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

Due to the risks that the debris satellites pose to missions, one of the more recent study subjects in space is the removal of these debris masses from orbit. The usage of tethered satellites is one of the various approaches that are suggested for this objective and is taken into consideration in this research. That is, a tether from an operational satellite moves the debris satellite to a lower Earth orbit. This is done by extracting the mathematical model of the in-plane motion of a flexible tethered satellite system. The assumption of large deformations is also used for flexible appendages, which results in highly nonlinear governing equations. Four different types of controllers have been developed with the intention of suppressing the oscillations of flexible panels with an orbital transfer at a certain velocity decrease. Except for the basic PID controller, the other three are extensions of the classical form of sliding mode controller. In theory, every controller has unique qualities. Applying these features to the system in a computer simulation allows for their verification. The controllers' relative levels of efficacy are contrasted.

The objective of this research is to examine the influence of internal fluid pressure on the development of imperfections when quadrilateral tubes undergo rotary draw bending. Both experimental and numerical methods are utilized to conduct the tests. The experimental setup involved using an aluminum sample with an outer cross section of 35 mm × 35 mm and 1.5 mm thickness. The internal mandrel is replaced with fluid pressure introduced through a connection at one end of the sample while the other end is blocked. Several tests are carried out at various pressures with a bend radius ratio of 3 and a bending angle of 90°. The findings of this research indicate that in the absence of internal pressure, the profiles experienced buckling in the bending area at a 90-degree angle. As the internal pressure increases up to 24 bar, the rupture load is determined. Both experimental tests and simulations confirmed that the impact of internal fluid pressure on tube thinning is much greater than on thickening. Increasing internal fluid pressure caused thinning in the extrados, whereas the intrados thickness is not significantly affected. Instead, thickening is reduced due to material flow direction at higher pressures. The formed tube under pressures of 6 and 10 bar experience wrinkling and cross-sectional distortion of 20% and 10%, respectively. However, samples bent under 20 bar pressure show the best results regarding defects of the bend zone, with less than 1% distortion.

An analytical modeling to predict the bending behavior of functionally graded core sandwich beams designed with plaster and cork inclusion core and polymer skins is carried out within the framework of the present study. In addition, a microscopic analysis of the beams core using scanning electron microscope (SEM) was conducted in order to better understand the microstructural material degradation and the interaction of the cork aggregates within the plaster matrix. Accordingly, the main objective of this work is to complement the experimental observations through a theoretical prediction using high-order beam theories. In this respect, the originality of this study is to confront the modeling based on different material laws of functionally graded material (FGM)-based sandwich beams advocated in the literature to the experimental observations. Therefore, the emphasized results in terms of deflection, stiffness and stresses are compared with a good agreement to the experimental data and the advocated laws of the normalized standards. As main findings, the outcomes analysis provides a practical validated equations enabling reliable prediction of the elastic flexural response of plaster/cork FGM core sandwich beams.

The present paper investigates the dynamic responses and associated damage of GLARE 5–2/1 plates subjected to successive repeated low-velocity impacts (LVIs) by spherical impactors having varied masses. For low-energy LVIs characterized by surface dents on the outer aluminium layer, the progression of damage of the internal plies is evaluated by incorporating a continuum damage model based on Hashin’s criteria considering the in situ 3D stress state. For the present analysis, a 3D finite element code is implemented to obtain the dynamic responses of the target GLARE plate by incorporating the Newmark-β method and Hertzian contact law, considering the effect of local indentation on the contact stiffness. Results show that the impactor mass, the impact energy divisions and their order of occurrence significantly influence the indentation at the impact site, thereby affecting the dynamic responses and the damage sustained by the GLARE plates. Results also show that the indentation post the first impact leads to an increase in the local stiffness at the impact site of GLARE, though the same does not indicate the absence of internal damage.

This paper investigates the fluid pressure response at the outlet of a vertical fluid delivery straight pipe under random axial vibration. Based on the classical fluid–structure interaction (FSI) 4-equation model and forced vibration theory, the FSI equations of motion of the pipe under random axial vibration are established. Then, the variance of the pressure response at the pipe outlet is solved by combining the pseudo-excitation method and the characteristic line method. The correctness of the proposed method is verified by comparing the results obtained by the proposed method with the Monte Carlo simulation method. Since the pseudo-excitation method can directly obtain the pressure variance without many sample calculations, the method in this paper has high computational efficiency. The influence laws of fluid velocity, pressure, pipe structural parameters, and power spectral density of random vibration on the pressure response of pipe outlet are analyzed. The results show that the effect of random axial vibration on the fluid pressure response at the pipe outlet is significant and cannot be ignored. Increasing the pipe's inner diameter or shortening the pipe's length is beneficial in reducing the fluctuation of the pressure response at the outlet of the pipe. The analytical method in this paper can effectively analyze the outlet pressure of the pipe under random axial excitation and can provide a theoretical basis for reducing the fluid pressure fluctuation in the pipe under random vibration.

Soft bellows robots exhibit exceptional movement capabilities owing to their considerable retractability and high flexibility. Nonetheless, accurately describing the relationship between their actual movements and the forces they exert remains a significant challenge. To address this challenge, this paper proposes a dynamic modeling method for soft bellows robots. Initially, a soft bellows robot is designed as the subject of study, and its movement is categorized into two modes: straight crawling and steering, based on their respective functions. Subsequently, leveraging the constant curvature bending assumption, the relationships between the deformation and pose of the soft bellows actuators (SBAs) constituting the soft bellows robot are meticulously analyzed. Dynamic models for the SBAs are then established. Finally, the validity of these dynamic models for the SBAs is confirmed through controlled testing, thereby verifying the two movement modes of the soft bellows robot. In summary, the dynamic modeling method presented in this paper enhances the theoretical framework of soft bellows robots and provides crucial theoretical support for precise control.

In response to the challenge of unclear characteristics within the internal flow field and operational performance of internal twin screw pumps, this study employs computational fluid dynamics to investigate the internal flow field variations during operation. Numerical simulation models are established for both internal twin screw pumps and conventional single screw pumps. Through three-dimensional transient dynamic mesh simulations, a comparative analysis of the internal flow field of these two screw pump types leads to the observation that the internal twin screw pump exhibits a remarkable advantage in volumetric efficiency and superior sealing performance compared to the single screw pump. Furthermore, examining the impact of parameters such as internal and external rotor clearances, medium viscosity, inner rotor speed, and single-stage pressure difference on the outlet flow and volumetric efficiency of the internal twin screw pump reveals overarching trends and underlying mechanisms. The findings indicate that the outlet flow of the internal twin screw pump diminishes with increasing pressure difference, and the influence of pressure difference on flow reduction is mitigated by higher medium viscosity. It is deduced that internal twin screw pumps are more suitable for application in medium or high-viscosity oil wells. With volumetric efficiency being modulated through prudent adjustments in speed. Conversely, internal twin screw pump leakage rises with augmented outer rotor clearance and reduced medium viscosity. These research outcomes hold significant implications for enhancing performance and refining the structural design of internal twin screw pumps in practical applications.