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SCHUBERT, FRANK, BERND KOEHLER et ALEXANDER PEIFFER. « TIME DOMAIN MODELING OF AXISYMMETRIC WAVE PROPAGATION IN ISOTROPIC ELASTIC MEDIA WITH CEFIT — CYLINDRICAL ELASTODYNAMIC FINITE INTEGRATION TECHNIQUE ». Journal of Computational Acoustics 09, no 03 (septembre 2001) : 1127–46. http://dx.doi.org/10.1142/s0218396x0100098x.
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The Elastodynamic Finite Integration Technique (EFIT), originally developed by Fellinger et al.,1–3 represents a stable and efficient numerical code to model elastic wave propagation in linearly-elastic isotropic and anisotropic, homogeneous and heterogeneous as well as dissipative and nondissipative media. In previous works, the FIT discretization of the basic equations of linear elasticity, Hooke's law and Cauchy's equation of motion, was exclusively carried out in Cartesian coordinates. For problems in cylindrical geometries it is more suitable to use cylindrical coordinates. By that, axisymmetric problems can be treated in a two-dimensional staggered grid in the r,z-plane. The paper presents an EFIT version for axisymmetric problems in cylindrical coordinates called Cylindrical EFIT (CEFIT). After demonstrating the accuracy of the numerical code by a comparison between simulation results and analytical solutions, different examples of application are given. These examples include modeling of sound fields of ultrasonic transducers, thermoelastic laser sources, geophysical borehole probes, impact-echo measurements in layered media, and load simulations of the European Spallation Source (ESS) mercury target.
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Piquet, Arthur, Boubakr Zebiri, Abdellah Hadjadj et Mostafa Safdari Shadloo. « A parallel high-order compressible flows solver with domain decomposition method in the generalized curvilinear coordinates system ». International Journal of Numerical Methods for Heat & ; Fluid Flow 30, no 1 (5 juin 2019) : 2–38. http://dx.doi.org/10.1108/hff-01-2019-0048.
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Purpose This paper aims to present the development of a highly parallel finite-difference computational fluid dynamics code in generalized curvilinear coordinates system. The objectives are to handle internal and external flows in fairly complex geometries including shock waves, compressible turbulence and heat transfer. Design/methodology/approach The code is equipped with high-order discretization schemes to improve the computational accuracy of the solution algorithm. Besides, a new method to deal with the geometrical singularities, so-called domain decomposition method (DDM), is implemented. The DDM consists of using two different meshes communicating with each other, where the base mesh is Cartesian and the overlapped one a hollow cylinder. Findings The robustness of the present implemented code is appraised through several numerical test cases including a vortex advection, supersonic compressible flow over a cylinder, Poiseuille flow, turbulent channel and pipe flows. The results obtained here are in an excellent agreement when compared to the experimental data and the previous direct numerical simulation (DNS). As for the DDM strategy, it was successful as simulation time is clearly decreased and the connection between the two subdomains does not create spurious oscillations. Originality/value In sum, the developed solver was capable of solving, accurately and with high-precision, two- and three-dimensional compressible flows including fairly complex geometries. It is noted that the data provided by the DNS of supersonic pipe flows are not abundant in the literature and therefore will be available online for the community.
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Danielson, K. T., et A. K. Noor. « Finite Elements Developed in Cylindrical Coordinates for Three-Dimensional Tire Analysis ». Tire Science and Technology 25, no 1 (1 janvier 1997) : 2–28. http://dx.doi.org/10.2346/1.2137529.
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Abstract Finite elements developed in cylindrical coordinates are presented for three-dimensional analysis of tires. In contrast to elements formulated in Cartesian coordinates, these elements allow the exact representation of circular shapes. The exact modeling of circular geometries can provide better finite element predictions and reduce the number of elements needed around the tire circumference. Numerical results are presented for the application of this formulation to the analysis of a radial automobile tire subjected to rim mounting, nonconservative inflation pressure, and rigid pavement contact. The predictions of the foregoing finite elements are compared to experimental data and to predictions of a commercial code using finite elements developed in Cartesian coordinates. The comparisons demonstrate the accuracy and the advantages of the cylindrical coordinate formulation for the three-dimensional finite element analysis of tires.
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Tsega, Endalew Getnet. « Numerical Solution of Three-Dimensional Transient Heat Conduction Equation in Cylindrical Coordinates ». Journal of Applied Mathematics 2022 (4 janvier 2022) : 1–8. http://dx.doi.org/10.1155/2022/1993151.
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Heat equation is a partial differential equation used to describe the temperature distribution in a heat-conducting body. The implementation of a numerical solution method for heat equation can vary with the geometry of the body. In this study, a three-dimensional transient heat conduction equation was solved by approximating second-order spatial derivatives by five-point central differences in cylindrical coordinates. The stability condition of the numerical method was discussed. A MATLAB code was developed to implement the numerical method. An example was provided in order to demonstrate the method. The numerical solution by the method was in a good agreement with the exact solution for the example considered. The accuracy of the five-point central difference method was compared with that of the three-point central difference method in solving the heat equation in cylindrical coordinates. The solutions obtained by the numerical method in cylindrical coordinates were displayed in the Cartesian coordinate system graphically. The method requires relatively very small time steps for a given mesh spacing to avoid computational instability. The result of this study can provide insights to use appropriate coordinates and more accurate computational methods in solving physical problems described by partial differential equations.
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Gavrus, Adinel, Daniela Pintilie et Roxana Nedelcu. « Studies Concerning Numerical Prediction of Metal Fibering Obtained by Cold Bulk Forming Using Sensitivity Analysis of Tribological and Rheological Properties on a Cylindrical Crushing Process ». Applied Mechanics and Materials 841 (juin 2016) : 29–38. http://dx.doi.org/10.4028/www.scientific.net/amm.841.29.
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The present research paper concerns a numerical and experimental analysis of the tribologic and rheological constitutive behavior influence on prediction of metallic material forging fibering. Numerical analysis using finite element Forge® code and Abaqus software show the high importance of the friction law formulation and of the material rheological softening on the fibers morphology and on their position coordinates. Calibration and sensitivity of friction law together with the numerical sensitivity of the softening term corresponding to a Hansel-Spittel rheological equation have been studied for a cylindrical crushing test of a 16MnCr5 steel.
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Könies, Axel, Jinjia Cao, Ralf Kleiber et Joachim Geiger. « A numerical approach to the calculation of the Alfvén continuum in the presence of magnetic islands ». Physics of Plasmas 29, no 9 (septembre 2022) : 092102. http://dx.doi.org/10.1063/5.0102239.
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A numerical approach is devised to calculate the shear Alfvén continuum inside and outside magnetic islands in cylindrical and stellarator plasmas. Equations for an appropriate set of coordinates and the arising equations for the continuum are derived and implemented in the CONTI code. An experiment-oriented representation of the results is chosen to allow a radial localization of the modes and a comparison of different magnetic configurations. Comparison is made with results of earlier analytic work for validation. Agreement is good but more details of the spectrum, such as the generation of island induced gaps inside and outside the separatrix, are found. While the code is easily usable and can be applied to any magnetic equilibrium accessible with VMEC, the calculations are plagued with convergence issues close to the separatrix. A calculation for a realistic W7-X equilibrium with islands is done where the island width is estimated with the HINT code.
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Peponis, Dimitrios V., George P. Latsas, Zisis C. Ioannidis et Ioannis G. Tigelis. « Dispersion properties of rectangularly‐corrugated waveguide structures by the in‐house 3D FDTD code COCHLEA in cylindrical coordinates ». IET Microwaves, Antennas & ; Propagation 13, no 1 (10 octobre 2018) : 28–34. http://dx.doi.org/10.1049/iet-map.2018.5129.
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Lee, M., et Y. J. Cho. « On the migration of smooth particle hydrodynamic formulation in Cartesian coordinates to the axisymmetric formulation ». Journal of Strain Analysis for Engineering Design 46, no 8 (15 août 2011) : 879–86. http://dx.doi.org/10.1177/0309324711409656.
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The smooth particle hydrodynamic (SPH) method has been extended for application to large deformation problems such as high velocity impacts by including the effect of material strength. This paper presents a simple modification of the kernel function that allows the SPH formulation in Cartesian coordinates to be migrated into an axisymmetric formulation. The proposed procedure is first applied to analyse transient deformations of a cylindrical rod impacting a rigid wall (Taylor impact test). A good agreement with published experimental data for the deformed shape is obtained. A sensitivity study of the key parameters required in the SPH formulation is conducted to provide better insight into the SPH modelling approach. Impacts between two bodies at high speed have also been simulated using an axisymmetric SPH code.
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Glasser, A. H., et S. A. Cohen. « Simulating single-particle dynamics in magnetized plasmas : The RMF code ». Review of Scientific Instruments 93, no 8 (1 août 2022) : 083506. http://dx.doi.org/10.1063/5.0101665.
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The RMF (Rotating Magnetic Field) code is designed to calculate the motion of a charged particle in a given electromagnetic field. It integrates Hamilton’s equations in cylindrical coordinates using an adaptive predictor-corrector double-precision variable-coefficient ordinary differential equation solver for speed and accuracy. RMF has multiple capabilities for the field. Particle motion is initialized by specifying the position and velocity vectors. The six-dimensional state vector and derived quantities are saved as functions of time. A post-processing graphics code, XDRAW, is used on the stored output to plot up to 12 windows of any two quantities using different colors to denote successive time intervals. Multiple cases of RMF may be run in parallel and perform data mining on the results. Recent features are a synthetic diagnostic for simulating the observations of charge-exchange-neutral energy distributions and RF grids to explore a Fermi acceleration parallel to static magnetic fields.
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Luan, Zhaogao, et M. M. Khonsari. « Computational Fluid Dynamics Analysis of Turbulent Flow Within a Mechanical Seal Chamber ». Journal of Tribology 129, no 1 (27 juin 2006) : 120–28. http://dx.doi.org/10.1115/1.2401220.
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Turbulent flow inside the seal chamber of a pump operating at high Reynolds number is investigated. The K−ε turbulence model posed in cylindrical coordinates was applied for this purpose. Simulations are performed using the fractional approach method. The results of the computer code are verified by using the FLUENT and by comparing to published results for turbulent Taylor Couette flow. Numerical results of four cases including two rotational speeds with four flush rates are reported. Significant difference between the laminar and the turbulence flow in the seal chamber is predicted. The behavior of the turbulent flows with very high Reynolds number was also investigated. The physical and practical implications of the results are discussed.
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Zweigle, J., M. Bremer et M. Grewing. « Twodimensional Axialsymmetrical Hydrodynamical Simulations of PN-Evolution ». Symposium - International Astronomical Union 155 (1993) : 373. http://dx.doi.org/10.1017/s0074180900171621.
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In order to investigate the early evolution of planetary nebulae (PNe) we solved numerically the hydrodynamical equations in cylindrical coordinates (r, z) assuming azimutal symmetry. The numerical method used is described in detail by Mair et al. (1988). Our simulations model the interaction of a fast, tenuous, spherical symmetrical central star wind with a slow, dense, aspherical Red Giant Envelope (RGE) expelled from the progenitor star. For the aspherical RGE with a polar/equatorial density contrast we used the initial model given by Mellema et al. (1991) in cylindrical coordinates. We have investigated the influence of each initial model parameter upon the evolution of PNe. Thereby we confirm that the polar/equatorial density contrast in the RGE and the thickness of the RGE-disk play an important role for the morphology of PNe. In agreement with the results from Mellema et al. (1991). The polar/equatorial density contrast in the RGE influences the ratio of the distances of the bright inner rim to the central star in z- and r-direction. This ratio increases with decreasing polar/equatorial density contrast. We find the thickness of the RGE-disk to be a key parameter for getting an elliptical or a butterfly PN: thin RGE-disks produce the first type of nebulae, thick disks the latter. We thank G. Mair, E. Müller and W. Hillebrandt for making available to us a copy of the SADIE code.
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Amabili, M. « Effect of Boundary Conditions on Nonlinear Vibrations of Circular Cylindrical Panels ». Journal of Applied Mechanics 74, no 4 (6 février 2006) : 645–57. http://dx.doi.org/10.1115/1.2424474.
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Geometrically nonlinear vibrations of circular cylindrical panels with different boundary conditions and subjected to harmonic excitation are numerically investigated. The Donnell’s nonlinear strain–displacement relationships are used to describe geometric nonlinearity; in-plane inertia is taken into account. Different boundary conditions are studied and the results are compared; for all of them zero normal displacements at the edges are assumed. In particular, three models are considered in order to investigate the effect of different boundary conditions: Model A for free in-plane displacement orthogonal to the edges, elastic distributed springs tangential to the edges and free rotation; Model B for classical simply supported edges; and Model C for fixed edges and distributed rotational springs at the edges. Clamped edges are obtained with Model C for the very high value of the stiffness of rotational springs. The nonlinear equations of motion are obtained by the Lagrange multimode approach, and are studied by using the code AUTO based on the pseudo-arclength continuation method. Convergence of the solution with the number of generalized coordinates is numerically verified. Complex nonlinear dynamics is also investigated by using bifurcation diagrams from direct time integration and calculation of the Lyapunov exponents and the Lyapunov dimension. Interesting phenomena such as (i) subharmonic response; (ii) period doubling bifurcations; (iii) chaotic behavior; and (iv) hyper-chaos with four positive Lyapunov exponents have been observed.
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Ringle, R. « 3DCylPIC—A 3D particle-in-cell code in cylindrical coordinates for space charge simulations of ion trap and ion transport devices ». International Journal of Mass Spectrometry 303, no 1 (mai 2011) : 42–50. http://dx.doi.org/10.1016/j.ijms.2010.12.015.
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Ngor Thiam, Omar, Samba Dia et Cheikh Mbow. « STUDY OF THE TEMPERATURE DISTRIBUTION IN A PARABOLIC CYLINDRICAL CONCENTRATORUSING A NANOFLUID AS HEAT TRANSFER FLUID ». International Journal of Advanced Research 10, no 11 (30 novembre 2022) : 687–94. http://dx.doi.org/10.21474/ijar01/15716.
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We have numerically studied the heat transfers in a Cylindrical-parabolic concentrator using a nanofluid as heat transfer fluid for its use in Solar Thermodynamics. After an analysis of the work relating to solar concentrators and nanofluids, we have, after having described our physical system and posed working hypotheses, written the equations which govern the transfers in our collector. The latter as well as the associated boundary conditions were then dimensionless in order to generalize the problem and reveal the parameters that control the operation of the absorber. To solve our equations, we used the method of finite differences and the algebraic system obtained is solved thanks to the Thomas method combined with an iterative process of line-by-line relaxation type. The computer code that we developed made it possible to find the temperature distributions according to the spatial coordinates and at different times. The effects and influences of wind effect, axial and transverse thermal dispersion, absorber length, geometric shape factor on the average temperature distributions of the coolant is analyzed. At the end of the study, we were able to identify the most important physical and geometric parameters which give our system optimum operation for its use in Solar Thermodynamics.
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Eiamsa-ard, S., et P. Promvonge. « Numerical investigation of turbulent swirling flows through an abrupt expansion tube ». ASEAN Journal on Science and Technology for Development 23, no 1&2 (30 octobre 2017) : 55. http://dx.doi.org/10.29037/ajstd.87.
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A numerical investigation of turbulent swirling flows through an abrupt expansion tube is reported. The TEFESS code, based on a staggered Finite Volume approach with the standard k-ε model and first-order numerical schemes built-in, was used to carry out all the computations. The code has been modified in the present work to incorporate the ASM and two second-order numerical schemes. The ASM, which includes the non-gradient convection terms arising from the transformation from Cartesian to cylindrical coordinates, was investigated for isothermal flows by applying it to the flow through an abrupt expansion tube with or without swirl flows. In addition, to investigate the effects of numerical diffusion on the predicted results, two second-order differencing schemes, namely, second-order upwind and the quadratic upstream interpolation, were used to compare with the first-order hybrid scheme. An abrupt expansion tube with non-swirling flow, predicted results using both the k-ε model and the ASM were in good agreement with measurements. For swirling flows, the calculated results suggested that the use of the ASM with a second-order numerical scheme leads to better agreement between the numerical results and experimental data, while the k-ε model is incapable of capturing the stabilizing effect of the swirl.
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Horn, Susanne, Olga Shishkina et Claus Wagner. « On non-Oberbeck–Boussinesq effects in three-dimensional Rayleigh–Bénard convection in glycerol ». Journal of Fluid Mechanics 724 (29 avril 2013) : 175–202. http://dx.doi.org/10.1017/jfm.2013.151.
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AbstractRayleigh–Bénard convection in glycerol (Prandtl number $\mathit{Pr}= 2547. 9$) in a cylindrical cell with an aspect ratio of $\Gamma = 1$ was studied by means of three-dimensional direct numerical simulations (DNS). For that purpose, we implemented temperature-dependent material properties into our DNS code, by prescribing polynomial functions up to seventh order for the viscosity, the heat conductivity and the density. We performed simulations with the common Oberbeck–Boussinesq (OB) approximation and with non-Oberbeck–Boussinesq (NOB) effects within a range of Rayleigh numbers of $1{0}^{5} \leq \mathit{Ra}\leq 1{0}^{9} $. For the highest temperature differences, $\Delta = 80~\mathrm{K} $, the viscosity at the top is ${\sim }360\hspace{0.167em} \% $ times higher than at the bottom, while the differences of the other material properties are less than $15\hspace{0.167em} \% $. We analysed the temperature and velocity profiles and the thermal and viscous boundary-layer thicknesses. NOB effects generally lead to a breakdown of the top–bottom symmetry, typical for OB Rayleigh–Bénard convection. Under NOB conditions, the temperature in the centre of the cell ${T}_{c} $ increases with increasing $\Delta $ and can be up to $15~\mathrm{K} $ higher than under OB conditions. The comparison of our findings with several theoretical and empirical models showed that two-dimensional boundary-layer models overestimate the actual ${T}_{c} $, while models based on the temperature or velocity scales predict ${T}_{c} $ very well with a standard deviation of $0. 4~\mathrm{K} $. Furthermore, the obtained temperature profiles bend closer towards the cold top plate and further away from the hot bottom plate. The situation for the velocity profiles is reversed: they bend farther away from the top plate and closer towards to the bottom plate. The top boundary layers are always thicker than the bottom ones. Their ratio is up to 2.5 for the thermal and up to 4.5 for the viscous boundary layers. In addition, the Reynolds number $\mathit{Re}$ and the Nusselt number $\mathit{Nu}$ were investigated: $\mathit{Re}$ is higher and $\mathit{Nu}$ is lower under NOB conditions. The Nusselt number $\mathit{Nu}$ is influenced in a nonlinear way by NOB effects, stronger than was suggested by the two-dimensional simulations. The actual scaling of $\mathit{Nu}$ with $\mathit{Ra}$ in the NOB case is $\mathit{Nu}\propto {\mathit{Ra}}^{0. 298} $ and is in excellent agreement with the experimental data.
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Canli, Eyub, Ali Ates et Sefik Bilir. « Comparison of turbulence models and CFD solution options for a plain pipe ». EPJ Web of Conferences 180 (2018) : 02013. http://dx.doi.org/10.1051/epjconf/201818002013.
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Present paper is partly a declaration of state of a currently ongoing PhD work about turbulent flow in a thick walled pipe in order to analyze conjugate heat transfer. An ongoing effort on CFD investigation of this problem using cylindrical coordinates and dimensionless governing equations is identified alongside a literature review. The mentioned PhD work will be conducted using an in-house developed code. However it needs preliminary evaluation by means of commercial codes available in the field. Accordingly ANSYS CFD was utilized in order to evaluate mesh structure needs and asses the turbulence models and solution options in terms of computational power versus difference signification. Present work contains a literature survey, an arrangement of governing equations of the PhD work, CFD essentials of the preliminary analysis and findings about the mesh structure and solution options. Mesh element number was changed between 5,000 and 320,000. k-ϵ, k-ω, Spalart-Allmaras and Viscous-Laminar models were compared. Reynolds number was changed between 1,000 and 50,000. As it may be expected due to the literature, k-ϵ yields more favorable results near the pipe axis and k-ωyields more convenient results near the wall. However k-ϵ is found sufficient to give turbulent structures for a conjugate heat transfer problem in a thick walled plain pipe.
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Liu, HanChen, et XueWu Cao. « Numerical Study on Hydrogen Flow Behavior in Two Compartments with Different Connecting Pipes ». Science and Technology of Nuclear Installations 2017 (2017) : 1–10. http://dx.doi.org/10.1155/2017/4709503.
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Hydrogen accumulation in the containment compartments under severe accidents would result in high concentration, which could lead to hydrogen deflagration or detonation. Therefore, getting detailed hydrogen flow and distribution is a key issue to arrange hydrogen removal equipment in the containment compartments. In this study, hydrogen flow behavior in local compartments has been investigated in two horizontal compartments. The analysis model is built by 3-dimensional CFD code in Cartesian coordinates based on the connection structure of the Advanced Pressurized Water Reactor (PWR) compartments. It consists of two cylindrical vessels, representing the Steam Generator compartment (SG) and Core Makeup Tank compartment (CMT). With standard k-ε turbulence model, the effects of the connecting pipe size and location on hydrogen concentration distribution are investigated. Results show that increasing the diameter of connection pipe (IP) which is located at 800 mm from 150 mm to 300 mm facilitates hydrogen flow between compartments. Decreasing the length of IP which is located at 800 mm from 1000 mm to 500 mm can also facilitate hydrogen flow between compartments. Lower IP is in favor of hydrogen mixing with air in non-source compartment. Higher IP is helpful for hydrogen flow to the non-source term compartment from source term compartment.
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Allet, A., et I. Paraschivoiu. « Viscous Flow and Dynamic Stall Effects on Vertical-Axis Wind Turbines ». International Journal of Rotating Machinery 2, no 1 (1995) : 1–14. http://dx.doi.org/10.1155/s1023621x95000157.
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The present paper describes a numerical method, aimed to simulate the flow field of vertical-axis wind turbines, based on the solution of the steady, incompressible, laminar Navier-Stokes equations in cylindrical coordinates. The flow equations, written in conservation law form, are discretized using a control volume approach on a staggered grid. The effect of the spinning blades is simulated by distributing a time-averaged source terms in the ring of control volumes that lie in the path of turbine blades. The numerical procedure used here, based on the control volume approach, is the widely known “SIMPLER” algorithm. The resulting algebraic equations are solved by the TriDiagonal Matrix Algorithm (TDMA) in the r- and z-directions and the Cyclic TDMA in the 0-direction. The indicial model is used to simulate the effect of dynamic stall at low tip-speed ratio values. The viscous model, developed here, is used to predict aerodynamic loads and performance for the Sandia 17-m wind turbine. Predictions of the viscous model are compared with both experimental data and results from the CARDAAV aerodynamic code based on the Double-Multiple Streamtube Model. According to the experimental results, the analysis of local and global performance predictions by the 3D viscous model including dynamic stall effects shows a good improvement with respect to previous 2D models.
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SARIFUDDIN, SANTABRATA CHAKRAVARTY et PRASHANTA KUMAR MANDAL. « EFFECT OF ASYMMETRY AND ROUGHNESS OF STENOSIS ON NON-NEWTONIAN FLOW PAST AN ARTERIAL SEGMENT ». International Journal of Computational Methods 06, no 03 (septembre 2009) : 361–88. http://dx.doi.org/10.1142/s0219876209001887.
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Numerical investigations of non-Newtonian blood flow are carried out through an asymmetric arterial constriction (stenosis) obtained from casting of mildly stenosed artery [Back et al. [1984] Effect of mild atherosclerosis on flow resistance in a coronary artery casting by man, J. Biomech. Eng., Trans. ASME106, 48]. The Marker and Cell method, for governing equations of motion for the flow in primitive variables formulations is developed in a staggered grid to discretize the momentum equations representing the non-Newtonian viscous incompressible flow characterized by the generalized Power-law model in cylindrical coordinates system under axial symmetric conditions so that the problem effectively becomes two-dimensional. The modified pressure equation has been solved by Successive-Over-Relaxation method and the pressure–velocity correction formulae have been derived. Satisfactory level of convergence namely, the mass conservation of the order of 0.5 × 10-12 and consequently the steady-state criteria have been achieved. The separation points, reattachment points, pressure drop, and the wall shear stress distribution resulting from the present simulation agree well with the available numerical and experimental results. Secondary separation has also been predicted at higher Reynolds numbers. Further, in-depth study of the flow patterns reveals that shear-thickening model of generalized Power-law fluid experiences excess pressure drop more than that of shear-thinning model as in the case of flow past through cosine and smooth-shaped constrictions than irregular ones. The efficiency of the numerical code is illustrated by applying it to a test problem in order to validate the applicability of the technique as well as the simulation under consideration.
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Ghernoug, Chahinez, Mahfoud Djezzar, Hassane Naji et Abdelkarim Bouras. « Towards numerical computation of double-diffusive natural convection within an eccentric horizontal cylindrical annulus ». International Journal of Numerical Methods for Heat & ; Fluid Flow 26, no 5 (6 juin 2016) : 1346–64. http://dx.doi.org/10.1108/hff-10-2014-0330.
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Purpose – The purpose of this paper is to numerically study the double-diffusive natural convection within an eccentric horizontal cylindrical annulus filled with a Newtonian fluid. The annulus walls are maintained at uniform temperatures and concentrations so as to induce aiding thermal and mass buoyancy forces within the fluid. For that, this simulation span a moderate range of thermal Rayleigh number (100RaT100,000), Lewis (0.1Le10), buoyancy ratio (0N5) and Prandtl number (Pr=0.71) to examine their effects on flow motion and heat and mass transfers. Design/methodology/approach – A finite volume method in conjunction with the successive under-relaxation algorithm has been developed to solve the bipolar equations. These are written in dimensionless form in terms of vorticity, stream function, temperature and concentration. Beforehand, the implemented computer code has been validated through already published findings in the literature. The isotherms, streamlines and iso-concentrations are exhibited for various values of Rayleigh and Lewis numbers, and buoyancy ratio. In addition, heat and mass transfer rates in the annulus are translated in terms of Nusslet and Sherwood numbers along the enclosure’s sides. Findings – It is observed that, for the range of parameters considered here, the results show that the average Sherwood number increases with, while the average Nusselt number slightly dips as the Lewis number increases. It is also found that, under the convective mode, the local Nusselt number (or Sherwood) increases with the buoyancy ratio. Likewise, according to Lewis number’s value, the flow pattern is either symmetric and stable or asymmetric and random. Besides that, the heat transfer is transiting from a conductive mode to a convective mode with increasing the thermal Rayleigh number, and the flow structure and the rates of heat and mass transfer are significantly influenced by this parameter. Research limitations/implications – The range of the Rayleigh number considered here covers only the laminar case, with some constant parameters, namely the Prandtl number (Pr = 0.71), and the tilt angle (α=90°). The analysis here is only valid for steady, two-dimensional, laminar and aiding flow within an eccentric horizontal cylindrical annulus. This motivates further investigations involving other relevant parameters as N (opposite flows), Ra, Pr, Le, the eccentricity, the tilt angle, etc. Practical implications – An original framework for handling the double-diffusive natural convection within annuli is available, based on the bipolar equations. In addition, the achievement of this work could help researchers design thermal systems supported by annulus passages. Applications of the results can be of value in various arrangements such as storage of liquefied gases, electronic cable cooling systems, nuclear reactors, underground disposal of nuclear wastes, manifolds of solar energy collectors, etc. Originality/value – Given the geometry concerned, the bipolar coordinates have been used to set the inner and outer walls boundary conditions properly without interpolation. In addition, since studies on double-diffusive natural convection in annuli are lacking, the obtained results may be of interest to handle other configurations (e.g., elliptical-shaped speakers) with other boundary conditions.
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Muñoz-Cobo, José, Sergio Chiva, Mohamed El Aziz Essa et Santos Mendes. « Experiments performed with bubbly flow in vertical pipes at different flow conditions covering the transition region : simulation by coupling Eulerian, Lagrangian and 3D random walks models ». Archives of Thermodynamics 33, no 1 (1 août 2012) : 3–39. http://dx.doi.org/10.2478/v10173-012-0001-4.
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Experiments performed with bubbly flow in vertical pipes at different flow conditions covering the transition region: simulation by coupling Eulerian, Lagrangian and 3D random walks modelsTwo phase flow experiments with different superficial velocities of gas and water were performed in a vertical upward isothermal cocurrent air-water flow column with conditions ranging from bubbly flow, with very low void fraction, to transition flow with some cap and slug bubbles and void fractions around 25%. The superficial velocities of the liquid and the gas phases were varied from 0.5 to 3 m/s and from 0 to 0.6 m/s, respectively. Also to check the effect of changing the surface tension on the previous experiments small amounts of 1-butanol were added to the water. These amounts range from 9 to 75 ppm and change the surface tension. This study is interesting because in real cases the surface tension of the water diminishes with temperature, and with this kind of experiments we can study indirectly the effect of changing the temperature on the void fraction distribution. The following axial and radial distributions were measured in all these experiments: void fraction, interfacial area concentration, interfacial velocity, Sauter mean diameter and turbulence intensity. The range of values of the gas superficial velocities in these experiments covered the range from bubbly flow to the transition to cap/slug flow. Also with transition flow conditions we distinguish two groups of bubbles in the experiments, the small spherical bubbles and the cap/slug bubbles. Special interest was devoted to the transition region from bubbly to cap/slug flow; the goal was to understand the physical phenomena that take place during this transition A set of numerical simulations of some of these experiments for bubbly flow conditions has been performed by coupling a Lagrangian code, that tracks the three dimensional motion of the individual bubbles in cylindrical coordinates inside the field of the carrier liquid, to an Eulerian model that computes the magnitudes of continuous phase and to a 3D random walk model that takes on account the fluctuation in the velocity field of the carrier fluid that are seen by the bubbles due to turbulence fluctuations. Also we have included in the model the deformation that suffers the bubble when it touches the wall and it is compressed by the forces that pushes it toward the wall, provoking that the bubble rebound like a ball.
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Meisenberg, Oliver. « Virtual Igor : an analytical phantom for the simulation of the Saint Petersburg brick phantom in arbitrary layouts in MCNP ». Radiation and Environmental Biophysics, 28 août 2021. http://dx.doi.org/10.1007/s00411-021-00939-1.
Texte intégralRésumé :
AbstractA computer code called Virtual Igor is presented. The code generates an analytical representation of the Saint Petersburg brick phantom family (Igor, Olga, Irina), which is frequently used for the calibration of whole-body counters, in arbitrary user-defined layouts for the use in the Monte-Carlo radiation transport code MCNP. The computer code reads a file in the ldraw format, which can easily be produced by simple freeware software with graphical user interfaces and which contains the types and coordinates of the bricks. Ldraw files with the canonical layouts of the brick phantom are provided with Virtual Igor. The code determines the positions of (2.75 cm)3 segments of the bricks, where 2.75 cm is the smallest length in the layout and, therefore, represents the spacing of the segment lattice. Each segment contains the exact geometry of the respective part of the brick, using cuboid and cylindrical surfaces. The user can define which rod source drill holes of which bricks contain the rod-type radionuclide sources. The method facilitates the comparison of different layouts of the Saint Petersburg brick phantom with each other and with anthropomorphic computational phantoms.
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Worgan, Karen, Michael Apted et Rolf Sjöblom. « Performance Analysis of Copper Canister Corrosion Under Oxidizing or Reducing Conditions ». MRS Proceedings 353 (1994). http://dx.doi.org/10.1557/proc-353-695.
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AbstractThe finite-difference CAMEO code for modeling general corrosion of copper canisters is described. CAMEO represents the engineered barrier system and surrounding fractured host rock in 3-dimensional cylindrical coordinates. The time of containment failure is evaluated using CAMEO, as constrained by transport rates of corrodants to the canister or by transport rates of corrodant products away from the canister. Additional chemical processes explicitly modeled in CAMEO include 1) copper corrosion, and 2) kinetics of Cu(I) oxidation to Cu(II), both as a function of near-field pore water chemistry, specifically pH, Eh, and chloride concentration. The diffusional transport and sorption behavior of Cu(I) and Cu(II) are also separately incorporated.
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Saxena, Anil Kumar, Sanjay Limaye et P. K. Bhaumik. « EXPERIMENTAL TECHNIQUES ». International Journal of Engineering Applied Sciences and Technology 6, no 2 (1 juin 2021). http://dx.doi.org/10.33564/ijeast.2021.v06i02.040.
Texte intégralRésumé :
-There may be several aspects in any experiment conducted to achieve a well defined goal. It is considered more useful to cite number of experimental techniques employed in a single large scale experiment. For the rewetting of vertical cylindrical surface under bottom flooding conditions, it is reasonable to assume uniformity of temperature in the peripheral coordinate. Code RAMM (Rewetting Analysis using Moving Mesh) has been developed by the author of this paper [1] to calculate rewetting velocity. Experiments were also conducted for determination of rewetting velocities [2], the rewetting velocity in mm/s is100.0 by [3]; 33.3 by [4] ;51.0 by [5]. This paper is aimed to cover experimental techniques employed in the determination of rewetting velocity (RV) in Nuclear Reactor Channel under the scenario of Loss Of Coolant Accident (LOCA). For determining RV, many experimental methodology and techniques were employed. Experimental simulation of nuclear fuel pin clad named as fuel pin simulator, was carried out by taking hot vertical annular channel where rewetting of outer surface was studied. Experimental rewetting studies requires multidisciplinary approach namely (i) selection of material for the fuel pin simulator. (ii) Installation of thermocouple wires at many locations into wall of a long and narrow tube (iii) Electrical resistance Joules heating of S. S. tube of 3.03m long, 0.015m outer and 0.012m inner diameters (iv) selection of power source for heating (v) Instrumentation required to capture parameters and (vi) Programming and connecting the Data Acquisition System (DAS) for recording the temperature transients.
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Zhang, Jiecheng, George Moridis et Thomas Blasingame. « Message Passing Interface (MPI) Parallelization of Iteratively Coupled Fluid Flow and Geomechanics Codes for the Simulation of System Behavior in Hydrate-Bearing Geologic Media. Part 1 : Methodology and Validation ». SPE Reservoir Evaluation & ; Engineering, 1 mars 2022, 1–21. http://dx.doi.org/10.2118/206161-pa.
Texte intégralRésumé :
Summary The Reservoir GeoMechanics Simulator (RGMS or RGM simulator), a geomechanics simulator based on the finite element method (FEM) and parallelized using the Message Passing Interface (MPI), is developed in this work to model the stresses and deformations in subsurface systems. RGMS can be used standalone or coupled with flow and transport models. pTOUGH+ HYDRATE (pT+H) V1.5, a parallel MPI-based version of the serial TOUGH+HYDRATE (T+H) V1.5 code that describes mass and heat flow in hydrate-bearing porous media, is also developed. Using the fixed-stress split iterative scheme, RGMS is coupled with the pT+H V1.5 codes to investigate the geomechanical responses associated with gas production from hydrate accumulations. In the first paper of this series, we discuss the governing equations underlying physics and their mathematical representation in the modeling of the geomechanics, methane hydrate, and coupled problems as well as the numerical methods and the parallelization processes (involving a domain decomposition method based on the MPI approach) used for the parallel simulators. Two 2D problems (in Cartesian and radial-cylindrical coordinates) and a 3D Cartesian coordinate problem are created to validate the FEM and the parallelization method in RGMS. The displacements and the maximum principal effective stresses obtained from the RGMS solution of these three problems are compared to those from the commercial software Ansys Mechanical and are shown to practically coincide. The parallelization of pT+H V1.5 is validated by comparing its results to those from the serial T+H V1.5 code in a study that involved (a) fluid production from a large-scale 2D cylindrical system describing a real-life oceanic hydrate deposit and (b) a simplified geomechanical model based on hydrate-dependent pore compressibility. The coupling method is validated by comparing the numerical results to the analytical solutions of the Terzaghi and the McNamee-Gibson problems. The parallelization validation of the coupled simulator is achieved by comparing the results obtained for different numbers of processes in the solution of the problems used for the pT+H V1.5 parallelization validation with the full geomechanical model. The results clearly demonstrate the validity and reliability of the parallel codes (a) RGMS, (b) pT+H V1.5, and the (c) coupled pT+H V1.5 and RGM simulators, which can be used to solve the large-scale physics of complex problems.
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Wang, Wei, Kenji Imadera, Haruki Seto et Masatoshi Yagi. « Global gyro-kinetic study of magnetic shaping effects on linear trapped electron mode instability in normal/reversed magnetic shear plasmas ». Nuclear Fusion, 19 avril 2022. http://dx.doi.org/10.1088/1741-4326/ac6818.
Texte intégralRésumé :
Abstract A linear δf version of gyro-kinetic Vlasov code GKNET (Gyro-Kinetic Numerical Experiment of Tokamak) is extended to the global cylindrical coordinates (R,φ,Z) and include the kinetic electron response, to study the shaping effect on linear drift-wave instabilities in Tokamak plasmas. Cross-verifications are performed between three GKNET versions that use different electron models, i.e., adiabatic electron model, hybrid electron model (only trapped electrons are calculated kinetically) and full-kinetic electron model (all electrons are calculated kinetically). A destabilizing effect of non-adiabatic passing electrons is observed in the full-kinetic case for the Ion Temperature Gradient (ITG) mode in short wavelength region and the Trapped Electron Mode (TEM). The ion-to-electron mass ratio and the electron-electron collisionality have weak impacts on the destabilization of ITG/TEM. Utilizing MHD equilibria designed with normal and reversed magnetic shear (NS and RS), characteristics of linear TEMs and corresponding impact of plasma shaping are studied based on the GKNET code with full-kinetic electrons. Due to the change of temperature/density gradient and magnetic shear either measured locally in the low field side (LFS) or averaged over the flux surface, plasma shaping shows different impacts on linear TEMs in NS and RS configurations. For the elongation κ, the increase of κ always stabilizes linear TEMs due to the reduction of effective profile gradient over the flux surface. For the triangularity δ, in the NS case the change of δ shows weak dependence to TEM linear growth rates due to the balance between variations of profile gradients and magnetic shear in the LFS. In the RS case, local magnetic shear in the peak gradient region is nearly zero, thus the variation of local profile gradient plays a dominated role on the linear growth in plasma shaping scan. As a result, the negative triangularity (δ<0) has destabilizing effects to the linear TEMs in the RS configuration due to the upshift of local profile gradient in LFS.
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Fernandes, Fernando Bastos. « Perturbative-Integro-Differential Solution for the Nonlinear Hydraulic Diffusivity Equation for Infinite-Acting-Oil Flow in a Permeability-Pressure-Sensitive Reservoir ». SPE Reservoir Evaluation & ; Engineering, 1 mars 2022, 1–38. http://dx.doi.org/10.2118/208593-pa.
Texte intégralRésumé :
Summary The nonlinear hydraulic diffusivity equation (NHDE) models the isothermal single-phase Darcian flow through porous media considering the variation in the properties of the rock and the fluid present inside its pores. Typically, the dimensionless solution of the linear hydraulic diffusivity equation (LHDE) pD(rD,tD) for constant permeability oil flow in porous media is computed through Laplace and Fourier transform or Boltzmann transformation. For these cases, the dimensionless general solution in cylindrical coordinates is expressed by the transcendental function exponential integral Ei(rD,tD). This work develops analytically a new coupled perturbative-integro-differential model to solve the NHDE for oil flow in a permeability-pressure-sensitive reservoir with source. The general solution is computed combining a first-order asymptotic series expansion, Green’s functions (GF), and a Volterra’s second kind integro-differential formulation. A set of pore pressure and permeability values for two sandstones samples in an offshore reservoir from Brazil is obtained experimentally using the geomechanical elastic parameters (e.g., the Young’s modulus and Poisson’s ratio in addition to a uniaxial cell). These data are used as input in the computational code to run the analytical model and evaluate the reservoir permeability change. After these data input, the model runs and it allows to compute the instantaneous reservoir permeability values over the well-reservoir life cycle. The model calibration is performed by comparing the developed solution with a numerical porous media oil flow simulator named IMEX®, widely used in reservoir engineering and well-testing field operations and scientific works. The general solution of the NHDE mD(rD,tD) is computed by the sum of the linear solution pD(rD,tD) (constant permeability) and the first-order term of the asymptotic series expansion mD(1)(rD,tD), composed of the nonlinearity present in solution caused by the reservoir permeability variation. The results have shown that the developed solution is accurate, when compared to the numerical simulator, providing to be an attractive mathematical tool to help the well-reservoir management due to its low computational costs, when compared to the numerical simulators acquisition costs.