JOURNAL OF SOLID AND FLUID MECHANICS
Year:2019 | Volume:8 | Issue:4|Papers Count:21

Achieving to the higher out-of-plane displacement for a piezoelectric microcantilever enhances sensitivity and accuracy of the related microsensors and causes increase in displacement and performance of the related microactuators. In this paper, out-of-plane displacement of a piezoelectric microcantilever with TShaped cross section has been modeled using finite element method. With the aim of increase in out-ofplane displacement of this microcantilever, effect of the geometrical parameters on the out-of-plane displacement of the microcantilever has been investigated using the Taguchi method. Optimum levels of the piezoelectric microcantilever geometrical parameters to achieve the maximum out-of-plane displacement were obtained using analysis of the signal to noise ratios and order of the effect importance of geometrical parameters on the out-of-plane displacement was specified using analysis of variance (ANOVA). Among the studied parameters, length of the microcantilever (L) has the most influence on the out-of-plane displacement. The higher the length of the microcantilever, the more the out-of-plane displacement. Then, beam web depth (h) has the most effect on the out-of-plane displacement of the microcantilever. The less the web depth, the more the out-of-plane displacement of the microcantilever. Using optimum levels of the geometrical parameters, out-of-plane displacement of 296. 3 µ m was obtained that is about 2. 3 times of the result of the latest research conducted in this field.

Dynamic behavior of continuous systems, such as beams and plates under the application of moving concentrated loads, is an important issue in engineering. In this study, a meshfree method is presented for the analysis of the dynamic response of thick plates under the influence of concentrated moving loads. The displacement field is based on the third-order shear deformation theory. In this numerical method, the field variables are interpolated only by using nodes distributed purposively in the computational domain. Since there is no conectivity between the nodes, it is possible to add nodes in the areas of application of the force. Another feature of the proposed method is the use of the radial point interpolation method (RPIM) shape functions which possess the Kronecker delta function property and therefore satisfies the essential boundary conditions easily. Also, due to the high density of nodal points in the vicinity of the point of application of the load, the background decomposition method (BDM) is used in order to achieve a high accuracy with appropriate speed. In this paper, nodes are re-arranged in the path of the moving load adaptively which leads to high accuracy and speed of the final solution. To validate the proposed method, the obtained results are compared with the analytical solutions.

Resin pocket area is a common defect in manufactruring of sandwich composites using vacuum infusion process (VIP). A numerical study is performed on crack growth behavior and failure modes of a sandwich composite wind turbine blade by means of extended finite element method (XFEM) and considering virtual crack closure technique (VCCT). The effect of resin pocket area on crack growth is investigated by considering different sizes for this area. Results of numerical analysis have shown that crack growth in the specimen initiates in foam core under loading nose and propagates through the middle of foam core and decreases its angle and grows towards the tapered area until it reaches to the core-face interface. Calculation of stress intensity factors has shown that first and second fracture modes are dominant modes in crack initiation and propagation steps, respectively. It is also observed that small and average sizes of resin pocket area in sandwich composite specimens delays the damage propagation and large resin pocket area accelerates damage progress. Finally, numerical and experimental results of crack growth path and load-displacement behavior of four-point bending test have shown a good accordance.

One of the main problems in the classical methods for analyzing crack is a discontinuity in materials and specific conditions at the crack tip. Peridynamic theory, which has been introduced in recent years, could be used to improve the analysis of cracked structures. In this theory, the points of a body whose displacement or displacement derivatives are discontinuous are not distinguished from other material points. In this paper, using the bond-based peridynamic theory, the crack growth in a beam with initial crack under the impact load has been investigated. The governing equation is developed and solved using Peridynamic theory and the results are validated using other investigations. Two models for the initial crack definition and two projectile shapes have been considered and in addition the effect of some peridynamic parameters on the results has been studied. The results demonstrate the ability of the peridynamic theory to model the crack growth in the studied problems.

Explosion problems can be examined in different environments. Due to the lesser-known nature of soil types and extent of the equations of state, explosion problems need careful analysis. Because of difficulties in laboratory explosion modeling, numerical models use to analyze this phenomenon Using the SPH methodology avoids the disadvantages of traditional numerical methods in treating large diformations in the extremely transient explosion process. Since explosion crater in the soil is an important problem and most of the studies are experimental, In this article it is tried to investigate the craters diameter and height caused by the different amounts of explosives. The model is programmed with Fortran language and smooth particle hydrodynamics, SPH, the craters, pressure caused by the explosion in the soil and the soil surface changes are also studied. To validate the model, the results of a laboratory study were used and it is shown that they are consistent with the numerical results of this study. Finally, craters in a two layer soil is studied. This program can be used for modeling of soil explosion and craters.

Vibration of postbuckled cracked plate has been investigated using the differential quadrature element method. The crack modeled as an open crack using a no-mass linear spring. The governing equations of vibration of a buckled cracked plate are derived using the Mindlin theory and considering the effect of initial imperfection. The answer consist of static and dynamic parts. First, differential equations are discretized using the differential quadrature element method and then the resulting nonlinear algebraic equations are solved using the arc-length strategy. Then, assuming small amplitude vibrations of the plate about its buckled state and exploiting the static solution in the linearized vibration equations, the dynamic equations are converted to a non-standard eigenvalue problem. Finally, natural frequencies and mode shapes of the buckled cracked plate are obtained solving the eigenvalue problem. The accuracy of the proposed approach is verified using the results obtained by an experimental setup and those obtained by the finite element method. Moreover, several case studies of buckled cracked plates have been solved and effects of selected parameters have been studied.

Friction stir welding (FSW) process is a method for joining the aluminum alloys. Nowadays, it is considered to form the blanks fabricated by this method. Single point incremental forming (SPIF) is used to manufacture complex shapes with high depth which is not possible with traditional methods. SPIF is a flexible method for low production or manufacturing a prototype model. In this paper, experiments are performed on the blanks fabricated by FSW process to study the effect of the SPIF parameters. The first step conducted to investigate the influence of rotational speed and feed rate of friction stir welding process on mechanical properties of AA 6061-T6. The output of this step is the appropriate samples for next step. In the next step, the effect of the lubrication, rotational speed, feed rate and tool trajectory has been studied on thickness reduction (thinning), surface roughness and formability. The results show the lubricant and tool trajectory increase the depth of formation up to 1. 6 times. Also, these two parameters improve the effects of thickness reduction and surface quality.

In order to avoid flutter phenomena in blades of a turbine stage, the blades have not been made equal and they have some differences in their masses and stiffness. These small differences are called mistuning. In this study, the effect of the mistuning on vibration response of blades connecting with two lacing wires is studied. First, the system has modeled by mass-spring-damper and then the governing equations are derived. After that, the vibration response of the mistuned system is compared with the vibration response of the tuned system in the different type of blades numbers connection. The vibration response of the mistuned system is also investigated when all of the blades are connected. The results show that a small change in the stiffness of the tuned system causes the vibration amplitude of some of the blades of the system to change considerably in some of the blades connection arrangements. For example, it can be seen that the mistuning up to about 0. 5 percent, in the case of connecting eight blades to each other in a row of turbine blades, increases about 11 percent the amplitude of vibration response of the system.

An analytical solution procedure based on the power series method and the first order shear deformation plate theory is developed for analysis of FG rectangular plates. For the first time, a system of five second order coupled partial differential equations is solved as general form by using power-series solution. Most of presented analytical solutions for analysis of the rectangular plates can be applied for plates with specific load and edge conditions. Based on the developed analytical method in the present paper, plates under various boundary conditions, various transverse and shear loads and plates rested on non-uniform twoparameter elastic foundation can be analyzed. Firstly, a sensitivity analysis regarding the number of terms of the series solution is performed as convergence criterion. Then, the obtained results are compared with the presented results by other researchers. Finally, effects of various parameters are examined as 3D figures. This study shows that the developed method has very good accuracy and can be applied for analysis of various plates. Also, it can be seen that results can be obtained as a function of various parameters, so the presented analytical solution can be easilyapplied for analysis of the various parameters.

Research in field of explosions effects on hybrid and composite structures is expanding. One of the loads that defense structures needs to withstand and not lose their performance is the explosion wave. In this thesis, fiber-metal laminates were made using hand layup. Then mechanical properties were obtained using standard tensile tests for composites. The explosion test was carried out using a Shock tube machine. Finally, the results of the empirical test were compared with the numerical simulation of these plates by the finite element software. It was found that experimental and numerical results are in good agreement. At the end, the results of the experimental test and finite element simulation were compared and it was observed that a good match between the results was observed. The results of the experiments have shown that these plates do not even in loading less than 10 grams of C4 (equivalent to a pressure of 28 MPa) inside the shuck tube, and they are delaminated and in Loading 20 grams ruptured. In all experiments, it can be seen that the back aluminum plate, due to the reflection of the compressive wave that converts to the tensile wave, is removed from the panel and deforms the plastic And makes the composite less damaged.

In this paper, fatigue analysis and life estimation in the bracket of an airplane emergency exit door was investigated. The design and static analysis of door has already been carried out. The critical parts of door structure were selected based on static stress analysis and principal structural elements criteria. The bracket is one of 4 critical parts of door, selected due to those criteria. The stress spectrum on the bracket was obtained from airplane flight profiles and the loads of door existing in a flight envelope. By using the rain flow cycle counting algorithm, the fatigue life in bracket has been calculated. Two codes were developed by using Matlab software. One code was obtained the stress spectrum in a flight block and another code was count the stress cycle based on the rain flow method. The results were shown that the bracket was safe at flight envelope. Finally, some fatigue tests has been carried out on the bracket and good agreement was found in the results evaluated numerically and that obtained experimentally.

In this research, the compression properties of fiber-metal laminates including 2024-T3 aluminum sheet and composite of epoxy reinforced by the hybrid of Jute-glass fibers were investigated. In order to to improve the adhesion of aluminum sheets with reinforcement fibers, chemical etching was used for surface modification of this sheets. Also to improve the mechanical properties and adhesion behavior of jute fibers, alkali surface modification was performed and verified by Fourier transform infrared spectroscopy. Samples with eight different stacking sequence of jute-glass fibers were made by hand-laying up technique. Edgewise compression was performed and the maximum applied loading, compression strength, absorbed energy during failure and specific absorbed energy were calculated. Three failure modes including, buckling and debonding one of the facing metals from the fiber, columnar collapse with facing buckling in opposite directions and Euler buckling mode were observed. According to the comparison of the failure modes and the results of the edgewise compression test, it was found that Euler's buckling mode is the most favorable failure mode. Also, investigating the force-displacement and failure modes of the samples showed that hybrid sample with ordering of glass-jute-glass-jute-glass fibers has the highest compressive strength (102. 1 MPa) and specific absorbed energy (1123. 6 kJ/kg) and its failure (Euler Bucking mode) is multi-step and controlled.

In this paper, we investigate the vibrational behavior of a double-beam doubly clamped beam subjected to the harmonic external load with different amplitudes using a passive absorber. This system actually provides a simple and localized model of marine structures stimulated by external fluid. For modeling of the beam, the Euler-Bernoulli theory and for modeling of nonlinear energy sink, nonlinear springs and linear dampers have been used. The system response is obtained by two analytical methods (complexification averaging method) and numerical (fourth order Rang-Kuta method) and accordingly, the proper range of system and absorber’ s parameters are extracted to optimally reduce vibrations. In addition, the effects of system damping, the effect of higher modes, quasi-periodic response regions and instability conditions on the relative displacement and center of mass of the system response are investigated. The results showed that the load thresholds for the occurrence of various phenomena such as the detached resonance frequency region and the Hopf and saddle node bifurcations, the probability of occurrence of the jump phenomenon in the system and the nonlinear adsorbent efficiency will change with the change of the adsorbent location.

The aim of this paper is to study the buckling analysis of power law functionally graded rectangular microplates. The modified couple stress theory based on the exponential shear deformation theory has been used to obtain the dimensionless critical buckling load of the functionally graded microplate. In exponential shear deformation theory, exponential functions are used in term of thickness coordinate to include the effect of transverse shear deformation and rotary inertia. To obtain the critical buckling loads for all boundary conditions, the equations of motion are obtained using Rayleigh– Ritz method based on the modified couple stress theory that the this theory contains only one material length scale parameter. The temperature is assumed to be constant in the plane of the plate and to vary in the thickness direction. Material properties are assumed to be temperature dependent and vary continuously through the thickness according to a power law distribution in term of the volume fraction of the constituents. Finally, the effect of various parameters such as n Power Law indexes, aspect ratio (a/b), length to thickness ratio and the length scale parameter on the non-dimensional critical buckling load of rectangular FG micro nano-plates are presented.

Synthetic jet is a novel means for various industrial applications and has received a lot of attention by researchers because of its small size and zero-net mass flux (ZNMF) characteristics. The aim of the present study is to investigate the flow field of the synthetic jet in the presence of the crossflow in order to gain a better understanding of the flow mechanism and also assessing high Reynolds turbulence models. For this purpose, three turbulence models (Realizable k-ε (RKE), RNG k-ε (RNG) and Standard k-ε (SKE)) are applied. The results show that contrary to Standard k-ε and Realizable k-ε turbulence model, RNG k-ε model is capable of capturing the vortical structures generated in the flow field. Furthermore, comparison of the normalized instantaneous velocity magnitude at the orifice exit confirmed that unlike the standard model, RNG and RKE showed a better prediction of relative maximum and minimum peaks in the suction cycle.

in this study two general geometries of microchannels (Straight and V-shaped) with four different types of interruption are studied. The effects of geometries and pin-fins interruption on performance enhancement of microchannel heat sinks were investigated at various Reynolds number (100-900). Important parameters such as base temperature, Nusselt number, pressure drop, heat transfer coefficient and hydrothermal performance factor were evaluated. The simulations have been carried out using Fluent 17 software. The results show that interrupted microchannels improve the heat transfer coefficient and Nusselt number compared to integral microchannels. Microchannels with a V-shaped pin report better results due to turbulence in the bulk flow and the generation of vortex. Through different configurations, the Interrupted-Staggered configuration for both straight and V-shaped geometries shows the highest hydrothermal performance factor with increase of about 1. 5 times in comparison to the Straight-Integral model. adding Al2O3 nanoparticles to water increased the hydrothermal performance factor approximately 1. 83 times in the case of Straight, Interrupted-Staggered and about 1. 77 times in the case of Vshaped, Interrupted-Staggered. Increasing the concentration of nanoparticles also improved the hydrothermal performance.

In this paper the forced convection of Cu and Fe3O4 and Cu/Fe3O4 hybrid nanofluid in the laminar regime under constant heat flux codition is investigated experimentally. Experiments are carried out in three volume fractions of 1, 2, 4 % and three Re number of 600, 1200 and 1800, and local Nusselt number is measured. The results show that for nanofluid in simple and hybrid mode, with increasing the volume fraction of nanoparticles and Re number, the heat transfer coefficient is increased. results revealed that the heat transfer rate is augmented for both cases of simple and hybrid nanofluids with a rise in the particle volume fractions or the Re number. In addition, the comparison of the experimental data of Cu, Fe3O4 and hybrid nanofluids indicated that the heat transfer enhancement is more remarkable in the case of hybrid nanofluid. In the case of Cu/Water nanofluid, the greatest increase in the heat transfer vs. pure Water is 7. 8% and in the hybrid nanofluid 11. 9%. Also, the volume fraction of hybrid nanofluids is very effective in increasing the coefficient of heat transfer, so that in a 2% volume state, an increase is observed over other simple nanofluid volumetric fraction.

In this paper the effect of roughness on hydrodynamical friction reduction of superhydrophobic surfaces were studied. For this purpose, different non-wettable microchannel with various processing method was fabricated and then the amount of drag reduction in laminar flow was investigated on them. The surfaces were from Aluminum and the four different methods were used to fabricate superhydrophobic surfaces. According to the results, whereas superhydropobic surfaces with hierarchical roughness could lead to a significant skin friction reduction (about 20 %), non-wettable smooth surface did not show a tangible reduction in drag force. Beside this for study the effect of preprocessing method the boiling process was added to the fabrication method. the results indicated that boiling process alongside roughening the substrates as a part of preparation of superhydrophobic surfaces intensified durability of the coated layer and drag reduction (up to 45 %). In addition surfaces which was prepared by adding boiling process were more stable in flow field.

The aim of this article is to develop a high order splitting scheme for the simulation of multi-layer core-annular flow of two fluids with different viscosities inside the two-dimensional channel. For this simulation, the incompressible fluids flow equations (Navier-Stokes) and concentration (volume fraction) equation are solved. The two-phase flow is modeled by the volume of fluid technique and with harmonic interpolation. The spectral element method is used for the spatial discretization and Adams-Bashforth method is adopted for the time integration. Velocity correction scheme is developed here as a high order splitting scheme for the coupling issue. To validate the numerical results they are compared with the analytic solution of fully developed flow. This comparison includes outflow velocity profile and pressure gradient. Also, the accuracy of numerical method has been investigated spatially and temporally. The form of core-annular flow has been investigated for various parameters and the results have been compared with experimental and other numerical works. Investigations show that the Reynolds number and core inlet thickness are two important parameters on the pattern of core-annular flow.

The main objective of this paper is to study the characteristics of flow-induced noise in high pressure reducing valve (HPRV) and to provide some guidance for noise control. Based on computational fluid dynamics (CFD), numerical method was used to compute flow field. Ffowcs Williams and Hawkings Model was applied to obtain acoustic signals. The unsteady flow field shows that noise sources are located at the bottom of plug for valve without perforated plate, and noise sources are behind the plate for valve with perforated plate. Inlet pressure has great effects on sound pressure level (SPL). The higher inlet pressure will lead to larger SPL at high frequency. When the maximum Mach is close to 1, SPL at low frequency becomes very high. Therefore the advantage Ansys Fluent on Numerical Simulation Method have been used and variations in the intensity of current turbulency and frequency variations in different noise have been studied. For this simulation via an angle globe valve with two inch size has been used with a water vapor that is analyzed in two cage in simple & perforated Cage.

In this paper, the effect of uniform sinusoidal roughness elements on natural convection heat transfer of nanofluids within an enclosed cavity is studied by adopting the lattice Boltzmann Model. The uniform sinusoidal roughness elements are presented on the vertical walls, while the Right and left walls are kept at hot and cold constant temperatures, respectively. The variation of density is slight thus; hydrodynamics and thermal fi elds equations are coupled using the Boussinesq approximation. Effective viscosity and thermal conductivity of nanofl uid are obtained using KKL model implementing Brownian motion of nanoparticles. The velocity and temperature distribution are both solved by D2Q9 scheme by using a Fortran code. The study have been carried out for Rayleigh number, location of roughness elements, frequency of roughness elements, dimensionless amplitude of uniform sinusoidal roughness elements and various volume fractions of Al2O3 nanoparticles in the base water fluid. Results show that the heat transfer increases with the increment of Rayleigh number and nanoparticles volume fractions, but Nusselt number decreases by the increment of the frequency of roughness elements and dimensionless amplitude of uniform sinusoidal roughness elements. The rate of increase or decrease of Nusselt number is a function of roughness elements locations.