Cobblestone effect on surface effect ship (SES)

Dear Friends,

I am naval architecture and recently in a project to design a surface effect ship (SES), I come across to the problem of cobblestone phenomena.
This is a phenomenon which must be pay attention in design step. I searched around and couldn't find enough information on this specifically.

My understanding is that cobblestone phenomena have two aspects: Dynamic and control which should be study carefully in design step.
Would you please advice me, first to understand this phenomena and second to consider the best design and devices to minimize this effect.

I am looking forward to your reply
Best regards and


Ahmad

 

first time i hear this term and looked it up http://www.google.nl/search?hl=nl&s...oogle zoeken&meta=&rlz=1R2GGIE_nl&aq=null&oq=

"The concept of a surface effect ship (SES) is to lift the hull partly by the air cushion enclosed within two side hulls, a bow skirt and a stern seal. Consequently, it results in lower draft, resistance and motions than equivalent length catamarans in most sea states. In very low sea states, however, there is a significant design problem, which is high vertical accelerations, referred to as the cobblestone effect. The oscillations are based on resonance phenomena and are caused by the change of the cushion volume due to the incident waves. The resonance oscillations have an important damping mechanism which is derived from the air leakage flow under the stern seal bag of a SES. Hence, the accurate prediction of the leakage flow is required for the estimation of the cobblestone effect. In order to solve the unsteady flow field under the stern seal bag, a viscous flow code for numerically simulating two-dimensional incompressible flows has been developed. The governing equations to be solved are the time-dependent Navier–Stokes equations, using the artificial compressibility approach. The spatial discretization is based on a cell-centred finite volume formulation. The inviscid fluxes are evaluated by Roe's scheme with the third-order-accurate MUSCL approach. Time integration is conducted by the second-order accurate backward Euler formula and the linear equation system is solved by an approximate Newton relaxation scheme with the symmetric Gauss–Seidel iteration approach. For the resulting time integration to be conservative on a moving grid system, a geometric conservation law is introduced. A numerical procedure is presented and contributions of the viscous effects to the cobblestone effect problem are discussed."

 

Ya, what he said.

 

In addition, the frequency of the pressure oscillations within the cushion have been occurring in frequency bands that cause resonance within the physical structure of the vessel. Thus the cobblestone effect is of concern, not only in terms of personal comfort, but also because of possible fatigue breakdown in structural components.

 

Bill McFann of Island Engineering posts as BMcF here on the forum. He has talked little about cobblestoning in his posts (an expert).

Do search on his user name and also see what you can pick up off the www.foils.org site.

Bill's Website:
http://www.islandengineering.com/

 

Also, search for papers on the cobblestone effect by Prof. Odd Faltinsen.

 

SES seems to have problems my SSE does not.

Interesting discussion on problems with SES designed ships that may need to be upgraded to have the FINS in my invention - where a boat or a Ship was not designed to use the SSE "Superior Surface Effects Technologies solutions that Superior hulls has developed and owns.

As you can see from my picture, a deep V cruiser is lifted to run on it keel just by installing the Fins to make it fly with more comfort ride - more revolutionary then the Deep V invention, as time will show, as I get older...

 

The so-called 'cobblestone effect' associated with SES has been understood well for many years now and has not been a 'problem' for a very long time. The fundamental heave resonance and longitudinal acoustic resonances are dealt with effectively through a combination of proper design details and active damping.

Comparing an SES to a foil-assisted planing hull is very much apples and oranges, btw.