1. Energo Engineering, Inc.
Vessel Collisions Case Studies of an LNG Ship and an Offshore Supply Vessel
Energo Engineering, Inc.
3100 Wilcrest Drive, Suite 240
Houston, Texas
(713)
June 2004

2. 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.
Ship Collision Case Study – June 2004

3. 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
Ship Collision Case Study – June 2004

4. 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
Ship Collision Case Study – June 2004

5. 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
Ship Collision Case Study – June 2004

6. 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 (> 10 knots)
Ship Collision Case Study – June 2004

7. 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
Ship Collision Case Study – June 2004

8. Case 1 – Lightly Designed LNG Ship General View Animation
Click on the Energo logo to start animation
Ship Collision Case Study – June 2004

9. Case 1 – Lightly Designed LNG Ship Section View Animation
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Ship Collision Case Study – June 2004

10. Case 1 – Lightly Designed LNG Ship View 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.
Ship Collision Case Study – June 2004

11. Case 2 – Stronger LNG Ship Section View Animation
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Ship Collision Case Study – June 2004

12. Case 3 – Strongest LNG Ship Section View Animation
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Ship Collision Case Study – June 2004

13. 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
Ship Collision Case Study – June 2004