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

In recent years, numerous studies have consistently demonstrated the remarkable impact of nanofluids on augmenting heat transfer processes. In the present study, the numerical investigation focuses on the analysis of MWCNT-Fe₃O₄/water hybrid nanofluid natural convection within a vibrating cavity. The governing equations are solved by the IB-STLBM, which combines the immersed boundary method with the simplified and highly stable lattice Boltzmann method. The results indicate a positive correlation between the Nusselt number and both Ra and ϕ, indicating an increase in heat transfer performance with higher Ra and ϕ values. The study further reveals that variations in a and ω have minimal impact on the overall averaged heat transfer characteristics (Nu_mean), yet do influence the instantaneous heat transfer characteristics in terms of frequency and amplitude (Nu_avg). Specifically, when Ra = 10⁵, Ar = 2.5 and ϕ = 0.003, adjusting a and ω can result in a maximum increase of 2.4% in the Nu_mean. Moreover, while changes in Ar do not affect the amplitude and frequency of Nu_avg fluctuations due to the unchanged motion modes of the system, they do impact Nu_mean.

The main objective of this investigation is to evaluate the relationship between the Entropy Generation Rate (EGR) and the performance of a Gorlov Hydrokinetic Turbine (GHT). Experimental and numerical research is conducted on a fully submerged GHT in an open channel. The numerical results of the power coefficient are validated using experimental data. ANSYS CFX 23.1 is applied for CFD simulation of the two-phase, transient and turbulent flow around the GHT in the open channel. (k - omega) SST and the homogeneous multiphase model are the tools that are utilized for modeling turbulence and the two-phase flow. The numerical results are used for calculating the turbulent, direct and total EGR in the open channel and also the rotating domain around the rotor. The results show that the 95% of the total entropy is produced by the turbulence. Comparing the variations of (C_{P}) and the integral of the total EGR at one rotation of the turbine showed that the minimum (or maximum) generated entropy is not in correspondence with the maximum (or minimum) power coefficient. This phenomenon is due to the fact that the maximum (frac{Lift}{{Drag}}) (or the (C_{Pmax })) occurs at a bigger attack angle in comparison to the minimum drag force at which the total EGR is minimum. Evaluating EGR contours on a plane crossing the mid-section of the rotor and on the surfaces of the blades showed that the leading edge, the separated boundary layer region, and the wake zone near the trailing edge are the main sources of entropy generation in the rotating domain.

Cracks are common faults in micro-electromechanical structures that affect the performance and dynamic behavior of the structure. Cracks can change the structure’s stiffness, and parameters like resonance frequency, voltage and output power and could lead to the failure of that structure after a specific time. Hence, it is imperative to diagnose and detect structural cracks. In this study, we introduce a semi-analytical method to examine transverse cracks occurring within the mid-layer of a bimorph piezoelectric energy harvester. The investigation encompasses reductions in stiffness and variations in capacitance resulting from mid-layer transverse cracks. From a microscale perspective, we employ a stress transfer technique based on crack density to quantify stiffness reduction caused by mid-layer cracks. Analytical outcomes concerning the influence of cracks in the mid-layer of the bimorph are obtained using assumptions derived from the Euler–Bernoulli beam theory and substantiated through finite element analysis. The consequences of these imperfections on mechanical parameters such as resonance frequency, as well as electrical parameters like output electrical power, are deliberated upon. It is observed that the existence of cracks in the mid-layer of the bimorph piezoelectric energy harvester leads to a decline in its resonance frequency, accompanied by an increase in voltage and output power, indicative of impending device malfunction. This research facilitates the identification of defects in MEMS by monitoring the harvester's operational performance.

This work specifically examines the modeling of the transient thermodynamic reaction of a Kirchhoff–Love thermoelastic thin circular plate that is simply supported and set on an elastic base of Winkler type. The plate experiences a time-varying external load. The Kelvin-Voigt model is employed to simulate the viscoelastic behavior of the plate in this investigation. The modified dual-phase-lag (DPL) thermoelasticity model is used to represent the intricate thermoelastic properties of the plate accurately. The DPL thermoelastic model includes the effects of restricted thermomechanical diffusion, which considers the connection between thermal and mechanical events in the plate. This model offers a more extensive depiction of the plate's reaction, considering both temperature and mechanical factors. Analytical solutions for the studied variables, such as deflection, temperature, displacement, bending moment, and thermal stress, were extracted using the Laplace transform. The viscoelastic coefficient, Winkler base, and the angular frequency of the distributed load greatly affect how circular plate structures behave, as shown by numerical examples and insightful discussions. Finally, to verify the validity of the results and the proposed model, they were compared with previously published studies and their corresponding thermoelastic models.

The impact and rebound dynamics of water droplets on surfaces featuring triply periodic minimal surfaces (TPMS) are examined, investigated, and compared against flat and solid substrates in this numerical study. Water droplets’ collision, spreading, retraction and ability to jump off from TPMS surfaces are evaluated using kinetic energy analysis. Two types of geometry, cuboid and cylindrical, in the form of four distinct types of triply periodic minimal surfaces are generated as porous substrates to study their ability for water repellency. At high contact angles, the droplets’ kinetic energy profiles are found to be considerably higher than the flat substrates, at low impact velocity/Weber numbers. At smaller contact angles, the difference between the kinetic energy profiles is considerably higher for TPMS surfaces compared to flat substrates. Thus, droplets on periodic porous substrates are able to jump off such surfaces while failing to detach from a purely flat surface. At the same time, higher speed impacts at the smaller contact angles result in droplets failure to jump off on certain TPMS substrates, and could be attributed to excessive impalement characteristics that are not present with the other three types of substrates. For the cylindrical substrates, a similar observation has been made, where at lower contact angles, the droplets fail to jump off the solid substrate but repellency occurs on the TPMS substrates. The variation of the radial ratios of the substrates is also presented to elucidate the different characteristics of TPMS substrates at the end of the study.

This paper explores the effects of an electromagnetic field, variable thermal conductivity, and gravity on the behavior of elastic porous thermo-microstretch media immersed in an inviscid fluid. The study incorporates the Green-Naghdi theory mode III (G-N III) and the three-phase-delay model (3PHL), which considers the coexistence of thermal waves, porous microstretch waves, and phase delay effects. The analytical strategy for deriving ordinary differential equations is normal mode analysis, then using the eliminating method between six ordinary differential equations, and finally using the characteristic equation to obtain the precise formulas for the physical quantities covered with an infinite fluid of G-N III theory to those of the model 3PHL. Thermal conductivity, the magnetic field, and the gravity have been shown to have a significant impact on all physical quantities.

Metamaterial composites are a rapidly developing field of engineered materials. These materials are typically created by incorporating periodic inclusions, such as coated spheres, into a matrix. It has been shown that the reduced micromorphic model enables the analysis of the static and dynamic behaviors of metamaterial composites. Based on the reduced micromorphic model, a novel approach for estimating the effective bulk modulus of metamaterial composites is proposed. Utilizing the reduced micromorphic model, a hydrostatic compression test is simulated to derive a closed-form expression for the effective bulk modulus. The material coefficients of the reduced micromorphic model are identified according to the elastic properties of all phases of the composite, and the obtained numerical results are compared with those reported in the literature. Additionally, this study examines the influences of various physical parameters on the effective bulk modulus.

One therapeutic method to treat cancer is hyperthermia, in which temperature control is crucial so that only the temperature of the tumor site increases with healthy tissues remaining intact. In regards to the physics governing this phenomenon, the heat transfer equations are of the non-Fourier type. Using inverse heat transfer based on the conjugate gradient method, the present article aims to control the tumor temperature considering the dual-phase lag effect of heat flux and temperature. To increase the tumor temperature up to 42 °C, three different protocols including sinusoidal, triangular and step shape desired temperatures are considered, the results of which revealed that the proposed method can effectively control the tumor temperature with high accuracy during the hyperthermia process. The relative root mean square of the difference between desired and estimated temperatures are 0.51%, 0.69%, and 2.58% for sinusoidal, triangular and step shape desired temperatures, respectively.

To tackle the issue of magnetic force loss caused by the air gap in the electromagnetic permanent magnet (EPM) blank holder process magnetorheological elastomer (MRE) is used to fill the air gap of the magnetic circuit as magnetic matrices. This allows for the construction of a controllable magnetic force blank holder system with magnetorheological elastomers (EPM-MRE) for sheet metal forming. Additionally, EPM-MRE blank holder deep drawing tools were designed. MREs with different mass ratios were developed and tested for their magnetic properties. Air and MREs of varying mass ratios were filled into the magnetic circuit gaps of a four-pole magnetic force model, and a finite element analysis of the magnetic force coupling field was conducted, followed by experimental verification. The results show that the inclusion of MRE in the magnetic circuit gap can significantly enhance magnetic force, with an increase of over 50% across gaps ranging from 0.5 mm to 3.0 mm, and the enhancement effect becomes more pronounced as the gap widens, and the enhancement effect of the prepared MREs with different mass fractions is not significantly different, with the difference being no more than 1%. The EPM-MRE blank holder process was further verified through deep drawing experiments and the results demonstrate that the designed process device can be matched with the press to effectively complete the drawing process. At last, the energy consumption using the EPM-MRE blank holder technique is predicted, and it is estimated to save more than 50% of energy compared with EMP blank holders and more than 80% of energy compared to conventional blank holders.

This study reports an improved design optimization method that incorporates profile shift and a modified tooth sum strategy to reduce both the weight and contact stress across the contact line of spur gears. The emphasis is on the optimal design of addendum-shifted spur gears with altered tooth sums, using a multi-objective optimization approach complemented by stress analysis and experimental validation. A detailed comparison of the optimization results reveals that addendum shifted gears with a negatively altered tooth sum achieve a weight reduction of 18.42% and a contact stress decrease of 9.17% compared to standard gears. Experimental evaluations further confirm that addendum modified and negatively altered tooth sum gears exhibit an 11.68% improvement in efficiency over standard gears. The experimental results demonstrate that there is 24.41% less reduction in tooth thickness, a 10.83% lesser decrease in surface roughness, a 21.74% lesser rise in oil bath temperature, and a 53.28% less rise in gear tooth contact surface temperature of the negatively altered tooth sum in comparison to the standard gear set. This indicates that there is a possibility of obtaining improved performance in profile modified altered tooth sum gear.