Hydrodynamic moment acting on a moving deformable body in a linear potential flow of an ideal incompressible liquid

1978 ◽  
Vol 12 (5) ◽  
pp. 714-718
Author(s):  
S. D. Vil'khovchenko
Keyword(s):  
Potential Flow ◽  
Incompressible Liquid ◽  
Deformable Body ◽  
Linear Potential ◽  
Ideal Incompressible Liquid

Linear and non-linear potential-flow calculations of free-surface waves with lift and induced drag

2000 ◽  
Vol 214 (6) ◽  
pp. 801-812
Author(s):  
C-E Janson
Keyword(s):  
Free Surface ◽  
Potential Flow ◽  
Lift Force ◽  
Radiation Condition ◽  
Linear Potential ◽  
Surface Boundary ◽  
Model Approximation ◽  
Non Linear ◽  
Lifting Surfaces ◽  
The Waves

A potential-flow panel method is used to compute the waves and the lift force from surface-piercing and submerged bodies. In particular the interaction between the waves and the lift produced close to the free surface is studied. Both linear and non-linear free-surface boundary conditions are considered. The potential-flow method is of Rankine-source type using raised source panels on the free surface and a four-point upwind operator to compute the velocity derivatives and to enforce the radiation condition. The lift force is introduced as a dipole distribution on the lifting surfaces and on the trailing wake, together with a flow tangency condition at the trailing edge of the lifting surface. Different approximations for the spanwise circulation distribution at the free surface were tested for a surface-piercing wing and it was concluded that a double-model approximation should be used for low speeds while a single-model, which allows for a vortex at the free surface, was preferred at higher speeds. The lift force and waves from three surface-piercing wings, a hydrofoil and a sailing yacht were computed and compared with measurements and good agreement was obtained.

Applicability and limitations of highly non-linear potential flow solvers in the context of water waves

2017 ◽  
Vol 142 ◽  
pp. 233-244 ◽  
Author(s):  
Guillaume Ducrozet ◽  
Félicien Bonnefoy ◽  
Yves Perignon
Keyword(s):  
Potential Flow ◽  
Water Waves ◽  
Linear Potential ◽  
Non Linear

Note on the Smith-Stone theory of fish propulsion

1964 ◽  
Vol 280 (1382) ◽  
pp. 398-408 ◽  
Keyword(s):  
Incompressible Liquid ◽  
Velocity Potential ◽  
Present Note ◽  
Flexible Plate ◽  
Two Dimensional ◽  
Ideal Incompressible Liquid ◽  
Wake Effect ◽  
Fish Propulsion ◽  
Perturbation Velocity ◽  
Two Dimensional Flow

The present note extends the theory of fish propulsion by E. H. Smith & D. E. Stone, taking into account the wake effect which was not discussed in the original paper. The motion of a fish is simulated by a flexible plate of infinitesimal thickness, infinite span, and constant chord length, moving in the two-dimensional flow field of an ideal incompressible liquid. The perturbation velocity potential for the flexible plate is obtained by solving the Laplace equation in an elliptic cylindrical co-ordinate system, while the wake velocity potential follows from the application of a method which is due to Theodorsen. The results are shown to be identical with those derived previously by Siekmann. A simple example is given for illustration and results predicted by theory are compared with experimental data.

Hydrodynamics of Side-by-Side Fixed Floating Bodies

2016 ◽  
Author(s):  
Kie Hian Chua ◽  
Rodney Eatock Taylor ◽  
Yoo Sang Choo
Keyword(s):  
Free Surface ◽  
Energy Dissipation ◽  
Skin Friction ◽  
Viscous Dissipation ◽  
Potential Flow ◽  
Flow Model ◽  
Time Window ◽  
Distance Estimation ◽  
Linear Potential ◽  
Potential Flow Model

Safety of cargo transfer operations between side-by-side vessels depends on accurate modelling of hydrodynamic behavior, especially in terms of predicting the gap free surface elevations between the two vessels. The common industry practice of using linear potential flow models to study these interactions over-predicts the free surface elevations, due to the fact that potential flow does not include viscous dissipation effects such as flow separation at hull corners and skin friction. This may result in inaccurate projections of the time-window when these operations can safely take place. This is an important aspect for developments such as Floating Liquefied Natural Gas (FLNG) platforms, where side-by-side cargo offloading is an essential operation. In a recent research [1], an approach of splitting the amount of energy lost through viscous dissipation (calculated from three-dimensional viscous CFD simulations) into components representative of the flow phenomena has been proposed. Using the approach, referred to as component energy dissipation, the amount of energy lost due to vortex shedding and skin friction can be estimated. Modifications to linear potential flow were also proposed in the referenced research, such that the energy loss components can be converted into dissipative coefficients that are used in terms added to the free surface and body boundary conditions. By combining use of the component energy dissipation approach and the modified dissipative potential flow model, better predictions of gap hydrodynamic interaction can be obtained, compared to using conventional potential flow. In this paper, results from viscous simulations of two identical fixed-floating side-by-side barges of 280m (length) × 46m (breadth) × 16.5m (draught) under excitation from regular incident waves are presented, and compared with corresponding results from the modified dissipative potential flow model. Two types of side-by-side hull configurations were investigated, the first using rectangular barges with sharp bilge corners at varying gap distances and the second using barges with rounded bilge corners of varying radii at a fixed gap distance. Estimation of the dissipative coefficients used in the modified potential flow model, calculated from the viscous results, will also be discussed. The comparison of results serves both as a validation of the modified potential flow model, and to highlight the importance of including viscous dissipation when analyzing hydrodynamic interactions.

Swimming due to transverse shape deformations

2009 ◽  
Vol 631 ◽  
pp. 127-148 ◽  
Author(s):  
EVA KANSO
Keyword(s):  
Potential Flow ◽  
Deformable Body ◽  
Three Dimensional ◽  
Point Vortices ◽  
Vortex Wake ◽  
Balance Laws ◽  
Reactive Force ◽  
Slender Bodies ◽  
Shape Changes ◽  
Shape Deformations

Balance laws are derived for the swimming of a deformable body due to prescribed shape changes and the effect of the wake vorticity. The underlying balances of momenta, though classical in nature, provide a unifying framework for the swimming of three-dimensional and planar bodies and they hold even in the presence of viscosity. The derived equations are consistent with Lighthill's reactive force theory for the swimming of slender bodies and, when neglecting vorticity, reduce to the model developed in Kanso et al. (J. Nonlinear Sci., vol. 15, 2005, p. 255) for swimming in potential flow. The locomotion of a deformable body is examined through two sets of examples: the first set studies the effect of cyclic shape deformations, both flapping and undulatory, on the locomotion in potential flow while the second examines the effect of the wake vorticity on the net locomotion. In the latter, the vortex wake is modelled using pairs of point vortices shed periodically from the tail of the deformable body.

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