Showing papers in "Journal of The Brazilian Society of Mechanical Sciences and Engineering in 2011"
TL;DR: The article purpose is to pave the way to the construction of generic calibration systems easily adapted to any type of robot, regardless of their application, such as modular robots and robot controllers specifically designed for non-standard applications.
Abstract: One of the greatest challenges in today's industrial robotics is the development of off-line programming systems that allow drastic reduction in robots' reprogramming time, improving productivity. The article purpose is to pave the way to the construction of generic calibration systems easily adapted to any type of robot, regardless their application, such as modular robots and robot controllers specifically designed for non-standard applications. A computer system was built for developing and implementing a calibration system that involves the joint work of computer and measurement systems. Each step of this system's development is presented together with its theoretical basis. With the development of a remote maneuvering system based on ABB S3 controller experimental tests have been carried out using an IRB2000 robot and a measurement arm (ITG ROMER) with 0.087 mm of position measurement accuracy. The robot model used by its controller was identified and the robot was calibrated and evaluated in different workspaces resulting in an average accuracy improvement from 1.5 mm to 0.3 mm.
51 citations
TL;DR: In this paper, a half-vehicle dynamic model with a two-point delayed base excitation was developed to correlate with the spectral density function of the pavement roughness, to obtain the system spectral transfer function in the frequency domain.
Abstract: The goal of the present study is the development of a spectral method to obtain the frequency response of the half-vehicle subjected to a measured pavement roughness in the frequency domain. For this purpose, a half-vehicle dynamic model with a two-point delayed base excitation was developed to correlate with the spectral density function of the pavement roughness, to obtain the system spectral transfer function, in the frequency domain. The vertical pavement profile was measured along two roads sections. The surface roughness was here expressed in terms of the spectral density function of the measured vertical pavement profile with respect to the evenness wave number of the pavement roughness. A frequency response analysis was applied to obtain the vertical and angular modal vehicle dynamic response with the excitation of the power spectral density (PSD) of the pavement roughness. The results show that at low speed, the vehicle suspension mode is magnified due to the unpaved track signature. At 120 km/h in an undulated asphalted road, the first vehicle vibration mode has a significant motion amplification, which may cause passenger discomfort.
37 citations
TL;DR: In this article, three nonintrusive optical techniques were combined and employed to determine the velocity field and bubble shape: particle image velocimetry (PIV), Pulsed Shadow Technique (PST) and Laser-Induced Fluorescence technique (LIF).
Abstract: The present paper reports the results of an ongoing project aimed at providing statistical information on slugs in two-phase flow in a horizontal pipe. To this end, the flow was examined experimentally and numerically. On the experimental side, three non-intrusive optical techniques were combined and employed to determine the velocity field and bubble shape: particle image velocimetry (PIV), Pulsed Shadow Technique (PST) and Laser-Induced Fluorescence technique (LIF). Statistical information was provided by photogate cells installed at two axial positions. The flow was numerically determined based on the one-dimensional Two-Fluid Model. The tests were conducted on a specially built transparent pipe test section, using air and water as the working fluids. The velocity fields were obtained for flow regimes where the slugs were slightly aerated to facilitate the utilization of the optical methods employed. The main parameters for characterizing the statistically steady flow regime such as slug length and velocity obtained numerically were compared with the experimental data and good agreement was obtained.
36 citations
TL;DR: In this article, the performance of four material model sets of the Johnson-Cook constitutive equation in modeling the deformation behavior of Ti6Al4V alloy is compared with results from orthogonal cutting experiments on a tube of the work material.
Abstract: The machining of titanium alloys poses several inherent difficulties owing to their unique mechanical properties and cutting characteristics. Finite element (FE) simulations have reduced the burden of extensive experimental trials in understanding the deformation behavior and optimize the cutting process. The FE code relies on the qualitative nature of inputs such as material flow stress model, friction conditions, fracture criterions and the accuracy of the modeling process. The aim of this paper is to assess the performance of four material model sets of the Johnson-Cook (JC) constitutive equation in modeling the deformation behavior of Ti6Al4V alloy. The FE output at steady state conditions is compared with results from orthogonal cutting experiments on a tube of the work material. The effect of the parameters of the JC law and the capabilities of the constitutive equation are analyzed. The FE model is excellent in predicting the effective stress, strain and temperature, but produces marginal deviations in cutting force and chip morphology predictions and under predicts the feed forces. The material model constants computed through an evolutionary computational optimization process and those with conditions similar to machining produced good correlation with experiments.
32 citations
TL;DR: In this paper, the surface analysis of nanomachined AISI D2 tool steel materials is measured using atomic force microscopy, the results indicate that the fractal dimension changed according to the smoothness of the machined surface.
Abstract: The surface analysis of nanomachined AISI D2 tool steel materials is measured using atomic force microscopy. The surface roughness and fractal dimensional analysis are the important factors in nano tribology and evaluating the quality of nanomachined surface. Carbon nanotube increases the heat carrying capacity, thermal conductivity of the lubricating oil and thus prevents any damage to the work piece. The surface morphology of different machined surface was studied by Fractal Dimension analysis and roughness characterization was carried out. The results indicate that the fractal dimension changed according to the smoothness of the machined surface. The Power Spectrum Density (PSD) method based Root mean square (Rms) surface roughness was calculated for carbon nano tube based nanofluids in grinding process. The fractal dimension and roughness are decreased due to single wall carbon nano tube based nanofluids and smooth surface finish has been obtained.
28 citations
TL;DR: In this paper, an analysis of active-passive damping performance of beams with extension and shear APPN is presented and a coupled finite element model with mechanical and electrical degrees of freedom is developed and used to design passive and active control parameters.
Abstract: Active-Passive Piezoelectric Networks (APPN) integrate active voltage sources with passive resistance-inductance shunt circuits to a piezoelectric patch. This technique allows to simultaneously passively dissipate vibratory energy through the shunt circuit and actively control the structural vibrations. This work presents an analysis of active-passive damping performance of beams with extension and shear APPN. A coupled finite element model with mechanical and electrical degrees of freedom is developed and used to design passive and active control parameters. Then, stochastic modeling and analyses of two cantilever beam configurations, with extension and shear APPN, are performed to evaluate the effect of uncertainties in circuit components on passive and active-passive vibration control. Results show that active-passive shunt circuits can be very interesting since they may combine an adequate passive control performance with an increase of active control authority when a control voltage is applied to the circuit. For the extension configuration, vibration amplitude reductions of up to 22 dB and 28 dB are obtained for passive and active-passive cases, respectively. Considering relative dispersions of 10% for the resistance and inductance values, the passive and active-passive amplitude reductions are found to be in the ranges 16-24 dB and 27-28 dB, respectively. For the shear configuration, increases in the active control authority of up to 29 dB due to a properly tuned resonant circuit are observed. When subjected to uncertainties in the resistance and inductance values, with 10% relative dispersions, the control authority increase is in the range of 6-29 dB.
23 citations
TL;DR: In this paper, a new equation is suggested to predict the bending forces in V-shaped dies for parts with holes on the bending surfaces, and the influence of the area of the holes, die angles, die widths and punch radius on the value of the spring-back and the bending force in V die bending is studied.
Abstract: Sheet metal bending is one of the most widely applied sheet metal operations. The bending operations present several technical problems in production, such as prediction of spring-back and the punch load. In this paper, the value of the spring-back and bending forces are investigated for a low carbon steel material. Two thicknesses of material (0.95 and 0.75 mm) are applied. Sheet metal components, which are used in the experiments, have oblong holes on their bending surfaces. The influence of the area of the holes, die angles, die widths and punch radius on the value of the spring-back and the bending forces in V-die bending is studied. It is found that all these parameters affect the spring-back and the bending forces, but not in the same way. A new equation is suggested in this paper to predict the bending forces in V-shaped dies for parts with holes on the bending surfaces.
23 citations
TL;DR: In this paper, the authors present a methodology for mapping the thermodynamic losses of vapor compression refrigeration systems, which consists of a theoretical model that splits the coefficient of performance into four terms: (i) the Carnot coefficient, (ii) the efficiency of real cycle running with an ideal compressor, (iii) the compression efficiency of a real compressor, and (iv) the cycling efficiency.
Abstract: The present study introduces a methodology for mapping the thermodynamic losses of vapor compression refrigeration systems which consists of a theoretical model that splits the coefficient of performance into four terms: (i) the coefficient of performance of an ideal cycle (Carnot), (ii) the efficiency of a real cycle running with an ideal compressor, (iii) the compression efficiency of a real compressor, and (iv) the cycling efficiency. In addition, measurements of the relevant variables at several positions along the refrigeration loop are also required, generating performance data not only for the whole unit but also for each one of the system components. The proposed methodology points out the thermodynamic losses of the refrigeration system, identifying opportunities for energy performance improvement. In addition, the methodology is suitable for comparing different refrigeration systems with respect to the same thermodynamic baseline. Albeit the methodology was originally developed for household refrigerators, it can be easily extended to any kind of vapor-compression refrigeration systems.
22 citations
TL;DR: In this paper, a wire-mesh sensor was applied to experimentally investigate two-phase horizontal pipe flow and some physical flow parameters were extracted based on the raw measured data obtained by the sensor.
Abstract: The monitoring and visualization of two-phase flow is of great importance either from technical/practical point of view for process control and supervision or from scientific/theoretical point of view, for the understanding of physical phenomenon. A wire-mesh sensor was applied to experimentally investigate two-phase horizontal pipe flow. Furthermore, some physical flow parameters were extracted based on the raw measured data obtained by the sensor. In this article, first, the work principle of wire-mesh sensors is revised and, second, the methodology of flow parameter extraction is described. A horizontal flow test section comprising of a pipe of 26 mm i.d. 9 m long was employed to generate slug flows under controlled conditions. An 8 × 8 wire-mesh sensor installed at the end of the test section delivers cross-sectional images of void fraction. Based on the raw data, mean void fraction, time series of void fraction and characteristic slug frequency are extracted and analyzed for several experiments with different liquid and gas superficial velocities.
22 citations
TL;DR: In this article, the authors investigated the influence of an EP additive on the drilling process of a CNC machine with 7.64 kW of power and a maximum rotation of 5000 rpm.
Abstract: Compacted Graphite Iron (CGI) is a good option for the manufacturing of engine blocks, because of the possibilities to decrease the wall thickness and to operate at higher pressures. However, due to its greater tensile strength and hardness compared with grey cast iron, the pearlitic CGI structure makes its machining more difficult. Thus, the aim of this paper is to investigate the improvements in CGI drilling achieved through the use of cutting fluids with EP additives. Experimental investigation of the influence of an EP additive on the drilling process was carried out using a CNC machine with 7.64 kW of power and maximum rotation of 5000 rpm. The cutting parameters were a cutting speed of 110 m/min, feed velocity of 350 mm/min and hole-depth of 20 mm. Three cutting fluids were analyzed, with and without EP additives. The results showed that the EP additive influenced the CGI drilling performance due to a layer comprised of sulphur (EP additive) and metal. Adhesion was avoided and the friction and wear behavior was improved.
18 citations
TL;DR: In this article, the authors analyzed the literature on single and two-phase frictional pressure drop inside tubes with twisted tape inserts focusing on the physical mechanism and the effects of the use of twisted-tape in comparison to plain tubes.
Abstract: Twisted-tape inserts are frequently used in heat exchangers as a passive and inexpensive heat transfer enhancement method. However, their use results not only heat transfer coefficient increments, but also pressure drop penalties. The present study analyses the literature on single and two-phase frictional pressure drop inside tubes with twisted-tape inserts focusing on the physical mechanism and the effects of the use of twisted-tape in comparison to plain tubes. Experimental data were gathered from the open literature and compared against the available correlations developed in order to predict two-phase frictional pressure drop in tubes containing twisted-tape inserts. It was found that none of the correlations was able to predict such a database accurately. A new correlation to estimate the friction factor for two-phase flows inside tubes with twisted-tape is also proposed. Contrarily to previous studies, the proposed correlation presents reasonable predictions under single and two-phase flow conditions and obeys the trends when the twisted-tape ratio tends to zero and infinite.
TL;DR: This work describes the steps required to construct a hydrodynamic model of the Guajara Bay, using Geographic Information Systems and the Finite Element Method, and the methods used to obtain field data and the results obtained.
Abstract: This work describes the steps required to construct a hydrodynamic model of the Guajara Bay, using Geographic Information Systems and the Finite Element Method. An overview of the problem that motivates this modelling procedure, i.e., the pollutant dispersion, is presented. The computer software used is then discussed, stressing the links between the data model entities. The calibration procedure is described. The methods used to obtain field data and the results obtained are presented, alongside the main flow patterns of the water. The simulations and applications of the model are discussed at the end of the paper.
TL;DR: In this article, the effects of different cutting parameters on performance characteristics are studied empirically during the drilling of Al7075, and the work piece surface roughness and the temperature changes due to the incurred heat at the cutting process are taken as performance outputs.
Abstract: Cutting fluids are difficult and expensive to recycle. These drawbacks mentioned can be reduced or eliminated by performing the cutting operations with minimum quantity lubrication or without using any cutting fluid. In this study, the effects of different cutting parameters on performance characteristics are studied empirically during the drilling of Al7075. The work piece surface roughness and the temperature changes due to the incurred heat at the cutting process are taken as performance outputs. In the experiments, HSS tools with a diameter of 8 mm and an angle of 118o were used. Minimum quantity lubrication (MQL), compressed air and dry processing (without the usage of any cooling liquid) techniques are used as the applied cooling technique. In the processing technique with MQL, the cooling liquid is sent pulverized on the interface between the work piece and the tool. Boron oil-water emulsion is used as the cutting liquid. As a result of the experiments, it is determined that better results are achieved with the MQL technique than with other cooling techniques. The best surface roughness is achieved at 20 m/min cutting speed and 0.1 mm/rev feed rate.
TL;DR: In this article, a comparison between several detailed chemical kinetic models recently developed and available experimental data is presented, and the results of numerical simulations are compared with existing experimental data of the combustion process in two simplified physical systems.
Abstract: This work presents a systematic comparison between several detailed chemical kinetic models recently developed and available experimental data. The aim is to assess the predictive capabilities of the combustion with air of the following fuels: hydrogen, methane, ethanol and liquefied petroleum gas, in a large range of equivalence ratio. The prevailing thermodynamical conditions range from ambient to the more stringent ones, such as high pressure combustion. In order to assess the predictive performance of the twelve chosen chemical kinetics models, the results of numerical simulations are compared with existing experimental data of the combustion process in two simplified physical systems: the perfectly stirred reactor and the freely propagating premixed laminar flame. When ambient conditions are considered, the comparisons reveal a good agreement among most of detailed kinetic mechanisms, on the prediction of thermochemical properties of practical interest with respect to the corresponding experimental data only, as far as lighter fuels such as hydrogen, methane and ethanol are considered. The chosen mechanisms are shown to meet with di fficulties when mixtures of liquefied petroleum gas and air are considered, even in ambient conditions. The obtained results highlight the necessity for (i) updating the existing mechanisms with the use of recent experimental results and (ii) the development of new comprehensive models. Keywords: detailed kinetic mechanisms, hydrogen, natural gas, ethanol, liquefied petroleum gas
TL;DR: In this paper, a mathematical modeling and calculation procedure for problems of electromagnetic forming of thin circular metal sheets using a flat spiral coil as actuator is presented, focusing specifically on the calculation of the electromagnetic field generated by the flat coil and analysis of the circuit that models the electromagnetic forming system to the initial time, before the plastic deformation of the sheet.
Abstract: This study presents mathematical modeling and calculation procedure for problems of electromagnetic forming of thin circular metal sheets using a flat spiral coil as actuator. The methodbased on the Biot-Savart Law focuses specifically on the calculation of the electromagnetic field generated by the flat coil and analysis of the circuit that models the electromagnetic forming system to the initial time, before the plastic deformation of the sheet. The solution of magnetic induction integral equations is performed by numerical methods specifically with the use of Matlab® software, providing important information that serves as feedback for system design. Free bulging experiments were performed to demonstrate a good relationship with the mathematical model predictions for electrical discharge current in the coil and induced currents in the metal sheet, behavior of the transient electromagnetic force between coil and workpiece, and distribution of magnetic field, electromagnetic density force along the coil.
TL;DR: In this paper, the roll gradient, understeer gradient and steering sensitivity vehicle dynamics metrics are compared with real vehicle measurements and more detailed multibody simulation models, and improvements for these available analytical formulations are proposed for the cases where the initial results do not present satisfactory correlation with measured values.
Abstract: Analytical models to evaluate vehicle dynamic handling properties are extremely interesting to the project engineer, as these can provide a deeper understanding of the underlying physical phenomena being studied. It brings more simplicity to the overall solution at the same time, making them very good choices for tasks involving large amounts of calculation iterations, like numerical optimization processes. This paper studies in detail the roll gradient, understeer gradient and steering sensitivity vehicle dynamics metrics, starting with analytical solutions available in the literature for these metrics and evaluating how the results from these simplified models compare against real vehicle measurements and more detailed multibody simulation models. Enhancements for these available analytical formulations are being proposed for the cases where the initial results do not present satisfactory correlation with measured values, obtaining improved analytical solutions capable of reproducing real vehicle results with good accuracy.
TL;DR: In this paper, an experimental investigation using adaptive control in a refrigeration system was performed using Programmable Logic Controller (PLC) and then sent to the computer through a PC serial port.
Abstract: This paper reports an experimental investigation using adaptive control in a refrigeration system. This system is composed basically of a semi-hermetic compressor, concentric tubes heat exchangers, the condenser and evaporator, and thermostatic expansion valve (TXV). The refrigerant used in the refrigeration system was the HCFC-22 and also an AC frequency inverter was used to control the speed of the compressor. The temperatures were measured by PT-100 sensors and the pressures using piezoresistive pressure transducers. Data acquisition was implemented using the Labview software. An electronic card with analogical signal output was also used. These analogical signals were converted into digital through a Programmable Logic Controller (PLC) and then sent to the computer through a PC serial port. Tests were performed with a variable speed compressor in the range from 30 to 70 Hz and the experimental results showed that the highest performance (COP) was attained by working in the range of 50 Hz, using adaptive fuzzy control.
TL;DR: In this article, the authors present the results of the first test, that is, with the oil recommended by the manufacturer in extreme conditions, and observe that if in a system an abnormal occurrence takes place, for example an extra load during a certain period of time, the lubricant analysis can be used together with the vibration analysis to complement it.
Abstract: Among all Predictive Maintenance techniques the oil analysis and vibration analysis are the most important for monitoring some systems. The integration of these techniques has the potential to revolutionize industrial practices and provide a large economic gain for industries. To study the integration of both techniques a bench test was set up and put to work to the extreme limit of use. Tests were carried out with the lubricant recommended by the manufacturer of the equipment, using lubricants supplemented with various percentages of liquid contaminant and lubricants supplemented with several percentages of solid contaminant. This paper presents the results of the first test, that is, with the oil recommended by the manufacturer in extreme conditions. From the results it was observed that if in a system an abnormal occurrence takes place, for example an extra load during a certain period of time, the lubricant analysis can be used together with the vibration analysis to complement it.
TL;DR: In this paper, the use of a robotic arm as a machine tool to machine aluminum alloys AA2024 applying high speed machining (HSM) technique was investigated, assessing surface finishing as a function of different orientation angles between end mill and machined surface.
Abstract: The needs to comply with an increasingly competitive international market lead industries to some innovative solutions, such as the use of robotic arms as machine tools. Although these solutions present some well known drawbacks, there are some advantages and niches of application where success is possible. The present work investigates the use of such pieces of equipment to machine aluminum alloys AA2024 applying high speed machining (HSM) technique, assessing surface finishing as a function of different orientation angles between end mill and machined surface. It also tests the best condition to machine foam for prototyping applications. Results indicate that the directions close to the normal are the best compromises because of dynamic stability of the robot arm structure and roughness as low as 4 µm Ra are possible to be achieved in aluminum alloys. A complex shape such as a semi sphere can be easily machined in foam for rapid and accurate prototype machining. Surface finishing can be very smooth and well suitable for industrial applications in such materials.
TL;DR: A phase-field model with a grid based on the Finite-Difference Method is presented, for improvement of computational efficiency and reducing the memory size requirement, showing that the dendrite with well-developed secondary arms can be obtained with low computation time and moderate memory demand.
Abstract: In this paper, we present a phase-field model with a grid based on the Finite-Difference Method, for improvement of computational efficiency and reducing the memory size requirement. The numerical technique, which is based on the temperature change of the pure material, enables us to use, in the initial steps of the computation, a very small computational domain. Subsequently, in the course of the simulation of the solidification process, the computation domain expands around the dendrite. The computation showed that the dendrite with well-developed secondary arms can be obtained with low computation time and moderate memory demand. The computational efficiency of this numerical technique, the microstructural evolution during the solidification, and competitive growth between side-branches are discussed.
TL;DR: In this paper, a theoretical model of a porous-inclined slider bearing lubricated with magnetic fluid has been considered together with slip velocity boundary condition and the influence of various dimensionless parameters arising out of the analysis of the model has been studied.
Abstract: A theoretical model of a porous-inclined slider bearing lubricated with magnetic fluid has been considered together with slip velocity boundary condition. Our aim is to study the influence of various dimensionless parameters arising out of the analysis of the model. By assuming the viscosity µ = µ0 exp [-β(tm - t0)] of magnetic fluid, the expressions for mean temperature and load capacity have been obtained. It has been observed that both mean temperature field and load capacity are the functions of slip parameter, magnetic parameter, thermal parameter and permeability parameter. The dependence of the mean temperature field as well as of load capacity on these parameters has been seen graphically.
TL;DR: In this article, a hydrodynamic modeling and morphological analysis of Lake Agua Preta in Belem city, Para State, Brazil has been performed, showing that the annual mean rate of sedimentation varies between 23,065 and 29,081 m3/year.
Abstract: The main contribution from this paper includes the hydrodynamic modeling and morphological analysis of Lake Agua Preta in Belem city, Para State, Brazil. The lake bathymetry was taken through the data provided by COSANPA (the local sanitation and water supply company) dating back to 1975, and from a 2009 field study. Both bathymetries produced two terrain elevation models, which were used for morphological analysis and hydrodynamic simulations. The morphological analysis has revealed that, from 1975 to 2009, the annual mean rate of sedimentation varies between 23,065 and 29,081 m3/year. Through this result, the sedimentation time of Lake Agua Preta, from 2009, has been calculated, which varies between 295 and 381 years, maintaining the same rate of sedimentation, water consumption and pumping. The hydrodynamic model simulated the depths and velocities, showing a slight flow with velocities ranging from 0 to 33 cm/s. This flow is established between water input and output of the lake, which is used as reservoir of Belem city.
TL;DR: In this article, a magneto-rheological vehicle suspension system built on the variable structure control approach is considered in order to improve the ride comfort obtained by a standard passive suspension, and the numerical results show that the proposed suspension outperforms the passive suspension and presents a performance comparable to that of the active ones when the vehicle body may be assumed as rigid.
Abstract: The synthesis of a magneto-rheological vehicle suspension system built on the variable structure control approach is considered in the present work. The suspension is synthesized in order to improve the ride comfort obtained by a standard passive suspension. Although a nominal half-vehicle model with rigid body is considered in the synthesis of the suspension, phenomenological models for the MR dampers and for the seat-driver subsystem, along with the flexibility of the vehicle body, are considered in the performance assessment. For comparison purposes, active and magneto-rheological suspensions built on the optimal control approach and an active suspension built on the variable structure control approach are also considered. The numerical results show that the proposed suspension outperforms the passive suspension and presents a performance comparable to that of the active ones when the vehicle body may be assumed as rigid. Besides, when its flexibility is an important issue, a great performance drop may be observed, depending on the road quality, the damper characteristics and the adopted control strategy.
TL;DR: In this paper, a computational model for a typical stranded cable based on the basic principles of Verification and Validation is proposed, and the model calibration and model tracking are guided based on a pool of validation metrics suitable for data which are commonly used in structural dynamics.
Abstract: The present work is aimed at building a computational model for a typical stranded cable based on the basic principles of Verification and Validation. The model calibration and model tracking are guided based on a pool of validation metrics suitable for data which are commonly used in structural dynamics. The estimator used for the associated inverse problem is the Maximum a Posteriori estimator and the parameter estimation process is performed sequentially over experiments. Experimental tests have been performed at CEPEL's (Electric Power Research Center) laboratory span with the overhead conductor Grosbeak in order to provide the measured data. The predictive capacity of the computational model is assessed by means of frequency-and time-domain validations through FRFs, band limited white-noise and sine sweep excitations. We also present novel and reliable estimates for the bending stiffness and damping parameters of a widely used transmission line conductor.
TL;DR: In this article, a mathematical model is developed for a liquid flow on solid particles in a trickle bed reactor, and a mathematical formulation is followed based on the liquid-solid model approach where the liquid phase with the (KCl) tracer is treated as a continuum.
Abstract: A mathematical model is developed for a liquid flow on solid particles in a trickle bed reactor. A mathematical formulation is followed based on the liquid-solid model approach where the liquid phase with the (KCl) tracer is treated as a continuum. The physical modeling is discussed, including the formulation of initial and boundary conditions and the description of the solution methodology. Results of mathematical model are presented and validated. The model is validated through comparison using three experimental cases. The optimized values of the axial dispersion (Dax), liquid-solid mass transfer (kLS), and partial wetting efficiency (FM) coefficients are obtained simultaneously using the objective function. The behavior of Dax, kLS, and FM is analyzed by the empirical correlations.
TL;DR: In this paper, natural convection heat and mass transfer along a vertical plate embedded in a doubly stratified power-law fluid saturated non-Darcy porous medium with uniform heat and flux is presented.
Abstract: Natural convection heat and mass transfer along a vertical plate embedded in a doubly stratified power-law fluid saturated non-Darcy porous medium with uniform heat and mass flux is presented. The governing partial differential equations are transformed into ordinary differential equations using similarity transformations and then solved numerically. The effects of magnetic parameter, stratification parameter and power-law index on the velocity, temperature and concentration are illustrated graphically.
TL;DR: In this paper, the analysis of diffusion coupled with temporary retention motivated by the challenge to solve the problem of population spreading is presented, where the authors use the discrete approach to deal with this problem due to its relative simplicity and straightforward mathematical treatment.
Abstract: This paper deals with the analysis of diffusion coupled with temporary retention motivated by the challenge to solve the problem of population spreading. Retention may be associated to colonization of the occupied territory in this case. The discrete approach was selected to deal with this problem due to its relative simplicity and straightforward mathematical treatment. Two types of problems are analyzed namely: symmetric spreading with temporary retention, and propagation with temporary retention. It is clearly shown that higher order differential terms must be included in the governing equations of diffusion and propagation to represent the temporary retention effect. Specifically third and fourth order terms are associated to the retention effect in propagation and diffusion processes respectively. Control parameters regulating the relative influence of the diffusion and the retention terms in the governing equations come up naturally from the analysis. After the appropriated operations the finite difference equations reduce to partial differential equations. The control parameters are kept in the partial differential equations. These parameters are essential in the governing equations to avoid uncontrolled accumulation of particles due to the retention effect. The diffusion-retention problem appearing in several physicochemical problems are governed by the same equations derived here. The current literature refers to several types of diffusion-retention problems, but all solutions assume the classical second order equation as the basic reference. A short analysis of the equilibrium conditions for diffusion-retention problems with a source helps to show the coherence of the theory. In order to explore the potentialities of the discrete approach the problem of asymmetric distribution is also analyzed.
TL;DR: In this paper, the problem of automatic inspection of ceramic tiles using Infrared Images and Artificial Neural Network (ANN) has been addressed, and the performance of the technique has been evaluated theoretically and experimentally from laboratory and on-line tile samples.
Abstract: In the ceramic industry, rarely testing systems were employed to on-line detect the presence of defects in ceramic tiles. This paper is concerned with the problem of automatic inspection of ceramic tiles using Infrared Images and Artificial Neural Network (ANN). The performance of the technique has been evaluated theoretically and experimentally from laboratory and on line tile samples. It has been performed system for IR image processing and, utilizing an Artificial Neural Network (ANN), detecting defected or no defected tile. The system has been applied to detect on-line measurement results achieved at the exit of the press. The above automatic inspection procedures have been implemented and tested on a number of tiles using synthetic and real defects. The results obtained confirmed the efficiency of the methodology defect detection in raw tile and its relevance as a promising approach on-line, as well as included in quality control and inspection programs.
TL;DR: In this article, a comparison between experimental data and numerical simulation results for the natural circulation phenomenon in single and two-phase flow regime is presented, and the comparison demonstrated that the numerical simulations are very close to the experimental data.
Abstract: The study of natural circulation phenomenon has been object of crescent interest in scientific community in recent years. The new generation of compact nuclear reactors uses natural circulation of the fluid as a residual heat removal cooling system in case of accident or shutdown. The objective of this paper is to present a comparison between experimental data and numerical simulation results for the natural circulation phenomenon in single and two-phase flow regime. Experimental data were obtained from a circuit built with glass tubes, through which thermal hydraulic phenomenon visualization was possible. The circuit is composed of an electric heater as the heat source, a heat exchanger as the heat sink and an expansion tank to accommodate fluid density changes. Instrumentation data acquisition is performed through thermocouples and pressure meters, and controlled by a computer interface developed using LABVIEW. Numerical modeling and simulations were done with the thermal hydraulic code RELAP5, which is widely used for this purpose. The cyclic reverse flow observed in the circuit was well represented by the numerical model. The comparison demonstrated that the numerical simulations are very close to the experimental data.
TL;DR: The paper reviews in detail the classical BEM formulation in order to be able to address the possible parallelization steps in the numerical implementation and reports the performance of the GPU-CPU system compared to the classical CPU-based system for an increasing number of boundary elements.
Abstract: Numerical simulation of engineering problems has reached such a large scale that the use of a parallel computing approach is required to obtain solutions within a reasonable time. Recent efforts have been made to implement these large scale computational tasks on general-purpose programmable graphics hardware (GPGPU). The Graphics Processing Unit (GPU) is specially well-suited to address problems that can be formulated in form of data-parallel computations with high arithmetic intensity. This work addresses the implementation of the direct version of the Boundary Element Method (DBEM) on a complementary GPU-CPU system. In this article, constant elements were used for the solution of 2D potential problems. A serial implementation of the BEM was rewritten under the SIMT (Single Instruction Multiple Thread) parallel programming paradigm. The code was developed on an NVidiaTM CUDA programming environment. The efficiency of the implemented strategies is investigated by solving a representative 2D potential problem. The paper reviews in detail the classical BEM formulation in order to be able to address the possible parallelization steps in the numerical implementation. The article reports the performance of the GPU-CPU system compared to the classical CPU-based system for an increasing number of boundary elements.