ICPC Presentation April 2016 Hamburg Rev 3

Introducing Hengtong Marine• Hengtong Marine manufacture Submarine Cable Systems • Power, Optical Fibre, Hybrid and Umbilical Cables• Submarine Optical Cables are UJ & UQJ certified• Current optical cable capacity 6500km, which is being

upgraded to 12,000km by end 2016

On-Bottom (Sea Bed) Stability Design of CablesHengtong Marine Presentation to ICPC Plenary April 2016

Hengtong Group – Fibre Products

kilometers of fiber per year

Sold in more than countries and regions

12 production bases around the world

50 million

Hengtong Industry Chain

Fiber Preform

Optical Fiber

Cable

Component and connection system

EPC and turn-key project service


On-Bottom (Sea Bed) Stability Design of Cables

Hengtong Marine Cable Systems

Presenter : Dr. Jerry Brown

ICPC Plenary Meeting: 12 April 2016 Hamburg

ICPC Plenary April 2016

www.hengtongmarine.com

Audience Participation(Wake Up & Stretch Your Arms)

• How many people know about DNV-RP-F109 ?• How many people have used DNV-RP-F109 ?• Do you think a DNV recommended practice for

pipelines (typically 76mm to 1800mm diameter & concrete coated) is really applicable to flexible cables (typically 18mm to 40mm diameter) ?


Why is On-Bottom Cable Stability Important ?• The cable should remain on the as laid cable route

– for ease of location – recovery during future maintenance operations

• For the convenience of other seabed users – to avoid damaging any adjacent equipment, – sensitive or protected marine organisms and

• To avoid cable damage – due to abrasion, – kinking,– fatigue failure due to repeated flexing and bending.


• Seabed Type• Roughness• Properties• Friction

coefficient• Cable

penetration• Trench

Depth


Factors which affect Cable Stability ?

• Cable Diameter

• Cable Weight• Cable Lay

direction• Marine

Growth & density

• Wave direction• Significant Wave

Height• Peak Wave Period• Current Speed &

Direction• Reference height

for current• Water depth


Cable Design For Stability• TIMING - During the Cable system route engineering, the cable on-

bottom stability should be checked.• CHECK LIST - These checks are often not completed at the design

stage due to a lack of environmental data, or they are over-looked by clients / suppliers.

• DESIGN - On-bottom stability checks completed at the correct time, allows the cable design (armouring) and engineering to be adjusted to meet the site conditions and client requirements… for a reasonable cost.

• TOO LATE - Often the reality is that the cable is manufactured (or deployed) before on-bottom stability is considered.

• FIX - A retro-fitted solution has to be engineered = increased costs.


Classical Theory for On-Bottom Stability

V90 = √ { ( 2 . g . Ww ) / (d . ρ . [ (CDrag / μ ) + CLift ] ) }

CDrag = CLift= 1.2 μ = 0.5 for armoured cables on rock and sandμ = 0.2 for armoured & LW cables on clay, silt, mud



penetration• Trench Depth


The Classical Theory uses some parameters

• Cable Diameter


direction• Marine

Growth & density






Cable

Marine Growth

Knowing the density of the Marine Growth and assuming the cross section of growth shown above, allows an equivalent ‘cable with growth’ diameter & weight in water to be calculated


LWP


DNV-RP-F109 On-Bottom Stability Design of Submarine Pipelines

• DNV-RP-F109 2007, revised in 10/10, and amended in 11/11. • Analyses the stability characteristics of a circular CSA pipeline

(diameter and weight). Considers water depth, seabed type and environmental conditions (i.e. current and wave profiles).

• Three different design approaches to analyzing pipeline stability • 1st …. calculations for absolute (zero movement) static stability, • 2nd …. calculations for a generalized stability method with design

curves for virtually stable pipes (allowing up to 0.5 diameters lateral displacement) and for up to 10 pipe diameters displacement in an extreme storm condition.

• 3rd …. is based on a full dynamic analysis method.


DNV-RP-F109 - Parameters Used … … … … … … but are they all necessary ?

• Cable Diameter


direction• Marine

Growth & density







penetration• Trench Depth


DNV-RP-F109 – DNV have released STABLELINES … … … … … …Hengtong Marine have verified our software against STABLELINES



The Effect of Waves on Seabed Stability of DA cable using DV-RP-F109 (Absolute Stability Method)

DNV-RP-F109 (Absolute Stability Method) Versus Classical Theory for DA cable

Considering the effect of only Current on the Sea Bed Stability of Cables

DNV-RP-F109 provides more conservative results when using a reference height = cable diameter


Affect of Bottom Roughness on Current Profiles


Affect of Trench Depth on Stability



For a cable bundle dimensions D x 2D, the stability analysis can be simplified and approximated to a circular cable, diameter D with a perpendicular current V90 which is half the current acting on the bundle.

Stability Analysis of Cable Bundles

Affect of Cable Aspect Ratio (Dmax/Dmin)

• As the Cable Body Aspect Ratio increases, seabed stability increases• The current reduction factor allows a circular cable stability analysis with a

reduced V90.• Low profile cross-section (large Aspect Ratio) increase seabed stability


Methods of Improving Seabed Stability of Cables• Change the weight of the cable

– Cable design (additional layers of armour)– Addition of modular ballast elements– Application of protective pipes– Clamp or Pin the Cable to the seabed

• Change the cable profile– Attachment of Ballast Wire (Cable Bundle)– Cover with Mattress (low profile shape)

• Burial of the cable– Rock Dumping– Trenching


Comparison of Stability Methods



Conclusions• Two On-Bottom Stability Calculation methods have been

introduced & results compared • The comprehensive capability of DNV-RP-F109 has been

demonstrated. There are limitations. DNV is working on a joint program to develop an amendment to enhance RP-F109 for flexible cables

• An analysis technique for cable bundles proposed• Some methods of improving on-bottom stability of cables

have been reviewed• Hengtong Marine are developing new methods of

stabilising cables.

THANK YOU FOR YOUR ATTENTION …

ANY QUESTIONS ?

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ICPC Presentation April 2016 Hamburg Rev 3

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