THE JOURNAL OF COMPUTATIONAL APPLIED MECHANICS
Year:2018 | Volume:49 | Issue:2|Papers Count:22

Modal signals of transverse sensing of truncated conical shells with simply supported boundary condition at both ends are investigated. The embedded piezoelectric layer on the surface of conical shell is used as sensors and output voltages of them in considered modes are calculated. The Governing sensing signal displacement equations are derived based on the Kirchhoff theory, thin-shell assumption, piezoelectric direct effect, the Gauss theory and the open circuit assumption. A conical shell with fully covered piezoelectric layer is considered as a case study and the layer is segmented into 400 patches. Modal voltages of the considered model are calculated and evaluated. The ideal locations for sensor patches are in the middle of conical shell surface in the longitudinal direction and locations near the ends of the conical shell are not recommended. The longitudinal membrane strain signal has a leading role on the total signal in comparison with other strain signal components. The output signals of the sensor can be used as a controller input for later active vibration control or structural health monitoring.

In this study, the effects of Prandtl number on the primary and secondary instability of the Rayleigh-Benard convection problem has been investigated using the lattice Boltzmann method. Two different cases as Pr=5. 8 and 0. 7 representing the fluid in liquid and gas conditions are examined. A body forces scheme of the lattice Boltzmann method was presented. Two types of boundary conditions in the presence of body forces are analyzed by the moment method and applied to a Poiseuille flow. Characteristic velocity was set in such a way that the compressibility effects are negligible. The calculations show that the increment of Prandtl number from 0. 7 to 5. 8 causes to create a secondary instability and onset of the oscillation in the flow field. Results show that at Pr=5. 8, when the Rayleigh number is increased, a periodic solution appeared at Ra=48, 000. It is observed that the dimensionless frequency ratio for Ra= 105 with Pr=5. 8 is around 0. 0065. The maximum Nusselt number for Ra = 105 with Pr=5. 8 are estimated to be 5. 4942.

The aim of this study is to investigate the effect of boundary conditions on the accuracy and stability of the numerical solution of fluid flows in the context of single relaxation time Lattice Boltzmann method (SRT-LBM). The fluid flows are simulated using regularized, No-slip, Zou-He and Bounce Back boundary conditions for straight surfaces in a lid driven cavity and the two-dimensional flow in a channel. The solutions for all types of the boundary conditions show good agreement with numerical references and exact solutions. The cavity pressure contours at low relaxation time show drastic perturbations for Zou-He boundary condition, whereas, the perturbation is ignorable for regularized boundary condition. At High Reynolds number, severe velocity gradients are major reason for numerical instabilities. Therefore, regularized boundary condition, which considers the velocity gradient in its calculation, has better numerical stability comparing the Zou-He boundary condition. Overall, the selection of appropriate boundary condition depends on the flow regime and Geometry. The proper boundary conditions at low Reynolds numbers are Zou-He and Bounce Back boundary conditions, and at high Reynolds numbers, regularized and No-slip boundary conditions are recommended.

In the present study, free vibration behaviors of carbon nanotube (CNT) and boron nitride nanotube (BNNT) have been investigated via Eringen’ s nonlocal continuum theory. Size effect has been considered via nonlocal continuum theory. Nanotubes have become popular in the world of science thanks to their characteristic properties. In this study, free vibrations of Boron Nitride Nanotube (BNNT) and Carbon Nanotube (CNT) are calculated using the Nonlocal Elasticity Theory. Frequency values are found via both analytical and finite element method (FEM). Galerkin weighted residual method is used to obtain the finite element equations. BNNT and CNT are modeled as Euler-Bernoulli Beam and solutions are gained by using four different cross-section geometries with three boundary conditions. Selected geometries are circle, rectangle, triangle, and square. Frequency values are given in tables and graphs. The effect of cross-section, boundary conditions and length scale parameter on frequencies has been investigated in detail for BNNT.

In the present work, the Rayleigh-Taylor instability of two rotating superposed magnetized fluids within the presence of a vertical or a horizontal magnetic flux has been investigated. The nonlinear theory is applied, by solving the equation of motion and uses the acceptable nonlinear boundary conditions. However, the nonlinear characteristic equation within the elevation parameter is obtained. This equation features a transcendental integro-Duffing kind. The homotopy perturbation technique has been applied by exploitation the parameter growth technique that results in constructing the nonlinear frequency. Stability conditions are derived from the frequency equation. It's illustrated that the rotation parameter plays a helpful result. It's shown that the stability behavior within the extremely uniform rotating fluids equivalents to the system while not rotation. A periodic solution for the elevation function has been performed. Numerical calculations area unit created for linear analysis furthermore the nonlinear scope. Moreover, the elevation function has been premeditated versus the time parameter. The strategy adopted here is vital and powerful for solving nonlinear generator systems with a really high nonlinearity arising in nonlinear science and engineering.

The development and production of high performance equipment necessitate the use of passive cooling technology. In this paper, heat transfer study of convective-radiative straight fin with temperature-dependent thermal conductivity under the influence of magnetic field is carried out using Legendre wavelet collocation method. The numerical solution is used to investigate the effects of magnetic, convective and radiative parameters on the thermal performance of the fin. From the results, it is established that increase in magnetic, convective and radiative parameters increase the rate of heat transfer from the fin and consequently improve the thermal performance of the fin. The results obtained are compared with the results established results in literature and good agreements are found. The analysis can help in enhancing the understanding and analysis of the problem. Also, they can provide platform for improvement in the design of extended surfaces in heat transfer equipment under the influence of magnetic field.

Structures consisting of cables and membranes have been of interest to engineers due to their higher ratio of strength to weight and lower cost compared to other structures. One of the challenges in such structures is presence of holes in membranes, which leads to non-uniform stress and strain distributions, even under uniform far-field deformations. One of the approaches suggested for controlling this non-uniformity is reinforcing the hole edge using a cable, such that stretch changes near the hole are minimized compared to that of the far field in the membrane. In this study, considering an optimization problem, it is illustrated that for different geometries and stretch ratios in a biaxial loading of the membrane, a suitable cable of varying stiffness can be chosen such that stretch non-uniformity in the membrane is minimum, thus presenting a state of a pseudo-neutral hole in the membrane. The presented form of parametric functionally graded cable and the optimization problem solved for a couple of hole shapes show that the cable can induce a state of close to uniform stretch distribution for certain values of far field stretch ratios, it also proves effective for a range of such a ratio. Relative non-uniformity indices as low as 2 percent are achieved from optimization.

Developing artificial neural network (ANN), a model to make a correct prediction of required force and torque in ring rolling process is developed for the first time. Moreover, an optimal state of process for specific range of input parameters is obtained using Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) methods. Radii of main roll and mandrel, rotational speed of main roll, pressing velocity of mandrel and blank size are considered as input parameters. Furthermore, the required load and torque in ring rolling process are taken into account as process outputs. Various three dimensional finite element simulations are performed for different sets of process variables to achieve preliminary data for training and validation of the neural network. Besides, the finite element model is approved via comparison with the experimental results of the other investigators. The Back Propagation (BP) algorithm is considered to develop Levenberg– Marquardt feed-forward network. Additionally, Model responses analysis is carried out to improve the understanding of the behavior of the ANN model. It is concluded that results of ANN predictions have an appropriate conformity with those from simulation and experiments. Moreover, GA and PSO methods have been implemented to obtain the optimal state of process while their outcomes have been also compared.

Torsional dynamic analysis of carbon nanotubes under the effect of longitudinal magnetic field is carried out in the present study. Torque effect of an axial magnetic field on a carbon nanotube has been defined using Maxwell’ s relation. Nonlocal governing equation and boundary conditions for carbon nanotubes are obtained by using Hamilton’ s minimum energy principle. Eringen’ s nonlocal stress gradient elasticity theory is used in the formulation. Fourth order nonlocal equation of motion is solved by utilizing differential quadrature method. Clamped-clamped and clamped-free nonlocal boundary conditions are considered. Nonlocal and axial magnetic field effects on torsional vibration of carbon nanotubes are investigated. The magnetic field has significant effects on the dynamics of carbon nanotubes and may lead to torsional buckling. Critical torsional buckling load reduces with nonlocal effects. Nonlocality shows softening effect on carbon nanotube’ s lattice structure. Present results can be used in the design and analysis of nanoelectromechanical products like nano-motors.

The accurate prediction of wellbore temperature distribution helps to accurately estimate well pressure profile and bottom-hole pressure (BHP) which is important in the under-balanced drilling (UBD) operation. In this paper effect of temperature variation due to heat transfer of drilling fluid with the formation and also oil and gas production from the reservoir into the annulus in under-balanced drilling condition were investigated. Gas-liquid two-phase flow model considering thermal interaction with the formation is used to numerically simulate a well with real dimensions. Based on drilling fluids flow and heat transfer characteristics in wells, conservations of mass and momentum and energy equations have been developed to compute BHP and wellbore temperature and pressure profile. After temperature and pressure validation of the numerical model, the effect of heat transfer between drilling fluid inside the well and the formation was considered on the pressure distribution and bottom-hole pressure. The results of two-phase flow, considering thermal effect gives better results compared to two-phase flow with geothermal temperature distribution analysis and better accuracy in comparison with other models.

The defect in work rolls directly influence the forming cost and the final shape of the product. The researchers tend to investigate the thermo-mechanical stress in work roll of rolling machines. These stresses may reduce the roll life. Since the investigation of the thermo-mechanical stress in work roll with real-conditions is complex, comprehensive studies by means of numerical methods are available in numerous literature. However, simulating the thermo-mechanical stress is time-consuming. So, most researchers desire to simplify the geometry and boundary conditions in order to reduce simulation cost. This paper proposes an integrated finite element model to study the thermo-mechanical behavior of work rolls during hot ring rolling process. Various methods were simulated and advantages and disadvantages of each method were discussed. Due to complexities of ring rolling process, the presented model was used in flat rolling in order to verify model integrity. After that work rolls of ring rolling mill subjected to partial boundary conditions are investigated. The results of thermal and thermo-mechanical simulations show stresses in the contact region of work rolls are rather different. However, they expressed the same results in other regions. Based on the obtained results, it is revealed that the effect of mechanical loads in the equivalent stresses should be considered and the location of equivalent maximum stress is below the surface.

Finite element method (FEM) is one of the most famous methods which has many applications in varies studies such as the study of crack propagation in engineering structures. However, unless extremely fine meshes are employed, problem arises in accurately modelling the singular stress field in the singular element area around the crack tip. In the present study, the crack growth simulation has been numerically simulated by using the dens mesh finite element source code program using Visual FORTRAN language. This code includes the mesh generator based on the advancing front method as well as all the pre and post process for the crack growth simulation under linear elastic fracture mechanics theory. The stress state at a crack tip has been described by the stress intensity factor which is related to the rate of crack growth. The displacement extrapolation technique is employed to obtain crack tip singular stresses and the stress intensity factors values. The crack direction is predicted using the maximum circumferential theory. Verification of the predicted stress intensity factors and crack path direction are validated with relevant experimental data and numerical results obtained by other researchers with good agreements.

The governing equations of three dimensional elasticity problems include the six Beltrami– Michell stress compatibility equations, the three differential equations of equilibrium, and the six material constitutive relations; and these are usually solved subject to boundary conditions. The system of fifteen differential equations is usually difficult to solve, and simplified methods are usually used to achieve a solution. Stress-based formulation methods, and displacement-based formulation methods are two common simplified methods for solving elasticity problems. This work adopts a stress-based formulation for a three dimensional elasticity problem. In this work, the Maxwell’ s stress functions for solving three dimensional problems of elasticity theory are derived from fundamental principles. It is shown that the three Maxwell stress functions identically satisfy all the three differential equations of static equilibrium when body force components are ignored. It is further shown that the three Maxwell stress functions are solutions to the six Beltrami-Michell stress compatibility equations if the Maxwell stress functions are potential functions. It is also shown that the Airy’ s stress functions for two dimensional elasticity problems are special cases of the Maxwell stress functions.

A two dimensional deformation due to internal heat source in a thermoelastic solid with micro-temperatures under the effect of dependence of reference temperature on all elastic and thermal parameters have been studied. A mechanical force is applied at the free surface of thermoelastic half space. The normal modes technique has been applied to obtain the exact expressions for the components of normal displacement, micro temperature, normal force stress, temperature distribution, heat flux moment tensor and tangential couple stress for thermoelastic solid with micro-temperatures. The effect of internal heat source, reference temperature and micro-rotation on the derived components have been depicted graphically.

Now a day centrifugal pumps are vital components of industries. Certainly, one of the most important specifications of centrifugal pumps are the performance curves. In the present work, performance curves of a centrifugal pumps are obtained by Computational fluid dynamics (CFD) and as an outcome, CFD results compare by practical curves. At the first step impeller and volute are designed with two standards and at the end former design completed by automatic design process using CFturbo software. For this purpose, full 3D-RANS equations in coupled with SST turbulence model are solved for several flow rate between 20% and 140% of the operation condition by means of a commercial code, CFX. This simulation is defined by means of the multi-reference frame technique in which the impeller is situated in the rotating reference frame, and the volute is in the fixed reference frame. Proposed simulation is based on a steady state flow, non-Newtonian, incompressible and constant property condition. Operation point is simulated to get the total head and then non-operation points are simulated to obtain performance curves. Practical curves and numerical ones are in good agreement, so numerical approach could be a perfect way to make centrifugal pump design better and easier. Indeed pump simulation with CFD approach can increase our knowledge about pump behavior such as consumption energy, trimming process and saving energy before we have any activities on the pump so the predictions have bettering and excise about any process on the pump.

This study examines the fatigue and anisotropy behaviour of cold rolled AA1200 aluminum alloy for light weight automotive connecting rod application. Aluminum (Al) 1200 ingots were melted at temperature of 680 0C (after one hour of heating) cast in sand mould and cast samples homogenized for 6 hrs at 480 0C. The cold rolling process was carried out after homogenisation for 10, 20, 30, 40 and 50% thickness reductions. The samples were characterised in 00, 150, 300, 450, 600, 750 and 900 to the rolling direction. The results show that degree of deformation increase linearly with mean stress, stress range, stress ratio, stress amplitude, thickness and area ratio for all the reductions and directions examined. Area and thickness ratio increases linearly with deformation at higher inclination (> 150). The fatigue life obtained in this work shows life cycles at different degrees of deformation: 7. 5 x 104 cycles at 10% reduction, 1. 3 x105 cycles at 20% reduction, 4. 3 x 104 cycles at 30% reduction; 2. 6 x 105 cycles at 40% reduction and 1. 09 x 105 cycles at 50% reduction). The results of this study provide evidence that systemic controlled cold deformation can potentially be used to significantly enhance the fatigue life of AA1200 aluminum alloy components subjected to cyclic loadings.

During the solidification of binary metal alloys, chemical heterogeneities at product scale over a long distance range (1cm-1m) develop and this has detrimental effect on the resulting mechanical properties of cast products. Macrosegregation is of great concern to alloy manufacturers and end users as this problem persist. In this study, the use of process parameters namely casting speed and runner angle to reduce macro-segregation in aluminum-copper binary alloy solidification is reported. The results from optical microscope, scanning electron microscope and energy dispersive spectrometry show that these parameters significantly influenced the development, size and volume of macrosegregation. The combination of parameters namely the pouring height between 96 mm/s, 100mm/s, and runner angles between 1200, 1500 produced less segregations with improved mechanical properties within standard specification. The modulus of elasticity (6800 MPa), tensile strength (110 MPa) and 2. 5 % elongation obtained in this study are within standard 7100 MPa, (88-124 MPa) and (1-25 %) respectively for this class of alloy.

The need to design blast resistant civilian structures has arisen due to aggressor attacks on many civilian structures around the world. Achieving vibration and wave attenuation with locally resonant metamaterials has attracted a great deal of consideration due to their frequency dependent negative effective mass density. In this paper, metaconcrete, a new material with exceptional properties is formed. The aggregates in concrete are substituted with spherical inclusions consisting of a heavy metal core coated with a soft outer layer. The physics of the metamaterial was first established, and mass in mass spring and effective mass system were shown to be equivalent. Then the engineered aggregate was tuned so that band gap was activated due to resonant oscillations of the replaced aggregate. In the numerical experiment conducted, the resonant behaviour causes the wave to be forbidden in the targeted frequencies. The proposed metaconcrete could be very useful in various civil engineering applications where vibration suspension and wave attenuation ability are in high demand.

Mechanical interaction of cells and their surroundings are prominent in mechanically active tissues such as cartilage. Chondrocytes regulate their growth, matrix synthesis, metabolism, and differentiation in response to mechanical loadings. Cells sense and respond to applied physical forces through mechanosensors such as integrin receptors. Herein, we examine the role of mechanical stimulation of integrins in regards to their mechanotransduction ability to promote chondrogenesis. For this purpose, magnetic nanoparticles were chemically bonded to cell membrane mechanoreceptors and stimulated. Histological results showed the endocytosis of nanoparticles over the experimental period, pointing out the inefficient mechanical stimulation of the mechanoreceptors. Moreover, gene expression analysis only showed significant upregulation for SOX9, whereas type II collagen and aggrecan gene expression were not significantly different from the control group. Our results suggest that magneto-mechanical stimulation studies using magnetic nanoparticles should not only focus on the mechanical aspects, but also the interaction of magnetic nanoparticles with intracellular machinery should be investigated as well.

In this study, the vibration behavior of functional graded (FG) circular and annular nanoplate embedded in a Visco-Pasternak foundation and coupled with temperature change is studied. It is assumed that a uniform radial magnetic field acts on the top surface of the plate and the magnetic permeability coefficient of the plate along its thickness are assumed to vary according to the volume distribution function. The effect of in-plane pre-load and temperature change are investigated on the vibration frequencies of FG circular and annular nanoplate. To obtain the vibration frequencies of the FG circular and annular nanoplate, two different size dependent theories are utilized. The material properties of the FGM nanoplates are assumed to vary in the thickness direction and are estimated through the Mori– Tanaka homogenization technique. The FG circular and annular nanoplate is coupled by an enclosing viscoelastic medium which is simulated as a Visco-Pasternak foundation. By using the modified strain gradient theory (MSGT) and the modified couple stress theory (MCST), the governing equation is derived for FG circular and annular nanoplate. The differential quadrature method (DQM) and the Galerkin method (GM) are utilized to solve the governing equation to obtain the frequency vibration of FG circular and annular nanoplate. The results are subsequently compared with valid result reported in the literature. The effects of the size dependent, the in-plane pre-load, the temperature change, the magnetic field, the power index parameter, the elastic medium and the boundary conditions on the natural frequencies are investigated. The results show that the size dependent parameter has an increasing effect on the vibration response of circular and annular nanoplate. Also, the temperature change play important role in the mechanical behavior of the FG circular and annular nanoplate. According to the results, the application of radial magnetic field to the top surface of the plate changes the state of stress in both tangential and radial direction. The present analysis results can be used for the design of the next generation of nano-devices that make use of the thermal vibration properties of the nanoplate.

Variable fill fluid couplings are used in the speed control units. Also, variation in coupling oil volume is used in adapting one size of coupling to a wider range of power transmission applications. Available model for the partially filled fluid couplings, has a good performance for couplings with fixed amount of oil but their performance will be degraded if they are used for the variable fill couplings. In this paper, the current model for partially filled fluid couplings is modified to have better performance for variable fill couplings. For this purpose, the circulation loss calculation is modified and also, the effect of oil temperature variations and blade thickness are included in the model. The effect of these modification on the model performance are investigated in couple of simulations. Comparing the simulation results with the available experimental data shows that the suggested modifications can improve the model performance very well.

In this study, analytical models considering different material and geometry for both single and double-lap bolted joints were reviewed for better understand how to select the proper model for a particular application. The survey indicates that the analytic models selected for the adhesively single or double bolted lap joints, as well as T, scarf, and stepped joints, with linear material properties are mostly two dimensional and the studies on stress distribution and/or failure of the joint are performed either experimentally, analytically or by finite element method. The results seem to be generally accurate and adequate. Additionally, it was shown that any increase in the bolt-hole clearance leads to an increase in bolt rotation, as well as a decrease in bolt-hole contact area, and hence, a reduction in joint stiffness. Moreover, studies on hybrid joints have revealed that the proper choice of adhesive material in conjunction with bolts or rivets in a joint, allows for significant increase in the static and fatigue strength compared to similar pure bonded joints. Additionally, the results on hybrid scarf joints showed that it is vital to place fasteners closer to the ends of the overlap to suppress the peak peeling stresses and hence, delay the effects of early crack initiation in the adhesive layer. Experimental studies on fatigue behavior and strength of bolted joints have shown that compared to clearance fit specimens, clamping force increases the fatigue life of a bolted joint. Moreover, higher tightening torque, in general, results in higher fatigue lives in bolted joints.