Showing papers in "Journal of The Brazilian Society of Mechanical Sciences and Engineering in 2004"
TL;DR: In this paper, the authors provide an overview on the recent developments and their application in the aerospace industry, including dry machining at high speed conditions, the use of high pressure and/or ultra high pressure coolant supplies, minimum quantity lubrication, cryogenic machining and rotary (self-propelled) machining technique.
Abstract: Materials used in the manufacture of aero-engine components generally comprise of nickel and titanium base alloys. Advanced materials such as aero-engine alloys, structural ceramic and hardened steels provide serious challenges for cutting tool materials during machining due to their unique combinations of properties such as high temperature strength, hardness and chemical wear resistance. These materials are referred to as difficult-to-cut since they pose a greater challenge to manufacturing engineers due to the high temperatures and stresses generated during machining. The poor thermal conductivity of these alloys result in the concentration of high temperatures at the tool-workpiece and tool-chip interfaces, consequently accelerating tool wear and increasing manufacturing cost. The past decade has witnessed a radical approach to product manufacture, particularly in the developed economy, in order to remain competitive. Modern manufacturing philosophies, principles and techniques geared primarily towards reducing non value added activities and achieving step increase in product manufacture have been widely adopted. Recent advances in the machining of aero-engine alloys include dry machining at high speed conditions, the use of high pressure and/or ultra high pressure coolant supplies, minimum quantity lubrication, cryogenic machining and rotary (self-propelled) machining technique. Tool materials with improved hardness like cemented carbides (including coated carbides), ceramics, polycrystalline diamond and polycrystalline cubic boron nitride are the most frequently used for high speed machining of aero-engine alloys. These developments have resulted to significant improvement in the machining of aero-engine alloys without compromising the integrity of the machined surfaces. This paper will provide an overview on these recent developments and their application in the aerospace industry.
138 citations
TL;DR: In this article, the numerical and experimental analysis of the turbulent flow of air inside a channel of rectangular section, containing two rectangular baffle plates, is presented, where the velocity field was measured with a hot wire anemometer, and the pressure field with an electronic manometer.
Abstract: The present work presents the numeric and experimental analysis of the turbulent flow of air inside a channel of rectangular section, containing two rectangular baffle plates. This is an important problem in the scope of heat exchangers where the characterization of the flow, pressure distribution, as well as the existence and the extension of possible recirculations need to be identified. The differential equations that describe the flow were integrated by the Finite Volumes Method, in two dimensions, employing the Fluent software with the k-e model to describe the turbulence. The mesh is structured, with rectangular volumes. Several boundary conditions were explored, being the more realistic results obtained by prescribing the inlet velocity field and atmospheric pressure at the exit. The obtained results are compared with experimental data, being analyzed and commented the deviations. The velocity field was measured with a hot wire anemometer, and the pressure field with an electronic manometer. The largest variations in the pressure and velocity fields occur in the regions near to the deflectors, as expected.
105 citations
TL;DR: In this paper, a new development, the Cranfield Automated Pipe-welding System (CAPS), is described, where tandem GMAW in a narrow groove has been applied to pipeline girth welding with two tandem torches in a single welding head.
Abstract: Installation of new pipelines is predicted to grow at a rapid rate over the next twenty years, due in part to the increase use worldwide of combined cycle power generation plant using natural gas a fuel. The need to construct large diameter pipelines over long distances has led to an increased demand to improve the productivity of pipeline girth welding. Many novel techniques have been tried in the past to achieve productivity gains, including laser welding, flash butt welding, homopolar welding, and radial friction welding. In spite of the failure to gain wide acceptance, there is still current development aimed at achieving their eventual implementation. Single wire mechanised gas metal arc welding (GMAW) remains the dominant pipe girth welding technique, and has been optimised in the past to produce the maximum productivity possible with this process. Continued development of GMAW with dual torch, tandem GMAW welding and novel techniques for GMAW roots is leading to further significant gains in arc welding productivity. This paper describes a new development, the CAPS project, (Cranfield Automated Pipe-welding System), where tandem GMAW in a narrow groove has been applied to pipeline girth welding with two tandem torches in a single welding head. The CAPS system offers welding productivity three to four times higher than that possible with the conventional single wire GMAW technique, while still producing a weld which is very similar to that generated by single wire welding. The development of the system is described, as well as recent successful trials under field conditions. The development of high power lasers has spurred a current high level of interest in the possibility of application to pipeline welding, and current research is described in which the feasibility of pipeline laser welding has been established.
87 citations
TL;DR: In this article, the authors investigated the ultrasonic abrasion of different workpiece materials - alumina, zirconia, quartz, glass, ferrite and LiF - by using a stationary ultrasonic machine.
Abstract: Precision abrasive processes are commonly employed to machine glasses, single crystals and ceramic materials for various industrial applications. Until now, precision machining of hard and brittle solids are poorly investigated in Brazil from the fundamental and applied point of views. Taking into account the major technological importance of this subject to the production of functional and structural components used in high performance systems, the present study investigated the ultrasonic abrasion of different workpiece materials - alumina, zirconia, quartz, glass, ferrite and LiF - by using a stationary ultrasonic machine. Experiments were conducted using a rectangular shaped cutting toll and SiC particles with mean grain size of 15mm. The machined surfaces were characterized by surface profilometry and scanning electron microscopy. In the case of alumina, zirconia and quartz, the rates of material removal decrease with the depth of machining. The rate of material removal remained constant for the others materials. The micrographs showed that brittle microcracking was the primary mechanism involved with material removal. The rates of material removal and the machined surface topographies were discussed as a function of intrinsic stiffness, hardness and fracture toughness of workpiece materials.
71 citations
TL;DR: In this paper, the authors demonstrate the use of modal analysis techniques to select brake dampers for reducing braking squeal noise, which reduces the simulation of braking events in dynamometers and allows an optimized use of the brake dynamometer to validate selected insulators.
Abstract: Squeal noise generation during braking is a complicated dynamic problem which automobile manufacturers have confronted for decades. Customer complaints result in significant yearly warranty costs. More importantly, customer dissatisfaction may result in rejection of certain brands of brake systems. In order to produce quality automobiles that can compete in today's marketplace, the occurrence of disc brake squeal noise must be reduced. The addition of a constrained layer material to brake pads is commonly utilized as a means of introducing additional damping to the brake system. Additional damping is one way to reduce vibration at resonance, and hence, squeal noise. The simulation of braking events in dynamometers has typically been the preferred insulator selection process. However, this method is costly, time consuming and often does not provide an insight into the mechanism of squeal noise generation. This work demonstrates the use of modal analysis techniques to select brake dampers for reducing braking squeal. The proposed methodology reduces significantly the insulator selection time and allows an optimized use of the brake dynamometer to validate selected insulators.
68 citations
TL;DR: In this article, the authors explored the possibility of using Genetic Algorithms (GAs) as a method to decide near-optimal settings of a GMAW welding process, where the problem was to choose the near best values of three control variables (welding voltage, wire feed rate and welding speed) based on four quality responses (deposition efficiency, bead width, depth of penetration and reinforcement), inside a previous delimited experimental region.
Abstract: This article explores the possibility of using Genetic Algorithms (GAs) as a method to decide near-optimal settings of a GMAW welding process. The problem was to choose the near-best values of three control variables (welding voltage, wire feed rate and welding speed) based on four quality responses (deposition efficiency, bead width, depth of penetration and reinforcement), inside a previous delimited experimental region. The search for the near-optimal was carried out step by step, with the GA predicting the next experiment based on the previous, and without the knowledge of the modeling equations between the inputs and outputs of the GMAW process. The GAs were able to locate near-optimum conditions, with a relatively small number of experiments. However, the optimization by GA technique requires a good setting of its own parameters, such as population size, number of generations, etc. Otherwise, there is a risk of an insufficient sweeping of the search space.
63 citations
TL;DR: In this paper, rough and finish machining conditions were tested using copper and tungsten-copper as materials for the electrodes, and appropriate parameters settings for EDM of the investigated alloy were suggested.
Abstract: High-strength copper alloys are used as materials for injection molding tools or as cores and inserts in steel molds because of their high thermal conductivity, corrosion and wear resistance. Unfortunately, there is little technological knowledge on the electrical discharge machining (EDM) of copper-beryllium ASTM C17200 alloy. In this work, rough and finish machining conditions were tested using copper and tungsten-copper as materials for the electrodes. Cross-sectional micrographic and hardness examinations as well as surface roughness measurements were also carried out on workpieces after machining in order to study the thermally affected zones. Appropriate parameters settings for EDM of the investigated alloy are suggested.
57 citations
TL;DR: In this paper, the performance of the Rohsenow's type of correlation when applied to the nucleate boiling of halocarbon refrigerants over cylindrical surfaces of different material was investigated.
Abstract: This paper reports results from an investigation on the performance of the Rohsenow's type of correlation when applied to the nucleate boiling of halocarbon refrigerants over cylindrical surfaces of different material. Experimental data for refrigerants R-11, R-123, R-12, and R-134a have been raised and fitted according to two different procedures. It has been determined that exponents m and n are weakly affected by the refrigerant, and surface material and finishing. Liquid/surface combinations and surface roughness affect the coefficient Csf. A correlation has been developed for Csf in terms of the liquid/surface combination and surface roughness. The resulting correlation has been evaluated through the experimental data used in the fitting process and results obtained elsewhere. Deviations of correlation with respect to the experimental heat transfer coefficient are within acceptable ranges.
54 citations
TL;DR: In this article, the authors presented the numerical modeling of a plate structure containing bonded piezoelectric material using the Hamilton's principle to derive the finite element equations using the mechanical energy of the structure and the electrical energy of a material.
Abstract: This paper presents the numerical modeling of a plate structure containing bonded piezoelectric material. Hamilton's principle is employed to derive the finite element equations using the mechanical energy of the structure and the electrical energy of the piezoelectric material. Then, a numerical model is developed based on Kirchhoff's plate theory. A computational program is implemented for analyzing the static and dynamic behavior of composite plates with piezoelectric layers symmetrically bonded to the top and bottom surfaces. A set of numerical simulations is performed and the results are compared with those from analytical formulation available in the literature and with software ANSYS® .
53 citations
TL;DR: In this article, the Shape and Directivity Index (SDI) of journal filtered orbits is used to detect rotor-to-stator rubs in a turbine-generator unit.
Abstract: The full spectrum analysis of rotating machine vibrations is a diagnostic tool that enables the symptoms of some special types of fault to be clearly detected. The Shape and Directivity Index (SDI) of journal filtered orbits is an additional diagnostic parameter whose evaluation can be combined with the full spectrum analysis. The ellipticity of the filtered orbit, as well as the amplitude and the inclination angle of the major axis of the orbit, are parameters whose analysis can provide important diagnostic information. In order to validate the proposed approach, the vibrations of a large turbine-generator unit that was subjected to rotor-to-stator rubs have been analyzed in this paper. The results of this investigation have been used to update the model of the rotor-system that has been used to identify the location and the severity of the fault. In the paper, the improvements in the accuracy of the fault identification provided by the model updating enabled by the SDI analysis are shown.
47 citations
TL;DR: This paper presents an application of the Simulated Annealing method to the optimization of trusses considering the cross sections of the members as discrete variables.
Abstract: At present, several methods are available for optimization of structures. The application of such methods to real structural problems, however, has not been as intense as the development of the techniques themselves. One of the main reasons is that the great majority of the methods, based on mathematical programming, consider a continuous search space. This paper presents an application of the Simulated Annealing method to the optimization of trusses considering the cross sections of the members as discrete variables. The constraints imposed to the analysis were the allowable stresses and the displacements on nodes. Some examples are presented in order to demonstrate the effectiveness of the method when compared with other methods found in literature.
TL;DR: In this paper, an analytical method is applied in which the time-varying directional dynamic milling forces coefficients are expanded in Fourier series and integrated in the width of cut bound by entry and exit angles.
Abstract: The prediction of chatter vibrations between the cutter and workpiece is important as a guidance to the machine tool user for an optimal selection of depth of cut and spindle rotation, resulting in maximum chip removal rate without this undesirable vibration. This can be done by some approaches. In this work, an analytical method is applied in which the time-varying directional dynamic milling forces coefficients are expanded in Fourier series and integrated in the width of cut bound by entry and exit angles. The forces in the contact zone between cutter and workpiece during the cut are evaluated by an algorithm using a mathematical model derived from several experimental tests with a dynamometer located between the workpiece and machine table. The algorithm results depend of the physical properties of the workpiece material and the cutter geometry. The modal parameters of the machine-workpiece-tool system like natural frequencies, damping and residues must also be identified experimentally. At this point, it is possible to plot the stability lobes to this dynamic system. These curves relates the spindle speed with axial depth of cut, separating stable and unstable areas, allowing the selection of cutting parameters resulting maximum productivity, with acceptable surface roughness and absence of chatter vibrations. Experimental face milling tests were performed in a knee-type machine, using a five inserts cutter. The results showed perfect agreement between chatter prediction and experimental tests.
TL;DR: In this article, the machinability of the referred material is compared to five different CGI alloys by means of drilling experiments, and a new alloy called CGI-450 was developed with excellent potential qualities for engine block and other auto parts manufacturing.
Abstract: CGI - Compacted Graphite Iron - has reached an important status for automotive industry, mainly in the last ten years. The material has been used for manufacturing parts as brake discs, exhaust manifolds, engine heads and diesel engine blocks. The superior strength characteristics of CGI, as compared to gray iron, allows the manufacturing of engines for higher pressure operating combustion chambers, therefore more efficient and with lower emissions levels. Also thinner walls are possible, generating lighter engines. However there are some technical challenges to overcome, mainly related to the machining process of the parts. This research intends to study the machinability of CGI, in order to develop a new alloy with improved characteristics of machinability, so the production costs for CGI automotive parts can be reduced. The study uses a reference material, gray iron FC-250, widely used for engine blocks manufacturing. The machinability of the referred material is compared to five different CGI alloys by means of drilling experiments. The considered machinability criteria are the tool wear and the cutting forces. The experiments led to the development of a CGI-450 with machinability 83% (relative to FC-250), therefore with excellent potential qualities for engine block and other auto parts manufacturing.
TL;DR: The applicability of the vortex element methods to various engineering problems has been developed and improved dramatically and it has become encouragingly clear that the vortex methods have so much interesting features that they provide easy-to-handle and completely grid-free Lagrangian calculation of unsteady and vortical flows without use of any RANS type turbulent models as discussed by the authors.
Abstract: The purpose of this paper is to explain the attractive applicability of the advanced vortex element methods and their contribution to the beginning of the new generation of CFD, with introduction of epoch-making application of the methods to simulation of unsteady flows around bluff bodies and virtual operation of fluid machinery. The vortex methods have been developed and applied for analysis of complex, unsteady and vortical flows in relation to problems in a wide range of industries, because they consist of simple algorithm based on physics of flow. Nowadays, applicability of the vortex element methods to various engineering problems has been developed and improved dramatically and it has become encouragingly clear that the vortex methods have so much interesting features that they provide easy-to-handle and completely grid-free Lagrangian calculation of unsteady and vortical flows without use of any RANS type turbulent models. In this paper, the mathematical background and numerical procedure of a vortex method developed by the group of the present author are briefly explained, and topics of calculated flows around bluff bodies, an oscillating airfoil, a swimming fish, virtual operation of fluid machinery (pumps and water turbines) are introduced.
TL;DR: In this article, the authors assess the operational behavior of ANSI/AWS A5.1-91 E6013 type electrodes when 0, 8 and 16 % of quartz (100 % SiO2) is replaced with wollastonite (Calcium Silicate, 50 % Si O2 - 50 % CaO) in the coating composition.
Abstract: The main objective of this work was to assess the operational behavior of ANSI/AWS A5.1-91 E6013 type electrodes when 0, 8 and 16 % of quartz (100 % SiO2) is replaced with wollastonite (Calcium Silicate, 50 % SiO2 - 50 % CaO) in the coating composition. The electrodes were tested through bead-on-plate welds in flat position on DC, both polarities, and on AC currents. Arc stability, fusion rate and deposition rate were used as operational characteristics evaluation criteria. The results suggested that the replacement of quartz with wollastonite, that increased slag basicity, kept, or even improved, the typical excellent operational characteristics of E6013 type electrodes.
TL;DR: In this paper, the tensile and Charpy V toughness testing and microhardness measurements were used to evaluate the low-alloy steel weld metals (WM) microstructure.
Abstract: In equipment manufacturing, there are occasions that the base metal (BM) need to be hot or cold worked prior to welding. After welding, the components have to be submitted to a normalizing heat treatment in order to recover its original mechanical properties. In this work four different low alloy steel weld metals (WM) both in the as welded condition and after normalizing heat treatment have been studied. Optical and scanning electron microscopy were used to observe the WM microstructure. Tensile and Charpy V toughness testing and microhardness measurements were used to evaluate the WM mechanical properties. Results show that normalizing breaks the original columnar structure in the as welded condition to an equiaxial structure similar to the one of the BM. Due to low carbon content of the WM it was observed a high decrease on the tensile properties specially the yield strength after normalizing. In respect of toughness, the normalizing heat treatment was observed to increase the Charpy V energy, except for one WM where a great content of martensite-austenite-bainite constituent was formed. Opposite to others post weld heat treatments, normalizing modifies significantly the microstructure and the resulting mechanical properties of the WM. Although normalizing is always beneficial to the BM, care must be taken in order to select welding consumables.
TL;DR: In this article, a mechanistic approach for modeling the thread milling process is presented, where the geometry of threads is added to the end milling tool to calculate the chip load area.
Abstract: A mechanistic approach for modeling the thread milling process is presented. The mechanics of cutting for thread milling is analyzed as an end milling process with modified cutting edge. The geometry of threads is added to the geometry of the end milling tool to calculate the chip load area. The linear path is simulated and values of the specific energy from end milling are used to compute the cutting forces involved. A comparison between the simulation of the cutting forces for a specific tool in two different situations is made to present the force behavior acquired from the model.
TL;DR: In this article, a modified Fowler-Milne method was applied on data taken from TIG welding arc, at low current (40 A), which is selected to contrast to and amplify the current literature focus, i.e., high currents.
Abstract: It is possible to assess the thermal efficiency of welding shielding gases by means of the arc temperature field analysis. Since this approach opens a remarkable study field to assess different shielding gases, giving support for dealing with advantages and disadvantages of commercial gas mixtures, there is a research line under development, which goal is to find techniques to measure arc temperatures. This work describes a proposed method containing different procedures to quantify plasma jet temperature profiles from experimental data. This method was applied on data taken from TIG welding arc, at low current (40 A). This low current was selected to contrast to and amplify the current literature focus, i.e., high currents. The experiment was conducted using emission spectroscopy, picking punctual luminescence from the plasma through an optic system. The TIG arc was stroked on a water-cooled copper plate and shielded by pure argon. The temperature field was determined through the modified Fowler-Milne method. The introduced modification aimed to overcome the limitation that this method has for low radiation intensity presents in low current arcs: the Fowler-Milne method has an intrinsic threshold of 10,000 - 25,000 K. For a 40-A arc, the lower 10,000-K limiting isotherm is reached close to the cathode, restricting the analysis field, especially for the anode region. The proposed modification suggests a linear distribution of the particle density instead of a Maxwellian one, at temperatures below 12,500 K. The experimental temperature field was compared to a previous publication that deals with numerical simulation and the results were found in good agreement, what indicates the supposition of a linear distribution it is not far from the reality.
TL;DR: In this article, the optimal placement of actuators, the model reduction and the controller design through techniques involving linear matrix inequalities (LMI) are considered as constraints in LMI: the decay rate, voltage input limitation in the actuators and bounded output peak (output energy).
Abstract: The study of algorithms for active vibrations control in flexible structures became an area of enormous interest, mainly due to the countless demands of an optimal performance of mechanical systems as aircraft and aerospace structures. Smart structures, formed by a structure base, coupled with piezoelectric actuators and sensor are capable to guarantee the conditions demanded through the application of several types of controllers. This article shows some steps that should be followed in the design of a smart structure. It is discussed: the optimal placement of actuators, the model reduction and the controller design through techniques involving linear matrix inequalities (LMI). It is considered as constraints in LMI: the decay rate, voltage input limitation in the actuators and bounded output peak (output energy). Two controllers robust to parametric variation are designed: the first one considers the actuator in non-optimal location and the second one the actuator is put in an optimal placement. The performance are compared and discussed. The simulations to illustrate the methodology are made with a cantilever beam with bonded piezoelectric actuators.
TL;DR: In this article, the efficiency of the High Velocity Combustion Wire Spray Process (HVCW) for the deposition of X46Cr13 stainless steel coatings is evaluated.
Abstract: Thermally sprayed metallic coatings have been frequently applied over low carbon steel components, aiming at protecting against corrosion and wear. However, these coatings always contain pores, oxides and cracks in the microstructure, which affect the protection performance. The spraying process employed determines not only the amount and distribution of these defects, but also several coating properties (e.g. thickness, hardness and adhesion to the substrate). Therefore, the final coating quality is strongly related to the spray parameters definition, such as: fuel gas type, oxygen pressure, particle velocity and spray distance. This research aims at verifying the efficiency of the High Velocity Combustion Wire spray process (HVCW) for the deposition of X46Cr13 stainless steel coatings. This process submits the particles to higher velocities than those in conventional processes (e.g. flame spraying (FS) and arc spraying (AS)), normally producing more refined microstructures with better properties. The influence of spray parameters has been investigated considering characteristics of the microstructure and mechanical properties, as well as, with respect to the corrosion behavior in synthetic marine solution. The results have confirmed the favorable performance of the HVCW process, which has produced a sufficiently dense coating to prevent damages to the substrate. Additionally, the absorbed oxygen content has been considered adequate to obtain optimized mechanical properties, including wear resistance.
TL;DR: In this article, a methodology for modeling and analyzing fault-tolerant manufacturing systems that not only optimizes normal productive processes, but also performs detection and treatment of faults is presented.
Abstract: This paper introduces a methodology for modeling and analyzing fault-tolerant manufacturing systems that not only optimizes normal productive processes, but also performs detection and treatment of faults. This approach is based on the hierarchical and modular integration of Petri Nets. The modularity provides the integration of three types of processes: those representing the productive process, fault detection, and fault treatment. The hierarchical aspect of the approach permits us to consider processes on different levels of detail (i.e. factory, manufacturing cell, or machine). Case studies considering detection and treatment of faults are presented, and a simulation tool is applied for verifying the models.
TL;DR: In this article, an unstructured finite volume vertex centered formulation, which was implemented using an edge-based data structure, is deduced and detailed for the solution of heat conduction problems.
Abstract: In recent years, there has been a significant level of research on the application of unstructured mesh methods to the simulation of a variety of engineering and scientific problems. Great progress has been achieved in such area and one of the most successful methodologies consists on the use of the Finite Volume Method (FVM). The unstructured FV formulation is very flexible to deal with any kind of control volume and therefore any kind of unstructured meshes, which are particularly important when complex geometries or automatic mesh adaptation are required. In this article, an unstructured finite volume vertex centered formulation, which was implemented using an edge-based data structure, is deduced and detailed for the solution of heat conduction problems. The numerical formulation is initially described considering a tri-dimensional model and latter particularized for bi-dimensional applications using triangular meshes. The presented procedure is very flexible and efficient to solve potential problems. It can also be extended to deal with a broader class of applications, such as models involving convection-diffusion-reaction terms, after considering the appropriate discretization of the convection-type term. In order to demonstrate the potentiality of the method, some model problems are investigated and the results are validated using analytical or other well-established numerical solutions.
TL;DR: In this article, the performance of recently developed nano-grain size ceramic tool materials were evaluated when machining nickel base, Inconel 718, in terms of tool life, tool failure modes and wear mechanisms as well as component forces generated under different roughing conditions.
Abstract: High-speed machining of aerospace alloys can be enhanced by the use of advanced cutting tool materials such as nano-grain size ceramics that exhibit improved physical and mechanical properties than their micron grain counterparts. The performance of recently developed nano-grain size ceramic tool materials were evaluated when machining nickel base, Inconel 718, in terms of tool life, tool failure modes and wear mechanisms as well as component forces generated under different roughing conditions. The tools were rejected mainly due to wear on the tool nose. It is also evident that chemical compositions of the tool materials played significant role in their failure. The alumina base ceramics performed better than the silicon nitride base ceramics. Severe abrasion wear was observed on both rake and flank faces of the cutting tools while cutting forces increased with increasing cutting speed when machining with the silicon nitride base nano-ceramic tools. This is probably due to the lower superplastic flow temperature of the nitride base nano-ceramics. The alumina base ceramics are more susceptible to chipping at the cutting edge than the silicon nitride base ceramics despite their higher edge toughness.
TL;DR: In this article, a methodology that can be applied to complex and simple reservoirs in a reasonable amount of time is presented, discussing especially the influence of the model used to predict recovery, choice of production strategies to be used in the process, number of attributes and type of information necessary to obtain reliable results.
Abstract: Decision analysis applied to petroleum field development is always strongly related to risk due to the uncertainties present in the process. Methodologies to quantify the impact of uncertainties are still not well established due to the amount of variables that have to be considered. The complete analysis usually depends on geological, economical and technological uncertainties that have different degrees of impact in the recovery process and may affect the decision process at different levels depending on the problem, reservoir characteristics, recovery mechanism and stage of field development. This paper shows several details of a methodology that can be applied to complex and simple reservoirs in a reasonable amount of time, discussing especially the influence of the model used to predict recovery, choice of production strategies to be used in the process, number of attributes and type of information necessary to obtain reliable results. A discussion of data integration among geology, reservoir engineering and economic analysis also is presented in order to reduce the amount of information necessary and time for the process. Some results are presented to show the advantages of automation and parallel computing to reduce the total time of the procedure where reservoir simulation is necessary for reservoir performance prediction.
TL;DR: In this paper, a dynamic elastic analysis of semi-rigid plane frames subjected to wind pressures is presented, where the frame material and connections are modeled as zero-length rotational springs.
Abstract: In the analysis and design of framed structures, the traditional methods are based on the simplified assumption that the joints are completely either pinned or rigid. However, the experimental investigations show that the frame connections present an intermediate behaviour between these two extreme cases. The present work is concerned with the dynamic elastic analysis of semi-rigid plane frames subjected to wind pressures. The dynamic excitation induced by the wind is estimated by adopting the simulation method of Monte Carlo. The wind flutuation pressures are decomposed into a limited quantity of harmonic components that are then combined many times, making possible the accomplishment of a probabilistic analysis and the choice of a characteristic response. The frame is considered as a set of contiguous bar elements, connected to each other at the nodes, and the connections are modelled as zero-length rotational springs. A nodal description of the kinetic and kinematic laws is given under the restriction of small displacements. The behaviour of the frame material and connections is described by linear elastic moment-rotation relationships, which are presented in the stiffness form. In order to take into account the effect of the semi-rigid behaviour of beam-to-column connections, the mass and stiffness matrices are developed as the sum of the conventional finite element matrices and correction matrices that incorporate the flexibility of the end joints. The problem of forced vibrations is then solved by means of the numerical integration of the motion equations.
TL;DR: In this paper, the authors evaluated the stress field inside elastic rolling bodies with an elliptic area of contact and showed that shear stress reaches the maximum magnitude below the surface of contact, which explains the presence of shelling defects in service.
Abstract: Railroad wheels fail in two main modes: rolling surface defects like spalling, shelling and wear, and internal defects including cracks propagating after a change takes place in the original stress pattern. Although the effects of the latter are almost always catastrophic, the former is more usual. The onset of rolling surface defects depends on the strength of the surface and the applied loads. The strength is related to surface hardness and can be determined through experimental evaluation under controlled conditions. Evaluating the loads is one of the challenges for contact researchers. This paper presents the evaluation of the stress field inside elastic rolling bodies with an elliptic area of contact. This kind of model can be applied to wheel-rail contact phenomena. Typical high freight transportation loads are used in conjunction with regular recommended wheel and rail sizes. The results have shown that shear stress reaches the maximum magnitude below the surface of contact, and this explains the presence of shelling defects in service. They have also shown that a new model including plasticity is required, because the range of the stresses reached surpasses, by far, the elastic limit
TL;DR: In this paper, a single wire conductive probe was used to measure the void fraction distribution in vertical upward air-water bubbly flows in a square cross-section channel, and the average void fraction ranged from 3.3% to 15%.
Abstract: In this work one shows experimental data and numerical results of the void fraction distribution in vertical upward air-water bubbly flows in a square cross-section channel. To measure the void fraction distribution one used a single wire conductive probe. The averaged void fraction ranged from 3.3% to 15%; the liquid and the gas superficial velocities varied from 0.9 m/s to 3.0 m/s and 0.04 m/s to 0.5 m/s, respectively. The experimental results for the void fraction distribution were compared with numerical calculation performed by an Eulerian-Eulerian implementation of the Two-Fluid Model. In this work one performs the turbulence modeling with three approaches: using an algebraic model, the k-e two-phase model and the k-e two-phase two-layer model. Comparisons between the experimental and numerical data revealed, in general, good agreement.
TL;DR: In this paper, a conductivity probe, consisting in two ring electrodes flush mounted to the pipe, delivered signals from which the time-frequency covariance was calculated from the corresponding Gabor transform, which is capable of detecting transitions by assessing the unstationarity associated with the corresponding transitions.
Abstract: One of the main features associated to multiphase flows is the existence of characteristic dynamic structures according to which the different phases of a mixture of immiscible fluids can flow. The manifestation of one of these structures, known as flow pattern or regime, is determined by the flow rates as well as by physical and geometrical properties of the fluids and piping. The development of flow pattern characterization and diagnostic methods, and the associated transitions in between, is of crucial importance for an efficient engineering of such phenomena. Time-frequency analysis is used in this work to characterize horizontal air-water intermittent flow regimes. More specifically, our main objective is to reveal the existence of sub-regimes inside the intermittent regimes region with the help of the corresponding time-frequency covariance, which is capable of detecting transitions by assessing the unstationarity associated with the corresponding transitions. Experimental tests were conducted at the TALC facility at CEA-Grenoble and an extensive database was obtained, covering several types of intermittent flow. A conductivity probe, consisting in two ring electrodes flush mounted to the pipe, delivered signals from which the time-frequency covariance was calculated from the corresponding Gabor transform.
TL;DR: In this article, a comparative study was performed with two austenitic stainless steels: one of the standard type AISI 304 (18% Cr / 8% Ni/ 1,3% Mn/ 0,07% Cu / 0,033% N, in weight) and other where nickel was partially replaced by manganese, nitrogen and copper.
Abstract: In this work, a comparative study was performed with two austenitic stainless steels: one of the standard type AISI 304 (18% Cr / 8% Ni / 1,3% Mn / 0,07% Cu / 0,033% N, in weight) and other where nickel was partially replaced by manganese, nitrogen and copper (16,3% Cr / 1,5% Ni / 7,4% Mn / 2,9% Cu / 0,184% N, in weight). The aim was to reduce the cost of the final product preserving its good formability and corrosion resistance properties. In order to determine the degree of stability of the austenite, isothermal tensile tests were performed on samples of the two steels in the range of temperature from -25 to 70 oC. The amount of a' martensite formed was measured with a ferrite detector. Microhardness tests showed that the hardness of both steels increase with the amount of induced martensite. Microstructural characterization of the deformed samples was performed by Optical Microscopy and Atomic Force Microscopy. The mechanical properties were studied by tension and formability tests (Erichsen and Swift). It was verified that the AISI 304 steel presents better formability (stretch formability) than the steel with partial substitution of Ni by Mn, Cu and N.
TL;DR: In this article, a numerical model for the simulation of fixed wings aeroelastic response is presented, which treats the aerodynamics and the structural dynamics separately and then couple them in the equations of motion.
Abstract: A numerical model for the simulation of fixed wings aeroelastic response is presented. The methodology used in the work is to treat the aerodynamics and the structural dynamics separately and then couple them in the equations of motion. The dynamic characterization of the wing structure is done by the finite element method and the equations of motion are written in modal coordinates. The unsteady aerodynamic loads are predicted using the vortex lattice method. The exchange of information between the aerodynamic and structural meshes is done by the surface splines interpolation scheme, and the equations of motion are solved iteratively in the time domain, employing a predictor-corrector method. Numerical simulations are performed for a prototype aircraft wing. The aeroelastic response is represented by time histories of the modal coordinates for different airspeeds, and the flutter occurrence is verified when the time histories diverge (i.e. the amplitudes keep growing). Fast Fourier Transforms of these time histories show the coupling of frequencies typical of the flutter phenomenon.