Rolling

The Roulis is a rotation movement of a mobile around its longitudinal axis (axis of rolling). The angular velocity of this rotation is also called rate of roll .

Aviation

In aviation, this movement is ordered by a side action on the manche.
The sleeve orders from its tower the deflection of mobile surfaces located on the wing: ailerons.
The deflections in opposite direction of these surfaces generate aerodynamic loads and a moment of rolling.

Axe of roulis
If the plane presents a dihedral sufficient, rolling can be obtained by actuating the control surface of direction.
Certain planes not equipped with ailerons (sailplanes known as " two axes" , planes of the " type; Louse of the ciel") carry out the turn in this way. See induced Rolling.

Navy

Definition

Rolling is the reciprocating motion of the ship around the longitudinal axis, the ship being inclined alternatively on Tribord and Bâbord.
If it is inclined on a side only one says that it lodging. Example, a sailing ship except for the pace of (against the wind).

Causes

The state of the sea is the cause of this phenomenon. The ship runs if the Houle or the Vague S arrives transversely on its road. It also happens that certain ships run with a sea of the front one. (Container ships) The phenomenon can be accentuated by a too strong stability. The amplitude of rolling can be accentuated by a Résonance, if the period of rolling approaches the period of the swell.

Clean period

As in any stable system, to rolling one clean period of the free oscillations is attached which grows with inertia and decrease with the stiffness. Inertia is then the sum of the traditional added inertia and moment of inertia I Ia corresponding to the acceleration of the fluid particles (see Notion of added mass). The stiffness in rotation is equal to the product of displacement P by the metacentric height, outdistances between the center of gravity G and the metacenter M (see Poussée of Archimedes)). The period is written:

T = 2 \ pi \ sqrt

Consequences

The movement of rolling that it is abrupt or slow can involve problems on board: Shifting of cargo, désarrimage of vehicles, draining of pumps, breakings of material, accidents human. This movement disturbs the balance and generates the Sea sickness at the not accustomed people.

Fight against rolling

  • Certain ships, especially the Transporter S and Steamer S, but also the Porte-conteneurs have active stabilizing systems (anti-roll ailerons controlled by an autostabilizer) making it possible to counter this movement. In a general way, on a hull which lends itself from its form to rolling one adds small side skittles (known as skittles of rolling ). In fact passive stabilizers do nothing but slow down the movements of rolling.
  • For the comfort of the passengers, a steamer as the Queen Mary 2 has 4 folding stabilizers:
Each one weighs approximately 70 tons, measures 2,50 meters of cord and 6,25 meters of scale, has a surface of 15,63 m2, ensures a bearing pressure positive or negative of 1.070 kN (109 tons) to cruising speed, spreads themselves or retracts in 30 seconds approximately. This system can reduce rolling by 90%.
  • It exists ships having a surface of very weak floating, less sensitive to rolling: the type SWATH , (Small Waterplane Area Twin Hull). This kind of ship in extreme cases of instability requires active stabilizers.

Railway

Movement of the train around its longitudinal, unpleasant axis for the travellers, and consequence of defects on the way.

See too

External bonds

  • Relations between period of rolling and transverse stability for the ships

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