1,721,042 research outputs found
ATTIVITA’ DI RICERCA E STRUMENTI DISPONIBILI PRESSO L’UNIVERSITA’ DI STRATHCLYDE and GLASGOW
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Added Mass and Damping Coefficient Prediction - Results of Different Methods
No full textAdded Mass And Damping Coefficient Prediction - Results Of Different
Methods
Ermina Begovic, University of Naples Federico II, Naples/Italy, [email protected]
Guido Boccadamo, University of Naples Federico II, Naples/Italy, [email protected]
Abstract
The evaluation of ship motions and loads obtained through seakeeping calculations is continuing to
be one of the most important research subject. Numerical procedures used for this purpose are
generally validated by ship motions experiment; evaluation of motion equation coefficients is carried
out experimentally by forced motions and measurement of exciting forces on restrained model in
regular seaway.
Even if the motion prediction by some numerical method is satisfactory, the predicted values of
particular coefficients from the motion equation (added mass and damping coefficients) and of
exciting forces are not always satisfactory. This can affect heavily loads assessment that is
fundamental for structure scantlings. In particular, for the widely studied Wigley based hulls (Journee
(1992)), big discrepancies between numerical and experimental values have been noted.
In this work the review of experimental results for added mass and damping coefficients for heave and
pitch available in literature is given. Fo r two Wigley models (Journee (1992)) and for high speed Blok
and Beukelmann Model 5 (Keuning (1990)) heave and pitch added mass and damping coefficients are
calculated by 2 1⁄2 D high speed theory by Faltinsen and Zhao (1990) with and without cross-flow
corrections as proposed by Authors in previous works. Results are compared with numerical results
of similar works where different 3D time domain calculation methods were used.
Significant differences in some coefficients are found, calling for further investigation on the matter
Wake Wash Analysis of HSC Catamarans
No full textIn this paper the wake wash phenomenon produced by High Speed Craft (HSC) is analysed. Briefly the hydrodynamic phenomenon of wake wash is described indicating the parameters influencing the generation of wake wash from HSC at different speed and depth. The critical conditions for typical dimensions and speed of HSC are identified. In presented case study the wake wash generated by three catamarans actually operating in Croatian coastal waters is assessed. For each of them the actual route is analysed and flow regimes and critical points where wake wash could occur are identified. The wake wash values are assessed using the database of field measured wake wash for similar size catamarans published in literature. These values are propagated to shoreline and the obtained results are used to propose the maximum speed for which the generated wave height is still complying with the International Rules
Resistance and Stability Characteristics of Different Trimaran Configurations for Medium Distance Transportation
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PRISMATIC HULL TESTS IN REGULAR WAVES IN DIN TOWING TANK
No full textPRISMATIC HULL TESTS IN REGULAR WAVES IN DIN TOWING TANK
Begovic Ermina, Boccadamo Guido, Bove Andrea, Caldarella Sebastiano
Department of Naval Architecture, University of Naples Federico II, Naples, Italy
1. Introduction
Dipartimento di Ingegneria Navale (DIN) of Università degli studi di Napoli
Federico II has a towing tank of 137.2 m length, equipped with towing carriage with
maximum forward speed of 10 m/s to perform the model tests for ship resistance
prediction. This dimension of towing tank and carriage maximum speed allow relatively
huge models and very good tank-sea correlation. Resistance and powering
characteristics have been conducted both for conventional ship and for fast planning
hulls. Furthermore, multi hull configurations like catamaran, trimaran and pentamaran
ship models have been subject of research during last years.
State of the art in naval architecture indicates that the significant improvements in
ship resistance characteristics were obtained using the optimised hull forms and
consequently the cruising speed was increased. On the other hand, increasing speed and
security of vessels calls for a better understanding of the seakeeping so ship behaviour
in rough water become one of the principal interests of scientific community both as
development of numerical prediction method and as experimental determination of ship
responses.
Considering seakeeping of ships means practically to constrain the attention mainly
at vertical accelerations, relative vertical motions between ship and waves, slamming,
water on deck and wave bending moments and shear forces. Vertical motions and
accelerations result in loads on structures, cargo and equipment and are the main reason
for seasickness. It is evident that this aspect will be the most important for the passenger
ships in order to increase the comfort on board. Relative vertical motions are used to
evaluate the possibility and damage due to slamming and water on deck and therefore
are important to be improved the safety of ship. As regard the exciting loads (i.e. wave
bending moments and shear forces) generated in the interaction of ship advancing at
“constant” speed in confused sea it is of paramount importance for the structure to be
dimensioned appropriately.
Within the frame of the Competence Regional Centre “Transport”, a project financed
by the Campania Region (Mesure 3.16 POR Campania 2000- 2006), started in
November 2002, to develop a research structure equipped with some technological
laboratories and capable to integrate the competences of Universities and Research
Corporations, acting in the Campania Region, DIN was one of Departments of
University of Naples Federico II selected to get financial resources for technological
development and improvement of laboratory facilities. At towing tank new electric
feeding system has been installed and new acquisition system has been developed.
Recently, a wave maker designed by Edinburgh Designs Ltd, chosen in open bid, has
been installed at DIN towing tank with the aim to extend the tank possibilities also to
seakeeping tests.
In this work, the first seakeeping tests conducted at DIN towing tank equipped with
new wavemaker for the prismatic hull form, typical for the planning ships are presented.
The idea for the project demonstrator was to highlight the possibility of towing tank –
towing carriage – wavemaker for the prediction of high speed craft behaviour in rough
sea, as it is considered one of the most important subject of scientific research. For the
validation of ship performance in rough sea, the vertical motions i.e. heave and pitch
have been considered as the most influencing for comfort on board.
The tests are relative to 28 m length high speed craft cruising at speed of 30 knots in
regular waves
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