1,721,017 research outputs found
Fatigue Collapse of Ship Structural Components: a Case Study
No full textMost 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
Low - Frequency analysis of super yacht free vibrations
No full textAfter a long period of crisis and uncertainty the yacht market seems to exit from the tunnel. Many shipyards are developing new interesting projects, especially for vessels over 50 m in length. The high intrinsic value of these vessels fosters technical offices to deepen the research on some critical subjects to increase competitiveness. The onboard comfort, with particular reference to vibrations, is probably one of the key aspects of this trend which nowadays drives most of the design choices relatively to structure lay out and materials for interior outfit. A great help comes from Classification Society new rules and regulations for the evaluation of noise and vibration. The so called "Comfort Class Rules" contain the general criteria for noise and vibration measurements in various yacht areas and suggest maximum limit values as a function of the required quality level of the yacht. In this paper a study carried out in cooperation between the University of Genova and a leading Italian shipyard on the dynamic behaviour of superyacht structures is presented. A detailed FEM analysis of the global and local natural frequencies of a 60 m superyacht was carried out in order to evaluate the reliability of simplified procedures based on reduced numerical models. The investigation has been carried out by two different FEM codes and the numerical results have been compared with experimental data measured during the construction of the vessel
The Evolution of Large Pleasure Vessel Towards a Green Future
No full textThe future of transportation means is quickly moving towards green solutions in order to reduce the emission of COx and SOx firstly and, secondly, to progressively abandon the fossil fuels. In this perspective, alternative propulsion such as fully electric engine, biofuels, hydrogen, LNG are now largely used in the automotive field and for mass transportation means. The naval field is now moving on the same trend by using hybrid and fully electric engine especially for pleasure vessels, where the relatively small engine power allows the installation of battery stacks onboard without adding unreasonable weight for only few navigation miles. In this paper, the transformation of a traditional pleasure vessel towards a new hybrid version is proposed; after a more comprehensive view of the modifications that are necessary to install hybrid engine and battery onboard, highlighting all the critical aspects of these new design, a FE numerical analysis of the basement of electric variable speed generators is presented
Experimental and numerical analysis of absorber materials for steel decks
No full textNowadays, comfort is becoming the principal goal for designers. But what does onboard comfort really mean? It is possible to define it as a sense of physical or psychological ease, often characterized as a lack of hardship, and it is therefore a subjective sensation. In fact, the perception of a comfort condition is due to a complex mechanism in which the different senses are involved and interact with each other. When trying to improve the comfort onboard, it should be considered that the interaction between the surrounding environment and the people on board is realized through the perception of stimuli related to hearing (noise), smell, breathing and transpiration (air quality and temperature), the sight (aspect of the environment), physical contact (vibration) and the sensation of movement of the body in space (ship motions). Until now, the most important Classification Societies impose severe rules and regulations only for the evaluation of noise and vibration maximum levels for different zones of the ship. Many other aspects that influence the comfort on board are currently under study. The incentive to provide the market with more comfortable products gave rise to high awareness for the analysis of sound transmission and absorption of the main materials used in shipbuilding. There are two driving parameters to describe the behavior of sound absorber materials: Transmission Loss (TL) and Insertion Loss (IL). In case of metals, with particular reference to steel, it is well known that the internal damping is very low. In contrast, there are so-called viscoelastic materials, which show high dissipation of mechanical energy. In this paper, a measurement campaign in real scale, carried out to investigate the dynamic behavior of different materials used to absorb vibration and sound propagating through steel decks, is described. During the tests, a comparison of velocity level measured under the naked metal plate obtained from experimental data and from finite element analyses has been carried out. Furthermore, the TL and IL values of the four different floor configurations obtained from experimental data are compared to understand which type of floor shows the best damping behavior
Numerical tools and experimental activities for the prediction of noise propagation on board superyachts
No full textThe Italian Classification Society, RINA S.p.A., is developing a new set of Rules regarding comfort conditions on board large motor-yachts. According to present owner requirements and technical enhancement, the new limit values will be more restrictive especially for yachts with more than 65 meter in length. In this perspective designers and shipyards should consider structure borne noise and vibration level as leading parameters since the earliest design stages.
In this paper some numerical tools, which allow to predict noise propagation on board before sea trials are carried out, are presented. The reliability of the proposed tools has been tested by means of experimental activities for the evaluation of damping loss factor on the viscoelastic materials employed in different parts of the vessel such as floating floors and engine foundations
Dynamic Loads on Fast Ferry Hull Structures Induced by the Engine-Propeller Coupling
No full textIn this paper the problem of the vibrations induced on the hull by the propulsion system is considered. Although the problem has been widely studied in the technical literature, some new aspects concerning the propulsion system model are here investigated. In particular the engine is modelled taking into account its exact crankshaft dynamics, leading to variable inertia effects and parametric excitation. The pulsating propeller torque in the hull wake is studied as well, by solving the flow about the propeller by a boundary element technique. The derived model allows an accurate calculation of the reaction forces transmitted by the engine-propeller system to the ship structures; in this way the characteristic time history of the vibrational motion of important parts of the ships can be predicted. The attention is focused on a typical fast passenger ship, the finite element model of which is developed. Preliminary test results are shown and the performed numerical simulations suggest that the global propeller-engine-structure model could be a useful tool in the frame of the optimization of the vibrational ship design
Thermal load effects on side plates of superyachts
No full textFrom the commercial point of view the aesthetics of large luxury yachts has the same importance of their technical performances and reliability. In this perspective the first impact that a new construction can exert on a potential owner takes place through the overall appearance of the hull and superstructures. The hull colour, in particular, is becoming more and more determinant to make a yacht more attractive. After a long, undisturbed supremacy of white and cream colours, now an increasing number of owners are opting for dark colours, like blue, green or black. For a perfect painting output these colours needs a perfectly smooth surface as they have the tendency to emphasize every small defect of the hull surface. This aspect can be further amplified by those shape defects affecting hull sides, such as bump and hollows, coming from welding plates each other and plates to frames. For this reason, in case of steel and aluminium vessels, the surface finishing must be achieved by a long and delicate process of filling and fairing. Notwithstanding very accurate preparation, hull surfaces can undergo undesired alteration because of long expositions to solar radiation. This phenomenon is amplified when the surface is painted with dark colours which have the tendency of absorbing much greater solar heat. As stated by a previous investigation carried out on superyachts painted with dark colours, the surface of hull sides after a long exposition to solar radiation can reach temperatures close to 70–80°. In order to evaluate possible distortions of hull sides caused by thermal loads, an investigation has been carried out on the influence of temperature on the mechanical behaviour of steel plates coated by epoxy filler. The study has been developed by FEM structural analyses on a portion of a superyacht hull in the region of aft sides where the flatness of shell makes more visible possible distortions. Both steel and aluminium material have been considered covered by filler layers of different kind and thickness. A preliminary experimental investigation has been performed on a number of steel and aluminium specimens in order to calibrate the numerical models
An experimental-driven methodology for the evaluation of pre-tension of stays and shrouds for large sailing vessels
No full textSince numerical structural calculations of sailing yachts' rigs strictly depend on the dock tuning load (DTL), it is necessary to evaluate it during vessels' normal operations even when it cannot be estimated by load cells installed onboard. In this paper, a novel approach for the determination of the pre-tension load of stays and shrouds for large sailing vessels is presented and it based on the coupling of an analytical approach to the cables’ dynamics and the evaluation of natural modes by using Experimental Modal Analysis (EMA). The validation of the method herein proposed as been validated by numerical non linear Finite Element calculations
A simplified method for the evaluation of inertial loads on sailing yachts
No full textThe aim of this work was to improve the understanding of dismasting, in view of the development of a new set of Rig Certification Rules specifically aimed at sailing yacht design, In the first phase of this project a preliminary systematic analysis of the dismastings of a large set of boats of different type and size has been carried out. By examining all these events, typical collapse modes have been identified, showing that whereas the traditional approach to mast scantlings is based on static loads, many of the failures took place as a result of severe dynamic loads. For this reason attention has been focused on the dynamic loads acting on the rigging caused by the response of the sailing yacht to waves. Especially in the case of boats with large displacement, these loads could be of a greater magnitude than static ones, and their evaluation must be earned out through seakeeping analysis. In particular pitching motions are extremely important, since they can cause severe accelerations to mast and rigging, possibly leading to mast collapse. Indeed dismasting is a significant event, very dangerous for the crew and very expensive to be repaired. In this paper a systematic study of the pitching behaviour of a database of sailing yachts was carried out. Using these results a simplified formulation is given to quickly evaluate the longitudinal acceleration at the mast centre of gravity. A state-of-the-art process is then used to obtain results in irregular sea states and to compute time series. Despite the small size of the database, this could be regarded as a first step towards the formulation of a simplified method based only on the boat length; this method would be able rapidly to estimate inertial loads due to waves
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