مجله مهندسی مکانیک
پیاپی 142 (فروردین و اردیبهشت 1401)

Today, due to the increasing weight of cars, the addition of turbochargers to internal combustion engines increases performance and at the same time, produces high noise in the range of 72 dB to 154 dB when the engine is running at high speeds and during the initial acceleration. To reduce the negative effects of these noises and increase the comfort of the car occupants, various methods such as including finite element analysis and numerical analysis of compressor blades to optimize pressure drop coefficients (ratio of turbine input to compressor output), sound pads and acoustic materials around engine parts including turbocharger parts and air manifold, are used. The purpose of this article is to express and classify the research done in the field of reducing annoying noises resulting from the operation of the car engine and turbocharger.

In this research, the efficiency of granular dampers in improving the vibration performance of a composite engine seat structure in a vessel has been investigated. Due to the time-consuming computation process of dynamic analysis of these dampers using processes such as discrete elements, an optimal alternative process based on multiphase flow theory has been developed. First, the characteristics of a unit of this type of damper are extracted and its equations are developed to estimate the equivalent damping coefficient. For this purpose, multiphase flow theory is used, in which the kinetic theory of dense fluid flow and the Moore-Columb theory are used to model the collision and friction between particles within the cell. Due to nonlinear dependence, a Python code has been used as a convergent loop in the ABAQUS software environment to implement the damping estimation process. In the result section, after performing validation and proving the accuracy and speed of calculations, it was shown that the amplitude of vibrational acceleration in this model has significantly decreased.

Recent progress in robotic industry has increased efforts on robot ability enhancement to use them in factories and services instead of labors and human workers. One of the important ability which plays an important role to reach this aim, is tactile sensation which is not compensated by other ability including image processing. In this paper, a robot fingertip with tactile sensation is designed and fabricated which has a configuration very close to human fingertip for griping or other robotic applications. This fingertip consists of rigid body and elastic flexible cover which the area between these two parts is filled with a fluid which is connected to the pressure sensor. When the elastic cover which plays a skin role, touch the external body, regarding to the speed and amplitude of touch, the reaction of the cover is transferred to the fluid and also pressure sensor. Pressure sensor sense the pressure change and convert this to the output voltage which is detectable by designed electrical circuit. Outer layer of the elastic cover is corrugated to increase sensitivity of the sensor. The fabricated tactile sensor was tested to verify its performance in different experiments which was in good agreement with our expectation.

Using twin web disks instead of single disks in turbine rotor is the new idea, which provides the necessary space for cooling and thus reducing the temperature level and the resulting stresses. The disk is subject to mechanical and thermal loading. Mechanical loading involves the effect of the disk rotation and the centrifugal load caused by the blade rotation at the external surface. Thermal loading is applied due to thermal changes between the internal and external surfaces on the disk. Disk boundary conditions are considered as dual-cantilever. Using the analytical solution method, the theory of elasticity of the plate is derived from the relations that govern the thickness of a rotating disk in a plane stress state. In the following, the disk was analysed under consideration the actual thickness profile using the TimoshenkoGrameel’s numerical method. In order to reach a twin web disk with a proper profile, this disk is studied with stepped holes in 400 different geometrical modes, and the state with the lowest possible mass and acceptable reliability coefficient is obtained. The results of the analysis show the reduction of mass, reduction of stress levels and improvement of the coefficient of confidence through the use of an optimal twin web disk.

Today, global demand for energy has increased due to economic and population growth. Turbines play an important role in generating power in order to generate electricity. This industry is one of the important factors in the global economy and has experienced continuous growth from the early years. To achieve higher thermodynamic efficiency in turbines from higher inlet temperature and pressure, advanced aerodynamics, efficient blade cooling systems, advanced alloys with higher temperature tolerance, heat treatment and metal and thermal barrier ceramic coatings is used. Under turbine operating conditions, some damage may occur that will decrease its life. In present study, mechanical and metallurgical aspects of turbine blade destruction and the development of materials to overcome it have been analyzed. Failure mechanisms must be identified to estimate blade life. The combination of different variables causes stress and complex damage mechanisms such as creep and fatigue are created by changing mechanical and heat stresses. In addition to the above, the importance of coating on gas turbine blades is mentioned. After investigation of various aspects of damage to clarify the issue, some case studies of failure during operation are briefly described.

Suspension system is undoubtedly one of the most important and basic subsystems of a vehicle. In this research, in order to fully analyze the vibrations of the car body and chassis movements that enter the occupants, a complete car model with 10 degrees of freedom has been used. After simulating the car suspension system and designing an active suspension system to eliminate disturbances, a comparison between the two types of PID controllers and an adaptation for the mentioned suspension systems will be made and the differences in vibration control will be studied. Due to the constant gains of the PID controller and also the uncertainty in the vehicle suspension, the PID controller is not able to control and decrease the vibrations on the car body, so in this work of the adaptive controller with non-fixed interest to control and reduce vibrations applied by road surface roughness to the car body. The innovation of this research is the design of two types of PID and adaptive controllers to reduce the vibrations of the car in three feedback of displacement, speed and acceleration for the model of 10 degrees of freedom (complete) of the vehicle.