Part 4 Systems and components Chapter 2 Rotating machinery, general

Transcription

1 RULES FOR CLASSIFICATION Ships Edition July 2016 Amended January 2017 Part 4 Systems and components Chapter 2 The content of this service document is the subject of intellectual property rights reserved by ("DNV GL"). The user accepts that it is prohibited by anyone else but DNV GL and/or its licensees to offer and/or perform classification, certification and/or verification services, including the issuance of certificates and/or declarations of conformity, wholly or partly, on the basis of and/or pursuant to this document whether free of charge or chargeable, without DNV GL's prior written consent. DNV GL is not responsible for the consequences arising from any use of this document by others. The electronic pdf version of this document, available free of charge from is the officially binding version.

2 FOREWORD DNV GL rules for classification contain procedural and technical requirements related to obtaining and retaining a class certificate. The rules represent all requirements adopted by the Society as basis for classification. July 2016 Any comments may be sent by to rules@dnvgl.com 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 shall pay compensation to such person for his proved direct loss or damage. However, the compensation shall not exceed an amount equal to ten times 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, 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.

3 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. Part 4 Chapter 2 Changes - current Sec.5 Electric power generation Sec.5 [1.4]: A reference to Pt.4 Ch.3 for applicable load tests has been included. Editorial corrections In addition to the above stated changes, editorial corrections may have been made. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 3

4 CONTENTS Changes current... 3 Section 1 Introduction General Application and scope Design principles General Material and testing specifications General Welding specification Special materials and processes General Foundations for machinery General Documentation requirements Installation Certification requirements Part 4 Chapter 2 Contents Section 2 Torsional vibrations General Application Symbols and definitions Ice class Documentation requirements Calculation General Free vibration Forced vibration frequency domain Forced vibration time domain Acceptance criteria Shipboard testing Check of barred speed range Check of gear hammer Check of stability for systems with flexible couplings when misfiring Check of transients during clutching-in procedure Closed loop stability Test procedure...24 Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 4

5 4.1 Measurements Section 3 Lateral and axial shafting vibrations General Application Definitions Documentation requirements Lateral vibration Analysis Axial vibration Analysis Measurements Axial vibration Measurement program Measurement results Part 4 Chapter 2 Contents Section 4 Shaft alignment General Application Definitions Documentation Calculation General Installation Inspection...36 Section 5 Electric power generation Prime mover driving electrical generators Transient loads Detrimental speed variation Speed recovery Load demand Two step on-loading Multistep on-loading Emergency generator Load sharing Reactive load Rated speed adjustment Synchronization Electric power supply system...40 Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 5

6 Changes historic...41 Part 4 Chapter 2 Contents Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 6

7 SECTION 1 INTRODUCTION 1 General 1.1 Application and scope These rules apply to rotating machinery used for the main functions defined in Pt.1 Ch.1 Sec.1 Table 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 Part 4 Chapter 2 Section General All machinery shall be designed so that expected deviations of influence parameters do not result in unacceptable 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 per minute, denoted by P and n 0, the values applied are maximum continuous power (kw) measured on engine output shaft and corresponding revolutions per minute. However, for plants where overload occurs frequently (intermittent load), the scantling criteria may have to be based on the overload, due to accumulated fatigue All parts shall be capable to withstand the stresses and loads peculiar to shipboard service, e.g. those due to movements of the ship, vibrations, intensified corrosive attack, temperature changes and wave impact, and shall be dimensioned in accordance with the requirements set out in the present chapter. In the absence of rules governing the dimensions of parts, a relevant international standard (to be stated) or the manufacturers standard shall be applied. Where connections exist between systems or plant items which are designed for different forces pressures and/or temperatures (stresses), safety devices shall be fitted which prevent the over-stressing of the system or plant item designed for the lower design parameters. To preclude damage, such systems shall be fitted with devices affording protection against excessive pressures and temperatures and/or against overflow 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 may carry out random inspections at any time. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 7

8 The manufacturer (and designer, if producing under license) is committed to involve the Society in corrective actions whenever failures occur to products certified by the Society and addressed in these rules, including parts for which documents are submitted for information. The corrective actions include changes to design and/or quality control. Failing to involve the Society, or to carry out proper corrective actions, may result in withdrawal of the type approval as well as restrictions of future approvals and/or certification When the rules require calculations and or analyses, this shall contain objectives, premises, assumptions and the conclusions The reliability and safety of components and complete units may also be documented by means of approved tests or service experience. The latter shall only be considered if a relevant load history can be documented. Acceptance of load history shall be decided case-by-case by the Society. Relevant load history means a suitable operation period (e.g. more than hours for propulsion) under running conditions similar to the expected running conditions for the product to be approved. 3 Material and testing specifications 3.1 General Part 4 Chapter 2 Section 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) 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 as keyways, 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 with class guideline DNVGL-CG-0051, or other recognized standards. The surveyor may require that the procedure is approved or qualified for the work. Unless otherwise specified in these rules or in approved manufacturer's specification, acceptance criteria from the 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 with in Ch.3 to Ch 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 in the form of a gap analysis, and justified by use of the principle of equivalency Blanks for gears and short shafts may be cut from forged bars without further forging. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 8

9 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 specification For 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 Part 4 Chapter 2 Section For materials which are more tolerant towards fatigue loading than ordinary materials for example due to high cleanliness (see Pt.2 Ch.2 Sec.6 [1.6.10]), and for processes which lead to improved fatigue properties such as continuous grain flow forging, shot peening, cold rolling etc., special approval may be given based on adequate testing and documentation. 6 Foundations for machinery 6.1 General Foundation is a device transferring loads from a heavy or loaded object to the vessel structure while supporting structure is strengthening of the vessel structure, see Pt.3 Ch.3 Sec 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 propulsion thruster. As power generating machinery is considered: driving engine or turbine and generator. As steering gear machinery is considered: steering gear rudder actuator The foundation shall be of sufficient strength to transmit loads and keep the machinery fixed under all operation conditions. Foundations for reciprocating combustion engines shall be in compliance with DNVGL-CG-0372 Foundation and mounting of machinery. Equivalent solutions may be accepted on a case by case basis Resin casting compounds shall be type approved according to DNVGL-CP-0432 Pourable compounds for foundation chocking Resilient mounts shall be type approved according to DNVGL-CP-0144 Flexible mounts used for propulsion or auxiliary machinery. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 9

10 6.2 Documentation requirements For foundations for propulsion, steering and auxiliary machinery, the builder shall submit the documentation required by Table 1. The documentation shall be reviewed by the Society as a part of the class 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 and fitted elements. Chocks, fixed C030 Detailed drawing AP Chocks, adjustable C030 Detailed drawing AP Cast synthetic foundations Z100 Specification Including material and design loads. AP, TA C040 Design analysis Loads and fastening devices. FI AP Part 4 Chapter 2 Section 1 Z100 Specification Including stiffness and damping. AP, TA Resilient mounts C040 Design analysis Vibration analysis, including maximum deflections. AP AP = For approval; FI = For information; TA = Covered by type approval For general requirements for documentation, including definition of the info codes, see Pt.1 Ch.3 Sec For a full definition of the documentation types, see Pt.1 Ch.3 Sec Installation Foundations for machinery for propulsion, power generation and steering are subject to survey by the Society. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 10

11 6.4 Certification requirements 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. Cast synthetic foundations Certificate issued by the manufacturer may be accepted for standard bolts up to thread size M39 PC Builder Measured tightening torque for foundation bolts TA Society For resin Part 4 Chapter 2 Section 1 Resilient mounts TA Society Type approval required for standard designs * Unless otherwise specified the certification standard is the rules For general certification requirements, see Pt.1 Ch.3 Sec For a definition of the certification types, see Pt.1 Ch.3 Sec.5. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 11

12 SECTION 2 TORSIONAL VIBRATIONS 1 General 1.1 Application Scope The 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 rated power Simplification Only mechanical active systems shall be included in the analysis. De-clutched branches shall not be required in the model. Electric power transmission, hydrodynamic couplings and torque converters shall not be seen as components transferring torsional vibrations; consequently systems in both ends can be handled as independent mass elastic systems Acceptance criteria Acceptance criteria are found in the respective rule chapters for the components. Part 4 Chapter 2 Section Coupled vibrations Axial vibrations initiated by torsional vibrations are handled in Sec Forced vibration analysis Time domain simulation can be used as alternative to conventional forced torsional vibration calculation. This is suitable for determination of vibration outside the engine itself, such as in nonlinear couplings and gear meshes. Relevant cases for simulation are presented in [2.4.3]. 1.2 Symbols and definitions Table 1 Symbols Symbol Unit Explanation n 0 rpm Rotational speed at maximum continuous power (mcr) n rpm Rotational speed at which vibration are considered λ - Speed ratio defined as n/n 0 T 0 knm Rated torque (at maximum continuous power) T knm Mean torque at n T v knm Vibratory torque amplitude at n τ N/mm 2 Torsional stress corresponding to T τ v N/mm 2 Torsional stress corresponding to T Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 12

13 Table 2 Definitions Term amplitude of vibratory torque Definition T v = 0.5 (maximum torque - minimum torque) during a time interval that covers the period of the lowest order, including possible beat orders This definition also applies for non-linear vibration and for synthesized linear vibration where the average torque (which is the average between the maximum torque and the minimum 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 the average torque. Part 4 Chapter 2 Section 2 driver engine frequency domain mass elastic system misfiring order natural frequency time domain unit acting as power source to the shafting system, e.g. engine, electric motor, gas turbine, steam turbine in this context engine is associated with reciprocating combustion engines independent of fuel type calculation where frequency is used as free variable, usually with rad/s or Hz as unit model consisting of inertias, springs and dampers representing the shafting system misfiring in a cylinder is defined as no fuel injection. The compression - expansion cycle is assumed to be maintained under the same charge air pressure as normal number of excitation cycles per cycle of an engine. One engine cycle is one revolution for two-stroke engines and two revolutions for four stroke engines natural frequency (or modal frequency) is the frequency at which a system tends to oscillate in the absence of any driving or damping force. Number of natural frequencies is equal to number of independent inertias calculation where time is used as free variable, usually with seconds as unit Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 13

14 transient torsional vibration non periodic external excitation of the system. In this context it is associated with operations as: vibration mode shape 1.3 Ice class 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 K dyn /T 0 > 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 speed because the excitation increases due to the feedback from the speed governor. pattern with non-dimensional angular displacements of inertias along the shafting for a given natural frequency Part 4 Chapter 2 Section 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 the Northern 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 to propeller ice impact excitations. Definition of loads and how to apply them are found in the respective ice rule chapters. 1.4 Documentation requirements The builder, or a sub-supplier acting on behalf of the builder, shall submit the documentation required by Table 4. The documentation shall be reviewed by the Society as a part of the class contract. Table 4 Documentation requirements Object Document type Additional description Info Conventional propulsion arrangement C040 Design analysis Forced vibration calculation, see [2.3] AP C040 Design analysis Systems with large transients. AP, R Forced vibration in time domain, see [2.4] C040 Design analysis Fatigue calculation AP, R Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 14

15 Propulsion and steering thruster arrangement Manoeuvring thruster arrangement Z241 Measurement report Measurement of torsional vibrations if requested during approval C040 Design analysis Forced vibration calculation, see [2.3] AP C040 Design analysis Z241 Measurement report C040 Design analysis C040 Design analysis C040 Design analysis Z241 Measurement report Systems with large transients. Forced vibration in time domain, see [2.4] Measurement of torsional vibrations if requested during approval Tunnel thruster hydraulic or electric driven. Free vibration calculation see [2.2] *) All other manoeuvring thrusters. Forced vibration calculation, see [2.3] *) Systems with large transients. Forced vibration in time domain, see [2.4] *) Measurement of torsional vibrations if requested during approval *) AP, R AP, R AP, R AP AP AP, R AP, R Part 4 Chapter 2 Section 2 Electric power generation C040 Design analysis Forced vibration calculation, see [2.3] **) AP C040 Design analysis Z241 Measurement report Systems with large transients. Forced vibration in time domain, see [2.4] **) Measurement of torsional vibrations if requested during approval **) AP, R AP, R Emergency electric power generation C040 Design analysis Forced vibration calculation, see [2.3] **) AP Z241 Measurement report Measurement of torsional vibrations if requested 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 used for 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 For general requirements to documentation, including definition of the info codes, see Pt.1 Ch.3 Sec For a full definition of the documentation types, see Pt.1 Ch.3 Sec.3. 2 Calculation 2.1 General Analysis conclusion All analysis reports shall have a conclusion. In case of forced vibration analysis the conclusion shall be based on a comparison between calculated dynamic response and the permissible values for all the sensitive parts in the plant. Assumptions, conditions and restrictions shall be presented. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 15

16 2.1.2 Input data quality General Parameters 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 the influence shall be quantitatively considered and also addressed in the conclusions. Uncertain parameters Variation of essential data such as dynamic characteristics of elastic couplings and dampers shall be considered. Especially rubber couplings and certain types of vibration dampers have wide tolerances of stiffness and damping. Variation of parameter values For components like couplings having stiffness with strong dependency on vibratory torque and/or temperature (as a consequence of power loss) calculation where these dependencies are included may be requested. Nonlinear characteristics Systems with components having a strong nonlinear characteristic within the operation range with large influence on the system dynamics shall be simulated in time domain. Source of data In vibration calculations the source of all essential data shall be listed. For data that cannot be given as constant parameters the assumed parameter dependency and tolerance range shall be specified. Part 4 Chapter 2 Section Free vibration Analysis content Natural frequency calculations of the complete system are required. These shall include tables of relative displacement amplitudes, relative inertia torques, vector sums and, if used later, also their phase angles. Specification of input data Mass elastic system: Moments of inertia and inertia-less torsional elasticity/stiffness for each element in the complete system Components: 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, also their phase angles. Graphs: Vibration mode shapes Calculation method Calculation of relevant natural frequencies and their corresponding mode shapes shall be carried out by recognised calculation methods. Guidance note: Examples of recognised methods obtaining natural frequencies and their mode shapes are methodologies for direct matrix solutions calculating eigenvalues. Alternatively, approximate methods as the iterative Holzer s method can be used. Damping has very little effect on natural frequency of the system, and hence the calculations for natural frequencies may be made on the basis of no damping. 2.3 Forced vibration frequency domain Analysis content Free vibration Forced vibration shall include free vibration calculation see [2.2]. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 16

17 Specification of input data Data 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 rod ratio, 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 various components in the system. The results shall be presented as synthesis, including amplitude and phase from the orders representing the 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. Part 4 Chapter 2 Section 2 Guidance note: Propeller moment of inertia for entrained water shall be specified by propeller designer, see Ch.5 Sec.1 [1.2.5] Calculation method and model Method and mass elastic system The forced torsional vibration shall be calculated by means of linear differential equations, one for each lumped 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 on mass. Other recognized methods may be accepted upon request. Representative parameter values The 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 on the level of the vibratory torque and used in a linear vibration calculation, then the whole calculation may have to be made by iteration. Two-stroke engine Engine designer s model and parameters shall be applied. Propeller damping In order to best represent the damping properties of a propeller, the Archer s or Frahm s approach with torque dependent damping coefficients should be used. Alternative methods using a dynamic magnifier or Schwanecke s empirical approach or other approaches shall be subject to special consideration. For planing crafts damping shall be based on derivation of the actual torque characteristics, see guidance note. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 17

18 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 = n m, 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 is typically in the range for conventional propellers. Dynamic magnifier for absolute damping is defined as M = Jω/C, where J is propeller inertia and ω is actual vibration frequency. The corresponding relative damping is ζ = (ω/ω n )/2M. Dynamic magnifier or relative damping should only be applied based on experience from measurements of similar plants Excitation Two-stroke engine Engine excitation shall be based on harmonic tables of tangential crank pressure from engine designer relevant for the actual engine with respect to type approval. Alternatively it can be based on measurements of cylinder pressure for the actual engine. Four stroke engine In addition to the methods for two-stroke engines, simplified methods with generic predefined pressure-time characteristics based on main engine data may be accepted. Propeller excitation Propeller excitation can be taken as a percentage of the actual mean torque according to Table 5 unless other values are substantiated by the propeller manufacturer. The values are representative for max continuous forward operation. Propeller excitation for extreme steering manoeuvres of azimuth thrusters shall be taken as 3 times the excitation in Table 5, unless other figures can be documented. Part 4 Chapter 2 Section 2 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 excitations Other excitation sources as electric drive control system, water jet impeller pulses, universal joints (second order), etc. may have to be taken into accountwhen it influences the system behaviour 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 take off gear integrated in the main gear or at the forward crankshaft end for loaded and idling generator, clutches for engaged and disengaged branches. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 18

19 Selection of misfiring cylinder For 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 domain Analysis content Free vibration Forced vibration shall include free vibration calculation, see [2.2]. Specification of input data Engine data to be specified as applicable; brand, model, bore, stroke, piston rod length, number of cylinders, V-angle, firing sequence and max rpm Calculation method and model Method and mass elastic system The forced torsional vibration shall be calculated by numerical integration of differential equations as found relevant for the system modelled. Simplified model The 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 the same lower (only the important) frequencies as the detailed system. Presentation of results Simulation results shall be presented by graphs. Resolution and choice of parameters shall reflect the intention of the simulation. Part 4 Chapter 2 Section Relevant cases for simulation Passing through a barred speed range Simulation of fixed pitch propeller plants shall take into account the most important properties of the propulsion, 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 the equivalent number of cycles. The acceptance criterion is the peak torque (or stress) and the corresponding equivalent 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 partial damage (Miner s theory) as the real load spectrum. This equivalent number of cycles for passing up and down through the barred speed range shall be multiplied with the expected number of passages during the foreseen lifetime of the ship. A detailed method for evaluating the equivalent number of cycles and expected number of passages is presented in class guideline DNVGL-CG Ice impact loads Response of non-harmonic impact loads from ice as described in the ice rules (see [1.3]) shall be simulated in the time domain when shaft speed cannot be maintained due to ice loads. Frequency domain calculation in resonant speed can be used as an option. Large inertia loads For plants that have a major critical resonance below idling speed and a low ratio of engine inertia to driven machinery inertia, the transient vibration torque shall be considered. This applies e.g. to diesel generator sets with highly elastic couplings and similar propulsion plants without clutch. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 19

20 Clutching-in The 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 changing coefficient 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 addition to 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 peak torques or amplitudes near the approved limits. Short circuit in PTO driven generators A possible short circuit in a generator is not to be detrimental for the power transmitting elements such as couplings and gears. The purpose of the calculation shall determine the peak torques and amplitudes that occur 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: Part 4 Chapter 2 Section 2 T = T 0 [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 governor When the speed governor influence has be taken into account it shall be done in the time domain. 2.5 Acceptance criteria If any result is close to the acceptance limit and there are uncertainties in the calculations, vibration measurements may be required, see [4] Availability of main functions In specifying prohibited ranges of operation it has to be observed that the navigating and manoeuvring functions are not severely restricted Determination of barred speed range Speed ranges or operating conditions where the following acceptance criteria are exceeded, shall be barred for continuous operation. Corresponding signboards shall be fitted at all manoeuvring stands and all tachometers marked with red. The tachometers shall be accurate within the tolerance +/-0.01 n 0. A barred speed 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 result in a too slow passage with the consequence of higher vibratory stress level and increased number of cycles with high stress level. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 20

21 2.5.3 Misfiring condition Exceeding 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 (slow heating 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 Shafts Design 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) shall be designed for at least the same vibration level as the gearing. Unless significantly higher vibration are expected to occur somewhere in the shafting, documentation of the vibration levels in the shafts is not required. For direct coupled plants the vibration level (τ v ) is not to exceed the values used for the shafting design with regard to continuous operation. Alternatively, the calculated vibration for continuous operation may be used for the shafting design. For shafts that are designed on the basis of transient vibration, the torque amplitudes as well as number of equivalent cycles per passage are not to exceed the prerequisites for the shaft design Extended documentation to be submitted for designs where it is likely to expect high cycle fatigue due to passing of barred speed range, see guidance note. Part 4 Chapter 2 Section 2 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. A large number of cycles shall be understood as above 10 5 cycles. Extended documentation shall contain fatigue analysis supported by engine and propeller curves as relevant. Classification guideline DNVGL-CG-0038 Calculation of shafts in marine applications can be used for fatigue analysis. DNVGL-CG-0038 calculates fatigue capacity based on Wöhler curve (S-N curve) and Miner sum Crankshafts Design 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 at mass for cam drive branch or journal movements in bearings Vibration dampers Design 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 Torsional elastic couplings Design 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. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 21

22 These limits are for continuous operation. Higher values may be accepted for a limited time of operation if twist amplitudes are monitored. Transient vibration which occur occasionally (i.e. less than times) such as clutching-in is not to exceed neither T Kmax1 nor ΔT Kmax. Transient vibration which occur very infrequently indeed such as short circuit [2.4.3] are not to exceed T Kmax2. Power loss need not be considered for transient operation Other couplings Design 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 T 0 unless especially approved Gear transmissions Design 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 (K A - 1) T 0 where K A is the application factor used in the gear transmission approval. 2) The vibration torque is limited to 35% of T 0 throughout the entire operation range. 3) Gear hammer (negative torque) is not permitted except in unloaded power take off branches, where 10% of T 0 (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 T 0. 5) Transient peak torques shall not exceed T 0. 6) Transient peak torques shall not exceed the approved (K AP T 0 ) or (1.5 T 0 ). Part 4 Chapter 2 Section Shrink fits including propeller fitting Design 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 when the peak torque in a barred speed range exceeds the peak torque at full load. Peak torque values during misfiring operation shall be subject to special consideration Propellers Design 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 Thrusters See Ch.5 Sec Electric rotating machines generators, pumps, compressors etc. The vibration level shall not exceed any limitation specified by designer of the electric generator or motor Speed governor The vibration levels at the sensor location of flexibly coupled propulsion engines shall not exceed the value specified by the engine manufacturer. If no value is specified and approved, tests and measurements shall be made in order to verify that the governor response is insignificant. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 22

23 3 Shipboard testing 3.1 Check of barred speed range Time recording Where a barred speed range (BSR) is required, passages through this BSR, both accelerating and decelerating, are to be demonstrated. The times taken are to be recorded and are to be equal to or below those times stipulated in the approved documentation. This also includes when passing through the BSR in reverse rotational direction, especially during the stopping test. This applies both for manual and automatic passing-through systems. The ship's draft and speed during all these demonstrations is to be recorded. In the case of a controllable pitch propeller, the pitch is also to be recorded (IACS UR M51 [4.5]) Border stability The engine is to be checked for stable running (steady fuel index) at both upper and lower borders of the barred speed range. Steady fuel index means an oscillation range less than 5% of the effective stroke (idle to full index) (IACS UR M51 [4.5]). For controllable pitch propellers, this shall be tested with both zero and full pitch unless otherwise agreed. Part 4 Chapter 2 Section Quick pass through Passing 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 foreseen operational conditions Signboard When a barred speed range is required, signboards describing how to pass through shall be provided at all engine operating stands. 3.2 Check of gear hammer Reduction gears and power take off gears shall be detected for gear hammer in misfiring condition in ranges specified in connection with the approval. Speed ranges where gear hammer occurs shall be barred for continuous operation. However, in power take off gears light gear hammer in unloaded condition is acceptable. 3.3 Check of stability for systems with flexible couplings when misfiring Engines with elastic couplings shall be checked for stability of the speed governing system when provoked by misfiring. 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 on board: 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 engines shall be combined. This may be done by keeping the selected misfiring for engine one, and first select a cylinder 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. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 23

24 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 engines are misfiring in order to have enough imbalances to simulate worst case with 0.5 order resonance. Fuel rack oscillations peak to peak (with combined misfiring for twin engines) less than 20% of the effective stroke (idle to full) are normally considered as acceptable. For engines without fuel rack similar parameters are taken from engine monitoring system. 3.4 Check of transients during clutching-in procedure After the clutch characteristics (pressure - time) are checked, the clutching-in shall be checked at the minimum respectively the maximum permissible engine speed for clutching-in. The speed governing system shall respond with quickly damped oscillations. 3.5 Closed loop stability The following may be requested, see type of speed governor type and position of speed sensor. Part 4 Chapter 2 Section 2 Guidance note: Evaluation of the torsional vibration system should be considered in case of conditions with high vibration at the governor pick up position. 4 Test procedure 4.1 Measurements Instrumentation When 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 Measurement report When vibration measurements are required by the Society, a 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. Rules for classification: Ships DNVGL-RU-SHIP Pt.4 Ch.2. Edition July 2016, amended January 2017 Page 24