SINCE the 1980s, after Steger et al. solved two- and three-dimensionalmultibody configurations, overset (chimera) grid systems became very popular because of theiradvantages in easing the grid generation. Later in 199...
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SINCE the 1980s, after Steger et al. solved two- and three-dimensionalmultibody configurations, overset (chimera) grid systems became very popular because of theiradvantages in easing the grid generation. Later in 1994, Kao et al. used overset grids in order toperform grid adaptation in the flow regions where higher gradients exist. Tuncer preferred to useoverset grids for unsteady Navier-Stokes solutions of sinusoidally pitching airfoil. Cho et *** the generic wing/pylon/finned store (WPFS) configuration as a steady three-dimensionalproblem by using the overset grids. Later Lee et al. used overset grid system for the solution of astore release problem. Furthermore, Hoist also developed a new search algorithm for locating thedonor cells associated with the overset grid system used in the solution of wing-fuselage geometryby full potential equations. In the present work, a three-dimensional finite differencing scheme,multiblock structured Euler and thin-layer Navier-Stokes solver is modified in order to enhanceoverset grid capability and to run in a parallel-computing environment. A wing-store configurationand Eglin WPFS configuration are selected as the test cases for the validation purposes.
The statement and solution algorithm are proposed for the problem on the stress-strain state of a kimberlite body, filling massif, and enclosing rock during slice chamber mining with filling. The equations of nonlinea...
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The statement and solution algorithm are proposed for the problem on the stress-strain state of a kimberlite body, filling massif, and enclosing rock during slice chamber mining with filling. The equations of nonlinear hereditary viscoelasticity are used as the constitutive relations for saliferous rocks.
Finite element (FE)-based motion points are developed for use in particlemethods. These motion points are advantageous for boundary treatment in the hybrid particle *** resulting approach considers boundary motion poi...
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Finite element (FE)-based motion points are developed for use in particlemethods. These motion points are advantageous for boundary treatment in the hybrid particle *** resulting approach considers boundary motion points as finite element nodes, whereas theneighboring stress points are considered as the integration points of an explicit finite elementmethod (FEM) formulation. The stability of employing FE-based motion points is discussed. Numericalresults are presented to demonstrate the feasibility, accuracy, and stability of the presentdevelopment. These developments can facilitate methodologies to combine the hybrid particle methodand the explicit FEM in a single analysis.
A modular approach to the formulation and a solution of mixed-integer non-linear programming (MINLP) problems are presented, which reduce the size of MINLP and the computational expenses effectively. The method decomp...
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A modular approach to the formulation and a solution of mixed-integer non-linear programming (MINLP) problems are presented, which reduce the size of MINLP and the computational expenses effectively. The method decomposes the synthesis task into three hierarchical levels-the superstructure, the structure, and the modules, with the layer of modules being the most critical to the problem solution. The strategy has been implemented in a simulation environment in which the variables of interest are defined as implicit functions of the optimization variables. The implicit relationships are handled using a data-oriented process simulation technique (DOPS) that significantly simplify the simulation. The method has been effectively applied to two case studies, one from literature for the synthesis of hydrodesalkylation, and another from industrial process manufacturing methylene diphenylene diisocyanates.
Unsteady, viscous flows over flapping airfoils in a biplane configuration are computed on moving overset grids. The overset grid solutions are obtained in parallel in a distributed memory environment. Unsteady flowfie...
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Unsteady, viscous flows over flapping airfoils in a biplane configuration are computed on moving overset grids. The overset grid solutions are obtained in parallel in a distributed memory environment. Unsteady flowfields are described by particle traces: Time-averaged thrust values are obtained from the integration of the unsteady drag coefficient. It is shown that airfoils in a biplane configuration and oscillating in a combined pitch and plunge motion with a proper phase shift between them produce 20-40% more thrust than a single flapping airfoil. Turbulence in the flow further augments the thrust generation. For a maximum thrust at a given flapping frequency, an optimization of the flapping motion parameters is needed.
A grid fin is an unconventional aerodynamic lifting and control device consisting of an outer frame with internal grid framework of small chord. The present study performs the Navier-Stokes computations of turbulent f...
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A grid fin is an unconventional aerodynamic lifting and control device consisting of an outer frame with internal grid framework of small chord. The present study performs the Navier-Stokes computations of turbulent flows past 1) a grid fin alone and 2) fin/body combination shapes at Mach numbers of 2.5 and 0.7. This work designs a procedure to generate a structure grid with a simple and efficient algorithm combining "block-off" and "multiblock" methods for the complex configurations. Full Navier-Stokes equations with a pointwise version of the Baldwin-Barth one-equation turbulence model are discretized into finite difference form and solved by an algorithm in a fully coupled, implicit, and large block structure, and the solution algorithm achieves satisfactory convergence. The comparisons between computations and experimental data are made, and the detailed flow structure near grid fins can be obtained and examined.
An anisotropic viscous Cartesian grid method based on a 2(N) tree data structure is developed. The method is capable of handling complex geometries automatically. In addition, viscous boundary layers can be computed w...
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An anisotropic viscous Cartesian grid method based on a 2(N) tree data structure is developed. The method is capable of handling complex geometries automatically. In addition, viscous boundary layers can be computed with high resolution, using automatically projected high aspect ratio viscous layer grids. Compared with a widely used Octree data structure, the 2(N) tree data structure supports anisotropic grid adaptations in any of the coordinate directions. Therefore, key flow features such as shock waves, wakes, and vortices can be captured in a very efficient manner. To handle the adaptive viscous Cartesian grid, an implicit, second-order, finite volume flow solver supporting arbitrary grids has been developed. A linearity-preserving least-squares solution reconstruction algorithm is used to achieve second-order accuracy. Furthermore, several directional adaptation criteria are developed and tested, The overall grid generation, flow simulation, and grid adaptation methodology is then demonstrated for a variety of flow problems, including a case of supersonic turbulent flow over a high-angle-of-attack missile configuration.
An analytical solution is provided to the nonlinear diffusion equation, with the thermal conductivity given as a linear function of temperature. The derivation of the solution, and implications of it, are presented. T...
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An analytical solution is provided to the nonlinear diffusion equation, with the thermal conductivity given as a linear function of temperature. The derivation of the solution, and implications of it, are presented. The boundary and initial conditions associated with the solution provide applicability to specific cases. The solution is useful for verifying numerical (computer) solutions to thermal diffusion with temperature-dependent thermal conductivity. The (nonlinear) analytical solution is compared to a numerical solution from a finite element code to verify the accuracy of the code and to establish the order of convergence for the spatial discretization error.
A method is presented for estimating the laminar/turbulent transition location in three-dimensional boundary layers for computational fluid dynamics (CFD) applications requiring numerous transition estimates with no u...
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A method is presented for estimating the laminar/turbulent transition location in three-dimensional boundary layers for computational fluid dynamics (CFD) applications requiring numerous transition estimates with no user intervention. Given the Reynolds number and the C-P distribution, the location of transition is estimated based on the attachment-line state, the potential for relaminarization, the occurrence of laminar separation, and the growth of instabilities. Transition caused by instability is estimated based on N factors calculated for Tollmien-Schlichting waves and for stationary crossflow instabilities. A neural network is used (in place of solving the Orr-Sommerfeld stability equation) for determining the instability growth rates. The current version of the method assumes incompressible How. The boundary-layer flow and instabilities are calculated based on an infinite-sweep (strip boundary layer) approximation;the instability calculations also employ the parallel-How approximation. Comparisons with traditional stability codes show good N-factor agreement over a practical range of C-P distributions. The method is several hundred times faster than traditional stability calculations, and it is robust enough to function as a simple "subroutine" in CFD codes. The method is biased toward application efficiency and simplicity as balanced against improvements in the detailed physical modeling.
A local time-stepping algorithm has been developed to improve the numerical efficiency of Lagrangian particle-based Monte Carlo methods for obtaining the steady-state solutions of the modeled probability density funct...
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A local time-stepping algorithm has been developed to improve the numerical efficiency of Lagrangian particle-based Monte Carlo methods for obtaining the steady-state solutions of the modeled probability density function equations of turbulent reacting flows. On each step in the pseudo-time-marching algorithm, the properties of each particle are advanced by a time step, the magnitude of which depends on the particle's spatial location. This algorithm has been incorporated into the consistent hybrid finite volume/particle method. The performance of the local time-stepping method is evaluated in terms of numerical efficiency and accuracy through application to a non-reacting bluff-body flow. For this test case, it is found that local time stepping can accelerate the global convergence of the hybrid method by as much as an order of magnitude, depending on the grid stretching. Additionally, local time stepping is found to improve significantly the robustness of the hybrid method mainly due to the accelerated convection of error waves out of the computational domain. The method is very simple to implement, and the small increase in CPU time per step (typically 3%) is a negligible penalty compared to the substantial reduction in the number of time steps required to reach convergence.
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