Modelling of foam degradation in lost foam casting process

In this investigation a new model was developed to calculate gas pressure at the melt/foam interface (Gap) resulting from foam degradation during mould filling in the lost foam casting (LFC) process. Different aspects of the process, such as foam degradation, gas elimination, transient mass, heat transfer, and permeability of the refractory coating were incorporated into this model. A computational fluid dynamic (CFD) code was developed based on the numerical technique of the SOLution Algorithm-Volume of Fluid (SOLA-VOF) utilizing model, for the simulation and prediction of the fluid flow in the LFC process. In order to verify the computational results of the simulation, a thin plate of grey iron was poured into a transparent foam mould. The mould filling process was recorded using a 16 mm high-speed camera. Images were analysed frame by frame, in order to measuring foam depolymerization rate and the gap volume during mould filling. Comparison between the experimental method and the simulation results, for the LFC filling sequence, has shown a good agreement.     

Effect of foaming temperature on the mechanical properties of produced closed-cell A356Aluminum foams with melting method

In this study an attempt was carried out to determine the effect of production temperature on the mechanical properties and energy absorption behavior of closed-cell A356 alloy foams under uniaxial compression test. For this purpose, three different A356 alloy closed-cell foams were synthesized at three different casting temperatures, 650 °C, 675 °C and 700 °C by adding the same amounts of granulated calcium as thickening and TiH₂ as blowing agent. The samples were characterized by SEM to study the pore morphology at different foaming temperatures. Compression tests of the A356 foams were carried out to assess their mechanical properties and energy absorption behavior. The results indicated that increasing the foaming temperature from 650 °C to 675 °C and 700 °C reduces the relative density of closed cell A356 alloys by 18.3% and 38% respectively and consequently affects the compressive strength and energy absorption of cellular structures by changing them from equiaxed polyhedral closed cells to distorted cells. Also at 700 °C foaming temperature, growth of micro-pores and coalescence with other surrounding pores leads to several big voids.     

Multi-Objective Surface Water Resource Management Considering Conflict Resolution and Utility Function Optimization

In the present research, a multi-objective model is developed for surface water resource management in the river basin area which is connected to the lake. This model considers different components of sustainable water resource management including economic, social and environmental aspects, and simultaneously tries to resolve conflicts between different stakeholders by means of non-symmetric Nash bargaining, which is linked to the multi-objective optimization method. This study proposes a new methodology to improve Nash Conflict Resolution through finding the optimum degree of the utility function. The proposed model is examined in the Zarrineh River basin in Iran. The results show that the amount of available resources or volume of reservoirs play a significant role in determining the optimal degree of the utility function and efficiency of the proposed method in such a way that the higher amount of resources or the larger reservoirs will result in the higher optimal degree of the utility function. In the proposed multi-objective model, two different amounts of surface water inflow are considered. The first assumed amount is the long-term average flow rate and the second one is equal to 80% of the first mode, which is reduced based on the estimated impacts of climate changes. This multi-objective allocation model could supply 100 and 97.5% of the environmental demand of Lake Urmia in the first and second situations, respectively.     

Effect of Titanium Addition on As Cast Structure and Macrosegregation of High‐Carbon High‐Chromium Steel

In casting heavy ingots of high‐chromium high‐carbon cold work steels, macrosegregation develops in the center of the ingot, causing difficulties during subsequent hot working. Heat transfer and solidification of an industrial scale high‐carbon high‐chromium steel ingot was simulated and thereafter a laboratory scale representative ingot was designed to model the solidification of the industrial scale ingot. Titanium in the range of 0.3–1% was added to the high‐chromium high‐carbon (12%Cr–2%C) steel during melting process. Microstructures, macrosegregation and phase formations were studied using optical microscopy, scanning electron microscopy, energy dispersive X‐ray spectrometry, wave dispersive X‐ray spectrometry, optical emission spectroscopy, and X‐ray diffraction. Addition of 0.3% titanium was sufficient to diminish the macrosegregation; however it did not have a significant effect on the grain size. Addition of 0.7 and 1% titanium had a substantial effect on grain size in the longitudinal direction and refined the primary carbides structure. The formation of small TiC carbides that precipitated before solidification of liquid iron acted as nuclei for primary pro‐eutectic austenite grains.     

Simulation of surface roughness on the flow pattern in the casting process

In this investigation a mathematical model has been developed for simulation of the incompressible flow with free surface during mould filling. The simulation 3D melt flow with free surface is based on the SOLA-VOF technique. In the model the effects of variations parameters including heat and mass transfer as well as influences of backpressure, and friction have been considered. The solid and free boundary conditions have been modified and a new algorithm has been developed to calculate the effect of wall–slip ratio, during mold filling. In this algorithm, the effect of wall–slip ratio on the filling pattern has been modeled with an experimental function. In order to verify the computational results, a thin Al–7.5 Si% alloy plate has been poured into a sand mould with a transparent face to take into account the effect of surface roughness on flow pattern, the amount of erosion, and impact of the molten metal on the sand mould, utilizing photography. The comparison between the experimental and the simulation results of sequence filling shows a good consistency that confirms the accuracy of the model for predicting the erosion phenomenon in the moulding materials.     

Modelling of metal flow during hot forging with regard to microstructural aspects

A mathematical model has been proposed for evaluation of velocity and temperature fields in hot forging operations for axisymmetric parts. The model can be applied to determine forging load, strain rate, strain and temperature distributions. In addition, the effects of temperature and strain rate on metal flow have been considered through simultaneous modelling of dynamic phase transformation within the deforming metal. Hot forging experiments have been carried out under different working conditions and the results have been compared with the predictions. A good agreement between the simulated and experimental results was found.     

An enhanced widely linear CDMA receiver with OQPSK modulation

This paper studies an enhanced widely linear (WL) receiver for direct-sequence code-division multiple-access (DS-CDMA) systems that employ aperiodic spreading sequences with offset quadrature phase-shift keying (OQPSK) modulation. The modulation scheme generates improper complex multiple-access interference (MAI) and necessitates the use of WL receivers. Focus is on bandlimited pulse shapes and the inherent cyclostationarity (CS) of the uncoded received signal. The enhanced WL receiver replaces the conventional chip-matched filter with new filters that exploit the CS of the received signal through frequency shifting. The proposed WL receiver is shown to outperform the classical strictly linear (SL) receiver when the interfering users are (quasi-)synchronous with respect to the user of interest. High-powered interfering users, that may exist to support high data rates, increase the performance improvement delivered by the WL receiver. Moreover, it is shown that MAI can become proper, either identically or asymptotically, when users are asynchronous and equally powered. This is despite the fact that individual interfering signals are improper. Numerical results demonstrate that the WL receiver can outperform the SL receiver by 1-3 dB under the examined scenarios with current CDMA standards settings. In asynchronous or quasi-synchronous transmission modes, performance gain of the WL receiver degrades unless the number of high-powered active users remains small. An example for implementation of the WL receiver is proposed and compared with that of the SL receiver when minimum-shift keying modulation, a special case of OQPSK, is used. The implementation is based on a fractionally spaced equalizer whose taps are updated by an adaptive algorithm. It is shown that the proposed structure is capable of delivering the maximum signal-to-noise ratio predicted by theory.     

Design and fabrication of a novel vibrational system for ultrasonic assisted oblique turning process

We designed and fabricated suitable vibrational equipment for ultrasonic assisted oblique turning process to enable researchers to perform experimental tests with the operating conditions closest to common assumptions of cutting mechanics theories. Applying ultrasonic vibrations to the tool cutting edge along tangential direction and in the presence of inclination and tool cutting edge angles necessitates a novel design and fabrication of vibrational horn with special oblique geometry. In this vibrational horn, the natural frequency of longitudinal vibration mode is forced to be in a certain frequency range of the ultrasonic power supply. The novel tool-workpiece assembly was designed using modal analysis to provide the most conformity of cutting geometry and process parameters between theory and practice. Three-dimensional cutting forces were measured experimentally in vibrational oblique turning process carried out by the mentioned horn. The most suitable conditions to profit from ultrasonic vibrations in oblique turning process were determined, and these experimental results were in agreement with modal analysis results.