Sohreiberj Bentkowsky and Kerr 



II. FREE STREAM DSRV DYNAMICS SIMULATION 



EQUATIONS OF MOTION 



The development of a dynamic simulation of the Deep Sub- 

 mergence Rescue Vehicle (DSRV) follows a different approach than 

 the methods used in most submarine studies. This deviation fronn 

 the standard approach is necessary because of the basic differences 

 in the mode of operation of the DSRV compared to that of conventional 

 submarines. While the analysis of a submarine is generally con- 

 fined to prediction of the vehicle dynamics at speed in an infinite 

 fluid, the DSRV dynamics must also be simulated while hovering and 

 docking in the presence of a downed submarine. The conventional 

 method used to simulate the dynamics of a submarine is to calculate 

 the position of the center of gravity of the vehicle using linear force 

 and moment coefficients for the complete vehicle which are refer- 

 enced to its center of gravity. The basic equations of motion for 

 the DSRV differ in two ways from this conventional method, first In 

 the choice of an axis system and secondly In the naanner of handling 

 the forces on the vehicles and appendages. 



Axis System 



Since the DSRV Is required to assume angles of 45° to the 

 horizontal In pitch and roll (very unrealistic for a conventional sub- 

 naarlne) a mercury trim and list system Is Incorporated which moves 

 the vehicle's center of gravity (e.g.) to accomplish these attitudes. 

 The fact that the vehicle's e.g. moves with respect to the vehicle 

 during maneuvers makes It a poor choice as a reference point for 

 describing force and moment coefficients since they would have to be 

 changed as a function of e.g. position. Using the e.g. as a refer- 

 ence axis system would also lead to complications In describing the 

 vehicle's motion with respect to the distressed submarine since the 

 motion of the axis system with respect to the vehicle would be In- 

 cluded In the velocity of the axis system. Therefore, an axis system 

 fixed to the body was used as a reference point. Since the axis sys- 

 tem is not always at the center of gravity and terms to account for 

 this shift must be Included In the equations of motion there Is no 

 advantage In choosing the nominal vehicle eg, as the center of the 

 cLxls system. There are, however, advajitages to having the x-axls 

 lie along the vehicle centerllne since the basic DSRV shape Is a body 

 of revolution. This axial symmetry provided by having one axis of 

 the system lie along the vehicle centerllne greatly reduces the number 

 of cross coupling coefficients required to describe the forces and 

 moments on the body. The positive direction of this axis Is forward 

 so that positive vehicle velocities are associated with vehicle forward 

 motion. Similarly with the z-axls through the centerllne of the transfer 

 skirt (280.8 Inches aft of the forward perpendicular) the number of 

 cross coupling coefficients are reduced and the direct reference to 

 the centerllne of the transfer skirt simplifies the description of 

 relationships between transfer skirt and the hatch during mating 



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