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

Large amplitude vibrational characteristics of variable section thin beams with edge rotations restrained by elastic torsional springs and supported on a cubic non-linear elastic foundation are studied. The motion equations and the corresponding boundary conditions are derived by employing Green’s strain together with von Kármán geometric non-linearity assumptions. The derived equations are discretized in the spatial domain using the differential quadrature method. The reliability and accuracy of the method are assessed through a comparative analysis of various available methods for beams with different geometrical parameters and boundary conditions. The study investigates the impact of various parameters on the non-linear to linear frequency ratios (NLFRs) of doubly linear and parabolic tapered beams. It is found that for double-linear tapered beams, the first three frequency ratios approach maximum values and then decrease by increasing the truncation factors. For double-parabolic tapered beams, first and third frequency ratios have maximum values, while the second frequency ratio increases initially and then remains constant. In addition, the transverse elastic coefficients depend on the shearing layer coefficient, especially for the doubly linear tapered beams. Also, in most cases, the frequency ratios decrease by increasing the transverse elastic coefficients. However, for the great values of shear layer elastic constant, the first NLFR of beams with a double-linear taper increases as the transverse elastic constants increase.

The current investigation centers on exploring the impact of sinusoidal wall surfaces on C-shaped cavities. The analysis aims to scrutinize the influence of both the Ra number and the sinusoidal wall shape function on fluid flow and heat transfer within the system. Four different sinusoidal wall shapes (y = sin(x), y = sin(6x), y = 4sin(x), y = 4sin(6x)) along with a smooth wall are being considered. The influence of Ra on the heat transfer mechanism within the cavity is prominently evident in the observations. For Ra ≤ 10⁴, the flow intensity is weak, and heat conduction predominantly governs the heat transfer mechanism. As Rayleigh (Ra) values surpass 10⁵, convective heat transfer emerges as the prevailing mechanism. Notably, heat transfer characteristics exhibit an uptick with higher Ra values. The variability in heat transfer characteristics attributed to changes in the wall shape function can be delineated based on the magnitude of change. The initial category encompasses walls with smooth surfaces, such as y = sin(x) and y = sin(6x). Conversely, the subsequent category comprises walls represented by y = 4sin(x) and y = 4sin(6x). Among these scenarios, the one featuring a smooth wall shape demonstrates the lowest heat transfer characteristics. Conversely, the case with y = 4sin(6x) walls exhibits the maximum heat transfer characteristics.

Liquid metallurgy is a cost-effective way to produce aluminium (Al) alloy products. Alloying and reinforcing in aluminium-matrix is the most practiced one in the liquid metallurgical technique, especially for mass production. Numerous developments have been observed in this technique over the past decade. This paper reviews most of the developments in processing techniques, along with providing basic information and parameters. Also, the shortcomings of each process have been significantly summarized, and potential research opportunities have been discussed. The developments in the batch and mass liquid metallurgical technique for Al have been discussed. The latest development recommendation for processing parameters and techniques to reduce the cost and time of production has been studied in detail. Based on the literature review and various published patents, the most relevant technique is a bottom-feeding continuous casting technique to produce metal matrix composites and aluminium alloys.

Composite structures are widely used in various engineering sectors, such as ships, aerospace, and automobiles due to their specific mechanical properties. In service operations like maintenance (dropping of tools), these structures are often subjected to low velocity impact (LVI), which leads to a decrease in the strength of laminates. Parameters such as fiber orientation, stacking sequence, boundary condition (BC), impactor geometry, and angle of impact affect the performance of composites. Therefore, it is essential to study the response of composites under LVI for different parameters. The role of fiber orientation and geometrical factors (oblique impact, impactor geometry, and off-center loading) on the dynamic response of composites under LVI needs to be investigated. The initial section of the research validates the presented numerical simulation results of reference layup A i.e. [0₂/45₂/90₂/45₂]_s with previously published experimental results. In the second part, finite element analysis to study the effect of normal and oblique impact and the effect of off-center loading on three different combinations of CFRP layups under LVI with three nose geometries of the impactor are presented. Simulation performed on CFRP T700GC/M21 material for normal and 45° oblique impacts to study the dynamic response using Abaqus/Explicit modeling software. This parametric study shows that the effects of fiber orientations, oblique impact, and impact location with different geometries of impactors plays an essential role in designing composite structures. Under oblique impact, layup B i.e. [0₂/90₂]_2s exhibits the highest fluctuations in all impactor geometries, which signify intra- and interlaminar failure. Additionally, the hemispherical impactor for layup A shows smooth curves and less fluctuation under off-center loading.

This article presents a comparative study of the aerodynamic and thermal behavior of various types of flat-plate solar collectors. The study is based on computational fluid dynamics (CFD) which solves turbulent airflow with different types of baffles. Four models of flat-plate solar collectors were investigated: solar collectors with inclined baffles (SCIB), solar collectors with arched baffles (SCAB), solar collectors with perpendicular baffles (SCPB), and solar collectors with a maze of baffles (SCMB). The reduction in flow passage surface area due to the presence of baffles results in significant increases in airspeed, reaching 254%, 266%, 290%, and 502% of the inlet speed for SCIB, SCAB, SCPB, and SCMB, respectively.

Fractures in the lower extremities are sometimes accompanied by severe damage, so definitive treatments with extensive surgical exposure are impractical. Extensive traumatization and swelling of surrounding tissue often dictate the use of external fixators as a temporary treatment for immediate stabilization of compound fractures. External fixation offers a variety of possible spatial configurations. Adequate fracture stabilization demands a good understanding of the stiffness, strength, sustainability, and tilting of external fixators of different frames. An improper frame can result in nonunion, malunion, delayed healing, and bone re-fracture, some of which are indications for revision surgery. This study employs a numerical approach to assess the stiffness, stress distribution, pin loosening, and interfragmentary displacement in different configurations of external fixators applied to a comminuted fracture in the diaphyseal region of the tibia. Unilateral fixators with single and double rods, bilateral, biplanar, and triangular frames with and without end cross-links are different configurations examined in-silico. Results show that the triangular frame with cross-links exhibits the stiffest, strongest, and most sustainable construct in axial, bending, and torsion modes. Except for the torsion mode, adding the end cross-links does little to increase the stiffness and strength of biplanar and triangular frames. Moreover, doubling the rod considerably improves construct stiffness and strength under axial compression load while appearing to be less superior in torsional stiffness and pin loosening. Furthermore, the bilateral frame demonstrates the most uniform displacement across the fracture gap. The results of this study could be used for preoperative planning of diaphyseal fracture management with external fixators.

In this study, saturation efficiency and pressure drop, two critical parameters for the direct evaporative cooling phenomenon, were numerically investigated and optimized. For this purpose, the direct evaporative cooling process was simulated at inlet air velocities in the range of 1–3 m/s on different thicknesses of CELdek 7090 evaporative cooling pad from 100 to 300 mm. The mathematical model of pressure drop and saturation efficiency was developed by analyzing variance at R-squared values of 99.53% and 99.99%, respectively. Finally, the non-dominated sorting genetic algorithm II (NSGA-II) was applied to minimize the pressure drop while maximizing the saturation efficiency simultaneously. The results indicate that applying mathematical models makes it possible to predict the saturation efficiency and pressure drop of direct evaporative cooling systems with a 4% and 7.9% deviation, respectively. It can also be concluded that the pad thickness effect is more significant on the saturation efficiency than on the pressure drop. On the other hand, the inlet velocity has a greater impact on the pressure drop. NSGA-II optimization demonstrated that, regardless of the pad thickness, optimal saturation efficiency and pressure drop were obtained at the inlet air velocity of 1 m/s. Accordingly, when using direct evaporative cooling systems, efficiency and pressure drop can be optimized whenever the fan is set at a low speed. Depending on the researchers’ and designers’ goals, the findings of this research can be used in the design of direct evaporative cooling systems for different applications to achieve maximal saturation efficiency at the minimum possible energy consumption.

In order to improve the wrist rehabilitation training effect, a 3RPUP_c-UPS metamorphic parallel mechanism is designed according to the physiological structure, motion characteristics and rehabilitation training requirements of the human wrist. Two motion modes of the mechanism, three-rotation and one-translation and two-rotation and one-translation, are obtained by locking or not locking the active joint of the metamorphic limb UPS. The motion output characteristics of the mechanism under two motion modes are analyzed based on the screw theory. The inverse kinematics solutions including the displacement, velocity and acceleration equations are derived. The singularity is discussed and all singular configurations are provided. The attitude workspace of the mechanism is analyzed using the Monte Carlo method. The structural optimization is performed based on the artificial bee colony algorithm. Research results show that the mechanism can fulfil all wrist rehabilitation training actions, such as the flexion/extension, ulnar/radial, traction/extrusion and pronation/supination motions.

The purpose of this article is to introduce the concept of a bi-facial floating solar photovoltaic plant (FSPV_B) and evaluate its technological and economic performance in comparison to an established simulated mono-facial floating solar power plant (FSPV_M). This study evaluates the practicality of floating solar photovoltaic projects in Water Works, Chandigarh, by assessing a 2 MW grid-connected system with a bi-facial PV configuration. The study involves simulating the outcomes of both FSPV_B and FSPV_M plants to identify the most efficient design to achieve maximum power output. The performance parameters, i.e. performance ratio, energy production, levelized cost of energy, and payback period of the floating solar PV plant are evaluated using the PVsyst software. The findings demonstrate that the FSPV_B plant can produce 2887 MWh of energy per year, with a superior performance ratio of 92.90%. Furthermore, the economic analysis indicates that the FSPV_B plant had a shorter payback period (PBP) of 8.3 years compared to the FSPV_M plant with a PBP of 12.7 years. Additionally, the FSPV_B plant has a lower LCOE than the FSPV_M plant. Hence, the study suggests that the proposed bi-facial floating solar power plant would be better, technologically, economically, and environmentally.

Ceramic bearings are widely used in industrial production. They can be used to maintain accurate operations over a long period of time. However, the bearing model that was so thoroughly investigated has not been adapted for ceramic bearings. To better calculate the characteristics of ceramic bearings, the existing model may be modified to account for the high stiffness of ceramics. In this paper, the vibration response is investigated and used to modify the analytical model of bearing-rotor dynamics. Under the influence of thermal deformation, the dynamic parameters of the bearing components, including stiffness, traction forces, and Hertz contact force, are analyzed first. On the basis of the modified dynamic model, the vibration response of the bearing-rotor system, time domain, Poincaré phase diagram, phase trajectory, and bifurcation diagram are simulated under various cage pocket hole diameters. The simulation results indicate that increasing the cavity diameter can appropriately improve the dynamics of the rotor system at high speeds. The established model is highly accurate, with an error of less than 8% when comparing the simulation and experimental results. The study’s relevance to bearing structural design has been confirmed.