ABS releases the revised Guidance Notes on Ship Vibration

The American Bureau of Shipping on 1 September 2023 released the revised Guidance Notes on Ship Vibration.

This edition introduces new recommendations for modeling engine and propeller excitations, as well as combining excitations and modeling of cargo and fluid inside tanks.

It aligns the measurement procedures with the ABS Guide for Vibration of Machinery Equipment and Related Structures and references that Guide for vibration criteria regarding machinery, equipment, and local structures.

Introduction

With the increase of ship size and speed, shipboard vibration is an increasing concern in the design and construction of vessels.

Excessive ship vibration should be avoided for passenger comfort and crew habitability.

In addition to undesired effects on humans, excessive ship vibration may result in the fatigue failure of local structural members and malfunction of machinery and equipment.

These Guidance Notes provide users, specifically shipyards, naval architects and ship owners, with guidance on the concept design to avoid excessive ship vibration at an early design stage.

If appropriate procedures are followed with insight and good judgment in the concept design stage, then the difficult countermeasures 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 procedure to predict the vibration response and evaluate the design in detail design stage.

The vibration analysis procedure represents the most current analysis practice in ABS.

These Guidance Notes also offer guidelines on the vibration measurement procedure during the sea trials and the acceptance criteria on vibration limits based on international standards and practice in ABS.

Application

These Guidance Notes are applicable to vessels of all lengths, including ship-type floating production units.

Scope

These Guidance Notes provide overall guidelines on ship vibration excited by the main engine, propeller, or slamming.

In these Guidance Notes, the following subjects are considered:

i) Concept Design
ii) Vibration Analysis
iii) Measurements
iv) Acceptance Criteria

The concept design in Sections 2, 3 and 4 provides users with guidance on dealing with ship vibration in the concept design stage.

In the concept design, local vibration is not addressed because detail information is not usually available in the early design stage.

Instead, the concept design is focused on those areas that have been known to be of critical importance in avoiding harmful ship vibration.

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 should be addressed in the detail vibration analysis.

The analysis procedure provides guidelines on FE modeling, engine and propeller excitation and free and forced vibration analysis.

The procedure for calculating slamming excitation can be found in the ABS Guide for Slamming Loads and Strength Assessment for Vessels.

Site-specific wave scatter diagram should be used for slamming calculations for ship-type floating production installations.

For the assessment of ship vibration performance, the actual vibration levels at the most critical locations should be measured and evaluated during the sea trials.

Section 6 provides guidelines on the vibration measurement procedure on the instrumentation, measurement conditions and locations, data processing and reporting.

Section 7 provides acceptance criteria on the vibration limits for human comfort and habitability, local structures and machinery based on international standards and practice in ABS.

The shaft alignment and torsional vibration are not directly addressed in this document.

For the requirements of the shaft alignment and torsional vibratory stress, refer to 4-3-2/7 of the ABS Marine Vessel Rules.

The overall procedure for ship vibration assessment recommended in these Guidance Notes is shown in Figure 1 below.