مجله مهندسی مکانیک امیرکبیر
سال پنجاه و چهارم شماره 10 (دی 1401)

In this paper, the size-dependent vibration of nanoscale beams with simultaneously longitudinal and rotational motions is analyzed based on Eringen nonlocal theory. Also, for the first time, a parametric study is performed to explain the surface effects, viscoelastic-Pasternak substrates characteristics, thermal loads, geometric properties, symmetric and asymmetric cross-sections, axial and follower loads on the dynamics and stability of the system. First, the dynamic equations of the system are obtained using the Hamilton principle. Then, with the help of the Galerkin discretization method, the natural frequencies of the system are determined. To ensure the accuracy of the proposed model and method, the present study results are compared and validated with those of published articles. Stability maps and Campbell diagrams are drawn for different working conditions. The results showed that increasing the surface elastic modulus and residual stress improves the vibration frequencies and the dynamic instability threshold of the system. It is also found that with increasing system thickness/length, the axial velocity of static instability decreases/increases. In addition, it is observed that in contrast to the nonlocality effects, the system performance improves with increasing the elastic and shear coefficients of the substrate. The results of the present study significantly help designers and engineers control the vibration of bi-gyroscopic nanostructures.

Microfluidics has many applications in modern sciences such as medicine and biomedical engineering. There are usually two ways of injecting fluids; using pressure regulations in fluid flow lines and using syringe pumps, which using syringe pumps is the most common way. Today, a lot of research has been done in this field, but a limited number of them have focused on active control of the droplet size. In this research, a microchannel was first fabricated using photolithography. To inject fluids into the channels, a syringe pump is designed and built using a DC motor with suitable speed and torque and the L298N module. The fluids used in this research are double distilled water as a discrete phase and oil as a continuous phase. An Arduino Mega 2560 board has also been used as the processor to automatically control this system. The droplet diameter is calculated using a digital microscope and its image processing with a high-speed algorithm. The sliding mode control algorithm has been used to control the droplet size due to the nonlinearity of the system behavior as well as the disturbances. The obtained results for three different diameters i.e. 82, 90, and 100 µm, show the accurate performance of the sliding mode controller.

Today, the use of drones to automate activities such as civil works, rescue operations and military missions is expanding to increase speed and accuracy, retaining manpower and reducing costs. According to this approach, in this paper, hybrid control of position and force for a spherical inverted pendulum on top of a quadrotor which its motion is constrained in the vertical direction, is studied to enable the quadrotor - spherical inverted pendulum system to perform operations such as painting and cleaning on high ceilings. In this regard, first using Newton-Euler laws, the equations of motion governing the quadrotor-inverted pendulum system in the constrained motion are extracted and then by presenting a model for the constraint force, a hierarchical control system including position-force control loop, inverted pendulum orientation control loop and quadrotor orientation control loop are provided. Proposed Control laws for the inverted pendulum orientation control loop and the quadrotor orientation control loop are designed using some theorems of geometric control methods. Finally, to study performance of the proposed control method, some numerical simulations have been performed.

A rotating composite shaft can be used with the application of power transmission in the rotating machinery industry. Compared to the conventional metal power transmission shaft, the composite power transmission shaft has more natural frequencies and higher critical speeds usually. Accurate determination of the natural frequency of the shaft is of great importance in its design, especially in the case of composite shafts due to the anisotropy of composite materials. In this paper, first in a rotating state, finite element results of a composite shaft eight layers of carbon/epoxy in case of two steel discs in the middle are symmetric with different diameters are compared with the results of previous research and the accuracy of the results is verified. A hollow composite shaft of eight layers of carbon/epoxy and glass/epoxy is modeled with two steel discs on the elastic supports. Applying the Lagrange equations, the equations of motion of the hybrid composite shaft are obtained using the modified equivalent modulus beam theory. By writing code in MATLAB software and numerical solution, the amplitude diagram in terms of frequency in the rotating state is obtained and compared with the results of the composite shaft simulation in Ansys, and validation is performed. Finally, the effect of stacking sequence parameters such as fiber angle, arrangement of use carbon/epoxy, and glass/epoxy on natural frequencies is investigated.

In current research, a strategy is proposed for designing an error tolerant control system using a combination of adaptive neuralnetwork and backstepping method. Any defect in the flight control system may cause an irreparable problem. Typically, a highly reliable system with human decision-making power is used to prevent or correct such errors in a flying vehicle. The fault tolerant control system is designed to deal with various types of errors that may occur in the system. Fault-tolerant control systems are divided into two main parts. The first part is the error detection and isolation phase (FDI) and the second part is the control system design phase to overcome the error effects in the system, depending on the type of error and the location of the error, whether sensor, operator or components, the control system must be able to eliminate effects. In this paper, a neural-adaptive observer is used in the error detection stage and a backstepping method is used in the controller design stage. Finally, nonlinear six-degree-of-freedom simulation results for an F-18 aircraft model are presented to demonstrate the effectiveness of the proposed control law.

In this paper, the nonlinear forced vibrations of carbon nanotubes conveying magnetic nanofluids under a longitudinal magnetic field are investigated. Using Von Karmen nonlinear strain field and Euler-Bernoulli beam theory, the equations governing the nonlinear vibrations of simply supported carbon nanotubes are extracted. Using the multiple scale method, the frequency response is obtained in primary resonance, supperharmonic resonance and subharmonic resonance. The stress driven nonlocal integral model has been used to consider the effects of nano size. Finally, the effect of magnetic fluid and magnetic field strength on frequency response and force response is investigated. From the results it can be found that the presence of a magnetic field causes the vibrational amplitude of the system to be unstable and to have a limit cycle. Under these conditions the vibrational response is quasi-alternative. However, the presence of a magnetic fluid causes the vibration amplitude to be stable and the temporal response to be alternative; So that the Poincaré diagram shows a point on the phase plane. In primary resonance, despite the longitudinal magnetic field, with increasing excitation amplitude, the frequency response curves include two sub-amplitudes. One is an asymptotic curve with a horizontal axis and the other consists of a closed curve.

Today, various treatments such as surgery, chemotherapy, radiotherapy and hyperthermia are used to treat cancer. The best treatment for cancer treatment is to predict and accurately control the distribution of temperature in the damaged tissue, which has been the subject of many studies in recent years. In most studies, it has been observed that, due to the increased temperature in cancer treatment, and especially in the hyperthermia, the healthy tissue adjacent to the damaged tissue also disappears and results in bad consequences. In this paper, the optimal laser control for cancer therapy has been done. To this end, according to the non-Fourier behavior of temperature transitions in laser treatments, the time-dependent transient temperature distribution in one-dimensional mode, along with the heat of metabolism and perfusion of blood, using the Pence heat transfer equation, is analyzed. In order to minimize the damage to the healthy tissues adjacent to the damaged tissue, the objective function includes the difference between the calculated thermal damage with the desired thermal damage is defined. Therefore, the thermal flux value is optimized as an optimal control problem and the lowest and most useful value is obtained. Finally, the results of the numerical solution of this problem are extracted and shown for triangular thermal flux and square heat pulses.

Electromechanical impedance spectroscopy is among the most effective technologies for online damage detection in maintenance.This technique can be used for damage localization by estimating the electromechanical impedance spectrum with numerical or analytical models. The existence of several sources of uncertainty however leads to a significant mismatch between the numerical and experimental results. Therefore, uncertainty quantification for high-frequency coupled electromechanical vibration response of the piezoelectric patch is necessary. Polynomial chaos expansion (PCE) is an efficient method for assessing uncertainty when dealing with time-consuming models. For the probabilistic analysis of modal features of the impedance spectrum, surrogate models derived by polynomial chaos expansion were used. The statistical moments and probability distributions of the quantity of interest were computed analytically using surrogate models. By post-processing the coefficients of PCE models with relatively minimal computing cost, global sensitivity analysis was performed to rank the relevance of input variable variation on response variance. According to the results, due to the common uncertainties in the material properties and geometry of the piezoelectric patch, the coefficient of variation in the peak amplitudes is substantially higher than the peak frequencies. In addition, modal frequencies are most sensitive to mechanical properties (compliance and density), whereas modal amplitudes are most sensitive to mechanical damping, electrical permittivity, and the piezoelectric constant.

In this paper, the effect of porosity on the thermo-elastoplastic bending response of temperature-dependent functionally graded (FG) plates exposed to a combination of thermal and mechanical loads is studied using a three-dimensional meshless model based on the radial basis reproducing kernel particle method. To describe the plastic behavior of the FG plate, the von Mises yield criterion, isotropic strain hardening, and the Prandtl-Reuss flow rule are adapted. The material properties, which are assumed to be temperature-dependent, are continuously varying in the thickness direction according to a power-law function in terms of the ceramic and metal volume fractions. The modified rule of mixtures is employed to locally evaluate the effective thermomechanical parameters of the FG material. To show the accuracy and efficiency of the present method, the obtained results are compared with the analytical and numerical results in the literature and very good agreements have been observed. In addition, the effect of significant parameters such as porosity coefficient, material gradient index, thickness ratio and boundary conditions on the bending response of FG plates has been investigated.

Nowday, due advancement of technology, the number of oscillations applied to some parts reaches range of 107 and higher. Recently, researchers have used ultrasonic fatigue test to study the fatigue behavior in these parts. This device is considered because of the high frequency of loading and as a result, achieving a higher number of oscillations in a shorter time. There is no universally accepted standard for this test, so one of the most commonly used geometries in this test is the hourglass. while examining this geometry in order to achieve optimal geometry or maximum stress, the effect of geometric parameters on temperature increase during high frequency vibration or the thermal elasticity effect which is known as one of the disadvantages of ultrasonic fatigue test. has been studied to minimize this effect. For this purpose, the dimensions of the hourglass geometry were defined as a parameter and its changes were investigated using simulations.The results show that by decreasing radius of curvature along with constant diameter of middle part and diameter of cylindrical part, the amount of stress increases and also the amount of temperature changes decreases increasing diameter of the cylindrical part while middle diameter and amount of curvature is constant increases the amount of stress and temperature. The above results were evaluated using experimental arrangement and good agreement was observed in them.

In this study, the effect of microtextures parallel to cutting edge on the rake face of cutting tools during the turning process of 17-4PH steel was investigated. The depth, width, and distance of micro-textures were studied. Turning tests were performed with the created tools and the cutting force was measured by a dynamometer. The results showed that by increasing the width of microgrooves, the cutting force first decreases and then increases. This trend shows that the width of the microgrooves has an optimal value in which the cutting force during the turning process is minimal. Also, the cutting force is reduced with increasing the depth of microgrooves. By increasing the distance of microgrooves, it was found that the cutting force has increased. Based on the optimization results, the optimal values of the parameters of width, depth, and distance of the microgrooves are 126 µm, 15 µm, and 200 µm, respectively. The calculated error percentage for optimization validation was 5.81%, which indicates the high accuracy of the optimization process in the Design-Expert software. The deflection of the workpiece was achieved with a tool with an optimal microgroove of 30 µm and with a plane tool equal to 62 µm, which shows a 51.6% reduction with a textured tool. In fact, the accuracy of the machined part was improved with microtextured tools.

In recent years, the use of welded joints in fiber-reinforced composite structures is developing strongly. Welded joints have inherent defects caused by the manufacturing process. Initial cracks start from these defects and eventually lead to component failure. Therefore, the extraction of important parameters at the joint layer is a great help to engineers in designing and predicting the initiation time and development of interlayer crack in the weld layer. In this article, to investigate the second mode of fracture, the experimental and numerical calculation of the release rate of interlayer shear strain energy in the ultrasonic welding of composite materials has been done. In this research, 3 data reduction methods (CCM), (CBT) and (CBBM) have been used to calculate the strain energy release rate and the trapezoidal traction-separation model has been used to model the weld layer in Abaqus software. Then, the coupling of experimental and numerical results has been used to extract the parameters of the traction-separation law. Finally, the force-displacement diagrams obtained from experimental investigations and the force-displacement diagrams extracted from numerical modeling are compared. The results show that the models extracted using CBBM and CBT methods have good predictions for CCM method. Also, the contribution of bridging fracture toughness in crack growth is greater than the initial fracture toughness.