Section 1 - Introduction Flashcards
The ultimate test is that the ship shall perform at the required speed …
… with mininum shaft power.
The assumption that a hull form is optimum in calm water will also be optimum in rough seas …
… is not necessarily valid.
In general, the basic contractual obligation laid on the shipbuilder is that the ship may achieve a ___________ with ___________ in good weather on trial, and for this reason ___________ performance is of great importance.
certain speed / specified power / smooth water
The effect of sea condition is customarily allowed for by the provision of a ________________ above the power required in smooth water.
service power margin
Resistance of a ship at a given speed is ..
.. force required to tow the ship at that speed in smooth water, assuming no interference from the towing ship.
Bare-hull resistance
when hull has no appendages
Tow-rope or effective power
power necessary to overcome the resistance
Components of the total calm water resistance:
- frictional
- wave-making
- eddy
- air resistance
Residuary resistance
eddy and wave-making taken together
Simplest case of resistance
streamlined body moving in a straight horizontal line at constant speed, deeply immersed
Concerning submerged bodies, since there is no __________ , there is no _____________and therefore no _____________ resistance.
free surface / wave formation / wave-making
Perfect fluid
- without viscosity
- no eddy resistane
- no frictional resistance
In a perfect fluid, the pressure distribution around a submerged body can be determined theoretically from considerations of the _______________.
potential flow
Since the fluid has been assumed to be without viscosity , the pressure forces will be everywhere be _____________ to the hull.
normal
In a real fluid the boundary layer alters the virtual shape and length of the __________, the pressure distribution there is changed and its forward component is ___________.
stern / reduced
There is therefore a net force on the body acting against the motion, giving rise to a resistance which is variously referred to as ___________ or ______________.
form drag / viscous pressure drag
Types of resistance the body experiences in a real fluid:
- frictional resistance
- eddy resistance
- form drag or viscous pressure drag
Boundary layer
layer of water, which get gradually thicker from the bow to the stern, and in which the velocity varies from that of the body at its surface to that appropriate to the potential flow pattern at the outer edge of the layer
If the body is blunt at the aft end, the flow may leave the form at some point, called ___________________, thus reducing the pressure on the after body and adding to the resistance.
separation point
A ship moving in the surface of the sea experiences ____________, ____________, _____________ and _____________ in the same way as does submerged body.
frictional resistance / eddy-making / separation / viscous pressure drag
A surface ship has a _____________ pressure acting over the bow, and the pressure increase at the stern, in and just below the surface, is always ___________ than a submerged body.
greater / less
The presence of the ________________ modifies the skin friction and other resistances.
wave systems
