Method and device for allocating thrust
View Patent ↗Force balance and moment balance associated with thrust of air and water craft equipped with thrust generators are preset in view of non-linear characteristics and dynamic characteristics of thrust generators. A performance index for minimizing thrusts generated by the thrust generators is defined. Using the balance as restricting condition, propeller thrusts of the thrust generators and rudder angles and changing speeds of rudders that minimize the performance index are calculated.
1. A device for allocating thrusts in air and water craft equipped with a plurality of thrust generators that generate thrusts corresponding to manipulated variables, the device being configured to calculate the manipulated variables given to the plurality of thrust generators to allow the air and water craft to run with a given targeted thrust or to be held at a fixed point, comprising:
a calculating means for calculating the manipulated variables of the thrust generators that satisfy balance between the manipulated variables and the targeted thrust and a predetermined condition of a predetermined performance index,
based on force balance and moment balance between the thrusts generated by the thrust generators and a thrust of the air and water craft, which is predetermined based on non-linear characteristics of the thrust generators, and
based on the predetermined performance index associated with state variables relating to states of the thrust generators and/or the thrusts generated by the thrust generators, for minimizing the thrusts generated by the thrust generators, wherein
the balance is given by formulae (1) to (3):
∑
i
=
1
n
f
xi
=
X
(
1
)
∑
i
=
1
n
f
yi
=
Y
(
2
)
∑
i
=
1
n
(
k
1
i
f
xi
+
k
2
i
f
yi
)
=
N
(
3
)
where
X is a longitudinal component of the thrust of the air and water craft,
Y is a lateral component of the thrust of the air and water craft,
N is a thrust moment in a turning direction of the air and water craft,
f xi is a longitudinal component of the thrust generated by an i-th thrust generator,
f yi is a lateral component of the thrust generated by the i-th thrust generator,
k 1i and k 2i are coefficients, and
i is 1 to n (n: natural number); and wherein
the thrusts F(t)=[f x1 . . . f xn f y1 . . . f yn ] T generated by the thrust generators are given by a non-linear equation (4)
F ( t )= h[x ( t ), u ( t ), t] (4)
when the manipulated variables of the thrust generators are represented by u(t)=[u 1 . . . u m ] T (m: positive integer) of the thrust generators,
where
t is time variable, and
x are state variables given by non-linear differential equations (5):
{dot over (x)} ( t )= g[x ( t ), u ( t ), t] (5).
2. The device according to claim 1 , wherein the balance is predetermined based on the non-linear characteristics and dynamic characteristics of the thrust generators.
3. The device for allocating thrusts of claim 2 , wherein the craft is selected from the group consisting of a watercraft and an aircraft.
4. The device according to claim 1 , wherein the manipulated variables u satisfy relationship represented by a formula (6):
| u j ( t )|< u j max (6)
where
u jmax is a constant, and
j is 1 to m (m: natural number).
5. The device for allocating thrusts of claim 4 , wherein the craft is selected from the group consisting of a watercraft and an aircraft.
6. The device for allocating thrusts of claim 4 , wherein the craft is a watercraft.
7. The device according to claim 1 , wherein the state variables x satisfy relationship represented by a formula (7)
|x i ( t )|< x i max (7)
where
X imax is a constant.
8. The device for allocating thrusts of claim 7 , wherein the craft is selected from the group consisting of a watercraft and an aircraft.
9. The device according to claim 1 , wherein the thrust generators are azimuth thrusters and the balance is given by formulae (8) to (10)
∑
i
=
1
n
T
i
cos
θ
i
=
X
(
8
)
∑
i
=
1
n
T
i
sin
θ
i
=
Y
(
9
)
∑
i
=
1
n
T
i
(
-
yo
i
cos
θ
i
+
xo
i
sin
θ
i
)
=
N
(
10
)
where
T i is a propeller thrust of an i-th thrust generator,
θ i is a turning angle of the i-th thrust generator,
xo i is a position of the i-th thrust generator that is relative to a center of gravity of the air and water craft in a longitudinal direction of the craft, and
yo i is a position of the i-th thrust generator that is relative to the center of gravity of the air and water craft in a lateral direction of the craft.
10. The device for allocating thrusts of claim 9 , wherein the craft is selected from the group consisting of a watercraft and an aircraft.
11. The device according to claim 1 , wherein the performance index J is given by a formula (11)
J
=
ϕ
[
x
(
t
+
T
)
]
+
∫
t
t
+
T
L
[
x
(
t
′
)
,
u
(
t
′
)
]
ⅆ
t
′
(
11
)
where
Φ and L are scalar value functions differentiable up to a predetermined order or more,
T is a constant, and
t′ is a variable that satisfies t≦t′≦t+T, and
the predetermined condition is given to minimize or maximize the value of the performance index J.
12. The device according to claim 11 , wherein the performance index J includes weighting factors relating to the state variables x and/or the manipulated variables u, further comprising:
a changing means capable of changing the weighting factors on line.
13. The device according to claim 12 , further comprising:
a detecting means for detecting occurrence of failure in the thrust generator, wherein
when the detecting means detects occurrence of the failure in the thrust generator, the changing means changes the weighting factor relating to the state variables x and/or the manipulated variables u of the thrust generator in which the failure occurs.
14. The device for allocating thrusts of claim 12 , wherein the craft is selected from the group consisting of a watercraft and an aircraft.
15. The device for allocating thrusts of claim 11 , wherein the craft is selected from the group consisting of a watercraft and an aircraft.
16. The device for allocating thrusts of claim 1 , wherein the craft is a watercraft.
17. The device for allocating thrusts of claim 1 , wherein the craft is an aircraft.
18. The device for allocating thrusts of claim 1 , wherein the craft is selected from the group consisting of a watercraft and an aircraft.