboxylic acids via two synthesis methods: reconstruction and co-precipitation. The reconstruction method involves the rehydration of the products of LDH calcination. The co-precipitation method involves the addition of a base to solutions containing a mixture of the MII and MIII ions found in the metallic layers of an LDH. The intercalated compounds were then compounded with flexible grade PVC to see if these compounds had any effect on the heat stability of the PVC. Complete intercalation of these stabilisers did not occur; however layered double hydroxides did form for almost every synthesis. The organic acids that were to be intercalated were also present in every synthesised stabiliser. Neat hydrotalcite was the best overall stabiliser with an early stability time of 32.40 min and a final or long term stability time of 106.51 min. The best modified layered double hydroxide (LDH) in terms of early stability was 4-hydroxybenzoic acid + HTC synthesised with the reconstruction method. This stabiliser had an early stability time of 25.40 min. The best performing modified stabiliser in terms of late stability was salicylic acid + HTC synthesised with the co-precipitation method. This stabiliser had a late stability time of 71.32 min. The highly activating nature of the hydroxyl substituent group should make hydrotalcites intercalated with hydroxybenzoic acids good free radical scavengers. The substituent group positions that give the best PVC heat stability are the ortho and para positions. The pKa 2 value for an organic acid may be used as a selection parameter for intercalation into hydrotalcite. If a high pKa 2 value organic acid is intercalated into hydrotalcite, the resulting compound will have good PVC heat stabilisation properties. / Dissertation (MEng)--University of Pretoria, 2017. / Chemical Engineering / MEng / Unrestricted