Showing papers in "Journal of The Brazilian Society of Mechanical Sciences and Engineering in 2008"

Optimal design of passenger car suspension for ride and road holding

Abstract: The primary function of a vehicle suspension system is to isolate the road excitations experienced by the tyres from being transmitted to the passengers. In this paper, a suitable optimizing technique is applied at design stage to obtain the suspension parameters of a passive suspension and active suspension for a passenger car which satisfies the performance as per ISO 2631 standards. A number of objectives such as maximum bouncing acceleration of seat and sprung mass, root mean square (RMS) weighted acceleration of seat and sprung mass as per ISO2631 standards, jerk, suspension travel, road holding and tyre deflection are minimized subjected to a number of constraints. The constraints arise from the practical kinetic and comfortability considerations, such as limits of the maximum vertical acceleration of the passenger seat, tyre displacement and the suspension working space. The genetic algorithm (GA) is used to solve the problem and results were compared to those obtained by simulated annealing (SA) technique and found to yields similar performance measures. Both the passive and active suspension systems are compared in time domain analyses subjected to sinusoidal road input. Results show passenger bounce, passenger acceleration, and tyre displacement are reduced by 74.2%, 88.72% and 28.5% respectively, indicating active suspension system has better potential to improve both comfort and road holding.

Development of Asbestos-Free Friction Lining Material from Palm Kernel Shell

Abstract: Friction materials are applicable for braking and transmission in various machines and equipment. Their composition keeps changing to keep pace with technological development and environmental/legal requirements. For more than 80 years asbestos has been used as a friction material because of its good physical and chemical properties. However, due to the health hazard associated with its handling, it has lost favour and several alternative materials are being increasingly used. Thus, in this work, a non - asbestos friction material was developed using an agro-waste material base - palm kernel shell (PKS)- along with other constituents. Among the agro-waste shells investigated the PKS exhibited more favourable properties. Taguchi optimization technique was used to achieve optimal friction material formulation and manufacturing parameters. The derived friction material was used to produce automobile disk brake pads. The laboratory brake pads were tested for wear and effectiveness on a car. When compared with a premium asbestos-based commercial brake pad they were found to have performed satisfactorily. However, more pad wear was observed on the PKS pad at high vehicular speeds beyond 80km/hour. The results suggest that palm kernel shell could be a possible replacement for asbestos in friction lining materials.

Turning hardened steel using coated carbide at high cutting speeds

Abstract: The present work studies some aspects of the turning process applied on hardened steel using multilayer coated carbide tools at high cutting speeds. The influence of cutting parameters (vc, f, and depth of cut - d.o.c.) on tool temperature, tool wear, cutting forces, and surface roughness were analyzed. The current literature reports many studies using PcBN on hardened steel, but it is also important to know the results when using coated carbide tools, mainly for economical reasons. Temperature was measured by a thermocouple positioned at the lowest insert face, underneath it. Temperature near the rake face was calculated using the measured gradient within the insert thickness. To measure the gradient a special technique was used with one embedded thermocouple near the rake face and one underneath. Tool wear measurements demonstrated the capability of such tools in turning hardened steel with reasonable tool life. Forces measured resulted in relatively low values, being the radial component the largest of all. For the different cutting conditions studied, the doc has the greatest influence on force and temperature. Additionally, the best surface roughness values were smaller than 0,4 µm Ra.

Timoshenko beam with uncertainty on the boundary conditions

Abstract: In mechanical system modeling, uncertainties are present and, to improve the predictability of the models, they should be taken into account. This work discusses uncertainties present in boundary conditions using the model of a vibrating Timoshenko beam, free in one end and pinned with rotation constrained by a linear elastic torsional spring in the other end. The Finite Element Method is used to discretize the system and two probabilistic approaches are considered to model the uncertainties: (1) the stiffness of the torsional spring is taken as uncertain and a random variable is associated to it (parametric probabilistic approach); (2) the whole stiffness matrix is considered as uncertain and a probabilistic model is constructed for the associated random matrix (nonparametric probabilistic approach). In both approaches, the probability density functions are deduced from the Maximum Entropy Principle. In the first approach only the uncertainty of a parameter is taken into account, and in the second approach, the uncertainties of the model are taken into account, globally. Both approaches are compared and their capability to improve the predictability of the system response is discussed.

Hygrotermal effects evaluation using the iosipescu shear test for glare laminates

Abstract: Fiber-metal laminates (FML) composed of alternating layers of unidirectional fiber-reinforced plastic (FRP) laminae and aluminum-alloy sheets offer some superior mechanical properties, compared with either conventional laminates consisting of only FRP laminae or high-strength monolithic aluminum alloys. The environmental factors can limit the applications of composites by deteriorating the mechanical properties during service. Usually, polymeric matrix absorbs moisture when exposed to humid environments and metals are prone to surface corrosion. On the other hand, FML laminates presents more resistance of moisture when compared with their constituents. Evaluation of shear properties is particularly important in the design of mechanically fastened parts and components, which are subject to parallel and opposing loads. In this work, the shear behavior was studied for Glare laminates and its constituents in dry and wet conditions.

An Optimal Linear Control Design for Nonlinear Systems

Abstract: This paper studies the linear feedback control strategies for nonlinear systems. Asymptotic stability of the closed-loop nonlinear system is guaranteed by means of a Lyapunov function, which can clearly be seen to be the solution of the Hamilton-Jacobi-Bellman equation thus guaranteeing both stability and optimality. The formulated Theorem expresses explicitly the form of minimized functional and gives the sufficient conditions that allow using the linear feedback control for nonlinear system. The numerical simulations the Duffing oscillator and the nonlinear automotive active suspension system are provided to show the effectiveness of this method.

Modeling of dynamic rotors with flexible bearings due to the use of viscoelastic materials

Abstract: Nowadays rotating machines produce or absorb large amounts of power in relatively small physical packages. The fact that those machines work with large density of energy and flows is associated to the high speeds of rotation of the axis, implying high inertia loads, shaft deformations, vibrations and dynamic instabilities. Viscoelastic materials are broadly employed in vibration and noise control of dynamic rotors to increase the area of stability, due to their high capacity of vibratory energy dissipation. A widespread model, used to describe the real dynamic behavior of this class of materials, is the fractional derivative model. Resorting to the finite element method it is possible to carry out the modeling of dynamic rotors with flexible bearings due to the use of viscoelastic materials. In general, the stiffness matrix is comprised of the stiffnesses of the shaft and bearings. As considered herein, this matrix is complex and frequency dependent because of the characteristics of the viscoelastic material contained in the bearings. Despite of that, a clear and simple numerical methodology is offered to calculate the modal parameters of a simple rotor mounted on viscoelastic bearings. A procedure for generating the Campbell diagram (natural frequency versus rotation frequency) is presented. It requires the embedded use of an auxiliary (internal) Campbell diagram (natural frequency versus variable frequency), in which the stiffness matrix as a frequency function is dealt with. A simplified version of that procedure, applicable to unbalance excitations, is also presented. A numerical example, for two different bearing models, is produced and discussed.

An experimental study on ultrasonic machining of pure titanium using designed experiments

Abstract: In the present research work, the effect of several process parameters on the machining characteristics of pure titanium (ASTM Grade-I) has been reported. The machining characteristics that are being investigated are tool wear rate and the quality of the machined surface in terms of the surface finish. The mechanism of material removal was has also been correlated with the machining conditions. Four different process parameters were undertaken for this study; Tool material, abrasive material, grit size of the slurry used and power rating of the machine. The optimal settings of parameters are determined through experiments planned, conducted and analyzed using Taguchi method. The significant parameters are also identified and their effect on tool wear rate and surface roughness is studied. The results obtained have been validated by conducting the confirmation experiments.

Mixture experiments and their applications in welding flux design

Abstract: The traditional welding flux development has been by cost, material, time and labour intensive experiments. The extensive and expensive trial and error experimentation is needed because it is often difficult to know a priori how the flux ingredients interact to determine the operational characteristics of the flux and the final performance of the welded structure. The limitation of the traditional approach includes: (1) long lead-time (2) expensive experiments in terms of materials and energy consumption and labour requirements (3) the flux developed can not be guaranteed to be optimal and (4) inability to identify and quantify direct and interaction effects of flux ingredients. These constraints are due to the paucity of statistical modelling tools in welding flux technology. Since prediction models are derived from designed experiments, flux researchers need other methods by which flux experiments may be designed. This paper discusses a statistical modelling tool known as mixture experiment which has the potential to revolutionize welding flux development technology. Mixture design is discussed but not fully developed. The procedure of mixture experiment, analytical model forms and the sequence of model fitting are discussed. Areas of welding flux research where the various mixture designs may be useful are suggested.

Performance profiling of boric acid as lubricant in machining

Abstract: Turning is a widely used metal removal process in manufacturing industry that involves generation of high cutting forces and temperature. Lubrication becomes critical to minimize the effects of these forces and temperature on cutting tool and workpiece. The conventional cutting fluids employed in machining have certain limitations with regard to their use for ecological and economic reasons. Development of lubricants that are eco friendly is acquiring importance. In this context, application of solid lubricants has proved to be a feasible alternative to the conventional cutting fluids. In the present work, Boric Acid is used as a lubricant in turning process. Variations in cutting force, tool wear, tool temperature and surface roughness are studied under different machining conditions. The results indicate that there is considerable improvement in the machining performance with Boric Acid assisted machining compared to dry and wet machining.

Reliability analysis of I-section steel columns designed according to new Brazilian building codes

Abstract: This paper presents an evaluation of the safety of I-section steel columns designed according to the new revision of the Brazilian code for design of steel buildings (NBR8800) and to the code for loads and safety of structures (NBR8681). The safety evaluation is based on structural reliability analysis of columns designed to comply with these codes, and on advanced (FE-based) analysis of actual column resistance. The effects of geometrical imperfections and residual stresses in column resistance are taken into account. The uncertainty in yield stress, elasticity modulus, geometrical imperfections and dead and live loads are considered in the reliability evaluation. Reliability indexes are obtained for several column configurations. These indexes reflect the safety of the columns designed according to the two building codes. Reliability indexes are compared with target reliability indexes used in calibration of the ANSI code and with indexes proposed in the new EUROCODE. Keywords: steel columns, structural safety, building codes, nonlinear finite element analysis

Rotational placement of irregular polygons over containers with fixed dimensions using simulated annealing and no-fit polygons

Abstract: This work deals with the problem of minimizing the waste of space that occurs on a rotational placement of a set of irregular bi-dimensional small items inside a bi-dimensional large object. This problem is approached with an heuristic based on simulated annealing. Traditional “external penalization” techniques are avoided through the application of the no-fit polygon, that determinates the collision-free region for each small item before its placement. The simulated annealing controls: the rotation applied ch non-placed small item, a limited depth binary search is performed to find a scale factor that when applied to the small item, would allow it to be fitted in the large object. Three possibilities to define the sequence on which the small items are placed are studied: larger-first, random permutation and weight sorted. The proposed algorithm is suited for non-convex small items and large objects.

Hollow cathode discharge: application of a deposition treatment in the iron sintering

Abstract: The influence of a previous deposition treatment on the final amount of alloying elements (Cr and Ni) deposited and diffused into the surface of iron parts sintered in hollow cathode discharge (HCD) was studied. Cylindrical pure iron pressed samples, being a central cathode, were placed concentrically in the interior of an AISI 310 steel machine-made outer cathode, resulting in a 6 mm inter-cathode radial spacing. The study was divided in two steps: a) deposition treatment with the outer cathode acting as target and the iron sample acting as substrate (1123K -850 oC- and 60 minutes deposition temperature and time, respectively); and b) deposition treatment plus HCD sintering (1423K -1150 oC- and 60 minutes sintering temperature and time, respectively). The electrical discharge was generated using a pulsed voltage power source. The results indicate the presence of 6.5 at.% Cr and 6.9 at.% Ni on the samples surface. The concentration profiles were mathematically treated to quantify the actual amounts of Cr and Ni deposited on and diffused into the samples, and the integration of the fitted equations yielded the calculated areas of 133 (µm × at.% Cr) and 105 (µm × at.% Ni), respectively.

Identification of temperature-dependent thermal properties of solid materials

Abstract: This work proposes an experimental technique for the simultaneous estimation of temperature-dependent thermal diffusivity, α, and thermal conductivity, λ, of insulation materials. The thermal model used considers a transient one-dimensional heat transfer problem. The determination of these properties is done by using the principle of the Mixed technique. In this technique two objective functions are defined, one in the frequency domain and the other in the time domain. The objective function in the frequency domain is based on the square difference between experimental and calculated values of the phase angle, while the other objective function is the least square error function of experimental and calculated signals of temperature. The properties α and λ are obtained by using an experimental apparatus that basically consists of a Polyvinyl Chloride (PVC) sample exposed to different temperatures inside an oven. The temperature inside the oven is controlled by a PID temperature controller. The properties α and λ were estimated for 7 (seven) points of average temperature in a range from 20 oC to 66 oC. The properties were determined with an additional heating of approximately 4.5 K on the frontal surface. Analyses of sensitivity, sensors location and sample dimensions were also made. Keywords : thermal properties estimation, heat conduction, optimization, experimental methods

A Carbon Monoxide Transport Model of the Human Respiratory System Applied to Urban Atmosphere Exposure Analysis

Abstract: The aim of this work is to analyze the carbon monoxide (CO) transport in the human body submitted to several physical activity levels. A complete mathematical model of the human respiratory system was developed, considering the exchanges of CO, oxygen (O2) and carbon dioxide (CO2) in the lung, blood and tissues. The human body was divided in the following compartments: alveolar, pulmonary capillaries, arterial, venous, tissue capillary and tissues. The gas transport in the blood and tissues is represented by empirical equations. The physiological parameters were described in function of physical activity. The model was validated by comparing its results with experimental data of controlled CO exposition. The agreement was excellent. CO concentration curves for critical days of Sao Caetano do Sul city (SP, Brazil) atmosphere were used as model input. The simulation results for some physical activities show that the more intense the activity, the larger the blood carboxyhemoglobin (COHb) level variations. The COHb level was compared with a CO quality air criteria, which showed to be adequate for low and moderate physical activity levels.

Alternative fuels mixture in cement industry kilns employing Particle Swarm Optimization algorithm

Abstract: Most of the works accomplished in the optimization area in the cement industry are addressed to solve problems just considering only one variable, forgetting that it includes too many variables and they act at the same time. Among the main variables it can be mentioned the quality of the final product, the environmental ones, the costs along the process and the reduction of the fossil fuels (primary) employed through the use of alternative fuels (secondary), among others. The present work intends to build a mathematical model using optimization tools seeking to improve the cement production process foreseeing what can happen with the clinker and the emissions when the industrial residues co-processing technology is used as alternative or secondary fuel. In the optimization process a new approach called Particle Swarm Optimization (PSO) is employed, which is based on the Cauchy and Gauss distribution considering several process restrictions such as the specific fuel consumption, the cement quality and the environmental impact. The results obtained with PSO were precise and promising and they were compared with the classical Sequential Quadratic Programming (SQP). It was also possible to evaluate the levels of primary fuels substitution through the alternative or secondary ones.

Minimum pressure coefficient criterion applied in axial-flow hydraulic turbines

Abstract: The recent development of computer-based tools with more efficient algorithms has allowed a substantial improvement in hydraulic turbine design. The definition of an initial geometry capable to assist certain characteristics of turbine performance is a first step for useful numerical turbine analysis. This paper presents an application of the minimum pressure coefficient criterion for axial-flow hydraulic turbines cascade geometry design. In recent works, the criterion was tested for axial fan and it was showed that it is suitable to define the initial geometry for machine design. The global parameters that supply the principal dimensions of the turbine are obtained from the literature as based upon statistical data of installed power plants. The grid of the simulation domain was generated with CFX-TURBO grid software package and the results were obtained using the commercial package Navier-Stokes 3-D CFX-TASCflow to analyze the fluid flow through blade runner. Using this procedure, a study was carried out on a small axial-flow turbine, specifically designed to operate in a small river in the Amazon region. An interpretation of the flow through the turbine’s hydraulic channels is presented for nominal flow rate operation points. Finally, the results are evaluated to hydraulic efficiency prediction of blade runner turbines

Trajectory Planning of Jumping over Obstacles for Hopping Robot

Abstract: Trajectory planning strategy is proposed to jump over an obstacle integrated three various dynamics in one-legged multi-joint hopping robot. A concept of inertia matching ellipsoid and directional manipulability are extended to optimize take-off postures. Optimized results have been used to plan hopping trajectory. Aimed at the sensitivity of motion trajectory to constraint conditions, a 6th polynomial function is proposed to plan hopping motion and it has a better robustness to the parameters change of constraint conditions than traditional 5th polynomial function. During flight phase, an iterative method and angular momentum theory are used to control posture to a desired configuration. In order to lift foot over an obstacle, correction functions are constructed under unchanged boundary constraint conditions. During stance phase, robot trajectories are planned based on internal motion dynamics and steady-state consecutive hopping motion principle. A prototype model is designed, and the effectiveness of the proposed method is confirmed via simulations and experiments.

Stagnation point flow and heat transfer of a micropolar fluid with uniform suction or blowing

Abstract: The steady laminar flow of an incompressible non-Newtonian micropolar fluid impinging on a permeable flat plate with heat transfer is investigated. A uniform suction or blowing is applied normal to the plate, which is maintained at a constant temperature. Numerical solution for the governing nonlinear momentum and energy equations is obtained. The effect of the uniform suction or blowing and the characteristics of the non-Newtonian fluid on both the flow and heat transfer is presented and discussed.

MHD flow of micropolar fluid in a rectangular duct with hall and ion slip effects

Abstract: The steady flow of incompressible and electrically conducting micropolar fluid flow through a rectangular channel is considered taking Hall and ionic effects into consideration An external uniform magnetic field is applied which is directed arbitrary in a plane perpendicular to the flow direction The governing partial differential equations are solved numerically using finite difference method, and the effects of micropolar parameters, magnetic parameter, Hall parameter and ion slip parameter on the velocity and microrotation are discussed

Experimental Investigation on the Influence of the Lubricant Type in the Punch Stretching of Extra Deep- Drawing Steel

Abstract: In sheet metal stamping, several variables must be taken into account such as the material's mechanical properties, the tool's geometry, interface lubrication between punch and sheet metal and deformation rate, among others. This paper reports on a study of the lubricant's influence on the stretching forming process. The lubricants used ranged from liquid, such as mineral and vegetable oils with extreme pressure additives and synthetic fluids to solid PVC (polyvinyl chloride) and polyurethane films. In this work, the main objective was to study a minor strain profile as an alternative method to analyze the influence of solid and liquid lubricants on stretching forming of high stampability steels (DC 06). The minor true strain distribution profile was obtained, from the die radius to the punch pole, from stamping tests with stretching characteristics. Analyses of the strain distribution profile and of the fracture position allow an evaluation of the lubrication efficiency. Of the five lubricants studied, the results indicated that the solid polyurethane film yielded the best performance, promoting a more homogeneous distribution profile of the minor true strain (e2), increasing from the die radius to the punch pole, where tearing of the metal sheet occurred.

Influence of machining parameters on fatigue endurance limit of AISI 4140 steel

Abstract: The general purpose of this research is to study the influence of commercial machining parameters on fatigue limits of steels. Specifically in this work, the influence of cutting speeds, depth of cut, feed rate and residual stresses of turned surfaces of AISI 4140 steel specimens on fatigue strength were analyzed. In some specimens, the residual stress was eliminated by heat treatment. The fatigue experiments were carried out at room temperature, applying a cyclical frequency of 58Hz, with mean stress equal to zero (R=-1), on a rotating-bending fatigue testing machine of the constant bending moment type. It was used the staircase (or up-and-down) method to determine the fatigue limit of the specimens.

Geometry, dynamics and fractals

Abstract: Consider a collection of elastic wires folded according to a given pattern induced by a sequence of fractal plane curves. The folded wires can act as elastic springs. Therefore it is easy to build up a corresponding sequence of simple oscillators composed by the elastic springs clamped at one end and carrying a mass at the opposite end. The oscillation periods of the ordered sequence of these oscillators are related following a power law and therefore display a fractal structure. The periods of each oscillator clearly depend on the mechanical properties of the wire, on the mass at the end and on the boundary conditions. Therefore there are infinitely many possibilities to design a dynamical fractal sequence in opposition to the well defined fractal dimension of the underneath geometric sequence. Nevertheless the geometric fractal dimension of the primordial geometric curve is always related somehow to the dynamical fractal dimension characterizing the oscillation period sequence. It is important to emphasize that the dynamical fractal dimension of a given sequence built up after the geometry of a primordial one is not unique. This peculiarity introduces the possibility to have a broader information spectrum about the geometry which is otherwise impossible to achieve. This effect is clearly demonstrated for random fractals. The present paper deals with a particular family of curves, namely curves belonging to the Koch family. The method is tested for the simple Koch triadic and for random Koch curves. The method has also proved to be useful to identify the fractal dimension of a sequence given just one of its terms. Remarkable is the quality of information obtained with this technique based on very simple and basic concepts. Some of these aspects will be presented in this paper but much more, the authors believe, is still hidden behind the dynamic properties of fractal structures.

Wind tunnel test for vortex-induced vibration of vehicle-bridge system section model

Abstract: Vortex-induced vibration of bridges happens at a relatively low wind speed and while vehicles often run on a bridge at that wind speed. Thus, it is necessary to study how the vehicles influence vortex-induced vibration of vehicle-bridge systems. Based on the project of Shanghai Bridge over Yangtse River, the wind tunnel test for vortex-induced vibrations of vehicle-bridge system of a 1:60 model is presented. The wind tunnel test is introduced in detail including the equipments, test procedures and discussion of results. The results show that the vehicles have much influence on vortex-induced vibration of vehicle-bridge system for the Shanghai Bridge over Yangtse River. With speed increasing, the displacement of the bridge with vehicles fluctuates larger than that of the bridge without vehicles. The frequencies of vibration could be divided into three stages, vertical vibration frequency for the first stage, torsional vibration frequency for the second stage, and suspension system vibration frequency for the third stage. For the bridge with vehicles, vertical vortex-induced vibration was accompanied with torsional vibration and the frequencies of the two vibrations are equal. The displacement of vortex-induced vibration for the bridge with vehicles was larger than that of vortex-induced vibration for the bridge without vehicles. Due to the disturbance of vehicles, the lock-in wind speed region of the vortex-induced vibration appears ahead.

Performance of aerodynamic baffles in cylindrical grinding analyzed on the basis of air layer pressure and speed

Abstract: Over the years, grinding has been considered one of the most important manufacturing processes. Grinding is a high precision process, and the loss of a single workpiece in this stage of the production is unacceptable, for the value added to the material is very high due to many processes it has already undergone prior to grinding. This study aims to contribute toward the development of an experimental methodology whereby the pressure and speed of the air layer produced by the high rotation of the grinding wheel is evaluated with and without baffles, i.e., in an optimized grinding operation and in a traditional one. Tests were also carried out with steel samples to check the difference in grinding wheel wear with and without the use of baffles. Keywords : grinding, aerodynamic baffle, optimized process

High Reynolds Number Oscillations of a Circular Cylinder

Abstract: This paper concerns the numerical simulation of the flow around an oscillating circular cylinder, which moves with constant velocity in a quiescent Newtonian fluid with constant properties. For each time step of the simulation a number of discrete Lamb vortices is placed close to the body surface; the intensity of each of these is determined such as to satisfy the no-slip boundary condition. The aerodynamic loads acting on the surface of cylinder are computed using the integral formulation derived from the pressure Poisson equation. The influence of the frequency and amplitude oscillation on the aerodynamic loads and on the Strouhal number is presented and discussed.

Geometrically nonlinear static and dynamic analysis of composite laminates shells with a triangular finite element

Abstract: Geometrically nonlinear static and dynamic behaviour of laminate composite shells are analyzed in this work using the Finite Element Method (FEM). Triangular elements with three nodes and six degrees of freedom per node (three displacement and three rotation components) are used. For static analysis the nonlinear equilibrium equations are solved using the Generalized Displacement Control Method (GDCM) while the dynamic solution is performed using the classical Newmark Method with an Updated Lagrangean Formulation (ULF). The system of equations is solved using the Gradient Cojugate Method (GCM) and in nonlinear cases with finite rotations and displacements an iterative-incremental scheme is employed. Numerical examples are presented and compared with results obtained by other authors with different kind of elements and different schemes.

Immiscible liquid-liquid displacement in capillary tubes: viscoelastic effects

Abstract: The displacement of a fluid by liquid injection occurs in some practical applications like oil recovery in porous media and cementation of drilling wells. The dimensionless numbers that govern this problem are the capillary number, Reynolds number and viscosity ratio. An overview of selected oil recovery processes shows that hydrolyzed polyacrilamide and bio-polymers, as xanthan gun, are commonly pumped into oil reservoir in order to aid oil recovery. These materials are non-Newtonian, presenting high viscoelastic effects. The fractional mass deposited on the tube wall and the shape of the interface on liquid-liquid displacement of two Newtonian materials was studied previously by Soares et al. (2005). The goal of the present work is to conduct an experimental investigation analyzing viscoelastic effects on the fractional coverage and on the shape of the interface for both: a polymer displacing a Newtonian liquid and a Newtonian liquid displacing a polymer.

Eurocode structural fire design and its application for composite circular hollow section columns

Abstract: The tabular structural fire design method for centrally loaded composite columns consisting of concrete filled steel circular hollow sections proposed in EN 1994-1-2:2005 (Eurocode 4: Design of Composite Steel and Concrete Structures - Structural Fire Design) is described here. A design procedure is then discussed, based on the determination of the temperature distribution in the cross sectional area and along the column length. A finite element based computer program is developed to implement the three-dimensional thermal analysis of different materials and geometries for given time versus temperature fire data. An example problem is shown, comparing the tabular method proposed in EN 1994-1-2:2005 and the method presented in this work.

Energy-rate method and stability chart of parametric vibrating systems

Abstract: The Energy-Rate method is an applied method to determine the transient curves and stability chart for the parametric equations. This method is based on the first integral of the energy of the systems. Energy-Rate method finds the values of parameters of the system equations in such a way that a periodic response can be produced. In this study, the Energy-Rate method is applied to the following forced Mathieu equation: y" + hy' + (1 - 2β + 2β cos (2rt)) y = 2β sin2 (rt) This equation governs the lateral vibration of a microcanilever resonator in linear domain. Its stability chart in the β-r plane shows a complicated map, which cannot be detected by perturbation methods.