Flow sign in the pipe component (#385)

* Replaced Q^2 by Q*abs(Q) in the pipe

Signed-off-by: Nabil YOUSSEF <nabil.youssef@metroscope.tech>

* Update the changelog

---------

Signed-off-by: Nabil YOUSSEF <nabil.youssef@metroscope.tech>

Author: nabily-met

CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Sensors now contain a flow model to ease convergence [PR#383](https://github.com/Metroscope-dev/metroscope-modeling-library/pull/383)
 
 ### Fixed
+- Pipes now can have a unique flow direction according to the pressure difference direction [PR#385](https://github.com/Metroscope-dev/metroscope-modeling-library/pull/385)
 
 ## MML-v3.4.0
 

MetroscopeModelingLibrary/Partial/Pipes/Pipe.mo

@@ -21,8 +21,8 @@ equation
     fouling = 0;
   end if;
 
-  DP_f = - (1+ fouling/100)  * Kfr * Q^2 / rho;
-  DP_z = -rho *Constants.g  * delta_z;
+  DP_f = - (1+ fouling/100)*Kfr*Q*abs(Q)/rho;
+  DP_z = - rho*Constants.g*delta_z;
 
   DP = DP_f + DP_z;
   annotation (