# Mode 14 Calculator v1

Price: £15.25 (£15.25 Inc. VAT)

## Subject

A free-spanning beam or pipe is susceptible to vibration through continuous and/or recurrent inducements such as wave or wind loads. So long as the vibration frequency is not close to the natural frequency of the pipeline, excitation is not expected and failure is unlikely.

This problem can occur in any pipe, beam or structure spanning a gap that is exposed to free flowing or gusty fluid (air or water), or attached to vibrating equipment. The consequences of a structural failure of this type can be at worst; devastating and at best; expensive.

DnV generated its Guidelines No. 14 (June 1998) to address this issue for submerged pipelines, Sub-Section 3.7.2 of which is dedicated to defining the expected natural frequency based upon either constant horizontal fluid flow (e.g. current) or pipeline (submerged) weight including the effect of axial tension or compression along with recommended coefficients for end conditions.

## Calculator

Mode 14 calculates the natural frequency of a submerged pipe according to DnV's guidelines No. 14 for free spanning piplines, including the effects of axial tension or compression in the pipe due to the combined effects of laying, internal and external pressure differential and temperature when exposed to fluid flowing accross the pipe (current deflection load option) or simply due to the pipe's own submerged weight (weight deflection load option)

The mode 14 calculator also provides you with guidance on the appropriate use of DnV's recommended bending, axial and sagging coefficients (C₁, C₂ & C₃)

Mode 14 can be used to ensure that a pipeline’s natural frequency does not coincide with:

1) a sensitive piece of vibrating equipment
(see CalQlata's Engineering Basics, Rotary Balancing, Vibration Damping, Shafts calculators), or

2) the effects of a fluid flowing across it
(see CalQlata's Vortex Shedding)

Note: This calculator has not been officially endorsed by DnV. It is CalQlata’s interpretation of the guidelines

For help using this calculator see Technical Help

You enter: and the mode 14 calculator will provide:
• lay-tension in pipe
• pipe outside diameter
• pipe wall thickness
• coating thickness
• unsupported length
• internal pressure
• external pressure
• temperature change
• static/constant water velocity
• bending stiffness coefficient
• axial force coefficient
• sagging coefficient
• pipe tensile modulus
• temperature coefficient
• pipe material density
• medium density
• internal fluid density
• coating density
• drag coefficient
• gravitational acceleration
• natural frequency
• C₂.Sᵉᶠᶠ/Pᴱ
• L/D
• pipe second moment of area
• outside diameter
• inside area
• outside area
• effective mass per unit length
• effective unsupported length
• effective axial force