Analysis of window structures for super and megayachts

In the last years, after the economic crisis that modified the super and megayacht market and construction, the project focus of shipyards and owners has been moved from the research of higher performances and whimsical exteriors to more classic aesthetics and higher level of onboard comfort. This first aspect has led to the use of larger openings on superstructures\u2019 sides in order to enlarge windows and bring more natural light onboard vessels. The request of more comfortable units has granted a strong effort to find new solutions in order to reduce the noise and vibration level, dealing in particular to the structural elements that with higher noise radiations, such as dampers, pillars and windows. The aforementioned trends is reflected on a more intensive use of glazed windows onboard, that have led to non-trivial problem of both structural response (since the structural component are reduced in order to enlarge opening) and NVH assessment, considering that glued glass panes act as an harmonic speakers, having natural frequencies closed to ones of the main superyacht excitations. In this PhD thesis, the use of glass onboard superyacht has been focused with particular attention to finding new, simpler numerical and experimental procedure to take into account the vibroacustic properties of glass, that are actually ignored by Classification Societies, during their structural scantling and mounting. The proposed simplified methods has been tested also in two different global models, for the assessment of the vertical hull girder vibration at low frequency and for the NVH assessment in the mid-high frequency respectively. Moreover, the role of openings has also been tested from a structural point of view, as a first step of a wider research that should verify the stress transfer mechanisms between metallic structures and glazed windows

Local and Global Analysis of Large Motoryacht Superstructure

The superyacht manufacturing industry is currently facing big challenges, mainly related to the present economic crisis. Manufacturers are then competing on the ground of better and more aesthetic external and interior designs. This trend often leads to structural strength related issues, which can compromise the static or dynamic stability of superyacht hull. In several instances, the aforementioned fact is met, as in large openings and docks to recover tenders, the enlargement of windows to allow for better lighting of internal living spaces. So, for what the hull is concerned, large windows replaced small portholes on the yacht sides at mid length, rising non trivial problems about longitudinal strength. The same trend appeared on superstructures sides where traditional windows have been enlarged till to became glass doors extended from deck to deck which allow passengers to enjoy full sea landscapes. Despite the positive effect on the general design performance, this nice innovation implies serious structural problems. In fact in side areas where these doors are fitted the only structural elements are represented by very slender vertical stiffeners. The combined action of bending and compressive loads, together with the fact that superstructures are usually made by aluminium light alloy, can be the cause of buckling phenomena with severe consequences on structure and glass integrity. In this paper the contribution to steel hull strength of light alloy superstructures with large openings is studied by the finite element approach. A deep investigation of local strength of the superstructure has been assessed as well

A simplified approach to the dynamic effective thickness of laminated glass for ships and passenger yachts

In the last years, after the economic crisis that modified the super and megayacht market and construction, the project focus of shipyards and owners has been moved from the research of higher performances and whimsical exteriors to more classic aesthetics and higher level of onboard comfort. This first aspect has led to the use of larger openings on superstructures\u2019 sides in order to enlarge windows and bring more natural light onboard vessels. The request of more comfortable units has granted a strong effort to find new solutions in order to reduce the noise and vibration level, dealing in particular to the structural elements with higher noise radiations, such as dampers, pillars and windows. The aforementioned trends is reflected on a more intensive use of glazed windows onboard, that have led to non-trivial problem of both structural response (since the structural component are reduced in order to enlarge opening) and NVH assessment, considering that glued glass panes act as an harmonic speakers, having natural frequencies closed to ones of the main superyacht excitations. In this paper, a simplified interactive design procedure for laminated glass used onboard super and megayacht is provided; in particular, authors developed a model for the calculation of a simplified dynamic effective thickness of laminated glasses, in order to increase the reliability of the modelling of glazed panes, with the same dynamic properties, in global numerical models of vessels

Fatigue Collapse of Ship Structural Components: a Case Study

Most damages to structural components of ships are due to fatigue phenomena. Particular care should then be devoted to fatigue evaluation since the first phases of any ship project. All main Classification Societies have in their Rules simplified procedures for fatigue evaluation, in order to make all designers able to perform structure scantling complying with fatigue principles. Apart from design necessities, there is another aspect for which it becomes important to assess and evaluate fatigue phenomena; this happens when it is necessary to ascertain the causes of occurred an accident. While for design purposes the aim is to calculate the fatigue life of a structural detail based on a probabilistic approach, in the case of an occurred accident the driving philosophy is to accurately analyse the life history of the structure and to calculate, by a deterministic approach, the cumulative damage of the component up to the event time. The aim of this paper is to set up a procedure to analyse and verify the causes of the failure of a ship structure component due to fatigue phenomena

Vibration analysis for the comfort assessment of a superyacht under hydrodynamic loads due to mechanical propulsion

Yacht designers and builders are continuously looking for new solutions to reduce construction costs and to improve the quality and innovation of their vessels. In the case of superyachts over 30 m in length, performances are no longer a primary goal and the efforts of technical offices are mostly addressed on other aspects related to the aesthetic impact of the project and to the on board comfort. From this point of view, vibrations and noise represent a difficult issues to deal with for designers, both in the initial phase of the project, when it is necessary to have preliminary information about the response of the structure not yet defined, and during construction, in case some critical behaviors arose in any part of the structure. In this paper, the dynamic behavior of a 40 m motor yacht is investigated. The Vibration Velocity Spectra obtained by the numerical model of the yacht are compared with the value of level limits imposed by the ISO6954:1984. Different structural solutions are investigate to improve the comfort level in same area not in compliance with the rule

NUMERICAL TOOLS AND EXPERIMENTAL PROCEDURES FOR THE PREDICTION OF NOISE PROPAGATION ON BOARD SUPERYACHTS

The Italian Classification Society, RINA S.p.A., is developing a new set of Rules regarding comfort conditions on board large motor-yachts. Relative to present owner requirements and technical enhancement, the new limit values will be more restrictive especially for yachts of more than 65 metres in length. In this respect designers and shipyards should consider structure borne noise and vibration level as leading parameters from the earliest design stages. In this paper some numerical tools, which allow prediction of noise propagation on board before sea trials to be carried out, are presented

The preliminary design of rubber mounted pillars for pleasure and passenger yachts

In this research, the Naval Section of the Department of Electrical, Electronic, Telecommunications Engineering and Naval Architecture of the University of Genoa has developed a preliminary study for the use of pillars mounted on rubber supports that should be able to accomplish their structural role and concurrently reduce the vibration transmission. In particular, in this paper, the results of static and natural mode analyses has been carried out on FE mock up models of a simplified two-deck ship structure in order to verify the impact of rubber mountings on pillars, both in the transmission of loads and vibrations

Static and dynamic comparison of megayacht deck structure\u2019s layouts

The growing increase in length of super and megayachts has driven structural designers to adopt longitudinal layouts as a main point in the structural scantlings. By the way, the optimization of weights, strength, deformations and dynamic behaviour has to be evaluated separately for each new unit because of the particular and unique characteristics of each vessel. For this evaluation, especially for what the dynamic behaviour of ribbed plates is concerned, the use of numerical software based on the Finite Element Method is widely used since the early design stages in order to highlight benefits and weaknesses of a particular structural design. In this paper, two different structural layouts of megayacht decks have been studied and tested by using a FE software: the first one has been created with longitudinal and transversal stiffeners with the same cross section. In the second layout, transversal stiffeners are smaller in dimension but with lower span. The comparison has been carried out making reference to maximum strengths, deformations and dynamic behaviour. This work, starting from an initial lay out obtained by a CS rule approach, made it possible to converge to an optimal structural configuration, at least for what the starting geometries are concerned

Hull\u2013furniture interaction in the primary response to global loads of a carbon fibre sailing yacht

High performance sailing yachts are generally designed assuming high local and global loads transmitted by rigs to hull structures. The above-mentioned loading conditions can become critical for large hulls also in terms of displacements when composite materials are used. In this scenario, it is very important to use lightweight and high-performance materials, such as carbon fibres. In fact, also some \u2018non structural\u2019 components, such as outfit and furniture, are built in carbon fibres and, therefore, can be considered contributing to the hull local and global strength. The aim of this work is to investigate the contribution level of those \u2018non-structural\u2019 components to the hull strength. Two different finite element models of a 94 ft sailing yacht, with and without \u2018non structural components\u2019, have been carried out in order to evaluate their contribution to the primary hull response to longitudinal bending moment and dock tuning load

Buckling Numerical Analysis of Stiffened Cylindrical Structures

In this research, a buckling numerical analysis of stiffened and unstiffened cylindrical shells is presented; in the first part of this work, the numerical FE code has been validated by comparing the numerical results with an experimental campaign carried out at the Department of Naval Architecture of the University of Genova. In the second part, the buckling occurrence of stiffened cylindrical shells representing a real submarine vehicle has been analysed in order to verify which is the limit state design of these type of unit