Thermal Finite Element Analysis and Optimization of Carbon Steel Stud Arc Weld

This work investigates the temperature distribution during the stud arc welding process by building a thermal finite element (FE) model with the aid of Comsol- program. Also, the aim of this study was to optimize the ultimate applied torque of the welded stud and the total input heat during welding process by individual and composite desirability. A stud of carbon steel- B7 is welded to a plate of carbon steel- grade- C. The welding machine parameters are; current, welding time and plunge. Three levels for each parameter, mentioned above, are used to optimize the resistance torque and the total heat flux using the design of experiments according to Taguchi method. The finite element model is built depending on the input heat source, convection and radiation heat transfer during stud welding process. The tests include the torsional test and actual heat transfer depending on the record of temperatures at different locations. The suggested FE model gave a good agreement with the experimental temperature record with approximately errors of 5%. The results indicate that the torsional resistance increase with increasing of the weld time at a small welding current of I= 400 A. While, at higher welding current, I= 800 A, the torsional resistance decrease with increasing of the plunge welding value. The maximum temperature value lies at the centre of the FE welded model and reduced gradually away from it with a symmetrical distribution. A sufficient welding heat input can make the torsional resistance of the weld line more than those of stud. Due to the higher temperature gradient during the welding process, the microstructure of the welded joint exhibits three regions; nugget zone (NZ), thermo-mechanical affected zone (TMAZ) and the heat affected zone (HAZ). The first region consists of Martensite and ferrite phase with a higher plastic deformation, in which, the peak value of temperature is obtained from the finite element method. A coarse grain size with higher dislocations is found in the second stage. While, the HAZ gave a fine grain size without deformation due to, hence, only thermal cycle is occurred in this region.In this work an investigation to the temperature distribution during the stud arc welding process by building a thermal finite element (FE) model with the aid of Comsol- program was conducted. Also, an optimization to the ultimate applied torque of the welded stud and the total input heat during welding process by individual and composite desirability was intended.  A stud of carbon steel-B7 is welded to a plate of carbon steel-grade-C. The welding machine parameters are; current, welding time and plunge. Three levels for each parameter, mentioned above, are used to optimize the resistance torque and the total heat flux using the design of experiments according to Taguchi method. The finite element model is built upon the input heat source, convection and radiation heat transfer during stud welding process. The tests include the torsional test and actual heat transfer depending on the record of temperatures at different locations. The suggested FE model gave good agreement with the experimental temperature record with an approximate error of 5%. The results indicated that the torsional resistance increases with the increasing of weld time at small welding current of 400 A. At higher welding current (I = 800 A) the torsional resistance decreases with the increasing of the plunge welding value. The maximum temperature region lies at the center of the FE welded model and reduced gradually away from it with a symmetrical distribution. A sufficient welding heat input can make the torsional resistance of the weld line more than those of the stud. Due to the higher temperature gradient during the welding process, the microstructure of the welded joint exhibits three regions; nugget zone (NZ), thermo-mechanical affected zone (TMAZ) and the heat affected zone (HAZ). The first region consists of Martensite and ferrite phase with a higher plastic deformation, in which, the peak value of temperature was observed numerically. A coarse grain size with higher dislocations was found in the second stage. While, th

Application of optimization algorithms in the design of a superconducting A.C. generator rotor

The superconducting a.c. generator is expected to be the optimum choice among a.c. generation systems in future because of its reduced size, high efficiency, high terminal voltage and its contribution to the stability of the power system. Such machines also exhibit unique design problems which remain unsolved. The optimal selection of the basic design parameters is a current problem of interest. This thesis is intended as a contribution in this direction, and a general design strategy has been developed for the superconducting a.c. generator. Elements of the design process include magnetic field analysis, losses, and mechanical performance all which of are discussed in the thesis. An analytical model has been developed to help determine the distribution of magnetic flux density inside the superconducting machine. This model takes into account the number, and the geometric structure, of the winding slots and allows the rotor of the superconducting machine to be designed with optimum magnetic field distribution. A general design strategy has been developed for the superconducting a.c. generator rotor for predicting the optimum design. The design optimization process incorporates "direct search" and random-shrinkage methods. Two direct search methods of minimization have been compared on mathematical functions and also on machine design problems. The best method is highlighted and discussed. A general computer program package is presented that will optimize and analyse machine design problems. The package is organised in such away that future addition or deletion of performance specifications, constraints, optimization methods and design process elements are readily implemented

Essays on labour migration in Canada

The immigration literature generally concludes that the assimilation of immigrants mainly depends on individual characteristics of the person. Following Hatton and Leigh (2011), we study whether immigrants assimilate as communities, not only as individuals. Using the 1981, 1991, 2001 and 2006 Canadian Census data, the relationship between the assimilation of immigrants and the past stock of given ethnic origin groups are studied. Alongside the past stock, other group-level variables are used. The results suggest that a large number of immigrants from a given origin group depress the relative hours worked whilst a history of past immigration raises the relative hourly wages. Thus, the history of the individual’s ethnic group in the host country matters in the assimilation process. In addition, the years since migration of a given origin group raises both the relative annual earnings and hourly wages. In chapter two, using data from the Canadian censuses of 2001 and 2006, the role of the migrant’s community in their time choices compared to native Canadians is studied. A Tobit regression in which the dependent variables are, the number of hours per week spent on childcare, housework and looking after the elderly, is estimated. The results show that immigrants spend less time on these three activities compared to natives and there is evidence to suggest that the migrant’s community positively aids in the assimilation process of nonmarket activities. The province of Quebec in Canada has two official languages, English and French, with French being the majority-spoken language. Similarly, the Montreal metropolitan area in Quebec has a majority of native French speakers but also a significant proportion of native English speakers and allophone immigrants. Using the 1971, 1981, 1991, 2001 and 2011 Canadian Census data, the paper Payoff to official language knowledge in Quebec studies the wage premium associated to having knowledge of an official language(s) that is different from one’s mother tongue and whether it pays for one to learn a second official language given that communication can already take place with a different mother tongue language group (network externality). The results suggest that for the English mother tongue group, there is a positive payoff associated to having knowledge of French in Quebec and Montreal, while having knowledge of the English language for Francophone individuals only pays in Quebec but not in Montreal. For the allophone immigrants, there is a positive payoff to having knowledge of French only, higher than having knowledge of English only. However, having knowledge of both official languages pays more than knowing just one. Finally, evidence is found in Francophone individuals to support the network externality hypothesis

Experimental investigation on a novel integrated solar chimney and liquid desiccant system for simultaneous power and fresh water generation

Electric power and water play a pivotal role in all aspects of daily life. In attempts to provide renewable energy-sourced systems for the concurrent generation of power and fresh water, a few studies have been conducted over the last two decades to combine solar chimney power plant (SCPP) with fresh water production systems (FWPS). These studies have mostly been theoretical approaches with significant feasibility limitations. In this article, a novel solar-powered hybrid generator of power and fresh water is presented, where SCPP has been combined with liquid desiccant system( LDS) to simultaneously produce power and fresh water. This combination utilizes the advantages of LDS of calcium chloride to turn the SCPP working air humidity into fresh water. A pilot plant of this technology was designed, constructed, and tested on an hourly basis over ten randomly selected days in October-December 2018. Consequently, its concept of operation was proven. It was concluded that using this technology and under daily averages of solar irradiance of 500 W/m2 and atmospheric air humidity ratio of 0.019 (kg water vapour/ kg dry air), a combination of power generation capacity higher than 50 MW could economically produce power and fresh water. Furthermore, an average of 5.6 l/hr of fresh water could be produced per 1 kg/s of SCPP working air. Nevertheless, the current technology enables using a wide controllable range (0%-100%) of SCPP produced power to generate fresh water

Sclerosing peritonitis presenting as complete mechanical bowel obstruction: A case report

Introduction: Sclerosing peritonitis or abdominal cocoon syndrome is characterized by small bowel loops completely encapsulated by a fibrocollagenous membrane in the center of the abdomen. Although cocooning of the abdomen is mostly seen in patients on peritoneal dialysis, it can occur de novo; it very rarely manifests as complete mechanical bowel obstruction.Case Presentation: A 46-year-old Asian man presented with complete mechanical bowel obstruction. He had previous attacks of partial bowel obstruction during the past 6 to 8 months, which was misdiagnosed as abdominal tuberculosis because tuberculosis is very prevalent in the region in which he lives. He took anti-tuberculosis therapy for 3 months but this did not result in resolution of his symptoms. This time he had diagnostic laparoscopy followed by laparotomy in which a fibrocollagenous membrane, resulting in entrapment of his bowel, was excised and his entire small bowel was freed. Postoperatively he again had a mild episode of partial bowel obstruction but this was relieved with a short course of steroids.Discussion: Sclerosing peritonitis is a rare benign etiology of complete mechanical bowel obstruction. Patients might have suffered recurrent attacks of partial bowel obstruction in the past that were falsely managed on lines of other conditions such as tuberculosis, especially in endemic areas like Pakistan or India.Conclusion: Sclerosing peritonitis is a rare benign diagnosis which can manifest as complete bowel obstruction and a high index of suspicion is required to diagnose it. Contrast-enhanced computed tomography of the abdomen is a useful radiological tool to aid in preoperative diagnosis. Diagnostic laparoscopy is usually confirmatory. Peritoneal sac excision and adhesiolysis is the treatment and a short course of steroids in relapsing symptoms

Disclosing bad news of cancer diagnosis: Patients\u27 preference for communication

The majority of relatives of cancer patients in Pakistan request their clinicians to adopt a do not tell approach while counselling the patients regarding their disease. The current study aimed to assess patients\u27 understanding of their disease and how they would prefer the physicians to deliver news about cancer diagnosis and its management plan. This was a cross-sectional study in which both patients and their immediate relatives were interviewed. The study enrolled 55 patients with six different types of cancers. The study showed that 35 (65.5%) patients did not know the stage of their illness at the time of diagnosis, while 40 (72.7%) patients did not know the current stage of their disease. In 22 (40%) cases, the patient\u27s family knew the diagnosis ahead of the patient, and 19 (86.3%) families asked the clinicians to hide the diagnosis from the patient. This study, which used a scoring questionnaire, demonstrates that specialist oncologists for breaking the bad news, family counselling, helping patients to figure out how to inform others, giving the news directly to the patient and the effects of cancer on daily life are preferred areas to communicate with cancer patients

A Comparative Study on the Electrical Characteristics of Generating Plasma by Using Different Target Sources

In this research, the electrical characteristics of glow discharge plasma were studied. Glow discharge plasma generated in a home-made DC magnetron sputtering system, and a DC-power supply of high voltage as input to the discharge electrodes were both utilized. The distance between two electrodes is 4cm. The gas used to produce plasma is argon gas which flows inside the chamber at a rate of 40 sccm. The influence of work function for different target materials (gold, copper, and silver), - 5cm in diameter and around 1mm thickness - different working pressures, and different applied voltages on electrical characteristics (discharge current, discharge potential, and Paschen’s curve) were studied. The results showed that the discharge current and potential increase by increasing the applied voltage ranging between 300-700 V. Discharge current increased as working pressure increased in the beginning, and then semi-stabilized (slight increase) starting from 1×100 mbar, while discharge potential decreased at the beginning as working pressure increased and then semi-stabilized at the same point at which discharge current stabilized. The Paschen’s curves were compared with each other. It was concluded that the lower breakdown voltage was associated with lower work function of the (Au, Cu, and Ag) cathode material. Breakdown voltages were (395, 398, and 420) for Ag, Cu and Au respectively

Hot Press Joining Optimization of Polyethylene to Aluminium Alloy AA6061-T6 Lap Joint Using Design of Experiments

The hot press method is used to join a poly-ethylene (thickness = 4 mm) with an aluminium alloy (AA6061-T6, thickness = 1.5 mm). In order to achieve the joint success, anodizing processes have been done on the surface of the aluminium samples. The conditions are; current density (200Amp. /m2), temperature (24 oC), sulfur acid (15%) and anodizing time (60 minute). Three joint parameters are used with different levels; Two values of temperature (115 and 135 oC), three values of pressure (2, 6, 10 bar) and the pressing time are (1, 2, 3, 4 and 5 min.). The welded specimens are tested by shear, microstructure, energy dispersive spectrometry (EDS) and differential scanning calorimetric (DSC) test. The shear test results are analyzed using design of experiments (DOE). Minimum and maximum shear tensile strength are found at the first level of temperature (T = 115 oC), (F min = 680N, F max = 2800N). From Pareto chart, the applied pressure has the heights effect on the shear tensile strength of the welded specimens as comparing with temperature and welding time. The main effect plot shows that the optimum value of shear tensile strength is obtained at the welding conditions (T = 135 oC, P = 6 bar, t = 3 minute).The tested specimens exhibit a dislocation, extension and necking in the region of polymer with a ductile fracture. The interlock percentage of polymer element is approximately (11 micron). The melting point and glass transmission temperature of (PE) are decreased.The hot press method is used to join a poly-ethylene plate of thickness 4 mm with an aluminium alloy AA6061-T6 plate of thickness 1.5 mm. A preanodizing process is crucial for the success of such joint. The anodizing was performed under a current density of 200 A/m2, temperature 24°C, sulphuric acid 5 wt.% and for a 60 minutes. Three period parameters were considered in the hot pressing process; temperature: 115 and 135°C, pressure: 2, 6, and 10 bar and pressing time: 1, 2, 3, 4 and 5 minutes. The joint specimens are tested by shear tensile test, microstructure, energy dispersive spectrometry, differential scanning calorimetric and thermo grvanometric analysis. The results of shear tensile were analyzed using design of experiments. Minimum and maximum shear tensile force were found at temperature T = 115°C where; Fmin = 680N and Fmax = 2800 N. From Pareto chart, the applied pressure had the most significant effect on the shear tensile force of the joint specimens compared to temperature and joining time. The main effect plot showed that optimum value of shear tensile force was obtained at joining conditions of T = 135°C, P = 6 bar and t = 3 minutes. The tested specimens exhibited an interfacial shear failure, extension and necking in the region of polymer with a ductile fracture. The mechanical interlocking of polymer element in the anodizing surface is approximately 15 µm. The melting point and glass transmission temperature of PE are decreased after the hot press