Iranian Journal of Science and Technology-Transactions of Mechanical Engineering最新文献

The application of constant air pressure to control a stepper actuator is introduced in this study. This actuator consists of a piston that reciprocates inside a cylinder. At the end of each stroke, the piston strikes the end of the cylinder and changes the position of the inlet and outlet valves. Each impact at the end of the cylinder causes the cylinder to move one step forward. By semi-closing the outlet valves at one end, the magnitude of the impulsive force acting on each end of the cylinder can be adjusted once before driving the actuator, and their status is not changed during the actuation. The impact force is adjusted to be greater than the friction force, causing the actuator to move in one direction. A fluid–structure interaction analysis was performed using the finite element method to evaluate the feasibility of the proposed design and to conduct an initial evaluation of the required parameters. The impulsive force can be adjusted by inputting constant air pressure. For this purpose, the experiment was conducted in two different modes. In the first case, the actuator was placed horizontally without an angle, and the finest resolution of movement was 1 µm. In the second experiment, the actuator was placed on slopes with angles of 1.5 and 2.5 degrees. The displacement of the actuator per pulse was 2 and 3 µm, respectively. According to the mentioned specifications, this stepper actuator can be used in different applications, such as X–Y positioning stages in metrology, electrical discharge machines, and miniaturized robots.

This paper aims to investigate the effect of using a side mirror on the north side of the field and tilting the field to the south on the efficiency of a short-length Linear Fresnel Reflector based on tentative information. Taking into account the design parameters, a prototype with specific dimensions was designed and built. The performance of the device was evaluated under different conditions. The effect of flow rate on the efficiency of the device was examined and it was found that due to the existence of vacuum tubes, increasing the discharge has little effect on the overall efficiency of the device (less than 1%). It was recommended to use a side mirror in the northern part of the field aimed at reflecting again the lost sun rays and consequently increasing efficiency by 6% compared to a field without a side mirror. Based on the experiments, it was concluded that tilting the field to the south improves the performance of the short-length Linear Fresnel Reflector by about 2.5% and 5% for tilt angles of 3 and 6 degrees respectively. Moreover, the simultaneous use of a side mirror on the north side of the field and tilting the field to the south were investigated, which revealed that the use of a side mirror on lower slopes has a greater impact on efficiency.

One Way Clutch (OWC) is a machinery component widely used in mechanical industries for transmitting a large amount of torque in one direction while running freely in the reverse. Load reversal in OWC results in highly stressed contact regions and damage leading to fatigue wear initiated from subsurface microcracks. A linear elastic–plastic material model is utilized to capture the effects of microplasticity for case hardening steel in conjunction with continuum damage mechanics. The damage evolution material parameters for case hardening steel are derived using a torsion fatigue curve generated by empirical relationships. A 2D representative volume element (RVE) is considered to predict fatigue lives using damage coupled finite element analysis. The microstructure randomness of the material volume is taken into account by Voronoi tessellation. Fatigue lives and their dispersions are observed to follow the Weibull distribution. The simulation results of this study show a good correlation with experimental results. The influence of residual stress distribution and case hardening depth on fatigue lives is also studied.

The present paper investigates the buckling behavior of grid-stiffened composite annular spherical shells with geodesic lattice cores subjected to external pressure, using analytical and numerical approaches. Using a smeared stiffener technique, the grid structure is transformed into an equivalent composite layer. To achieve the overall stiffness of the grid-stiffened shell, the stiffness of the stiffeners should be superimposed by the stiffness of the shells. The governing equations are formulated based on the classical Donnell’s thin shell theory. The Galerkin method has been applied to extract the buckling loads. To corroborate the analytical results, a finite element model is provided. The comparisons indicate satisfactory agreement between the two approaches. Moreover, the effect of meridian angle, stiffener orientation, and skin thickness are investigated. The results obtained are new and can be used for future studies.

Aiming at the effect of cavitation on the propeller performance of underwater vehicles during navigation, this paper is based on the Reynolds Averaged Navier Stokes method combined with the Schnerr-Sauer cavitation model and the RNG (k - varepsilon) turbulence model. The comprehensive effects of cavitation number, advance coefficient, rotational speed and skew angle on the cavitation hydrodynamic characteristics of the MAU4-40 propeller widely used in marine industry are systematically analyzed. The results show that the cavitation phenomenon will gradually decrease with the increase of the advance coefficient or the cavitation number. With the increase in cavitation number, the thrust and torque of the propeller increase gradually. With the increase in propeller rotational speed, the hydrodynamic characteristics of the propeller show the trend of first increasing and then decreasing, with the maximum value appearing at (n = 30rps). The blade vorticity cloud and wake tip vorticity of the propeller show different changing trends. The cavitation area and hydrodynamic force of the propeller decrease with the increase of the skew angle, and thrust and torque reach their maximum when the skew angle (theta = 18^{^circ }). This study not only focuses on the overall effect of cavitation on propeller performance, but also goes deep into the details of thrust and torque, blade vorticity cloud map and wake tip vortex morphology, so as to conduct a comprehensive and in-depth analysis of propeller cavitation hydrodynamic characteristics. The complex effects of several key parameters on its performance are revealed, which provides powerful theoretical support and practical guidance for the optimal design of the propeller.

The current research deals with the rapid surface heating of cylindrical panels made of functionally graded materials (FGMs). The investigation encompasses the temperature-dependent nature of all thermo-mechanical properties within the FG media. Applying the uncoupled linear thermoelasticity theory establishes a one-dimensional transient heat conduction equation modelled by the Fourier type. Various distinct rapid heating boundary conditions are imposed on the top and bottom surfaces of the panel. First, the finite element method (FEM) is utilized to discretize the heat conduction equation across the panel thickness. As a result of the temperature dependence of the material properties, the heat conduction equation takes on a nonlinear form. Consequently, the time-dependent ordinary differential equations system is tackled through the iterative Crank–Nicolson time-stepping method. The thermal force and thermal moment outcomes acquired at each time increment from the temperature distribution are integrated into the equations of motion. The equations of motion are derived using the first-order shear deformation theory (FSDT). Due to the accuracy and suitable convergence rate , the Ritz method is used to discretize the equations of motion. The direct integration method based on the Newmark time marching scheme is employed to determine the unknown displacements at any given time. The accuracy of the formulation and solution method is verified through comparison investigations. Numerous examples are presented for functionally graded material consisting of SUS304 as the metal component and Si(_3)N(_4) as the ceramic component to examine the effects of various parameters such as power law index in the FGM formulation, temperature dependence, panel opening angle, in-plane and out-of-plane boundary conditions, and type of rapid heating on the thermally induced response of the FGM panel under thermal shock.

Our paper focuses on wave propagation in a circular annular piezoelectric plate with hexagonal elastic symmetry used in Micro-Electromechanical Systems (MEMS). The objective is to examine the properties of two piezoelectric materials: PZT-5A, a soft ceramic used in ultrasonic sensors, and PZT-4, a strong ceramic used in ultrasonic actuators. We developed the Legendre orthogonal polynomial method to obtain semi-analytical solutions for the governing equations. One strength of our method is that it can analyze the global structure using a single formalism calculation. The analysis takes into consideration the alternating current excitation and directly includes the boundary conditions into the vibration equations. As a result, we found that the limit value of voltage ({V}_{0}) across the electrodes equals (160 V) that can be applied to determine the maximum von Mises stress without exceeding the yield stress value of (31.2text{ MPa}) for the PZT4. The electromechanical coupling coefficient shows that the fundamental mode is the most piezoactive mode in the structure. Furthermore, we present the natural frequencies, electrical input impedance, field profiles, and dispersion curves. To validate the efficiency and accuracy of our approach, we compared our results with those obtained using voltage excitation and analytical data. Ultimately, we achieved a good agreement between them.

The left ventricular assist device (LVAD) is a blood pump that boosts the pumping ability of the bottom left chamber of the heart in patients with advanced stage of heart failure. This study aims to present a detailed investigation into the hemolytic characteristics associated with an LVAD, while scrutinizing the impact of valves on blood damage in a reciprocating blood pump. To this end, a numerical approach is utilized to explore the effect of valves movement and leakage flow as the two critical causes of red blood cell damage (hemolysis) by capturing the full range of the valve motion. To predict both blood flow and the hemolysis index, corresponding time-dependent nonlinear partial differential equations are integrated into the governing formulation system. The fluid dynamic characteristics are derived from the Navier–Stokes equations, while the degree of hemolysis is determined by incorporating two additional scalar transport equations using an Eulerian transport method. To simulate valves closure, we consider different methods namely, dynamic mesh technique, viscosity valve closure model and the combination of both. The findings reveal that the hemolysis index is minimum at the inlet region and acquires its maximum value at the valves and clearance subdomains. Moreover, the results depict a favorable reduction in the hemolysis index through a simultaneous increase in frequency and decrease at a specific Reynolds number. It is observed that valves movement and valves leakage flow lead to a sensible one and two order of magnitude increase in the hemolysis index, respectively.

Recent years have seen significant advancements in micro-robotics technology. The reason for the use of micro-robots lies in their unique advantages over larger robotic systems. Their small size allows them to perform tasks in inaccessible spaces, offering a level of precision and flexibility that is unmatched. This makes them particularly useful in the medical field, where they can be used for targeted drug delivery, tissue engineering, and minimally invasive surgeries, significantly reducing recovery times and improving patient outcomes. So far, micro-robots have been designed and controlled using various flagella and configurations. This study introduces a new flagella arrangement for micro-robots, utilizing five flagella: one at the center of the micro-robot and four surrounding it at equal 90-degree angles and distances. The results indicate that this flagella arrangement enhances the speed and maneuverability of the micro-robot compared to previous models. Additionally, this research explores different motions by varying the rotational frequencies of the flagella, enabling the micro-robot to reach its goal from a starting point through controlled sequences of motions.

The fuel sloshing in the vehicle fuel tank can cause adverse consequences, especially under resonance conditions, and the vertical baffle may efficiently restrain the fuel sloshing. The current work couples mesh motion and volume of fluid to investigate the effect of baffle height on the liquid sloshing damping effect at different filling levels under resonance conditions. The aim is to explore the optimal baffle height at different fuel filling levels. The results indicate that the best damping performance can be obtained when using baffles with the same height as the fluid height. To reduce the impact pressure on the tank walls, a baffle slightly higher than the free surface height should be used at low filling levels, and a baffle slightly lower than the free surface height should be used at medium filling levels. Compared with high filling level, the baffle is more effective in reducing the sloshing force and moment at low and medium filling levels. A new formula for calculating the energy damping ratio is proposed. At 20% fuel filling level, the energy damping ratio increases continuously as the baffle height increases, and reaches the maximum value of 85.31% when h_b/h_w = 1.2. At 50% and 80% fuel filling level, the damping ratio reaches the maximum when h_b/h_w = 1, which is 79.79% and 56.39% respectively. This study provides important theoretical support for the anti-sloshing design of a vehicle fuel tank.