مجله مهندسی مکانیک
پیاپی 144 (امرداد و شهریور 1401)

In this article, various methods have been introduced regarding the movement of robots and the advantages and disadvantages of these methods. By combining the methods of potential function, virtual structure and leader tracking, an algorithm is obtained that, while having the merits of the mentioned methods, also overcomes the disadvantages and challenges of these methods to a large extent. The resulting algorithm is used to design the desired movement path of the robots, and a sliding mode controller acts as a useful tool to force the robots to follow these desired paths. Finally, to evaluate the performance of the designed system, the movement of a group of six non-holonomic robots that surround a target in a triangular formation has been simulated in MATLAB software. The obtained results is compared with the works done by other researchers. It was found that the introduced algorithm has important advantages over previous works, such as reducing the volume of calculations, removing the local minima of potential functions, reducing the range of input changes, the reduction of the number of weight coefficients to adjust the potential functions. It should be noted that the resulting advantages make this method more suitable for practical applications.

Today, measuring the flow parameters of the oscillating airfoil wake is of great importance due to its wide applications in industry and nature. Therefore, the aim of this research is to provide an innovative method for the experimental measurement of the NACA0012 oscillating airfoil. For this purpose, three one-dimensional hot-wire sensors were used, one of which is fixed, and the others are mobile. By using MATLAB code and the connection between the data of these three sensors, the spatial and time correlation of the flow velocity at all points of the wake was obtained. The results showed that measuring different parameters of the wake with less hardware equipment than other researches is possible. In this method, the flow parameters have been measured with higher accuracy by eliminating the errors caused by the large number of sensors and by increasing the number of data collection points in the wake. The results showed that the combination of the free stream flow momentum with the oscillating momentum of the airfoil creates a sinusoidal flow with the same frequency of the airfoil oscillation in the wake. Moving vortices area and the area of diffusing vortices momentum form the two parts of the oscillating airfoil wake.

In this paper, a comparison was made between super hydrophobic surfaces resulted from SiO2 and TiO2 nanoparticles on chemical modification wood and bamboo Substrate. The super hydrophobicity of surface was evaluated based on its morphological properties, mechanical stability, long term stability, and self-cleaning ability by measuring WCA and SA angles. The super hydrophobicity of the surface was obtained by applying sandpaper mesh size 1500 and exposing the surface to the atmosphere for more than 180 days with a contact angle of 155±2° and a sliding angle of 6±2°, and surface showed a self –cleaning property. Taking into consideration the flexibility and simplicity of the method, it is a feasible and low-cost method to acquirable the lotus effect and demonstrated potential for practical applications.

Today, in order to reduce noise and vibrations, meta-materials are used as a barrier, attenuator or absorber of vibration and sound in various fields such as aerospace, automotive and pollutant control. Meta-materials are synthetic materials made from single cells with dimensions smaller than the desired wavelength of sound waves, repeated alternately in a larger scale, which can effectively reduce the amplitude of sound waves in the desired frequency range. In this review article, research conducted in the field of various metamaterials, especially acoustic and elastic metamaterials, and their applications and results in reducing noise and unwanted vibrations of the environment have been studied. In most researches, numerical calculations have been performed using the Bloch-Floquet theorem to calculate the Bloch cell phase of a single metamaterial cell. The results of this research show that by using acoustic and elastic meta-materials, the vibrations and low frequency noise of a system can be reduced to a desirable level. It becomes a means of increasing the energy band gap. Increasing the degree of release of local resonators is another way to increase energy gap and further reduce vibration.

Nowadays, extrusion-based additive manufacturing is an emerging manufacturing method that is receiving much attention and is the basis of FFF 3D printers. In this method, molten polymer is deposited layer by layer through a nozzle to create a three-dimensional object. Due to the rapid freezing of the layers, small gap and cavities may be created between the layers and lead to a decrease in the mechanical properties, including the strength of the parts. Since predicting and improving the mechanical properties is one of the challenges of this production method, the purpose of this study is to investigate the factors affecting the strength of parts produced by FFF. Investigation of the previous studies shows that the influencing factors are the nozzle temperature, filling percentage, sample alignment, filament deposition angle, layer thickness and nozzle diameter. Furthermore, it is concluded that increasing the nozzle temperature, filling percentage, and nozzle diameter and decreasing the layer thickness improve the strength of the produced parts. This is due to an increase in the contact surface of the deposited filaments as well as a decrease in the empty gaps between them. Also, considering the deposition angle in the tension axis of the part can greatly increase its strength.

In this paper, a dual-axis inclinometer based on a micro-machine chip is introduced. The main purpose of this paper is to present a high-speed inclinometer with a wide measurement range and high accuracy for use in self-leveling systems. The inclinometer can measure the slope of the ground and generate the information of the slope in each direction as 11-bit digital data. The generated digital data is sent to the outside of the chip using the traditional SPI protocol. The part number of the chip is SCA100T-D02, which is controlled by an ATMEGA 32 microcontroller. The entire inclinometer circuit is placed inside an aluminum box and can be installed on any surface. The test results are shown that the proposed inclinometer can measure the slope of the ground with a speed of 18 Hz in both horizontal and longitudinal directions, with a range of ±90 degrees and an accuracy of 0.1 degrees. The operating temperature range of the inclinometer is from -40 to 125 degrees Celsius, and the slope information can be seen on a 4×20 display. So, this inclinometer can be used in a wide range of industrial, agricultural, etc. equipment.