نشریه علوم کاربردی و محاسباتی در مکانیک
سال سی و پنجم شماره 4 (زمستان 1402)

In the macro scale, surface forces such as friction and adhesion are of little importance and can be ignored. But in the micro/nano world, these forces are of great importance. For this purpose, in order to simulate the manipulation of nanoparticles based on the atomic force microscope, various friction models can be used, including the HK friction model. Accurate calculation of force and critical time, respectively, in order not to damage the particle and to reach the target point in the manipulation process is important and necessary. In this research, data were collected using the Taguchi test design method in three levels. The amount of force and critical time were calculated for each test. Then, with the help of analysis using the signal-to-noise ratio method, to investigate the effect of the input parameters of the HK friction model including, , ,B and M The reduction of the critical force and the increase of the critical time in mamipulation the gold nanoparticle with a radius of 50 nm on the silicon oxide substrate have been discussed. Based on the obtained results, parameter B as the first parameter and M as the second parameter with the lowest signal-to-noise ratio on reducing the critical force and with the highest signal-to-noise ratio at the critical time at level 3 with values of -1.869 and -0.3419.

In the membrane humidifier, the characteristics of the membrane as the heart of the humidifier and the selection of Nafion as the most common membrane for use in the process of separating two wet and dry streams have a great impact on its performance. In this study, a numerical and three-dimensional investigation of a flat membrane humidifier including the dry flow channels, membrane, wet flow channels and plates on the two sides of the membrane has been investigated by Ansys Fluent software and the effect of membrane characteristics including: thickness, permeability and porosity coefficient on the mass (water) and heat transfer through the membrane and as a result the performance of the humidifier has been investigated. The results show that the use of Nafion 111 due to its lower thickness compared to Nafion 115, 117 and 211, leads to improved heat and mass transfer and therefore improves the performance of the membrane humidifier. Considering the dew point which shows the simultaneous effect of mass and heat transfer; increasing the permeability coefficient of the membrane from 10-15 to 10-21 square meters, the dew point temperature at the outlet of the dry side increases by about 3.5K. In the common limits of the porosity coefficient of common commercial membranes, the change of the porosity coefficient does not have much effect on the performance of the membrane humidifier.

Monopropellant hydrazine thrusters are widely used in situation control, orbital transmission, and position correction systems of satellites. In these thrusters, hydrazine is decomposed into the hot gaseous products by passing through a catalyst bed during a highly exothermic reaction. In this paper, the decomposition chamber of a monopropellant hydrazine thruster is numerically simulated in the granule scale of the catalyst bed. The effect of the catalyst granule size is investigated on the performance of the decomposition chamber with catalyst bed with a length of 2.48 cm. Simulations have been performed for catalyst granules with diameters of 0.88, 1, and 1.15 mm at the porosity equal to 0.4 and the chamber inlet pressure equal to 15 bar. The results show that the size of the catalyst granules affects the chamber performance so that with its increase, the hydrazine decomposition and the bed temperature increase respectively 8% and 5% and the mass flow decreases about 25%, which in turn reduces the bed loading about 5%. Finally, further increase in the temperature of the decomposition chamber causes an increase in the outer wall temperature.

The purpose of this study is to investigate the behavior of a cylinder with three fins in the presence of free air flow. This study aims to investigate the unsteady aerodynamic flow with respect to its practical significance in aviation. Considering the degree of freedom of movement within the geometry and the complexity of the vortex masses that cause instability, it is essential to accurately predict the different dynamic behaviors. We have investigated the dynamic behavior of the model with different length ratios, free flow speeds, and angles of attack. According to the results of the study, rotational and oscillating behaviors, as well as a combination of both, are observed, and they are dependent upon the geometrical characteristics of the model, such as the ratio of the length of the plates to the radius of the cylinder, as well as the angle of attack When the aspect ratio and free flow speed are low, the motion pattern is damped around 60 degrees and the motion regime is oscillatory in nature, which changes to rotational motion as the aspect ratio and flow speed increase. The maximum oscillation or rotation is related to the initial angle of attack of zero degrees. It has been observed that rotational motion regimes occur with an increase in the longitudinal ratio and free flow speed at low initial angles of attack.

Incremental sheet metal forming is one of the promising sheet forming processes, in which local nature of the applied forming forces and independency of the process on the die, induces higher formability in the sheet and increases flexibility of the process in producing intricated geometries. In current study, from damage mechanics window, one of the prominent features of the process, i.e. forming limits of AA5052 sheets has been investigated. For this purpose, firstly, Bao-Wierzbicki damage model is coded and implemented into Abaqus finite element program via VUMAT subroutine. The constants of the damage model, hardening model and Hill48 yield model have been obtained utilizing the uniaxial tensile experiments in three directions of 0º, 45º and 90º with respect to rolling direction. To examine the formability, truncated cone and pyramid geometries with variable increasing wall angles have been considered and the experimental tests and simulation of the process were conducted. Using the stress and strain distribution, fracture phenomena and onset of fracture were described. The results show that the sheet metal fractures before it reaches the designed final height, so that for the geometries of truncated pyramid and truncated cone, the fracture height is obtained 19.9 mm and 16.9 mm, respectively. Considering the sheet anisotropy properties in the process simulation, the fracture height of specimens was predicted with an average accuracy of 9%, and the results reveal that with excluding the anisotropy properties of the sheets, the prediction accuracy decreases. Also, an acceptable agreement was obtained in predicting the fracture location.

A composite structure is a non-uniform solid that consists of two or more different materials with different kinds that are mechanically bonded together. These structures have completely different chemical and physical properties and they merge together to make a substance that is not similar to any of these materials. In previous studies, the construction and investigation of sandwich structures of polymer materials were done with two materials with similar physical properties (two hard materials), but in this research, two polymers with completely different physical properties were combined and a new sandwich structure was made. This study aims to investigate and try to increase the mechanical performance of single-layer and multi-layer composite (sandwich) structures printed from hard (ABS) and soft (TPU) polymer materials and comparing these samples by preparing different composite structures from these polymers. The method of making polymer materials used in this research is the use of 3D printing technology (incremental layering). The results have been obtained in the form of laboratory tensile test and simulation in the Abaqus software environment. These results indicate that with the change of layers and materials, the amount of strain to failure of the composite samples has increased up to about 4 times. It should be noted that the construction of the tensile test samples in this project was done according to the standard of the American Association of Materials and Testing.

In this study, a modified phenomenological model has been proposed by merging the Suzen-Huang model and the Yoon-Han thrust model for two types of single plasma actuators and plasma synthetic jet actuators, in different geometries and different working and environmental conditions. The model introduced in the present work is based on the thrust induced by plasma. With this generalization and modification, this model overcomes the drawbacks of the standard Suzen-Huang model (lack of correct estimation of the nonlinear relationship between the applied voltage and the amount of thrust induced by the plasma and not considering the influence of parameters such as the thickness of dielectric and dielectric constant, the thickness of the exposed electrode, and the alternating current frequency). Applying this model on a single plasma actuator shows the accuracy and correctness of this model. Also, by generalizing the present model for the annular plasma synthetic jet actuators, the dependence of the maximum charge density and body force on the diameter of the actuator was included in the model. Validation of the present model for the annular plasma synthetic jet actuator shows that the model is able to adapt itself well to changing the diameter of the actuator, working conditions, geometry and materials of the actuator and make a good estimate of the results.

This paper investigates the deflection of chromium nanobeams using the design of experiments method. Using the full factorial method, a number of 100 experiments were designed in which the length and the force on the nanobeam were considered input variables at 25 and 4 levels, respectively and the deflection of the nanobeam was considered output. First, all 4 force levels (8, 9.5, 11, and 12.5 nN) were used for the analysis, and closed-form equations were obtained to estimate the deflection of the nanobeam. The results showed that the effect of the length is more than the force, by increasing the length so that the deflection changes with third degree. The third-order regression model predicts the deflection with high accuracy, and its error value is lower than the first and second-order regression models. Afterward, two levels of force (8 and 11 nN) were used for analysis, and new equations were obtained to estimate the deflection of the nanobeam. The new equations were used for interpolation and extrapolation of the nanobeam's deflection in forces of 9.5 and 12.5 nN, respectively. The results demonstrated that the regression model using two force levels accurately predicts the deflections of nanobeams as well. The results of this research demonstrated that it is possible to estimate the nanobeam's deflection without the need to perform more experiments and spend cost, perform complex calculations, and solve differential equations; the nanobeam's deflection can be accurately estimated with algebraic formulas.