pipeline dynamics with flowing contents in abaqus/standard · pipeline dynamics with flowing...

Pipeline Dynamics with Flowing Contentsin Abaqus/Standard

Dr. Barry TrippitSimuserv, Perth, Australia

Coauthors

Kin Yin Chee, INTECSEA, Perth, Australia

Sinan Aizad, Simuserv, Perth Australia

Barry Trippit Slide 2

Overview

Simuserv the company

Why model pipeline contents

Existing approaches

New concept

Sleeper example

Spool example

Benefits & Limitations

Novel applications

Summary


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


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


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”, 28th International Conference of Ocean, Offshore and Arctic

Engineering, 2009


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/m3

Fatigue concerns Pipeline free spans Sharp bends

Three effects: Changing weight/loading Momentum changes Inertia changes


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


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 MastersCoupled Masters Coupled Masters

1 432

Potential MastersPipe Elements


Simple Test

Cantilever beam Single coupled heavy mass element Gravity loading Dynamic analysis

………*MPC,USER,MODE=NODE1100,100,1,2,3,4,5**………***STEP,NLGEOM*DYNAMIC0.01,1.0,,0.01***FIELD,VARIABLE=1100,-10.0***END STEP


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

1 432

Slave Mass

Coupled Masters


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 axisPipe shown smaller than realInstallation steps not shown


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


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


Jumper Spool

Static & Dynamic Highly damped Less damped

Higher dynamic stresses Change in momentum at

corners

Some vibrations present Real damping unknown

SlugPosition

Static

DynamicHighly

Damped

DynamicLess

Damping

Displacements x50


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


Limitations

Masses traversing a bend, ideal stepping

Masses continually moving


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)

Masters controlling axial position(convergence)

Load transfer masters

(constraint equilibrium)

1 2 43

For convergence of axial position derivatives will have terms from nodes 1 and 2For correct force transfer derivatives will have terms from nodes 2 and 3 only


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

Mass elements transported while stiffness elements held stationaryContact with rollers/pulleys essentially unchanging

Same as pipeline


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


Thank you

Questions?

pipeline dynamics with flowing contents in abaqus/standard · pipeline dynamics with flowing...

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