Effect of heat generation and absorption on mixed convection flows in a sinusoidal heated lid-driven square cavity filled with a porous medium is investigated numerically. Both the vertical walls of the enclosure are insulated while the bottom wall is uniformly heated or cooled. The top wall is moving at a constant speed and is heated sinusoidally. The governing equations and boundary conditions are non-dimensionalized and solved numerically by using finite volume method approach along with SIMPLE algorithm together with non-uniform grid system. The effect of Darcy and heat generation parameters are investigated in terms of the flow, heat transfer, and Nusselt number. The results for stream function and isotherm are plotted and it is found that there have significant influence with the presence of heat generation and porous medium.
The specific enthalpy of fracture due to ductile crack propagation in commercial polycarbonate sheet is calculated as * =A1c/R1c, whereA1c is the critical energy release rate associated with the onset of unstable crack propagation andR1c is the corresponding amount of damage (yielded material) formed per unit crack extension.A1c andR1c are determined from fatigue crack propagation experiments conducted at different maximum loads, load ratios and frequencies. The value of * obtained from all experiments is found to be 9.8±1.4 cal g–1 (1cal = 4.184 J) which indicates that * is a material constant. This finding substantiates predictions of the crack layer theory. 相似文献
In this paper, the Rama distribution (RD) is considered, and a new model called extended Rama distribution (ERD) is suggested. The new model involves the sum of two independent Rama distributed random variables. The probability density function (pdf) and cumulative distribution function (cdf) are obtained and analyzed. It is found that the new model is skewed to the right. Several mathematical and statistical properties are derived and proved. The properties studied include moments, coefficient of variation, coefficient of skewness, coefficient of kurtosis and moment generating function. Some simulations are undertaken to illustrate the behavior of these properties. In addition, the reliability analysis of the distribution is investigated through the hazard rate function, reversed hazard rate function and odds function. The parameter of the distribution is estimated based on the maximum likelihood method. The distributions of order statistics for ERD are also presented. The performance of the suggested model is compared with several other lifetime distributions based on some goodness of fit tests on a real dataset. It turns out that the suggested model is more flexible than its competitors considered in this study, for modeling real lifetime data. 相似文献
A novel wide range electrostatic microelectromechanical system floating Fabry Perot optical tunable filter (MEMS f-FPOTF)
is modelled and analyzed in terms of its electro-mechanic behaviour. The composite beam approach has been used to model the
floating Fabry Perot cavity. The floating dual membrane FPOTF consists of multi layer Si/SiO2/Si thin films with an optical cavity in the middle structure. The filter tuning range has been improved by utilizing bonded
silicon on insulator wafers that permits the floating cavity to be deflected both ways; up and down. Electro-mechanic analysis
shows a 7% (STRUCTURE1) and 5% (STRUCTURE2) difference between analytical and finite element modelling in which the 7% difference
in light incident angle contributes to a 0.5 nm shift while the 5% difference in length of cavity indicates a 4 nm shift in
MEMS f-FPOTF operating wavelength. This analysis validates the analytical modelling of this device as a wavelength selector
in coarse wavelength division multiplexing. 相似文献
The substitution of the oxyanion Q114 with Met and Leu was carried out to investigate the role of Q114 in imparting enantioselectivity on T1 lipase. The mutation improved enantioselectivity in Q114M over the wild-type, while enantioselectivity in Q114L was reduced. The enantioselectivity of the thermophilic lipases, T1, Q114L and Q114M correlated better with log p as compared to the dielectric constant and dipole moment of the solvents. Enzyme activity was good in solvents with log p < 3.5, with the exception of hexane which deviated substantially. Isooctane was found to be the best solvent for the esterification of (R,S)-ibuprofen with oleyl alcohol for lipases Q114M and Q114L, to afford E values of 53.7 and 12.2, respectively. Selectivity of T1 was highest in tetradecane with E value 49.2. Solvents with low log p reduced overall lipase activity and dimethyl sulfoxide (DMSO) completely inhibited the lipases. Ester conversions, however, were still low. Molecular sieves employed as desiccant were found to adversely affect catalysis in the lipase variants, particularly in Q114M. The higher desiccant loading also increased viscosity in the reaction and further reduced the efficiency of the lipase-catalyzed esterifications. 相似文献
This paper presents the engine performance and optimum injection timing for 4-cylinder direct injection hydrogen fueled engine. The 4-cylinder direct injection hydrogen engine model was developed utilizing the GT-Power commercial software. This model employed one dimensional gas dynamics to represent the flow and heat transfer in the components of engine model. Sequential pulse injectors are adopted to inject hydrogen gas fuel within the compression stroke. Injection timing was varied from 110° before top dead center (BTDC) until top dead center (TDC) timing. Engine speed was varied from 2000 rpm to 6000 rpm, while the equivalence ratio was varied from 0.2 to 1.0. The validation was performed with the existing previous experimental results. The negative effects of the interaction between ignition timing and injection duration was highlighted and clarified. The results showed that optimum injection timing and engine performance are related strongly to the air fuel ratio and engine speed. The acquired results show that the air fuel ratio and engine speed are strongly influence on the optimum injection timing and engine performance. It can be seen that the indicated efficiency increases with increases of AFR while decreases of engine speed. The power and torque increases with the decreases of AFR and engine speed. The indicated specific fuel consumption (ISFC) decreases with increases of AFR from rich conditions to lean while decreases of engine speed. The injection timing of 60° BTDC was the overall optimum injection timing with a compromise. 相似文献
The ever-increasing amount of waste from electrical and electronic equipment (WEEE) has become a common problem due to the significant environmental and health impacts associated with inappropriate End-of-Life (EoL) management. The current ad hoc applications of WEEE recycling are often based on limited knowledge and cannot cope with the complex range of materials and products in such waste. A knowledge-based approach has been utilised to investigate the realisation of a recycling process planner which aims to determine the most suitable EoL options for WEEE. A number of case studies have been used to show that a 20-30% improvement on economical and environmental performance could be achieved through adoption of such a systematic approach to recycling process planning. 相似文献