Showing papers in "Journal of The Brazilian Society of Mechanical Sciences and Engineering in 2013"

The influence of nano additive blended biodiesel fuels on the working characteristics of a diesel engine

Abstract: The present study reports the results of Alumina and CNT (carbon nanotube) nanoparticles blended biodiesel fuel on the performance, emission, and combustion characteristics of a diesel engine. The biodiesel is produced from the raw jatropha oil by standard transesterification process, and subsequently, the nanoparticles such as Alumina, CNT, and Alumina–CNT are blended with the biodiesel fuel in the mass fractions of 25 and 50 ppm with the aid of an ultrasonicator. The characterization studies of the nanoparticles such as TEM and XRD are carried out to analyze their morphology. The whole investigation is carried out in a constant speed diesel engine in four phases using neat biodiesel fuel, Alumina blended biodiesel, CNT blended biodiesel, and Alumina–CNT blended biodiesel fuels. The results revealed a considerable enhancement in the brake thermal efficiency and marginal reduction in the harmful emissions for the nanoparticles blended biodiesel fuels compared to those of neat biodiesel fuel. Furthermore, the hot-plate evaporation test confirmed a shorten ignition delay effect, and improved heat transfer rate associated with the nanoparticles blended biodiesel fuels, owing to their enhanced surface area/volume ratio, and heat conduction properties.

Development of cold spray from innovation to emerging future coating technology

Abstract: Cold spray is one of the various names for describing an all-solid-state coating process that uses a high-speed gas jet to accelerate powder particles toward a substrate where they plastically deform and consolidate upon impact. Traditional thermal spray coating technologies require the melting or partial melting of feedstock material, and then quenching the molten droplets to produce coating. Cold spray technology belongs to the wide family of thermal spray technology and is a future of deposition of coating especially on temperature sensitive materials. In this paper the historical background of the cold spray process, fundamentals of this process and influence of the process parameters on coating properties are summarized. The main motivation for this review is to summarize the rapidly expanding common knowledge on cold spray for the researchers and engineers already or soon to be involved for their future endeavors with this new technology.

Influence of thermal stratification on the radiative flow of Maxwell fluid

Abstract: We carried out analysis of the effects of thermal stratification in the boundary layer mixed convection flow of Maxwell fluid. The thermal radiation effect is considered. The derived equations with appropriate boundary conditions are solved for series solutions of velocity and temperature. Graphical results lead to the interesting observations. Local Nusselt number is tabulated and discussed. It is found that there is an opposite effect of fluid characteristics on the velocity and temperature. However, the velocity and temperature have similar effects for thermal stratification and radiation.

Assessment of the grinding wheel active surface condition using SEM and image analysis techniques

Abstract: The grinding wheel active surface (GWAS) condition assessment after the grinding processes is one of the crucial elements of diagnostics of abrasive tools used in modern production industry. At present there exist a number of measurement methods which facilitate such evaluation (e.g. stylus, optical, pneumatic). These may include also imaging methods using the scanning electron microscopy (SEM). This paper presents and discusses a proposal for obtaining additional information concerning the GWAS condition based on the acquired, properly processed, and computer-analyzed SEM micrographs. In the experimental investigations SEM micrographs of the selected GWAS areas with abraded vertexes and microsmearings of the abrasive grains active vertexes, macrosmearings of grains and intergranular spaces, as well as intergranular spaces filled with sulfur introduced during the impregnation process were acquired. For acquisition the scanning electron microscope JSM-5500LV by JEOL Ltd. (Japan) was used. Image analysis of selected GWAS areas was carried out by specialized research environment Image-Pro® Plus 5.1. It was concluded that the applied techniques were highly useful and could complement the typically used ones, especially in complex tests.

The first frequency of cantilevered bars with geometric effect: a mathematical and experimental evaluation

Abstract: In engineering, a large number of structures may be modeled as cantilevers. Due to their intrinsic characteristics, some of these structures are sensitive to dynamic actions. Gusts of wind are dynamic excitations for which the fundamental frequency of vibration is an important factor when calculating the structural response. Modeling the effects of the axial force on the natural frequencies of a structure usually results in systems of differential equations that are not solvable from a practical engineering perspective. This article develops a simple mathematical expression for calculating the fundamental frequency of cantilevered structures, within small ranges, that considers the presence of an axial demand. This expression has been validated by dynamic laboratory testing.

Modeling and analysis of correlations between cutting parameters and cutting force components in turning AISI 1043 steel using ANN

Abstract: Predictive modeling is essential to better understanding and optimization of machining processes. Modeling of cutting forces has always been one of the main problems in metal cutting theory. In this paper, artificial neural networks (ANNs) were used for modeling correlations between cutting parameters and cutting force components in turning AISI 1043 steel. Cutting force components were predicted by changing cutting speed, feed rate, depth of cut and cutting edge angle under dry conditions. In order to improve generalization capabilities of the ANN models, Bayesian regularization is used in ANN training. Considering experimental data for ANN training, five ANN models were tested. For evaluating the predictive performance of ANN models, three performance criteria were given consideration. The overall mean absolute percentage error for cutting force components was around 3 %. This study concludes that Bayesian regularized ANN of quite basic architecture using small training data is capable of modeling multiple outputs with high prediction accuracy.

Adaptive neuro-fuzzy interference system modelling of carbon nanotube-based electrical discharge machining process

Abstract: This study deals with modelling of surface roughness with carbon nanotube (CNT)-based electrical discharge machining (EDM) of AISI D2 tool steel material by means of adaptive neuro-fuzzy inference system (ANFIS) approach. The full factorial design of experimental techniques was adapted to conduct the experimental works. The CNT mixed dielectric nanofluids were prepared and used in the EDM process to analyze the surface roughness. The first-order sugeno type fuzzy interference modeling was used to predict the output parameters and compared with experimental values. The ANFIS model has been developed in terms of machining parameters for the prediction of surface roughness using trained data. The ANFIS predictions for the surface roughness with CNT the testing error was 0.20276 and correlation coefficient was 0.997 with the experimental data and for without CNT the testing error was 0.26529 and correlation coefficient was 0.889. The developed ANFIS model were compared in terms of their performances and shows that high residual R 2 value indicate that the predicted model very well fits with the experimental data for using CNT on EDM process. The proposed model can also be used for estimating surface roughness on-line.

Influence of HSM cutting parameters on the surface integrity characteristics of hardened AISI H13 steel

Abstract: The purpose of this study is to evaluate the influence of the cutting parameters of high-speed machining milling on the characteristics of the surface integrity of hardened AISI H13 steel. High-speed machining has been used intensively in the mold and dies industry. The cutting parameters used as input variables were cutting speed (v c), depth of cut (a p), working engagement (a e) and feed per tooth (f z ), while the output variables were three-dimensional (3D) workpiece roughness parameters, surface and cross section microhardness, residual stress and white layer thickness. The subsurface layers were examined by scanning electron and optical microscopy. Cross section hardness was measured with an instrumented microhardness tester. Residual stress was measured by the X-ray diffraction method. From a statistical standpoint (the main effects of the input parameters were evaluated by analysis of variance), working engagement (a e) was the cutting parameter that exerted the strongest effect on most of the 3D roughness parameters. Feed per tooth (f z ) was the most important cutting parameter in cavity formation. Cutting speed (v c) and depth of cut (a p) did not significantly affect the 3D roughness parameters. Cutting speed showed the strongest influence on residual stress, while depth of cut exerted the strongest effect on the formation of white layer and on the increase in surface hardness.

Implementation of the extended finite element method for coupled dynamic thermoelastic fracture of a functionally graded cracked layer

Abstract: The effect of thermal shock on a cracked functionally graded material (FGM) layer is considered using the extended finite element method. Classical coupled thermoelastic equations are used in the calculations. The coupled dynamical system of equations obtained from the extended finite element discretization is solved by the Newmark method in the time domain. Micromechanical models for conventional composites are used to estimate the material properties of functionally graded layer. The interaction integral is then employed to calculate the dynamic thermal stress intensity factors (SIFs) at each time step. The effects of initial crack angle and volume fraction profiles of FGMs on SIFs are studied. Also crack propagation phenomenon is investigated in this paper. We have used MATLAB software to do the different stages of simulation from mesh generation to numerical computation of SIFs. Some numerical examples are implemented to investigate the validity and accuracy of attained results.

Nonlinear aerostatic stability analysis of new suspension bridges with multiple main spans

Abstract: In order to solve the aerostatic stability problem of long-span bridges more effectively, an upper limit of the external iteration number is set optimally to improve the incremental double iteration method, and an optimum iteration method is brought forward. For new suspension bridges with multiple main spans, the assumption of the spatial uniformity of wind speed is invalid due to their long decks and high towers. Taking into account the spatial non-uniformity of wind speed, a program corresponding to the optimum iteration method is developed and used to analyze the full-range aerostatic stability of the Maanshan Bridge, which is a long-span suspension bridge with double main spans in China, and the effect of wind speed spatial non-uniformity on the aerostatic stability of the bridge is investigated analytically. The result shows that the lowest critical wind speed of aerostatic instability is gained when the distribution of wind speed is non-uniform and the spatial non-uniformity of wind speed has a considerable effect on the aerostatic stability of suspension bridges with multiple main spans. The optimum iteration method is compared with the method without improvement in analysis, and the result indicates that the accuracy and efficiency of the optimum iteration method are much better, so the validity and advancement of the optimum iteration method are proved.

Application of RCGA-ANN approach for modeling kerf width and surface roughness in CO2 laser cutting of mild steel

Abstract: This paper presents an artificial intelligence approach for the development of predictive models for a CO2 laser cutting of mild steel by using artificial neural networks (ANNs) and real coded genetic algorithm (RCGA). Laser cutting experiment, conducted according to Taguchi’s experimental design using L 25 orthogonal array, provided a set of data for the development of ANN models for the prediction of the kerf width and surface roughness. Both ANN models considered cutting speed, laser power, and assist gas pressure as input parameters. Considering the disadvantages of the back propagation, the RCGA was applied for training of the ANNs. Statistical results indicate good correlation between the experimental results and ANN predictions, which confirms the validity of the applied approach. Finally, using the developed models, the combined effects of input process parameters on the quality characteristics were studied.

Numerical simulation of filling process of natural gas onboard vehicle cylinder

Abstract: The accurate modeling of the filling compressed natural gas-fuelled vehicle storage cylinders is a complex process, and should be studied deeply. The minimum filling time has positive impact on commercialization of natural gas vehicles. On the other hand, very fast filling may result in unexpected temperature rise, violating the safety standards. This study investigates flow and heat transfer in natural gas vehicle’s onboard cylinder during filling. The cylinder is assumed to be a type III onboard storage cylinder. An axisymmetric computational model for unsteady, compressible turbulent flow has been built. A computational fluid dynamics has been developed for predicting the temperature and pressure change during the fill based on using commercial software Fluent. The natural gas (NG) as working fluid is treated as a real gas. The Redlich–Kwong equation of state has been employed to compute the thermodynamic properties of NG. The computation results have been compared with previously measured values and shows good agreement. The results show that the temperature rise for NG is about 35 K. Most of the heat dissipation from the in-cylinder gas is stored in the cylinder wall during the fill and the heat lost to the ambient is small.

Surface integrity of moulds for microcomponents manufactured by micromilling and electro-discharge machining

Abstract: Milling is one of the most important processes to manufacture dies and moulds. However, it cannot machine regions with small sizes and difficult access to the cutting tool. Such regions must be machined by electro-discharge machining (EDM). It is known that EDM can damage the integrity of the machined surface, and also requires long processing time, due to both, the necessity to manufacture the electrode and its low material removal rate. The micromilling process, using high-frequency spindle together with cutting tools smaller than 1 mm of diameter has been emerging as an option for machining small regions in dies and moulds. In this context, this paper aims to help the understanding of the cutting phenomenon to manufacture small areas using both machining techniques, in order to identify the adequacy to replace EDM for micromilling in such circumstances. Machining experiments were carried out on AISI P20 (29HRC) and AISI H13 (45HRC) steels. These materials are commonly used in the mould and die industry. Residual stress on machined surface, surface finishing (2D and 3D), SEM images, microstructure and microhardness were accessed. The residual stress was tensile for the EDM pieces and compressive for the milled parts. The material had more influence on the residual stresses values than the process and H13 had higher values than P20. The surface roughness from the EDM machining pieces was not influenced by the material. The EDM caused white layer and microcracks on both materials, but much more intensely on H13. These occurrences were not found on the milled workpieces. Plastic deformation occurred on the micromilled surfaces, but without phase transformation of the material’s microstructure. Unexpectedly, the roughness on the hardest material (H13) was worse than P20 for the milling experiments. It was attributed to more intense tool deflection when milling H13. In general, roughness obtained in micromilling was about six times lower than that obtained using EDM and it presented a regular surface topography, unlike the EDM specimens.

A three-dimensional SPH model for detailed study of free surface deformation, just behind a rectangular planing hull

Abstract: Transom wave behind planing hulls is a complicated physical phenomenon that has lead to computational challenge for many researchers. On the other hand, smoothed particle hydrodynamics (SPH) which is known as a meshless Lagrangian approach can simulate free surface flows with strongly nonlinear physics. Therefore, effort has been made in the current study to develop a 3D-SPH code for three-dimensional simulation of transom stern flow behind a rectangular planing hull. It is also aimed to give some new physical insights into this highly nonlinear problem. Different techniques such as sub particle scale turbulence model and moving least square density filter among others are also implemented. To validate the developed 3D-SPH code, the benchmark problem of dam breaking is investigated. Moreover, to verify the capability of the presented SPH model for transom flow simulation, previous experimental studies at low Froude numbers are considered. Comparisons display good agreement between the numerical results and experimental findings. Furthermore, a detailed discussion about rooster tail formation is presented.

Control of instabilities in non-Newtonian free surface fluid flows

Abstract: Free surface flows in inclined channels can develop periodic instabilities that are propagated downstream as shock waves with well-defined wavelengths and amplitudes. Such disturbances are called “roll waves” and are common in channels, torrential lava, landslides, and avalanches. The prediction and detection of such waves over certain types of structures and environments are useful for the prevention of natural risks. In this work, a mathematical model is established using a theoretical approach based on Cauchy’s equations with the Herschel–Bulkley rheological model inserted into the viscous part of the stress tensor. This arrangement can adequately represent the behavior of muddy fluids, such as water–clay mixture. Then, taking into account the shallow water and the Rankine–Hugoniot’s (shock wave) conditions, the equation of the roll wave and its properties, profile, and propagation velocity are determined. A linear stability analysis is performed with an emphasis on determining the condition that allows the generation of such instabilities, which depends on the minimum Froude number. A sensitivity analysis on the numerical parameters is performed, and numerical results including the influence of the Froude number, the index flow and dimensionless yield stress on the amplitude, the wavelength of roll waves and the propagation velocity of roll waves are shown. We show that our numerical results were in agreement with Coussot’s experimental results (1994).

Effect of the gray cast iron microstructure on milling tool life and cutting force

Abstract: Gray cast irons are frequently used in machine tool beds due to low cost, high vibration damping capacity, and easiness of manufacturing. The guiding standards for production of these alloys determine their classes based on the range of tensile strength and shape of graphites. This research project aims at investigating the differences in machinability between two gray cast irons belonging to the same class (GG25), i.e., within the same standard tolerance, but with different pearlitic/ferritic concentrations. Machinability was evaluated in terms of tool life and cutting forces in milling operations using carbide and ceramic tools and two different cutting speeds. Two different materials were used as samples, one containing 100 % pearlite and another with 50 % pearlite + 50 % ferrite. The results showed that milling of the 100 % pearlitic alloy led to faster tool wear and higher cutting forces than in the 50 % ferritic alloy. Ceramic tools exhibited longer life than carbide tools. The observed wear mechanisms were diffusion, attrition, and thermal cracks. However, material microstructure was observed to be far more significant for tool life and cutting force than the other input variables (cutting speed and tool material).

Cutting forces, friction coefficient and surface roughness in machining Ti-5Al-4V-0.6Mo-0.4Fe using carbide tool K313 under low pressure liquid nitrogen

Abstract: This work presents a study on the effect of low pressure cryogenic liquid nitrogen on cutting forces, friction coefficient, surface roughness of the machined surface and tool wear under high speed machining of a relatively new titanium alloy, Ti-5Al-4V-0.6Mo-0.4Fe. The experiments were conducted in dry and cryogenic conditions. The experimental results show that liquid nitrogen can reduce the friction force, friction coefficient and improve the surface roughness.

Comparison of different WSGG correlations in the computation of thermal radiation in a 2D axisymmetric turbulent non-premixed methane–air flame

Abstract: This study makes an analysis of the radiation heat transfer in a turbulent non-premixed methane–air cylindrical combustion chamber. The highly complex dependence of the radiative properties with the wavenumber spectrum is modeled with the weighted-sum-of-gray-gas (WSGG), making use of the classical correlations of Smith et al. (J Heat Transfer 104:602–608, 1982) and of the more recently in obtained correlations of Dorigon et al. (IJHMT 64:863–873, 2013), based on HITEMP2010. The reaction rates were considered as the minimum values between the Arrhenius and Eddy Break-Up rates. A two-step global reaction mechanism was used, and turbulence modeling was considered via standard k–e model. The source terms of the energy equation consisted of the energy involved in the reaction rates and radiation exchanges. The discrete ordinates method (DOM) was employed to solve the radiative transfer equation (RTE). The results show that the temperature, the radiative heat source, and the wall heat flux can be importantly affected by the WSGG correlations, while their influence on the species concentrations tends to be negligible. Numerical results considering the WSGG model with the new correlations were closer to experimental data presented in the literature.

A reactor network model for predicting NOx emissions in an industrial natural gas burner

Abstract: A chemical reactor network (CRN) is developed and applied to the modeling of a natural gas burner. The CRN development is based on experimental and CFD simulation results of the BERL 300 kW test. The CRN element arrangement, reactor volumes, and flow splits are adjusted based on the best agreement with characteristic temperatures of the reactive flow, aiming to reproduce the experimental NOx emissions data. A sensitivity analysis and a parametric study of the CRN are carried out to evaluate its sensitivity to the flow splits adjustments and its ability to predict emission with air preheat and turndown operation, as well as the influence of the reaction mechanism employed. The best agreement was obtained in the air preheat simulations using Konnov 0.4 mechanism, while the GRI-Mech 3.0 is accurate only within 110 K preheating. The turndown operation results are relatively accurate for turndown ratio between 1.0 and 1.3.

Fast acoustic scattering predictions with non-uniform potential flow effects

Abstract: Acoustic scattering simulations with non-uniform potential flow effects are performed by two formulations described in the literature, valid under specific flow conditions. Both formulations require the solution of the Helmholtz equation for the acoustic scattering computation and the solution of the Laplace equation for the steady potential base flow. These equations are solved using the boundary element method (BEM), and the fast multipole method (FMM) is used to accelerate the matrix-vector products arising from the Helmholtz and Laplace BEM equations. An assessment of the solutions obtained by the two formulations is presented for a verification test case where analytical and full unsteady Euler solutions are available. Results of acoustic scattering for large-scale simulations of realistic airframe configurations are presented. Good agreement is found between Taylor’s low Mach number scattering formulation and the solution of the full unsteady Euler equations for high-frequency simulations of plane waves scattering from a rigid cylinder. The computational cost per iteration of the FMM–BEM for the acoustic scattering around a full airplane configuration discretized by 550,000 boundary elements in a non-uniform potential flow is 19 s.

A new theory for anomalous diffusion with a bimodal flux distribution

Abstract: This paper deals with a new governing equation for anomalous diffusion encompassing a large spectrum of phenomena with particular attention on delaying processes. The analysis starts with a discrete approach and a law of evolution introducing a partial retention of the diffusing particles at each time step. The resulting differential equation assuming that the concentration function belongs to class C3 is a fourth-order differential equation. To fit this result into the framework of a new theory, a bi-modal flux distribution for the diffusion process associated with two energy states is proposed. The first energy state is related to the set of particles flowing according to the Fick’s law and the complementary set follows a new law. Two key parameters are introduced, namely, a parameter β indicating the fraction of the particles in the principal energy state and a parameter R controlling the effect of the secondary flux. Some examples are presented characterizing different types of phenomena as function of the relative values of β and R. The necessary conditions for the retention behavior are discussed for some particular cases.

Development of volume of fluid methods to model free surface flow using new advection algorithm

Abstract: In this paper, a new advection algorithm is presented to model free surface flows using volume of fluid method. To model the fluid flow, Navier–Stokes equations are solved as governing equations using two-step projection method on the Cartesian staggered grids. In the volume of fluid method, several algorithms such as flux-corrected transport (FCT) and Youngs’ algorithms are used to model the free surface. In these methods, for staggered grids, fluxes to neighboring cells are estimated based on cell face velocities. It means that fluid particles in the cell have the same velocity of the cell faces. However, in practice, the particles velocity varies between two adjacent cell faces velocities. In the present research, modified Youngs’ and flux-corrected transport methods are presented. In these methods, the velocity in mass center of fluid cell is estimated and used to calculate cell face fluxes. The performance of the modified schemes has been evaluated using a number of alternative schemes taking into account translation, rotation, shear test and dam break on dry bed. The results showed that the modified Youngs’ method is more accurate than the original one particularly in coarse grid. It is also more accurate than the modified flux-corrected transport method.

Experimental study of the bistability in the wake behind three cylinders in triangular arrangement

Abstract: By means of hot wire anemometry technique and flow visualizations, the presence of the phenomenon of the bistability around three cylinders in two triangular arrangements is investigated in an aerodynamic channel and in a water channel. Bistability occurs in flows over sets of bluff bodies forming a flip-flopping wake characterized by a biased flow switching at irregular intervals, which can represent an additional source of dynamic instabilities. Results of flow around three cylinders in triangular arrangement are presented for two configurations: one cylinder upstream and two downstream, and vice versa. The experimental data are analyzed by means of statistical, spectral and wavelet tools. The joint analysis in time and frequency domains through wavelets allows the detection of non-permanent flow structures. The results show the presence of bistable flow in the configuration with one cylinder upstream and two downstream, but no bistable effect was detected in the second configuration, where the flow shows a distinct shedding frequency.

A hopping-righting mechanism analysis and design of the mobile robot

Abstract: This paper presents a hopping-righting device inspired by a locust hind leg and its posture turnover for the ground-based mobile robot to enhance its adaptability and ability of overcoming large obstacles. Based on the analysis of locust morphology, the simple hopping-righting mechanism is designed, focusing on jumping and righting functions. Firstly, it deals with design and optimization of a simple four-bar linkage jumping mechanism according to the analysis of the thrust force against the ground and the speed during takeoff. In addition, the design of a novel righting mechanism for the jumping mobile robot is described. In the next section, the model design and simulation are performed, and ultimately jumping and righting experiments are conducted. The results show that the hopping-righting mechanism enables the mobile robot to jump and upright itself in testing area, which makes the mobile robot more feasible and portable. That lays the foundation for further innovative research of jumping mechanisms.

Squeezed screw trajectories for smooth regrasping movements of robot fingers

Abstract: In dextrous robotic manipulation we are often confronted with the problem that the robot fingers need to be repositioned on the object surface, either because a finger reaches its workspace limits or because the manipulation planner decides to do so due to its manipulation strategy. In this paper we propose a trajectory type for the purpose of regrasping, named “Squeezed Screw”. It is smooth and has a relatively simple shape. It is a superposition of a movement on an ellipse with a translation in an arbitrary direction in 3D. It can be generated from only eight input parameters. An algorithm was developed to calculate the path geometry from these parameters. A comparison with a Rapidly-exploring Random Tree algorithm points out the advantages of this novel trajectory type.

An automated design system for compound washer dies

Abstract: The designing of stamping dies is a complex process influenced by numerous design parameters, which can be classified into independent and dependent parameters. Before starting the design process a designer must identify, analyze, and calculate these parameters needing a wide range of knowledge. The design task is then accomplished on the basis of these parameter values that must be incorporated into the die design’s elements, in order to achieve workable and quality designs. Since most of the 3D CADs provide insufficient help in this regard, an automated system has been developed in CATIA V5 for the automatic designing of compound dies intended for production of various washer configurations. This system operates on the basis of an integrated design knowledge embedded inside washer, strip, and die-parts’ generative models using user parameters and a programmatically established relations between them. The use of this system significantly shortens the design time, and denotes design quality.

Numerical simulation of an ethanol turbulent spray flame with RANS and diffusion combustion model

Abstract: A detailed numerical simulation of ethanol turbulent spray combustion on a rounded jet flame is presented in this article. The focus is to propose a robust mathematical model with relatively low complexity submodels to reproduce the main characteristics of the coupling between both phases, such as the turbulence modulation, turbulent droplets dissipation, and evaporative cooling effect. A RANS turbulent model is implemented. Special features of the model include an Eulerian–Lagrangian procedure under a fully two-way coupling and a modified flame sheet model with a joint mixture fraction–enthalpy β-PDF. Reasonable agreement between measured and computed mean profiles of temperature of the gas phase and droplet size distributions is achieved. Deviations found between measured and predicted mean velocity profiles are attributed to the turbulent combustion modeling adopted.

Mechatronic design concept and its application to pick-and-place robotic systems

Abstract: Mechatronic design can be defined as the integrated design of mechanical systems and their embedded control system. Two main challenges in designing mechatronic systems are treated in this manuscript: challenges in modeling mechatronic systems and challenges in optimizing mechatronic systems. Modeling methodologies, model-reduction strategies, control system evaluation have been discussed in order to overcome some of the challenges regarding modeling issues. Regarding the optimization issues, two methodologies have been proposed: the nested and the direct strategies. In this manuscript, the design of a mixed kinematic pick-and-place robot demonstrates the main challenges regarding mechatronic design. It can be concluded that, for this case study, tighter performance requirements and robustness have been achieved using more advanced control strategies, such as the ones derived using model-based control design. These control strategies can only be considered when using the nested design strategy. In both strategies, design tradeoffs can be evaluated qualitatively and quantitatively aiding the designer during mechatronic design of robotic systems.

The study of the efficiency enhancement of bionic coupling centrifugal pumps

Abstract: The objective of this paper is to investigate a new method to increase the efficiency of the centrifugal pump under the guidance of the bionic coupling theory. A centrifugal pump with a bionic coupling impeller called a bionic coupling centrifugal pump (BCCP) was developed. Either riblets or concave dimples were engraved on the flank or blade back of the impellers and then coated with polyurethane. This design was inspired by the specific skin structure of living creatures and the theory of biological coupling. The BCCP efficiency was investigated using the method of pseudo-level orthogonal testing. The results show that the efficiency of BCCPs obviously improved and the efficiency curve became more compressed than that of a conventional centrifugal pump over the effective working range. This indicates that the BCCPs would still function within a higher efficiency range even when they deviate from the highest efficiency point. The efficiency enhancement of the BCCP could be attributed to the effect of the delayed release of energy because of the elastic deformation of polyurethane. Polyurethane coupled with non-smooth surface structures stabilized the turbulent flow. This coupling consequently reduced the turbulence and stabilized the water in the boundary layer of the impeller blade.

Natural convection inside cubical cavities: numerical solutions with two boundary conditions

Abstract: The study deals with the three-dimensional natural convection in closed cubic cavities. The boundary conditions were set as two walls (forward and backward) at constant but different temperatures and adiabatic and conducting walls in top and bottom. In the remaining walls the adiabatic condition was used. The Navier–Stokes and energy equations were discretized with the finite volume method using staggered Cartesian meshes. The characteristic flow patterns for a few values of the Rayleigh number up to 107 and of the Prandtl number Pr = 0.71 are shown. Analysis of the different boundary conditions influence on the thermal field and the effects in the determination of local and averaged heat transfer coefficient are also performed. We noticed a good agreement with experimental data.