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Kongsberg cJoy OT
The Kalman Filter
The Kalman Filter estimates the vessel's heading, position and velocity in each of the
three degrees of freedom - surge, sway and yaw. It also incorporates algorithms for
estimating the effect of sea current and waves.
The Kalman Filter uses a vessel model which includes hydrodynamic characteristics
such as drag coefficients and virtual mass data. This model, called the Mathematical
Vessel Model, describes how the vessel responds to an applied force, e.g. wind and
thrusters. The mathematical model itself is never a 100% accurate representation of
the real vessel. However, by using the Kalman filtering technique, the model can be
continuously corrected.
The vessel's heading and position are measured using the gyrocompass and
position-reference system, and are used as input data to the system. These measurements
are compared with the predicted or estimated data produced by the mathematical model,
and the differences are then used to correct the model.
Figure 4
Block diagram showing the Kalman filter
Model
Update
Sea Current
Estimate
Mathematical
Vessel Model
Kalman Filter
Measurements from
Position-
Reference System
Sensors and
Thruster
Allocation
Controller
Thruster
Feedback
Wind
IndividualThruster
Commands
Wanted Heading
and Speed
Position
Forces and
Moment Demand
Heading,
and Speed Estimates
Position
-
+
(CD2879A)
The Kalman Filter provides the following advantages:
• Optimum self-adaptive noise filtering of heading and position measurements
according to noise level and measurement-update rate.
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