VehiQle Dynamics Associated with Submarine Rescue 



each command axis is fed into a "signed square" circuit, so that the 

 commands represent forces rather than propeller RPM. After 

 mixing the signals appropriately, they are fed into square root cir- 

 cuits so that the commands to the actuators represent RPM. Each 

 actuator is represented by a delay network which includes a maximum 

 motor acceleration limit. The effectors are represented by an 

 (RPM) network (to convert RPM to thrust) and a "thrust refinement" 

 circuit. The latter accounts for the variations of thrust with the 

 forward speed of the vehicle. The approximations used in the thrust 

 refinement are shown in Fig. 30. 



The actuator/effector simulation shown in Fig, 29 ignores 

 the lead-lag thrust effect of the thrusters which results from the 

 delay in accelerating the water in the thruster duct. Exploratory 

 experiments showed that, in manual control, the thrusters are used 

 in a bang-bang fashion, and the effects of ignoring the lead-lag 

 response of the thrusters are minimal. 



In the more sophisticated control modes used aboard the 

 DSRV, the mercury list system control is integrated into the right- 

 hand stick, and the pitch control motion of the right-hand stick 

 affects both thrusters and mercury trim control. 



NORMAL 

 I FORCE 



FORWARD 



AXIAL 

 FORCE 



0.2 0.4 0.6 0.8 1.0 



FORWARD VELOCITY FT/SEC 

 IMPtLLER VELOCITY ' ~m~' 



0.2 0.4 0.6 0.8 1.0 

 FORWARD VELOCITY FT/SEC 



IMPELLER VELOCITY ' nO^T" 



Fig. 30, Effect of Forward Speed on Thruster Forces and Moments 



1171 



