Journal of Computational Applied Mechanics
Volume:47 Issue: 1, Jun 2016

Nano fillers are part of new studies to enhance various properties of fluids and solids. For example, adding nanoparticles as an enforcement in nanocomposites or as an additive to improve thermal or electrical properties in nano-fluids are of extreme importance in science and industry. There are numerous methods to uniformly disperse nanoparticles in fluid and solid phase. One of the well-used techniques is utilizing ball mills. Milling method is treated widely to uniformly disperse Carbon Nano Tubes (CNTs) in solid or fluid state materials. However, the issue is that this method abolishes some part of CNTs' structure. As a result, this defect adversely decreases the improvement of designated properties. In this research, two methods of milling conditions have been analyzed to find out their impacts on CNTs' structure. The first method is milling Multi-Wall Carbon Nano Tubes (MWCNTs) in ambient temperature. On the other hand, in the second method the temperature dwindled to -196°C by Retsch new generation ball mills (Cryo-mill). This apparatus flows liquid nitrogen (LN2) around the shaking jar and decreases the temperature as low as -196°C. To analyze the impact of these methods of milling on MWCNTs, Field Emission Gun-Scanning Electron Microscopy micrograph, X-Ray Diffraction, Raman Spectroscopy, and Thermo Gravimetric Analysis are scrutinized on MWCNTs’ structure. In conclusion, all the aforementioned experiments provide sufficient support to implicitly convince that cryo-milling method has less defective impact on initial MWCNTs.

In this paper, a general elastoplastic-damage constitutive model considering the effect of strain rate has been developed. The derivation of this model has been cast into the irreversible thermodynamics with internal variables within the fundamentals of Continuum Damage Mechanics (CDM). The rate effect has been involved as an additional term into the plastic yield surface (dynamic plastic yield surface). Therefore, the plastic surface has been presented in the category of Consistency–type model in which the rate of state variables is considered as independent state variables. The damage has been assumed as a tensor type variable and based on the energy equivalence hypothesis the damage evolution has been developed. The proposed model has been validated for both rate-independent and rate-dependent deformation. For this manner, the generalized trapezoidal stress integration algorithm of the model has been explained and the model has been implemented into user-defined subroutines (UMAT and VUMAT) in the finite element program ABAQUS. The results of numerical simulation, statically and dynamically, have been compared to the experimental results of three aluminum and two steel alloys. Also, the results of simulation for shear and double-notched tests have been compared to their experiments. By comparing the predicted results with experimental data, the capability and validity of the model have been verified.

Dynamically stable biped robots mimicking human locomotion have received significant attention over the last few decades. Formerly, the existence of stable periodic gaits for straight walking of passive biped walkers was well known and investigated as the notion of passive dynamic walking. This study is aimed to elaborate this notion in the case of three dimensional (3D) walking and extend it for other maneuvers, specifically curved walking or turning. For this purpose, the motion of a general 3D compass gait model on a ramp has been analyzed theoretically in detail. A comprehensive dynamic modeling with respect to the vertical fixed frame is used based on Lagrangian and augmented methods. In addition to 3D passive straight walking, the results confirm the existence of some passive turning motions for the biped walker towards the steepest decent of the ramp. It was shown that the value of passive turning is strictly concerned to the value of initial perturbed condition of the walker, especially to the value of heading angle. A parameter analysis was also accompanied to examine the change in the characteristics of such passive motions caused by the change in model parameters.

The primary cilium which is an organelle in nearly every cell in the vertebrate body extends out of the cell surface like an antenna and is known as cell sensor of mechanical and chemical stimuli. In previous numerical simulations, researchers modeled this organelle as a cantilevered beam attached to the cell surface. In the present study, however, we present a novel model that accommodates for both pivoting and bending of primary cilium in response to the fluid flow. In this model, primary cilium is attached to the cell using a thin elastic layer. This layer, which comprises the bottom boundary of the cilium, provides the possibility of pivoting of the cilium around its base so that we are able to analyze the other part of ciliary response to the fluid flow. In this study, we have used finite element method and fluid-structure interaction techniques to simulate the problem. Domains of solid cilium and the surrounding fluid were meshed using triangular elements. The governing equations in this problem were fully coupled and were solved by the direct method. Graphs of maximum stress in the cilium base versus elastic constant of the thin layer depict two different trends. By scrutinizing colored plots of stress distribution in the cilium base it is construed that these trends represent two different mechanisms in ciliary deformation due to the flow of the fluid. In case of low elasticity constants, for which attachment of the cilium to the cell is soft, pivoting mechanism is essential, while in case of harder attachments, bending mechanism dominates.

In the present study, modelling and vibration analysis of Carbon nanotubes/ fiber/ polymer composite microplates are investigated. The governing equations of the Carbon nanotubes/ fiber/ polymer composite microplates are derived based on first order shear deformation plate theory, rather than other plate theories, due to accuracy and simplicity of polynomial functions. The modified couple stress theory is employed because of its capability to interpret the size effect. Halpin-Tsai model is utilized to evaluate the material properties of two-phase composite consisted of uniformly distributed and randomly oriented Carbon nanotubes through the epoxy resin matrix. Afterwards, the structural properties of carbon nanotubes reinforced polymer matrix, which is assumed as a new matrix, and then, reinforced with E-Glass fiber, they are calculated by fiber micromechanics approach. Employing Hamilton’s principle, the equations of motion are obtained and solved by Hybrid analytical numerical method. The influences of various parameters such as the weight percentage of single-walled carbon nanotube, aspect ratio, and size effect on the vibration characteristics of microplate are discussed in details. Results indicate that the stability of Carbon nanotubes/fiber/polymer composite microplates can be improved by adding appropriate values of Carbon nanotubes. In addition, increase in the frequencies is more pronounced in the case of microplates reinforced with SWCNT compared with MWCNT. These findings can be used in design and manufacturing of marine vessels and aircrafts.

In this paper, the 10-minutes period measured wind speed data at different heights (10 m, 30 m, and 40 m) are presented for Khvaf, which is one of the major counties with high wind potential in Khorasan provinces in Iran. To the author’s knowledge, there hasn’t been any assessment works in the mentioned site. From the primary evaluation and by determining mean wind speed and also the Weibull function, the results show that the measurement site falls under class 7 of the International System Wind Classification, which means that the station has very suitable conditions for installing and operating wind farms. On the other hand, a new approach is utilized for evaluating potential power of a region based on comparison between maximum power generation pattern and daily and monthly energy consumption patterns. Furthermore, by using wind roses of speed and turbulence simultaneously, the best direction for installing wind turbines is determined. On the other hand, the situation of topography and surface conditions of Khvaf station has been analyzed; because of its smooth surface, it is appropriate for installing wind turbines. Besides, several types of Vestas Company turbines have been compared by their capacity factors and three of them with highest capacity factor are selected for economic evaluations. One of the important issues in the assessment of wind energy potential is the economic evaluation. This is a major gap that many researches do not have sufficient attention to it. Hence, an economic analysis was performed based on NPV, IRR, and Normal Payback methods in order to select the best wind turbine for this site.

On the onset of triple-diffusive convection in a horizontal layer of nanofluid heated from below and salted from above and below is studied both analytically and numerically. The effects of thermophoresis and Brownian diffusion parameters are also introduced through Buongiorno model in the governing equations. By using linear stability analysis based on perturbation theory and applying normal modes analysis method, the dispersion relation accounting for the effect of various parameters is derived. The influences of solute-Rayleigh number, analogous solute-Rayleigh number, thermo-nanofluid Lewis number, modified diffusivity ratio and nanoparticle Rayleigh number on the stability of stationary convection are presented analytically and graphically. The solute Rayleigh number and analogous solute Rayleigh number have stabilizing effects on the onset of stationary convection for both top-heavy and bottom-heavy arrangements. The thermo-nanofluid Lewis number and diffusivity ratio have stabilizing effects on the onset of stationary convection while nanoparticle Rayleigh number has destabilizing effect on the onset of stationary convection. The necessary conditions for the existence of oscillatory modes are also obtained. A very good agreement is found between the results of present paper and earlier published results.

One of the most crucial elements of each country is electricity distribution networks (EDN). Awareness of accidents in EDN could be very important in the conservation and utilization of them. The accurate and periodic inspections can provide a good service to subscribers. The goal of this project is to fabricate a quad rotor, which can do an accurate and a periodic inspection. The design and implementation procedure are explained. The mechanical parts are designed by SolidWorks software then the structure of robot is fabricated with AL8080 by machining and milling. Then the dynamic model of the robot is generated and based on it the controller is designed. The two PID controller are proposed and simulated with MATLAB Simulink.

In this paper the dynamic of a droplet on a surface with a hole is investigated under gravitational effect by using lattice Boltzmann method. Incompressible two-phase flow with high density ratio proposed by Lee is considered. Cahn’s theory is used to observe the wettability of the surface in contact with liquid and gas phases. Several parameters such as contact angle, surface tension and gravitational acceleration are studied to demonstrate their effects on the deformation of the droplet. To evaluate the results, the benchmark problems for equilibrium contact angle, capillary rise and Laplace law are conducted and a satisfactory agreement with analytical results is shown. Based on this study, four typical deformations of a droplet dripping down a hole can be observed; equilibrium drop on the top of the surface, equilibrium drop under the bottom of the surface, splashing and dripping of the drop. It is seen that at low Ohnesorge numbers the droplet deforms slightly and tends to retain its state. Moreover any increase in the Archimedes number magnifies the tendency to pass through the hole. Also, the relationship between the volume of the remaining droplet on the surface and Archimedes and Ohnesorge numbers is investigated. It is found that by increasing the Archimedes number, the volume of the remaining droplet on the surface reaches a constant value that is dependent on geometric parameters.

In this paper, the effect of autofrettage process parameters on the ultimate pressure that functionally graded spherical vessel can tolerate are investigated. FGM properties and autofrettage pressure are considered as important parameters. Assumptions are variation of properties of FGM in radial direction, the residual stress in the absence of Bauschinger effect with the operation of variable material property method for bilinear material and power law fraction distribution for FG vessel calculated. The stress distribution in loading phase is computed using projection method and rule of mixture for FGM and elastic solution for thick spherical vessel. In unloading phase the material behavior is assumed to be isotropic and residual stress computed by using superposition method for loading and unloading phase. For reloading phase the rules of linear mixture employed for estimating the ultimate strength of FGM. By assuming functionally graded material properties and autofrettage process as effective parameters on amount of pressure capacity of autofrettaged vessel, the effects of parameters discussed separately. The results illustrate considerable effect of volume fraction used in FGM (up to 35% compared to full metal case) and inhomogeneity exponent (up to 154% compared to homogeneous case) on amount of ultimate pressure which is mentioned in results of parametric analyzing.

Evaporation of micro-liter drops from solid surfaces at room condition is mainly governed by diffusion. Therefore, there should be no difference between evaporation rate of sessile and pendant drops. However, some studies indicate a difference and explain the difference using buoyancy. The objective here is to reconcile the inconsistency in the literature. For that, first, by comparing two identical suspended drops, one with a plate on top and the other underneath with a space between drop and plate, we showed the contribution of buoyancy in evaporation is at most less than 8%. When a plate was placed on top, water (its vapor is lighter than air) evaporated slower and hydrocarbons (their vapors are heavier than air) evaporated faster. Interestingly, it was observed when drops touch the plates (i.e. sessile and pendant drops), both water and hydrocarbon drops evaporated faster in sessile configuration. The observation for hydrocarbons is in contradiction with what buoyancy explains. To describe the difference, different scenarios were studied. It was found that sessile drops stay longer in the “constant wetted area” (CWA) mode, before switching to the CCA (constant contact angle) mode, e.g. a 4 µl sessile water drop on a Poly(methyl methacrylate) coated silicon stays in the CWA mode for 318 s whereas for a similar pendant drop this time is 274 s. Considering the fact that evaporation rate in the CWA mode is 30–40% higher compared to the CCA mode, the faster evaporation rate of sessile drops may be explained.

Structural health monitoring of cracked structures is one of beloved subject of researchers recently. Consider of crack behavior in the water and energy pipeline is important because of environmental problems. In this paper consider of crack parameters in the underwater pipe subjected to mechanical transient load is investigated. For this purpose, three- dimensional parametric model of cracked pipe has been presented for calculation of J integral values. Underwater explosion load model has been used for applying the transient load and J integral values have been obtained in circumferential and axial semi-elliptical internal cracks. Obtained results is shown that under mentioned condition, pipe isn’t safe and crack grow is happening in the inner surface of crack. According to results for integrity of structure must be safe stand-off distance (distance of charge with respect to pipe) greater than previous state. Obtained values in this paper is used for estimation of structure life and Repair and maintenance are useful.