Vessel Collisions Case Studies of an LNG Ship and an Offshore Supply Vessel

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Vessel CollisionsCase Studies of an LNG Ship
and an Offshore Supply Vessel

• Energo Engineering, Inc.
• 3100 Wilcrest Drive, Suite 240
• Houston, Texas 77042
• [phone]
• www.energoeng.com

June 2004
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Summary

• This presentation shows examples of an advanced
  structural analysis used to determine the
  potential damage caused by ship-to-ship
  collisions.
• The presentation demonstrates that vessel
  collision studies need to account for the
  specific geometry and strength of the colliding
  vessels. The typically used empirical
  relationships can be misleading and wrong.
• In this example case an LNG ship is struck by an
  Offshore Supply Vessel (OSV). The LNG ship could
  also be an offshore LNG terminal Floating or
  Gravity Base.

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Objectives

• This type of analysis are useful in defining data
  needed for risk studies as well as LNG ship or
  LNG terminal design.
• This includes
• Critical speed of impact that breaches the ship
  outer hull and containment (e.g., LNG, oil,
  chemical)
• Size of containment breach hole needed for
  consequence analyses
• Specific vessels that are of concern some
  vessels do not penetrate the containment
• Areas of the ship that can be improved in design
  to prevent excessive collision damage

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Characteristics of Collisions

• Collisions are a complex nonlinear, dynamic
  impact problem
• The examples shown are state-of-the-art and
  account for
• Hull damage to the LNG ship
• Bow crushing of the striking vessel
• Energy dissipation via global motions of the LNG
  and striking vessel
• The structural models account for this by
  considering
• Multiple contact surfaces
• Contact friction
• Material and geometric nonlinearity
• Material failure
• Strain rate dependency

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Ship Specific Controlling Factors

• The following factors are accounted for in the
  examples shown
• Traveling speed
• Vessel draft and weight (LNG and striking vessel)
• Striking angle
• Initial impact location
• These can be varied from case to case to
  represent typical field conditions

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Example Cases - Background

• Three example collision cases are shown
• Specifics are as follows
• Struck Vessel Typical LNG ships (or FSRU or
  GBS) considering light and strong designs
• Striking Vessel 6600 BHP OSV, LOA 85 m, Beam 19
  m
• Striking angles 45 degrees and 90 degrees
• High striking speed (gt 10 knots)

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Example Cases

• Case 1 45 degrees Lightly Designed LNG ship
• The LNG outer hull and containment is breached
• Case 2 45 degrees Stronger Designed LNG Ship
• The LNG outer hull is breached but not the LNG
  containment
• Case 3 90 degrees Strongest Designed LNG Ship
• The OSV bow crushes and there is localized breach
  of the LNG side shell but not the LNG containment
• This is the preferred design configuration

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Case 1 Lightly Designed LNG ShipGeneral View
Animation
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Case 1 Lightly Designed LNG ShipSection View
Animation
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Case 1 Lightly Designed LNG ShipView of the
Containment Hole
View is looking from outboard the LNG
ship. Black portion of the damaged area is the
resulting hole in the LNG containment.
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Case 2 Stronger LNG ShipSection View Animation
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Case 3 Strongest LNG Ship Section View Animation
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Conclusions

• Ship-to-ship collisions are very dependant upon
  many factors including the specific ship
  geometries
• Empirical approaches can result in inaccurate
  findings
• Detailed engineering analysis, as shown here, is
  the most accurate approach
• This approach can be used to provide input to
• Ship or LNG terminal design in terms of optimum
  bulkheads and scantlings to limit collision
  damage
• Risk studies in terms of types of ships of
  concern and critical impact speeds
• Consequence studies in terms of containment hole
  sizes (if any) and associated shape