Experimental and finite element analysis of EDM process and investigation of material removal rate by response surface methodology

In this study, thermal modeling and finite element simulation of electrical discharge machining (EDM) has been done, taking into account several important aspects such as temperature-dependent material properties, shape and size of the heated zone (Gaussian heat distribution), energy distribution factor, plasma flushing efficiency, and phase change to predict thermal behavior and material removal mechanism in EDM process. Temperature distribution on the cathode has been calculated using ANSYS finite element code, and the effect of EDM parameters on heat distribution along the radius and depth of the workpiece has been obtained. Temperature profiles have been used to calculate theoretical material removal rate (MRR) from the cathode. Theoretically calculated MRRs are compared with the experimental results, making it possible to precisely determine the portion of energy that enters the cathode for AISI H13 tool steel. Also in this paper, the effect of EDM parameters on MRR has been investigated by using the technique of design of experiments and response surface methodology. Finally, a quadratic polynomial regression model has been proposed for MRR, and the accuracy of this model has been checked by means of analysis of residuals.     

Plasma surface modification and characterization of collagen‐based artificial cornea for enhanced epithelialization

Argon plasma treatment enhanced the attachment of epithelial cells to a collagen‐based artificial cornea crosslinked using glutaraldehyde (GA) and glutaraldehyde‐polyethylene oxide dialdehyde (GA‐PEODA) systems. The epithelialization of untreated and treated surfaces was evaluated by the seeding and growth of human corneal epithelial cells. Characterization of polymer surface properties such as surface hydrophilicity and roughness was also made by contact angle measurement and atomic force microscopy, respectively. Contact angle analysis revealed that the surface hydrophilicity significantly increased after the treatment. In addition, AFM characterization showed an increase in surface roughness through argon plasma treatment. Based on the biological and surface analysis, argon plasma treatment displays promising potential for biocompatibility enhancement of collagen‐based artificial corneas. It was also found that the cell attachment to artificial cornea surfaces was influenced by the combined effects of surface chemistry (i.e., surface energy), polymer surface morphology (i.e., surface roughness), and polar interactions between functional groups at the polymer surface and cell membrane proteins. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Mechanical and Morphological Studies of Poly(propylene)‐Filled Eggshell Composites

Poly(propylene) (PP) composites were prepared by using eggshell (ES) as filler and their mechanical properties were compared with those using talc (TA) and calcium carbonate (CC) of different grain sizes (X₅₀). A decrease in impact strength and deformation at break with increase in filler content was observed. The PP composite with ES (X₅₀ = 8.4 µm) was stiffer than those with CC (X₅₀ = 0.7 µm). The hybrid composite PP‐ES‐TA showed a similar stiffness as the PP‐TA composites due to the similar morphology of TA (X₅₀ = 0.5 µm) and ES, when TA was replaced up to 75 wt.‐% by ES. SEM study revealed evidence of improved interfacial bonding between PP and ES in theirs composites.

     

Performance evaluation of modified rotating-jet electrospinning method by investigating the effect of collector size on the nanofibers alignment

Modified rotating-jet electrospinning method (MRJM) is a new electrospinning technique with a novel setup including two metallic concentric hollow cylinders for generating highly aligned fibers. In this report, an experimental study was carried out to evaluate the effectiveness of MRJM for generating highly aligned nanofibers. For this purpose, the effect of voltage in the range of 10–22 kV, inner collector diameter in the range of 20–50 cm, and outer collector diameter in the range of 30–60 cm, on alignment degrees of electrospun fibers were explored and the results for each set of parameters were compared with those obtained for rotating-jet electrospinning method (RJM). The obtained results indicated that the alignment degrees of electrospun fibers in MRJM were significantly higher than those of RJM. The maximum achievable alignment degree in MRJM was around 82 % that was higher than the corresponding maximum value (40 %) of RJM. Although the effect of applied voltage on the degree of alignment in MRJM was observed to be negligible, it was experimentally proved that by manipulating the outer cylinder diameter, the degree of alignment can be increased up to 20 %. To achieve a conceptual understanding of the reason for significant influence of the outer cylinder on the elecrospinning performance, a formula was derived according to the Gauss’s law in the last part of this paper that relates the electric field strength inside the region between the inner cylinder and the spinneret to the radii of inner and outer cylinders.     

Investigation of sediment transport pattern and beach morphology in the vicinity of submerged groyne (case study: Dahane Sar Sefidrood)

Marine structures, such as Groynes, Sea walls and Detached Breakwaters, are constructed in coast of area to improve coast stability against bed erosions due to changing wave and current pattern. Marine mechanisms and interaction with the hydraulic structures need to be intensively studied. Groynes are one of the most prominent structures that are used in shore protection and littoral sediment. The main hydraulic function of the groyne is to control the long shore current and littoral sediment transport. This structure can be submerged and provide the necessary beach protection without negative aesthetic impact. However, for submerged structures adopted for beach protection, the shoreline response to these structures is not well understood. The objective of this study is to predict sediment transport in the vicinity of submerged groyne and comparison with non-submerged groyne focusing on a part of the coast at Dahane Sar Sefidrood, Guilan Province, Iran, where serious coast erosion has been occurred. The simulations were designed using a one-line model which can be used as a first approximation of shoreline prediction in the vicinity of groyne. The results of the proposed model are compared with experimental data to determine the shape of the coast. The results of predicted beach deformation show that when submerged groyne construct in the beach, sediment accumulation will be slightly less than the non-submerged groyne; because transfer coefficient for the submerged groyne is more than non-submerged groyne. This result will cause more sediment passing on submerged groyne. Finally, the result of the present study show that using submerged groyne is an efficient way to control the sediment and beach erosion without causing severe environmental effect on the coast.     

Untertagevergasung tiefliegender Steinkohle

Bisherige Entwicklungen zur Untertagevergasung von Kohle. Neuere Überlegungen zur Untertagevergasung in Anlehnung an die Methoden bei der Gewinnung von Erdöl und Erdgas. Erörterung über die Verfahren des Bohrlochbergbaus im Durchdringungsverfahren, Kanalverfahren und Blockumströmungsverfahren. Beurteilung der Möglichkeiten der Untertagevergasung bei tiefliegenden Steinkohlelagerstätten. Bericht über die Aktivitäten einer Arbeitsgruppe des Instituts für Eisenhüttenkunde der Technischen Hochschule Aachen mit Angaben über Versuche im Autoklaven zur Simulation der Untertagevergasung und zur Ermittlung grundlegender Stoffdaten. Beurteilung der Zukunftsaussichten der Untertagevergasung.     

A novel algorithm for frequency dependent modeling of ferrite ring and its optimum design to study VFTO behaviors within GIS

One of the fundamental issues in gas insulated substations (GIS) which has destructive effects on GIS equipment is the very fast transient over-voltages (VFTOs). This paper models a 400/230 kV substation in order to study the effects of VFTO extensively implemented on EMTP-RV. In addition, the application of ferrite rings for suppressing VFTOs is assessed thoroughly. The main advantage of this paper is its new proposed algorithm according to the ferrite ring frequency dependent modeling that is validated with experimental results. This paper examines the effects of three compositions of the ferrite ring on VFTO suppression. Moreover, it estimates the dimension of the ferrite ring based on the SF6 gas insulation withstand and the maximum effect of ferrite rings on VFTO suppression constraint with the COMSOL multiphysics software. Furthermore, it gains VFTO attenuated percentages due to the installation of the ferrite ring in different GIS nodes. Finally, it analyzes the offered VFTO amendment technique in various GIS switching scenarios.     

基于进化算法的多目标闭环物流网络设计

为了帮助生产企业建立科学合理的闭环物流网络系统,提高废旧产品材料的再循环利用率,提出了一个多周期、多产品、多阶段的闭环物流网络选址与运输模型。该模型中,不仅考虑建造混合分销回收中心,还提出了2个优化目标:经济成本最小和时间成本最小。针对该多目标优化问题,本文采用了一种基于优先值编码方法的进化算法对模型求解,最终得到该问题的帕累托(Pareto)前沿。通过与约束法的计算结果相比较,求得误差均值小于5%,说明该进化算法对Pareto前沿的拟合程度较好,计算结果是正确有效的。     

Prediction of Gas Flow Through Short and Long 2-D Micro- and Nanochannels Using a Generalized Slip Model

This article reports the outcome of our recent effort in prediction of gas slip flow through micro- and nanochannels. Slip nitrogen flow through short (length to height ratio of 20) and long (length to height ratio of 2,500) microchannels is analyzed and discussed using the spectral element method and the generalize slip model boundary condition of Karniadakis and Beskok. The well-known curvature in pressure distribution, due to the compressible behavior of the gas flow, is observed. Comparison of numerical results with the experimental and direct simulation Monte Carlo (DSMC) data as well as previous reported numerical results showed that the generalized slip model is able to produce reliable results for both short and long microchannels.