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The most important application of explosive welding in cylindrical geometry is cladding of cylindrical surfaces in order to increase corrosion and wear resistance and also improving the mechanical properties of bimetal product. In this study, the explosive welding of bimetal tubes made of steel and Phosphor-Bronze was investigated using two explosives (TNT and Amatol 5-95) with different explosion velocity. At first the explosive window of two metals was achieved using the theoretical-experimental relations, and then using different experiments, the key role of explosion velocity and also the position of selected parameters of explosive window in the metals weldability were determined. At the end, the successfull method of manufacturing of this bimetal tubes is presented and commented upon.

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The flow field around the axisymmetric streamlined bodies which forms the main body of the airplanes and submarines has been the subject of several researches. The present study aimed to investigate the flow field around a standard submersible model in various angles of attack by employing two visualization methods. The vortex structures around the model are qualitatively studied at the 40-degree angle of attack in a vertical wind tunnel. These structures are visualized by the laser sheet illumination of the smoke injected flow. The shear stress field lines on the model surface in the 0≤ α ≤35° angles of attack became visible by oil and pigments. Noteworthy and distinct aspect of the present study is the application of two empirical visualizing methods which made three dimensional vortical field more understandable. Formation and development of the primary and secondary vortex along the model length are qualitatively interpreted by the results of the smoke and laser light visualization technique. Moreover, the primary and secondary separation lines along model length for various angles of attack were deduced from the results of the oil flow visualization.

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This study focuses on transition of laminar to turbulent flow around a symmetrical airfoil at a low Reynolds number in free flow and flow near the ground at different angles of attack. Finite volume method is adopted to solve the unsteady Reynolds-averaged Navier–Stokes (RANS) equation. Flow around the symmetrical airfoil SD8020 at a low Reynolds number (4000) at 5 and 8 degree angle attack has been simulated in free stream and near the groundnumerically. Current numerical result is compared with other’s experiment and numerical result in free flow at low Reynolds number and flow in ground effect that good agreement has been obtained in aerodynamic coefficient prediction. SIMPLEC method is used for pressure and velocity coupling and flow equations discrete with Quick method. Transition-SST model is used for modeling turbulence of flow. Result shows that the current numerical method can detect adverse pressure gradient, laminar separation bubble and transition of laminar flow to turbulent. According to the result, in ground effect location of laminar separation bubble, length of bubble and location of transition is moved to leading edge and pressure distribution is effected by location of laminar separation bubble.

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The fThe flow field around the axisymmtric stream lined bodis which forms the main body of the airplaines and submarines has been the subject of several researches. Turning maneuvers of submarines result in cross flow separation that generates large hydrodynamic forces. The separation of a simple axisymmetric body is very complex in nature. Understanding these vortical flows is paramount to improving vehicle performance and design. A suitable way to reduce the effects of this separated flow is to use vortex generators. The main goal of the present study is to investigate the flow field around a Suboff standard underwater model employing the vortex generator by using the oil flow visualization method and CFD method (OpenFOAM code) at 0° ≤ α ≤ 30° angles of attack. The novelty of the this study is the application of oil flow visualizing method and CFD simulation which can help us to precisely study the structure of three-dimensional vortical flow field. The results show that Vortex Generators placed along the submarine do indeed significantly reduce cross flow separation, size of vortices and drag forces.

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In present study, the wake flow field of a submarine model was investigated experimentally in a wind tunnel. These experiments were conducted in four different locations X/L= 0.85, 1, 1.25 and 1.5 downstream of the model at Reynolds number of 3.85×105 by a five hole probe. The effect of various factors such as the variation of Reynolds number, the installation of the trip strip on the model nose surface, the mounting of the appendages on the submarine bare hull model and the nose shape effect on the wake structure were investigated in this study. The results showed that the installation of the trip strip on the nose surface did not have recognizable effects. By Increasing the Reynolds number, the amount of the dropping velocity in the wake field decreased due to the decreasing of the separation region on the after-body section. Presentation of the appendages on the model surface lead to the increasing of the wake area. The effect of the nose shape on the wake of the submarine model is the main innovation in the present work. Investigations showed that the velocity in the central part of the wake for non-axisymmetric nose shape (TANGO) decreased in comparison with the axisymmetric nose shape (SUBOFF and STANDARD).

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This work aims to prediction of laminar/turbulent transition which plays an important role on aerodynamics of wing section. In this respect the flow around the NACA2415 airfoil simulated in a Computational Fluid Dynamics (CFD) solver in different regimes with and without propeller flowfield. For predicting the transition onset, two approaches were used: The first is based on time history of the skin-friction coefficient for determining the transition onset and the transition length on the airfoil. The second is to apply transition γ-〖Re〗_θ model for laminar/turbulent transition simulation. For investigation of transition effect, the simulation repeated by use of a classical turbulent model and both results was compared with experimental data. The comparison shows that taking into account the transition effects gives a good agreement with experiment. Relative error of calculated drag coefficients for the transition based simulation is lower than 10%, while fully turbulent simulation are 70% overestimated in some incidences. Slipstream of upstream propeller changes flow pattern and boundary layer characteristics over the wing. Indeed in presence of propeller, spanwise load distribution and laminar/turbulent transition onset were affected. In propeller flowfield, increasing of velocity normal component over wing surface causes transition delay. Movement of transition onset to trailing edge on the upper surface in propeller downwash is representative of such phenomenon. On the other hand, in upwash region, the transition onset moves upstream. With the increasing propeller rotational speed, this tendency augments and so the transition onset on the wing upper surface moves far downstream in propeller downwash.

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In the present research aeroacoustic characteristics of flow over a finite height wall mounted square cylinder at different angles of attack is investigated. The aspect ratio of the model and the boundary layer thickness were 7 and δ⁄D=4.27, respectively. The experiments were done in a acoustically improved aerodynamic wind tunnel. The purpose of this study is to identify correlation between the fluid and the acoustic fields. The flow-induced noise was measured using single microphone. The measured noise is related to aerodynamic characteristics of the flow using a single hot wire. The flow-induced noise of the cylinder is characterized in terms of frequency and magnitude. A sharp pick was observed in the far-field pressure at the vortex shedding frequency in which measured with hot wire anemometer. So, one could be concluded that vortex shedding is a source of aerodynamic noise generation. The strouhal number obtained from two devices was almost equal to 0.11 that is in agreement with previous studies. Also, maximum vortex shedding frequency was measured for α=15°. It is observed that sound pressure level is increased with increasing upstream velocity. The overall sound pressure level ranged between 84.2 and 110.95 (dB) for upstream velocities in the range of 5-15 (m/s). The angle of attack has no important effect on overall sound pressure level.

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One of the most important parts of the polymer fuel cell is the bipolar plate, which through the channel paths as the flow field in these plates, the availability of reactive gases to the surface of the catalyst layer is possible to carry out the electrochemical reactions of the fuel cell. So far, many researchers have been designing different flow streams for fuel cells, although each of the models has its own advantages and disadvantages, but a suitable design for the fuel cell flow field, which has a uniform distribution of reactive gases on the surface of the catalyst layer, Access to higher performance and longer fuel cell life is very important. In this paper, we introduce a new flow pattern for fuel cell flow field, and the numerical results obtained with a conventional parallel model are compared. The flow-shaped designs have been modified with a spiral and the total dimensions of the cell are 6400 mm 2, which has allowed access to uniform distribution of reactive gases, flow density and temperature distribution. An increase of 66% was achieved with a limited density and increased 1.7 times the power density by adjusting the arrangement for the flow field. Therefore, considering the design of the fuel cell based on the power density curve presented in the new model, the specific characteristics and power of the fuel cell in an air mission have been addressed and the availability of high specific power that is of particular importance in aerial applications is achieved.

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The interaction between institutional quality and the mechanism of oil shock diffusion might have a significant effect on macroeconomic dynamics in an oil-exporting country. The literature lacks a formal model to address the role of institutional quality in the economic performance of an oil-rich developing economy. Using a new Keynesian dynamic stochastic general equilibrium (DSGE) framework, this study develops a model to investigate the response of macroeconomic variables to changes in institutional quality resulted from oil shocks in Iran as an important oil-exporting country. Our modeling allows us to show how institutional quality and oil revenues affect households, firms, government, and the central bank. The model is solved and calibrated for the period 1959-2017. The results indicate that the destruction of institutional quality caused by a positive oil shock prevents the Iranian economy from reaping the fruits of an increase in oil revenues. Oil revenues and their shocks by destroying the institutional quality through the expansion of rent-seeking ‎activities, increasing transaction costs of production, reducing the impact of government spending, and ‎diverting monetary and fiscal policies from the targets result in negative effects on Iran's non-oil ‎production in the long run.‎ To reduce the destructive effects of oil shocks on institutional quality in the Iranian economy, we suggest the policymakers in Iran reduce the dependency of the government budget on oil revenues.

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In the present study, the wake flow field of a submarine model was investigated experimentally in a wind tunnel. The experiments were conducted to determine the effect of the location of control surfaces on the wake inflow to the impeller of the submarine. In order to investigate the effect of the location of control surfaces as the most important innovation of the present study, the aforementioned surfaces were installed in three longitudinal positions X/L=0.89, 0.92, 0.95 on the heel of the submarine model, and the wake flow was measured at position X/L=1.7 and the Reynolds number 6*10^5  by a five-hole probe and a hotwire anemometer. Finally, the longitudinal position X/L=0.95 was selected as the optimal location for the stern planes to improve the wake inflow to the impeller in terms of reducing its total area and the least amount of turbulence and non-uniformity. The results obtained during this study showed that arriving of the holder basechr('39')s wake to the stern area increases ​​the area and average velocity and subsequently reducing the non-uniformity of the wake flow.

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In this paper, solution of inverse problems in a plane linear elastic bodies are investigated. For this purpose, sampling method in frequency domain is introduced for cavity/crack detection in a structural element such as plate. This method is categorized as a qualitative approach to image the geometrical features of unknown targets. This goal is followed by partitioning the investigated region into an arbitrary grid of sampling points, in which a linear equation is solved. The main idea of the linear sampling method is to search for a superposition of differential displacement fields which matches with a prescribed radiating solution of the homogeneous governing equation in Ω(D), for each sampling point. Although this method has been used in the context of inverse problems such as acoustics, and electromagnetism, there is no specific attempt to apply this method to identification of crack/cavities in a structural component. This study emphasizes the implementation of the sampling method in the frequency domain using spectral finite element method. A set of numerical simulations on two-dimensional problems is presented to highlight many effective features of the proposed qualitative identification method.

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The main approach in the study of fluid flow instabilities is the theory of linear stability, which is based on linearizing the governing equations and finding unstable eigenvalues. In many flows, like shear flows, the results of linear stability theory fail to match most experiments. In a linear system, even if all the eigenvalues are stable, the perturbations can lead to instability, if the eigenfunctions are not orthogonal. The transient features of these non-normal dynamical systems, can be described with low-dimensional structures, i.e. a few modes. It is possible to suppress the asymptotic and transient growth by identification of time-dependent modes. In this paper, a method of order reduction based on optimally time-dependent modes has been implemented. This method identifies the growth behavior of disturbances in short and long times. Also, a control algorithm based on the above method has been implemented to stabilize the growth of disturbances. The DNS solution of the flow and the implementation of the reduction and control algorithms is based on the NEKTAR++ open-source solver. At first problem, to validate the solution method, the order reduction and control algorithm has been implemented on the flow over a cylinder with Re=50. At second problem, for the first time, the control algorithm is implemented on the flow over a cylinder subjected to persistent time-varying disturbances. The results show that by applying a control force, the Von-Karman vortices are stabilized and a constant lift is obtained and body vibrations are cancelled.