Determination of Supercavity Shape for Axisymmetric Cavitators at Different Non-Zero Attack Angles, Using Boundary Element Method

2012 ◽  
Vol 28 (2) ◽  
pp. 383-389
Author(s):  
R. Shafaghat ◽  
S. M. Hosseinalipour ◽  
A. Vahedgermi
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Body Cavity ◽  
The Body ◽  
Cavity Surface ◽  
Closure Model ◽  
Potential Flows ◽  
Unbounded Potential ◽  
Cavity Closure ◽  
Element Method

AbstractWhen fluid passes a cavitator in the supercavitating flow, a supercavity forms behind the cavitator. Variation of the cavitator attack angle can influence theshape of the formed supercavity behind the cavitator. Consequently, it will affect the stability of supercavity behind the supercavitating cavitator with after body. In this study, a direct boundary element method (DBEM) is being formulated and numerically solved for3D unbounded potential flowspassing supercavitating bodies of revolution at different attack angles. In the analysis of potential flows passing supercavitating bodies at non-zero attack angles, a cavity closure model must be employed in order to close the mathematical formulationand guarantee the solution uniqueness. In the present study, we employ modified Riabouchinsky closure model. Since the location of the cavity surface is unknown at prior, an iterative scheme is used and for the first stage, an arbitrary cavity surface is assumed. The flow field is then solved and by an iterative process, the location of the cavity surface is corrected. Upon convergence, the exact boundary conditions are satisfied on the body-cavity boundary. A powerful CFD codeis developed to solve the 3D supercavitating flows behind all types of axisymmetric cavitators (such as disk, cone, etc) at zero and non-zero attack angles. The predictions of the CFD code are compared with those generated by verified existing data. The predictions of the code for supercavitating cones and disks seem to be excellent. Using the obtained data from CFD code, we investigate the supercavity shapesand corresponding stability at different attack angles with a fixed cavitation number.

Mathematical Approach to Investigate the Behaviour of the Principal Parameters in Axisymmetric Supercavitating Flows, Using Boundary Element Method

2009 ◽  
Vol 25 (4) ◽  
pp. 465-473 ◽  
Author(s):  
R. Shafaghat ◽  
S. M. Hosseinalipour ◽  
N. M. Nouri ◽  
A. Vahedgermi
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
The Body ◽  
Cavity Surface ◽  
Power Functions ◽  
Closure Model ◽  
Potential Flows ◽  
Unbounded Potential ◽  
Wide Range ◽  
Element Method

ABSTRACTIn this paper, a direct boundary element method (DBEM) is formulated numerically for the problems of the unbounded potential flows past supercavitating bodies of revolution (cones and also disks which are special case of cones with tip vertex angle of 180 degree) at zero degree angle of attack. In the analysis of potential flows past supercavitating cones and disks, a cavity closure model must be employed in order to make the mathematical formulation close and the solution unique. In the present study, we employ Riabouchinsky closure model. Since the location of the cavity surface is unknown at prior, an iterative scheme is used. Where, for the first stage, an arbitrary cavity surface is assumed. The flow field is then solved and by an iterative process, the location of the cavity surface is corrected. Upon convergence, the exact boundary conditions are satisfied on the body-cavity boundary. For this work, powerful software, based on CFD code, is developed in CAE center of IUST. The predictions of the software are compared with those generated by analytical solution and with the experimental data. The predictions of software for supercavitating cones and disks are seen to be excellent. Using the obtained data from software, we investigate the mathematical behavior of axisymmetric supercavitating flow parameters including drag coefficients of supercavitating cones and disks, cavitation number and maximum cavity width for a wide range of cone and disk diameters, cone tip angles and cavity lengths. The main objective of this study is to propose appropriate mathematical functions describing the behavior of these parameters. As a result, among all available functions such as linear, polynomial, logarithmic, power and exponential, only power functions can describe the behavior of mentioned parameters, very well.

The Optimum Design of a Cavitator for High-Speed Axisymmetric Bodies in Partially Cavitating Flows

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
I. Rashidi ◽  
Mo. Passandideh-Fard ◽  
Ma. Pasandideh-Fard
Keyword(s):  
Boundary Element Method ◽  
Numerical Simulations ◽  
Drag Coefficient ◽  
Boundary Element ◽  
Cavitation Number ◽  
The Body ◽  
Total Drag ◽  
Conical Section ◽  
Disk Cavitator ◽  
Element Method

In this paper, the partially cavitating flow over an axisymmetric projectile is studied in order to obtain the optimum cavitator such that, at a given cavitation number, the total drag coefficient of the projectile is minimum. For this purpose, the boundary element method and numerical simulations are used. A large number of cavitator profiles are produced using a parabolic expression with three geometric parameters. The potential flow around these cavitators is then solved using the boundary element method. In order to examine the optimization results, several cavitators with a total drag coefficient close to that of the optimum cavitators are also numerically simulated. Eventually, the optimum cavitator is selected using both the boundary element method and numerical simulations. The effects of the body radius and the length of the conical section of the projectile on the shape of the optimized cavitator are also investigated. The results show that for all cavitation numbers, the cavitator that creates a cavity covering the entire conical section of the projectile with a minimum total drag coefficient is optimal. It can be seen that increasing the cavitation number causes the optimum cavitator to approach the disk cavitator. The results also show that at a fixed cavitation number, the increase in both the radius and length of the conical section causes the cavitator shape to approach that of the disk cavitator.

Hydrodynamic Issues of FLNG Systems

2013 ◽  
Author(s):  
Xiao-Bo Chen ◽  
Louis Diebold ◽  
Guillaume de-Hautecloque
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Wave Diffraction ◽  
Coupling Effect ◽  
Dynamic Effect ◽  
Complex Interaction ◽  
Liquid Motion ◽  
Potential Flows ◽  
Seakeeping Analysis ◽  
Element Method

Advanced hydrodynamic analyses of floating LNG terminals are presented in the paper. They consist of the complex interaction of multiple bodies and the coupling effect of seakeeping (wave diffraction and radiation around bodies) and sloshing (liquid motions in tanks). Based on the recent development to introduce the dissipation in potential flows and new formulations of boundary element method, the seakeeping analysis is enhanced to be able to make accurate predictions of gap resonances and major dynamic effect of liquid motion in tanks.

Realistic Design of a Floating Breakwater Design with Moonpools

2015 ◽  
Vol 69 (7) ◽  
Author(s):  
Faisal Mahmuddin ◽  
Rahimuddin Rahimuddin
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
High Performance ◽  
3D Model ◽  
Longitudinal Direction ◽  
Realistic Model ◽  
The Body ◽  
Efficient Design ◽  
Floating Breakwater ◽  
Element Method

In an attempt to obtain a 2D floating breakwater model with high performance in wave reflection, genetic algorithm (GA) was combined with boundary element method (BEM) in the previous study. The performance of the obtained model was verified with numerical relations as well as an experiment in towing tank. Moreover, its performance and characteristics in 3D case were also evaluated in the subsequent study. However, because the 3D model is formed by simply extruding the 2D shape in longitudinal direction, it only produces a model with uniform transversal shape which is considered to be less effective and efficient in terms of technical and economical points of view. Consequently, it is needed to modify the model to obtain a more realistic and efficient design without reducing significantly the high performance obtained previously. In the present study, several modifications of the original 3D model are performed which include placing moonpools inside the body. The performance and characteristics of the modified models in terms of wave elevations on the free surface are evaluated at various wavelengths by using higher order boundary element method (HOBEM). The accuracy of the computed results is confirmed with Haskind-Newman and energy conservation relations. From the modifications and evaluations of the models, it could be realized that the moonpools inside the body could be used to obtain a more realistic model without reducing the optimum performance of the original model shape.  

Higher Order Boundary Element Method Applied to the Hydrofoil Beneath the Free Surface

2009 ◽  
Author(s):  
Hassan Ghassemi ◽  
Ahmad Reza Kohansal ◽  
Abdollah Ardeshir
Keyword(s):  
Free Surface ◽  
Boundary Element Method ◽  
Boundary Element ◽  
Three Dimensional ◽  
Wave Pattern ◽  
Higher Order ◽  
The Body ◽  
Hydrodynamic Characteristics ◽  
Good Agreement ◽  
Element Method

In this paper a three-dimensional numerical model using the higher order boundary element method (HOBEM) is developed to analyze hydrodynamic characteristics of hydrofoils beneath the free surface. The method uses combinations of the source and doublet by linear disctribution on each element of the body and free surface. The geometry of the element is represented by quadratic bilinear elements. The method is applied to three-dimensional hydrofoils of the symmetric Joukowski and NACA4412 profiles moving beneath the free surface in constant speed. Some results (pressure distribution, lift, wave-making drag and wave elevation and wave pattern) are presented. It is shown that this approach is accurate, efficient and the results are in good agreement with the experimental measurements and other calculated results.

A Meshless Boundary Element Method for Simulating Slamming in Context of Generalized Wagner

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Jens B. Helmers ◽  
Geir Skeie
Keyword(s):  
Free Surface ◽  
Boundary Element Method ◽  
Boundary Element ◽  
The Body ◽  
Body Contour ◽  
Analytical Functions ◽  
Smooth Body ◽  
Body Velocity ◽  
Body Location ◽  
Element Method

A boundary element method (BEM) designed for solving the symmetric generalized Wagner formulation is presented. The flow field is parameterized with analytical functions and can describe the kinematics at any free surface or body location using a small set of parameters obtained from a collocation scheme. The method is fast and robust for all deadrise angles, even for flat plate impacts where classical BEMs usually fail. The method is easy to implement and is easy to apply. Given a smooth body contour the only additional input is the requested accuracy. There is no mesh involved. When solving the temporal problem, we exploit the analytical distribution of free surface velocities and apply an integral equation formalism consistent with the Wagner formulation. The output of the spatial and temporal scheme is a set of functions and parameters suitable for fast computation of the complete kinematics for any impact trajectory given the position of the keel and the body velocity. The method is developed to be combined with seakeeping programs for statistical impact and whipping assessment.

AZ80 Magnesium Alloy Mold Temperature Field Analysis in Isothermal-Forging by the Boundary Element Method

2015 ◽  
Vol 723 ◽  
pp. 919-923
Author(s):  
Wei Min Li
Keyword(s):  
Temperature Field ◽  
Magnesium Alloy ◽  
Boundary Element Method ◽  
Boundary Element ◽  
Maximum Temperature ◽  
Cavity Surface ◽  
Base Temperature ◽  
Isothermal Forging ◽  
Az80 Magnesium Alloy ◽  
Element Method

Using the boundary element method, AZ80 magnesium alloy isothermal forging mould temperature field has be calculated. the outer wall of mold base temperature control at 360 °C, the model of cavity surface minimum temperature at 281.382 °C, the model of cavity on the surface of the highest temperature at 282.319 °C. Mold base outside the cavity wall and the model shows that the maximum temperature at 78.618 °C, the model of the maximum temperature difference between the cavity surface is 0.937 °C.

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