Journal of Simulation and Analysis of Novel Technologies in Mechanical Engineering
Volume:13 Issue: 1, Feb 2021

This paper investigates the bending vibration of single-walled carbon nanotubes based on a new theory called doublet mechanics with a scale parameter. A sixth order partial differential equation that governs the bending vibration for such nanotubes is derived. Euler-Bernoulli beam model is used in this paper. Using doublet mechanics, the relation between natural frequency and scale parameter is derived in the bending vibration mode. It is proven that scale parameter plays significant role in the vibration behavior of such nanotubes in lateral direction. Such effect decreases the natural frequency compared to the predictions of the classical continuum mechanics models. However, with increasing the tube length, the scale effect on the natural frequency decreases. To validate this method, the results obtained herein are compared with the existing nonlocal and molecular dynamics results and good agreement is observed. It is the first time that DM is used to model the bending vibration of carbon nanotube.

Vertical take-off and landing (VTOL) unmanned aircrafts have many applications due to their floating capability, their ability in vertical take-off and landing and flying in limited areas. Since providing a safe flight without causing any damages whether to itself or its surrounding environment is very important for this vehicle, a particular kind of VTOL aircraft is presented in this article which satisfies the above-mentioned requirement. To increase safety, a cylindrical chamber called duct is used around the propellers. This enhances the efficiency of the system while reducing losses, increasing the thrust, decreasing noises, and improving the safety of the aircraft and its surrounding area. Moreover, aerodynamic characteristics of the aircraft are modified. This vehicle is applied in indoor environments. In this research, firstly, aerodynamical and mechanical design of a kind of VTOL aircrafts called ducted fan is accomplished. Then, the desired controller is designed and the simulations results are given. Finally, the proposed scheme is improved and implemented on which navigation and control systems are installed, and many practical experiments are performed. In order to control the vehicle, optimization techniques are used, and the desired properties are evaluated

The hybrid composites have exceptional properties such as strength to weight and hardness ratios. These characteristics make the application of these materials in the aerospace industry. In composite materials, there are various fittings, such as a bolt and a rivet, which is the focus of stress concentration in the joints because the fibers are damaged. In this research in hybrid composite materials, a high elastic modulus fiber (HM) and a low elastic modulus fiber (LM) are used. It is also assumed that the length of the sheet is infinite. The force on the lamina is tensile force which applies on matrix and fibers while the fibers in the layers are one directed. In this paper the effects of different parameters such as ,number of broken fibers and the ratio of (LM) to (HM) fiber extensional stiffness.By using finite element method (FEM) modeling and investigation geometrical and crack modeling, stress concentration factor (SCF) around a elliptical hole is calculated and compared with the results obtained from reference.The results of the validation showed that compared to the reference data are close to each other, indicating the correctness of the code written for the analysis.

Dynamics and vibrations of the aircraft at the moment of impact with the ground is an important issue in aircraft design and its suspension systems. Different models for spring and damper have been used in the design of aircraft. One of the innovative ideas is MR Fluid Technology in its design. These shock absorbers are actually created a semi-active control system which by setting a magnetic field, the viscosity of the fluid can be adjusted and led to the desired damper so that the vibrations of the aircraft at the moment of landing reach the minimum amount. To achieve this purpose in the present study at First, a passive shock absorber is modeled and then an MR shock absorber which could provide the necessities of a landing gear system, have been analyzed. Finally, after writing the differential equations, the vibrational charts of the passive mode with semi active have been compared and the results confirmed and confirmed.

Nowadays the application of plasma actuators has drawn much attention due to the possibility of creating a volumetric force and, therefore, controlling airflow around rigid bodies. These actuators are among common flow control methods because of availability, lack of need for special repairs, very short response time, and low power consumption. The aim of this study is to reduce the flow separation region and delay the stall angle. Therefore, the airflow over a NACA 0012 airfoil and with a Reynolds number of 1.4×10^6 was simulated using Spalart-Allmaras turbulence model. In the first step, the lift coefficients in the plasma-off mode were investigated at different angles. The stall angle of attack was shown to be 15°. Then, the lift coefficients and the stall angle for different Reynolds numbers were compared. In the second step, the plasma (DBD) actuator was defined using UDF code in Ansys Fluent software as the body force exerted on the airfoil. Plasma activation led to an increase in the lift coefficients at different angles compared to the plasma-off mode. Subsequently, it was shown that the plasma actuator minimizes the flow separation area on the airfoil. Defining this actuator at an optimal position at a constant RE of 1.4×10^6 on a NACA 0012 airfoil where flow separation occurs changed the stall angle of the airfoil from 15° under normal conditions to 19°. The results of the lift coefficient with the help of plasma actuators showed that the airflow on the airfoil is well controlled at sensitive attack angles.

Based on the distributed dislocation technique, an analytical solution for the orthotropic layer with functionally graded material (FGM) orthotropic coating containing multiple axisymmetric interfacial cracks subjected to torsional loading is investigated. It is assumed that the material properties of the FGM orthotropic coating vary power-law form along the thickness of the layer. At first, by using the Hankel transform, the solution for Somigliana type rotational ring dislocation in the layer and its coating is obtained. Then, the dislocation solution is used to derive a set of singular integral equations for a system of coaxial axisymmetric interface cracks, including penny-shaped and annular cracks. cracks with Cauchy type kernel. The integral equations are of Cauchy singular type, which are solved by Erdogan’s collocation method for dislocation density on the surface of interfacial crack and the results are used to determine stress intensity factors (SIFs) for axisymmetric interface cracks. Finally, several examples are provided to study the effects of the non-homogeneity constant, orthotropy parameter and thickness of FGM coating on the SIFs for interfacial cracks.. The effects of the non-homogeneity constant, orthotropy parameter and thickness of FGM coating as well as the interaction of multiple interfacial cracks on the SIFs are investigated. The results reveal that the value of the SIFs decreases with increasing the non-homogeneity parameter, orthotropy and thickness of FGM coating. The SIFs for inner tips of annular interface crack are larger than the outer tips.