ON-BOTTOM STABILITY CALCULATIONS FOR FIBRE OPTIC SUBMARINE CABLES - PowerPoint PPT Presentation

conference & convention enabling the next generation of networks & services ON-BOTTOM STABILITY CALCULATIONS FOR FIBRE OPTIC SUBMARINE CABLES Inge Vintermyr Nexans Norway AS

conference & convention enabling the next generation of networks & services Presenter Profile Inge Vintermyr graduated from the Norwegian Institute of Technology in 1989 with a Ph.D in Materials Science. He joined Nexans Norway AS (previous Alcatel Kabel Norge AS) the same year. He has Kabel Norge AS) the same year. He has been working with research, development and engineering of energy and telecom cables since 1989. In 2000 he was appointed Technical Manager for the communications cable division. Inge Vintermyr Technical Mgr Email: Inge.Vintermyr@Nexans.com Tel: (+47) 22 88 62 29 Mobile Tel: (+47) 95 23 57 43

conference & convention enabling the next generation of networks & services OUTLINE • INTRODUCTION/BACKGROUND • THEORY AND MODELS • STANDARDS AND SOFTWARE PROGRAMS • STANDARDS AND SOFTWARE PROGRAMS • CALCULATIONS AND RESULTS • SUMMARY AND CONCLUSIONS

conference & convention enabling the next generation of networks & services INCREASING DEMAND FOR FOR FO IN OFFSHORE INDUSTRY ������� ������ ������� ������ ����� ����� �������� �������� �������� �������� ������ ������ ����������������������� ����������������������� �������������������� �������������������� � � �������� �������� �� �� � � ����������������������� ����������������������� ����� ������������� ����� ������������� � � ����������������� ����������������� ��������� ��������� ������� ��������������� ������� ��������������� ������ ������� ������ �������

conference & convention enabling the next generation of networks & services ON-BOTTOM STABILITY • FO cables are installed along with other cables, umbilicals and pipelines. • Commonly specified that all installed items shall be stable. shall be stable. • Typically referred to DNV-RP-F109 ”On Bottom Stability Design of Submarine Pipelines”.

conference & convention enabling the next generation of networks & services FO CABLES MUST OPERATE WITH OTHER SUBSEA INSTALLATIONS

conference & convention enabling the next generation of networks & services FO CABLES, POWER CABLES AND UMBILICALS URC -Cables ROC -Cables ROC -Cables Power/Umb

conference & convention enabling the next generation of networks & services CABLE CHARACTERISTICS ����� ���� �� ��� ���� ����$ � ����$�# �� �!"#� �!"�#� �!"�#�% �&�'(')�($* �� ���� ���� ����� �&�'('�+,$% �� ���� ���� ����� �&�'('�+% �� ���� ���� ����� �&�'('&� �&�'('&� �� �� ����� ����� ����� ����� ������ ������ &��')� �� ���� ���� ����� &��'�+,$- ���� ���� ���� ����� ����� . %/ !0 ���� ����� ���� ������ ����� '(/1 !0 ����� ����� ����� ������ ��������� ����� ����� ����� ������ %/2 �������� ��� ������ ������ ������

conference & convention enabling the next generation of networks & services SEABED STABILITY THEORY • Driving forces: -Drag and inertia forces from flowing water, waves and current • Resisting forces: -Interaction with soil, friction + passive resistance due to penetration F L FLOW F I +F D (w s –F L )u+ F R (z) w s

conference & convention enabling the next generation of networks & services SEABED STABILITY THEORY • Drag and lift forces are proportional to velocity squared 1 ( ( ) ) 2 sin = ρ ⋅ ⋅ ω + F D C U t U Drag: D w D w C 2 1 ( ( ) ) 2 sin = ρ ⋅ ⋅ ω + F D C U t U Lift: L w L w C 2 π π dU dU     2 2 = = 4 ρ ρ ⋅ ⋅ ⋅ ⋅ Intertia: Intertia: F D C  w  I w M dt   F L FLOW F I +F D (w s –F L )u+ F R (z) w s High W s /D ratio is positive for stability

conference & convention enabling the next generation of networks & services SEABED STABILITY THEORY • Interaction between cable and soil provides resistance – Consists of pure coulomb friction and resistance due to penetration into the seabed F L FLOW F I +F D (w s –F L )u+ F R (z) w s

conference & convention enabling the next generation of networks & services SEABED STABILITY BASIS Operation – For permanent operational conditions and temporary phases with duration in excess of 12 months, a 100-year return period applies. – When detailed information about the joint probability of – When detailed information about the joint probability of waves and current is not available, this condition may be approximated by the most severe condition among the following two combinations: 1) The 100-year return condition for waves combined with the 10-year return condition for current. 2) The 10-year return condition for waves combined with the100-year return condition for current.

conference & convention enabling the next generation of networks & services SEABED STABILITY BASIS Temporary Phase – For temporary phases with duration in excess of three days and less than12 months, a 10-year return period applies. – This condition may be approximated by the most – This condition may be approximated by the most severe condition among the following two combinations: 1) The 10-year return condition for waves combined with the 1-year return condition for current. 2) The 1-year return condition for waves combined with the10-year return condition for current.

conference & convention enabling the next generation of networks & services STABILITY - APPROACHES • Allowing accumulated displacement – A certain maximum displacement allowed – Will break out of its cavity during extreme sea state state • No break-out (virtual stability) – Allowing small displacement, normally less than 0.5XD. No accumulated displacements • Absolute stability – All loads less than the resistance forces, no lateral movement

conference & convention enabling the next generation of networks & services STANDARS AND SOFTWARE PROGRAMS • Time Domaine Dynamic Analysis – A three hour severe storm is typically simulated – Results are a timeseries througout the storm: • Lateral displacement • Load effects (forces, stress, strain) • Load effects (forces, stress, strain) – Few companies use this method – Commercial software products: • PONDUS (Marintek) • AGA Level III (PRCI, USA)

conference & convention enabling the next generation of networks & services STANDARDS AND SOFTWARE PROGRAMS • DNV-RP-F109, 2007 ”On-Bottom Stability Design of Submarine Pipelines” (Replaces DNV-RP-E305, 1988 • RP-F109 provides design curves that are based on a large set of full dynamic analyses performed by using PONDUS • • Simplified approach compared with the time domain dynamic Simplified approach compared with the time domain dynamic analysis • Includes four sets of design curves for the following methods: – Sandy seabed with displacement < 0.5 x OD – Sandy seabed with displacement < 10 x OD – Clayey seabed with displacment < 0.5 x OD – Clayey seabed with displacement < 10 x OD • Absolute stability -No displacement allowed

conference & convention enabling the next generation of networks & services INPUT PARAMETERS Pipe outer diameter [mm] D: Pipe submerged weight per unit length [kgf/m] w s : Hs : Significant wave height [m] for extreme sea states ( 1, 10 and 100 years return period) Tp : Wave Peak period [s] for Hs Uc : Current speed [m/s] for extreme events (1, 10 and 100 years return period) (1, 10 and 100 years return period) d : Water Depth [m] Un-drained clays shear strength [kPa] s u : γ ’ s : Submerged unit soil weight. For sand normally in the range 7000 (very loose) to 13 500 N/m (very dense) d 50 : Mean sand grain size [mm] The oceanographic data (Hs, Tp, Uc) have to be derived by statistical methods from long term measurement of both wave and current Seabed data( s u , γ ’ s , d 50 ) are established by taking soil samples at different locations in the area where the pipe is going to be installed