From fdca2bef42ab641a54663de03d55dca3ebad78f1 Mon Sep 17 00:00:00 2001 From: Lew Rossman Date: Mon, 3 Sep 2018 10:34:03 -0400 Subject: [PATCH] Edits made to 2.2 Release Notes --- ReleaseNotes2_2.md | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/ReleaseNotes2_2.md b/ReleaseNotes2_2.md index d09fbf8..65f1574 100644 --- a/ReleaseNotes2_2.md +++ b/ReleaseNotes2_2.md @@ -1,6 +1,4 @@  - - Release Notes for EPANET 2.2 (Draft) ============================ @@ -49,15 +47,18 @@ These new parameters augment the current `EN_ACCURACY` option which always remai ## Improved Linear Solver Routine EPANET's hydraulic solver requires solving a system of linear equations over a series of iterations until a set of convergence criteria are met. The coefficient matrix of this linear system is square and symmetric. It has a row for each network node and a non-zero off-diagonal coefficient for each link. The numerical effort needed to solve the linear system can be reduced if the nodes are re-ordered so that the non-zero coefficients cluster more tightly around the diagonal. -EPANET's original node re-ordering scheme has been replaced by the more powerful **Multiple Minimum Degree (MMD)** algorithm. On a series of eight networks ranging in size from 7,700 to 100,000 nodes **MMD** reduced the solution time for a single period (steady state) hydraulic analysis by an average of more than 50%. +EPANET's original node re-ordering scheme has been replaced by the more powerful **Multiple Minimum Degree (MMD)** algorithm. On a series of eight networks ranging in size from 7,700 to 100,000 nodes **MMD** reduced the solution time for a single period (steady state) hydraulic analysis by an average of 58%. ## Pressure Dependent Demands EPANET has always employed a Demand Driven Analysis (**DDA**) when modeling network hydraulics. Under this approach nodal demands at a given point in time are fixed values that must be delivered no matter what nodal heads and link flows are produced by a hydraulic solution. This can result in situations where required demands are satisfied at nodes that have negative pressures - a physical impossibility. To address this issue EPANET has been extended to use a Pressure Driven Analysis (**PDA**) if so desired. Under **PDA**, the demand *D* delivered at a node depends on the node's available pressure *P* according to: -$$D =D_f\left(\frac{P-P_{min}}{P_{req}-P_{min}}\right)^{P_{exp}} for P_{0}<=P<=P_{req}$$where *Df* is the full demand required, *Pmin* is the pressure below which demand is zero, *Preq* is the pressure required to deliver the full required demand and *Pexp* is an exponent. When *P < Pmin* demand is 0 and when *P > Preq* demand equals *Df*. -To implement pressure dependent analysis four new parameters have been added to the [OPTIONS] section of the EPANET input file: +*D = Df [ (P - Pmin) / (Preq - Pmin) ]Pexp* + +where *Df* is the full demand required, *Pmin* is the pressure below which demand is zero, *Preq* is the pressure required to deliver the full required demand and *Pexp* is an exponent. When *P < Pmin* demand is 0 and when *P > Preq* demand equals *Df*. + +To implement pressure driven analysis four new parameters have been added to the [OPTIONS] section of the EPANET input file: | Parameter | Description | Default | @@ -81,7 +82,8 @@ for the thread-safe API. Some additional points regarding the new **PDA** option - If no DEMAND MODEL and its parameters are specified then the analysis defaults to being demand driven (**DDA**). - This implementation of **PDA** assumes that the same parameters apply to all nodes in the network. Extending the framework to allow different parameters for specific nodes is straightforward to do but is left as a future feature to implement. - - *P0* is allowed to equal to *Preq*. This condition can be used to find a solution that results in the smallest amount of demand reductions needed to insure that no node delivers positive demand at a pressure below *Pmin*. + - *Pmin* is allowed to equal to *Preq*. This condition can be used to find a solution that results in the smallest amount of demand reductions needed to insure that no node delivers positive demand at a pressure below *Pmin*. + ## Code Changes