Local RBF-DQ method for two-dimensional transient heat conduction problems

The meshless local radial basis function-based differential quadrature (RBF-DQ) method is applied on two-dimensional heat conduction for different irregular geometries. This method is the combination of differential quadrature approximation of derivatives and function approximation of radial basis function. Four different geometries with regular and irregular boundaries are considered, and numerical results are compared with those gained by finite element (FE) solution achieved by COMSOL commercial code. Outcomes prove that current technique is in very good agreement with FEM and this fact that RBF-DQ method is an accurate and flexible method in solution of heat conduction problems.     

Design optimization of shell and tube heat exchangers using global sensitivity analysis and harmony search algorithm

This study explores the use of global sensitivity analysis (GSA) and harmony search algorithm (HSA) for design optimization of shell and tube heat exchangers (STHXs) from the economic viewpoint. To reduce the size of the optimization problem, non-influential geometrical parameters which have the least effect on total cost of STHXs are identified using GSA. The HSA which is a meta-heuristic based algorithm is then applied to optimize the influential geometrical parameters. To demonstrate the effectiveness and accuracy of the proposed algorithm, an illustrative example is studied. Comparing the HSA results with those obtained using genetic algorithm (GA) reveals that the HSA can converge to optimum solution with higher accuracy.     

Emulsified jet fuel flame characterization with image processing

This work describes a RGB digital image processing approach of emulsified jet fuel flame, which allows the characterization of the combustion phenomenon in the case of new fuels through color chemiluminiscence measurements. By applying RGB techniques, the image processing of the flame reveals useful parameters in an effective and cost-efficient technique for the determination of relevant chemical species, such as CH* and C₂*, equivalence ratio, and temperature estimation.Second generation emulsified aviation fuels containing water-jet fuel have been a challenge for simultaneous thrust augmentation and pollution diminution, with subsequent cost reduction and fossil fuel dependence. Testing new fuels would normally require expensive equipment and reliable investigation techniques, while image processing proved to be a reliable method for the estimation of combustion chemical species and temperature in the case of classic fuels.For the combustion behavior of emulsified jet fuel, a co-annular spray burner was used, allowing the complex investigation with UV-VIS spectrometer and flame photography. RGB image processing techniques showed good agreement with more complicated diagnosis tools, such as spectrometers.     

Parameter retrieval of chiral metamaterials based on the causality principle

The parameter retrieval method based on the causality principle and Kramers‐Kronig relations, which has been proposed for extracting effective parameters of metamaterials (MTMs) is extended to extract effective parameters of chiral metamaterials (CMMs) as well. Using Kramers‐Kroning relations, the branch selecting problem which is the challenge of effective media parameters retrieval methods could be simply removed. To demonstrate the validity of the method, first, the constitutive parameters of a homogeneous chiral media are retrieved in the excellent agreement with the supposed parameters. Second validation is achieved by extracting the effective parameters of two well‐known CMM structures whose effective parameters have been reported in the literature. The results are in excellent agreement with the reports of the previous works. Finally, a new type of CMMs called windmill structure is suggested, and its effective parameters are then extracted using the proposed method. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Crosstalk analysis of multi‐microstrip coupled lines using transmission line modeling

This article presents a new analytical method to predict crosstalk of a homogeneous terminated two microstrip coupled lines over a ground plane using transmission line theory. The derived formula is frequency and location dependent, which can be used to quickly estimate the crosstalk of a coupled line. Also, the effect of the geometrical parameters of the lines and load are included in the derived formula. Presented method can be used for the other types of coupled lines including lossy or lossless lines. To verify the accuracy of the introduced method, a few microstrip coupled line structures with different geometrical parameters are considered numerically and experimentally. The results of crosstalk based on the proposed analytical methods, simulation study using high frequency structure simulator and those obtained by measurements are reported and compared with each other. It is shown that our proposed method accurately estimates the amount of crosstalk for a two microstrip coupled lines.     

Unconfined compressive strength of loose sandy soils grouted with zeolite and cement

Cement production requires a lot of energy and is also one of the most important sources of carbon dioxide emissions. Consequently, the replacement of part of the cement with a more environmentally friendly material, such as zeolite, is of great importance. The present research involves the conducting of a series of laboratory tests on loose sand specimens ($D_r\approx 30\%$) grouted with cementitious materials (cement and zeolite) to investigate the effect of different parameters, such as the size of the sand particles, the ratio of water to cementitious materials (W/CM) and the replacement of a certain percentage of the cement in the grout with zeolite (Z), on the unconfined compressive strength (UCS) of the grouted sand specimens. The results indicate that for all the grout W/CM and sand grain sizes, when Z is increased from zero zeolite (Z₀), the UCS initially increases. Then, after reaching an optimal amount (Z₃₀), it decreases. Moreover, increasing both the size of the sand particles and the W/CM of the grout is seen to reduce the UCS of the grouted specimens. The UCS of the grouted sand specimens increases with the equilibrium of SiO₂ and Al₂O₃ with CaO elements in the grouting suspension. Finally, equations with a high performance are proposed to predict the UCS of sands grouted with zeolite-cement using a multiple regression model (MRM) and a group method of data handling (GMDH)-type neural network.     

Monitoring simple linear profiles in the presence of generalized autoregressive conditional heteroscedasticity

In this paper, monitoring of simple linear profiles is investigated in the presence of nonequality of variances or heteroscedasticity, ie, generalized autoregressive conditional heteroscedasticity. In this condition, using of the common methods regardless of the heteroscedasticity leads to the fault interpretations. We consider a simple linear profile and assume that there is a generalized autoregressive conditional heteroscedasticity (GARCH) (1,1) model within the profiles. Here, we particularly focus on Phase II monitoring of simple linear regression. We studied the generalized autoregressive conditional heteroscedasticity effect, briefly GARCH effect, on the average run length criterion. As the remedial measures, the weighted least squares method to estimate the regression parameters and the heteroscedasticity‐consistent approaches to estimate the covariance matrix of regression parameters, are used to extract the GARCH effect. Two control chart methods namely T² and exponentially weighted moving average 3 are discussed to monitor the simple linear profiles. Their performances are evaluated by using the average run length criterion. Finally, a real case from an industry field is studied.     

Crosstalk analysis of uniform and nonuniform lossy microstrip‐coupled transmission lines

In this article, an analytical method is presented to precisely estimate the crosstalk of uniform and nonuniform microstrip‐coupled transmission lines (TLs) in frequency domain using modified transmission matrix. The obtained expression is quantitatively related in terms of the geometrical parameters of the coupled lines. A straightforward procedure is presented to obtain a closed form formula to accurately determine the crosstalk of a microstrip‐coupled line. For a nonuniform structure, the TL is divided into a few series of uniform sections with a specific modified transmission matrix. The total modified transmission matrix is determined by multiplying the modified transmission matrix of different sections and then the crosstalk can be calculated using the total modified transmission matrix. Several structures are considered to confirm the validity of the presented method. It is shown that the obtained results are in a good agreement with those obtained by simulation and measurement.