Computational fluid dynamics geometric modeling

Computational fluid dynamics (CFD) is essentially a computer-based numerical analysis approach for fluid flow, heat transfer and related phenomena. CFD techniques typically consist of the following five subprocesses geometrical modelling, geometry discretisation, boundary condition definition, CFD-based problem solving, and post-processing for solution visualisation. 

Computational fluid dynamics models were developed over the years that include the effects of leaflet motion and its interaction with the flowing blood (Bellhouse et al., 1973 Mazumdar, 1992). Several finite-element structural models for heart valves were also developed in which issues such as material and geometric nonlinearities, leaflet structural dynamics, stent deformation, and leaflet coaptation for closed valve configurations were effectively dealt with (Bluestein and Einav, 1993 1994). More recently, fluid-structure interaction models, based on the immersed boundary technique. 

A multi-zone model similar to the finite volume methods used in Computational Fluid Dynamics (CFD, see Section 12.5) is based on geometrical zones and assumes uniform conditions within each zone, that is, completely mixed (CSTR) zones, while essentially allowing conditions to differ between zones. For statistically stationary flow, the species balance equations for species A in zone i of iVcan then be written as ... 

As a model system a cylindrical reactor of the length L = 60 mm and inner diameter di = 7 mm packed with 400 uniform, nonporous spherical particles of the diameter dp = 1.8 mm was studied. The geometrical dimensions, as well as the average porosity, e = 0.47, of the packed bed were adjusted to those used in Section 5.2. Spatial discretization with the resolution of 30 lattice constant per sphere diameter was performed resulting in the computational domain of dimension 1300 X 117 X 117 points. The selected results given below intend to illustrate substantial differences and characteristics in the fluid dynamics in a FBR (Frs/Fss = 00) and PBMR. All the simulations presented were carried out on a Hewlett Packard Superdome parallel computer (64 processors, 120GB RAM). Typical simulation times for the complete model were about 24h on this architecture. 

West, Nick. Practical Fluid Dynamics Part 1. Game Developer 14, no. 3 (March, 2007) 43-47. Introduces the application of geometric principles in the modeling of smoke, steam, and swirling liquids in the graphics of computer games and simulations. 

As discussed in Section 6.4 for ammonia oxidation at a single Pt wire, that is, where the cylindrical wire is heated by an exothermic chemical reaction, the variation of temperature around a cylinder can nowadays be modeled by computer programs, for example, by the finite element method. The geometric structure is approximated by a meshing procedure that is used to define and break the model up into small elements. The differential equations of heat transfer and of the fluid dynamics (Navier-Stokes equations) are then numerically solved. The temperature gradients at the surface of the cylinder (Tcyi = const. = at... 

The COAST computer program is used to calculate the reactor coolant flow coast down transient for any combination of active and inactive pumps and forward or reverse flow in the hot or cold legs. The equations of conservation of momentum are written for each of the flow paths of the COAST model assuming unsteady one-dimensional flow of an incompressible fluid. The equation of conservation of mass is written for the appropriate nodal points. Pressure losses due to friction, and geometric losses are assumed proportional to the flow velocity squared. Pump dynamics are modelled using a head-flow curve for a pump at fiill speed and using four-quadrant curves, which are parametric diagrams of pump head and torque on coordinates of speed versus flow, for a pump at other than full speed. 

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