A Two-Dimensional Potential Flow Model of the Wave Field Generated by a Semisubmerged Body in Heaving Motion

1988 ◽  
Vol 32 (02) ◽  
pp. 83-91
Author(s):  
X. M. Wang ◽  
M. L. Spaulding
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Potential Flow ◽  
Flow Model ◽  
Second Order ◽  
Two Dimensional ◽  
Third Order ◽  
The Third ◽  
Potential Flow Model ◽  
Good Agreement

A two-dimensional potential flow model is formulated to predict the wave field and forces generated by a sere!submerged body in forced heaving motion. The potential flow problem is solved on a boundary fitted coordinate system that deforms in response to the motion of the free surface and the heaving body. The full nonlinear kinematic and dynamic boundary conditions are used at the free surface. The governing equations and associated boundary conditions are solved by a second-order finite-difference technique based on the modified Euler method for the time domain and a successive overrelaxation (SOR) procedure for the spatial domain. A series of sensitivity studies of grid size and resolution, time step, free surface and body grid redistribution schemes, convergence criteria, and free surface body boundary condition specification was performed to investigate the computational characteristics of the model. The model was applied to predict the forces generated by the forced oscillation of a U-shaped cylinder. Numerical model predictions are generally in good agreement with the available second-order theories for the first-order pressure and force coefficients, but clearly show that the third-order terms are larger than the second-order terms when nonlinearity becomes important in the dimensionless frequency range 1≤ Fr≤ 2. The model results are in good agreement with the available experimental data and confirm the importance of the third order terms.

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.

A Free-Streamline Model for Bluff Bodies in Confined Flow

1977 ◽  
Vol 99 (3) ◽  
pp. 585-592 ◽  
Author(s):  
V. J. Modi ◽  
S. E. El-Sherbiny
Keyword(s):  
Potential Flow ◽  
Bluff Body ◽  
Flow Model ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Flat Plates ◽  
Surface Loading ◽  
Confined Flow ◽  
Potential Flow Model

A potential flow model is presented for two-dimensional symmetrical bluff bodies under wall confinement. It provides a procedure for predicting surface loading on a bluff body over a range of blockage ratios. Experimental results with normal flat plates and circular cylinders for blockage ratios up to 35.5 percent substantiate the validity of the approach.

scholarly journals Two-Dimensional Supercavitating Plate Oscillating Under a Free Surface

1965 ◽  
Vol 9 (02) ◽  
pp. 40-55
Author(s):  
C. S. Song
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Potential Flow ◽  
Flow Region ◽  
Integral Form ◽  
Cavitation Number ◽  
Two Dimensional ◽  
First Order ◽  
Upper Half Plane ◽  
Order Quantities

The problem of a supercavitating flat plate at zero and nonzero cavitation numberoscillating under a free surface is analyzed by a linearized method using the accelerationpotential. The analysis is based on the concept of small velocity perturbations where in all second-order quantities are neglected. The flow is assumed two-dimensional, irrotational, incompressible, and gravitation-free. The potential-flow region is mapped on to an upper half-plane and the solution is expressed in an integral form using Cheng andRott's method. Special attention is given to the effect of approximate wake boundary conditions on the computed force and moment. It was estimated that the effect is of secondorder when the cavitation number is a first-order small quantity.

scholarly journals Effect of Roof Impacts on Coupling Between Wave Response and Sloshing in Tanks of LNG-Carriers

2008 ◽  
Author(s):  
Bernard Molin ◽  
Fabien Remy ◽  
Alain Ledoux ◽  
Nicolas Ruiz
Keyword(s):  
Potential Flow ◽  
Large Amplitude ◽  
Flow Model ◽  
Nonlinear Effects ◽  
Free Surfaces ◽  
Irregular Wave ◽  
Experimental Campaign ◽  
Wave Response ◽  
Potential Flow Model ◽  
Good Agreement

An experimental campaign is reported on the wave response of a rectangular barge supporting two rectangular tanks partly filled with water. Flat and chamfered tank roofs are successively tested, at varying heights above the free surfaces inside the tanks. The tests are carried out in irregular wave systems coming from abeam. The measured barge roll and sloshing motions in the tanks are compared with numerical results from a linearized potential flow model. Good agreement is reported in mild seastates. Nonlinear effects, associated with large amplitude sloshing motion and/or roof impacts, are investigated.

scholarly journals Modelling of depth-induced wave breaking in a fully nonlinear free-surface potential flow model

2019 ◽  
Vol 154 ◽  
pp. 103579 ◽  
Author(s):  
Christos E. Papoutsellis ◽  
Marissa L. Yates ◽  
Bruno Simon ◽  
Michel Benoit
Keyword(s):  
Free Surface ◽  
Surface Potential ◽  
Potential Flow ◽  
Wave Breaking ◽  
Flow Model ◽  
Fully Nonlinear ◽  
Nonlinear Free Surface ◽  
Potential Flow Model

On higher-order wave theory for submerged two-dimensional bodies

1969 ◽  
Vol 38 (2) ◽  
pp. 415-432 ◽  
Author(s):  
Nils Salvesen
Keyword(s):  
Free Surface ◽  
Wave Theory ◽  
Order Theory ◽  
Wave Drag ◽  
Higher Order ◽  
Second Order ◽  
Two Dimensional ◽  
Third Order ◽  
Free Surface Waves ◽  
Body Shapes

The importance of non-linear free-surface effects on potential flow past two-dimensional submerged bodies is investigated by the use of higher-order perturbation theory. A consistent second-order solution for general body shapes is derived. A comparison between experimental data and theory is presented for the free-surface waves and for the wave resistance of a foil-shaped body. The agreement is good in general for the second-order theory, while the linear theory is shown to be inadequate for predicting the wave drag at the relatively small submergence treated here. It is also shown, by including the third-order freesurface effects, how the solution to the general wave theory breaks down at low speeds.

Experimental and theoretical analysis of the wave decay along a long array of vertical cylinders

2002 ◽  
Vol 456 ◽  
pp. 113-135 ◽  
Author(s):  
H. KAGEMOTO ◽  
M. MURAI ◽  
M. SAITO ◽  
B. MOLIN ◽  
š. MALENICA
Keyword(s):  
Free Surface ◽  
Numerical Model ◽  
Potential Flow ◽  
Flow Model ◽  
Numerical Code ◽  
Normal Velocity ◽  
Numerical Predictions ◽  
Head Waves ◽  
Vertical Cylinders ◽  
Potential Flow Model

A row of fifty identical, truncated vertical cylinders is submitted to regular head waves, with wave periods in a narrow range around the period of the so-called Neumann trapped mode. The free-surface elevation is measured at 14 locations along the array. Response amplitude operators of the free-surface motion are compared with numerical predictions from a potential flow model. Resonance effects, at wave periods equal to or larger than the critical one, are found to be much less than given by the numerical model. It is advocated that these discrepancies are due to dissipative effects taking place in the boundary layers at the cylinder walls. An artificial means is devised to incorporate dissipation in the potential flow model, whereby the cylinder walls are made slightly porous; the inward normal velocity of the flow is related to the dynamic pressure. The coefficient of proportionality is based on existing knowledge for circular cylinders in oscillatory flows. With this modification in the numerical code, excellent agreement is obtained with the experiments. The numerical model is further used for the case of a very long array composed of 1000 cylinders; it is found that with dissipation at the cylinder walls, the wave action steadily decreases along the array, even for wave periods substantially larger than the critical one. On the other hand, at wave periods less than the critical one, dissipation plays a negligible role; the observed decay is solely due to diffraction effects. Implications of these results for very large structures such as column-supported floating airports are discussed. In particular, it is concluded that scale effects may be an important issue in the experimental analysis of such multi-column structures.

A novel potential flow model for granular flow in two-dimensional flat-bottomed packed bed with centric discharge

2019 ◽  
Vol 342 ◽  
pp. 545-554 ◽  
Author(s):  
Chengshan Wang ◽  
Xiaojing Mu ◽  
Youyou He ◽  
Dandan Li ◽  
Yanwen Shi
Keyword(s):  
Granular Flow ◽  
Potential Flow ◽  
Flow Model ◽  
Packed Bed ◽  
Two Dimensional ◽  
Potential Flow Model
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