Section 3 Design
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Naval Ships, January 2023 - Volume 2 Machinery and Engineering Systems - Part 5 Shaft Vibration and Alignment - Chapter 2 Axial Vibration - Section 3 Design

Section 3 Design

Parent topic: Chapter 2 Axial Vibration

3.1 Symbols

3.1.1 The symbols used in this Section are as follows:

D = outside diameter of shaft, taken as an average over length l, in mm
d = internal diameter of shaft, in mm
l = length of shaft line between propeller and thrust bearing, in mm
m = mass of shaft line considered, in kg
= 0,785 (D2 – d 2) Gl
M = dry mass of propeller, in kg
A =
M e = M (A + 2)
n = number of propeller blades
k = estimated stiffness at thrust block bearing, in N/m
E = modulus of elasticity of shaft material, in N/mm2
G = density of shaft material, in kg/mm3
N c = critical speed, in rev/min.

3.2 Critical frequency of axial vibration

3.2.1 For those systems as defined in Vol 2, Pt 5, Ch 2, 2.2 Scope of calculations 2.2.1.(b) the propeller speed at which the critical frequency occurs may be estimated using the following formula:

where
a =
b =

3.2.2 Where the results of this method indicate the possibility of an axial vibration resonance in the vicinity of the maximum service speed, calculations using a more accurate method will be required.

3.3 Restricted speed ranges

3.3.1 The limits of any speed restriction are to be such as to maintain axial amplitudes within recommended levels during continuous operation.

3.3.2 Limits of a speed restriction, where required, may be determined from calculation or on the basis of measurement.

3.3.3 Where a speed restriction is imposed for the contingency of a damper malfunction, the speed limits are to be entered in the operating manual and regular monitoring of the axial vibration amplitude is required. Details of proposals for monitoring are to be submitted.

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