Flow Due to a Moving Pressure Distribution on Free-Surface With Finite-Depth Bottom

2002 ◽  
Author(s):  
Iskender Sahin ◽  
Noriaki Okita
Keyword(s):  
Free Surface ◽  
Pressure Distribution ◽  
Current Method ◽  
Finite Depth ◽  
Steady State Solution ◽  
Wave Resistance ◽  
Surface Elevation ◽  
Bottom Pressure ◽  
Approximation Techniques ◽  
Pressure Profiles

Surface elevation and dynamic bottom pressure profiles caused by a moving pressure distribution over the free-surface are obtained. A direct numerical integration approach for the linear, two-dimensional, and steady-state solution has been developed. The behavior of the surface elevation and bottom pressure profiles along with wave resistance for increasing Froude number or depth are presented. The agreement of the wave resistance calculations using the profiles obtained by the current method and the expression given by Newman and Poole (1962) indicates that the current method can be used as a reliable tool for prediction as well as validation for other numerical approximation techniques.

Disturbance During Steady and Unsteady Motion of a Two-Dimensional Pressure Distribution

2001 ◽  
Vol 45 (03) ◽  
pp. 165-176 ◽  
Author(s):  
Noriaki Okita ◽  
Iskender Sahin ◽  
Mark C. Hyman
Keyword(s):  
Pressure Distribution ◽  
Finite Depth ◽  
Unsteady Motion ◽  
Wave Resistance ◽  
Two Dimensional ◽  
Bottom Pressure ◽  
Integration Algorithm ◽  
Pressure Profiles ◽  
Principal Value ◽  
Depth Water

A two-dimensional study of flow due to a moving pressure distribution in subcritical Froude numbers over finite-depth water was conducted by a linearized ideal flow approach. A numerical integration algorithm was developed to evaluate the analytical solution given by Cauchy principal-value integrals. The surface elevation, bottom pressure profiles, and wave resistance were computed as functions of speed and water depth. The calculated results agreed well with published values.

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.

The translation of two bodies under the free surface of a heavy fluid

1950 ◽  
Vol 46 (3) ◽  
pp. 453-468 ◽  
Author(s):  
A. Coombs
Keyword(s):  
Free Surface ◽  
Large Range ◽  
Three Dimensional ◽  
Finite Depth ◽  
Arbitrary Cross Section ◽  
Wave Resistance ◽  
Vertical Force ◽  
First Approximation ◽  
Special Case ◽  
Two Bodies

1. Many investigations have been made to determine the wave resistance acting on a body moving horizontally and uniformly in a heavy, perfect fluid. Lamb obtained a first approximation for the wave resistance on a long circular cylinder, and this was later confirmed to be quite sufficient over a large range. In 1926 and 1928, Havelock (4, 5) obtained a second approximation for the wave resistance and a first approximation for the vertical force or lift. Later, in 1936(6), he gave a complete analytical solution to this problem, in which the forces were expressed in the form of infinite series in powers of the ratio of the radius of the cylinder to the depth of the centre below the free surface of the fluid. General expressions for the wave resistance and lift of a cylinder of arbitrary cross-section were found by Kotchin (7) using integral equations, and the special case of a flat plate was evaluated. He continued with a discussion of the motion of a three-dimensional body. More recently, Haskind (3) has examined the same problem when the stream has a finite depth.

scholarly journals Modelling free surface flow with curvilinear streamlines by a non-hydrostatic model

2016 ◽  
Vol 64 (3) ◽  
pp. 281-288
Author(s):  
Yebegaeshet T. Zerihun
Keyword(s):  
Free Surface ◽  
Hydrostatic Pressure ◽  
Pressure Distribution ◽  
Free Surface Flow ◽  
Higher Order ◽  
Surface Flow ◽  
Pressure Profiles ◽  
Proposed Model ◽  
Saint Venant Equations ◽  
Gravity Driven

Abstract This study addresses a particular phenomenon in open channel flows for which the basic assumption of hydrostatic pressure distribution is essentially invalid, and expands previous suggestions to flows where streamline curvature is significant. The proposed model incorporates the effects of the vertical curvature of the streamline and steep slope, in making the pressure distribution non-hydrostatic, and overcomes the accuracy problem of the Saint-Venant equations when simulating curvilinear free surface flow problems. Furthermore, the model is demonstrated to be a higher-order one-dimensional model that includes terms accounting for wave-like variations of the free surface on a constant slope channel. Test results of predicted flow surface and pressure profiles for flow in a channel transition from mild to steep slopes, transcritical flow over a short-crested weir and flow with dual free surfaces are compared with experimental data and previous numerical results. A good agreement is attained between the experimental and computed results. The overall simulation results reveal the satisfactory performance of the proposed model in simulating rapidly varied gravity-driven flows with predominant non-hydrostatic pressure distribution effects. This study suggests that a higher-order pressure equation should be used for modelling the pressure distribution of a curvilinear flow in a steeply sloping channel.

Blockage with a Free Surface

1976 ◽  
Vol 20 (04) ◽  
pp. 199-203
Author(s):  
J. N. Newman
Keyword(s):  
Free Surface ◽  
Velocity Potential ◽  
Finite Depth ◽  
Wave Resistance ◽  
Steady Flows ◽  
Two Dimensional ◽  
Present Context ◽  
Two Dimensional Flow ◽  
Field Radiation ◽  
Radiation Conditions

The occurrence of blockage, or a jump in the velocity potential between the upstream and downstream infinities, is well known for steady two-dimensional flow past a body in a rigid channel. This paper considers the analogous situation where there is a free surface, as in the wave resistance problem for submerged two-dimensional bodies in a fluid of finite depth. It is shown that blockage occurs in spite of the free surface, taking values which depend not only on the dipole moment but also upon the Froude number based on depth. The occurrence of blockage, in the present context, has a bearing primarily upon the correct formulation of far-field radiation conditions for steady flows with finite depth.

Waves on a shear flow

1974 ◽  
Vol 11 (2) ◽  
pp. 263-277 ◽  
Author(s):  
K.K. Puri
Keyword(s):  
Free Surface ◽  
Steady State ◽  
Shear Flow ◽  
Initial Value Problem ◽  
Finite Depth ◽  
Steady State Solution ◽  
State Solution ◽  
Wave System ◽  
Initial Value ◽  
Oscillatory Pressure

The propogation of disturbance when a shear flow with a free surface, in a channel of infinite horizontal extent and finite depth, is disturbed by the application of time-oscillatory pressure, is studied. The initial value problem is solved by using transform techniques and the steady state solution is obtained therefrom in the limit t → ∞. The effect of the initial shear on the development of the wave system is investigated.

Forced Oscillations in a Two-Layer Fluid of Finite Depth

1983 ◽  
Vol 50 (3) ◽  
pp. 506-510
Author(s):  
R. K. Manna
Keyword(s):  
Free Surface ◽  
Internal Wave ◽  
Pressure Distribution ◽  
Fourier Transformation ◽  
Finite Depth ◽  
Forced Oscillations ◽  
Wave System ◽  
Initial Value ◽  
Oscillatory Pressure ◽  
Generalized Fourier Transformation

An initial value investigation is made of the development of surface and internal wave motions generated by an oscillatory pressure distribution on the surface of a fluid that is composed of two layers of limited depths and of different densities. The displacement functions both on the free surface and on the interface are obtained with the help of generalized Fourier transformation. The method for the asymptotic evolution of the wave integrals is based on Bleistein’s method. The behavior of the solutions is examined for large values of time and distance. It is found that there are two classes of waves—the first corresponds to the usual surface waves with a changed amplitude and the second arises entirely due to stratification. Some interesting features of the wave system have also been studied.

The Wave and Induced Drag of a Hydrofoil of Finite Span in Water of Limited Depth

1961 ◽  
Vol 5 (03) ◽  
pp. 15-21
Author(s):  
J. P. Breslin
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Finite Depth ◽  
Wave Resistance ◽  
Finite Span ◽  
Induced Drag ◽  
Special Cases ◽  
The Waves ◽  
Limited Depth ◽  
Good Agreement

The wave resistance and the induced drag of a simple hydrofoil of finite span moving at a fixed submergence in water of finite depth are derived from a knowledge of the shallow water potential of a source. From this the waves produced by the semi-infinite doublet sheet which represents the undisturbed mathematical model of the hydrofoil are computed and the wave resistance is then inferred from the formula for the waves. Special cases which have been published previously are recaptured from the formulas. The induced drag is computed from a knowledge of the nature of the potential functions needed to satisfy the boundary conditions on the bottom and free surface. A comparison with one set of experimental data shows the theory to underestimate the experimentally determined lift-dependent drag curve at low Froude numbers F and to agree very well as high F. It is conjectured that the lack of good agreement at low F is due to the neglect of the influence of the free surface on the lift which has been omitted in this analysis.

Dead-Water Effects of a Ship Moving in Stratified Seas

1993 ◽  
Vol 115 (2) ◽  
pp. 105-110 ◽  
Author(s):  
T. Miloh ◽  
M. P. Tulin ◽  
G. Zilman
Keyword(s):  
Free Surface ◽  
Numerical Solutions ◽  
Fluid Model ◽  
Finite Depth ◽  
Prolate Spheroid ◽  
Wave Resistance ◽  
Water Effects ◽  
Linearized Theory ◽  
Dead Water ◽  
Surface Disturbances

A linearized theory is presented for the dead-water phenomena. A two-layer fluid model of finite depth is assumed and the solutions for both the wave resistance, as well as the interface and free-surface disturbances, are obtained in terms of Green’s function. Numerical solutions are given for the case of a semi-submersible slender-body (prolate spheroid) moving steadily on the free-surface.

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