Modares Mechanical Engineering
Year:2015 | Volume:14 | Issue:13|Papers Count:39

Cardiovascular diseases area major cause of death in the world and are closely related to the dynamics of the blood and arterial wall mechanics. Not only in the cardiovascular system, but also in the whole body system, the heart is the most important organ, if the blood vessels of the heart are blocked heart function will be impaired. Effective solutions to resolve blockage of coronary is the bypass surgery in which are placement vessel for the blood supply to the heart. So studying the behavior of the vessels that are used for the bypass is important. The goal of this study is the investigation of the mechanical behavior of saphenous vein by using the tensile biaxial tests. Eight human saphenous samples were obtainedand the planar biaxial tests were performed on the tissue specimens by applying simultaneous loads along the circumferential and longitudinal directions. Then the measured data were fitted into the four-parameter Fung-type model and also to the five-parameter Mooney-Rivlin model, this could be used in finite element packages for numerical analysis. The specimens were stiffer in the longitudinal than in the circumferential direction. The specimens showed some degree of anisotropy.

In this paper an efficient algorithm of system design with reliability approach is presented. Using this algorithm in subsystem designing of spatial systems may lead to systematically optimized design with reliability parameters attitude. By applying item tree parameters, including general subsystem parameters into the algorithm and by knowing failure modes and the occurrence rate of each failure mode, the design may be improved and necessary reconsiderations can be applied in order to prevent or reduce the probability of failure mode. Moreover, dynamic behavior of system is determined and steady state response of system is obtained according to initial conditions. First, some basic conceptual definitions including reliability, availability, capacity and failure rate are explained, then various reliability analysis methods like Fault Tree Analysis (FTA), Failure Mode Effect Analysis (FMEA), Reliability Block Diagram (RBD) and Markov analysis are discussed. Reliability and availability distribution over different phases of unlocking and deploying mechanisms are illustrated using Windchill solution. Subsequently the effect of the different ranges of failure rates of added components on reliability, availability and capacity of whole system is investigated. By analyzing the reliability and availability of system for different phases, it was found that the whole system is under stable situation at the end of each phase. Also, results showed that the reliability, availability and capacity of whole system increased and reached a stable level by minimizing the failure rate of the redundant components.

In this study, forced convective heat transfer and pressure drop behavior of multi walled carbon nanotubes (CNT) - water nanofluid were evaluated under constant heat flux in a circular tube. For this purpose, first, homogeneous aqueous suspension of CNT using gum Arabic (GA) surfactant was prepared in concentrations 0.05%, 0.1% and 0.2% wt. Then, the above mentioned nanofluids were evaluated in Reynolds number range of 800-2000 under constant heat flux. The results indicatea significant increase in convective heat transfer coefficient of nanofluids with the addition of small amounts of CNT in deionized water. Also, heat transfer coefficient is enhanced with increasing concentration and Reynolds number. However, the effect of increasing concentrations of CNT is higher than the increase in Reynolds number. In addition, the pressure drop data on the different concentrations and Reynolds numbers are also investigated. At low weight concentrations of CNT, the deal of pressure drop of nanofluids containing CNT and base fluids is approximately similar and the gap between them is negligible. This means that no extra pump power is required for low concentration CNT/water nanofluid. The maximum increase in heat transfer coefficient is 42.8%, which occurred at Re=2027, anda concentration of 0.2% wt.

The need for complex surfaces in CAD motivates researchers for methods which can produce smooth and visually pleasing surfaces. In this research, a new method is presented for creating compatible cross-sectional curves for surface fitting to certain sections or lofting. In this method, the distribution of sections' data points along with basis knot vectors are improved in order to reacha desired smooth surface. In compatibility process, the section curves' degrees and their knot vectors must be set equal before implementing lofting process. Based on proposed algorithm, in this research, the constructed smooth and faired surfaces can be used in many engineering applications such as reverse engineering, biomedical engineering, quality control, etc. The main focus of the method is improvement of data points' distributions and their assigned parameters in a way that by a few iterations, data points' distribution are improved in order to reacha common knot vector for all cross-sectional curves. The method is implemented on some benchmarking examples and its efficiency are confirmed. In addition, the amount of final data points' deviation from the initial section curve is analyzed using the vigorous Hausdorff method. It is worth mentioning that the quality of obtained final surface is visually pleasing. In order to quantitatively confirm that the proposed method will result in smooth and fair surfaces, MVS is used. Finally the application of the method in modeling the root joint zone of a wind turbine blade is presented.

In this paper, the buckling of rectangular plates subjected to non-uniform in-plane loading is investigated. At first the equilibrium equations of plate based on the first order shear deformation theory have been extracted. The kinematic relations have been assumed based on the von-Karman model and the Hook’s law has been considered as the constitutive equations. The adjacent equilibrium method has been used for deriving the stability equations. The equilibrium equations which are related to the prebuckling stress distribution have been solved using the differential equations theory. To determine the buckling load of a simply supported plate, the Galerkin method has been used for solving the stability equations which area system of differential equations with variable coefficients. In this paper, four types of in-plane loading, including the uniform, parabolic, cosine and triangular loading, have been considered and the effects of the plate aspect ratio and thickness on the buckling load has been investigated and the results have been compared with the finite element method and the classical plate theory. The comparison of the results show that for all loading cases, the buckling load computed by the classical plate theory is higher than the value obtained based on first order shear deformation theory.

In the present paper, mixed convection of TiO2-water nanofluid in a laminar flow within a vertical rectangular duct is investigated numerically. A single phase and a two phase method is applied to simulate nanoparticles dispersion in the base fluid. An Euler-Lagrange approach is employed to track particles individually. In this approach, the base fluid is assumed to be a continuous phase while the particles are dispersed through it. The presence of particles in the base fluid is modeled as a source term in the momentum and energy equations. Governing equations are discretized using Control Volume based Finite Element Method (CVFEM). Effects of nanoparticles concentration, particles size, aspect ratio of cross section, asymmetrical boundary condition and buoyancy on the hydrodynamics and thermal parameters are presented and discussed. It is observed that increasing nanoparticles concentration enhances heat transfer rate and this enhancement is more considerable in higher aspect ratios. Also, at smaller values of Richardson number (Ri) where the effect of forced convection is more than natural convection, dispersion of nanoparticles in the base fluid improves heat transfer rate more considerably. Whilst an improvement in convective heat transfer is shown to be more than 6.5% at Ri=0.5, it does not exceed 4% at Ri=5.

In this paper, the efficiency of PEM fuel cell system by using ejector for returning the additional fuel in the fuel supply circuit and comparison with conventional systems with compressor in fuel supply circuit, are studied. For this purpose a semi-analytical developed model for calculating the amount of efficiency increment, as well as the amount of power saving as a result of employing ejector in the fuel cell return line is provided by extending the previous models. In this developed model the important stack design parameters and ejector design parameters are correlated by presenting a new dimensionless parameter. The results for a typical fuel cell show that the amount of efficiency increment at different values of current density is different and there is a maximum point for it. The amount of power saving as a result of employing ejector compared with fuel cell power is considerable and will increase with increasing the current density. These results indicate that the ejector for those applications that require high power (for instance the transport applications) is more efficient.

Compression stiffened panels are reinforced skins that are mainly subjected to axial compressive load and are widely used in aerospace structures. Iterative design loops are the common methods for these types of structure. Design methodology based on structural index concept is a coupled design and analysis method. In this method detailed design of the compression stiffened panel is fully accomplished based on the key parameters of structural index and material properties of the panel. The complete design is obtained in single stage in an analytical and explicit manner. In this paper the design methodology of stiffened panel using structural index concept that could be applied on selective configuration of compression stiffened panel (including selection of stiffener type and the type of panel: integral or skin-stringer) is analyzed. The results are extracted and modified from two different approaches to manage the results of common iteration methods that are currently used in the preliminary sizing of stiffened panel. This procedure could be regarded as a near optimum design and therefore would be more conservative with respect to common methods. Final results of the derived methodology are compared with reported and FEM results. The results could be considered an acceptable design; furthermore, they can be used as an appropriate starting point in numerical optimization methods.

Nowadays, using renewable energies, specifically ocean wave energy, is of importance in the world. One of the methods by which this energy can be harnessed is through using axial turbines with low head. In this study, performance of an ocean wave axial turbine of Wells type installed on the floating oscillating platform has been numerically studied. The length of the oscillating platform is equal with the wave length of the ocean and the Wells turbine is installed at the center of oscillation platform. This design causes the inlet flow rate to be doubled which in turn increases the power. In this way, the governing equations include continuity and momentum equations have been solved considering k-wSST turbulence model in the rotating frame. The obtained results have been verified through mesh independency analysis and have been validated by comparison with the available experimental data. The results show that with decreasing the clearance by 2% of the chord length, the maximum efficiency, which is approximately 35%, will be gained. Moreover, by varying the blade angles from0 to 12oatthe different flow coefficients, the turbine performance is improved at the off-design points. Also, employing a blade with variable profile will lead to postponing stall phenomena. Moreover, employing multistage turbines with guide vanes at the mid stage can improve efficiency by 9 percent.

The present numerical study investigates the effect of a bluff body on outer wall temperature in micro scale combustor. Combustion of lean premixed hydrogen-air mixture is simulated in two dimensions domain utilizing the detailed chemistry of Li et al. (13 species with 19 chemical reactions) and different mass diffusivity for each species. The effect of bluff body in combustor is studied in two viewpoints: shape of bluff body and number of bluff bodies. Two shapes of bluff body including square and triangular shape are considered to study the combustion efficiency and outer wall temperature. The results illustrate that the shape of bluff body does not have an obvious effect on outer wall temperature so triangular shape outer wall temperature is slightly higher than square shape. However combustion efficiency of the square bluff body is larger than the triangular one. In the second part, the effect of bluff body number (i.e. one, two and four bluff bodies) in micro scale combustor is examined on combustion characteristics. With the increasing number of bluff bodies, the outer wall temperature increases. This is because of the creation of a uniform temperature field in micro scale combustor.

In hydroforming process, applying hydraulic pressure to the inner surface of tube along with axial loads to two ends of tube simultaneously causes the tube to be formed to the die shape. Application of finite element simulation is a common practice to predict the geometrical dimensions of the produced part and analysis of probable defects. For finite element simulation, precise mechanical properties of tube material are required. Obtaining these properties from a test similar to the tube hydroforming process is desirable. In this study hydraulic bulge test using T-shape die has been introduced to obtain the stress-strain curve of the tube material. Using hydroforming set-up, several experiments were carried out on C12200 copper alloy samples. Geometrical parameters required to be used in analytical solutions have been identified and the stress-strain curve has been plotted. The results of the proposed experiment have been compared to the results of the tensile test. In addition, the effects of anisotropy on the obtained stress-strain curve of both tests have been determined. The stress-strain curve obtained has been used to plot the forming limit diagram. The bulge test mechanical properties and the forming limit diagram have been applied to simulate the tube bursting and prediction of the final part of geometrical dimensions in T-shape tube hydroforming and these results have been compared to the part being experimentally produced by hydroforming. The results show that when stress-strain curve obtained by the proposed experiment is used, there is good agreement between the simulated hydroformed part and the part being produced experimentally.

In this paper, the Finite Cell Method (FCM) is used to predict the ductile damage and crack evolution in ductile materials under small strains and nonlinear isotropic hardening conditions. In the first step, a fully coupled elastic-plastic-damage model based on modified Lemaitre ductile damage model was developed and implemented into FCM implicit codes. Also, the effect of micro crack closure, which may dramatically decrease the rate of damage growth under compression, was incorporated and its computational implementation discussed. The FCM is the result of combining the p-version finite element and fictitious domain methods, and has been shown to be effective in solving problems with complicated geometries for which the meshing procedure can be quite expensive. It, therefore, combines fast and simple mesh generation with a high convergence rate inherited from p-FEM. The performance of the FCM and damage model was verified by means of numerical examples and the results were compared with experimental observation. The results showed that modified Lemaitre damage model can be used as a quick and accurate tool to predict ductile damage and fracture in metal forming processes.

In this research, dynamic behavior of non-linear finite element model of a drillstring is investigated. By considering total length of drillstring, a three-dimensional timoshenko beam element is employed. In addition the geometric stiffening effect, the added fluid mass and the contact between different parts of the drillstring and the borehole wall has been considered, with a more complete model than previous studies, the effects of these factors have been analyzed separately. The equations of motion are obtained and full order equations are used to drive the results. For the first time, a domain of drillstring points that the possibility of contact occurrence in them is more than other points, have been identified. The natural frequencies of the drillstring are evaluated and compared with the available commercial software results and recorded results for the actual drillstring. Coupling of vibrations of model is tested and the effect of linear and nonlinear model in analysis of dynamic behavior and vibration of drillstring, especially in contact with the borehole wall and the effect of weight on bit change on the contact at stabilizers are analyzed and for the first time, the contact time in each of stabilizers have been evaluated.

In this research, a Mach reflection and its effect on explosive free forming of confined cylindrical shells are studied numerically. This shells were manufactured from extruded 6063-T5 Aluminum alloy. The diameter of shell was 1.5 times larger than its length. Its ends were sealed with rigid sheets. The simulation of formation of Mach reflection and plastic response of shell were done with Autodyne hydrocode and coupled Lagrangian-Eulrian spatial discretization. Formation of Mach reflection occurred on end plates. It is observed that the generated pressure in an area that is affected by Mach stem is higher than elsewhere. This phenomena causes rupture in boundaries area of shell to plate connections, before forming process. The maximum of transverse deformation that obtained from this study compared with experimental results which done in explosion mechanic laboratory in K. N. Toosi university of technology. The experimental and numerical results shows more than 93% agreement. Meanwhile, because of blast waves reflection and interaction of waves, coupled Lagrangian-Eulrian method is suitable method for investigation of internal explosion problems. In addition failure modes was simulated with finite element software Abaqus and good agreement was found between the results.

Optimal trajectory planning is an important task which is required in most of guidance missions. This paper introduces a new method that utilizes the most important characteristics of global optimization methods along with a new gradient -based method in a two layered scheme for the trajectory planning. In the first layer to construct a convenient shooting method based algorithm, some of the most important global methods of optimization are used in an information transform structure. Exchanging the information between selected algorithms helps for increasing the efficiency of problem solving. To do this, a comprehensive model for parameterization of the control history is introduced which allows the method to search for the best profile in a variety of different profiles. Results of this layer are transformed to the second layer that uses one of direct methods of solving the optimal control problems. This gradient based method named Radau pseudospectral method using of the results of global methods, completes the optimization process. Finally, developed algorithm is used to find the optimal trajectory of a reentry capsule and effects of the path constraint values on the total heat absorbed is investigated.

This paper presented a theoretical model to investigate steady plastic shock wave on FCC metals.The method included shear flow stress according to effective parameters and based on microstructure and dynamics of dislocation method. The aim of this paper was to achieve final relation between shear stress and plastic stretch with presenting constitutive equations for shock loading. Then, Shear flow stress to effective plastic strain was plotted with solving final relation between shear flow stress and plastic stretch. Presented constitutive equations were based on loading under one dimensional strain and were validated just for shock loadings. The main innovation of this investigation included using from energy constitutive law with considering entropy generation rate. Entropy generation rate expressed as dislocation generation, dislocation annihilation and dislocation glide. Also, the effect of shock velocity, total stretch and input stress according to plastic stretch were investigated. Furthermore, shock structure was investigated according to different input stresses. Maximum input stress was 25 GPa. Relations and diagrams were verified with published experimental works on Al 6061 alloy. Good agreement was found between presented model and experimental works.

A vibration absorber is used to reduce vibration of an Euler-Bernoulli beam with elastic supports subjected to a moving oscillator. Dynamic response of the beam under moving harmonic exciter with different moving velocities and different parameters are obtained. The critical velocity of the moving oscillator is determined and absorber parameters are optimized by numerical algorithm and effect of mass and damping on the absorber performance is investigated. When absorber is applied to the beam, effect of crack occurrence on its performance is investigated. Crack is assumed to be open and is modeled by sectional flexibility increase. Two different cases considered for crack severity. In each case, optimal absorber for intact beam is applied and dynamic response of the midpoint of the beam with different velocities of moving exciter is obtained. Results show although crack can increase dynamic deflection of the beam with absorber, dynamic deflection of cracked beam without considering absorber is higher than dynamic deflection of cracked beam with absorber used. It is found that the vibration absorber designed for intact beam keeps its performance in dynamic deflection reduction after crack occurrence and changing in structural dynamic.

In this study, static/dynamic instability and nonlinear vibrations of FG plates resting on elastic foundation under parametric forcing excitation are investigated. Based on CPT, applying the von-Karman nonlinear strain–displacement relation and the Hamilton’s principle, the governing nonlinear coupled partial differential equations are derived. By considering six vibration modes, the Galerkin’s procedure is used to reduce the equations of motion to nonlinear Mathieu equations. In the absence of elastic foundation, the validity of the formulation for analyzing the static buckling, dynamic instability and nonlinear deflection is accomplished by comparing the results with those of the literature. Then, in the presence of the foundation and by deriving the regions of dynamic instability, it is shown that as the parameters of the foundation increases, the natural frequency and the critical buckling load increase and the dynamic instability occurs at higher excitation frequencies. The frequency response equations in the steady-state condition are derived by applying the multiple scales method, and the parametric resonance is analyzed. Then the conditions of existence and stability of nontrivial solutions are discussed. Moreover, the effects of the system parameters, including excitation frequency, amplitude of excitation, foundation parameters and damping, on the nonlinear dynamics of the FG plate are investigated.Also, it is shown that the presence of the foundation has a considerable influence on the resonance characteristic curves.

In this paper, steady creeping motion of non-Newtonian falling drop through a viscous fluid is investigated analytically. Here, the Upper Convected Maxwell model (UCM) is used for drop phase and Newtonian model is considered for external fluid. The perturbation technique is used to solve both exterior and interior flows and Deborah number, which indicate the elastic effect is considered as the perturbation parameter. The present solution is derived up to second order of perturbation parameter so this solution has suitable accuracy for drops made from dilute polymeric solutions. It was found that the Newtonian drop has a spherical shape during the creeping motion but the non-Newtonian drop loses this shape and takes an oblate form. By increasing the elastic effect, a dimple at the rear end of the drop is created and developed. Here, it is shown that the present results have better agreement with experimental data than the previous analytical studies. The origin of drop deformation is also considered and it is proved that the elastic property of drop phase creates a concentrated normal stress at the rear end of the drop that causes the dimple shape in this region.

In this paper, the free vibration and low velocity impact response of a sandwich plate with a Magneto Rheological (MR) flexible core have been studied. The rectangular sandwich plate contains a Magneto Rheological (MR) flexible core and two constrained layers. The MR materials have different properties with respect to different magnetic field intensities. The governing equations of motion have been derived using Hamilton principles. The solution of these equations was obtained using Fourier series and analytical systematic procedure. Using the proposed solution method, the natural frequencies, structural loss factors, impact load and transverse deflection of the plate were calculated. Also, the contact force history was derived using a two degrees of freedom spring mass model analytically. The effects of variations of magnetic field intensity on the natural frequency, loss factors, contact force and deformations of the plate and impactor were investigated. In order to calculate the equivalent mass of the plate, the obtained fundamental natural frequency from solution of eigen value problem was used. The obtained equivalent mass of the plate was used in analytical spring mass model. The results show that with systematic variation of magnetic field, the magnitudes of transverse stiffness, structural loss factors and maximum contact force can be changed and controlled, respectively.

Bolt joints play an important role in the industries, so the estimation of fatigue life of bolts is an essential task. The aim of present study is estimation of fatigue life of connection bolts of two flanges in reinforced cylindrical shell with cutout. Two groups of data are needed for mentioned bolt: fatigue properties of bolt and value of stress of bolt due to applying load to structure. So, two paths have been gone. First, the fatigue properties of bolt have been measured in laboratory according to ISO 3800 standard. For this purpose a specific fixture was designed and manufactured which provided testing different bolts. By doing fatigue experiments, the fatigue properties of mentioned bolt such as fatigue limit and Basquin’s equation constants (fatigue strength coefficient and fatigue strength exponent) have been measured. Fracture mechanism and fracture surface have been investigated, too. Afterward, in the next step the value of stress in bolt that is subjected to mix loading has been calculated by using of FE modeling. Because of problem complexities, cost of three dimensional analysis of this problem increases, so analysis of the problem has been performed by shell-to-solid sub-modeling technique. At the end, by calculating the nominal stress of bolt from FE modeling and using fatigue properties witch obtained from experiments, life of the mentioned bolt has been estimated.

Conceptual design optimization of spacecraft systems is a complex and multidisciplinary process. In this case evaluation of the objective functions relies heavily on running iterative simulation models and analysis codes between various subsystems (such as structures, payload, electrical power supply, attitude determination and control, communication, command and data handling). The conventional sequential optimization approaches to such a complex design problem is time consuming and does not guarantee to achieve the best compromise among the various competing coupled subsystems, and may even lead to non-optimal design. In addition, the design search space can be multi-modal, non-convex with multiple local minima and hence it is time consuming or difficult to rapidly evaluate trade-offs between various subsystems (disciplines). To address these issues, in this paper an efficient surrogate (response surface) model-based multidisciplinary spacecraft systems design optimization technique with discrete and continuous design variables is presented. The methodology is based on the utilization of genetic algorithms (GA) for both system level and discipline level as an optimizer. Surrogate-modeling as an efficient tool is also used to decrease computational cost in discipline (subsystem) level within a collaborative optimization (CO) framework. Results obtained in this study show that the method introduced in this paper provides an effective way of improving computational efficiency of a complex space system design such as conceptual design optimization of a spacecraft.

Polishing is considered as the last and most important step in the manufacturing of optical components. Computer control polishing (CCP) methods are usually used to polish complex surfaces. In this method, material removal is controlled at each point, depending on error at that point. In contact polishing mechanism, tool feed rate is often controlled to eliminate local errors. It means that the higher the tool feed rate, the lower the material removal would be and vice versa. Tool influence function (TIF), which is defined as the instantaneous material removal under the polishing tool for a given tool motion, is the most important parameter in CCP and its predictability during the polishing process leads to reliable result. In this study, a new spherical tool which can polish complex surfaces by using a 3-axis CNC machine is presented. Because of spherical geometry of both tool and work piece, tool, material removal rate is variable because of changing the angle between tool axis and surface normal vector which leads to variation of relative speed. Tool influence function which depends on tool engagement’s angle was modeled based on Preston equation. Moreover, the simulation is modeled based on discretization of tool path. To evaluate the methodology, some polishing experimental tests were performed. The experimental results show that a 130 mm spherical convex lens with initial surface roughness of 1.114 micrometer for PV was decreased to 395 nm for PV using the CCP method developed in this study.

In this paper, with the aim of providing a new test pattern for empirical prediction of FLD of 304 stainless steel tube, first, numerical investigation of hydro-bulging process with various load paths and die geometries has been performed on strain path and plastic instability. Study on geometry of dies has been performed by varying die corner radius (R) and bulging length (W). Here, effect of axial feeding on strain ratio (b) has been studied. In this condition, by increasing W, strain ratio (b) tends to a value of zero, a situation that is independent of boundary condition. By increasing die corner (R) in free loading condition, reduction of b occurs and the strain path approaches to plane strain state; while in loading with axial feeding condition, increasing of R has negligible effect on strain path and ratio. In loading with axial feeding condition, increase in axial feeding strain ratio (b) is reduced drastically. From the simulated tests, number of 10 tests with distributed loading path on strain diagram was selected for empirical study. Meshed tubes are loaded controllably until tearing and the FLCs were drawn using strains obtained near tearing locations.

A prerequisite in the majority of control processes is modeling. The model used to design a controller must be both accurate and real-time. Utilizing prevalent approaches of modeling, namely modeling based on (numerically) solving the equations governing the fluid in the combustion chamber, is too time - consuming and not suitable for control purpose. This paper aims to model combustion in an SI engine by means of neural networks and present an accurate and fast-response model for combustion. Obviously, any training procedure of neural networks involves empirical data acquisition. On the other hand, engine testing is highly expensive, and testing data tables available (in industry) is not sufficient to train neural networks. In this paper, first with the aid of CFD software, a one-dimensional model of an engine is constructed, and then calibrated using the factual experimental data at hand. Afterwards, acquiring data required is performed via the validated CFD model. As a matter of fact, because of the lack of access to necessary experimental coefficients, calibration is an extremely complicated and time-consuming process. An attempt is made to accomplish and spell out the calibration of the engine model in the GT-Power software, in a scientific practice. After a brief survey on the methods employed in designing the neural networks, modeling of the combustion chamber will be stated. Eventually, the response of the constructed NN model will be compared to the results gained from the GT Power software, and the great accuracy of the NN model will be shown.

The creating scratch by an abrasive grit is mostly investigated to enhance the finishing processes. In grinding, many distributed abrasive grits on grinding wheel surface are engaged with the workpiece to remove material. To investigate the material removal mechanism in grinding process a scratch and removed material by an abrasive grit is assumed and simulated. The results are developed for all engaged abrasive grits on grinding wheel surface. This leads to improve the machining process and gaining deeper insight to the grinding mechanism. By analyzing a creating scratch by a single abrasive grit, the material removal mechanism is scrutinized from a different view. The effect of grinding wheel surface topography and input parameters on material removal mechanism is investigated. Results show that increasing cutting speed leads to changing material removal mechanism from ploughing to cutting. The shape of abrasive grits has more effect on material removal mechanism. In worn grits increasing the cutting depth causes the ploughing to become the dominant mechanism in machining. This leads to less cutting efficiency. But in abrasive grits with sharp single cutting edge the converse result is achieved. When grit breaks down and self dressing occurs during machining, the multiple edges are formed on grit and the grit acts like a dull abrasive.

In this work, A 3-dimensional model is developed to investigate fluid flow in a magneto-hydrodynamic micropump. The equations are numerically solved using the finite volume method and the SIMPLE algorithm. This study analyzes the performance of the magnetohydrodynamic micropump. For this purpose, a magnetohydrodynamic micropump built in 2000, is simulated. The micropump has a channel with 20mm length, width of 800mm, height of 380mm and an electrode with 4mm length. The applied magnetic flux density was 13mT and the electric current was different for various solution (10-140 mA). The results show that the intensity of the magnetic field, the electric current and the geometry has an effect on the magnetohyrodynamic micropump performance. By increasing the amount of magnetic flux and electric current the average velocity increases. decreasing the channel length would increase the mean flow velocity. by increasing the channel depth, the mean flow velocity initially increases and then decreases, while at a depth of approximately 700-800mm the maximum averaged velocity will be resulted. The velocity increases by Increasing the channel width to 1500mm, however the velocity remained unchanged for larger values.

In this article, an improved 3D finite element (FE) model of low velocity transverse impact on armchair and zigzag single-walled carbon nanotubes (SWNTs) has been developed. Numerical examples for estimating the Young’s modulus of nanotubes are presented based on explicit and implicit analysis to illustrate the accuracy of this simulation technique. Based on explicit finite element model, maximum dynamic deflections of single-walled carbon nanotubes with different boundary conditions, geometries, as well as chiralities are obtained and then compared with theory investigation. Impact of mass on simply supported and clamped nanobeams is investigated by using nonlocal Euler–Bernoulli and Timoshenko beam theory. The simulation results demonstrated good agreement with analytical results based on Euler–Bernoulli and Timoshenko nonlocal theory. When aspect ratio is increased, maximum dynamic deflection at the center of the beam is increased for both the simply supported and the clamped-clamped nanobeams. The inclusion of the nonlocal effect increases the magnitudes of dynamic deflections. The dynamic deflections predicted by the classical theory are always smaller than those predicted by the nonlocal theory due to the nonlocal effects.

AISI 4340 steel is a low alloy steel with high tensile strength that has numerous applications in industry. Machinability of this alloy steel is difficult due to its low heat conduction and high heat concentration in cutting zone. Therefore, use of cutting fluids in machining of this steel is inevitable. On the other hand, environmental problems of using mineral lubricants lead industries to use of biodegradable oils such as Vegetable-based cutting fluids. The aim of this study is to investigate the drilling of AISI4340 alloy steel in presence of semi-dry lubricant using soybean vegetable-based oil. For this purpose, drilling parameters including feed rate and cutting speed at three levels and workpiece hardness at two levels were chosen. Totally 18 experiments were carried out using coated carbide drill. Results revealed that vegetable-based oil can be used effectively in drilling using a semi-dry lubrication method. In addition, feed rate was the most effective parameter on cutting force and surface roughness and by increasing it, the cutting force increased, and the surface quality deteriorated. Also, workpiece hardness showed significant effect on surface roughness.

Predicting wind flow pattern around high rise building, because of some important issues like pedestrian comfort, air pollution. in weak wind region and etc. has great position in wind engineering. Turbulent wind flow over buildings due to the complexity like sharp corners, ground effect, different vortexes and other factors is one of the best choices to evaluate efficiency and accuracy of turbulence methods. Moreover in a large building collection due to high velocity region between buildings, simulating wind flow is more complex. Therefore reaching acceptable result needs a fine grid with an accurate turbulence model that increases computational cost. DES is hybrid RANS-LES models for simulating turbulent flow which for their characteristic, treat near wall as RANS and farther the wall act as LES model. onsequently computational time will decrease compared to traditional LES models. In this article turbulent wind flow over Tarbiat Modares University with DES method in different wind velocities is simulated. Because cells number is great parallel processing has been used. For verification, DES results are compared with traditional LES models such as smagorinsky. The DES results show good agreement with smagorinsky model.

This paper aims to obtain the dynamic models of two over-constraint parallel mechanisms (PM) with 3-DOF (degree of freedom) and 4-DOF, the Tripteron and the Quadrupteron. The reasoning used in this paper is based on a judicious concept in detaching the whole mechanism into several subsystems and consecutive synergies between kinematic analysis, Lagrangian and Newtonian approaches. In this regard, the mechanisms are made equivalent to some subsystems and the equations of kinematic constraints are derived for all subsystems. Afterwards, upon resorting to Lagrangian approach and blending it with the latter kinematic relations, the dynamic model of each leg in task space is obtained. The dynamic model of the end-effector is written in virtue of Newton-Euler’s approach where it yields to three differential equations. Finally, the problem leads to a system of 12 equations for the Tripteron and 16 equations for the Quadrupteron, which do not require the usual simplifications in such problems. For the sake of comparison, the results are put into contrast by the one obtained with a dynamic analyzer software. The results obtained by both approaches are coherent, which affirms the correctness of the proposed algorithm.

Thermo-mechanical control processing is used to produce API pipeline steels. To design a proper thermo-mechanical cycle, it is necessary to determine the critical temperatures including nonrecrystallization temperature (Tnr) and austenite to ferrite transformation start and finish temperatures (Ar3 and Ar1). In this research, average schedule and continuous cooling torsion after areal schedule were used to determine critical temperatures of API X65 steel for the first time in Iran. This steel is imported from abroad and is extensively used in Iran for large diameter, high pressure gas transportation pipelines and for oil transmission networks. It was found that the average schedule was a proper method to determine Tnr; while, continuous cooling torsion was proper to determine Ar3 and Ar1. The obtained results were compared with Boratto and Ouchi experimental relations (with the purpose of evaluating the reliability of these relations) for determination of Tnr and Ar3 critical temperatures. The obtained 4 percent relative error from both relations showed the need for conducting the experimental studies. Regarding the lack of experimental data, the obtained results can be used to design the optimum thermo-mechanical control process (through the selection of proper temperature ranges for rough and finish rolling stages) in domestic manufacturing of the test steel.

In this study, considering slippage between a robot end-effector and an object, adaptive control of a one-finger hand manipulating an object is explored. This system is a good sample to develop different techniques such as grasp analysis, grasp synthesis, stability analysis and designing different types of controller for cooperative manipulator systems. Due to the presence of inequality equations in frictional point contact modeling, a novel formulation is developed to replace the equality and inequality equations with a single second order differential equation with switching coefficients. Introducing this new friction contact model, an input-output conventional form is derived using the equality and inequality equations of motion of the system. Using this new form of motion equations, two adaptive controllers with simple update laws are proposed that both of them ensure the asymptotic convergence of the object position tracking as well as slippage control while compensating the system uncertainties. The first controller compensates the uncertain masses of the manipulator links and the object while the second one compensates the uncertain coefficients of friction. Numerical simulation is utilized to evaluate performance of the proposed controllers.

Occlusion of cerebrospinal fluid path increases the pressure exerted by the liquid on the walls of the ventricles and ultimately leads to hydrocephalus. This research investigated a numerical index to diagnose the non-communicating hydrocephalus disease. First, the diagram of velocity in Sylvius aqueduct of a healthy subject, obtained through a 3D FSI analysis was compared to a similar velocity diagram extracted from CINE-PC-MRI of the same subject. Then, after ensuring that the two diagrams coincide with each other, the problem assumptions and solution were confirmed. The Reynolds number in Sylvius aqueduct of a healthy subject was less than 275.7 and the maximum pressure of CSF was 616.3 Pa. Further, the conditions of ventricular system ina patient suffering from non-communicating hydrocephalus were modeled. The maximum pressure increased to 2958.5 Pa. Regarding the cause of hydrocephalus, the maximum pressure of CSF on the brain tissue in Sylvius aqueduct was introduced as an index to assess non-communicating hydrocephalus. Finally, calculated CSF pressure data of this study were compared to the data obtained through the lumber puncture (LP) test and it was found that these values are proportional to each other. Based on this finding, the CSF pressure obtained by LP test was introduced as a practical numerical index for diagnosis of non-communicating hydrocephalus.

The investigation of failure modes of plates and behavior of various resistive structures to destructive effects of explosive waves, due to its importance in design of blast resistive structures, has been of interest to researchers for a long time. In this study, three different methods of numerical simulation of blast wave issues were carried out to evaluate and compare with the experimental results. As a consequence, by the means of study of clamped isotropic square plates under shockwave loading from various weight and distance of charges, the couple of ALE and ConWep methods were approved to have 8.54 per cent error in comparison with ALE and ConWep methods individually. Given that in the coupled approach and ConWep method, the equivalent weight of TNT for different types of explosives is needed, the equivalent weight of TNT for C4 was estimated by 1.14, and according to the empirical pressure-time chart and empirical equation for pressure in the air, this coefficient was proved to be right and the pressure and impulse charts for TNT and C4 explosives with the same weights was studied.