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.

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

2013 ◽  
Author(s):  
Jens B. Helmers ◽  
Geir Skeie
Keyword(s):  
Free Surface ◽  
Boundary Element Method ◽  
Boundary Element ◽  
The Body ◽  
Boundary Element Methods ◽  
Body Contour ◽  
Smooth Body ◽  
Body Velocity ◽  
Body Location ◽  
Element Method

A boundary element method 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 boundary element methods usually fails. 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.

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.

Study on the Dynamics of the Bubble under the Combined Action of the Bjerknes Effect of the Free Surface and the Buoyancy

2014 ◽  
Vol 644-650 ◽  
pp. 628-631
Author(s):  
Ke Yi Li ◽  
Zhong Cai Pei
Keyword(s):  
Free Surface ◽  
Boundary Element Method ◽  
Boundary Element ◽  
Potential Flow ◽  
Flow Theory ◽  
Motion Direction ◽  
Potential Flow Theory ◽  
Combined Action ◽  
Element Method

When the bubble moves in the vicinity of a free surface, the movement will be affected by the buoyancy and the Bjerknes effect. Blake and Gibson proposed the criterion which determined the motion direction of the jet and the dynamics of bubble. They proposed the jet wouldn’t be formed in the condition that . Based on the potential flow theory, boundary element method (BEM) is used to calculate three typical examples in this paper in order to study the dynamics of the bubble under the combined action of the Bjerknes effect of the free surface and the buoyancy. It is found out during the analysis that the Blake criterion is applicable to predict the conditions that and .

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.

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