Noise and Vibration analysis services case study and overview by Gorm Dannesboe, Senior Consultant. Presentation covers: > Measuring Noise and vibrations > Noise and vibration modelling methods > How to mitigate noise and vibration on offshore platforms > Case study from Lloyd's Register Energy. You can read Gorm's accompanying bog here: For more information about our services, click here: http://www.lr-ods.com/expertise/noise-and-vibration-control.aspx This paper was originally presented at the International Petroleum Technology Conference 2014.

1. Noise and vibrations in the petroleum industry
IPTC, Doha, 21st January 2014
Working together
for a safer world

2. Consultancy in Lloyd’s Register
•
Lloyd’s Register started out as a classification
society 250 years ago
•
Now Lloyd’s Register covers a wide range of
services to the marine and energy business
including consulting.
•
Consulting includes among several areas
Engineering Dynamics and hereunder Noise and
Vibrations
Noise and vibrations in the petroleum industry

3. Measuring Noise
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We use state of the art tools for measuring and analysing noise.
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What can we measure?
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Noise level
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Sound power of machines
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Reverberation time of rooms
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Absorption
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Insulation
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Etc.
Sound Pressure: dB
Pow Watts
er:
(sound)
Noise and vibrations in the petroleum industry

4. Measuring Vibrations
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What can we measure
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Vibration levels
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Mobility
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Natural frequencies
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Impact test or operational modal analysis
(OMA)
Noise and vibrations in the petroleum industry

5. Pre-construction analysis
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Finding and preventing the problems before they occur.
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Internal noise
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0.5
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Noise and vibrations in the petroleum industry

6. Noise and vibrations in the petroleum industry

7. Calculating acoustic absorption and insulation needed for living
quarters
Lp,1
Noise and vibrations in the petroleum industry
Lp,2 = ?

8. Outdoor noise modelling
Noise and vibrations in the petroleum industry

9. Modelling of structure-borne noise
Lv4
LW4
Lv2
LW2
LW3 Lv3
LW1
Lv1
Noise and vibrations in the petroleum industry

10. Reducing vibrations from machinery
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Finite Element Modelling (FEM) to calculate mobility of support structures
Excitatio
n points:
Noise and vibrations in the petroleum industry

11. Modelling as part of troubleshooting
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Modelling coupled with measurements is a powerful tool for solving many different
problems
Noise and vibrations in the petroleum industry

12. Case study
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High levels of tonal noise from 45 t/h steam boiler
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Tones increase in frequency with increase in boiler load
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Increase in flow speed and temperature
Tones appear very suddenly following a small increase in load
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Preventing delivery of an oil tanker
And disappear just as suddenly at higher loads
Several tones observed simultaneously
Noise and vibrations in the petroleum industry

13. Measurements: Waterfall plot
Noise and vibrations in the petroleum industry

14. Noise and vibrations in the petroleum industry

15. •
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Fan tone
• Frequency doesn’t change with fan speed
Combustion instability
• Frequency too high
• Unlikely with oil fired nearly stoichiometric burn
Side branch resonance in exhaust stack
• Frequency too high
• No vibrations around side branch
Flow-structural interaction in heat exchanger
• Change in frequency with load too great
Flow-acoustic interaction in heat exchanger…
Noise and vibrations in the petroleum industry

16. Theory: Flow-acoustic interaction
Noise and vibrations in the petroleum industry

17. •
Scaling analysis
• Flow induced noise
• Important variables: flow speed U (function of temperature in the boiler),
pin diameter a
• [U] ~ ms-1, [a] ~ m, [f] ~ s-1 so St = fa /U
• Acoustic resonance
• Important variables: sound speed c (function of temperature), size of
boiler d
• [c] ~ ms-1, [d] ~ m, [f] ~ s-1 so He = f d / c
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U and c are functions of temperature in the boiler
• Sweep
Noise and vibrations in the petroleum industry

18. fd
= He1
c0 (T )
fd
= He 4
c0 (T )
fd
= He 2
c0 (T )
fa
=St 1
U
fd
= He 3
c0 (T )
fa
=St 2
U
Noise and vibrations in the petroleum industry

19. •
Frequency of tones scale with sound speed
• Acoustic, correspond to eigenfrequencies of the cavity
• Frequency of tones are determined by acoustic response
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Existence of tones corresponds to a certain range of Strouhal numbers
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As the boiler load increases
• The flow speed increases
• The Strouhal number of a given tone falls into the unstable range when it
appears, and eventually to below the unstable range, where it disappears
• The temperature increases
• The sound speed increases and
• The frequency of a given tone increases
Noise and vibrations in the petroleum industry

20. •
Simple solution is to fit a silencer
•
But…
• Large silencer = large back pressure
• Effects boiler efficiency
• No guarantee a larger boiler (or indeed a smaller) won’t fail
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Motivation for a long term solution
Noise and vibrations in the petroleum industry

21. •
Scale model built
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0.9 x 0.6 x 2.5 metres
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Cold air up to ca. 20m/s
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132 dB(A) 1m from outlet
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Complaints received from golf course 7 km away
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Staff threatened strike
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Tests stopped by police
Noise and vibrations in the petroleum industry

22. •
Unsteady flow behind pipes generates fluctuating lift on pins
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This is a source of sound
Noise and vibrations in the petroleum industry

23. •
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Acoustic response of cavity characterized by resonant acoustic modes
• Interaction between noise generated by unsteady flow and acoustic resonances
• Enhances the noise generating capability of the flow (nonlinear phenomenon)
• Synchronization
• Correlation
• Source amplification
• Not simply a case of broadband excitation exciting an acoustic resonance (linear
phenomenon)
Resulting in flow-acoustic self-sustaining oscillations, a.k.a. Boiler tones
Ordinary aeroacoustic prediction gives background noise level of 70 dB with broad
peaks up to about 90 dB.
• Peaks are too narrow and too high
Noise and vibrations in the petroleum industry

24. An analogy: The Millennium Bridge
Noise and vibrations in the petroleum industry

25. •
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Opened 10 June 2000
• Closed 12 June 2000
Bridge basically well engineered
• Calculated the structural response of 100,000 people per day walking across
• Assume stochastic, uncorrelated excitation (foot steps)
• Huge safety margin
• But possibly a little soft
But when the bridge starting swinging, the people on the bridge started swinging too
• Walking in time with the swing of the bridge
• Excitation no longer random
• Synchronized at the resonant frequency of the bridge
• Correlated in space because everyone sways the same way
Noise and vibrations in the petroleum industry

26. •
Same story in the boiler
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Simple (70 dB) model assumes the flow behind each pin is uncorrelated and
stochastic
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But the flow “feels” the acoustic field and starts “swaying” in time to the response
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The unsteady flow behind the pins corresponds to the people on the bridge
Excitation becomes correlated and synchronized
New prediction 140 dB
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Measured 120
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Not fully correlated everywhere
Nonlinear damping mechanisms
Flow-acoustic self-sustaining oscillation
Noise and vibrations in the petroleum industry

27. Numerical analysis: Test boiler at 50%
Noise and vibrations in the petroleum industry

28. Treatment
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Geometrical modification
• Reduce source power by modifying geometry
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Acoustic attenuation
• Increase dissipation in critical modes by introducing absorbing materials
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High temperatures – standard fibrous solutions will melt
Perforated plates
• Located at velocity maxima of critical modes
• Hole sized scaled to account for changes in acoustic conditions with temperature
and gas properties
• Significant levels of attenuation
• Self-cleaning
•
Noise and vibrations in the petroleum industry

29. Noise and vibrations in the petroleum industry

30. Noise and vibrations in the petroleum industry

31. •
If you are interested in learning more about Noise and Vibration control click here.
Noise and vibrations in the petroleum industry

32. Gorm Dannesboe
Senior Consultant
Energy
T +974 445 699 52
M +974 550 992 91 E gorm.dannesboe@lr.org
Connect with me on LinkedIn
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