Scientia Iranica
Volume:25 Issue: 6, Nov - Dec 2018

This paper presents a new non-gradient nature-inspired method, Lion Pride Optimization Algorithm (LPOA) for solving optimal design problems. This method is inspired by the natural collective behavior of lions in their social groups "lion prides". Comparative studies are carried out using fifteen mathematical examples, two benchmark structural design problems, in order to verify the effectiveness of the proposed technique. The LPOA algorithm is also compared with other algorithms for some mathematical and structural problems. The results have proven that the proposed algorithm provides desirable performance in terms of accuracy and convergence speed in all the considered problems.

In this paper, a simulation of asymmetric cold rolling is being presented by using an explicit analysis procedure. A two-dimensional finite element model with adaptive meshing technique has been employed to simulate asymmetrical condition, due to difference of the roll radius and velocity. Some conditions have been found to make sheet without curvature, in order to achieve this goal, different velocities have been made in rolls in each radius ratio. To validate the simulation, the results of the simulation has been compared with experimental papers which was done in the past. The effects of asymmetric process have been discussed, which is caused by radius ratio and velocity ratio on the rolling force, rolling torque and on the sheet curvature. Also the optimum velocity ratio in each radius ratio that causes the sheet without curvature was obtained. It was found that the appropriate speed ratio to produce flat sheets (i.e. sheets without curvature) is almost 1.067 being independent of the radius ratios between 1 and 1.05.

Traumatic brain injury (TBI) often happens due to assaulting loads such as blast on the human head. Finite elements (FEs) can approximately simulate the blast interactions with the human head. An important parameter in the FE modelling procedures is the accuracy of constitutive formulation of the brain tissue. This paper is focusing on implementation of three brain tissue constitutive relations to measure and compare the dynamic behaviour of the brain under identical blast loads. For the geometry, we employ a simple spherical head model to monitor the brain tissue response and examine the uncertainties in FE brain tissue constitutive modelling. The brain tissue is constitutively modelled as hyperelastic, viscoelastic, and hyperviscoelastic type material. Intracranial pressures (ICP), strains, and shear stresses as the dynamic parameters are measured with time. These biomechanical parameters can be compared against the injury thresholds. Our analyses show that although the results for ICPs and strains are close for the three models, however, shear stresses are considerably different. The study will further provide new insight into selecting a proper constitutive model of the brain tissue under dynamic conditions.

In this paper vibrational analysis of size dependent micro-ring gyroscope under electrostatic DC voltage is performed. Based on the modified couple stress theory, Hamilton’s principle and in-extensionality approximation governing equations of size dependent micro rings and corresponding finite element formulation of circular micro ring along with eight half circular stiffeners embedded inside the ring is derived. Frequency analysis indicate that the obtained ring gyroscope mode shape is slightly different from the one previously reported in the literature. Size dependent behavior of the gyroscope is studied and findings confirmed the gap between classic and non-classic natural frequencies and pull-in voltage when the ring thickness is in order of material length scale parameter. Two different orientations for the actuation electrodes of the micro-ring gyroscope are implemented and effect of these orientations on the static deflection, pull-in instability and device frequencies in the sense ( direction) and drive ( direction) directions is investigated. Results reveal that the pull-in phenomena take place under lower voltage for & orientation of electrodes in comparison with orientation and frequency split occurs in higher voltages for & orientation. A comparison between finite element numerical natural frequencies of single ring and previously obtained analytical ones shows excellent agreement.

Flow through a twisted-tape (swirler) creates a complicated vortex structure downstream in the pipe. Detailed velocity measurements with Laser Doppler Velocimetry (LDV) along horizontal and vertical axes perpendicular to the axial flow direction have shown a strange flow pattern at the center of the rotating flow - a counter-rotating vortex seems to be present at the center with periodically varying magnitude in the axial direction. In more detailed measurements, it is shown that this behavior is the result of a pair of co-rotating secondary vortices that are superimposed on the primary rotating flow in a helical formation. The source of these secondary vortices has remained unclear. This study presents numerical simulations of the flow through 180o twisted-tape in a pipe, complementing the previous experimental results. The simulations reproduce the characteristics of the helical co-rotating vortices observed in experiments and provide details of the flow field. The results provide insight into the formation of the secondary vortices inside the twisted-tape, explaining the experimental observations. Mechanism of the vortex formation is described, showing that the secondary co-rotating helical vortices are produced by a pair of single co-rotating vortex formed on each side of the twisted-tape.

In this study a new hybrid RANS/LES turbulence model within the frame work of the Multi Relaxation Time (MRT) Lattice Boltzmann method (LBM) was used to study particle dispersion and deposition in a room. For the hybrid RANS/LES method the near wall region was simulated by the RANS model, while the rest of the domain was analyzed using the LES model within the framework of the LBM. In the near wall layer where RANS was used, the turbulence model was employed. To simulate the particle dispersion and deposition in the room, particles with diameters of 10nm to 10 µm were investigated. The simulated results for particle dispersion and deposition showed that the predictions of the present hybrid method were quite similar to the earlier LES-LBM. In addition, the predictions of the hybrid model for the particle deposition and dispersion were closer to LES simulation results compared to those of the model.

In this study, shape of water droplets with different sizes on various inclined smooth surfaces is simulated numerically and advancing and receding contact angles are determined by using the molecular dynamics approach. Experimental measurements are also carried out to validate the numerical predictions of droplet shape on inclined surfaces. Based on the verified code, shape of water droplets in different sizes around smooth circular cylinders with various diameters is simulated. Furthermore, advancing and receding contact angles along with the hysteresis values of the sessile and pendant droplets with various sizes around the cylinders are evaluated. Finally, based on the numerical results, two correlations are developed to predict advancing and receding contact angles of droplets on the circular cylinders. According to the results, maximum advancing and minimum receding angles take place on both sides of the cylinder on a horizontal line passes through the cylinder center. As a result, contact angle hysteresis reaches its maximum value in these two positions. In addition, advancing and receding angles have the same values on the top and bottom of the cylinder. Moreover, droplet size and cylinder diameter have minor effect while drop position has major effect on the shape of droplets over the cylinder.

Numerical simulations of three-phase gas-liquid-particle flows under 1g and 2g gravitational conditions were performed with an Eulerian-Lagrangian method. In this study, the liquid was treated as continuous phase and modeled by a volume-averaged system of governing equations. Bubbles and particles were modeled as discrete phases using Lagrangian method. Drag, lift, buoyancy, and virtual mass forces were included in the Lagrangian equation. Bubbles were treated as spherical without shape variations. The two-way coupling between bubble-liquid and particle-liquid were included and interactions between bubble-bubble and particle-particle were considered with the hard sphere model. Particle-bubble interactions and bubble coalescences were also included in the analysis. The results under 1g normal gravity condition were compared with the available experimental data in earlier simulation with good agreement. The transient flow characteristics of the three-phase flow under 1g and 2g gravitational condition were studied and the effects of gravity were analyzed. The results show that gravity has magnificent effect on the flow characteristics of three-phase gas-liquid-particle flows in bubble columns. The three-phase velocities under higher gravity are larger than that of the flow under normal gravity. The flow under higher gravity develops fast. Bubbles and bubble volume fraction in the higher gravity flow are smaller.

Strain is sensitive to damage, especially in steel structures. But traditional strain gauge does not fit bridge damage identification because it only provides the strain information of the point where it is set up. While traditional strain gauges suffer from its drawbacks, long-gage FBG strain sensor is capable of providing the strain information of a certain range, which all the damage information within the sensing range can be reflected by the strain information provided by FBG sensors. The wavelet transform is a new way to analyze the signals, which is capable of providing multiple levels of details and approximations of the signal. In this paper, a wavelet packet transform-based damage identification is proposed for the steel bridge damage identifications numerically and with experimental experiment to validate the proposed method. The strain data obtained via long-gage FBG strain sensors are transformed into a modified wavelet packet energy rate index first to identify the location and severity of damage. The results of numerical simulations show that the proposed damage index is a good candidate which is capable of identifying both the location and severity of damage under noise effect.

In gas and oil industry, erosion damages to pipe lines bends and elbows due to the presence of sand particles have been a challenging issue. In this study a computational model approach was for evaluating the erosion rates in different vertical return bends including sharp bend, standard elbow, 180° pipe bend and long elbow. The airflow in the pipe was simulated using the SIMPLE method and the k-ω SST turbulence model. An Eulerian-Lagrangian approach was used for predicting particle trajectories and the corresponding erosion rates. Different particle sizes and mass flow rates were considered and Oka model for evaluating the erosion rate was used in these simulations. Under the same conditions, the simulation results indicated that the sharp return bends experience the highest erosion rates and the 180° bends experience the lowest erosion among the studied configurations. It was also found that the erosion rate is linearly proportional to the mass flow rate of particles for all cases studied.

Predicting multiphase flows in curved pipes is of great importance in industrial equipment. In the present study, a computational model for predicting the velocity profile is developed and used to study the developing turbulent gas-liquid- solid three dimension flow in curved pipes. In order to discretize and solve the three-dimensional steady-state momentum equations, the finite volume scheme on staggered grids besides central difference and QUICK scheme have been used. Moreover, the k-ε model is employed to reflect the nature of turbulence in the flow. In order to address the needs for sooner convergence and convenient mapping of the physical domain, the computations have been performed in an extended toroidal coordinate system. Particle tracking has been done using Lagrangian approach in which two-way coupling regime is considered. In terms of validation, the numerical simulation results for the straight duct (infinite curvature), have been compared with the analytical solution and previous experimental results. Moreover, injection of particles through the flow indicates that, in each section of the bend, trade-off between centrifugal and pressure gradient forces plays a key role on particles motion. In last section, the effects of particle diameter and bend curvature on particle motion have been examined.

Nonlinear dynamic behaviour of structural systems has a significant role in many engineering applications. The analysis methods are typically numerical. Accordingly, for verification and test of accuracies, availability of nonlinear systems with exact closed form solutions is important. In this paper, a three-parameter system, with exact analytical solution, consisted of two synchronized colliding mass-spring-dashpot systems, is introduced and the validity of the exact solutions is demonstrated. Simplicity of the exact response, and the capability to control the frequency content, are addressed as the main features of the introduced system. Selection of appropriate values of the parameters entailing desired response features is discussed, and practical implementations of the model are described.