Engenharia Mecânica

URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/23

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Residual compressive stresses applied due to shot peening process in the Ti 6al 4v alloy
(2010-07-26) LAVOR, P. R. U.; MOURA-NETO, C. DE; Sergio Delijaicov; DE CAMPOS, V. S.
The objective is to measure the residual stresses in the Ti 6Al 4V alloy due the shot peening process. The specimens were manufactured in the conditions: 1st machined without Shot Peening; 2nd machined and submitted to Shot Peening in the range: 0,13 N(mm) - 0,46 N(mm); 3rd Machined and submitted to Shot Peening in the range: 0,15 A(mm) - 0,25 A(mm). The residual stresses were measured through the incremental hole drilling technique and the data obtained in a graphic form and are important for stress analysis in order to verify the influence of the residual stresses in the fatigue life. The graphics show the curves of the compressive tensions through the thickness of the three conditions studied and herein follows an idea of the obtained measurements: 1st Machined test specimens without shot peening application: residual compressive stresses of 200 MPa. 2 ndMachined test specimens and submitted to Shot Peening application in the range: 0.13 N(mm) - 0.46 N(mm): Residual Compressive Stresses of 500 MPa. 3rd: Machined test specimens and submitted Shot Peening application in the range: 0.15 A(mm) - 0.25 A(mm): Residual Compressive Stresses of 1000 MPa.
Plastic eta factors to determine experimental J-integral and ctod using homogeneous and mismatched SE(T) specimens
(2010-07-26) MOREIRA, F. C.; OLIVEIRA, G. P. DE; Gustavo Donato
This work presents procedures for experimental estimation of J - integral and CTOD (d) using the eta (h) method and SE(T) specimens in clamped and pin-loaded conditions. Homogeneous materials and also specimens containing mismatched welded joints are considered. The conceptual background is presented, followed by the details of the various finite element models developed for the analyses. As results, are presented h factors for J and CTOD experimental estimation. The main objective is to allow fracture toughness experimental evaluation using SE(T) specimens to reduce the conservatism in integrity assessments of pipelines and pressure vessels, which present very similar fracture conditions. Consequently, the results contribute for a better understanding of SE(T) specimens and encourage further developments since they are not available in current standards.
Investigation of residual stress in laser welding dissimilar materials Investigação da tensão residual na soldagem laser de mate riais dissimilares
(2010-07-26) MIRIM, D. DE C.; BERRETTA, J. R.; ROSSI, W. DE; LIMA, N. B. DE; OLIVEIRA, R. R. DE; Sergio Delijaicov; GOMES, D. O.
One of the most critical problems found in the different materials welding is the residual stress formation, that happens mainly for the fact of those materials they possess coefficients of thermal expansion and different thermal conductivities. Like this in this work the residual tension was evaluated in the technique of welding laser among the steel low carbon, AISI 1010 and AISI 304. The materials were united for it welds autogenous of top with a laser of continuous Nd:YAG in that they were varied the potency, speed and the focus of the laser stayed constant in relation to surface of the sample. The main objective of the study went identification and to analysis of the residual stress in HAZ on both sides of seem. Um planning factorial of two factors at two levels each it was executed for optimization the combination of the factors potency and speed. The obtained answers were the residual stress in different depths in HAZ. In the surface of the sample measures of residual stress were accomplished by the technique of X-ray difraction. The hole drilling strain gage method it was applied to measure the residual stress on both sides of the union. The results were analyzed using the variance analysis and the statistical regression based on the different influences of the entrance and combination of the factors in the residual stress generated in that union. The results indicate that the development of models can foresee the answers satisfactorily.
Thermal performance and pressure drop in a ceramic heat exchanger evaluated using CFD simulations
(2011-07-07) MONTEIRO, D. B.; Paulo de Mello
There is one potential demand for heat exchangers capable of supporting high temperatures, typically higher than 800°C, for use in thermal power plants. These heat exchangers could be used in the implementation of EFGT (Externally Fired Gas Turbines) cycles. To support these working conditions the heat exchanger must be constructed with ceramics. This work presents the results obtained with CFD simulations of one plate-fin ceramic heat exchanger. Correlations for the Colburn and friction factors, for a range of Reynolds number between 500 and 1500, are evaluated from the numerical results obtained with CFD. These correlations may be used for the thermal design of ceramic heat exchangers. One validation procedure is conducted comparing the simulation results with experimental data for a compact heat exchanger of similar configuration.
Using linear programming for the optimal control of a cartpendulum system
(2011-01-05) PUGLIA, L. V.; Fabrizio Leonardi; Marko Ackermann
This paper discusses the use of linear programming for the optimal control of a cart pendulum system. The objective function and the constraints are designed to minimize the control effort and the time duration of the operation. Simulations and experimental tests were performed. Restrictions of null angle and angular velocity at the extremes were incorporated in the design specification as well as other physical constraints. In order to compensate for the modeling errors and disturbances, the optimal trajectory was kept within a prescribed precision by means of a closed loop system. The obtained results illustrate that the technique is simple, powerful and always conclusive.
Using linear programming for the optimal control of a cartpendulum system
(2011) PUGLIA, L. V.; Fabrizio Leonardi; Marko Ackermann
This paper discusses the use of linear programming for the optimal control of a cart pendulum system. The objective function and the constraints are designed to minimize the control effort and the time duration of the operation. Simulations and experimental tests were performed. Restrictions of null angle and angular velocity at the extremes were incorporated in the design specification as well as other physical constraints. In order to compensate for the modeling errors and disturbances, the optimal trajectory was kept within a prescribed precision by means of a closed loop system. The obtained results illustrate that the technique is simple, powerful and always conclusive.
Thermodynamic study of an EFGT (Externally Fired Gas Turbine) cycle with one detailed model for the ceramic heat exchanger
(2011-07-07) Paulo de Mello; MONTEIRO, D. B.
The EFGT cycle has been considered as an option to burn biomass in gas turbines. One key element on the implementation of one EFGT cycle is the ceramic heat exchanger necessary to support the high temperatures of operation. The performance of the ceramic heat exchanger, its effectiveness and pressure drop imposed to the gas flow, may have significant influence over the thermal efficiency of the EFGT cycle. The simulations of the EFGT cycle presented herein use correlations for the pressure drop and heat transfer of one ceramic heat exchanger of the plate and fin type, evaluated numerically. The results obtained show that the type of ceramic heat exchanger simulated presents adequate performance to be implemented in one EFGT cycle.
Reducing vibrations on flexible rotating arms through the movement of sliding masses: Modeling, optimal control and simulation
(2012-01-05) TERCEIRO, E.; FLEURY, A. T.
This paper brings contributions on the proposal of use of translational motions of sliding masses to minimize vibrations induced by the rotational motion of a light flexible manipulator (rotating arm). This system is inspired by rotating cranes used to transport loads. Optimal control methods have been used to generate the slider trajectories while the flexible manipulator performs a rotational maneuver from a fixed to other fixed configuration. This approach has led to good solutions even in case of quite quick maneuvers, as, for example, a 90° beam rotation in just 1 second, using 1 or 2 sliders (Terceiro, 2002). In the present paper, the complete motion equations for any number of masses are firstly presented, in order to emphasize the complexity of the coupled elastic-rotational-translational motions. Simplifying assumptions are pointed out and the corresponding optimal control problems (OCP) are obtained. Optimal trajectories, generated according to different Indexes of Performance and different problem parameters, are analysed and compared in order to get feasible movements for the set.
Reducing vibrations on flexible rotating arms through the movement of sliding masses: Modeling, optimal control and simulation
(2012-09-19) TERCEIRO, E.; FLEURY, A. DE. T.
This paper brings contributions on the proposal of use of translational motions of sliding masses to minimize vibrations induced by the rotational motion of a light flexible manipulator (rotating arm). This system is inspired by rotating cranes used to transport loads. Optimal control methods have been used to generate the slider trajectories while the flexible manipulator performs a rotational maneuver from a fixed to other fixed configuration. This approach has led to good solutions even in case of quite quick maneuvers, as, for example, a 90o beam rotation in just 1 second, using 1 or 2 sliders (Terceiro, 2002). In the present paper, the complete motion equations for any number of masses are firstly presented, in order to emphasize the complexity of the coupled elastic-rotational-translational motions. Simplifying assumptions are pointed out and the corresponding optimal control problems (OCP) are obtained. Optimal trajectories, generated according to different Indexes of Performance and different problem parameters, are analysed and compared in order to get feasible movements for the set.
The effect of altitude and intensity of physical activity on the exergy efficiency of respiratory system
(2013-07-16) HENRIQUES, I. B.; Carlos Mady; Cyro Albuquerque; YANAGIHARA, J. I.; OLIVEIRA JUNIOR, S.
The effect of altitude on exercise performance of lowlanders has long been discussed, but it is still unclear whether the performance reduction is related to inefficiency of the respiratory system, tissues or both. In the present work, exergy analysis was applied to the human body in order to compare its exergy efficiency under basal conditions and during physical activity at sea level and high altitudes for different periods of acclimatization. Two control volumes were analyzed: the respiratory system, which comprises the lungs and the airways, and the human body as a whole. In the first control volume, the exergy rates and flow rates are associated with the venous blood and the inspired air in the inlet and the arterial blood and expired air in the outlet. An internal exergy variation due to the exergy metabolism of the lung, an exergy transfer rate associated with the metabolism of the lung and the power performed by the respiratory muscles were also taken into account. Analyzing the second control volume, the exergy transferred rate to the environment due to the heat losses by convection and radiation were considered, as well as the exergy flow rate associated with respiration and transpiration. The temperatures of different parts of the body and the heat losses to the environment were obtained from a heat transfer model of the human body. The data concerning gas and blood flows were obtained from a model of the respiratory system. The last one was modified based on medical literature to simulate the response to physical activity at high altitude for different periods of acclimatization, from the first moment that the body is exposed to a high altitude environment to three months of acclimatization. The results obtained indicated that the respiratory system exergy efficiency is reduced at high altitudes and under physical activity, while the exergy efficiency of the body increases for both parameters. Concerning the acclimatization period, its influence was more pronounced in the respiratory system. It was possible to observe a decrease in the exergy efficiency of the respiratory system in the first two days. From this moment on, the efficiency increased continuously until the twentieth day, when it is stabilized and remains constant.

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