Radiation Hydrodynamics of a Surface Effect Ship

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.

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

2014 ◽  
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.

Finite Element Contact/Impact Modeling Capability of Complex Surface Effect Ship Dynamics: Preliminary Assessment

2013 ◽  
Author(s):  
Ravi Challa ◽  
David Newborn ◽  
Solomon Yim
Keyword(s):  
Finite Element ◽  
Free Surface ◽  
Numerical Simulations ◽  
Water Surface ◽  
Large Scale ◽  
Surface Effect ◽  
Numerical Models ◽  
Channel Water ◽  
Surface Effect Ship ◽  
Air Cushion

Experimental tests were conducted on a large scale captive Surface Effect Ship (SES) specimen at the US Navy’s Large Cavitation Channel (LCC) to primarily determine the mechanics of bow finger seal motions. In this paper, preliminary qualitative comparisons between the experimental and numerical simulations comprised of test dependent variables such as spatially distributed channel water elevation, channel water speed and air-cushion pressure are presented. A surface effect ship is an air-cushion supported vessel with two side hulls and fore and aft flexible seals. The side hulls of the SES along with the wet deck, seals and the fluid-water surface constitute the boundary of the air-cushion. An evaluation of the predictive capabilities of the existing technology of a state-of-the-art nonlinear multi-physics finite element code (LS-DYNA) with its arbitrary Lagrangian Eulerian (ALE) technique in modeling the coupled fluid-structure interaction (FSI) behavior of the boundary of a SES with the water surface is studied. The predictive capability of the code to model a single stern seal deployment, a single seal impacting a rigid flat surface, multiple seals impacting a water free surface and the centerline profile of multiple stern seal deployment between two rigid surfaces were verified. Simple numerical models for a five-finger bow seal with partial submergence in uniform current have been developed. Additional features including the mechanism to pressurize the air cushion chamber were included. Preliminary finite element (FE) simulation results show that the robust contact and impact algorithm is shown to capture the physics of the complex flexible body FSI problem well. In view of the good qualitative comparison between the experimental and numerical simulations, the ALE feature is being employed for studying the complex flexible structural mechanics including bow and stern seal motions interacting with air cushion and free-surface hydrodynamics.

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

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.

scholarly journals Roll damping of a surface effect ship with split air cushion

2018 ◽  
Vol 51 (29) ◽  
pp. 450-456
Author(s):  
Jonas Tønnessen ◽  
Håkon E. Bryn ◽  
Jan T. Gravdahl ◽  
Vahid Hassani ◽  
Øyvind F. Auestad
Keyword(s):  
Surface Effect ◽  
Roll Damping ◽  
Surface Effect Ship ◽  
Air Cushion

Air Cushion Vehicles and Surface Effect Ships for Great Lakes and Great Rivers Transportation

1990 ◽  
Vol 27 (06) ◽  
pp. 337-355
Author(s):  
John L. Allison
Keyword(s):  
Great Lakes ◽  
Surface Effect ◽  
Coast Guard ◽  
Rapid Expansion ◽  
Short Paper ◽  
Surface Effect Ship ◽  
Present Design ◽  
Air Cushion ◽  
Hull Forms ◽  
The U.S

A brief introduction to air cushion vehicle (ACV) and surface effect ship (SES) technology is presented, with past and present examples, to show that this technology may now be considered mature. Applicability of ACVs and SESs to transportation on the Great Lakes and rivers of Canada and the U.S. is discussed, with some emphasis on year-round service in the regions affected by ice. An indication of present design capabilities is provided with some examples of application to typical sets of requirements. Future developments are outlined in the light of the rapid expansion of air-supported ferry operation in other parts of the world, and military and Coast Guard applications in the U.S. and Canada. Some data on acquisition and operating costs are presented in comparison with those for other hull forms, with information on the type of technical and port support required for ACV and SES operation. Numerous references are provided to enable the reader to pursue the topics discussed in greater detail than is possible in a short paper.

Flow along a horizontal plate near a free surface

1993 ◽  
Vol 252 ◽  
pp. 399-418
Author(s):  
Milan Hofman
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
Flat Plate ◽  
Viscous Liquid ◽  
Gravity Waves ◽  
Asymptotic Expansions ◽  
Small Amplitude ◽  
Surface Effect ◽  
Matched Asymptotic Expansions ◽  
Horizontal Plate

The problem of flow along a horizontal semi-infinite flat plate moving in its own plane through a viscous liquid just below the free surface is considered. The method of matched asymptotic expansions is used to analyse the interaction between the free surface and the boundary layer formed on the plate. It is found that, due to viscosity, small-amplitude gravity waves on the free surface can be formed. The formulae for the resistance of the plate containing the free-surface effect and for the lift, appearing as a new phenomenon, are derived.

scholarly journals The Motion of a Point Vortex near Large-Amplitude Topography in a Two-Layer Fluid

2004 ◽  
Vol 34 (12) ◽  
pp. 2808-2824 ◽  
Author(s):  
Andrew J. White ◽  
N. Robb McDonald
Keyword(s):  
Dispersion Relation ◽  
Linear Theory ◽  
Large Amplitude ◽  
Small Amplitude ◽  
Lower Layer ◽  
Point Vortex ◽  
Step Change ◽  
Wave Radiation ◽  
Contour Dynamics ◽  
Analytic Expression

Abstract This work examines the dynamics of point vortices in a two-layer fluid near large-amplitude, sharply varying topography like that which occurs in continental shelf regions. Topography takes the form of an infinitely long step change in depth, and the two-layer stratification is chosen such that the height of topography in the upper layer is a small fraction of the overall depth, enabling quasigeostrophic theory to be used in both layers. An analytic expression for the dispersion relation of free topographic waves in this system is found. Weak vortices are studied using linear theory and, if located in the lower layer, propagate mainly because of their image in the topography. Depending on their sign, they are able to produce significant topographic wave radiation in their wakes. Upper-layer vortices propagate much slower and produce relatively small amplitude topographic wave radiation. Contour dynamics results are used to investigate the nonlinear regions of parameter space. For lower-layer vortices, linear theory is a good approximation, but for upper-layer vortices complicated features evolve and linear theory is only valid for weak vortices.

Multihull and Surface-Effect Ship Configuration Design: A Framework for Powering Minimization

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Ronald W. Yeung ◽  
Hui Wan
Keyword(s):  
High Speed ◽  
Surface Effect ◽  
Early Stage ◽  
Base Line ◽  
Total Displacement ◽  
Surface Effect Ship ◽  
Linearized Theory ◽  
Air Cushion ◽  
New Formula ◽  
Analytical Expressions

The powering issue of a high-speed marine vehicle with multihulls and air-cushion support is addressed, since there is an often need to quickly evaluate the effects of several configuration parameters in the early stage of the design. For component hulls with given geometry, the parameters considered include the relative locations of individual hulls and the relative volumetric ratios. Within the realm of linearized theory, an interference-resistance expression for hull-to-hull interaction is first reviewed, and then a new formula for hull-and-pressure distribution interference is derived. Each of these analytical expressions is expressed in terms of the Fourier signatures or Kochin functions of the interacting component hulls, with the separation, stagger, and speed as explicit parameters. Based on this framework, an example is given for assessing the powering performance of a catamaran (dihull) as opposed to a tetrahull system. Also examined is the wave resistance of a surface-effect ship of varying cushion support in comparison with that of a base line catamaran, subject to the constraint of constant total displacement.

Disturbance Induced by a Pressure Distribution Moving Over a Free Surface

1970 ◽  
Vol 14 (03) ◽  
pp. 195-203
Author(s):  
T. T. Huang ◽  
K. K. Wong
Keyword(s):  
Free Surface ◽  
Pressure Distribution ◽  
Surface Effect ◽  
Surface Profile ◽  
Wave Theory ◽  
Local Flow ◽  
Closed Form Solutions ◽  
Pressure Trace ◽  
Surface Effect Ship ◽  
Free Surface Profile

This paper uses the linearized water-wave theory to analyze the disturbances induced by a constant pressure distribution with a rectangular planform moving over calm water. The methods developed, however, can be applied to other pressure distributions. Numerical schemes and computation results for typical speeds and beam/length ratios are presented for the pressure trace on the sea floor when the water depth is finite and the local flow pattern when the depth is infinite. For shallow waters, closed-form solutions for both the pressure trace and free-surface profile are obtained. A surface-effect ship acts like a moving pressure distribution as far as the induced disturbances in the water are concerned. Thus, the results of the present study may be useful for the design of surface-effect ships.

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