the absorption performance of anechoic coatings depends on the material properties، layer thicknesses and cavity distribution density and cavity size. In this paper a design method based on numerical simulation was presented by combining FEM and acoustic duct method (ADM). Analyzing of anechoic coatings was performed under active sonar impinging plane wave by normal incident angle. In this approach considering a unit cell of anechoic coating and two ducts of the fluid on its both sides، the reflection characteristics، transmission and reflection coefficients of anechoic coating were calculated using acoustic duct theory. Validation was performed by comparing the results of simulation with the available experimental data. Also a design code in ANSYS software was developed. Finally using this code and the proposed model، the acoustical behavior of anechoic coatings was investigated. The results show that sound transmission coefficient for coating with cylindrical cavity is larger than that of spherical cavity. Furthermore unlike the transmission coefficient، for all frequencies upper than 1500 Hz، coating with cylindrical cavity has a greater echo reduction and therefore its anechoic performance is better than that of spherical cavity.

The discharge process in two- and three-electrode pure-nitrogen spark gaps is simulated using Finite Element Method (FEM) to solve for the electric potential and field. The effects of secondary electron emission. Photo-ionization and recombination mechanisms are taken into account. Current growth and the evolution of ion and electron distributions in the discharges are studied and an oscillation due to cathode streamer movements has been observed, in agreement with the theoretically estimated values. The study of complete discharges has been possible by introducing proper absorbing boundary conditions over the electrodes, by which numerical instabilities have been suppressed. The simulation results for different values of applied voltage. pressure, gap distance. series resistance and series inductance are discussed. In the case of three electrode spark gaps. the effect of the trigger voltage on the current buildup speed is considered.Agreement between the calculated dosing time for the two-electrode spark gap and a reported empirical formula is observed.

Applying numerical methods in the analysis of forming processes, results in the prediction of the process parameters without performing costly and time-consuming laboratory test procedures. The purpose of this study is to evaluate the feasibility of manufacturing a dental drill body using a hydroforming process. Due to the hygienic issues, the selected material for this part is stainless steel grade 304. The main reason for applying stainless steel in the main body is its hygienic characteristics such as antibacterial surface and washability which makes it appropriate for use in many medical instruments. The hydroforming process is simulated in ABAQUS software and the required parameters of the initial material are obtained from engineering tables. The thickness of the initial part is 0. 5 mm and after simulation, it is decreased to 0. 38mm. The maximum Von Misses stress of the part reached in this simulation is 708 MPa and the maximum strain rate is 1. 233 mm/mm.

Waveguides, used in electronic industries, are structures for transferring electromagnetic waves. A twist waveguide is a device used to change the polarization of waves. In this study, a process for fabricating an aluminum rectangular twist waveguide was designed and some guidelines were introduced. The preliminary profile was obtained by a forward extrusion process. In order to study the effect of strain hardening, the twisting process was studied for annealed and non-annealed samples after the extrusion process. The results revealed the necessity of annealing the samples before the twisting; otherwise, local deformation would occur. Measuring the applied torque showed that as the process progressed, the required torque for an annealed sample would increase due to work hardening, while for a non-annealed sample the torque would decrease after local deformation. Furthermore, the simulation of twisting process was performed using Deform software. No inconsistency was observed between numerical and experimental results. Moreover, investigating the cross sectional distortion showed an undesirable cross sectional distortion for the unfilled sample whereas the cross section in the sand-filled sample stayed rectangular.

Cold roll forming is the most popular process that is widely for manufacturing pipe by forming strips into a cylindrical shape which are then welded by electric resistance welding. In this study, an elastic-plastic deformation behavior of the strip was investigated by using the FEM method. Therefore a 2D modeling has been done by means of FEM software, Ansys, to examine effective parameters on the final shape of the strip edge. Also the effects of the parameters such as fin angle at fin rolls and the proportion of the strip thickness per final pipe diameter (t/D) were considered on the final shape of product. Some experimental works have been done in Ahvaz Pipe Company that successfully there were an acceptable consistency among experimental results and obtained outcomes from 2D simulations and also results from other researchers.

Since transformers are one of the most important and most used equipment in power network, investigating the factors which affect the loss of these equipments is of particular importance. Nowadays Amorphous metal core transformers have a significant place in today power market, since they exhibit 60-70% lower no-load losses compared to the Silicon crystalline steel core transformers. In order to enhance the design and cost and also to shorten the time to produce Amorphous metal core transformers, numerical analysis of the no-load as well as load conditions are of paramount importance and hence should be considered. On the other hand, temperature is one of the important and effective factors in transformer life, because increasing the transformer temperature leads to reduction of its rated life. In this paper, a 100 kVA unit transformer has been simulated by coupling ANSYS Maxwell and ANSYS FLUENT softwares and no-load and load losses are investigated. The results show that amorphous core transformer compared to Silicon Crystalline Steel core transformer reduce no-load losses about 65 percent. Furthermore, thermal analysis shows amorphous core transformer has lower temperature compared to the Silicon core transformer in no-load conditions.

In this paper, the drawing process of multilayer sheet metal through a wedge-shaped die has been analyzed using stream function and upper bound method. Typically, a sandwich sheet contains three layers of metal, where the outer layers are of the same thickness and material and different from those of the inner layer. In this study, a new deformation model has been introduced in which inlet and outlet shear boundaries are considered flexible and the effect of work hardening of sheet layer materials has been considered. According to the suggested stream function, velocity field, strain rates and powers have been calculated. The optimized geometry of the deformation zone and the required drawing force have been determined depending on the process conditions. Analytical results including the drawing force and thickness of the sheets in the outlet of the die have been compared with the finite element (FE) results. The FE results have good congruence with the analytical ones. Finally, the effects of friction factor and reduction in thickness have been investigated on the drawing force and the optimum die angle.

Manufacturing of the Autonomous Underwater Vehicle (AUV) is a challenge for researchers because of the hazardous ocean environment. The propeller is the most complex part in AUV because of its elaborately shaped blade designed to increase the thrust. The selection of the manufacturing process, flash-less cold forging die design and optimization of the work-piece are the major issues to reduce the overall cost of the propeller. Numerous investigations have been carried out in this area by many researchers using various tools and techniques. However, cold forging of complex geometries such as the propeller blade is still lacking. Moreover, volumetric analysis and optimization of work-piece have not been reported so far for complex geometries. In this work, the cold forging process is adopted to produce the propeller blade. Three-dimensional finite element (FE) analysis and experimental flash-less cold forging of aluminum blade of the AUV propeller is presented. The work-piece used is of AISI AL6061 and the die material is die steel (AISI D2). Based on the simulation results, the flash-less cold forging is successfully done on a 100 ton C-type machine.