Bibliografie tematiche / Global parametrization

Letteratura scientifica selezionata sul tema "Global parametrization"

Autore: Grafiati

Pubblicato: 8 giugno 2024

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Articoli di riviste sul tema "Global parametrization":

Shen, Hanxiao, Leyi Zhu, Ryan Capouellez, Daniele Panozzo, Marcel Campen e Denis Zorin. "Which cross fields can be quadrangulated?" ACM Transactions on Graphics 41, n. 4 (luglio 2022): 1–12. http://dx.doi.org/10.1145/3528223.3530187.

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We describe a method for the generation of seamless surface parametrizations with guaranteed local injectivity and full control over holonomy. Previous methods guarantee only one of the two. Local injectivity is required to enable these parametrizations' use in applications such as surface quadrangulation and spline construction. Holonomy control is crucial to enable guidance or prescription of the parametrization's isocurves based on directional information, in particular from cross-fields or feature curves, and more generally to constrain the parametrization topologically. To this end we investigate the relation between cross-field topology and seamless parametrization topology. Leveraging previous results on locally injective parametrization and combining them with insights on this relation in terms of holonomy, we propose an algorithm that meets these requirements. A key component relies on the insight that arbitrary surface cut graphs, as required for global parametrization, can be homeomorphically modified to assume almost any set of turning numbers with respect to a given target cross-field.

Campen, Marcel, David Bommes e Leif Kobbelt. "Quantized global parametrization". ACM Transactions on Graphics 34, n. 6 (4 novembre 2015): 1–12. http://dx.doi.org/10.1145/2816795.2818140.

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Myles, Ashish, Nico Pietroni e Denis Zorin. "Robust field-aligned global parametrization". ACM Transactions on Graphics 33, n. 4 (27 luglio 2014): 1–14. http://dx.doi.org/10.1145/2601097.2601154.

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Myles, Ashish, e Denis Zorin. "Controlled-distortion constrained global parametrization". ACM Transactions on Graphics 32, n. 4 (21 luglio 2013): 1–14. http://dx.doi.org/10.1145/2461912.2461970.

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Myles, Ashish, e Denis Zorin. "Global parametrization by incremental flattening". ACM Transactions on Graphics 31, n. 4 (5 agosto 2012): 1–11. http://dx.doi.org/10.1145/2185520.2185605.

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Bright, Alon, Edward Chien e Ofir Weber. "Harmonic global parametrization with rational holonomy". ACM Transactions on Graphics 36, n. 4 (20 luglio 2017): 1–15. http://dx.doi.org/10.1145/3072959.3073646.

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Pietroni, Nico, Marco Tarini, Olga Sorkine e Denis Zorin. "Global parametrization of range image sets". ACM Transactions on Graphics 30, n. 6 (dicembre 2011): 1–10. http://dx.doi.org/10.1145/2070781.2024183.

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Veira, A., S. Kloster, N. A. J. Schutgens e J. W. Kaiser. "Fire emission heights in the climate system – Part 2: Impact on transport, Black Carbon concentrations and radiation". Atmospheric Chemistry and Physics Discussions 15, n. 5 (6 marzo 2015): 6695–744. http://dx.doi.org/10.5194/acpd-15-6695-2015.

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Abstract. Wildfires represent a major source for aerosols impacting atmospheric radiation, atmospheric chemistry and cloud micro-physical properties. Although former studies indicated that the height of the aerosol–radiation interaction crucially affects the overall climate impact, the importance of fire emission heights in particular remains to be quantified. In this study we use the general circulation model ECHAM6 extended by the aerosol module HAM2 to investigate the impact of wildfire emission heights on atmospheric long-range transport, Black Carbon (BC) concentrations and atmospheric radiation. We simulate the wildfire aerosol release using either various versions of a semi-empirical plume height parametrization or prescribed standard emission heights in ECHAM6-HAM2. Extreme scenarios of near-surface or free-tropospheric only injections provide lower and upper constraints on the emission height climate impact. We find relative changes in mean global atmospheric BC burden of up to 7.9±4.4% caused by average changes in emission heights of 1.5–3.5 km. Regionally, changes in BC burden exceed 30–40% in the major biomass burning regions. The model evaluation of Aerosol Optical Thickness (AOT) against MODIS, AERONET and CALIOP observations indicates that the implementation of a plume height parametrization slightly reduces the ECHAM6-HAM2 biases regionally, but on the global scale these improvements in model performance are small. For prescribed emission release at the surface, wildfire emissions entail a total sky Top Of Atmosphere (TOA) Radiative Forcing (RF) of −0.16±0.06 W m−2. The application of a plume height parametrization which agrees reasonably well with observations introduces a slightly stronger negative TOA RF of −0.20±0.07 W m−2. The standard ECHAM6-HAM2 model in which 25% of the wildfire emissions are injected into the free troposphere and 75% into the planetary boundary layer, leads to a TOA RF of −0.24±0.06 W m−2. Overall, we conclude that simple plume height parametrizations provide sufficient representations of emission heights for global climate modeling. Significant improvements in aerosol wildfire modeling likely depend on better emission inventories and aerosol process modeling rather than on improved emission height parametrizations.

Du, Zhang Peng, Christoph Steindl e Stefan Jakubek. "Efficient Two-Step Parametrization of a Control-Oriented Zero-Dimensional Polymer Electrolyte Membrane Fuel Cell Model Based on Measured Stack Data". Processes 9, n. 4 (18 aprile 2021): 713. http://dx.doi.org/10.3390/pr9040713.

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This paper proposes a new efficient two-step method for parametrizing control-oriented zero-dimensional physical polymer electrolyte membrane fuel cell (PEMFC) models with measured stack data. Parametrizations of these models are computationally intensive due to the numerous unknown parameters and the typically nonlinear, stiff model properties. This work reduces an existing model to decrease its stiffness for accelerated numerical simulations. Subdividing the parametrization into two consecutive subproblems (thermodynamic and electrochemical ones) reduces the solution space significantly. A parameter sensitivity analysis further reduces each sub-solution space by excluding non-significant parameters. The method results in an efficient parametrization process. The two-step approach minimizes each sub-solution space’s dimension by two-thirds, respectively three-fourths, compared to the global one. An achieved R2 value between simulation and measurement of 91% on average provides the required accuracy for control-oriented models.

Veira, A., S. Kloster, N. A. J. Schutgens e J. W. Kaiser. "Fire emission heights in the climate system – Part 2: Impact on transport, black carbon concentrations and radiation". Atmospheric Chemistry and Physics 15, n. 13 (1 luglio 2015): 7173–93. http://dx.doi.org/10.5194/acp-15-7173-2015.

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Abstract. Wildfires represent a major source for aerosols impacting atmospheric radiation, atmospheric chemistry and cloud micro-physical properties. Previous case studies indicated that the height of the aerosol–radiation interaction may crucially affect atmospheric radiation, but the sensitivity to emission heights has been examined with only a few models and is still uncertain. In this study we use the general circulation model ECHAM6 extended by the aerosol module HAM2 to investigate the impact of wildfire emission heights on atmospheric long-range transport, black carbon (BC) concentrations and atmospheric radiation. We simulate the wildfire aerosol release using either various versions of a semi-empirical plume height parametrization or prescribed standard emission heights in ECHAM6-HAM2. Extreme scenarios of near-surface or free-tropospheric-only injections provide lower and upper constraints on the emission height climate impact. We find relative changes in mean global atmospheric BC burden of up to 7.9±4.4 % caused by average changes in emission heights of 1.5–3.5 km. Regionally, changes in BC burden exceed 30–40 % in the major biomass burning regions. The model evaluation of aerosol optical thickness (AOT) against Moderate Resolution Imaging Spectroradiometer (MODIS), AErosol RObotic NETwork (AERONET) and Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) observations indicates that the implementation of a plume height parametrization slightly reduces the ECHAM6-HAM2 biases regionally, but on the global scale these improvements in model performance are small. For prescribed emission release at the surface, wildfire emissions entail a total sky top-of-atmosphere (TOA) radiative forcing (RF) of −0.16±0.06 W m−2. The application of a plume height parametrization which agrees reasonably well with observations introduces a slightly stronger negative TOA RF of −0.20±0.07 W m−2. The standard ECHAM6-HAM2 model in which 25 % of the wildfire emissions are injected into the free troposphere (FT) and 75 % into the planetary boundary layer (PBL), leads to a TOA RF of −0.24±0.06 W m−2. Overall, we conclude that simple plume height parametrizations provide sufficient representations of emission heights for global climate modeling. Significant improvements in aerosol wildfire modeling likely depend on better emission inventories and aerosol process modeling rather than on improved emission height parametrizations.

Più fonti

Tesi sul tema "Global parametrization":

Coiffier, Guillaume. "Global Parametrization Algorithms for Quadmeshing". Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0273.

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Les maillages quadrangulés sont une structure de données centrale au domaine du traitement automatique de la géométrie, trouvant des applications en infographie comme en simulation numérique. De nos jours, les techniques de génération automatique calculant les maillages quads de meilleure qualité se basent sur le calcul d'une représentation à plat de la surface à mailler. Pour que des quadrilatères puissent être extraits, cette paramétrisation se doit d'être "sans couture", c'est-à-dire de respecter un ensemble de contraintes sur son bord et ses découpes. Cela demande une quantification en nombre entier de certains degrés de liberté. Ces contraintes sont généralement imposées petit à petit dans un pipeline d'opérations désormais bien étudié, consistant en un calcul de champ de repères lisse, définissant un champ de singularités au défaut d'angle multiple de "pi/2", une phase d'intégration pour obtenir une paramétrisation aux coutures sans rotation, suivie d'une phase de quantification déterminant les degrés de liberté en translation. Cette thèse s'intéresse à l'amélioration des différentes étapes du pipeline de génération de maillages quadrilatéraux. En nous appuyant sur des notions de géométrie différentielle, nous proposons des formulations du problème évitant les écueils de l'approche actuelle. Premièrement, nous abandonnons la résolution de problèmes en nombre entier pour certaines étapes (connue pour être difficiles à résoudre) pour la remplacer par la minimisation de fonctions objectif continues (bien que non convexe). Deuxièmement, nous fusionnons certaines étapes du pipeline en une seule optimisation déterminant en un seul coup les degrés de liberté correspondants. Cela permet plus de versatilité et de contrôle utilisateur sur le maillage quad final, et évite les cas d'échecs classiques causés par l'approche gloutonne du pipeline actuel. Ces formulations théoriques du problème de paramétrisation sans couture s'accompagnent d'implémentations pratiques dans lesquelles nous démontrons la viabilité de nos approches sur une grande variété de modèles CAO. Finalement, notre travail est théoriquement généralisable au problème plus difficile du maillage hexaédrique, là où les algorithmes de paramétrisation actuels sont soit uniquement valables pour les surfaces, soit échouent à produire des résultats de façon robuste
Quadrangular meshes are a central data structure in the domain of geometry processing, with applications ranging from computer graphics to numerical simulation. Nowadays, techniques for automatic generation of quadmeshes with the highest quality results rely on a flat representation of the surface to mesh. For quads to be extracted from this so-called surface parametrization, it has to be seamless, that is to say satisfy a set of constraints on its boundary and its cuts. This needs a quantization as integer values of some of its degrees of freedom. These constraints are usually enforced progressively in a well-studied pipeline of operations, consisting in the computation of a smooth frame field, defining a singularity distribution with angle defects multiple of "pi/2", an integration phase from which a rotationally seamless parametrization is recovered, and a quantization step to determine the translational degrees of freedom. In this work, we focus on improving the steps of the parametrization-based quadmeshing pipeline. Using notions from differential geometry, we propose formulations of the problem that avoids the drawbacks of the current approaches. Firstly, we get rid of the mixed-integer optimization problems (known to be hard to solve) used in some steps. We replace them by the minimization of smooth (yet non-convex) objective functions. Secondly, we merge some of the pipeline's steps into a single optimization determining the corresponding degrees of freedom in one go. This allows for more versatility and user control over the final quadmesh, and avoids typical failure cases caused by the greedy approach of the current pipeline. These theoretical formulations of the seamless parametrization problems are accompanied by practical implementations where we demonstrate the viability of our approach on a vast array of CAD models. Finally, our work is theoretically generalizable to the more difficult problem of hexahedral meshing. As current parametrization-based approaches are only suitable for surfaces or simply fail at reliably producing results in the volume case, this opens the way for more robustness and qualitative hexmeshes

Ramos, João Paulo Augusto. "Calibração e avaliação de modelos para estimativa da radiação solar global para o Brasil". Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/11/11152/tde-25082017-093906/.

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A radiação solar global (RG) é uma das variáveis meteorológicas mais importantes para a compreensão de processos biofísicos em ferramentas ao suporte de decisão na agricultura. Atualmente, ela pode ser medida por diferentes sensores de custo relativamente baixos e, de modo geral, apenas estações meteorológicas instaladas mais recentemente registram RG. Na falta de dados observados, torna-se necessário estimá-la através de modelos tão simples quanto possível e baseados em dados de entrada de fácil obtenção. O presente trabalho teve por objetivo analisar dois modelos (Bristow e Campbell (1984) (BC) e Hargreaves e Samani (1982) (H)) e otimizá-los estatisticamente, ajustando seus parâmetros, tomando como referência uma base de dados observados de 32 localidades pelo Instituto Nacional de Pesquisas Espaciais em todas as regiões brasileiras. O desempenho de cada modelo foi avaliado através do erro médio (EM), erro médio absoluto (EAM), coeficiente de determinação (R2), coeficiente de correlação (r), índice de concordância de Willmott (d) e raiz do erro médio quadrático (RMSE). Utilizando os parâmetros originais, o modelo H apresentou melhor desempenho, analisando RMSE, para todas as regiões brasileiras, com valores de 4.24 MJ.m-2d-1 para a região Norte, 4.55 MJ.m-2d-1 para a região Nordeste, 4.39 MJ.m-2d-1 para a região Centro Oeste, 4.61 MJ.m-2d-1 para a região Sul e 4.21 MJ.m-2d-1 para a região Sudeste. Após a otimização, o melhor desempenho foi dado pelo modelo BC, em todas as regiões do Brasil, com RMSE de 3.44 MJ.m-2d-1 para a Região Norte, 3.70 MJ.m-2d-1 para a região Nordeste, 3.62 MJ.m-2d-1 para a região Centro Oeste, 4.43 MJ.m-2d-1 para a região Sul e 3.50 MJ.m-2d-1 para a região Sudeste. Com a otimização dos parâmetros, encontraram-se valores médios para KT, utilizada pelo modelo de H: 0.152 °C-0,5 para a região Norte, 0.173 °C-0,5 para a região Nordeste, 0.145 °C-0,5 para a região Centro Oeste, 0.163 °C-0,5 para a região Sul e 0.152 °C-0,5 para a região Sudeste. Para os parâmetros adimensionais \"A\", \"B\" e \"C\" do modelo BC obteve-se para cada região, respectivamente, os seguintes valores: 0.619, 0.026 e 1.845 para a região Norte, 0.694, 0.074 e 1.489 para a região Nordeste, 0.635, 0.029 e 1.697 para a região Centro Oeste, 0.671, 0.044 e 1.580 para a região Sul e 0.702, 0.025 e 1.747 para a região Sudeste.
Global solar radiation (RG) is one of the most important weather variables for understanding the biophysical processes in agricultural support tools. Currently, it can be measured by different low cost sensors. In Brazil, weather stations just recently start to record RG values. In the absence of long term observed data, models for estimating RG are needed, and the objective of this study was to analyse two Bristow and Campbell (1984) (BC) and Hargreaves and Samani (1982) (H) models for different regions in Brazil against a reference database of 32 places collected the National Institute of Space Research (INPE) through the coefficient of determination (R2), correlation coefficient (r), Willmott concordance index (d), modelling efficiency (E), and root mean square error (RMSE). They were also statistically optimized based on an iterative approach. Using the original parameters, the H model presented the best performance for all Brazilian regions, with values with RMSE of 4.24 MJ.m-2d-1 for a North region, 4.55 MJ.m-2d-1 for the Northeast Region, 4.39 MJ.m-2d-1 for a Midwest region, 4.61 MJ.m-2d-1 for a South region and 4.21 MJ.m-2d-1 for a Southeast region. After the optimization process, the best performance was given by the BC model for all Brazilian regions, with RMSE of 3.44 MJ.m-2d-1 for a North Region, 3.70 MJ.m-2d-1 for a Northeast region, 3.62 MJ.m-2d-1 for a Midwest region, 4.43 MJ.m-2d-1 for a South region and 3.50 MJ.m-2d-1 for a Southeast region. After the parameter optimization, mean values for KT for H model were 0.152 °C-0.5 for the North region, 0.173°C-0.5 for the Northeast region, 0.145°C-0.5 for the Midwest region, 0.163 °C-0.5 for the South region and 0.152°C-0.5 for the Southeast region. For the BC´s dimensionless parameters \"A\", \"B\" and \"C\" it was found the following values, respectively: 0.619, 0.026 and 1.845 for the North region, 0.694, 0.074 and 1.489 for the Northeast region, 0.635, 0.029 and 1.697 for the Midwest region, 0.671, 0.044 and 1.580 for the South region, and 0.702, 0.025 and 1.747 for the Southeast region.

Desobry, David. "Génération de maillages hexaédriques pour des simulations de grandes déformations". Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0163.

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Cette thèse se concentre sur le développement de méthodes de maillage hexaédrique adaptées aux simulations de grandes déformations en mécanique non-linéaire. Les méthodes de paramétrisation du domaine basées sur les champs de repère sont utilisées pour générer des maillages hexaédriques de haute qualité alignés sur les bords du domaine. Cependant, lors de grandes déformations, la qualité du maillage peut se dégrader et potentiellement bloquer la simulation. Cette thèse explore l'idée de déterminer une connectivité optimale pour les éléments du maillage en tenant compte des déformations prévues. En 2D, un pipeline complet est développé pour réaliser ce défi en combinant des travaux antérieurs et des contributions scientifiques. En 3D, des contributions sont apportées pour se rapprocher de cet objectif, notamment en contrôlant les valences de bord des maillages hexaédriques produits à partir de champs de repère. Les différentes parties de la thèse abordent les étapes de la simulation numérique de grandes déformations, les avantages des méthodes de paramétrisation globale, les résultats de simulations sur des maillages industriels 2D, ainsi que des contributions pour améliorer la flexibilité et la robustesse du processus de maillage hexaédrique. L'objectif final est de réduire le temps passé par les ingénieurs à générer un maillage adéquat pour une simulation en prenant en compte des informations a priori sur la déformation à laquelle le maillage et l'objet seront soumis
This thesis focuses on the development of hexahedral meshing methods suitable for large deformation simulations in non-linear mechanics. Domain parameterization methods based on frame fields are used to generate high-quality hexahedral meshes aligned with the domain boundaries. However, during large deformations, the mesh quality may degrade and potentially block the simulation. This thesis explores the idea of determining an optimal connectivity for the mesh elements while taking into account the anticipated deformations.In 2D, a complete pipeline is developed to tackle this challenge by combining previous work and scientific contributions. In 3D, contributions are made to approach this objective, particularly by controlling the boundary valences of hexahedral meshes produced from frame fields. The different parts of the thesis address the steps of large deformation numerical simulations, the advantages of global parameterization methods, the results of simulations on industrial 2D meshes, and contributions to improving the flexibility and robustness of the hexahedral meshing process.The ultimate goal is to reduce the time spent by engineers in generating an adequate mesh for a simulation by considering a priori information on the deformation to which the mesh and the object will be subjected

Capitoli di libri sul tema "Global parametrization":

Sudholt, Dirk. "Parametrization and Balancing Local and Global Search". In Handbook of Memetic Algorithms, 55–72. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-23247-3_5.

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Blanchi, Victor, Étienne Corman, Nicolas Ray e Dmitry Sokolov. "Global Parametrization Based on Ginzburg-Landau Functional". In Lecture Notes in Computational Science and Engineering, 251–62. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-76798-3_16.

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Brechbühler, Ch, G. Gerig e O. Kübler. "Towards Representation of 3D Shape: Global Surface Parametrization". In Visual Form, 79–88. Boston, MA: Springer US, 1992. http://dx.doi.org/10.1007/978-1-4899-0715-8_9.

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Yigitsoy, Mehmet, Javad Fotouhi e Nassir Navab. "Hough Space Parametrization: Ensuring Global Consistency in Intensity-Based Registration". In Medical Image Computing and Computer-Assisted Intervention – MICCAI 2014, 275–82. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-10404-1_35.

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Jensen, Hector, e Costas Papadimitriou. "Parametrization of Reduced-Order Models Based on Global Interface Reduction". In Sub-structure Coupling for Dynamic Analysis, 49–65. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-12819-7_3.

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Götz, Georg. "The Large Scale Dynamics Are Reasonably Well Understood, Un-Certainty Lies in the Parametrization of Small-Scale Processes". In Global Change, 25–32. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-23444-6_4.

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Peckham, Bruce B. "Global Parametrization and Computation of Resonance Surfaces for Periodically Forced Oscillators". In The IMA Volumes in Mathematics and its Applications, 385–405. New York, NY: Springer New York, 2000. http://dx.doi.org/10.1007/978-1-4612-1208-9_17.

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Nikolaidou, Thalia, Felipe Nievinski, Kyriakos Balidakis, Harald Schuh e Marcelo Santos. "PPP Without Troposphere Estimation: Impact Assessment of Regional Versus Global Numerical Weather Models and Delay Parametrization". In International Symposium on Advancing Geodesy in a Changing World, 107–18. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/1345_2018_44.

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Ferrentino, Enrico, e Pasquale Chiacchio. "Redundancy Parametrization in Globally-Optimal Inverse Kinematics". In Advances in Robot Kinematics 2018, 47–55. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-93188-3_6.

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Shem-Tov, Shachar, Guy Rosman, Gilad Adiv, Ron Kimmel e Alfred M. Bruckstein. "On Globally Optimal Local Modeling: From Moving Least Squares to Over-parametrization". In Mathematics and Visualization, 379–405. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-34141-0_17.

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Atti di convegni sul tema "Global parametrization":

Ganacim, Francisco, André Maximo e Luiz Velho. "Base mesh construction using global parametrization". In ACM SIGGRAPH 2012 Posters. New York, New York, USA: ACM Press, 2012. http://dx.doi.org/10.1145/2342896.2343000.

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Pietroni, Nico, Marco Tarini, Olga Sorkine e Denis Zorin. "Global parametrization of range image sets". In the 2011 SIGGRAPH Asia Conference. New York, New York, USA: ACM Press, 2011. http://dx.doi.org/10.1145/2024156.2024183.

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Pedersen, Pauli, e Velaja B. Hammer. "On Global Design Description for Orientational Strength Optimization". In ASME 1994 Design Technical Conferences collocated with the ASME 1994 International Computers in Engineering Conference and Exhibition and the ASME 1994 8th Annual Database Symposium. American Society of Mechanical Engineers, 1994. http://dx.doi.org/10.1115/detc1994-0131.

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Abstract The idea of global design description used frequently in shape optimization, is extended from curve to surface parametrization. The design is given as a linear combination of orthogonal functions. Application to orientational design of laminates for strength optimization is used as an example, but the technique is directly applicable to design also of thickness distribution. The advantages by this design description are many, including control on smoothness, control on slopes, and control on connections at the boundaries. This simplified parametrization of the design makes it possible to work with only a few design variables, say 25 for a whole design domain.

Akhtar, Adeel, Sajid Saleem e Steven L. Waslander. "Feedback Linearizing Controllers on SO(3) using a Global Parametrization". In 2020 American Control Conference (ACC). IEEE, 2020. http://dx.doi.org/10.23919/acc45564.2020.9147963.

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Cirillo, Giuseppe I., Alexandre Mauroy, Ludovic Renson, Gaëtan Kerschen e Rodolphe Sepulchre. "Global Parametrization of the Invariant Manifold Defining Nonlinear Normal Modes Using the Koopman Operator". In ASME 2015 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/detc2015-46366.

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Nonlinear normal modes of vibration have been the focus of many studies during the past years and different characterizations of them have been proposed. The present work focuses on damped systems, and considers nonlinear normal mode motions as trajectories lying on an invariant manifold, following the geometric approach of Shaw and Pierre. We provide a novel characterization of the invariant manifold, that rests on the spectral theory of the Koopman operator. A main advantage of the proposed approach is a global parametrization of the manifold, which avoids folding issues arising with the use of displacement-velocity coordinates.

KRAUSKOPF, B., e H. M. OSINGA. "GEODESIC PARAMETRIZATION OF GLOBAL INVARIANT MANIFOLDS OR WHAT DOES THE EQUADIFF 2003 POSTER SHOW?" In Proceedings of the International Conference on Differential Equations. WORLD SCIENTIFIC, 2005. http://dx.doi.org/10.1142/9789812702067_0068.

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Bošković, Jovan D. "A Nonlinear Parametrization for Stable Neural Network-Based Identification and Control". In ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-0399.

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Abstract In this paper a stable neural network-based identification and control method for a class of first-order nonlinear plants is suggested. The method is based on neural networks built using a rational activation function. The paper discusses a method for stable adjustment of the network parameters and robustness issues in the resulting closed-loop system. The overall control scheme also includes a robust global controller that guarantees that the state of the system is confined to a region in the state space. The combination of robust global and neural network-based controllers appears to be well suited for performance improvement in complex nonlinear systems.

Kume, Keita, e Isao Yamada. "A Global Cayley Parametrization of Stiefel Manifold for Direct Utilization of Optimization Mechanisms Over Vector Spaces". In ICASSP 2021 - 2021 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP). IEEE, 2021. http://dx.doi.org/10.1109/icassp39728.2021.9414157.

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Loureiro, Juliana B. R., e Atila P. Silva Freire. "Law of the Wall Formulation for Separating Flow Over a Rough Hill". In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-67382.

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Simple asymptotic arguments together with the mixing length hypothesis are used to derive a local analytical solution that accounts for adverse pressure gradient and separation effects for flows over rough walls. To model the wall roughness effects, a new parametrization method is advanced for the proposed solution in terms of the friction velocity (u∗), the local pressure gradient (∂xp) and the roughness length (z0). The near-wall solution and the parametrization function are validated against some DNS (smooth wall flow) and LDA (smooth and rough wall flows) data. The experiments were carried out in a water-channel and the extent of separated flow was made to vary as a function of the roughness and the Reynolds number. Global optimization algorithms based on four different direct search methods are used to assess the relevant flow parameters. The analysis includes regions of attached as well as separated flow. Forty two velocity profiles are tested against the proposed expression for the parametrization function, including two profiles that satisfy the solution of Stratford. The present theory furnishes consistent results that might be implemented in predictive numerical models for complex flows.

Maithripala, D. H. S., e Jordan M. Berg. "Geometric PID Control for Almost-Global Stabilization of a Quadrotor With Parameter Error and Constant Disturbances". In ASME 2014 Dynamic Systems and Control Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/dscc2014-5995.

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Intrinsic controllers are invariant under the coordinates used for their representation. In the case of rigid-body motion in two and three dimensions, the intrinsic approach eliminates problems with singularity or over-parametrization that may occur in specific choices such as Euler angles or quaternions. Intrinsic PD controllers that combine almost-global stabilization with a familiar and intuitive PD design framework have been known for several years. In this paper we show how intrinsic integral action may be added to intrinsic PD control. We apply the result to stabilize the attitude of a quadrotor UAV model, and demonstrate in simulation that performance is significantly improved in the presence of parameter uncertainty and constant disturbance forces. We also consider the effect of bounded, time-varying, disturbances.

Rapporti di organizzazioni sul tema "Global parametrization":

Seifert, Miriam, Claudia Hinrichs, Judith Hauck e Christoph Völker. New / improved model parametrizations for responses in phytoplankton growth and calcification to changes in alkalinity implemented. OceanNets, marzo 2023. http://dx.doi.org/10.3289/oceannets_d4.5.

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Global biogeochemical ocean models that are currently in place to investigate alkalinity enhancement at a global scale do usually not consider the effects of a changing carbonate system on phytoplankton. We introduce new and modified parameterizations of phytoplankton carbonate systems sensitivities into the biogeochemistry model REcoM. We then compare phytoplankton biomass and net primary production at different atmospheric CO2 concentrations to results from other deliverables (D5.3, 5.6, 5.7) based on experiments and models. The resilience of phytoplankton biomass towards low CO2 concentrations in our model compares well with the results of mesocosm experiments. Or model results differ in the phytoplankton responses compared to the results of a 1D biogeochemical model that employs similar parameterizations regarding the effects on calcifying phytoplankton and total net primary production, which we explain primarily with differences in the spatial scales and phytoplankton communities investigated.