Browsing by Subject "steady state"
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Item An Experimental and Numerical Investigation of the Steady State Forces in Single Incremental Sheet Forming(2012-10-19) Nair, MaheshIncremental sheet forming process is a relatively new method of forming which is increasingly being used in the industry. Complex shapes can be manufactured using this method and the forming operation doesn't require any dies. High strains of over 300 % can also be achieved. Incremental sheet forming method is used to manufacture many different components presently. Prototype examples include car headlights, tubs, train body panels and medical products. The work done in the thesis deals with the prediction of the steady state forces acting on the tool during forming. Prediction of forces generated would help to design the machine against excessive vibrations. It would help the user to protect the tool and the material blank from failure. An efficient design ensures that the tool would not get deflected out of its path while forming, improving the accuracy of the finished part. To study the forces, experiments were conducted by forming pyramid and cone shapes. An experimental arrangement was set up and experimental data was collected using a data acquisition system. The effect that the various process parameters, like the thickness of the sheet, wall angle of the part and tool diameter had on the steady state force were studied. A three dimensional model was developed using commercial finite element software ABAQUS using a new modeling technique to simulate the deformation of the sheet metal blank during incremental sheet forming. The steady state forces generated for any shape, with any set of parameters used, could be predicted using the numerical model. The advantage of having a numerical model is that the forces can be predicted without doing experiments. The model was used to predict the steady state forces developed during forming of pyramid and cone shapes. The results were compared and were seen to be reasonably close to the experimental results. Later, the numerical model was validated by forming arbitrary shapes and comparing the value obtained from simulations to the value of the measured steady state forces. The results obtained from the numerical model were seen to match very well with the experimental forces for the new shapes. The numerical model developed using the new technique was seen to predict forces to a reasonable extent with less computational time as compared to the models currently available.Item Heat Transfer Enhancement in Rectangular Channel with Compound Cooling Techniques(2013-11-27) Krad, BelalVarious compound internal cooling techniques were investigated in this experiment to see which combinations can offer the greatest heat transfer. Combinations of rib turbulators as well as pin0fins were used in different configurations in order to analyze heat transfer and pressure loss characteristics to determine which configuration had the overall best performance. Two different flow configurations were considered, a uniform channel flow setup as well as a jet impingement setup. There were a total of sixteen cases performed for the experiment, eight for the channel flow and eight for the jet impingement. The types of cases that were performed were: a smooth surface case, two cases of only copper rib turbulators (P/e ratios of 5 and 10), two cases of only copper pin0fins (P/e ratios of 5 and 10), and three cases of a combinations of copper rib turbulators and pin0fins (P/e ratios of 2.5, 5, and 10). All of the cases were performed at four different Reynolds numbers to explore the effect of Reynolds number on the heat transfer. In terms of the channel flow experiment, the results indicate that the all ribs case with a P/e ratio of 5 had the highest heat transfer coefficients but also produced the highest friction factor. If the total area is considered and not just the projected area, than the case of all pins P/e ratio of 10 is the best candidate due to its extensively low pressure drop and moderate heat transfer. In terms of the jet impingement experiment, none of the cases significantly enhanced heat transfer and many of them had results lower than the smooth case. The case of all pins P/e ratio of 5 performed the best out of all the rough cases but the case of all pins P/e ratio of 10 perform the best when taking into account the total surface area. Cross0flow contributed to the jet impingement results, lowering the local Nusselt number due to the bending of the jet beams in the low x/d regions but started increasing the local Nusselt number at further x/d due to the cross flow heat transfer.Item Passive load follow analysis of the STAR-LM and STAR-H2 systems.(Texas A&M University, 2004-09-30) Moisseytsev, AntonA steady-state model for the calculation of temperature and pressure distributions, and heat and work balance for the STAR-LM and the STAR-H2 systems was developed. The STAR-LM system is designed for electricity production and consists of the lead cooled reactor on natural circulation and the supercritical carbon dioxide Brayton cycle. The STAR-H2 system uses the same reactor which is coupled to the hydrogen production plant, the Brayton cycle, and the water desalination plant. The Brayton cycle produces electricity for the on-site needs. Realistic modules for each system component were developed. The model also performs design calculations for the turbine and compressors for the CO2 Brayton cycle. The model was used to optimize the performance of the entire system as well as every system component. The size of each component was calculated. For the 400 MWt reactor power the STAR-LM produces 174.4 MWe (44% efficiency) and the STAR-H2 system produces 7450 kg H2/hr. The steady state model was used to conduct quasi-static passive load follow analysis. The control strategy was developed for each system; no control action on the reactor is required. As a main safety criterion, the peak cladding temperature is used. It was demonstrated that this temperature remains below the safety limit during both normal operation and load follow.