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From one port to another one, much faster as possible. Much cheaper as possible. Much more comfortable. 
Bulbous bow’s purposes are to fight against head wave impact and decrease drag from wave generating resistance. These two actions cover such important sections as financial costs (fuel consumption, hull maintenance cost), transportation time (seakeeping, ship’s velocity), comfort for passengers and crew (vibration, wave shock impact). 
Application of bulbous bow helps to significantly reduce all above listed costs, journey time and improve people’s health condition onboard. Electronic equipment undergoes less shock and has less risk to be damaged due to wave impact on fore-part. Hull vibration levels may also be reduced by high values and frequencies. 
But still, there is no limit to try to improve bulbous bow’s performance further. 
In this thesis the author will describe and provide the results from research made to find out about applicability of new concept of bulbous bow – blade bulbous bow – on a middle-size semi-displacement cruise yachts. 
The new bow application already had obtained positive reviews in naval/maritime theme magazines. Here below some articles will be provided as side overview of existing vessels aiming such a bow.

Ingénierie, informatique & technologie > Ingénierie civile

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The purpose of this report is the study of the prediction of noise propagation generated on board a motor yacht (40m) still under the construction at Cerri Cantieri Navali shipyard. This investigation is carried out because of the shipyard’s necessity to collect the information about the dynamic and vibration behavior of the structures of the motor yacht. The structure of the yacht is not a conventional one: it is considerably stiffer than the regular semi-displacement motor yacht of nearly the same size because it is of Ice Class. Prediction of noise propagation is of great importance in luxury ships like motor yachts. It is more or less concerned with the vibration of the structures on the ship. Generally, the more vibration there is, the more is the noise production and propagation. Noise propagation issues are determinant not only for the structural reasons but also when the high standards are expected on comfort and well-being. If the limits established by the standards are not exceeded, the habitability will be good which means no health damage will occur. For this study, the complete motor yacht including hull, decks, structures and insulations are going to be finished. Because it is a perfect condition to perform the predictions, measurements and analyze the comparison of the generated results with the noise criteria from RINA measurements, considering that there is less uncertainties regarding the damping in the vibration analysis and induced errors in the input data. The objective of this study is to know the nature of the Vibroacoustic One software which is applied to perform the SEA analysis, to know the acoustic theory of the structures, to make the prediction of noise in each room throughout the analyzed yacht model, to check whether the estimated sound pressure level of noise satisfy the criteria proposed by RINA and whether the created yacht model can be used to make further investigations on this particular field of study. And the behavior of the glass windows especially around the owner’s cabin such that how they contribute to the sound pressure level according to the variation of particular thickness and the behavior of changes in insulation thickness surrounding the acoustic cavity of interest. Moreover, the transmission loss behavior around the critical coincidence frequency of one of the SEA plate panels which contributes the highest power input to the acoustic cavity of interest will be analyzed. The design of yacht, construction plans and technical information will be provided by the shipyard’s responsible office. On the side of software, the analysis of this study is developed through the application of VA One (Vibroacoustic One) software. The creation of yacht model is done through the marine modeler tab inside the software.

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The cumulative damage due to fluctuating loads leads to fatigue fracture which is the main cause of the fracture of offshore vessels and structures. Knuckle joints are the most critical area due to its susceptibility to fatigue failure. This is mainly due to a high-stress concentration at knuckle joints. Also, the area is inaccessible for inspection and repair due to cargo tank containment arrangement. In this report, the spectral fatigue analysis is presented for 148k, Moss type spherical tank LNG carrier. The study is focused on the fatigue damage evaluation of hopper knuckle joint details by full spectral fatigue analysis. 

The full spectral fatigue analysis involves the computations of hydrodynamic response, global structural analysis, local structural analysis and calculation of fatigue damage. The structural response is assessed by performing linear FE–analysis with a linear material response. In order to simulate structural response, a linear hydrodynamic analysis using unit wave amplitude is carried out to simulate the wave-induced loads on the LNG carrier, which is followed by a linear FE global analysis to assess stress transfer function. The wave loading is calculated by linear hydrodynamic analysis is based on 3D diffraction theory. The wave amplitude of 1.0m considering wave headings from 0 to 360 degrees with an increment of maximum 30 degrees is used to calculate the ship response. For each wave heading 25 wave frequencies are included to describe the shape of the transfer functions. The inertia loads, internal and external pressures are calculated in the hydrodynamic analysis and transferred directly to the global structural model. Direct wave load computations by the numerical method improve the accuracy of the calculated loads compared to the approach of using the classification society‘s formulae. Two type of loading cases i.e. full load and normal ballast condition are considered for the damage calculation. For each heading of sea state, fatigue damage is calculated by combing the hotspot transfer functions with stress cycle (S-N) curve data and wave scatter diagram. 

Fatigue damage computations involve design variables such as S-N curve data, wave scatter data, wave spectrum, etc. Current rules of classification societies DNV GL and ABS are used to evaluate the fatigue damage of knuckle joint. In general, the spectral fatigue calculation is cumbersome due to time-consuming calculation process. However, the study also provides information about the procedures involved in the spectral fatigue calculation

Spectral Fatigue, Fatigue damage, design variable --- Ingénierie, informatique & technologie > Ingénierie civile