probability density function

In this paper sensitivity analysis of a wideband backward-wave directional coupler due to fabrication imperfections is done using Monte Carlo method. For using this method, a random stochastic process with Gaussian distribution by 0 average and 0.1 standard deviation is added to the different geometrical parameters of the coupler and the frequency response of the coupler is estimated. The applied process must be done several times for converging Monte Carlo method. Therefore, a large number of simulations is reqired for the coupler. This may take a long time if one uses High Frequency Structure Simulator (HFSS) as the simulation software. To decrease the required time of analysis, neural network model of the coupler incnjuction with Mone Carlo is used. Results showed that the bandwidth of the coupler, minimum return loss in passband and minimum isolation in passband won’t be change considerably using the sepecified value of random process. The obtained results for a prototype of a backward wave coupler is presented, which confirm the results of the sensitivity analysis.

The present study attempts to improve heat transfer efficiency of a domestic gas burner by enhancing heat transfer from flue gases. Heat transfer can be augmented using the obstacles that are inserted into the flow field near the heated wall of the domestic gas burner. First, to achive the maximum efficiency, the insert geometry is optimized by the multi-objective genetic algorithm so that heat transfer is maximized while minimizing the skin frication. Then, the heating unit is modeled as a three dimensional physical domain. The conservation equations of mass, momentum, energy and species are discretized over the meshing system of control volumes in the domain. The experimental set-up is equally established to measure and validate the numerical results. The effect of the inserts on heat transfer enhancement is studied both numerically and experimentally. The results show that the optimal insert is a triangle with the scaled area of 12.4 mm2. Also, the results indicate that the optimal inserts led to the improvement of heat transfer efficiency by 2.7% compared with the case of similar environment with no insert.