Chapter 3 - Dynamics of Marine Vessels

Chapter 3 - Dynamics of Marine Vessels Chapter 3 - Dynamics of Marine Vessels

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22 3.3.2 Linearized Equations of Motion The gravitational and buoyancy forces can also be expressed in terms of VP coordinates. For small roll and pitch angles: g Notice that this formula confirms that the restoring forces of a leveled vessel ( ) is independent of the yaw angle . 0 ≈ PG PGP p Gp G 0 For a neutrally buoyant submersible (W=B) with x g =x b and y g =y b we have: G diag0, 0, 0, 0, zg − zbW, zg − zbW,0 For a surface vessel G is defined as: G 022 032 023 G r 0 0 0 0 0 0 0 0 0 0 , G r −Zz 0 −Z 0 −K 0 −Mz 0 −M P Notice that: GP ≡ G Ivar Ihle – TTK4190 Spring 2006

23 3.3.2 Linearized Equations of Motion Low-Speed Maneuvering and DP: ≈ 0 implies that the nonlinear Coriolis, centripetal, damping, restoring, and buoyancy forces and moments can be linearized about 0 and 0. Since C(0)=0 and Dn (0)=0 it makes sense to: approximate: Ṁ C D Dn 0 D The resulting state-space model becomes: A ̇ p Ṁ D G p w 0 I −M−1G −M−1D P p , B g Gp 0 M−1 g o w ̇x Ax Bu Ew x p , , u , E 0 M−1 which is the linear time invariant (LTI) state-space model used in DP. Ivar Ihle – TTK4190 Spring 2006

22<br />

3.3.2 Linearized Equations <strong>of</strong> Motion<br />

The gravitational and buoyancy forces can also be expressed in terms <strong>of</strong> VP<br />

coordinates. For small roll and pitch angles:<br />

g<br />

Notice that this formula confirms that the restoring forces <strong>of</strong> a leveled vessel<br />

( ) is independent <strong>of</strong> the yaw angle .<br />

0<br />

≈ PG PGP p Gp G<br />

0 <br />

For a neutrally buoyant submersible (W=B) with x g =x b and y g =y b we have:<br />

G diag0, 0, 0, 0, zg − zbW, zg − zbW,0<br />

For a surface vessel G is defined as:<br />

G <br />

022<br />

032<br />

023<br />

G r<br />

0 0 0 0 0 0<br />

0<br />

0<br />

0<br />

0<br />

, G r <br />

−Zz 0 −Z<br />

0 −K 0<br />

−Mz 0 −M<br />

P Notice that:<br />

GP ≡ G<br />

Ivar Ihle – TTK4190 Spring 2006

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