Forward-Speed Vertical Wave Exciting Forces on Ships

1985 ◽  
Vol 29 (02) ◽  
pp. 105-111
Author(s):  
P. D. Sclavounos
Keyword(s):  
Velocity Potential ◽  
Reverse Flow ◽  
Diffraction Problem ◽  
Three Dimensional ◽  
Forward Speed ◽  
Direct Solution ◽  
Radiation Problem ◽  
Strip Theory ◽  
Exciting Forces ◽  
Wave Exciting Forces

Expressions are derived for the heave and pitch exciting force and moment on a ship advancing in waves. They are obtained in the form of an integral over the ship axis of the outer source strength of the reverse-flow radiation problem multiplied by the value of the incident-wave velocity potential. Their performance is tested for two slender spheroids. Comparisons are made with predictions obtained from a three-dimensional numerical solution at zero speed—the expression common to strip-theory programs which uses the ship hull as the integration surface—and the direct solution of the diffraction problem.

scholarly journals Wave forces on three-dimensional floating bodies with small forward speed

1991 ◽  
Vol 227 ◽  
pp. 135-160 ◽  
Author(s):  
Jan Nossen ◽  
John Grue ◽  
Enok Palm
Keyword(s):  
Velocity Potential ◽  
The Body ◽  
Wave Forces ◽  
Forward Speed ◽  
Floating Bodies ◽  
Wave Drift ◽  
Exciting Forces ◽  
Wave Exciting Forces ◽  
Wave Drift Damping ◽  
The Mean

A boundary-integral method is developed for computing first-order and mean second-order wave forces on floating bodies with small forward speed in three dimensions. The method is based on applying Green's theorem and linearizing the Green function and velocity potential in the forward speed. The velocity potential on the wetted body surface is then given as the solution of two sets of integral equations with unknowns only on the body. The equations contain no water-line integral, and the free-surface integral decays rapidly. The Timman-Newman symmetry relations for the added mass and damping coefficients are extended to the case when the double-body flow around the body is included in the free-surface condition. The linear wave exciting forces are found both by pressure integration and by a generalized far-field form of the Haskind relations. The mean drift force is found by far-field analysis. All the derivations are made for an arbitrary wave heading. A boundary-element program utilizing the new method has been developed. Numerical results and convergence tests are presented for several body geometries. It is found that the wave exciting forces and the mean drift forces are most influenced by a small forward speed. Values of the wave drift damping coefficient are computed. It is found that interference phenomena may lead to negative wave drift damping for bodies of complicated shape.

On the Radiation and Diffraction of Surface Waves by Submerged Spheroids

1989 ◽  
Vol 33 (02) ◽  
pp. 84-92
Author(s):  
G. X. Wu ◽  
R. Eatock Taylor
Keyword(s):  
Degrees Of Freedom ◽  
Velocity Potential ◽  
Three Dimensional ◽  
Added Mass ◽  
Wave Radiation ◽  
Legendre Functions ◽  
Incoming Wave ◽  
Six Degrees Of Freedom ◽  
Damping Coefficients ◽  
Exciting Forces

The problem of wave radiation and diffraction by submerged spheroids is analyzed using linearized three-dimensional potential-flow theory. The solution is obtained by expanding the velocity potential into a series of Legendre functions in a spheroidal coordinate system. Tabulated and graphical results are provided for added mass and damping coefficients of various spheroids undergoing motions in six degrees of freedom. Graphs are also provided for exciting forces and moments corresponding to a range of incoming wave angles.

Time-Domain Simulations of Radiation and Diffraction Forces

2010 ◽  
Vol 54 (02) ◽  
pp. 79-94 ◽  
Author(s):  
Xinshu Zhang ◽  
Piotr Bandyk ◽  
Robert F. Beck
Keyword(s):  
Free Surface ◽  
Time Domain ◽  
Three Dimensional ◽  
The Body ◽  
Surface Boundary ◽  
Two Dimensional ◽  
Forward Speed ◽  
Time Step ◽  
Surface Boundary Conditions ◽  
Strip Theory

Large-amplitude, time-domain, wave-body interactions are studied in this paper for problems with forward speed. Both two-dimensional strip theory and three-dimensional computation methods are shown and compared by a number of numerical simulations. In the present approach, an exact body boundary condition and linearized free surface boundary conditions are used. By distributing desingularized sources above the calm water surface and using constant-strength flat panels on the exact body surface, the boundary integral equations are solved numerically at each time step. The strip theory method implements Radial Basis Functions to approximate the longitudinal derivatives of the velocity potential on the body. Once the fluid velocities on the free surface are computed, the free surface elevation and potential are updated by integrating the free surface boundary conditions. After each time step, the body surface and free surface are regrided due to the instantaneous changing wetted body geometry. Extensive results are presented to validate the efficiency of the present methods. These results include the added mass and damping computations for a Wigley III hull and an S-175 hull with forward speed using both two-dimensional and three-dimensional approaches. Exciting forces acting on a Wigley III hull due to regular head seas are obtained and compared using both the fully three-dimensional method and the two-dimensional strip theory. All the computational results are compared with experiments or other numerical solutions.

Radiation and diffraction of water waves by a submerged sphere at forward speed

1988 ◽  
Vol 417 (1853) ◽  
pp. 433-461 ◽  
Keyword(s):  
Water Waves ◽  
Velocity Potential ◽  
Surface Condition ◽  
Wave Resistance ◽  
The Body ◽  
Legendre Functions ◽  
Forward Speed ◽  
Submerged Sphere ◽  
Exciting Forces ◽  
Similar Equation

A submerged sphere advancing in regular deep-water waves at constant forward speed is analysed by linearized potential theory. A distribution of sources over the surface of the sphere is expanded into a series of Legendre functions, by extension of the method used by Farell ( J . Ship Res . 17, 1 (1973)) in analysing the wave resistance on a submerged spheroid. The equations governing the velocity potential are satisfied by use of the appropriate Green function and by choosing the coefficients in the series of Legendre functions such that the body surface condition is satisfied. Numerical results are obtained for the wave resistance, hydrodynamic coefficients and exciting forces on the sphere. Some theoretical aspects of a body advancing in waves are also discussed. The far-field equation of Newman ( J . Ship Res . 5, 44 (1961)) for calculation of the damping coefficients is extended, and a similar equation for the exciting forces is derived.

Wave-Body Interactions Among an Array of Truncated Vertical Cylinders

2016 ◽  
Author(s):  
Qian Zhong ◽  
Ronald W. Yeung
Keyword(s):  
Velocity Potential ◽  
Wave Radiation ◽  
Fast Computation ◽  
Array Configuration ◽  
Point Absorber ◽  
Exciting Forces ◽  
Wave Exciting Forces ◽  
Matched Eigenfunction Expansions ◽  
Wave Farm ◽  
Vertical Cylinders

A semi-analytical method is developed to investigate water-wave radiation and diffraction by an array of truncated vertical cylinders as a model for a point-absorber wave farm. Each cylinder can have independent movements in six modes. The method of matched eigenfunction expansions is applied to obtain the velocity potential for the fluid. To achieve fast computation, the effects of evanescent modes of locally scattered waves from one cylinder are neglected in the near fields of the neighboring cylinders. Wave-exciting forces and moments on an individual cylinder or a group of cylinders, situated among an array, are evaluated by a new, generalized form of Haskind relation that is applicable to an array configuration. In results, hydrodynamic coefficients and wave-exciting loads are presented for arrays of different configurations. Comparisons between wave-exciting loads obtained from the generalized Haskind relation and those from direct diffraction solutions show excellent agreements.

Three-Dimensional Effects for a Ship Experiencing Large Amplitude Roll Motion

2011 ◽  
Author(s):  
Christopher C. Bassler ◽  
Ronald W. Miller
Keyword(s):  
Large Amplitude ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Roll Motion ◽  
Ship Motions ◽  
Forward Speed ◽  
Strip Theory ◽  
Calm Water ◽  
Large Amplitude Motions ◽  
3D Effects

Recent advancements have been made to consider the effects of large amplitude motions for roll damping models used for numerical ship motion performance assessments. These advancements have been focused on the development and expansion of models for potential flow simulation tools with sectional formulations. However, additional 3D effects due to vortex shedding, flow convection downstream, waves, and bilge keel emergence and submergence during large roll motion may be important, but are typically neglected in the sectional formulations. A series of RANS computations were performed for both 2D and 3D conditions of large amplitude ship roll motion, with and without forward speed, and in calm water and in waves. Comparisons were made to available experimental data for the 2D calm water conditions at zero-speed. These results were then assessed with the 3D conditions to develop improved understanding of additional 3D effects, including forward speed and waves, which should be considered for future developments of strip-theory approaches for ship motions prediction.

On the Motion of a Slender Body Submerged Beneath Surface Waves

1988 ◽  
Vol 32 (03) ◽  
pp. 208-219 ◽  
Author(s):  
P. Wilmott
Keyword(s):  
Velocity Potential ◽  
Axisymmetric Body ◽  
The Body ◽  
Body Motion ◽  
Vertical Force ◽  
Forward Speed ◽  
Body Velocity ◽  
Exciting Forces ◽  
Deep Fluid ◽  
The Mean

A slender axisymmetric body is submerged beneath a regular train of waves on an inviscid, incompressible, infinitely deep fluid. Using the method of matched asymptotic expansions, the velocity potential in the neighborhood of the body is calculated, thus determining the mean second-order vertical force when the body is permitted to respond to the exciting forces and moment but is otherwise moving with constant forward speed and depth beneath a head sea. To stablilize the body motion, the effects of a hydrofoil placed on the body axis are included. Several examples are computed showing the dependence of mean vertical force on body velocity.

Contracting ducts of finite length

1951 ◽  
Vol 2 (4) ◽  
pp. 254-271 ◽  
Author(s):  
L. G. Whitehead ◽  
L. Y. Wu ◽  
M. H. L. Waters
Keyword(s):  
Stream Function ◽  
Finite Length ◽  
Velocity Potential ◽  
Three Dimensional ◽  
Relaxation Method ◽  
Two Dimensional ◽  
Dimensional Flow ◽  
Hodograph Plane ◽  
Two Dimensional Flow ◽  
Working Section

SummmaryA method of design is given for wind tunnel contractions for two-dimensional flow and for flow with axial symmetry. The two-dimensional designs are based on a boundary chosen in the hodograph plane for which the flow is found by the method of images. The three-dimensional method uses the velocity potential and the stream function of the two-dimensional flow as independent variables and the equation for the three-dimensional stream function is solved approximately. The accuracy of the approximate method is checked by comparison with a solution obtained by Southwell's relaxation method.In both the two and the three-dimensional designs the curved wall is of finite length with parallel sections upstream and downstream. The effects of the parallel parts of the channel on the rise of pressure near the wall at the start of the contraction and on the velocity distribution across the working section can therefore be estimated.

Sign in / Sign up

Export Citation Format

Share Document