Comparison of Flow Characteristics of Different Sphere Geometries Under the Free Surface Effect

The safety of underwater operation depends on the accuracy of its speed logs which depends on the location of its probe and the calibration thoroughness. Thus, probes are placed in areas where the flow of water is smooth, continuous, without high velocity gradients, air bubbles, or vortical structures. In the present work, the flow around two different submarines is numerically described in deep-water and near-surface conditions to identify hull zones where probes could be installed. First, the numerical setup of a multiphase solver supplied with OpenFOAM v7 was verified and validated using the DARPA SUBOFF-5470 submarine at scaled model including the hull and sail configuration at H/D=5.4 and Fr=0.466. Later, the grid sensitivity of the resistance was assessed for the full-scale Type 209/1300 submarine at H/D=0.347 and Fr=0.194. Free-surface effect on resistance and flow characteristics was evaluated by comparing different operational conditions. Results shows that the bow and near free-surface regions should be avoided due to high flow velocity gradient, pressure fluctuations, and large turbulent vortical structures. Moreover, free-surface effect is stronger close to the bow nose. In conclusion, the probe could be installed in the acceleration region where the local flow velocity is 15% higher than the navigation speed at surface condition. A 4% correction factor should be applied to the probe readings to compensate free-surface effect.

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Irreversible Adsorption Erases the Free Surface Effect on the Tg of Supported Films of Poly(4-tert-butylstyrene)

ACS Macro Letters ◽

10.1021/acsmacrolett.7b00129 ◽

2017 ◽

Vol 6 (4) ◽

pp. 354-358 ◽

Cited By ~ 59

Author(s):

Natalia G. Perez-de-Eulate ◽

Michele Sferrazza ◽

Daniele Cangialosi ◽

Simone Napolitano

Keyword(s):

Free Surface ◽

Surface Effect ◽

Irreversible Adsorption

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Free-surface flow simulations for discharge-based operation of hydraulic structure gates

Journal of Hydroinformatics ◽

10.2166/hydro.2013.215 ◽

2013 ◽

Vol 16 (1) ◽

pp. 189-206 ◽

Cited By ~ 13

Author(s):

C. D. Erdbrink ◽

V. V. Krzhizhanovskaya ◽

P. M. A. Sloot

Keyword(s):

Free Surface ◽

Hydraulic Structure ◽

Flow Characteristics ◽

Surface Flow ◽

Water Levels ◽

Surface Model ◽

Local Flow ◽

Gate Operation ◽

Flow Equations ◽

Flow Simulations

We combine non-hydrostatic flow simulations of the free surface with a discharge model based on elementary gate flow equations for decision support in the operation of hydraulic structure gates. A water level-based gate control used in most of today's general practice does not take into account the fact that gate operation scenarios producing similar total discharged volumes and similar water levels may have different local flow characteristics. Accurate and timely prediction of local flow conditions around hydraulic gates is important for several aspects of structure management: ecology, scour, flow-induced gate vibrations and waterway navigation. The modelling approach is described and tested for a multi-gate sluice structure regulating discharge from a river to the sea. The number of opened gates is varied and the discharge is stabilized with automated control by varying gate openings. The free-surface model was validated for discharge showing a correlation coefficient of 0.994 compared to experimental data. Additionally, we show the analysis of computational fluid dynamics (CFD) results for evaluating bed stability and gate vibrations.

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Practical Evaluation of Steady Flow Resulting from a Free-Surface Pressure Patch

Journal of Ship Research ◽

10.5957/jsr.2009.53.3.137 ◽

2009 ◽

Vol 53 (03) ◽

pp. 137-150

Author(s):

Francis Noblesse ◽

Gérard Delhommeau ◽

Chi Yang

Keyword(s):

Free Surface ◽

Surface Pressure ◽

High Speed ◽

Surface Effect ◽

Practical Method ◽

Analytical Approximation ◽

Surface Boundary ◽

Steady Flows ◽

Local Flow ◽

The Green Function

The linearized potential flow resulting from a distribution of pressure that advances at constant speed along a straight path at the free surface of calm water, of effectively infinite depth and lateral extent, is considered. A practical method for evaluating the free-surface elevation caused by the moving free-surface pressure patch—which can be used to model steady flows of air-cushion vehicles, high-speed planing boats, surface-effect ships, and some types of hybrid ships—is given. The key ingredient of this method is a highly simplified analytical approximation to the local-flow component in the expression for the Green function associated with the classic Michell-Kelvin linearized free-surface boundary condition.

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An Analysis of Heave Added Mass and Damping of a Surface-Effect Ship

Journal of Ship Research ◽

10.5957/jsr.1981.25.1.44 ◽

1981 ◽

Vol 25 (01) ◽

pp. 44-61

Author(s):

C. H. Kim ◽

S. Tsakonas

Keyword(s):

Free Surface ◽

High Speed ◽

Surface Effect ◽

Practical Method ◽

Added Mass ◽

Damping Coefficients ◽

Calm Water ◽

Surface Effect Ship ◽

Long Time ◽

Computational Procedures

The analysis presents a practical method for evaluating the added-mass and damping coefficients of a heaving surface-effect ship in uniform translation. The theoretical added-mass and damping coefficients and the heave response show fair agreement with the corresponding experimental values. Comparisons of the coupled aero-hydrodynamic and uncoupled analytical results with the experimental data prove that the uncoupled theory, dominant for a long time, that neglects the free-surface effects is an oversimplified procedure. The analysis also provides means of estimating the wave elevation of the free surface, the escape area at the stern and the volume which are induced by a heaving surface-effect ship in uniform translation in otherwise calm water. Computational procedures have been programmed in the FORTRAN IV language and adapted to the PDP-10 high-speed digital computer.

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Radiation Hydrodynamics of a Surface Effect Ship

Volume 9: Odd M. Faltinsen Honoring Symposium on Marine Hydrodynamics ◽

10.1115/omae2013-10310 ◽

2013 ◽

Author(s):

Palaniswamy Ananthakrishnan

Keyword(s):

Free Surface ◽

Large Amplitude ◽

Small Amplitude ◽

Stokes Equations ◽

Surface Effect ◽

Wave Radiation ◽

Absolute Pressure ◽

Radiation Hydrodynamics ◽

Surface Effect Ship ◽

Air Cushion

The radiation hydrodynamics of a heaving surface effect ship (SES) is examined including the effect of air compressibility on the hydrodynamic forces and surface waves. Of particular focus of the study has been on determining the nonlinear viscous and air compressibility effects at natural frequencies corresponding to the piston and sloshing wave modes between the hulls and at the natural frequency corresponding to the heave motion of a surface effect ship with the restoring force dominated by the compressibility of the air cushion. In the present paper, the air cushion pressure is assumed to be uniform with its variation due to change of volume modeled using the adiabatic gas law pVγ = constant, where p denotes the absolute pressure of the air, V the air volume bounded by the side hulls, the free surface and the wet deck, and γ the ratio of specific heats Cp/Cv which is about 1.4 for air. The incompressible Navier-Stokes equations governing the nonlinear viscous wave-air-body interaction problem is solved in the time domain using a finite-difference method based on boundary fitted coordinates. New results presented in this paper show that air cushion compressibility affects the generation of waves and wave radiation forces significantly even at small amplitude of hull motion. As already well known, the free surface nonlinearity due to hull motion is significant for large amplitude of oscillation. At small amplitude of body oscillation, significant nonlinearity can be caused by air compressibility resulting in the generation of higher harmonic waves and forces. The results also highlight the significance of viscosity and flow separation, in conjunction with air compressibility, in the case of large amplitude hull motion with a small draft.

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Comparison of Single and Overset Grid Techniques for CFD Simulations of a Surface Effect Ship

Volume 2: CFD and VIV ◽

10.1115/omae2014-24207 ◽

2014 ◽

Cited By ~ 2

Author(s):

Colton G. Clark ◽

David G. Lyons ◽

Wayne L. Neu

Keyword(s):

Free Surface ◽

Surface Effect ◽

The Body ◽

Computational Domain ◽

Overset Grid ◽

Hexahedral Mesh ◽

Surface Effect Ship ◽

Mesh Resolution ◽

Refined Meshes ◽

Air Cushion

Overset, or Chimera meshes are used to discretize the governing equations within a computational domain using multiple meshes that overlap in an arbitrary manner. The overset mesh technique is most applicable to problems dealing with multiple or moving bodies. In order to extend existing full craft CFD (RANS) simulations of a surface effect ship (SES) into shallow water and maneuvering cases, an overset mesh is needed. Deep water simulations were carried out using both single and overset grid techniques for evaluation of the overset grid application. The single grid technique applies a hexahedral mesh to the fluid domain and SES geometry. An adequate mesh resolution was determined by performing a grid convergence study on a series of systematically refined meshes. An overset mesh of the same resolution was then constructed and was fixed to the body. Drag and pitch results are compared among the two simulations. Free surface elevations around the craft and under the air cushion for simulations with the single and overset meshes are compared. Steady-state simulations using the overset mesh and the single mesh show general similarities in drag, pitch, and free surface elevations.

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