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Noise and vibrations in the petroleum industry

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Information about Noise and vibrations in the petroleum industry
Technology

Published on January 20, 2014

Author: LRUpstream

Source: slideshare.net

Description

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

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

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

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

Pre-construction analysis • Finding and preventing the problems before they occur. • Internal noise 100 99 98 97 96 97 98 98 95 95 97 96 96 95 95 96 97 96 96 1 0.5 0 97 96 97 95 95 10 18 95 16 14 94 93 12 10 5 8 92 6 4 2 0 0 91 90 Noise and vibrations in the petroleum industry

Noise and vibrations in the petroleum industry

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

Outdoor noise modelling Noise and vibrations in the petroleum industry

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

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

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

Case study • High levels of tonal noise from 45 t/h steam boiler • • Tones increase in frequency with increase in boiler load • • Increase in flow speed and temperature Tones appear very suddenly following a small increase in load • • 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

Measurements: Waterfall plot Noise and vibrations in the petroleum industry

Noise and vibrations in the petroleum industry

• • • • • 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

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

• 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 • U and c are functions of temperature in the boiler • Sweep Noise and vibrations in the petroleum industry

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

• Frequency of tones scale with sound speed • Acoustic, correspond to eigenfrequencies of the cavity • Frequency of tones are determined by acoustic response • Existence of tones corresponds to a certain range of Strouhal numbers • 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

• 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 • Motivation for a long term solution Noise and vibrations in the petroleum industry

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

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

• • • 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

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

• • • 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

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

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

Treatment • Geometrical modification • Reduce source power by modifying geometry • Acoustic attenuation • Increase dissipation in critical modes by introducing absorbing materials • 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

Noise and vibrations in the petroleum industry

Noise and vibrations in the petroleum industry

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

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 Lloyd’s Register Qatar LLC Regus Building, D Ring Road, Doha, State of Qatar Working together for a safer world Lloyd’s Register and variants of it are trading names of Lloyd’s Register Group Limited, its subsidiaries and affiliates. Copyright © Lloyd’s Register [Entity]. 2013. A member of the Lloyd’s Register group.

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