Design of Offshore Structures For Extreme Ice Conditions Prepared - PowerPoint PPT Presentation

CJK ENGINEERING Design of Offshore Structures For Extreme Ice Conditions Prepared for SNAME 2017 Arctic Section by John Fitzpatrick P. Eng. CJK Engineering Ltd. jfitzpat@telus.net Graphics by Jakub Ciring and Associates Inc. jakubciring@shaw.ca

Overview CJK ENGINEERING • Why a Gravity Based Structure (GBS) will not work in 100 to 200 meters of water under extreme tabular ice conditions! • Two alternative solutions for permanent platforms in 200 meters of water. • First: Gravity Fendered Structure (GFS). • Second: Rock Island Structure. • Costs for both concepts.

Transfer Equations for Energy to Force CJK ENGINEERING Non-deformable Structures: F = 2 E 2/3 σ 1/3 / (H/D) 2/3 Large potential for error in σ and H/D Deformable Structures: F S = E = MgH No potential for error

Energy vs. Force, depending on shape & crushing strength of the ice feature CJK ENGINEERING MN 10,000 MN 10,000 10 -2 , 100m 10 -2 , 200m 10 -4 , 100m 10 -4 , 200m 700 million tonnes Ice Island @ 0.22m/s 5,000 2,500 MN Hibernia 1,000 10,000 5,000 15,000 MNm

GBS vs. 100m Thick Tabular Ice CJK ENGINEERING E = 1,700,000 Tm = 17,000 MNm F = 2 x (17,000) 2/3 x 4 1/3 / 0.1 2/3 = 10,000 MN (“Flat”) F = 2 x (17,000) 2/3 x 1 1/3 / 0.4 2/3 = 2,500 MN (“Bump”)

GBS vs. 100m Thick Tabular Ice CJK ENGINEERING

GFS Concept CJK ENGINEERING

GFS for 200m water depth – principal particulars and design energy parameters CJK ENGINEERING

Size comparison with existing large structures CJK ENGINEERING

GFS vs. size of the Design Tabular Ice Island, 3000m in diameter and 100m thick CJK ENGINEERING

Timeline of absorption of energy: 0 sec. CJK ENGINEERING

Timeline of absorption of energy: 90 sec. CJK ENGINEERING

Timeline of absorption of energy: 180 sec. CJK ENGINEERING

Timeline of absorption of energy: 275 sec. CJK ENGINEERING

Timeline of absorption of energy: 390 sec. Interaction and force transfer complete CJK ENGINEERING

Timeline in plan view: 0 sec., 700 million tonne Ice Island contacting Fender at 0.22m/s CJK ENGINEERING

Timeline in plan view: 390 sec., Ice Island stopped, after displacing Fender by 56m horizontally and 17m vertically. CJK ENGINEERING

Energy to Force for Deformable Structures CJK ENGINEERING F S = E = MgH (68,000t ÷ 2) × 50m = 0.5 × 700,000,000t × 0.22^2 ÷ 9.81=100,000t × 17m =1,700,000 tm No potential for error in Base Shear if Mass and Velocity are known. F maximum = 68,000 metric tonnes = 680MN Base overturning moment = 12,000,000 tonne meters

Fender response to ‘rogue wave’ embedded in 15m significant sea state CJK ENGINEERING Base Shear Departure [m] Force [ T ] 40 60,000 See detail 30 45,000 20 30,000 10 15,000 -10 -15,000 -20 -30,000 -30 -45,000 -40 -60,000 t = 0 sec 800 1600 2000 400 1200 10 min 20 min

Wave induced Fender motions. 15m wave Steady State plus Transient ‘Rogue’impact CJK ENGINEERING m 30 20 10 20 40 60 80 100 120 140 160 180 sec. m 30 20 10 20 40 60 80 100 120 140 160 180 sec. m 30 20 10 20 40 60 80 100 120 140 160 180 sec.

Wave Loads and Input to dynamics program CJK ENGINEERING H=15m, T=16 secs, WL=400m • • Fender mass (including annulus water) = 3,240,000 tonnes • K=15,000kn/m, Cm = 1.5, Cd=0.7 • Fender natural period 160 seconds • Resonance not possible Steady state total Base Shear = 30,000 tonnes • • Confused irregular sea state = 50,000 tonnes • Wave Base Moment = 8,000,000 tonne meters Steady state departure +/- 6m . •

15m high (Steady State) Regular Wave action CJK ENGINEERING 0 sec.

15m high Regular Wave action – 4 sec. CJK ENGINEERING

15m high Regular Wave action – 8 sec. CJK ENGINEERING

15m high Regular Wave action – 12 sec. CJK ENGINEERING

15m high Regular Wave action – 16 sec. CJK ENGINEERING

Additional benefits CJK ENGINEERING • In the event of a blowout the inner annulus of the Fender could act as an effective oil containment boom with a capacity of 15,000,000 bbls. The Fender itself could contain an additional 5,000,000 bbls. • The Fender provides a 200m wide approach channel for tankers in which to approach and load from the platform • The inner annulus could provide a safe haven and mooring location for ice breakers or supply ships under 100 meters in length.

GFS Cost Estimate (excluding topsides) CJK ENGINEERING Steel quantity input: Base 150,000T 1 st Step 40,000T 2 nd Step 20,000T Pillar 50,000T Deck 40,000T Subtotal 300,000T Fender 100,000T Total 400,000T Total steel: 400,000T x $4,000/T = $1.60 Billion 250 cables x 100m x $1,100/m = $30 Million + $10 Million for Ends = $0.04 Billion Ballast: 300,000m 3 x $200/m 3 = $0.06 Billion Capital cost subtotal $1.70 Billion Towing & installation: 300days x $1 Million/day = $0.30 Billion Contingency: $0.50 Billion Grand total $2.5 Billion

Rock Island for 200m water depth - principal quantities and design energy CJK ENGINEERING

Concept of Rock Island for 200m water depth CJK ENGINEERING

Rock Island construction sequence using 10 new self- propelled, ice strengthened Rock Barges, each with 15,000 CJK ENGINEERING DWT capacity

Comments on Rock Island CJK ENGINEERING • Virtually no limit to the amount of energy that can be absorbed. An indentation of 25m would absorb some 10,000,000 tonne meters of energy or 6 times more than the 10,000 year design energy. • The central platform should not have a draft any deeper than 30m as this could result in overload. • The central platform needs to be surrounded by a protective berm • The Rock Island cannot be built with sand due to quantities and instability. (D 50 ≈ 350 kg ≈ 600 mm Φ ).

Rock Island Cost Estimate (excluding topsides) CJK ENGINEERING Input for the cost of rock: Open pit mine to provide 60,000T/day $35/m 3 Transport & loading/ conveyer system $10/m 3 Fleet of 10 self propelled ice strengthened barges, 15,000DWT each + assistance $35/m 3 Total unit cost for rock $80/m 3 Octagonal platform 100m x 110m x 90m, with 3,000,000 bbl. storage $0.60 Billion Berm: 30,000,000 m 3 x $80/m 3 $2.40 Billion Grand total $3.0 Billion Construction time 3 to 4 years

Conclusions CJK ENGINEERING • Gravity based non-deformable structures are not feasible in extreme tabular ice conditions. • Alternative ``deformable`` solutions exist for reasonable costs.

Thank you for your attention. CJK ENGINEERING