Littérature scientifique sur le sujet « Structural kinetic modelling »
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Articles de revues sur le sujet "Structural kinetic modelling"
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Aftandiliants, Ye G. « Modelling of structure forming in structural steels ». Naukovij žurnal «Tehnìka ta energetika» 11, no 4 (10 septembre 2020) : 13–22. http://dx.doi.org/10.31548/machenergy2020.04.013.
Texte intégralRésumé :
The study showed that the influence of alloying elements on the secondary structure formation of the steels containing from 0.19 to 0.37 wt. % carbon; 0.82-1.82 silicon; 0.63-3.03 manganese; 1.01-3.09 chromium; 0.005-0.031 nitrogen; up to 0.25 wt.% vanadium and austenite grain size is determined by their change in the content of vanadium nitride phase in austenite, its alloying and overheating above tac3, and the dispersion of ferrite-pearlite, martensitic and bainitic structures is determined by austenite grain size and thermal kinetic parameters of phase transformations. Analytical dependencies are defined that describe the experimental data with a probability of 95% and an error of 10% to 18%. An analysis results of studying the structure formation of structural steel during tempering after quenching show that the dispersion and uniformity of the distribution of carbide and nitride phases in ferrite is controlled at complete austenite homogenization by diffusion mobility and the solubility limit of carbon and nitrogen in ferrite, and secondary phase quantity in case of the secondary phase presence in austenite more than 0.04 wt. %. Equations was obtained which, with a probability of 95% and an error of 0.7 to 2.6%, describe the real process.
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Liebermeister, Wolfram. « Structural Thermokinetic Modelling ». Metabolites 12, no 5 (11 mai 2022) : 434. http://dx.doi.org/10.3390/metabo12050434.
Texte intégralRésumé :
To translate metabolic networks into dynamic models, the Structural Kinetic Modelling framework (SKM) assumes a given reference state and replaces the reaction elasticities in this state by random numbers. A new variant, called Structural Thermokinetic Modelling (STM), accounts for reversible reactions and thermodynamics. STM relies on a dependence schema in which some basic variables are sampled, fitted to data, or optimised, while all other variables can be easily computed. Correlated elasticities follow from enzyme saturation values and thermodynamic forces, which are physically independent. Probability distributions in the dependence schema define a model ensemble, which allows for probabilistic predictions even if data are scarce. STM highlights the importance of variabilities, dependencies, and covariances of biological variables. By varying network structure, fluxes, thermodynamic forces, regulation, or types of rate laws, the effects of these model features can be assessed. By choosing the basic variables, metabolic networks can be converted into kinetic models with consistent reversible rate laws. Metabolic control coefficients obtained from these models can tell us about metabolic dynamics, including responses and optimal adaptations to perturbations, enzyme synergies and metabolite correlations, as well as metabolic fluctuations arising from chemical noise. To showcase STM, I study metabolic control, metabolic fluctuations, and enzyme synergies, and how they are shaped by thermodynamic forces. Considering thermodynamics can improve predictions of flux control, enzyme synergies, correlated flux and metabolite variations, and the emergence and propagation of metabolic noise.
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Korla, Kalyani, et Chanchal K. Mitra. « Kinetic modelling of mitochondrial translation ». Journal of Biomolecular Structure and Dynamics 32, no 10 (13 septembre 2013) : 1634–50. http://dx.doi.org/10.1080/07391102.2013.833135.
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TĂNASE, DOBRE, OANA CRISTINA PÂRVULESCU et CRISTIAN RĂDUCANU. « Stochastic modelling of polysaccharide hydrolysis ». Journal of Engineering Sciences and Innovation 3, no 1 (10 janvier 2018) : 25–38. http://dx.doi.org/10.56958/jesi.2018.3.1.25.
Texte intégralRésumé :
A stochastic model was selected and developed to describe polysaccharide hydrolysis kinetics. This model can accurately predict the hydrolysis kinetics and covers the limitations of some classical kinetic models (e.g., complexity of mathematical models, large number of parameter estimations, change in parameters with a change in hydrolysis conditions, etc.). One of the main advantages of the stochastic mathematical model approach is represented by the fact that the polysaccharide structural characteristics and operating parameters can be separately incorporated into the model. The stochastic process characterizing the model considers that the breakdown of a polysaccharide by hydrolysis is a random process based on the cleavage of a parent macromolecule within a molecular mass range into two descendants within lower molecular mass ranges. The model description and its implementation in the hydrolysis of a hypothetical polysaccharide were presented.
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Christensen, F. R., G. Holm Kristensen et J. la Cour Jansen. « Biofilm Structure – An Important and Neglected Parameter in Waste Water Treatment ». Water Science and Technology 21, no 8-9 (1 août 1989) : 805–14. http://dx.doi.org/10.2166/wst.1989.0283.
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Experimental investigations on the kinetics of wastewater treatment processes in biofilms were performed in a laboratory reactor. Parallel with the kinetic experiments, the influence of the biofilm kinetics on the biofilm structure was studied at macroscopic and microscopic levels. The close interrelationship between biofilm kinetics and structural changes caused by the kinetics is illustrated by several examples. From the study, it is evident that the traditional modelling of wastewater treatment processes in biofilm reactors based on substrate removal kinetics alone will fail in many cases, due to the inevitable changes in the biofilm structure not taken into consideration. Therefore design rules for substrate removal in biofilms used for wastewater treatment must include correlations between the removal kinetics and the structure and development of the biological film.
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Huang, P. Y. H., et Y. Ch Fu. « Modelling the kinetics of water loss during deep-fat frying of potato particulates ». Czech Journal of Food Sciences 32, No. 6 (27 novembre 2014) : 585–94. http://dx.doi.org/10.17221/99/2014-cjfs.
Texte intégralRésumé :
We developed an empirical model to describe the water loss during deep-fat frying. Raw potato particulates were sliced to form cylinders and subjected to the deep-fat frying at isothermal temperatures of 160, 190, and 220°C. The microstructure properties were assessed by Field Emission Scanning Electron Microscope (FESEM). The plot of the water content versus the frying time showed two distinct regions. A first-order kinetic model correlated with the two irreversible serial rate processes, rapid process and slow process, was hypothesised to describe the water loss during frying. The results showed the simultaneous two first-order kinetic models adequately predicted the water loss of potato particulates during isothermal frying. The effect of temperature on the rate constants, k<sub>1</sub> and k<sub>2</sub>, for the two processes was adequately modelled by the Arrhenius relationship. The observations of structural changes on the surface and in the inner section of potato particulates are critical. These physical pieces of evidence support our assumption that the mechanisms of the water loss (two-stage rate processes) before and after the transition time are different.
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Telenius, Jelena, Anders E. Wallin, Michal Straka, Hongbo Zhang, Erika J. Mancini et Roman Tuma. « RNA Packaging Motor : From Structure to Quantum Mechanical Modelling and Sequential-Stochastic Mechanism ». Computational and Mathematical Methods in Medicine 9, no 3-4 (2008) : 351–69. http://dx.doi.org/10.1080/17486700802168502.
Texte intégralRésumé :
The bacteriophages of theCystoviridaefamily package their single stranded RNA genomic precursors into empty capsid (procapsids) using a hexameric packaging ATPase motor (P4). This molecular motor shares sequence and structural similarity with RecA-like hexameric helicases. A concerted structural, mutational and kinetic analysis helped to define the mechanical reaction coordinate,i.e.the conformational changes associated with RNA translocation. The results also allowed us to propose a possible scheme of coupling between ATP hydrolysis and translocation which requires the cooperative action of three consecutive subunits. Here, we first test this model by preparing hexamers with defined proportions of wild type and mutant subunits and measuring their activity. Then, we develop a stochastic kinetic model which accounts for the catalytic cooperativity of the P4 hexamer. Finally, we use the available structural information to construct a quantum-chemical model of the chemical reaction coordinate and obtain a detailed description of the electron density changes during ATP hydrolysis. The model explains the results of the mutational analyses and yields new insights into the role of several conserved residues within the ATP binding pocket. These hypotheses will guide future experimental work.
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Хамидуллина, Зульфия Абударовна, Альбина Сабирьяновна Исмагилова et Семен Израилевич Спивак. « Determination of the basis for nonlinear parametric functions of chemical reactions ». Вычислительные технологии, no 3 (15 juillet 2020) : 29–34. http://dx.doi.org/10.25743/ict.2020.25.3.004.
Texte intégralRésumé :
Настоящая работа посвящена математическому и компьютерному моделированию кинетики сложных химических реакций. Сформулирована и доказана теорема о соответствии структуры механизма сложной химической реакции с матрицей связей. Разработан и автоматизирован алгоритм определения базиса нелинейных параметрических функций. Реализована теоретико-графовая интерпретация механизма сложной химической реакции Mathematical and computer modelling of the kinetics of complex chemical reactions is considered in the present study. It was formulated that the structural mechanism of complex chemical reaction corresponds to the matrix of bonds. The appropriate theorem was proved. A graph and theoretical technique that allows determining the functional dependences of kinetic parameters directly from the graph of the reaction mechanism is developed. Based on the proposed algorithm, a program for determining the basis of nonlinear parametric functions of kinetic parameters is proposed. The program implements a graph and theoretic interpretation of the mechanisms of complex chemical reactions for constructing stationary kinetic models of catalytic reactions. An algorithm for determining the basis of nonlinear parametric functions is developed and automated. A graph and theoretical interpretation of the mechanism of a complex chemical reaction is implemented
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Krayovskyy, Volodymyr, Volodymyr Pashkevych, Mariya Rokomanyuk, Petro Haranuk, Volodymyr Romaka, Yuriy Stadnyk, Lyubov Romaka et Andriy Horyn. « KINETIC AND ENERGETIC PERFORMANCES OF THERMOMETRIC MATERIAL TiCo1-xMnxSb : MODELLING AND EXPERIMENT ». Measuring Equipment and Metrology 82, no 1 (2021) : 19–25. http://dx.doi.org/10.23939/istcmtm2021.01.019.
Texte intégralRésumé :
The results of a complex study of the semiconductor thermometric material TiСo1-xMnxSb, х=0.01–0.10, for the producing of sensitive elements of thermoelectric and electro resistive sensors are presented. Microprobe analysis of the concentration of atoms on the surface of TiСo1-xMnxSb samples established their correspondence to the initial compositions of the charge, and X-ray phase analysis showed the absence of traces of extraneous phases on their diffractograms. The produced structural studies of the thermometric material TiСo1-xMnxSb allow to speak about the ordering of its crystal structure, and the substitution of Co atoms on Mn at the 4c position generate structural defects of acceptor nature. The obtained results testify to the homogeneity of the samples and their suitability for the study of electrokinetic performances and the manufacture of sensitive elements of thermocouples. Modeling of structural, electrokinetic and energetic performances of TiСo1-xMnxSb, х=0.01–0.10, for different variants of spatial arrangement of atoms is performed. To model energetic and kinetic performances, particularly the behavior of the Fermi level, the band gap, the density of states (DOS) distribution was calculated for an ordered variant of the structure in which Co atoms at position 4c are replaced by Mn atoms. Substitution of Co atoms (3d74s2) by Mn (3d54s2) generates structural defects of acceptor nature in the TiСo1-xMnxSb semiconductor (the Mn atom contains fewer 3d- electrons than Co). This, at the lowest concentrations of impurity atoms Mn, leads to the movement of the Fermi level from the conduction band to the depth of the band gap. In a semiconductor with the composition TiCo0.99Mn0.01Sb, the Fermi level is located in the middle of the band gap, indicating its maximum compensation when the concentrations of ionized acceptors and donors are close. At higher concentrations of impurity Mn atoms, the number of generated acceptors will exceed the concentration of donors, and the concentration of free holes will exceed the concentration of electrons. Under these conditions, the Fermi level approach, and then the level of the valence band TiСo1-xMnxSb cross: the dielectric-metal conductivity transition take place. The presence of a high-temperature activation region on the temperature dependence of the resistivity ln(ρ(1/T)) TiСo1‑xMnxSb at the lowest concentration of impurity atoms Mn, х=001, indicates the location of the Fermi level in the band gap of the semiconductor thermopower coefficient α(Т,х) at these temperatures specify its position - at a distance of ~ 6 meV from the level of the conduction band . In this case, electrons are the main carriers of current. The absence of a low-temperature activation region on this dependence indicates the absence of the jumping mechanism conductivity. Negative values of the thermopower coefficient α(Т,х) TiСo0,99Mn0,01Sb at all temperatures, when according to DOS calculations the concentrations of acceptors and donors are close, and the semiconductor is maximally compensated, can be explained by the higher concentration of uncontrolled donors. However, even at higher concentrations of impurity Mn atoms in TiСo0,98Mn0,02Sb, the sign of the thermopower coefficient α(Т,х) remains negative, but the value of resistivity ρ(х,Т) increases rapidly, and the Fermi level deepens into the forbidden zone at a distance of ~ 30 meV. The rapid increase in the values of the resistivity ρ(х,Т) in the region of concentrations х=0.01–0.02 shows that acceptors are generated in the TiСo1-xMnxSb semiconductor when Co atoms are replaced by Mn, which capture free electrons, reducing their concentration. However, negative values of the thermopower coefficient α(Т,х) are evidence that either the semiconductor has a significant concentration of donors, which is greater than the number of introduced acceptors (х=0.02), or the crystal simultaneously generates defects of acceptor and donor nature. The obtained result does not agree with the calculations of the electronic structure of the TiСo1-xMnxSb semiconductor. It is concluded that more complex structural changes occur in the semiconductor than the linear substitution of Co atoms by Mn, which simultaneously generate structural defects of acceptor and donor nature by different mechanisms, but the concentration of donors exceeds the concentration of generated acceptors. Based on a comprehensive study of the electronic structure, kinetic and energetic performances of the thermosensitive material TiСo1-xMnxSb, it is shown that the introduction of impurity Mn atoms into TiCoSb can simultaneously generate in the semiconductor an acceptor zone (substitution of Co atoms for Mn) and donor zones and of different nature. The ratio of the concentrations of ionized acceptors and donors generated in TiСo1-xMnxSb will determine the position of the Fermi level and the mechanisms of electrical conductivity. However, this issue requires additional research, in particular structural and modeling of the electronic structure of a semiconductor solid solution under different conditions of entry into the structure of impurity Mn atoms. The investigated solid solution TiСo1-xMnxSb is a promising thermometric material.
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Yang, Qi, Jie Dong, Tongju Xing, Yi Zhang, Yong Guan, Xiaoli Liu, Ye Tian et Peng Yu. « RANS-Based Modelling of Turbulent Flow in Submarine Pipe Bends : Effect of Computational Mesh and Turbulence Modelling ». Journal of Marine Science and Engineering 11, no 2 (3 février 2023) : 336. http://dx.doi.org/10.3390/jmse11020336.
Texte intégralRésumé :
Pipe bend is a critical integral component, widely used in slurry pipeline systems involving various engineering applications, including natural gas hydrate production. The aim of this study is to assess the capability of RANS-based CFD models to capture the main features of the turbulent single-phase flow in pipe bends, in view of the future investigation of the hydrate slurry flow in the same geometry. This is different from the available literature in which only a few accounted for the effects of a combination of computational mesh, turbulence model, and near-wall treatment approach. In this study, three types of mesh configuration were adopted to carry out the computations, namely unstructured mesh and two structured meshes with a uniform and nonuniform inflation layer, respectively. To explore the influence of the turbulence model, standard k-ε, low-Reynolds k-ε, and nonlinear eddy viscosity turbulence model were selected to close RANS equations. Pressure coefficient, mean axial velocity, turbulence intensity, secondary flow velocity, and magnitude of secondary flow were regarded as the critical variables to make a comprehensive sensitivity analysis. Predicted results suggest that turbulent kinetic energy is the most sensitive variable to the computational mesh while others tend to stabilize. The largest difference of turbulence kinetic energy was around 26% between unstructured mesh and structured mesh with a nonuniform inflation layer. Additionally, a fully resolved boundary layer can reduce the sensitivity of mesh on turbulent kinetic energy, especially for a nonlinear turbulence model. However, the large gradient and peak value of turbulence intensity near the inner wall of the bend was not captured by the case with a fully resolved boundary layer, compared with that of the wall function used. Furthermore, it has been confirmed that the same rule was detected also for different curvature ratios, Reynolds numbers, and dimensionless wall distance y+.
Thèses sur le sujet "Structural kinetic modelling"
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Garcia, Pereira Jose Carlos. « Atomistic modelling of the structure and kinetics of silica-based sol-gel processes ». Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266429.
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Erdös, Zoltan. « Modélisation couplée tectonique et processus de surface de l'extension et l'inversion dans les Pyrénées ». Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU024/document.
Texte intégralRésumé :
Orogenic belts are fundamental features of plate tectonics. The crustal structure of orogens around the world shows a wide range of deformation styles from narrow, asymmetric wedges like the Pyrenees to wide, plateau-like orogens such as the Zagros or the Himalaya. The primary controlling factor on the size and structure of an orogen is the amount of convergence between the colliding plates. However, there are important additional factors providing major controls on the structural development of orogens. Among the potential parameters that can affect the style of deformation are the crustal strength, inherited weaknesses, and the surface processes. These parameters have been studied extensively in the past but their relative importance remains unclear. The aim of this thesis is to improve our understanding of: (1) How surface processes affect mountain building, with a special focus on the relationship between thin-skinned foreland and thick-skinned internal deformation of orogens. (2) How inherited extensional structures affect mountain building. The study was carried out using the Pyrenees as a special reference case. To answer our research questions we have used a wide range of state-of-the-art numerical modelling tools. In paper 1 we present a new method where we couple a structural-kinematic model and a thermo-kinematic model to evaluate the consistency of existing balanced section reconstructions with independent thermochronology data. In papers 2 and 3 we use 2D lithospheric scale thermo-mechanical models with surface process algorithms. Using the above toolset, we demonstrate that syntectonic sedimentation results in longer basement thrust sheets as well as longer thin-skinned thrust sheets and a generally wider orogen. Conversely erosion tends to narrow the wedge and reduce the orogenic loading of the colliding plates, limiting the space available for deposition in the flexural foreland deeps. We also demonstrate that inherited extensional structures play a crucial role in mountain building as they facilitate the migration of deformation into the undeformed basement of the overriding plate. Moreover, a significant amount of lower-crustal/mantle-lithospheric material is preserved at shallow depths only in the presence of extensional inheritance, but significant erosion is needed in order to bring this material to the surface. Our models also show that thin-skinned thrust sheets are generally rooted in the footwall of basement thrusts as they form outward-propagating sequences. As soon as a new basement thrust forms, the thin-skinned sequence situated on top of the new basement thrust-sheet is abandoned in favour of starting a new sequence in the footwall of the new thrust. Regarding our case study, it was possible to reproduce the section restoration using a structural-kinematic model with high accuracy up to the 36-Ma time slice and with limited accuracy up to the 50-Ma time slice. The thermochronometric ages predicted by the thermo-kinematic modelling are generally in good agreement with both the high- and low-temperature thermochronology data available in the Central Pyrenees; hence we conclude that the restoration is to a first order consistent with these datasets. The predicted thermochronological ages approximate the available low-temperature thermochronology data better by taking into account the late-stage burial and re-excavation scenario affecting the southern flank of the Pyrenean wedge presented by Coney et al. (1996), and quantified by Fillon and van der Beek (2012). In conclusion, our model experiments suggest, that extensional inheritance played a prime role in the structural evolution of the Pyrenees, with the major characteristics of the North Pyrenean Unit, including the presence of steep, inverted normal faults, the relative tectonic quiescence of the area after the early inversion and the presence of a lower-crustal body at shallow depth below the unit, best recaptured by our accordion modelsOrogenic belts are fundamental features of plate tectonics. The crustal structure of orogens around the world shows a wide range of deformation styles from narrow, asymmetric wedges like the Pyrenees to wide, plateau-like orogens such as the Zagros or the Himalaya. The primary controlling factor on the size and structure of an orogen is the amount of convergence between the colliding plates. However, there are important additional factors providing major controls on the structural development of orogens. Among the potential parameters that can affect the style of deformation are the crustal strength, inherited weaknesses, and the surface processes. These parameters have been studied extensively in the past but their relative importance remains unclear. The aim of this thesis is to improve our understanding of: (1) How surface processes affect mountain building, with a special focus on the relationship between thin-skinned foreland and thick-skinned internal deformation of orogens. (2) How inherited extensional structures affect mountain building. The study was carried out using the Pyrenees as a special reference case. To answer our research questions we have used a wide range of state-of-the-art numerical modelling tools. In paper 1 we present a new method where we couple a structural-kinematic model and a thermo-kinematic model to evaluate the consistency of existing balanced section reconstructions with independent thermochronology data. In papers 2 and 3 we use 2D lithospheric scale thermo-mechanical models with surface process algorithms. Using the above toolset, we demonstrate that syntectonic sedimentation results in longer basement thrust sheets as well as longer thin-skinned thrust sheets and a generally wider orogen. Conversely erosion tends to narrow the wedge and reduce the orogenic loading of the colliding plates, limiting the space available for deposition in the flexural foreland deeps. We also demonstrate that inherited extensional structures play a crucial role in mountain building as they facilitate the migration of deformation into the undeformed basement of the overriding plate. Moreover, a significant amount of lower-crustal/mantle-lithospheric material is preserved at shallow depths only in the presence of extensional inheritance, but significant erosion is needed in order to bring this material to the surface. Our models also show that thin-skinned thrust sheets are generally rooted in the footwall of basement thrusts as they form outward-propagating sequences. As soon as a new basement thrust forms, the thin-skinned sequence situated on top of the new basement thrust-sheet is abandoned in favour of starting a new sequence in the footwall of the new thrust. Regarding our case study, it was possible to reproduce the section restoration using a structural-kinematic model with high accuracy up to the 36-Ma time slice and with limited accuracy up to the 50-Ma time slice. The thermochronometric ages predicted by the thermo-kinematic modelling are generally in good agreement with both the high- and low-temperature thermochronology data available in the Central Pyrenees; hence we conclude that the restoration is to a first order consistent with these datasets. The predicted thermochronological ages approximate the available low-temperature thermochronology data better by taking into account the late-stage burial and re-excavation scenario affecting the southern flank of the Pyrenean wedge presented by Coney et al. (1996), and quantified by Fillon and van der Beek (2012). In conclusion, our model experiments suggest, that extensional inheritance played a prime role in the structural evolution of the Pyrenees, with the major characteristics of the North Pyrenean Unit, including the presence of steep, inverted normal faults, the relative tectonic quiescence of the area after the early inversion and the presence of a lower-crustal body at shallow depth below the unit, best recaptured by our accordion models
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Steinmetz, Fabian. « Integration of data quality, kinetics and mechanistic modelling into toxicological assessment of cosmetic ingredients ». Thesis, Liverpool John Moores University, 2016. http://researchonline.ljmu.ac.uk/4522/.
Texte intégralRésumé :
In our modern society we are exposed to many natural and synthetic chemicals. The assessment of chemicals with regard to human safety is difficult but nevertheless of high importance. Beside clinical studies, which are restricted to potential pharmaceuticals only, most toxicity data relevant for regulatory decision-making are based on in vivo data. Due to the ban on animal testing of cosmetic ingredients in the European Union, alternative approaches, such as in vitro and in silico tests, have become more prevalent. In this thesis existing non-testing approaches (i.e. studies without additional experiments) have been extended, e.g. QSAR models, and new non-testing approaches, e.g. in vitro data supported structural alert systems, have been created. The main aspect of the thesis depends on the determination of data quality, improving modelling performance and supporting Adverse Outcome Pathways (AOPs) with definitions of structural alerts and physico-chemical properties. Furthermore, there was a clear focus on the transparency of models, i.e. approaches using algorithmic feature selection, machine learning etc. have been avoided. Furthermore structural alert systems have been written in an understandable and transparent manner. Beside the methodological aspects of this work, cosmetically relevant examples of models have been chosen, e.g. skin penetration and hepatic steatosis. Interpretations of models, as well as the possibility of adjustments and extensions, have been discussed thoroughly. As models usually do not depict reality flawlessly, consensus approaches of various non-testing approaches and in vitro tests should be used to support decision-making in the regulatory context. For example within read-across, it is feasible to use supporting information from QSAR models, docking, in vitro tests etc. By applying a variety of models, results should lead to conclusions being more usable/acceptable within toxicology. Within this thesis (and associated publications) novel methodologies on how to assess and employ statistical data quality and how to screen for potential liver toxicants have been described. Furthermore computational tools, such as models for skin permeability and dermal absorption, have been created.
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Papadias, Dennis. « Mathematical Modelling of Structured Reactors with Emphasis on Catalytic Combustion Reactions ». Doctoral thesis, Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3212.
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Cipolletta, Mariasole. « Kinetic modelling and structure-reactivity study for the production of GVL from levulinic acid and its esters ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Trouver le texte intégralRésumé :
This work is based on an experimental research activity in which direct hydrogenation reaction of biomass-derived compounds was performed to produce gamma-valerolactone (GVL), a relevant organic platform molecule in bio-refinery industry. After defining the best operative, levulinic acid (LA) and its alkyl esters (AL) were tested as starting substrates and a kinetic model was obtained from the data.
The kinetic study was the starting point to compare the chemical reactivity of the four chosen substrates in the defined system in order to evaluate their advantages and disadvantages from the reaction point of view and taking into account their implications in a further applicative perspective. Finally, a discussion about a possible correlation between the kinetics and the chemical structures of the different substrates is presented.
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Gutierrez, Acebo Ester. « Impact of the topology of the zeolite structure on the mechanism and selectivity of ethylcyclohexane bifunctional isomerization : experiments, ab initio calculations and multi-scale kinetic modelling ». Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1240/document.
Texte intégralRésumé :
Le paraxylène (pX), utilisé dans la fabrication de l'acide téréphtalique pour la production de nylon, est principalement produit par isomérisation de la coupe aromatique C8. Cette dernière est principalement composée des trois isomères du xylènes (para, ortho et méta) et de l'éthylbenzène (EB). L’EB est transformé en xylènes grâce à un catalyseur bifonctionnel comprenant à la fois une fonction acide comme la zéolithe EU-1 et une fonction hydro-déshydrogénante (HD/DHD) comme le platine. L’hydrogénation de l’EB conduit également à la production d’éthylcyclohexane, qui peut subir des réactions non désirées d’ouverture de cycle et de craquage sur la fonction acide du catalyseur. Au cours de ce travail, nous avons cherché à comprendre les facteurs influant sur la sélectivité du catalyseur bifonctionnel en hydroconversion de l’éthylcyclohexane (ECH), et à identifier des phases acides zéolithiques très sélectives. L’effet de paramètres tels que le ratio et la proximité entre sites acides et sites HD/DHD, la localisation des sites acides au sein du réseau zéolithique, et la topologie de ce réseau zéolithique, a été examiné. Des études catalytiques ont été mises en œuvre sur des séries de catalyseurs bifonctionnels à base de zéolithe EU-1, et interprétées à la lueur de calculs ab initio focalisés sur les mécanismes d’isomérisation et d’ouverture de cycle de l’ECH sur la phase acide EU-1. L’intégration de données thermocinétiques déterminées ab initio dans un modèle cinétique en champ moyen a permis de valider l’approche et d’identifier les étapes réactionnelles clés dictant la sélectivité. Un criblage rationnel de structures zéolithes a ensuite été proposé pour identifier les paramètres topologiques influantThe paraxylene (pX), used in the manufacture of terephtalic acid for the production of nylon, is mainly produced by isomerization of the C8 aromatic cut. The latter is mainly composed of the three xylene isomers (para, ortho and meta) and ethylbenzene (EB). EB is converted into xylenes by mean of a bifunctional catalyst comprising both an acid function, such as EU-1 zeolite, and a hydro-dehydrogenating function (HD / DHD), such as platinum. The hydrogenation of EB also leads to the production of ethylcyclohexane, which can undergo undesired ring-opening and cracking reactions on the acid function of the catalyst. In this work, we tried to understand the factors influencing the selectivity of the bifunctional catalyst in the hydroconversion of ethylcyclohexane (ECH), and to identify very selective zeolitic acid phases. The effect of parameters such as the ratio and proximity between acid and HD / DHD sites, the location of acid sites within the zeolite network, and the topology of this zeolite network, was evaluated. Catalytic studies have been carried out over bifunctional catalysts series based on the EU-1 zeolite, and interpreted considering ab initio calculations focused on the isomerization and ring-opening mechanisms of ECH on the EU-1 acid phase. The integration of thermokinetic data (determined by ab initio calculations) in a mean field kinetic model made it possible to validate the approach and to identify the key reaction steps dictating the selectivity. A rational screening of zeolite structures was then proposed to identify the influential topological parameters
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Kaganjo, James Chege. « Structure-function studies of 5-aminolevulinic acid (ALA) synthases ». Bowling Green State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1510583488812729.
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Shukla, Deepak R. « Three-dimensional computational investigations of flow mechanisms in compound meandering channels ». Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/8392.
Texte intégralRésumé :
Flow mechanisms of compound meandering channels are recognised to be far more complicated than compound straight channels. The compound meandering channels are mainly characterised by the continuous variation of mean and turbulent flow parameters along a meander wavelength; the existence of horizontal shear layer at the bankfull level and the presence of strong helical secondary flow circulations in the streamwise direction. The secondary flow circulations are very important as they govern the advection of flow momentum, distort isovels, and influence bed shear stress, thus producing a complicated and fully three-dimensional turbulent flow structures. A great deal of experiments has been conducted in the past, which explains flow mechanisms, mixing patterns and the behaviour of secondary flow circulations. However, a complete understanding of secondary flow structures still remains far from conclusive mainly because the secondary flow structures are influenced by the host of geometrical and flow parameters, which are yet to be investigated in detail. The three-dimensional Reynolds-averaged Navier-Stokes and continuity equations were solved using a standard Computational Fluid Dynamics solver to predict mean velocity, secondary flow and turbulent kinetic energy. Five different flow cases of various model scales and relative depths were considered. Detailed analyses of the measured and predicted flow variables were carried out to understand mean flow mechanisms and turbulent secondary flow structures in compound meandering channels. The streamwise vorticity equation was used to quantify the complex and three-dimensional behaviour of secondary flow circulations in terms of their generation, development and decay along the half-meander wavelength. The turbulent kinetic energy equation was used to understand energy expense mechanisms of secondary flow circulations. The strengths of secondary flow circulations were calculated and compared for different flow cases considered. The main findings from this research are as follows. The shearing of the main channel flow as the floodplain flow plunges into and over the main channel influences the mean and turbulent flow structures particularly in the crossover region. The horizontal shear layer at the inner bankfull level generates secondary flow circulations. As the depth of flow increases, the point of generation of secondary flow circulations moves downstream. The secondary shear stress significantly contributes towards the generation of streamwise vorticity and the production of turbulent kinetic energy. The rate of turbulence kinetic energy production was found to be higher than the rate of its dissipation in the crossover region, which demonstrates that the turbulence extracts more energy from the mean flu\\' than what is actually dissipated. This also implies that, in the crossover region, the turbulence is always advected downstream by the mean and secondary flows, The strength of geometry induced secondary flow circulation increases with the increase in the relative depth.
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Bouin, Emeric. « Propagation de fronts structurés en biologie - Modélisation et analyse mathématique ». Thesis, Lyon, École normale supérieure, 2014. http://www.theses.fr/2014ENSL0960/document.
Texte intégralRésumé :
Cette thèse est consacrée à l'étude de phénomènes de propagation dans des modèles d’EDP venant de la biologie. On étudie des équations cinétiques inspirées par le déplacement de colonies de bactéries ainsi que des équations de réaction-diffusion importantes en écologie afin de reproduire plusieurs phénomènes de dynamique et d'évolution des populations. La première partie étudie des phénomènes de propagation pour des équations cinétiques. Nous étudions l'existence et la stabilité d'ondes progressives pour des modèles ou la dispersion est donnée par un opérateur hyperbolique et non par une diffusion. Cela fait entrer en jeu un ensemble de vitesses admissibles, et selon cet ensemble, divers résultats sont obtenus. Dans le cas d'un ensemble de vitesses borné, nous construisons des fronts qui se propagent à une vitesse déterminée par une relation de dispersion. Dans le cas d'un ensemble de vitesses non borné, on prouve un phénomène de propagation accélérée dont on précise la loi d'échelle. On adapte ensuite à des équations cinétiques une méthode basée sur les équations de Hamilton-Jacobi pour décrire des phénomènes de propagation. On montre alors comment déterminer un Hamiltonien effectif à partir de l'équation cinétique initiale, et prouvons des théorèmes de convergence.La seconde partie concerne l'étude de modèles de populations structurées en espace et en phénotype. Ces modèles sont importants pour comprendre l'interaction entre invasion et évolution. On y construit d'abord des ondes progressives que l'on étudie qualitativement pour montrer l'impact de la variabilité phénotypique sur la vitesse et la distribution des phénotypes à l'avant du front. On met aussi en place le formalisme Hamilton-Jacobi pour l'étude de la propagation dans ces équations de réaction-diffusion non locales.Deux annexes complètent le travail, l'une étant un travail en cours sur la dispersion cinétique en domaine non-borné, l'autre étant plus numérique et illustre l’introductionThis thesis is devoted to the study of propagation phenomena in PDE models arising from biology. We study kinetic equations coming from the modeling of the movement of colonies of bacteria, but also reaction-diffusion equations which are of great interest in ecology to reproduce several features of dynamics and evolution of populations. The first part studies propagation phenomena for kinetic equations. We study existence and stability of travelling wave solutions for models where the dispersal part is given by an hyperbolic operator rather than by a diffusion. A set of admissible velocities comes into the game and we obtain various types of results depending on this set. In the case of a bounded set of velocities, we construct travelling fronts that propagate according to a speed given by a dispersion relation. When the velocity set is unbounded, we prove an accelerating propagation phenomena, for which we give the spreading rate. Then, we adapt to kinetic equations the Hamilton-Jacobi approach to front propagation. We show how to derive an effective Hamiltonian from the original kinetic equation, and prove some convergence results.The second part is devoted to studying models for populations structured by space and phenotypical trait. These models are important to understand interactions between invasion and evolution. We first construct travelling waves that we study qualitatively to show the influence of the genetical variability on the speed and the distribution of phenotypes at the edge of the front. We also perform the Hamilton-Jacobi approach for these non-local reaction-diffusion equations.Two appendices complete this work, one deals with the study of kinetic dispersal in unbounded domains, the other one being numerical aspects of competition models
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Wang, Yanjun. « Production of γ-valerolactone from the hydrogenation of levulinic acid or alkyl levulinates : calorimetry and kinetic study Application of the concept of Linear Free Energy Relationships to the hydrogenation of levulinic acid and its corresponding esters Thermal risk assessment of levulinic acid hydrogenation to γ-valerolactone ». Thesis, Normandie, 2020. http://www.theses.fr/2020NORMIR02.
Texte intégralRésumé :
Les énergies fossiles jouent un rôle fondamental dans l'économie, la société et la politique. Il existe différentes énergies renouvelables pouvant présenter une alternative telles le solaire, l'éolien, l'hydro-électrique ou encore la biomasse. Parmi ces énergies renouvelables, la biomasse est la seule source de carbone pouvant être utilisée pour la production de carburants, produits chimiques ou matériaux. Parmi les produits chimiques issus de la biomasse, la production de molécules plateformes comme l'acide lévulinique (AL) et ses esters est une voie attractive. Ces molécules peuvent être obtenues par solvolyse de la cellulose ou hémicellulose. L’hydrogénation de ces molécules plateformes conduit à la production de γ-valerolactone (GVL) qui peut aussi être considéré comme une molécule plateforme. Pour favoriser le passage à l'échelle industrielle et trouver les conditions opératoires optimales vis-à-vis de la sécurité et des coûts de production, les questions suivantes doivent être répondues : - Quel est le risque thermique de cette réaction d' hydrogénation? ; - Quel réactif doit-on utiliser : AL ou ses esters? ; - Afin de favoriser l’intégration énergétique, comment mesurer les enthalpies de réactions? Dans un premier temps l'évaluation des risques thermiques pour l' hydrogénation de l’acide lévulinique en GVL catalysée par Ru/C dans l'eau a été effectuée. Un modèle cinétique simple incluant un bilan énergétique en condition pseudo-adiabatique a été développé pour estimer les constantes cinétiques et les paramètres de risque thermique. Par cette étude, il a été possible de déterminer des conditions opératoires sûres pour ce système afin de prévenir les emballements thermiques. Dans un deuxième temps, une approche structure-réactivité a été effectuée en utilisant le concept de relation linéaire de l’énergie libre, à savoir l’équation de Taft. Cette équation a été utilisée pour l'hydrogénation de l'acide lévulinique et de ses esters en GVL catalysée par Ru/C. Le GVL a été utilisé comme solvant pour solubiliser les différents réactifs : AL, lévulinate de méthyle (LM), d'éthyle (LE) et de n-butyle (LB). Il a été démontré que la première étape cinétique, à savoir l'hydrogénation de LA, LM, LE ou LB en leurs intermédiaires et la cinétique de la deuxième étape, à savoir la cyclisation suivent l'équation de Taft. Les effets polaires et stériques ont été évalués et il a été montré que l'effet polaire gouverne ces étapes réactionnelles. La dernière partie de cette thèse consiste à estimer les enthalpies de réaction par calorimétrie. L'estimation de ces constantes thermodynamiques peut s'avérer complexe parce que le GVL est utilisé comme solvant et qu'il n'y a pas d'informations sur les intermédiaires. L’hydrogénation du lévulinate de méthyle a été sélectionnée pour cette étude. Une méthode utilisant les données calorimétriques et analyse chimique a permis d’évaluer l'enthalpie réactionnelle globale et les enthalpies des 2 réactions consécutives. Il a été montré que l'enthalpie globale a une valeur de -51.5 kJ/mol de GVL produits montrant que le système est dans sa globalité exothermique. L’enthalpie d'hydrogénation a été estimée à -58-66 kJ/mol de LM consommé et celle de cyclisation à +7,16 kJ/mol de GVL produitsFossil energy plays a fondamental role in the economy, society and politics. Till now, different renewable energy are explored to be an alternative for energy supply, such as wind, solar, hydro and biomass energy. Among these renewable energy, biomass is regarded as the organic carbon source which can be applied for production of fuels, chemicals or materials. Among the bio-based chemicals, production of platform molecules such as levulinic acid (LA) and its esters is one of attractive way for biomass valorization. LA and its esters can be obtained through hydrolysis and alcoholysis of cellulose or hemicellulose. By further hydrogenation, γ-valerolactone (GVL) is produced and it is also regarded as a platform molecule for further upgrading to biofuels and chemicals with wide application. To scale-up the hydrogenation reaction and to find the optimum operating conditions towards safety and cost, the following questions must be answered : - What is the thermal risk of this reaction? ; - Which starting materials to choose (LA or esters)? ; - For a better energy integration of this process, how to measure the reaction enthalpies? Herein, at first, thermal risk assessment for hydrogenation of LA to GVL catalyzed by Ru/C in water was performed. A simplified kinetic model including energy balance under near-adiabatic conditions was developed to estimate the kinetic constants and thermal risk parameters of this reaction system. Through this thermal risk assessment, it was possible to know the safe operation conditions for this reaction system, i.e., preventing the risk of thermal runaway. Secondly, a structure-reactivity approach was carried out using the concept of Linear Free Energy Relationships (LFER). i.e., Taft equation. The Taft equation (LFER) was applied to hydrogenation of LA and its corresponding esters to GVL catalyzed over Ru/C. GVL was used as a solvent to allow the solubility of the different reactants, namely, LA, methyl levulinate (ML), ethyl levulinate (EL) and n-butyl levulinate (BL). It was demonstrated that the kinetics of the first step, i.e., hydrogenation of LA, ML, EL or BL to the corresponding intermediates and the kinetics of the second step, i.e., ring-closure follow Taft equation. The polar and steric effect of the substituents were evaluated, and it is shown that polar effect governs the kinetics of both reaction steps. Thirdly, the estimation of reaction enthalpies by calorimetry experiments was done. The estimation of such thermodynamic constants by using different thermodynamic models can be hazardous, because in this study GVL was used as a solvent and there are no data concerning the intermediates. Hydrogenation of methyl levulinate (ML) to GVL catalyzed over Ru/C was selected for this study. A method which links calorimetry measurement with composition analysis was developed to determine the reaction enthalpies of the overall reaction and two consecutive steps. It was found that the overall reaction enthalpy was -51.5 kJ/mol of GVL produced, which indicates that the reaction for production of GVL from ML is exothermic. The reaction enthalpy for the first hydrogenation step was calculated to be -58.66 kJ/mol of ML consumed, and for the reaction enthalpy for the second ring-closure step was calculated to be +7.16 kJ/mol of GVL produced
Chapitres de livres sur le sujet "Structural kinetic modelling"
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Leermakers, Frans A. M., et J. Mieke Kleijn. « Molecular Modelling of Biological Membranes : Structure and Permeation Properties ». Dans Physicochemical Kinetics and Transport at Biointerfaces, 15–111. Chichester, UK : John Wiley & Sons, Ltd, 2004. http://dx.doi.org/10.1002/0470094044.ch2.
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Izadifar, Mohammadreza, Neven Ukrainczyk, Eduardus Koenders, K. M. Salah Uddin et Bernhard Middendorf. « Portlandite dissolution : Part 2. Forward rates by Kinetic Monte Carlo (KMC) ». Dans Computational Modelling of Concrete and Concrete Structures, 652–56. London : CRC Press, 2022. http://dx.doi.org/10.1201/9781003316404-78.
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Abu Bakar, Muhamad Husaini, Ahmad-Fazireen Ahmad-Fauzi et Nor Liyana Maskuri. « Kinetic Modelling of a Particle Grinding Process in a Planetary Ball Mill Jar ». Dans Advanced Structured Materials, 183–97. Cham : Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-05621-6_16.
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Alex, Aleena, et Enrico Masoero. « Autogenous healing in cement : A kinetic Monte Carlo simulation of CaCO3 precipitation ». Dans Computational Modelling of Concrete and Concrete Structures, 102–6. London : CRC Press, 2022. http://dx.doi.org/10.1201/9781003316404-12.
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Yamanoi, Y., et K. Maekawa. « Transient shear band and its kinetics around interfaces of cementitious materials and soil/rock foundation ». Dans Computational Modelling of Concrete and Concrete Structures, 381–88. London : CRC Press, 2022. http://dx.doi.org/10.1201/9781003316404-45.
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Ranzi, Gianluca, Graziano Leoni, Raymond Ian Gilbert, Luigino Dezi et Riccardo Zandonini. « State-of-the-art review on the time-dependent behaviour of composite steel-concrete beams ». Dans Time-dependent behaviour and design of composite steel-concrete structures, 61–82. Zurich, Switzerland : International Association for Bridge and Structural Engineering (IABSE), 2021. http://dx.doi.org/10.2749/sed018.ch4.
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<p>This chapter provides an overview of the work carried out to date on the long-term behaviour of composite steel-concrete beams. In the first part of the chapter, a description of the components forming a composite member is presented. This is followed by an outline of the main kinematic concepts, such as full and partial shear interaction, that influence the structural response of this form of construction due to the flexibility of the shear connection provided between the concrete and steel components. The review of the work performed on the time-dependent behaviour of concrete and its influence on the long-term structural response of composite beams for building and bridge applications is then presented. The modelling and experimental work considered in the review highlights the importance of considering concrete time effects, when predicting the in-service response of composite beams.</p>
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Becquet, M. « Direct and Inverse Dynamic Modelling for Complex Kinematic Structure Robots ». Dans Robotics and Factories of the Future ’87, 389–95. Berlin, Heidelberg : Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-73890-6_45.
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Tönshoff, H. K., S. Rehling et K. Tracht. « An Alternative Approach to Elasto-Kinematic Modelling of Machine Tool Structures ». Dans AMST’02 Advanced Manufacturing Systems and Technology, 215–23. Vienna : Springer Vienna, 2002. http://dx.doi.org/10.1007/978-3-7091-2555-7_22.
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Milia, Alfonsa, et Maurizio Maria Torrente. « Genetically Linked Sedimentary Basins to Define a Kinematic Model of the Central Mediterranean Extension ». Dans The Structural Geology Contribution to the Africa-Eurasia Geology : Basement and Reservoir Structure, Ore Mineralisation and Tectonic Modelling, 221–23. Cham : Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-030-01455-1_47.
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Chen, Qing, Anders Engström, Lars Höglund, Henrik Strandlund et Bo Sundman. « Thermo-Calc Program Interface and Their Applications - Direct Insertion of Thermodynamic and Kinetic Data into Modelling of Materials Processing, Structure and Property ». Dans Materials Science Forum, 3145–48. Stafa : Trans Tech Publications Ltd., 2005. http://dx.doi.org/10.4028/0-87849-960-1.3145.
Texte intégralActes de conférences sur le sujet "Structural kinetic modelling"
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Martin, Blake, et Armaghan Salehian. « Vibration Modelling of String-Harnessed Beam Structures Using Homogenization Techniques ». Dans ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-37039.
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Harnessing structural elements with strings, power cables, and signal cables increases the complexity in modelling the dynamic behaviour of such structures. Developing models capable of accurately predicting the dynamic behaviour of these systems is of great importance for space structures that cannot be tested prior to launch. The focus of this work is obtaining an equivalent continuum model for string-harnessed beam-like structures with periodic wrapping patterns. The tension in the string is assumed to vary as the beam deflects. The displacement field with second-order terms is determined and from which the Green-Lagrange strain tensor is obtained. After finding kinetic and potential energy expressions Hamilton’s principle is used to obtain the partial differential equation and boundary conditions. Numerical results for the shift in the natural frequencies are presented for various string properties to investigate their effects on the structure.
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Pacciani, Roberto, Michele Marconcini, Andrea Arnone et Francesco Bertini. « A CFD Study of Low Reynolds Number Flow in High Lift Cascades ». Dans ASME Turbo Expo 2010 : Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-23300.
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A study of the separated flow in high-lift, low-Reynolds-number cascade, has been carried out using a novel three-equation, transition-sensitive, turbulence model. It is based on the coupling of an additional transport equation for the so-called laminar kinetic energy with the Wilcox k-ω model. Such an approach takes into account the increase of the non-turbulent fluctuations in the pre-transitional and transitional region. Two high-lift cascades (T106C and T108), recently tested at the von Ka´rma´n Institute in the framework of the European project TATMo (Turbulence and Transition Modelling for Special Turbomachinery Applications), were analyzed. The two cascades have different loading distributions and suction side diffusion rates, and therefore also different separation bubble characteristics and loss levels. The analyzed Reynolds number values span the whole range typically encountered in aeroengines low-pressure turbines operations. Several expansion ratios for steady inflow conditions characterized by different freestream turbulence intensities were considered. A detailed comparison between measurements and computations, including bubble structural characteristics, will be presented and discussed. Results with the proposed model show its ability to predict the evolution of the separated flow region, including bubble bursting phenomena, in high-lift cascades operating in LP-turbine conditions.
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Temesvari, E., B. Batki et M. Gren. « Neutronic Methodological Benchmarks With Simplified Geometries for the Gas Cooled Reactor Group Constant Generating Tools ». Dans 2018 26th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/icone26-81427.
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In the ESNII+ EU FP7 project, a reactor physics benchmark aiming at the whole core calculation with the reflectors and detailed description of the structural elements was specified. This benchmark is based on the 2009 CEA concept of the ALLEGRO core. Fixed nominal technological data at nominal reactor state (geometry, composition) were prescribed which had to be modified in specified calculation branches according to different types of the thermal expansion and control rod positions. The parameters of the point kinetic model to be applied in a system thermal hydraulic code had to be determined this way. Static mechanical models of the expansion processes were specified by the benchmark. The goal of the calculation exercise was to verify the reactor physics codes, namely to get information about the modelling uncertainties and — after — their influence on the calculated results of the safety analyses. The obtained deviations between the participants are characterizing the user effects, the modelling uncertainties and the influence of the nuclear data differences all, without the possibility of their separation because of the complexity of the benchmark problem. A conclusion could be drawn that a step by step procedure starting from simple problems (homogenous material, Wigner-Seitz cell or subassembly in asymptotic approach) is necessary if we wish to identify the reasons of the deviations. For the Doppler effect, a decision was made in this direction already in the ESNII+ project where an infinite regular lattice problem without any leakage had to be solved. This approach of the simplicity is followed by the present benchmarks (one rod and one assembly), but extending the simple benchmarks with burnup calculations and taking into account leakage in asymptotic approximation by neglecting the complicated processes necessary in the reflector regions.
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Howell, Richard M., et Anthony D. Lucey. « Energy Production Characteristics of a Spring-Mounted Cantilevered-Free Flexible Plate in a Uniform Flow ». Dans ASME 2012 Fluids Engineering Division Summer Meeting collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/fedsm2012-72071.
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We study a new fundamental system that comprises a cantilevered thin flexible plate exactly aligned with the direction of a uniform flow in which the upstream end of the flexible plate is not fixed. Instead, it is attached to a spring-damper system that allows the entire system to oscillate perpendicularly to the flow direction as a result of the mounting’s dynamic interaction with the flow-induced oscillations of the flexible plate. This models an energy-harvesting system whereby the rate of energy extraction by the damper represents power generation from the kinetic-energy flux of the mean flow transferred via fluttering motions of the flexible plate to the motion of the mounting system. The two-dimensional modelling presented is an extension of the methods in [1,2] that mixed numerical simulation with eigenvalue analysis to study a fixed cantilevered flexible plate. The present system also includes a rigid inlet surface upstream of and fixed to the spring-mounted cantilever. Ideal flow is assumed wherein the rotationality of the boundary-layers is modelled by vortex elements on the solid-fluid interface and the imposition of the Kutta condition at the plate’s trailing edge. The Euler-Bernoulli beam model is used for the structural dynamics. Results presented first show how the replacement of the fixed leading edge with an interactively oscillating mounting modify the well-known linear-stability characteristics of a fluttering plate. The overall effect is that the critical flow speed for flutter onset is reduced and this is desirable for the present energy-harvesting application. This entails some subtle but important changes to the destabilisation mechanisms. The power generating potential of the fluid-structure interaction system is then illustrated. The present model of the dynamics of the plate-support interaction has been simplified so as to demonstrate proof-of-concept; thus, a discussion of the way forward to a more complete model is presented to close the paper.
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Franitza, Daniel, et Timo Lichtneckert. « Fast Simulation of Nonlinear Compliant Mechanisms Using Convective Rate Formulation ». Dans ASME 2005 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/detc2005-84286.
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The current paper addresses modelling and simulation of spatial compliant mechanisms, which links are of one dimensional structure. Applications of compliant mechanisms in macroscopic devices (i.e. clutches, switches) offer the advantages of cost reduction due to a lower number of parts or reduced assembly time and the avoidance of friction and wear. In microscopic devices compliant mechanisms usually apply because classical joints cannot be scaled down to the desired measurements. Usually these structures can be described with respect to their kinematic and kinetic variables for beam elements. Here the basic ideas for the calculation of compliant mechanisms at finite deformations from the viewpoint of continuum mechanics and numerics are applied. A common approach to model and simulate these structures is the use of beam elements with shape functions. Usually problems occur regarding accuracy or convergence if large deformations have to be faced. Here the beam structure is described with respect to the rates of its kinematic and kinetic variables. Using a finite element approach based on transfer matrices leads to a linear Boundary Value Problem embedded into a nonlinear Initial Value Problem. The result of this method is a fast analysis program (KOBA3D), whose abilities are presented in two examples and which results are compared to reference calculations in ABAQUS.
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Zhang, Guangcheng, Yueh-Jaw Lin et Christian Klumpner. « A Flow-Induced Structure-Based Kinetic Energy Harvester ». Dans ASME 2017 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/detc2017-67711.
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In this paper, a strategy utilizing a pair of cylinders which are put on both sides of the cantilever beam and perpendicular to the water flow direction to harvest the energy is demonstrated. The novel flow-induced structure-based energy harvester consists of a pair of inducing objects (cylinders) and one L-type cantilever beam. Macro fiber composite (MFC) is attached at the fixed end of the cantilever beam to convert the kinetic energy into electric power. The structure could induce the vortex shedding from the upstream flow and harvest the energy from it. Compared with the former studies regarding one or series layout inducing objects, the proposed structure could both improve the power output of the flow-induced energy harvester and avoid the damage happening in complex working conditions. Analytical modelling and experiment methods are both utilized in the research to cross verify the results. The characteristics related with water flow speed and center distance variations between inducing objects are discussed in the paper as well. It is found that when the water flow speed is 0.2m/s and the center distance is 30mm, the output power is optimal of 0.16μW and the power density is 0.4mW/m2.
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Nizina, Tatyana, Dmitriy Nizin, Nadezhda Kanaeva et Denis Artamonov. « Method for analyzing the kinetics of damage accumulation in the structure of polymer materials under tensile stresses ». Dans 29TH RUSSIAN CONFERENCE ON MATHEMATICAL MODELLING IN NATURAL SCIENCES. AIP Publishing, 2021. http://dx.doi.org/10.1063/5.0059899.
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SAZHIN, SERGEI, et IRINA SHISHKOVA. « Kinetic and MD modelling of automotive fuel droplets heating and evaporation : recent results ». Dans ILASS2017 - 28th European Conference on Liquid Atomization and Spray Systems. Valencia : Universitat Politècnica València, 2017. http://dx.doi.org/10.4995/ilass2017.2017.4593.
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Recent results of the investigation of kinetic and molecular dynamics (MD) models for automotive fuel droplet heating and evaporation are summarised. The kinetic model is based on the consideration of the kinetic region in the close vicinity of the surface of the heated and evaporating droplets, where the motion of molecules is described in terms of the Boltzmann equations for vapour components and air, and the hydrodynamic region away from this surface. The effects of finite thermal conductivity and species diffusivity inside the droplets and inelastic collisions in the kinetic region are taken into account. A new self-consistent kinetic model for heating and evaporation of Diesel fuel droplets is briefly described. The values of temperature and vapour densities at the outer boundary of the kinetic region are inferred from the requirement that both heat flux and mass flux of vapour components in the kinetic and hydrodynamic regions in the vicinity of the interface between these regions are equal. At first, the heat and mass fluxes in the hydrodynamic region are calculated based on the values of temperature and vapour density at the surface of the droplet. Then the values of temperature and vapour density at the outer boundary of the kinetic region, obtained following this procedure, are used to calculate the corrected values of hydrodynamic heat and species mass fluxes. The latter in their turn lead to new corrected values of temperature and vapour density at the outer boundary of the kinetic region. It is shown that this process quickly converges and leads to self-consistent values for both heat and mass fluxes. Boundary conditions at the surface of the droplet for kinetic calculations are inferred from the MD calculations. These calculations are based on the observation that methyl (CH3 ) or methylene (CH2 ) groups in n-dodecane (approximation of Diesel fuel) molecules can be regarded as separate atom-like structures in a relatively simple United Atom Model. Some results of the application of quantum chemical methods to the estimation of the evaporation/condensation coefficient are discussed.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4593
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Nuzhnov, Yu V. « Testing the ASMTurb Method on the Example Modelling of the Budget Equation of Turbulent Kinetic Energy ». Dans ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-38022.
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The statistical modeling of fluctuating kinetic energy in turbulent and non-turbulent fluid of a turbulent flow are presented and self-similar solutions applied to budget equations of conditionally averaged fluctuating kinetic energy are obtained. The equations were constructed on basis of the method of autonomous statistical modeling of turbulent flows (ASMTurb method) and allow to calculate the conditional averages both fluctuating kinetic energy and terms of the budget equations. The total statistical averages are found with help algebraic ratios between total and conditional averages through the agency of external intermittency factor. Testing the ASMTurb method is presented in the form of ASMTurb model for self-similar region of the two-stream plane mixing layer. Test results showed that the constructed here ASMTurb model is deeper and more accurate than RANS model. A comparison is performed between predictions and known experimental data for energy-containing fluctuating structure of the turbulent flow in mixing layer and excellent agreements are noted.
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Centea, Dan N., Herve Lacheray, Frederic Audren, Richard Teltz et Mohamed A. Elbestawi. « Development of the TIARA Hexapod : A Machine Tool Based on Parallel Kinematic Structures ». Dans ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0752.
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Abstract The paper focuses on the TIARA Hexapod — a parallel kinematic machine tool that is being developed at McMaster University. The design uses fixed length struts, and an inclined layout for the motion axes that results in the mechanism resembling a ‘tiara’. In addition to the novelty of the design, these characteristics have several advantages from both a performance and economic perspective. The paper presents an overview of the development program for this machine tool, discussing issues related to design, modelling, inverse and forward kinematics, workspace, and dynamics analysis. Later sections of the paper detail the kinematic and dynamic models developed for the TIARA machine tool, and demonstrate their use for workspace analysis and the specification of actuator requirements.
Rapports d'organisations sur le sujet "Structural kinetic modelling"
1
Waganet, R. J., John Duxbury, Uri Mingelgrin, John Hutson et Zev Gerstl. Consequences of Nonequilibrium Pesticide Fate Processes on Probability of Leaching from Agricultural Lands. United States Department of Agriculture, janvier 1994. http://dx.doi.org/10.32747/1994.7568769.bard.
Texte intégralRésumé :
Pesticide leaching in heterogeneous field soils is relatively unstudied and is the focus of this project. A wide variety of heterogeneous soils exist, characterized by processes that result from the presence of structural cracks, worm holes, and other preferred pathways within which the majority of transport can occur (called physical non-equilibrium processes), along with the presence of sorption processes that are both equilibrium and kinetic (chemical non-equilibrium processes). Previous studies of pesticide leaching have focused primarily on relatively homogeneous soils, which are less widely distributed in nature, but more studied due to the relative ease with which quantitative theory can be applied to interpret experimental results. The objectives of the proposed project were: first, to gain greater insight into the basic physical and chemical processes that characterize non-equilibrium systems, second, to improve our ability to predict pesticide leaching in heterogeneous field soils, and third, to estimate the consequences of non-equilibrium processes at the field scale by conducting an analysis of the probability of pesticide leaching when non-equilibrium processes prevail. The laboratory, theoretical and modelling aspects of the project were successful; the field aspects less so. We gained greater insight into basic processes in heterogeneous field soils, and we improved and tested tools (simulation models) and the methodology of using such tools for assessing the probability of pesticide leaching as a contribution to broader risk analysis efforts.
2
Perdigão, Rui A. P., et Julia Hall. Spatiotemporal Causality and Predictability Beyond Recurrence Collapse in Complex Coevolutionary Systems. Meteoceanics, novembre 2020. http://dx.doi.org/10.46337/201111.
Texte intégralRésumé :
Causality and Predictability of Complex Systems pose fundamental challenges even under well-defined structural stochastic-dynamic conditions where the laws of motion and system symmetries are known. However, the edifice of complexity can be profoundly transformed by structural-functional coevolution and non-recurrent elusive mechanisms changing the very same invariants of motion that had been taken for granted. This leads to recurrence collapse and memory loss, precluding the ability of traditional stochastic-dynamic and information-theoretic metrics to provide reliable information about the non-recurrent emergence of fundamental new properties absent from the a priori kinematic geometric and statistical features. Unveiling causal mechanisms and eliciting system dynamic predictability under such challenging conditions is not only a fundamental problem in mathematical and statistical physics, but also one of critical importance to dynamic modelling, risk assessment and decision support e.g. regarding non-recurrent critical transitions and extreme events. In order to address these challenges, generalized metrics in non-ergodic information physics are hereby introduced for unveiling elusive dynamics, causality and predictability of complex dynamical systems undergoing far-from-equilibrium structural-functional coevolution. With these methodological developments at hand, hidden dynamic information is hereby brought out and explicitly quantified even beyond post-critical regime collapse, long after statistical information is lost. The added causal insights and operational predictive value are further highlighted by evaluating the new information metrics among statistically independent variables, where traditional techniques therefore find no information links. Notwithstanding the factorability of the distributions associated to the aforementioned independent variables, synergistic and redundant information are found to emerge from microphysical, event-scale codependencies in far-from-equilibrium nonlinear statistical mechanics. The findings are illustrated to shed light onto fundamental causal mechanisms and unveil elusive dynamic predictability of non-recurrent critical transitions and extreme events across multiscale hydro-climatic problems.