Title: Vessel Collisions Case Studies of an LNG Ship and an Offshore Supply Vessel
1Vessel CollisionsCase Studies of an LNG Ship
and an Offshore Supply Vessel
- Energo Engineering, Inc.
- 3100 Wilcrest Drive, Suite 240
- Houston, Texas 77042
- (713) 532-2900
- www.energoeng.com
June 2004
2Summary
- 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.
3Objectives
- 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
4Characteristics 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
5Ship 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
6Example 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)
7Example 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
8Case 1 Lightly Designed LNG ShipGeneral View
Animation
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9Case 1 Lightly Designed LNG ShipSection View
Animation
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10Case 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.
11Case 2 Stronger LNG ShipSection View Animation
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12Case 3 Strongest LNG Ship Section View Animation
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13Conclusions
- 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