Pipeline Dynamics with Flowing Contents in Abaqus/Standard

Transcription

1 Pipeline Dynamics with Flowing Contents in Abaqus/Standard Dr. Barry Trippit Simuserv, Perth, Australia Coauthors Kin Yin Chee, INTECSEA, Perth, Australia Sinan Aizad, Simuserv, Perth Australia

2 Overview Simuserv the company Why model pipeline contents Existing approaches New concept Sleeper example Spool example Benefits & Limitations Novel applications Summary Barry Trippit Slide 2

3 Simuserv Dassault Systemes PLM Solution Partner and Education Partner for SIMULIA solutions in Australia Provision of advanced Simulation Services Offices in Melbourne and Perth Experience across a range of industries Automotive Packaging Railway Aerospace Mining Oil & Gas Perth Melbourne Barry Trippit Slide 3

4 Oil and Gas Significant Oil and Gas developments in Australia Abaqus primarily used for: Subsea pipeline buckling Pipeline walking Pipeline installation Simuserv Abaqus customisations Various Pipeline to Seabed friction models Wave loading Interest in modelling changing pipeline mass Some complexity in achieving this Barry Trippit Slide 4

5 Slugging Reservoirs produce mixture of: Fluid (Oil, Condensate, Water) Gas Mix varies with conditions and reservoir life Products transported in single pipeline Flow condition within a pipe: Low velocity separate but even High velocity mixed Intermediate velocity slugging can occur Fluid forms slugs gas forms bubbles Courtesy Cooper, P. Fatigue Design of Flowline Systems with Slug Flow, 28 th International Conference of Ocean, Offshore and Arctic Engineering, 2009 Barry Trippit Slide 5

6 Slugging Occurs naturally Develops from uniform inflow conditions Sizing of pipes is conducent to slug flow 8m/s, 75% fluid Actual condition highly variable Perhaps 60m slug followed by 20m bubble Perhaps 1 slug per 10 seconds Slug significantly more dense Perhaps 900 vs. 100 kg/m 3 Fatigue concerns Pipeline free spans Sharp bends Three effects: Changing weight/loading Momentum changes Inertia changes Barry Trippit Slide 6

7 Modelling Changing Mass Ideally want to model this in Abaqus/Standard Model effect of density change without fluid detail However no convenient method to change/transport mass Potential Approaches: Moving distributed load, perhaps DLOAD routine Captures weight Ignores inertia and perhaps momentum Activate/deactivate additional masses Captures weight and inertia Ignores momentum Multiple steps cumbersome Transport masses, perhaps with slideline contact Captures weight, inertia, momentum Contact iterations (no tied option) Mass movement cumbersome Barry Trippit Slide 7

8 MPC User Routine MPC routine supports implementation of arbitrary nonlinear constraint equations Concept: Create moving tie constraint to transport additional mass along the path of the pipeline at a predefined speed Extra mass node is slave All pipeline nodes define path and are potentially masters Couple slave only to close masters Slave location updated and moves along path Use many constraints to tie many masses to form slug Slave Mass Coupled Masters Coupled Masters Coupled Masters Potential Masters Pipe Elements Barry Trippit Slide 8

9 Simple Test Cantilever beam Single coupled heavy mass element Gravity loading Dynamic analysis *MPC,USER,MODE=NODE 1100,100,1,2,3,4,5 ** ** *STEP,NLGEOM *DYNAMIC 0.01,1.0,,0.01 ** *FIELD,VARIABLE=1 100,-10.0 ** *END STEP Barry Trippit Slide 9

10 Constraints Lateral constraint: Linear between master nodes in current segment Investigating option of cubic Significantly more complex Axial constraint options: 1. Defined speed relative to pipeline, forces reacted to pipeline 2. Defined speed relative to pipeline, forces reacted to ground 3. Slider Slave Mass Coupled Masters Barry Trippit Slide 10

11 Pipeline Sleeper Sleepers form buckle initiators Relieves thermal strains 0.5m high sleeper, 300m of pipeline modelled Potential slug induced fatigue Four consecutive slugs modelled 60m long slug, 600 masses per slug, 600 user MPC s 8m/s slug velocity Dynamic implicit analysis View almost along axis Pipe shown smaller than real Installation steps not shown Barry Trippit Slide 11

12 Pipeline Sleeper Response mostly quasi-static Sag due to weight change most important Significant free span changes Varies between 27 and 72m, original 60m Significant stress cycles Double peaked response Maximum peak with central slug Smaller peak central bubble Trough with slug to side Initial and final gas only Barry Trippit Slide 12

13 Jumper Spool Connects various subsea equipment Maybe supported only at ends Potential for slug induced fatigue Four consecutive slugs modelled 60m long slug, 600 masses per slug 8m/s slug velocity Jumper Spool Barry Trippit Slide 13

14 Jumper Spool Static & Dynamic Highly damped Less damped Higher dynamic stresses Change in momentum at corners Some vibrations present Real damping unknown Slug Position Static Dynamic Highly Damped Dynamic Less Damping Displacements x50 Barry Trippit Slide 14

15 Benefits Relatively easy user setup *MPC bit cumbersome for many MPC s Easily automated Velocity and path easily defined Reasonably efficient even with many slaves Small time steps can be required for dynamic Captures all desired effects Barry Trippit Slide 15

16 Limitations Masses traversing Barry Trippit a bend, ideal stepping Masses continually moving Slide 16

17 Limitations MPC routine called for three purposes: 1. Define slave degrees of freedom Position slave nodes 2. Transfer loads from slave to masters Constraint equilibrium 3. Eliminate slave from stiffness matrix Convergence of Newton iteration Abaqus assumes derivatives for 2 and 3 are same Appropriate for many constraints In this case causes non-quadratic convergence Although no issues observed to date (small steps) Load transfer masters (constraint equilibrium) Masters controlling axial position (convergence) For convergence of axial position derivatives will have terms from nodes 1 and 2 For correct force transfer derivatives will have terms from nodes 2 and 3 only Barry Trippit Slide 17

18 Novel Applications Movement of nodes along path and connected to body Moving loads/mass, similar to slideline (without contact) Transport of mass with stationary stiffness Semi-eulerian Same as pipeline Mass elements transported while stiffness elements held stationary Contact with rollers/pulleys essentially unchanging Barry Trippit Slide 18

19 Summary Slugging occurs naturally in many subsea pipelines Potential for fatigue damage at various locations, this is a design driver Abaqus capable of solving slugging User MPC routine developed to conveniently model the phenomenon Thanks to Co-authors INTECSEA Barry Trippit Slide 19

20 Thank you Questions? Barry Trippit Slide 20