DNV GL © 2013 SAFER, SMARTER, GREENER DNV GL © 2013

31 Oct 2016

Aravind Nair

Vibration Assessment of Complex Pipework

1

DNV GL Technology Week

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Overview

Vibration Induced Fatigue- Sources, Consequence; State of the art-pipeline VIV

Complex Pipework- Jumper System

– VIV assessment challenges

Jumper VIV JIP

Future study

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Vibration Induced Fatigue

Main sources:

Internal Flow Induced Vibration

– Common sources- major discontinuities such as

valves, pipe bends, intersections etc.

External Flow Induced Vibration

– Vortex induced vibration -shedding of vortices

downstream of the pipe system

– Flow past dead legs

Mechanical Excitation

– Presence of pumps/ compressors, chokes etc

Internal and External Flow Induced & Acoustic

Vibration

Even this can result in Vibration!

Identify source of vibration

Frequency and consequence of vibration

Failure & Mitigation Study

Ensure operational integrity

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Failures

4

PHMSA bulletin: ADB 2015

– Missouri river

– Montana

Cook Inlet Span

Offshore Jumper Failure

www.Oilprice.com Mobilisation for repair – several

million US$

Offshore time – 0.5-1 million

US$/day

Loss of income –15-20 million

US$/day

Cost may be huge!

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What is VIV and state of the art?

Non-linear fluid structure interaction phenomenon

Cross-flow vibration amplitudes of the order of one diameter

Extensively studied for risers/pipeline free spans

Design guidelines and tools available for risers/pipeline free spans

Relatively less knowledge/studies for Complex pipe systems

Cross-flow (Lift)

In-line

(Drag)

Image courtesy: Cesareo de La Rosa Siqueira (www.wikipedia.org)

Current

5

𝑓𝑠ℎ𝑒𝑑𝑑𝑖𝑛𝑔 = 𝑆𝑡𝑈

𝐷

𝑓𝑠ℎ𝑒𝑑𝑑𝑖𝑛𝑔 = vortex shedding frequency

St = Strouhal number (0.17 to 0.25)

U = current speed

D = diameter

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Uneven seabed - Subsea

Reinertsen Engineering

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What has been done

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State of the Art on VIV Analysis

Response Based Models

Force Based Models

Flow Based Models

Empirical Models (FatFree): Cross and Inline Vibration

•Sheared Flow Force Based Models (Shear7): Cross Vibration; Sheared flow

• Inline Vibration Flow Based Models (CFD):

• Promising

Report from the vortex induced vibration, specialist committee of the 25th ITTC (2008)

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Jumper VIV Challenges

9

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Jumper Systems

Subsea Jumper: short connection- transports fluid between two subsea components

• Connects Pipeline end terminations. • Typical length: >100ft

• Shapes: U, M, Z, V and any such complex shapes; manifold piping

Complex: anything that potentially deviates from DNV RP F105.

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Jumper VIV: Common Industry Practice

Extend existing VIV concepts and methodology for

risers/pipelines to jumpers (e.g. use DNV-RP-F105)

Use engineering judgment, exercise caution and understand

limitations when using DNV-RP-F105 for subsea jumpers

DNV-RP-F105 Response Models

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Challenges-Category

CHALLENGES

STRUCTURE FLUID INTERACTION

DAMAGE ESTIMATION

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Studied Shapes

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Effect of Geometry- Modal Response

• Frequency Differences

• Mode Shape Differences

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Modal Response

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Modal Response

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Modal Response- VIV Damage

• There is no empirical data to validate any of the damage assessment

calculations on non-straight geometries.

• Comparison of fatigue damage due to the modal differences – Only a 1st step

The calculated damage assumes all other parameters (such as vortex shedding patterns), are similar to straight pipelines and that the currently available response model (DNV RP F105) is valid.

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Fluid Interaction: Available Studies

ExxonMobil’s Model test- M Shaped

Jumper

– Wang et.al, “VIV Response of a Subsea

Jumper in Uniform Current”, OMAE 2013

– 1st and ONLY model test data available

for jumper systems.

CFD Study

– Holmes, S (Red Wing Engineering) and

Constantinides, Y. (Chevron Energy

Technology Company); “Vortex Induced

Vibration Analysis of a Complex Subsea

Jumper”, OMAE 2010.

DNV’ Study- CFD:

– M shaped Jumper form DNV’s ISOPE

2013 paper

– M shaped Jumper from ExxonMobil’s

OMAE 2013 paper

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Damage Estimation: Available Studies

There are few studies

available for damage

estimation.

Studies typically use

parameters in DNV RP F105

(Free span pipelines) for VIV

damage estimation

Limited studies account for

unique factors affecting

jumper systems

No study is Validated

Studies: • Nair, A, Sharma, P, Grytoyr, G., Fyrileiv, O, and Vedeld, K

(2013), “VIV Assessment of Rigid Jumper Systems-A Comparative Study on Jumper Shapes”, 23rd International Offshore and Polar Engineering Conference ( ISOPE 2013), June 30-July 5, 2013, Anchorage, USA

• Nair, A, Kadiyala, R and Whooley, A (2010).“Vortex Induced Vibrational Assessment of Multi-planar Geometry-New Methodology”, Proc. Of the Deep Offshore Technology Conf., Amsterdam, The Netherlands, DOT 2010, PennWell Corp.

• Vedeld, K., Sollund, H., Fyrileiv, O. (2011), “Fatigue and Environmental Loading of Large Bore Manifold Piping”, Proc. of the ASME 2011 30th International Conference on Ocean, Offshore and Artic Engineering, OMAE2011, OMAE2011-49381.

• Vedeld, K., Sollund, H., Fyrileiv, O. (2011), “Fatigue and Environmental Loading of Large Bore Manifold Piping”, Proc. of the ASME 2011 30th International Conference on Ocean, Offshore and Artic Engineering, OMAE2011, OMAE2011-49379.

• Hariharan, M, Cerkovnik, M (2H Offshore Inc.), Thomson, H. (Chevron Texaco), “The Significance of Low Velocity Near Bottom Currents on the In-Line Vortex-Induced Vibration Response of Rigid Subsea Jumpers”

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The issue

Designers discretion and judgement: What am I comfortable with?

“New Approach to the Design of Rigid Jumpers for Free Standing Hybrid Risers”, S Plouzennec, M. Sonawane, T. Eyles,IBP1708-1

“VIV Assessment of Rigid Jumper Systems-A comparative study on Jumper shapes”, A. Nair, P. Sharma, G. Grytøyr, O. Fyrileiv, K. Vedeld, ISOPE 2013

“The Significance of Low Velocity Near Bottom Currents on the In-Line Vortex-Induced Vibration Response of Rigid Subsea Jumpers:, Madhu Hariharan, Mark E. Cerkovnik (2Hoffshore Inc) and Hugh M. Thompson (ChevronTexaco), ?

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Damage Estimation Contd..

Geometry/ Client: Undisclosed

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JIP Study

22

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JIP Study- Phase I (Completed)

Generate Jumper specific Response

Curve

Compare against DNV-RP-F105

FEA-CFD Study

Key Deliverable part of the Guidance Report

DNV-RP-F105 Curve

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JIP to address Jumper VIV started in December 2014

Objective:

EITHER update DNV-RP-F105 incorporating Jumper response

OR a new standalone recommended practice on Jumper VIV

Five participants in phase 1

– BP

– DNV GL

– ExxonMobil

– Petrobras

– Saipem

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Phase-1: Data Collection and Analysis

Exxon Mobil’s model test data

– 10” OD jumper Base case

– 141 towing experiments

Mode shapes

Ay/D plots Wang, H et.al “VIV Response of Subsea Jumper in Uniform

Current”, OMAE 2013 [ExxonMobil Paper]

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Raw

Acceleration

Velocity

Displacement

Total RMS

Displacement

Detr

en

d

In

teg

r

ate

Detr

en

d

In

teg

r

ate

Data Assessment

Sample Processing Approach Only- Not JIP data

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Approach

X

Y

Z

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New Jumper Specific Response Curve

DNV-RP-F105 Response Models

Jumper Response Curve currently shows differences with DNV-

RP-F105 curve. NEW Guidance Report issued.

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FSI CFD Study

The purpose of the study is to evaluate the

applicability of CFD as a response prediction

tool in-lieu of model tests.

Five cases selected for preliminary comparison

against the model test results.

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Jumper VIV CFD Activity

Flow around stationary cylinder (Pre-JIP)

– 2D Simulations

– 3D Simulations - RANS vs DES

Fluid-Structure Interaction (JIP)

– Analysis methodology

– Couple FE Structural solver and CFD solver

– Solve structural response within CFD code using linear mode

superposition (PFSI – Practical FSI)

– Both methodologies used in the JIP CFD Study

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Stationary Cylinder Study Cases

Flow Past 2D Rigid Cylinder at U= 0.3 m/s (CASE1-2D), 0.7 m/s (CASE2-2D)

,0.9 m/s (CASE3-2D)

Calculate quantities such as CD, CL, St with respect to Re.

Compare with experimental results

D (m) 0.06

L (m) 0.3 ( 5D)

U (m/s) 0.3, 0.7,0.9

Re (x103) 18.6, 45.0, 55.5 L

D

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2D Mesh Set Up

2.4 m (40D)

1.2

m (2

0D

)

Mesh Size = 16,111 FV’s, ∆x=∆y = 0.003m (0.05D) around cylinder, y+ < 1

SYMM

SYMM

OUTLET INLET

U

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Case 1,2 and 3: Comparison of force quantities

CASES U (m/s) Re (x103) Cd (CL)rms St

Case 1 0.3 18.6 1.51 1.13 0.241

Case 2 0.7 45.0 1.15 0.91 0.247

Case 3 0.9 55.5 1.10 0.88 0.248

St* = 0.2 for 104<Re<105

CD = 1.2

CD= 1.2 for 104<Re<2.8x105

DNV RP-C205

*St = fs D /U

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3D Mesh Set Up

• ∆t = 0.005 s

• ∆x=∆y=∆z=0.003m (0.05D)

• RANS: k- Model

• DES

5D

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Flow Around Cylinder - Comparison of Aerodynamic Coefficients (RANS)

CASES U (m/s) Re (x103) Cd (CL)rms St

Case 1-2D 0.3 18.6 1.50 1.13 0.24

Case 2-2D 0.7 45.0 1.15 0.91 0.25

Case 3-2D 0.9 55.5 1.10 0.88 0.25

CASES U (m/s) Re (x103) Cd (CL)rms St

Case 1-3D 0.3 18.6 1.34 0.92 0.21

Case 2-3D 0.7 45.0 1.05 0.68 0.22

Case 3-3D 0.9 55.5 1.00 0.62 0.23

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JIP FEA-CFD

Comparison between AcuSolve PFSI study and Ansys-Fluent Study

Similarity and Differences with Experiment

Preliminary Guidance for using CFD study

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Remaining Challenges

Effect of current direction; and the differences in the vortex pattern based on

current direction and the angle of the structural members (legs).

Shielding effect from adjacent legs

Hydrodynamic damping

Presence of coupled flexure-torsion and shear – Fatigue Estimation

Response model for range of jumper sizes and shapes

Current

Cross-flow

(horizontal leg)

Cross-flow

(vertical leg)

Current

Cross-flow

Freespan

M-shaped Jumper FSI: Fluid-Structure

Interaction

In-line

In-line

In-line

Multiple competing excitation regions possible

on an M-shaped jumper

The FSI for jumper is more complex than for a freespan

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Phase II JIP Plan

Desk Top Study

Additional load cases (esp. off angle cases) using FEA-CFD

– Special topics such as fatigue estimation.

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SAFER, SMARTER, GREENER

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Thank You

Aravind Nair

Aravind.Nair@DNVGL.COM

(970) 204 9657 [Mobile]