Reliability challenge for impedance network‐based DC‐DC boost converters

In this paper, reliability evaluation is proposed for some of the most famous impedance network‐based DC‐DC boost converters. Markov reliability approach is used to evaluate the reliability of the converters. Also, some other factors such as components' failure rates, reliability functions, and mean time to failures are introduced and evaluated. Detailed explanations for the evaluation methods of the mentioned factors are also provided in the context of the paper. In addition to the mathematical analysis, numerical calculations are also done through the simulation results of the converters. Simulations are done in PSCAD/EMTDC. Finally, a numerical and graphical reliability comparison is provided for the mentioned converters. The purpose of this paper is to give a comprehensive reliability evaluation and comparison for some of the most popular impedance network‐based DC‐DC converters. In addition, this paper gives a detailed reliability analysis that can be used in reliability assessment of all types of power electronic converters, so it can help the researchers to consider reliability calculations into their designing.     

Evaluation of ground convergence and squeezing potential in the TBM driven Ghomroud tunnel project

One of the new components of water conveyance system in central Iran is the Ghomroud water conveyance tunnel that is being excavated by a double shield TBM. The 36 km long tunnel mainly passes through the metamorphic weak rocks of Jurassic age. Key geotechnical design issues for the tunnel, which has up to 650 m of overburden, include the potential for high ground pressure due to high in situ stress. In order to prevent the shield jamming in these weak rocks, it was necessary to evaluate the amount of ground pressure on the outer surface of TBM shield in the vicinity of the tunnel face. The stress and strain condition in the vicinity of the tunnel face has a 3D nature and it is not realistic to assume a two-dimensional stress state at the tunnel face area. In the convergence-confinement method, it is possible to simulate the tunnel face effect with an internal fictitious pressure that is imposed on the tunnel perimeter. In this study, based on the convergence-confinement method, a new method was introduced to calculate the tunnel face effect on ground pressure distribution around the tunnel face region. Then by using this method, critical areas with potential for shield jamming was predicted along the Ghomroud water conveyance tunnel. The obtained results by this method are in good agreement with the current TBM jamming situations along the Ghomroud tunnel.     

Applications of linear inverse finite element method in prediction of the optimum blank in sheet metal forming

A linear inverse finite element method has been developed and investigated to predict the optimum blank. To reduce the computation time, the part is unfolded properly on the flat sheet and treated as a 2D problem. This approach is employed primarily to design the optimum blank shape from the desired final shape with the linear formulations. The procedure is based on the minimization of energy for the unfolded elements. Two solution methods, Direct and Newton–Raphson methods have been examined for the solution of nodal displacements in the equilibrium equations. The convergence show high sensitivity to the initial guess for the strain path when assumed to be linear at the first step. Two applied examples are implemented to show the efficiency of this method. In S rail example, the thickness distributions have been compared with experimental analysis after obtaining the optimum blank with Linear IFEM. In circular cup example, the results have been compared with conventional forward incremental method. New calculation of the external forces vector has been displayed. In this calculation, both blank holder force (BHF) vector and in-plane force vector have been shown. Finally, in this approach good agreement was found between the forward incremental and Linear IFEM results.     

Polarization dependence of the C 1s X-ray absorption spectra of individual multi-walled carbon nanotubes

The polarization dependence (linear dichroism) of the C 1s X-ray absorption spectrum of individual multi-walled carbon nanotubes (MWCNTs) is measured using scanning transmission X-ray microscopy. A very strong dichroic effect is found in the C 1s --> pi* transition, with almost complete disappearance of this transition when the electric-field (E)-vector is aligned parallel to high-quality (low-defect) MWCNTs and maximum intensity when the E-vector is orthogonal to the tube axis. In contrast, there is very little dichroism in the C 1s --> sigma* transitions. The origin of this polarization effect is explained. The magnitude of the polarization dependence is found to differ in MWCNTs synthesized by different methods (arc discharge versus chemical vapor deposition). This is ascribed to differences in densities of sp(2)-type defects. The potential for use of this signal to characterize defects in single-carbon-nanotube devices is discussed.     

Moisture sorption isotherms and isosteric heat for pistachio

The equilibrium moisture contents (EMC) of pistachio were determined using the standard static-gravimetric method at 15, 25, 35 and 40 °C for pistachio powder at 15, 35 °C for pistachio kernel and pistachio nut for water activity (a _w) ranging from 0.11 to 0.9. At a given water activity, the results show that the moisture content decreases with increasing temperature. The experimental sorption curves are then described by the BET, GAB, Henderson, Oswin, Smith and Halsey models. A nonlinear regression analysis method was used to evaluate the constants of the sorption equations. The Smith model was found to be suitable for describing the sorption curves. The isosteric heat of adsorption of water was determined as a function of moisture content from the equilibrium data at different temperatures using the Clasius–Clapeyron equation.     

Surface roughness and cutting forces modeling for optimization of machining condition in finish hard turning of AISI 52100 steel

An experimental investigation was conducted to analyze the effect of cutting parameters (cutting speed, feed rate and depth of cut) and workpiece hardness on surface roughness and cutting force components. The finish hard turning of AISI 52100 steel with coated Al₂O₃ + TiC mixed ceramic cutting tools was studied. The planning of experiment were based on Taguchi’s L₂₇ orthogonal array. The response table and analysis of variance (ANOVA) have allowed to check the validity of linear regression model and to determine the significant parameters affecting the surface roughness and cutting forces. The statistical analysis reveals that the feed rate, workpiece hardness and cutting speed have significant effects in reducing the surface roughness; whereas the depth of cut, workpiece hardness and feed rate are observed to have a statistically significant impact on the cutting force components than the cutting speed. Consequently, empirical models were developed to correlate the cutting parameters and workpiece hardness with surface roughness and cutting forces. The optimum machining conditions to produce the lowest surface roughness with minimal cutting force components under these experimental conditions were searched using desirability function approach for multiple response factors optimization. Finally, confirmation experiments were performed to verify the pertinence of the developed empirical models.     

Selective separation of contaminants from paper mill effluent using nanofiltration

Biologically treated newsprint mill effluent containing 57 mg L⁻¹ DOC and 1430 TDS was used in a screening study of nine commercial NF membranes for use as pretreatment for reverse osmosis in an end of pipe water recycling application. A salt-organic-separation (SOS) efficiency factor was developed to help rank the performance of the membranes. The SOS measures the ratio of the sum of the percentage rejection of organics and divalent cations over the percentage rejection of monvalents. It can be used to discriminate between NF membranes that are not too permeable to divalent cations or organics in which case the NF permeate will have a high chlorine demand due to the carryover of organics, or too retentive in which case all the material in the effluent will be retained and fouling problems are likely to occur. The optimum SOS efficiently for this study appeared to range from 3.5 to 5.6 for six membranes, DK, HPA-150, ESNA1-LF2, DL, TFC-SR2 and NF-270, which were categorised as membranes with an intermediate rejection. Out of these membranes ESNA1-LF2, TFC-SR2 and NF-270 were capable of operating up to 90% recovery with high permeabilities ranging from 17.7 to 22.3 L m⁻² h⁻¹ bar⁻¹.     

Estimation of mid‐distillates production rate in a low temperature Fischer–Tropsch process

BACKGROUND: The Fischer–Tropsch process is the most important path for converting natural gas to high quality liquid hydrocarbons. Low temperature Fischer–Tropsch synthesis in slurry bubble column reactors with cobalt‐based catalysts is used for mid‐distillates production. RESULTS: In this work the slurry bubble column reactor was simulated by applying the two‐bubble class mathematical model. In addition, the effect of operating parameters on synthesis gas conversion was studied. The distribution of products was also predicted from the simulation framework. CONCLUSIONS: The effect of synthesis gas inlet velocity on mid‐distillates production rate was studied in the present work. A maximum production rate for mid‐distillates of about 23 kg s^?1 was predicted from the simulation program. Copyright © 2011 Society of Chemical Industry     

An investigation on the correlation between rheology and morphology of nanocomposite foams based on low‐density polyethylene and ethylene vinyl acetate blends

This article presents the correlation between rheology and morphology of nanocomposite foams of low‐density polyethylene (LDPE), ethylene vinyl acetate (EVA), and their blends. LDPE/EVA nanocomposites were prepared via melt mixing and then foamed using batch foaming method. To assess the rheological behavior of polymer melts, frequency sweep and creep recovery tests were done. Morphology of the samples was also studied by scanning electron microscopy and X‐ray diffraction. The results showed that with increase in clay content, storage modulus, complex and zero shear viscosities will be increased, which affect the foam morphology. In addition, elasticity plays an important role in foaming process, in a way that samples with more elasticity percentage have the highest cell density and the lowest cell size. POLYM. COMPOS., 31:1808–1816, 2010. © 2010 Society of Plastics Engineers.