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Ritz method is widely used in variational theory to search for an approximate solution. This paper suggests a Ritz-like method for integral equations with an emphasis of pantograph delay equations. The unknown parameters involved in the trial solution can be determined by balancing the fundamental terms. [ABSTRACT FROM AUTHOR]

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The use of detailed chemical reaction mechanisms of aviation fuels is still very limited in analyzing the combustion process concerning complex multidimensional fluid dynamics issues. In this work, a reduced chemical kinetic mechanism containing 210 elemental reactions (including 92 reversible reactions and 26 irreversible reactions) and 50 species was introduced and studied in the kinetic simulation of the ignition and combustion of n-decane (n-C10H22) at various combustion regimes. Moreover, it was validated with the experimental results obtained from both premixed flame of a flat-flame burner and n-C10H22shock-tube ignition. The results show that the calculated ignition delay time of fuel n-C10H22in the shock-tube under typical conditions viz. a pressure of 12 or 50 bar and corresponding equivalence ratio at 1.0 or 2.0, as well as the calculated mole fractions of the main reactants and products of fuel n-C10H22in the premixed combustion process, agree very well with the experimental data. The combustion processes in the single flame tube of a tube annular combustor were simulated through coupling this reduced reaction mechanism of surrogate fuel n-C10H22and one step reaction mechanism of surrogate fuel C12H23into the computational fluid dynamics (CFD) software, and this combustion process was also experimentally studied. It is found that the reduced reaction mechanism exhibits clear advantages in simulating the combustion processes and certain species formation in the single flame tube over the one step reaction mechanism. In particular, the temperature radial distribution at the outlet of the single flame tube computed by using reduced reaction mechanism of surrogate fuel n-C10H22is found to be more reasonable and agreed better with the experimental data than that computed by one step reaction mechanism of surrogate fuel C12H23. [ABSTRACT FROM AUTHOR]

To improve predicting accuracy further, this paper modified original Pareto dominance relation among the candidate solutions, and proposed a new method named d-Pareto dominance prediction using nearest neighbor. Combined with the characteristics of multi-objective optimization, it described the framework of d-Pareto and the conclusion that a d-Pareto dominance prediction could obtain a lower average prediction error rate comparing with Pareto demonstrated dominance prediction. Besides, it also explored the interaction between d-Pareto dominance prediction and multi-objective evolutionary algorithms. Experiments on several classic MOPs were conducted and the simulation results show that prediction of d-Pareto dominance is feasible and effective. [ABSTRACT FROM AUTHOR]

This paper presents a numerical simulation of the fluid flow and heat transfer in the shell-side of a large-scale shell-and-tube heat exchanger with longitudinal flow through porous-medium and distributed-resistance model. Such characteristics as flow field distribution, shell-side pressure drop, heat transfer performance and overall performance factor of the shell-side were studied with change in L/D and Re. It was shown that when L/D decreased from 6.0 to 1.5 with the same Re, the fluid flow maldistribution became intense, pressure drop increased sharply, and that the overall performance factor η decreased sharply. Particularly, when L/D≤ 2.0, the problems became more and more serious. Through a detailed analysis of the pressure field distribution, it was discovered that >80% of the total pressure drop occurred in the region of the inlet and the outlet, where the fluid flow mainly cross the tube bundle. In order to solve the problems, the use of a novel structure of multi-parallel-channel inlet and outlet (MPC) in the shell-side was proposed. A comprehensive investigation showed that MPC is very effective not only in optimizing the fluid flow distribution of the shell-side and enhancing the global heat transfer performance of a heat exchanger, but also in decreasing shell-side pressure drop. [ABSTRACT FROM AUTHOR]

Abstract: Through amending the SENKIN code of CHEMKIN III chemical kinetics package, a computational model of gas explosion in a constant volume bomb was built, and the detailed reaction mechanism (GRI-Mech 3.0) was adopted. The mole fraction profiles of reactants, some selected free radicals and catastrophic gases in the process of gas explosion were analyzed by this model. Furthermore, through the sensitivity analysis of the reaction mechanism of gas explosion, the dominant reactions that affect gas explosion and the formation of catastrophic gases were found out. At the same time, the inhibition mechanisms of water on gas explosion and the formation of catastrophic gases were analyzed. The results show that the induced explosion time is prolonged, and the mole fractions of reactant species such as CH4, O2 and catastrophic gases such as CO, CO2 and NO are decreased as water is added to the mixed gas. With the water fraction in the mixed gas increasing, the sensitivities of the dominant reactions contributing to CH4, CO2 are decreased and the sensitivity coefficients of CH4, CO and NO mole fractions are also decreased. The inhibition of gas explosion with water addition can be ascribed to the significant decrease of H, O and OH in the process of gas explosion due to the water presence. [Copyright &y& Elsevier]

By coupling the KIVA-3V engine computational fluid dynamic(CFD) package with the CHEMKIN III and DETCHEM chemical kinetics packages, the effects of catalytic combustion on the combustion process and emissions of homogeneous charge compression ignition(HCCI) engine were simulated. Methane was used as fuel and the detailed surface and gas reaction mechanisms were adopted. The effects of catalytic combustion on the ignition timing, temperature field and HC, CO and NOx emissions of a HCCI engine whose piston surface was coated with catalyst (rhodium or platinum) were discussed. The results show that the ignition timing is advanced and the emissions of HCand CO are decreased, but the NOx emission is increased slightly by using catalyst coating on the piston surface. In the same conditions, compared with catalyst Pt, the ignition timing is more advanced, and the emissions of HC are lower, but the emissions of CO and NOx: are higher with catalyst Rh on the piston surface. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, an algorithm for sparse channel estimation, called least-absolutes (), and an algorithm for equalization, called linear least-absolutes (LLA), in non-Gaussian impulsive noise are proposed. The proposed approaches are based on the minimization of the absolute error function, rather than the squared error function. By replacing the standard modulus with the of complex numbers, the resulting optimization problem can be efficiently solved through linear programming. The selection of an appropriate regularization parameter is also addressed. Numerical results demonstrate that the proposed algorithms, compared with the classical methods, are more robust to impulsive noise and have a superior accuracy. [Copyright &y& Elsevier]

Thrust vectoring can provide fighter with advantages regarding performance, survivability and detectability. Two types of fluidic control Convergent-Divergent nozzle thrust vector technology, which are Shock Vectoring controlling and Throat Shift, are numerically simulated and their performances are analyzed. A nozzle with fixed geometry from nozzle inlet to throat, and fixed length of divergent flap is researched. The relative position of the secondary injecting flow is fixed, and the injecting direction is always vertical to the nozzle main flow. The nozzle flow fields are obtained via CFD numerical simulation. It can be seen from the results that, Throat Shift method is suitable for the nozzle expansion ratio less than 1.5, and Shock Vectoring controlling method is contrary to Throat Shift method, which is suitable for the nozzle expansion ratio greater than 1.5. The Throat Shift method can restrict the nozzle mass flow besides thrust vectoring. The main influence of the secondary mass flow is the ratio of secondary total pressure to main flow total pressure. [ABSTRACT FROM AUTHOR]