Finite Element Simulation of Laser Welding of 904L Super Austenitic Stainless Steel

Experiments on Laser butt welding of 904L super austenitic stainless steel was conducted using diffusion cooled 3.5 kW slab CO₂ laser welding system. The weld geometries such as bead width and depth of penetration were measured. The laser welding process has also been simulated using ANSYS a Finite Element Analysis tool. The effect of laser power, welding speed and focal point position on the bead geometry was investigated. The experimental plan was developed based on the Taguchi technique. The comparison of the results of the simulation indicates that Finite Element Method (FEM) can predict the responses adequately within the limits of welding parameters being used. It is suggested that FEM can be used as a tool for predicting the bead geometry at low values of heat input on laser welding.     

Conjugate heat transfer enhancement of laminar slot jets with various nanofluids on an array of protruding hot sources using MPM approach

Conjugate heat transfer in laminar slot jets impinging on multiple protruding hot sources using various nanofluids has been investigated numerically by employing (i) a mass-based modeling and an (ii) Eulerian-based multi-phase modeling (MPM). Various parameters such as streamline contours, isotherm profiles, local Nusselt number (Nu), average Nusselt number (Nuavg) are evaluated for different nanofluids (Ag–water, Al₂O₃–water, CuO–water and TiO₂–water), various range of Reynolds number (Re), particle volume fraction (?), diameter of the nanoparticle (d) and thermal conductivity ratio (kr). The steady, laminar, incompressible and two-dimensional flows are considered for the analysis. Finite-volume method with SIMPLE algorithm is used to solve continuity, momentum and energy equations along with boundary conditions. The highest heat transfer rate is achieved at ??=?0.05 for any protruding blocks and Reynolds number. Conjugate heat transfer rate of nanofluids increases with decreasing the diameter of nanoparticles. Here, Al₂O₃–water nanofluid is found to exhibit highest average Nusselt number compared to other nanofluids. The mixture based MPM approach with considering slip velocity yields higher heat transfer rate compared to the results obtained by single phase modeling approach.     

Effect of rotation of feed and seed rods on the quality of Na0.75CoO2 single crystal grown by traveling solvent floating zone method

High purity Na_0.75CoO₂ single crystals have been grown by floating zone method. We found the rotation of feed and seed rods play a crucial role in growing high quality single crystal. Systematic investigations suggest the occurrence of a phase separation at microscopic level, such as the separation into Na-rich and Na-poor domains during the growth, and formation of impurity phase(s) depending on growth conditions. Na_xCoO₂ (x = 0.30, 0.60) crystals have been prepared by sodium deintercalation from Na_0.75CoO₂. Powder X-ray and energy dispersive X-ray analyses have confirmed the phase purity and homogeneity of the samples. Magnetic susceptibility measurements of x = 0.60 and 0.75 crystals indicate a bulk phase transition at 22 K and an anomaly around 339 K and 334 K respectively which are attributed to structural transition. In addition some unique features related to Na_0.60CoO₂ were observed.     

Lung computed axial tomography image segmentation using possibilistic fuzzy C-means approach for computer aided diagnosis system

Soft computing is an associate rising field that plays a crucial half in the area of engineering and science. One of the most significant applications of soft computing is image segmentation. It focuses on an exploiting tolerance of imprecision and uncertainty. Segmentation supported soft computing remains a difficult task within the medical field. Medical images are habitually used in the segmentation process to extract the meaningful portions and to know and clarify the condition of the particular patient. In this article, we implement an efficient possibilistic fuzzy C-means (PFCM) approach to segment the lung portion in the computed tomography (CT) image and the result shows that it improves the segmentation accuracy upto 98.5012% and results are compared with existing segmenting approaches like fuzzy possibilistic C-means method, fuzzy bitplane method and so forth. Also, the PFCM approach increases the diagnostic accuracy of the computer aided diagnosis system using CT images. The radiologist may utilize this computer aided diagnosis system results as a second opinion of their diagnosed results.     

Beneficial impact of channel correlations on MIMO capacity

The potential beneficial impact of channel correlations on the capacity of MIMO systems is investigated. In contrast to most previous work, the present analysis is based on a comprehensive model of the channel correlation structure. It is therefore illustrated that fading cross-correlations may increase the ergodic capacity, sometimes even beyond the supposedly ideal case of independent channels. Starting from considerations on an analytical upper bound of the capacity, the study is then supported by simulation results of the actual ergodic capacity in arbitrary MIMO channels using a simple geometry-based stochastic model.     

Optimization for friction welding parameters with multiple performance characteristics

Friction Welding is a variation of pressure welding method. Though some experience has already been accumulated in the industrial application of friction welding, achieving the optimal processing parameters is still a difficult task. This work is putting a step forward to achieve the best possible design. This paper presents an investigation on the optimization and the effect of welding parameters on multiple performance characteristics (tensile strength and the metal loss) obtained by friction welded joints. A plan of experiments based on the Taguchi method was designed. The output variables were the tensile strength and metal loss of the weld. These output variables were determined according to the input variables, which are the Heating Pressure (HP), Heating Time (HT), Upsetting Pressure (UP) and Upsetting Time (UT). The main objectives of this study are maximization of tensile strength and minimization of metal loss. By statistical analysis, an optimal level of combination of processing parameters is achieved. To validate the optimization, experience were conducted at optimum parameters.     

Forming limit diagram for Indian interstitial free steels

In this work, the suitability of interstitial free steel sheets of thickness 0.6 and 1.6 mm for press forming operations were examined by obtaining the forming limit diagram. The microstructural aspects, tensile properties and formability parameters were studied. Forming limit diagrams (FLD) were evaluated for the above sheet metals of two different thicknesses and they were compared. Strain distribution profiles were obtained from the forming experiment. The fracture surfaces of the formed samples were observed using scanning electron microscope. Using the fractography, the fracture behaviour and formability were analyzed. The tensile properties and formability parameters were correlated with the FLD. It was found that the formability of both sheets is good and the sheet with 1.6 mm thickness was superior.     

MIMO Wireless Linear Precoding

This article provides a tutorial of linear precoding for a frequency- flat, single-user MIMO wireless system, examining both theoretical foundations and practical issues. The article first discusses principles for CSIT (channel-side information at the transmitter) acquisition and develops a dynamic CSIT model, which spans perfectly to statistical CSIT, taking into account channel temporal variation. It then presents the capacity benefits of CSIT and information theoretic arguments for exploiting the CSIT by linear precoding. A precoded system structure is then described, involving an encoder and a linear precoder. Criteria for designing the precoder are then discussed, followed by specific designs for different CSIT scenarios.     

A structured channel estimator for maximum likelihood sequencedetection in multipath fading channels

This paper describes a channel estimator using known prior information about the transmit and receive filters, it is shown that the composite channel lies in a certain subspace obtained from the impulse responses of these filters. A structured linear channel model is then developed that is linearly parameterized by an unknown vector. To illustrate the potential usefulness of such an approach, the estimated structured channel is used in a multisensor and oversampled maximum likelihood sequence estimation (MLSE) receiver. We also present expressions on the pairwise error probability for the MLSE receiver based on the structured channel model. Using these results, we investigate the phenomenon of error flooring