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Objective: Ischemic preconditioning (IPC) is an endogenous phenomenon that can induce ischemic tolerance (IT) in variety of organs such as brain. In this study, we examined the intermittent and prolonged normobaric hyperoxia (HO) on neurologic deficit scores, infarct volume, and superoxide dismutase activity. Materials and Methods: The rats were divided to four main groups. First two main groups were exposed with HO in prolonged (24 h; PrHO) and intermittent (4 h×6 days; InHO) groups and second two main group acted as controls, and were exposed to 21% oxygen in the same chamber (room air, RA) continuously (24 h; PrRA) and discontinuously (4 h×6 days; InRA). Each group subdivided to three subgroups. After 24 h, first subgroup were subjected to 60 minutes MCAO followed by 24 h of reperfusion. Then, IT induced by InHO and PrHO were measured by neurologic deficit scores and infarct volume. Second and third subgroups were called sham-operated and intact subgroups for assessment of the effect of HO on superoxide dismutase activity. Results: Our findings indicate that InHO and PrHO are involved in the induction of IT. Pretreatment with InHO and PrHO reduced neurologic deficit scores and infarct volume significantly. InHO and PrHO increase superoxide dismutase activity significantly. Conclusion: Although further studies are needed to clarify the mechanisms of ischemic tolerance, InHO and PrHO seem to partly exert their effects via increase superoxide dismutase activity.

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Effect of boundary layer and its local separation on lift and drag coefficients, especially in the analysis of hydrodynamic behavior of hydrofoils is considered as an interesting subject for fluid mechanics researchers. Boundary layer control methods to increase the lift coefficient and reduce the drag coefficient, are very common. Aerodynamic study of flows at low Reynolds to special applications such as micro unmanned underwater vehicles, underwater robots and explorers are interested. For this reason in this study, the effect of fluid blowing and suction through upper surface of hydrofoils on flow control, lift and drag coefficients for flow under Re =500 and Re=2000 are investigated. Jameson’s finite volume method and power-law preconditioning method for analyzing viscous incompressible flows are presented. To control the boundary layer a jet with a width of 2.5% of chord length is placed on hydrofoil’s upper surface and results for different blowing (suction) parameters are introduced. Results show that, blowing far from leading edge at low blowing angel and perpendicular suction far from leading edge increase the lift coefficient. Also blowing with law velocity ratio and suction with large velocity ratio, has the better impact on increasing lift coefficient.

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Numerical analysis and simulation of cavitating flows due to appearance and its application in the maritime industry, water turbomachinery, hydrofoils, underwater vehicles, etc. have specific importance. For this reason in this research, the effect of blowing on hydrodynamic behavior of cavitating flows over hydrofoils has been investigated. Jameson's finite volume method and power-law preconditioning method with single-phase cavitation model (Barotropic model) have been used to the analyzing of cavitating flow. The stabilization of solution has been achieved with help of the second and fourth-order dissipation term. Explicit four step Runge-Kutta method has been used to achieve the steady state condition. As regards the cavitation often occurs at high Reynolds number, to facilitate the simulation the inviscid flow equations are considered. For apply the blowing from hydrofoil surface, a jet has been placed on hydrofoil’s upper surface. The parameters of jet location, blowing velocity ratio, blowing angle and width of jet are investigated and simulation has been performed for two different cavitation numbers. The numerical results show that the power-law precondition increases the convergence speed significantly. Blowing reduces the cavity length, lift and pressure drag coefficients compared to no blowing case. Also the increase of blowing velocity ratio, blowing angle and width of jet, decrease the cavity length, lift and pressure drag coefficients.

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Aerodynamic study of flows at low Reynolds for special applications such as micro unmanned underwater vehicles, underwater robots and explorers are interested. In this paper, an improved progressive preconditioning method named power-law preconditioning method, for analyzing unsteady laminar flows around hydrofoils is presented. In this method, the 2D Navier-Stokes equations modifies by altering the time derivative terms of the governing equations. The preconditioning matrix is adapted from the velocity flow-field by a power-law relation. The governing equation is integrated with a numerical resolution derived from the cell-centered Jameson’s finite volume algorithm and a dual-time implicit procedure is applied for solution of unsteady flows. The stabilization is achieved via the second- and fourth-order artificial dissipation scheme. Explicit four-step Runge–Kutta time integration is applied to achieve the steady-state condition. The computations are presented for unsteady laminar flows around NACA0012 hydrofoil at various angles of attack and Reynolds number. Results presented in the paper focus on the velocity profiles, lift and drag coefficient and effect of the power-law preconditioning method on convergence speed. The results show satisfactory agreement with numerical works of others and also indicate that using the power-law preconditioner improves the convergence rate and decreases the computational cost, significantly.

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In this paper, an implicit finite element-discontinuous Galerkin method for compressible viscous and inviscid flow is developed using Newton-Krylov algorithm with the objective of increasing the accuracy and convergence rate. For inviscid flows, an artificial viscosity is implemented in sharp gradient flow regions especially at high-order cases, increasing the accuracy of the solution. Moreover, for viscous flows, the accuracy is improved by using compact discontinuous Galerkin discretization method for elliptical terms. To reduce the computing CPU time and increase the convergence rate, an iterative Krylov type preconditioned linear solver is applied. For preconditioning, restarting, Block-Jacobi and block incomplete-LU factorization are employed for solving the linear system of the Jacobian matrix. The Jacobian matrix is constructed via finite difference perturbation technique. In this context, the performance of preconditioning matrix for three types of flow regimes of inviscid subsonic, inviscid transonic and viscous laminar subsonic are studied. In addition to complete the discussions, multigrid smoother with special conditions is applied for all preconditioning matrices. To improve the solver performance for higher order discretization, a lower order solution may be used as higher orders initial condition. Therefore, a middle phase is needed to transfer calculations from low to high order discretized domain and then the final Newton phase is continued. In addition, local time stepping is implemented to improve the rate of convergence. Consequently, the presented numerical method can be used as an efficient algorithm for high-order Discontinuous Galerkin flow simulation, especially for transonic inviscid and laminar viscous flows.

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Abstract In this paper, a viscous all-speed flow solver has been developed based on Roe upwind scheme in unstructured database. In the presented method, stiffness of the compressible governing equations in low-speed region reduces using the preconditioning form. In calculating the artificial viscosity of a Roe upwind scheme, multiple matrices multiplication are needed. Frink reduced these costly operations by simplification of the matrices multiplication to some flux components which are related to distinct eigenvalues. In this research similar to Frink work, the equations of artificial viscosity in preconditioning Roe upwind scheme obtained and presented in the flux components form. This is a generalized form that can be easily switched to the preconditioned or non-preconditioned form. This is useful in converting any original Roe upwind scheme to the preconditioning form and also has application in adjoint optimization method. Results of the computer code were compared with experimental data of single and two-element airfoils in both preconditioning and non-preconditioning form. The results show that the non-preconditioning compressible solver hardly converged in low-speed regions while the preconditioned form converged more rapidly.