Offshhore Ppt

8/2/2019 Offshhore Ppt

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SUBMITTED BY-

AJENDRA SINGHMTECH IST YEAR

MPE-11002


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STABILITY Stability is the ability of a body to remain afloat

Based on the Archimedes's principle mass of the

liquid displaced by the body should be equal to themass of the vessel

For this condition the metacentre should lie above thecentre of gravity of the vessel & centre of buoyancy


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Archimedess Principle


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4

Some Definitions

Freeboard

Draft

Width

Freeboard

Draft


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Structure of Vessel Heeling


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Terminologies Draft- Depth of submerged hull

GZ-Heel lever arm

TCB-Transverse centre of bouyancy G- Location of centre of gravity

K-Keel

KMT-Transverse metacentre height above keel

KML-Longitudinal metacentre height above keel

TPI-Tonnes per inch


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Stability for a particular rig is furnishedusing a Stability Booklet which contains-:

1. Hydrostatic Properties

2. Cross curve of stability

3. Statical stability curve

4. Dynamic stability curve


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Hydrostatic Properties


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Hydrostatic properties are generated fromthe shape of underwater portion of the rigand can be used to determine the weightof rig and location of centroidlongitudinally &transversely


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Cross curve stability Cross curve stability are also generated from the

underwater portion of rig and are used by the designengineer to detemine the stability of vessel when it isnot in upright posiion

It basically shows the variation of GZ and KG


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Statical stability curve


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Statical stability curve are developed fromthe the cross curve of stability and arecurves of righting arm

They are referred to as GZ Curves


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Dynamic stability curves


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Righting Moment-Displacement multiplied by GZ

Heeling Moment-Overturning moment produced by

wind Downflooding Angle-Angle at which water will enter

the hull through an opening

Second Intercept-Second crossing of righting moment

and heel moment curves


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Other information that may found be useful but arenot considered essential are-:

1. Allowable dynamic stability KG curves

2. Damaged stability calculation3. Motion response analysis

4. Lightship characteristics


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These are generated from the dynamic stabilitycalculation. These are a growth of dynamicstability curves and they simplify the rig movers

job by eliminating need to prepare calculation ofdynamic stability every time he decides on a towcondition

Allowable dynamic stability KG curves


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Damaged Stability

If a ship floods, the loss of stability is caused by theincrease in B, the centre of buoyancy, and the loss of

waterplane area - thus a loss of the waterplane moment of

inertia - which decreases the metacentric height.Thisadditional mass will also reduce freeboard (distance from

water to the deck) and the ship's angle of down floodingangle.

These calculations show that vessel have sufficient reservestability to survive either damage or flooding


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Motion Response Analysis It is the study of rig inhovetostate This is

the positon when going on location and

results of this analysis are used to determinethe stresses induced by mooring forces etc.


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Lightship Characteristic

This is prepared from the series of accurate weightcalculation or from an inclining test or both.

From this the operator determine the condition ofrig at any time.

These are the foundation of all calculation forafloat and elevated position and an inaccurate

measurement could endanger the safety of rig.


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Stability comparision for different structures


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Conclusion Thus stability is a very important parameter that

must be taken into consideration while designing

,installing or towing a rig .For this designers andoperators have to work on peculiarities of each rig.Stability means Safety and safety can only meanmore operating time and more return on

investment


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Offshhore Ppt