Seakeeping – Wet Deck Slamming on Offshore Ships

How can we accurately predict wave impact loads on ships for seakeeping? Some of the important parameters related to ship hull design include ship motions, vertical accelerations, wave impact/slamming loads, and deck wetness. The ABS Guide for Building and Classing High Speed Naval Craft (HSNC 2007) clearly states that slamming impact load is one of the most critical factors for the scantling design of hull structures. Accurate prediction of wave impact loads requires solving three problems. First is the prediction of wave kinematics, second is the prediction of the pressure and viscous forces and the third is the prediction of ship motion during the wave impact. It is possible to simulate all of these problems with ANSYS computational fluid dynamics (CFD) software.

I am delighted to present our paper at the Offshore Technology Conference (OTC) 2014 in Houston on May 5th focusing on the wet deck slamming analysis of twin-hulled offshore ship in irregular sea waves using ANSYS Fluent (OTC2014-25213).

Twin-hulled ships are well-known for their excellent performance with respect to speed, safety, resistance and transversal stability even in high sea. Volume of Fluid (VOF) method was used to model the free surface and Six Degrees of Freedom Model (6DOF) was used to predict the motion of the ship. JONSWAP spectrum is used for generating unidirectional random waves in deep sea. We verified the model for pure random wave propagation problem where the numerical results for free surface elevation are compared with analytical results with very good agreement even at higher value of sea steepness and for a long period of time.

The CFD analysis was carried out in calm sea and survival condition with significant wave height 9m with different ship loadings and ship speeds. The peak impact pressure was highest when the wave crest hits the ship during the ship reentry to the water surface and was localized in space. The current study showed the dependency of ship accelerations, impact pressures and the peak pressure locations on the operating conditions and the sea state and demonstrated the usage of CFD for wetdeck slamming analysis.

I hope you can attend my talk at OTC and visit ANSYS booth 5001 to discuss how ANSYS CFD modeling can predict the wave impact loads, motions and vertical accelerations of offshore ship in irregular sea waves accurately and efficiently. If you are not attending OTC, I would welcome your comments and questions below this post or any other questions related to seakeeping.

image of free surface elevation CFD simulation

Comparison of Free surface elevation of CFD simulation with Analytical results for irregular wave

Comparison of Wave Impact Pressure for two different Ship Loadings

Comparison of Wave Impact Pressure for two different Ship Loadings

image during wave loading peak impact pressure incident

Snapshot during wave loading at a peak impact pressure incident

image during wave loading peak impact pressure incident

Snapshot during wave loading at a peak impact pressure incident

 

This entry was posted in Fluid Dynamics, Oil & Gas by Madhusuden Agrawal. Bookmark the permalink.
Madhusuden Agrawal

About Madhusuden Agrawal

Madhusuden Agrawal is a principal engineer at ANSYS, Inc. He has 20+ years’ experience in numerical modeling of fluid flow and mass/heat transfer. His expertise includes cutting-edge, industrial-strength CFD analysis, simulations and optimization in wide range of applications in oil and gas, chemical, biomedical, pharmaceutical, petrochemical, materials and consumer products. Mr Agrawal obtained his master’s degrees from the Indian Institute of Technology, Kanpur India; his MBA is from Franklin Pierce College, NH.