مجله مهندسی مکانیک
پیاپی 153 (بهمن و اسفند 1402)

Given the growing importance of emissions in maritime transportation and the need to reduce ship fuel consumption, efforts have been made to address this concern. Recently, the hull vane, serving as an energy storage device, has been introduced to the ship's stern area, reducing resistance. Additionally, recent studies have explored the use of tubercles on hydrofoils. This study aims to assess the impact of hull vane, with and without tubercles, on total resistance and propeller coefficients in self-propulsion conditions, as well as their effect on vessel power consumption. Results show that for a vessel with a smooth leading-edge hull vane, the total resistance coefficient decreased by 1.77%, propeller thrust coefficient by 2.853%, and torque coefficient by 1.14% compared to a vessel without a hull vane. Furthermore, for a vessel with a leading-edge tubercles hull vane, these coefficients decreased by 1.85%, 3.488%, and 1.94% respectively. Additionally, power consumption decreased by 0.789% compared to a vessel with a regular hull vane.

In the present study, the wool porous material is used to cover the steps of a stepped solar still and the effect of wool porous material thickness on the energy and exergy efficiencies, distilled water production rate and the temperatures of internal zone and steps are studied experimentally. Experiments are carried out for porous material thicknesses of 4, 6, 8 and 12 mm and without it. Results indicate that solar irradiation affects the amount of distilled water, and the porous material besides affecting the internal temperature of the solar still, causes to produce higher distilled water and higher efficiency than the solar still without the porous material. For example, the amount of distilled water and energy effeciency of solar still with 12 mm-thick of porous material are 0.35 litre and 7.8% higher than the system without porous material.

Analytical, numerical, and experimental solution of the rotating system in the stages of design, construction, and operation is important in order to prevent resonance phenomenon. In this research, the numerical and experimental analysis of a rotor is studied using Jeffcatt’s 8 DOF model. The equations of motion by considering the gyroscopic effects and the mass of the bearings are formulated using the Lagrange method. After introducing a model of the system, the terms of potential, kinetic, and dissipation energy are obtained according to the boundary conditions. Then, by placing the system parameters, the natural frequencies of the system and the Campbell diagram have been obtained in order to predict the critical speeds. Validation of the presented model has been done by comparing with the results of Finite Element Solution (ANSYS) and approximate solution, and also percentage error of the first critical frequency compared to the experimental value is 15%. Then, the effect of changing the position of the disk from the first bearing on the natural frequencies of the system is studied. In the end, the system's frequency response is presented at the different unbalanced distances and the position of the disk. Observations show that changes in unbalanced distance and position of the disk can affect the frequency and resonance peak of the system.

Nowadays, due to the increasing need of various military, aerospace, automotive, etc. industries for materials with high strength-to-weight ratio, good resistance to wear and fatigue, etc. the use of composite materials, especially metal-based composites, has increased significantly. Machining to achieve high dimensional accuracy is an integral part of the production process of products made with metal-based composites. Due to the presence of reinforcing materials such as silicon carbide, etc. the machining of this category of materials always faces many challenges, including tool wear, increased machining forces, decreased surface quality, etc. Therefore, it is to study the parameters affecting the machining of metal composites. Many studies have been done in this field by different researchers. In this article, by reviewing the most important articles published in this field, comprehensive and at the same time summary information on the influencing factors in conventional machining processes such as turning, milling, etc. or non- conventional machining processes such as electrical discharge, electrochemical machining, etc. has been tried to be available to the readers. Also, the performance of different types of tools during the machining of metal composites was investigated. In the end, the existing gaps and new and studyable topics for researchers were pointed out.

The use of empirical and semi-empirical models to model the properties of nano composites to predict mechanical properties and failure leads to cost and time reduction and optimal design. In this study, discontinuous (short) fiber models were used to model the mechanical properties and fracture behavior of carbon nanotube reinforced polymer nanocomposites with volume fractions of 0.5%, 0.75%, and 1%. In previous studies, the discontinuous fiber model was used to determine the macro scale properties of composites reinforced with discontinuous fibers. In this study, a model that considers the geometric similarity between short fibers and nanotubes was used. Using this model and the model of random distribution of nanotubes in the epoxy matrix, simulations were performed using the Python programming language and the mechanical properties and fracture behavior were investigated at the Nano and mesoscales.

This article aims to investigate the stability and estimate the aerodynamic coefficients of an aircraft based on experimental flight data. The least squares method was used to estimate these coefficients by using data from an inertial measurement unit (IMU) and global positioning system (GPS). This research, for the first time, has estimated these coefficients on a high-wing aircraft and during various flight maneuvers, including takeoff, landing and variant turns. It has been conducted utilizing time and frequency response data based on actual flight. In this article, the match between the recorded flight path of the aircraft and the flight path plotted by MATLAB software output was evaluated, and the output of the flight path model confirmed this match. Moreover, to improve the estimation of aerodynamic coefficients, the least squares method was modified using past inputs to estimate a value. The method explained in this article was evaluated in 5 experiments using actual flight data from the aircraft. Finally, the maximum estimation error generated by the modified method is 6.7%, which was related to the pitching moment coefficient.