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Vibration, dynamics and noise

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Flow-Induced Turbulence (FIT) Analysis

for High Kinetic Energy Flow

FIT analysis applies to rotating pumps (or compressors) to determine if low-frequency vibration will cause piping vibration. This study can be conducted on a standalone basis, and it is also part of Wood’s comprehensive Piping Vibration Assessment (per Energy Institute Guideline – see link below). 

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1 Background

Turbulent energy is created in piping systems when fluid flows past significant flow discontinuities in the system.Typical examples are process equipment, partially closed valves, short radius or mitered bends, tees or reducers. The majority of the turbulent energy concentrates at low frequency (typically below 100 Hz). The level of excitation is higher at lower frequencies.

A FIT analysis is recommended for high flow systems with flexible and infrequent supports. One quick way to judge the risk of piping vibration related to FIT is to evaluate fluid kinetic energy:

Fluid Kinetic energy =  pv^2 where
p=density (kg/m^3) and v = fluid velocity (m/s)

risk of fit-related piping vibration
< 5000 kg/m-s^2 Low
< 20,000 kg/m-s^2 Medium
=> 20,000 kg/m-s^2 High 
2 Scope

The methodology used for this study is the Energy Institute’s Guidelines for the Avoidance of Vibration Induced Fatigue Failure in Process Pipework (AVIFF)

The FIT analysis considers the interaction between turbulent energy and low-frequency piping modes and makes recommendations to increase the stiffness of the piping support structure. Other recommendations include flow smoothing and dampers/snubbers.

An advanced FIT evaluation looks at the actual natural frequency of the piping system and makes recommendations to stiffen up the system.

The FIT study is a component of Wood’s Piping Vibration and Integrity Assessment 
This assessment includes the excitation sources illustrated in the chart.

Excitation Sources (FIT, FIV, AIV, STA)

-FIT (Flow-Induced Turbulence)

-FIV (Flow-Induced Vibration)

-AIV (Acoustic-Induced Vibration)

-STA (Shell Transverse Acoustical)

Excitation sources studied in Wood's Piping Vibration Assessment 

Note that the each of these excitation sources is caused by a different phenomenon and occurs at a different frequency. For more information on the other excitation sources, refer to the related services below.

3 Related Services
4 Related Information
5 Keywords
  • Vortex shedding
  • Vortex-induced vibration
  • Flow-induced pulsations
  • Flow-induced excitations
  • Energy Institute Guideline (2008)
  • Centrifugal compressor vibration
  • Avoidance of vibration induced fatigue failure in process pipework (AVIFF)

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