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 Cables
Hengtong 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

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 sand
μ = 0.2 for armoured & LW cables on clay, silt, mud

• Seabed Type
• Roughness
• Properties
• Friction
coefficient
• Cable
penetration
• Trench Depth
The Classical Theory uses some parameters
• Cable
Diameter
• Cable Weight
• Cable Lay
direction
• Marine
Growth &
density
• Wave direction
Height
• Current Speed &
Direction
for current
• Water depth

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
• Cable Weight
• Cable Lay
direction
• Marine
Growth &
density
• Wave direction
Height
• Current Speed &
Direction
for current
• Water depth
• Seabed Type
• Roughness
• Properties
• Friction
coefficient
• Cable
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 ?

ICPC Presentation April 2016 Hamburg Rev 3

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