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.     

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.     

Chromium accumulation and distribution in crop plants

Crop plants accumulated chromium from nutrient solutions labelled with either ⁵¹CrIII or ⁵¹CrVI and retained approximately 98 % of the elements in the roots. Of the 9 crop species examined, cauliflower plants accumulated the most chromium in both shoots and roots and mung bean seedlings the least. Species differences of approximately 10-fold in the tops and 5-fold in the roots were recorded. The roots of each species supplied with ⁵¹CrIII contained more chromium than those supplied with ⁵¹CrVI but the reverse was found in the shoots. There was a greater proportion of soluble chromium in plants supplied with ⁵¹CrVI than in those supplied with ⁵¹CrIII, the major soluble compound being tentatively identified as trioxalato-CrIII. Little chromium was associated with cell organdies or soluble proteins.     

Evaluating the development of elastic anisotropy with plastic flow

It has been observed that many initially isotropic materials show the development of anisotropic elastic response after plastic flow. It is desirable to be able to model this change in the elastic properties as a function of the extent of plastic flow. This is particularly important when considering the traveling of waves in some glassy polymers that exhibit large differences in the wave moduli along the different directions resulting from unequal plastic flow in these directions. A thermodynamically based model of plasticity is developed and used to evaluate the elastic moduli associated with infinitesimal elastic deformations around the unloaded configuration. It is shown that for this model there are at least four independent material functions describing the elastic moduli of an initially isotropic material. These moduli are functions of the isotropic invariants of the right plastic Cauchy stretch tensor.     

Anisotropic loss of toughness with physical aging of work toughened polycarbonate

We have studied the response of mechanically toughened and physically aged polycarbonate primarily using Charpy impact and ultrasonic wave speed measurements. The toughening was conducted through plastic compression on as‐received PC. The Charpy impact tests showed anisotropic toughening, both in the absorbed energy and in the mode of fracture. The amount of toughening with plastic compression, even though anisotropic, is centered around the response of annealed and quenched samples, which represent the response of an unaged PC. There was an anisotropic drop in the toughness of some samples with aging. The time of this drop was uncorrelated in the different directions and disappeared for the highly toughened samples. This transition was bimodal and statistically distributed between either a fully ductile or a fully brittle failure. As the samples were prepared in a manner to remove induced residual stresses, this drop in toughening may be associated with an intrinsic anisotropic thermal aging of the deformed material. POLYM. ENG. SCI., 54:794–804, 2014. © 2013 Society of Plastics Engineers