Current Issue : January - March Volume : 2014 Issue Number : 1 Articles : 5 Articles
The biologically inspired concept of hidden genes has been recently introduced in genetic algorithms to solve optimization\r\nproblems where the number of design variables is variable. In multigravity-assist trajectories, the hidden genes genetic algorithms\r\ndemonstrated success in searching for the optimal number of swing-bys and the optimal number of deep space maneuvers. Previous\r\ninvestigations in the literature for multigravity-assist trajectory planning problems show that the standard differential evolution is\r\nmore effective than the standard genetic algorithms. This paper extends the concept of hidden genes to differential evolution. The\r\nhidden genes differential evolution is implemented in optimizingmultigravity-assist space trajectories. Case studies are conducted,\r\nand comparisons to the hidden genes genetic algorithms are presented in this paper....
The design of an intake for a gas turbine engine involves CFD-based investigation and experimental assessment in an intake test\r\nrig. In both cases, the engine is represented by a mass flux sink, usually positioned a fewfan radii aft of the real fan face. In general,\r\nthis approach is sufficient to analyze intake geometry for low distortion at the fan face, because in this case the interaction of the\r\nfan with the inlet flow can be neglected. Where there are higher levels of distortion at the fan face, the interaction could become\r\nmore significant and a different approach would be preferable. One alternative that takes into account the interaction in such cases\r\nincludes the fan in the analysis of the intake, using either a steady or unsteady flow model approach. However, this solution is\r\nexpensive and too computationally intensive to be useful in design mode. The solution proposed in this paper is to implement\r\na new boundary condition at the fan face which better represents the interaction of the fan with the flow in the air intake in the\r\npresence of distortion. This boundary condition includes a simplified fanmodel and a coupling strategy applied between the fan and\r\nthe inlet. The results obtained with this new boundary condition are compared to full 3D unsteady CFD simulations that include\r\nthe fan....
Film cooling is vital to gas turbine blades to protect them from high temperatures and hence high thermal stresses. In the current\r\nwork, optimization of film cooling parameters on a flat plate is investigated numerically. The effect of film cooling parameters such\r\nas inlet velocity direction, lateral and forward diffusion angles, blowing ratio, and streamwise angle on the cooling effectiveness is\r\nstudied, and optimum cooling parameters are selected. The numerical simulation of the coolant flow through flat plate hole system\r\nis carried out using the ââ?¬Å?CFDRC packageââ?¬Â coupled with the optimization algorithm ââ?¬Å?simplexââ?¬Â to maximize overall film cooling\r\neffectiveness. Unstructured finite volume technique is used to solve the steady, three-dimensional and compressible Navier-Stokes\r\nequations. The results are compared with the published numerical and experimental data of a cylindrically round-simple hole, and\r\nthe results show good agreement. In addition, the results indicate that the average overall film cooling effectiveness is enhanced\r\nby decreasing the streamwise angle for high blowing ratio and by increasing the lateral and forward diffusion angles. Optimum\r\ngeometry of the cooling hole on a flat plate is determined. In addition, numerical simulations of film cooling on actual turbine\r\nblade are performed using the flat plate optimal hole geometry....
A proper orthogonal decomposition (POD)method is used to interpolate the flow around an airfoil for variousMach numbers and\r\nangles of attack in the transonic regime. POD uses a few numerical simulations, called snapshots, to create eigenfunctions. These\r\neigenfunctions are combined using weighting coefficients to create a new solution for different values of the input parameters. Since\r\nPOD methods are linear, their interpolation capabilities are quite limited when dealing with flow presenting nonlinearities, such\r\nas shocks. In order to improve their performance for cases involving shocks, a new method is proposed using variable fidelity.\r\nThe main idea is to use POD to interpolate the difference between the CFD solution obtained on two different grids, a coarse one\r\nand a fine one.Then, for any new input parameter value, a coarse grid solution is computed using CFD and the POD interpolated\r\ndifference is added to predict the fine grid solution. This allows some nonlinearities associated with the flow to be introduced.\r\nResults for various Mach numbers and angles of attack are compared to full CFD results. The variable fidelity-based POD method\r\nshows good improvement over the classical approach....
Solid carbon is deposited on the surfaces of an inductively coupled plasma torch operating with a Titan like atmosphere plasma\r\ngas. The frame of the initial research is the study of the radiative properties of plasma encountered around a spacecraft during its\r\nhypersonic entry in upper layers of planetary atmosphere. Deposition of carbon is observed not only on the quartz tube outside the\r\ninductor but also on the ceramic protection of the torch injector. Carbon exhibits two types of morphology more or less dense and\r\nit is analyzed by various analytic devices as MEB, SEM, TEM, EDS and Raman spectroscopy.The gathered carbon powder shows\r\nthe presence of nanostructured particles....
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