Showing papers in "Journal of The Brazilian Society of Mechanical Sciences and Engineering in 2007"
TL;DR: In this paper, a discussion on the particularities of the pressure drop equations being used in the design of natural gas pipelines is carried out and several versions are presented according to the different flow regimes under consideration and the basic physical support for each one is discussed as well as their feasibility.
Abstract: In this work a discussion on the particularities of the pressure drop equations being used in the design of natural gas pipelines will be carried out. Several versions are presented according to the different flow regimes under consideration and through the presentation of these equations the basic physical support for each one is discussed as well as their feasibility.
94 citations
TL;DR: In this paper, the results of an experimental finish machining with graphite and copper as tool electrodes were investigated, and the measured technological outputs were the material removal rate Vw, volumetric relative wear ϑ and workpiece surface finish Ra.
Abstract: The machining parameter settings installed at CNC EDM machines are developed under optimum process conditions. Standard workpiece and electrode materials are used traditionally by machine manufacturers to establish the EDM parameter settings. However, this is not the usual situation of the tooling industry, where many different grades of workpiece and tool electrode materials are used. Consequently, the customers are required to develop their own process parameters, which normally demand many experimental tests. According to the aforementioned argument an experimental er finish machining has been carried out. The tests were performed with graphite and copper as tool electrodes. Important EDM electrical parameters that influence the process performance were investigated. The measured technological outputs were the material removal rate Vw, volumetric relative wear ϑ and workpiece surface finish Ra . The main conclusions can be summarized as follows: the best results for material removal rate Vw were reached when EDM with negative graphite electrodes. Graphite and copper tools presented similar results of Vw for positive polarity. For graphite and copper tools the lowest values of volumetric relative wear were achieved for positive polarity. The best surface roughness Ra was obtained for copper electrodes under negative polarity. Keywords : sinking EDM, graphite and copper electrodes, tool steel, process parameters
75 citations
TL;DR: In this paper, specific cutting energy measurements as a function of the cutting speed and tool cutting edge geometry were performed on a vertical CNC machining center with 7,500 rpm spindle rotation and 7.5 kW power.
Abstract: This paper presents specific cutting energy measurements as a function of the cutting speed and tool cutting edge geometry. The experimental work was carried out on a vertical CNC machining center with 7,500 rpm spindle rotation and 7.5 kW power. Hardened steels ASTM H13 (50 HRC) were machined at conventional cutting speed and high-speed cutting (HSC). TiN coated carbides with seven different geometries of chip breaker were applied on dry tests. A special milling tool holder with only one cutting edge was developed and the machining forces needed to calculate the specific cutting energy were recorded using a piezoelectric 4-component dynamometer. Workpiece roughness and chip formation process were also evaluated. The results showed that the specific cutting energy decreased 15.5% when cutting speed was increased up to 700%. An increase of 1o in tool chip breaker chamfer angle lead to a reduction in the specific cutting energy about 13.7% and 28.6% when machining at HSC and conventional cutting speed respectively. Furthermore the workpiece roughness values evaluated in all test conditions were very low, closer to those of typical grinding operations (~0.20 mm). Probable adiabatic shear occurred on chip segmentation at HSC.
60 citations
TL;DR: In this article, an experimental study of both wear and friction responses of lubricated sliding tests, considering both responses in Stribeck diagram were also done. And the use of a wear coefficient similar to that of Archard equation for characterizing sliding wear behavior is discussed.
Abstract: This paper deals with an experimental study of both wear and friction responses of lubricated sliding tests, considering both responses in Stribeck diagram. Analyses concerning the wear coefficient by Archard equation were also done. Tests were oil-bath lubricated, performed through a machine with devices for rotating pin-on-disk and reciprocating pin-on-plate tests. Tested specimens were pins of AISI52100 steel and counter-bodies of AISI8640 steel. Presence of additives and contamination in lubricant oil was investigated under two mechanical loading levels, determined by the velocity/load ratio. Wear was studied by means of optical microscope and dimensional analysis of the worn surfaces. The use of a wear coefficient similar to that of Archard equation for characterizing sliding wear behavior is discussed. Differences were observed in the wear trend of the rotating and the reciprocating tests in terms of Stribeck parameters considerations.
50 citations
TL;DR: In this paper, a two-step autoregressive and auto-regressive with exogenous inputs (AR-ARX) model was used for linear prediction of damage diagnosis in structural systems.
Abstract: Structural health monitoring (SHM) is related to the ability of monitoring the state and deciding the level of damage or deterioration within aerospace, civil and mechanical systems. In this sense, this paper deals with the application of a two-step auto-regressive and auto-regressive with exogenous inputs (AR-ARX) model for linear prediction of damage diagnosis in structural systems. This damage detection algorithm is based on the monitoring of residual error as damage-sensitive indexes, obtained through vibration response measurements. In complex structures there are many positions under observation and a large amount of data to be handed, making difficult the visualization of the signals. This paper also investigates data compression by using principal component analysis. In order to establish a threshold value, a fuzzy c-means clustering is taken to quantify the damage-sensitive index in an unsupervised learning mode. Tests are made in a benchmark problem, as proposed by IASC-ASCE with different damage patterns. The diagnosis that was obtained showed high correlation with the actual integrity state of the structure.
40 citations
TL;DR: In this paper, a skin friction equation for the turbulent flow of Carreau-Yasuda fluids was derived assuming a logarithmic behavior of the turbulent mean velocity for the near wall flow out of the viscous sub layer.
Abstract: In this work the turbulent flow of the Non-Newtonian Carreau-Yasuda fluid will be studied. A skin friction equation for the turbulent flow of Carreau-Yasuda fluids will be derived assuming a logarithmic behavior of the turbulent mean velocity for the near wall flow out of the viscous sub layer. An alternative near wall characteristic length scale which takes into account the effects of the relaxation time will be introduced. The characteristic length will be obtained through the analysis of viscous region near the wall. The results compared with experimental data obtained with Tylose (methyl hydroxil cellulose) solutions showing good agreement. The relations between scales integral and dissipative obtained for length, time, velocity, kinetic energy, and vorticity will be derived for this type of fluid. When the power law index approach to unity the relations reduces to newtonian case.
31 citations
TL;DR: A validation of the hybrid method for numerical simulation of room acoustics in an international inter-comparison with other softwares and measurements data is presented, showing the efficiency and the accuracy of the proposed hybrid method over non-hybrid ones.
Abstract: A new hybrid simulation method for room acoustics is presented. It is grounded on two well known numerical simulation techniques for room acoustics. The hybrid method takes geometric acoustics for granted and uses an improved version of the classical ray-tracing technique for computing the specular reflections and a slightly modified energy transition method for simulating the diffuse reflections. The impulse responses (IRs) are then computed by superposition of the specular and diffuse ones. The reverberant part of the IRs gains a much more realistic aspect than the one obtained from either ones method alone. Both the ray-tracing technique and the energy transition method are reviewed and some improved features are discussed. The sound source and the receiver modeling are presented, including a new method for simulating the head related transfer functions (HRTFs), and based on the wavelet technique, which provides a shorter time computation of the binaural impulse responses for auralization purposes. In a companion paper, entitled Hybrid method for numerical simulation of room acoustics: Part 2 – Validation of the computational code RAIOS 3, a validation of the method in an international inter-comparison with other softwares and measurements data is presented, showing the efficiency and the accuracy of the proposed hybrid method over non-hybrid ones. Keywords: computer modeling, room acoustics, hybrid method, auralization
22 citations
TL;DR: In this paper, a two-dimensional numerical simulation of flows around different bluff bodies, at Re = 100 and 200, using the Immersed Boundary (IB) method, as a sequence of a previous work is presented.
Abstract: This paper presents a two-dimensional numerical simulation of flows around different bluff bodies, at Re = 100 and 200, using the Immersed Boundary (IB) method, as a sequence of a previous work. The force density term required by the IB method is obtained with the Virtual Physical Model (VPM). Simulations were carried out for two circular cylinders of different diameter in tandem, two cylinders of the same diameter in tandem and two cylinders placed in side by side arrangement. The configurations of seven cylinders in a 'V' arrangement, for angles of 40o < a < 180o, were also simulated. A configuration of 23 different bluff bodies, representing a transverse cut in a central tower of an offshore structure, has been also simulated and the results were compared with a single compact square, of equivalent size. The Strouhal number, the drag and the lift coefficients were also calculated. The Strouhal number is calculated using the Fast Fourier Transform (FFT) of the lift coefficient temporal distribution. Visualization of the vorticity and pressure fields and the streamlines are presented for each simulation showing the flow dynamics and patterns. It was possible to verify that the IB method with VPM is a powerful methodology to simulate flows in the presence of complex geometries.
21 citations
TL;DR: In this paper, the weak patch test of the graded element for non-homogeneous materials is used to assess convergence of the finite element method (FEM) in the boundary value problem.
Abstract: Functionally graded materials have an additional length scale associated to the spatial variation of the material property field which competes with the usual geometrical length scale of the boundary value problem. By considering the length scale of nonhomogeneity, this paper presents the weak patch test (rather than the standard one) of the graded element for nonhomogeneous materials to assess convergence of the finite element method (FEM). Both consistency (as the size of elements approach zero, the FEM approximation represents the exact solution) and stability (spurious mechanisms are avoided) conditions are addressed. The specific graded elements considered here are isoparametric quadrilaterals (e.g. 4, 8 and 9-node) considering two dimensional plane and axisymmetric problems. The finite element approximate solutions are compared with exact solutions for nonhomogeneous materials.
20 citations
TL;DR: In this article, the authors present the results and methodology used to calibrate the thermal power of the TRIGA Mark I IPR-R1 Research Reactor at the Nuclear Technology Development Centre (CDTN), in Belo Horizonte, Brazil.
Abstract: This paper presents the results and methodology used to calibrate the thermal power of the TRIGA Mark I IPR-R1 Research Reactor at the Nuclear Technology Development Centre (CDTN), in Belo Horizonte, Brazil. The TRIGA Mark I is a pool type reactor, cooled by water natural convection. The method used in the calibration consisted in the steady-state energy balance of the primary cooling loop of the reactor. For this balance, the inlet and outlet temperatures and the water flow in this primary cooling loop were measured. The heat transferred through the primary loop was added to the heat leakage from the reactor pool. The thermal losses from the primary loop were not evaluated since the inlet and outlet temperatures were measured just above the water surface of the reactor pool. The temperature of the water in the reactor pool as well as the reactor room temperature were set as close as possible to the soil temperature to minimize heat leakages. These leakages are mainly due to the conduction through the concrete and metal walls and also due to the evaporation and convection through the water surface of the reactor pool.
20 citations
TL;DR: In this article, the steady state vibration of a rotor bearing system is modeled as two degrees of freedom elements where the kinematics of the rolling elements are considered, so are the internal clearance and the Hertz contact nonlinearity.
Abstract: This work is about the steady state vibration of a rotor bearing system. The rolling bearings are modeled as two degrees of freedom elements where the kinematics of the rolling elements is considered, so are the internal clearance and the Hertz contact nonlinearity. The steady state solution of the system is achieved by the harmonic balance method, validated by a numerical integration using a three-point-centered finite difference scheme. The number of harmonics employed in the harmonic balance method is examined to find the satisfactory quantity of harmonics that can describe the system dynamics. The contact regimes in the rolling elements are also explored.
TL;DR: In this article, the numerical simulation of internal recirculating flows encompassing a two-dimensional viscous incompressible flow generated inside a regularized square driven cavity and over a backward-facing step is performed by using the projection method combined with a Chebyshev collocation spectral method.
Abstract: This paper concerns the numerical simulation of internal recirculating flows encompassing a two-dimensional viscous incompressible flow generated inside a regularized square driven cavity and over a backward-facing step. For this purpose, the simulation is performed by using the projection method combined with a Chebyshev collocation spectral method. The incompressible Navier-Stokes equations are formulated in terms of the primitive variables, velocity and pressure. The time integration of the spectrally discretized, incompressible Navier-Stokes equations is performed by a second-order mixed explicit/implicit time integration scheme. This scheme is a combination of the Crank-Nicolson scheme operating on the diffusive terms and a second-order Adams-Bashforth scheme acting on the advective terms. The projection method is used to split the solution of the incompressible Navier-Stokes equations in two decoupled problems: the Burgers equation to predict an intermediate velocity field and the Poisson equation for the pressure, which is used to correct the intermediate velocity field and satisfy the continuity equation. Numerical simulations for flows inside a two-dimensional regularized square driven cavity for Reynolds numbers up to 10000 and over a backward-facing step for Reynolds numbers up to 875 are presented and compared with numerical results previously published, where good agreement is demonstrated.
TL;DR: It will be shown that the proposed hybrid method for numerical simulation of room acoustics with auralization results in very reliable and accurate predictions of the main acoustical parameters: T30, EDT, C80, D50, TS, G, LF and LFC.
Abstract: In the companion paper "Hybrid method for numerical simulation of room acoustics with auralization: Part 1- Theoretical and numerical aspects" a new hybrid method for numerical simulation of room acoustics, implemented by the software RAIOS 3, was presented. Here, the software itself and its main features are discussed. It will be shown that the proposed method actually results in very reliable and accurate predictions of the main acoustical parameters: T30, EDT, C80, D50, TS, G, LF and LFC. The performance of RAIOS 3 was assessed in an international intercomparison, coordinated by the Physikalisch-Technische Bundesanstalt, in Germany, where measured acoustical parameters where compared to those predicted by 9 different software. Due to the hybrid method proposed, the comparative results shown a very good agreement between the parameters predicted by our software and the measurements, even in a somewhat diffuse condition. In a statistical evaluation, the results obtained by the numerical code RAIOS 3, stayed among the top 10%. The strong dependency of the predicted acoustical parameters on reliable room data, especially absorption and diffusion coefficients, is also discussed.
TL;DR: In this paper, the authors analyse the behavior of steel beams under uniform temperature rising and three boundary conditions: simply supported (pin-roller), simply supported with axial restraint (pinned-pinned), and both ends fixed (fixed-fixed).
Abstract: Structures load resistance is reduced when subject to high temperatures in fire. Nevertheless, it is not enough to take into account strength and modulus of elasticity reduction. One must know with great accuracy the behaviour of the structures including the realistic boundary conditions at high temperatures, in order to determine for safe and of low cost solutions. This work is intended to analyse the behaviour of steel beams under uniform temperature rising. It covers beams under several uniform load levels and three boundary conditions: simply supported (pin-roller), simply supported with axial restraint (pinned-pinned) and both ends fixed (fixed-fixed). The variation of deflection, critical temperature, bending moment, normal force and stresses, with the temperature is presented. The analyses were made with the aid of ANSYS computer software taking into account material and geometric non-linearities and the variation of the stress-strain diagram with the temperature.
TL;DR: An algorithm for converting CSG models into triangulated solid models through propagation based marching cubes algorithm is proposed and three main new concepts are used in the algorithm: open boundary, B-Rep/CSG Voxelization mapping and constructive triangulation of active cells.
Abstract: The purpose of this work is to define a new algorithm for converting a CSG representation into a B-Rep representation. Usually this conversion is done determining the union, intersection or difference from two B-Rep represented solids. Due to the lack of explicit representation of surface boundaries, CSG models must be converted into B-Rep solid models when a description based on polygonal mesh is required. A potential solution is to convert a CSG model into a voxel based volume representation and then construct a B-Rep solid model. This method is called CSG voxelization, conceptually it is a set membership classification problem with respect to the CSG object for all sampling points in a volume space. Marching cubes algorithms create a simple mesh that is enough for visualization purposes. However, when engineering processes are involved, a solid model is necessary. A solid ensures that all triangles in the mesh are consistently oriented and define a closed surface. It is proposed in this work an algorithm for converting CSG models into triangulated solid models through propagation based marching cubes algorithm. Three main new concepts are used in the algorithm: open boundary, B-Rep/CSG Voxelization mapping and constructive triangulation of active cells. The triangles supplied by the marching cubes algorithm need not be coherently oriented; the algorithm itself finds the correct orientation for the supplied triangles. The proposed algorithm restricts the exploration to the space occupied by the solid's boundary. Differently from normal marching cubes algorithms that explore the complete sampled space.
TL;DR: In this paper, a method to use free form features to improve the automatic generation of high speed machining information for specific geometric areas to create HSC free form manufacturing features is presented.
Abstract: High speed cutting (HSC) offers the opportunity to significantly reduce machining times as well as to minimize manual rework for complex free form surfaces in the die and mould making industry. To achieve the best results it is also necessary to apply HSC-suitable machining strategies to perform optimal high speed milling operations. This paper presents a method to use free form features to improve the automatic generation of high speed machining information for specific geometric areas to create HSC free form manufacturing features. By examining the geometrical and topological information of the work pieces virtual model, the feature elements can be extracted and joined with the required information. This covers several important high speed cutting aspects in the CAM system, like optimal technology and strategy suggestion, machining safety requirements and process stability of different strategies. Using this approach the programming time to produce HSC appropriate tool paths is reduced significantly, while it is quality is secured.
TL;DR: In this paper, a study of the BUE geometry of a SAE 12L14 steel machined at low speeds with and without a cutting fluid was performed on three quick-stop samples.
Abstract: A well known phenomenon, the “built-up edge – BUE”, occurs at the chip/tool interface when multiphase materials are machined at low cutting speeds. Under high compressive stresses, seizure prevents the material from sliding over the tool’s rake face. Although many reports have been published on the subject, studies of the BUE phenomenon have been marked by a lack of precision in determining its dimensions. This paper reports on a study of the BUE geometry of a SAE 12L14 steel machined at low speeds with and without a cutting fluid. Three quick-stop samples were prepared for each test condition (9 cutting speeds, with and without cutting fluid). The quick-stop samples were mounted perpendicularly in transparent acrylic resin to facilitate observation and the hardened resin sandpapered. The opposite face of the mounted sample was then ground to make the front and back faces parallel. After sandpapering and polishing, the samples were digitally photographed and their BUE geometries determined using an image analyzer. The measurements were done along the cutting width at five different points. It was found that the BUE dimensions varied considerably along the cutting width, and that the fluid reduced the BUE at the lowest cutting speed tested. Keywords: built-up-edge, quick-stop, SAE 12L14 steel
TL;DR: In this article, the authors proposed an alternative structural analysis modeling strategy for guyed steel towers design, considering all the actual structural forces and moments, by using three-dimensional beam and truss finite elements.
Abstract: The usual structural analysis models for telecommunication and transmission steel tower design tend to assume a simple truss behaviour where all the steel connections are considered hinged. Despite this fact, the most commonly used tower geometries possess structural mechanisms that could compromise the assumed structural behaviour. A possible explanation for the structure stability is related to the connections semi-rigid response instead of the initially assumed pinned behaviour. This paper proposes an alternative structural analysis modelling strategy for guyed steel towers design, considering all the actual structural forces and moments, by using three-dimensional beam and truss finite elements. Comparisons of the above mentioned design models with a third alternative, that models the main structure and the bracing system with 3D beam finite elements, are made for three existing guyed steel telecommunication towers (50m, 70m and 90m high). The comparisons are initially based on the towers static and dynamic structural behaviour later to be followed by a linear buckling analysis to determine the influence of the various modelling strategies on the tower stability behaviour.
TL;DR: In this paper, a numerical method based on the vortex methodology is presented in order to obtain unsteady solution of the aerodynamic coefficients of a thin airfoil in either compressible subsonic or supersonic flows.
Abstract: A numerical method based on the vortex methodology is presented in order to obtain unsteady solution of the aerodynamic coefficients of a thin airfoil in either compressible subsonic or supersonic flows. The numerical model is created through the profile discretization in uniform segments and the compressible flow vortex singularity is used. The results of the proposed model are presented as the lift and the pressure coefficient along the profile chord as a function of time. The indicial response for the unit step change of angle of attack and unit sharp-edged gust response of the profile are also obtained numerically. The results yielded by the present methodology are also compared with solutions available in the literature.
TL;DR: In this paper, the authors demonstrate that scratch test techniques can be used to provide a quick and cost effective evaluation of cutting fluids, and demonstrate that the linear scratch test was not efficient while the pendular scratch test is efficient tool in the classification of cutting fluid.
Abstract: This work demonstrates that scratch test techniques can be used to provide a quick and cost effective evaluation of cutting fluids. Apparent coefficient of friction and specific energy for the scratch steel samples under several lubrication conditions provides a good indicator of cutting fluid performance. This is followed by evaluation of the surface finish and the cutting force of the ABNT NB 8640 steel with emulsion and synthetic cutting fluids, at 5% of concentrations, and neat mineral oil in the turning process. Comparative tests were carried out under dry and wet conditions. Results show that the linear scratch test was not efficient while the pendular scratch test was efficient tool in the classification of cutting fluids. The results can be transferred to conventional machining due to its dynamic nature.
TL;DR: In this paper, a study about the use of the out-of-phase current pulses technology applied to the double-wire MIG/MAG welding process with insulated potential on welded coating is presented.
Abstract: The part 1 of this work presents a study about the use of the out-of-phase current pulses technology applied to the Double Wire MIG/MAG welding process with Insulated Potentials on welded coating. High-speed digital back-lighted images were recorded to evaluate the influence of the levels of out-of-phase current pulses on the behavior of both metallic transfer modes and voltaic arcs configurations. The results showed that, with the electrodes positioned side by side and the mean currents below the transition current, the out-of-phasing parameter setting reduces the deviations of the arcs and changes the paths of the droplets. However, no significant effect was noticed on bead finishing or arc stability.
TL;DR: This work analyses a real time orbit estimator using the raw navigation solution provided by GPS receivers, which considers a Kalman filter with a rather simple orbit dynamic model and random walk modeling of the receiver clock bias and drift.
Abstract: This work analyses a real time orbit estimator using the raw navigation solution provided by GPS receivers. The estimation algorithm considers a Kalman filter with a rather simple orbit dynamic model and random walk modeling of the receiver clock bias and drift. Using the Topex/Poseidon satellite as test bed, characteristics of model truncation, sampling rates and degradation of the GPS receiver (Selective Availability) were analysed.
TL;DR: In this article, the effects of synthetic jet actuators on the flow of the boundary layer developed on a flat plate and on a hypothetical airfoil were analyzed using a spatial Direct Numerical Simulation (DNS).
Abstract: This work has as a fundamental objective the numerical study of the effects of synthetic jet actuators on the flow of the boundary layer developed on a flat plate and on a hypothetical airfoil. The aim is to obtain computational data to indicate how these effects may be used as a means of flow control, describing the dynamics of the synthetic jet in the presence of external flow. The present paper uses a spatial Direct Numerical Simulation (DNS) to solve the incompressible Navier-Stokes equations, written in vorticity-velocity formulation. The spatial derivatives are discretized with a sixth order compact finite difference scheme. The Poisson equation for the normal velocity component is solved by an iterative Line Successive Over Relaxation Method and uses a multigrid Full Approximation Scheme to accelerate the convergence. The results of simulations with different values of frequency, amplitude and slot length were analyzed through a temporal Fourier analysis. Through this analysis the decision as to which are the better parameters to delay the separation of the boundary layer is examined.
TL;DR: In this article, a flexible mount system was developed for flutter tests in wind tunnels and the dimensions of the system were determined by finite element analysis and verified with an Aeroelastic Model.
Abstract: Aeroelastic instabilities may occur in aircraft surfaces, leading then to failure. Flutter is an aeroelastic instability that results in a self-sustained oscillatory behaviour of the structure. A two-degree-of-freedom flutter can occur with coupling of bending and torsion modes. A flexible mount system has been developed for flutter tests in wind tunnels. This apparatus must provide a well-defined 2DOF system on which rigid wings encounter flutter. Simulations and Experimental Tests are performed during the design period. The dimensions of the system are determined by Finite Element analysis and verified with an Aeroelastic Model. The system is modified until first bending and torsion modes become the first and second modes and other modes become higher than these. After this, a Modal Analysis is performed. An identification algorithm, ERA, is used to determine modes shape and frequencies from experimental data. Detailed results are presented for first bending and torsion modes, which are involved in flutter. The flutter mechanism is demonstrated by Frequency Response Functions obtained in several wind tunnel velocities until flutter achievement and by a V-g-f plot obtained from an identification process performed with an extended ERA. Mode coupling, damping behaviour and the self-sustained oscillatory behaviour are verified characterising flutter.
TL;DR: In this paper, a Pulse Width Modulation (PWM) speed controller for an electric mini-baja-type car is presented, which is implemented by a low-cost 8-bit microcontroller with optimized ROM charts for distinct speed value implementations, synchronized transition between different charts and reduced odd harmonics generation.
Abstract: This paperwork presents a Pulse Width Modulation (PWM) speed controller for an electric mini-baja-type car. A battery-fed 1-kW three-phase induction motor provides the electric vehicle traction. The open-loop speed control is implemented with an equal voltage/frequency ratio, in order to maintain a constant amount of torque on all velocities. The PWM is implemented by a low-cost 8-bit microcontroller provided with optimized ROM charts for distinct speed value implementations, synchronized transition between different charts and reduced odd harmonics generation. This technique was implemented using a single passenger mini-baja vehicle, and the essays have shown that its application resulted on reduced current consumption, besides eliminating mechanical parts.
TL;DR: In this paper, the developing region of an axially symmetric laminar flow from a reservoir to a sharp-edged tube is numerically simulated with a primitive-variables solver of the Navier-Stokes equations, using a plenum upstream of the tube inlet in order to avoid arbitrary specification of the profile at the inlet.
Abstract: The developing region of an axially symmetric laminar flow from a reservoir to a sharp-edged tube is numerically simulated with a primitive-variables solver of the Navier-Stokes equations, using a plenum upstream of the tube inlet in order to avoid arbitrary specification of the profile at the inlet. Development region lengths, velocity profiles and head losses for varying Reynolds numbers are obtained. Results are compared to available experimental and theoretical results.
TL;DR: In this article, the effects of design parameters viz. mass flow rate of air, immersion ratio, diameter of rising main etc. on the performance of air lift pump are presented.
Abstract: Airlift pumps are finding increasing use where pump reliability and low maintenance are required, where corrosive, abrasive, or radioactive fluids must be handled and when a compressor is readily available. The objective of the present study is to evaluate the performance of a pump under predetermined operating conditions and to optimize the related parameters The effects of design parameters viz. mass flow rate of air, immersion ratio, diameter of rising main etc. on the performance of airlift pump are presented. The larger diameter of rising main is found to be suitable for high flow rate of water. The injecting device used in the system has considerable effect on the performance of the pump. The paper is focused on the general mathematical expression to determine the effective diameter of nozzle applicable to air lift pump installations in the diameter range of 25.4 mm < d < 101.6 mm. The various types of flows are visualized in the rising main of a pump and the corresponding airlift pump performance is analyzed. It is observed that the slug flow is more predominant for improving the performance of the pump.
TL;DR: In this paper, a simple model for roll stack deflection at the finishing mill has been illustrated where a modified Misakas equation has been used to obtain mean flow-stress.
Abstract: Predictive models are required to provide the bending set point for bending for the flatness control devices at rolling stands of finishing mill of Hot Strip Mill (HSM). A simple model for roll stack deflection at the finishing mill has been illustrated where a modified Misakas equation has been used to obtain mean flow-stress. Investigation has been performed to understand the effect of width of roll on roll stack deflection. The bending on the deflection has been found to have a positive effect to reduce the amount of the stack deflection. The results from the sensitivity analysis of the roll width on roll deflection are also described.
TL;DR: In this article, the results of in-situ re-crystallization annealing of micromachined silicon were monitored by micro-Raman spectroscopy, and it was also shown that the annesaling heat treatment influenced surface roughness.
Abstract: Mechanical material removal during ultraprecision machining of semiconductors crystals normally induces surface damage. In this article, Raman micro-spectroscopy has been used to probe structural alteration as well as residual stresses in the machined surface generated by single point diamond turning. The damage found is characterized by an amorphous phase in the outmost surface layer. In addition, it is reported, for the first time, the results of in-situ re-crystallization annealing of micromachined silicon monitored by micro-Raman spectroscopy. It is also shown that the annealing heat treatment influenced surface roughness: results were Rmax equal to 24.2 nm and 47.3 nm for the non treated and for the annealed surfaces, respectively.
TL;DR: In this paper, the authors demonstrate the importance of adequately estimating the discretization error intrinsic in the result of any numerical simulation, and propose a method to analyze the effect of the distance between the tubes, aiming to optimize the heat exchanger's geometrical configuration.
Abstract: This paper aims to demonstrate the importance of adequately estimating the discretization error intrinsic in the result of any numerical simulation. The problem under consideration is forced convection in a staggered circular tube heat exchanger. The problem is solved to analyze the effect of the distance between the tubes, aiming to optimize the heat exchangers geometrical configuration by two Reynolds numbers (50 and 100). The present work did not confirm the existence of an optimal geometrical point for the operation of staggered circular tube heat exchangers, as claimed in a numerical study published in the literature.