شبیه سازی عددی

In this article, the numerical simulation of the behavior of metallic plates in the process of high-speed forming with female die is discussed. Also, the repeated underwater explosive loading was applied to the sample so that 4 and 8 gr of explosive charge were used in the 1st and 2nd blast, respectively. In the following, the Coupled Eulerian-Lagrangian method along with Johnson-Cook viscoplasticity model was used for the numerical simulation of the process. The numerical model was validated using the experiments conducted in Ref [1]. It was shown that the numerical model well shows the deformation profile as well as the thickness distribution in the longitudinal direction of the plate. Using the validated numerical model, quantities such as changes in horizontal deformation velocity and vertical deformation velocity, pressure, stress and JC damage criteria in the radial direction of the plate were investigated. The results showed that unlike the results obtained for explosive forming in the previous references, the test specimen in the 1st and 2nd blasts after passing through the transient deformation area does not undergo fluctuations or so-called springback phenomenon and its value quickly approaches the maximum amount (depth of the female die). Also, after hitting the die, the plate does not experience the reverse deformation or reduction of the deformation. The cause of this issue can be found in the appropriate selection of the amount of the charge mass of the and also the use of the female die. Therefore, it is very efficient to use the idea of a female die without central venting hole for forming metals under repeated underwater explosive loading.

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%.

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.

In this article, a forced circulation crystallizer under vacuum, which consists of crystallizer, pump and heat exchanger, is proposed for the purpose of providing fresh water for consumption. In order to simultaneously supply the heating load of the crystallizer and also to distill the water vapor coming out of the crystallizer, a heat pump has been used as a new method. A laboratory set is designed and built to demonstrate the feasibility of the proposed system, which includes a forced circulation crystallizer cycle. The average error percentage between the laboratory and simulation results was reported as 4.8%. The results indicate that by changing the inlet temperature and pressure of the crystallizer, the rate of salt crystal production and fresh water production increases by 0.65 and 19.81 kg/h, respectively. Electric energy consumption also decreases with the increase of feed water inlet temperature and the heat capacity of the heat exchanger, and the lowest amount of electric energy consumption occurs at the temperature of 50 degrees Celsius, the pressure of the crystallizer is 0.085 bar, and the heat capacity of the heat exchanger is 13.25 kw.

This study investigates the anisotropic damage growth and martensitic phase transformation in AISI-316 austenitic stainless steel at room temperature. Initially, tensile and torsion tests were performed on samples at various displacements. Following these tests, the samples were analyzed using X-ray diffraction (XRD) to identify the present phases and determine the martensite volume fraction. The experimental data obtained were then used to develop a numerical model implemented in Abaqus software using the UMAT code. The simulation covers two main aspects: martensitic phase transformation and anisotropic damage growth, with the code capable of predicting both phenomena at room temperature. Damage mechanics is a relatively new tool in mechanical engineering, complementing the theories of plasticity and fracture mechanics. This study experimentally examined the process of damage growth and phase transformation in 316 stainless steel. The innovation of this model lies in its simultaneous consideration of anisotropic damage growth and austenite-to-martensite phase transformation at room temperature. The damage model used in this study is the Limiter model. Experimental tests, including tensile and torsion tests, were conducted to assess damage in different dimensions, involving both loading and unloading conditions. The model by Shin and colleagues was utilized to determine the phases present in the material. For greater accuracy in phase transformation testing, the samples were prepared using a water jet and then subjected to X-ray diffraction to measure the extent of martensite phase development. Finally, the numerical simulation was calibrated against experimental results for 316 stainless steel, ensuring the model's accuracy. Austenitic stainless steels transform into the martensite phase under strain, where the unstable austenite phase converts into stable martensite due to plastic deformation. This martensitic phase transformation hardens the austenitic steels. This study examines the anisotropic damage growth resulting from plastic strain and the martensitic phase transformation in austenitic stainless steels, specifically AISI-316, at room temperature. Initially, tensile and torsion tests are conducted on the samples at various displacements. Subsequently, these samples undergo X-ray diffraction tests to determine the existing phases and the martensite volume fraction in the samples. Using the obtained results, an empirical model is created from numerical tests using the UMAT code in Abaqus software. This simulation includes both the martensitic phase transformation and anisotropic damage growth. The code can predict any phenomenon under environmental conditions. Finally, the effectiveness of the proposed model is compared and analyzed against experimental results for AISI-316 steel.

This study focuses on the precise production of droplets in a droplet-based microfluidic device, where monodisperse oil-in-water emulsions with controlled droplet sizes are generated. The primary objective is to achieve uniform emulsions by examining key parameters such as additives in the continuous aqueous phase, internal phase flow rates, and the microfluidic device's geometric characteristics. Initially, the geometric parameters of the microchip for emulsion formation were selected using numerical simulations, and the results were validated through experimental tests of emulsion production with the microchip. The precision of the outcomes is enhanced using an innovative 3D printing method for microchip manufacturing, enabling the creation of identical microdevice copies. In the experimental phase, the optimal conditions for producing uniform droplets were identified by examining the effects of various additives in the external aqueous phase, different internal phase flow rates, and the geometric parameters of the microfluidic device. The results demonstrate that the distance between the two capillaries can control droplet size and frequency, the internal phase flow rate, and the type of additive in the external phase, allowing for emulsions with droplet sizes ranging from 500 to 1000 microns. Specifically, the distance between the capillary tubes significantly affects droplet size, contributing to 30% of the variation when this distance is increased sixfold. Additionally, the study reveals that the increase in droplet diameter due to a higher internal phase flow rate varies with different additives in the external phase. For instance, sodium dodecyl sulfate (SDS) results in a 6.65-fold increase in droplet production frequency with a sixfold increase in the internal phase flow rate. Furthermore, the type of additive in the external phase can independently control droplet size. For example, with a specific internal-to-external phase ratio, oil droplets measure 600.8 μm in an external phase containing SDS, 582.2 μm with polyvinyl alcohol (PVA), and 615.4 μm with Triton X-100. This method can precisely control droplet size and frequency, making it suitable for generating precursor emulsions for engineered micro- and millimeter-sized polymer particles aimed at drug delivery or cell culture applications. The study successfully ensures consistent and uniform emulsions by manipulating these critical parameters through this combined approach of numerical simulations and experimental validation.

In this study, numerical simulations are used to investigate the dynamic stall phenomenon at two advance ratios, μ = 0.3 and μ = 0.35, on a single blade with cyclic pitching motion. To simulate the three-dimensional compressible flow field, the unsteady Reynolds-averaged Navier-Stokes (URANS) equations are solved using the finite volume discretization method. A hybrid mesh is employed, and turbulence is modeled using the k-ω SST model. To validate and verify the numerical method, flight test data from the AH-1G helicopter was used. The comparison results confirm the accuracy and reliability of the numerical approach applied in this study. The findings of this study indicate that contrary to expectations, the intensity and number of stalls on the retreating side of the rotor at the studied radial section (r/R = 0.778) are greater at µ = 0.3 compared to µ= 0.35. On the advancing side, the stall is more severe at µ = 0.35, with the post-stall pitching moment coefficient differing by 89%, resulting in a significant increase in negative aerodynamic damping at this ratio. An analysis of the flow pattern reveals that the dynamic stall development at both advance ratios begins with flow separation near the trailing edge, which then propagates upstream while simultaneously bend to outboard region due to radial flow.

The present research has investigated the simulation of the aerodynamic heating of a missile with regard to the placement and non-placement of the control block and its connection components. In this research, he investigated four different geometries of a commercialized missile sample, including a missile without a block, a missile with a control block, a missile with a control block and a shaft connected to it, and a missile with a control block and a shaft connected to it, considering the wedge. The results showed that the presence of control block as an obstacle in the way of air flow has increased the heat flux on the missile surface by about 27% compared to the first phase. In the upstream of the shaft, t in the amount of heat flux is 5 times compared to the case without the shaft. Also, with the simulation of the fourth phase, the effect of the presence of the wedge in guiding the fluid flow and reducing the damaging effects of heating around the location of the shaft was revealed. The results showed that the presence of the wedge caused the heat flux of the missile surface to decrease by about 52% compared to the third phase. Also, the wedge has reduced the maximum heat flux created on the shaft surface by about 74% compared to the third phase.

In this research, a numerical investigation of the steady flow around an air-to-surface missile has been done using Fluent and Missile Datcom software at different speeds and angles of attack. Force and moment coefficients and contours of Mach number, pressure and temperature around the missile have been investigated. In order to reduce the numerical error of the grid, the flow in the critical aerothermal conditions is examined around the nose of the missile using a structured mesh. The results show that the missile has static stability at all speeds and a vortical flow is formed on the body and control surfaces, and with the increase of the angle of attack, these vortices become larger and cover more areas of the body and control surfaces. Examining the temperature distribution on the surface of the missile showed that the point of maximum temperature is located at the tip of the missile and at the leading edge of the control surfaces, and with the increase of the angle of attack, this point inclines towards the bottom of the missile tip. Also, with the increase of Mach number, the temperature value at this point increases. The temperature distribution on the surface of the missile in steady conditions showed that these conditions are equivalent to a very long flight of the missile with the maximum Mach number of 3.7.

The semi-submerged propeller is a type of marine propeller that is used in high-speed vessels. This propeller has attracted designers attention; because it resists the destructive phenomenon of cavitation. also Semi-submerged propellers have suitable thrust and torque stability at high speeds and offer high maneuverability. Therefore, further investigation around it is important. The current research aims to examine the effect of creating a vertical groove on the surface of the blades of a semi-submerged propeller, an idea inspired by the grooved or corrugated surface on the bottom of some high-speed vessels. The propeller examined in this study is the semi-submerged propeller 841-B known as Olofsson. The 3D domain meshing and numerical simulation have been done in the Star CCM software. The specific condition considered in this numerical simulation is a submergence depth ratio of 33%, an advance coefficient of 0.8, a cavitation number of 2.3, a Froude number of 6, and a shaft angle of zero degrees (horizontal position). The results showed that the efficiency of the grooved propeller is 44.5%, which is less than the efficiency of the ungrooved propeller. In the end, it can be said that the created groove has an adverse effect on the efficiency and performance of the propeller and it is not recommended to use it in the working conditions of the investigated propeller.

In the present study, the effect of the angle and pitch of the spiral pipe on the rate of heat transfer through the wall of the pipe to the fluid passing through it in quiet, transition and turbulent flows has been studied Next the changes in Nusselt number due to the addition of nanoparticles TiO2 were investigated. Finally, the effect of applying a magnetic field with an intensity of 1 Tesla on the rate of heat transfer in different situations has been investigated. To do this, the spiral tube is considered in three different pitches of 10, 12.5 and 15 cm and three angles of 0, 45 and 90 degrees. According to the results, the Nusselt number increases with decreasing pitch and in different Reynolds, the Nusselt number reaches its highest value in 10 cm pitch. This number also changes with changing angle and has the highest and lowest values at 45° and 90° angles, respectively. Then TiO2 nanoparticles with mass percentages of 0.1%, 0.3% and 0.5% were added to the fluid, which increased the Nusselt number. It was observed that increasing the concentration of nanoparticles causes a higher Nusselt number. Finally, Hartmann number was calculated for the spiral tube, the maximum value of which was obtained in pitch of 15 cm and a concentration of 0.5% TiO2 and was equal to 43.83.

In this research, one of the widely used control systems of tailless aircraft, named Crow Flap, has been simulated by numerical method and the appropriate opening direction of this system has been investigated. By creating a differential drag on both sides of the aircraft, this system creates the necessary yawing moment and directional control. This system consists of two moving surfaces that are deflected against each other to neutralize each other's force and produce drag. One of the important issues in control systems is the reduction of disturbing moments. Determining the suitable opening direction with the least drag and disturbing moment and increasing the useful moments is the aim of this research. For this purpose, the measurement of these moments and forces are compared in two states of normal and reverse-opening. The UAV under investigation is a lambda-shaped UAV named Swing. Experiments have been carried out at AOAs of 0 to 12° for three opening angles. The created Mesh is unstructured. In this simulation, the continuity, momentum, and scalar equations have been solved by the Simple C algorithm after discretization with the finite volume method, and the turbulence model (K-ω-SST) has also been used. In this research, the opposite opening direction of the Crow Flap, unlike the usual opening direction mentioned in some articles, had a better result, so that at high AOAs, this opening direction has between 5 and 32% less drag and it has produced 10.5 to 35% more Yawing moment along with reducing disturbing moments.

In the present research, the performance of the combustion chamber for use in thermo-photovoltaic systems depending on some factors such as the material of chamber, wall thickness, and the presence of porous medium, has been numerically investigated. In the numerical simulation, the realizable k-ε and the finite rate- eddy dissipation models have been used to model flow turbulence and hydrogen gas combustion, respectively. Three different wall thicknesses at constant equivalence ratio of 0.8 and velocities of 2 m/s and 3 m/s have been studied. The results show that decreasing the wall thickness increases the temperature of the outer wall and the radiation efficiency of the chamber. The maximum temperature increases by 111 and 141 °C at the velocity of 2 m/s and at the thickness of 0.2 mm as compared to the thicknesses of 0.5 mm and 0.8 mm and by 79 and 107 °C at the velocity of 3 m/s. Also, the combustion chamber has been simulated with three different materials of walls, Al2O3, SiC and Stainless Steel (SS316). The results show that when the wall is made of Al2O3, the efficiency is higher. In another part of this research, the presence of two porous zones in the chamber has led to a change in the place of flame formation. The radiation efficiency in the combustion chamber with the presence of two porous zones increases by 24%, 27%, and 28%, respectively, in the equivalence ratios of 0.6, 0.8, and 1.

In this article, to investigate the severity of damage to the helicopter pilot under the crash impact, the numerical simulation of the actual helicopter cockpit seat has been done. To limit the complexity of the problem, a fully vertical impact was considered as a reference scenario for the assembly consisting of a collapsible helicopter seat, an energy absorption section, and a humanoid dummy. For this purpose, the three-dimensional model of the chair in the laboratory was studied in two states with and without the addition of the energy absorption mechanism. A honeycomb structure was used in the seat cushion section. The results of the research showed that the use of UPVC damper to test the crash impact with a certain mass based on biomechanical criteria, an average 80 % decrease in serious injuries to the skull and spine has been achieved. Also, based on the results obtained in this research, although the aluminum honeycomb structure meets the criterion of damage to the head and is within the permissible range, it has rejected the criteria of damage to the spine and permissible acceleration range. However, compared to the case without honeycomb, it has performed much better and has been able to absorb the energy of the crash impact.

Due to the very high importance of gas turbine in electricity production and also its increasing development in the electricity industry, one of the most important methods to increase the efficiency of gas turbine blades is to add thermal barrier coating to their outer surface. These coatings improve the cooling of gas turbine blades, but they also have disadvantages such as roughness of their surface cause to the separation of the hot fluid flow around the turbine blades. The rough surfaces of thermal barrier coatings should be used optimally and purposefully. In this research, using commercial software of Fluent, this type of coating has been investigated and analyzed in order to find the most optimal possible mode for its use. The influence of surface parameters such as roughness, thickness and material of thermal barrier coatings have been investigated. The most optimal state for the mentioned parameters are: 0.1 mm, 0.38 mm and 2.7 W/m.K respectively.

In this paper, the low velocity impact response of sandwich panels with composites face sheets and aluminum based corrugated cores is modeled with numerical simulation, and the amount of energy absorption, contact force, deformation of the impact area and dimensions of the damage area are calculated and compared with experimental results. Sandwich panels with composite face sheets reinforced with carbon fibers and glass fibers and corrugated aluminum-based cores are in square, trapezoidal, arched, sinusoidal and triangular shapes. Through numerical simulations ten examples have been analyzed. Dimensions and weights of face sheets and cores of the samples are the same. The obtained results show that in the sandwich panel with trapezoidal and square corrugated cores, the contact force is applied to a larger area and the energy absorption and dimensions of the damage area are greater. Also, sandwich panels with arc and sinusoidal wave shape cores have the greatest displacement at the point location compared to other sandwich panels.

To evaluate the acoustic performance of the muffler at zero flow, different methods of determining transmission loss were studied. Both numerical and experimental approaches were used to calculate transmission loss. The numerical method employed was the Herschel-Quincke tube method (case 1) as well as simulation methods using COMSOL (2) and ANSYS (3). The experimental approach utilized the transfer matrix method with the aid of software developed by the B&K software (4) and the sound card with MATLAB software (5) was used to calculate the transmission loss. Furthermore, the mesh independence of numerical methods and the uncertainty of the experimental method were examined. Results were evaluated between 20 and 1900 Hz, which is an appropriate frequency range and reliable range for evaluating mufflers and comparing different cases to transmission loss calculations. According to the results, the equivalent transmission loss for cases 1 to 5 is approximately 5.81 dB, 5.35 dB, 5.21 dB, 4.08 dB, and 3.77 dB, respectively Based on the results obtained, it can be concluded that the equivalent transmission loss of ANSYS and COMSOL numerical methods is almost consistent, and COMSOL simulation results in a 8% lower equivalent transmission loss than Herschel-Quincke's one-dimensional numerical method. Similarly, the equivalent transmission loss of experimental calculation methods indicates that the sound card approach has a 7.5% lower equivalent transmission loss than the B&K software approach.

Characteristics such as excellent mechanical properties, high heat resistance, corrosion resistance and low density have made composites like carbon fiber widely used in various industries including medical, aerospace and automotive. However, due to characteristics such as poor thermal conductivity, low cutting surface quality and high strength, it is difficult to cut it using conventional methods. The aim of this article is to design and build a type of cutting tool that uses ultrasonic waves to reduce the cutting force and improve the cutting surface quality of carbon fiber workpieces. In this research, the design and construction of the horn part of the cutting tool is specifically discussed. First, a stepped horn is designed by performing analytical calculations, and then by adding a conical part with different angles to it, the effect of changing the angle on the amplitude amplification, modal spacing and stress distribution has been investigated by finite element simulation method.The results of numerical simulation show the insignificant effect of changing the angle of the conical part on the result. Finally, the optimized design is built.The results of experimental tests show that the use of ultrasonic waves has a significant effect in reducing the cutting force up to one-sixteenth and significantly improving the quality and straightness of the cutting edge of the carbon fiber workpiece compared to the case without ultrasonic assistance.

In this study, a three dimensional numerical simulation of an industrial entrained flow combustion reactor has been conducted. The governing equations and reactions are implemented and the operating parameters are considered according to the experimental works. The results obtained from the numerical simulation are validated by comparing with existing experimental data and similar published papers. Four different devolatilization models are investigated and the simulation results are compared to each other. The obtained results show that although the Kobayashi model has a higher calculation time, it provides more accurate results compare to the experimental results. The effect of increasing/decreasing of injected coal particle sizes are studied. The results show that increasing of the coal particle sizes from 55 to 120 μm has led to a decrease in the gas temperature inside the reactor. By reducing the average coal particle size from 55 to 30μm, the gas temperature close to the flame has increased from 1800 K to 1900 K.