numerical simulation

In the sheet metal bending process, springback at the end of the operation often leads to inaccuracies in the workpiece geometry. One innovative approach to reducing springback is the application of ultrasonic vibrations. In this research, an ultrasonic tool and concentrator for bending operation were designed and manufactured to investigate the effect of ultrasonic vibrations on springback. First, the concentrator dimensions were calculated using analytical relations, and numerical simulations were conducted using Abaqus software to determine the vibration node location. The resonant frequency of the constructed assembly was then measured using an impedance analyzer. Samples of aluminum Al3105 and Al6061, as well as CK65 steel, were bent both with and without ultrasonic vibrations, and the springback was measured. Experimental results demonstrated that ultrasonic vibrations reduce springback by up to 58% in steel sheets and 29% in aluminum sheets, with a more significant effect observed in materials with higher yield strength.

In recent years, 3D printing technology has played an important role, especially in prototyping and manufacturing parts with high speed and low cost. Among the various methods, fused deposition modeling (FDM) is known as one of the most economical and widely used. This method uses materials such as polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS), and parameters like nozzle temperature, layer thickness, and print speed directly affect the final quality of the part. Due to their significant impact on properties such as tensile strength, Young's modulus, flexural strength, and dimensional stability, many experimental and numerical studies have been conducted. The growing industrial use of this method highlights the need to review and evaluate these studies. This research aims to review and critically analyze them from both experimental and numerical perspectives to identify the key parameters in optimizing mechanical properties and reducing costs. Results show that parameters such as layer thickness and print speed have a greater effect on tensile strength and production time/cost. Achieving a proper balance among printing parameters is essential to produce parts with optimal properties and low cost. The findings are also consistent with previous research.

Biogas is a low-calorie fuel comprises 50-70% methane and 30-50% carbon dioxide, with small amounts of other particles. Combustion of low-calorie fuels often involves significant challenges related to flame stability in most burners. Combustion of porous media is an effective method of directing flame heat to the input mixture, which can increase flame stability. In most studies, biogas has been used in experimentaly work or numerical simulation with simple geometry. In this paper, researchers simulate a two-layer porous burner with biogas fuel, based on an experimental design, in two dimensions. They evaluate the effect of the burner geometry, which was not investigated in previous researches, on the temperature distribution and the radiation efficiency. The results show that reducing the amount of carbon dioxide increases the burner surface temperature. Additionally, changes in the interface of the porous layers, simulated in two conical and spherical forms in two converging and diverging states, cause changes in the place of flame, the maximum combustion temperature, the temperature of the burner surface, and the radiation efficiency. The maximum combustion temperature and the maximum burner surface temperature occur for the conical geometry in convergent mode. Increasing 10% of carbon dioxide in the biogas fuel reduces the radiation efficiency by 25% on average. The radiation efficiency of the divergent burner is more than the convergent mode, about 37% for conical geometry and about 25% for spherical geometry. The maximum radiation efficiency is achieved when the burner is divergent and the amount of carbon dioxide is 30%.

One of the important passive techniques to reduce the drag force is the use of microstructured surfaces. The structures of these surfaces, which are from the order of nanometers to several hundred micrometers, can be created randomly or in a regular and controlled manner, with different geometries and configurations on the surface, and by affecting the fluid flow, they can change the amount of drag. With the aim of studying the physics governing microstructures, this article will investigate the parameters resulting from air flow passing them, which include drag components, velocity profiles and shear stress. For this purpose, triangular microstructures with the same base and height of 50, 100, 200, 400 and 800 µm have been used, which are transversely exposed to air flow with velocity of 5 m/s and 25 m/s. Due to the emphasis of some articles on the flow slipping over the microstructures, the velocity profiles on these surfaces have been investigated, but finally, the change in the amount and direction of the shear stress has been described as the main mechanism of viscous drag reduction. Then, the effect of the size of the structures and the velocity of the flow has been investigated. The obtained results show that the trapped vortices among the transverse structures can reduce the viscous drag by reducing the amount of shear stress around the peaks and reversing its direction in the valleys. On the other hand, creating a pressure gradient inside and around the structures will lead to creating pressure drag. The sum of these two drag components, which depend on the size of the microstructures and the flow velocity, will finally determine the increase or decrease of the total drag.

Heavy turbofan engines with high thrust values have a special place among air engines. Between the components of gas turbine engines, the turbine part is very sensitive and important due to the high temperature and long-distance operation of its components. In the present study, based on the results of the cycle design, the conceptual design of the turbine of the considered turbofan engine has been done by using the defined software and algorithms. The pressure ratio of the designed turbines in the conceptual design and numerical simulation section differed only by 0.7 and 0.5%. However, the efficiency of the high pressure turbine differed by about 5.6% between the conceptual design and the numerical simulation due to not considering the cooling in the numerical simulation.