ice loads and dynamic response of offshore structures
TRANSCRIPT
THE HAMBURG SHIP MODEL BASINSetting the Standard in Ship Optimisation
CFD CAD Office Resistance & Propulsion Propellers & Cavitation Seakeeping, Manoeuvring & Offshore Arctic Technology www.hsva.de
Ice Loads and Dynamic Response of Offshore
StructuresGesa Ziemer, HSVA
Sea Ice – Structure Interaction WorkshopBritish Antarctic Survey, November 13th, 2017
THE HAMBURG SHIP MODEL BASINSetting the Standard in Ship Optimisation
CFD CAD Office Resistance & Propulsion Propellers & Cavitation Seakeeping, Manoeuvring & Offshore Arctic Technology www.hsva.de
Introduction
• Ice loads on offshore structures are hard topredict
• If ice is present, limiting design case is usuallyice load
• Structures in ice-infested waters becomeincreasingly complex (multi-legged, flexible, ..)
• Ice-structure interaction is in many aspects not well understood yet
THE HAMBURG SHIP MODEL BASINSetting the Standard in Ship Optimisation
CFD CAD Office Resistance & Propulsion Propellers & Cavitation Seakeeping, Manoeuvring & Offshore Arctic Technology www.hsva.de
Structuralresponse
Ice Ice Loads
Offshore Structure
Thickness, strength, drift speed, feature…
Geometry, stiffness, natural frequency, …
THE HAMBURG SHIP MODEL BASINSetting the Standard in Ship Optimisation
CFD CAD Office Resistance & Propulsion Propellers & Cavitation Seakeeping, Manoeuvring & Offshore Arctic Technology www.hsva.de
Challenges
Ice
Ice Loads
Structuralresponse
• Good forecast needed, but limited data available• Ice properties hard to predict for specific sites• risk of over- or underestimation at high costs• worst case scenario often inhomogeneous condition
(e.g. pressure ridges, rafted ice)
• Rules inaccurate / oversimplified (e.g. ISO 19906)• Complex interaction mechanisms not fully understood• Prediction and numerical simulation especially difficult
for complex structures and at transition conditions
• Not yet reliably predictable in dynamic ice-structureinteraction
• mechanism of ice-induced vibration not fullyunderstood
THE HAMBURG SHIP MODEL BASINSetting the Standard in Ship Optimisation
CFD CAD Office Resistance & Propulsion Propellers & Cavitation Seakeeping, Manoeuvring & Offshore Arctic Technology www.hsva.de
Recent advances in model testing• Project BRICE „breaking the ice“• Fraunhofer IWES, VTT, HSVA• Aid numerical models with physical modelling of complex
ice-structure interaction scenarios:– Transition to non-linear response (ice-induced resonant
vibrations)– Transition of failure modes
THE HAMBURG SHIP MODEL BASINSetting the Standard in Ship Optimisation
CFD CAD Office Resistance & Propulsion Propellers & Cavitation Seakeeping, Manoeuvring & Offshore Arctic Technology www.hsva.de
Example: Norströmsgrund Lighthouse
• Wide, cylindrical structureclose to Swedish Coast
• Instrumented in LOLEIF / STRICE projects
• Measurement of forces, accelerations, ice properties
• Physical model at 1:8.7
THE HAMBURG SHIP MODEL BASINSetting the Standard in Ship Optimisation
CFD CAD Office Resistance & Propulsion Propellers & Cavitation Seakeeping, Manoeuvring & Offshore Arctic Technology www.hsva.de
• Video!!!!!!!
THE HAMBURG SHIP MODEL BASINSetting the Standard in Ship Optimisation
CFD CAD Office Resistance & Propulsion Propellers & Cavitation Seakeeping, Manoeuvring & Offshore Arctic Technology www.hsva.de
Model test results• Different interaction types
captured well• Good agreement with full
scale data• Only few data points
THE HAMBURG SHIP MODEL BASINSetting the Standard in Ship Optimisation
CFD CAD Office Resistance & Propulsion Propellers & Cavitation Seakeeping, Manoeuvring & Offshore Arctic Technology www.hsva.de
Example: Cone angle variation• Crushing on vertical
structures; risk of ice-induced resonant vibrations
• Flexural failure on conicalstructures (ice cones); lowbreaking frequency
• Transition?
THE HAMBURG SHIP MODEL BASINSetting the Standard in Ship Optimisation
CFD CAD Office Resistance & Propulsion Propellers & Cavitation Seakeeping, Manoeuvring & Offshore Arctic Technology www.hsva.de
Model test results• Maximum ice loads decrease
on conical structures, but velocity effect increases withincreasing slope
• Structural displacementincreases with increasingslope
• Oscillations can arise on all cones when ice drift speed ishigh enough
• 80° cone experiences periodsof crushing
THE HAMBURG SHIP MODEL BASINSetting the Standard in Ship Optimisation
CFD CAD Office Resistance & Propulsion Propellers & Cavitation Seakeeping, Manoeuvring & Offshore Arctic Technology www.hsva.de
Model test results• Maximum ice loads decrease
on conical structures, but velocity effect increases withincreasing slope
• Structural displacementincreases with increasingslope
• Oscillations can arise on all cones when ice drift speed ishigh enough
• 80° cone experiences periodsof crushing
THE HAMBURG SHIP MODEL BASINSetting the Standard in Ship Optimisation
CFD CAD Office Resistance & Propulsion Propellers & Cavitation Seakeeping, Manoeuvring & Offshore Arctic Technology www.hsva.de
Closing remarks• Ice loads and structural response of offshore structures
are subject to extensive research, but knowledge isinsufficient
• Validated numerical models required for designers toassess risks and define realistic design cases
• Physical model tests needed to monitor ice behaviourand provide validation data
• Model tests attractive for complex structures to get a feeling for their behaviour in ice