245MI - Architettura Navale

245MI - Architettura NavaleA.A. 2020/21

Introduction

Docente: Prof. Mitja MorgutUniversità degli Studi di TriesteDipartimento di Ingegneria e ArchitetturaVia A. Valerio 10, 34127 TriesteEdificio C5 - Stanza C5_2.44mail: [email protected]

Resistance prediction Classification on marine vessels Calm Water

Why resistance predictions are important

Architettura Navale, A.A. 2020/21

When a new ship is ordered, a contract containing a specification of the ship is signedÏ One of the most strict specifications is the contract speed i.e. the speed reached

at a specific power consumption in a trial run before delivery.Ï The trial run carried out to certify the contract speed is supposed to take place

under ideal conditions.

For a successful ship design, it is fundamental to accurately predict the powernecessary to achieve the desired/expected speed

Ï Due to a strong competition between shipyards the offer must be at least as goodas that of the competitors.A few percent higher power for a given speed can lead in a lost of order.

Ï On the other hand, if the prediction is performed in too optimistic fashion and onthe trial day the ship does not reach the expected speed, the customer mighteven refuse the ship.

The difficulty of this task is augmented by the fact that reliable information regardinghull shape, resistance and propulsion is required early in the design.The hull shape needs to be defined as soon as possible is since it affects not onlyresistance and propulsion, but also stability, structure.. of the vessel.


Why resistance predictions are important


When a new ship is ordered, a contract containing a specification of the ship is signedÏ One of the most strict specifications is the contract speed i.e. the speed reached

at a specific power consumption in a trial run before delivery.Ï The trial run carried out to certify the contract speed is supposed to take place

under ideal conditions.

For a successful ship design, it is fundamental to accurately predict the powernecessary to achieve the desired/expected speed

Ï Due to a strong competition between shipyards the offer must be at least as goodas that of the competitors.A few percent higher power for a given speed can lead in a lost of order.

Ï On the other hand, if the prediction is performed in too optimistic fashion and onthe trial day the ship does not reach the expected speed, the customer mighteven refuse the ship.

The difficulty of this task is augmented by the fact that reliable information regardinghull shape, resistance and propulsion is required early in the design.The hull shape needs to be defined as soon as possible is since it affects not onlyresistance and propulsion, but also stability, structure.. of the vessel.


Different ways to predict resistance


Three different methods are used at different stages of the design task

1) Empirical methodsÏ Employed in the initial design stageÏ Simple and rapid, but not always accurateÏ Usefull to identify the main particulars of the hull

2) Numerical methodsÏ Having an idea of the hull main dimensions, they may (are) employed to further

optimize of the shape of the hullÏ Time consuming, may require a significant amount of computational resourcesÏ Currently the CFD (Computational Fluid Dynamics) simulations are routinely

used

3) Model testsÏ Performed in the later stages of the designÏ Well established and arguably the most reliable performance prediction methodÏ Expensive but cheap compared to the cost of the shipÏ The model test data have to be extrapolated to full scale. This can introduce

significant errors if not done properly.


Classification based on the way the weight is supported



Surface piercing foils



Fully submerged foils



ACV - Air Cushion Vehicles



WIG - Wing in Ground (Craft)









Natural environment



Calm water


Documents

245MI - Architettura Navale