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In this research behavior of bubble due to under water explosion and it’s effects on ship structure have been studied. For determination of these effects field equations must be derived and solved them by mathematical simulation. Mathematical model is com in follow, it show physical rules on impression of bubble oscillation on body ship. This model is solved by combination of Euler method, 5 step Adams-Beshforse method and 4 step Adams-Moltone method for explaining the response of ship structure due to oscillation bubble. In order to agreement of solution way, stress-strain curves that obtained in this paper, is compared with experimental results. Also this results compared with FEMA results. Ship structure is modeled in ANSYS software in free beam form with variable mass and stiffness elements. Internal ship’s equipments and buoyancy are modeled by local mass and spring. The effect of explosion depth and explosive mass on stress in ship structure is studied. These result show when explosion depth is increased, stress is decreased and when explosive mass is increased, stress is increased.

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In this study, a single bubble behavior in dielectric viscous fluid under the uniform magnetic field has been simulated numerically by using a level set method in two-phase bubbly flow. The two-phase bubbly flow considered to be laminar and homogenous. Deformation of the bubble was considered due to buoyancy and magnetic forces induced from the external applied magnetic field. A computer code was developed to solve the problem with flow field, interface of two-phases, and the magnetic field. The Finite Volume method was applied using SIMPLE algorithm to differentiate the governing equations. Using this algorithm enables us to calculate the pressure parameter which was eliminated by previous researchers due to complexity of the two-phase flow. The Finite Difference method was used to solve the magnetic field equation. The results outlined in the present study well agree with the existing experimental data and numerical results. The results show that the magnetic field affects and controls the shape, size, velocity and location of the bubble.

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In this paper the behavior of framee, the process of plastic hinge formation and energy absorption of frames with two spans and one floor with three types of slab including bubble deck slab, hollow core slab and reinforced slab under three earthquake accelerations have been analyzed and compared. The results show that bubble deck slab and hollow core slab as rigid as normal reinforced slab, although bubble deck slab has higher strength and stiffness compared to other slabs. Partnering slab in analysis make period of slab reduce more over bubble deck slab and hollow core to the comparison of reinforced slab, have more effect on period reduction. Ultimate displacement of frame with reinforced slab reach to failure mechanism is more than two mentioned case, however frame with bubble deck slab reach to failure mechanism under stronger earthquake acceleration and smaller displacement than reinforced slab. Comparison base shear of three discussed case shows that maximum base shear is in bubble deck slab and minimum base shear is in normal reinforced slab. Formation of plastic hinge in frame with bubble deck slab is similar with that in frame with hollow core slab with the difference that plastic hinge in former occurs later at the top end of the middle column and two ends of middle beams. In fact, formation of plastic hinges in this frame requires higher acceleration because of the higher amount of concrete and stiffness. In all samples, plastic hinge first occur in the frame and then yielding lines occur in the tensile region of the slabs. The failure mechanism of slab and steel frame occur at the same time in frame with hollow core slab and reinforced slab; however, this is not the case in the frame with bubble deck slab and even though with occurring of yielding lines, the slab does not fail. The stress distribution due to gravity loads is symmetric across all the slabs; however, the increase rate of stress is different. This difference is particularly notable in seismic behavior of slabs in a way that the formation of plastic hinge and yielding lines in hollow core slab, because of the holes, is totally different with that of in reinforced slab. In comparison with other slabs and due to the formation of plastic hinge, reinforced slab absorb lower energy. Columns, beams and connections play different role in energy dissipation. In all frame, the contribution of connections to dissipate energy is minor and this is because yielding does not occur in connections. Contrary to the frame with reinforced slabs, because of yielding in several places of columns, columns dissipate energy more than beams in the frames with hollow core slabs. It was concluded that hollow core slab and bubble deck slab have maximum and minimum contributions to the energy dissipation, respectively.

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The effect of bubbles on frictional drag reduction has been studied experimentally using a vertical Taylor-Couette system. Air bubbles are injected into water flow at the bottom of the system. The flow between cylinders is a fully turbulent flow and Taylor vortices are formed in annulus gap. In these experiments, the variations range of rotational Reynolds number is 5000<=Re_w<=70000 . The variations of drag reduction in the presence of bubbles have been investigated by measuring the exerted torque on the inner cylinder. The results show that increasing rotational Reynolds number up to a certain amount leads to enhancement of bubbles effects on drag reduction while the effects are inversed for higher rotational Reynolds number. In this work, the acquired maximum drag reduction is about 5%.

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In the present article, velocity and deformation of an air bubble have been considered in quiescent liquid at different consecutive slopes from 5 to 90 degrees in respect to horizontal condition. To establish these purposes, air-water two-phase flow has been simulated numerically by using volume of fluid method. The two-phase flow interface has been traced by using Piecewise Linear Interface Calculation (PLIC) method. Surface tension force was estimated by Continuum Surface Force (CSF) model. The simulation results show that maximum bubble velocity occurred at 45 degrees which is in agreement with the previous researchers result. Simulation of bubble movement was also continued to two consecutive slopes at different angles. At slope deviation location, a vortex was generated due to liquid movement governed by gravity forces. This vortex changes the bubble velocity as well as bubble shape. This vortex also reduces the bubble velocity and changes the bubble nose shape from sharp to flatten at deviation from low to high slope values. However, at deviations from high to low slope values, the bubble nose becomes more sharpened in addition to bubble velocity increase. The maximum average velocity of bubble movement at two consecutive slopes was obtained during the condition that the first and second slopes were set to 60 and 30 degrees, respectively.

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Experimental investigation conducted on Taylor bubble characteristics in a large bend including three consecutive inclinations. For this purposes, flow maps were obtained for the bend and horizontal section of upstream of the bend to define the area of this regime and mechanism of Taylor bubble formation. The effect of superficial gas-liquid velocities and the duct slope were studied on average velocity, length and frequency of bubbles. The results show, the bubble velocity and length increase as gas superficial velocity increases and the duct slope decreases. However, liquid velocity increase has decreasing effect on this characteristics. Bubble frequency is independent of slope change and reduces as gas superficial velocity increase. However, bubble frequency reduces at first and then increase as liquid superficial velocity increases. Regarding the safety regulation for industry, the minimum of the bubble frequency should be generated for the required liquid mass flow rate. Meanwhile, for the gas velocity, some optimization is required between frequency reductions with Taylor bubble velocity increase in addition to bubble length reduction. Regarding the background of the present field with shortage of results on Taylor bubbles frequency, some correlations based on the superficial Reynolds number of phases were presented for each inclination.

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Dry bubble disease is one of the most important serious diseases of the cultivated white button mushroom (Agaricus bisporus (Lange) Imbach). It is a cosmopolitan disease having a worldwide distribution. Ten isolates of Lecanicillium fungicola var. fungicola (Preuss) Zare and Gams were collected from mushroom farms. Sensitivity of the isolates to benomyl, carbendazim, carbendazim+iprodione and prochloraz manganese were studied. All the isolates were resistant to benomyl(ED50= 415.45-748.12 mg L^-1), carbendazim (ED₅₀= 1123.87-1879.59 mg L^-1) and iprodione+carbendazim (ED₅₀= 415.45-748.12 mg L^-1). However, most of the isolates were sensitive to prochloraz manganese (ED₅₀=1.62–12.58 mg L^-1). As the primary source of the pathogen inoculum is casing soil and insects, stringent environmental hygiene of the mushroom houses will play a very important role in preventing and controlling the disease.

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At moderate Reynolds numbers, the perturbations may be intensified and laminar flow regime changes to turbulent flow regime. In transition process from laminar to turbulence, the flow tends to separate from a surface and then reattaches with it. As a result, some bubbles are formed which are called laminar separation bubbles. Understanding the physics of the separation bubble phenomenon and controlling of them are needed to proper aerodynamic devices design at moderate Reynolds numbers. This study has tried to enhance the aerodynamic efficiency of a low speed UAV airfoil and wing by using geometric heterogeneity like groove and bump. In this study; firstly, around CLARK-Y airfoil a proper turbulence model is proposed and effective value of Reynolds numbers on bubbles are obtained; secondly, a geometric heterogeneity is build and moved from leading edge to trailing edge on the airfoil and the performance of this airfoil is evaluated; Thirdly, geometric heterogeneity around the transition zone is changed and its effect on the performance of this airfoil is evaluated; and fourthly, some grooves and bump are arranged on the wing and their aerodynamic performance are compared relative to the clean wing. The results show that, the K-Kl-ω turbulence model is more accurate than others, higher Reynolds number lower bubble size, nearby transition point position is a good option for heterogeneity building, grooves enhance aerodynamic performance more than bumps, and a continues groove is obtained higher aerodynamic performance than clean wing but discontinues aligned grooves obtained lower aerodynamic performance than clean wing.

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Air entrainment in liquids via a fluid jet, is a complex phenomenon that has important applications in industry and the environment. The impact of a vertical laminar water jet translating over the quiescent pool of water at constant velocity was studied empirically, and the penetration depth as well as distribution of the bubbles formed by this jet was measured for both fresh and sea water with two different optical methods. This experiment was conducted at different flow rates (corresponding to different vertical velocities). In each case, the jet was moved at different horizontal velocities relative to the pool surface. As the jet started its horizontal translation, air began entering the pool from the bottom of the point of impact. Bubbles penetration depth was measured through a high-speed imaging technique, and pulse shadowgraphy was used for measuring the bubbles distribution. Increasing the vertical velocity of the jet while simultaneously decreasing the horizontal velocity of the same led to increased bubble penetration depths, and similar results were obtained for fresh water and sea water. This result was obtained in spite of the fact that the number and size of the bubbles formed in sea water were dramatically different from those formed in fresh water. Moreover, the significant role of buoyant forces in the distribution of the bubbles was obvious. The penetration depth and distribution of the bubbles were measured and reported for various jets with different diameters at different vertical and horizontal velocities.

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In the present paper, a two dimensional numerical analysis of the dynamic stall phenomenon associated with unsteady flow around the NACA 0012 airfoil at low Reynolds number (Re ≈ 130000) is studied. For this purpose, a thin blade with height of 0.005 chord length was placed vertically on the airfoil to control the bursting of the laminar leading edge separation bubble. The numerical simulation of flow is based on discretization of convective flaxes of the turbulent unsteady Navier-stokes equations by second-order Roe’s scheme and an explicit finite volume method in a moving coordinate system. Because of the importance of the time dependent parameters in the solution, the second-order time accurate is applied by dual time stepping approach. Three oscillating patterns with different frequencies and angular amplitudes were used to study the dynamic stall phenomenon. In order to validate the operation of computer code, some results for static and dynamic stall are compared with experimental data. The results of this study showed that the burst control blade had the acceptable effects on the dynamic stall control; so that these effects were increased while the oscillation frequency was raised. The best result occurs in 5 deg angular amplitude and reduced frequency of 0.15; so that the lift stall reduced 50% and there was not any obvious stall in drag coefficient.

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In this study, bubble dynamic and the mechanisms to cause net vapor generation (NVG) were explored experimentally in a rectangular vertical upward subcooled flow boiling under atmospheric pressure, and new results was found on various conditions of surface wettability. In the course of observation, two different vapor bubble behavior were observed and in low void fraction region new mechanism for incipience of net vapor generation was proposed. On a hydrophilic heated surface, at boiling incipience all the bubbles were lifted off the heated surface at atmospheric pressure and immediately collapsed in the subcooled liquid. On the contrary, when the surface was hydrophobic, bubbles mostly stuck on the nucleation sites at ONB condition. Furthermore, in this study, experiments were performed using rather hydrophilic and hydrophobic heated surface to propose the new mechanisms of NVG. An important result revealed in this work was that on a hydrophobic heated surface with high contact angle around 90°, bubble departure from all the nucleation sites which is a necessary condition to cause NVG, occurs in proximity to onset of significant void (OSV). The direct cause of OSV for the hydrophilic and hydrophobic surfaces was reattachment of lift-off bubble to heated surface, but bubble departure from nucleation sites was a good indication of OSV at hydrophobic surface.

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Present research has been done with the aim of investigating hydrodynamic behavior of slug flows in a transparent acrylic tube with inner diameter of 40 mm and height of 3.33 m. The vertical experimental system constructed in Two-Phase Flow lab in Tarbiat Modares University was used to perform needed experiments. By using image processing technique, recorded movies of flow structures were analyzed and some important characteristics of slug flow such as length and velocity of Taylor bubbles and liquid slugs between them were extracted. In addition, the average path line of Taylor bubble nose was computed in a proper range of the tube length. The acquired probability density functions show that there is a direct relationship between the increasing of Taylor bubble length and liquid slug length moving after it. Also rising velocity of shorter Taylor bubbles is more than longer ones. Results show that bubble nose does not violate ± 20 % around the center line of the tube. An experimental correlation based on the Taylor bubble velocity and total superficial velocities of phases is presented which shows that the famous Nicklen correlation does not work well for this tube diameter.

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In present study, impact of single bubble on an inclined wall and its movement are investigated by applying volume of fluid method (VOF) in OpenFOAM open source cfd package using a solver called interFoam. Both phases are incompressible and surface tension between two phases is estimated by CSF method. The effect of some parameters such as contact angle, wall slope and Bond and Morton dimensionless numbers on bubble shapes and velocity are studied. The numerical results show bubble velocity along wall increases with the increase of wall slope angle. The maximum bubble velocity happens at 50 degree. Three bubble regimes are recognized and introduced in this study named as: sliding, bouncing, and zigzagging based on wall slope. The bubble regime changes from sliding to bouncing when wall slope changes from 30 to 40 degrees. In constant Morton number, increment of Bond number increases both velocity and amplitude of fluctuations. In addition, an increment of Morton number in constant Bond number, decreases velocity and amplitude of fluctuations. Moreover, by increment of Morton number, the bubble motion will change from an accelerating motion to a constant velocity condition.

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The encounter between bubble pairs can be happened in the bubble flows and may result in coalescence, which is one of the most important elementary physical processes occurring in liquid columns. Sufficient knowledge of the coalescence process of two bubbles can lead to a better description of the bubbly flow’s behavior. Effects of uniform magnetic fields on the interactions and coalescence of dielectric bubbles were not studied up to now; therefore in this research, interactions and coalescence of two bubbles in a viscous stagnant liquid has been simulated numerically. Considered bubbles are spherical and fluids are stagnant, initially. Both liquid and gas phases considered being incompressible and dielectric where applied magnetic field is uniform. In the numerical simulation of the problem, the Finite Volume method was applied using the SIMPLE algorithm to discretizing the governing equations while the finite difference method was used for discretizing of the magnetic field equation. For simulating the interface of two phases, the level set method has been incorporated. The results outlined in the present study well agree with the existing experimental and numerical results. Obtained results show that applied uniform magnetic field affects shape, dynamics and also interactions and coalescence of bubble pairs. Applied magnetic field enhances coalescence between in-line rising bubbles. Therefore, the external uniform magnetic field could be used for contactless control of the coalescence process between bubbles.

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In this article bubbly flow under the specified axial pressure gradient in a curved channel is studied numerically. To do so, a second order parallelized front-tracking/finite-difference method based on the projection algorithm is implemented to solve the governing equations including the full Navier-Stokes and continuity equations in the cylindrical coordinates system using a uniform staggered grid well fitted to the geometry concerned. In the absence of gravity the mid-plane parallel to the curved duct plane, which is the symmetry plane in the single fluid flow inside the curved duct, separates the bubbly flow into two different flow regions not interacting with each other. Twelve bubbles with diameters of 0.125 wall units are distributed in the equally spaced distances from each other. The numerical results obtained indicate that for the cases studied here, the bubbles reach the statistical steady state with an almost constant final orbital motion path due to the strong secondary field. Furthermore, the effects of different physical parameters such as Reynolds number, and curvature ratio on the flow field at the no slip boundary conditions, are investigated in detail.

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In this paper, a single bubble free ascending in a vertical channel was studied experimentally. Five different Newtonian fluids were used where the surface tension force is dominant. The bubble trajectory was considered in water, glycerin 30 and 50 Vol% that is zigzag, however, linear behavior is observed while the weight concentration of the glycerin reaches to 80 and 100 percent. The bubble rise velocity and aspect ratio coefficient are calculated by image analysis via MATLAB software. The results are in a very good agreement with the literature for the bubble velocity. The effect of magnetic field (perpendicular to the bubble flow) on the hydrodynamic characteristics of the bubble for each of the working fluids has been scrutinized. Although the presence of the magnetic field does not affect the bubble trajectory type or change the flow pattern from zigzag to linear, but it reduces the flow domain where this descending trend decreases with the increase in viscosity. It should be also noted that the magnetic field causes the bubble rise velocity to increase while this enhancement increases with higher viscosity. The magnetic field effect on the bubble aspect ratio was also considered and it was found that as viscosity increases the aspect ratio change is decreases.

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Numerical simulation of multi material or multi-phase flows are one of the most challenging problems between computational fluid dynamics researches. The main difficulty of these problems is producing some unexpected and non-physical oscillation at material interface which causes entering some error in to computation domain. For eliminating this source of error, many sophisticated algorithm have been proposed recently. By neglecting diffusion processes, Euler equations and HLLC reimann solver are applied. In addition, Level set algorithm is implemented to track interferences between two materials. An accurate, easily developed and low computation cost algorithm, proposed by Abgrall and Karni, is used to prevent generating the oscillations in the interfaces. In the current work, the algorithm is developed to 2 dimensional algorithm. Afterwards, the result of 1 and 2 dimensional code are evaluated to verify the developed algorithm by some standard problems such as sod problem. Finally, shock –bubble (Air – Helium) interaction problem is simulated to investigate the effect of the algorithm in 2 dimensional simulation. The comparison shows that the code and its result have very good accuracy with very low computational cost.

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In this paper, the convection-diffusion process in a two-phase air-water flow is investigated. Two-phase flows of air and water are important and are widely used in the industrial applications. Simulation of such a flow needs a proper understanding of the interface between two phases where these is a change in fluids properties. Smoothed Particle Hydrodynamics (SPH) is a fully Lagrangian and meshless method which can simply detect the interface of multiphase flows. Here, we develop the open-source SPHyiscs2D code into two phase and implement the convection-diffusion equation by looking carefully at surface tension forces. To validate, first the still-water problem is investigated to ensure that the hydrostatic pressure at the interface is predicted and then the dam-break problem on an infinite bed is compared with the available experimental data. Results show that the combination of surface tension formulations and an additional artificial force gives a better result. Finally, the convection-diffusion process and the concentration distribution are shown for the air-bubble rising problem for different diffusive coefficients. It will be shown that the SPH method is a useful tool for studying multiphase flows and convection-diffusion processes.

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Analysis of air bubbles entrainment in liquid slug body is one of the most important and complicated phenomena during slug flow regime. In the present attempt, a method is proposed for slug modeling to consider the air bubble entrainment into slug liquid body. The effect of consequencies and their impact on slug behaviour to predict more accurate correlations for slug parameters are estimated and calculated. This method considers a two-fluid single pressure model, combined with population balance model for equal bubble diameter series and solves using volume of fluid. In this regard based on slug and hydraulic jump similarity, a correlation for air bubble entrainment rate and its mechanism selected. This correlation developed in the form of a user defined function code and coupled with other models in FLUENT solver to calculate slug flow. Finally the result of this numerical modeling is validated with the result of other numerical and experimental results where exist in the related literature. The result is consist of the slug flow profile, entrained air bubble profile and their diameter distribution, vortex at slug front, pressure distribution during slugging, slug mixture velocity, turbullent model parameters and etc.

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Pool boiling has the ability to remove large heat flux at low difference temperature of wall and this can be further enhanced by using surface modification methods. This article investigates pool boiling heat transfer on 4 levels with different orientations. For this purpose, a laboratory device was designed and built. The main goal of providing a simple and cost-effective manner with high durability in industrial applications, to having the highest amount of critical heat flux at the lowest level of super-heated temperature difference. The results show that surface roughness factor causing a delay in connecting the bubbles and heat flux increased slightly. In addition to roughness factor, two factors separating bubbles from the fluid in the heat dissipation and more power nucleation sites and micro-bubble layer can be more important than the surface roughness. The surface polished in one direction with lower roughness has higher critical heat flux than circular rough surface. Ultimately to combine bubble separation and more feed the micro layer with made micro channel. With this method it could be increased 131% critical heat flux and 211% heat transfer coefficient.