laminar flow. a core concept of the hwss is that a streamlined body passing through water generates...
TRANSCRIPT
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