SHIP VIBRATION - ABS

Guidance Notes on Ship VibrationGUIDANCE NOTES ONSHIP VIBRATIONFEBRUARY 2018American Bureau of ShippingIncorporated by Act of Legislature ofthe State of New York 1862 2018 American Bureau of Shipping. All rights reserved.1701 City Plaza DriveSpring, TX 77389 USA

ForewordForeword (1 February 2018)The American Bureau of Shipping recognizes the overall ship vibration as an important measure to ensurethe habitability, safety and functionality of the vessels. The ABS Guidance Notes on Ship Vibration havebeen developed to provide users with specific guidance on the design, analysis, measurement proceduresand criteria in order to achieve the goal of limiting the ship vibration to an acceptable level. In the textherein, this document is referred to as “these Guidance Notes”.The design and construction of the hull, superstructure, and deckhouse of a steel vessel are to be based onall applicable requirements of the ABS Rules for Building and Classing Steel Vessels (Steel Vessel Rules).Specifically, for the Container Carriers over 130 meters in length, the ABS Steel Vessel Rules require theconsideration of vibratory responses of hull structures, as applicable (5C-5-3/13.1). For the LNG Carriers,the ABS Steel Vessel Rules require special attention to the possible collapse of membrane due to hullvibration (5C-8-4/13.5). In conjunction with the propulsion shaft alignment, the ABS Steel Vessel Rulesrequire the consideration of propulsion shaft vibrations (4-3-2/7). For the cargo and passenger vessels,ABS provides optional classification notations for crew habitability and passenger comfort (ABS Guide forPassenger Comfort on Ships and Guide for Crew Habitability on Ships). Also ABS provides ConditionMonitoring Program for machinery vibration (7-A-14/5.1.2 of the ABS Rules for Survey After Construction(Part 7)).These Guidance Notes provide practical guidelines on the concept design to assist ship designers to avoidexcessive shipboard vibration at an early design stage. These Guidance Notes also assist with the finiteelement analysis (FEA) based vibration analysis procedure to calculate the vibration response and evaluatethe design at detail design stage. The analysis procedure represents the current analysis practice in ABS.These Guidance Notes also offer guidelines on the vibration measurement procedure at sea trials and theacceptance criteria on vibration limits based on the international standards and the practice in ABS.The 2018 edition provides guidance on quick local vibration analysis methods for ships.These Guidance Notes become effective on the first day of the month of publication.Users are advised to check periodically on the ABS website www.eagle.org to verify that this version of theseGuidance Notes is the most current. Comments or suggestions can be sent electronically to rsd@eagle.orgTerms of UseThe information presented herein is intended solely to assist the reader in the methodologies and/or techniquesdiscussed. These Guidance Notes do not and cannot replace the analysis and/or advice of a qualifiedprofessional. It is the responsibility of the reader to perform their own assessment and obtain professionaladvice. Information contained herein is considered to be pertinent at the time of publication, but may beinvalidated as a result of subsequent legislations, regulations, standards, methods, and/or more updatedinformation and the reader assumes full responsibility for compliance. This publication may not be copiedor redistributed in part or in whole without prior written consent from ABS.iiABS GUIDANCE NOTES ON SHIP VIBRATION . 2018

Table of ContentsGUIDANCE NOTES ONSHIP VIBRATIONCONTENTSSECTION 1General . 11Introduction . 13Application . 15Scope . 1FIGURE 1SECTION 2Concept Design . 31Introduction . 33Design Considerations . 35Concept Design Approach . 4FIGURE 1SECTION 3Overall Procedure for Ship Vibration Assessment. 2Items to be Considered During Concept Design . 5Excitations . 61Introduction . 63Low-speed Main Diesel Engine . 65Hull Wake . 85.17Hull-Propeller Clearance . 11Propeller . 137.1Alternating Thrust . 137.3Hull Pressure Forces . 17TABLE 1 . 8FIGURE 1FIGURE 2FIGURE 3FIGURE 4FIGURE 5FIGURE 6FIGURE 7FIGURE 8ABS GUIDANCE NOTES ON SHIP VIBRATION . 2018External Forces and Moments . 6Guide Force Couples . 7Nominal Wake Distribution for a Typical Merchant Ship(DTMB Model 4370, CB 0.6) . 9Alternative Shafting Arrangements: Open Strut Stern(upper); Conventional Skeg Stern (lower) . 10Open Strut Stern Arrangement . 12Conventional Skeg-Stern Arrangement . 12Maximum Skew Angle . 13Burrill Cavitation Inception Chart . 16iii

SECTION 4SECTION 5Structural Resonances . 191Introduction .193Hull Girder Vertical Vibration Excited by the Main Diesel Engine.195Main Machinery/Shafting System Longitudinal Vibration Excitedby the Propeller .227Superstructure Fore-and-Aft Vibration Excited .26TABLE 1Comparison of 2-node Vertical Vibration NaturalFrequencies .20TABLE 2Flexible Base Correction Factors .27FIGURE 1FIGURE 2FIGURE 3FIGURE 4FIGURE 5FIGURE 6Natural Frequencies of Vertical Hull Vibration .213-mass Longitudinal Model of Main Propulsion System .23Example of Natural Frequencies vs. Foundation Stiffness .25Deckhouse Types .27Fixed-base Superstructure Natural Frequencies .27Deckhouse Stiffening .29Vibration Analysis . 311Introduction .313579iv1.1Scope and Objective. 311.3Procedure Outline of Ship Vibration Analysis . 32Finite Element Modeling .333.1Global Model . 333.3Engine, Propeller Shaft and Stern/Skeg . 333.5Lightship Weight Distribution . 353.7Cargo, Water Ballast in Tanks and Fuel Oil in Tanks . 363.8Local Structural Component Models . 363.9Local Structural Panel Models . 36Loading Condition .365.1Selection of Loading Conditions and Ship Speed . 365.3Added Mass . 365.5Buoyancy Springs . 375.7Special Conditions . 37Free Vibration .377.1Analysis Procedure . 377.3Checking Points . 39Propeller Excitation .399.1Introduction . 399.3Propeller Shaft Forces . 399.5Hull Surface Forces Induced by Propeller Cavitation. 409.7Direct Calculation of Bearing and Surface Forces . 4411Engine Excitation .4513Forced Vibration .4513.1General . 4513.3Critical Areas . 4613.5Damping . 46ABS GUIDANCE NOTES ON SHIP VIBRATION . 2018

SECTION 6TABLE 1Propeller Bearing Forces and Moments for 20 Real ShipCase Study. 40FIGURE 1Procedure to Perform Ship Vibration Analysis. 32FIGURE 2Global FE Model Example . 33FIGURE 3Engine Model Example . 34FIGURE 4Turbine Engine and Propeller Shaft Modeling Example . 35FIGURE 5Propeller Shaft . 35FIGURE 6First Two Vertical Mode Shapes . 38FIGURE 7First Two Horizontal Mode Shapes . 38FIGURE 8Scale Effect due to Propeller Inflow Condition. 44Measurements . 471General . 473579111.1Scope . 471.3Application . 471.5Terminology. 47Instrumentation . 483.1General Requirements . 483.3Calibration . 48Measurement Conditions . 495.1Environment Condition . 495.3Loading Condition . 495.5Course . 495.7Speed and Engine Power . 50Measurement Locations. 507.1Stern . 507.3Superstructure . 507.5Main Engine and Thrust Bearing . 507.7Lateral Shaft Vibration . 517.9Torsional Shaft Vibration . 517.11Local Structures . 517.13Local Deck Transverse . 517.15Local Machinery and Equipment . 517.17Shell Near Propeller . 51Data Processing Analysis . 519.1Measured Data . 519.3Performance of Measurements . 529.5Analysis Methods . 52Measurement Report . 5511.1Analysis and Reporting of Data . 55TABLE 1Typical Frequencies Ranges . 52TABLE 2Examples of Alternate Vibration Measurements. 54ABS GUIDANCE NOTES ON SHIP VIBRATION . 2018v

SECTION 7Acceptance Criteria . 571General .573Vibration Limits for Crew and Passengers.573.1ABS Criteria for Crew Habitability and Passenger Comfort . 573.3ISO 6954 (1984) Criteria for Crew and Passenger Relating toMechanical Vibration . 583.5ISO 6954 (2000) Criteria for Crew and Passenger Relating toMechanical Vibration . 605Vibration Limits for Local Structures .607Vibration Limits for Machinery.617.1Main Propulsion Machinery . 617.3Machinery and Equipment . 62TABLE 1Maximum Weighted RMS Acceleration Levels for CrewHabitability.58TABLE 2Maximum Weighted RMS Acceleration Levels forPassenger Comfort .58TABLE 3Overall Frequency-Weighted RMS Values(ISO 6954: 2000).60TABLE 4Vibration Limits for Main Propulsion Machinery.62FIGURE 1ISO 6954 (1984).59FIGURE 2Vibration Limits for Local Structures .61APPENDIX 1 References . 631General References .633Concept Design .635FE Analysis .647Measurement .64APPENDIX 2 Corrections . 651Corrective Investigations.653General Approach .665Hydrodynamic Modifications .667Structural Modifications.689Case Study.68vi9.1Determination of Model Constants. 699.3Structural Rectification Analysis. 709.5Propeller Change . 72FIGURE 1Wake Improvement with Special Lines-adapting SternDevices Conventional Stern Cargo Ship .67FIGURE 2Mass-elastic Model of Deckhouse and Support Structure .69FIGURE 3Equivalent One-mass System.71ABS GUIDANCE NOTES ON SHIP VIBRATION . 2018

APPENDIX 3 Seaway Excitation and Response . 741General . 743Springing . 745Bow Flare Slamming and Whipping. 747Bottom Impact Slamming . 75APPENDIX 4 Concept Design Checklist . 76ABS GUIDANCE NOTES ON SHIP VIBRATION . 2018vii

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Section 1: General1SECTION1GeneralIntroductionWith the increase of ship size and speed, shipboard vibration becomes a great concern in the design andconstruction of the vessels. Excessive ship vibration is to be avoided for passenger comfort and crewhabitability. In addition to undesired effects on humans, excessive ship vibration may result in the fatiguefailure of local structural members or malfunction of machinery and equipment.These Guidance Notes are to provide users, specifically shipyards, naval architects, and ship owners, withpractical guidance on the concept design to avoid excessive ship vibration at an early design stage. If simpleprocedures are followed with insight and good judgment in the concept design stage, then the difficultcountermeasures and corrections at the subsequent design stages may be avoided in most cases.These Guidance Notes also assist with the finite element analysis (FEA) based vibration analysis procedureto predict the vibration response and evaluate the design in detail design stage. The vibration analysis procedurerepresents the most current analysis practice in ABS. These Guidance Notes also offer guidelines on thevibration measurement procedure during the sea trials and the acceptance criteria on vibration limits basedon international standards and practice in ABS.3ApplicationThese Guidance Notes are applicable to the vessels of all lengths.5ScopeThese Guidance Notes provide overall guidelines on ship vibration excited by the main engine and prope

The vibration analysis in Section 5 provides the FE-based vibration analysis procedure based on first principles direct calculations. The FE-based vibration analysis is recommended to evaluate the design during the detail design stage. If found necessary, the local vibration is tobe addressed in the detail vibration analysis. The