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

Vessel Collisions Case 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. Summary.

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

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  1. Vessel 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

  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 ShipGeneral View Animation Click on the Energo logo to start animation Ship Collision Case Study – June 2004

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

  10. 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. Ship Collision Case Study – June 2004

  11. Case 2 – Stronger LNG ShipSection View Animation Click on the Energo logo to start animation Ship Collision Case Study – June 2004

  12. Case 3 – Strongest LNG Ship Section View Animation Click on the Energo logo to start animation 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

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