VSP efficiency + retrieving efficiency directly (#81)

* VSP efficiency + retrieving efficiency directly

Changes to the getenergy function (in hydraulic.c) to compute the
correct efficiency of variable speed pumps according to the affinity
laws.
Changes to epanet2.h and epanet.c are for retrieving the efficiency of
pumps throught the ENgetlinkvalue function (code 16 for efficiency)

* Update epanet.c

* VSP efficiency (incl. bas and vb file)

- bas and vb file have been updated with code 16 for efficiency.
- Retrieving efficiency case has been improved.

src/epanet.c

@@ -1458,7 +1458,11 @@ int DLLEXPORT ENgetlinkvalue(int index, int code, EN_API_FLOAT_TYPE *value)
          if (Link[index].Type == PUMP)
             v = (double)Pump[PUMPINDEX(index)].Upat;
          break;
-         
+
+      case EN_EFFICIENCY: 
+         getenergy(index, &a, &v);  
+         break; 
+
       default: return(251);
    }
    *value = (EN_API_FLOAT_TYPE)v;

src/hydraul.c

@@ -998,6 +998,7 @@ void  getenergy(int k, double *kw, double *eff)
 {
    int   i,j;
    double dh, q, e;
+   double q4eff; //q4eff=flow at nominal speed to compute efficiency
 
 /*** Updated 6/24/02 ***/
    /* No energy if link is closed */
@@ -1019,7 +1020,11 @@ void  getenergy(int k, double *kw, double *eff)
       j = PUMPINDEX(k);
       e = Epump;
       if ( (i = Pump[j].Ecurve) > 0)
-         e = interp(Curve[i].Npts,Curve[i].X,Curve[i].Y,q*Ucf[FLOW]);
+      { 
+         q4eff = q/LinkSetting[k]; 
+         e = interp(Curve[i].Npts,Curve[i].X, Curve[i].Y, q4eff*Ucf[FLOW]); 
+      } 
+      //   e = interp(Curve[i].Npts,Curve[i].X,Curve[i].Y,q*Ucf[FLOW]); //old line of code
       e = MIN(e, 100.0);
       e = MAX(e, 1.0);
       e /= 100.0;