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SHIP LOADS AND STRESSESSHIP LOADS AND STRESSES

GROUP B:GROUP B:

Bhullar Kunwar Puneet SinghBhullar Kunwar Puneet Singh

Krishnan PrashantKrishnan Prashant

Kulhari SundeepKulhari Sundeep

Mahadik RohanMahadik Rohan

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With the aid of diagrams, describe theWith the aid of diagrams, describe thevarious types of deformations in shipvarious types of deformations in shipstructures due to external forces andstructures due to external forces and

classify them as due to Static or Dynamic classify them as due to Static or Dynamic forces.forces.

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The ship at sea or lying in still water is constantly being The ship at sea or lying in still water is constantly being subjected to a wide variety of stresses and strains, which subjected to a wide variety of stresses and strains, which result from the action of forces from outside and within result from the action of forces from outside and within

the ship.the ship.

These forces may initially be classified intoThese forces may initially be classified into

STATIC FORCESSTATIC FORCESDYNAMIC FORCES DYNAMIC FORCES

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STATIC FORCESSTATIC FORCES

These are due to These are due to

Internal forces resulting from structural weight, cargo Internal forces resulting from structural weight, cargo and machinery weight.and machinery weight.

External static forces including the hydrostatic External static forces including the hydrostatic pressure of the water on the hull.pressure of the water on the hull.

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DYNAMICDYNAMIC FORCESFORCES

They result fromThey result from

The ship’s motion at sea.The ship’s motion at sea. The action of wind and waves.The action of wind and waves. The effects of operating machinery.The effects of operating machinery.

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DEGREES OF FREEDOMDEGREES OF FREEDOM A ship is free to move A ship is free to move

about six degrees of about six degrees of freedom.freedom.

Three linear and three Three linear and three rotational.rotational.

Various forces acting on Various forces acting on ship are constantly ship are constantly varying in degree and varying in degree and frequency.frequency.

This movement of the This movement of the ship introduces ship introduces dynamic forces which dynamic forces which result in stresses on the result in stresses on the ship’s structure.ship’s structure.

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HOGGINGHOGGING

Wave crest at mid-ships, buoyancy Wave crest at mid-ships, buoyancy in this region is increased.in this region is increased.

Wave trough at the ends of the ship, Wave trough at the ends of the ship, buoyancy is reduced.buoyancy is reduced.

This loading condition will result in This loading condition will result in a significantly increased bending a significantly increased bending moment.moment.

This causes the ship to hog.This causes the ship to hog. Extreme condition giving maximum Extreme condition giving maximum

bending moment in a ship’s bending moment in a ship’s structure.structure.

This is a result of Dynamic forces.This is a result of Dynamic forces.

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SAGGINGSAGGING

Wave trough at mid-ships, Wave trough at mid-ships, buoyancy in this region is reduced.buoyancy in this region is reduced.

Wave crest at the ends of ship, Wave crest at the ends of ship, buoyancy is increased.buoyancy is increased.

This loading condition will result This loading condition will result in a significantly increased in a significantly increased bending moment.bending moment.

This causes the ship to sag.This causes the ship to sag. This is a result of Dynamic forces.This is a result of Dynamic forces.

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RACKINGRACKING

When a ship rolls, it results in When a ship rolls, it results in forces tending to distort it forces tending to distort it transversely.transversely.

This may cause deformation at This may cause deformation at corners.corners.

Deck tends to move laterally Deck tends to move laterally relative to bottom structure.relative to bottom structure.

Shell on one side tends to move Shell on one side tends to move vertically relative to other side.vertically relative to other side.

This is termed racking.This is termed racking. Greatest effect felt when ship is Greatest effect felt when ship is

in light or ballast condition.in light or ballast condition. This is a result of Dynamic This is a result of Dynamic

forces.forces.

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TORSIONTORSION

When a ship is subjected to a When a ship is subjected to a twisting moment, it is said to twisting moment, it is said to be in Torsion.be in Torsion.

Ship heading obliquely(45 Ship heading obliquely(45 degrees) to a wave will be degrees) to a wave will be subjected to righting subjected to righting moments of opposite moments of opposite direction at its ends. direction at its ends.

This tends to twist the hull This tends to twist the hull putting it in Torsion.putting it in Torsion.

This is a result of Dynamic This is a result of Dynamic forces.forces.

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STRESSES DUE TO STRESSES DUE TO WATER PRESSUREWATER PRESSURE

Water pressure increases Water pressure increases with depth and tends to set with depth and tends to set in the ship’s plating below in the ship’s plating below the water line.the water line.

Transverse section of a ship Transverse section of a ship is subjected to static pressure is subjected to static pressure from the surrounding water. from the surrounding water.

Considerable distortion of Considerable distortion of structure can occur in structure can occur in absence of adequate absence of adequate stiffening.stiffening.

This is a result of Static This is a result of Static forces.forces.

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STRESSES DUE TO STRESSES DUE TO DRY-DOCKINGDRY-DOCKING

Tends to set the keel Tends to set the keel upwards.upwards.

Due to the up-thrust of the Due to the up-thrust of the keel blocks.keel blocks.

Tendency for the ship’s sides Tendency for the ship’s sides to bulge outwards.to bulge outwards.

Bilges tend to sag.Bilges tend to sag. This is a result of Static This is a result of Static

forces.forces.

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SLAMMING OR POUNDINGSLAMMING OR POUNDING While heaving or pitching, the forward end leaves and re-enters While heaving or pitching, the forward end leaves and re-enters

the water with a slamming effect.the water with a slamming effect. Flat areas of plating are brought into violent contact with water Flat areas of plating are brought into violent contact with water

at a very acute angle.at a very acute angle. There is a loud bang and the ship shudders.There is a loud bang and the ship shudders. Momentum of the ship receives a check and energy is imparted Momentum of the ship receives a check and energy is imparted

to the ship girder to make it vibrate.to the ship girder to make it vibrate. This is also known as pounding and is a result of Dynamic This is also known as pounding and is a result of Dynamic

forces.forces.

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SLAMMINGSLAMMING

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SLAMMING OR POUNDINGSLAMMING OR POUNDING

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PANTINGPANTING Movement of waves along a ship Movement of waves along a ship

causes fluctuations in water causes fluctuations in water pressure on the plating.pressure on the plating.

This tends to create an in-and-This tends to create an in-and-out movement of the shell out movement of the shell plating, known as panting.plating, known as panting.

Effect is particularly evident at Effect is particularly evident at the bows as the ship pushes its the bows as the ship pushes its way through the water. way through the water.

Pitching motion of the ship Pitching motion of the ship produces additional variations produces additional variations in water pressure, particularly in water pressure, particularly at the bow and stern, which also at the bow and stern, which also causes panting of the plating.causes panting of the plating.