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Acoustical performance of Helmholtz resonators used as vehicular silencers.
(2018) Martins, Lucas Rodrigues; Guimarães, Gustavo Paulinelli; Fragassa, Cristiano
This study proposes to evaluate the acoustical performance of a reactive vehicular silencer made entirely of Helmholtz resonator. Four or seven resonators are idealized to be in a series configuration, all the dimensions except cavity length and resonators are fixed. An algorithm processes inputted characteristic engine noise signal obtained from literature, identify peaks, and calculates ideal cavity length for attenuation. The transmission loss of the system is analytically calculated. Attenuation levels obtained are satisfactory. The required volume of the resonator to achieve the same resonance frequency as low frequency noise peak demands impractical cavity length, proving it to be flawed. It is suggested to use resonators of two or three different diameter for different frequency range in order to overcome this problem.
An approach to torque and temperature thread by thread on tapping.
(2020) Pereira, Igor Cezar; Vianello, Pedro Ivo Alves; Boing, Denis; Guimarães, Gilmar; Silva, Marcio Bacci da
During internal threading, small alterations in cutting parameters, tool geometry, or process characteristics produce considerable effects on torque and temperature behavior. Understanding these effects is critical to the design and development of new taps. In this work, the torque behavior for a tap operation is evaluated as a function of the number of threads, tool manufacturer, and angle of the taper region of the tool. The chip–tool interface temperature was analyzed, considering the influence of cutting speed and number of threads. Experimental tests were carried out using M10x1.5 taps and cutting speeds of 10 m/min and 25 m/min. Taps with two different geometries were considered in this analysis. The results show a difference in the distribution of the torque along the threads of the conical part between the tools. The presence of adhered material increased the torque during the reverse stage. The torque during the reverse stage for a tap with a damaged tooth was approximately 50% of the torque during the cutting stage. The temperature showed an increase with the number of threads stabilizing between the fourth and fifth threads and increasing again in the sixth filled due to adhesion of workpiece material.
Análise da temperatura filete a filete no rosqueamento interno por machos de corte.
(2018) Souza, R. F. A.; Vianello, Pedro Ivo Alves; Silva, Marcio Bacci da; Pereira, Igor Cézar
Among the manufacturing processes, threading stands out, as it can be accomplished by machining or by forming. This process is responsible for the creation of internal and external threads, which has great applicability in production lines. Due to the market’s great competitiveness, methods are sought to increase production by decreasing the time of each unit process. However, tapping is usually performed at low cutting speeds due to limitations related to the manufacturing process. The study of the tapping can bring benefits, such as the reduction of wear mechanisms, resulting in an increase in tool life. In this research, the temperature was measured from fillet to fillet in the conical part of the tool, varying the cutting speed and the number of fillets. The tap used is, M 10 x 1.5 HSS, uncoated in threading process for internal thread production in SAE 1045. To analyze the temperature was used the tool-workpiece thermocouple method on each fillet of the tap. The cutting speeds used were 10 and 25m / min. From the second fillet on the temperature is constant, even with the increase in the number of fillets, as expected.
Análise e comparação do torque filete a filete no rosqueamento interno por machos de corte.
(2018) Vianello, Pedro Ivo Alves; Souza, R. F. A.; Silva, Marina Carla Bezerra da; Pereira, Igor Cezar
The thread process is responsible for internal and external threads creation which are of large application in several areas. Even though its large usage in industry, there are few papers about this process. In this paper, it was carried out torque fillet by fillet measurements over the chamfer portion of the tap and the torque comparation between tools from two distinct manufacturers. It was used M 10 x1,5 HSSE straight flute taps, with and without coating in tapping process on a grey cast iron GG30, in order to analyse the relation between the number of fillets in the tap’s chamfer and its geometry in torque signal behaviour.
Analysis of a hybrid molten carbonate fuel cell and gas turbine cycle.
(2020) Leal, Elisângela Martins; Silva, Barbara Emanuelle Sanches; Leal Júnior, Amauri Menezes
Background: Hybrid systems with fuel cells and thermal engines are studied with promising results. Molten carbonate fuel cells (MCFC) show many advantages compatible with the current demands for energy production in a sustainable competitive way. Materials and Methods: This paper focuses on the computational investigation of an indirect internal reforming MCFC coupled to a gas turbine (GT) system. The technical analysis comprises of energy analysis of the hybrid cycle, using the Gibbs function minimization technique for the methane steam reforming process. The assessment is performed to determine the influence of the hybrid cycle operating temperature and pressure, steam-to-carbon ratio, and fuel and oxidant usage in the fuel cell. Results: Results show that the increase in temperature and in operating pressure of the fuel cell and the fuel reform rate improves the hybrid system performance. Variation in the utilization factor, however, did not determine an expressive increase in system efficiency. For the same fuel mass flow rate, it is possible to see that the variation in the operating temperature of the fuel cell resulted in an increase in the total power of the hybrid system when compared to the results of the pressure increase. The increase in temperature resulted in a maximum increase of 12% in delivered power and corresponding to about 7% system efficiency increase. Instead, an increase in pressure of about 4% corresponding to an increase of about 2% system efficiency. Conclusion: Although an increase in the fuel cell's power density was observed for the same mass flow rate in the system, the pressure negatively influenced the total delivered power by the fuel cell.
Analysis of the coefficient of friction at the workpiece-tool interface in milling of high strength compacted graphite cast irons.
(2019) Silva, Leonardo Rosa Ribeiro da; Ruzzi, Rodrigo; Teles, Vinicius C.; Sales, Wisley Falco; Guesser, Wilson L.; Machado, Alisson R.
The coefficient of friction at the workpiece-tool interface is one of the main influencing parameters in machining. It can be tribologically investigated using conventional and open tribometers, however, there is no consensus as to which type of test has the best correlation with the real machining process. This work aims at investigating the use of three different methods to measure the coefficient of friction in the machining of three types of high strength compacted graphite cast irons, with variations in the size of the free graphite phase and the presence or absence of molybdenum carbides in the matrix. The coefficient of friction of the process was measured using two progressive load conventional tribological tests, the progressive load single sliding test with load ranging from 0.5 to 40 N and the progressive load reciprocate sliding test in both dry and starved lubrication regimen, with load ranging from 48 to 83 N. The coefficient of friction was also measured in a conventional machining center used as an open tribometer, where ramp milling tests were performed in workpieces fixed on a piezoelectric dynamometer, with a cutting depth varying from 100 μm to 0, to simulate a regressive load. The following machining parameters were varied: cutting speed, feed rate, tool geometry, tool coating and the use of minimum quantity of lubrication in contrast to dry machining. As the main results, the predominance of lubrication, even in small quantities, was observed as the most influential parameter in the coefficient of friction. An inverse relationship was also observed between the hardness of the materials and the coefficient of friction independent of the lubrication condition used. The results of the coefficient of friction obtained in progressive load re- ciprocate sliding and open tribometer tests showed the best correlation with those found in the literature for this kind of materials.
Analysis of the energy efficiency of diesel oil consumption in the Brazilian Iron Ore Mining Company.
(2018) Fernandes, Eunírio Zanetti; Leal, Elisângela Martins; Figueiredo, Robson Lage; Reis, Gemírson de Paula dos
This paper aims to evaluate the diesel oil consumption between 2008 and 2015 in the production of iron ore in Brazil, creating correlations between energy intensity (production), economy and checking the impact of fuel prices on the commodity. During the analyzed period, the years 2008-2009 indicated economic crises, which interfered in the price and the commercialization of iron ore products. The physical intensity was 0.2% higher than the economic intensity. In the period from 2010 to 2014, economic activity remained more stable, with a decreasing trend, mainly due to the increase of iron ore prices. The physical intensity is much higher than the economic intensity influenced by the expansion of the Chinese economy. The year of 2014 indicated the end of the high iron ore price cycle and the beginning of supply and demand stabilization with consequent reduction in prices. In 2015, the market entered the stabilization phase, with a continuous reduction in unit production costs and transportation logistics. There was an abrupt change due to the strong increase of the economic intensity due to the fall of the international prices of iron ore. The diesel oil consumption plays a vital role in the scenario of cost reduction in iron ore production and a deeper analysis must be done in order to discover some options to change the energy matrix.
Chua circuit based on the exponential characteristics of semiconductor devices.
(2022) Rocha, Ronilson; Torricos, Rene Orlando Medrano
The use of non-ideal features of semiconductor devices is an interesting option for implementations of nonlinear electronic systems. This paper analyzes the Chua circuit with nonlinearity based on the expo- nential hyperbolic characteristics of semiconductor devices. The stability analysis using describing func- tions predicts the dynamics of this nonlinear system, which is corroborated by numerical investigations and experimental results. The dynamic behaviors and bifurcations of this nonlinear system are mapped in parameter space in order to create a base for studies, analyses, and designs. The dynamic behavior of the experimental high speed implementation of this version of Chua circuit differs from the expected dynamics for a conventional Chua circuit due to effects of unmodelled non-idealities of the real semicon- ductor devices, displaying that new and different dynamics for the Chua circuit can be obtained exploring different nonlinearities.
Corrosion behavior of low carbon steel processed by ECAP in neutral and alkaline environment.
(2021) Braga, Jorgimara de Oliveira; Lins, Jefferson Fabricio; Castro, Gabriel Pessoa de; Almeida Junior, Helder Alves de; Santos, Igor Cuzzuol dos; Sousa, Gustavo Henrique; Criscuolo, Izabel Lima; Santana, Cláudio Márcio; Pereira, Ursula Cid
The purpose of this study was to evaluate the corrosion behavior of 1010 steel processed by Equal Channel Angular Pressing (ECAP), a technique that induces severe plastic deformation (SPD) in materials. The samples were processed by one and two passes of ECAP throught routes A and C. The corrosion behavior was evaluate using the potentiodynamic polarization and electrochemical impedance spectroscopy, using NaCl (pH= 6.5) and sodium hydroxide/sodium phosphate (pH= 10.5) solutions. The polarization tests showed better performance for the samples processed by ECAP than in the as cast samples both in alkaline and neutral solutions. The results showed that alkaline solution presented higher corrosion rate for the as cast and one ECAP pass materials. It is seen that samples processed throught routes A and C develop a film stabilization on the surface of these samples. In addition, the values of polarization resistance obtained from the electrochemical impedance spectroscopy in NaCl environment were higher for sample processed in route C.
Development of a low-cost instrumentation system applied to an electrolytic cell.
(2020) Reis, Gemírson de Paula dos; Matos, Saulo Neves; Rêgo Segundo, Alan Kardek; Leal, Elisângela Martins; Figueiredo, Robson Lage
Humanity’s growing long-term energy demand will be the opportunity for new energy generation sources. In this scenario, the use of hydrogen as an energy source has become an interesting alternative to energy production, as the use of fossil fuels can lead to harmful consequences, such as the emission of greenhouse gases. This paper presents the development of a low-cost instrumentation system for monitoring the temperature, current, voltage, and gas flow rate of a dry electrolytic cell. Through the electrolysis process, the cell generates a hydrogen-rich gas which is used as an additive in an internal combustion engine to reduce pollutant gas emissions and primary fuel consumption. The measured variables are presented as a function of the time to analyze the behavior of the electrolyzer. The main advance reported in this work is related to the use of a low-cost sensor for a hydrogen-rich gas flow measurement, in which calibration was performed indirectly using a rotameter as a reference. The calibration curve adjusted to the experimental data by linear regression presented a coefficient of determination of 0.9957. Thus, the use of the low-cost sensor is a feasible alternative for measuring the electrolysis gas generated by the cell.
Dynamic behavior of tapping axial force.
(2021) Pereira, Igor Cezar; Mapa, Lidianne de Paula Pinto; Barros, Thamiris Nogueira de; Fortes, Reinaldo Clemente; Silva, Marcio Bacci da; Guimarães, Gustavo Paulinelli
Background Tapping is one of the processes that most requires attention in the industry, due to the stage in which it occurs and its characteristics. In the case of tapping, it is common to use components and equipment with less rigidity, which com promises the dynamic behavior in several situations and can lead to process distortion or failure. Purpose The objective of this paper is to study the dynamic behavior of tapping in relation to several characteristics of the process. Methods The dynamic behavior of the force signal was used to evaluate the process, varying the cutting parameters and the clamping system of the workpiece. Results The experimental results indicate that the foating system did not present a good dynamic behavior at high cutting speeds, this greater application of vibration is due to the resonance due to the combination of oscillations under forced and natural vibration. Conclusions The natural frequency of the foating fxture system infuenced the behavior of the axial forces. The increase in cutting speed resulted in a direct increase in the axial force vibrations as its frequency came close to the natural frequency of the system. Through dynamic analysis of the axial force signal observed the dynamic characteristics of the process and the machine tool. This allowed the dynamic evaluation of the system through the measurement of force signals generated in the threading process.
Experimental analysis between performance parameters for an internal combustion engine fueled by gasoline and ethanol when submitted to engine block vibration.
(2022) Santana, Cláudio Márcio; Barros, José Eduardo Mautone; Almeida Junior, Helder Alves de
Ethanol and gasoline are widely used as fuels in Otto cycle engines. These fuels have diferent heating power and octane numbers and the engine behaves diferently depending on the type of fuel used. The objective of this study is to measure, compare and investigate the factors that afect the block vibration of an internal combustion engine, which uses ethanol or gasoline as its fuel, as a function of shaft torque and shaft power engine, main efective pressure, advanced ignition, pressure combustion engine and other parameters. The experiment consisted of instrumenting the side of the engine block with a triaxil accelerometer to measure the level of the vibration acceleration value of the engine running on a bench dynamometer, while varying the engine speed under full load conditions. The results showed that the engine vibration level was infuenced by engine speed, load, type of fuel and performance parameters of the engine. The highest level of vibration was noted in the region of maximum torque and maximum pressure combustion. The combustion process is primarily responsible for the highest level of vibration reached when using ethanol as a fuel. Under all operating conditions, the vibration level of the engine block was highest when using ethanol. On average, the longitudinal, vertical and transverse engine vibration was 3%, 31% and 56% higher in the engine running on ethanol compared to the engine run on gasoline. This study holds relevance as it correlates the longitudinal, vertical and transverse vibration level of the block of an internal combustion engine, as is found in an engine combustion process fueled by ethanol and gasoline.
Experimental investigation of flameless combustion of biodiesel.
(2022) Silva, Edson Orati da; Veríssimo, Anton Skyrda; Rocha, Ana Maura Araújo; Costa, Fernando de Souza; Carvalho Junior, João Andrade de
A laboratory-scale combustor was investigated under flameless biodiesel combustion. The biofuel was used due to its importance as a green fuel substitute for conventional fossil diesel, in order to reduce the emission of greenhouse gases. The combustor design was based on the phenomenon of internal recirculation, whose intensity is determined by the airflow jet momentum rate through its air intake nozzle. This investigation is important to identify the physicochemical phenomena that govern flameless combustion of liquid fuels, in addition to determining the operating parameters of the burner. A pressure swirl atomizer was used to atomize the biodiesel. The influence of biodiesel temperature and pressure on the droplet size was investigated. Results show that after a certain liquid pressure and preheating temperature, the droplet size does not vary. The combustor aerodynamics promoted adequate mixing of fuel vapor in the vicinity of the droplet interface with diluted oxidant, as a result of high airstream jet momentum rate, leading to distributed combustion reactions. The experimental results showed that combustion at high rates of excess air and preheated air fulfilled the typical characteristics of flameless combustion due to the indistinguishable flame limits, reduced combustion noise levels, absence of soot emissions and low emissions of NOx and CO, simultaneously. On the other hand, combustion in low excess air resulted in the stabilization of a bright yellowish flame with high soot emissions together with a sharp increase in CO emissions. The droplet size has a significant influence on the establishment of stable combustion. For droplet sizes above 35 mm it was impossible to keep the burning of the biodiesel. NOx and CO emissions were affected by the excess air and temperature variations.
Finding hidden oscillations in the operation of nonlinear electronic circuits.
(2016) Rocha, R.; Torricos, Rene Orlando Medrano
Several dynamic behaviours can simultaneously coexist in the operation of a nonlinear electronic circuit. However, some of these dynamics are difficult to be observed due to their sensibility to initial conditions. The use of describing functions to determine the coexistence of multiple dynamics in the operation of an electronic circuit with nonlinear feedback is proposed.
Heat fux in machining processes : a review.
(2022) Figueiredo, Alisson Augusto Azevedo; Guimarães, Gilmar; Pereira, Igor Cezar
The models of temperature prediction in manufacturing processes have advanced considerably in the last decades, either by applying numerical methods or by the development of techniques and methods of temperature measurement, which feed and compare the results of models. Associated with the advancement of prediction models is the improvement in the analysis of heat generation and distribution during materials machining. This work presents state of the art in research related to heat fux estimation in metal cutting processes using direct and inverse methods, through analytical, numerical, and empirical models. Pioneering and current research approaching the problem of estimating heat fux, as the main focus or means to predict the temperature distribution during the process, are reviewed. Its particularities, such as boundary conditions, techniques used, and innovations concerning previous works, are discussed. Therefore, this paper will present and detail diferent methods to estimate the heat fux during machining, aiming to help researchers identify the advantages and limitations in several cases discussed. The heat fux estimation using inverse methods can be more accurate with the development of data acquisition systems, reducing errors in measured temperatures during the process. In addition, multiphysics numerical simulations characterizing plastic deformation and heat transfer can be improved to help estimate the heat generated in machining.
Influence of metallurgical texture on the abrasive wear of hot-rolled wear resistant carbon steels.
(2019) Damião, Carlos Alberto; Alcarria, Gabriela; Teles, Vinicius C.; Mello, Jose Daniel Biasoli de; Silva Junior, Washington Martins da
Hot-rolled wear resistant carbon steel sheets are commonly applied in mining equipment as abrasive wear- resistant material for front loaders, chutes, etc. The rolling process can induce metallurgical texture in the form of alternating bands of ferrite and pearlite known as "banding" which affect the mechanical properties of the material. The goal of this work was to verify the impact of metallurgical texture on the abrasion resistance of hot- rolled wear resistant carbon steels. SEM images of the field specimens showed that the prevailing wear me- chanism was parallel scratches. This wear mechanism was replicated in the laboratory using a dry sand-rubber wheel wear tester. The particle size used in the abrasive wear test (0.15–0.30 mm) was defined by the topo- graphical analysis of the field sample. In addition, linear scratch tests were conducted to determine the specific scratch energy. The block specimens used in the abrasion wear tests were cut from hot rolled plates with and without metallurgical texture taking into account the rolling direction. Metallographic analysis of these samples showed an anisotropic microstructure related to the lateral and transversal surfaces of the plates. The wear rate of the lateral surface was up to 40% lower than that of the upper surface. This result was attributed to the presence of metallurgical texture that increased hardness. In addition, the wear rate presented a linear re- lationship to the scratch specific energy. In this case, samples without metallurgical texture were more difficult to scratch. The analysis of the specific energy and wear rate parameters clearly showed the anisotropy of the samples presenting metallurgical texture, which corresponded to the highest abrasive wear rate.
Investigations on complex acoustic modes of rocket engines combustion chambers for damping allocation.
(2021) Guimarães, Gustavo Paulinelli; Pirk, Rogério; Souto, Carlos D'Andrade; Góes, Luiz Carlos Sandoval
Combustion instability can severely impair the operation of many kinds of combustion engines. Acoustic resonators are widely used to suppress the pressure oscillations caused by the coupling between the combustion process and the combustion chamber acoustic modes. Combustion chambers with subsonic flow in its inlets and outlets, like gas turbine combustors, exhibit some acoustical damping due to the presence of openings. In such chambers, the acoustic modes are complex. In a complex mode, the antinode regions can be shifted from its position in the corresponding real mode. In this work an experimental acoustic modal analysis of a cavity with an opening was performed. Acoustic frequency response functions were obtained by using a volume acceleration source, a microphone and a data acquisition system. The PolyMAX algorithm was used to estimate longitudinal modes in its real and complex versions. A comparison was performed and the results show that, for some modes, the antinode region placement could change reasonably. This suggests that the use of complex modes for location of antinode regions provides more accurate results and consequently could be a better way to identify positions, where resonators provide maximum damping in order to minimize combustion instability in subsonic combustion chambers.
Measuring and comparing the ignition delay time of the reference diesel, convectional diesel, additive ethanol and biodiesel from soybean oil using a shock tube.
(2020) Santana, Cláudio Márcio; Barros, José Eduardo Mautone; Almeida Junior, Helder Alves de; Braga, Jorgimara de Oliveira; Bosch Neto, Juan Canellas
The objective of this work is to correlate the ignition delay times of reference diesel, convectional diesel, ethanol and biodiesel from soybean oil measured in a shock tube with a 5% additive increase in the cetane number. The results were correlated with the cetane number of the respective fuels and compared with the ignition delay times available in the studies by oth- ers authors. The shock tube is a metal tube in which gas at low pressure and at high pressure is separated by a diaphragm. When the diaphragm breaks in predetermined conditions (high pressure in this case) produces shock waves that move from the high-pressure chamber (known driver section) to the low-pressure chamber (known driven section). The tests were per- formed under the following initial conditions: refected shock wave temperature from 903 to 1260 K, equivalence ratio of 1 and refected shock wave pressures of 24 bar. For determining and recording the ignition delay time, pressure sensors with high acquisition rate and luminosity sensors were used. With information from pressure sensors and the luminosity sensor, ignition delay times of reference diesel, convectional diesel, additive ethanol and biodiesel from soybean oil were recorded. We concluded that the ignition delay time of additive ethanol was twice as large as the ignition delay time of reference diesel. The ignition delay time of biodiesel from soybean oil was approximately three times greater than the ignition delay time of reference diesel. The ignition delay time of the reference diesel was smaller than the convectional diesel. The contribution of this work is that it shows why additive ethanol and pure biodiesel should not be used as substitutes for diesel compression ignition engines without any major changes in the engines. The ignition delay times of these fuels are at least two to three times longer than the ignition delay time of reference diesel.
Stability analysis for the Chua circuit with cubic polynomial nonlinearity based on root locus technique and describing function method.
(2020) Rocha, Ronilson; Medrano Torricos, Rene Orlando
This work investigates the dynamics of the Chua circuit with cubic polynomial nonlinearity using methods for stability analysis based on linearization and frequency response. Root locus technique maps eigenvalues of the linearized system in order to analyze the local stability, which allows to verify dynamic features, motion patterns, and attractor topologies. The method based on describing functions allows analyze effects of the cubic nonlinearity in the system, as well as predict equilibrium and fixed points, periodic and chaotic orbits, limit cycles, multistability and hidden dynamics, unstable states, and bifurcations. The stability of the Chua circuit with cubic polynomial nonlinearity is analyzed using both approaches in order to identify and map dynamics in parameter spaces. Numerical investigations based on computational simulations corroborate the theoretical results obtained using this stability analysis. This theoretical analysis and the numerical investigations present interesting insights about the dynamics of the Chua circuit with cubic polynomial nonlinearity and provides a design tool for electroelectronic implementations.
Study of the project parameters influence in the performance of solar collectors.
(2019) Mapa, Lidianne de Paula Pinto; Mendes, Bárbara de Morais; Bortolaia, Luis Antônio; Leal, Elisângela Martins
This paper aims to observe the influence of design parameters on the performance of plane solar collectors. From the energy balance of the plane solar collector, the mathematical model was implemented varying the following design parameters: (i) Thickness of the absorber plate; (ii) Distance between the absorber and the cover; (iii) Edge insulation thickness; (iv) Absorber emittance; (v) Conductivity of the absorber; (vi) Convective heat transfer coefficient inside the tubes; (vii) Distance between tubes; (viii) Wind velocity; (ix) Solar radiation incident; and (x) Back insulation thickness. These parameters were altered observing the influence on the optical efficiency; the coefficient of energy loss; the instantaneous efficiency; and the useful energy gain. From the results, it is possible to see that the parameters that most influence the performance of the solar collector are the distance between the absorber and the cover, the absorber emittance, the thermal conductivity of the absorber, the distance between tubes, wind speed and solar radiation incident.

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