Convergence issues in the EPANET solver

EPANET assumes that the nodal outflows are constant regardless of the network pressures - known as the Demand-Driven Approach (DDA). This approach is quite accurate when the system operates under adequate positive pressures, but not when pressures are not sufficient enough. In scenarios of insufficient pressure is required an alternative approach to the DDA in order to compute the available demand as a function of nodal pressure, known as the Pressure-Driven Approach (PDA); for example, through the use of a pressure-demand relationship. However, the embedding of the pressure-demand relationship into the hydraulic solver can lead to convergence problems.This paper details the measures taken in WaterNetGen to avoid the convergence issues, namely the use of relaxation coefficients and the use of a more stable linear system solver. The paper also analyses the DDA and the PDA performances and draws relevant conclusions.