Showing papers in "Journal of The Brazilian Society of Mechanical Sciences and Engineering in 2014"

Microstructure and mechanical behavior of A356/SiC/Fly-ash hybrid composites produced by electromagnetic stir casting

Abstract: Electromagnetic stir casting is one of the simplest ways of producing defect free aluminum matrix composites. This work focuses on the fabrication of aluminum matrix composites reinforced with various weight percentages of SiC particulates and Fly-ash by modified electromagnetic stir casting route. The distribution of SiC and Fly-ash particles in the matrix was improved by providing externally argon gas into the melt during electromagnetic stirring. Five samples of hybrid composite with different combination of Fly-ash and SiC (25 μm) were prepared by electromagnetic stir casting method. Mechanical properties (tensile strength, hardness, toughness and fatigue strength) and microstructure of all five samples were analyzed. Microstructure presents that the reinforcements (SiC particulates and Fly-ash) are uniformly distributed in the matrix (A356). The results reveal that sample of A356/15 %SiC/5 % Fly-ash shows best result among all the selected samples. Density, porosity, specific strength and thermal expansion were also calculated to see the effect of Fly-ash addition.

Evaluation of stiffness and strength in fused deposition sandwich specimens

Abstract: New technologies known as additive manufacturing (AM) are now available for producing prototypes directly from a 3D CAD model. However, prototypes made by AM usually have mechanical characteristics inferior to those of the final product. AM technologies are in increasing demand for use in the development of functional prototypes and the manufacture of final products. The main aim of this work was to evaluate the influence of deposition strategies on the mechanical behavior of the AM process known as fused deposition modeling (FDM) and to gain a better understanding of the stiffness behavior of the parts. Specimens with different raster orientations in each layer (sandwich-like configurations) were built. The final stiffness and strength of the specimens were determined in tensile and bending tests, and the stiffness was predicted using classical lamination theory. The stiffness in the two main directions for the specimens manufactured with the sandwich deposition configurations was higher than or at least equal to the stiffness of the specimens produced with the default FDM configuration. However, the results indicate that the analytical model used did not accurately predict the behavior in the experimental tests.

Multi-objective process optimization of wire electrical discharge machining based on response surface methodology

Abstract: Determining the optimal cutting parameters has always been a critical matter to achieve high performance in different types of machining. In this study the behavior of four major control parameters includes pulse on time (T on), pulse off time (T off), peak current (IP), and servo voltage base on design of experiment method during wire electrical discharge machining of titanium alloy (Ti6Al4 V) experimentally studied. A zinc-coated brass wire of 0.25 mm diameter was used as a tool electrode to cut the specimen. Analysis of variance (ANOVA) technique was used to find out the parameters affecting the surface roughness, sparking gap, wire lag, wire wear ratio, and white layer thickness. Assumptions of ANOVA were discussed and carefully examined. This work has been established as a second-order mathematical model based on the response surface methodology. The residual analysis and confirmation runs indicate that the proposed model could adequately describe the performance of the factors those are being investigated. The results are particularly useful for scientists and engineers to determine which subset of the process variable has the maximum influence on the process performance.

Correlating tool wear, surface roughness and corrosion resistance in the turning process of super duplex stainless steel

Abstract: Super duplex stainless steels are extremely corrosion-resistant alloys designed for very demanding applications that expose them to corrosive environments, such as seawater. Due to their chemical composition and microstructure, which provide high mechanical strength and thermal resistance as well as high ductility, the machinability of these alloys is generally poor, resulting in long production cycles and high tooling costs. Moreover, machining may be harmful for the corrosion resistance of the alloy. The goal of this research is to study the turning operation of UNS 32750 alloy, known commercially as SAF 2507, and its influence on the alloy’s corrosion resistance in practical applications. Tests were performed, using cutting speed and cooling conditions with low and high fluid pressure as the input variables. The results indicate that turning with PVD-coated inserts under high-pressure cooling resulted in long tool lives, good workpiece roughness and high corrosion resistance of the material after machining. The most frequent wear mechanism found during the tests was notch wear, while the main tool wear mechanism was attrition.

Wire electrical discharge machining of AA7075/SiC/Al 2 O 3 hybrid composite fabricated by inert gas-assisted electromagnetic stir-casting process

Abstract: This paper investigated the effect of wire electrical discharge machining process parameters like discharge duration, pulse interval time, discharge current and the wire drum speed on the kerf width while machining newly developed hybrid metal matrix composite (Al7075/7.5 % SiC/7.5 % Al2O3). The hybrid composite was prepared by inert gas assisted electromagnetic stir-casting process. Taguchi method was used for parameter optimization and the level of importance was determined using analysis of variance. The results show that discharge duration, discharge current and wire drum speed were significant parameters. The discharge current was the most significant parameter that contributed maximum (47.16 %) to the kerf width followed by discharge duration (38.36 %), wire drum speed (5.16 %), and interaction, discharge duration × discharge peak current (5.47 %). The pulse interval time had insignificant effect on the kerf width. In confirmation test, the average experimental value of kerf width (228.7 μm) was within an error of 2.56 % of the predicted value at the optimum level of process parameters.

Identification of nonlinear structures using discrete-time Volterra series

Abstract: Mathematical modeling of mechanical structures is an important research area in structural dynamics. The goal is to obtain a model that accurately predicts the dynamics of the system. However, the nonlinear effects caused by gaps, backlash, joints, as well as large displacements are not as well understood as the linear counterpart. In this sense, the Volterra series is an interesting tool for the analysis of nonlinear systems, since it is a generalization of the linear model based on the impulse response function. This paper applies the discrete-time Volterra series expanded in orthonormal Kautz functions to identify a model of a nonlinear benchmark system represented by a Duffing oscillator. The input and output data are used to identify the Volterra kernels of the structure. After the identification of the model, the linear and nonlinear components of the response of the system can be analyzed separately. The paper concludes by indicating the main advantages and drawbacks of this technique to model the behavior of nonlinear systems.

Optimal point-to-point motion planning of non-holonomic mobile robots in the presence of multiple obstacles

Abstract: This paper presents theoretical and experimental investigations in dynamic modeling and optimal path planning of a non-holonomic mobile robot in cluttered environments. A mobile robot in the presence of multiple obstacles was considered. Nonlinear dynamic model of the system was derived with respect to non-holonomic constraints of robot’s platform. Motion planning of the system was formulated as an optimal control problem, and efficient potential functions were employed for collision avoidance. Applying the Pontryagin’s minimum principle was resulted in a two-point boundary value problem solved numerically. The effectiveness and capability of the proposed method were demonstrated through simulation studies. Finally, for verifying the feasibility of the presented method, results obtained for the Scout mobile robot were compared with the experiments.

Determining of the hydrodynamic forces on the multi-hull tunnel vessel in steady motion

Abstract: The research described in this paper was carried out to determine the hydrodynamic forces on the multi-hull tunnel vessel in steady motion. The hull form of vessel is fairly generated by the tunnel hull form generator code using the non-uniform rational B-Spline method. Then, the hydrodynamics simulation is carried out based on finite volume discretization method using volume of fluid model to consider free surface between water and air phases around the vessel. A dynamic mesh restructuring method is applied for grid generation regarding to the heave and pitch motions of vessel in each time step. The calculations of the center of gravity arising, trim angle, pressure, resistance and effective power are studied at various vessel’s speeds. The resistance plot versus velocity has an increasing trend having a hump velocity while the power curve shows a linear-like changes respect to speed increasing. Pressure calculations show that the ratio of hydrostatic pressure to total pressure is decreased at the end point of keel from 100 to 1 % as velocity increases from 5 to 20 m/s. The proposed numerical algorithm is a promising method for hydrodynamic analyses of wide-ranging high speed vessel types, particularly tunnel vessels.

Simulation machining of titanium alloy (Ti-6Al-4V) based on the finite element modeling

Abstract: Titanium alloy is the most significant material used in the aviation industry because of their properties such as high strength and corrosion resistant. However, it is considered one of the most challenging areas for all industrialists due to their poor machinability. Therefore, machining process needs to be controlled by selecting the optimal cutting conditions to obtain the best machining responses at the same time which is very difficult and involves high cost. Hence, this review paper presents the investigation of an agreement between the simulation results and experimental findings to evaluate the finite element modeling (FEM) for prediction of the machining parameters of titanium alloy (Ti-6Al-4V). Computer-aided engineering tools, especially software which was used to perform the simulation. Four types of finite element software have been focused during the machining process of titanium alloy (Ti-6Al-4V) such as AdvantEdge, ABAQUS/EXPLICIT, DEFORM, and FORG software. The simulation results of FEM proved an agreement with the experimental data during the machining process of titanium alloy (Ti-6Al-4V). The FEM permits to reduce the cost of manufacturing in terms of prolonging the cutting tool life and saving machining time.

Dynamic and phenomenological vibration models for failure prediction on planet gears of planetary gearboxes

Abstract: Faults detection in planet gears of planetary gearboxes by vibration analysis is not as straightforward as the detection of failures in conventional gear transmissions. This is because the driving flanks are different between the inner contact (ring–planet gear) and the external contact (sun–planet gear). Furthermore, the failure position varies with respect to the fixed transducer located on the ring gear, a situation leading to differences in the transient amplitude of the acceleration signals. In the present study, the planet gear fault is simulated based on two models: dynamic and phenomenological. These models have been used in other publications for the study of non-faulty planetary gearboxes. For the first model, the equations of motion are solved by temporal integration using HHT; whereas the second model is solved using algebraic equations. The fundamental results from the simulation of both models are shown in terms of waveforms and spectral content. They are also compared and validated later with the experimental results extracted from two test benches. It is concluded that the dynamic model has larger difficulties for spectral analysis, due to numerical errors from the temporal integration and mainly by the non-inertial reference frame used. Regarding the detection of failures in planet gears through vibration signals, this will not necessarily generate periodic transients every half rotation of this component, as it depends on if the planet gear is damaged on one or both flanks of the tooth. The conducted analysis also permits to conclude that when one flank is damaged, it can be detected more clearly when it meshes with the sun gear than when it meshes with the ring gear.

Guideline tool based on design for manufacturing and assembly (DFMA) methodology for application on design and manufacturing of aircrafts

Abstract: This paper presents a guideline which uses the concepts of design for manufacturing and assembly methodology for specific application on design and manufacturing of aircrafts. The main goal of this guideline was to orient the engineers during the aircraft development phases, such that a better aircraft design is achieved. The guideline comprises a set of tables to drive the engineers for a better evaluation of manufacturing processes, assembly, maintenance and human factors (ergonomics). It aims to improve the manufacturing and assembly for easy manufacturing of parts that build the aircraft with low costs, high quality and the best optimized condition. A case study is shown to testify the advantages and benefits achieved when the proposed guideline tool is used.

Optimization of tribological parameters for a brake pad using Taguchi design method

Abstract: In this study, the weight loss of brake pad in automotive brake system was investigated using Taguchi’s method. Wear tests of the brake pad versus cast iron disk were carried out for a dry sliding condition in a so-called a pad-on-disk rig. The wear tests were realized at the sliding speeds of 7, 9, and 11 ms−1 and under the pressures of 0.5, 1, and 1.5 bars. The obtained lowest weight loss for the brake pad contains the copper flake volume fraction of 20 % by weight under the same test conditions. The experimental results are transformed into a signal-to-noise (S/N) ratio using Taguchi method. Volume fraction of copper flake, pressure, and interaction between volume fraction of copper flake and pressure exert a great effect on the weight loss, at 58.11, 16.35, and 20.86 %, respectively. The estimated S/N ratios of the weight loss, using the optimal testing parameters, were calculated and a good agreement was observed between the predicted and actual weight loss, with a confidence level of 99.5 %.

Investigations into the surface quality and micro-hardness in the ultrasonic machining of titanium (ASTM GRADE-1)

Abstract: In the current study, the influence of various process parameters such as tool material, abrasive type, slurry grit size and power rating on the surface quality and the micro-hardness of the machined surface has been reported while machining pure titanium (ASTM Grade-I) using ultrasonic machining. Taguchi’s robust design approach has been utilized for planning the experiments and optimizing the experimental results of surface roughness and micro-hardness. The surface topography of the machined samples revealed that the mode of material removal is related to the energy input rate. The mode of material removal may change from plastic deformation to brittle fracture under varied conditions of energy input rate. The hardness gradient has also been evaluated for selected process conditions and correlated with the energy input rate corresponding to each of the conditions.

An integration of TRIZ and the systematic approach of Pahl and Beitz for innovative conceptual design process

Abstract: Conceptual design has a considerable effect on costs of products and product innovation. Therefore, it is known as the most critical phase of engineering design process. We envision that new generation CAD/E systems will hinge on innovative conceptual design. Despite its importance, the relevant works and commercial efforts have usually concentrated on embodiment and detail design, which are the last two phases of engineering design process. Because the conceptual design phase includes time-consuming and tedious methods. Moreover, they do not sufficiently incorporate creativity methods that trigger designers to find more creative and innovative solutions. To cope with this issue, we propose an integration of TRIZ and conceptual design process based on Pahl and Beitz’s Systematic Approach. In the proposed integration model, TRIZ is used as a problem solver in the step of determination of problems; as a solution finder in the step of searching for solutions to subfunctions, and as a solution improver after the step of evaluation in the design process. To demonstrate the applicability of the model, a case study is conducted. The case study shows that the integration model is superior to other similar works in terms of inventiveness level, applicability to practice, and efforts to use.

Influence of substrate roughness on adhesion of TiN coatings

Abstract: Titanium-nitride coatings were prepared by ion beam assisted deposition. In order to provide adequate adhesion between TiN films and steel substrates, ion beam mixing of Ti atoms with atoms of steel base was applied prior to deposition. The effect of substrate surface roughness on adhesion strength of TiN coatings was evaluated in this research. A scratch test was used to characterize the adhesive properties of the coatings. Optical microscopy was employed to examine scratch-induced channels, while atomic force microscopy was used to determine sample roughness prior and after the deposition of TiN coatings. It has been revealed that adhesion increases with increase in substrate roughness.

Optimization of nonlinear characteristics of ball burnishing process using Sugeno fuzzy neural system

Abstract: Aluminium alloy (Al 63400) is burnished using different burnishing parameters. It deals with the modelling of nonlinear characteristics of ball burnishing using Sugeno fuzzy neural system. A fuzzy neural network or neuro-fuzzy system is a learning machine that finds the parameters of the fuzzy systems (i.e. fuzzy sets, fuzzy rules) by exploiting approximation techniques from neural networks. Input parameters are designed for experimental process using Box–Behnken method. Ball burnishing tool is used in CNC machining centre to surface finish the milling process. The tool and work-piece material are tungsten carbide and aluminium, respectively. The input parameters are force, table feed, step over, ball diameter and number of passes. The output parameters are surface roughness along feed direction, surface roughness across feed direction and surface micro-hardness. The minimum surface roughness obtained for ball burnishing process along the tool path (x-axis) is 0.032 μm and across the tool path (y-axis) is 0.232 μm and its micro-hardness is 91.63 HV. Sugeno fuzzy neuro system is used to model the nonlinear characteristics of the surface roughness (along the tool path and across the tool path) and micro-hardness. The Pearson product moment correlation is used to validate the fuzzy neuro model.

Electrical discharge machining parameters optimization using response surface methodology and fuzzy logic modeling

Abstract: This paper describes the application of the fuzzy logic analysis coupled to Central Composite Design to optimize the parameters of the carbon nanotube (CNT) mixed in dielectric fluids used in electrical discharge machining (EDM) process This work investigates the surface characteristics of AISI D2 Tool Steel with graphite as a tool electrode during EDM process The multiwall carbon nanotube is mixed with dielectric fluids to analyze the surface roughness and micro-cracks using atomic force microscope measurements Response surface model has been developed to predict the surface roughness for EDM parameters Analysis of variance and F test have been used to check the validity of response surface model and determine the significant process parameter affecting the surface roughness A fuzzy logic model has been used to investigate relationships between the machining parameters and determine the efficiency of each parameter with and without using CNT-based EDM process

New heuristics for the no-wait flowshop with sequence-dependent setup times problem

Abstract: In this paper, we address the problem of scheduling jobs in a no-wait flowshop with sequence-dependent setup times with the objective of minimizing the makespan and the total flowtime. As this problem is well known for being NP hard, we present two new constructive heuristics to obtain good approximate solutions for the problem in a short CPU time, named GAPH and QUARTS. GAPH is based on a structural property for minimizing makespan and QUARTS breaks the problem in quartets to minimize the total flowtime. Experimental results demonstrate the superiority of the proposed approaches over three of the best-known methods in the literature: BAH and BIH, from Bianco et al. (INFOR J 37(1):3–19, 1999) and TRIPS, by Brown et al. (J Oper Res Soc 55(6):614–621, 2004).

Investigation of burr formation and surface roughness in drilling engineering plastics

Abstract: Engineering plastic components are generally drilled owing to the need for bolted, riveted or screwed structures, but formation of burr induces some difficulties in the assembly stage. The most practical method for deburring is to select proper cutting parameters and tool during drilling. This study investigates the formation of the exit burr height during drilling of ultra-high molecular weight polyethylene under three different cutting speeds (30, 40, 50 m/min) and feeds (0.006, 0.0125, 0.250 mm/rev). Also, three different types of HSS-based tools such as TiN-coated, TiCN-coated and uncoated HSS twist drill tools were used. The effects of cutting parameters and tools were the controllable factors in the experimental study. Experimental design and multiple regression analysis were utilized in determining the optimal parameters. The results showed that highest feed (0.025 mm/rev), lowest cutting speed (30 m/min) and uncoated HSS tool gave lower burr height due to the less deformation of the work material. Surface roughness of the drilled holes was also measured and almost similar effects of the controllable factors on surface roughness and burr height were observed. Finally, a relation between the burr height and type of chip was observed and it has been observed that the process variables increasing burr height gave irregular and highly deformed chips.

Nucleate boiling of water using nanostructured surfaces

Abstract: The aim of this study was to analyze the effect of nanostructured surfaces on the nucleate boiling of distilled water at saturation temperature and atmospheric pressure. The nanostructures studied consisted of nanoparticles of molybdenum (obtained by the sputtering method) and of maghemite, deposited on a substrate of very thin Constantan tape. The results obtained with the nanostructures were compared with experimental data for smooth and rough tapes (substrate). The nanostructures increased the surface wettability, especially in the case of the maghemite deposition, and consequently increased the critical heat flux values. An increase in the heat transfer coefficient was observed only for high heat fluxes. The measurement of the apparent contact angle showed that the rough substrates are highly hydrophobic and enhance the heat transfer coefficient.

Influence of intake pipe length and diameter on the performance of a spark ignition engine

Abstract: This work shows the influence of intake pipe length and diameter on the performance of a spark ignition engine. A production four-stroke, four-cylinder, eight-valve, 1.0-l engine was tested in a bench dynamometer, fuelled by a blend of 78 % gasoline and 22 % ethanol. Experiments were carried out in the engine speed range from 1,500 to 6,500 rev/min. Three intake pipe lengths—0.3, 0.6 and 0.9 m—and three intake pipe diameters—0.044, 0.053 and 0.067 m—were investigated. The effects of intake pipe geometry on intake air mass flow rate and volumetric efficiency and the impacts on engine performance parameters—torque, power, thermal efficiency and specific fuel consumption—were evaluated. The results revealed that, for low engine speeds, the intake pipe with longer length and smaller diameter produced the best performance. On the other hand, the intake pipe with shorter length and larger diameter delivered the best engine performance at high speeds.

Study of ECAE mechanics by upper bound rigid block model with two degrees of freedom

Abstract: The mechanics of equal channel angular extrusion (ECAE) in a rectangular die was studied by upper bound method and rigid block model of deformation with two variables (two degrees of freedom). The appearance of a dead zone in the die external corner was assumed and verified by physical simulation using plasticine as a modeling material. The obtained dependences of ECAE pressure, total ECAE shear and geometrical parameters of dead zone upon friction factor were compared with corresponding results of upper bound rigid block analysis with one variable (one degree of freedom) and with the results of slip line analysis published by the authors elsewhere. It was demonstrated that an increase in degrees of freedom in an ECAE rigid block model from one to two results in much better approximation of the reference data of slip line analysis. The authors believe that an increase in the numbers of degrees of freedom and flexibility of a rigid block model generally leads to a better accuracy in modeling of other metal forming processes as well. As an example, the ECAE pressure of the aluminum 6061 alloy was calculated and compared with the experimental data from literature. A good agreement between them was found. The importance of consideration of friction in the inlet and outlet die channels was emphasized.

Development and analysis of series elastic actuators for impedance control of an active ankle–foot orthosis

Abstract: This paper deals with force and impedance control of a series elastic actuator specially designed for driving an ankle–foot orthosis. Series elastic actuators are devices where elastic components are introduced between the motor’s output and the load. From the deflection of these components, it is possible to measure the force applied to the load and to control it. Furthermore, the mechanical impedance of the actuator/load interface can be regulated to typical values of joint’s stiffness and damping presented by humans during walking. Experimental results of force and impedance control applied to an active ankle–foot orthosis driven by the series elastic actuator are presented. Also, a variable impedance control strategy is performed to reproduce the behavior of an actual ankle joint.

Thermoanalysis and reaction kinetics of heavy oil combustion

Abstract: The present study deals with fingerprinting the oxidation behavior of a Brazilian crude (12° API) oil. It focuses on the determination of reaction kinetic parameters through classical thermal analysis techniques such as thermogravimetry (TG), differential thermal analysis (DTG) and scanning calorimetry (DSC). The required experimental data are collected from oil and oil–sand samples. The reaction data are treated following distinct conventional and isoconversional non-isothermal models, using integral and differential approaches based on Arrhenius’ model. The thermoanalytical study is successful in identifying three oxidation temperature ranges: the low-temperature (LTO) range, a transition zone, and the high-temperature (HTO) range. TG and DSC analyses show that the highest variation of mass and the highest level of energy generation occur at the HTO range. At the high end of the LTO range, a mass transfer resistance (skin effect) was evident. Values of activation energy obtained for oil samples are 103 kJ mol−1 for LTO and 278 kJ mol−1 for HTO oxidation reactions by the most straightforward method used—the unity model. By all kinetic models, HTO’s values are higher than those for LTO, observation also valid for the results of oil–sand samples. Results also evidence that the presence of sand contributes to the so-called skin effect.

Concomitant vortex-induced vibration experiments: a cantilevered flexible cylinder and a rigid cylinder mounted on a leaf-spring apparatus

Abstract: This paper presents experimental results of vortex-induced vibrations (VIV), concomitantly carried out in water with a flexible cylinder, rigidly fixed, and with a ‘rigid’ cylinder, mounted on an elastic apparatus. The experiments were run at IPT towing tank facility, in a side-by-side arrangement. The flexible cylinder is simply fixed at the upper end. For the flexible cylinder, two degrees of freedom (2DOF) are implied for each vibration mode: crosswise and aligned with respect to the incident flow. The elastic support to which the ‘rigid’ cylinder is mounted is made of two vertical leaf-springs, fixed to two thick horizontal plates, conferring to the cylinder a single degree of freedom (SDOF) to oscillate transversally with respect to the incident flow. The mass ratios of the cylinders are almost the same, around 1.2 and 1.4, respectively, very low values, typical of long ocean pipe structures, as risers and pipelines. The structural damping ratio is also typically low and such as to guarantee high-amplitude responses. Besides usual spectral and statistical analysis, the Hilbert–Huang spectral analysis technique is applied, as, strictly, VIV is a non-stationary oscillation emerged from a nonlinear dynamic system. A discussion is made on the distinct VIV behaviors of the SDOF and the 2DOF systems.

Investigation on stator vibration characteristics under air-gap eccentricity and rotor short circuit composite faults

Abstract: This paper investigates the stator vibration characteristics of turbo-generator, respectively, under normal condition and the air-gap eccentricity and rotor interturn short circuit composite fault, with the effects of the eccentricity factor and the short circuit factor on the stator vibration characteristics presented. The air-gap magnetic flux density and the unit magnetic pull under the composite fault are firstly deduced. Then three kinds of eccentricities are, respectively, considered to analyze the stator vibration characteristics. Finally, experiments are taken on a SDF-9 non-salient fault-simulating generator to verify the theoretical results. The study shows that when the composite faults occur, the eccentric kind determines the vibration components. 1st to 4th harmonic vibrations will be produced when the eccentricity is the static one, while 1st to 6th harmonic vibrations will be produced when the eccentricity is the other two. The increment of the interturn short circuit will increase the 4th harmonic vibration, but decreases the 2nd harmonic for the static eccentricity situation, and increase the 6th harmonic vibration for the other two eccentricities. However, no matter which kind of eccentricity increases, each stator vibration component will be increased. The presented work has reference value and positive meaning for the diagnosis of composite faults.

Modeling of piezoelectric energy harvesting considering the dependence of the rectifier circuit

Abstract: Harvesting energy with piezoelectric materials has been a process of many practical applications in structural health monitoring, either to recharge batteries or feed directly sensors and also electronic devices. In general, the amount of energy provided by a vibration source requires converting the alternating current (AC) to direct current (DC) through rectifier circuits before using it as a power supply of electronic devices. However, modeling the harvesting system, usually a PZT sensor bonded on a cantilever beam and coupled to a rectifier circuit, using the same software package is pointed out by some authors as a drawback to overcome, due to its multidisciplinary requirements, involving topics of both mechanical and electrical engineering. In this sense, the goal of the present paper is describe a comprehensive and simple modeling strategy, which considers a single computational platform and accounts for both the electromechanical model of a clamped piezoelectric beam and the practical energy harvesting circuit, seeking further application when optimizing the entire energy harvesting system. Numerical simulations and experimental tests are performed to illustrate the proposed approach, considering a full-wave diode bridge as the non-controlled rectifier circuit and a resistive load, which are directly connected to the cantilevered piezoelectric beam.

Combined effects of micropolarity and surface roughness on the hydrodynamic lubrication of slider bearings

Abstract: In this paper, theoretical analysis of combined effects of micropolarity and surface roughness on the performance characteristics of hydrodynamic lubrication of slider bearings with various film shapes such as plane slider bearing, exponential slider bearing, secant-shaped slider bearing and hyperbolic slider bearing is presented. A stochastic random variable with non-zero mean, variance and skewness is assumed to mathematically model the surface roughness of the slider bearing. The Eringen’s (J Math Mech 16:1–18, 1) micropolar fluid is used to characterize the rheological behavior of the lubricant with polymer additives. The averaged modified Reynolds equation is derived and the closed form of expressions for the bearing characteristics such as load carrying capacity, frictional force, center of pressure are obtained. Numerical results are compared for various film shapes under consideration, the negatively skewed surface roughness increases the load carrying capacity, frictional force and temperature.

Analysis of syngas formation and ecological efficiency for the system of treating biomass waste and other solid fuels with CO2 recuperation based on integrated gasification combined cycle with diesel engine

Abstract: This paper presents the analysis of ecological and economical availability for using syngas from gasification of biomass waste or other solid fuels into diesel with ICE-based combined cycle (CC). The new approach is proposed to improve the ecological efficiency of the CC system and decrease the cost of electricity which can be produced with electric generator. For optimization of design of the combined system the new diagrams were obtained to determine characteristics of mixed fuel (diesel + syngas) for the engine at varied syngas fuel parameters after the gasifier with steam agent (plasma or other type). Based on these diagrams it is possible to obtain total reducing CO2 emission in atmosphere of ~1.5 times in the CC system with biomass gasifier.

Inverse determination of blood perfusion coefficient by using different deterministic and heuristic techniques

Abstract: This work aims to establish an estimation of the blood perfusion coefficient in cancerous tissues, using inverse problem techniques. The blood perfusion coefficient is modeled as a constant parameter or as a function of the position. Several optimization methods are studied for the constant parameter model. The function estimation approach is performed by the conjugate gradient method with adjoint problem to evaluate the model with spatial variation of the blood perfusion coefficient. The heat transfer problem is represented by the Pennes’ equation. It is a standard heat diffusion equation with a sink term and a source term. The sink term accounts for the blood flow within the biological tissue and the source term accounts for the combined effect of the internal metabolic heat generation together with an external heat flux associated to the cancer treatment. The results are obtained for different functions of blood perfusion coefficients, simulating measurements with and without errors. The performances of the studied inverse problem techniques are analyzed.