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Sizing a water distribution network using genetic algorithms with Urbano Hydra and EPANET

18.03.2021.

Urbano Hydra connects AutoCAD drawing (detailed water distribution network (WDN) design) with EPANET hydraulic calculation. EPANET calculation engine is built inside of Urbano Hydra which allows you to draw the network inside of AutoCAD, input all the EPANET parameters (such as water demands, pipe roughness, equipment parameters, etc.) and perform EPANET single period (snapshot) hydraulic calculation without even having EPANET installed on your computer. All the results are immediately available in your familiar AutoCAD user interface. In Urbano Hydra you can review all the calculated values using Urbano data tables, you can show all the values in profiles and label all the elements in plan, you can draw piezometric lines, do thematic mappings, create various reports, etc.

In EPANET, it is not possible to size a WDN. You first have to input pipe diameters and then EPANET can calculate hydraulic values according to those pipe diameters, selected headloss equation and other input parameters. In small, dead-end (tree) networks this is not a big problem, but in large networks, especially circular (ring) networks, this can be very time consuming and can represent quite a problem for WDN designers. Urbano Hydra can size a new WDN (or optimize an existing one) using EPANET engine and genetic algorithm method. The purpose of the algorithm is to determine optimal pipe diameters based on target flow velocity in WDN. Genetic algorithms significantly accelerate and facilitate the achievement of the optimal solution, since with the brute-force method (all possible variations) this would last for days.

Genetic algorithm is a method of solving complex problems based on natural selection process similar to biological evolution. The algorithm repeatedly modifies a population of individual WDN solutions. At each step, algorithm selects individual WDN solutions from previous generation and uses them as “parents” to produce the “children” solutions for the next generation. Each generation contains certain number of WDN solutions. New generation population is produced using WDN solutions from previous generation with methods that mimic mutation, biological crossover and selection. The population “evolves” towards an optimal solution due to successive generations.

For the algorithm to be able to recognize better solutions, the program calculates “fitness factor” for each WDN solution. Fitness factor represents deviation from target flow velocity. Lower fitness factor means that the flow velocity is closer to target value. You can set the program to discard solutions where the flow velocity deviates from the target velocity more than limited value. In the first step, the program generates solutions in a way to assign pipe diameters randomly. In later steps, the program chooses solutions with better fitness factor. The generational process is repeated until the termination condition has been reached.

Just like in EPANET, it is possible to choose between three headloss equations: Hazen-Williams, Darcy-Weisbach and Chezy-Manning, but it is also possible to choose which water demand scenario will be relevant for the calculation (in Urbano Hydra you can have various parallel water demand scenarios (alternatives) and those scenarios can be simultaneously previewed and compared – e.g. winter and summer period scenario or scenario with and without firefighting demand, etc.). This will be a topic of another article.

You can define different parts of the network with different values of target flow velocity and different set of pipe diameters. Since the whole process is iterative, graphical representation shows you the calculation progress and the occurrence of convergence. Simultaneously, you can preview all the values (pipe diameters and resulting flow velocities, headlosses, etc.) in editable Urbano data tables for the entire network or just for the selected parts. After the calculation is completed, you can review all the assigned pipe diameters and results of the hydraulic calculation. When you save the results, program automatically writes all the values in the drawing, draws piezometric lines in profiles and updates labels in plan. See more in the video below:

Urbano Hydra works on Autodesk AutoCAD, Map3D and Civil3D 2013-2018.

To watch more videos about Urbano Hydra please go to our official YouTube channel.