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Auswahl der wissenschaftlichen Literatur zum Thema „Numerical schemes coupling“
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Zeitschriftenartikel zum Thema "Numerical schemes coupling"
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Mani Aouadi, S., W. Mbarki und N. Zemzemi. „Stability Analysis of Decoupled Time-stepping Schemes for the Specialized Conduction System/myocardium Coupled Problem in Cardiology“. Mathematical Modelling of Natural Phenomena 12, Nr. 5 (2017): 208–39. http://dx.doi.org/10.1051/mmnp/201712513.
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The Purkinje network is the rapid conduction system in the heart. It ensures the physiological spread of the electrical wave in the ventricles. In this work, we consider a problem that models the coupling between the Purkinje network and the myocardium. We first prove the stability of the space semi-discretized problem. Then we present four different strategies for solving the Purkinje/ myocardium coupling. The strategies are based on different time discretization of the coupling terms. The first scheme is fully coupled, where the coupling terms are considered implicit. The second and the third schemes are based on Gauss-Seidel time-splitting schemes where one coupling term is considered explicit and the other is implicit. The last is a Jacobi-like time-splitting scheme where both coupling terms are considered explicit. Our main result is the proof of the stability of the three considered schemes under the same restriction on the time step. Moreover, we show that the energy of the problem is slightly affected by the time-splitting schemes. We illustrate the theoretical result by different numerical simulations in 2D. We also conduct 3D simulations using physiologically detailed ionic models.
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Miller, Scott T., Gregory Bunting und Nicholas A. Reynolds. „Numerical investigation of coupling schemes for structural acoustics“. Journal of the Acoustical Society of America 143, Nr. 3 (März 2018): 1717. http://dx.doi.org/10.1121/1.5035592.
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Best, M. J., A. Beljaars, J. Polcher und P. Viterbo. „A Proposed Structure for Coupling Tiled Surfaces with the Planetary Boundary Layer“. Journal of Hydrometeorology 5, Nr. 6 (01.12.2004): 1271–78. http://dx.doi.org/10.1175/jhm-382.1.
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Abstract A generalized coupling is proposed between atmospheric models and surface schemes (land and ocean). A set of input and output variables is defined for this purpose in such a way that it can be used by many current and future models, including mosaic or tile schemes. The basic concept is to pass atmospheric variables from the lowest model level and their relation to corresponding fluxes to the surface scheme. The surface scheme returns the fluxes. In this framework, there is no need for the atmospheric model to have detailed information about the surface. Only the result of the surface computations is needed; namely, the fluxes, which are applied as a boundary condition. The equations for fully implicit coupling are derived, and the relevance for numerical stability is demonstrated. It is also shown that fully implicit coupling in a tile scheme leads to more robust results than partially implicit coupling.
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Tang, Jinyun, und William J. Riley. „Predicted Land Carbon Dynamics Are Strongly Dependent on the Numerical Coupling of Nitrogen Mobilizing and Immobilizing Processes: A Demonstration with the E3SM Land Model“. Earth Interactions 22, Nr. 11 (01.05.2018): 1–18. http://dx.doi.org/10.1175/ei-d-17-0023.1.
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AbstractWhile coupling carbon and nitrogen processes is critical for Earth system models to accurately predict future climate and land biogeochemistry feedbacks, it has not yet been analyzed how numerical methods that land biogeochemical models apply to couple soil mineral nitrogen mobilizing and immobilizing processes affect predicted ecosystem carbon and nitrogen cycling. These effects were investigated here by using the E3SM land model and an evaluation of three plausible and widely used numerical couplings: 1) the mineral nitrogen–based limitation scheme, 2) the net uptake–based limitation scheme, and 3) the proportional nitrogen flux–based limitation scheme. It was found that these three schemes resulted in large differences (with a range of 316 PgC) in predicted cumulative land–atmosphere carbon exchanges under the RCP4.5 atmospheric CO2 simulations. This large uncertainty is without accounting for the different representations of the many land biogeochemical processes, but is about 73% of the range (434 PgC) reported for CMIP5 RCP4.5 simulations. These results help explain the large uncertainty found in various model intercomparison experiments and suggest that more robust numerical implementations are needed to improve carbon–nutrient cycle coupling in terrestrial ecosystem models.
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Regazzoni, Francesco. „Stabilization of loosely coupled schemes for 0D–3D fluid–structure interaction problems with application to cardiovascular modelling“. Numerische Mathematik 157, Nr. 1 (25.01.2025): 249–306. https://doi.org/10.1007/s00211-025-01452-z.
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Abstract In this paper we analyze the numerical oscillations affecting loosely coupled schemes for hybrid-dimensional 0D–3D fluid–structure interaction (FSI) problems, which arise e.g. in the field of cardiovascular modeling, and we propose a novel stabilized scheme that cures this issue. We study several loosely coupled schemes, including the Dirichlet–Neumann (DN) and Neumann–Dirichlet (ND) schemes. In the first one, the 0D fluid model prescribes the pressure to the 3D structural mechanics model and receives the flow. In the second one, on the contrary, the fluid model receives the pressure and prescribes the flow. The terms DN and ND, employed in the FSI literature, are borrowed from domain decomposition methods, although here a single iteration is performed before moving on to the next time step (that is, the coupling is treated explicitly). Should the fluid be enclosed in a cavity, the DN scheme is affected by non-physical oscillations whose origin lies in the balloon dilemma, for which we provide an algebraic interpretation. Moreover, we show that also the ND scheme can be unstable for a range of parameter choices. Surprisingly, increasing either the viscous dissipation or the inertia of the structure favours the onset of oscillations and, for certain parameter choices, the ND is unconditionally unstable. In the presence of inertial terms, by reducing the time step size below a certain threshold, the amplitude of the numerical oscillations is even amplified. We provide an explanation for these facts and establish sharp stability bounds on the time step size. Our analysis extends to Robin–Robin schemes, based on linear combinations of the conditions of pressure continuity and either volume or flux continuity. While appropriate choices of Robin coefficients can achieve numerical stability, tuning these coefficients can be challenging in practice. To address these issues, we propose a numerically consistent stabilization term for the Neumann–Dirichlet scheme, inspired by physical insight on the onset of oscillations. We prove that our proposed stabilized scheme is absolutely stable for any choice of time step size. Notably, the proposed scheme does not require parameter tuning. These results are verified by several numerical tests. Finally, we apply the proposed stabilized scheme to an important problem in cardiac electromechanics, namely the coupling between a 3D cardiac model and a closed-loop lumped-parameter model of blood circulation. In this setting, our proposed scheme successfully removes the non-physical oscillations that would otherwise affect the numerical solution.
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Banda, Mapundi K., Axel-Stefan Häck und Michael Herty. „Numerical Discretization of Coupling Conditions by High-Order Schemes“. Journal of Scientific Computing 69, Nr. 1 (18.04.2016): 122–45. http://dx.doi.org/10.1007/s10915-016-0185-x.
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QI, GUANXIAO, HONGBIN HUANG und HAIJUN WANG. „SIZE INSTABILITIES IN THE RING AND LINEAR ARRAYS OF CHAOTIC SYSTEMS“. Advances in Complex Systems 10, Nr. 03 (September 2007): 301–13. http://dx.doi.org/10.1142/s0219525907001185.
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We investigate the dynamical stabilities of ring and linear arrays of chaotic oscillators with asymmetric nearest-neighbor and long-range couplings. It is shown that the instabilities of complete chaotic synchronization occur as the numbers of oscillators are increased beyond critical values which depend on the coupling schemes and coupling parameters of the systems. Based on the master stability function and eigenvalue analysis methods, we give the semi-analytical relations between the critical values and the coupling parameters. Results are demonstrated with numerical simulations in a set of coupled Lorenz oscillators.
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An, Xingwei, Tonghui Deng, Lei Chen, Saiyun Ye und Zhirong Zhong. „Generation of Schrödinger Cat States in a Hybrid Cavity Optomechanical System“. Entropy 24, Nr. 11 (29.10.2022): 1554. http://dx.doi.org/10.3390/e24111554.
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We present an alternative scheme to achieve Schrödinger cat states in a strong coupling hybrid cavity optomechanical system. Under the single-photon strong-coupling regime, the interaction between the atom–cavity–oscillator system can induce the mesoscopic mechanical oscillator to Schrödinger cat states. Comparing to previous schemes, the proposed proposal consider the second order approximation on the Lamb–Dicke parameter, which is more universal in the experiment. Numerical simulations confirm the validity of our derivation.
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Ketata, Ahmed, Zied Driss und Mohamed Salah Abid. „1D gas dynamic code for performance prediction of one turbocharger radial turbine with different finite difference schemes“. Mechanics & Industry 20, Nr. 6 (2019): 627. http://dx.doi.org/10.1051/meca/2019073.
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The turbine, a key component of a turbocharger, is usually characterized by steady flow solutions. This method seems to be physically unrealistic as the fluid flow within a turbine is strongly unsteady due to the pulsating nature of the flow in the exhaust manifold of a reciprocating engine. This paper presents a new 1D gas dynamic code, written in the FORTRAN language, to characterize a radial turbine of one turbocharger embedded to a small gasoline engine. This code presents the novelty of meanline-1D coupling and the feature of numerical schemes choice. In this study, the turbocharger turbine is simulated with six different finite difference schemes. The computed distribution of the downstream mass flow rate, from the different cases, is compared to test data in order to choose the most suitable scheme. Test data are gathered from a developed test facility. Based on the computed results, unsteady performance of the turbine has been computed and discussed for the different schemes at two engine frequencies of 50 and 83.33 Hz. The results showed a significant impact of the numerical scheme on the 1D prediction of the turbine performance. Results indicated that the MR2LW finite-difference scheme has led to the minimum deviation of the numerical results to test data compared to the other considered schemes.
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Bishop, Michael P., Brennan W. Young und Jeffrey D. Colby. „Numerical Modeling and Parameter Sensitivity Analysis for Understanding Scale-Dependent Topographic Effects Governing Anisotropic Reflectance Correction of Satellite Imagery“. Remote Sensing 14, Nr. 21 (25.10.2022): 5339. http://dx.doi.org/10.3390/rs14215339.
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Anisotropic reflectance correction (ARC) of satellite imagery is required to remove multi-scale topographic effects in imagery. Commonly utilized ARC approaches have not effectively accounted for atmosphere-topographic coupling. Furthermore, it is not clear which topographic effects need to be formally accounted for. Consequently, we simulate the direct and diffuse-skylight irradiance components and formally account for multi-scale topographic effects. A sensitivity analysis was used to determine if characterization schemes can account for a collective treatment of effects, using our parameterization scheme as a basis for comparison. We found that commonly used assumptions could not account for topographic modulation in our simulations. We also found that the use of isotropic diffuse irradiance and a topographic shielding parameter also failed to characterize topographic modulation. Our results reveal that topographic effects govern irradiance variations in a synergistic way, and that issues of ARC need to be formally addressed given atmosphere-topography coupling. Collectively, our results suggest that empirical ARC methods cannot be used to effectively address topographic effects, given inadequate parameterization schemes. Characterizing and removing spectral variation from multispectral imagery will most likely require numerical modeling efforts. More research is warranted to develop/evaluate parameterization schemes that better characterize the anisotropic nature of atmosphere-topography coupling.
Dissertationen zum Thema "Numerical schemes coupling"
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Alnafisah, Yousef Ali. „First-order numerical schemes for stochastic differential equations using coupling“. Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/20420.
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We study a new method for the strong approximate solution of stochastic differential equations using coupling and we prove order one error bounds for the new scheme in Lp space assuming the invertibility of the diffusion matrix. We introduce and implement two couplings called the exact and approximate coupling for this scheme obtaining good agreement with the theoretical bound. Also we describe a method for non-invertibility case (Combined method) and we investigate its convergence order which will give O(h3/4 √log(h)j) under some conditions. Moreover we compare the computational results for the combined method with its theoretical error bound and we have obtained a good agreement between them. In the last part of this thesis we work out the performance of the multilevel Monte Carlo method using the new scheme with the exact coupling and we compare the results with the trivial coupling for the same scheme.
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Qirezi, Fatmir. „Discrete schemes for thermoviscoelasticity with thermorheologically-simple nonlinear coupling“. Thesis, Brunel University, 2014. http://bura.brunel.ac.uk/handle/2438/13456.
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Usman, Muhammad. „Performance Assessment and Management of Groundwater in an Irrigation Scheme by Coupling Remote Sensing Data and Numerical Modeling Approaches“. Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-203578.
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The irrigated agriculture in the Lower Chenab Canal (LCC) of Pakistan is characterized by huge water utilization both from surface and groundwater resources. Need of utilization of water from five rivers in Punjab province along with accelerated population growth has forced the construction of world’s largest irrigation network.
Nevertheless, huge irrigation infrastructure, together with inappropriate drainage infrastructure, led to a build-up of shal-low groundwater levels, followed by waterlogging and secondary salinization in the soil profile. Following this era, decreased efficiency of irrigation supply system along with higher food demands had increased burdens on groundwater use, which led to a drop in groundwater levels in major parts of LCC. Previous studies in the study region revealed lacking management and maintenance of irrigation system, inflexible irrigation strategies, poor linkages between field level water supply and demands. No future strategy is present or under consideration to deal with this long time emerged groundwater situation particularly under unchanged irrigation water supply and climate change. Therefore, there is an utmost importance to assess the current profile of water use in the irrigation scheme and to device some workable strategies under future situations of land use and climate change. This study aims to investigate the spatio-temporal status of water utilization and performance of irrigation system using remote sensing data and techniques (SEBAL) in combination with other point data.
Different irrigation performance indicators including equity, adequacy and reliability using evaporation fraction as main input parameter are utilized. Current profiles of land use/land cover (LULC) areas are assessed and their change detections are worked out to establish realistic future scenarios. Spatially distributed seasonal net recharge, a very important input parameter for groundwater modeling, is estimated by employing water balance approaches using spatial data from remote sensing and local norms. Such recharge results are also compared with a water table fluctuation approach. Following recharge estimation, a regional 3-D groundwater flow model using FEFLOW was set up. This model was calibrated by different approaches ranging from manual to automated pilot point (PP) approach. Sensitivity analysis was performed to see the model response against different model input parameters and to identify model regions which demand further improvements. Future climate parameters were downscaled to establish scenarios by using statistical downscaling under IPCC future emission scenarios. Modified recharge raster maps were prepared under both LULC and climate change scenarios and were fed to the groundwater model to investigate groundwater dynamics.
Seasonal consumptive water use analysis revealed almost double use for kharif as compared to rabi cropping seasons with decrease from upper LCC to lower regions. Intra irrigation subdivision analysis of equity, an important irrigation performance indicator, shows less differences in water consumption in LCC. However, the other indicators (adequacy and reliability) indicate that the irrigation system is neither adequate nor reliable. Adequacy is found more pronounced during kharif as compared to rabi seasons with aver-age evaporation fraction of 0.60 and 0.67, respectively. Similarly, reliability is relatively higher in upper LCC regions as compared to lower regions. LULC classification shows that wheat and rice are major crops with least volatility in cultivation from season to season. The results of change detection show that cotton exhibited maximum positive change while kharif fodder showed maximum negative change during 2005-2012. Transformation of cotton area to rice cultivation is less conspicuous. The water consumption in upper LCC regions with similar crops is relatively higher as compared to lower regions. Groundwater recharge results revealed that, during the kharif cropping seasons, rainfall is the main source of recharge followed by field percolation losses, while for rabi cropping seasons, canal seepage remains the major source. Seasonal net groundwater recharge is mainly positive during all kharif seasons with a gradual increase in groundwater level in major parts of LCC. Model optimization indicates that PP is more flexible and robust as compared to manual and zone based approaches. Different statistical indicators show that this method yields reliable calibration and validation as values of Nash Sutcliffe Efficiency are 0.976 and 0.969, % BIAS are 0.026 and -0.205 and root mean square errors are 1.23 m and 1.31 m, respectively. Results of model output sensitivity suggest that hydraulic conductivity is a more influential parameter in the study area than drain/fillable porosity. Model simulation results under different scenarios show that rice cultivation has the highest impact on groundwater levels in upper LCC regions whereas major negative changes are observed for lower parts under decreased kharif fodder area in place of rice, cotton and sugarcane. Fluctuations in groundwater level among different proposed LULC scenarios are within ±1 m, thus showing a limited potential for groundwater management. For future climate scenarios, a rise in groundwater level is observed for 2011 to 2025 under H3A2 emission regime. Nevertheless, a drop in groundwater level is expected due to increased crop consumptive water use and decreased precipitations under H3A2 scenario for the periods 2026-2035 and 2036-2045. Although no imminent threat of groundwater shortage is anticipated, there is an opportunity for developing groundwater resources in the lower model regions through water re-allocation that would be helpful in dealing water shortages. The groundwater situation under H3B2 emission regime is relatively complex due to very low expectation of rise in groundwater level through precipitation during 2011-2025. Any positive change in groundwater under such scenarios is mainly associated with changes in crop consumptive water uses. Consequently, water management under such situation requires revisiting of current cropping patterns as well as augmenting water supply through additional surface water resources.
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Ritzenthaler, Valentin. „Stratégies de couplage des méthodes Compatible Discrete Operators appliquées aux équations de Maxwell dans le domaine temporel“. Electronic Thesis or Diss., Toulouse, ISAE, 2024. http://www.theses.fr/2024ESAE0060.
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Dans le domaine de la simulation numérique des équations de Maxwell, l'un des principaux objectifs consiste à rendre compte numériquement de la réalité physique des champs électromagnétiques avec une haute précision et un faible coût calcul. Il existe aujourd'hui de nombreuses méthodes permettant de résoudre le système de Maxwell en domaine temporel, présentant chacune, en fonction des situations, des qualités et des défauts. Dans cette thèse, on s’intéresse à deux stratégies de couplagedes méthodes Compatible Discrete Operators (CDO) appliquées aux équations de Maxwell dans le domaine temporel. La première, consiste à définir localement la métrique du schéma en fonction de la géométrie du maillage. La seconde, consiste à partitionner le domaine de calcul en deux sous-domaines et à coupler les méthodes par la définition d'opérateurs sur l’interface. Pour cela, les équations de Maxwell sont étudiées en deux parties : les relations topologiques, d’une part, et les relations constitutives, d’autre part. Dans le cadre CDO, les relations topologiques sont formulées au moyen d’opérateurs différentiels discrets correspondant à la discrétisation des opérateurs vectoriels classiques. Afin de prendre en compte des conditions au bord non homogènes, ces opérateurs sont étendus au bord. Les relations constitutives sont quant à elles formulées au moyen d’opérateurs de Hodge discrets. Ils définissent la métrique du schéma et dépendent des paramètres matériels. Le schéma discret en espace et en temps est alors analysé en terme de stabilité et de consistance. Il est ensuite testé numériquement sur différentes configurations de maillages hybridesIn numerical simulations of Maxwell's equations, one of the main goals is to accurately represent the physical reality of electromagnetic fields while keeping a low computational cost. Numerous methods exist for solving the system in the time domain, each with its own strengths and weaknesses, depending on the situation. In this thesis, we focus on two coupling strategies of Compatible Discrete Operators (CDO) schemes applied to Maxwell's equations in time domain. The first consists in locally defining the metric of the scheme by considering the mesh geometry. In the second approach, the computational domain is partitioned in two subdomains and the coupling is achieved by defining operators on the interface. To this end, Maxwell's equations are studied in two parts: the topological relations and the constitutive relations. In the CDO framework, the topological relations are formulated using discrete differential operators corresponding to the discretization of the classical vector operators. In order to take into account non-homogeneous boundary conditions, these operators are extended using a dual boundary mesh. The constitutive relations are formulated using discrete Hodge operators. They define the metric of the scheme and depend on the material parameters. The discrete scheme in space and time is then analyzed in terms of stability and consistency. We then test it on different configurations using hybrid meshes
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Viot, Louis. „Couplage et synchronisation de modèles dans un code scénario d’accidents graves dans les réacteurs nucléaires“. Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLN033/document.
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La thèse s'inscrit dans le contexte des accidents graves dans les réacteurs nucléaires qui sont étudiés au laboratoire de physique et modélisation des accidents graves (LPMA) du CEA de Cadarache. Un accident grave survient lors de la perte du caloporteur au niveau du circuit primaire ce qui provoque une dégradation du combustible et la création d'un bain de corium. Celui-ci va ensuite se propager en cuve et fortement endommager les structures du réacteur. Pour la sûreté nucléaire, il est donc nécessaire de pouvoir prévoir la propagation de ce corium, d'où la création en 2013 de la plateforme PROCOR (Java) permettant aux travers d'applications industrielles de simuler cette propagation. Ces applications sont un ensemble de modèles physiques, couplés sur une macro boucle en temps, ayant chacun un ensemble d'équations algébriques et différentielles qui sont résolues en interne des modèles. Les modèles de la plateforme sont généralement des modèles OD dont la discrétisation spatiale est remplacée par des corrélations généralement issues de l'expérience. Chaque modèle a aussi un ensemble d'états et de règles de transition, et un changement d'état peut alors survenir à l'intérieur de la macro boucle en temps. Au début de la thèse, le couplage était simplement un chaînage des modèles sur la macro boucle en temps : chaque modèle est résolu l'un après l'autre, l'ordre étant défini par le créateur de l'application, et les modèles sont synchronisés à la fin de cette boucle. Les résultats des applications industrielles de la plateforme en modifiant simplement le pas de temps de la macro boucle en temps montrent une forte dépendance du schéma avec ce pas de temps. On a par exemple 10 % d'écart sur les flux imposés sur la cuve du réacteur en passant d'un pas de temps de 100 s à 50 s, ce qui a un fort impact sur les résultats de sûreté nucléaireThis thesis focuses on solving coupled problems of models of interest for the simulation of severe accidents in nuclear reactors~: these coarse-grained models allow for fast calculations for statistical analysis used for risk assessment and solutions of large problems when considering the whole severe accident scenario. However, this modeling approach has several numerical flaws. Besides, in this industrial context, computational efficiency is of great importance leading to various numerical constraints. The objective of this research is to analyze the applicability of explicit coupling strategies to solve such coupled problems and to design implicit coupling schemes allowing stable and accurate computations. The proposed schemes are theoretically analyzed and tested within CEA's procor{} platform on a problem of heat conduction solved with coupled lumped parameter models and coupled 1D models. Numerical results are discussed and allow us to emphasize the benefits of using the designed coupling schemes instead of the usual explicit coupling schemes
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Tschisgale, Silvio. „A numerical method for fluid-structure interactions of slender rods in turbulent flow“. TUDpress - Thelem Universitätsverlag, 2018. https://tud.qucosa.de/id/qucosa%3A38706.
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This thesis presents a numerical method for the simulation of fluid-structure interaction (FSI) problems on high-performance computers. The proposed method is specifically tailored to interactions between Newtonian fluids and a large number of slender viscoelastic structures, the latter being modeled as Cosserat rods. From a numerical point of view, such kind of FSI requires special techniques to reach numerical stability. When using a partitioned fluid-structure coupling approach
this is usually achieved by an iterative procedure, which drastically increases the computational effort. In the present work, an alternative coupling approach is developed based on an immersed boundary method (IBM). It is unconditionally
stable and exempt from any global iteration between the fluid part and the structure part.
The proposed FSI solver is employed to simulate the flow over a dense layer of vegetation elements, usually designated as canopy flow. The abstracted canopy model used in the simulation consists of 800 strip-shaped blades, which is the
largest canopy-resolving simulation of this type done so far. To gain a deeper understanding of the physics of aquatic canopy flows the simulation data obtained are analyzed, e.g., concerning the existence and shape of coherent structures.
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Usman, Muhammad [Verfasser], Rudolf [Akademischer Betreuer] [Gutachter] Liedl, Niels [Gutachter] Schütze und Martin [Gutachter] Sauter. „Performance Assessment and Management of Groundwater in an Irrigation Scheme by Coupling Remote Sensing Data and Numerical Modeling Approaches / Muhammad Usman. Betreuer: Rudolf Liedl. Gutachter: Rudolf Liedl ; Niels Schütze ; Martin Sauter“. Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://d-nb.info/1105876535/34.
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Ramsamy, Priscilla. „Modélisation de la morphodynamique sédimentaire par une méthode distribuant le résidu“. Thesis, Antilles, 2017. http://www.theses.fr/2017ANTI0206/document.
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Ce travail de thèse, propose un schéma numérique d'ordre élevé, distribuantle résidu (RD) pour l'approximation d'un problème hydro-sédimentairehyperbolique non conservatif, couplant les modèles de Grass et de Saint-Venant. Il fait appel à des méthodes de Runge-Kutta à variation totale diminuanteet de stabilisation (méthode de décentrement amont, dit Upwind),avec ou sans adjonction de limiteurs et présente de bonnes propriétés.L'une des facettes importantes de ce qui a été réalisée, repose sur la conceptionet le développement d'un programme Python 2D-espace, sous la formed'un logiciel faisant appel à un ensemble de modules créés pour l'occasion.Le développement du code de calcul, qui se propose d'approcher la solutiondu problème hydro-sédimentaire, a été e_ectué avec une orientation Objetet pour être e_cace sur calculateur parallèle (utilisant le parallélisme multithreadsOpenMP). L'une des particularités du schéma numérique dans cecadre, est liée à son application à des quadrangles.Un programme 1D-espace, qui se présente également sous forme de logiciel,a aussi été mis en place. Pour des raisons de portabilité et d'e_catité, il aété écrit multilangages (Python-Fortran : via numpy.ctypes pour Python etvia l'interface standard de Fortran pour C). Le schéma RD avec ou sansadjonction de limiteurs de _ux, a été implémenté à la manière d'un schémaprédicteur-correcteur. Des comparaisons avec d'autres schémas ont été e_ectuées a_n de montrer son e_cacité, son ordre de précision élevé a été mis enévidence, et la C-propriété a été testée. Les tests ont révélé que, pour le casd'un transport d'un pro_l sédimentaire parabolique, c'est le limiteur de _uxMUSCL MinMod, qui est le plus adapté parmi ceux testés.Dans le cas scalaire, des tests numériques ont été réalisés a_n de validerle second ordre de précisionThe present work, proposes a high order Residual Distribution (RD) numericalscheme to solve the non conservative hyperbolic problem, coupling Shallow Water and Grass equations. It uses Total Value Diminishing Runge Kutta and stabilisation Upwind methods, with or without limiters. It also has some good properties.A part of the work realised in this thesis, is about the conception and the developpement of a 2D-space Python program, under the form of a software,using a set of moduls created for the occasion. the code developpement, whichis said to approach the _uid-sediment model, coupling Shallow-Water and sedimentequations, has been made with an Object orientation and in orderto be e_cient on parallel architecture (using multithreads OpenMP parallelism). One of the features of the scheme in this case, is due to its application on quadrangles.A 1D-space program, also writen as a software, has been estabished. In order to be portable and e_cient, It has been developped multilinguals (Python- Fortran : by numpy.ctypes for Python and by standart interface FORTRAN for C). The RD scheme with or without Flux Limiters, has been implemented like predictor-corrector one. Comparisons with other schemes results have been realised, in order to show its e_ciency, moreover its high order accuracy has been focus on, and the C-proprerty has been tested. The tests show that MUSCL MinMod _ux limiters, is the most adaptated for a dune test case, between all tested.In the scalar case, numerical tests have been realised, for validating the secondorder of accuracy
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Zhang, Yumeng. „Modélisation et simulation des dispositifs de ventilation dans les stockages de déchets radioactifs“. Thesis, Nice, 2015. http://www.theses.fr/2015NICE4132/document.
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L'objectif de cette thèse est de fournir des modèles et des outils de simulation pour décrire les échanges de masse entre les circuits de ventilation (galeries) et les milieux poreux des ouvrages souterrains d'enfouissement des déchets nucléaires. La modélisation prend en compte le couplage à l'interface poreux-galerie entre les écoulements liquide gaz compositionnels dans le milieu poreux constituant le stockage et les écoulements gazeux compositionnels dans le milieu galerie libreThe objective of this thesis is to develop models and algorithms to simulate efficiently the mass exchanges occurring at the interface between the nuclear waste deep geological repositories and the ventilation excavated galleries. To model such physical processes, one needs to account in the porous medium for the flow of the liquid and gas phases including the vaporization of the water component in the gas phase and the dissolution of the gaseous components in the liquid phase. In the free flow region, a single phase gas free flow is considered assuming that the liquid phase is instantaneously vaporized at the interface. This gas free flow has to be compositional to account for the change of the relative humidity in the free flow region which has a strong feedback on the liquid flow rate at the interface
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Clair, Guillaume. „Etudes théorique et expérimentale de plasmas produits par laser en vue de leur application a l'analyse chimique des matériaux en environnement complexe“. Thesis, Aix-Marseille 2, 2011. http://www.theses.fr/2011AIX22019/document.
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Ce travail présente une étude originale de l'interaction laser-matière en régime nanoseconde à l'aide d'une double approche expériences-modélisation numérique. L'approche expérimentale vise à caractériser les plasmas produits par laser et l'empreinte laissée par le faisceau laser sur la cible. L'approche numérique s'appuie sur un modèle 1D qui permet de décrire le chauffage de la cible par le laser, l'ablation de matière et la formation d'un plasma dans cette matière ablatée dûe à l'interaction avec le laser. Des comparaisons des résultats obtenus par les deux approches permettent d'évaluer le degré de précision des résultats issus du modèle. Ces comparaisons se limitent aux 100 premières nanosecondes d'expansion du plasma. Nous montrons ainsi que le modèle décrit assez bien l'écrantage du faisceau laser par le plasma, l'expansion du plasma et la propagation de l'onde de choc dans le gaz ambiant. De plus, les valeurs des seuils d'ablation et de formation du plasma sont calculées avec une bonne précision. En revanche, des écarts sont constatés pour la modélisation des processus d'interaction entre le laser et la cible. Le degré de précision du modèle est au final suffisamment bon pour nous permettre d'étudier précisément l'effet du gaz ambiant sur les propriétés et la dynamique du plasmaThis work provides an original study about laser-matter interaction in the nanosecond regime, based on a coupling between the experiments and the modelling. The experimental study provides a description of the dynamics of the laser produced plasmas. The modelling, based on a 1D numerical scheme, is aimed to describe the heating of the target by the laser pulse, the process of matter ablation and the formation of a plasma in this ablated material due to the interaction with the laser. The comparisons between both experimental and numerical results give the order of accuracy of the results obtained by modelling. These comparisons are limited to the first hundred nanoseconds of plasma expansion. We show that the plasma shielding, the plasma expansion and the propagation of the shockwave are well modelled. Furthermore, the values of both ablation and plasma formation threshold are accurately computed. However, many differences are observed in the results concerning the laser-target interaction process. Finally, the degree of accuracy of the model is sufficiently high to study precisely the background gas effet on both plasma dynamics and properties
Buchteile zum Thema "Numerical schemes coupling"
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Klar, Axel. „Domain Decomposition Schemes and Coupling Conditions for Kinetic and Hydrodynamic Equations“. In Notes on Numerical Fluid Mechanics (NNFM), 128–38. Wiesbaden: Vieweg+Teubner Verlag, 1995. http://dx.doi.org/10.1007/978-3-322-86859-6_12.
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Dörfel, Michael R., und Bernd Simeon. „Analysis and Acceleration of a Fluid-Structure Interaction Coupling Scheme“. In Numerical Mathematics and Advanced Applications 2009, 307–15. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-11795-4_32.
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Xu, Liu-Jun, und Ji-Ping Huang. „Theory for Hele-Shaw Convective Cloaks: Bilayer Scheme“. In Transformation Thermotics and Extended Theories, 65–86. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-19-5908-0_6.
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AbstractThermal convection is one of the three basic heat transfer mechanisms, profoundly influencing the natural environment, social production, and daily life. However, the high complexity of governing equation, which describes the coupling of heat and mass transfer, makes it challenging to manipulate thermal convection at will in both theory and experiment. Here, we consider the heat transfer in Hele-Shaw cells, a widely-used model of Stokes flow between two parallel plates with a small gap, and apply the scattering-cancellation technology to construct convective thermal materials with bilayer structures and homogeneous isotropic materials. By tailoring thermal conductivity and viscosity, we demonstrate cloaking devices that can simultaneously hide obstacles from heat and fluid motion and verify their robustness under various thermal-convection environments by numerical simulations. Our results show that about 80% of the temperature and pressure disturbances in the background caused by obstacles can be eliminated by the cloak. The developed approach can be extended to control other convection-diffusion systems or multiphysics processes. The results pave a promising path for designing various metadevices such as concentrators or sensors.
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Barfusz, Oliver, Felix Hötte, Stefanie Reese und Matthias Haupt. „Pseudo-transient 3D Conjugate Heat Transfer Simulation and Lifetime Prediction of a Rocket Combustion Chamber“. In Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 265–78. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-53847-7_17.
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Abstract Rocket engine nozzle structures typically fail after a few engine cycles due to the extreme thermomechanical loading near the nozzle throat. In order to obtain an accurate lifetime prediction and to increase the lifetime, a detailed understanding of the thermomechanical behavior and the acting loads is indispensable. The first part is devoted to a thermally coupled simulation (conjugate heat transfer) of a fatigue experiment. The simulation contains a thermal FEM model of the fatigue specimen structure, RANS simulations of nine cooling channel flows and a Flamelet-based RANS simulation of the hot gas flow. A pseudo-transient, implicit Dirichlet–Neumann scheme is utilized for the partitioned coupling. A comparison with the experiment shows a good agreement between the nodal temperatures and their corresponding thermocouple measurements. The second part consists of the lifetime prediction of the fatigue experiment utilizing a sequentially coupled thermomechanical analysis scheme. First, a transient thermal analysis is carried out to obtain the temperature field within the fatigue specimen. Afterwards, the computed temperature serves as input for a series of quasi-static mechanical analyses, in which a viscoplastic damage model is utilized. The evolution and progression of the damage variable within the regions of interest are thoroughly discussed. A comparison between simulation and experiment shows that the results are in good agreement. The crucial failure mode (doghouse effect) is captured very well.
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Li, Zhe, und Julien Favier. „Fluid-Structure Interaction Using Lattice Boltzmann Method Coupled With Finite Element Method“. In Advances in Computer and Electrical Engineering, 262–92. IGI Global, 2018. http://dx.doi.org/10.4018/978-1-5225-4760-0.ch008.
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This chapter presents several partitioned algorithms to couple lattice Boltzmann method (LBM) and finite element method (FEM) for numerical simulation of transient fluid-structure interaction (FSI) problems with large interface motion. Partitioned coupling strategies allow one to solve separately the fluid and solid subdomains using adapted or optimized numerical schemes, which provides a considerable flexibility for FSI simulation, especially for more realistic and industrial applications. However, partitioned coupling procedures often encounter numerical instabilities due to the fact that the time integrations of the two subdomains are usually carried out in a staggered way. As a consequence, the energy transfer across the fluid-solid interface is usually not correctly simulated, which means numerical energy injection or dissipation might occur at the interface with partitioned methods. The focus of the present chapter is given to the energy conservation property of different partitioned coupling strategies for FSI simulation.
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Luo, Zhuoran, Jingzheng Li und Xiaojie Zhou. „Numerical Simulation of Extreme Precipitation in Beijing“. In Advances in Transdisciplinary Engineering. IOS Press, 2024. https://doi.org/10.3233/atde241150.
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The numerical simulation of urban extreme precipitation is a hot spot direction in urban hydrology. To more accurately reproduce the spatial and temporal distribution process of precipitation in Beijing, this study coupled the urban canopy model (UCM) and WRF model to conduct numerical simulation of the spatial distribution of precipitation in Beijing during typical periods in 2020. The results show that the precipitation in most areas of the northwest of Beijing is less than 40 mm, while the precipitation in the eastern, southern and central areas is more than 60 mm. Compared with NON scheme, the precipitation of UCM scheme in urban areas is increased by 10–20 mm. The increase of specific humidity and temperature of air promotes the increase of precipitation. The coupling simulation of UCM and WRF makes the model more comprehensive description of urban extreme precipitation process.
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Luo, Zhuoran, Jiahong Liu, Shanghong Zhang und Xiaojie Zhou. „Simulation and Mechanism of Extreme Precipitation Data in Greater Bay Area“. In Advances in Transdisciplinary Engineering. IOS Press, 2023. http://dx.doi.org/10.3233/atde230799.
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Recently, the frequent occurrence of urban extreme precipitation has become the focus of academic and social attention. To systematically analyze the impact of urbanization factors on the spatial components of extreme precipitation, this study uses the coupling method of WRF and UCM to conduct numerical simulation analysis of extremely typical extreme precipitation events in the Greater Bay Area. The results showed that the daily precipitation in the Greater Bay Area exceeded 300 mm, which was significantly higher than other surrounding areas. Compared with the NON scheme, the UCM scheme had a higher precipitation simulation result in Greater Bay Area, and it was more than 20mm higher in a few areas. Urbanization factors have enhanced extreme precipitation. The increase of air specific humidity and temperature jointly promoted the formation of convective precipitation above urban and built-up land.
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Sharma, Vishal Kumar, Shyam Krishan Joshi und Avnish Bora. „Quantum Control of Networked Robotic Systems“. In Advances in Marketing, Customer Relationship Management, and E-Services, 357–68. IGI Global, 2024. https://doi.org/10.4018/979-8-3693-7673-7.ch015.
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In the present work we propose a scheme to control the network of wheeled mobile robots using Quantum computing. This scheme provides a fast and efficient way to navigate a system of networked robots from one position to another using a PID Controllers. It is a well established fact that the robotic systems aredefined using Lagrangian dynamics and PID control is an efficient way to control the movement of robotic systems . In the present work we propose a framework to use Quantum Computers and Photic couplings among robots to form a consensus and move a the coupled robotic system from one place to another. We propose that all the computations must be carried out on quantum computers for efficient control and fast execution. We propose an algorithm that enables the proposed scheme. Numerical Simulations that show synchronized motion of coupled robots have been reported.
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„A numerical simulation on centrifuge liquefaction model using microscopic fluid coupling scheme with Discrete Element Method“. In Numerical Methods in Geotechnical Engineering, 217–22. CRC Press, 2010. http://dx.doi.org/10.1201/b10551-39.
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Spaulding, Malcolm. „Drift Current under the Action of Wind and Waves“. In Wind-over-Wave Couplings, 243–56. Oxford University PressOxford, 1999. http://dx.doi.org/10.1093/oso/9780198501923.003.0025.
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Abstract Accurate estimates of sea surface drift currents are critical to forecast ing oil spill transport and fate and the movement of objects lost at sea. The majority of existing models employ a drift factor and deflection angle, based on the local wind speed and direction, to estimate the wind induced sea surface drift vector. The effects of wind induced shear and wave induced transport are lumped together in this formulation. In the present study the conservation of momentum and turbulent kinetic energy equations are solved using an implicit finite difference scheme to predict the vertical distribution of currents, turbulent kinetic energy, and vertical eddy viscosity at one point. The model includes coupling between the wave and shear induced currents. Inputs of momentum and energy from the atmosphere to the current and turbulent energy fields are parameterized through free surface boundary conditions. The numerical model has been extensively tested against analytic solutions for wind forced shear flow and prior work on wave current interaction with very good results. The model was applied to predict the steady state surface drift currents for varying wind speeds in deep water.
Konferenzberichte zum Thema "Numerical schemes coupling"
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Bunel, T., M. Conforti, Z. Ziani, J. Lumeau, A. Moreau, A. Fernandez, O. Llopis, G. Bourcier und A. Mussot. „Kerr frequency comb generation in normal dispersion fiber Fabry-Pérot resonators via switching waves excitation“. In CLEO: Science and Innovations, SF1Q.5. Washington, D.C.: Optica Publishing Group, 2024. http://dx.doi.org/10.1364/cleo_si.2024.sf1q.5.
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We report the generation of optical frequency combs in fiber Fabry-Perot resonator operating in the normal dispersion regime. Thanks to the compact design and the easy coupling of the resonator, switching waves can be generated in an all-fiber experimental setup employing a pulsed pumping scheme. The influence of dispersion is thoroughly discussed, revealing the potential to create a frequency comb spanning a 15 THz bandwidth through the utilization of a flattened low dispersion cavity. The experimental results are in good agreement with the theory and the numerical simulations.
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Longatte, E., Z. Bendjeddou, V. Verreman und M. Souli. „Explicit and Implicit Code Coupling Schemes in Fluid Structure Interaction“. In ASME 2005 Pressure Vessels and Piping Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/pvp2005-71647.
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In multi-physics numerical computations a good choice of code coupling schemes is required. Several methods are possible like: an explicit synchronous scheme an Euler implicit method and no interpolation on velocity pressure; an explicit asynchonous scheme using a Crank-Nicholson time integration scheme and interpolation on velocity and pressure; an implicit scheme using a fixed iterative method. In the present paper these different schemes are compared for application in fluid structure interaction field. In the first part numerical coupling schemes are presented. Then their capability to ensure energy conservation is discussed according to numerical results obtained in analytical test cases. Finally application of coupling process to fluid structure interaction problems is investigated and results are discussed in terms of added mass and damping induced by a fluid for a structure vibrating in fluid at rest.
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Bendiksen, Oddvar O. „Fluid-Structure Coupling Requirements for Time-Accurate Aeroelastic Simulations“. In ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-0161.
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Abstract In this paper we study the requirements that must be satisfied by a fluid-structure coupling scheme, in order to obtain a dynamically consistent aeroelastic code. Both spatial compatibility and time synchronization requirements must be met, to assure that the time-marching simulations exhibit the physically correct stability behavior. Inconsistent or inaccurate implementation of the fluid-structure boundary conditions can cause the aeroelastic code to converge to an incorrect aeroelastic solution. It is shown that CFD codes based on linear interpolations for the velocities cannot be fully compatible with structural FE codes that use plate or shell elements to model the wing skin. Numerical examples are presented for three different nonlinear aeroelastic models, using Euler-based aerodynamics and two different fluid-structure coupling schemes. The results indicate that for Mach numbers in the upper transonic range, past the transonic dip, the aeroelastic solution appears very sensitive to the fluid-structure coupling scheme used. In the case of the NACA 0012 model, the two different schemes studied predicted entirely different stability behaviors.
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Rajaomazava, Tolotra Emerry, Mustapha Benaouicha und Jacques-Andre´ Astolfi. „A Comparison Study of Coupling Algorithms for Fluid-Structure Interaction Problems“. In ASME 2011 Pressure Vessels and Piping Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/pvp2011-57573.
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The influence of numerical schemes for solving coupled problem in fluid-structure interaction is addressed. A non-linear Burgers equation in a bounded domain with moving interface is solved by finite element method (FEM). The implicit and explicit coupling algorithms are studied with interface equation solved at outside then inside of Newton iterative procedure (referred to as implicit-outer, implicit-inner, explicit and semi-implicit schemes respectively). Iteration numbers and computing time are compared for each algorithm. The interface position and energy conservation condition at the interface are discussed.
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Cui, X. „Solving Coupled Partial Differential Equations in Porous/Fractured Geomaterials“. In 58th U.S. Rock Mechanics/Geomechanics Symposium. ARMA, 2024. http://dx.doi.org/10.56952/arma-2024-0836.
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ABSTRACT: Exploring efficient and robust algorithms to solve the simultaneous Partial Differential Equations (PDEs) is essential to model the prevalent multiphysics processes in deep rock engineering activities, such as the thermo-hydro-mechanical coupling in nuclear waste disposal and geothermal exploitation. In this study, the staggered and monolithic solution schemes are developed in the context of poroelastic and fractured geomaterials, and the applicability of the two solution schemes is analyzed in detail. It is found that the degree of coupling between primary variables plays a pivotal role in determining the performance of the staggered and monolithic solution schemes. Two-way coupling can only be tackled by the monolithic solution scheme, while the staggered solution scheme is very robust and efficient to deal with one-way coupling. This study provides an overarching principle to solve simultaneous PDEs: Understand the degree of coupling between primary variables, and use the staggered and monolithic solution schemes to address one-way and two-way couplings, respectively. 1. INTRODUCTION Rock mechanics, as an applied geoscience, has its roots deeply entangled with various rock engineering activities. The pioneers and early generations of rock engineering practitioners established the framework and theory of rock mechanics mainly from on/near ground surface projects, such as rock foundations, rock slopes, and shallowly buried tunnels. In the last two decades, rock engineering activities started to go deeper and deeper to serve increasingly complex engineering purposes. Examples include nuclear waste disposal, hydraulic fracturing, geothermal exploitation, CO2 sequestration, and injection-induced earthquakes. The above new rock engineering activities pose great challenges to the existing rock mechanics theory, but at the same time, they provide a fertile ground for rock mechanics to extend and prosper. Future rock mechanics will interact more closely with computer science, seismology, petroleum engineering and many other disciplines to further highlight its interdisciplinary attributes. A common feature of rock engineering at a great depth is the potential coexistence of in-situ stress, high temperature, fluid pressure in pores/fractures, and chemical reactions. These factors are coupled together, and each of them plays a considerable role in the entire system. Therefore, deep rock engineering is a typical multiphysics system. It is not trivial to replicate such a complex working environment in the laboratory, neither can the field tests be readily conducted at such a depth. Numerical simulation, however, provides an insightful, economical and effective approach to understand the multiphysics system.
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Li, Na, Zhenchun Li, Jianping Huang, Kun Tian und Qingyang Li. „The high-order FD numerical simulation of coupling Lebedev and standard staggered-grid schemes for complex anisotropic media“. In SEG Technical Program Expanded Abstracts 2013. Society of Exploration Geophysicists, 2013. http://dx.doi.org/10.1190/segam2013-0937.1.
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Das, Shankhadeep, Battalgazi Yildirim, Sanjay R. Mathur, Alina Alexeenko und Jayathi Y. Murthy. „A Parallel Coupled Ordinates Method for Rarefied Gas Dynamics Simulations“. In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-89256.
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Deterministic solution techniques for non-equilibrium rarefied flows in RF MEMS switches are frequently based on the ellipsoidal statistical Bhatnagar-Gross-Krook (ESBGK) form of the Boltzmann kinetic equation. These numerical schemes involve the sequential solution of the distribution function in velocity space. However, these schemes have poor convergence rates, especially at low Knudsen numbers, because of the explicit coupling of the distribution functions in velocity space. Furthermore, parallel implementation of these schemes is inefficient, making simulation of real-life devices practically impossible. In this paper we describe the parallel performance of a recently-developed numerical procedure called the coupled ordinates method (COMET) to solve ESBGK equations. In this method, the distribution functions for all velocity ordinates are strongly coupled at each physical point, resulting in an implicit solution procedure in velocity space. The coupled procedure is used as a relaxation sweep in a geometric multigrid scheme to promote spatial coupling. Results show that COMET gives excellent CPU scaling on multiple processors even for very small workload per processor. The solver is also shown to have very good strong and weak scaling characteristics. The parallel COMET solver also gives significantly faster solutions than the parallel implementation of the conventional sequential solution procedure. It is believed that the parallel COMET solver can become an efficient tool to model real-life RF MEMS switches.
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Srinivasan, Vedanth, und De Ming Wang. „Numerical Simulation of Free Surface Flows Using STACS-VOF Method“. In ASME/JSME 2007 5th Joint Fluids Engineering Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/fedsm2007-37569.
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This paper presents a numerical method that couples the incompressible Navier-Stokes equations with the Volume of Fluid method in a Cartesian co-ordinate system for tracking immiscible interfaces in multiple dimensions. The governing equations are discretized based on a finite volume method on a non-staggered fixed grid. The free surface flow problem is solved as a single phase flow system in which the free surface is captured using a Switching Technique for Advection and Capturing of Surfaces (STACS) scheme. The effects of surface tension at the interfaces are treated using a Continuum Surface Force (CSF) model. The pressure velocity coupling is achieved using a SIMPLE strategy. The coupled system, implemented in the commercial CFD software, AVL FIRE/SWIFT, is applied to a two dimensional dam breaking problem. The simulation results reveal a multitude of phenomena such as, free surface vortex generation, air entrapment and splashing of the liquid surge front. The computational results are in good agreement with experimental data, wherever available. The effects of time and grid resolution on the solution behavior are elaborated in detail. Different convection schemes are tested and the current method is compared to another existing interface capturing methodology.
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Longatte, E., V. Verreman, Z. Bendjeddou und M. Souli. „Comparison of Strong and Partioned Fluid Structure Code Coupling Methods“. In ASME 2005 Pressure Vessels and Piping Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/pvp2005-71251.
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As far as flow-induced vibrations are concerned, fluid structure interactions and fluid elastic effects are involved. They may be characterized by parameters like added mass, added damping and added stiffness describing fluid and flow effects on structure motion. From a numerical point of view, identifying these parameters requires numerical simulation of coupled fluid and structure problems. To perform such a multi-physics computation, several numerical methods can be considered involving either a partitioned or a monolithic fluid structure code coupling procedure. Monolithic process is a fully implicit method ensuring the energy conservation of the coupled system. However its implementation may be difficult when specific methods are required for both fluid and structure solvers. The partitioned procedure does not feature the same disadvantage because fluid and structure computations are staggered in time. However a specific attention must be paid to the energy conservation of the full coupled system and one must choose code coupling schemes in order to avoid or to reduce as much as possible numerical dissipation polluting the results. In the present paper, several techniques for fluid structure code coupling are compared. Several configurations are considered and numerical results are discussed in terms of added mass and damping for structures vibrating in fluid at rest. These results contribute to the validation of a full fluid structure code coupling procedure with many possible applications in the fields of fluid structure interactions and flow-induced vibrations.
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Jung, Jin-Young, und Michael M. Chen. „Numerical Simulation of Dendritic Solidification“. In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1481.
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Abstract It is well known that the dendritic microstructure of alloys is a consequence of morphological instability of the solidification process, which is a result of the coupling of heat and mass transfer with the composition-dependent phase equilibrium condition mediated by the surface energy. There have been many numerical simulations of dendritic solidification. However, many successful simulations of dendritic growth have used non-discrete front tracking method such as artificial source method or phase field method, with demonstrably first order accuracy. Many also found it necessary to continuously inject random noise during simulation. The continuous injection of random noise raises the suspicion that the numerical schemes used may be overly dissipative. The noise is apparently capable of creating nonuniform solidification, but not sufficient to ensure growth with a clear dendritic pattern. In the present study, to rule out the numerical diffusivity as a cause of the damping of dendritic perturbations, artificial perturbations are either not used, or injected only as initial conditions. Under the unstable solidification mode, the initial perturbation triggers the onset of interface instability. Computations were performed for both sub-cooled pure material as well as directional solidification of alloys. The successful simulation of dendritic solidification without the intentional injection of random noise provided evidence that the present method has less numerical diffusion than many existing front tracking methods.