Account for mass lost in tank overflow

This change addresses issue #769.

src/qualreact.c

@@ -7,7 +7,7 @@ Description:  computes water quality reactions within pipes and tanks
 Authors:      see AUTHORS
 Copyright:    see AUTHORS
 License:      see LICENSE
-Last Updated: 05/15/2019
+Last Updated: 03/12/2024
 ******************************************************************************
 */
 
@@ -492,6 +492,13 @@ void tankmix1(Project *pr, int i, double vin, double win, double vnet)
        seg->v += vnet;
        seg->v = MAX(0.0, seg->v);
        tank->C = seg->c;
+       
+        // Account for mass lost in tank overflow
+        if (seg->v > tank->Vmax)
+        {
+            qual->MassBalance.outflow += ((seg->v) - tank->Vmax) * tank->C;
+            seg->v = tank->Vmax;
+        }
     }
 }
 
@@ -513,7 +520,8 @@ void tankmix2(Project *pr, int i, double vin, double win, double vnet)
 
     int    k;
     double vt,          // Transferred volume
-           vmz;         // Full mixing zone volume
+           vmz,         // Full mixing zone volume
+           vsz;         // Full stagnant zone volume
     Pseg   mixzone,     // Mixing zone segment
            stagzone;    // Stagnant zone segment
     Stank  *tank = &pr->network.Tank[i];
@@ -559,8 +567,19 @@ void tankmix2(Project *pr, int i, double vin, double win, double vnet)
     if (vt > 0.0)
     {
         mixzone->v = vmz;
-        if (vnet > 0.0) stagzone->v += vt;
+        if (vnet > 0.0)
-        else            stagzone->v = MAX(0.0, ((stagzone->v) - vt));
+        {
+            stagzone->v += vt;
+            
+            // Account for mass lost in overflow from stagnant zone
+            vsz = (tank->Vmax) - vmz;
+            if (stagzone->v > vsz)
+            {
+                qual->MassBalance.outflow += ((stagzone->v) - vsz) * stagzone->c;
+                stagzone->v = vsz;
+            }
+        }
+        else stagzone->v = MAX(0.0, ((stagzone->v) - vt));
     }
     else
     {
@@ -612,10 +631,13 @@ void tankmix3(Project *pr, int i, double vin, double win, double vnet)
         else addseg(pr, k, vin, cin);
     }
 
-    // Withdraw flow from first segment
+    // Find volume leaving tank, adjusted so its volume doesn't exceed Vmax
+    vout = vin - vnet;
+    if (tank->V >= tank->Vmax && vnet > 0.0) vout = vin;
+
+    // Withdraw outflow from first segment
     vsum = 0.0;
     wsum = 0.0;
-    vout = vin - vnet;
     while (vout > 0.0)
     {
         seg = qual->FirstSeg[k];
@@ -643,6 +665,10 @@ void tankmix3(Project *pr, int i, double vin, double win, double vnet)
     if      (vsum > 0.0)                tank->C = wsum / vsum;
     else if (qual->FirstSeg[k] == NULL) tank->C = 0.0;
     else                                tank->C = qual->FirstSeg[k]->c;
+    
+    // Account for mass lost in overflow from 1st segment
+    if (tank->V >= tank->Vmax && vnet > 0.0)
+        qual->MassBalance.outflow += vnet * tank->C;
 }
 
 
@@ -669,7 +695,7 @@ void tankmix4(Project *pr, int i, double vin, double win, double vnet)
     k = net->Nlinks + i;
     if (qual->LastSeg[k] == NULL || qual->FirstSeg[k] == NULL) return;
 
-    // Find inflows & outflows
+    // Find inflow concentration
     if (vin > 0.0) cin = win / vin;
     else           cin = 0.0;
 
@@ -687,6 +713,33 @@ void tankmix4(Project *pr, int i, double vin, double win, double vnet)
 
         // Update reported tank quality
         tank->C = qual->LastSeg[k]->c;
+        
+        // If tank full then remove vnet from leading segments
+        if (tank->V >= tank->Vmax)
+        {
+            wsum = 0.0;
+            while (vnet > 0.0)
+            {
+                seg = qual->FirstSeg[k];
+                if (seg == NULL)  break;
+                vseg = seg->v;               // Flow volume from leading seg
+                vseg = MIN(vseg, vnet);
+                if (seg == qual->LastSeg[k]) vseg = vnet;
+                wsum += (seg->c) * vseg;
+                vnet -= vseg;               // Remaining flow volume
+                if (vnet >= 0.0 && vseg >= seg->v)  // Seg used up
+                {
+                    if (seg->prev)
+                    {
+                        qual->FirstSeg[k] = seg->prev;
+                        seg->prev = qual->FreeSeg;
+                        qual->FreeSeg = seg;
+                    }
+                }
+                else seg->v -= vseg;   // Remaining volume in segment
+            }
+            qual->MassBalance.outflow += wsum;
+        }
     }
 
     // If tank emptying then remove last segments until vnet consumed