فهرست مطالب

  • Volume:50 Issue: 2, 2020
  • تاریخ انتشار: 1399/02/16
  • تعداد عناوین: 24
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  • Ali Falavand Jozaei, Ebrahim Hajidavalloo *, Aziz Azimi, Younes Shekari Pages 210-218
    Analysis of the drilling fluid temperature due to heat transfer of drilling fluid with the formation in under-balanced drilling operation is the main objective of this study. Gas-liquid two-phase flow model considering thermal interaction with the formation is used to numerically simulate a well with real dimensions. In the present study, the continuity, momentum, and energy equations are developed to compute the wellbore temperature profile. In this simulation, the effects of oil and gas production from the reservoir into the annulus and heat generated by viscous dissipation within the drilling fluid, heat generated by friction between the rotating drill string and the wellbore wall, and heat generated by the drill bit were included in the model. The results are validated with actual field data and also with two-phase flow model using the geothermal temperature gradient given in the literature. Comparisons of the present results show that two-phase flow numerical simulation with thermal consideration gives more accurate results compared to other models for the prediction of the bottom-hole pressure. Results show that the fluid temperature at the bottom-hole increases with increasing well depth, the flow rate of gas, and source terms consideration. Whereas the fluid temperature at the bottom-hole decreases with increasing liquid flow rate and specific heat of liquid and gas.
    Keywords: Under-Balanced Drilling (UBD), Bottom-Hole Pressure (BHP), Two-fluid model, Two-phase flow, Temperature profile
  • Mahmoud Chahartaghi *, Sayed Ehsan Alavi, Ali Sarreshtehdari Pages 219-227
    During hot seasons the inlet temperature of Nitrogen increases, as a result compressor consumes more power for compressing a specific mass ratio of fluid and consequently total energy consumption of the compressor increases as well. In this research, a three stage centrifugal compressor with intercooler was modeled thermodynamically in order to decreases the energy consumption of the compressor. In each compressor, isentropic efficiency, outlet temperature of the Nitrogen gas and power compression was investigated. The effect of inlet Nitrogen temperature and cooling water temperature on intercoolers’ efficiency were investigated. In this study, Nitrogen gas is considered as an ideal gas. It is found that, in each compressor any growth in inlet temperature of the Nitrogen gas will result in linear increase in the outlet temperature of the Nitrogen gas and power compression furthermore, it is observed that increasing the temperature of Nitrogen gas has the most negative effect on efficiency and power compression of the first compressor in comparison to the second and the third compressor consequently, it will result in a 10 percent decrease in special power compression specially during summer time. According to the results, it is figured out that any growth in inlet Nitrogen temperature causes a smooth decline in isentropic and Power Compression of the first, second and third compressors besides increasing the temperature of the Nitrogen gas increases the isentropic efficiency up to 3 Percent and increasing the cooling water temperature decreases the intercooler efficiency up to 7 Percent.
    Keywords: Three Stage Centrifugal Compressor, Shell, tube heat exchanger, Isentropic Efficiency, Compression Power
  • Ali Falavand Jozaei *, Asad Alizadeh, Ashkan Ghafouri Pages 228-238
    In the present study, the combination of lattice Boltzmann and immersed boundary methods is used to simulate the motion and deformation of a flexible body. Deformation of the body is studied in microchannel with stenosis and the effect of the flexibility changes on its deformation is investigated. The obtained results in the present manuscript show that by increasing the elasticity modulus, the deformation of the body and its speed decrease. In this case, the flow pressure around the body increase. When the body is initially located outside the microchannel center, tank-treading motion occurs due to the difference in velocity of the shear layers. In addition, with a decrease in the size of microchannel stenosis, the body is less deformed and goes faster and reaches to the end of the microchannel in less time. The faster or slower movement of the biological membranes than the normal state causes the proper exchange of materials between the membrane wall and the surrounding flow and that disturbs its most important duty i.e. the exchange of materials with tissues. The analysis in this study shows that the results of the simulation are in good agreement with the available results and demonstrates the efficiency of the combination of lattice Boltzmann and immersed boundary methods to simulate the dynamic behavior of biological membranes, red blood cells and deformable particles inside the flow.
    Keywords: Flexibility, Stenosis, Poiseuille Flow, Lattice Boltzmann method, Immersed Boundary Method
  • Ahmad Reza Ghasemi *, Masood Mohandes Pages 239-245
    A comparison between the vibration of fiber-metal laminate (FML) and composite cylindrical shells has been studied in this manuscript. Love’s first approximation shell theory has been applied to obtain Strain-displacement relations. In addition, beam modal function model has been used to analyze the cylindrical shell with different boundary conditions. In this manuscript, the frequencies of FML and composite cylindrical shells have been compared to each other for different materials, lay-ups, boundary conditions, axial and circumferential wave numbers. The most commercially available FMLs are CARALL (carbon reinforced aluminium laminate), and GLARE (glass reinforced aluminium laminate), which are studied in this research. The results showed although the frequencies of carbon/epoxy are greater than glass/epoxy for all of the n, this process is not constant for FML. Also, with increasing the n, the frequencies of FML cylindrical shells are converged more faster than the composite one. Moreover, the frequencies of both boundary conditions are converged with increasing n for both FML and composite cylindrical shells.
    Keywords: Free Vibration, FML, Circular Cylindrical Shell, Beam Modal Function, Different Lay-ups
  • Mahmood Chahartaghi *, Sayed Ehsan Alavi Pages 246-255
    Improving heat transfer and performance in a radial, finned, shell and tube heat exchanger is studied in this study. According to the second law of thermodynamics, the most irreversibilities of convective heat transfer processes are due to fluid friction and heat transfer via finite temperature difference. Entransy dissipations are due to the irreversibilities of convective heat transfer. Therefore, the number of entrancy dissipation is considered as the optimization objective. Thirteen optimization variables are considered, such as the number of tubes, tube diameter, tube length, fin height, fin thickness, the number of fins per inch length of tube and baffle spacing ratio. The “Delaware modified” technique is used to determine heat transfer coefficients and the shell-side pressure drop. In this technique, the baffle cut is 20 percent. The results show that using genetic algorithm the optimization can be improve the heat transfer by 13 percent and performance of heat exchanger increased by 18 percent. In order to show the accuracy of the algorithm the results compared to the particle swarm optimization.
    Keywords: Entransy dissipation, Genetic Algorithm, Optimization, Shell, tube heat exchanger
  • Farokh Alipour *, Aminreza Noghrehabadi, Alireza Danehdezfuli Pages 256-262
    This study aimed at linear stability analysis of the stratified two-phase liquid-gas flow in a horizontal pipe. First, equations governing the linear stability of flow in each phase and boundary conditions were obtained. The governing equations were eigenvalue Orr Sommerfeld equations which are difficult and stiff problems to solve. After obtaining the velocity profiles of the gas and liquid phases in the pipe, the instability equations for each phase with related boundary conditions were coupled and simultaneously solved by using the Chebyshev Tau - QZ polynomial method. The instability spectra for some points has been plotted and some curves about instability conditions the same as neutral stability curve which shown stable and unstable region respect to Reynolds number had been drown. According to the neutral stability curve for each phase, the liquid phase is more exposed to instability than the gas phase. The liquid phase was unstable in low Reynolds numbers and a large amplitude of the wave velocity α but gas was unstable in higher Reynolds number and small amplitude of α.
    Keywords: Two phase flow, stratified, Instability equations, Eigenvalue equations, Chebyshev polynomial
  • Hamid Basaeri, Mohamadreza Zakerzadeh *, Aghil Yousefikoma, Nafise Faridi Rad, Mohammad Mahdavian Pages 263-274
    In this paper, hysteretic behavior modeling, system identification and control of a mechanism that is actuated by shape memory alloy (SMA) wires are presented. The mechanism consists of two airfoil plates and the rotation angle between these plates can be changed by SMA wire actuators. This mechanism is used to identify the unknown parameters of a hysteresis model. Prandtl–Ishlinskii method is employed to model the hysteresis behavior of SMA actuators, and then, a self-tuning fuzzy-PID controller is designed based on the obtained model and implemented experimentally on the mechanism. The process of designing the controller has been implemented based on the model which results in compensating time and price. Self-tuning fuzzy-PID controller is applied to the closed control loop in order to control the position of the morphing wing. The performance of the controller has been investigated under different input signals including square and sinusoidal waves, and the results show the proper effectiveness of the method.
    Keywords: Hysteresis Modeling, Fuzzy-PID Control, SMA Actuator
  • Sadegh Ghorbanhosseini *, Faramarz Fereshteh, Saniee Pages 275-281
    One of sheet severe plastic deformation (SPD) operation, namely constrained groove pressing (CGP), is investigated here in order to specify the optimum values for geometrical variables of this process on pure aluminium sheets. With this regard, two different objective functions, i.e. the uniformity in the effective strain distribution and the necessary force per unit weight of the specimen, are selected to be minimized. To examine the effects of the sheet thickness, die groove angle and the die-tooth number on these objective functions, several finite-element (FE) analyses of the operation are carried out. Using the values of objective functions attained via these numerical simulations, an artificial neural network (ANN) is trained with good regression fitness. Employing a two-objective genetic algorithm (GA), a series of optimum conditions is obtained as a Pareto front diagram. The best optimum point in this diagram is the closest one to the origin which, at the same time, makes both the objective functions smallest. With this regard, a sheet thickness of 2 mm, a groove angle of  and an 8-tooth die are found to be an appropriate optimal condition for performing a CGP process. The finite-element simulation with these enhanced geometrical variables is conducted and the values of the objective functions gained from the numerical analysis is found to be in good agreement with those obtained from the genetic algorithm optimization.
    Keywords: Constrained Groove Pressing, Multi-objective optimization, Genetic Algorithm, Geometrical Parameters, Pure Aluminum Sheet
  • Mahmood Yaghoubi *, Zafar Namazian Pages 282-288
    Heat generation in an exothermic reaction during the curing process and low thermal conductivity of the epoxy resin produces high peak temperature and temperature gradients which result in internal and residual stresses, especially in large epoxy samples. In this paper, an optimization algorithm was developed and applied to predict the thermal cure cycle to minimize the temperature peak and thermal gradients within the material of an industrial epoxy model during the curing process. An inverse analysis was used to obtain the new coefficients of Kamal’s equations for the model. To validate and verify the developed model, temperature profiles for several points of the material in the model were obtained by numerical simulation and compared with the previously experimentally measured data. With validated curing simulation, the mentioned inverse analysis and optimization algorithm were utilized to find the thermal curing cycle with several isothermal holds and temperature ramps. The new objective reference was proposed for the first time and used to optimize the cure cycle, which subsequently produced the same temperature profiles for all points. The results showed that the obtained optimized thermal curing cycle was most effective to decrease the peak temperature as well as temperature gradients of the material.
    Keywords: Cure cycle optimization, Inverse analysis, Temperature gradients, Large epoxy model, Peak temperature
  • Naeem Zolfaghari, Mahdi Moghimi Zand *, Roozbeh Dargazany Pages 289-294
    In this paper, we analyze the effect of stress-fiber inclusion on the stiffness of an actin random network. To do this, use a discrete random network model to analyze the elastic response of this system in terms of apparent Young’s modulus. First, we showed that for a flat-ended cylindrical AFM indenter the total indentation force has a linear relation with the indentation depth and the indenter radius in a fibrous network. Using this relation, we concluded that the stiffening effect of the stress-fiber on the fibrous network has a range of effectivity and surprisingly, the stiffening is not maximum when the stress-fiber is immediately under the indenter but, when has a certain distance with it. In addition, when the stress-fiber axis has a specific distance from the loading region, it has negligible effect on the local stiffness of the network. These results shed light on some aspects of the widely used AFM stiffness measurements of cells.
    Keywords: CELL CYTOSKELETON, ACTIN CORTEX, RANDOM FIBROUS NETWORK, ATOMIC FORCE MICROSCOPY, STIFF INCLUSION
  • Mohsen Mahdavi Adeli, Faramarz Sarhaddi *, Said Farahat Pages 295-302
    Nowadays, the increase of fossil fuel consumption intensifies the crucial role of architects. As buildings consume over one-third of the used energy, the society of architects is held responsible for this consumption. Therefore, the amount of energy used by a building is directly related to its design; meaning that reduction of energy consumption should be targeted at the design stage. In this research, the proper building form with the lowest energy consumption for heating, cooling, and lighting was obtained after studying different shapes in Design Builder Software, and it was concluded that the building form has a significant impact on energy consumption. After the parametric studies, the best building orientation of 60 degrees north-east and a window-wall ratio (WWR) of 40% was obtained. Moreover, the building considered for this study had annual CO2 emissions of 30 tons, which was reduced to around 15 tons of CO2 emissions in a year at the optimum degree and WWR, i.e. a reduction of CO2 emissions to half of its previous amount.
    Keywords: Window To Wall Ratio (WWR), Environmental impact, Energy Efficiency, Parametric Design, Zero-Energy Building
  • Ahmed Hamoud *, Kirtiwant Ghadle Pages 303-307
    Integral and integro-differential equations are one of the most useful mathematical tools in both pure and applied mathematics. In this article, we present a variational iteration method for solving Fredholm integro-differential equations. This study provides an analytical approximation to determine the behavior of the solution. To show the efficiency of the present method for our problems in comparison with the exact solution we report the absolute error. From the computational viewpoint, the variational iteration method is more efficient, convenient and easy to use. The method is very powerful and efficient in nding analytical as well as numerical solutions for wide classes of linear and nonlinear Fredholm integro-differential equations. Moreover, It proves the existence and uniqueness results and convergence of the solution of Fredholm integro-differential equations. Finally, some examples are included to demonstrate the validity and applicability of the proposed technique. The convergence theorem and the numerical results establish the precision and efficiency of the proposed technique.
    Keywords: Variational iteration method, Fredholm integro-differential equation, Approximate solution
  • Amir Vosough, Mohammad Reza Assari *, Seyed Mohsen Peyghambarzadeh Pages 308-314
    Fouling is a common, fundamental and costly problem in heat transfer systems, which reduces thermal efficiency of equipment, increases the energy loss and causes strong damage to the heat transfer equipment in various industries. The main causes of fouling on the heat transfer surfaces are salts with inverse temperature-solubility in the fluid which calcium sulfate is one of the most important of them. In this paper, the effect of calcium sulfate fouling on the heat transfer coefficient in subcooled flow boiling was investigated. The fouling mass of calcium sulfate on the heat transfer surface was also calculated. In the experiments carried out in this study, flow rate (2.5–11.5 l/min), solution concentration (1.75–2.2 g/l), bulk fluid temperature (55–75 ℃), and heat flux (8-95 kW/m2) were variables at the mentioned ranges. The results showed that the maximum deviation in the uncertainty analysis was related to the difference between the inlet and outlet temperature of the fluid, followed by the temperature difference between the wall temperature and the bulk fluid temperature. Also, the analysis of the experimental data revealed that increasing the salt concentration, the bulk temperature, and the heat flux of the solution, the mass of deposited calcium sulfate on the heat transfer surface increases with time, resulting in a decrease in the heat transfer coefficient. Careful analysis of the experimental data also showed that the solution concentration has more important role than the heat flux and the fluid bulk temperature in fouling formation.
    Keywords: CaSO4 solution, Inverse solubility, Fouling, Subcooled flow boiling
  • Bouras Abdelkarim *, Taloub Djedid Pages 315-323
    A numerical study of the natural convection of the laminar heat transfers in the stationary state was developed in a horizontal ring and compared between a heated trapezoidal internal cylinder and a cold elliptical outer cylinder. This annular space is traversed by a Newtonian and incompressible fluid. The Prandtl number is set to 0.7 (air case) for different Rayleigh numbers. The system of equations governing the problem was solved numerically by the calculation code Fluent based on the finite volume method. In these simulations the Boussinesq approximation was considered. The inner and outer surfaces are kept at a constant temperature. The study is performed for Rayleigh numbers ranging from 103 to 105. Indeed, the effects of different numbers of thermal Rayleigh on natural convection were studied. The results are presented in the form of isotherms, isocurrents, local and average numbers of Nusselt. The purpose of this study is to study the influence of the thermal Rayleigh number, and the change of the angle of inclination of the trapezoidal lateral walls on the structure of the flow and the distribution of the temperature.
    Keywords: Natural convection, thermal Rayleigh number, Boussinesq approximation, elliptic, Triangular, trapezoidal
  • Hamed Gharooni *, Mehdi Ghannad Pages 324-340
    In this study, nonlinear analysis for thick cylindrical pressure vessels with arbitrary variable thickness made of hyperelastic functionally graded material properties in nearly incompressible state and clamped boundary conditions under non-uniform pressure loading is presented. Thickness and pressure of the shell are considered in axial direction by arbitrary nonlinear profiles. The FG material properties of nearly incompressible hyperelastic shell are graded in the radial direction with a power law distribution. Effective combination of shear deformation theory and match asymptotic expansion of perturbation theory are used to derived and solve the nonlinear governing equations, respectively. A numerical modelling based on finite element method is presented to validate the results of the current analytical solution. The effect of material constants, non-homogeneity index, geometry and pressure profiles on displacements, stresses and hydrostatic pressure distributions are illustrated for different hyperelastic material properties and case studies. This approach enables insight to the nature of the deformation and stress distribution through the thickness of rubber vessels and may offer the potential to study the mechanical functionality of blood vessels such as artificial or natural arteries in physiological pressure range.
    Keywords: Hyperelastic FGMs, FG cylindrical shells, Variable thickness, Perturbation theory, Hyperelastic pressure vessel
  • Siavash Haddad Soleymani *, Mohammad Shishesaz, Reza Mosalmani Pages 341-357
    In this study, shear and peel stress distributions in the viscoelastic adhesive layer of a single-lap joint (SLJ) with functionally graded (FG) adherends are investigated. The study focuses on the effect of different adherend profiles and material composition on the time-dependent stress concentration/distribution in balanced and unbalanced SLJs. For this purpose, the Reddy model is applied to the FG adherends and a three-parameter solid viscoelastic model is used to simulate the adhesive layer behavior. Using the first-order shear deformation theory for the FG adherends, the governing differential equations are derived and then transformed into the Laplace domain. A finite element model of the joint was also developed to further backup the numerical solution. The numerical inverse Laplace transform method was used to extract the desired results that were then compared with those of finite element method (FEM) findings. Very good agreements were observed between the results of both methods. Results show that the geometric and mechanical properties of the FG adherends have an essential role in reducing the shear and peel stress concentrations as well as the uniformity of shear stress distribution in the overlap region. Results also show that either method (finite element or the proposed semi-analytical method) can be utilized with confidence for prediction of stress relaxation in the adhesively bonded SLJs with FG adherends.
    Keywords: Adhesively bonded single-lap joint, Viscoelastic adhesive, Functionally graded adherend, Semi-analytical method, finite element method
  • Mohammad Orak, Mehdi Salehi * Pages 358-365
    In this study, vibration of initially imperfect cracked thick plate has been investigated using the differential quadrature method. The crack modeled as an open crack using a no-mass linear spring. The governing equations of vibration of a cracked plate are derived using the Mindlin theory and considering the effect of initial imperfection in Von-Karman equations. Differential equations are discretized using the differential quadrature method and are converted to a non-standard eigenvalue problem. Finally, natural frequencies and mode shapes of the cracked plate are obtained solving this eigenvalue problem. The accuracy of the proposed approach is verified using the results presented in other references. Various examples of the cracked plate problem have been solved utilizing the proposed method and effects of selected parameters such as crack depth, length and position have been checked. It is demonstrated that increasing the length and the depth of the crack decrease the plate stiffness and natural frequencies. Moreover, the effects of crack location on natural frequencies are more complicated, since they depend on the mode shapes, and when the crack is placed at a node-line, it will not influence the frequencies.
    Keywords: Crack, Thick plate, Vibration, Differential quadrature method
  • Amirhossein Azami, Ashkan Heydarian *, Armin Jarrahi Khameneh, Siamak Khorramymehr, Behnoosh Vasaghi Gharamaleki Pages 366-374

    The effect of UV beam, which has been emitted from a natural or a manmade source on cells has been studied in previous studies for several times. Radiation of this beam can have different effects on DNA of the cell, cytotoxicity, the structure of cellular proteins and their mechanical properties based on radiation period or frequency. The effect of radiation of two types of beams, namely UVB and UVC on stiffness and deformation of the cell are studied in such studies based on different durations of radiation. Viscoelastic properties of skin fibroblast cells were measured using the magnetic tweezer method for a number of groups under UVC radiation with radiation durations of 38, 60 and 120 seconds and for a group under UVB radiation with radiation duration of 38 seconds, also for a control group. In addition, three and four-element discrete differential models were used for creep analysis. Cells deformation had a considerable change after radiation, while such deformation decreased as the frequency increased, however, no comment can be stated regarding radiation duration. Furthermore, cell stiffness reduced after radiation. Such decrease in cell stiffness after radiation could be due to the destruction of the biological macromolecules bonds. Furthermore, the extent of cell deformation was much lower in the radiation groups in comparison to the control group.

    Keywords: Ultraviolet Effects, Cell Biomechanics, Creep Response, Viscoelastic
  • Yusuf YUuml Ksel *, Şeref Akbaş Pages 375-380

    Fiber-reinforced laminated composites are frequently preferred in many engineering projects. With the development in production technology, the using of the fiber reinforced laminated composites has been increasing in engineering applications. In the production stage of the fiber-reinforced laminated composites, porosities could be occurred due to production or technical errors. After a level of the porosity, the mechanical behaviors of composite materials change significantly. This paper presents buckling analysis of fiber-reinforced laminated composite plate with porosity effects within the first shear deformation plate theory. In the porosity effect, three different porosity models are used in the laminated composite plate. The material properties of the laminas are considered as orthotropic property. In the solution of the problem, the Navier procedure is used for the simply supported plate. Influences of the porosity coefficients, the porosity models, the fiber orientation angles and the sequence of laminas on the critical buckling loads are presented and discussed.

    Keywords: Laminated Plate, Porosity, Buckling, First Shear Deformation Plate Theory
  • S Ramakrishna *, Gautham Ajay Pages 381-386
    Composite propellers offer high damping characteristics and corrosion resistance when compared with metal propellers. But the design of a hybrid composite propeller with the same strength of metal propeller is the critical task. For this purpose, the present paper focusses on fluid-structure interaction analysis of hybrid composite propeller with Carbon/Epoxy, R-Glass/Epoxy and S2-Glass/Epoxy to find its strength at the same operating conditions of the baseline aluminium propeller. The surface and solid models of the hybrid composite propeller are modelled using modelling software (CATIA) and these models are imported into mesh generation software (Hypermesh) to generate the surface mesh and solid mesh respectively. This surface model of the hybrid composite propeller is imported into computational fluid dynamics software (Fluent) to estimate the pressure loads on propeller blades. These pressure loads from Fluent are imported into FEA software (Abaqus) and applied on the propeller to find the deformation and strength of hybrid composite propeller due to fluid-structure interaction loads. Optimization study is carried out on hybrid composite propeller with different layup sequences of Carbon/R-Glass/S2-Glass to find the optimum strength. From the optimization study, it is found that the hybrid composite propeller with layup-3 of 55/55/90/0/0/90/450/90/ 0/90/45/90/45/90/0/90/0 degrees generates the least stress compared with other layups for the same pressure load obtained from fluid flow simulations. Damage initiation analysis is also carried out on hybrid composite propeller with optimized layup-3 based on Hashin damage criteria and found that the design is safe.
    Keywords: Composite Propeller, Carbon, Epoxy, R-Glass, Epoxy, S2-Glass, Epoxy, Hashin Damage Criteria
  • Javad Bayat, Homayoun Emdad, Omid Abouali * Pages 387-394
    Partially liquefied vitreous humor is a common physical and biochemical degenerative change in vitreous body which the liquid component gets separated from collagen fiber network and leads to form a region of liquefaction. The main objective of this research is to investigate how the oscillatory motions influence flow dynamics of partial vitreous liquefaction (PVL). So far computational fluid dynamics modeling of the PVL has not yet been well studied. To this end, a spherical model of the vitreous is subjected to harmonic motion and the numerical simulations are performed for various planar interface conditions in linear viscoelastic regimes. A numerical solver is developed in the OpenFOAM toolbox which is based on finite volume method and uses the PIMPLE algorithm and the dynamic mesh technique. This solver also uses modified classic volume-of-fluid approach to capture the interface effects and dynamic characteristics of two-phase viscoelastic-Newtonian fluid flow. The numerical model is validated by comparing the obtained results with the analytical solution which excellent agreement was observed. The results showed that the intensity of secondary flow in the vertical direction was much higher for the PVL with a higher liquefied fraction. Also, the obtained maximum stresses were dependent on the liquefied fraction of the PVL and located on the equatorial plane at the cavity wall near the interface layer and within the vitreous gel.
    Keywords: Two-phase flow, Viscoelastic-Newtonian fluid, Partial vitreous liquefaction, Harmonic motion, Vitreous
  • Hamed Gharooni *, Mehdi Ghannad Pages 395-412
    In this paper, nonlinear analytical solution of pressurized thick cylindrical shells with variable thickness made of hyperelastic materials is presented. The governing equilibrium equations for the cylindrical shell with variable thickness under non-uniform internal pressure are derived based on first-order shear deformation theory (FSDT). The shell is assumed to be made of isotropic and homogenous hyperelastic material in nearly incompressible condition. Two-term Mooney-Rivlin type material is considered which is a suitable hyperelastic model for rubbers. Boundary Layer Method of the perturbation theory which is known as Match Asymptotic Expansion (MAE) is used for solving the governing equations. In order to validate the results of the current analytical solution in analyzing pressurized hyperelastic thick cylinder with variable thickness, a numerical solution based on Finite Element Method (FEM) have been investigated. Afterwards, for a rubber case study, displacements, stresses and hydrostatic pressure distribution resulting from MAE and FEM solution have been presented. Furthermore, the effects of geometry, loading, material properties and incompressibility parameter have been studied. Considering the applicability of the rubber elasticity theory to aortic soft tissues such as elastin, the behaviour of blood vessels under non-uniform pressure distribution has been investigated. The results prove the effectiveness of FSDT and MAE combination to derive and solve the governing equations of nonlinear problems such as nearly incompressible hyperelastic shells.
    Keywords: Variable thickness, Blood vessel, Hyperelastic material, Mooney-Rivlin model, Match Asymptotic Expansion
  • Saeed Norouzi *, Abbas Barati, Reza Noroozi Pages 413-419
    Computational methods can play a significant role in characterization of the carbon-based nanocomposites by providing simulation results. In this paper, we prepared a brief review of the mechanical properties of carbon nanotubes (CNTs), Graphene, and coiled carbon nanotube (CCNTs) reinforced nanocomposites. Varies simulation studies in mechanical properties of nanocomposites including representative volume element (RVE) approaches using the finite element, multiscale simulation and molecular dynamics studied is mentioned. All the simulation results show a significant role of interphase properties, interphase thickness, elastic properties of nanostructure, various loading conditions and orientation of the nanostructure on mechanical behavior of nanostructure reinforced nanocomposite. Some researchers employed various approaches for comparing simulation results of the effective elastic properties of nanostructures reinforced nanocomposite. Although it is a huge challenge for scientists to make a connection between MD simulations and continuum mechanics, in some researches scientists tried to couple MD and continuum mechanics for more precise results in nanocomposites.
    Keywords: Carbon nanostructures, Nanocomposites, Representative Volume Element (RVE)
  • Mehdi Mousavi Khoram, Mohammad Hosseini *, Mohammad Shishesaz Pages 420-429
    Recent works done by nano-engineers and nano-sciences about mechanical behavior of nano-plates including bending, buckling and vibration response were reviewed. The authors used non-classical elasticity theories to explain these behaviors of plate structures. Some of them employed Hamilton’s principle along with stain gradient theory, nonlocal theory, surface theory and couple stress theory to derive the governing equation of nanostructures. Also, the authors have used various plate theories such as classical plate theory (CPT), first-order shear deformation theory (FSDT) and higher-order shear deformation plate theory (HSDT) to explain the linear and nonlinear behavior of nano-plates. Few researchers utilized molecular dynamics or experimental tests to explain size-dependent behavior of nano-plates. Investigated nano-plates were made of homogeneous and functionally graded materials (FGM) and were under mechanical and/or thermal loads. The effect of the magnetic field was considered, in other few researches. Governing equations solved using numerical methods such as differential quadrature method (DQM). The results of recent researches were presented and discussed.
    Keywords: Nano-plate, Non-classical elasticity theory, Bending, Buckling, Vibration