Vibration analysis for the comfort assessment of superyachts

Abstract

Comfort levels on modern superyachts have recently been the object of specific attention of the most important Classification Societies, which issued new rules and regulations for evaluating noise and vibration maximum levels. These rules are named "Comfort Class Rules" and set the general criteria for noise and vibration measurements in different vessels' areas, as well as the maximum noise and vibration limit values. As far as the vibration assessment is concerned, the Comfort Class Rules follow either the ISO 6954:1984 standard or the ISO 6954:2000. After an introduction to these relevant standards, the authors herein present a procedure developed to predict the vibration levels on ships. This procedure builds on finite element linear dynamic analysis and is applied to predict the vibration levels on a 60 m superyacht considered as a case study. The results of the numerical simulations are then benchmarked against experimental data acquired during the sea trial of the vessel. This analysis also allows the authors to evaluate the global damping ratio to be used by designers in the vibration analysis of superyachts.

Vibration analysis of super-yachts: Validation of the Holden Method and estimation of the structural damping

“…Following the procedure presented in Ref. [32], a damping ratio of the hull structures is estimated in a frequency range which includes the first harmonics of the diesel engines. Step 4 is described in Subsection 2.5.…”

“…A 3D Finite Element model of the ship structures was developed with MSC.Patran to study the dynamic response of the vessels structures and is presented in Ref. [32]. That model is also used in this work to evaluate the dynamic response of the ship structures via linear frequency response analyses performed in MSC.Natran.…”

“…The average size of the plane strain and beam elements is 300 mm, which corresponds to the half-span of two consecutive transversal frames of the ship structures. This element size allows for a proper simulation of the structural dynamics up to 100 Hz [32], which is the frequency range of interest to evaluate the ship comfort [20].…”

“…It was deliberately chosen to use the first version of this Standard, rather than the most recent version issued in 2016 [20], as it is more suitable to evaluate the overall structural damping, and to identify the response to each harmonic of the vibration sources, as explained in Ref. [27,32].…”

“…The present paper examines the outcomes of a study carried out to validate the use of the Holden Method for the vibration analysis of super-yacht structures. This study is part of a wider research project involving thorough experimental and numerical studies on super-yachts structural dynamics [28,32,47], on-board structure-borne noise [6], and simulation of the hull frequency dependent added mass [31].…”