LAMINAR FLOW

• A Core Concept of the HWSS is that a streamlined body passing through water generates a smooth laminar flow without creating turbulence in the form of eddy vortexes. Vortexes reduce speed and create cavitation.

• A streamlined body here consists of hydrodynamically shaped hulls/pontoons and tower columns in the water.

• This factor is best expressed in the drag co-efficient formula; lower being better. The HWSS has a much lower drag co-efficient than conventional 6th generation semi submersibles or other conventionally shaped ships.

• This enables the vessel to work in much more extreme marine environments as the rough seas & high winds associated with bad weather pass around the HWSS because the vortex fields, cavitation and turbulent flows are greatly reduced & lessened.

Any object moving through a fluid experiences drag - the net force in the direction of flow due to pressure and shear stress forces on the surface of the object.

Drag force can be expressed as:

Fd = cd 1/2 ρ v2 A

where

Fd = drag force (N)

cd = drag coefficient

ρ = density of fluid (1.2 kg/m3 for air at NTP)

v = flow velocity

A = characteristic frontal area of the body

The drag coefficient is a function of several parameters like shape of the body, Reynolds Number for the flow,Froude number, Mach Number and Roughness of the Surface.

The characteristic frontal area - A - depends on the body.

Any object moving through a fluid experiences drag - the net force in the direction of flow due to pressure and shear stress forces on the surface of the object.

Drag force can be expressed as:

Fd = cd 1/2 ρ v2 AwhereFd = drag force (N)cd = drag coefficientρ = density of fluid (1.2 kg/m3 for air at NTP)v = flow velocityA = characteristic frontal area of the bodyThe drag coefficient is a function of several parameters like shape of the body, Reynolds Number for the flow,Froude number, Mach Number and Roughness of the Surface.The characteristic frontal area - A - depends on the body.

3 stages of flow around a foil1. Laminar 2. Transitional 3. Turbulent

Turbulent Vortex field behind a conventional ship.

6th Gen Semi-submersible: ‘Brick’ Pontoon & Square Column

Detail of ‘Brick’ Pontoon

6th generation semisubmersible; bow pontoon & column

Note K-bracing at pontoon level

Note square shape of column

Note “Rounded-off brick” shape of bow

Vortex field on semi-submersible with bow submerged

Semi submerged, note vortex field

SSBN 598 George Washington

SS-580 Barbel