Modares Mechanical Engineering
Year:2016 | Volume:16 | Issue:7|Papers Count:50

The application of woven fabrics in composites manufacturing has increased because of their special mechanical behavior. Due to the complexity of modeling and simulation of these composites, in this research a micromechanics based analytical model has been developed to predict the elastic properties of woven fabric composites. The present model is simple to use and has a high accuracy in predicting the elastic properties of woven fabric composites. One of the most important effective factors on the modeling accuracy is utilizing a proper homogenization method. Therefore, a new homogenization method has been developed by using a laminate analogy based method for the woven fabric composites. The proposed homogenization method is a multi-scale homogenization procedure. This model divides the representative volume element to several sub-elements, in a way that the combination of the subelements can be considered as a laminated composite. To determine the mechanical properties of laminates, instead of using an iso-strain assumption, the assumptions of constant in-plane strains and constant out of plane stress have been considered. Then, the proposed homogenization model has been combined with a micromechanical model to propose the new micromechanical model. The applied assumptions improve the prediction of mechanical properties of woven fabrics composites, especially the out-of-plane elastic properties. The proposed model is evaluated by comparing the predicted results with five available experimental results available in the literature, and the accuracy of the present model is shown.

In this paper simulation of steady super cavitation phenomenon has been considered by using partial non-linear model of Boundary Element Method (BEM).The grid mesh used is fixed and the strength of dipole and source are constant on each element. With the assumption of a partial non-linear model the cavity condition is applied on the body with the assumption that cavity height is low. Thus there is not any calculation on the cavity surface, but it is restricted to only the panels on the body surface. Cavitation number is known at first and the cavity length is determined in every iteration. When the lengths obtained in two successive iterations are very close to each other it is assumed to be the answer. Based on this method two Kutta conditions including Morino condition and Iterative Pressure Kutta Condition (IPKC) are studied to satisfy the wake surface condition. The application is a wing with NACA16006 section. IPKC condition compared to Morino one needs higher computational costs, but on the other hand leads to more accurate results. It has been shown that simulation of the flows with super cavitation over wing leads to a pressure difference at the trailing edge of each strip if Morino’s Kutta condition is used. While if Iterative Pressure Kutta Condition is used the results are satisfactory. Comparison of the results shows that this method leads to very accurate predictions for the behavior of flows with cavitation, while significantly lower computational cost is required if the simple cavity closure condition is used.

In this paper, the interaction between aluminum facing and honeycomb structure in the quasi-static and the impact loading has been investigated experimentally. The structural elements used in this research were aluminum plate, aluminum 5052 honeycomb structure. The quasi-static penetration tests and ballistic impact experiments were performed on aluminum plate, honeycomb structure and sandwich panel by flat ended penetrator and flat ended projectile respectively. The failure mechanisms, ballistic limit velocities, absorbed energies due to penetration, the damage modes and some structural responses were studied. Also, the effect of interaction between aluminum facing and honeycomb structure in the quasi-static penetration and the ballistic impact response in this honeycomb sandwich panel were discussed and commented upon. Comparing energy absorption in these structures showed that the amount of absorbed energy by the sandwich panel with honeycomb core is more than the absorbed energy by the aluminum plate and honeycomb structure in the quasi-static penetration. These results indicated that, using the honeycomb structure as the core of sandwich panel resulted in increasing the stiffness and the strength of the sandwich panel. The ballistic impact results showed that the absorbed energy and the ballistic limit velocity in the sandwich panel compared with the individual components were increased. Therefore, the sandwich structure can be used as a suitable energy absorber.

In this paper, a trajectory tracking control strategy for a quadrotor flying robot is developed. At first, dynamic model is obtained by Lagrange-Euler approach. Then, control structure, consisting of a model based predictive controller, has been used based on state space error to track transitional movements for reference trajectory and also robust nonlinear H¥ control is applied for stabilizing the rotational movements and rejecting the external disturbance. In both controllers the integral of the position error is considered, allowing the achievement of a null steady-state error when sustained disturbances are acting on the system. The external disturbances are considered as aerodynamic torques. If uncertainties increase, the designed control system unable to path tracking properly. So finally, in order to eliminate the effects of parameter uncertainties the recursive least squares is used for estimating mass and moment inertia parameters which are linear and it is applied to the control system. Simulation results show that by using estimation of system parameters, the proposed control system has a promising performance in terms of stabilization and position tracking even in the presence of external disturbance and parametric uncertainties.

The slab method can rapidly predict the rolling force and torque in metal forming processes and a large amount of CPU time can be saved. Up to now, the work hardening effect has not been considered in the slab analysis for forging process of double-layer clad sheet. Evaluation of considering or eliminating the work hardening effect on material behavior in the slab analysis of three layer clad sheet forging process and investigating the subsequent effects on the process outputs are novel subjects considered in this paper. The pressure distribution as well as the forging force is investigated for both conditions. In addition, three layer clad sheet forging process is entirely simulated using ABAQUS/Explicit software. The results show that considering the work hardening effect on material behavior will result into having higher stresses and forces in the process. Moreover, the results of considering the work hardening effect have better agreements with those from simulation. Finally, some experiments were performed on forging process of two layer Al/Cu clad sheet to evaluate the bonding quality of sheets. Therefore, forging process can be used for producing multi-layer clad sheets in various industries.

Uncertainty inherently exists in quantity of a system’s parameters (e.g., loading or elastic modulus of a structure), and thus its effects have always been considered as an important issue for engineers. Meanwhile, numerical methods play a significant role in stochastic computational mechanics, particularly for the problems without analytical solutions. In this article, spectral finite element method is utilized for stochastic spectral finite element analysis of 2D continua considering material uncertainties. Here, Lobatto family of higher order spectral elements is extended, and then influence of mesh configuration and order of interpolation functions are evaluated. Furthermore, Fredholm integral equation due to Karhunen Loeve expansion is numerically solved through spectral finite element method such that different meshes and interpolation functions’ orders are also chosen for comparison and assessment of numerical solutions are solved for this equation. This method needs fewer elements compared to the classic finite element method, and it is specifically useful in dynamic analysis as it supplies desirable accuracy by having diagonal mass matrix. Also, these spectral elements accelerate the computation process along with Karhunen Loeve and polynomial chaos expansions involving numerical solution of Fredholm integral equation. This research examines elastostatic and elastodynamic benchmark problems to demonstrate the effects of the undertaken parameters on accuracy of the stochastic analysis. Moreover, results demonstrate the effects of higher-order spectral elements on speed, accuracy and efficiency of static and dynamic analysis of continua.

The incremental forming process which can be used in low quantity production of the components is a relatively new forming process for sheet metal components. One of the problems of this method is thinning and non-uniform thickness distribution of the component in radial direction. In the incremental forming process, the sheet thickness in the wall of the formed cup is reduced considerably while the thickness in the bottom of the formed cup is unchanged. This problem hinders the wide application of the incremental forming process in the industry. In this paper, a new method is presented for the improvement of the thickness distribution in the incremental forming process. In the presented method, a new preform is added to forming stages which reduces the sheet thickness in the bottom of the formed cup, increases the minimum thickness in the wall of the formed cup and improves its thickness distribution. The incremental forming process is simulated using the software ABAQUS and verified using the experiments available in the literature. Then the proposed method is simulated and its result indicates the capability of the presented method in thickness improvement.

The present study was done to evaluate the effect of parameters like trip strip installation, free stream velocity, geometry of model nose (SUBBOF nose and DRDC nose) and putting up model in pitch and yaw angle, on drag coefficient. Also, the effect of stand geometry of an axially symmetric model in wind tunnel on wake flow structure and drag coefficient in zero and ten degree angles of attack was investigated. Choosing the best distance behind the model for data acquisition in order to calculate drag coefficient under consideration of turbulence effects in one dimension is the other item investigated in present study. All experiments have been done in an open circuit wind tunnel at university of Yazd and data acquisitions has been done with a one dimensional hot wire. According to calculations, installation of trip strip enhanced drag coefficient in all cases. Also, drag coefficient decreased with increasing free stream velocity. Putting up the model in pitch and yaw angle of attack increased drag coefficient. Between two nose shapes that were tested, the SUBBOF nose shape was chosen as suitable nose. A stand with NACA0012-64 geometry and Rod stand were selected as the most appropriate stands for zero and 10 degree angles of attack.

Study of air infiltration into a building in several ways such as energy, air quality, thermal comfort and pollution entering in the building is very important. In this context, many studies have been conducted in different countries. In our country due to the use of steel doors and windows, independent research on the gap size and air infiltration is necessary .In this study, by practical view and in order to localize results, based on a field study, the actual dimensions of the gaps around conventional doors and windows in Iran are measured. The results of these measurements are used to simulate gaps, then, with experimental study air infiltration rate of these gaps is calculated at different pressures. In present study, after investigating the effect of different aspects of gaps on air infiltration rate, two common equations, power law and quadratic equation, were compared in order to fit data. Results show that power law equation can adapt better to the experimental data. Coefficients of the power law equation to estimate the air infiltration rate through the gaps were presented. Due to the proximity factor of the pressure difference to the number 0.5 in most of the results, it was concluded that the Bernoulli equation can be used to predict the air infiltration rate through the gaps. This equation is in better compliance with laws and physical principles. Discharge coefficient of the Bernoulli equation for gaps with different dimensions is calculated.

This paper is seeking to add a CNC G-code to hexapod CNC system. The mentioned G-code is five axis tool radius compensation. Once the tool radius is changed, especially in the case of tool size changing with tool wear in machining, a new NC program has to be recreated. Five axis tool radius compensation corrects cutter path automatically. This G-code contains all the main parts of a standard code such as: interpreter, interpolator and inverse kinematics unit. The interpreter unit extracts the position and orientation from the received code and sends it to the interpolation and kinematics units to correct the errors and achieve the desired six pods lengths. In the tool radius compensation algorithm, the unique vector of the movement direction of the tool tip and the normal vector of the machining surface have been used to calculate the direction of the tool radius compensation. The offset path is calculated by offsetting the tool path along the direction of the offset vector. Accuracy of the proposed method is tested with a number of experiments. The experimental results confirmed the accuracy of the proposed methods.

This study dealt with the flutter and biaxial buckling of composite sandwich panels based on a higher order theory. The formulation was based on an enhanced higher order sandwich panel theory in which the vertical displacement component of the face sheets were assumed as quadratic while a cubic pattern was used for the in-plane displacement components of the face sheets and the all displacement components of the core. The transverse normal stress in the face sheets and the in-plane stresses in the core were considered. For the first time, the continuity conditions of the displacements, transverse shear and normal stress at the layer interfaces, as well as the conditions of zero transverse shear stresses on the upper and lower surfaces of the sandwich panel are simultaneously satisfied. The aerodynamic loading was obtained by the first-order piston theory. The equations of motion and boundary conditions were derived via the Hamilton principle. Moreover, effects of some important parameters like lay-up of the face sheets, length to width ratio, length to panel thickness ratio, thickness ratio of the face sheets to panel, fiber angle, elastic modulus ratio and thickness ratio of the face sheets on the stability boundaries were investigated. The results were validated by those published in the literature. The results revealed that by increasing length to width ratio, length to panel thickness ratio and elastic modulus ratio of the face sheets, the stability boundaries were decreased and the largest nondimensional buckling loads occurred at the angle ply sandwich panel.

A practical method for improving the COP of an air-cooled chiller is pre-cooling the air entering its condenser via a water mist system. This article studies a water mist system with hollow-cone spray nozzles and investigates the effects of water flow rate, water droplet diameter and the number of spray nozzles on system performance. Simulations were run by FLUENT software, applying Eulerian-Lagrangian method. Solution grid independency was obtained and was validated with experimental data. According to the results, in a constant air flow rate of 8.3 (kg/s), with increasing the water flow rate from 0.05 to 0.4 (kg/s), percent increase of COP increases from 3 to about 14, but the percentage of evaporated water decreases from 12.13 to 7.62 (however the value of evaporated water increases). Besides, decreasing the water droplets diameter from 200 to 50 micrometer, results in percent increase of COP from 4 to 24. Due to less water evaporation in higher flow rates, the number of spray nozzles was raised in a constant total flow rate which, according to the results, increasing the number of nozzles improves the system performance. Also, with other simulations it was observed that increasing the number of nozzles is more effective in higher flow rates and less drop diameters. Finally, the case study demonstrated that using sufficient number of nozzles, it is possible to achieve higher COPs in lower flow rates and therefore in addition to energy consumption, the water consumption could be reduced.

In this study, experimental and analytical unsteady flow around a cylinder model with rotational degrees of freedom is discussed. Experimental studies at different speeds and angles of attack for two cylinder models with different length ratios have been done. Meanwhile the analyses of numerical technique known as vortex panel method have been used. Analytical and experimental results show that the rotational and vibrational motion and a combination of these behaviors occur. These types of behaviors depend on ratio of length plates to cylinder radius, primary object angle of attack and free stream velocity. At different speeds and at all angles of attack for a length of less than 1, the model has vibrational motion around a specific angle. This angle for cylinder with two plates is 90 degrees. Generally, the model tends toward vibrational motion at low angles of attack with increasing length ratio and free stream velocity occurring and by increasing the primary angle of attack the desire for vibration motion around a specific angle occurs. Also, in free stream velocity 10 (m/sec) and higher, for length ratio 4, the model had a steady rotational motion. In addition, angular velocity models and Strouhal number on rotational motion are calculated. The results show that by increasing the Reynolds Number, Strouhal number becomes fixed.

One of the main challenges existing in the field of missile aerodynamics is how to reduce the aerodynamic drag of aerospace vehicles through different mechanisms. Thus far, many investigations have been performed to determine the performance and influence of various parameters on the effectiveness of these mechanisms. The challenge is particularly more pronounced in missiles with a blunt nose. The aim of this study is to reduce the aerodynamic drag of such missiles using hybrid employment of mounted spike at the stagnation point of the nose in addition to jet injection at different positions on the spike. To this aim, spike and jet injection configurations are extracted from the literature. Jet injection is considered in the sonic regime and perpendicular to the surface of spike. All analyses are performed using Fluent software along with Navier-Stokes equations for compressible and three-dimensional flow in both steady and unsteady states considering free stream at a Mach number of 1.89 and different angles of attach. Since the numerical simulation of these models requires high processing speed and memory, parallel processing system is employed. Additionally, structure grid and k-w-SST turbulence models are utilized. Results indicate that a significant drop in the drag is achieved using the hybrid utilization of jet injection and spike.

In this paper the arrangement of the fiber metal laminate for cylindrical shells to achieve the maximum natural frequencies is optimized. In order to maximize the FML shell natural frequencies the sequence of the composite –metal layers and fiber orientation are changed frequently and for each case, the sample natural frequency is calculated. Finally FML shell with maximum natural frequencies is found. Hamilton‘s principle and energy method is used to define the equation of motion and First order shear deformation theory (FSDT) is utilized for vibration analysis in the shell’s equilibrium equation .In order to solve free vibration problem the double Fourier series is used to obtain the eigenvalue problem. For this purpose, through a MATLAB program linked to the finite element software of ABAQUS, different shells with various layer sequence and fiber orientation are created and studied from optimization aspect. This comprehensive program is able to analyze the FML shells with various arrangements of composite –metal layers, fiber orientation and boundary condition. The simply-simply and clamp-clamp boundary conditions are applied on edges. The applicable fiber orientations are 0,30,60,90 degrees.

Nanofluids are engineered by suspending nanoparticles with average sizes below 100 nm. The ever increasing thermal loads in such applications require advanced operational fluid characteristics, for example, high thermal conductivity dielectric oils in transformers and car radiators. These fluids require high thermal conduction, as well as electrical insulation. In the present work the thermophysical and rheological properties of the nanofluids such as thermal conductivity, viscosity and density are obtained from molecular dynamics simulations. These results serve as initial data for computational fluid dynamics simulations to calculate heat transfer coefficient. The results show that, adding titanium oxide nanosheet in the base fluid enhanced the thermal conductivity and increased the viscosity and density of the base fluid. The theoretical calculations confirmed the molecular dynamics simulation results and the simulation methods accuracy. The computational fluid dynamics results show that increasing the amount of titanium oxide nanosheet in the base fluid increases the heat transfer coefficient and increasing ethylene glycol ratio in base fluid leads to lower heat transfer coefficient. Also, nonequilibirium molecular dynamics method can be used as an effective and accurate method for nanofluids investigation. The coding that is used to obtain the thermal conductivity of nanofluid is a novel and modified type of non-equlibiruim molecular dynamics method. By using this coding the error persentages of simulations is decreased. The other advantage of this code is reducing the simulation process, because the molecular dynamics simulations need a long time for processing.

In the nonlinear elastoplastic finite element analysis, the stresses must be updated at each Gauss point of the elements in each iteration of each load increment by a stress-updating process. The stress-updating process is performed by integration of the constitutive equations in plasticity. It should be noted that the accuracy of integrating the constitutive equations significantly affects the accuracy of the final results of the structural analysis. In this study, the von-Mises plasticity model along with the isotropic and kinematic hardening mechanisms is considered in the small strain realm. The constitutive equations are converted to a nonlinear equation system in an augmented stress space. The aforementioned nonlinear equation system is solved by a semi implicit technique. The precision of the solution is dependent on the radius of the yield surface which is used in the process of the solution. Therefore, the relations are derived so that the yield surface radius can be picked up from each arbitrary part of plasticity step. Finally, to determine the best time of loading step for calculating the radius of the yield surface, a wide range of numerical tests is performed.

In this study, aluminum- brass bimetal composite was produced by centrifugal casting process. Four preheat temperatures (100, 200, 300, and 400oC), three rotational speeds (800, 1600, and 2000 rotationper- minute) and two volume ratios (1.5 and 2.5) were investigated. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction analysis (XRD) were used for microstructure observations and phase characterization. Mechanical tests, based on Chalmers model, and fracture studies were performed on some specimens. According to the results, interface contains three discrete zones. Zone 1 includes diffusional layers (Al3Cu5Zn4- Al3Cu3Zn), zone 2 contains Al3Cu precipitates distributed in Al11Zn matrix, and lastly zone 3 includes anomalous eutectic microstructure (a-Al/Al3Cu). Pressure test results showed that brittleness is associated with interface thickening so that bond strength is weakened. Interface fracture surface contains two fracture modes, brittle and ductile. Brittle fracture seems to be related to Al3Cu precipitates and ductile fractures to a-Al/Al3Cu anomalous eutectic microstructure.

Due to high humidity, high air temperature and hazardous compounds including chlorine, indoor swimming pools are called an unhealthy environment. Therefore, the pollutants’ concentration, relative humidity and thermal comfort conditions must be simultaneously considered in designing the air conditioning systems of indoor swimming pools. In this study, a new approach has been presented for concurrent modeling of water evaporation mechanism, chlorine concentration level, occupants’ thermal sensation and temperature and velocity fields in a championship-size indoor swimming pool. In this regard, a new algorithm has been developed in order to apply adaptive boundary conditions at water-air interface in the pool. In the mentioned pool, the air enters the environment through a linear ceiling diffuser at temperature of 35oC, relative humidity of 30% and air exchange rate of 4 times per hour. The results show that the distribution of temperature, relative humidity and concentration of chlorine contaminant are significantly dependent on the height from the water surface. So, the volumetric average of relative humidity from the floor to 0.5m height is about 62%; while the volumetric average of relative humidity in the occupied zone is about 50%. Moreover, results indicate that in the distance of floor to 0.5 m height, the mean value of chlorine’s concentration is about 60% larger than its mean value in the occupied zone. Also, the temperature field and distribution of thermal comfort index are significantly dependent on the height.

The major purpose of this paper is to illustrate statistical design accuracy using trajectory simulation for launch vehicles design in conceptual design phase and also sensitivity analysis of velocity relative to effective external forces. Considering the advantages of statistical design in prevention of time and cost losses, system specification of sample launch vehicle is calculated based on statistical data of the studied population. Then, by solving the equations of motion, design parameters are calculated in such a way that difference of the final velocity of trajectory simulation and needed orbital speed is less than 1 percent. Studied launch vehicles are two-stage liquid propellant vehicles, with Portability 2.5-3.5 tons mass to the low earth orbit. For validating, curves of speed, altitude and angle of path of launch vehicle are designed using statistical method, then compared with curves of Tsiklon launch vehicle, therefore correct operation of the mission and accuracy of the statistical design algorithm is proved. By comparing ideal speed and speed of simulation, speed changes of any effective force are obtained. Eventually, speed loss factor at each stage and sensitive percent of each stage speed relative to the force for both launch vehicles, statistical design and tsiklon, are analyzed.

Roughness of vanes’ outer surface and that of cooling channels’ inner surface have considerable impact on temperature distribution. Using a rougher surface leads to increased turbulence in near-surface flows and increases the rate of heat transfer. In this study, vane of a C3X turbine cooled via 10 cooling channels was simulated -three-dimensionally- by ANSYS-CFX software based on SST turbulence model, and then the effects of roughness of said surfaces were examined. The results showed that increasing the roughness of the blade’s outer surface, which absorbs the heat of the hot fluid, to values below the threshold of fully rough regime (Reks<70) makes no significant impact on vane’s surface temperature distribution; but increasing the roughness to values higher than this threshold leads to 8% increase in surface temperature. This indicates that outer surface of the blade should always exhibit a transitionally rough regime. Contrary to the outer surface, increasing the roughness of cooling channels’ inner surface, which transfers the heat to the cooling fluid, has been found to be the very beneficial, as even a slight increase in the roughness of this surface (within the domain of transitionally rough) decreases the blade’s surface temperature by up to 8%, and improves the hydraulic-thermal performance factor by about 250%.

Air staging is defined as the supply of inadequate air from the primary stage to the reaction zone, and the completion of the air supply through the next stage or stages. This study is concerned with the optimization of the air staging system of a burner with two air inlets and one fuel (natural gas) inlet with the help of numerical modeling. The equivalence ratio of the primary air (with the assumption of a fixed total air mass flow rate), and the distance between the two air inlets constitute the design variables of the problem. In the previous research works, the air staging technology has been mainly employed as a method to reduce the emission of NO. However, in the current study, in addition to the emission of NO, the emissions of CO and soot, and radiative heat transfer from the flame are considered as the objective functions. The results show that increasing the level of air staging (or the equivalence ratio of the primary air) has contradictory effects on the objective functions so that, as a positive influence, it increases the radiative heat transfer from the flame and decreases the emission of NO, and as a negative effect, it increases the emission of both CO and soot. The results also indicate that when all the previously mentioned objectives are considered simultaneously, the optimal case, which is selected based on the Pareto front concept, is the case in which the primary air is about 20% of the theoretical air.

In this paper, the energy absorption capacity of A356 aluminum foam reinforced by SiC particles under impact loading was studied. The foam was manufactured by direct foaming of melts with blowing agent CaCO3. The drop-weight impact testing machine was designed and fabricated. The dynamic load-cell circuit was designed and mounted on the impactor. The impact test was carried out using a hemispherical indenter with a velocity of 6.70 m/s on the foam specimens, and the load-time history data was obtained. The results were compared with the results reported by a piezoelectric force sensor and validated. The obtained impact response of A356/SiCp composite foam is stable, which represents the suitable design of the machine and its reliable output. This is emphasized by comparison of material behavior with the results of other researchers. The response includes three stages: an initial linear behavior, a plateau of load and failure of the foam. In plateau region, the plastic deformations can be tolerated by the foam at nearly constant load. The end of plateau region and beginning of the failure region occur at the moment when the rate of energy absorbed by the foam is decreasing. The values of plateau load and absorbed energy estimated from load-cell are 1.62 kN and 22.04 J respectively, which has a relative error of 1.8% and 7.7% in comparison with piezoelectric sensor. The value and percentage of absorbed energy were obtained as 6.07 J, 6.58 J, 9.39 J and 27.5%, 29.9%, 42.6% for elastic, plateau and failure regions respectively.

In this paper, magnetogasdynamics with outlet Knudsen of 0.2 is studied in a pressure-driven micro channel. By using a developed code, the effects of changing magnetic field parameters including power and length with implementation of slip velocity at the walls have been simulated numerically. The geometry is a two dimensional planar channel having a constant width throughout. The flow is assumed to be laminar and steady in time. In order to analyze the variation of velocity, pressure, Lorentz force and induction magnetic field, the governing equations for flow and magnetic fields have been solved simultaneously using the lattice Boltzmann. No assumption of being constant for parameters like Knudsen and volumetric forces is made. Another feature of this research is to improve the quantity of results, which is a major problem in this method and many studies have been done in this area. This study presents the results which have more quantitative agreement with that of analytical relations by using a second order accuracy for calculation of slip velocity and correction of pressure deviation curve in comparison with the past studies if a proper relaxation time is determined. The simulation results show a change in Fx profile to M if the length of external magnetic field length reduces to 40% of the whole. Removing applied magnetic field from both ends of the channel will increase pressure gradient at the intermediate part and displace the section at which the maximum pressure deviation occurs. Slip velocity and centerline velocity behave differently for the reduced magnetic field length.

Nowadays, in order to reduce costs and increase safety, utilizing test devices like conic shock tube has been popularized to investigate the explosion under-water phenomenon and its impact on constructions. A shock tube is designed, manufactured and utilized in the mechanic of explosion laboratory of mechanic faculty of K.N. Toosi University of Technology to study the effect of isotropic metal plates’ material in this research. The source which creates the shock in the utilized shock tube is explosive material and the positive point is that in such tube a high pressure can be produced with a tiny explosive charge. In order to investigate the effect of the material and the geometry of the utilized metal plate, three materials with two different thicknesses are considered in the experimental tests. The behavior of the plate can be measured when the amount of the pressure produced by the explosive charge and the amount of plate’s transformation is specified. From the results of the experimental tests, in order to give a semi experimental relation, the behavior of plate under explosion load with water interface is utilized. Finally, with the combination of experimental and theoretical results, the effect of material and thickness change are studied separately and with increase in weight parameter of the load, equations are given to predict the transformation of the metal plates.

In this study, dynamic bending of FG circular and annular plates with stepped thickness variations is examined. System of governing differential equations is derived based on the first order shear deformation theory and solved by using a semi-analytical method based on the power series and the fourth-order Runge-Kutta methods. On the basis of presented solution procedure, dynamic behavior may be obtained for the plates under various dynamic loads such as stepped, stepped pulse, triangular pulse and harmonic loads which can be imposed on the arbitrary parts of plates. Also, transverse asymmetric plates with various stepped segments with various boundary conditions may be analyzed. For derivation of system of governing differential equations, Stepped annular plates are divided into multiple constant thickness annular segments and stepped circular plates are divided into multiple annular and one circular segment with constant thickness. Governing equations are written for each segment, individually. Then, continuity conditions of displacements and stresses are imposed between various segments. Comparisons made with results of a numerical finite element code (ABAQUS software) on the basis of the three dimensional theory of elasticity reveal that the obtained results by using the proposed solution procedure have very good accuracy for various stepped plates under various dynamic loads.

Reduction of unwanted noises is an important issue in the current societies regarding their potential negative impact on the mental and physical health of the peoples. Researchers are trying to find a new method to reduce the damage unwanted sound. Accordingly, the use of sound absorbing materials with appropriate acoustic properties has increased in recent years.In this article, first the production of polyurethane foam is explained and sound absorption coefficient of pure PUF is measured. In order to improve the mechanical and acoustical properties of polyurethane foam, various quantities of Nano-Alumina powder are added to the structure of the foam. The effects of this additive material on the acoustic and mechanical properties of the foam are then measured. In this work, for the first time, the mechanical, physical and acoustical properties of the polyurethane foam improved by Nano-Alumina are studied. Finally, the change of the sound absorption coefficient of the produced composite material is analyzed based on the mechanical and physical experimental results. The sound absorption coefficient of this foam is then measured using Two microphone method with Impedance tubes.

Rotating stall alleviation in an axial compressor with deployment of air injection at its rotor blade row tip region has been experimentally investigated. Twelve air injectors were mounted evenly spaced around the compressor casing upstream the rotor blade row. Initially, improvement of the compressor overall performance was examined through air injection, especially at stall point condition. Instantaneous flow velocities at various radial and circumferential positions were measured simultaneously utilizing hot wire anemometry. Results obtained from these latter measurements together with signal frequency analyses, provided to describe the stall inception process and consequent flow induced fluctuations and also stall alleviation during the air injection process. Results show that a small amount of air injection at the rotor blade tip region can affect the rise in total pressure and more specifically, increase the compressor stall margin efficiently. Air injection of less than 1% of the compressor main flow rate through the injectors has improved the stall margin by 9%. Air injection at the blade row tip enables this beneficial effects to extend throughout the blade whole span, especially while working at the near stall conditions.

Inlet performance is an important field in aerodynamic design of aerial vehicle engines. This study focuses on numerical investigation of Mach number effects on a supersonic axisymmetric mixed compression inlet performance. For this purpose, a density based finite volume CFD code has been developed. A structured multi-block grid and an explicit time discretization of Reynolds averaged Navier-Stokes (RANS) equations have been used. Furthermore, Roe’s approximated Riemann solver has been utilized for computing inviscid flux vectors. Also, the monotone upstream centered schemes for conservation laws (MUSCL) extrapolation with Van Albada limiter have been used to obtain second order accuracy. In addition, Spalart-Allmaras one-equation turbulence model has been used to close the governing equations. The code is validated in three test cases by comparing numerical results against experimental data. Finally, the code has been utilized for numerical simulation of a specific supersonic mixed compression inlet. The effects of free stream Mach number on performance parameters, including mass flow ratio (MFR), drag coefficient, total pressure recovery (TPR), and flow distortion (FD) have been discussed and investigated. Results show that increase in Mach number, leads to decrease in TPR and drag coefficient; however, MFR and FD increase. Also, FD variations with respect to other performance parameters are significant, such that increase in Mach number from 1.8 to 2.2 leads to more than 100% FD increment while increase in MFR is less than 10%. By using this code it will be possible to design, performance parametric study, and geometrical optimization of axisymmetric supersonic inlet.

The management of air quality in enclosed parking lots has many challenges such as increasing pollution concentration and pollution movement between floors. In this article, the complete calculation of ventilation system in multilevel parking lots is presented and the effect of supply and exhaust vents height on pollution concentration and movement is investigated by using numerical simulation. Also, a new criterion for recognition of flow pattern is presented. In the numerical simulation, the conservation equations are solved by using openFoam. For validating the numerical simulation, the results are compared with available experimental results. Comparison of results showed good accuracy of numerical simulation. After that, the common multilevel parking lots are introduced and the effect of supply and exhaust vent heights on the amount of pollution in these parking lots is investigated. The results showed that, if the supply vents are installed on the non-dimensional heights of about 0.55 and exhaust vents are installed on the non-dimensional heights of about 0.55 to 0.7, the best ventilation flow pattern in the multilevel parking lots is obtained. Furthermore, by using the novel method of this paper, the ideal bulk flow velocity for development of piston flow in parking lot is obtained and the flow pattern tends to piston flow by optimizing the supply and exhaust vent heights.

In this paper, the non-Newtonian immiscible two-phase polymer flow in a petroleum reservoir has been investigated numerically. The fluid flow in a porous medium is simulated as a compressible flow. The Carreau-Yasuda constitutive equation is employed as the model of non-Newtonian fluid. The IMPES method is used for numerical simulation, in which the pressure equation is discretized and solved by an implicit approach and the saturation equation is solved by an explicit method. Results reveal that zeroshear rate viscosity has a high impact on the sweep efficiency of the reservoir and also controls the channeling and viscous fingering effects. In addition, increasing the viscosity of non-Newtonian fluid improves cumulative oil production and diminishes the viscous fingering phenomenon caused by injected fluid. The relaxation time of Carreau-Yasuda fluid, which is the elastic characteristic of the non-Newtonian fluid, cannot influence flow characteristics inside the reservoir for low permeability values, however, for higher permeability values its effect becomes more sensible. Increasing the injection rate leads to the increase of fluid production, while the injection rate has an optimum range to reach the optimum oil production. In addition, the effect of variation of the injected fluid properties on the polymer breakthrough time has been investigated and results presented.

In this study, the combined steam and organic Rankine cycles have been stimulated with high temperature wasted hot gases recovery from the energy and exergoeconomic points of view. In configuration of the combined cycles, the high-temperature wasted gases act as the source of steam cycle evaporator, then the decreased temperature exhaust gas of the steam cycle evaporator is used as the low temperature source of organic cycle evaporator. After this, the effects of changing different parameters such as evaporator temperature, condenser pressure and pinch temperature difference in steam cycle on the amount of total output work, total irreversibility, energy efficiency, exergy efficiency and exergoeconomic variables have been checked. The results in base state show that, energy and exergy efficiency of combined cycles are 0.2782 and 0.5279 respectively and the amount of output work and total irreversibility are 71401kW and 43616kW, respectively. Total exergoeconomic factor for the combined cycles is 12.47 percent, which represents a high exergy destruction in components and raising the initial cost of components in order to improve the performance of system is recommended. The evaporator, turbine and condenser are the components that should be considered from the perspective of exergoeconomics, as they contain the maximum amount of total initial costs and the cost of exergy destruction.

The design of complex mechanical systems usually involves multiple mutually coupled disciplines and competing objectives which require complicated and time-consuming interactive analysis during the design process. Multidisciplinary design optimization (MDO) is a systematic design methodology to improve the design efficiency of complex mechanical systems, specifically in non-cooperative design environments. On the other hand, game theory is a set of mathematical constructs that study the interaction between multiple intelligent rational decision makers. In this paper, a new game theoretic approach is proposed and applied for multi-objective MDO problems in non-cooperative design environments, considering the intrinsic similarity between the MDO and game theory. In this way, genetic programming is used as a surrogate to construct the approximate rational reaction sets (RRS) of players. Furthermore, in order to find the intersection of RRS of players in Nash game models, an objective function is proposed which should be minimized. The effectiveness of the proposed framework is demonstrated by the design of three case studies in the field of engineering design optimization in non-cooperative environment. The results show that the presented approach is able to approximate complicated RRS, and, in addition has the ability to find multiple Nash solutions when the Nash solution is not a singleton and generally found solutions better than those reported in the literature.

Parallel manipulators are mechanisms with closed kinematic chains that have been developed in different forms, but these manipulators have several drawbacks such as small workspace, existence of singular points in their workspace, and complex kinematics and dynamics equations that lead to increased difficulty in their control. In spite of this, these mechanisms have been conventionally used in many different industrial applications such as machining, motion simulators, medical robots, etc. To overcome these drawbacks, design and manufacturing of a manipulator with three translational degrees of freedom are provided. Design of this manipulator was based on the possibility of three translational motions for its end-effector. The manipulator degrees of freedom are obtained via screw theory. Basic features, consisting of forward and inverse kinematics, workspace and singularity analyses and also velocity analysis, are considered in this paper. A numerical algorithm is implemented to determine the workspace regarding applied joint limitations and the design parameters were extracted based on whether the desired workspace was achieved or not. The robot motion was created by three pneumatic actuators which receive their commands from pneumatic servo valves. After design steps, the required elements were provided and assembled in a robotic lab. Finally, the simulation results have clearly approved the robot improvement.

Ultrasonic waves have a variety of applications in bio field. The most important applications are diagnosis and treatment of diseases, drug delivery, cell separation and cell study. Passing ultrasonic waves through tissues and organs, which creates heat, bubble, stress and vibration, can result in chemical reactions, physical and biological changes. Scientific activities of many researchers in this area are focused to reduce the harmful effects and increase the usefulness of this beneficial tool. In current research, the interaction of two nonlinear phenomena, acoustic streaming due to passing ultrasonic waves through bio-fluid and non-Newtonian viscosity is studied numerically. Taking into account nonlinear effects of ultrasonic field, continuity, momentum and state equations are used. In this paper, parametric effects of wall impedance, inlet flow velocity and non-Newtonian viscosity models on acoustic streaming are investigated. Results indicate influence of inlet speed on acoustic streaming velocity magnitude and its ineffectiveness on acoustic streaming profile. By increasing wall impedance, acoustic streaming magnitude decreases. This reduction is more intense for non-Newtonian fluid. Considering non-Newtonian viscosity model for bio-fluid leads to velocity changes near boundaries, while it has less influence at domain middle.

Detonation engines are expected to be used as propulsion system in aerospace applications in the future. Several types of detonation engines are currently under examination, including the rotating detonation engine (RDE). In this work, the feasibility study for design of a laboratory sample RDE which has an annular geometry with diameter of 76 mm has been performed. In this sample, hydrogen and standard air are separately injected into the combustion chamber of detonation engine. First, numerical studies are validated comparing the FLUENT results with the experimental ones. Then, the geometry and equivalence ratio of injection mixture are investigated parametrically. Considering the negligible variations of thermodynamics parameters in the radial direction of flow field to reduce the computational costs, also a 2D model is used for numerical simulations. Three different equivalence ratios were employed. Results show for the case with the equivalence ratio of 1.2, detonation speed, pressure, and temperature behind detonation front is more than the equivalence ratio of 0.8. Also, maximum detonation speed and pressure behind detonation take place in stoichiometric conditions. The parametric study of the chamber length effects was also conducted using a length 0.5 and 2 times of the main chamber. Because the chamber outflow is subsonic at some regions, chamber length change has a significant effect on the engine performance and flow field. The results point out that increasing the chamber length in low injection pressure and high injection pressure leads to increasing and decreasing the height of detonation front, respectively.

Shape memory alloys (SMAs) are suitable candidates in various fields of engineering. One advantage of these alloys is their capabilities in developing high strain and force. In addition to these great features, lightweight and super-elastic behavior are other traits of these materials. These specifications are of such importance and allow SMAs to be suitably used in further engineering applications. However, their intrinsic hysteresis non-linear behavior makes their usage as position actuators difficult. Despite this challenge there are various methods proposed in the literature to model the hysteresis behavior of such materials. In this paper, a generalized Prandtl-Ishlinskii model, because of its simplicity, efficiency and inverse analytical capability, has been used for modeling the SMA behavior. In addition, the hysteresis modeling has been validated via experimental data of one of the articles. In the control section, however, two control systems consisting of PID and fuzzy sliding mode controllers have been used. Fuzzy sliding mode control system is a method that can be used in systems without mathematical model and leads to increased robustness. It is shown in this paper that by using this method, it is possible to apply a suitable control input to the system in order to remove the error signal. However, by using PID controllers, the error signal is not acceptable due to the constant controller coefficients. The results illustrate a more efficient performance of fuzzy sliding mode controller with respect to the classical PID controller.

In this paper, an explicit formulation of optimal line-of-sight strategy is derived in closed-loop for integrated guidance and control (IGC) system without consideration of fin deflection limit. The airframe dynamics is modeled by a second-order non minimum phase transfer function, describing short period approximation. In the derivation of our optimal control problem, the actuator is assumed to be perfect and without limitation on fin deflection, whereas fin deflection limit is applied for the performance analysis of the presented optimal IGC solution. The problem geometry is assumed in one dimension and the final position and final time are fixed. The formulation is obtained in four different normalized forms to give more insight into the design and performance analysis of the optimal IGC strategy. In addition, guidance gains are obtained analytically in explicit form for steady-state solution. In most cases, the performance of IGC is better than that of IGC with steady-state gains, but has more computational burden; however, it is reasonable for today’s microprocessors. Curve fitting or look-up table may be used instead for implementation of optimal IGC strategy. Moreover, parametric study of nondimensional IGC parameters is carried out, such as weighing factor, dc gain, and short period frequency. Finally, the performance of both IGC strategies is evaluated with airframe model uncertainties.

In this paper, simultaneous impact of two parallel drops on a thin liquid film is investigated using the lattice Boltzmann method. The purpose of this study is to investigate the effects of surface tension (characterized by Weber number), distance between two drops, and gas kinematic viscosity on the impact. The developed numerical model in this paper which is based on the Shan and Chen pseudo potential two-phase model makes it possible to access large density ratios, low viscosities, and tunable values of surface tension independent of the density ratio. The model is validated by comparing the coexistence densities with those of Maxwell analytical solution, evaluating the Laplace law for a droplet, and simulating single droplet impact on a thin liquid film. Simulation results of two drops simultaneous impact show that after impact, two jets raised between the drops join each other and form a central jet. Height of this jet increases with time leading to separation of secondary droplets from its tip. When the surface tension value is decreased, the central jet height is increased, but the size of the separated droplets is reduced. The crown shape observed in single drop impact is also seen in simultaneous impact of two drops. Increasing distance between two drops leads to a smaller central jet height and an increase in the crown radius. The crown height, however, was found to be independent of the distance. Finally, increasing gas kinematic viscosity reduces the central jet rising speed and delays separation of secondary droplets from the jet.

Alzheimer's is the most common form of dementia. Amyloid beta peptides play a key role in the pathology of Alzheimer's disease and the recent surveys have demonstrated that amyloid beta oligomers are the most toxic component of them. Among oligomers, considering the high durability of dimer in comparison to other kinds has more toxic effects. Prefoldin is a molecular chaperone which prevents accumulation of misfolded proteins. Prefoldin has demonstrated that it can also operate as a nano actuator. In this article, the interaction between the prefoldin nano actuator and dimeric pathogenic nano cargo in molecular dimensions is investigated; hence all-atom molecular dynamic simulation in explicit solvent was performed at physiological temperature. Visualizing the results and investigating the atomic distance between nano actuator and pathogenic nano cargo revealed that two arms of six arms of prefoldin nano actuator have been able to capture cargo and during the simulation they have made hydrogen bonds. Furthermore, investigating the hydrophobic effects between the hydrophobic amino acids in the cargo and nano actuator revealed that these effects have positively affected the stability of the binding between arms and the cargo. This article introduces prefoldin as an inhibitory factor for dimeric oligomer from amyloid beta.

Today, in most of the mining projects, especially with high operating capacity, using of AG and SAG mills become more common, due to their special features, comparing with other conventional grinding mills. Usually in comminution process a small percentage of energy is merely consumed by grinding and crushing processes. Also, the comminution process is dependent on many parameters such as: ore hardness, charge volume, size and geometry of ore, charge and size of balls, percentage of critical velocity of mill and liner profile. Therefore, achieving the optimum mentioned factors and consumed energy is of particular importance. Since, it is impossible to consider interaction of all effective parameters simultaneously, by employing experimental methods because of their high expenses and being time consuming, so in this research the effect of liner profile on comminution process was investigated by changing the height and angle of liners using numerical method (finite element methods, FEM). In this approach the height and angle of liners were determined by estimating the stress of the particles impacts with liners. The results showed that a liner with a height of 140 mm and an angle of 15 degrees has the maximum impact and breakage of particles. The results achieved from FEM model for the Sarcheshmeh Copper Complex SAG mill were in good agreement with the measured data from experimental SAG mill.

Serious increase of pollution from cars in the enclosed residential parking lots is an important challenge. Forecast and estimation of generated pollution from cars is applicable for proper design of residential car parks. In this article, the pollution concentration in a residential parking lot is measured experimentally and the results are used for validation of numerical solution. In the second part, the pollution is simulated in several parking lots and the equation of pollution incensement with time is proposed and offered in the form of analytical equation. By using this equation, the allowable time of man’s presence in these parking lots is offered.