Hydrodynamic Forces on a Marine Riser: A Velocity-Potential Method

1982 ◽  
Vol 104 (1) ◽  
pp. 53-57 ◽  
Author(s):  
J. S. Chung
Keyword(s):  
Free Surface ◽  
Velocity Potential ◽  
Potential Method ◽  
Hydrodynamic Forces ◽  
Marine Riser ◽  
Morison Equation ◽  
Wave Damping ◽  
Drag Forces ◽  
Vessel Motion ◽  
Semi Empirical

A linear equation is mathematically derived for hydrodynamic forces on a marine riser under effects of free surface and floating-vessel motion using a velocity-potential method. It accounts for inertia and wave damping forces, including the force caused by riser motion, and empirically includes the drag force caused by viscosity. The equation, when reduced to a simpler form, is basically identical to the semi-empirical Morison equation for the inertia and drag forces. Theoretical validity of the simpler equation and the Morison equation is discussed. Previously, practical, semi-empirical force equations on the riser have been suggested, ignoring the effects of the free surface and the wave damping. The equations in current practice are compared with the present simpler equation.

A Numerical Calculation of Hydrodynamic Forces on a Seagoing Ship by 3-D Source Technique With Forward Speed

2004 ◽  
Author(s):  
Yoshiyiki Inoue ◽  
Md. Kamruzzaman
Keyword(s):  
Free Surface ◽  
Velocity Potential ◽  
Hydrodynamic Forces ◽  
The Body ◽  
Source Distribution ◽  
Accurate Estimation ◽  
Forward Speed ◽  
Surface Ship ◽  
Wave Patterns ◽  
Wigley Hull

In this paper, the hydrodynamic forces of a surface ship advancing in waves at constant forward speed are numerically calculated by using the 3-D source distribution techniques. The paper also deals with the numerical calculations of free surface flow around an advancing ship in calm water as well as in waves. The body boundary condition is linearised about the undisturbed position of the body and the free surface condition is linearised about the mean water surface. The potential is represented by a distribution of sources over the surface of the ship and its waterline. The problem is solved by the method of singularities distributed over the hull surface. Hess & Smith method is used to obtain the density of these singularities. The numerical solution of the surface ship case is approximately obtained by considering the hull as a position of plane polygonal elements, bearing a constant singularity distribution. The velocity potential of any particular point in the free surface around the moving hull is determined by using the 3-D Green function with forward speed which satisfies the boundary conditions for a pulsating source in the fluid. Contours of wave patterns around moving surface ships are calculated from the velocity potential. The numerical accuracy of the computer code is firstly checked by calculating the velocity potential of a translating, pulsating unit source with arbitrary frequency and forward speed. Free surface wave patterns generated by a Wigley hull advancing with steady forward speed are calculated by using this code. Some corresponding hydrodynamic coefficients of heave and pitch modes for the Wigley hull has been calculated. Exciting forces and motion amplitudes are also investigated. The numerical result of this code is validated by comparing the calculated results with the experimental ones and those calculated by other methods. From the comparison, the results predicted by the present calculations are found in fairly good agreement with the experiment. Finally, the effects of motion amplitude on the free surface elevation are analyzed. These will be helpful for the accurate estimation of sea keeping problems for a ship advancing in waves.

Response of a Liquid Bridge With Rotationally Excited Bottom

1992 ◽  
Vol 59 (1) ◽  
pp. 191-195 ◽  
Author(s):  
Helmut F. Bauer
Keyword(s):  
Free Surface ◽  
Velocity Distribution ◽  
Liquid Bridge ◽  
Transient Behavior ◽  
Liquid Column ◽  
Semi Empirical

The response of a cylindrical liquid column consisting of an incompressible and frictionless liquid has been investigated for a pitching bridge bottom. The response of the free surface and velocity distribution has been determined and numerically evaluated. In addition, the transient behavior of the column has been treated. Since for nonviscous liquid the response exhibits at the resonances singularity, a semi-empirical damping was introduced in the resonance terms. Its magnitude has to be determined by experiments.

Drag Forces on, and Deformation of, Closed Flexible Bags

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Pål Lader ◽  
David W. Fredriksson ◽  
Zsolt Volent ◽  
Jud DeCew ◽  
Trond Rosten ◽  
...  
Keyword(s):  
Drag Force ◽  
Hydrodynamic Forces ◽  
Towing Tank ◽  
Drag Forces ◽  
Uniform Current ◽  
Salmon Production

The use of closed flexible bags is among the suggestions considered as a potential way to expand the salmon production in Norway. Few ocean structures exist with large, heavily compliant submerged components, and there is presently limited existing knowledge about how aquaculture systems with flexible closed cages will respond to external sea loads. The flexibility and deformation of the bag are coupled to the hydrodynamic forces, and the forces and deformation will be dependent on the filling level of the bag. In order to get a better understanding of the drag forces on, and deformation of, such bags, experiments were conducted with a series of closed flexible bags. The bags were towed in a towing tank in order to simulate uniform current. Four different geometries were investigated, cylindrical, cubical, conical, and pyramidal, and the filling levels were varied between 70% and 120%. The main findings from the experiments were that the drag force was highly dependent on the filling level, and that the drag force increases with decreasing filling level. Comparing the drag force on a deflated bag with an inflated one showed an increase of up to 2.5 times.

scholarly journals HYDRODYNAMIC FORCES ACTING ON A SUBMERGED OBSTRUCTION IN STEADY FREE SURFACE FLOWS

2004 ◽  
Vol 48 ◽  
pp. 877-882
Author(s):  
Mirei SHIGE-EDA ◽  
Juichiro AKIYAMA ◽  
Masayuki NONAKA ◽  
Takanori ASANO
Keyword(s):  
Free Surface ◽  
Free Surface Flows ◽  
Hydrodynamic Forces ◽  
Surface Flows

On Line Distributions of Kelvin Sources

1964 ◽  
Vol 8 (04) ◽  
pp. 45-52
Author(s):  
E. O. Tuck
Keyword(s):  
Free Surface ◽  
Physical Properties ◽  
Velocity Potential ◽  
Fourier Transforms ◽  
Point Sources ◽  
Straight Line ◽  
On Line ◽  
New Form ◽  
Line Of Singularities

The velocity potential for the flow due to point sources distributed arbitrarily along a straight line near to or at a linearized gravitational free surface is obtained in a new form by use of Fourier transforms. Such a method of representing the potential facilitates the determination of its behavior near to the line of singularities; this behavior is derived formally and its physical properties discussed. A brief illustration is given of a method of using this result in o theory for the motion of a slender ship.

scholarly journals A variational principle for fluid sloshing with vorticity, dynamically coupled to vessel motion

2019 ◽  
Vol 475 (2224) ◽  
pp. 20180642 ◽  
Author(s):  
H. Alemi Ardakani ◽  
T. J. Bridges ◽  
F. Gay-Balmaz ◽  
Y. H. Huang ◽  
C. Tronci
Keyword(s):  
Boundary Condition ◽  
Free Surface ◽  
Variational Principle ◽  
Stream Function ◽  
Fluid Motion ◽  
Two Dimensional ◽  
Euclidean Group ◽  
Fluid Sloshing ◽  
Pressure Boundary Condition ◽  
Vessel Motion

A variational principle is derived for two-dimensional incompressible rotational fluid flow with a free surface in a moving vessel when both the vessel and fluid motion are to be determined. The fluid is represented by a stream function and the vessel motion is represented by a path in the planar Euclidean group. Novelties in the formulation include how the pressure boundary condition is treated, the introduction of a stream function into the Euler–Poincaré variations, the derivation of free surface variations and how the equations for the vessel path in the Euclidean group, coupled to the fluid motion, are generated automatically.

scholarly journals Study on liquid sloshing characteristics of a swaying rectangular tank with a rolling baffle

2019 ◽  
Vol 119 (1) ◽  
pp. 23-41 ◽  
Author(s):  
Jing-Han Wang ◽  
Shi-Li Sun
Keyword(s):  
Free Surface ◽  
Present Method ◽  
Velocity Potential ◽  
Solution Procedure ◽  
Liquid Sloshing ◽  
Published Data ◽  
Free Surface Elevation ◽  
Separate Variable ◽  
Rectangular Tank ◽  
Vertical Baffle

Abstract This study addresses the sloshing characteristics of a liquid contained in a tank with a vertical baffle mounted at the bottom of the tank. Liquid sloshing characteristics are studied through an analytical solution procedure based on the linear velocity potential theory. The tank is forced to sway horizontally and periodically, while the baffle is fixed to the tank or rolling around a hinged point. The rectangular tank flow field is divided into a few sub-domains. The potentials are solved by a separate variable method, and the boundary conditions and matching requirements between adjacent sub-domains are used to determine the sole solution. The free surface elevations with no baffle or a low fixed baffle are compared with those in published data, and the correctness and reliability of the present method are verified. Then the baffle is forced to rotate around the bottom-mounted point. It is found that the baffle’s motion, including the magnitude and the phase together, can be adjusted to suppress the free surface elevation, and even the sloshing wave can be almost eliminated.

scholarly journals A non-local formulation of rotational water waves

2011 ◽  
Vol 689 ◽  
pp. 129-148 ◽  
Author(s):  
A. C. L. Ashton ◽  
A. S. Fokas
Keyword(s):  
Free Surface ◽  
Water Waves ◽  
Velocity Potential ◽  
Vries Equation ◽  
Travelling Waves ◽  
Explicit Dependence ◽  
Local Equation ◽  
Constant Vorticity ◽  
Small Parameters ◽  
Non Local

AbstractThe classical equations of irrotational water waves have recently been reformulated as a system of two equations, one of which is an explicit non-local equation for the wave height and for the velocity potential evaluated on the free surface. Here, in the two-dimensional case: (a) we generalize the relevant formulation to the case of constant vorticity, as well as to the case where the free surface is described by a multivalued function; (b) in the case of travelling waves we derive an upper bound for the free surface; (c) in the case of constant vorticity we construct a sequence of nearly Hamiltonian systems which provide an approximation in the asymptotic limit of certain physical small parameters. In particular, the explicit dependence of the vorticity on the coefficients of the Korteweg–de Vries equation is clarified.

Sign in / Sign up

Export Citation Format

Share Document