Sharif Digital Repository

A new shock-detecting sensor for properly switching between a second-order and a higher-order filter is developed and assessed. The sensor is designed based on an order analysis. The nonlinear filter with the proposed sensor ensures damping of the high-frequency waves in smooth regions and at the same time removes the Gibbs oscillations around the discontinuities when using high-order compact finite difference schemes. In addition, a suitable scaling is proposed to have dissipation proportional to the shock strength and also to minimize the effects of the second-order filter on the very small scales. Several numerical experiments are carried out and the accuracy of the nonlinear filter with... 

The numerical solution to the parabolized Navier-Stokes (PNS) and globally iterated PNS (IPNS) equations for accurate computation of hypersonic axisymmetric flowfields is obtained by using the fourth-order compact finite-difference method. The PNS and IPNS equations in the general curvilinear coordinates are solved by using the implicit finite-difference algorithm of Beam and Warming type with a high-order compact accuracy. A shock-fitting procedure is utilized in both compact PNS and IPNS schemes to obtain accurate solutions in the vicinity of the shock. The main advantage of the present formulation is that the basic flow variables and their first and second derivatives are simultaneously... 

High-order accurate solutions of parabolized Navier-Stokes (PNS) schemes are used as basic flow models for stability analysis of hypersonic axisymmetric flows over blunt and sharp cones at Mach 8. Both the PNS and the globally iterated PNS (IPNS) schemes are utilized. The IPNS scheme can provide the basic flow field and stability results comparable with those of the thin-layer Navier-Stokes (TLNS) scheme. As a result, using the fourth-order compact IPNS scheme, a high-order accurate basic flow model suitable for stability analysis and transition prediction can be efficiently provided. The numerical solution of the PNS equations is based on an implicit algorithm with a shock fitting procedure... 

The numerical solution of the parabolized Navier-Stokes (PNS) and globally iterated PNS (IPNS) equations for accurate computation of hypersonic axisymmetric flowfields is obtained by using the fourth-order compact finite-difference method. The PNS and IPNS equations in the general curvilinear coordinates are solved by using the implicit finite-difference algorithm of Beam and Warming type with a high-order compact accuracy. A shock fitting procedure is utilized in both the compact PNS and IPNS schemes to obtain accurate solutions in the vicinity of the shock. The main advantage of the present formulation is that the basic flow variables and their first and second derivatives are... 

Thermal cracking of hydrocarbons converts them into valuable materials in the petrochemical industries. Multiplicity of the reaction routes and complexity of the mathematical approach has led us use a kind of black-box modelingsartificial neural networks. Reactor feed type plays an essential role on the product qualities. Feed type is a qualitative character. In this paper, a method is presented to introduce a range of petroleum fractions to the neural network. To introduce petroleum cuts with final boiling points of 865 °F maximum to the neural network, a real component substitute mixture is made from the original mixture. Such substitute mixture is fully defined, it has a chemical... 

Olefin industry came to a commercialization maturity, but still energy consumption, coke formation and thermal cracking optimization seem hot debates. The typical use of static mixers or fins inside the pipes itself leads to significant pressure drop, leading to higher power consumption and lower selectivity of olefins production. Herein we propose an innovative approach, i.e., accelerated sinusoidal heat transfer through mixing at viscous sublayer pipe-fluid interface. CFD simulation by SOLIDWORKS, ANSYS FLUENT computer-aided computations visualized hydrodynamic wave effects on heat transfer in corrugated tube taking bare tubes as reference. The length and outside diameter of tube were... 

In this paper, we consider the coherent radar detection of rapid fluctuating signals in the Gaussian noise. This problem has been previously solved by employing the GLR technique, but we use the ALR to improve the detection performance. So, after deriving an approximate ALR detector, we compare the new detector with the GLR and ' Square-law detectors and we show its superiority  

In this paper, sliding friction and wear behaviors of gray cast iron A35 and white cast iron manufactured by quenching from the same cast iron in water were studied and compared by employing pin-on-disk wear tests. Microstructure of the worn surfaces before and after the wear tests were investigated by optical microscope observations. These images show that flakes separated from the surface in gray cast iron due to delamination process, while in white cast iron, the separation of materials from its surface is in the form of powder. In addition, the gray cast iron had higher graphite volume fraction with Type-A graphite flake morphology. The results show that white cast iron has less rate of...