THE MANUAL STEERING CRITERION BASED UPON PHASE MARGIN. 指導教授 : 曾 慶 耀 學 生 : 潘 維 剛. Outline. MATHEMATICAL MODEL MANUAL STEERING CRITERIA MANUAL STEERING MAP CONCLUSION. MATHEMATICAL MODEL.
THE MANUAL STEERING CRITERION BASED UPON PHASE MARGIN
指導教授:曾 慶 耀學 生:潘 維 剛
-180 deg , so that if the phase is say -120 deg , then the
close loop system will be stable . Alternatively , if the phase
is less than -180 deg , say -210 deg , then the system is un- stable .
The magnitude of the ship plus steering engine transfer function (4) may be express in logarithmic
and for an unstable system the phase can be written as
, so that
It can be seen that as long as L/U>10 , then from the
last equation , will be much small than and will not have a great effect on system .However when the reverse is true and L/U<10 , then the steering engine cause an increasing time lag which can greatly detract from the manual handlng ability of the ship.
so that r=
Large yaw rates and rudder angles in reality the steady
state behavior is non-linear . This may be represented
here by the inclusion of a cubic term , so that
The loop width can be found by differentiating equation
(7) respect to r and setting the right hand side to zero ,
Then the loop width can be shown to be
Now for all the family of ships examined by Nomoto,
, so that in this case we can eliminate
From the last expression yield