JOURNAL OF SOLID AND FLUID MECHANICS
Year:2016 | Volume:6 | Issue:3|Papers Count:25

An incompressible and unsteady flow problem in free falling of cylindrical particles was investigated in the intermediate Reynolds Number. Shape of the body that is used in an initial value problem in a vertical channel for the free falling was considered circular, square and rectangular cylinders. Fluid flow was computed by the Navier-Stokes equations for moderate Reynolds numbers. The particles were moved by effect of hydrodynamic, gravity and buoyancy forces. The governing equations for particle included second Newton law and torque were exerted over the particle. The particle-fluid interaction may treat by introducing a fully two dimensional overset grid Scheme. Overset grid Scheme may allow each component of a flow to be treated accurately and efficiently. The amounts of drag coefficients, free falling velocity, angular velocityand deviation for free falling cylinders were obtained for different Reynolds numbers (0.5£Re<50) and then were compared with experimental results. Free falling of rectangular and square cylinders in different situations were treated and the results compared with available data in fair agreement.

A bird strike incident is one of the most dangerous threats to flight safety. In this study, Smoothed Particles Hydrodynamics (SPH) method has been used for simulating the bird strike to an airplane wing leading edge structure using Ls-Dyna software. In order to verify the model, first, experiment of bird strike to a flat Aluminum plate has been simulated and strains and deformations on target plate have been compared with experimental results. Simulation outputs are in good agreement with experimental results. Then bird impact on an airplane wing leading edge structure has been investigated. At the next stage, considering dimensions of wing internal structural components like ribs, skin and spar as design variables, it has been tried to minimize structural mass and wing skin deformation simultaneously. To do this, relations between design variables and cost functions have been predicted by Response Surface Method (RSM), then Pareto based multi objective genetic algorithm has been used to minimize structural mass and wing skin deformation due to the bird strike. Finally dimensions of wing internal structural components are determined in such a waythat wing’s damage after the collision with a bird becomes minimal.

Microstructure reconstruction from statistical microstructure descriptors is a strong field of interest for researchers worldwide, due to its importance in material design. A new methodology is presented in this paper to reconstruct microstructure with a large number of representative volume elements. The proposed methodology provides a stable input for a deterministic method which can be used to simulate performance and effective properties. The Monte Carlo technique is used as the basis of the reconstruction methodology in this work. In this paper statistical correlation functions are extracted from the images of the experimental samples. The proposed algorithm reconstructs new samples which has similar statistical correlation functions in comparison to the experimental samples. The information of the geometric distribution of the nanotubes of the composites is stored in a database of the node locations of the unit cylinder segments and the corresponding waviness, Instead of using a discrete image matrix. These node locations are attractive results which can be utilized in the simulation software in order to obtain the properties of the studied composite. In this way, robust microstructures with a large number of representative volume elements were reconstructed for the future evaluation.

The flange joints are widely used in mechanical and aerospace structures. Hence, the static and dynamic behaviors of these joints are very important to be investigated. In the present study, a flange joint is described using linear and torsional springs. The equivalent stiffness of these springs are theoretically obtained. In doing so, the edge of flange is modeled as a cantilever beam and its deformation under various loading is calculated. Then the nonlinear deformed curvature due to the enforced loading is obtained. Having the curvature, the joint stiffness is calculated separately for axial and lateral loadings. It has been observed that the equivalent linear and torsional springs have bilinear stiffness due to different behaviors in positive and negative loadings. An experimental setup consisting a single bolt flange joint specimen has been designed to investigate the load-deflection behavior. The specimen puts into different loading configurations to obtain moment-rotation and force-deflection curves. A finite element model has been developed and result of the presented analytical model are compared with the experimental, FEM and previous numerical results. Finally, using the presented model, effect of changing the practical parameters of flange, like the bolt preload and flange thickness is investigated.

In this paper, instability behavior of cracked column equipped with piezoelectric patch is investigated, analytically. Polarization orientation is in such a way that axial force is induced in column. Crack is modeled as a torsional spring that connects two intact portion of column. After considering boundary conditions and continuity at the crack position and edges of piezoelectric patch positions, governing equations of buckling behavior of cracked column are obtained. Effects of effective parameters on the first and second buckling capacity of cracked column such as cracked parameters (position and depth), position, length and voltage of piezoelectric patch is investigated using suitable sketches. The results show that crack decreases buckling capacity, prominently. This decrease depends on position and depth of crack. Using appropriate position and length of piezoelectric patch, buckling capacity of cracked column is improved. The appropriate position of piezoelectric patch is not analogues to the crack position, necessarily and may be determined according to the column boundary conditions and crack position. The results show that positive voltage has opposite effects on the first and second buckling capacity of column.

One of the important subjects in aerodynamic design of high speed train is the slipstream or air flow around the train. This issue not only waste a significant amount of energy and fuel but also reduce the overall efficiency of the train. Due to irregularity the turbulence air flow around the high speed trains aerodynamic drag, noise and vibration are the most phenomenon that concern in this area. The slipstream is one of these aerodynamics features that directily related to the safety of passengers and workers near the line. When high speed train passes near to a standing human body, the produced presuer wave forces on the body surface and may lead to fall. In this numerical simulation we used dynamic mesh method and turbulence equation k-e in computational fluid dynamic software (Fluent). The aim of this study is to investigate the effects of air pressure around the train of moving with 300 km/hr velocity. The pressure waves are calculated in both modes of regular passage and passing with operation of aerodynamic brake. The resules are determined as the safty distance of the passenger from the line due to the different speed.

Due to wide range of engineering application of noncircular journal bearings in industry, their performance analysis is important. Shear stresses and friction forces in lubricant film cause variation of temperature condition in the bearing. Parameters such as increasing in rotational speed of shaft, decreasing in clearance space of bearing and low coefficient of heat transfer of lubricant, shaft and bearing cause the intensity changes in lubricant film temperature conditions. In the present work, the effects of design parameters such as speed of shaft, thickness of bearing shell, bearing length and micropolar lubricant characteristics on changes of temperature, lubricant film pressure distribution, load carrying capacity and attitude angle of bearing are investigated. By comparing the performance of noncircular three lobe bearings with and without considering temperature effects, it is found that pressure of lubricant film as well as load carrying capacity of bearing system decrease with increasing temperature, especially at high rotational speed of rotor. Also, the results show that with increasing micropolarity properties of lubricant, the effect of temperature on performance of mentioned bearings can be increased.

In the present paper, dynamic behavior of a multilayer composite plate with viscoelastic structural damping is investigated against a low-velocity impact by a spherical indenter. Hertz contact law is refined to include effect of the lower layers on the stiffness of the contact region and used in a non-linear form. Voltra hierarchical integral is employed for modeling the viscoelastic material and the layerwise theory and non-linear strain-displacement relations are used to model the plate more accurately. To solve the governing integro-differential equations, a combination of the finite element method, trapezoidal integration method for the Volterra integrals, and the Newmark numerical time integration method is used. In the results section, effects of the various viscoelasticity parameters and the indenter velocity on the time histories of the contact force, indentation, and lateral deflection of the plate are investigated. Results show that due to the damping nature of the viscoelastic materials, the plate rigidity and contact force increase whereas the maximum lateral deflection and the indentation decrease. Furthermore, higher contact forces do not necessarily indicates higher indentations.

Many researchers in the science of human behavior explore the role and function of the central nervous system (CNS) in planning and controlling of human movements. To this end, researchers have presented several different models. In present research a computer simulation of CNS's performance in designing the Sit-to-Stand transfer, which has been recently presented, is developed. This motion simulator is a modular and hierarchical movement planner (MHMP), based on decomposition hypothesis. In this paper the effect of foot position, as an environmental condition, is explored. The performance of the MHMP is evaluated with experimental captured motion. To this end, sit to stand motion is captured for five different foot position. Among these five motions, three motions are used to train the MHMP and the remaining motions are used for evaluating its performance. Results show that the maximum error of ankle, knee and hip angles are 0.122, 0.069 and 0.092 (radian) respectively. The maximum allowed error, suggested in researches, is 0.17 (radian). The results show that the MHMP has a good performance in planning the motion phases under this condition.

The delamination defects in the laminated composite structures are detected using the transient response analysis in the lock-in thermography test. The analysis procedure is implemented for a laminated composite plate subjected to harmonic heat flux in the top surface. The plate has some delamination defects with different sizes and locations. The thermal wave propagation due to heat loading is simulated in the plate thickness along the healthy and defective regions and the amplitude and phase differences are determined in such regions. The phase difference of reflected waves is more sensitive to the defects than the amplitude variation of the thermal waves. The results show that the phase difference between reflected waves from healthy and defective regions increases up to a specific frequency value and the optimum frequency is determined using the present simulation. The results also show that the logarithmic phase difference depends linearly on the depth of delamination and such dependency can be used to determine the defect depth. The simulation results of lock-in thermography test are used to determine the optimum parameters required to detect the delamination in the laminated composite materials.

This paper is the study of the effects of thermal environment on vibration analysis of a two-dimensional functionally graded rectangular plate on Pasternak elastic foundation. The natural frequencies of the plate are calculated by using the Rayleigh–Ritz method based on minimizing the total energy of the plate. The transverse displacement of the plate based on the third-order shear deformation plate theory (TSDT) is approximated by a set of admissible trial functions which is required to satisfy the clamped (CL) and simply supported geometric boundary conditions. For verifying the accuracy of this method, results are compared with those reported in the literature. As it is shown a good conformance is derived from the obtained results and the exact solution. In the numerical results, the effects of volume fraction coefficients, thickness ratios, aspect ratios of the FG plates, foundation stiffness parameters, temperature and boundary conditions on the natural frequencies are examined and discussed in detail.

This paper introduces an artificial neural network (ANN) application to a hot strip mill to improve the model’s prediction ability for rolling force and rolling torque, as a function of various process parameters. To obtain a data basis for training and validation of the neural network, numerous three dimensional finite element simulations were carried out for different sets of process variables. Experimental data were compared with the finite element predictions to verify the model accuracy. Thus the ABAQUS and MATLAB soft wares are used to simulate the finite element method and an artificial neural network, respectively. The back-propagation algorithm and Levenberg-Marquardt Training function were used in the artificial neural network. The input variables are selected to be, initial temperature of the strip, interface heat-transfer coefficient between strip and work roll, percentage of thickness reduction, initial thickness and rolling speed. The resulted ANN model is feasible for on-line control and rolling schedule optimization and can be easily and rapidly predicted the roll force and roll torque.

In this study, stresses and strains history of nanocomposite thick walled sphere wich is made of Polyimide reinforced by SiO2 nanoparticles are investigated using the viscoelastic Bergurs model. Loading of sphere includes the thermal and magnetic uniform field under hydrostatic inner pressure. Constitutive model of the problem based on elasticity relationship is obtained. Solving this equation with respect to mechanical boundary conditions leads to stresses and strains at zero time so called thermo-elastic solution in which these stresses are used at beginning creep problem procedure. With differentiating of constitutive differential equation with respect of time and using relationship between Bergurs model and Prandtl–Reuss relations drives a new constitutive equation for creep. History of stresses and strains are provided by solving this equation using numerical strain rate method. Results show that maximum effective stress and creep strains occurs at inner surface. Also the primary creep stage occurs up to 1000 second with quick change of stresses and strains. After this stage the value of stresses and strains change with uniform speed.

Use of adhesively bonded joints in structures has been increased in recent years because of their advantages. In structural applications, fatigue is generally considered to be the most important form of loading in respect to long-term service life. In this paper, experimental tests have been performed in order to examine the fatigue damage process of double lap adhesive joints, composed of E-glass laminates and epoxy adhesive with TiO2 P25 particles, under fatigue loading and then a method was proposed for fatigue life prediction based on initial stiffness. The scatter in results shows that the fatigue life is mostly dependent on initial stiffness. According to this, an exponential equation based on the initial stiffness has been proposed to have an initial estimation of fatigue life of the adhesive joints. In addition to the initial stiffness, stiffness degradation of the joints under fatigue loading influences on their final performance and therefore the initial estimation of fatigue life based on the initial stiffness could be modified. Also to have an online control of the fatigue damage process during the fatigue loading, a damage index using stiffness degradation was introduced.

Open pit mines have very high economic and operational risk because of high rate of production and using large scale machines. So, it is necessary to guarantee the availability of the operational equipment. First stage of mining in these mines is drilling for blasting and the availability of related machines has direct effect on all subsequent operations and consequently on overall economy of the operation. Today, operation conditions and machines availability can be assessed and analyzed due to development of reliability methods in different engineering fields. Markov method is one of the potent methods in this context which is based on stochastic process theory. In this study, reliability of rotary drilling machines in Golgohar Mine No.1, Sirjan, is analyzed using this method. In this way, reliability is calculated by investigating failure dad of these machines during 5 years and modeling different conditions of their availability. So, at least 2 machines will be ready and available for drilling operation with the probability of 95.42% corresponding to 347 days out of total 363 working days.

Vertical axis wind turbine, divided into Darrieus and Savonius, have been considered by many scientists owing to simplicity of design and operation independent of wind direction. Although Darrieus turbine has higher efficiency than Savonius, it faces to essential problem of self-starting. The aim of the present study is the combination of Darrieus and Savonius turbine in order to reach to a model with high starting torque and proper performance range. First, a model involving 3 straight-bladed Darrieus with 2 Savonius blades is simulated. For improving the performance, Savonius blade arc angle and airfoil solidity are changed. By optimizing the arc angle and solidity, the initial hybrid model performance is improved. Two-dimensional simulation using computational fluid dynamics is conducted using moving mesh for rotating part. According to results, the combination of Darrieus and Savonius turbine has favorable impact on self starting and makes performance curve smooth. It was also observed that solidity of 0.75 for Darrieus and angle of 150 for savonius blade arc are the optimized mode for maximum power coefficient, starting torque and performance range. In other words, The hybrid model with maximum performance is achieved by using these values at the same time.

In this paper, genetic and particle swarm algorithms were applied to optimize a recuperator in a microturbine, with the net present value (NPV) considered as the objective function. Examined for the optimization purposes is a plate-fin heat exchanger of offset strip fin configuration as well as counter- and cross-flow arrangements. Fin pitch, fin height, fin offset length, recuperator flow length, recuperator width, and recuperator height were considered as the six design parameters investigated. A sensitivity analysis is performed in order to investigate the effect of design parameters on the objective function. Comparing the results of genetic algorithm (GA) to those of particle swarm algorithm indicated that, the particle swarm optimization (PSO) approach had succeeded to achieve better results from computations’ volume and optimum value perspectives. As the used objective function in this research was a function of total cost and efficiency of the recuperator, the results of the present research were compared to thermo-economic optimization results. Being based on NPV and cycle efficiency criteria, the comparisons indicated superiority of the results of the present study, when viewed from technical and economic perspectives. Results show that in the present study NPV and cycle efficiency have increased up to 11.54% and 11.69%.

Increase in pressure drop due to the use of rifled tubes and also increase the heat transfer coefficient in two-phase flow and during boiling length (single-phase region) caused that using evolutionary genetic algorithm to optimize the parameters of rifled tubes, with the goal of increasing the heat transfer coefficient over the single-phase region and reduce the pressure drop in natural circulation system of drum should be dicussed in this paper. Choice of objective function was done with respect to the analysis of the pressure drop in each part of the drum circle and its large changes relative to the change of rifled tubes parameters. The optimization was done using two scenarios based on constant number of tubes (scenario I) and constant mass flux (scenario II). The results showed that the design in case of constant number of tubes which is defined base on no changes in length and width of the Shazand Arak power plant boiler, led to reduce the height of boiler from 60m to 27.23m. Finally, the role of rifled tubes parameters and mass flux in this scenario relative to first scenario in reduce of pressure drop was led to set values of the rifled tubes parameters.

In present work, the fluid flow around the cylinder has been controlled to change the pattern flow. Flow control methods are classified into two types, that were called active and passive methods.In this work, the compound method is applied, the splitter plate in the wake zone as passive method and EHD actuators as active method have been applied simultaneously. For simulation of fluid flow, Navier Stoks equations for fluid flow and conversation of electric charge and Poisson equations for electric field are calculated numerically by finite volume approach. The length of the splitter plate is equal the diameter of the cylinder and it is connected to the ground as well as the cylinder surface., The wire electrodes and the cylinder are used as EHD actuators. Calculations are done for the low Re number, Re=40 and the applied voltage V=10, 20 kV. The results show that the presence of the splitter plate at low Re number does not stabilize the wake zone and the vortexes behind the cylinder start to move.

In the present study, the effect of outlet opening location on providing appropriate and uniform thermal conditions and distribution of carbon dioxide species which is produced by high temperature radiant heaters under nonuniform flow field in an industrial environment have been investigated. For this reason, two dimentional environment with one inlet and one outlet opening have been considered. Two locations of air outlet opening near the floor and near the ceiling and also, two different types of radiantheaters’ arrangement have been considered as: single radiant heater, couple radiant heaters. For the mentioned conditions, continuity equation, momentum equations, energy equation, radiative transfer equation and species concentration equation have been solved by OpenFoam numerical solver. Also energy consumption have been evaluated in the present study. The results show that location of air outlet opening near the ceiling effects significantly on decreasing carbon dioxide concentration. As well as, usage of couple radiant heaters makes temperature distribution more uniform. The results indicate that energy consumption increases in presence of couple radiant heaters for outlet opening which is near the floor 3 percent and near the ceiling 15 percent in comparison with single radiant heater.

In the recent years, the baseboard heating system has attracted the attention of many HVAC engineers due to its uniform temperature distribution and low feed water temperature. Despite this, lack of ventilation equipment’s in the buildings with the mentioned heating system, can cause to decrease the indoor air quality. Therefore, the main goal of this study is to evaluate the effects of fresh air supply diffuser layout on the indoor air quality and occupants’ thermal comfort conditions in a baseboard heated building in winter. For this reason, the thermal sensation and indoor air quality indices have been numerically investigated in a standard case room and under the climatic conditions of 0°C as winter outdoor design temperature. The results show that the location of air supply diffuser has a significant influence on air temperature, thermal comfort conditions and indoor air quality. So that, changing the location of ceiling air diffuser from near the exterior wall to the center, can cause the average of air temperature to increase about 1.1oC (from 21.4 to 22.5oC). Moreover, the results indicate that selectiong the proper location for fresh air supply diffuser can lead to increase in the indoor air quality improvement index from 0.44 to 0.67.

In the current study, a solar shimney is analyzed and designed using computational fluid dynamics (CFD). The optimal dimensions of the chimney is determined. The chimney has a rectangular cross section and it is modeled in three-dimenstional space. The chimney has been modeled in various dimensions and with various geometric sections and impact of chimney geometries have been investigated on internal air flow and its performance. In addition to the geometry of the chimney effect, impact of change heat flux received from environment, entrance positive pressure and inlet air temperature were studied on outlet air mass flow rate from the chimney. The results indicated that there is optimum width in order to maximize air flow rate in the chimney. Optimum width is increased with Increase in inlet cross section, entrance pressure and chimney height in addition to increased air mass flow rate and performance improvement. The results of this plan can be used for appropriate design of a solar chimney and finally making it.

In this paper, elasto-plastic time dependent impact of high-speed projectile on water surface is simulated numerically using Arbitrary Lagrangian- Eulerian (ALE) method. The projectile is considered as elasto-plastic solid and its mesh is generated by Lagrangian approach. The water is also assumed as compressible fluid so its mesh is produced by Eulerian method. Three steps simulation are performed in this research; static, dynamic stress analysis and also impact analysis of full degrees of freedom (DOF) projectile on water surface using ALE method. The effects of fluid compressibility and cavitation are considered in last analysis. In order to validate results, the stress wave propagation produced in the projectile due to water impact is compared with exact ones. The results show that the maximum error compare with exact ones is 5%. Also the magnitude of maximum stress and location/path of fracture in the projectile are compared with experimental data. The good agreement between the predicted and analytical/experimental values shows the accuracy of this numerical algorithm. The impact of projectile on water surface is simulated with different angles. The results show that the safe zone of impact angle for present projectile is±0.5o.

This paper presents the numerical study on the mechanical properties of polypropylene (PP) reinforced with1 wt.% (weight percentage) mesoporous silica (MCM-41), Hydroxy Apatite (HA) and the composite of MCM-41 and HA (MCM41-HA or MH) nanoparticles. Numerical simulation according to macromechanical method (continuum method) was performed for differentform of StrainEnergy Density Function containing: Marlow, Ogden and Van der Waals using the commercial software ABAQUS/CAE.In this research the hyperelastic behavior of porous polymeric nanocompositscontaining: mesoporous silica/ polypropylene (PMCM), hydroxyapatite/polypropylene (PHA) nanocomposites and mesoporous silica- hydroxyapatite /polypropylene (PMH) nanohybridin the uniaxial tensile test, three point bending test and Izod impact test were studied.In order to verify the numerical results, values obtained from the simulation of mechanical properties were compared With similar functional tests. The performed simulation results are in good accordance with the experimental data and the Marlow model has the best agreement with results of experiment.

In this article, the free convection heat transfer of water-alumina Nano fluid is investigated in a baffle L-shaped cavity. The governing equations are solved numerically using the finite volume method and the SIMPLE algorithm. The left and bottom vertical walls are warm, the horizontal intermediate wall and the baffle are cold. Other walls are well insulated. The effect of Righly Number, nanofluid volume fraction, aspect ratio of the cavity and the baffel′s length on the heat transfer are investigated and discussed. The results show that the presence of the baffle is effective on the heat transfer enhancement and by increasing the Righly Number, nanofluid volume fraction and the aspect ratio of the cavity the heat transfer increases. Also in higher aspect ratio, Nano fluids have more influence on the Nusselt number enhancement.