APPENDIX: 

 DEPLOYED CABLE DYNAMICS AND COST FACTORS 



A cable dynamics model and computer program were developed at NOSC and used as 

 the bases for the deployment model of a fiber-optics cable. The original program was devel- 

 oped to calculate the nonequilibrium movement of a towed cable with a payload. A tow 

 ship or powered clump moves horizontally at a constant speed, pulling cable and payload 

 behind. The user specifies the initial configuration of a fully deployed cable. The model is 

 two-dimensional, showing movements vertically and horizontally in the X, Y plane. X and Y 

 thrusts are specified for tiie payload, and there is the capability of varying the thrust at set 

 intervals. The varying payload thrusts, along with tow speed, cable drag, cable weight, and 

 payload drag, are used to determine the cable configurations as a function of time. The 

 tensions at the top and bottom of the cable are also calculated. 



The main modification to the original program provides for cable deployment, since 

 the original program models a fully deployed cable with a fixed length. In the deployment 

 model, which features an expendable tether case, cable is paid out continually to form ever- 

 increasing scopes. To begin the deployment program, the user inputs the characteristics of 

 the tether and payload (tethered vehicle). The cable is modeled by straight-line segments. 

 The initial cable configuration is calculated from the number of straight-fine segments, the 

 length of these segments, and the locations of the nodes at the end points of the segments. 

 After the initial length is specified, the total amount of tether in the payout reel available 

 for deployment is specified. The user specifies the intervals at which the computer is to 

 print out tlie catenary configuration, and how often. 



To start the deployment, the tow ship starts forward at a fixed speed. The capabihty 

 of simulating a ship with automatic stationkeeping can be achieved if the coordinate system 

 is translated to have the origin move with the top of the cable. In this case, the tow speed 

 becomes the uniform current speed that is moving past the stationary ship. The simulation 

 either starts with a tow ship moving at a fixed speed with no current, or with a ship on auto- 

 matic stationkeeping with a constant, uniform current. 



The submersible starts on a course whose speed and heading are specified by the user. 

 The program calculates the location of the underwater vehicle and deploys new lengths of 

 tether to keep up with the moving vehicle. At the same time, the cable configuration and 

 tensions are calculated for the deploying cable in response to ship movement, vehicle move- 

 ment, and current. The program keeps track of how much tether is deployed and continues 

 even after full deployment. 



The payout of cable is assumed to take place only from a canister on the tethered 

 vehicle. A pullout tension of zero is assumed. Thus the tethered vehicle cannot provide any 

 pull on the cable during deployment. Any movement or thrust from the tethered vehicle 

 merely pays out more tether. This approximates the unarmored f-o tether well, but there 

 will probably be a substantial pullout tension for the S-glass tether. Because of this, the 

 program actually gives a "worst-case" condition. The reason is that a nonzero tension will 

 result in less cable being pulled out by the current. 



The program starts with an initial cable configuration and either a current or tow 

 ship speed, as well as a tethered vehicle speed. The current (or tow ship) movement and the 

 movement of the tethered vehicle will pay out tether until all available cable is deployed. 

 The program continuously calculates the cable tensions, configuration, and scope. 



The different fiber-optic tether configurations can be simulated with this deployment 

 model for different test conditions. The tensions during and after deployment help to 



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