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

In this study, experimental and numerical methods have been used in order to obtain the elastic modulus of the gradient structure with auxetic unit cells (negative Poisson’s ratio). Stress shielding is the most significant issue at the bone-implants interface. The difference in elastic modulus between bone and implant provides stress shielding. The development of mechanical properties in the porous structure can provide opportunities to resolve this mechanical properties mismatch between bone and implant. In this study, firstly, the uniform auxetic unit cells with negative Poisson’s ratio were introduced, and their mechanical properties were investigated by numerical and experimental methods in the x and y direction, and the results were verified. Then, numerical methods were used to achieve the uniform distribution of the elastic modulus in the gradient structure. Therefore, in the gradient structure, the elastic modulus in the outermost layer (assumed the contact surface with the bone) is considered lower to reduce the stress shielding at the bone-implant contact surface. In the next layers approaching the center of gradient structure, the elastic modulus is increased gradually in order to increase the mechanical properties of the whole porous structure. It is noted that the difference in elastic modulus between two contact layers is approximately 15% to reduce stress shielding. The results showed that stress shielding could be reduced by using the gradient structure. In addition, using negative Poisson’s ratio unit cells can establish good surface contact between the bone and implant.

The vibration of bends or T-sections excites flexural modes, which require a numerically complex fourth-order differential term in the fluid–structure interaction (FSI) simulation. This paper presents an efficient approximate approach as an alternative to the full simulation of the bending vibration equations. The flexural stiffness of one pipe is lumped at the boundary of the other pipe to eliminate the corresponding problematic differential equation describing lateral vibration. FSI results obtained by the full simulation of the lateral vibration equations are compared with the corresponding proposed approach for intact and blocked L-shaped pipes. The results reveal that the approximate simulation is approximately ten times faster than the full simulation and easier to program. It can simulate different pipe lengths, valve closure times, pipe diameter to wall thickness ratios, blockage lengths, blockage ratios, and blockage locations with sufficient accuracy. Therefore, it can be a promising alternative for the full simulation of blocked pipe systems. As observed in several studies, junction vibration can generate significant signatures on the transient pressure response, which are similar to those of pipe defects and flow blockages meaning that it is important for the simulation model to be able to reflect these dynamics in order to be able to be reliably used to interpret the measured signal. The approximate model can lead to an accurate and simple junction-coupling transient solver for defect detection in pipeline systems without the inconvenience of solving the equation of lateral motion where the FSI effect is not negligible.

In this paper, a modification of the mast, which is the main part of a vortex-induced wind generator was considered in order to improve the performance. Numerical simulations were applied to investigate the change in vortex shedding frequency behind an oscillating structure. Considering the identical vortex shedding frequencies throughout the whole mast, an expression for the characteristic length (ϕ) was defined. The numerical simulations were conducted for an oscillating cylinder at different wind speeds and for different A/D to present a formula for designing of the mast. The FFT was implemented to determine the frequencies. The results showed that for A/D > 0.2, the variations in characteristic length were not significant. It was found that for Re < 2 × 10⁴, the variation in (phi /D) was considerable and was taken into account in the design of the mast. Using these results, an expression for calculation of the diameter of the mast at different heights was generated. Finally, a small mast with a height of 3 m was designed based on this method. For evaluation of the modified mast, a 3D simulation was conducted. Results showed that the vortex shedding frequencies were the same throughout the whole mast, which is desired.

The failure to consider thermal radiation in addition to free convection heat transfer in many cases such as heat exchangers will cause an unavoidable error in the flow analysis. Due to the complexity of volumetric radiation modeling in solving various problems, it is difficult to simulate this issue, especially through computer coding. The reason for this numerical study is the lack of extensive investigation of the effect of volumetric radiation on non-Newtonian nanofluid flow under magnetic field and heat absorption. By using the LBM and simulating the natural convection phenomenon, the cooling of a square-shaped component within a sector of a ring containing a non-Newtonian nanofluid has been modeled in the present research. The findings indicate that the presence of radiation increases the average value of the Nusselt number for the shear thickening, the Newtonian, and the shear thinning fluids by about 17%, 11%, and 8.5%, respectively. The growth of the thermal performance index and the mean Nusselt Number value is observed via the enhancement of the fluid power-law index, especially in the absence of heat absorption. In most cases, the presence of nanoparticles improves the heat transfer rate, especially in cases where thermal conduction dominates convection. There is the lowest cooling performance index and magnetic field effect for the cavity placed at the angle of 45°. By designing the system in such a way that the magnetic field is imposed on the system at different angles and positions, the thermal performance can be improved to a great extent.

Abstract

Compared with the single working fluid, the binary mixture working fluid can further extend the operating temperature range and enhance the heat transfer performance of a thermosyphon. In this paper, an experimental test system was designed and implemented to study the heat transfer characteristics of the thermosyphon. Methanol employed as the base fluid, 10 kinds of binary mixtures were prepared by adding different volume fractions of deionized water and ethanol separately. The effects of filling ratio, heat flux, and working fluid type on the heat transfer characteristics of the thermosyphon were analyzed and discussed. Moreover, the start-up characteristics were also explored. The experimental result shows that the filling ratio has a significant impact on the performance of the thermosyphon, and the optimal filling ratio is about 30% in this study. The start-up times of the thermosyphon with different binary mixture working fluids remain consistently, which are in the range of 200–300 s. It is worth mentioning that the start-up time of methanol-based binary mixture working fluid with 5% DW is 200 s, which is nearly 33% earlier than that with 50% ethanol. The thermosyphon with methanol-based binary mixture working fluid containing 5% DW presents a reduction of 7.3 °C in the maximum temperature difference and a remarkable 57.0% decrease in thermal resistance when contrasted with the thermosyphon using methanol working fluid. The results of this paper have important significance for the practical application of methanol-based binary mixture working fluid.

Since quadcopters are hugely limited by their short flight duration, it is of significant importance to employ an optimal design for the structure of the vehicle in order to reduce energy costs. Tilting-rotor quadcopter designs have shown promise in high speed maneuvers. However, the effects of different structural parameters on the stability of quadcopters have not been thoroughly investigated. In this paper, the effects of the Center of Mass (CoM) location and the inward tilting of rotors (dihedral angle) are analyzed. Additionally, a formula for the optimal selection of the dihedral angle based on the CoM position is derived. Furthermore, the effects of uncertainties in the dihedral angle on the quadcopter’s behavior are studied. The results indicate that increasing the dihedral angle makes the robot more sensitive to small uncertainties in adjusting the dihedral angle of different rotors. By considering these analyses during the design phase of a new quadcopter, a more optimal structure can be proposed to achieve the most efficient behavior.

Energy harvesting has received considerable attention in the last two decades. Piezoelectric energy harvesting has been widely used in this field. This study investigates energy harvesting from vibration of two beams in a rotating piezoelectric nonlinear system. The presence of two factors, the nonlinear spring and the nonlinear strain, causes the system to be nonlinear, and consequently, it is possible to harvest energy over a wider range of frequencies. The coupled nonlinear differential equations of the system are derived using Lagrange electromechanical equations. Then, the approximate analytical solution of the multiple scales method and also the numerical solution of the equations using the Runge–Kutta method have been obtained. The resulting voltage and power are presented as a function of the rotating frequency, physical, and geometric parameters of the system. It is shown that the results of the perturbation solution are near to the numerical solution. Moreover, an experiment has been done on the constructed model to verify the theoretical results. The test results showed that the maximum difference between the power values in practice and theoretical results was less than 8%. Power in the range of 20–288.05 µW is produced in the frequency range of 1–3.1 Hz, which is more than the power required for wireless data transmission systems. Also the nonlinear energy harvester is superior to the linear type due to produce of more power in a wider bandwidth. The maximum efficiency of the real sample is 88%, and its output power density is 1.47–23.49 µW/cm³ in the frequency range of 0.75–3.1 Hz.

Abstract

Hydrodynamic cavitation is a prevalent phenomenon within fluid dynamics, offering substantial advantages in various engineering applications. The alteration of cavitation venturi structure and the augmentation of hydrodynamic cavitation intensity have long represented a dynamic research domain. In this context, we introduce a novel cavitation venturi design with the explicit aim of amplifying cavitation intensity by expanding the flow channel within the venturi nozzle. In this study, we conducted a comprehensive analysis of the flow characteristics inside the nozzle using large eddy simulation and numerical simulation with the Zwart cavitation model. We compared the cavitation evolution process of two distinct nozzles under specific conditions: inlet pressure ranging from 0.2 to 0.6 MPa and a transient time interval of 0–1 ms. Additionally, we evaluated the average steam volume fraction within the nozzle. The numerical results demonstrate that, when subjected to identical boundary conditions, the multi-channel venturi nozzle exhibits a greater capacity to generate steam volume, consequently amplifying the cavitation energy produced at the nozzle outlet and intensifying cavitation. The results of our research provide a crucial reference for the design of nozzles in various engineering applications.

In the classical linear viscoelastic framework, materials exhibit more significant creep and stress relaxation at high temperatures, making thermoviscoelastic analyses of materials essential in the design of some polymers. In this paper, a new generalized thermo-viscoelastic model is developed by introducing the Kelvin-Voigt theory of viscoelasticity, and the transient response of an elastic rod under the action of a magnetic field and a moving heat source is investigated in the context of the three-phase lag heat conduction model and the Eringen nonlocal theory. The Kelvin-Voigt model is used to characterize the viscoelastic behaviour of the rod, and the analytical solution is obtained by the Laplace transform and its numerical inverse transform to show the distribution trends of temperature, displacement, and stress of the rod in a graphical way. The effects of time, moving heat source speed, delay time, memory-dependent effects, viscosity, nonlocal effects, and magnetic field on temperature, displacement, and stress are also discussed in detail.

Knowing the required muscle activation pattern of a determined movement can be used as an input to functional electrical stimulation in order to artificially activate the involving muscles in individuals with paralyzed limbs. Although there are muscles that are far from the skin, EMG data acquisition cannot be done noninvasively. There are several studies that estimate the muscle activations using the kinematics of the motion. The measurement devices for the joint angles can be volume occupying and may limit the dexterity of the motion. This article proposes to predict the missing anterior deltoid activation using the sEMG data of the long head and lateral head of triceps during shoulder press movement. First, the joint angles of the shoulder and elbow are estimated applying extended Kalman filter on an EMG-based state-space model. Having the kinematics of the motion, the joint torques can be determined using upper arm musculoskeletal model and inverse dynamics controller to track the estimated the joint angles. A static optimization method and Hill-based model are applied so the muscle activation of the muscles can be determined. An experimental setup is designed to obtain the biological and kinematic data needed to construct the equations, and the real values of the angle and activations can be used for the validation of this method. The RMSE of the real and estimated anterior deltoid activation is between 0.15 and 0.21 that is acceptable.