ABSs系统模糊控制器优化设计

已经开发了的ABSs系统改善了突然制动和特别是滑动路面状况时车辆控制。这样的控制目标是在保持车辆合适稳定性及可操纵性和缩短车辆刹车距离情况下在要求的方向增大车轮的牵引力。本文提出了ABSs系统优化的模糊控制器。从保持其车轮滑动值为目标函数获得车轮最大的牵引力和车轮最大的减速度。采用遗传算法优化模糊系统的全部组件。采用误差数整体优化方法收敛接近最优点。仿真结果表明快速收敛和对不同路况的控制器的最好性能。     

Orientation variance discrimination in amblyopia

Our previous results showed that while amblyopes can efficiently integrate visual signals, they are poor at segregating signals in noise. This could be either because integration detectors have broader bandwidths or because of a selective extrastriate segregation anomaly. One consequence of the former would be poorer variance discrimination. Using a two-alternative forced-choice paradigm, observers were asked to judge the orientational variance for arrays of 16 Gabors. All observers, be they normal or amblyopic, could perform the task similarly, although at high spatial frequencies, amblyopic eyes needed slightly more incremental variance than the normal eyes. We conclude that normals and amblyopes integrate signals in a similar way.     

Nanostructured Carbide-Free Bainite Formation in Low Carbon Steel

It is an important challenge to reduce the carbon content in nanostructured bainitic steels for commercialization purposes while still being able to gain the desired microstructural characteristics in nanoscale and not to deteriorate the strength-ductility combinations. That is the point at which an appropriate heat treatment procedure design would be an important parameter. This article aims to investigate how to obtain nanostructured bainite in steel with 0.26 wt% carbon content by applying multi-step austempering procedures. One-, two- and three-step austempering processes have been implemented, and proper heat treatment temperatures and approaches were selected based on dilatometry tests. Results indicated that it has become possible to achieve bainitic ferrites and austenite films with overall thicknesses of 164, 145 and 132 nm and 134, 105 and 90 nm at the end of one-, two- and three-step austempering heat treatments, respectively. Meanwhile, microstructural characteristics resulted in enhanced mechanical properties with ultimate tensile strength (UTS) of 1435, 1455 and 1428 MPa in combination with elongation levels of 15.4, 13.6 and 11.4% after implementing those heat treatments. Finally, it has been shown that applying the multi-step austempering heat treatments resulted in enhanced yield strength and impact toughness values due to the microstructural characteristics and proper heat treatment procedure design.     

喷丸强化对合金化奥贝球铁疲劳性能的影响

喷丸处理是改进金属工件疲劳性能最常规的表面处理方法。文中研究了喷丸处理对合金化奥贝球铁(AD)I疲劳性能的影响。等温淬火包括875℃保温90 min奥氏体化处理,然后在320℃、365℃和400℃进行等温处理。用直径0.4～0.6 mm的丸喷丸后的试样做旋转弯曲疲劳试验。对试样进行XRD和SEM分析,测定显微硬度和粗糙度,研究试样的疲劳性能。结果表明,在320℃、365℃和400℃等温处理的试样喷丸后疲劳强度分别增加了27.3%、33.3%和48.4%。     

Improved H2 production from the APR of polyols in a microreactor utilizing Pt supported on a CeO2Al2O3 structured catalyst

In this research, the activity and selectivity of a platinum-based catalyst for H₂ production through aqueous phase reforming (APR) in a fixed-bed reactor (FBR) as well as, a structured catalyst microreactor (MR) were investigated. In this venue, first, an in-house designed MR was fabricated and the catalytic material was deposited on the channel walls of this steel made reactor. After verification of the stability of the coated layer, the prepared reactor was employed to investigate the APR reaction. In this regard, APR of the ethylene glycol and glycerol over Pt/Al₂O₃ and Pt/CeO₂Al₂O₃ catalyst were conducted in an MR and FBR. Obtained results demonstrated that employing Pt/CeO₂Al₂O₃ as a highly active catalyst in an FBR, slightly reduced the H₂ selectivity for the APR reaction of the ethylene glycol. Moreover, this effect appeared even more pronounced in reforming of glycerol. On the other hand, utilization of an MR for the APR of glycerol improved the H₂ selectivity due to the more active Pt/CeO₂Al₂O₃ catalyst, for this process. Comparison of the results revealed that the highly active catalyst alongside a reactor alleviating mass transfer limitations were two complementary factors leading to better performance of such chemical systems. Moreover, this research emphasized that obtained values of the APR conversion and H₂ selectivity in an MR coated with the Pt/CeO₂Al₂O₃ catalyst was superior to those obtained from an FBR. Ultimately, the best results obtained for the aforementioned catalytic species indicated that the APR of glycerol in a structured catalyst MR led to 75.3% conversion of glycerol and 92.4% selectivity to hydrogen production both of which were considerably better than results determined in an FBR.     

Energy,exergy, economic and environmental (4E) analysis of using city gate station (CGS) heater waste for power and hydrogen production: A comparative study

This paper deals with energy, exergy, economic, and environmental (4E) analysis of two new combined systems for simultaneous power and hydrogen production. The combined systems are integrated from a city gate station (CGS) system, a Rankine cycle (RC), an absorption power cycle (APC), and a proton exchange membrane (PEM) electrolyzer. Since the pressure of natural gas (NG) in transmission pipeline is high, this pressure is reduced at CGS to a lower pressure. However, this NG has also ample potential to be recovered for multiple productions, too. In the proposed systems, the outlet energy of NG is used for power and hydrogen production by employing RC/APC and PEM electrolyzer. The power sub-cycles are driven by waste heat of CGS, while PEM electrolyzer is driven by this waste heat along with a portion of CGS-Turbine output power. A comprehensive thermodynamic modeling and parametric study of the proposed combined systems are conducted from the 4E analysis viewpoint. The results of two proposed systems are compared with each other, considering a fixed value of 1 MW for RC- and APC-Turbines power. Under the same external conditions and using steam as working fluid of RC, the thermal efficiency of the combined CGS/PEM-RC and -APC systems are obtained 32.9% and 33.6%, respectively. The overall exergy efficiency of the combined CGS/PEM-RC and -APC systems are also calculated by 47.9% and 48.9%, respectively. Moreover, the total sum unit cost of product (SUCP) and CO₂ emission penalty cost rate are obtained 36.9 $/GJ and 0.033 $/yr for the combined CGS/PEM-RC and 36 $/GJ and 0.211 $/yr for the combined CGS/PEM-APC systems, respectively. The results of exergy analysis also revealed that the vapor generator (in both systems) has the main contribution in the overall exergy destruction.     

A robust direct current control of DFIG wind turbine with low current THD based predictive approach

This paper presents a simple and robust direct current control based predictive approach for rotor side converter (RSC) of the doubly fed induction generator (DFIG), which operates at a constant switching frequency and has a fast dynamic response. First, sector of required rotor voltage vector is predicted in this strategy, and according to this predicted sector, two active vectors and two zero vectors are elected in each switching period. Derivatives of rotor current in the synchronous frame are determined for each predicted voltage vector in every period. These derivatives are used to compute the duration of the vectors in such a way that the current error at the end of the switching period gets minimized. The accuracy of the proposed control strategy under variation of rotor speed is evaluated in Matlab/Simulink environment for a 2 MW DFIG. Moreover, the impact of parameter variations on the system is examined for this suggested technique. Furthermore, the dynamic response and stator current total harmonic distortion (THD) of proposed strategy is compared with traditional vector control (VC), direct power control (DPC) and predictive direct power control (PDPC) methods. Finally, the performance of the proposed method is evaluated under disturbance voltage. The results demonstrate that suggested control technique has the lowest stator current THD and operates perfectly near the synchronous speed and under grid voltage dip. Copyright © 2015 John Wiley & Sons, Ltd.     

Methanol electrooxidation on synthesized PtRu nanocatalyst supported on acetylene black in half cell and in direct methanol fuel cell

We reported the direct reduction of H₂PtCl₆ and RuCl₃ solution containing acetylene black powder by Na₂S₂O₄ to make Pt–Ru (20–10 wt%) supported on acetylene black (Pt–Ru/AB) as a nanocatalyst for methanol electrooxidation in acidic media. The electrochemical activity of catalyst was studied by electrochemical impedance spectroscopy, linear sweep voltammetry, cyclic voltammetry and chronoamperometry. Structural aspects of the Pt–Ru (20–10 wt%)/AB were studied by transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The analysis of electrochemical results indicated lower charge transfer resistance, higher peak current for Pt–Ru (20–10 wt%)/AB compared to the commercial catalyst, Pt–Ru (20–10 wt%)/carbon Vulcan. XRD spectra verified a face centered cubic structure for the synthesized Pt–Ru/AB and its particle size was mostly 10 nm according to TEM and XRD images. In DMFC, Pt–Ru/AB had superior performance compared to the commercial catalyst in all current densities, which could be attributed to enhancement of the methanol oxidation kinetics, higher conductivity, and more uniform distribution of the ionomer in anode catalyst layer.     

Evaluation of Zefreh Dolomite (Central Iran) for Production of Magnesium via the Pidgeon Process

This study evaluates the production of magnesium metal from the Zefreh dolomite ore of Central Iran using the Pidgeon process. The investigation consisted of mineralogical and chemical characterization of the dolomite ore, calcining, chemical characterization, LOI (loss on ignition) determination, reduction tests on the calcined dolomite (dolime), using Iranian (Semnan) ferrosilicon and mineralogical, and chemical characterization of the reactants and products. Calcining of dolomite samples was carried out at approximately 1400°C in order to remove CO₂, moisture, and other easily volatilized impurities. The dolime was then milled, along with ferrosilicon, thoroughly mixed, and briquetted. The briquettes were heated at 1125°C--1150°C and 500 Pa in a tube reactor for 10--12 hours to extract the magnesium. The ferrosilicon to dolime ratio was determined based on the chemical analyses of the two reactants, using as a guide, and Mintek's Pyrosim software package. Magnesium extraction varied with ferrosilicon addition and with the dolime used, and reach about 80% under optimal conditions. The levels of major impurities encountered in the magnesium crown were similar to those in the crude metal production.     

On the particle–particle contact effects on the hole cleaning process via a CFD–DEM model

ABSTRACT

The accurate and precise computational models in order to predict the hole cleaning process is one of the helpful assets in drilling industries. Besides the bulk properties such as the flow velocity, particles average size, cleaning fluid properties, etc., that will affect the cleaning process, there is an unanswered question about the microscopic properties of the particles, particularly those which determines the contact characteristics: Do those play a major role or not? The rudimentary answer is not. The first purpose of the present work is to answer this question via a developed computational fluid dynamics coupled with discrete element method (CFD–DEM) in which the six unknown rolling and sliding friction coefficients of particle–particle contact, particle–wall contact, and particle–drill contact are considered as the main microscopic properties of the contacts. The second purpose is to search for optimum values of these coefficients in order to calibrate the CFD–DEM model with the experimental data for a near horizontal well cleaning available in the literature. The verification of the calibrated CFD–DEM model is checked by simulation of the hole cleaning process for different inclination angles of the deviated well. The results indicate the pivotal role of the microscopic properties of the particles on the characteristics of the particle transport mechanism.