Simple Calculation of Sheltering Effect on Ship-Wave Resistance and Bulbous Bow Design

1980 ◽  
Vol 24 (04) ◽  
pp. 232-243
Author(s):  
B. Yim
Keyword(s):  
Free Surface ◽  
Simple Calculation ◽  
Wave Resistance ◽  
Beam Length ◽  
Ship Wave ◽  
Surface Pressure Distribution ◽  
Wigley Hull ◽  
Bulbous Bow ◽  
Sheltering Effect ◽  
Optimum Volume

The sheltering effect on the ship wave resistance is treated by the free-surface pressure distribution inside the ship. The theory is developed and the numerical values of wave resistance are obtained for parabolic and sinusoidal hulls. The corrected wave resistance is shown to be reduced more than 20 percent from the Michell's wave resistance even for a Wigley hull with beam-length ratio 0.1. However, the humps and hollows of wave resistance still remain with the magnitude closer to the experimental results. The optimum volume of bulb for sinusoidal ships is also shown to be reduced from 7.6 percent to 18 percent of the values without sheltering effect for the range of Froude numbers from 0.15 to 0.35.

A Slender-Ship Theory of Wave Resistance

1983 ◽  
Vol 27 (01) ◽  
pp. 13-33
Author(s):  
Francis Noblesse
Keyword(s):  
Froude Number ◽  
Wave Resistance ◽  
Successive Approximations ◽  
Zeroth Order ◽  
Remarkable Effect ◽  
Ship Wave ◽  
First Order ◽  
Wigley Hull ◽  
Low Froude Number ◽  
The Waves

A new slender-ship theory of wave resistance is presented. Specifically, a sequence of explicit slender-ship wave-resistance approximations is obtained. These approximations are associated with successive approximations in a slender-ship iterative procedure for solving a new (nonlinear integro-differential) equation for the velocity potential of the flow caused by the ship. The zeroth, first, and second-order slender-ship approximations are given explicitly and examined in some detail. The zeroth-order slender-ship wave-resistance approximation, r(0) is obtained by simply taking the (disturbance) potential, ϕ, as the trivial zeroth-order slender-ship approximation ϕ(0) = 0 in the expression for the Kochin free-wave amplitude function; the classical wave-resistance formulas of Michell [1]2 and Hogner [2] correspond to particular cases of this simple approximation. The low-speed wave-resistance formulas proposed by Guevel [3], Baba [4], Maruo [5], and Kayo [6] are essentially equivalent (for most practical purposes) to the first-order slender-ship low-Froude-number approximation, rlF(1), which is a particular case of the first-order slender-ship approximation r(1): specifically, the first-order slender-ship wave-resistance approximation r(1) is obtained by approximating the potential ϕ in the expression for the Kochin function by the first-order slender-ship potential ϕ1 whereas the low-Froude-number approximation rlF(1) is associated with the zero-Froude-number limit ϕ0(1) of the potentialϕ(1). A major difference between the first-order slender-ship potential ϕ(1) and its zero-Froude-number limit ϕ0(1) resides in the waves that are included in the potential ϕ(1) but are ignored in the zero-Froude-number potential ϕ0(1). Results of calculations by C. Y. Chen for the Wigley hull show that the waves in the potential ϕ(1) have a remarkable effect upon the wave resistance, in particular causing a large phase shift of the wave-resistance curve toward higher values of the Froude number. As a result, the first-order slender-ship wave-resistance approximation in significantly better agreement with experimental data than the low-Froude-number approximation rlF(1) and the approximations r(0) and rM.

Analyses of Waves and the Wave Resistance due to Transom-Stern Ships

1969 ◽  
Vol 13 (02) ◽  
pp. 155-167
Author(s):  
Bohyun Yim
Keyword(s):  
Boundary Condition ◽  
Free Surface ◽  
Wave Resistance ◽  
Second Order ◽  
Surface Boundary ◽  
Exact Formulation ◽  
Wave Problem ◽  
Ship Wave ◽  
Free Surface Boundary Condition ◽  
Surface Boundary Condition

Waves and the wave resistance due to a ship with a transom stern are analyzed starting with an exact formulation of the general ship wave problem. Green's theorem is utilized together with the well-known Green's function which satisfies the linear free-surface boundary condition on the free surface. Here it is required to take at least the second-order terms in the formal development. It is found that the immersed transom stern acts to cancel stern waves. Using a limited form of Michell's wave-resistance formula, the wave resistance of the transom-stern ship is analyzed

Quasi-linear theory of waves and ship wave resistance in restricted waters

2004 ◽  
Vol 31 (10) ◽  
pp. 1231-1244 ◽  
Author(s):  
Eduard Amromin ◽  
Svetlana Kovinskaya ◽  
Igor Mizine
Keyword(s):  
Linear Theory ◽  
Wave Resistance ◽  
Ship Wave

Forces Exerted on a Hovercraft by a Moving Pressure Distribution: Robustness of Mathematical Models

2006 ◽  
Vol 50 (01) ◽  
pp. 38-48 ◽  
Author(s):  
Gregory Zilman
Keyword(s):  
Free Surface ◽  
Mathematical Models ◽  
Pressure Distribution ◽  
Constant Pressure ◽  
Wave Resistance ◽  
Excess Pressure ◽  
Physical Parameters ◽  
Rectangular Region ◽  
Heavy Fluid ◽  
Side Force

The wave resistance, side force, and yawing moment acting on a hovercraft moving on the free surface of a heavy fluid is studied. The hovercraft is represented by a distributed excess pressure. Various types of pressure and bounding contours are considered. The sensitivity of the results to numerous uncertainties in the problem's physical parameters is investigated. It is found that constant pressure over a rectangular region moving with an angle of drift results in peculiar side force values. Several robust mathematical models of a moving hovercraft are proposed and analyzed.

Nonlinear Local Analysis of Steady Flow About a Ship

1991 ◽  
Vol 35 (04) ◽  
pp. 288-294
Author(s):  
F. Noblesse ◽  
D. M. Hendrix ◽  
L. Kahn
Keyword(s):  
Free Surface ◽  
Fluid Velocity ◽  
Wave Profile ◽  
Local Analysis ◽  
Experimental Measurements ◽  
Surface Boundary ◽  
Nonlinear Method ◽  
Rapid Variation ◽  
Wigley Hull ◽  
Analytical Expressions

A nonlinear local analysis of the steady potential flow at a ship bow and stern, and more generally at any point along a ship waterline, is presented. The hull boundary condition and the nonlinear kinematic and dynamic free-surface boundary conditions are satisfied exactly, at the actual position of the free surface, in this analysis. The bow-flow analysis shows that the free surface at a ship bow is tangent to the stem. This theoretical result appears to agree with existing experimental measurements of steady bow waves of the Wigley hull. Simple analytical expressions defining the fluid velocity at the bow and the stern, and more generally at any point along the wave profile, in terms of the elevation of the free surface at the corresponding point are also given. These analytical expressions and the available experimental measurements of wave profiles along the Wigley hull show that the velocity of the flow disturbance due to this hull is fairly small compared to the hull speed everywhere along the wave profile except in very small regions around the bow and the stern, where the total fluid velocity is nearly equal to the hull speed in magnitude but directed vertically. Nonlinearities therefore appear to be quite important, although only in very small regions surrounding a ship bow and stern. A genuine nonlinear method of calculation must then be able to represent the very rapid variation in the direction of the fluid velocity occurring within small regions around a ship bow and stern. In particular, a sufficiently fine discretization is required in these regions.

From Bulbous Bow to Free-Surface Shock Wave—Trends of 20 Years’ Research on Ship Waves at the Tokyo University Tank

1981 ◽  
Vol 25 (03) ◽  
pp. 147-180
Author(s):  
Takao Inui
Keyword(s):  
Shock Wave ◽  
Free Surface ◽  
Field Measurements ◽  
Wave Pattern ◽  
Ship Waves ◽  
Second Stage ◽  
Initial Stage ◽  
Man And Nature ◽  
Bulbous Bow ◽  
The Relationship

Trends of 20 years' research on ship waves at the Tokyo University Tank since 1960 are briefly sketched. Stress is focused on the importance of dialogues between man and nature. The process of these dialogues is exemplified by some typical cases, including the development of bulbous bows and the finding of free-surface shock waves. Wave-pattern pictures are shown to be indispensable for the initial stage of the di alogues, while wave contours and velocity-field measurements serve well in the second stage. The current wave analysis and wake survey may be the third. The relationship between "wavebreaking" and the "free-surface shock wave" is also discussed.

Three-Dimensional Large Amplitude Body Motions in Waves

2007 ◽  
Author(s):  
Xinshu Zhang ◽  
Robert F. Beck
Keyword(s):  
Free Surface ◽  
Three Dimensional ◽  
Surface Boundary ◽  
Forward Speed ◽  
Time Step ◽  
Surface Boundary Conditions ◽  
Submerged Body ◽  
Calm Water ◽  
Wigley Hull ◽  
Constant Strength

Three-dimensional, time-domain, wave-body interactions are studied in this paper for cases with and without forward speed. 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 panels on the exact submerged body surface, the boundary integral equations are solved numerically at each time step. 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 submerged body geometry. The desingularized method applied on the free surface produces non-singular kernels in the integral equations by moving the fundamental singularities a small distance outside of the fluid domain. Constant strength panels are used for bodies with any arbitrary shape. Extensive results are presented to validate the efficiency of the present method. These results include the added mass and damping computations for a hemisphere. The calm water wave resistance for a submerged spheroid and a Wigley hull are also presented. All the computations with forward speed are started from rest and proceed until a steady state is reached. Finally, the time-domain forced motion results for a modified Wigley hull with forward speed are shown and compared with the experiments for both linear computations and body-exact computations.

Sign in / Sign up

Export Citation Format

Share Document