Chlorine Dosage Example

This example illustrates how the Toolkit could be used to determine the lowest dose of chlorine applied at the entrance to a distribution system needed to ensure that a minimum residual is met throughout the system. We assume that the EPANET input file contains the proper set of kinetic coefficients that describe the rate at which chlorine will decay in the system being studied. In the example code, the ID label of the source node is contained in SourceID, the minimum residual target is given by Ctarget, and the target is only checked after a start-up duration of 5 days (432,000 seconds). To keep the code more readable, no error checking is made on the results returned from the Toolkit function calls.

#include "epanet2_2.h"
 
double cl2dose(char *SourceID, double Ctarget)
{
    int i, nnodes, sourceindex, violation;
    double c, csource;
    long t, tstep;
    EN_Project ph;
 
    // Open the toolkit & obtain a hydraulic solution
    EN_createproject(&ph);
    EN_open(ph, "example3.inp", "example3.rpt", "");
    EN_solveH(ph);
 
    // Get the number of nodes and the source node's index
    EN_getcount(ph, EN_NODECOUNT, &nnodes);
    EN_getnodeindex(ph, SourceID, &sourceindex);
 
    // Setup the system to analyze for chlorine
    // (in case it was not done in the input file)
    EN_setqualtype(ph, EN_CHEM, "Chlorine", "mg/L", "");
 
    // Open the water quality solver
    EN_openQ(ph);
 
    // Begin the search for the source concentration
    csource = 0.0;
    do {
 
        // Update source concentration to next level
        csource = csource + 0.1;
        EN_setnodevalue(ph, sourceindex, EN_SOURCEQUAL, csource);
 
        // Run WQ simulation checking for target violations
        violation = 0;
        EN_initQ(ph, 0);
        do {
            EN_runQ(ph, &t);
            if (t > 432000) {
                for (i=1; i<=nnodes; i++) {
                    EN_getnodevalue(ph, i, EN_QUALITY, &c);
                    if (c < Ctarget) {
                        violation = 1;
                        break;
                    }
                }
            }
            EN_nextQ(ph, &tstep);
 
        // End WQ run if violation found
        } while (!violation && tstep > 0);
 
    // Continue search if violation found
    } while (violation && csource <= 4.0);
 
    // Close up the WQ solver and delete the project
    EN_closeQ(ph);
    EN_deleteproject(ph);
    return csource;
}