مجله مکانیک سازه ها و شاره ها
سال سیزدهم شماره 4 (مهر و آبان 1402)

In this article, thermo-elastic analysis of a thick hollow cylinder under internal pressure is investigated. The material properties are considered to be temperature-dependent and functionally graded in radial direction. This temperature dependency caused the heat conduction equations to be nonlinear. The perturbation theory is performed for solving nonlinear heat conduction equations of the cylinder. Arbitrary combined thermal boundary conditions containing temperature and temperature gradient are considered. As the temperature field is extracted, it can be used to solve decoupling thermal stress governing equations. These thermo-elastic equations and related boundary conditions are discretized in strong form using differential quadrature method. Numerical results extracted from the suggested semi-analytical approach in a linear regime are then compared to the existing results. It is depicted that the presented method benefits from the low computational and high convergence behavior. The stress distribution of the cylinder is computed by considering the approximation of the temperature in zeroth-order, one-order as well as second-order. In order to achieve proper accuracy, more terms of the perturbation approximation series should be considered for the higher temperature difference between the inner and outer surfaces of the cylinder.

The vibration of cylindrical shells with rigid disks attached at the edges is investigated and the results are compared by those obtained under the common simplifying assumption that the edges are clamped at points attached to the rigid disk. The shell is modeled using Sanders-Koiter shell theory, including the transverse shear deformation. The effect of the rigid disk on the edges displacements is also determined in a systematic manner by using the kinematic relations of the disk. To solve the problem, the semi-analytical finite element method is used and the stiffness and mass matrices of the element attached to the disks are completely determined for the first time. The reason that the disk affects the stiffness matrix is that some constraints appear between the displacement components of the shell edges due to the attached rigid disk. Numerous numerical studies are performed to investigate the effect of mass properties of the rigid disks on different shell natural frequencies and mode shapes. Results show that the rigid disk can significantly change the natural frequencies of the modes with zero and one circumferential wave number. It is also shown that by increasing the rigid disk mass, the mode with the smallest frequency would change from a mode with a high circumferential wave-number to a beam-like bending mode.

The paper discusses the design of an observer-based fault-tolerant control algorithm and active vibration control for attitude stailization of a flexible spacecraft (as a rigid-flexible system) subject to external disturbances. An iterative learning observer has been developed in order to estimate the torque deviation caused by actuator faults. One of the main features of the proposed observer is the consideration of external disturbances in its structure. Next, a fault-tolerant sliding mode control (SMC) law based on a proportional-integral-derivative (PID) structure with a time-varying switching gain is proposed in order to generate control signals with ideal performance. To minimize residual vibrations during and after the maneuver, the strain rate feedback (SRF) control algorithm is also activated simultaneously with fault-tolerant control. Using Lyapunov theory, the proposed control strategies guarantee global stability for the closed loop system. Numerical simulations as a comparative study have been used to demonstrate the effectiveness of the developed system compared to conventional algorithms, such as integral sliding mode control, when handling actuator failures, external disturbances, and flexible body excitations in rigid-flexible dynamic systems.

Since resonant micro/nanoresonators are very delicate devices with very small dimensions, therefore, any defects and faults caused by the process of manufacturing and laboratory implementation can lead to fundamental changes in their vibration behaviors. Therefore, the effects of the mentioned disadvantages should be considered as much as possible to obtain more accurate sensors with higher efficiency. In this study, a general model of a doubly clamped microbeam (nanotube) with an asymmetric cross-section with external excitation is considered. Then, linear and non-linear behaviors of an ideal nanotube with a circular cross-section are investigated. The results of the simulations indicate a good agreement with the experimental references available in the literature. Then, taking into account the asymmetry in the resonator cross-section, the system is moved away from an ideal model to a more real model, and the possible effects of the asymmetric cross-section in adjustment, reduction, and vanish of internal resonance are investigated and studied. Finally, the advantages and disadvantages caused by asymmetries and the optimal use of such an opportunity to obtain more innovative and complete models with higher efficiency are explained.

In this research, the influence of the parameters of metallic wires in the foam cores of sandwich panels as a reinforcement to improve the bending properties of sandwich panels has been investigated. In this regard, the three parameters including the number of wires (on a scale of 1, 2, and 3 wires), wire material (aluminum, iron, and steel) and their diameter (0.75, 1, and 1.5 mm) as the effective input parameters and specific bending strength and modulus of the structure have been selected as the output parameters of the design of experiment. In order to evaluate the parameters after validating the numerical model using the built prototype, an experiment has been designed using the Mini Tab software (Taguchi method) and simulation of the proposed tests has been carried out using the Abaqus software.The results showed that the optimal sample with priority of strength to weight includes three steel wires on each side, with the diameter of one millimeter. Also, with the increase in the number and diameter of the wires, the strength has increased, but this relationship is not always correct when assessing the strength to the weight of the sample. Increasing the mechanical properties of the wire increases the overall strength of the structure, so that the bending strength of the sandwich panel reinforced with three steel wires rises by about 43%, the bending modulus by about 80%, the specific strength by weight by 21%, and the special bending modulus by about 54%.

The physical and chemical properties of living tissues change with the change in their physiological conditions during disease. AFM can perform surface imaging and ultrastructural observation of living tissues at nanometer resolution under near-physiological conditions and collect force spectroscopic information, which enables the study of tissue mechanical properties. In this research, AFM was used to measure the elasticity modulus of stomach cancer tissue. For this purpose, in order to bring the theoretical results closer to the experimental reality, three-dimensional modeling of the developed contact theories has been done. Since in most of the past research, the shape of spherical target particles has been assumed, as an important innovation, in this research, cylindrical contact models including Hertz, Dawson, Nikpour, Hoeprich, and Lundberg have been modeled, and the simulation of each of these models has been done using MATLAB software. The simulation results of contact models have been compared with the results of experimental work. From the results obtained from this comparison, the modulus of elasticity in kilopascals at the most appropriate penetration depth of the AFM needle for biological tissue has been extracted. The results have shown that the Hoeprich model is a suitable model for theoretical simulation and is closest to the experimental results. By comparing the obtained results and the previous results, the difference percentage of the results for gastric cancer tissue is between 3 and 20% at the end, and the validity of the results was checked.

In this paper, the formability behavior of thin-walled aluminum tubes has been experimentally investigated using the hydraulic rotary draw bending process. At first, AA6063 tubes with a ratio of diameter to thickness of 13.88, outer diameter of 25 mm, and thickness of 1.8 mm were subjected to heat treatment operations; annealing and artificial aging. Then, bending experiments were carried out on as-received and heat-treated samples at fluid pressures of 0, 1, 1.8, 3.2, and 3.6 MPa. After performing the experiments, the amount of thinning and thickening of the bent tubes were measured. By examining the results, it was found that for all samples, the maximum thinning and thickening occur at an angle of 40 degrees to the pressure die. Also, the examination of the formability results of the tubes demonstrated that the heat treatment and the fluid pressure have interaction effects, so the effect of the heat treatment is not very noticeable at the fluid pressure of 0 MPa, but the effect of the heat treatment is remarkable at the maximum fluid pressure of 36 MPa. At maximum fluid pressure, aging heat treatment reduces thinning by 7% and annealing heat treatment increases thinning by 13% compared to the as-received sample. In addition, in comparison to the as-received sample, the thickening of aged tubes increases by 5% and decreases by 16%, respectively.

The present study investigates the optimal design of the die shape in the metal forming process using extrusion. Due to the large deformations that occur during the forming process and the resulting entry into the plastic deformation zone, the finite element method is used to analyze the problem in this area, and the modeling is performed in the Eulerian system. The objective function of this study is to minimize the total energy required for deformation in the extrusion process. The design variable is the die shape, and spline curves with multiple control points are used to generate the die shape. Due to the nonlinear nature of the forming problem, the complexity, and the large amount of computation required during the analysis, a powerful combination of two metaheuristic optimization methods, the Imperialist Competitive Algorithm and Ant Colony Algorithm (ICACO), has been inspired for the optimal design of the die shape. To validate the obtained results for the die geometry, they are compared with the results presented in previous studies, The error was less than 2%, showing a good agreement. The results obtained have led to a significant reduction in the total energy consumption during deformation by approximately 12% compared to the conventional linear mode.

Metal matrix composites have attracted a lot of attention for application in the aerospace, defense, and automotive industries. Machining these materials with traditional machining methods is very difficult due to the presence of abrasive particles. Electrical Discharge Machining (EDM) is one of the most widely used advanced machining methods and seems to be a good method for machining metal matrix composites. Tool wear occurs during the process and cannot be reduced to zero, but it can be reduced as much as possible. In this research, the effect of discharge peak current, pulse on time, and pulse off time on the workpiece made of AZ91 magnesium alloy, reinforced with 5% of powdered silicon carbide particles has been investigated. The effect of these parameters on the wear rate of copper electrode is studied. The tests of this process have been modeled using the response surface methodology. 17 experiments have been done to reach the results. Discharge peak current, pulse on time, the interaction effect of discharge peak current and pulse on time, and the interaction effect of pulse off time and discharge peak current are effective factors on electrode wear rate. The lowest electrode wear rate is on the 300 microseconds pulse on time, 11.69 amp discharge peak current, and pulse off time of 20 microseconds.

Clean electrical energy and freshwater are two basic human needs that can be met by using solar energy properly. In this article, the goal is to produce electricity and freshwater simultaneously by installing a solar still coupled with a semi-transparent solar module. The coupled solar system was simulated in ANSYS Workbench 2022 software environment.To check the water yield, the system was simulated at different brackish water temperatures of 60 , 70 , and 80 and different wind speeds of 1, 2, 3, 4, and 5 m/s. Also, ten scenarios were defined and simulated according to radiation intensity and brackish water temperature. The results showed that the increase in brackish water temperature and the wind speed increased the amount of freshwater production, and the effect of brackish water temperature was greater compared to wind speed. By increasing the brackish water temperature from 60 to 70 and from 70 to 80 , the average water yield increment for the wind speed of 3 m/s is 64% and 120%, respectively. Also, by increasing the wind speed from 1 m/s to 5 m/s at 70 , the output power of the system increases by 10.53%. The simulation results in ten different scenarios showed that the coupled solar system was more efficient than the independent solar system in eight cases. According to the results of this research, it is suggested that the southern regions of the country with high radiation intensity and high wind speed should be considered for installing the coupled solar system.

One method to improve heat convection is to increase the heat transfer coefficient of the working fluid. Adding metal or non-metal nanoparticles into the base fluid, known as nanofluid, is a technique to enhance the heat transfer coefficient. Research in the field of nanofluids has grown significantly in the last two decades. In this study, the effects of a homogenous combination of Al2O3 and TiO2 nanoparticles with deionized water are investigated. The thermohydraulic performance of the nanofluid inside the vertical channel is analyzed by experimental and numerical methods for turbulent and laminar flow. The turbulence model utilized in computational fluid dynamics is the k-ε model. The heating rod in the test section produces 1 kW cosine heat flux. The results show that increasing the concentration of nanoparticles significantly reduces the maximum temperature of the rod. The use of 1% homogeneous nanofluid reduces the maximum temperature by 20% at the Reynolds of 950 and 9.5% at the Reynolds of 4200 compared to pure water. Also, the heat transfer coefficient increases with the addition of nanoparticles. The difference between the results obtained by the k-ε turbulence model and the experimental method shows a difference of 10% to 13%. This research shows that the combined nanofluid with suitable thermal performance can be one of the working fluids in future thermal cycles.

Domestic refrigerators have become an essential part of modern life.Since these devices are connected to the power grid and operate continuously throughout the day and year, they consume a lot of energy.Experimental studies show that adding phase change materials in refrigerators in different places improves the energy efficiency of these appliances.In this study, the effect of adding a phase change material(PCM)box on the thermal performance and electricity consumption of a single-door refrigerator/freezer is studied.The box of phase change material is attached to the bottom surface of the evaporator with different materials.Water with a melting temperature of zero degrees Celsius has been used as a phase change material.To study the effect of increasing the thermal conductivity of water, fins with the same material(copper, aluminum and steel)as PCM box are placed in the box to evaluate their effect on temperature distribution and power consumption.The results show that the presence of the water box in contact with the bottom surface of the evaporator helps to reduce the temperature of the cabin due to the potential of water as a phase change material in absorbing and releasing cooling energy.Also, the results show that copper is more suitable for water storage because of its higher thermal conductivity and it helps to more evenly distribute the temperature.Furthermore, using a fin inside the water chamber, in addition to limiting the temperature range of the cabin, on average causes a further reduction in energy consumption by 1 to 4% compared to the case without a fin.