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DNV GL AS

RULES FOR CLASSIFICATION

Ships

Edition July 2016Amended January 2017

Part 4 Systems and components

Chapter 2 Rotating machinery, general

FOREWORD

DNV GL rules for classification contain procedural and technical requirements related to obtainingand retaining a class certificate. The rules represent all requirements adopted by the Society asbasis for classification.

© DNV GL AS July 2016

Any comments may be sent by e-mail to [email protected]

If any person suffers loss or damage which is proved to have been caused by any negligent act or omission of DNV GL, then DNV GL shallpay compensation to such person for his proved direct loss or damage. However, the compensation shall not exceed an amount equal to tentimes the fee charged for the service in question, provided that the maximum compensation shall never exceed USD 2 million.

In this provision "DNV GL" shall mean DNV GL AS, its direct and indirect owners as well as all its affiliates, subsidiaries, directors, officers,employees, agents and any other acting on behalf of DNV GL.

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Rules for classification: Ships — DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Rotating machinery, general

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CHANGES – CURRENT

This document supersedes the January 2016 edition.Changes in this document are highlighted in red colour. However, if the changes involve a whole chapter,section or sub-section, normally only the title will be in red colour.

Amendment January 2017

• Sec.1 Introduction— Sec.1 [6.1.5]: New paragraph added regarding resilient mounting.

Main changes July 2016, entering into force 1 January 2017

• Sec.2 Torsional vibrations— Sec.2 [2.3.1]: A new guidance note has been included regarding inertia of entrained water.

• Sec.4 Shaft alignment— Sec.4 [2.1.4]: Procedure from shaft alignment calculation shall include description of method and be

possible to re-use when in service.

• Sec.5 Electric power generation— Sec.5 [1.4]: A reference to Pt.4 Ch.3 for applicable load tests has been included.

Editorial correctionsIn addition to the above stated changes, editorial corrections may have been made.

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CONTENTS

Changes – current.................................................................................................. 3

Section 1 Introduction............................................................................................ 71 General................................................................................................ 7

1.1 Application and scope....................................................................... 72 Design principles................................................................................. 7

2.1 General........................................................................................... 73 Material and testing specifications...................................................... 8

3.1 General........................................................................................... 84 Welding specification...........................................................................95 Special materials and processes..........................................................9

5.1 General........................................................................................... 96 Foundations for machinery.................................................................. 9

6.1 General........................................................................................... 96.2 Documentation requirements............................................................106.3 Installation.....................................................................................106.4 Certification requirements................................................................ 11

Section 2 Torsional vibrations...............................................................................121 General.............................................................................................. 12

1.1 Application..................................................................................... 121.2 Symbols and definitions...................................................................121.3 Ice class........................................................................................ 141.4 Documentation requirements............................................................14

2 Calculation......................................................................................... 152.1 General..........................................................................................152.2 Free vibration.................................................................................162.3 Forced vibration frequency domain....................................................162.4 Forced vibration time domain........................................................... 192.5 Acceptance criteria..........................................................................20

3 Shipboard testing.............................................................................. 233.1 Check of barred speed range........................................................... 233.2 Check of gear hammer....................................................................233.3 Check of stability for systems with flexible couplings when misfiring...... 233.4 Check of transients during clutching-in procedure............................... 243.5 Closed loop stability........................................................................ 24

4 Test procedure...................................................................................24

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4.1 Measurements................................................................................ 24

Section 3 Lateral and axial shafting vibrations..................................................... 251 General.............................................................................................. 25

1.1 Application..................................................................................... 251.2 Definitions......................................................................................251.3 Documentation requirements............................................................26

2 Lateral vibration................................................................................ 272.1 Analysis......................................................................................... 27

3 Axial vibration................................................................................... 273.1 Analysis......................................................................................... 27

4 Measurements....................................................................................284.1 Axial vibration................................................................................ 284.2 Measurement program.....................................................................284.3 Measurement results....................................................................... 28

Section 4 Shaft alignment.....................................................................................291 General.............................................................................................. 29

1.1 Application..................................................................................... 291.2 Definitions......................................................................................291.3 Documentation............................................................................... 30

2 Calculation......................................................................................... 302.1 General..........................................................................................30

3 Installation........................................................................................ 363.1 Inspection...................................................................................... 36

Section 5 Electric power generation..................................................................... 381 Prime mover driving electrical generators........................................38

1.1 Transient loads............................................................................... 381.2 Detrimental speed variation............................................................. 381.3 Speed recovery.............................................................................. 381.4 Load demand................................................................................. 381.5 Two step on-loading........................................................................381.6 Multistep on-loading........................................................................381.7 Emergency generator...................................................................... 401.8 Load sharing.................................................................................. 401.9 Reactive load..................................................................................401.10 Rated speed adjustment................................................................ 401.11 Synchronization.............................................................................401.12 Electric power supply system..........................................................40

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SECTION 1 INTRODUCTION

1 General

1.1 Application and scope

1.1.1 These rules apply to rotating machinery used for the main functions defined in Pt.1 Ch.1 Sec.1 Table 2.

1.1.2 The rules cover design and construction, and provide procedural requirements for:

— design assessment— survey at manufacturer— certification of components— survey during installation on board the vessel and on board testing.

2 Design principles

2.1 General

2.1.1 All machinery shall be designed so that expected deviations of influence parameters do not result inunacceptable reduction of the reliability or safety. Influence parameters can be for example:

— power and speed *— number of times passing through a barred speed range— machining notches in inaccessible areas— diesel engine misfiring— variation of elastic coupling characteristics— variation of damper characteristics— normal tear and wear— deviation between actual material properties of the component and the minimum specified properties (as

verified by test specimen).

* Where requirements for dimensions in Ch.2, Ch.3, Ch.4 and Ch.5 are based on power and revolutions perminute, denoted by P and n0, the values applied are maximum continuous power (kW) measured on engineoutput shaft and corresponding revolutions per minute.However, for plants where overload occurs frequently (intermittent load), the scantling criteria may have tobe based on the overload, due to accumulated fatigue.

2.1.2 All parts shall be capable to withstand the stresses and loads peculiar to shipboard service, e.g. thosedue to movements of the ship, vibrations, intensified corrosive attack, temperature changes and waveimpact, and shall be dimensioned in accordance with the requirements set out in the present chapter. In theabsence of rules governing the dimensions of parts, a relevant international standard (to be stated) or themanufacturers standard shall be applied.Where connections exist between systems or plant items which are designed for different forces pressuresand/or temperatures (stresses), safety devices shall be fitted which prevent the over-stressing of the systemor plant item designed for the lower design parameters. To preclude damage, such systems shall be fittedwith devices affording protection against excessive pressures and temperatures and/or against overflow.

2.1.3 The manufacturer shall have a quality system in place that is suitable for the kind of certified product.The surveyor may check that the most important elements of this quality system are implemented and maycarry out random inspections at any time.

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The manufacturer (and designer, if producing under license) is committed to involve the Society in correctiveactions whenever failures occur to products certified by the Society and addressed in these rules, includingparts for which documents are submitted for information. The corrective actions include changes to designand/or quality control. Failing to involve the Society, or to carry out proper corrective actions, may result inwithdrawal of the type approval as well as restrictions of future approvals and/or certification.

2.1.4 When the rules require calculations and or analyses, this shall contain objectives, premises,assumptions and the conclusions.

2.1.5 The reliability and safety of components and complete units may also be documented by means ofapproved tests or service experience. The latter shall only be considered if a relevant load history can bedocumented. Acceptance of load history shall be decided case-by-case by the Society. Relevant load historymeans a suitable operation period (e.g. more than 2 500 hours for propulsion) under running conditionssimilar to the expected running conditions for the product to be approved.

3 Material and testing specifications

3.1 General

3.1.1 A material specification shall as a minimum contain the following:

— type of material— chemical composition— production method (cast, hot rolled, separately forged, blank cut out of a forged bar of specified size, etc.)— type of heat treatment— minimum mechanical properties (which normally includes impact energy Charpy-V for quenched and

tempered steels).

3.1.2 An NDT specification shall as a minimum contain the following:

— method of NDT— extent— acceptance criteria.

High stress areas shall be included in the NDT specification, in particular, zones with stress risers, such askeyways, holes, splines, teeth and shrinkage surfaces.For surfaces with specified hardness exceeding 400 HV, the extent of NDT shall be 100%.All NDT work shall be performed according to a written procedure. The procedure shall be in compliance withclass guideline DNVGL-CG-0051, or other recognized standards. The surveyor may require that the procedureis approved or qualified for the work.Unless otherwise specified in these rules or in approved manufacturer's specification, acceptance criteria fromthe following documents can be used for NDT of machinery components:

— For forged components: IACS Recommendation no.68.— For cast components: IACS Recommendation no.69.— For welds: ISO 5817 Level B.

The extent of material testing and documentation thereof is specified for the various components dealt within Ch.3 to Ch.5.

3.1.3 Material specifications including material testing and documentation shall be in accordance with Pt.2.If a material standard that deviates from Pt.2 is used, it may be required that the deviation is documented inthe form of a gap analysis, and justified by use of the principle of equivalency.

3.1.4 Blanks for gears and short shafts may be cut from forged bars without further forging.

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Such blanks are considered equivalent (regarding fatigue strength) to separate forgings (close to shape)provided that the forging process has been approved by the Society.Without this qualification the fatigue properties shall be assessed 20% below those of separate forgings.

4 Welding specificationFor welded connections in components dealt with in Ch.3 to Ch.5 the specification shall at least contain:

— welding procedure specification, see Pt.2 Ch.4 Sec.1 [3.2.1]— NDT specification containing:

— method of NDT— extent— acceptance criteria.

5 Special materials and processes

5.1 General

5.1.1 For materials which are more tolerant towards fatigue loading than ordinary materials for exampledue to high cleanliness (see Pt.2 Ch.2 Sec.6 [1.6.10]), and for processes which lead to improved fatigueproperties such as continuous grain flow forging, shot peening, cold rolling etc., special approval may begiven based on adequate testing and documentation.

6 Foundations for machinery

6.1 General

6.1.1 Foundation is a device transferring loads from a heavy or loaded object to the vessel structure whilesupporting structure is strengthening of the vessel structure, see Pt.3 Ch.3 Sec.5.

6.1.2 Foundations for machinery for propulsion, power generation and steering are subject to approval.Additionally, foundation for azimuthing thrusters is subject to approval independent of function.

Guidance note:As propulsion machinery is considered: driving engine or motor or turbine, reduction gear, separate thrust bearings and propulsionthruster.As power generating machinery is considered: driving engine or turbine and generator.As steering gear machinery is considered: steering gear rudder actuator.

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6.1.3 The foundation shall be of sufficient strength to transmit loads and keep the machinery fixed under alloperation conditions.Foundations for reciprocating combustion engines shall be in compliance with DNVGL-CG-0372 Foundationand mounting of machinery.Equivalent solutions may be accepted on a case by case basis

6.1.4 Resin casting compounds shall be type approved according to DNVGL-CP-0432 Pourable compoundsfor foundation chocking.

6.1.5 Resilient mounts shall be type approved according to DNVGL-CP-0144 Flexible mounts used forpropulsion or auxiliary machinery.

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6.2 Documentation requirements

6.2.1 For foundations for propulsion, steering and auxiliary machinery, the builder shall submit thedocumentation required by Table 1. The documentation shall be reviewed by the Society as a part of theclass contract.

Table 1 Documentation requirements

Object Documentation type Additional description Info

Foundation arrangement Z030 Arrangement plan Including specification of foundation type. FI

Fastening devices C030 Detailed drawing Including bolts, nuts, sleeves, stoppers andfitted elements. AP

Chocks, fixed C030 Detailed drawing AP

Chocks, adjustable C030 Detailed drawing AP

Z100 Specification Including material and design loads. AP, TACast synthetic foundations

C040 Design analysis Loads and fastening devices. FI

Z100 Specification Including stiffness and damping. AP, TA

Resilient mountsC040 Design analysis Vibration analysis, including maximum

deflections. AP

AP = For approval; FI = For information; TA = Covered by type approval

6.2.2 For general requirements for documentation, including definition of the info codes, see Pt.1 Ch.3 Sec.2.

6.2.3 For a full definition of the documentation types, see Pt.1 Ch.3 Sec.3.

6.3 Installation

6.3.1 Foundations for machinery for propulsion, power generation and steering are subject to survey by theSociety.

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6.4 Certification requirements

6.4.1 Certification requirements for foundations are summarized in Table 2.

Table 2 Certification requirements

Object Certificate type Issued by Certification standard* Additional description

Bolts MC Society Including nuts.

Certificate issued by themanufacturer may beaccepted for standardbolts up to thread sizeM39

PC Builder Measured tighteningtorque for foundationbolts

Castsyntheticfoundations

TA Society For resin

Resilientmounts

TA Society Type approval requiredfor standard designs

* Unless otherwise specified the certification standard is the rules.

6.4.2 For general certification requirements, see Pt.1 Ch.3 Sec.4.

6.4.3 For a definition of the certification types, see Pt.1 Ch.3 Sec.5.

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SECTION 2 TORSIONAL VIBRATIONS

1 General

1.1 Application1.1.1 ScopeThe rules in this section apply to all shafting used in rotating machinery for propulsion, power production,steering and manoeuvring independent of type of driver except auxiliary plants with less than 200 kW ratedpower.

1.1.2 SimplificationOnly mechanical active systems shall be included in the analysis. De-clutched branches shall not be requiredin the model. Electric power transmission, hydrodynamic couplings and torque converters shall not be seenas components transferring torsional vibrations; consequently systems in both ends can be handled asindependent mass elastic systems.

1.1.3 Acceptance criteriaAcceptance criteria are found in the respective rule chapters for the components.

1.1.4 Coupled vibrationsAxial vibrations initiated by torsional vibrations are handled in Sec.3.

1.1.5 Forced vibration analysisTime domain simulation can be used as alternative to conventional forced torsional vibration calculation. Thisis suitable for determination of vibration outside the engine itself, such as in nonlinear couplings and gearmeshes. Relevant cases for simulation are presented in [2.4.3].

1.2 Symbols and definitionsTable 1 Symbols

Symbol Unit Explanation

n0 rpm Rotational speed at maximum continuous power (mcr)

n rpm Rotational speed at which vibration are considered

λ - Speed ratio defined as n/n0

T0 kNm Rated torque (at maximum continuous power)

T kNm Mean torque at n

Tv kNm Vibratory torque amplitude at n

τ N/mm2 Torsional stress corresponding to T

τv N/mm2 Torsional stress corresponding to T

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Table 2 Definitions

Term Definition

amplitude of vibratorytorque

Tv = 0.5 (maximum torque - minimum torque) during a time interval that covers the periodof the lowest order, including possible beat orders

This definition also applies for non-linear vibration and for synthesized linear vibrationwhere the average torque (which is the average between the maximum torque and theminimum torque) differs significantly from the effective driving torque (mean torque T).In such cases the mean torque used in various fatigue criteria shall be replaced with theaverage torque.

driver unit acting as power source to the shafting system, e.g. engine, electric motor, gas turbine,steam turbine

engine in this context engine is associated with reciprocating combustion engines independent offuel type

frequency domain calculation where frequency is used as free variable, usually with rad/s or Hz as unit

mass elastic system model consisting of inertias, springs and dampers representing the shafting system

misfiring misfiring in a cylinder is defined as no fuel injection. The compression - expansion cycle isassumed to be maintained under the same charge air pressure as normal

order number of excitation cycles per cycle of an engine. One engine cycle is one revolution fortwo-stroke engines and two revolutions for four stroke engines

natural frequency natural frequency (or modal frequency) is the frequency at which a system tends tooscillate in the absence of any driving or damping force. Number of natural frequencies isequal to number of independent inertias

time domain calculation where time is used as free variable, usually with seconds as unit

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transient torsional vibration non periodic external excitation of the system. In this context it is associated withoperations as:

— acceleration or deceleration through a barred speed range— starting and stopping operations, especially when driven inertia is multiple of drivers

inertia— clutching in— short circuit in PTO driven generators, especially when Kdyn/T0 > 10 in the PTO branch— propeller out of water and water jet aeration— ice impact dependent of ice class notation— system instability

The latter condition is in principle a transient condition even if it occurs at constant speedbecause the excitation increases due to the feedback from the speed governor.

vibration mode shape pattern with non-dimensional angular displacements of inertias along the shafting for agiven natural frequency

1.3 Ice class

1.3.1 Ice class notations are presented in Table 3:

Table 3 Ice class notations

Rule reference Class Notations

Pt.6 Ch.6 Sec.1 Basic Ice Strengthening Ice(C), Ice(E)

Pt.6 Ch.6 Sec.2 Ice Strengthening for theNorthern Baltic

Ice(1A*), Ice(1A), Ice(1B), Ice(1C)

Pt.6 Ch.6 Sec.5 Polar Class PC(1), PC(2), PC(3), PC(4), PC(5), PC(6), PC(7),Icebreaker

All Ice class notations except Basic Ice strengthening require response torsional vibration analysis due topropeller ice impact excitations. Definition of loads and how to apply them are found in the respective ice rulechapters.


1.4.1 The builder, or a sub-supplier acting on behalf of the builder, shall submit the documentation requiredby Table 4. The documentation shall be reviewed by the Society as a part of the class contract.


Object Document type Additional description Info

C040 – Design analysis Forced vibration calculation, see [2.3] AP

C040 – Design analysis Systems with large transients.

Forced vibration in time domain, see [2.4]

AP, R

Conventional propulsionarrangement

C040 – Design analysis Fatigue calculation AP, R

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Z241 – Measurement report Measurement of torsional vibrations ifrequested during approval

AP, R

C040 – Design analysis Forced vibration calculation, see [2.3] AP


Forced vibration in time domain, see [2.4]

AP, R

Propulsion and steeringthruster arrangement

Z241 – Measurement report Measurement of torsional vibrations ifrequested during approval

AP, R

C040 – Design analysis Tunnel thruster – hydraulic or electric driven.Free vibration calculation see [2.2]*)

AP

C040 – Design analysis All other manoeuvring thrusters.

Forced vibration calculation, see [2.3]*)AP


Forced vibration in time domain, see [2.4]*)AP, R

Manoeuvring thrusterarrangement

Z241 – Measurement report Measurement of torsional vibrations ifrequested during approval *)

AP, R

C040 – Design analysis Forced vibration calculation, see [2.3] **) AP


Forced vibration in time domain, see [2.4] **)AP, R

Electric power generation

Z241 – Measurement report Measurement of torsional vibrations ifrequested during approval **)

AP, R

C040 – Design analysis Forced vibration calculation, see [2.3] **) APEmergency electric powergeneration

Z241 – Measurement report Measurement of torsional vibrations ifrequested during approval **)

AP, R

AP = For approval; FI = For information; R = On request

*) Not required for auxiliary thrusters of 300 kW or less as these have no certification requirements. Thrusters usedfor dynamic positioning is not auxiliary.

**) Generator set not used for propulsion is defined as auxiliary and not scope of approval if less than 200 kW.

1.4.2 For general requirements to documentation, including definition of the info codes, see Pt.1 Ch.3 Sec.2.


2 Calculation

2.1 General2.1.1 Analysis conclusionAll analysis reports shall have a conclusion. In case of forced vibration analysis the conclusion shall be basedon a comparison between calculated dynamic response and the permissible values for all the sensitive partsin the plant. Assumptions, conditions and restrictions shall be presented.

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2.1.2 Input data qualityGeneralParameters of importance which are uncertain, varying or nonlinear are handled by use of extreme values.It is not required to perform calculations with all combinations of these extreme data, but as a minimum theinfluence shall be quantitatively considered and also addressed in the conclusions.Uncertain parametersVariation of essential data such as dynamic characteristics of elastic couplings and dampers shall beconsidered. Especially rubber couplings and certain types of vibration dampers have wide tolerances ofstiffness and damping.Variation of parameter valuesFor components like couplings having stiffness with strong dependency on vibratory torque and/ortemperature (as a consequence of power loss) calculation where these dependencies are included may berequested.Nonlinear characteristicsSystems with components having a strong nonlinear characteristic within the operation range with largeinfluence on the system dynamics shall be simulated in time domain.Source of dataIn vibration calculations the source of all essential data shall be listed. For data that cannot be given asconstant parameters the assumed parameter dependency and tolerance range shall be specified.

2.2 Free vibration2.2.1 Analysis contentNatural frequency calculations of the complete system are required. These shall include tables of relativedisplacement amplitudes, relative inertia torques, vector sums and, if used later, also their phase angles.Specification of input dataMass elastic system: Moments of inertia and inertia-less torsional elasticity/stiffness for each element in thecomplete systemComponents: List of components with technical data as found relevant.Presentation of results

— Tables: Relative displacement amplitudes, relative inertia torques, vector sums and, if used later, alsotheir phase angles.

— Graphs: Vibration mode shapes.

2.2.2 Calculation methodCalculation of relevant natural frequencies and their corresponding mode shapes shall be carried out byrecognised calculation methods.

Guidance note:Examples of recognised methods obtaining natural frequencies and their mode shapes are methodologies for direct matrixsolutions calculating eigenvalues. Alternatively, approximate methods as the iterative Holzer’s method can be used. Damping hasvery little effect on natural frequency of the system, and hence the calculations for natural frequencies may be made on the basisof no damping.


2.3 Forced vibration frequency domain2.3.1 Analysis contentFree vibrationForced vibration shall include free vibration calculation see [2.2].

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Specification of input dataData to be specified as applicable:

— Engine: Engine maker including type designation, rated power, rated speed, cycles per revolution, design(in-line/V-type), number of cylinders, firing order, cylinder diameter, stroke, stroke to connecting rodratio, oscillating mass of one crank gear, excitation see [2.3.3].

— Vibration damper: Type, damping coefficient, moments of inertia, dynamic stiffness.— Elastic couplings: Type, damping coefficient, moments of inertia, dynamic stiffness.— Reduction/power take off (PTO) gears: Type, moment of inertia for wheels and pinions, individual gear's

ratios per mesh, effective stiffness.— Shafting: Shaft diameter of crankshafts, intermediate shafts, gear shafts, thrust shafts and propeller

shafts.— Propeller: Type, diameter, number of blades, pitch and expanded area ratio, moment of inertia in air,

moment of inertia of entrained water (for zero and full pitch for CP propellers).— Mass elastic system: Values of all inertias, stiffnesses and damping values including propeller damping.

Presentation of results

— The results of the forced torsional vibration calculations shall be presented as relevant for the variouscomponents in the system.

— The results shall be presented as synthesis, including amplitude and phase from the orders representingthe largest contributions.

— The results shall be presented by graphs including acceptance values, see [2.5].— Where barred speed range is required, maximum time for passing shall be specified.

Guidance note:Propeller moment of inertia for entrained water shall be specified by propeller designer, see Ch.5 Sec.1 [1.2.5].


2.3.2 Calculation method and modelMethod and mass elastic systemThe forced torsional vibration shall be calculated by means of linear differential equations, one for eachlumped mass. Each mass shall be described by its inertia, connected by torsional springs to adjacent masses,damping described as absolute (mass) damping and relative (shaft) damping, and excitation applied onmass. Other recognized methods may be accepted upon request.Representative parameter valuesThe parameters used in vibration calculations shall be representative for the actual speed, mean torque,frequency, temperature, and vibratory torque. The latter implies that if an element is strongly dependent onthe level of the vibratory torque and used in a linear vibration calculation, then the whole calculation mayhave to be made by iteration.Two-stroke engineEngine designer’s model and parameters shall be applied.Propeller dampingIn order to best represent the damping properties of a propeller, the Archer’s or Frahm’s approach withtorque dependent damping coefficients should be used. Alternative methods using a dynamic magnifier orSchwanecke’s empirical approach or other approaches shall be subject to special consideration. For planingcrafts damping shall be based on derivation of the actual torque characteristics, see guidance note.

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Guidance note:Propeller damping is a consequence of the propeller’s torque absorption characteristics, defined as C = dT/dω, where T is absorbed

torque and . The torque characteristic for non-planning vessels can be formulated as T = nm, where μ is 2 in steady

state condition, but is somewhat higher due to the superimposed vibratory torque. The Archer number is defined as .

The corresponding Frahm number is Q ≈ a/9,545. Archer number is depending on the actual propeller design and load, but istypically in the range 24-30 for conventional propellers. Dynamic magnifier for absolute damping is defined as M = Jω/C, where Jis propeller inertia and ω is actual vibration frequency. The corresponding relative damping is ζ = (ω/ωn)/2M. Dynamic magnifier orrelative damping should only be applied based on experience from measurements of similar plants.


2.3.3 ExcitationTwo-stroke engineEngine excitation shall be based on harmonic tables of tangential crank pressure from engine designerrelevant for the actual engine with respect to type approval. Alternatively it can be based on measurementsof cylinder pressure for the actual engine.Four stroke engineIn addition to the methods for two-stroke engines, simplified methods with generic predefined pressure-timecharacteristics based on main engine data may be accepted.Propeller excitationPropeller excitation can be taken as a percentage of the actual mean torque according to Table 5 unless othervalues are substantiated by the propeller manufacturer. The values are representative for max continuousforward operation. Propeller excitation for extreme steering manoeuvres of azimuth thrusters shall be takenas 3 times the excitation in Table 5, unless other figures can be documented.

Table 5 Propeller excitation as percent of mean torque

Number of blades Blade frequency Double blade frequency

3 8% 2%

4 6% 2%

5 4% 1.5%

6 4% 1.5%

Other excitationsOther excitation sources as electric drive control system, water jet impeller pulses, universal joints (secondorder), etc. may have to be taken into accountwhen it influences the system behaviour.

2.3.4 Conditions

— normal operation. For engines this shall be applied as uniform pressure distribution over all cylinders— misfiring operation, only applicable for engines— where the installation allows various operation modes, the torsional vibration characteristics shall be

investigated for all possible modes, see guidance note.

Guidance note:Examples of designs to investigate are installations fitted with controllable pitch propellers for zero and full pitch, power takeoff gear integrated in the main gear or at the forward crankshaft end for loaded and idling generator, clutches for engaged anddisengaged branches.


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Selection of misfiring cylinderFor calculation in misfiring condition the misfiring cylinder shall be selected as follows:

— for vibration modes and orders with vector sums almost equal zero, any cylinder may be selected— for vibration modes with significant vector sums (e.g. > 0.1 relative to maximum cylinder amplitude)

either:

— the cylinder which has the opposite phase angle of the vector sum should be selected or— calculating all combinations and presenting the worst.

2.4 Forced vibration time domain2.4.1 Analysis contentFree vibrationForced vibration shall include free vibration calculation, see [2.2].Specification of input dataEngine data to be specified as applicable; brand, model, bore, stroke, piston rod length, number of cylinders,V-angle, firing sequence and max rpm.

2.4.2 Calculation method and modelMethod and mass elastic systemThe forced torsional vibration shall be calculated by numerical integration of differential equations as foundrelevant for the system modelled.Simplified modelThe mass elastic system for numeric simulation can be simplified in order to remove high natural frequencies.It is required to verify by natural frequency calculations that the simplified system has approximately thesame lower (only the important) frequencies as the detailed system.Presentation of resultsSimulation results shall be presented by graphs. Resolution and choice of parameters shall reflect theintention of the simulation.

2.4.3 Relevant cases for simulationPassing through a barred speed rangeSimulation of fixed pitch propeller plants shall take into account the most important properties of thepropulsion, the ship mass and resistance (fully loaded) and the rpm control.The result of transient vibration documentation shall contain the peak vibration level and an estimation of theequivalent number of cycles. The acceptance criterion is the peak torque (or stress) and the correspondingequivalent number of cycles that shall be used for the shaft calculations.The equivalent number of cycles is defined as the number that results in the same accumulated partialdamage (Miner’s theory) as the real load spectrum. This equivalent number of cycles for passing up anddown through the barred speed range shall be multiplied with the expected number of passages during theforeseen lifetime of the ship. A detailed method for evaluating the equivalent number of cycles and expectednumber of passages is presented in class guideline DNVGL-CG-0038.Ice impact loadsResponse of non-harmonic impact loads from ice as described in the ice rules (see [1.3]) shall be simulatedin the time domain when shaft speed cannot be maintained due to ice loads. Frequency domain calculation inresonant speed can be used as an option.Large inertia loadsFor plants that have a major critical resonance below idling speed and a low ratio of engine inertia to drivenmachinery inertia, the transient vibration torque shall be considered. This applies e.g. to diesel generator setswith highly elastic couplings and similar propulsion plants without clutch.

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Clutching-inThe calculation of the system shall determine:

— the peak torque in couplings and gears— the first decreasing torque amplitudes— the heat developed in the clutch— the flash power in the clutch.

The clutch parameters such as the actuation pressure-time characteristics and if necessary also the changingcoefficient of friction shall be used in the calculation.The results are not to exceed the permissible peak torques and amplitudes in couplings and gears in additionto the permissible heat (J) and flash power (W) in the clutch.Torque measurements during the clutching-in may be required. This applies when calculations indicate peaktorques or amplitudes near the approved limits.Short circuit in PTO driven generatorsA possible short circuit in a generator is not to be detrimental for the power transmitting elements such ascouplings and gears. The purpose of the calculation shall determine the peak torques and amplitudes thatoccur before the safety system (circuit breaker) is in action. The duration to be considered is 1 s.

Guidance note:If the excitation torque (in the air gap between rotor and stator) is not specified, it can be assumed as:

T = T0 [10 e-t/0.4 sin(Ω t) – 5 e-t/0.4 sin(2Ω t)]where:

Ω/2π = the electric net frequency (50 or 60 Hz)

t = time in s.


Influence of speed governorWhen the speed governor influence has be taken into account it shall be done in the time domain.

2.5 Acceptance criteriaIf any result is close to the acceptance limit and there are uncertainties in the calculations, vibrationmeasurements may be required, see [4].

2.5.1 Availability of main functionsIn specifying prohibited ranges of operation it has to be observed that the navigating and manoeuvringfunctions are not severely restricted.

2.5.2 Determination of barred speed rangeSpeed ranges or operating conditions where the following acceptance criteria are exceeded, shall bebarred for continuous operation. Corresponding signboards shall be fitted at all manoeuvring stands and alltachometers marked with red. The tachometers shall be accurate within the tolerance +/-0.01 n0. A barredspeed range above λ = 0.8 is not permitted.The width of a barred speed range shall be determined as follows:

— range where permissible values are exceeded— extend with tachometer tolerance in both ends— further extension in case of unstable engine operation at any end of the barred range.

Guidance note:For 2-stroke fixed pitch plants the width of the barred speed range should not be made unnecessary wide because this can resultin a too slow passage with the consequence of higher vibratory stress level and increased number of cycles with high stress level.


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2.5.3 Misfiring conditionExceeding the acceptance limits in misfiring condition shall result in:

— restricted (e.g. < 0.5 hours) operation when the vibration level is acceptable for limited time (slowheating of rubber elements)

— restricted driving or load condition (barred speed range or speed reduction etc.)— rejection when the vibration level may be critical as e.g. speed governor response, heating of rubber

elements causing damping and stiffness to alter to further increase the vibration level, hard gear hammer,etc.

2.5.4 ShaftsDesign requirements with acceptance criteria for shafts are found in Ch.4 Sec.1.For plants with gear transmissions, the shafts (inside as well as outside the gearbox or thruster) shallbe designed for at least the same vibration level as the gearing. Unless significantly higher vibration areexpected to occur somewhere in the shafting, documentation of the vibration levels in the shafts is notrequired.For direct coupled plants the vibration level (τv) is not to exceed the values used for the shafting design withregard to continuous operation. Alternatively, the calculated vibration for continuous operation may be usedfor the shafting design.For shafts that are designed on the basis of transient vibration, the torque amplitudes as well as number ofequivalent cycles per passage are not to exceed the prerequisites for the shaft designExtended documentation to be submitted for designs where it is likely to expect high cycle fatigue due topassing of barred speed range, see guidance note.

Guidance note:In this context high cycle fatigue is expected when high transient stress amplitudes are combined with a large number of cycles.Total number of cycles is dependent of cycles for each passing of barred speed range (BSR) and the vessel's operation profile. Alarge number of cycles shall be understood as above 105 cycles. Extended documentation shall contain fatigue analysis supportedby engine and propeller curves as relevant. Classification guideline DNVGL-CG-0038 Calculation of shafts in marine applicationscan be used for fatigue analysis. DNVGL-CG-0038 calculates fatigue capacity based on Wöhler curve (S-N curve) and Miner sum.


2.5.5 CrankshaftsDesign requirements and acceptance criteria for crankshafts are found in Ch.3 Sec.1.The permissible vibration torque (or shear stresses) and peak torque (only applicable to semi-built shafts)are determined in connection with the engine approval. Other criteria may also apply, such as acceleration atmass for cam drive branch or journal movements in bearings.

2.5.6 Vibration dampersDesign requirements and acceptance criteria for dampers are found in Ch.3 Sec.1.Depending on the type of damper (viscous, rubber, steel spring) the following shall be considered:

— dissipated power (all kinds)— vibration torque (rubber type and some steel spring types)— vibration angle (some steel spring types).

The limits specified in the respective type approvals apply.

2.5.7 Torsional elastic couplingsDesign requirements and acceptance criteria for torsional elastic couplings are found in Ch.4 Sec.5.Torsional elastic couplings have design limitations with respect to:

— dissipated power— vibration torque.

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These limits are for continuous operation. Higher values may be accepted for a limited time of operation iftwist amplitudes are monitored.Transient vibration which occur occasionally (i.e. less than 50 000 times) such as clutching-in is not to exceedneither TKmax1 nor ΔTKmax.Transient vibration which occur very infrequently indeed such as short circuit [2.4.3] are not to exceedTKmax2.Power loss need not be considered for transient operation.

2.5.8 Other couplingsDesign requirements and acceptance criteria for actual components are found in Ch.4 Sec.4.For other couplings and similar components such as membrane couplings, universal joints, link couplings,elements of composite materials, etc. the approved vibration torque shall not be exceeded.Tooth couplings are limited with regard to cyclic torque reversals. The negative torque is not to exceed 20%of T0 unless especially approved.

2.5.9 Gear transmissionsDesign requirements and acceptance criteria for gear transmissions are found in Ch.4 Sec.2.The permissible vibration torque in gear transmissions is limited as:

1) In the full speed and load range (> 90% of rated speed and load) the vibration torque is not to exceed(KA - 1)·T0 where KA is the application factor used in the gear transmission approval.

2) The vibration torque is limited to 35% of T0 throughout the entire operation range.3) Gear hammer (negative torque) is not permitted except in unloaded power take off branches, where

10% of T0 (referred to the subject shaft speed) and 15% short duration misfiring is permitted.4) Transient vibrations shall not cause negative torques of more than 25% of T0.5) Transient peak torques shall not exceed T0.6) Transient peak torques shall not exceed the approved (KAP T0) or (1.5 T0).

2.5.10 Shrink fits including propeller fittingDesign requirements and acceptance criteria for shrink fits are found in Ch.4 Sec.1.The estimated vibration torque shall not exceed the value used in the approval of the shrink fit connection.Permissible vibration torque in shrink fit connections shall be considered for direct coupled plants and whenthe peak torque in a barred speed range exceeds the peak torque at full load. Peak torque values duringmisfiring operation shall be subject to special consideration.

2.5.11 PropellersDesign requirements and acceptance criteria for propellers are found in Ch.5 Sec.1.No specific limitations apply unless especially mentioned in connection with the propeller approval.

2.5.12 ThrustersSee Ch.5 Sec.3.

2.5.13 Electric rotating machines generators, pumps, compressors etc.The vibration level shall not exceed any limitation specified by designer of the electric generator or motor.

2.5.14 Speed governorThe vibration levels at the sensor location of flexibly coupled propulsion engines shall not exceed the valuespecified by the engine manufacturer. If no value is specified and approved, tests and measurements shall bemade in order to verify that the governor response is insignificant.

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3 Shipboard testing

3.1 Check of barred speed range3.1.1 Time recordingWhere a barred speed range (BSR) is required, passages through this BSR, both accelerating anddecelerating, are to be demonstrated. The times taken are to be recorded and are to be equal to or belowthose times stipulated in the approved documentation. This also includes when passing through the BSR inreverse rotational direction, especially during the stopping test. This applies both for manual and automaticpassing-through systems. The ship's draft and speed during all these demonstrations is to be recorded. Inthe case of a controllable pitch propeller, the pitch is also to be recorded (IACS UR M51 [4.5]).

3.1.2 Border stabilityThe engine is to be checked for stable running (steady fuel index) at both upper and lower borders of thebarred speed range. Steady fuel index means an oscillation range less than 5% of the effective stroke (idle tofull index) (IACS UR M51 [4.5]).

For controllable pitch propellers, this shall be tested with both zero and full pitch unless otherwise agreed.

3.1.3 Quick pass throughPassing through a barred speed range shall be made in an optimum way. This means as quickly as possible.If a specific procedure is given in the torsional vibration calculations, this shall be verified under the foreseenoperational conditions.

3.1.4 SignboardWhen a barred speed range is required, signboards describing how to pass through shall be provided at allengine operating stands.

3.2 Check of gear hammerReduction gears and power take off gears shall be detected for gear hammer in misfiring condition inranges specified in connection with the approval. Speed ranges where gear hammer occurs shall be barredfor continuous operation. However, in power take off gears light gear hammer in unloaded condition isacceptable.

3.3 Check of stability for systems with flexible couplings when misfiringEngines with elastic couplings shall be checked for stability of the speed governing system when provoked bymisfiring. For selection of misfiring cylinder, see approved torsional vibration calculations.Unless otherwise stated in the approved torsional vibration calculations, the following apply for each plant onboard:

— Single engine plant; The entire speed range with either full pitch or combination pitch shall be checked.This may be done by a slow sweep or stepwise speed increase.

— Two-engine plants (with common reduction gear); The same applies, but the misfiring of the enginesshall be combined. This may be done by keeping the selected misfiring for engine one, and first select acylinder at random for the second engine and afterwards select the adjacent cylinder, see guidance note.

— Plants with more than two engines; Special considerations apply.— Diesel generator sets shall be checked at a minimum of 50% load and with another set operating in

parallel. All sets shall be tested.— Speed ranges where gear hammer occurs due to one misfiring cylinder shall be restricted for continuous

operation in that operation mode.

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Guidance note:

Explanation to the two engine plant test: This is a test of low order (typical 0.5 order) instability and not two independent failures.Hence, it is important that the two engines have different phase shift after a clutching in-out sequence, and that both enginesare misfiring in order to have enough imbalances to simulate worst case with 0.5 order resonance. Fuel rack oscillations peak topeak (with combined misfiring for twin engines) less than 20% of the effective stroke (idle to full) are normally considered asacceptable. For engines without fuel rack similar parameters are taken from engine monitoring system.


3.4 Check of transients during clutching-in procedureAfter the clutch characteristics (pressure - time) are checked, the clutching-in shall be checked at theminimum respectively the maximum permissible engine speed for clutching-in. The speed governing systemshall respond with quickly damped oscillations.

3.5 Closed loop stabilityThe following may be requested, see type of speed governor

— type and position of speed sensor.Guidance note:Evaluation of the torsional vibration system should be considered in case of conditions with high vibration at the governor pick upposition.


4 Test procedure

4.1 Measurements4.1.1 InstrumentationWhen vibration measurements are required by the Society, the type of instrumentation, location of pickups,signal processing method, and the measurement procedure shall be approved by the Society.

4.1.2 Measurement reportWhen vibration measurements are required by the Society, a complete report containing results fromunfiltered signals (e.g. shaft stresses) as well as processed signals (e.g. frequency analyses) shall besubmitted for approval.

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SECTION 3 LATERAL AND AXIAL SHAFTING VIBRATIONS

1 General

1.1 Application1.1.1 ScopeThe rules in this section apply to all shafting used in rotating machinery for propulsion, power production,steering and manoeuvring independent of type of driver except auxiliary plants with less than 200 kW ratedpower.

1.1.2 Vibration regimesThe following vibration regimes are covered within this section:

— lateral vibrations are handled as whirling, see [2]— axial vibration see [3].

The following regimes are covered in other rule chapters:

— torsional vibrations see Sec.2— engine flexible mounting, see Ch.3 Sec.1— vibration level as environmental requirement, see Ch.1 Sec.3— class notations related to vibrations see Pt.6 Ch.8 Sec.1 and Pt.6 Ch.8 Sec.2.

1.1.3 Acceptance criteriaAcceptance criteria for components are found in the respective rule chapters for the components.

1.1.4 Coupled vibrationsAxial vibrations initiated by torsional vibrations can be handled as independent, but with the radialcomponent of excitation from the cylinder forces.

1.1.5 Forced vibration analysisTime domain simulation may be requested in addition to forced vibration calculation in the frequency domainfor transient analysis.

1.2 DefinitionsTable 1 Definitions

Term Definition

axial vibration vibration in the direction of the centre line

counter whirl whirl vibration has opposite direction as the mean shaft rotation

forward whirl whirl vibration has equal direction as the mean shaft rotation

lateral vibration vibration in orthogonal direction to the centre line

order number of excitations per shaft revolution

whirling run out of shaft and shafting components with nodes in the shaft bearings

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1.3.1 The builder, or a sub-supplier acting on behalf of the builder, shall submit the documentation requiredby Table 2. The documentation shall be reviewed by the Society as a part of the class contract.



C040 - Design analysis Lateral vibration *) AP, RConventional propulsion arrangement

C040 - Design analysis Axial vibration *) AP, R

C040 - Design analysis Lateral vibration *) AP, RPropulsion and steering thrusterarrangement


C040 - Design analysis Lateral vibration *) AP, RManoeuvring thruster arrangement


AP = For approval; R = On request*) Default is free vibration calculation, but more extended calculations may be requested.

Guidance note 1:Lateral vibration calculation may be requested during approval of shaft arrangement. Example of sensitive designs are; Shafts withlarge bearing span/shaft diameter ratio, propellers with large overhang from aft most bearing, flexible support of aft most bearingas typical for twin screw designs, large inertias without bearing support, tooth couplings without bending stiffness.


Guidance note 2:Axial vibration calculation may be requested during approval of shaft arrangement. Example of sensitive designs are; Long stroketwo-stroke engines without axial damper, shafting with length above 40 m, flexible couplings with interaction between torque andaxial deflection, propeller designs where natural blade bending frequency is equal to natural axial shaft frequency.




1.3.4 Drawings of the complete shafting arrangement shall be included in the design analysis. Typedesignation of prime mover, gear, elastic couplings, driven unit, shaft seals etc. shall be stated on thedrawings. The drawings shall show all main dimensions as diameters and bearing spans, bearing supportsand any supported elements as e.g. oil distribution boxes.

1.3.5 The vibration calculations shall be accompanied by an analysis, which shall compare the result ofthe calculation with the acceptance levels for all components in the system as relevant, and conclude withrespect to possible restrictions. Assumptions, conditions and restrictions shall be presented.

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2 Lateral vibration

2.1 Analysis2.1.1 Extent and method of calculationAs a minimum, the calculations shall include the natural frequencies and mode shapes of the relevantvibration modes.

2.1.2 Uncertain and variable parametersA variation of parameters shall be included in the analysis in case of uncertain or variable importantparameters.

Guidance note:Important but uncertain parameters as stiffness of aft stern tube bearing, resulting bearing load position, bearing load distributionover length (if calculating with distributed bearing reaction), entrained water on propeller, etc. shall be varied within their probablerange and natural frequencies to be presented as corresponding graphs.


2.1.3 Entrained water to propellerCalculation of entrained water shall be presented.

2.1.4 First order acceptance criteriaResonance with the shaft speed (1st order forward whirl) shall have a separation margin of at least 20% tothe operating speed range, guidance note.

Guidance note:Example: A system with idle at 20 rpm and MCR at 100 rpm shall not have a 1st order fwd whirl in the range 16 to 120 rpm.


2.1.5 Higher order acceptance criteriaResonance caused by propeller blade passing (blade order) shall be avoided in the upper operating speedrange unless it is substantiated that resonance will not cause harmful response, see guidance note.

Guidance note:Approval is based on an over-all evaluation, and resonance should be avoided above 80% of max rpm. Exceptions may be given: Along shafting with many bearings is not found sensitive if the propeller is the main excitation source and the mode shape indicatesresonance in forward end of shafting. Also bearing designs where good damping is expected, e.g. high bearing length to diameterratio combined with a bouncing vibration mode, may justify acceptable resonance response at high rpm.


2.1.6 Presentation of resultsResults shall be presented both in way of numerical values and graphical e.g. as a Campell diagram. Modeshapes of the natural frequencies shall be presented.

3 Axial vibration

3.1 Analysis3.1.1 Extent and method of calculationAs a minimum, the calculations shall include the natural frequencies and mode shapes of the relevantvibration modes.

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3.1.2 Uncertain and variable parametersIf the lowest vibration mode (with the node in the thrust bearing) is of significance to the conclusion, thecalculations shall be made with various thrust bearing stiffness in order to see the influence of an estimationerror.

3.1.3 Acceptance criteria free vibrationIf major critical resonance occurs near or in the operational speed range and no damper is foreseen, forcedaxial vibration calculations shall be required.

3.1.4 Acceptance criteria forced vibrationIn crankshafts, the stresses due to axial vibration shall not exceed the values used in connection with theengine approval. The amplitudes at the front end of the crankshaft shall be within the engine designer’sspecified limit.

3.1.5 Presentation of resultsResults shall be presented both in way of numerical values and graphical of the mode shapes of the naturalfrequencies.

4 Measurements

4.1 Axial vibrationMeasurements of axial vibrations shall be required if major critical resonance occurs near or in theoperational speed range and no damper is foreseen.

4.2 Measurement programWhen vibration measurements are required, the type of instrumentation, location of pick-ups, signalprocessing method, and the measurement procedure shall be approved by the Society.

4.3 Measurement resultsA complete report containing results from unfiltered signals (e.g. shaft stresses) as well as processed signals(e.g. frequency analyses) shall be submitted for approval.

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SECTION 4 SHAFT ALIGNMENT

1 General

1.1 Application1.1.1 ScopeThe shaft alignment rules are only applicable for propulsion plants. For geared plants, the calculations areonly applicable for the low speed shaft line, which shall include the output gear shaft with radial bearings.Vertical shaft alignment is always applicable, while horizontal alignment is applicable upon request.

1.1.2 Calculation versus specificationPropulsion plants as described in [1.3.2] require shaft alignment calculation.All other plants need a shaft alignment specification only, see [1.3.3].

1.1.3 Aft most bearingAcceptance criteria and modelling of aft most bearing are dependent of risk:

— White metal lined aft stern tube bearing which is either double sloped, or has a journal diameter 500 mmor greater, shall fulfil bearing lubrication requirement see [2.1.6].

— Other propulsion plants where alignment calculation is required shall fulfil requirements in [2.1.5].Guidance note:Aft most bearing is in most cases to be understood as aft stern tube bearing, but can also be other designs e.g. strut mountedbearings which are common in twin screw designs without skegs.


1.1.4 SurveyInstallation of propulsion plants requiring a shaft alignment calculation shall be verified by a surveyor.

1.2 DefinitionsTable 1 Definitions

Term Explanation

shaft alignment specification description of the shaft alignment sufficient to carry out the installation. It shallcontain a procedure, verification data and offset from a defined reference line

shaft alignment calculation all information required to evaluate the shaft alignment. It shall contain a shaftalignment specification in addition to calculations as described in [2]

reference line a straight virtual line defined by two chosen points in order to define vertical andhorizontal offsets

bearing reaction influence numbers bearing loads as a consequence of a unit offset of a bearing. It is described by a(N × N) sized table for a model with N bearings

Definitions and symbols used in oil film criteria only are presented in [2.1.6].

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1.3 Documentation

1.3.1 The builder shall submit the documentation required by Table 2. The documentation shall be reviewedby the Society as a part of the class contract.

1.3.2 Systems requiring shaft alignment calculationShaft alignment calculation report shall be submitted for approval for propulsion plants with one out of thefollowing criteria:

— minimum shaft diameters (low speed side) of 400 mm or greater for single screw and 300 mm for twinscrew

— gear transmissions with more than one pinion driving the output gear wheel, even if there is only onesingle input shaft as for dual split paths

— shaft generator or electrical motor as an integral part of the low speed shaft in diesel engine propulsion.

Upon request, shaft alignment calculations may also be required for other plants when these are consideredsensitive to alignment.For required content of a shaft alignment calculation report, see [2.1.4].

1.3.3 Systems only requiring shaft alignment specificationFor all propulsion plants other than those listed in [1.3.1], a shaft alignment specification shall be submittedfor information. The shaft alignment specification shall include the following items:

— bearing offsets from the defined reference line— bearing slope relative to the defined reference line if different from zero— Installation procedure and verification data with tolerances e.g. gap and sag and jacking loads (including

jack correction factors and jack positions) and verification conditions (cold or hot, propeller submersion,etc.).



C040 – Design analysis Shaft alignment calculation when required, see[1.3.1] AP

Conventional propulsionarrangement

Z170 – Installation manual Shaft alignment specification when calculation isnot required, see [1.3.2] FI

AP = For approval; FI = For information



2 Calculation

2.1 General2.1.1 Calculation input dataThe shaft alignment calculations shall at minimum include the following input data:

— propulsion plant particulars, e.g. rated power of main engine and propeller shaft rpm

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— equipment list, i.e. manufacturer and type designation of prime mover, reduction gear (if applicable) andbearings

— geometry data of shafts, couplings and bearings, including reference to relevant drawings. For directcoupled plants, the crankshaft model shall be according to the engine designer's guidelines

— propeller data— bearing clearances.

2.1.2 Alignment conditionsThe shaft alignment calculations shall include the following conditions:

— alignment condition (during erection of shafting)— cold, static, afloat, fully submerged propeller— hot, static, afloat, fully submerged propeller— hot, running with hydrodynamic propeller loads.

For geared shafting systems:

— running conditions as required to verify gear acceptance criteria— all relevant combinations of prime mover operation— horizontal alignment is upon request.

2.1.3 Influence parametersThe shaft alignment calculations shall take into account the influence of:

— buoyancy of propeller— thermal rise of machinery components (including rise caused by heated tanks in double bottom and other

possible heat sources)— gear loads (horizontal and vertical forces and bending moments)— angular working position in gear bearings for gears sensitive to alignment, see guidance note 1— bearing wear (for bearings with high wear acceptance e.g. bearings with water or grease lubrication)— bearing stiffness (if substantiated by knowledge or evaluation, otherwise infinite)— hull and structure deflections, see guidance note 2— hydrodynamic propeller loads, see guidance note 3.

Guidance note 1:For sensitive geared systems (e.g. gears with large face width or gears with more than one pinion driving the output wheel) evensmall alignment offsets may have large influence on the gear face load distribution. In such systems, angular position of the shafthas to be found by iteration. Vertical and horizontal offsets may be assessed by means of the vertical and horizontal forces in theprevious iteration step. Bearing clearances have to be taken into account, but the oil film thickness can usually be disregarded(except for very light bearing loads). For fluid film bearings the angular working position may be estimated to 20 to 30° off thedirection of the force (except for very light bearing loads).


Guidance note 2:Hull deflection is dependent of design, draught, trim, aft peak tank filling etc. Estimated deflections can be based on FEMcalculations, experience from similar designs etc. Larger safety margins should be applied when these deflections are unknown andare expected to have influence on the alignment.


Guidance note 3:Rule paragraph [1.1.3] defines scope of aft most tail shaft bearing analysis dependent of risk. For propulsion plants where theaft most bearing lubrication criteria are required; see [2.1.6]. For other plants, the hydrodynamic loads can be applied by eitherverified measurements on similar designs or a default bending moment. The default bending moment should not be less than0.05·T0 downward and 0.40·T0 upward, where T0 is propeller torque at mcr. For twin screw plants a range of ±0.3·T0 horizontallyand ±0.2·T0 vertical should be used.


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2.1.4 ResultsThe shaft alignment calculations shall at minimum include the following results:

— bearing offsets from the defined reference line— calculated bearing reaction loads and pressures— bearing reaction influence numbers— graphical and tabular presentation of the shaft deflections with respect to the defined reference line— graphical and tabular presentation of the shaft bending stresses as a result of the alignment— nominal relative slope between shaft and bearing centrelines in aft most propeller shaft bearing (see

[2.1.5]) and if applicable, details of proposed slope-bore— results from aft stern tube bearing lubrication criteria, see [2.1.6]— a shaft alignment procedure with verification method and data with tolerances (e.g. aft bearing slope

and geometry, reference line, stern tube bearing offsets, calculated gap & sag values and jackingloads including jack correction factors). The procedure shall clearly state at which vessel condition thealignment verification shall be carried out (cold or hot, submersion of propeller etc.). Positions of jacksand temporary supports have to be specified. The procedure shall be possible to use again when inservice.

2.1.5 Acceptance criteriaThe shaft alignment has to fulfil the following acceptance criteria for all relevant operating conditions in[2.1.2]:

— acceptance criteria defined by manufacturer of the prime mover, e.g. limits for bearing loads, bendingmoment and shear force at flange

— acceptance criteria defined by the manufacturer of the reduction gear, e.g. limits for output shaft bearingloads and load distribution between bearings

— bearing load limits as defined by bearing manufacturer and Ch.4 Sec.1— zero or very low bearing loads are only acceptable if these have no adverse influence on whirling vibration— tolerances for gap and sag less than 5/100 mm are not accepted.

Acceptance criteria for aft most tail shaft bearing:

— in hot static and hot running conditions the relative nominal slope between shaft and aft most propellershaft bearing should not exceed 3·10-4 rad (0.3 mm/m) and 50% of min. diametrical bearing clearancedivided by the bearing length, whichever is less. For definition of relative nominal slope, see Figure 1. Thiscriterion is only applicable for single slope or no-slope bearings.

A white metal lined aft stern tube bearing which is either double sloped, or has a journal diameter 500 mm orgreater, shall fulfil requirements regarding hydrodynamic lubrication performance as stated in [2.1.6].

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Figure 1 Relative nominal slope between bearing and shaft

2.1.6 Aft most bearing lubrication criteriaA white metal lined aft stern tube bearing which is either double sloped, or has a journal diameter 500 mmor greater, shall be designed to ensure hydrodynamic lubrication in all operational conditions. The minimumspeed giving hydrodynamic lubrication (n0), has to be lower than the actual shaft speed (n). Both low speedand full speed criteria have to be fulfilled, see guidance note 1.For multi slope bearings the method applies to the bearing segment with highest nominal bearing pressurefor each operational condition.

Low speed criterion:The minimum shaft speed ensuring hydrodynamic lubrication (n0,stat) is calculated for:

— Hot static condition: No hydrodynamic propeller loads, n0,stat

Full speed criterion:The minimum shaft speed ensuring hydrodynamic lubrication (n0,dyn) is calculated for the following conditionsdefined by the vertical hydrodynamic bending moment acting on the propeller, see guidance note 2 below:

— Hot running condition 1: 15% of full torque downwards, n0,dyn1— Hot running condition 2: 40% of full torque upwards, n0,dyn2

The hydrodynamic propeller loads are defined as vertical bending moments as percentage of full speedtorque, see guidance note 2.

Calculation to be used for both criteria:

Where:

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,

,

Table 3 Calculated parameters

n0 minimum rotational shaft speed ensuring hydrodynamic lubrication [rpm]

h0 minimum required lubrication film thickness [mm]

peff effective bearing pressure [N/m2]

Leff length of locally pressurized area [mm], Leff ≤ L

KD dimensionless size factor [ - ]

KL dimension less length to diameter ratio [ - ]

Table 4 Dimensions and physical parameters

nmin actual shaft speed for continuous slow speed operation [rpm]

nfull actual max shaft speed for continuous operation [rpm], typical at MCR

C diametrical bearing clearance [mm]. Use nominal diameter for std. double slope machining in lower part ofbearing, and actual diameter for trumpet shaped slope

L bearing length, or segment length in case of multi slope bearing [mm]

ν the kinematic viscosity at 40°C [cSt] of the lubricant. To be used as minimum viscosity acceptable for theinstallation

D bearing journal diameter [mm]

Table 5 Parameters from shaft alignment calculation, see Figure 2 and Figure 3

W radial bearing load, W1 + W2 [N]

Wmax max value of W1 and W2 [N]

Wmin min value of W1 and W2 [N]

α calculated relative slope between shaft and bearing at Wmax, either α1 or α2 [mm/m], see Figure 3

White metal lined stern tube bearings shall be modelled in the shaft alignment calculation as presented inFigure 3. This is achieved by modelling the bearing with a support point at either bearing end (or at eithersegment end for multi slope bearings). The total bearing stiffness shall not be taken less than 5·109 N/m,and stiffness of each individual support point not less than 2·109 N/m, unless documented otherwise.

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Figure 2 Model of a shaft resting in a single slope or no-slope bearing

Figure 3 Model of a shaft resting in a double slope bearing

The following results from the calculation shall be presented:n0,stat , n0,dyn1 , n0,dyn2 , ν

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Guidance note 1:The calculation of minimum speed ensuring hydrodynamic lubrication is based on a quasi-empiric solution of the Reynolds equationfor journal bearings. Special conditions typical for stern tube bearings such as uneven load distribution and misalignment areimplemented. This method shall ensure lubrication in areas with maximum bearing pressure. The method shall set a limit for theminimum continuous operational shaft speed and the minimum viscosity of the lubricant. Use of oil with high viscosity (above 200cSt) generate viscous losses and heat, hence care has to be taken. The chosen viscosity (ν) is the minimum value to be used asstern tube lube oil. The calculated oil film thickness (h0) is a parameter to be seen as an integrated element of the calculationmethod, and shall not be understood as an acceptance of actual oil film thickness. (L/D) < 2 is a limitation in the calculationmethod, and not a limitation of the actual bearing length.The centre load in a double slope bearing (see W2 in Figure 3) can be distributed to both bearing segments as there will be an oilfilm in both segments. The load shall then be distributed proportional to the end loads, from this it follows that W2aft is W2×W1/(W1

+ W3) and W2fwd is W2×W3/(W1 + W3).The low speed criterion is calculated for hot static condition without any dynamic load, and limits the slow speed operation. Use ofturning gear is not seen as a continuous operation. It is not possible to fulfil the low speed criterion for very low speeds, but it isrecommended that steam plants operating with auto-spin shall have n0,stat not higher than 20 rpm. Electric propulsion plants ableto operate at low rpm should be special considered. Engine driven propulsion plants will have idle speed as nmin.The full speed criterion includes the dynamic loads, and the criterion ensures that the oil film at full speed is able to handle a rangeof different loads.


Guidance note 2:The hydrodynamic propeller load range is chosen in order to safeguard the performance of the aft most propeller shaft bearing inall running conditions. This includes both straight running at MCR and manoeuvring.If the propeller tip in some operational conditions is above or in the vicinity of the water line, a downward bending moment shouldoccur even at slow speeds. Running with a semi-submerged propeller at high rpm may harm the bearing.For twin screw propulsion plants, the alignment calculations should also include the propeller induced horizontal loads.Manoeuvring at high vessel speed shall generate large vertical and horizontal loads. The propeller induced loads are influencedby the rotational direction of the propellers. Horizontal slope should be evaluated, but this requires a three dimensional analysiswhich is not within scope of this rule paragraph. The angular working position of the shaft should not conflict with longitudinal oilgrooves.It is not mandatory to carry out an independent hydrodynamic propeller load calculation.


2.1.7 Verification data and tolerancesThe tolerances in the alignment specification shall correlate with the tolerance ranges used in thecalculations. The final verification of the alignment shall be carried out afloat in at least one relevantcondition as mentioned in [2.1.2].In special cases, verification in running condition by means of strain gauges and/or proximity transducersmay also be required. In such cases the measurement program shall be submitted for approval.Tolerances for misalignment in way of slope and straightness of stern tube bearings shall be defined. Thetolerances shall reflect the calculation of lubricant film thickness see [2.1.6].

3 Installation

3.1 Inspection

3.1.1 All large welding work in the vicinity of the shafting shall be completed before sighting process andinsertion of propeller shaft. All large and heavy structure elements shall be in place before final verification ofshaft alignment, see guidance note in [3.1.4].

3.1.2 When shaft alignment calculations are required (see [1.3.2]), the stern tube bearing geometry shallbe measured and reported in presence of the surveyor after mounting of bearings, but prior to insertion ofthe propeller shaft. Straightness, slope and ovality shall be within the specified tolerances. Each stern tube

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bearing shall be checked at minimum three longitudinal positions. Equal procedure shall be applied on eachsegment in case of multi slope bearing, see guidance note in [3.1.4].

3.1.3 The shaft alignment shall be within the tolerances given in the shaft alignment specification, seeguidance note in [3.1.4].

3.1.4 When shaft alignment calculations are required (see [1.3.2]), the measured values of gap and sagand/or jacking loads with force-displacement diagrams and/or alternative verification data shall be reportedin presence of the surveyor, see guidance note.

Guidance note:Local effect verification: The designed geometry of stern tube bearings is based on the bearings ability to handle dynamic propellerloads and weight loads from propeller shaft and propeller. The condition inside stern tube bearings is dependent of accuracyboth in design and installation. It has to be verified that the bearing's slope(s), ovality and straightness are within the alignmentspecification with defined tolerances before propeller shaft is inserted. Global hull deflections should have limited influence to thealignment inside the stern tube, but welding in vicinity of the stern tube may disturb the alignment. Aftmost bearing mounted instruts should be evaluated case by case.Global effect verification: Mounting of large hull sections should introduce extra weight which should introduce global hulldeflections. Large welding works and launching should also introduce hull deflections. Final verification of global shaft alignmentsuch as gap and sag and/or jacking should preferably be carried out afloat with most of the hull completed.


3.1.5 For shafting installations not requiring approval (see [1.3.2]), documentation of the installation of theshafting in accordance with the alignment specifications shall be submitted to the surveyor.

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SECTION 5 ELECTRIC POWER GENERATION

1 Prime mover driving electrical generators

1.1 Transient loadsEach prime mover used to drive main or emergency generator shall be fitted with a governor which shallprevent transient frequency variations in the electrical network in excess of ±10% of the rated frequencywith a recovery time to steady state conditions not exceeding 5 seconds when the maximum electrical stepload is switched on or off.If a step load equivalent to the rated output of the generator is switched off, a transient speed variation inexcess of 10% of the rated speed may be acceptable, provided this does not cause the intervention of theoverspeed device as required by Ch.3 Sec.1 [5.3].

1.2 Detrimental speed variationAt all loads between no load and rated power, the permanent speed variation shall not deviate to a value thatmay be detrimental to the reliability of any electric consumer.

Guidance note:±5% of the rated speed is considered as a safe value.


1.3 Speed recoveryThe speed at the actual power after a load change shall be stabilized and in steady-state condition within fiveseconds, inside the permissible range for the permanent speed variation δr.

The steady-state condition is considered reached when the permanent speed variation, δr, does not exceed ±1% of the speed associated with the set power.

1.4 Load demandPrime movers shall be selected in such a way that they shall meet the load demand within the ship’s mains.See Ch.3 Sec.1 [9.3.4] and Ch.3 Sec.1 [9.4] for load tests.

1.5 Two step on-loadingPrime movers driving electric generators, shall be able to accommodate sudden loading from no-load to 50%,followed by the remaining 50% of the rated generator power, duly observing requirements of [1.1] and [1.3].

1.6 Multistep on-loadingApplication of the load in more than two steps is acceptable on the condition that:

— the ship's electrical system is designed for the use of such generator sets— load application in more than two steps is considered in the design of the ship's electrical system and is

approved when the drawings are reviewed— during shipboard trials the functional tests shall be carried out. Step loads caused by sudden

disconnection of running generators shall be tested, and it shall be verified that the main source of electricpower is maintained at all time.

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Guidance note:Typically limiting curves for diesel engines can be seen in Figure 1 and examples of maximum load acceptance of large bore gasengines with port injection depending on base load can be seen in Figure 2.


Figure 1 Example of limiting curves for loading 4-stroke diesel engines step by step from no loadto rated power as function of the brake mean effective pressure

Figure 2 Example of maximum load acceptance of a large bore gas engine with port injectiondepending on base load.

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1.7 Emergency generatorEmergency generator sets shall satisfy the governor conditions as per [1.1] and [1.2], even when:

a) their total consumer load is applied suddenly, orb) their total consumer load is applied in steps, subject to;

— the total load is supplied within 45 seconds since power failure on the main switchboard— the maximum step load is declared and demonstrated— the power distribution system is designed such that the declared maximum step loading is not

exceeded— the compliance of time delays and loading sequence with the above is to be demonstrated at ship's

trials.

1.8 Load sharingFor A.C. generating sets operating in parallel, the governing characteristics of the prime movers shall be suchthat within the limits of 20% and 100% total load the load on any generating set shall not differ from itsproportionate share of the total load by more than 15% of the rated power of the largest machine or 25%of the rated power of the individual machine in question, whichever is the less. For an A.C. generating setintended to operate in parallel, facilities shall be provided to adjust the governor sufficiently fine to permit anadjustment of load not exceeding 5% of the rated load at normal frequency. (IACS UR M3.2.6)

1.9 Reactive loadFor reactive load sharing between generators running in parallel, see Ch.8 Sec.5 [2.4.1].

1.10 Rated speed adjustmentThe governors of the engines shall enable the rated speed to be adjusted over the entire power range with amaximum deviation of 5%.

1.11 SynchronizationThe rate of speed variation of the adjusting mechanisms shall permit satisfactory synchronization in a shorttime.

Guidance note:Relating to Ch.3 Sec.1 [5.2.1] and [1]:The rated power and the corresponding rated speed relate to the conditions under which the engines are operated in the systemconcerned.


1.12 Electric power supply systemFor further requirements related to main electric power supply system including the use of shaft generator,see Ch.8 Sec.2 [2] and for emergency power supply system, see Ch.8 Sec.2 [3].

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CHANGES – HISTORIC

January 2016 editionThis document supersedes the October 2015 edition.

Main changes January 2016, entering into force 1 July 2016

• Sec.2 Torsional vibrations— Table 4: Added documentation requirement fatigue calculation for conventional propulsion arrangement.— [2.3.1]: Where barred speed range is required, maximum time for passing shall be specified.— [2.5.4]: Extended documentation to be submitted where it is likely to expect high cycle fatigue due to

passing of barred speed range including new guidance note.— [3]: Requirements for check of barred speed range have been updated to align with new IACS UR M51

[4.5].

October 2015 edition

GeneralThis is a new document.The rules enter into force 1 January 2016.

DNV GLDriven by our purpose of safeguarding life, property and the environment, DNV GL enablesorganizations to advance the safety and sustainability of their business. We provide classification andtechnical assurance along with software and independent expert advisory services to the maritime,oil and gas, and energy industries. We also provide certification services to customers across a widerange of industries. Operating in more than 100 countries, our 16 000 professionals are dedicated tohelping our customers make the world safer, smarter and greener.

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