Modares Mechanical Engineering
Year:2015 | Volume:14 | Issue:12|Papers Count:24

This research aims to provide new information about the mechanical behavior of double-stranded DNA (dsDNA). For this purpose, a series of extended atomic resolution molecular dynamics (MD) simulations of DNA dodecamer is performed. The MD calculations are carried out using Generalized Born solvent-accessible surface area method and Langevin dynamics. The stressstrain curves of DNA obtained under various pulling rates and pulling angles are analyzed, and the role of pulling angle and velocity in determining biomechanical properties of short dsDNA is discussed. The results illustrate that how much the behavior of DNA under action of tensile forces could be complicated. By means of at base pair level analyses of the molecule conformation during the stretching processes, the structural stability of the DNA molecule subjected to the angled pulling with different pulling rates and different pathways to the dsDNA rupture are studied. The structural stability of dsDNA can be dependent on the pulling velocity and pulling angle. Whereas the DNA stability can decrease significantly with the reduction of pulling velocity, stretching the DNA under different angles has different unpredictable effects on its structural stability.

This article describes the details in design and development of a satellite attitude dynamics simulator that is used to validate control algorithms, improve novel control methods, verify the operation of available actuators or sensors and exhibit the fundamentals of attitude dynamics to students or experts. This dumbbell style simulator is based on a spherical air-bearing and is able to produce a frictionless and torque-free environment for simulating spacecraft operational environment. The facility includes a variety of subsystems such as: cold-gas propulsion subsystem, inertial measurement unit, power-supply unit, on-board processor and semiautomatic mass balancing mechanism. The overall design of this system was pretty complicated especially when considering the mission requirements, operating constraints and functional limitations imposed by the ground-based simulation, thus, a detailed design procedure has been deployed and also, this procedure has been performed accurately. An explanation about dynamic equations of motion of simulator with on-off thrusters, software-based simulation, applying reliable control algorithm and balancing methodology is the next part of this article. Finally, the results of the realistic maneuvers of this satellite simulator are presented and investigated in detail.

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.

Due to the complexity in the control system of hybrid vehicles, the electronic control units should go through extensive testing before getting installed in a prototype vehicle. In the first stages of the development process, Hardware-in-the-Loop (HiL) simulation can not be performed because the hardware components of the vehicle are not yet available. In this case, Model-in-the-loop (MiL) simulation is used which couples the designed control software with an environment simulation with no need for a special hardware. In this paper, the MiL simulation is introduced for verification of the vehicle control software in a series hybrid electric bus. To do so, considering the dynamic behavior of various components of the vehicle, a simulator of the hybrid bus is designed by going through with the input/outputs of the vehicle control software. Using the designed test bench, the user can act as a real driver and experience different driving regimes and analyze the control software commands. In the designed simulator, all subsystems are simulated separately in LabVIEW environment and real-time simulation is achieved with an acceptable error. Therefore, it can be used in a HiL test bench for testing each of the vehicle components. The designed simulation model has been validated using real test results. Using that, results show that all control functions in the vehicle control software can be tested and verified with no cost and in the shortest possible time.

In this paper the creep behavior of a functionally graded (FG) rotating disc made of Aluminum 6061 and Silicon Carbide is investigated and the optimum volume fraction of FG disc and its profile has been obtained. For this purpose, the temperature gradiant along the disc radius is obtained by solving the govering heat transfer differential equation. All the thermal properties of the material are assumed to be the function of temperature and volume fraction. To obtain material properties, two models of Mori-Tanaka and Hashin-Schtrickman are used. To validate the results, they are compared with those given in the literature. Two solution methods: semianalytical and closed form are employed and the results are compared. The optimum design is carried out with one, and multi-objective methods which are based on genetic algorithm. The objectives are increasing the factor of safety, reducing the weight of the disc and reducing the range between minimum and maximum safety factors. The design variables are percentage of volume fraction, the power of material distribution formula, and the thickness of the disc. The Res ults show that two solution methods compare well. Also, it has been shown that high fraction of Silicon Carbide in the outer side the disc provide optimum results. Also, contradiction of the objectives is reviled, hence the results are presented as Pareto front.

Fuel metering system and controlling fuel-air mixture of spark ignition engines have been the major goals for the researcher. Management in mixture quality and fuel economy have resulted in changing carburetor systems to injection systems. Start of fuel injection position and injection duration play important role in engine performance. In the current work a single cylinder research engine with capability of adjusting spark timing and controlling gasoline injection start position and duration was utilized. Compression ratio, engine speed and injection start position were adjusted to 8, 1800 rpm and breathing top dead center (BTDC), respectively. Injection duration and spark timing were controlled so that to achieve maximum output torque at equivalence ratio of 0.90. Fixing them, the start of injection was only changed in the range of -180 to 180°CA relative to BTDC with a 30°CA increment. For each case, cylinder pressure of 500 successive cycles were recorded and stored. The obtained results showed that the dispersion of indicated mean effective pressure (imep) data of the cases with injection position start after BTDC were higher than those of the cases with injection position start before BTDC. Also, the average values of imep and peak pressure and their coefficient of variation changed with varying fuelinjection start position; and for the cases of high dispersion in imep data, the average values of imep and isfc appeared to be high and low respectively.

Asshown inthe previous studies, blades can cause resonance in bladed rotors under some specific conditions. In this paper, the nonlinear behavior of a rotor, which faces with this kind of  resonance, is investigated. In order to reach this goal, a model of bladed rotor, in which the disk and shaft are rigid, is considered. The blades are modeled by flexible beams. It is assumed that both ends of the shaftare supported by elastic and nonlinear bearings. The nonlinear term of the bearing stiffness functionis cubic. The rotor vibrations include both cylindrical and conical whirling. The bifurcation equation on the stability boundary is obtained by the method of multiple time scales. The nonlinear effects are studied by this equation. It is revealed that the system behavior, when it encounters Hamiltonian Hopf bifurcation, is dependent on the bearing stiffness nonlinearity type. Accordingly, both subcritical and supercritical Hopf bifurcationsare possible. Eventually, a numerical simulation is performed in order to study the effects of damping coefficients on the trajectory of rotating disk center. The results and methods, which are used in this paper, can be used for studying Hamiltonian Hopf bifurcation in other fields.

Experimental investigation of two-phase air-water flow was conducted at consecutive inclinations of a large bend (with three equal slopes in respect to each other) and including the horizontal sections of the inlet and outlet of the bend. The results show that the elongated bubble regime flows without any effect of duct inclination change and consistent for all three zones of horizontal sections of before and after the bend and the bend itself. It was also noticed, as the duct inclination decreases along the route, vortex misty flow transmits to misty annular flow at higher gas flow rates. The annular flow regime was noticed only at the first slop of the bend. Slug flow was observed at the horizontal sections upstream and downstream of the bend. The slug flow at the upstream generated by the interfacial instabilities but at the downstream formed by Taylor bubbles. Slug flow area in the flow diagram increases as liquid flow rate increase at both horizontal sections. In addition, the void fraction change rate with phases mass flow rate was considered at the duct inlet.

The purpose of this paper is a qualitative evaluation of the mechanical properties of nanostructured titanium aluminum nitride (TiAlN) hard coatings applied on cutting tools using Xray diffraction (XRD). Deposition of nanostructured TiAlN and TiN coatings were carried out by a pulse DC plasma-assisted vapor deposition (DC-PACVD) and a high power impulse magnetron sputtering (HIPIMS) machines. At first, for enhancement the adhesion of nanostructured TiAlN coating on the steel substrate, TiN inter-layer was deposited for the all samples. Nanoindentation, micro-hardness tester, and field emission scanning electron microscope (FE-SEM) were used in order to measured and compare the qualitative results with the real and experimental values. The results indicate that XRD pattern and their analysis can be a suitable qualitative method to evaluate the mechanical properties of the coatings. The lattice parameter, micro-strain, residual stress, texture coefficient, the crystal grain size and density of dislocation are used to demonstrate the relationship between the mechanical properties of the coatings and the XRD patterns. As a result, this method can be used as non-destructive and inexpensive method for quantitative comparison and evaluation of mechanical properties of thin film materials.  

Control engineers are interested in state estimation problems as one of the most interesting subject. In this way, Kalman filter, H-infinity, and Mixed Kalman/H-infinity filter are the most widely used filters for state estimation of the discrete linear dynamical system corrupted with Gaussian and white noises. These filters will be, however, suboptimal for state estimation when the process noise and/or measurement noise are color noises. In this paper, a multi-objective Pareto optimization (multi-objective genetic algorithm) approach is presented for the design of combined Kalman/H-infinity filters to estimate states corrupted with color noises. In this way, a state augmentation procedure is used to analyze the effect of the colored noises on states estimation of an inverted pendulum. Some Pareto curves are then obtained to compromise between the Kalman and H-infinity filters. It is shown that the use of such approach can evidently improve the effectiveness of the filters when the color noises are significant. Therefore, by using the proposed approach, we can employ the advantages of both Kalman and H-infinity filters simultaneously to minimize both the mean of squared errors and the upper bounds limit of estimation errors.

Micromechanical resonators are miniature devices that vibrate at high frequencies. Nowadays, with the recent advances in micro-electro-mechanical systems (MEMS) fabrication technology, micromechanical resonators are used widely in sensors, wireless communication and navigation systems. The commonly encountered energy loss mechanisms in micromechanical resonators include air damping, thermoelastic dissipation and anchor loss. In this paper, with regard to the dominated quality factor by anchor loss in some important applications including oscillators, electrical filters and gyroscopes, the closed-form expression is obtained for anchor loss quality factor in the plunging-mode vibrations of micromechanical rectangular-plate resonator with two support beams. The findings are validated by comparing with experimental data. As far as there is an acceptable match between the analytical and experimental results, the proposed model is confirmed. The results also show that the anchor loss quality factor increases with increasing substrate thickness. Moreover, a new design is proposed to enhance the anchor loss quality factor in the plunging-mode vibrations of micromechanical rectangular-plate resonators. For this purpose, the conventional support beams are replaced with T-shaped support beams. Besides, the results show that the anchor loss quality factor at the same resonant frequency is enhanced about 1.5 times.

The main aim of this experiment is to investigate the effects of Nano-size Al2O3 on the mechanical properties and microstructure of multi-passes friction stir welding of Al 2024 lap joint. Nano  particles were added into the joint line. A combination of rotational speed and travelling speeds were performed. Optical microscopy and scanning electron microscope were used to investigate the microstructure and fracture surface of samples respectively. Optimum condition (sample) was selected due to highest ultimate tensile strength (UTS). It was seen that sample which included Nano particles and fabricated by 1400 rev/min rotational speed and 16 mm/min travelling speed in second pass of continues welding had improvement in UTS in comparison to one pass welded sample of particle free and after that increasing the number of passes reduce the UTS. The average micro hardness of the sample which was particle rich were increased in comparison to particle free sample in nugget zone. Increasing the number of passes was not effect average micro hardness in nugget zone signiicantly. Grain sizes were reduced by 2 passes welding and after that no significant reduction has been seen.

Two incompressible SPH numerical solvers, including a modified explicit method and a new implicit method have been developed to simulate the sediment-laden free surface flow problems. Using consistent discretization schemes, the proposed explicit method improves somewhat the accuracy of the usual explicit ISPH methods. The implicit method additionally guarantees the incompressibility condition completely. In the presented methods, the liquid phase is modeled using Navier-Stokes equations and to predict the non-Newtonian behavior of the sediment phase, the Bingham plastic rheological model is used. The accuracy and capabilities of the developed incompressible SPH methods is first validated in comparison with available experimental and numerical results of a single-phase water-sediment mixture flow generated by unsteady dam break problem. Then, they are applied to simulate an eroding dam break problem with a twophase flow sediment transport. Comparison of the obtained results with the results in the literature shows that the developed methods particularly the implicit one, are very powerful tools for simulation of the problems including sediment transport induced by violent free surface flow, with interactions between flow and sediment and morphological changes in bed.

In this paper, dry an electro-discharge machining (Dry EDM), one of the newest machining process which differs mainly from conventional EDM in using gaseous dielectric along with tool electrode rotation, has been studied. Gap voltage, discharge current, pulse-on-time, pulse-off time, dielectric gas pressure, and electrode rotational speed have been considered as effective input parameters. Response surface methodology (RSM) has been used to optimize the machining performance with respect to material removal rate (MRR). Base on the results and analysis of running experiments, it can be concluded that MRR increases by increasing gap voltage, discharge current, the ratio of pulse-on time over pulse-off time, input gas pressure, and electrode rotational speed. There also exists an optimum amount of pulse-on time determined according to the machining circumstances. Also the material removal rate in dry EDM has been improved compared with that in conventional EDM in identical conditions.

In this paper, Free Vibration analysis of truncated conical shell Reinforced with single-walled carbon nanotubes for Uniformly Distribution (UD), resting on Pasternak elastic foundation, based on the first order shear deformation plate theory is investigated. The rule of mixture is used to effect of the properties of nanotubes in the mentioned structure. Based on the displacement field according to the first order shear deformation theory, after determining the strain components in the curvilinear coordinates and simplifying derived relation, we compute the strain components in conical coordinate. Then, the stress components are derived by the Hook’s law. In the next stage, by computing the total potential energy of system by regarding the effect of Pasternak elastic foundation and regarding the suitable functions for displacements, by applying the Ritz method the natural frequency of system have been derived. At the end, the effect of volume fraction of nanotubes, ratio of thickness to radius of cone, elastic constants and other parameters, on the natural frequency of structure have been investigated. Also, it can be observe close agreements between present results and other papers.

Experimental investigation conducted on Taylor bubble characteristics in a large bend including three consecutive inclinations. For this purposes, flow maps were obtained for the bend and horizontal section of upstream of the bend to define the area of this regime and mechanism of Taylor bubble formation. The effect of superficial gas-liquid velocities and the duct slope were studied on average velocity, length and frequency of bubbles. The results show, the bubble velocity and length increase as gas superficial velocity increases and the duct slope decreases. However, liquid velocity increase has decreasing effect on this characteristic. Bubble frequency is independent of slope change and reduces as gas superficial velocity increase. However, bubble frequency reduces at first and then increase as liquid superficial velocity increases. Regarding the safety regulation for industry, the minimum of the bubble frequency should be generated for the required liquid mass flow rate. Meanwhile, for the gas velocity, some optimization is required between frequency reductions with Taylor bubble velocity increase in addition to bubble length reduction. Regarding the background of the present field with shortage of results on Taylor bubbles frequency, some correlations based on the superficial Reynolds number of phases were presented for each inclination.

In this paper, the problem of the navigation error effect for the optimal and constraint Trajectory de of the UAVs that are required to fly at low altitude over terrains has been discussed. Due to the increasing deviation problem of inertial navigation systems in terms of time, having a safe flight and collision avoidance with terrain at low altitude is the main point in the trajectory design of this type of the vehicles. On the other hand, some of these vehicles use Terrain Contour Matching (TERCOM) as a navigation aiding system. This system is more efficient in rough terrains, and providing the requirements of this system beside other constraints is a complex task. In this paper is tried to meet these constraints in the trajectory design process. For this purpose, an algorithm based on the layered network flow on the digital terrain maps used in a manner that has a high potential in adoption of various constraints and optimal trajectory is generated. Then, using equations of motion on a terrain digital data in 3D space with the dynamical constraints and different optimality criteria, a complete model of navigation error and also parameters affecting TERCOM has been developed to generate feasible path reducing terrain collision probability to zero. The resulting algorithm applying initial conditions and in the least time possible, produces the trajectory. Numerical results show validity of this issue.

In this paper a new model is developed to describe the response of Magneto-rheological fluids (MRF) in transient state. The models which are developed so far, cover the steady-state flow, or address the transient state, with step-wise input electrical current and constant shear rate. In this paper, a new model for transient state of MRF is developed in which the input electrical current is an exponential function in different values of shear rate. Due to the magnetic inertia caused by the inductance of the coil, the real magnetic flux density could not be step-wise. Hence, compare with the other models, this model is in well agreement with reality. To verify the presented model and study the fluid properties as input parameters, an experimental coupling is designed and fabricated. The coupling applies magnetic field perpendicular to shear direction, and measures the shear stress as a function of time. The results of the proposed model show acceptable agreement with experimental observations. According to experimental and theoretical results, the presented model is applied to a controllable torque coupling and acceptable results were obtained.

Rotating machines are one of the kinds of mechanical systems that widely used in industry. The way of connecting axis and vibration of system are among the items that are always discussed in these systems. In the paper, mechanical rotating system is modeled. In the model, system consisting of two flexible axes (shafts) with different rotation axis which connected through cardan joint is investigated via two degrees of freedom model. The stability of the model is analyzed by means of monodromy matrix technique. The model is verified by comparing the results with the results of the previous researches and different natural frequencies. Then the effects of different system parameters such as axis rotational velocity, cardan angle, shaft's properties (stiffness and damping) on the stability of system are investigated. Also manner and conditions of each parameter on the stability of system are discussed. Finally, the stability charts constructed on various system parameters is presented. It is observed that decreasing shaft stiffness and cardan joint angle due to more stability, while decreasing shaft damping has the opposite effect.

In this paper, trajectory tracking control of a wheeled mobile robot is analyzed. Wheeled mobile robot is a nonlinear system. This system including three generalized coordinates ( x, y, Q), and a nonholonomic constraint. First, system kinematic and dynamic equations are obtained. A nonmodel- based control algorithm using PD-action filtered errors has been used in order to control the wheeled mobile robot. Non-model-based controllers are always more appropriate than model-based algorithms due to independency from dynamic models, lower computational costs and also robustness to uncertainties. Asymptotic stability of the closed loop system for trajectory tracking control of wheeled mobile robot has been investigated using appropriate Lyapunov function and also Barbalat’s lemma method. Finally, in order to show the effectiveness of the proposed approach simulation and experimental results have been presented. Obtained results show that without requiring a priori knowledge of plant dynamics, and with reduced computational burden, the tracking performance of the presented algorithm is quite satisfactory. Therefore, the proposed control algorithm is well suited to most industrial applications where simple efficient algorithms are more appropriate than complicated theoretical ones with massive computational burden.

In this paper, the result of a numerical study on the natural convection in an inclined T shap cavity filled with Water-Cu nanofluid with the presence of a constant magnetic field was investigated. A heat source embedded on the bottom wall of enclosure, the upper wall is cold and the other walls are adiabatic. Discretization of the governing equations are achieved through a finite volume method and solved with SIMPLE algorithm. The Hartmann number has been varied from 0 to 80 and the cavity has been twisted under the angles between 0 to 90 degrees. The  indings of study show that the effect magnetic field on the average Nusselt number is higher in high Reyleigh number. In Ra=105, the increase in nanofluid, to the Hartman number 20, contributes to decrease of the average number and in the Hartman number 40 and more, causes the average Nusselt number to increase. In Ra=106 , the increase in nanofluid, to the Hartman number 20, contributes to increase of the average number and in the Hartman number 40 and more, causes the average Nusselt number to decrease. The results also indicate that, the maximum heat transfer, in Ra=105 and Ra=106 accurse at 67.5° angle. The minimum heat transfer, in Ra=105 and Ra=106 accurse at 0° and 22.5° angle respectively.

Tube bending is used extensively in aerospace, automotive and other industries. Wrinkles in thinwalled Tubes, changes in cross section and thickness changes during tube bending are the main problems in this process. Compressive force and internal pressure can be used to better control the bending process. If the bend radius to tube diameter ratio (R/D) in the bending process could be between 1 and 1.5, the bending is not done with conventional methods. Providing a new method that results in preventing both wrinkles and minimum tube wall thickness changes is important. In this paper, tubes producing with closed end. Since tube producing with closed end is difficult, in this study, initially closed end seamless tubes are produced by deep-drawing and ironing processes, thereafter tube bending process with ratio (R/D) equal to one was analyzed using experiments and simulations by hydrobending the new method. The pressure, in which the tube takes the shape of the die completely without wrinkles, was obtained after investigating pressure changes. The effects of pressure changes on the thickness distribution of the tube inner radius and outer radius of the bent tube was also examined.

In mechanical assembly, errors arisingfrom part manufacturing or assembly process maycause significantvariationinfinalassembly withrespecttotheidealmodelandaffectthequalityand performanceof product. In sheet metal products dueto high order of compliancy of componentsrrorsgeneratedduringassemblyprocessareasimportantasparts’manufacturingtolerances. Therefore, it is crucial to have comprehensive model in order to analyze the assembly process of these structures and represent the relationship between part tolerances and final assembly errors. However, it should be noted that assembly processes are often complex and nonlinear in nature. In sheet metalstructures,the mostimportantfactorthat makestheassembly process nonlinearis contactinteractionbetweenmatingpartsduringassembly.Ifthisfactorisdisregardedandthe. assembly process is only represented based on linear force-displacement relationship, the model will result in part penetration and remarkable difference between theoretical and experimental results will occur. Another important featurein sheet metaltoleranceanalysis is the surface continuity of components which makes the deformation of the neighboring points of plate correlated. This paper aimsto present new methodologyfortolerance analysis of compliant sheet metal assembliesin which nonlinearfiniteelementanalysisisintegrated withimprovedsensitivity-freeprobability analysis in order to account for effects of contact interaction and surface continuity of components andcalculate theassemblyerror. Theaccuracyofthisapproachisconfirmedbyan experimental case study and Monte Carlo simulation.