A Simplified Approach to Free-Surface Wave Drag Theory

1968 ◽  
Vol 72 (687) ◽  
pp. 239-242 ◽  
Author(s):  
Peter R. Payne
Keyword(s):  
Free Surface ◽  
Classical Theory ◽  
Pressure Field ◽  
Practical Importance ◽  
Dynamic Modelling ◽  
Major Change ◽  
Wave Drag ◽  
Uniform Field ◽  
Simplified Approach ◽  
Linear Differential

Summary The problem of a two-dimensional pressure field moving over a free surface is analysed by dynamic modelling techniques. Using a simple second order linear differential equation, it is possible to obtain all the classical theory rersults for a uniform field in deep water. Squire’s results for the non-uniform pressure field of a planing wedge are also duplicated. Further results, not hitherto obtained with classical theory, may explain some anomalies associated with the classical theory. The method has the advantage that results for a large number of “pressure field distributions” have already been tabulated by workers studying the response of simple lumped parameter mechanical dynamic systems. A conclusion of some practical importance in applied hydrodynamics is that the wave drag of a pressure field varies with its distribution. The more non-uniform a pressure field the greater its wave drag. The theory also gives insight into the occurrence of “humps and hollows” in model resistance curves, and gives some insight as to why a minor change in form may cause a major change in wave resistance.

The Introduction of Micro Cells to Treat Pressure in Free Surface Fluid Flow Problems

1995 ◽  
Vol 117 (4) ◽  
pp. 683-690 ◽  
Author(s):  
Peter E. Raad ◽  
Shea Chen ◽  
David B. Johnson
Keyword(s):  
Fluid Flow ◽  
Free Surface ◽  
Pressure Field ◽  
Flow Simulation ◽  
New Method ◽  
Computational Domain ◽  
Critical Feature ◽  
Flow Problems ◽  
Macro Cell ◽  
Marker And Cell Method

A new method of calculating the pressure field in the simulation of two-dimensional, unsteady, incompressible, free surface fluid flow by use of a marker and cell method is presented. A critical feature of the new method is the introduction of a finer mesh of cells in addition to the regular mesh of finite volume cells. The smaller (micro) cells are used only near the free surface, while the regular (macro) cells are used throughout the computational domain. The movement of the free surface is accomplished by the use of massless surface markers, while the discrete representation of the free surface for the purpose of the application of pressure boundary conditions is accomplished by the use of micro cells. In order to exploit the advantages offered by micro cells, a new general equation governing the pressure field is derived. Micro cells also enable the identification and treatment of multiple points on the free surface in a single surface macro cell as well as of points on the free surface that are located in a macro cell that has no empty neighbors. Both of these situations are likely to occur repeatedly in a free surface fluid flow simulation, but neither situation has been explicitly taken into account in previous marker and cell methods. Numerical simulation results obtained both with and without the use of micro cells are compared with each other and with theoretical solutions to demonstrate the capabilities and validity of the new method.

Minimising wave drag for free surface flow past a two-dimensional stern

2011 ◽  
Vol 23 (7) ◽  
pp. 072101 ◽  
Author(s):  
Osama Ogilat ◽  
Scott W. McCue ◽  
Ian W. Turner ◽  
John A. Belward ◽  
Benjamin J. Binder
Keyword(s):  
Free Surface ◽  
Free Surface Flow ◽  
Wave Drag ◽  
Surface Flow ◽  
Two Dimensional ◽  
Flow Past

SPLASH Nonlinear and Unsteady Free-Surface Analysis Code for Grand Prix Yacht Design

1997 ◽  
Author(s):  
Bruce S. Rosen ◽  
Joseph P. Laiosa
Keyword(s):  
Free Surface ◽  
Free Surface Flow ◽  
Inviscid Flow ◽  
Wave Drag ◽  
Surface Flow ◽  
Viscous Drag ◽  
Accurate Estimation ◽  
Following Seas ◽  
Induced Drag ◽  
Lifting Surfaces

The SPLASH free-surface potential flow panel code computer program is presented. The 3D flow theory and its numerical implementation are discussed. Some more conventional applications are reviewed, for steady flow past solid bodies, and for classical linearized free-surface flow. New free-surface capabilities are also described, notably, steady nonlinear solutions, and novel unsteady partially­nonlinear solutions in the frequency domain. The inviscid flow method treats both free-surface waves and lifting surfaces. The calculations yield predictions for complex interactions at heel and yaw such as wave drag due to lift, the effect of the free­surface on lift and lift-induced drag, and unsteady motions and forces in oblique or following seas. These are in addition to the usual predictions for the simpler effects considered separately, for example double-body lift and induced drag, and upright steady wave resistance or added resistance in head seas. For prediction of total resistance, the use of computed variable wetted areas and wetted lengths in a standard semi-empirical, handbook-type "viscous stripping" algorithm provides a more accurate estimation of viscous drag than is possible otherwise. Results from a variety of IACC and IMS yacht design studies, including comparisons with experimental data, support the conclusion that the free­surface panel code can be used for reliable and accurate prediction of sailboat performance.

scholarly journals Flat vs. curved rigid-lid LES computations of an open-channel confluence

2019 ◽  
Vol 21 (2) ◽  
pp. 318-334 ◽  
Author(s):  
Pedro Xavier Ramos ◽  
Laurent Schindfessel ◽  
João Pedro Pêgo ◽  
Tom De Mulder
Keyword(s):  
Free Surface ◽  
Secondary Flow ◽  
Open Channel ◽  
Pressure Field ◽  
Large Eddy Simulations ◽  
Numerical Treatment ◽  
Mean Flow ◽  
Large Eddy ◽  
Flow Case ◽  
Channel Confluence

Abstract This paper describes the application of four Large Eddy Simulations (LES) to an open-channel confluence flow, making use of a frictionless rigid-lid to treat the free-surface. Three simulations are conducted with a flat rigid-lid, at different elevations. A fourth simulation is carried out with a curved rigid-lid which is a closer approximation to the real free-surface of the flow. The curved rigid-lid is obtained from the time-averaged pressure field on the flat rigid-lid from one of the initial three simulations. The aim is to investigate the limitations of the free-surface treatment by means of a rigid-lid in the simulation of an asymmetric confluence, showing the differences that both approaches produce in terms of mean flow, secondary flow and turbulence. After validation with experimental data, the predictions are used to understand the differences between adopting a flat and a curved rigid-lid onto the confluence hydrodynamics. For the present flow case, although it was characterized by a moderately low downstream Froude number (Fr ≈ 0.37), it was found that an oversimplification of the numerical treatment of the free-surface leads to a decreased accuracy of the predictions of the secondary flow and turbulent kinetic energy.

Hysteresis and nonlinear detuning in a spatial-resonance phenomenon

1973 ◽  
Vol 61 (2) ◽  
pp. 401-413
Author(s):  
Ian Huntley ◽  
Ronald Smith
Keyword(s):  
Free Surface ◽  
Experimental Work ◽  
Alternative Model ◽  
Pressure Field ◽  
Low Frequency ◽  
Theoretical Description ◽  
Resonance Phenomenon ◽  
Theoretical Problem ◽  
Frequency Wave ◽  
Spatial Resonance

The experimental work of Franklin, Price & Williams (1973) shows that for moderately large driving amplitudes there are features of spatial resonance that are not predicted by the model representation of Mahony & Smith (1972). We here derive an alternative model, which remains valid for moderately large driving amplitudes, and we are able to obtain a theoretical description of both hysteresis and nonlinear detuning of the low frequency wave response. An experiment in which surface waves were generated by a sinusoidal pressure field at the free surface (and which corresponds almost exactly to the theoretical problem) was conducted in order to test these predictions.

A simple example from flat-ship theory

1988 ◽  
Vol 189 ◽  
pp. 301-310 ◽  
Author(s):  
Susan Cole
Keyword(s):  
Exact Solution ◽  
Free Surface ◽  
Energy Balance ◽  
Aspect Ratio ◽  
Pressure Distribution ◽  
Wave Drag ◽  
Vortical Flow ◽  
Far Field ◽  
Low Aspect Ratio ◽  
Free Surface Waves

This paper describes the induced pressure distribution, free-surface waves, vortical flow and wave drag of an exact solution of low-aspect-ratio flat-ship theory. An energy balance is derived which relates the spray drag, the energy carried away by the far-field waves and the vortical flow to the total wave drag.

A Small Axisymmetric Obstacle in the Presence of an Underwater Point-Source Field

1997 ◽  
Vol 05 (03) ◽  
pp. 243-263 ◽  
Author(s):  
A. Charalambopoulos ◽  
G. Dassios ◽  
P. Ergatis
Keyword(s):  
Free Surface ◽  
Point Source ◽  
Pressure Field ◽  
Vertical Line ◽  
Source Field ◽  
Floating Object ◽  
Smooth Objects ◽  
Special Case

A small, acoustically hard and axisymmetric object is placed in a deep homogeneous sea environment with a hard plane bottom. The free surface of the sea is assumed to be soft. The source and the receiver are placed on the same vertical line, far away from the object. Given the positions of the source and the receiver, two problems are solved: the determination of the pressure field at the receiver from the position and the shape of the object, and the determination of the position and the shape of the object from the pressure field at the receiver. The special case of smooth objects generated by the rotation of differentiable curves is studied. We provide results for the case of a floating object and for the case of an object or a boss at the bottom of the sea.

Numerical Simulation of Violent Impinging Jet Flows with Improved SPH Method

2016 ◽  
Vol 13 (04) ◽  
pp. 1641001 ◽  
Author(s):  
J. R. Shao ◽  
S. M. Li ◽  
M. B. Liu
Keyword(s):  
Free Surface ◽  
Pressure Field ◽  
Surface Condition ◽  
Time History ◽  
Impinging Jet ◽  
Jet Flows ◽  
Solid Boundary ◽  
Sph Method ◽  
Pressure Time ◽  
Kernel Gradient Correction

This paper presents an implementation of an improved smoothed particle hydrodynamics (SPH) method for simulating violent water impinging jet flow problems. The presented SPH method involves three major modifications on the traditional SPH method, (1) The kernel gradient correction (KGC) and density correction are used to improve the computational accuracy and obtain smoothed pressure field, (2) a coupled dynamic solid boundary treatment (SBT) is used to remove the numerical oscillation near the solid boundary and ensure no penetration condition, (3) a free surface condition, which is obtained from the summation of kernel function and volume, is used to describe the water jet accurately. Different cases about violent impinging jet flows are simulated. The influences of impact velocity and angles are investigated. It is demonstrated that the presented SPH method has very good performance with accurate impinging jet patterns and pressure field distribution. It is also found that the pressure time histories of observation points are greatly influenced by the rarefaction wave from surrounding air. Closer distance from free surface can lead to quicker decay of the pressure time history.

Surface folds during the penetration of a viscoelastic fluid by a sphere

2002 ◽  
Vol 460 ◽  
pp. 337-348 ◽  
Author(s):  
THOMAS PODGORSKI ◽  
ANDREW BELMONTE
Keyword(s):  
Relaxation Time ◽  
Free Surface ◽  
Physical Mechanism ◽  
Pressure Field ◽  
Elastic Membrane ◽  
Anisotropic Elastic ◽  
The Stability ◽  
Stress Boundary ◽  
Settling Process ◽  
Present Experimental Evidence

When a sphere settles through the free surface of a viscous fluid, the interface is deformed and assumes a funnel shape behind the sphere. If the fluid is viscoelastic and the settling process is fast compared to the relaxation time of the fluid, elastic effects are dominant and an instability occurs. The interface loses its original axisymmetry and buckles, leading to a particular mode of pinch-off unseen in Newtonian fluids. We present experimental evidence that stress boundary layers form in this type of flow, and argue that a physical mechanism for this instability can be recovered, at least qualitatively, by considering the stability of a stretched anisotropic elastic membrane in a pressure field.

Dynamics and motion of a gas bubble in a viscoplastic medium under acoustic excitation

2019 ◽  
Vol 865 ◽  
pp. 381-413 ◽  
Author(s):  
G. Karapetsas ◽  
D. Photeinos ◽  
Y. Dimakopoulos ◽  
J. Tsamopoulos
Keyword(s):  
Effective Viscosity ◽  
Acoustic Pressure ◽  
Static Pressure ◽  
Pressure Field ◽  
Spherical Shape ◽  
Lagrangian Formalism ◽  
Acoustic Excitation ◽  
Bubble Motion ◽  
Viscoplastic Material ◽  
Simplified Approach

We investigate the dynamics of the buoyancy-driven rise of a bubble inside a viscoplastic material when it is subjected to an acoustic pressure field. To this end, we develop a simplified model based on the Lagrangian formalism assuming a pulsating bubble with a spherical shape. Moreover, to account for the effects of a deformable bubble, we also perform detailed two-dimensional axisymmetric simulations. Qualitative agreement is found between the simplified approach and the detailed numerical simulations. Our results reveal that the acoustic excitation enhances the mobility of the bubble, by increasing the size of the yielded region that surrounds the bubble, thereby decreasing the effective viscosity of the liquid and accelerating the motion of the bubble. This effect is significantly more pronounced at the resonance frequency, and it is shown that bubble motion takes place even for Bingham numbers (Bn) that can be orders of magnitude higher than the critical Bn for bubble entrapment in the case of a static pressure field.

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