Modares Mechanical Engineering
Year:2019 | Volume:19 | Issue:8 |Papers Count:28

High speed atomic force microscopy (HS-AFM) is one of the widely used techniques in nanotechnology applications due to high resolution and the ability of 3D imaging. Despite its advantages and although it is known as a nondestructive technique, tip or sample damage can occur if maximum repulsive force is higher than the failure stress of the sample or tip, as a result of tip-sample interactions. Several studies in understanding the peak repulsive forces in tapping mode AFM have been carried out, but mostly in steady state situations. In transient situation when tip encounters a sudden steep upward step, the repulsive force can be much higher than that in the steady state situation and, consequently, damage could happen. Therefore, if appropriate parameters’ values are not tuned, the tip-sample stress may exceed yield stress of the tip or the sample. This paper presents the comparison of maximum transient interaction forces in time periods of net attractive and repulsive forces and the effects of important scanning parameters on maximum transient stress of compliant samples with the elastic modulus in the range of 2GPa together with lateral resolution and scanning speed diagrams, using theoretical analysis as a novelty of this paper, so that selecting cantilever stiffness in the range of 0. 1-1N/m, free air amplitude 60-100nm, amplitude ratio 0. 8-0. 9, quality factor 50-100, tip radius 10-40 nm, and scanning speed 0. 1-0. 3mm/s relative to required lateral resolution indeed leads to safe high speed microscopy.

In this paper, a new method for determining the Young’ s modulus of structural elements, using the finite element model updating approach, is presented. The model updating is the correction of the numerical model of a structure based on measured data from the real structure. Therefore, after introducing a case study of an aluminum alloy (7075-T651) beam, the frequency of bending vibrations of the case study was measured, using frequency response functions derived from the modal test. Then, Young’ s modulus for the case study was calculated, using the relationships in the ASTM E 1876-01standard and also the analytical relations governing Euler– Bernoulli beam behavior. The results of the model updating method indicate that there is a very good adaptation with the results of the two recent approaches, the Standard and Euler– Bernoulli beam relations. As a result, this method can be developed with good precision to identify the Young’ s modulus in structural elements with more complex shapes, where the relations derived from the aforementioned standard and analytical relations are not efficient due to geometric constraints.

Since the invention of ultrasonic vibration assisted turning, this process has been widely considered and investigated. The reason for this consideration is the unique features of this process, which include reducing machining forces, reducing wear, and friction, increasing the tool life, creating periodic cutting conditions, increasing the machinability of difficult-to-cut material, increasing the surface quality, creating a hierarchical structure (micro-nano textures) on the surface and so on. Different methods have hitherto been used to apply ultrasonic vibration to the tip of the tool during the turning process. In this research, a unique horn has been designed and constructed to convert linear vibrations of piezoelectrics to threedimensional vibrations (longitudinal vibrations along the z axis, bending vibrations around the x axis, and bending vibrations around the y axis). The advantage of this ultrasonic machining tool compared with other similar tools is that in most other tools, it is only possible to apply one-dimensional (linear) and two-dimensional (elliptical) vibrations, while this tool can create three-dimensional vibrations. Additionally, since the nature of the designed horn can lead to the creation of three-dimensional vibrations, there is no need for piezoelectric half-rings (which are stimulated by 180 phase difference) to create bending vibrations around the x and y axes. The reduction of costs as well as simplicity of applying three-dimensional vibrations in this new method can play an important role in industrializing the process of three-dimensional ultrasonic vibration assisted turning.

In this study, flutter of functionally graded carbon nanotube (FG-CNT)-reinforced composite wing carrying a distributed patch mass is analyzed and presented. Wing is modeled by a rectangular plate with cantilever boundary conditions in supersonic flow. To evaluate the displacement fields of the moderately thick plate, First-order shear deformation theory (FSDT) and chebyshev polynomials series are applied. In supersonic airflow simulation effect, the firstorder piston theory was used and differential equation governing the system was adapted, using the Hamilton principle. In this study, 4 different types of CNT are considered through the thickness. CNT distribution patterns are as uniform, decreasing, decreasing-increasing, and increasing-decreasing. Finally, the effects of size, mass, and location of the distributed patch mass as well as various CNT distributions and fiber orientation angle in a two-layer antisymmetric composite on flutter boundaries were studies. In comparisons with the results of previous studies, a good agreement is observed. The results showed that the flutter boundary reduced with increasing mass ratio and increased in longer length of added mass. By increasing orientation’ s angle of CNT fiber of anti-symmetric composite, the flutter boundary is raised and has different behavior for different distribution patterns.

In this paper, the effect of geometric parameters of tube and die on the forming behavior of AA6061 step tube in hot metal gas forming process (HMGF) is investigated. For this purpose, empirical experiments and finite element simulations with ABAQUS software have been used. Investigations have been made at the different ratios of die to tube diameter (D/d) and the different ratios of tube thickness to diameter (t/d). A simple theoretical model for the relationship between these geometric parameters and the process parameters such as internal pressure and axial feeding is presented. The results show that under constant internal pressure and axial feeding conditions, the die filling percentage decreases with increasing the ratios of D/d and t/d. Also, in the constant D/d ratio, by increasing the t/d ratio to about 0. 05, the die filling percentage reduces gradually, but with increasing t/d to 0. 06, a sharp decrease occurs in the die filling percentage. Using different simulations, the internal pressure, and axial feeding are changed proportional to the t/d and D/d ratios. The results show that in accordance with the prediction of the theoretical model, the relative internal pressure and relative axial feeding should be increased linearly with increasing the t/d and expansion ratio (D/d-1), respectively, to give specimens with approximately the same die filling percentage.

In this paper, a nonlinear inverse dynamic controller is designed for a magnetic actuated satellite. Since the stability of linear control laws in nonlinear dynamics is not guaranteed far from the equilibrium point, a global stabilizing nonlinear control law is necessary. In this method, by changing the system parameters, the nonlinear dynamics of the system is converted to linear dynamics and the input controller compensates the changes. The stability of the closed loop system was, then, investigated and proved by the Lyapunov method. Dynamic and kinematic equations of satellite are also developed in the presence of aerodynamic disturbance, gravity gradient, magnetic and radiation moments, and the linearization of the motion equations is done around the equilibrium point. In order to evaluate the performance of the dynamic inverse controller, the proportional-derivative linear control law and linear quadratic regulator optimal control law are designed and the results are compared. By modeling satellite orbit, the disturbance moments and the local magnetic field vector are calculated instantaneously according to the satellite’ s position in the orbit. Finally, the system response is presented by considering the saturation range of magnetic actuators. The results show a better performance of the nonlinear dynamic inversion controllers in both accuracy and convergence time.

In this study, effect of shroud on dynamic characteristics of a rotating multi blade system is investigated. The main aim of this study is to investigate the effect of shroud stiffness and shroud configuration on the system natural frequency. For this purpose, natural frequencies of various systems (in terms of the position, where the blade is connected to the shroud and number of blades, which are connected together with a shroud) via different degrees of shroud stiffness and different configurations of shroud have been compared to show how this parameters affect the natural frequencies of the system. In this study, the shrouds have been considered as the discrete springs with corresponding stiffness values. The vibration frequency characteristics have been analyzed, using assumed mode method along with Hamilton’ s law. Since in multi blade systems such as turbines it is crusial to keep the system working frequencies far away from natural frequencies (in order to prevent the resonance phenomenon), based on the results of this paper, it is shown how the parameters of shroud can remove the natural frequencies associated with some of the modes of the system from the work area.

One of the applications of composite materials in the oil and gas industry is to repair worn metal pipelines. Calculating the strain energy release rate of the first failure mode is an important criterion for testing the bond strength and predicting the failure of these types of structures. In this paper, the rate of strain energy release during crack growth in bonding a composite patch to a steel substrate is investigated. In this regard, using the theory of elastic beam first, a new method is proposed to calculate the thickness of the metal and composite for Unlike Double Cantilever Beam (UDCB). This is due to the fact that the standard for experimental test procedure of strain energy release rate (ASTM-D5528) is for symmetric double cantilever beams. In this study, samples are fabricated from composite consisting of unidirectional fiberglass/ epoxy resin with harder in the upper and steel in the lower half of the beam. After sample fabrication, the strain energy release rate of UDCB and Asymmetric Unlike Double Cantilever Beam (AUDCB) are calculated experimentally. In addition, for the separation of first and second failure modes in symmetric and asymmetric samples, finite element simulation based on the virtual crack closure technique is presented. This analysis is to qualify the accuracy of the proposed equation for the thickness of unlike beams to achieve the first failure pure mode of symmetric samples. Also, it calculates the contribution of the first and second modes of failure in the strain energy release rate of AUDCB samples.

In the present study, the flutter and aeroelastic response of mistuned bladed disks to the engine order excitation are studied with the aim of determining the effects of disk structural properties and also establishing an efficient method of analysis. For modeling the solid-fluid interaction, the Whitehead’ s incompressible, two dimensional cascade theory is used. The structure is also modeled, using a 4 degrees of freedom lumped mass-spring system, which accounts for the bending and torsional deformation of the blade and the disk. This model would enable us to study the effect of structural coupling of adjacent sections as well as the disk flexibility. The solution is based on expansion of the mistuned-blade response in terms of the traveling-wave modes of a tuned bladed disk. The adopted method would be appropriate for determining the aeroelastic response, since the aerodynamic loads are available only for each individual traveling-wave mode. The obtained solution is used to study the effects of disk flexibility on the aeroelastic instability, variations of natural frequencies with different numbers of nodal diameters, and the sensitivity of the vibration amplitude response to the mistuning. Furthermore, the effects of mistuning in blades torsional frequencies and the mistuning in engine order excitation is considered. Parametric studies show that for disks with a lower bending stiffness, the mistuning can significantly influence the aeroelastic behavior such that the for a certain amount of the natural frequency, the disk response could be increased more than 8 times due to the presence of mistuning.

In this paper, a novel dynamic model is proposed for an actively damped boring bar equipped with electromagnetic actuator. The dynamic models of actuator and boring bar are obtained by using the suggested systematic identification approach, which is based upon the fundamental tools and techniques of system identification theory. The electro-mechanical system or the forward path is consisted of 3 basic components, i. e. linear power amplifier, electrodynamic shaker, and boring bar structure. In this paper, the dynamic models of forward path’ s sub-systems are simultaneously identified. The component-based identification approach has led to a remarkable finding about the source of nonlinearity in the dynamic model of forward path. According to the presented experimental observations, it has been concluded that electromagnetic actuator can be modeled as a linear dynamic system, while the boring bar structure exhibits nonlinear behavior, since the prediction accuracy of boring bar dynamic model is drastically reduced by changing the amplitude of excitation. As a result, a new parameter varying dynamic model is presented for describing the dynamic behavior of forward path in terms of both frequency and excitation level. The proposed dynamic model has a predefined representation with the least possible mathematical order. It can anticipate the time domain response of forward path due to chirp excitation with 88% accuracy. In addition, during the validation stage, the proposed model forecasts the dynamic response of system due to Gaussian white noise excitation with remarkable accuracy. Moreover, the dynamic model of electromagnetic actuator can predict the dynamic force signature of actuator with 85% accuracy.

Today, nanofluid is attracting intense research due to its potential to augment the heat transfer rate and the cooling rate in many systems. On the other hand, new research progresses indicate that graphene nanofluids even in very low concentrations could provide higher convective heat transfer coefficient in comparison to the conventional nanofluids. For this reason, we used nanofluid containing the CoFe2O4/GO nanoparticles as working fluid to perform experimental investigation of its effect on laminar forced convective heat transfer in the flow passing through a copper tube, which is under a uniform heat flux. It should be noted that utilizing magnetic field on nanoparticles is one of the active methods for improving the heat transfer rate. To achieve this objective, the effect of external magnetic field intensity and also the effect of applying different frequencies on the improvement of heat transfer in Reynolds number and different concentration is also investigated and the optimum frequency were obtained. The results showed that the heat transfer of the studied hybrid nanofluid has been improved in the presence of constant and alternating magnetic fields and the amount of heat transfer increment, due to an alternating magnetic field, is more significant compared with a constant magnetic field. The results also show that in the absence of magnetic field, using ferrofluid with concentration of φ =0. 6%, improves the average enhancement in convective heat transfer up to 15. 2% relative to the DI-water at Re=571, while this value is increased up to 19. 7% and 31% by using constant and alternating magnetic field, respectively.

In this research, Cu-30Zn alloy was subjected to severe plastic deformation (SPD) by Multi-Directional Forging (MDF) process up to 6 passes at room temperature. After the samples fabrication, microstructure, mechanical, and electrical properties were investigated. Mechanical properties of the samples were measured by shear punch, tensile, and hardness tests at room temperature after each pass of MDF process. In addition, electrical properties of the samples were evaluated by Eddy Current method. The results of microstructure characterization by scanning electron microscopy equipped with EBSD attachment showed that the grain size of the initial annealed specimen reduced from about 230 μ m to less than 1 μ m, after 6 passes of MDF process. Furthermore, grain size reduction was accompanied by slip process, formation of twinning, and shear bonds in a specific direction. According to the results, mechanical properties were significantly improved after 6 passes of MDF. MDF process led to a 212% increase in hardness, enhancement of 105% and 73% in shear yield and ultimate shear strengths, and also improvement of 298% and 190% in tensile yield and ultimate tensile strengths, respectively. The results of the electrical conductivity showed that the electrical conductivity of the Cu-30Z alloy reduced slightly during the MDF process. Comparison of mechanical and electrical properties results demonstrated that high-strength alloys can be obtained in the MDF process without significantly reduction in the electrical conductivity

In this study, the mechanical properties of one of the most widely used polymeric biomaterials in the body called Poly Lactic Acid (PLA) in the porous state were evaluated. Firstly, the initial regular porous structures, based on the tetrahedron-catheter model known as Kelvin model, were designed for simulating bone tissue, using 3D design software with FDM technique. Afterwards, pressure test was used to determine the mechanical properties and mode of failure. Finally, experimental results were compared with the simulation software analysis results. The results showed that increasing the porosity reduces the strength and the increasing the cell size in a constant porosity results in increased compressive strength. Also, by decreasing the porosity, the amount of the strain up to fracture increases in a relatively constant stress. The brittle failure at 45° in the samples of high porosity was shown. However, the samples with a lower porosity had a relative ductile behavior and as the pressure rises, the cells accumulate on each other and change the form to the fracture point. Comparing the empirical and the simulation results showed that there is a good agreement between them and the simulation model has a high reliability for the porous model.

In this paper, in order to minimize the required power of satellite thermal control subsystem, considering known geometric model and the orbital parameters and conditions, the optimal layout design of the satellite subsystems will be performed based on thermal and attitude control constraints. Since all of the satellite subsystems can act only in a certain temperature range, here, by considering the thermal dissipations of each subsystem and incoming thermal loads to each satellite faces in different orbital conditions, by optimally layout of components and sub-systems of the satellite, we will arrive to appropriate configuration plan. The constraints of the thermal subsystem should be satisfied by considering the temperature distribution within the satellite as far as possible. Finally, given that the main purpose of this layout is to provide thermal power, in addition to satisfication of the power budget system constraint, the power of the thermal control subsystem has been reduced by 66%. The superiority of this method is that by following the resulting layout, we obtain a model that needs a thermal control subsystem with less complexity and limited power. Consequently, in addition to decreasing the mass of the satellite, reliability will also be increased. Considering the importance of satellite stability, the layout algorithm and optimization are defined in such a way that the attitude control requirements are observed with the thermal requirements in this layout.

The present paper applies a multi-objective genetic algorithm for optimally design of a vehicle suspension. The vehicle model considers three-dimensional movements of vehicle body. In this full vehicle model having 8 degrees of freedom, vertical movement of passenger seat, vehicle body, and 4 tires as well as rotational movements of vehicle body create the degrees of freedom of the model. In this paper, applicable suspension parameters, consisting of passenger seat acceleration, vehicle body pitch angle, vehicle body roll angle, dynamic tire force, tire velocity, and suspension deflections are considered and optimized in optimization process. Different pairs of these parameters are selected as objective functions and optimized in multi-objective optimization processes, and Pareto solutions are obtained for pair of objective functions. In final optimization process, the Pareto solution related to the summation of dimensionless parameters in one suspension parameters group versus other group, is derived. In these Pareto solutions, there are important optimum points and designers can choose any optimum points for a particular purpose. Pareto optimization is better than other multi-objective optimization methods because there are more optimum points on Pareto front, where each point represents a level of optimization for the pairs of objective functions, and designers can choose any of the points to specific purpose.

Pulsed laser welding have a wide application in welding of thin sheet because of high intensity of its localized heat source. In the current study, 3 experimental tests with low, medium, and large level of energy and also, the 3D finite element simulation of Nd: YAG pulsed laser welding in thin sheet AISI316L have been done. Thermal analyzes were done with ABAQUS software in transient heat transfer. In order to increase the accuracy of thermal model, heat losses were considered as convection, radiation, and thermal conduction. 3 thermal models with different heat flux distribution as Gaussian surface, Gaussian volume, and conical volume were used. The main aim of this study is the selection of best thermal model between 3 mentioned thermal models to estimate the melt pool geometry with high accuracy. In addition, with defining and applying the shape factor in 3 thermal models, the finite element analyses were carried out in order to enhance the precision of estimated melt pool geometry. After thermal analysis, the melt pool geometry dimensions are extracted for each of the mentioned thermal models and compared with experimental results. Results show that thermal analysis with Gaussian surface model have the melt pool geometry accurately just in welding with low energy. Also, the conical model could estimate the melt pool geometry in all levels of energy with acceptable accuracy. Therefore, the pyramidal thermal model can be selected as the most suitable model for simulating pulsed laser welding in thin steel sheets.

In this study, the use of internal mechanical insert to prevent wrinkling defects in the process of T-shape tube hydroforming and expanding the window of the hydroforming process is presented. The study was performed both experimentally and by finite element simulation. In wrinkling limit testing, the use of internal mechanical insert for different modes prevented 100% of wrinkling and the T-joint was formed flawless, so that the wrinkles with high lengths such as 69. 5 and 67. 1 mm were prevented. Also, in the case of an internal pressure of 13 MPa and displacement of 33 mm, despite the high amount of axial displacement and the low internal pressure, the internal mechanical insert caused a reduction of 85. 06% of the wrinkling length and the wrinkling length reduced from 74. 3 to 11. 1 mm. To study the conditions of the hydroforming process for both cases of with and without internal mechanical insert, the simulation of finite element was used. Experimental tests were also carried out to verify the validity of simulation results. By comparing the results of the experimental study and the simulations, an appropriate match was found between them. The results showed that the use of internal mechanical insert prevents wrinkling in the piece. Therefore, it can be used to produce a piece without defects and develop the window of the hydroforming process.

The aim of this article is to present the methodology for modeling and simulation of start effects in spacecraft or satellite’ s propulsion system on the fuel sloshing in the tank by pendulum model in microgravity conditions. In other words, the main aim of this paper is pure sloshing study of fuel and ullage gas relative movement, neglecting the role of Propellant Management Device (PMD). To this end, fuel sloshing in tank is performed by utilizing the Fluent software based on pendulum model. Firstly, algorithm inputs are determined (exiting input, fuel and ullage gas volume, loading, dimensional specifications, etc. ); then, tank is modeled and designed and, finally, fuel sloshing simulation in micro-gravity conditions is developed. Fuel sloshing modeling and simulation outputs include determining the sloshing damping rate and its value in the simulation at 20 sec, velocity variation contour, velocity direction contour in the tank, and also ullage gas and fuel relative location in 0. 2, 0. 4, and 1 sec. The accuracy of the obtained results has been evaluated with the similar experimental results.

In this paper, the superelastic response of porous shape memory alloys (SMAs) containing spherical pore shape with pore volume fraction between 5% and 40% has been considered. Using digital images processing, the distribution of pores in 2D images of porous NiTi SMA has been extracted. In this method, the 3D distribution of pores has been appraised with the Monte Carlo method and 3D porous SMA models have been established. To investigate the superelastic behavior of shape memory alloys, the Lagoudas’ s phenomenological model was used, in which a phase transformation function was used. To homogenize the porous SMAs, the Young’ s modulus and the phase transformation function have been assumed to be a function of the pore volume fraction. Based on the proposed constitutive model a numerical procedure was proposed and executed by the commercial finite element code ABAQUS with developing a user material subroutine. The numerical results show that the Young’ s modulus and the phase transformation function are the approximately linear function of the pore volume fraction; furthermore, these results demonstrate the accuracy of the proposed homogenization method to predict the superelastic behavior of porous SMAs.

The development of built environment and increase of energy source utilization have led to paying attention to different procedures to optimized energy consumption in buildings. Designing different sort of double skin faç ade provides opportunities to keep building in more balanced environment and use less energy to provide comfort condition. As a natural process that optimizes energy consumption by balancing between different solutions, homeostasis is used as a pattern in designing this sort of homeostatic faç ade. Nowadays, different sorts of smart faç ade have been used on the boundary of building and environment. A sort of smart faç ade, which is designed based on homeostatic process, is able to create a sustainable balance between different solutions, adapting to environmental changes, and define the hierarchy of their use in different conditions, so as to provide thermal comfort conditions inside the building with higher efficiency than conventional smart faç ades. In this study, temperature fluctuation limits in homeostatic faç ade is determined and solutions are derived from a natural homeostasis system, and used in the design of the desired faç ade. The aim of this research is to compare the efficiency of temperature reduction solutions in different conditions and specified optimal one. For this end, a modulus of homeostatic faç ade is built and the operation under laboratory condition is evaluated, and also its behavioral relationship is examined with temperature fluctuations.

In recent years, scientific advances in navigation systems and technological development of low-power consumption and high-precision in magnetic sensors have made researchers to realize that earth’ s magnetic field can be applied for locating purposes. Earth’ s magnetic field is applied in the navigation method where the required data from earth’ s magnetic field can be read from high accuracy magnetic sensors. It is possible to determine the location by comparing the data with the reference maps through adaption of algorithms and/or filtering. Generally, in this method of locating, the inertia system is used to determine the velocity and condition, and the magnetic navigation system represents navigational assistance. In the first step toward obtaining a magnetic locating system, a reference magnetic map must be created; so, it is required to carefully analyze the earth’ s magnetic field, the quantity, and quality of the field variations over different time and places. In this paper, the possibility of obtaining the geographical location of an observatory by extracting available data of a magnetic observatory has been investigated and, then, the effect of the displacement of geographical location on the magnitude of the earth’ s magnetic field has been examined by an experimental test. The results of simulation and data collection confirm the fact that geographic location for a variety of vehicles can be attainable just using earth’ s magnetic field data and there is no need to use any other navigation sensors.

Due to the high demand of steel factories, the necessity of localization of mechanical laminar was introduced from Mobarakeh Steel Company of Isfahan. In this research, we first studied the working conditions and the extraction of the forces applied to the waterworks. The investigations showed that the forces are quasi-static and the pressure values are PH=225Pa and PGr=220Bar, and the torque TS=306. 07N. m. The results of the tensile test showed that the final strength for the waterworks and belt was 620. 3 and 594. 1 MPa, respectively. In order to make the desired waterworks, the belt was prepared in 6 steps from the mold and formed a circular shape. Using the matrix pitch matrix, the staircase was created on the waterworks. The results of static analysis on the mechanical laminar and domestic laminar showed that the maximum stresses, based on Von Mises theory, were 1. 39×108 Pa and 3. 2×108 and the confidence coefficient for each was 2. 808 and 1. 338, respectively.

Bistable mechanisms have two distinct stable positions that can move from one of these situations to other by a small stimulus. These stable positions, as well as the movement between them, have increased the use of these mechanisms in devices such as valves, switches, and etc. This bistable behavior is the result of the storage and release of the potential energy. Therefore, it is obvious that these mechanisms must have one or more flexible links or joints. In this paper, flexible members are modeled, using torsional springs based on the pseudo-rigid-body-model (PRBM). The existence of one flexible member is sufficient for bi-stability of the four-bar linkage. However, with changing the location of this flexible member as the input, the output, or the coupler link (or changing the location of equivalent torsional spring), various conditions are generated for the design of a four-bar linkage, which is discussed in this study. The results show that in all cases (the crank-crank, the crank-rocker, the rocker-crank, and the rocker-rocker), the equivalent torsion spring should not be connected to a smaller link in order to create a bistable four-bar linkage.

Micro-mixers are vital components of “ Lab-on-a-Chip” devices. Their main functionality is the mixing of two streams with desired quality and at minimum mixing time. In this work, numerical modelings of some active and passive micro-mixers with innovative designs are reported. Increasing mixing quality and decreasing mixing time are the design objectives. Our numerical model features solving the set of non-linear and inter-coupled Poisson-Nernst-Planck-Naiver-Stokes equations (PNP-NSE) instead of using simplified models like Poisson-Boltzmann (PB). These equations describe a more realistic model of the physics involved at continuum level by incorporating diffusion, electro-migration, and convection, which are the dominant phenomena in electro-kinetic micro-mixers especially those using AC voltage electrodes. The computations are carried out using Rayan (in-house code). The traditional Poisson-Boltzmann (PB) model relies on simplifying assumptions and is proven to lose its accuracy in complex geometries and near active electrodes. On the other hand, the PB model is much less sophisticated and therefore much less computationally expensive. One of the contributions of this research is to show that in passive micro-mixers making the obstacles smaller but more numerous increases the mixing quality (for the case studied by 13%). The other major contribution of this work is the introduction of the combination of the vertical and horizontal AC electrodes. This new design creates jets normal to the direction of the mainstream which is responsible for enhancing chaotic mixing. This results in a stable mixing quality of 99% at 2. 7s.

The optimal design of multilayer substrates containing the cutout under compression is very important to achieve maximum buckling resistance in comparison with structural weight, especially in aerospace structures. In this study, buckling and post-buckling behavior of composite laminated plates with orthogonal and symmetrical layup containing the cutout with different diameters has been investigated experimentally, semi-analytically, and numerically. To study the buckling of the composite plate with cutout semi-analytically, a finite strip method is developed. A finite element method was used for numerical analysis. The required material parameters for modeling were obtained from standard tests. The results of the current study show that the size of diameter of cutout does not have considerable effect on elastic rigidity of plate, but the buckling load significantly decreases by increasing cutout diameter. Also, buckling load and elastic rigidity of plate are considerably increased by increasing the number of composite layers. The thickness of plate has more effect on buckling load than the diameter of hole. Studies show that there is a good match between the results of buckling behavior derived from semi-analytical and finite element methods with experimental results.