نشریه مهندسی مکانیک مدرس
سال چهاردهم شماره 9 (آذر 1393)

Nowadays، solid tumor modeling and simulation results are used to predict how therapeutic drugs are transported to tumor cells by blood flow through capillaries and fluid flow in tissues. This model involves processes such as fluid diffusion، convective transport in extracellular matrix، and extravasation from blood vessels. In this paper، a complete model of interstitial fluid flow in tumor and normal tissue is presented with considering multi scale of solution such as blood flow through a capillary (as the smallest scale) to interstitial flow (as the biggest scale). The advanced mathematical model is used to generate a capillary network induce by tumor with two parent vessel around the tumor for the first time. In the following، the blood flow is modeled through the network with considering the non-continuous behavior of blood rheology and adaptability of capillary diameter to hemodynamics and metabolic stimuli. This flow is simultaneously simulated with interstitial flow which is coupled to blood flow through capillary with extravascular flow. The results predict elevated interstitial pressure in tumor region and heterogeneous capillary network which are introduced as barriers to drug delivery.

Calculation the cutting force in machining processes is of great importance. In this paper، undeformed chip thickness in one-dimensional ultrasonic vibration assisted milling is calculated and then، a model for determining the cutting force in this process is presented. Analytical relations show that in ultrasonic assisted milling (UAM)، the maximum cutting force is greater than in conventional milling (CM)، but the average cutting force is decreased. To verify the proposed relations، with the aid of a particular experimental setup، one-dimensional vibration in feed direction is applied to workpiece and cutting force in CM and UAM is measured experimentally. Greater maximum cutting force in UAM and decrease of average cutting force in UAM compared to CM is observed experimentally as well. Comparison of average values of cutting force shows that the analytical relations for predicting the cutting force have 16% average error in CM and 40% average error in UAM. Given that the analytical calculation of undeformed chip thickness and cutting force in UAM and also comparison of experimental forces with the modeled ones has been done in this paper for the first time، the accuracy of proposed relations are acceptable.

Due to the extreme increase in computational power over the recent years، numerical methods have gained the most proportion in analyzing composite structures and components because of the consideration complicated failure mechanisms such as delamination، fiber buckling and fiber breakage، matrix cracking، debonding ribs of skin and a combination of mentioned failure mechanisms. However exact three - dimensional modeling damages caused by impact phenomena is still a challenge. In present numerical work، the most advanced modeling techniques have been used to predict the behavior of composite structure under high velocity impact. The ribs and layers have been modeled using solid elements and a user defined material model with modified puck and Hashin (3D) failure criteria was implemented. Because these failure criteria do not exist in Commercial version of the Abaqus software، we have used Fortran software for writing these criteria so this capability was added to the software. Figures of velocity variations and force variations of projectile، damaged area، different mechanisms of fracture were reported as results and commented upon. In this study، The numerical results have been validated with experimental data and show very good agreement.

In this research، Discrete Element Method (DEM) or in other words، Molecular Dynamics (MD) is employed for simulation of sorting process of granular materials which is done by means of a linear vibratingscreen device. To model the interaction forces between the particles and walls، short range viscoelastic Hertz potential has been used. Spherical and rectangular shapeswere considered for the particles and the screen mesh aperturesrespectively; and a linear vibration is applied to the mesh surface. During the simulation، differential governing equations of the granules motions are solved numerically to predict their behavior. The required programs were developed to perform the simulations using the open source code، LIGGHTS; and the factors affecting numerical computationswere tuned to obtain suitable values. Numerous simulations were done to study the effects of different parameters includingmeshinclination،vibration frequency،vibration angle and apertures'' size onthe sorting performance; and the correlations are reported graphically. The obtained results are verified by comparison with the adequate ones reported in open literature. Although the current research is not limited to a special case، some data related to the characteristics of iron pellet and the screen device in Gol-e-Gohar pellet factory are employed for numerical studies.

In this study، the effect of inlet supply temperature on energy consumption optimization، thermal comfort and mean local air age has been investigated for a displacement ventilation inside a typical room. Based on the results obtained from this study، an increase in the inlet supply temperature for a displacement ventilation from 17. 8 to 25. 8 in summer leads to a 50% reduction of consumed energy. Owing to the fact that optimization of consumed energy is an action bound to maintain thermal comfort of occupants، PMV (predicted mean vote) and PPD (predicted percentage of dissatisfied) parameters as two general thermal comfort indices have been investigated. In addition temperature gradient in vertical direction as local thermal discomfort index and mean local air age as air quality index have been probed. All the aforementioned indices except that of mean local air age، lie within the sightly range of ISO7730 standard with an increase in temperature، but air quality index experiences some quality drop in inhalation region، This slight drop is negligible and displacement ventilation system can be used as a suitable ventilation system for summer applications.

Modeling of a Sport Utility Vehicle as it moves on two wheels studied in this paper. Our major purpose concentrated on developing a general criterion to specify rollover threshold. First، model of vehicle as it sustained on two wheels derived that its results used to develop rollover threshold of Sport Utility Vehicles. In addition، these results could be valuable to design new controllers، which are able to prevent rollover at the best state of vehicle dynamics. After vehicle modeling، appropriate model for tire forces and moments picked up from the most related and available references. Then validation accomplished as final part of modeling section. Stability of presented model studied as an important part of this paper. In order to specify rollover threshold as vehicle moves on two wheels، steady-state equations of motion used and based on steady state analyses a new criterion proposed. Next، by designing some maneuvers، simulations accomplished to show applicability of proposed criterion at different situations. As conclusion، presented criterion is more implementable and efficient than other proposed model for rollover threshold and can prospect rollover threshold at various steering angles and longitudinal speeds as model inputs.

In the present study، fabrication and performance testing of a flameless catalytic pad has been investigated. The catalyst was prepared with 1g of H2PtCl6. 6H2O solved in 0. 5 liter solvent contains 50% water and 50% ethanol and sprayed on the alumina - silica fiber mat as the catalyst support. The wet pad was dried and calcined before usage. The performance of the heater was evaluated by design and fabrication of a test stand which was capable of measuring parameters such as temperature at surface and in depth of the catalyst layer، the amount of pollutants such as CO and NOx، flow rate and pressure of the fuel and surface air circulation in front of the pad. In addition، by placing the panel containing the pad in an environmental test chamber، the effect of different climate conditions in five cities of Iran، i. e.، Borojerd، Khalkhal، Lavan، Mahshahr and Puladshahr were investigated. Average surface temperature of the pad was measured about 350°C. No NOx was detected and CO emission of the burner was measured up to 5ppm. In Khalkhal conditions with the lowest temperature and humidity، the highest temperature at surface was recorded and the maximum CO emissions in Mahshahr with the highest temperature and humidity was about 3ppm. It was shown that increasing the fuel flow rate increases the surface temperature and CO emissions. It was also shown that an increase of environment temperature and humidity، increases the surface temperature.

In this paper، an analytical method is presented to study thermo-elastic behavior of nanoscale spherical shell subjected to thermal shock based on nonlocal elasticity theory. The shell is considered as elastic، homogeneous and isotropic solid. The nonlocal differential equation of motion is derived in terms of radial displacement. The analytical solution of equation of motion is obtained by Laplace transform and differential transform method (DTM). Mechanical boundary conditions are used to obtain unknown parameters that get in recurrence equation in Laplace domain. The results in Laplace domain is transferred to time domain by employing the fast inverse Laplace transform method (FLIT). Accuracy of obtained results is evaluated by well-known similar articles. The results have a good agreement in comparison with published data in pervious literatures. Also، the effects of nonlocal parameter and wall thickness of shell on the dynamic characteristics of nanoscale spherical shell are studied in various points across the thickness of shell under thermal shock. The present analytical method provides an appropriate field for analysis of times histories of radial and hoop stresses in a nanoscale shells subjected to various time dependent thermo-mechanical loads.

A new complete system model of a flapping wing has been derived which consists of all effective parameters. Flapping mechanism can deliver maneuverability as well as low speed flight capability in MAVs. Here a validated aeroelastic model is being developed based on the wing torsional deformation assumption. Based on the proposed model complete parameter study could be performed and consequently the optimization requirements can be extracted. Experimental results of a static test stand have been used for validation. Performance indices، composed of force generated، power consumption and efficiency are depicted in terms of stiffness and kinematic properties. The average behavior is being referred. It is revealed that by changing frequency and speed، the optimum values for stiffness and amplitude are independent. Therefore using suitable kinematics one can utilize specified constant stiffness to optimize the flapping robot flight.

Multi-pass welding process is one of the most applicative methods of welding in various industries. In this paper، temperature and residual stress distribution due to three pass welding of two plates made of AISI 321 stainless steel having different thicknesses is studied. Welding process consists of three welding passes of two Shielded Metal Arc Welding (SMAW) process and one Gas Tungsten Arc Welding (GTAW) process. First، the benchmark plates are manufactured and welding process is performed. The transient temperature distribution during the welding process is recorded using thermocouples attached to the welding plates. First this process simulated experimentally and temperature distribution during to welding process was measured using thermocouples. Furthermore، the final residual stress distribution after welding process is measured using incremental center hole drilling technique (ICHD). The three pass welding process was then simulated using ABAQUS finite element (FE) code. The finite element model consists of temperature-dependent properties of base metal and weld metal. Furthermore، moving heat source and the element-birth technique is implemented in FE model. Experimentally measured temperature and residual stresses provide an in-depth knowledge insight the complicated welding process.. Comparing between the results shows that the numerical predictions and experimental measurements have good agreement and therefore the FE developed model can be employed in designing and evaluating of welded structures.

In this study، the first mode of stress intensity factor of semi-elliptical circumferential crack in the outer surface of a cylinder with radius to thickness ratio of 30، is investigated. The cylinder is applied in semi-submersible drilling platforms. First، the stress field of the cylinder under thermal and mechanical loads is extracted based on semi couple thermo-elastic equations. Then، the weight functions are derived for deepest and surface points using three reference loads results. Explicit expressions of stress intensity factors for surface and deepest points are presented using thermo-elastic stress field and the weight functions of the cracked cylinder. The results obtained by proposed weight functions and those obtained by finite element method and those presented in the literatures have a good accuracy. The interaction effects of thermal and mechanical loads on the stress intensity factors are studied. The results show that with increasing load ratio، the dimensionless stress intensity factors of deepest and surface points، decrease and increase، respectively.

Axial compression behavior of foam materials can be explained by two ideal deformation scenarios: discrete crush band process and progressive collapse. In this paper، a perfectly new model for strength assessment and quantitative/qualitative description of one-dimensional progressive collapse of aluminum foams under impulsive loadings is presented and its capability to split this way of crushing into two distinct regimes of shock wave and elastic- plasic wave propagation is highlighted. Then، using conservation relations and the new introduced model، the analytical solution of dynamic deformation of aluminum foams in the two mentioned regimes is developed. Regime 2 considers the case when the crushing front velocity is lower than the linear sound velocity of the foam; but remains higher than the effective sound velocity for a perturbation in which the amplitude lies in the so-called “plateau region’ of the static stress-strain diagram. The physical difference between this regime and the fiest one entails not only the creation a shock front associated with the collapsing foam، but also an acoustic precursor in the case of second regime. Finite element simulation is also performed to validate the analytical procedure. The numerical prediction is found to be in very good agreement with the analytical results.

One of the most applicable methods to study the mechanical behavior of reinforced polymers with CNTs is modeling of representative volume element (RVE). It has been shown that the mechanical behavior of RVE depends on its ingredients mechanical properties and its geometrical parameters. In this research، a RVE which includes a CNT and its surrounding polymer is chosen as a rectangular cube. In this research، effects of the length and depth of the RVE، the length of the CNT and the CNT caps on the elastic behavior of the RVE have been studied. Furthermore، the effect of the volume fraction of CNTs is also considered. First، an analytical solution has been developed to predict the elastic modulus of the RVE. Then، using a finite element method، the elastic behavior of the RVE is modeled. The analytical and numerical results show that at a constant volume fraction of the CNT، variation of each material and geometrical parameters can affect the longitudinal elastic modulus of the RVE significantly. However، it has been shown that the transverse elastic modulus of RVE is not sensitive to the geometrical parameters variations. Finally، using a combination of the Halpin-Tsai micromechanical model and the present analytical solution، a proper aspect ratio of the RVE for each volume fraction of the CNT has been determined and suggested.

In reverse engineering it may be required to perform multiple measurements due to the size and part complexity limitations of the physical equipment CMM / Optical Scanner and / or settings. To model the whole part it is required to bring different point sets obtained during different scans to a common coordinate system. Registration process for point clouds is to find the geometric transform between them in which all point clouds are transformed into a single absolute coordinate system. Theoretically، it is very straight forward to perform registration by finding the six components of transformation matrix (3 angles plus 3 displacements) and this can be mathematically determined if three non-linear points are known in both global and local coordinate systems. The process of registration is strongly affected by inaccurate data and may fail in the case of noisy data، hence other methods are usually sought to find the transformation matrix. This paper tries to solve the problem in practical applications. The Nelder-Mead method was employ for point clouds registration for the first time. The registration was also performed using Singular value decomposition and Genetic Algorithm methods. The three methods were compared in terms of convergence، accuracy and computation time.

The Prandtl-Ishlinskii (P-I) model is one of the powerful models which is used in modeling complex hysteretic nonlinear behavior in systems. The initial form of this model، called the Classical Prandtl-Ishlinskii model، cannot describe systems with output saturation and also results have considerable error when there is an asymmetric in hysteresis loops. In order to eliminate these defects، some modifications are applied to the Classical Prandtl-Ishlinskii model and these models are called the generalized or modified Prandtl-Ishlinskii models. This model is usually utilized in modeling complex hysteresis nonlinear behavior in piezoceramic، piezoelectric، magnetostrictive and shape memory alloy actuators، but in this work، the model is used for identification hysteresis behavior of hydraulic proportional relief valve consist of asymmetric hysteresis loops. This model is trained by the experimental data which are obtained of hydraulic proportional relief valve and then the parameters of the model are identified in order to adapt the model response to the real hysteretic behavior. The data consist of the descending reversal curves of major loop. Then the accuracy of the obtained model in predicting nonlinear hysteresis behavior of the valve is validated with some different experimental data. The results show this model has well accurate and good ability in behavior prediction of proportional relief valve.

The use of stop drill holes is one of the most convenient methods for reducing the stress intensity factors and crack growth rate. The efficiency of stop drill holes on the crack growth retardation depends on the amount of reduction in stress intensity factors. The curved plates are frequently used in engineering structures. Therefore، in this paper، by using the finite element method، the effects of configurations and diameters of crack flank holes on the variations of stress intensity factor are studied for a curved plate. The numerical results indicate that the location and the size of stop drill holes affect the stress intensity factors which is mainly due to their interaction with the crack tip stresses. Closer distances to the crack tip and larger diameters of the flank holes provide more reduction in the stress intensity factors. Also، the finite element results show that the use of stop drill hole method for the curved plates has the same efficiency as that of the flat plates.

In this article the effect of hot rolling process on properties and microstructure of Al-B4C composite is investigated. To produce the composite samples، 3 vol. % B4C particles with 300 nm average grain size added to melted Al-356 alloy. Rolling process was done at 350 °C on vortex samples that is made after 15 minutes mixing at 850 °C. Porosimetry، hardness and tensile strength tests were carried out to investigate the physical and mechanical properties of composite samples. Microstructures of the samples were also investigated by using scanning electron microscopy. The results indicate lowering the amount of porosity، increasing hardness and increasing tensile strength of rolling composites. The amount of porosity before rolling process was 2. 05% that is decreased to 0. 35% after rolling process. Tensile strength and hardness of composites before and after rolling process achieved 178 MPa and 293 MPa and 62 HBN and 101 HBN respectively. Also hot rolling process caused to more ductile fracture of composites that is produced by vortex. Tensile strength and hardness of composites before and after rolling process achieved 178 MPa and 293 MPa and 62 HBN and 101 HBN respectively. Also hot rolling process caused to more ductile fracture of composites that is produced by vortex.

Variation of the cross-sectional area of a channel affects the flow field and، therefore، convective heat transfer between the fluid and channel walls. In this paper، a geometrical model is proposed for a wavy channel carrying steady laminar flow of an incompressible fluid. The two-dimensional channel is modeled as a combination of a number of subsonic diffusers and nozzles. Effects of the geometrical characteristics such as length، boundary shape and symmetry of the channel، which describe the shape of these nozzles and diffusers، are investigated. Numerical studies at Re=200 show that the shape of the wall does not dramatically affect the convection heat transfer rate in the steady laminar regime. However، optimization studies can be carried out to change the shape of the channel and improve the average Nusselt number to some extent. It is shown that the average Nusselt number increases with the increase of the length of the diffuser part، but the asymmetry of the channel might increase or decrease the average Nusselt number. Finally، a genetic algorithm is introduced and used to optimize the geometrical parameters which describe the aforementioned nozzles and diffusers and، hence، the shape of the channel.

In the present study، central composite algorithm was used in order to model and optimize the mechanical behavior of “glass fiber reinforced epoxy composite - structural steel “connections. Initial tests showed that the polymer curing variables play a significant role as key process parameters in producing strong and reliable connections. After conducting Thermal Gravimeteric Analysis on polymer، by selecting curing time and curing temperature as input variables، the parameters were coded and each of them was studied in five levels. In order to estimate the desirable response and provide appropriate models، thirteen tests were conducted systematically. In order to assess the accuracy and to validate the proposed model، analysis of variance was performed successfully. The effect of curing time and curing temperature on the connection’s strength quality was studied utilizing two-dimensional graphs. Utilizing this approach the optimal bonding process variables was achieved at 40°C and 180 min for curing temperature and curing time respectively. Finally، the results obtained from micro structural characterization and fractography analyses of joints by Optical and Scanning Electron Microscope were in good agreement with the results achieved by the developed model.

Drowsy driving is a main cause of severe accidents. Drowsiness is responsible for 30% to 37% of fatal road accident in Iran. In this paper، driver drowsiness is detected based on features related to the steering wheel angle and the lateral position of the vehicle. Data from the vehicle and the virtual road are used to extract drowsiness features. Experimental results using a driving simulator are presented. Participants were 21 to 28 year-old males with a high tendency to sleep (Epworth Sleepiness Scale≥10). The subjects had to drive a lane keeping scenario on a long and monotonous virtual road in both drowsy and alert states. The drowsiness criteria are validated with Karolinska Sleepiness Scale (KSS) and video rating based on KSS measurements. The results illustrate that the phase diagram of the steering wheel angle (Ellipse criterion)، the standard deviation of the steering wheel angle، and the mean and the standard deviation of the lateral position of the vehicle are highly correlated with drowsiness. The accuracy of the diagnosis was 77% for the Ellipse criterion، 76% for the standard deviation of the steering wheel angle، 67% for the standard deviation of the lateral position، and 65% for the mean value of the lateral position.

The present research deals with the impact response of notched aluminum plates repaired by fiber metal laminate (FML) patches under various temperatures using drop weight impact test status. Some aluminum samples repaired by FML patches were prepaired to study their impact behavior and frcture mechanisms under drop weight tests at the temperature range of -20 ℃ to 60 ℃. An Energy Profiling Diagram (EPD) was used to obtain the penetration and perforation thresholds of hybrid composites. Besides، the effect of temperature on some impact characteristics such as endurance load، contact time and permanent deflection were also studied. The results showed that the amount of force for nearly all of the samples increased by increasing of the room temperature. The ability of energy absorption of the samples was also the most at the room temperature، therefore the energy thereshold of samples increases by increasing of the room temperature. Temperature variation also affects on the impact characteristics of composites patches and in some cases results in a 20 percent reduce in impact strength of the samples. It was also shown that the most value of impact parameters reaches at -20 ℃ and 60 ℃.

In this study، the effects of magnetic field on the flow field، heat transfer and entropy generation of Cu-water nanofluid mixed convection in a trapezoidal enclosure have been investigated، numerically. The side walls of the cavity are insulated، the top lid is cold and moving toward right or left and bottom wall is hot and the side walls angle from the horizon is 45˚. The results showed that with imposing the magnetic field and enhancing it، the nanofluid convection and the strength of flow decrease and the flow tends toward natural convection and finally toward pure conduction. For this reason، for all of the considered Reynolds numbers and volume fractions، by increasing the Hartmann number the average Nusselt number decreases. Furthermore، for any case with constant Reynolds and Hartmann numbers by increasing the volume fraction of nanoparticles the maximum stream function decreases. For all of the studied cases، entropy generation due to friction is negligible and the total entropy generation is mainly due to irreversibility associated with heat transfer and variation of the total entropy generation with Hartmann number is similar to that of the average Nusselt number. With change in lid movement direction at Reynolds number of 30 the average Nusselt number and total entropy generation are changed، but at Reynolds number of 1000 it has a negligible effect.

In this work، adhesion system for wall climbing robots، known as «vortex attractor»، has been studied analytically، numerically and experimentally. Vortex attractor system consists of the following components: vortex cup، centrifugal fan and an electrical motor. In this design، vortex flow which is generated at the fan impeller eye produces a considerable suction pressure. Knowing this fact that the air flow is trapped inside the cup، the suction force increases and also power consumption is reduced. Firstly، an attractor system is manufactured considering necessary measurement facilities. The effect of different parameters such as rotational speed and gap between system and surface on system performance is investigated. Numerical simulation of vortex attractor system is performed using CFX software. The numerical results were verified through grid independency and validated with comparison with those obtained from measurements. In the next step analytical study is carried out using Rankine vortex. Experimental results show that as gap increases، power consumption increases. In the case of vortex attractor stick to surface، repulsive force is observed. Analytical results show that generated force and pressure are proportional to square of rotational speed.

This study focuses on transition of laminar to turbulent flow around a symmetrical airfoil at a low Reynolds number in free flow and flow near the ground at different angles of attack. Finite volume method is adopted to solve the unsteady Reynolds-averaged Navier–Stokes (RANS) equation. Flow around the symmetrical airfoil SD8020 at a low Reynolds number (4000) at 5 and 8 degree angle attack has been simulated in free stream and near the groundnumerically. Current numerical result is compared with other’s experiment and numerical result in free flow at low Reynolds number and flow in ground effect that good agreement has been obtained in aerodynamic coefficient prediction. SIMPLEC method is used for pressure and velocity coupling and flow equations discrete with Quick method. Transition-SST model is used for modeling turbulence of flow. Result shows that the current numerical method can detect adverse pressure gradient، laminar separation bubble and transition of laminar flow to turbulent. According to the result، in ground effect location of laminar separation bubble، length of bubble and location of transition is moved to leading edge and pressure distribution is effected by location of laminar separation bubble.