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Ship Loads and stresses

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

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Ship Loads and stresses

  1. 1. DMS-DODMS-DO 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
  2. 2. DMS-DO With the aid of diagrams, describe theWith the aid of diagrams, describe the various types of deformations in shipvarious types of deformations in ship structures due to external forces andstructures due to external forces and classify them as due to Static or Dynamicclassify them as due to Static or Dynamic forces.forces.
  3. 3. DMS-DO The ship at sea or lying in still water is constantly beingThe ship at sea or lying in still water is constantly being subjected to a wide variety of stresses and strains, whichsubjected to a wide variety of stresses and strains, which result from the action of forces from outside and withinresult 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 FORCES DYNAMIC FORCESDYNAMIC FORCES
  4. 4. DMS-DO STATIC FORCESSTATIC FORCES These are due toThese are due to  Internal forces resulting from structural weight, cargoInternal forces resulting from structural weight, cargo and machinery weight.and machinery weight.  External static forces including the hydrostaticExternal static forces including the hydrostatic pressure of the water on the hull.pressure of the water on the hull.
  5. 5. DMS-DO 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.
  6. 6. DMS-DO DEGREES OF FREEDOMDEGREES OF FREEDOM  A ship is free to moveA ship is free to move about six degrees ofabout six degrees of freedom.freedom.  Three linear and threeThree linear and three rotational.rotational.  Various forces acting onVarious forces acting on ship are constantlyship are constantly varying in degree andvarying in degree and frequency.frequency.  This movement of theThis movement of the ship introducesship introduces dynamic forces whichdynamic forces which result in stresses on theresult in stresses on the ship’s structure.ship’s structure.
  7. 7. DMS-DO HOGGINGHOGGING  Wave crest at mid-ships, buoyancyWave 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 inThis loading condition will result in a significantly increased bendinga significantly increased bending moment.moment.  This causes the ship to hog.This causes the ship to hog.  Extreme condition giving maximumExtreme condition giving maximum bending moment in a ship’sbending moment in a ship’s structure.structure.  This is a result of Dynamic forces.This is a result of Dynamic forces.
  8. 8. DMS-DO 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 resultThis loading condition will result in a significantly increasedin 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.
  9. 9. DMS-DO RACKINGRACKING  When a ship rolls, it results inWhen a ship rolls, it results in forces tending to distort itforces tending to distort it transversely.transversely.  This may cause deformation atThis may cause deformation at corners.corners.  Deck tends to move laterallyDeck tends to move laterally relative to bottom structure.relative to bottom structure.  Shell on one side tends to moveShell 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 isGreatest effect felt when ship is in light or ballast condition.in light or ballast condition.  This is a result of DynamicThis is a result of Dynamic forces.forces.
  10. 10. DMS-DO TORSIONTORSION  When a ship is subjected to aWhen a ship is subjected to a twisting moment, it is said totwisting moment, it is said to be in Torsion.be in Torsion.  Ship heading obliquely(45Ship heading obliquely(45 degrees) to a wave will bedegrees) to a wave will be subjected to rightingsubjected to righting moments of oppositemoments of opposite direction at its ends.direction at its ends.  This tends to twist the hullThis tends to twist the hull putting it in Torsion.putting it in Torsion.  This is a result of DynamicThis is a result of Dynamic forces.forces.
  11. 11. DMS-DO STRESSES DUE TOSTRESSES DUE TO WATER PRESSUREWATER PRESSURE  Water pressure increasesWater pressure increases with depth and tends to setwith depth and tends to set in the ship’s plating belowin the ship’s plating below the water line.the water line.  Transverse section of a shipTransverse section of a ship is subjected to static pressureis subjected to static pressure from the surrounding water.from the surrounding water.  Considerable distortion ofConsiderable distortion of structure can occur instructure can occur in absence of adequateabsence of adequate stiffening.stiffening.  This is a result of StaticThis is a result of Static forces.forces.
  12. 12. DMS-DO STRESSES DUE TOSTRESSES DUE TO DRY-DOCKINGDRY-DOCKING  Tends to set the keelTends to set the keel upwards.upwards.  Due to the up-thrust of theDue to the up-thrust of the keel blocks.keel blocks.  Tendency for the ship’s sidesTendency for the ship’s sides to bulge outwards.to bulge outwards.  Bilges tend to sag.Bilges tend to sag.  This is a result of StaticThis is a result of Static forces.forces.
  13. 13. DMS-DO SLAMMING OR POUNDINGSLAMMING OR POUNDING  While heaving or pitching, the forward end leaves and re-entersWhile 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 waterFlat 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 impartedMomentum 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 DynamicThis is also known as pounding and is a result of Dynamic forces.forces.
  14. 14. DMS-DO SLAMMINGSLAMMING
  15. 15. DMS-DO SLAMMING OR POUNDINGSLAMMING OR POUNDING
  16. 16. DMS-DO PANTINGPANTING  Movement of waves along a shipMovement of waves along a ship causes fluctuations in watercauses 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 shellout movement of the shell plating, known as panting.plating, known as panting.  Effect is particularly evident atEffect is particularly evident at the bows as the ship pushes itsthe bows as the ship pushes its way through the water.way through the water.  Pitching motion of the shipPitching motion of the ship produces additional variationsproduces additional variations in water pressure, particularlyin water pressure, particularly at the bow and stern, which alsoat the bow and stern, which also causes panting of the plating.causes panting of the plating.

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