مجله مهندسی مکانیک امیرکبیر
سال پنجاه و چهارم شماره 4 (تیر 1401)

Liquid transport by UAVs is a necessary task in autonomous firefighting and field spraying missions. On the other hand, transient and residual sloshing of the liquid during and after the movement can cause instability, increase position error and control effort and create danger or damage if the liquid is flammable. Therefore, in this study, control of a liquid carrier quadrotor has been studied and a controller has been presented that, unlike previous studies, can provide stability in point-to-point transmission without the need to measure or estimate liquid states. For this purpose, a controller is first designed by linearizing the equations of motion of the system and assuming the liquid is rigid via pole placement. On the other hand, in order for the behavior of the system to be similar to the behavior of the design model and to maintain the stability of the system, the liquid sloshing must be reduced as much as possible. Therefore, a command smoother based on the natural frequencies of the liquid sloshing modes is used. The ability of the proposed control system has been investigated, validated and compared with a similar study by simulation. Also, the simulation results show that implementation of the designed command smoother can significantly reduce the amplitude of liquid sloshing, the deviation of the system states from the equilibrium state and the control effort.

In recent years, unmanned aerial vehicles (UAVs) have become popular in many countries in the industrial and scientific research fields because of their high speed and maneuverability. This research investigates a compound system consisting of a quadrotor and a series robotic manipulator. Joining of these two systems aims at utilizing the agility and flexibility of multi-rotor UAVs and dexterity of robotic arms. This configuration makes UAVs able to perform more complicated tasks. First, kinematics and dynamics of quadrotor are presented using quaternion and Newton-Euler equations. Next, a 3-DOF robotic arm connected to the bottom of the quadrotor is considered and its kinematics and dynamics is derived using Newton-Euler recursive algorithm. In order to control the quadrotor, two inner-outer loops are used for its orientation and position, respectively. The torque resulted from arm operation or exerted force to its end-effector is estimated using Kalman filter and is fed into quadrotor inner control loop. For trajectory tracking of arm end-effector an inverse kinematic algorithm is used. The compound system including UAV and arm is simulated with different scenarios in order to verify its satisfactory performance.

In this paper, an adaptive sliding mode controller (ASMC) with variable gains to cope the uncertainties is proposed for an electromechanical clutch position control system to apply in the automated manual transmission. Transmission systems undergo changes in parameters with respect to the wide range of driving condition, such as changing in friction coefficient of clutch disc and stiffness of diaphragm spring, hence, an adaptive robust control method is required to guarantee system stability and overcome the uncertainties and disturbances. As the majority of transmission dynamics variables cannot be measured in a cost-efficient way, a non-linear estimator based on unscented Kalman filter (UKF) is designed to estimate the state valuables of system. Also, a non-linear dynamic model of the electromechanical actuator is presented for the automated clutch system. The model is validated with experimental test results. Numerical simulation of a reference input for clutch bearing displacement is performed in computer simulation to evaluate the performance of ASMC controller and UKF estimator. To evaluate the performance of the proposed control system the root mean square( RMS) value of the position tracking error in the two systems for different uncertainties of 10 and 20% has been used. The results of the analysis indicate a higher efficiency of the ASMC designed to improve the RMS value of the position tracking error compared to the conventional SMC.

Particle displacement in Nano-dimensions, improvement of properties, studies on cellular tissues are some of the applications of the nanomanipulation process. All of these applications are performed with an efficient tool called an atomic force microscopy. In general, the manipulation process begins with the contact of the probe and the desired cell tissue and with the application of force to the atomic force microscope. The increase in force will continue until it overcomes resistant forces such as friction. In this situation, the critical time and the critical force will be recorded. Examining all environmental and geometric factors and eliminating unnecessary parameters will lead to more accurate information in the field of cancer studies. Therefore, in this article, colon cancer tissue has been studied. The important parameter evaluated in this study is the critical force and time according to different friction models in order to reduce the damage to cancerous tissue. Experimental tests have been performed on colon cancer tissue using an atomic force microscope. LuGre, Coulomb and HK friction models are used in the simulations. Finally, by comparing the force outcome diagrams considering different friction models, in three-dimensional manipulation, the maximum amount of force and the critical time of manipulation of colon cancer tissue were recorded for the Coulomb friction model and the lowest value for the LuGre friction model.

Inertial navigation systems are one of the main components in advanced equipment navigation systems such as drones and satellites. Therefore, their reliability is very important for system mission success. To increase reliability while developing advanced sensors, the issue of sensor placement and arrangement, the use of redundancy, and error detection should also be considered. In this paper, different sensor configurations and reliability analysis of fault detection and isolation of an inertial navigation system are evaluated. First, the design of the navigation system is analyzed in terms of the location of the sensors, then the detection and fault detection unit based on the excess sensors. The reliability of the system is calculated based on exponential distribution and reliability block diagram, then the reliability fault detection unit is calculated using the Monte Carlo method. the sensitivity analysis has been performed and results show that the reliability depends on the noise value. Because the reliability of this system is a function of the fault detection and its threshold values, the optimal values for fault detection threshold are obtained using two iterative methods and estimating the minimum nonlinear squares.

In this study, dynamic behavior of a micro scale parallelogram flexure under end load conditions is studied. To this end, by making use of the modified strain gradient elasticity along with the beam constraint model, the nonlinear strain energy of a single flexure beam and consequently a parallelogram flexure is derived in terms of its end displacements. Then, using the Lagrange equations, a dynamic model is presented for the parallelogram flexure. To enable the study of small amplitude oscillations around the operating point, the proposed dynamic model is linearized about the static equilibrium sate. Then the allowable regions for application of static axial and transverse forces, so that the utilized nonlinear theory is not violated and at the same time, the system remains stable, is found. Obtained results show that the classical theory underestimates the stability of the parallelogram flexure. Moreover, the natural frequencies and mode shapes of the system was also derived and their dependence to the length scale parameters and the static loading condition is analyzed. It is observed that with reducing the dimensions, or increasing the length scales, the difference between the predictions of the classical theory with that of the modified strain gradient theory is increased. Moreover, it is observed that increasing the transverse load leads to a decrease, while increasing the axial load, leads to an increase in natural frequencies.

In this study, the compression behavior of cardboard Egg Box cores with various stacking sequences used in sandwich structures are investigated both experimentally and numerically. A critical requirement of the design is that the structure is compatible with the environment (biodegradable), and its properties have been investigated through compression and tension testing. This study aims to investigate the bending characteristic of cardboard egg box to reduce the use of chemicals and get benefits of this shape in construction of biodegradable sandwich panels. Egg boxes were chosen as the core material for sandwich structures due to their mechanical strength, excellent insulation properties, and strength. Also, the core shape in various stacking sequences were model in ABAQUS FE code to simulate the behavior of the egg box core in bending. The results showed that the surrounding edges of the core crushed and the truncated top region compressed. The increase in thickness of the egg boxes directly affected the compression properties. By doubling the thickness of the layers, the amount of energy absorbed by the core increased by more than 110%. By comparison of various stacking sequence of the cores, the one with double layers of the egg boxes overlapped, showed an increase of 32% in stiffness, 64% in energy absorption, and 59% in strength.

In this study, the buckling of functionally graded graphene platelet-reinforced porous nanocomposite plates with various shapes such as, rectangular, elliptical and triangular ones embedded in an elastic medium is analyzed. To mathematically model the considered plate and elastic foundation, the first-order shear deformation plate theory and the Winkler-Pasternak model are used, respectively. Three types of graphene nanoplatelet distribution and porous dispersion patterns through the thickness direction are considered for the nanocomposite plate. The effective material properties are obtained via a micromechanical model. By writing the energy functional of system and using the analytical P-Ritz method, the influences of porosity coefficient, weight fraction of graphene nanoplatelets, elastic foundation coefficients, and also the length-to-width and -thickness ratios on the critical buckling loads are analyzed. It is illustrated that the plate with non-uniform porosity distribution pattern of the first type and GPLA pattern due to the greater concentration of graphene nanoplatelets on the upper and lower surfaces of the plate and the increase in the stiffness of the plate, it has higher critical buckling load. Also, the maximum critical buckling load is related to shear loading and the minimum critical buckling load is related to biaxial buckling load. Also, by increasing the porosity coefficient, the critical buckling loads of the plate associated with all patterns of graphene nanoplatelets are reduced.

Fretting fatigue (fatigue-wear) occurs when contact stresses cause cracks to form and continue to grow between two objects or surfaces in contact. By considering frictional abrasions and intermittent mechanical loads, the phenomenon of fretting fatigue can occur in vehicle engine parts. The presence of cyclic loads and the presence of wear in the engine cylinder head increase the probability of the fretting fatigue phenomenon. In this study, the effect of lubrication and abrasion force on the fretting fatigue behavior of the cylinder head aluminum alloy has been investigated. The results were also obtained to compare samples with and without nanoparticles. Microstructure and fracture surface were also examined by light microscopy and scanning electron microscopy. The results showed that lubrication and reduction of abrasive force improved the wear fatigue lifetime of cylinder head aluminum alloy. In addition, according to the results obtained from the diagram, the effect of oil and reduction of abrasive force, the lifetime of reinforced specimens was 7 and for cylinder head specimens 7000 times compared to the lifetime of aluminum specimens without lubricant and at contact force of 15 N.

Nanofluids are a new generation of fluids with very high potential in industrial applications. In this study, the effect of temperature and concentration of nanoparticles consisting of Al2O3 nanoparticles and graphene nanoplates on the rheological behavior of the base fluid consisting of water and ethylene glycol was studied. Also, 0.2% vol. of oleic acid (OA) and 0.2% wt. of sodium dodecyl sulfonate (SDS) were added to the base fluid as a surfactant to stabilize and disperse the nanoparticles. The volume fraction of nanoparticles in this study was considered 0.05, 0.1, 0.5, 1, 1.5, 2 and 2.5% by volume and also to investigate the effect of temperature, the tested temperatures were selected in the temperature range of 263-293 K. The morphology and microstructure of the nanoparticles were investigated by SEM and TEM. Detection of phases in nanoparticles was performed by XRD analysis. Also, specific area and porosity of nanoparticles were determined by BET analysis. Dynamic viscosity of hybrid nanofluids was measured and compared with the base fluid. The results showed that the rheological properties of water-ethylene glycol/nano graphene-nano alumina hybrid nanofluid were highly dependent on temperature and nanoparticle concentration, especially at sub-zero temperatures. Dynamic viscosity results showed that hybrid nanofluid samples with solid volume fractions less than 0.5% Newtonian behavior, while samples with higher solid volume fractions showed non-Newtonian shear thinning behavior.

This paper summarizes the experimental investigation of glass drilling using laser-induced plasma-assisted ablation. In the experiments, a nanosecond pulsed laser with a wavelength of 532 nm as the laser source and copper with 2 mm thickness as the metal substrate are used, and two permanent neodymium magnets (4500-4800 G) are used to apply an external magnetic field to drill holes in the laboratory slide glass. The laser fluence was selected in 4 levels of 1, 1.5, 3 & 3.5 J/cm2 and the characteristics of the holes produced with 50 laser shots were examined in terms of dimensions and morphology. It was observed that by applying a magnetic field, the material removal rate increases about 2 to 2.4 times in the lower fluences and 31 to 35 times in the higher fluences. In the magnetic field absence for different laser fluence, the hole depth and diameter changed from 1.6 to 32 and 10 to 100 microns, and in its presence, they change from 3 to 76 and 11 to 380 microns, respectively. So the drilled hole depth and diameter increase up to 230% and 320% respectively, by applying a magnetic field. Metal deposition on glass in magnetic field absence is distributed symmetrically around the hole entrance, but in magnetic field presence, it occurs with high density and cohesion on one side of the hole.

Forming limit diagrams (FLD) are a criterion to predict the necking for constructing optimal design in metal products. In this paper, the Marciniak-Kuczynski instability theory is used to determine the forming limits of the AA6111-T43 sheet. Also, Hill 48, Gotoh, and Yld2000-2d yield criteria are investigated to describe the yield behavior of the alloy, and their coefficients are computed based on the results obtained from uniaxial and bulge tests. Finally, forming limit diagrams are plotted by employing different yield functions and appropriate hardening models. The comparison between theoretical and experimental results indicated that the limit strains obtained by Yld2000-2d criterion and Swift model are in better agreement with experimental data than others. Since in complex forming processes, the strain path is rarely linear, the investigation of the forming limit diagram by considering the nonlinear strain path is important. In multi stage forming processes, while the limit strains are significantly path dependent, the forming limit stress diagram (FLSD) is less dependent on the loading path. However the sensitivity of the FLSD to strain path is lower than FLD, the limit stresses in large pre-strain are not completely loading path independent. The sensitivity of the limit stresses to strain path in addition to the magnitude of the pre-strain, it also depends on the used hardening model and yield function that are examined in detail in this study.