Browsing by Author "Sari, G"

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    Numerical Analysis of Vibrating Touch Screen Actuated by Piezo Elements
    Ak, AF; Sari, G; Akgül, MB; Kirisken, B; Akis, AA
    Audiovisual feedback generally is used on touch screens on portable electronic devices, which are frequently used in daily life. Tactile feedback is one of the issues that have recently gained importance in this technology. Tactile feedback occurs by stimulating the nerves at the fingertip by moving the touch screen. In this study, we have determined the vibration characteristics of touchscreens made from different materials used in the sector. The finite element method is employed to obtain the vibration modes of the screen. In addition to, the effects of the materials of piezo, applied voltage, the number of the piezo patches are investigated to produce the best vibration function and graphically are presented.
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    An Experimental Study of a Piezoelectrically Actuated Touch Screen
    Sari, G; Akgül, MB; Kirisken, B; Ak, AF; Akis, AA
    An audiovisual feedback is used on touch screens in portable electronic devices. When these devices are used in noisy and distracting environments, suitable available feedback methods is severely inadequate and the availability of the device severely reduced. For these reasons, touch screen technology has become a popular recently. These panels used in many sectors such as watches, cars, mobile devices, aerospace. Touch screens, which provide tactile feedback to the user, are activated using solenoid actuators, coil-type actuators or vibration motors. The use of evolving piezoelectric vibrators has attracted considerable attention in recent years to obtain high-resolution tactile feedback. Their higher bandwidth helps create more user-perceivable haptic effects. In this work, we experimented to observe the effect of the piezo vibrator on the screen. As a result, the various types of tactile feedback functions will be developed on the screen and compared. The best vibration functions depending on the settings are obtained through experiments.
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    Lie Group Analysis of Unsteady Flow and Heat Transfer over a Porous Surface for a Viscous Fluid
    Akgül, MB; Sari, G; Pakdemirli, M
    The problem of a two-dimensional, unsteady flow and a heat transfer of a viscous fluid past a surface in the presence of variable suction/injection is analyzed. The unsteadiness is due to the time dependent free stream flow. The governing equations are derived with the usual boundary layer approximation. Using Lie group theory, a group classification of the equations with respect to the variable free stream flow and suction/injection velocity is performed. Restrictions imposed by the boundary conditions on the symmetries are discussed. Adopting the obtained symmetry groups, governing partial differential equations are converted into ordinary differential equations and then solved numerically. Effects of the dimensionless problem parameters on the velocity and temperature profiles are outlined in the figures.
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    Vibrations of a Slightly Curved Microbeam Resting on an Elastic Foundation with Nonideal Boundary Conditions
    Sari, G; Pakdemirli, M
    An investigation into the dynamic behavior of a slightly curved resonant microbeam having nonideal boundary conditions is presented. The model accounts for midplane stretching, an applied axial load, and a small AC harmonic force. The ends of the curved microbeam are on immovable simple supports and the microbeam is resting on a nonlinear elastic foundation. The forced vibration response of curved microbeam due to the small AC load is obtained analytically by means of direct application of the method of multiple scales (a perturbation method). The effects of the nonlinear elastic foundation as well as the effect of curvature on the vibrations of the microbeam are examined. It is found that the effect of curvature is of softening type. For sufficiently high values of the coefficients, the elastic foundation and the axial load may suppress the softening behavior resulting in hardening behavior of the nonlinearity. The frequencies and mode shapes obtained are compared with the ideal boundary conditions case and the differences between them are contrasted on frequency-response curves. The frequency response and nonlinear frequency curves obtained may provide a reference for the choice of reasonable resonant conditions, design, and industrial applications of such systems. Results may be beneficial for future experimental and theoretical works on MEMS.
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    APPROXIMATE DETERMINATION OF POLYNOMIAL ROOTS
    Pakdemirli, M; Sari, G; Elmas, N
    Three theorems are given for approximate determination of magnitudes of polynomial roots. A definition for the order of a number is given first. The first theorem is for a polynomial equation with all coefficients the same order of magnitude. The second theorem deals with polynomial equations having only one coefficient of different magnitude from the others. Finally, the third theorem is a general theorem valid for any arbitrary polynomial equations. The theorems successfully determine the magnitudes of roots for arbitrary degree of polynomial equations. An additional fourth theorem predicts the roots for the special case of two dominant terms in the polynomial. Proofs and numerical applications of each theorem are presented. It is shown that the predictions of the theorems and the real roots are in reasonable agreement.
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    Effects of Non-Ideal Boundary Conditions on the Vibrations of a Slightly Curved Micro Beam
    Sari, G; Pakdemirli, M
    Response of a slightly curved resonant microbeam having non-ideal boundary conditions is investigated. Non-ideal boundary conditions are formulated using perturbation theory. These non-ideal conditions allow for small deflection at the right end of the microbeam. The curvature is taken as a sinusoidal function of the spatial variable. The initial displacement is due to the geometry of the microbeam itself. They are produced intentionally to be curved or made curved by buckling straight beams through compressive axial loads. The model accounts for mid-plane stretching, an applied axial load and an AC harmonic force. The ends of the curved microbeam are on immovable simple supports. Immovable end conditions introduce integral type nonlinearity. The integro-differential equations of motion are solved analytically by means of direct application of the method of multiple scales (a perturbation method). The amplitude and phase modulation equations are derived for the case of primary resonances. The effect of curvature on the vibrations of the microbeam is examined. It is found that the effect of curvature is of softening type. The frequencies and mode shapes obtained are compared with the ideal boundary conditions case and the differences between them are contrasted on frequency response curves.
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    Solution of a Quadratic Nonlinear Problem with Multiple Scales Lindstedt-Poincare Method
    Pakdemirli, M; Sari, G
    A recently developed perturbation algorithm namely the Multiple Scales Lindstedt-Poincare method (MSLP) is employed to solve an equation with quadratic nonlinearity. Approximate solutions are obtained with classical multiple scales Method (MS) and the MSLP method and they are compared with numerical solutions. It is shown that MSLP solutions are better than the MS solutions for the strongly nonlinear case.
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    Non-Linear Vibrations of a Microbeam Resting on an Elastic Foundation
    Sari, G; Pakdemirli, M
    In this study, response of a microbeam bonded to a non-linear elastic foundation is investigated. The model accounts for mid-plane stretching, an applied axial load, and an AC harmonic force. The microbeam is resting on a non-linear elastic foundation which introduces a cubic non-linear term to the equations of motion. Immovable end conditions introduce integral type nonlinearity. The integro-differential equations of motion are solved analytically by means of direct application of the method of multiple scales (a perturbation method). The amplitude and phase modulation equations are derived for the case of primary resonances. Frequency-response curves and non-linear frequencies are analyzed with respect to the effective physical parameters. Influence of elastic foundation coefficients, coefficients related to dielectric constants, and mid-plane stretching on the vibrations of the microbeam are investigated.
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    Nonstationary Vibrations of Piezoelectric Atomizer: Experimental Analysis and Mathematical Model
    Sari, G; Aydin, YN
    The nonstationary vibrations of an atomizer with time-varying drop mass were investigated in this study. The atomizer made use of brass and piezoceramic discs driven by a sine input voltage. When the acceleration applied by the piezoelectric disc reached a critical value, small droplets were ejected from the surface of the mass and the liquid drop mass decreased with respect to time. This study consisted of two parts. In the experimental one, a laser vibrometer was used to measure displacements and accelerations of the disc, while in the theoretical part, a mathematical model was developed for different applied acceleration values. It was observed that the atomization rates of the drop were exponentially proportional to applied accelerations. In the theoretical part, the mathematical model was developed for the behaviour of the atomizer with time-varying drop mass. The nonlinear equation of motion was solved analytically by means of the multiple scales method. The nonstationary response of the system obtained numerically and experimentally was compared. It was found that the experimental results are in good agreement with the theoretical solution. The aim of this work was to determine the effects of initial accelerations on the atomization rates, as well as mass variation and initial drop mass on the transient behaviour of the system. The authors concluded that the duration of the transient behaviour and the displacement amplitude of the system increased as the initial drop mass and atomization rate increased with acceleration.
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    A comprehensive perturbation theorem for estimating magnitudes of roots of polynomials
    Pakdemirli, M; Sari, G
    A comprehensive new perturbation theorem is posed and proven to estimate the magnitudes of roots of polynomials. The theorem successfully determines the magnitudes of roots for arbitrary degree of polynomial equations with no restrictions on the coefficients. In the previous papers Takdemirli and Elmas, Appl. Math. Comput. 216 (2010) 1645-1651' and Takdemirli and Yurtsever, Appl. Math. Comput. 188 (2007) 2025-2028', the given theorems were valid only for some restricted coefficients. The given theorem in this work is a generalization and unification of the past theorems and valid for arbitrary coefficients. Numerical applications of the theorem are presented as examples. It is shown that the theorem produces good estimates for the magnitudes of roots of polynomial equations of arbitrary order and unrestricted coefficients.
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    Non-Newtonian Fluid Effects on Surface Reactions in a Microfluidic Flow Cell
    Akgül, MB; Sari, G; Pakdemirli, M
    Mass transfer over a reactive surface in microfluidic flow cells plays a key role in understanding biomoleculer interactions and diagnosis of small molecules for biomedical and environmental applications. The effects of Non-Newtonian power law fluid on the binding reaction kinetic of immunoglobulin G in a flow cell are analyzed in this study. Governing equations for the fluid flow, mass transport and surface reaction are derived. The finite element method is employed to solve resulting equations. In addition, the effects of volumetric flow rate, fluid behavior index and reaction constants on the surface reaction are analyzed and presented graphically.
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    Dynamics of liquid drop on a vibrating micro-perforated plate
    Sari, G; Aydin, YN; Bilekli, ÜG; Göl, MB
    The present work presents the behavior of a liquid drop placed onto a surface of the perforated plate experimentally. Micro holes were created on the brass plate by a laser marking method. The actuator made of brass and piezoelectric discs driven by a sine input voltage, and it bonded rigidly to the perforated plate. This study aimed to reveal the behavior of the drop placed on the perforated plate and the effects of the initial acceleration value on the rate of change in the drop projected area onto the surface. For this purpose, a frequency-response function of the dry micro-perforated plate was measured by a laser vibrometer, and the acceleration distribution was determined on the perforated plate. Further, the drop was excited with five different initial acceleration values, and the drop projected area onto the surface was recorded by a camera during the atomization process. It was observed that droplets were atomized at the air-liquid interface on two sides of the perforated plate. The time-varying function of the drop projected area onto the surface for each initial acceleration value was presented graphically. The polynomial function was fitted to the experimental data points for each acceleration value, and thus the effects of the initial acceleration on the varying drop size were analyzed. The authors emphasized that the drop projected area onto the surface first increased and then decreased during the atomization process. The rate of change in the drop projected area onto the surface increased as the initial acceleration increased. The drop was atomized both by ejecting from the surface and sucking through the holes.
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    Boundary Layer Equations and Lie Group Analysis of a Sisko Fluid
    Sari, G; Pakdemirli, M; Hayat, T; Aksoy, Y
    Boundary layer equations are derived for the Sisko fluid. Using Lie group theory, a symmetry analysis of the equations is performed. A partial differential system is transferred to an ordinary differential system via symmetries. Resulting equations are numerically solved. Effects of non-Newtonian parameters on the solutions are discussed.
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    Displacement and stress distribution of Kilroy spring and nickel-titanium closed-coil spring during traction of palatally impacted canine: A 3-dimensional finite element analysis
    Sezici, YL; Gediz, M; Akis, AA; Sari, G; Duran, GS; Dindaroglu, F
    Objective To compare the stress distribution and initial displacements during traction of palatally impacted canine between Kilroy and nickel-titanium (NiTi) closed-coil springs by means of the finite element analysis. Setting and Sample Population A finite element method analysis of two traction methods for a maxillary impacted canine. Materials and Methods The corresponding periodontal ligaments (PDLs), brackets, molar tubes and a 0.019 x 0.025-in base stainless-steel (SS) wire were modelled and imported to ANSYS SpaceClaim version 2020 R1. Traction was simulated under two different set-ups with equal force magnitude (60 g); (1) the Kilroy spring, which is made of 0.016-inch SS, and (2) the NiTi closed-coil spring. Von Mises stress distributions and initial displacements of the maxillary teeth were analysed. Results In both mechanics, while the highest stress was seen on the impacted canine (Kilroy, 10.41 kPa; NiTi closed-coil, 5.27 kPa), the stress distribution decreased as the distance from the impacted canine increased. The Kilroy spring showed a greater total displacement (465.60 mu m) on the impacted canine. The higher stresses on the adjacent lateral (5.29 kPa) and premolar (6.41 kPa) occurred with the Kilroy spring. Conclusions The Kilroy spring yielded higher stresses than the NiTi closed-coil spring on the impacted canine and the adjacent teeth. The difference between distribution of the stresses over the impacted canine induced greater displacement with the Kilroy spring, particularly in the vertical direction.
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    HISTOLOGICAL EFFECTS OF POLLUTION ON GILL AND HEPATOPANCREAS TISSUES OF BLACK MUSSELS (M. GALLOPROVINCIALIS L.) FROM IZMIR BAY OF TURKEY
    Katalay, S; Yavasoglu, A; Yigitturk, G; Oltulu, F; Sari, G; Yavasoglu, NUK
    In the present study, the histological examination of the hepatopancreas (digestive gland) and gills of black mussels, Mytilus galloprovincialis was performed as a part of the biomonitoring programs carried out to assess the biological effects of the Izmir Bay (Western coast of Turkey). Mussels collected from five stations; Urla in the outer Bay and Inciralti, Goztepe, Konak, Pasaport in the inner Bay of Izmir Bay. While normal histology on hepatopancreas tissue was observed in Urla samples, vacuolar degenerations and hemocytic infiltrations were abundant in hepatopancreas throughout the other four stations. Also breakdown of digestive epithelium was determined in only Pasaport station. In gill tissues, while hemocytic infiltration was observed in Urla samples, gradually increasing cilia erosion, fusion, cell loss and necrosis was observed in Inciralti, Goztepe, Konak, Pasaport samples. Lumen was determined as normal in Urla and Goztepe samples and enlarged in Inciralti samples. The lumen in each filament was thinner and in some parts adjoined to each other and in Konak and Pasaport samples. Also the gills abfrontal tissue integrity was disturbed in these two stations.
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    Experimental and numerical studies on improvement of heat transfer of OLED TVs
    Nil, M; Öztürk, Y; Akgül, MB; Sari, G
    In this study, the thermal behaviors of organic light emitting diodes (OLED) televisions are investigated experimentally and numerically. Organic light emitting diodes are very sensitive to temperature. For this reason, the heat emitted from the diodes must be removed quickly from the environment. The study consists of two parts. In the first part, the use of an effective heat spreader between the screen and the metal casing is proposed as a mechanism for improving the temperature distributions for heat transfer. Pyrolytic graphite plate and tempered pyrolytic graphite plate were used as heat spreader. The graphical heat transfer coefficients of the graphite plates are considerably higher than in the normal direction. The effectiveness of these proposed mechanisms is demonstrated by simulation. As an example model, OLED TV was selected in 15 dimensions and both experimental and numerical thermal analyzes were performed. The temperature distributions of the OLED were obtained with the help of the ANSYS ICEPAK program, a commercial code that uses the finite volume method. Simulation and test results are obtained very close to each other. The thermal management contributions of OLED TVs using different thicknesses of pyrolytic and tempered pyrolytic graphite plates are presented experimentally and numerically. In the second part, a dual action piezo fan design is proposed. The design parameters of the piezo fan were determined and the numerical analyzes for these parameters were made with the Comsol Multiphysics program. Experimental measurements were made for design dimensions determined by numerical analysis. The result is that the use of a dual-acting piezo provides more efficient cooling than the existing synthetic jets.