حمید فاضلی

High strength aluminum alloy pipes (AA7075-T6) has been widely used in various industries due to their favorable properties, Such as high strength to weight ratio, excellent machinability and proper forming. On the other hand, according to the susceptible to phenomenon of stress corrosion cracking, the evaluation and monitoring of mechanisms related to this issue is of considerable importance in the industry. In this research, Fuzzy clustering method (FCM) has been used to detect acoustic emission signals related to stress corrosion cracking mechanisms of aluminum pipe. Using this method, while revealing the clusters in an unsupervised method, leads to more appropriate classification and separation of data. In this regard, a laboratory system including waveguide, corrosive solution chamber, and arc-shaped aluminum samples according to ASTM-E399 standard along with acoustic emission equipment was designed and prepared. Then, using the slow strain rate test (SSRT) and receiving AE signals simultaneously, the AA7075-T6 aluminum sample was placed in two corrosive environments (HCL9% and HCL33%) to identify the two main mechanisms of stress corrosion cracking, including anodic dissolution and hydrogen embrittlement (cathodic). Five descriptive acoustic parameters including rise time, count, energy, amplitude and duration were used to analyze the obtained signals. In order to select the most effective acoustic characteristics and reduce the amount of information, principal component analysis was used. Subsequently, with the fuzzy method (FCM clustering) based on the optimized data from the analysis of the main components, it was possible to distinguish and separate these two types of corrosion mechanisms. According to the obtained results, it was found that the dominant mechanism in the phenomenon of stress corrosion cracking in HCL corrosive solution is the anodic dissolution mechanism, which in addition to increasing the corrosion current density, increases the dependence of stress corrosion on this mechanism by increasing the concentration of H+ and C- ions.

Due to the lack of existence of control surfaces in entry capsules, the subject of static and dynamic stability is always important. In this paper, these coefficients are investigated experimentally for the case of forced oscillation at supersonic flow. In this experimental study, the effects of freestream Mach number, mean attack angle and pitch frequency on dynamic stability coefficients were evaluated. According to the results, in Mach 1.8, the geometry starts to be dynamically unstable. One approach to overcome this problem is to change the average attack of angle of the model. This change in the mean attack of angle, similar to the results presented for the five-degree mean angle, will lead to dynamic stability.

Discrete concrete targets show more resistance to penetration against shaped charges. The purpose of this study is to simulate the penetration of shaped charge in discrete concrete targets using LS-DYNA and ANSYS-AUTODYN and compare the results. For this purpose, the simulation process for one of the experimental results is performed and the results obtained from both software are validated. Finally, the results of two software in the fields of jet velocity, penetration depth, entry diameters, middle and exit crater, and run time are compared. Application of the ALE method for jet elements and the RHT concrete model to simulate the concrete behavior at high strain rates yielded good results. Differences in numerical solution method and command differences in the interaction of the Lagrangian and Eulerian elements in two software caused the depth of penetration in ANSYS-AUTODYN to be less than the LS-DYNA and the diameters of entry, middle and exit crater in ANSYS-AUTODYN become larger than the LS-DYNA and closer to the experimental results. The results of the two software are in good agreement with the experimental results. Continuous concrete was also simulated and it was found that the penetration depth of discrete concrete was lower than continuous concrete.

Casting simulation has been recognized as an efficient tool for analyzing mold filling behavior, solidification and cooling, and prediction of the position and type of internal defects. The main concern in the current study is to predict the occurrence of porosity defects with the current casting design of a conical part, and then presenting practical solutions to remove or reduce the defects. Niyama dimensionless criterion was used for precise quantification of micro-porosity. The results of the casting simulation with accordance to the current process parameters showed that the occurrence of shrinkage porosity defect took place considerably. In order to suggest a solution to decline the extent of porosity, the inclination of the part wall was utilized. The results indicated that with an increasing slope, the amount of porosity is successively reduced. Besides it was found that a slope in the order of 0.5° on the external wall would lead to a remarkable reduction in the shrinkage porosity by inducing the directional solidification. The effect of various designs of the casting including the positioning of the casting inside the mold on the extent of porosity is discussed.

Recently the use of reactive shaped charges with bimetallic liners are taken into consideration to increase destruction quality in water environments. In this research, according to the results of a series of valid experimental results, the analysis of a reactive shaped charge with a bimetallic liner made of copper-aluminum liner has been numerically verified. In this verification, a suggested theory for the cutoff velocity of bimetallic liners has been used to calculate the cutoff velocity. The amount of penetration depth using a numerical solution is in good agreement with the experimental value. These results have been compared with the values obtained from the analytical solution. Finally, the behavior of the shaped charge with bimetallic liner has been compared with a single metallic liner using the same target geometry in both and it has been shown that the overall penetration quality such as depth, diameter and the profile of reactive shaped charge with a bimetallic liner was found to be better than the single metal liner.

One of the main important components which are used in the shaped charges is liner that its material has a considerable influence on the jet formation and penetration profile. In recent years, researches have focused on the analysis of the effect of bimetallic liners and their effective behavior. In this paper, at the first step, the process of jet formation and the penetration in the steel target is numerically simulated for a shaped charge with copper liner using the Ansys-Autodyn software. Analytical solutions have been done using generalized PER theory for jet formation and hydrodynamics theory for penetration; as well the experimental tests were performed with copper liner. The comparison of penetration profiles obtained from numerical, experimental and analytical methods showed a good agreement. Then, the validated numerical simulations were developed for two single-metal liners of nickel and aluminum, and two bimetallic copper-nickels, and copper-aluminum liners. Also, the results of jet tip velocity, penetration depth and crater diameter have been compared between single and bimetallic liners. Regarding to jet formation and penetration in steel target, the comparison between single and bimetallic liners results shows that the using bimetallic liners, improve crater diameter and depth of penetration simultaneously.

of the main important components which are used in the shaped charges is liner that its material has a considerable influence on the jet formation and penetration profile. In recent years, researches have focused on the analysis of the effect of bimetallic liners and their effective behavior. In this paper, at the first step, the process of jet formation and the penetration in the steel target is numerically simulated for a shaped charge with copper liner using the Ansys-Autodyn software. Analytical solutions have been done using generalized PER theory for jet formation and hydrodynamics theory for penetration; as well the experimental tests were performed with copper liner. The comparison of penetration profiles obtained from numerical, experimental and analytical methods showed a good agreement. Then, the validated numerical simulations were developed for two single-metal liners of nickel and aluminum, and two bimetallic copper-nickels, and copper-aluminum liners. Also, the results of jet tip velocity, penetration depth and crater diameter have been compared between single and bimetallic liners. Regarding to jet formation and penetration in steel target, the comparison between single and bimetallic liners results shows that the using bimetallic liners, improve crater diameter and depth of penetration simultaneously.

Using heat shield, especially in throat area has a significant effect on combustion chamber pressure and thermal efficiency of solid fuel engines, and so many studies have been made in this field. A precise prediction of regression in throat surface is essential to optimum design of high burning time engines. In this study, ablation of graphite nozzle in solid fuel engines is investigated numerically for a special ingredient composite fuel .Navier Stocks equations together with thermodynamic equations inside the engine as well as thermochemical and thermal conductivity equations on nozzle surface are derived and written in their suitable forms and solved to determine the regression rate of nozzle throat surface. Furthermore, a cartridge full size solid motor by polyester binder fuel was tested and the ablation rate was measured by using a 3D scanner. The experimental pressure-time and thrust-time curves were also derived and used as input data for numerical calculations. Comparison between numerical and experimental results shows a satisfactory agreement. The experimental results show that the ablation has maximum value in the inlet area, and in divergent section is approximately constant and its value is 0.2mm. Because of important effect of ablation rate on the geometry of nozzle throat and so on the performance of the engine, the results of this study may have applicable usage in analyzing and designing solid fuel engines.

The purpose of this study is to demonstrate the advantages of computer simulation and parametric studies in improving the copper electroforming process. For this purpose, the finite element model for a cone geometry was prepared using the Comsol software, and the effect of key parameters including applied current density, solution electrical conductivity, electrode spacing, and anode length, on the thickness uniformity. In order to validate the model, a conical shell was produced in the laboratory by electroforming method, and the thickness distribution was compared with the simulation results. The comparison of the results showed that using the tertiary current distribution method to simulate the electroforming process is a precise and efficient model and can be used for parametric studies. Finally, after parametric study, it was determined that all selected variables had a significant effect on the thickness uniformity. In addition, it was found that the most to least significant variables were applied current density, solution conductivity, anode-cathode spacing, and anode length, respectively.

This paper aims to study the effect of nanofluid on the thermal performance of a heat pipe with three evaporators for satellite equipment cooling. Nanoparicls of Cuo and TiO2 were considerd for modeling. The mathematical expressions of temperature distribution of heat pipe wall, which are analytically derived by separation of variables technique, consist of infinite series that were solved by Matlab software. The accuracy of simulated results was validated against available experimental data and a good agreement was observed between them. The results show that the use of nanofluid instead of water leads to a more temperature reduction of satellite equipment as well as a more temperature uniformity throughout the wall of heat pipe. Moreover, increasing of nanoparticle concentration and reducing nanoparticle diameter have a remarkable effect on the heat transfer enhancement, thermal resistance reduction, and thus thermal performance of heat pipe. Under the best condition, growing CuO nanoparticle with diameter of 10nm up to 8% increases heat transfer coefficient up to 75%. The use of nanofluid reduced the required heat transfer surface and the weight of heat pipe in best cause (8% CuO nanoparticle with diameter 10nm) decreases down to 35%. The outcomes of this paper indicate that metal oxides nanofluids can have a great potential in satellite equipment cooling.

An analytical-numerical study on the thermal behavior of nanofluid in a cylindrical heat pipe is performed to investigate the nanofluid application in air conditioning systems. Pure water and Al2O3-water nanofluid are used as working fluids. A mathematical modeling is developed to predict the heat transferred by the heat pipe between precooling and reheating sections of the air conditioning system. The obtained results by proposed model are validated against experimental data and a good agreement between them is observed. The effect of nanoparticle concentration and size on the amount of energy required in precooling and reheating sections are evaluated. The results reveal that using nanofluid can dramatically decreases the temperature difference between condenser and evaporator sections of a cylindrical heat pipe under constant transferred thermal energy condition. Enhanced condition for precooling and reheating processes is provided for higher concentration and lower size of nanoparticles. Also, not a significant variation in heat transfer is observed by increasing nanoparticles size beyond 40 nm. The findings of this study prove the potential of nanofluid application for air conditioning of buildings located in regions with hot and humid climate.

It is obvious that the natural frequencies of a submerged structure are less than those of in vacuum and these are due to the effect of added mass of water to the structure.for marine structures, fluid inertial (added mass) effects cannot be neglected. This paper focuses on the experimental, analytical and numerical solution of natural frequencies of submerged stiffened plate. The analytical solution based on the deflection equation of submerged stiffened plate, Laplace’s equation and Rayleigh's method in vibration analysis.Considering small oscillations induced by the plate vibration in the incompressible and inviscid fluid.The velocity potential and Bernoulli’s equation are adopted to express the fluid pressure acting on the structure. The natural frequencies of the stiffened plate are obtained practically by using Fast Fourier Transformation functions (FFT) in experimental analysis. Experimental results demonstrate the validity of numerical and analytical solution and results.the experimental results validate the derived formulation for natural frequency of plate vibrate underwater.

Designing space propulsion systems as one of the important subsystems of the spacecrafts and upper stage space launch systems needs to bypass different and complicated steps. In this article the comprehensive process of designing liquid fuel low-thrust space propulsion systems was illustrated. In the presented pattern, first of all according to the requirements and mission constraints, the main characteristics of the system were determined and then other characteristics were extracted. Finally, for the evaluation of the presented pattern, a low-thrust space propulsion system was designed based on a special mission and the results were compared with a real model. Comparison between the designed space propulsion system and the real one showed an appropriate accuracy of the presented pattern.

In this paper، thermodynamic design of an axial flow power turbine for converting an existing turbojet to a turbo-shaft engine is presented. The exhaust nozzle of the turbojet is replaced by an axial flow power turbine. The turbine model is developed، based on Ainley-Mathieson model. The results of Ainley-Mathieson model were verified، using a 3D simulation and existing experimental data. The turbine performance was investigated for several blade angles of attack. Results show that the turbine stage has a minimum loss and a maximum efficiency، when angles of attack are -3 degrees for stator and -8 degrees for rotor blades.

In a large caliber gun, charge determination has vital significance for gaining maximum muzzle velocity. Geometry and material of grains and charge weight (or number of grains) are important variables for charge determination. using internal ballistic software, we can determine the appropriate values of these variables. Determining the shape and material of the grain, makes the charging of a projectile possible. In this simulation program, the changes of the shape of the grain and the changes of its material are applied through shape function and changing the burning rate and special force ratios of the propellant respectively. In this article, an internal ballistic model is explained and evaluated. Then, the appropriate charge for a large caliber APFSDS projectile is determined. Finally, by using determined charge, the experimental results are compared against three sets of predictions obtained with the software to show the simulation accuracy.