Wadiso Numeric Balancing Pressures and Flows

A number of numeric schemes have been proposed and used in the computation of the pressure and flow distribution in pipe networks. Each one has its specific characteristics: some schemes are simple to implement, others require the least amount of computer memory, or the least amount of computer time to find the answer. Again another characteristic is how the program performs under extreme conditions, does it easily "crash" or is it particularly "robust" when analyzing unusual situations, as might be encountered during extended time simulation or during optimization. The technique employed in Wadiso is a node method: the non-linear loss equation for each pipe (or pump) is linearized and substituted into the continuity equation at each node. The result is a system of linear equations with as many equations as there are nodes in the system which is solved through an iterative procedure. The major advantages of this technique include:

• A coefficient matrix which is symmetrical for all systems (even in the presence of pumps and pressure reducing valves).

• A network topology which does not change substantially if during the optimization pipes are removed.

• Excellent convergence characteristics.

• An algorithm which has hydraulic head (or pressures) as the primary unknown, allowing excellent control over required and achieved accuracy.