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Surge Tanks, SUR

Analysis and Stability of Surge Tanks, SUR (Version 3.0)

This program computes the transient-state conditions in a system of surge tanks using the lumped-system approach, commonly referred to as the rigid-column theory. It may be used to compute the maximum and minimum surge tank levels, the possibility of tank drainage and spill, the volume of spill, and to investigate the stability of surge tank oscillations.

It is a general program for a series system of surge tanks.  SI units are used throughout and all elevations are with respect to a specified datum.

The system may have up to 15 surge tanks (This number may be increased by modifying the DIMENSION statement, for which  the developer of the program should be contacted.) and the the surge tanks may be of the simple or orifice type.  The orifice may have different loss coefficients for the inflow into or outflow from the tank.  A surge tank may have up to 10 area changes.

The ordinary differential equations describing the transient conditions are computed by using Euler, Modified Euler, or Iterative Predictor-Corrector methods. The software has been verified by comparing the computed results with the analytical results.

Water level oscillations in the surge tanks may be caused by changes in the plant flows.  The following two types of variations in the plant flows may be investigated: (i) Plant flows at different times may be specified; (ii) Plant power output may be changed instantly at time t = 0 and then kept constant at that level. For the constant power case, the plant flow is computed for the final power output using the net head from the previous time step and taking into consideration the change in turbine efficiency if the net head is higher than the rated head; and the plant flow is computed from the full-gate opening relationship if the net head is less than the rated head. The flows and the output of all turbines in each plant are lumped together.

A number of options are available for printing the program output.  The computed results (tank water levels, inflows, outflows, and spill volume) may be printed after specified number of time steps and some of these results may be stored in a different file for post-processing.

A provision for the addition of a branching junction is scheduled to be done at a later date.

Boundary Conditions

The following boundary conditions are included:

  • Upstream reservoir
  • Tunnel
  • Surge tank (simple or orifice; orifice losses may differ for the inflows and outflows)
  • Turbine (Flow variation; or constant power for stability investigation);
  • Downstream reservior