PART IV: DYNLETl 



79. This chapter describes the general structure and operation of the 

 user interface of DYNLETl and preparations that must be made prior to running 

 the model. DYNLETl also generates graphs for display on the monitor, for 

 storing in graphics files, and for printing. The graphical display contains 

 plots of cross sections , plots comparing computed and measured velocities and 

 volume flow rates, and plots comparing measured and computed water surface 

 elevations. These plots are not intended to be true report quality graphics; 

 rather, they are provided to facilitate interpretation of the calculations and 

 measurements. Unless otherwise stated, plots shown in this report involving 

 use of DYNLETl were generated by the modeling system. In the following, focus 

 is on the input and output files comprising the interface. 



Preparation to Run DYNLETl 



Coordinate system and grid 



80. From the characteristics of the flow system, the various channels 

 to comprise the system must be identified. If more than two channels meet or 

 a channel branches into two forks, a junction must be identified. Appropriate 

 locations for the channel cross sections can be determined from a hydrographic 

 map. The distance between any two cross sections is arbitrary, but cross 

 sections should be placed at locations where channel properties (width, depth, 

 etc.) change significantly to represent the flow in regions of physical 

 importance. Cross sections are identified by nodes, a node being a grid point 

 on the chart representing the cross section passing through that grid point. 

 Once locations of the cross sections are known, the number of nodes N, that 

 is, the number of cross sections comprising the inlet system, is defined. 



81. For numbering of nodes, an initial flow direction must be assumed 

 to determine where a channel begins and ends. The selection of flow direction 

 is arbitrary, but once it is chosen, it cannot be changed during run time. It 

 is convenient, although not necessary, to assume the initial direction of the 

 flow to be from the sea toward land and to number the nodes in increasing 

 order away from the sea. 



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