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Ship Loads and stresses
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ship construction chapter 2.
ship stresses

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Ship stresses

  1. 1. SHIP STRESSESSHIP STRESSES Rishi Piravin Anmol Agilan Arief Immanuel
  2. 2. What is stress andWhat is stress and strain?strain? • STRESS – Is defined as the load put on a piece of material or a structure • STRAIN – Is defined as the permanent deformity or weakness caused by excessive stress
  3. 3. There are 3 main types of stress: •Tensile / Tensioning •Compressive / Compression •Shear
  4. 4. Tensioning Compression tendency to pull the material apart tendency to crush the material or to buckle
  5. 5. Shear Shear is the effect of two forces actingShear is the effect of two forces acting in opposite directions and alongin opposite directions and along parallel lines.parallel lines.
  6. 6. Mechanical Properties of Metals Elasticity - The case with which a metal may be bent or molded into a given shape. Brittleness - The opposite of plasticity, lack or elasticity Malleability - The property possessed by a metal of becoming permanently flattened or stretched.
  7. 7. Hardness - The property of a metal to resist wear and abrasion. Fatigue - A metal subjected to continually varying loads may eventually suffer from fatigue. Ductility - Ability to be drawn out lengthwise, the amount of the extension measures the ductility.
  8. 8. Brittle Fracture • Low temperatures at or near freezing points, •Load on material relatively light, •Defects or faults in a weld •Internal stresses within material ie. welding may initiate a fracture.
  9. 9. The ship at sea or lying in still water isThe ship at sea or lying in still water is constantly being subjected to a wideconstantly being subjected to a wide variety of stresses and strains, whichvariety of stresses and strains, which result from the action of forces fromresult from the action of forces from outside and within the ship.outside and within the ship. These forces may initially be classified into:These forces may initially be classified into: STATIC FORCESSTATIC FORCES DYNAMIC FORCESDYNAMIC FORCES
  10. 10. STATIC FORCESSTATIC FORCES These are due to • Internal forces resulting from structural weight, cargo and machinery weight. • External static forces including the hydrostatic pressure of the water on the hull.
  11. 11. Vessel at rest Static forceStatic force
  12. 12. DYNAMICDYNAMIC FORCESFORCES They result from • The ship’s motion at sea. • The action of wind and waves. • The effects of operating machinery.
  13. 13. Dynamic ForcesDynamic Forces • A ship is free to move about six degrees of freedom. • Three linear and three rotational. • Various forces acting on ship are constantly varying in degree and frequency. • This movement of the ship introduces dynamic forces which result in stresses on the ship’s structure.
  14. 14. • Heave is the motion of the ship when the ship have being up by a wave or sea. • Sway is the swing of a mast or bow of a ship from side to side as the vessel progresses in a heavy sea. • Surge is the movement forward as the bow of a ship rises and dips when it encounter waves which are strong enough to life it. The ship surge up the side of a wave, often shipping water as it passes through the crest, then dips down the other side of the wave.
  15. 15. • Pitch is the motion of a ship in rising the crest of a wave then descending into the following trough. • Roll is the motion of a ship from side to side as she moves through the water. • Yaw is where the bow of a ship falls away or sways erratically from side to side as the vessel moves through the water.
  16. 16. Forces produce stresses in the ship’sForces produce stresses in the ship’s structure which may be divided into twostructure which may be divided into two categories:categories: •Global stress – affects the whole ship •Local stress- affects a particular part of a ship
  17. 17. HOGGINGHOGGING • Hogging is when the ship bends upwards longitudinally. This occurs when there is more weight concentrated at the ends due to uneven cargo distribution or when the vessel rides a wave crest in its middle, causing excessive buoyancy.
  18. 18. SAGGINGSAGGING • Sagging is the reverse of hogging when the ship bends longitudinally in the downwards direction. This occurs when there is more weight concentrated in the mid length of the vessel due to uneven cargo distribution or when the vessel rides a wave trough in its middle causing excessive buoyancy at the ends.
  19. 19. RACKINGRACKING • When a ship is rolling, the accelerations on the ship’s structure are liable to cause distortion in the transverse section. • Greatest effect is under light ship condition.
  20. 20. TORSIONTORSION • A ship traversing a wave train at angle will be subject to righting moments of opposite directions at its ends. • The hull is subject to a twisting moment and the structure is in torsion.
  21. 21. STRESSES DUE TOSTRESSES DUE TO WATER PRESSUREWATER PRESSURE • Water pressure acts perpendicular to the surface and increases with depth
  22. 22. STRESSES DUE TOSTRESSES DUE TO DRY-DOCKINGDRY-DOCKING • Tends to set the keel upwards. • Due to the up-thrust of the keel blocks. • Tendency for the ship’s sides to bulge outwards. • Bilges tend to sag.
  23. 23. PANTINGPANTING • This is a stress, which occurs at the ends of a vessel due to variations in water pressure on the shell plating as the vessel pitches in a seaway. The effect is accentuated at the bow when making headway DMS-DO
  24. 24. Stresses caused by localized loadingStresses caused by localized loading Localized heavy loads may give rise to localized distortion of the transverse section. Such local loads may be the machinery (Main engine) in the engine room or the loading of concentrated ore in the holds.
  25. 25. Pounding Effect: 0.25L of the bow/stern Pounding due to heavy pitching as the whole ship is lifted in a seaway may be subject the forepart to severe impact from the sea. It gives greatest effect when in light condition. About 30% from forward strengthened.
  26. 26. Deck opening creates areas of high local stress due to lack of continuity of Structure
  27. 27. Thank you and haveThank you and have a great daya great day everyone!everyone! 
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ship construction chapter 2. ship stresses


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