7,121 research outputs found
Numerical simulation of two-dimensional blade-vortex interactions using unstructured adaptive meshes
No full textA two-dimensional Euler flow solver has been developed for the simulation of unsteady, blade-vortex interaction problems on unstructured meshes. The Euler solver is based on a second-order-accurate implicit time integration using a point Gauss-Seidel relaxation scheme and a dual time-step subiteration. A vertex-centered, finite volume discretization is used in conjunction with the Roe's flux-difference splitting. An unsteady solution-adaptive dynamic mesh scheme is used by adding and deleting mesh points at every adaptation step to take account of not only spatial but also of temporal variations of the flow field. Unsteady flow around a harmonically oscillating airfoil and traveling vortex in a freestream were simulated to validate the accuracy of the dynamic mesh adaptation procedure. Three blade-vortex interaction problems, two at transonic freestream speeds and one with vortex-airfoil collision, were investigated. Computed results show good agreements with existing experimental and computational results within the accuracy of the present inviscid solver. It is found that the evolution of vorticies and propagation of acoustic waves can be accurately simulated using the present unstructured dynamic mesh adaptation procedure
Time-accurate Navier-Stokes simulation of vortex convection using an unstructured dynamic mesh procedure
No full textA two-dimensional Navier-Stokes flow solver is developed for the simulation of unsteady flows on unstructured adaptive meshes. The solver is based on a second-order accurate implicit time integration using a point Gauss-Seidel relaxation scheme and a dual time-step. subiteration. A vertex-centered, finite-volume discretization is used in conjunction with Roe's flux-difference splitting. The Spalart-Allmaras one equation model is employed for the simulation of turbulence. An unsteady solution-adaptive dynamic mesh scheme is used by adding and deleting mesh points to take account of spatial and temporal variations of the flowfield. Unsteady viscous flow for a traveling vortex in a free stream is simulated to validate the accuracy of the dynamic mesh adaptation procedure. Flow around a circular cylinder and two blade-vortex interaction problems are investigated for demonstration of the present method. Computed results show good agreement with existing experimental and computational results. It was found that unsteady time-accurate viscous flows can be accurately simulated using the present unstructured dynamic mesh adaptation procedure. (C) 2002 Elsevier Science Ltd. All rights reserved
Deformations of coisotropic submanifolds and strong homotopy Lie algebroids
No full textIn this paper, we study deformations of coisotropic submanifolds in a symplectic manifold. First we derive the equation that governs C-infinity deformations of coisotropic submanifolds and define the corresponding C-infinity-moduli space of coisotropic submanifolds modulo the Hamiltonian isotopies. This is a non-commutative and non-linear generalization of the well-known description of the local deformation space of Lagrangian submanifolds as the set of graphs of closed one forms in the Darboux-Weinstein chart of a given Lagrangian submanifold. We then introduce the notion of strong homotopy Lie algebroid (or L-infinity-algebroid) and associate a canonical isomorphism class of strong homotopy Lie algebroids to each pre-symplectic manifold (Y,omega) and identify the formal deformation space of coisotropic embeddings into a symplectic manifold in terms of this strong homotopy Lie algebroid. The formal moduli space then is provided by the gauge equivalence classes of solutions of a version of the Maurer-Cartan equation (or the master equation) of the strong homotopy Lie algebroid, and plays the role of the classical part of the moduli space of quantum deformation space of coisotropic A-branes. We provide a criterion for the unobstructedness of the deformation problem and analyze a family of examples that illustrates that this deformation problem is obstructed in general and heavily depends on the geometry and dynamics of the null foliation.X112524Nsciescopu
Performance evaluation of absorption chiller using LiBr+H2N(CH2)(2)OH+H2O, LiBr+HO(CH2)(3)OH+H2O, and LiBr+(HOCH2CH2)(2)NH+H2O as working fluids
No full textIn order to check the theoretical performance of new working fluids LiBr + H2N(CH2)(2)OH + H2O, LiBr + HO(CH2)(3)OH + H2O, and LiBr + (HOCH2CH2)(2)NH + H2O [LiBr/H2N(CH2)(2)OH, LiBr/HO(CH2)(3)OH, and LiBr/(HOCH2CH2)(2)NH mass ratios were 3.5] which were developed particularly for the air-cooled cycle operation, the theoretical coefficients of performance (COPs) were calculated at various operating conditions. The cooling capacity and crystallization problem were also checked at a specific condition for air-cooled cycle operation. All the solutions were found to be of possibe use as working fluids for the air-cooled absorption chiller as alternatives to the conventional LiBr + H2O solution (C) 1998 Elsevier Science Ltd. All rights reserved
The multilayer modified Stoney's formula for the laminated polymer composites on a silicon substrate
No full textThe thermomechanical behavior of multilayer structures is a subject of perennial interest. Stoney's formula has long been one of the most important tools for understanding thermomechanical stress for single-layered structures like spin-coated polyimides or deposited metal thin film on substrates. In today's microelectronics, however, as multilayer substrates have become widely available, the "modified version" of Stoney's formula for multilayer applications is not only useful but necessary. While the majority of reports in the literature have focused on single-layer analysis, in this study, we examined an extended usage of Stoney's formula for multilayer analysis. A simple model, the multilayer-modified Stoney's formula, which predicts the stress contribution of each individual layer is proposed and verified through experiments and numerical analysis. Using various kinds of materials employed in a typical lamination-based multichip module technology, the thermomechanical behavior of the lamination-based multilayer substrates was measured by a laser profilometry during thermal cycling. The measured values were compared with calculated values using the multilayer-modified Stoney's formula. (C) 1999 American Institute of Physics. [S0021-8979(99)05822-3]
Solubilities, vapor pressures, densities, and viscosities of the LiBr+LiI+HO(CH2)(3)OH+H2O system
No full textThe lithium bromide + lithium iodide + 1,3-propanediol + water (LiBr/LiI mole ratio = 4 and (LiBr + LiI)/HO(CH2)(3)OH mass ratio = 4) solution was selected as the potential working fluid for an air-cooled absorption chiller, and its basic four thermophysical properties were measured. The solubilities were measured in the range of absorbent (LiBr + LiI + HO(CH2)(3)OH) concentration from 70.0 mass % to 77.8 mass %. The vapor pressures were measured in the ranges of temperature and absorbent concentration from 339.75 K to 444.35 K and from 55.0 mass % to 80.0 mass %. Both the densities and viscosities were measured in the temperature and concentration ranges of 283.15 K to 343.15 K and 25.0 mass % to 75.0 mass %, respectively. The individual data set was correlated with a regression equation with high accuracy. The absorption chiller using the new solution as a working fluid is expected to have a wide operation range without the danger of crystallization, which is the critical problem in constructing an air-cooled absorption chiller.This work was supported by Grant No. 97-2-10-03-01-3 from the
Basic Research Program of the KOSEF and also partially by the
Brain Korea 21 Project
Simultaneous Measurement and Compensation of 5-DOF Motion Errors Using Extended Twyman-Green Interferometry
No full textCompensation of Parasitic Motion Errors in Translational Stage Based on Twyman-Green Interferometry
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