Resumo em Inglês:

Abstract In this paper, torsional vibration of a micro-shaft in interacting with a micro-scale fluid media has been investigated. The presented mathematical model for this study is made up of a micro-shaft with one end fixed and a micro-cylinder at its free end which is immersed in a micro-scale fluid media. The micro-shaft can be actuated torsionally via applying an AC voltage to the capacitive plates around the micro-shaft and the outer fixed cylinder. As fluids and solids behave differently in micro scale than macro, the surrounding fluid field in the gap and also the micro-shaft have been modeled based on non-classical theories. Equation of motion governing angular displacement of the micro- shaft and also equations of motion of the fluid field have been derived based on non-local elasticity and micro-polar theories. The coupled differential equations have been transformed to an enhanced form with homogenous boundary conditions. The enhanced equations have been discretized over the beam and fluid domain using Galerkin method. Effects of non-local parameter of the micro-shaft and also micro-polar parameters of the fluid field on the response of the micro-shaft have been studied. We have shown that micropolar parameters of fluid due to having damping and inertial effects, changes resonance frequency and resonance amplitude of the shaft.

Resumo em Inglês:

Abstract This paper applies acoustic analysis of Sound Transmission Loss (STL) through infinite Functionally Graded (FG) thick plate employing Hyperbolic Shear Deformation Theory (HSDT). The procedure for applying a FG plate is followed by considering the material properties are changed continually based on power-law distribution of the materials in terms of volume fraction. The main benefit of HSDT can be justified knowing the fact that, it uses parabolic transverse shear strain across thickness direction. Therefore, no need to enter the extra effect of shear correction coefficient factor. Besides, the displacement field is extended as a combination of polynomial as well as hyperbolic tangent function by neglecting the effect of thickness stretching. Furthermore, the equations of motion are obtained employing Hamilton’s Principle. To provide an analytical solution based on HSDT, equations of motion are combined with acoustic wave equations. Moreover, some comparisons are made with the known theoretical and experimental results available in literature to verify the accuracy and efficiency of the current formulation. These comparisons reveal an excellent agreement. Consequently, some configurations are presented to demonstrate which parameters appear to be effective to improve the behavior of STL including the effects of modulus of elasticity and density in the thickness direction with respect to various power-law distributions.

Resumo em Inglês:

Abstract In this paper, acoustic power radiation of a submerged finite length ribbed cylinder subject to a harmonic point load is minimized by a new fast scheme. For this purpose, two arrangements of non-uniformly distributed sequential point masses and mass springs attached on stiffening ribs of the cylinder are used to optimally reduce the acoustic power radiation. A fully coupled analysis is here carried out based on Finite/Boundary element (FEM/BEM) model. Instead of direct BEM formulation, two beneficial procedures have been proposed for computing BEM matrices in each frequency line. In order to fast solving of equations, the Krylov vectors (produced via Ritz or Arnoldi iterative procedures) and structural mode shapes (modal truncation approach) have been used and validated before performing optimization. As a result, the best strategy for evaluation of response and cost function is using Taylor series expansion for computing BEM matrices and applying Krylov vectors for order reduction. The results show good agreement with previous studies and experiments. The optimization results show noticeable reductions in the acoustic power radiation. In point mass optimization, the most of additional masses has been placed in regions which are near to the excitation point whereas for the absorber design, they are put in the places in opposite side of the excitation point.

Resumo em Inglês:

Abstract In precast concrete segmental tunnels, radial and circumferential joints are often the most highly stressed parts and it is therefore important to use appropriate equations to accurately analysed these joints during design and provide adequate structural capacity to avoid failure. Different design codes have put forward equations for the estimation of bursting forces due to concentrated load on precast end blocks. The equations were specifically developed for pre-stressed concrete anchors and not specifically for precast concrete segmental tunnels. The design equations often account for the effects of load eccentricity in estimating bursting force but not the peak stress. This paper assesses the accuracy of published equations for bursting force and peak stress by conducting a high-resolution two-dimensional (2D) finite element (FE) based parametric studies. It was found that the effects of load eccentricity are significant for highly concentrated loads (load width ratios less than 0.3) and that they increase the peak bursting stresses significantly. Regression analysis is used to develop equations for estimating the peak bursting stress and bursting force due to load eccentricity for the design of precast concrete tunnel segments. These equations are more accurate as compared to pre-existing equations and important for practising engineers and designers.

Resumo em Inglês:

Abstract Free vibration of a bimaterial circular nano-tube is investigated. The tube is formed by bonding together a Si3N4/SUS304 functionally graded upper semi tube and a ZrO2/Ti-6Al-4V functionally graded lower semi tube. The material properties of the tube are assumed to vary along the radius according to power law with the power index of upper semi tube differing from that of lower semi tube. Based on non-local elasticity theory and Hamilton’s principle, a refined beam model considering the effect of transverse shear deformation is used to derive the governing equations, then analytical solution is obtained by using a two-steps perturbation method. Our results were compared with the existing ones. The effects on tube’s linear and non-linear frequency are analyzed of the factors, including small scale parameter, temperature, the double volume fraction indexes, slenderness ratio and different types of beam model. A new approach is suggested in this article to change the natural frequency of the tubes by adjusting constituent materials. In contrast to conventional approach, the new one can result in more accurate frequency control in the same dimensionless size of tubes.

Resumo em Inglês:

Abstract This paper presents some recent advances on the numerical solution of the classical Germain-Lagrange equation for plate bending of thin elastic plates. A meshless strategy using the Generalized Finite Difference Method (GFDM) is proposed upon substitution of the original fourth-order differential equation by a system composed of two second-order partial differential equations. Mixed boundary conditions, variable nodal density and curved contours are some of the explored aspects. Simulations using very dense clouds and parallel processing scheme for efficient neighbor selection are also presented. Numerical experiments are performed for arbitrary plates and compared with analytical and Finite Element Method solutions. Finally, an overview of the procedure is presented, including a discussion of some future development.

Resumo em Inglês:

Abstract Multi-bolted joints are adopted and designed to provide efficient load transfer within assembled engineering parts. Bearing failure is favorable during design phase due to more progressive failure mode, however, ability of by-pass stress to be transferred to adjacent bolts in multi-bolted joints prone to catastrophic net-tension failure. Former approach known as equivalent spring stiffness (ESS) was proposed but it requires experimental sliding load value. This has led to semi-empirical approach to require experimental set-up than incorporating a generic bolt preload value. This paper aims to provide a unified bolt preload (UBP) value to be implemented in each bolt independent upon plate properties and bolts arrangements. Strength prediction were taken place by 3-D Extended Finite Element Method (XFEM) framework of various staggered and non-staggered arrangements to include various lay-ups types and plate thickness. The failure loads predictions in each testing series were investigated and then validated against experimental datasets and also compared with previous technique (ESS approach). Crack patterns and failure modes from this approach were consistent with experimental observations, where net-tension failures were observed within all testing series. Less good prediction compared to from ESS technique, partly due to semi-empirical nature in former approach. Nevertheless, reasonable agreement in UBP technique with experimental datasets were obtained (average discrepancy of approximately 20%).

Resumo em Inglês:

Abstract A vehicle seat represents an automotive passive system because it limits the damage caused to passengers in the events of an accident or a crash. This way, the present work intends to evaluate the safety of an anchorage mechanism of a frontal vehicle driver seat considering two hazardous situations rear and frontal impacts. Performing a nonlinear FE in static and transient analyses provide the stress distribution in the main components of the mechanism, such as the inner track, the lock device and the bolts using Ansys®. Regulation Nº 17 from Un/ECE regulates the acceleration levels predicted in a crash test and therefore applied in the simulation. In addition, departing from a crash of 5g a fatigue analysis is carried out. From this particular analysis, it becomes possible to evaluate the actual safety of the vehicle seat after a minor crash.

Resumo em Inglês:

Abstract The Hankel transformation method was used in this work to determine the normal and shear stress distributions due to point, line and distributed loads applied to the surface of an elastic media. The elastic media considered in this study was assumed to be inextensible in the horizontal directions, and the only non-vanishing displacement component is the vertical component. Such materials were first considered by Westergaard as models of elastic half-space with alternating layers of soft and stiff materials with the stiff materials of negligible thickness and so closely spaced that the composite material characteristics is idealised as isotropic and homogeneous. The study adopted a displacement formulation. The Hankel transformation was applied to the governing Cauchy - Navier differential equation of equilibrium to reduce the problem to a second order ordinary differential equation (ODE) in terms of the deflection function in the Hankel transform space. Solution of the ODE subject to the boundedness condition yielded bounded deflection function in the Hankel transform space. Equilibrium of the internal vertical forces and the external applied load, was used to obtain the constant of integration, for the deflection function in the Hankel transform space. Inversion yielded the deflection in the physical domain variable. The stress displacement equations were then used to determine the Cauchy stresses. The vertical stress distributions due to line and distributed load over a rectangular area were also determined by using the point load solution for vertical stresses as Green functions, and then performing integration along the line and over the rectangular area of the load. The results obtained for vertical stresses due to point, line and distributed loads were determined in terms of dimensionless influence coefficients which were presented. The results obtained for the deflection, normal and shear stresses due to point, line and distributed load agreed with the solutions originally presented by Westergaard who used a stress function method.

Resumo em Inglês:

Abstract The wing leading edge is one of the aircraft structures which are vulnerable to birdstrike. Therefore, Federal Aviation Regulation has clear requirements of anti-birdstrike performance for wing leading edge. However, the impact location is not specified in aviation regulation. The forefront of the wing leading edge is selected as a critical location for the birdstrike in most researches. But the rationality of the selection is not given. This paper proposes an analytical method for determining the critical location that causes the most severe damage under impact due to birdstrike. The analysis is based on the concept of effective impact, i.e. the component of the bird velocity perpendicular to the surface of wing leading edge. A birdstrike model is established using Pam-crash and used to validate the analytical prediction. The numerical model proves its effectiveness compared to the birdstrike test. The residual compressive strength of the spar when the birdstrike is at the critical impact location determined by the proposed method is 44.5% of that at the traditional impact location. Moreover, the critical penetrating velocity of the traditional impact location is not the lowest. In other words, the traditional impact location is not the weakest. Airworthiness verification experiment of birdstrike on wing structure should pay attention to this aspect.

Resumo em Inglês:

Abstract The R-functions theory and Ritz approach are applied for analysis of free vibrations of laminated functionally graded shallow shells with different types of curvatures and complex planforms. Shallow shells are considered as sandwich shells of different types: a) face sheets of the shallow shells are made of a functionally graded material (FGM) and their cores are made of an isotropic material; b) face sheets of the shallow shells are isotropic, but the core is made of FGM. It is assumed that FGM layers are made of a mixture of metal and ceramics and effective material properties of layers are varied accordingly to Voigt’s rule. Formulation of the problem is carried out using the first-order (Timoshenko’s type) refined theory of shallow shells. Different types of boundary conditions, including clamped, simply supported, free edge and their combinations, are studied. The proposed method and the created computer code have been examined on test problems for shallow shells with rectangular planforms. In order to demonstrate the possibility of the developed approach, novel results for laminated FGM shallow shells with cut of the complex form are presented. Effects of different material distributions, mechanical properties of the constituent materials, lamination scheme, boundary conditions and geometrical parameters on natural frequencies are shown and analyzed.

Resumo em Inglês:

Abstract In this paper we calculated reflectance and transmittance of different optical birefringent networks sandwiched between two isotropic media. To model optical phenomena in the considered systems, we applied the 4×4 matrix method. Some interesting reflectance and transmittance spectra and polar plots for different system parameters and arbitrary incident monochromatic light were reported. The illustrated and discussed results can be useful for understanding optical phenomena in numerous birefringent media. Especially, the reflectance and transmittance spectra computed in this article can be suitable for analysis of more advanced contemporary optical systems, i.e. photonic band gap materials based on cholesteric liquid crystals.

Resumo em Inglês:

Abstract This work presents an analysis of an ocean wave energy harvesting system. This system is composed of a direct current (DC) power generator attached at the middle-top of a floating platform. A pendulum is connected to the generator’s shaft. It is considered that the ocean waves motion swings the platform in the vertical direction, which transfers energy to the pendulum, making possible to convert mechanical energy, induced by the ocean wave, into a rotational motion due the pendulum and after in electric energy due the generator. With the objective to optimize the harvested power, several analyses of the pendulum parameters, ocean wave amplitude and frequency were carried out. This work was based on the Brazilian’s coast characteristics. Numerical and experimental results were performed which shows the efficiency of the conversion of mechanical energy provided by the pendulum into electric power.

Resumo em Inglês:

Abstract The wheel-flat defect is one of the many issues decreasing the level of and comfort in light rail vehicles. The two main causes of wheel-flats are temporary or complete wheel blocking. The negative effect is the increase of the dynamic phenomenons in the wheel-rail interaction, which are impulsive in their nature. It could prove to be dangerous for the safety of the ride. Therefore, a regular wheel surface monitoring and wheel-flats detecting would be well-founded to the fast detection of a flat point and to take remedial measures. The main aim of the article is to present the algorithm, according to which the wheel-flat detection during tram passage is possible. Several vibration transducers were mounted on the rail and measured vibration amplitude during trams pass-by. The proposed method is based on the vibration signal processing in the time and frequency domain. The Hilbert transform was used in the algorithm and all research analyses. The carried out experimental study and the analysis of the results of the method, show a high efficiency in the wheel flat detection.

Resumo em Inglês:

Abstract In this paper a mathematical model was found, and numerical results obtained for the pendulum behavior when coupled to a DC generator. A simple pendulum is vertically excited on its support and consequently exhibiting oscillations and rotations. The motion of the pendulum spins the axis of a DC generator and inducing a current. The dynamic model involving the generator and the pendulum dynamics is developed and analyzed in this article. Bifurcation diagrams demonstrate doubling-period and saddle-node bifurcations with the chaos. The presence of chaos is verified by the Lyapunov exponents applied on the time series of the pendulum speed and position. Nonideal interactions of a DC motor with a pendulum by a crank-shaft-slider mechanism is analyzed and compared with an ideal excitation of the pendulum.

Resumo em Inglês:

Abstract The aim of the paper is to present the experimental results for material model of the sand, case of wet and dry probe. Since traction and side forces derivation methodology and tire-round interaction models for on-road vehicles are widely described, there is a lack of methods for off-road vehicles. The methodology, presented in this work, includes test in various ground conditions and different driving direction. Test results, presented in the paper were acquired for dry and humid sand, for various tire tilt angle. Traction and side forces were acquired and then will be used for black-box model parameters identification of the wheel-ground interaction.

Resumo em Inglês:

Abstract The work presents modeling of interface phenomena in biological structures. Selected ways of numerical modeling of phenomena at the boundary of two materials by means of FEM methods are discussed. The work focuses on phenomena related to biological structures and their mutual interactions. Using an example of an implant-bone system, various techniques of modeling interface phenomena are compared and referred to experimental results. The study reveals the main features of the selected modeling techniques, e.g. complexity of creating the model, time-consumption of computation, reliability of the obtained results. The obtained results proved that the most advantageous method is the one that makes it possible to regard interactions as numerical values, without an excessive generation of the finite elements (the grid) at the materials boundary. The contact modeling technique based on the contact indicator showed the lowest value of standard deviation in relation to contact modeling techniques: with the use of elastic-damping elements, based on the so-called boundary slip line and based on the so-called bio-layer. The contact indicator should be understood as a numerical value describing the interaction of the boundary surfaces of two objects cooperating with each other. The value of the indicator was determined experimentally. The value have oscillated +/- 0.0012mm. This is a very small value knowing that the standard deviation for the modeling technique of the contact employing damping-elastic elements gives a spread of +/- 0,1442 mm.