scholarly journals Generalizing WDN simulation models to variable tank levels

2011 ◽  
Vol 14 (3) ◽  
pp. 562-573 ◽  
Author(s):  
Orazio Giustolisi ◽  
Luigi Berardi ◽  
Daniele Laucelli
Keyword(s):  
Steady State ◽  
Mass Balance ◽  
Water Distribution ◽  
Extended Period ◽  
Water Distribution Network ◽  
Simulation Models ◽  
Gradient Algorithm ◽  
Initial State ◽  
Cross Sectional ◽  
Steady State Simulation

In water distribution network (WDN) steady-state modelling, tanks and reservoirs are modelled as nodes with known heads. As a result, the tank levels are upgraded after every steady-state simulation (snapshot) using external mass balance equations in extended period simulation (EPS). This approach can give rise to numerical instabilities, especially when tanks are in close proximity. In order to obtain a stable EPS model, an unsteady formulation of the WDN model has recently introduced. This work presents an extension of the steady-state WDN model, both for demand-driven and pressure-driven analyses, allowing the direct prediction of head variation of tank nodes with respect to an initial state. Head variations at those nodes are introduced as internal unknowns in the model, the variation of tank levels can be analyzed in the single steady-state simulation and EPS can be performed as a sequence of simulations without the need for external mass balances. The extension of mass balance at tank nodes allows the analysis of some technically relevant demand components. Furthermore, inlet and outlet head losses at tank nodes are introduced and large cross-sectional tank areas are allowed by the model and reservoirs become a special case of tanks. The solution algorithm is the generalized-global gradient algorithm (G-GGA), although the proposed WDN model generalization is universal.

scholarly journals Equivalent hydraulic resistance to simulate pipes subject to diffuse outflows

2011 ◽  
Vol 14 (1) ◽  
pp. 65-74 ◽  
Author(s):  
M. Ferrante ◽  
E. Todini ◽  
C. Massari ◽  
B. Brunone ◽  
S. Meniconi
Keyword(s):  
Hydraulic Resistance ◽  
Distribution System ◽  
Water Distribution ◽  
Water Distribution System ◽  
Distribution Network ◽  
Network Models ◽  
Water Distribution Network ◽  
Simulation Models ◽  
Gradient Algorithm ◽  
Present Generation

In water distribution network simulation models, pipes subject to diffuse outflow, either due to connections or to distributed demand or to leaks along their length, are generally converted into pipe elements only subject to lumped demand at their ending nodes. This approximation, which disregards the flow variation along the pipes, generates a loss of axial momentum, which is not correctly taken into account in the present generation of water distribution network models. In this paper a correction to the lumped demand approximation is provided and this equivalence is analyzed within the framework of the Global Gradient Algorithm. This is obtained through a correction of the pipe hydraulic resistance; this approach has proven to be more effective than the use of an asymmetrical lumped demand of the total distributed outflow at the pipe ending nodes. In order to assess the effect of the introduced correction, an application to a simple water distribution system is finally provided.

scholarly journals Simulation of Pressure Head and Chlorine Decay in a Water Distribution Network: A Case Study

2019 ◽  
Vol 13 (1) ◽  
pp. 58-68
Author(s):  
M. O. A. Alsaydalani
Keyword(s):  
Distribution Systems ◽  
Water Distribution ◽  
Distribution Network ◽  
Extended Period ◽  
Water Distribution Network ◽  
Simulation Models ◽  
Pressure Head ◽  
Minimum Requirement ◽  
Quality Of Water ◽  
Chlorine Decay

Background: The main issue in the operation of water distribution systems arises from the pressure deficiency resulting from events such as loss from leaks and bursts and loss of hydraulic capacity due to deterioration of aging water pipes. Such conditions affect the hydraulic performance of the system and the quality of water. Objective This paper investigates the hydraulic and water quality behavior of a selected water distribution network in Makkah city using the EPANET software. Methodology: The system was simulated under different hydraulic conditions including a loss of hydraulic capacity with pipe age and the presence of 30% leakage in the network over varying time conditions by employing extended period simulation models. Results and Conclusion: The results show that increasing pipe roughness with pipe age resulted in significantly low-pressure heads at the end of the network-particularly during peak demand hours. It also resulted in an increase in the rate of chlorine decay. Leakage in the network significantly affects the pressure head, resulting in pressure deficiency at some points in the network to below the minimum requirement during regular operation. The highest leakage rate occurs at periods of low demand where the pressure head in the network is high.

scholarly journals A Study on the Effects of Model Structure and Demand Allocation on Water Network Modeling

2020 ◽  
Vol 42 (3) ◽  
pp. 110-120
Author(s):  
Seonghan Kim ◽  
Kwansue Jung ◽  
Sukmin Yoon ◽  
No-Suk Park
Keyword(s):  
Steady State ◽  
Network Modeling ◽  
Extended Period ◽  
Model Structure ◽  
Water Network ◽  
Detailed Model ◽  
Water Head ◽  
Models Comparison ◽  
The Difference ◽  
Steady State Simulation

Objectives:In order to reduce the uncertainty of the pipe network modeling, the model structure was basically included all distribution pipes and several models were proposed according to the location of the water meters.Methods:For models verification, first, a steady state simulation of each model was made by constructing a model including all water supply pipes (All-meters Model), which are the bases of 3 simplified models, and considering the location of all water meters. The network analysis was performed by dividing into the steady state and the extended period simulation.Results and Discussion:From the results of models comparison, ‘All-meters Model’ and ‘All-connections Model’ were found to obtain more accurate results for constructing a water network model for simulation of water quality events in distribution network. When constructing an ‘All-meters Model’ in all networks, the model becomes complicated and data management does difficult. Therefore this study suggests a hybrid model construction.Conclusions:It would be reasonable to construct a detailed model (All-meters or All-connections Model) in looped network in which the water flow path can be changed according to the difference of water head, and a skeletonized model (Street-meters aggregation or Reduced-meters Model) for a branch network that does not have a significant impact on demand allocations.

scholarly journals Testing linear solvers for global gradient algorithm

2014 ◽  
Vol 16 (5) ◽  
pp. 1178-1193 ◽  
Author(s):  
Orazio Giustolisi ◽  
Naser Moosavian
Keyword(s):  
Linear System ◽  
Water Distribution ◽  
Direct Method ◽  
Mathematical Problem ◽  
Network Models ◽  
Water Distribution Network ◽  
Mass Conservation ◽  
Gradient Algorithm ◽  
Global Gradient Algorithm ◽  
Pressure Driven

Steady-state Water Distribution Network models compute pipe flows and nodal heads for assumed nodal demands, pipe hydraulic resistances, etc. The nonlinear mathematical problem is based on energy and mass conservation laws which is solved by using global linearization techniques, such as global gradient algorithm (GGA). The matrix of coefficients of the linear system inside GGA belongs to the class of sparse, symmetric and positive definite. Therefore a fast solver for the linear system is important in order to achieve the computational efficiency, especially when multiple runs are required. This work aims at testing three main strategies for the solution of linear systems inside GGA. The tests are performed on eight real networks by sampling nodal demands, considering the pressure-driven and demand-driven modelling to evaluate the robustness of solvers. The results show that there exists a robust specialized direct method which is superior to all the other alternatives. Furthermore, it is found that the number of times the linear system is solved inside the GGA does not depend on the specific solver, if a small regularization to the linear problem is applied, and that pressure-driven modelling requires a greater number which depends on the size and topology of the network and not only on the level of pressure deficiency.

Sizing Wet-Gas Pipelines and Slug Catchers With Steady-State Multiphase Flow Simulations

1998 ◽  
Vol 120 (2) ◽  
pp. 106-110 ◽  
Author(s):  
J. J. Xiao ◽  
G. Shoup
Keyword(s):  
Steady State ◽  
Multiphase Flow ◽  
Simulation Models ◽  
Gas Pipelines ◽  
Flow Simulations ◽  
Wet Gas ◽  
Starting Point ◽  
Operational Information ◽  
Exit Speed ◽  
Steady State Simulation

The design of wet-gas pipelines and slug catchers requires multiphase flow simulations, both steady-state and transient. However, steady-state simulation is often inadequately conducted and its potential not fully utilized. This paper shows how mechanistic steady-state simulation models can be used to obtain not only pressure drop, liquid holdup and flow regime, but also to extract important operational information such as pig transit time, pig exit speed, liquid buildup rate behind the pig, and the time for the pipeline to return to a steady-state after pigging. A well-designed set of steady-state simulations helps to determine pipeline size, slug catcher size, and pigging frequency. It also serves as a starting point for subsequent transient multiphase flow simulations.

scholarly journals Abnormal quality detection and isolation in water distribution networks using simulation models

2012 ◽  
Vol 5 (1) ◽  
pp. 435-453
Author(s):  
F. Nejjari ◽  
R. Pérez ◽  
V. Puig ◽  
J. Quevedo ◽  
R. Sarrate ◽  
...  
Keyword(s):  
Water Distribution ◽  
Water Distribution Network ◽  
Simulation Models ◽  
Distribution Networks ◽  
Fault Isolation ◽  
Sensitivity Matrix ◽  
Quality Detection ◽  
Fault Sensitivity ◽  
On Line ◽  
District Metered Area

Abstract. This paper proposes a model based detection and localisation method to deal with abnormal quality levels based on the chlorine measurements and chlorine sensitivity analysis in a water distribution network. A fault isolation algorithm which correlates on line the residuals (generated by comparing the available chlorine measurements with their estimations using a model) with the fault sensitivity matrix is used. The proposed methodology has been applied to a District Metered Area (DMA) in the Barcelona network.

scholarly journals Feasibility of Mass Balance Approach to Water Distribution Network Model Calibration

2017 ◽  
Vol 186 ◽  
pp. 551-558 ◽  
Author(s):  
Luigi Berardi ◽  
Antonietta Simone ◽  
Daniele Laucelli ◽  
Orazio Giustolisi
Keyword(s):  
Mass Balance ◽  
Network Model ◽  
Model Calibration ◽  
Water Distribution ◽  
Distribution Network ◽  
Water Distribution Network ◽  
Balance Approach ◽  
Mass Balance Approach

Change in Distillation Column Control Philosophy Using Dynamic Simulation

2019 ◽  
Vol 15 (3) ◽  
Author(s):  
Kanubhai Parmar ◽  
Sukanta Dash ◽  
Sunil Patil ◽  
Garimella Padmavathi
Keyword(s):  
Steady State ◽  
Dynamic Simulation ◽  
Operating Parameter ◽  
Simulation Models ◽  
Composition Control ◽  
Aspen Hysys ◽  
Steady State Model ◽  
Process Behavior ◽  
Steady State Simulation ◽  
Bottom Product

AbstractAt condensate stripper of a cracker plant with design control philosophy for composition control pant was facing operational difficulty. Due to disturbance in operating parameter column was becoming unstable and product was getting offspec w.r.t. desired purity. One of the applications of dynamic simulation is to troubleshoot the challenges related to control philosophy in practical application. Since steady-state simulation models cannot predict behavior with respect to time, initially steady state model and finally a dynamic model was developed in Aspen HYSYS. The model is used to study the process behavior for existing control philosophy and proposed philosophy. To avoid column puncture and without waiting for plant shut down the existing Temperature Indicator (TI) considered as Temperature Indicator Controller (TIC) for the study. A new control philosophy was developed based on the response of variables after disturbances in feed rate and composition. The revised control philosophy has been implemented and is now working satisfactorily, providing stabilized operation of the column with consistent bottom product quality. This has helped to reduce the loss of C2s in the bottom stream by about 700 ppm, for savings of about $100,000 USD per year.

scholarly journals Pumps as turbines (PATs) in water distribution networks affected by intermittent service

2013 ◽  
Vol 16 (2) ◽  
pp. 259-271 ◽  
Author(s):  
Valeria Puleo ◽  
Chiara Maria Fontanazza ◽  
Vincenza Notaro ◽  
Mauro De Marchis ◽  
Gabriele Freni ◽  
...  
Keyword(s):  
Energy Recovery ◽  
Water Distribution ◽  
Network Performance ◽  
Water Distribution Network ◽  
Distribution Networks ◽  
Monte Carlo Analysis ◽  
Gradient Algorithm ◽  
Baseline Scenario ◽  
Centrifugal Pumps ◽  
Operational Parameters

A hydraulic model was developed in order to evaluate the potential energy recovery from the use of centrifugal pumps as turbines (PATs) in a water distribution network characterized by the presence of private tanks. The model integrates the Global Gradient Algorithm (GGA), with a pressure-driven model that permits a more realistic representation of the influence on the network behaviour of the private tanks filling and emptying. The model was applied to a real case study: a District Metered Area in Palermo (Italy). Three different scenarios were analysed and compared with a baseline scenario (Scenario 0 – no PAT installed) to identify the system configuration with added PATs that permits the maximal energy recovery without penalizing the hydraulic network performance. In scenarios involving PAT on service connections, the specification of PAT operational parameters was also evaluated by means of Monte Carlo Analysis. The centralized solution with a PAT installed downstream of the inlet node of the analysed district, combined with local PATs on the larger service connections, proves to be the most energy-efficient scenario.

scholarly journals Extending the global gradient algorithm to unsteady flow extended period simulations of water distribution systems

2010 ◽  
Vol 13 (2) ◽  
pp. 167-180 ◽  
Author(s):  
Ezio Todini
Keyword(s):  
Unsteady Flow ◽  
Distribution System ◽  
Distribution Systems ◽  
Water Distribution ◽  
Extended Period ◽  
Distribution Networks ◽  
Gradient Algorithm ◽  
Integration Time ◽  
Original Algorithm ◽  
Global Gradient Algorithm

This paper introduces an extension of the Global Gradient Algorithm (GGA) to directly solve unsteady flow problems arising from the presence of variable head water storage devices, such as tanks, in Extended Period Simulations (EPS) of looped water distribution networks (WDN). Such a modification of the original algorithm was motivated by the need to overcome oscillations and instabilities reported by several users of EPANET, a worldwide available package, which uses the GGA to solve the looped WDN equations. The set of partial differential equations describing the time and space behaviour of a water distribution system is here presented. It is shown how an unsteady flow GGA can be derived by simple modifications of the original steady-state GGA. The performances of the new algorithm, referred to as EPS-GGA, are compared with the results provided by EPANET on an extremely simplified example, the solution of which is qualitatively known. As opposed to EPANET which shows significant instabilities, the EPS-GGA is stable under a wide variety of increasing integration time intervals.

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