مجله مهندسی مکانیک امیرکبیر
سال پنجاه و سوم شماره 2 (اردیبهشت 1400)

One of the main topics in the field of robotics is the modeling and control of the mobile robots intrajectory tracking problem. In this paper, the kinematic and dynamic models of a manipulator connetcted by revolute-prismatic joints and installed in a non-holonomic wheeled mobile platform are first derived by applying the recursive Gibbs-Appell method. Indeed, by employing this dynamic methodology, one gets rid of the difficulties of Lagrange Multipliers that originate from non-holonomic constraints. Then, a nonlinear predictive approach is applied to design the kinematic and dynamic control laws to generate trajectory tracking control commands of the non-holonomic robot. In this method, the nonlinear responses of the mobile robot are predicted using Taylor series. The optimal control laws are analytically developed by minimizing the difference between the predicted and the desired responses of the system outputs. The multivariable kinematic controller specifies the desired angular and linear velocities of the mobile base and the manipulator links. The obtained control inputs are then used as the desired values to be tracked by the dynamic controller. Finally, the results of numerical simulations are presented to emphasize the ability the proposed method in the mathematical modeling and simultaneous trajectory tracking control of the mobile base and end-effector of such complex robotic systems.

In this paper, kinematic modeling of a soft pneumatic robot, including a combination of 3 soft actuators, with the capability of spatial positioning is presented. The proposed kinematic model in this research, unlike former methods, corresponds the physics of robot and the main idea is modeling its configuration and movement by serial rigid robots which generate the same configuration and movement. The given kinematic model consists of forward and inverse problems and uses accurate geometrical solutions. In addition, velocity Jacobian of soft robot has been determined by two different approaches based on rigid serial robot principles. Furthermore, the robot work space and its configurations have been determined by considering the kinematic constraints. Modeling accuracy has been evaluated by finite element simulation and also experiments. Simulation results show the maximum error of 1.6% for the inverse kinematic model and the maximum error of forward kinematic model has been 13% in experiments due to manufacturing errors and gravity effects. These results demonstrate that the proposed model has proper accuracy for motion modeling and its control in future works.

Quadrotor is an unmanned aerial robot (UAR) from multi rotor drones group that has high maneuverability, vertical take off and landing (VTOL) and stationary flight capabilities. In the most applications, quadrotor system is subjected to disturbance forces due to wind and unbalanced weight or inertia of the payload. In the most applications, quadrotor system is subjected to disturbance forces due to wind and unbalanced weight or inertia of the payload.In order to maintain balance and hold the position, attitude stabilization of quadrotor is necessary in the presence of disturbances and unbalanced forces. Using conventional controllers with constant gains is not very efficient to eliminate variable disturbances that affect quadrotor in different conditions. In this paper, an adaptive fuzzy proportional- integral- derivative (PID) controller is designed for quadrotor attitude stabilization in which controller gains are regulated continuously based on the adaptive law and the fuzzy system. Performance of the proposed controller is examined in disturbance rejection test and is compared to conventional proportional- integral- derivative controller. Also, performance of the proposed controller is approved by the hardware in the loop (HIL) experimental tests using a 3 degree of freedom (DOF) pilot platform.

In this paper, by introducing a robust hybrid controller with an obstacle avoidance unit based on potential functions, the trajectory tracking control of quadrotors are discussed in the presence of obstacles. Quadrotors are underactuated systems and the design of a robust tracking controller has become one of the most challenging topics in recent researches. First, dynamic modeling of a quadrotor is considered using the Newton-Euler method by considering all its nonlinear terms. In the following, the system state space is represented. Then, a control method based on linear control algorithms is designed to control the outer loop and for the inner loop of the controller, the backstepping method is presented. The combination of the control methods is designed so that the best performance of the system is obtained in terms of convergence to the reference path, minimum steady-state errors and other transient response specifications of the system. In the following, an obstacle avoidance unit based on potential functions is designed to prevent the collision of the quadrotor with obstacles by creating a repulsive force between the system and the obstacles. Finally, trajectory tracking case studies are considered for a quadrotor in the presence of obstacles. Obtained results show the robust performance of the controller in tracking the trajectories and avoiding obstacles.

Hardware-In-the-Loop (HIL) can be used for testing of electronical controller of a closed-loop control system within computer-based real-time simulation of the rest of the system. In this paper, The Pitch Attitude Hold (PAH) mode controller of an unmanned aircraft vehicle is tested using networked hardware in the loop simulation. A computer is used for real-time simulation of flight and a PC/104 hardware is employed for controller implementation. The controller and the simulator are connected using network by UDP protocol. The hardware in the loop simulation can achieve unstable behavior or inaccurate results due to time-delay of network connection. Therefore, a polynomial-based predictor is designed for time-delay compensation of network connection. The consistency of the experimental real-time simulation and off-line simulation shows the applicability of the presented method for mitigating the effect of time-delay in the hardware in the loop simulation. Also, uncertainty of the model raised from stability and control derivatives are investigated. Also, uncertainty of the model raised from stability and control derivatives are investigated. Also, uncertainty of the model raised from stability and control derivatives are investigated.

Oncolytic viral therapy is a new promising strategy against cancer. Oncolytic viruses can replicate in cancer cells rather than in normal cells, leading to lysis of the tumor mass. Besides, oncotic viruses can stimulate the immune system. Since cancer viral therapy applies a virus infection, its complex dynamics should be analyzed using a mathematical model in order to identify its most effective treatment mechanism. During cancer viral therapy, there is a time delay from the initial virus infection of the tumor cells up to the time those infected cells reach the stage of being able to infect other cells. It is important to understand how the delay affects the cancer viral therapy. For this purpose, a mathematical model is introduced to identify this delay. To analyze the effects of delay on virus therapy, the model was reconstructed by adding both virus therapy and immunotherapy control. Finally, using a numerical simulation, a fuzzy PDC controller was designed for the first time. Numerical results showed that with proper control, the tumor cell population decreased to below 10% over time. It is also observed that the use of a delay-independent stability criterion for the design of the PDC controller has reduced the sensitivity of the system response to increasing time delay to an acceptable level. Since the studied system is introduced only in one reference and only the optimal controller is applied, the comparison shows the superiority and power of the designed fuzzy PDC controller.

The nonlinear dynamic and vibration behaviors of a cantilever carbon nanotube reinforced composite trapezoidal plate with two surface-bonded piezoelectric layers as an actuator in micro air vehicles which exposed to subsonic airflow under combined parametric and external excitations are considered in this paper. The plate is reinforced by single-walled carbon nanotubes. The large deflection Von Karman plate assumptions and the classical laminated plate theory are applied to derive the governing equations of the motion of the piezoelectric nanocomposite laminated trapezoidal plate by using the Hamilton’s principle. The geometry of trapezoidal plate is mapped into rectangular computational domain. The Galerkin’s approach is used to transform the nonlinear partial differential equations of motion into nonlinear two-degrees-of-freedom ordinary differential equations of cubic nonlinearities. The case of 1:3 internal resonance and primary resonance is considered and the multiple scales method is employed. The aerodynamic pressure distribution formula is modeled by linear potential flow theory. The frequency-response curves, time history responses and phase portrait in free, forced and actuated vibrations cases are obtained to analyze the nonlinear dynamic behavior of the plate. The effects of different parameters such as the plate geometry, volume fraction of carbon nanotubes and different excitations on the nonlinear vibration of the laminated thin plate are also discussed. A complex softening nonlinearity with two peak in the higher mode is observed in frequency response curves.

The purpose of this thesis is to study the free vibrations along a longitudinal line of a targeted graded nano-micro beam with an attached mass based on the theory of nonlinear elasticity using the asymptotic development method. Due to its small size and behavior depending on its size and the inability of classical therories to predict dependant mechanical behaviors, non classical therories have been used. The governing equations and boundary condition relations of targeted graded nano-micro beam with five boundary conditions simple-simple, clamped-free, clapmed-clamped, clapmed-simple and clamped-attached mass have derived by using Hamiltonian principle. Then differential equation is solved analytically to obtain the frequency equations for the five bondary conditions. In the following, non-dimension frequencies by using the solving zero and first order of numerical asymptotic development method have derived. Advantage of this method is simplicity, noncomplex mathematical relations and proper coding execution time. Eventually, effect of non-local parameter, material length scale, type of material, ratio of length to thickness and mode number on free vibration nano-beam has been investigated.

The length-scale parameter as a primary factor has an important role in approximation of natural frequencies of micro-structures. Applying the exact length scale parameters which are recently determined by researchers, natural frequencies of porous microstructures are determined. In view of the fact that assumption of constant length-scale parameter leads to deviation of natural frequencies from their exact value, this research applies a length scale parameter which is function of plate thickness and material. To model the porous structures of the plate, the proposed porous models including evenly porosity mode, unevenly symmetric porosity model, and unevenly asymmetric porosity model are employed. The micro-plate is assumed to be thin, and classical plate theory is applied to displacement field of the micro-plate. The modified stress couple theory is employed to approximate the behavior of the plate in micro-scale. The trial functions which satisfy the boundary conditions are taken as the polynomial form. Evaluating the energy values of the system, the Rayleigh-Ritz method is imposed to solve the governing equations of the system. Validated the solution procedure with data given in the literature search, effects of various parameters on natural frequency of the plate are studied in the form of tables and curves.

For the first time, in this work, Vibrations of the axially graded Rayleigh moving beams are studied. It is supposed that the material characteristics of the system change linearly or exponentially in longitudinal direction continuously. By using Galerkin method and eigenvalue problem, the natural frequencies and divergence of the system are computed numerically. In addition, the analytical relations are extracted for the critical velocity of the system. Critical velocity contours and stability maps are investigated for different distributions of material. As indicated, exponential and linear changes lead to a more stable system in the variable state of density and elastic modulus, respectively. Also, the results indicated that increasing the elastic modulus gradient parameter or decreasing the density gradient parameter results in an increase in the natural frequency of the system and a development in the stability. Hence, alteration in the density and elastic modulus gradient parameters has an opposite role in the dynamic behavior of the system. The results of this study can be useful for designing and optimizing high speed non-homogeneous axial movable structures.

Deposition of fatty substances and calcium in the artery is one of the factors that cause decrease of blood supply to the organs of the body. One of the common methods to resolve artery stenosis is insertion of a shape memory alloy (SMA) stent in the artery. The use of shape memory alloys in the manufacturing of self-expandable stent has expanded because of the superelastic behavior of this alloy. In this paper, we simulated the SMA stent insertion in an artery to explore stress and damage effects arising from the stent insertion on the artery by using ABAQUS software. In order to simulate mechanical behavior of artery, we considered the effect of the inelastic arterial properties (stress softening and recoverable inelastic deformation) that activated under supra physiological loading in stenting process and in order to simulate stent behavior, the Souza model is used. These two models were applied in ABAQUS by UMAT codes. By using damage model, the amount of damage in the artery, which is one of the factors of restenosis, is investigated. Also, in this paper, we use real diseased artery geometry, which were specified from high resolution Magnetic Resonance Images, therefor the analysis is more in line with reality and it is possible to determine the location of the maximum stress and damage in the artery.

Osteoporotic bone fracture is a significant public health problem. Therefore, it has become a fundamental goal for physicians and biomedical researchers. In this regard, the main objective of this study is to predict hip fracture location under various loading conditions. Nowadays, the use of bone densitometry in clinics has expanded to evaluate and predict osteoporosis. Therefore, in this research, finite element analysis is carried out using models based on images and reports of dual-energy X-ray absorptiometry system to predict the fracture pattern. Initially, the finite element models were created based on the bone mineral density reported in four distinct regions including neck, greater trochanter, intertrochanter, and total hip. To improve the accuracy of predictions, the pixel by pixel bone mineral density map was extracted based on the raw data of the HOLOGIC bone densitometry device. Linear finite element analysis was performed using the maximum risk factor that defined based on the ratio of the strain energy density to the yield strain energy density, and thus the location of femoral fractures were determined based on the location of critical elements. The results demonstrate that using the non-homogeneous distribution of bone mineral density in a finite element analysis of the 2D models based on dual-energy X-ray absorptiometry can be considered as a useful tool for predicting the location of the bone fracture.

Graphene helicoid is a man-made spiral structure that has recently been created with the advent of nanotechnology inspired by nature. In this study, the mechanical properties of multi-layer graphene helicoid with different geometric characteristics are studied using molecular dynamics simulation and the relationship between number of layers, geometric properties and mechanical properties of nanoparticles are investigated. The results show that the unique geometric properties of these nanoparticles produce interesting mechanical properties that are highly dependent on their structure. The stages of the tensile behavior of these nanoparticles are altered by increasing the number of layers corresponding to the geometric characteristics of the nanoparticles. One of the most important characteristics of these nanoparticles is their high stretchability, even for some specimens, up to 3000%, which, with the addition of a layer to their structure, decreases sharply. The results also indicate a strong increase in force in the small strain range with the onset of the stretching process due to the strong van der Walls forces between the adjacent layers. The spring constant for these nanoparticles is calculated in this initial area of the tensile test and, decreases with the addition of the layers. Identifying the properties of multilayered graphene helicoid can lead to an increase in their efficiency and their optimal performance in nanoscale devices and even improve multiscale performance.

A single-stage gas detonation apparatus was used for the free forming of metallic-polymeric structures. In the experimental section, to improve the performance of aluminum plates under gas mixture detonation loading, a layer of polyurea material was sprayed onto the back surface of the metallic plate. In order to investigate the effect of the thickness of the metallic and polymeric layers on the dynamic response of the structure, aluminum plates with different thicknesses of 1, 1.5, 2 and 2.5 mm, as well as polyurea coatings with different thicknesses of 3, 4, 5 and 6 mm, were used. Experimental results showed that spraying the polyurea coating onto the back surface of aluminum plates can significantly reduce the maximum permanent deflection of the structure and also prevent the rupture of the aluminum specimens. In the numerical modeling section, the Group Method of Data Handling (GMDH) neural network was used to present a mathematical model based on dimensionless numbers to predict the maximum permanent deflection of metallic-polymeric structures under impulsive loading. In order to increase the prediction capability of the proposed neural network for this process, the experimental data were divided into two training and prediction sets. The results showed that good agreement between the proposed model and the corresponding experimental results is obtained and all data points are within the ±10% error range.

Laser cladding is one of modification surface approaches which can lead to surface with an appropriate mechanical characteristics like high wear resistance, high resistance from oxidation in high temperature. The aim of this process is cladding one composite, ceramic or metal layer on the substratum. It should be noted that regardless of cladding process parameters, the type of material cladding layer is one of critical parameters which affects on mechanical characteristic in this process. In this research, cladding of composite powder TiC/316LSS with certain volume percentage (TiC/316LSS) 5, 10, 15 on steel 316LSS by using laser type Nd:YAG is investigated. Output parameters include the value of porosity in cladding, the value of transverse crack and the value of dilution of cladding. With designing experiment and analyzing output results by using CCD approach, the effect of input process parameters on the quality of cladding surface is investigated. In addition, by obtaining optimized value of input process parameters for creating cladding surface with lowest value of porosity and crack, cladding surface with hardness of 660 HV 0.1 is achieved, which is 4 times harder than substratum with hardness of 150 HV 0.1.

The automatic cortical bone milling process is being utilized in surgeries and orthopedic operations including knee joint replacement, ontological, spinal cord and hip replacement The behavior of forces generated by the cutting tool during the cortical bone milling process should be prudently evaluated. In this article, an adaptive neuro-fuzzy inference system is utilized to model the effect of important parameters in the cortical bone milling process including the rotational speed, feed rate, depth of cut and tool diameter so as to predict the cutting forces. To model the process force behavior, experimental tests are conducted on the fresh cow femur. Next, the results of performed experiments are used to train and test the employed inference system. In this model, the most influential parameters of automatic cortical bone milling process including the rotational speed, feed rate, tool diameter and depth of cut are taken as the input parameters, while the cutting forces in the feed direction, normal to the feed direction and normal to the bone surface as well as the resultant force are considered as the output. With regard to the network training section, the values of root mean square error and mean absolute error criteria are quite small, being close to zero. These criteria also yield relatively small values (less than 0.5) for the date related to the network test section. Overall, the average network errors for estimating the network cutting forces in the training part and test part are equal to 0.37% and 8.7%, respectively.

In the present paper, a predictive strain-rate-dependent model of localized necking is developed by using a modified Vertex theory. A novel ductile damage -based criterion is proposed to control the necking parameters including on stress triaxiality, strain hardening exponent and Lode parameters. As a characterization parameter, elastic modulus is eventually chosen to measure the ductile damage during process of plastic deforming. Furthermore, a vectorized user - defined material subroutine is developed to finite element simulation by ABAQUS software, according to original formulations, in order to create linkage between related essential models. A typical strain rate-dependent metal is selected to validate the modified Vertex theory. To examine the accuracy of the results from present simulated study, the applicability is considered to compare with the experimental results. Tests of forming are also performed for St 13 and St14 sheets to measure forming limit diagram (FLD). It should be noted that the simulated FLDs are in good agreement with the experimental data. However, this correlation at low strain rates is better than high strain rates. However, this increase will be infinitesimal for the lower strain rates as compared to the higher ones.

Adhesive joints have been employing in engineering structures such as marine, aerospace, automotive, oil and gas industry. Since the joints are the weakest part of engineering structures, the fracture possibility in adhesive joint is high. Therefore, structural health monitoring of adhesive joint is an important issue. The aim of this paper was condition monitoring of damage in the single lap adhesive joint by multiwall carbon nanotubes. This work is carried out by recording the electrical resistance change during the mechanical loading. This damage propagation is observed as a crack extension in adhesive joint. Firstly, MWCNTs with 9 wt.% are dispersed in an epoxy resin by ultrasonic device. Then, the hardener is added to the nonoadhesive. The obtained material is immediately poured into single lap adhesive joint mold. The defective adhesive joints were manufactured with circular and square defects in different sizes i.e. 10%, 30% and 70% overlap area. The specimen is subjected to tensile test and electrical resistance change are recorded during the shear load. The results showed that the maximum value of relative resistance change is occurring in the adhesive joint comprises of square defect with 30% overlap area of defect. In this situation, the crack was propagated in nanoadhesive and a small part of a crack was extended from defect boundary.

Flanged joints’ looseness is among the common causes for the failure of industrial structures with flanged joints the timely detection of which can prevent the imposition of heavy financial losses and in some cases injuries. There are conventional methods for detecting this fault and each of them has its own drawbacks. For instance, torque control methods have high error of measurement, impedance-based measurement methods, have high expenses, and vibration or ultrasonic methods lack accuracy due to the use of linear phenomena in fault detection. Vibro-Acoustic modulation method is one of the nonlinear fault detection methods that detect and assess looseness of flanged joints with high precision through the measurement of the intensity of the vibrational and ultrasonic signals modulation applied to the structure. This paper was an attempt to investigate the efficiency of the Vibro-Acoustic modulation method in the detection and evaluation of flanged joints numerically and experimentally. For this, a laboratory sample composed of two pipes connected with flanged joints is employed. It is revealed that this method can detect bolt looseness with 12.5% precision. In addition, the effect of parameters such as ultrasonic and vibrational frequency, amplitude of applied torque, sensors and actuators position, as well as excessive increase of torque have been examined and the model precision in the studied structure has been estimated.

Thread has been considered as a widely used technology in the industries. Thread milling is suggested as an alternative process of tapping. Thread milling includes a small tool which follows a helical path. This process includes significant advantages such as threading holes with different diameters using a specific tool. One of the important issues in machining is the tool wear. Besides a noticeable effect on the machining economy, tool wear has a direct impact on the surface roughness and dimensional accuracy of the workpiece. In thread milling, effective parameters on the tool wear include tool angles and geometry, infeed method in thread cutting, feed, and tool rotational speed. Tool wear and infeed method in thread milling have not been subjected in recent investigations. Hence, this research studies the infeed methods and effective parameters of the machining process on the tool wear during thread milling. Experimental results showed increasing of feed from 0.2 to 0.4 mm/rev led to 30 to 40% larger values of tool flank wear. Also, the variation of rotational speed from 500 to 900 rpm increased tool flank wear about 50 to 60%. Two cases of infeed method were employed which were incremental and modified flank infeed. Considering different rotational speeds, the incremental infeed method increased tool life about 100% while the modified flank infeed method achieved 300% higher tool life.