Journal of Computational Applied Mechanics
Volume:50 Issue: 1, Jun 2019

Purely elastic, partially and fully plastic stress states in a thick-walled spherical pressure vessel with an inner functionally graded material (FG) coating subjected to internal and external pressures are developed analytically in this paper. The modulus of elasticity and the uniaxial yield limit of the FG coating layer are considered to vary nonlinearly through the thickness. Using Tresca’s yield criterion and ideal plastic material behavior, the plastic model is established. Under pressure loading, the scenario in which the plastic deformation starts from inner surface of FG coating layer is taken into account. Having increased the pressure loading, it is assumed that the FG coating layer becomes fully plastic and the yielding commences subsequently at the inner surface of homogenous part. Essentially, the variation of FG parameters in the radial direction is properly adjusted in order to achieve the stated yielding scenario. Furthermore, axisymmetric finite element model is performed to validate the accuracy of the analytical results. It is concluded that the elastic and plastic response of the spherical pressure vessel are influenced by grading parameters and coating behavior.

Hydrodynamics of multiple rising bubbles as a fundamental two-phase phenomenon is studied numerically by lattice Boltzmann method and using Lee two-phase model. Lee model based on Cahn-Hilliard diffuse interface approach uses potential form of intermolecular forces and isotropic finite difference discretization. This approach is able to avoid parasitic currents and leads to a stable procedure to simulate two-phase flows. Deformation and coalescence of bubbles depend on a balance between surface tension forces, gravity forces, inertia forces and viscous forces. A simulation code is developed and validated by analysis of some basic problems such as bubble relaxation, merging bubbles, merging droplets and single rising bubble. Also, the results of two rising bubbles as the simplest interaction problem of rising bubbles have been calculated and presented. As the main results, square and lozenge initial configuration of nine rising bubbles are studied at Eotvos numbers of 2, 10 and 50. Two-phase flow behavior of multiple rising bubbles at same configurations is discussed and the effect of Eotvos number is also presented. Finally, velocity field of nine rising bubbles is presented and discussed with details.

In this paper, a novel approach is proposed to investigate the progressive collapse damage of prismatic thin walled metal columns with different regular cross sections, under the action of axial quasi-static and impact loads. The present work mainly focuses on implementation of some important factors which have been neglected in other studies. These factors include the effect of reducing impactor velocity and inertia effect during collapse, a mixed collapse mode for crushing mechanism, and consideration of a realistic elasto-plastic model for material. Taking all these factors into account, the analysis led to some parametric algebraic equations without a possible general solution in terms of collapse variables. Consequently, a new theoretical approach was proposed based on previously offered Super Folding Element (SFE) theory, to obtain the closed form explicit relations for the static and dynamic mean crushing forces and collapse variables. The proposed approach considers an analytic-numeric discretization procedure to solve these equations. To evaluate the results, a detailed finite element analysis on square mild steel models was conducted under an axial impact load, using LS-DYNA and ANSYS software programs. Comparison of the experimental results that are available in the literature with those of finite element analysis, shows the applicability of this approach in predicting the collapse behavior in such structures.

A preconditioned five-equation two-phase model coupled with an interface sharpening technique is introduced for simulation of a wide range of multiphase flows with both high and low Mach regimes. Harten-Lax-van Leer-Contact (HLLC) Riemann solver is implemented for solving the discretized equations while tangent of hyperbola for interface capturing (THINC) interface sharpening method is applied to reduce the excessive diffusion of the method at the interface. In this work, preconditioning technique is used in a system of equations including viscous and capillary effects. Several one- and two-dimensional test cases are used to evaluate the performance and accuracy of this method. Numerical results demonstrate the efficiency of preconditioning in low Mach number flows. Comparisons between results of preconditioned and conventional system highlight the necessity of using preconditioning technique to reproduce main characteristics of low-speed flow regimes. Additionally, preconditioned systems transform to the conventional systems at high Mach number flows thus exhibiting the same level of accuracy as the standard flow solver. Therefore, the preconditioned compressible two-phase method can be used as an all-speed two-phase flow solver accounting for capillary and viscous stresses.

The effect of the tip gap size on the performance of a multistage axial compressor was studied by means of computational fluid dynamics (CFD). It was found that the performance of the compressor was very sensitive to the size of the tip gap. By increasing the gap size, the stall margin value, the total pressure ratio and the compressor efficiency reduced considerably. The flow field at the tip region of the blades at the near-stall point showed that the size of the blockage grew with an increase in the gap size.  Afterward, the effect of various single circumferential grooves- having specified widths and depths at different placement positions- on the performance were investigated in the reference gap. The stall margin increased about 7% with negligible reduction of the peak efficiency using one of the grooves which placed next to the trailing edge of the first-stage rotor. Also, this groove increased the stall margin in other tip gap sizes. Investigation of the flow field of the tip region in the reference gap showed that when the groove was used, there was a reduction in the back-flow near the trailing edge of the first-stage rotor. Consequently, the stall occurred at a lower mass flow rate.

Thisstudy presents axially forced vibration of a cracked nanorod under harmonic external dynamically load. In constitutive equation of problem, the nonlocal elasticity theory is used. The Crack is modelled as an axial spring in the crack section. In the axial spring model, the nonrod separates two sub-nanorods and the flexibility of the axial spring represents the effect of the crack. Boundary condition of the nanorod is selected as fixed-free and a harmonic load is subjected at the free end of the nanorod. Governing equation of the problem is obtained by using equilibrium conditions. In the solution of the governing equation, analytical solution is presented and exact expressions are tained for the forced vibration problem. On the solution method, the separation of variable is implemented and the forced vibration displacements are obtained exactly. In the open literature, the forced vibration analysis of the cracked nanorod has not been investigated broadly. The objective of this study is to fill this blank for cracked nanorods. In numerical results, influences of the crack parameter, position of crack, the nonlocal parameter and dynamic load parameters on forced vibration responses of the cracked nanorod are presented and discussed.

This paper presents the analysis of vibration control of a laminated composite beam that including magnetostrictive layers. The formulation of problem is presented based on the shear deformation beam theory. For vibration suppression, the velocity feedback control with constant gain distributed is considered. Navier's method is applied to analyze the solution of vibration suppression of laminated beam with the simply-supported boundary conditions. The influence of lamination schemes, modes, number of smart layers at the structure, the control gain of the agnetic field intensity and smart layer position on suppress of the vibration are discussed. In addition, the  ntrolled motion of some special laminated composite beam is tested.

In this paper, we studied numerically both kinematic and dynamic models of a biologically inspired mammal-like octopod robot walking with a tetrapod gait. Three different nonlinear oscillators were used to drive the robot’s legs working as central pattern generators. In addition, also a new, relatively simple and efficient model was proposed and investigated. The introduced model of the gait generator allowed us to obtain better both kinematic and dynamic parameters of motion of the robot walking in different directions. By changing the length and the height of a single step of the robot, we introduced in a simple way the initial, rhythmic and terminal phases of the robot gait. For numerical research and to visualization of the walking process, we developed a simulation model of the investigated robot in Mathematica software. We computed displacement, velocity and acceleration of the center of the robot’s body, fluctuations in the zero moment point of the robot and the ground reaction forces acting on the feet of the robot. The obtained results indicated some advantages of the proposed central pattern generator regarding fluctuations in the robot’s body, the minimum value of dynamic stability margin as well as the minimum value of a friction coefficient which is necessary to avoid slipping between the ground and the robot’s feet during walking process. Eventually, the proposed model of gait also allowed us to control the vertical position of the robot during walking in different directions.

In this article, the thermoelastic interactions in an isotropic and homogeneous semi-infinite medium with variable thermal conductivity caused by an ultra-short pulsed laser heating based on the linear nonlocal theory of elasticity has been considered. We consider that the thermal conductivity of the material is dependent on the temperature. The surface of the surrounding plane of the medium is heated by an ultra-short pulse laser. Basic equations are solved along with the corresponding boundary conditions numerically by means of the Laplace transform technique. The influences of the rise time of the laser pulse, as well as the nonlocal parameter on thermoelastic wave propagation in the medium, have also been investigated in detail. Presented numerical results, graphs and discussions in this work lead to some important deductions. The results obtained here will be useful for researchers in nonlocal material science, low-temperature physicists, new materials designers, as well as to those who are working on the development of the theory of nonlocal thermoelasticity.

In this paper, the presented work aims to provide a designed model based on Finite element method for detection of Malaria protozoan parasites. Micro-cantilevers are next generation highly efficient biosensors for detection and prevention of any disease. Here, an E-shaped model for micro cantilevered biosensor is designed using COMSOL Multiphysics specifically for detection of Malaria. Microcantilever materials viz Au, Cu, Si and Pt are used for sensing Malaria protozoan with proper optimization of device structure. The studies were carried out for stress developed and displacement occurred due to force applied through these protozoan biomolecules and varying beam length. Further, the designed structure was analyzed for different beam materials available for biosensor and it was found that Au is best suitable material for detection of malaria protozoan parasites since it has best sensitivity profile among presented materials. The results were also verified through analytical approach and it was found that both results obtained through simulation and analytical methods do closely agree with each other.

This paper presents a new robotic mechanism for ultrasound imaging. The device is placed on a patient's body by an operator, and an ultrasound expert controls the motions of the device to obtain ultrasound images. The paper focuses on the robotic mechanism that performs ultrasound imaging. The design of the mechanism is based on two approaches to produce center of motion for an ultrasound probe. This center of motion which is located on the tip of the ultrasound probe helps to create clear ultrasound images. Detailed designs, kinematic relationships, prototyping and ultrasound imaging tests are presented. A novel cabling mechanism is developed to create the center of motion required for ultrasound imaging. The mechanism provides all four necessary motions for ultrasound imaging by using two actuators which significantly reduces the weight of the device to make it suitable for portable ultrasound applications. The device has been successfully used for ultrasound imaging of kidney, gallbladder, liver, ovary and uterus of volunteer patients.

The article is concerned with a new nonlocal model based on Eringen’s nonlocal elasticity and generalized thermoelasticity. A study is made of the magneto-thermoelastic waves in an isotropic conducting thermoelastic finite rod subjected to moving heat sources permeated by a primary uniform magnetic field and rotating with a uniform angular velocity. The Laplace transform technique with respect to time is utilized. The inverse transforms to the physical domain are obtained in a numerical manner for the nonlocal thermal stress, temperature, and displacement distributions. Finally, some graphical presentations have been made to assess the effects of various parameters; nonlocal parameter, rotating, applied magnetic field as well as the speed of the heat source on the field variables. The results obtained in this work should be useful for researchers in nonlocal material science, low-temperature physicists, new materials designers, as well as to those who are working on the development of the theory of nonlocal thermoelasticity.

Ball valve is one of valves that have many applications in industry especially in gas delivery systems. This kind of valve is categorized in the on- off flow control valve. This study aims to investigate unusual application of ball valve to control fluid flow in the oil and gas industry and its destructive effect including erosion of ball and body of valve. Simulation of industrial ball valve is done using ANSYS Fluent software and effect of erosion on it is investigated in different working conditions. In this study, working condition is performed regarding 3 different concentrations for suspended particles as well as four positions of ball in different angles. It is shown that rate of erosion for 25% open state of valve is increased to about 15000 times of complete open state of valve, and rate of erosion is increased to about 3500 times for half open state (50% open state); and rate of erosion is increased to about 220 times for 75% open state of valve.

In this article the instability of single phase flow in a circular pipe from laminar to turbulence regime has been investigated. To this end, after finding boundary conditions and equation related to instability of flow in cylindrical coordination system, which is called eigenvalue Orr Sommerfeld equation, the solution method for these equation has been investigated. In this article Chebyshev polynomial Tau-QZ algorithm has been selected for the solution technique to solve the Orr Sommerfeld equation because in this method some of complex terms in the instability equation in cylindrical coordination will be appeared. After finding Orr Sommerfeld parameters related to Chebyshev polynomial Tau-QZ algorithm the solution have been done for Re=5000 and Re=1000, then the results had been compared with the results of valid references where other methods had been used in them. It have been observed that the use of Chebyshev Tau-QZ algorithm has higher accuracy concerning the results and it also has a higher accurate technique to solve the Orr Sommerfeld instability equations in cylindrical coordination system.

Microtubules are used as targets for anticancer drugs due to their crucial role in the process of mitosis. Recent studies show that carbon nanotubes (CNTs) can be classified as microtubule-stabilizing agents as they interact with protein microtubules (MTs), leading to interference in the mitosis process. CNTs hold a substantial promising application in cancer therapy in conjunction with other cancer treatments such as radiotherapy and chemotherapy. In the current study, a size-dependent model is developed for the stability analysis of CNT-stabilized microtubules under radial and axial loads. A nonlocal shell theory with strain gradient effects is employed to take size influences into account. Moreover, Van der Waals interactions between CNTs and MTs are simulated. An excellent agreement is observed between the present model and reported data from experiments on protein MTs. In addition, the effects of taxol, as another stabilizing agent, on the stability of microtubules are studied. It is found that both nonlocal and strain gradient effects are essential to accurately obtain the stability capacity of MTs. Furthermore, CNTs have an increasing effect on the critical loads of microtubules while the critical loads reduce in the presence of taxol.

In this work, the vibrations of viscoelastic functionally graded Euler–Bernoulli nanostructure beams are investigated using the fractional-order calculus. It is assumed that the functionally graded nanobeam (FGN) is due to a periodic heat flux. FGN can be considered as nonhomogenous composite structures; with continuous structural changes along the thick- ness of the nanobeam usually, it changes from ceramic at the bottom of the metal at the top. Based on the nonlocal model of Eringen, the complete analytical solution to the problem is established using the Laplace transform method. The effects of different parameters are illustrated graphically and discussed. The effects of fractional order, damping coefficient, and periodic frequency of the vibrational behavior of nanobeam was investigated and discussed. It also provides a conceptual idea of the FGN and its distinct advantages compared to other engineering materials. The results obtained in this work can be applied to identify of many nano-structures such as nano-electro mechanical systems (NEMS), nano-actuators, etc.

Inertial microfluidics-based devices have recently attracted much interest and attention due to their simple structure, high throughput, fast processing and low cost. They have been utilised in a wide range of applications in microtechnology, especially for sorting and separating microparticles. This novel class of microfluidics-based devices works based on intrinsic forces, which cause microparticles to migrate laterally and locate at their equilibrium positions. In this article, a comprehensive theoretical formulation is presented for the dynamics of ultrasmall particles in microfluidics-based devices. Explicit expressions are presented for various important forces, which act on a microparticle, such as drag, Magnus, Saffman and wall-induced forces. In addition, the drag coefficient, diffusion phenomenon and Peclet number are formulated. Finally, the influences of particle size, as a crucial parameter, on various intrinsic forces including drag, Magnus and Saffman forces as well as the wall-induced force, are investigated. It is found that the drag, wall-induced and Saffman forces have an important role to play in the dynamics of microparticles in inertial microfluidics while the effects of Magnus force and diffusion can be ignored in most applications.

In this study, an investigation is carried out for laminar steady mixed 2D magnetohydrodynamic (MHD) flow of micropolar Casson fluid with thermal radiation over a horizontal circular cylinder with constant surface temperature. In the present study, an investigation is carried out on the effects of physical parameters on Casson fluid non dimensional numbers. The governing nonlinear partial differential equations and the controlling boundary conditions are derived for this case study. Furthermore, these equations are solved numerically using finite difference technique known as Keller Box Method (KBM). The effects of non-dimensional governing parameters, namely Casson parameter, mixed convection parameter, magnetic parameter, radiation parameter on the Nusselt number and local friction coefficient, as well as temperature, velocity and angular velocity are discussed and shown graphically. It is noticed that the local skin friction and the local Nasselt number has decrement behaviors when increasing the values the Casson parameter. But the opposite happens when the mixed convection parameter λ increase. It is found that the results in this study are in good agreement with previous studies. This proves that calculations using KBM method and the chosen step size are accurate enough for this type of problems.

Abstract In this work, the Mellin transform method was used to obtain solutions for the stress field components in two dimensional (2D) elasticity problems in terms of plane polar coordinates. the Mellin transformation was applied to the biharmonic stress compatibility equation expressed in terms of the Airy stress potential function, and the boundary value problem transformed to an algebraic  problem which was solved to obtain the Mellin transformed Airy stress potential function. The Mellin transform was similarly used to obtain the Mellin transformed stress field components. The use of Mellin transform inversion formula yielded the solutions to the 2D elasticity problem in the physical space domain variables. Specific illustration was considered of the solution by using the Mellin transform method for the Flamant problem and the Mellin transform solutions found to agree with solutions from the literature.

When the velocity of fluid flow in a cantilevered pipe is successively increased, the system may become unstable and flutter instability would occur at a critical flow velocity. This paper is concerned with exploring the dynamical stability of a cantilevered fluid-conveying pipe with an additional linear dynamic vibration absorber (DVA) attachment. It is endeavoured to show that the stability of the pipe may be considerably enhanced due to the presence of DVA. The quasi-analytical results show that the energy transferred from the flowing fluid to the pipe may be partially transferred to the additional mass. In most cases, thus, the critical flow velocity at which the pipe becomes unstable would become larger, meanwhile the flutter instability of the DVA is not easy to achieve. In such a fluid-structure interaction system, it is also found that flutter instability may first occur in the mode of the DVA. The effects of damping coefficient, weight, location and spring stiffness of the DVA on the critical flow velocities and nonlinear oscillations of the system have also been analyzed.

In this paper, the free vibration behaviors and flexural sensitivity of atomic force microscope cantilevers with small-scale effects are investigated. To study the small-scale effects on natural frequencies and flexural sensitivity, the consistent couple stress theory is applied. In this theory, the couple stress is assumed skew-symmetric. Unlike the classical beam theory, the new model contains a material-length-scale parameter and can capture the size effect. For this purpose, the Euler–Bernoulli beam theory is used to develop the AFM cantilever. The tip interacts with the sample that is modeled by a spring with constant of. The equation of motion is obtained through a variational formulation based on Hamilton’s principle. In addition, the analytical expressions for the natural frequency and sensitivity are also derived. At the end, some numerical results are selected to study the effects of material-length-scale parameter and dimensionless thickness on the natural frequency and flexural sensitivity.

This work presents a historical review of the researches procured by various scientists and engineers dealing with the nanocomposite materials and continuous systems manufactured from such materials. Nanocomposites are advanced type of well-known composite materials which have been reinforced with nanosize reinforcing fibers and/or particles. Such materials can be better suit for the industrial applications of which remarkable improved material properties are needed. In other words, the material properties of nanocomposites are superior to those of macroscale composites due to the enhanced features of materials in the nanoscale. These materials are being more and more employed by designers in the aerospace, mechanics and automotive applications as constituent elements instead of the conventional composite materials. Henceforward, it is of great significance to be aware of the researches conducted in this are by researchers to be able to predict the behaviors of structures consisted of such materials in real working conditions. In what follows, the mechanical analyses performed on different types of nanocomposite structures including carbon nanotube reinforced (CNTR), graphene reinforced (GR), graphene platelet reinforced (GPLR), graphene oxide reinforced (GOR) and multi-scale hybrid (MSH) nanocomposite ones will be reviewed and the most crucial highlights of the proposed scientific activities will be discussed.