Nonsmooth Hydraulics, Smooth Control: System Theory Framework for Analyzing Water Networks
Pith reviewed 2026-05-09 17:12 UTC · model grok-4.3
The pith
Regularized DAE models of water networks yield error bounds on stability and controllability while matching EPANET trajectories.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Regularization methods smooth flow and pressure trajectories under changing controls in a general nonlinear DAE model of water distribution networks, yielding explicit error bounds for linearization, local stability, and finite-horizon controllability that remain valid under network-induced parametric uncertainty; the resulting trajectories closely match those produced by EPANET on benchmark networks, and demand variation alters stability margins without removing local stability or pump authority.
What carries the argument
Regularization methods applied to the nonsmooth DAE model of WDN hydraulics that produce differentiable trajectories while preserving controllability and stability properties for error-bound analysis.
Load-bearing premise
The chosen regularization methods preserve the essential controllability and stability properties of the original nonsmooth DAE without introducing artifacts that invalidate the derived error bounds or local well-posedness results.
What would settle it
A side-by-side run of the smoothed DAE against EPANET on a benchmark network that produces trajectory deviations larger than the stated error bounds, or a specific demand-variation scenario in which the claimed local stability or pump authority is lost.
Figures
read the original abstract
This paper presents a comprehensive control-theoretic analysis of water distribution network (WDN) hydraulics. Starting from a general nonlinear differential algebraic equation (DAE) model of WDNs with arbitrary topology and network components (valves and pumps), we investigate three main questions. First, we study local well-posedness of the network dynamics and characterize the loss of differentiability introduced by pump and valve switching. Second, we introduce regularization methods that smooth flow and pressure trajectories under changing controls. Third, we establish error bounds for DAE linearization, local stability, and finite-horizon controllability, and quantify how network-induced parametric uncertainty impacts these properties. We demonstrate that the developed smoothed DAE models produce trajectories closely matching EPANET, a widely used WDN simulator, for various benchmark networks. The case studies also show that the WDN DAE exposes energy dissipation through a weighted Laplacian, ranks pipes by operating point sensitivity, and reveals that aggressive demand variation changes stability and controllability margins without eliminating local stability or pump authority. The developed theoretical foundations enable network analysis, mitigation strategies, and system design.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper develops a system-theoretic framework for water distribution networks modeled as nonsmooth DAEs with arbitrary topology and components. It analyzes local well-posedness and loss of differentiability at pump/valve switches, introduces smoothing regularization to restore differentiability, derives error bounds for DAE linearization, local stability, and finite-horizon controllability, quantifies the effect of network-induced parametric uncertainty on these properties, and validates that the smoothed models produce trajectories closely matching EPANET on benchmark networks. Additional insights include energy dissipation via a weighted Laplacian, pipe sensitivity ranking, and the impact of aggressive demand variation on stability/controllability margins.
Significance. If the error bounds and stability/controllability results transfer from the smoothed DAE to the original nonsmooth system, the work supplies a rigorous foundation for stability analysis and control design in WDNs under uncertainty and demand fluctuations. The pairing of theoretical derivations with external EPANET comparisons and the absence of free parameters in the core bounds are strengths that enhance applicability to infrastructure systems.
major comments (2)
- [error bounds and regularization sections] In the sections deriving error bounds for linearization, stability, and controllability (following the regularization): the bounds are established for the smoothed DAE, yet no explicit uniform estimate (in appropriate norms) is given for the trajectory or Jacobian distance between the smoothed and original nonsmooth DAE near switching surfaces. Without this, it is unclear whether the regularization perturbation dominates the linearization error term when assessing controllability Gramian or stability margins, undermining transfer of the quantitative claims to the physical network.
- [case studies and validation] Validation against EPANET: the claim of 'closely matching' trajectories for various benchmark networks is stated without reported quantitative error metrics (e.g., maximum deviation, L2 norms over time, or protocol details such as time-step alignment and switching event handling). This weakens support for the assertion that the smoothed models preserve essential properties of the original system.
minor comments (2)
- [analysis of energy dissipation] The definition and properties of the weighted Laplacian used to expose energy dissipation should be stated explicitly with an equation reference rather than assumed from context.
- [regularization methods] Notation for the smoothing parameter and its relation to switching thresholds could be made more uniform across the well-posedness and error-bound derivations to improve readability.
Simulated Author's Rebuttal
We thank the referee for the constructive and positive review, which highlights both the strengths and areas for improvement in our manuscript. We address each major comment below and will make revisions to strengthen the transfer of theoretical results and the validation evidence.
read point-by-point responses
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Referee: [error bounds and regularization sections] In the sections deriving error bounds for linearization, stability, and controllability (following the regularization): the bounds are established for the smoothed DAE, yet no explicit uniform estimate (in appropriate norms) is given for the trajectory or Jacobian distance between the smoothed and original nonsmooth DAE near switching surfaces. Without this, it is unclear whether the regularization perturbation dominates the linearization error term when assessing controllability Gramian or stability margins, undermining transfer of the quantitative claims to the physical network.
Authors: We agree that an explicit uniform estimate (in suitable norms) for the trajectory and Jacobian distance between the smoothed and original nonsmooth DAE near switching surfaces is needed to rigorously justify transferring the quantitative bounds. In the revised manuscript we will add a dedicated subsection deriving such an estimate. Under the standing local Lipschitz continuity of the DAE right-hand side away from switches and the O(ε) approximation property of the chosen regularization (with ε the smoothing parameter), we will prove that the trajectory deviation remains bounded by Cε (C independent of the linearization) in a neighborhood of any switching surface. This separates the regularization perturbation from the linearization error and allows the stability and controllability margins to be transferred to the original system for sufficiently small ε. revision: yes
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Referee: [case studies and validation] Validation against EPANET: the claim of 'closely matching' trajectories for various benchmark networks is stated without reported quantitative error metrics (e.g., maximum deviation, L2 norms over time, or protocol details such as time-step alignment and switching event handling). This weakens support for the assertion that the smoothed models preserve essential properties of the original system.
Authors: We concur that quantitative error metrics and protocol details are required to substantiate the 'closely matching' claim. In the revised manuscript we will expand the case-studies section with explicit quantitative comparisons: tables reporting maximum absolute deviations and time-integrated L2 norms for nodal pressures and pipe flows on each benchmark network; specification of the time-step sizes employed by the smoothed DAE integrator and by EPANET; description of time-grid alignment; and explicit handling of switching events (e.g., detection thresholds and interpolation). These additions will provide concrete, reproducible evidence that the smoothed models preserve the essential dynamics of the original system. revision: yes
Circularity Check
No significant circularity: derivations remain independent of inputs
full rationale
The paper begins with a general nonlinear DAE model of arbitrary WDN topology, characterizes loss of differentiability at switches, introduces regularization to obtain a smoothed DAE, derives error bounds and stability/controllability results for that smoothed system, and validates trajectories against the external EPANET simulator on benchmark networks. No quoted step reduces a claimed prediction, bound, or property to a fitted parameter or self-referential definition by construction; external simulator matching supplies independent evidence rather than internal fitting. The derivation chain is therefore self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
Reference graph
Works this paper leans on
-
[1]
U.S. Environmental Protection Agency,Drinking W ater Infrastructure Needs Survey and Assessment: Seventh Report to Congress, U.S. Environmental Protection Agency, Washington, DC, 2023, ePA 810-R-23-001
work page 2023
-
[2]
Water distribution systems analysis,
U. Shamir and C. D. D. Howard, “Water distribution systems analysis,”Journal of the Hydraulics Division, ASCE, vol. 94, no. 1, pp. 219–234, 1968
work page 1968
-
[3]
A gradient algorithm for the analysis of pipe networks,
E. Todini and S. Pilati, “A gradient algorithm for the analysis of pipe networks,” inComputer Applications in W ater Supply: V olume 1 – Systems Analysis and Simulation. London, UK: John Wiley & Sons, 1988, pp. 1–20
work page 1988
-
[4]
T. M. Walski, D. V . Chase, D. A. Savic, W. Grayman, S. Beckwith, and E. Koelle,Advanced W ater Distribution Modeling and Management. Waterbury, CT: Haestad Press, 2003
work page 2003
-
[5]
L. Rossman, H. Woo, M. Tryby, F. Shang, R. Janke, and T. Haxton,EP ANET 2.2 User Manual, U.S. Environmental Protection Agency, Washington, DC, 2020, ePA/600/R-20/133
work page 2020
-
[6]
Epyt: An EPANET-Python toolkit for smart water network simulations,
M. S. Kyriakou, M. Demetriades, S. G. Vrachimis, D. G. Eliades, and M. M. Polycarpou, “Epyt: An EPANET-Python toolkit for smart water network simulations,”Journal of Open Source Software, vol. 8, no. 92, p. 5947, 2023
work page 2023
-
[7]
K. A. Klise, M. L. Bynum, D. Moriarty, and R. Murray, “A software framework for assessing the resilience of drinking water systems to disasters with an example earthquake case study,”Environmental Modelling & Software, vol. 95, pp. 420–431, 2017
work page 2017
-
[8]
WaterModels.jl: An open source Julia/JuMP package for steady state water network optimization,
B. Tasseff, R. Bent, and C. Coffrin, “WaterModels.jl: An open source Julia/JuMP package for steady state water network optimization,” https://github.com/lanl-ansi/WaterModels.jl, 2019
work page 2019
-
[9]
S. Wang, A. F. Taha, L. Sela, M. H. Giacomoni, and N. Gatsis, “A new derivative-free linear approximation for solving the network water flow problem with convergence guarantees,”W ater Resources Research, vol. 56, no. 3, pp. no–no, 2020
work page 2020
-
[10]
M. H. Chaudhry,Applied Hydraulic Transients, 3rd ed. New Y ork, NY: Springer, 2014
work page 2014
-
[11]
E. B. Wylie, V . L. Streeter, and L. Suo,Fluid Transients in Systems. Englewood Cliffs, NJ: Prentice Hall, 1993
work page 1993
-
[12]
A review of water hammer theory and practice,
M. S. Ghidaoui, M. Zhao, D. A. McInnis, and D. H. Axworthy, “A review of water hammer theory and practice,”Applied Mechanics Reviews, vol. 58, no. 1–6, pp. 49–75, 2005
work page 2005
-
[13]
Improved rigid water column formulation for simulating slow transients and controlled operations,
J. Nault and B. Karney, “Improved rigid water column formulation for simulating slow transients and controlled operations,”Journal of Hydraulic Engineering, vol. 142, no. 4, p. 04015082, 2016
work page 2016
-
[14]
Parameterization of offline and online hydraulic simulation models,
J. Deuerlein, O. Piller, and A. Simpson, “Parameterization of offline and online hydraulic simulation models,” inProc. Procedia Engineering, vol. 119. Elsevier, 2015, pp. 559–568
work page 2015
-
[15]
A unified framework for pressure driven network analysis,
O. Piller and J. van Zyl, “A unified framework for pressure driven network analysis,” inProc. CCWI, 2007
work page 2007
-
[16]
Port hamiltonian based control of wa- ter distribution networks,
R. Perryman, C. Taylor, and A. Ramsey, “Port hamiltonian based control of wa- ter distribution networks,”Systems & Control Letters, vol. 162, p. 105197, 2022
work page 2022
-
[17]
Port hamiltonian models for flow of incompressible fluids in rigid pipelines with faults,
L. Torres and G. Besancon, “Port hamiltonian models for flow of incompressible fluids in rigid pipelines with faults,” inProc. IEEE Conf. Decision and Control (CDC). IEEE, 2019, pp. 8244–8249
work page 2019
-
[18]
Applications of graph spectral techniques to water distribution network management,
A. Di Nardo, M. Di Natale, G. Santonastaso, V . Tzatchkov, and V . Alcocer- Y amanaka, “Applications of graph spectral techniques to water distribution network management,”W ater, vol. 10, no. 1, p. 45, 2018
work page 2018
-
[19]
Complex network analysis of water distribution systems,
A. Y azdani and P . Jeffrey, “Complex network analysis of water distribution systems,”Chaos: An Interdisciplinary Journal of Nonlinear Science, vol. 21, no. 1, p. 016111, 2011, also available as arXiv:1008.1770
-
[20]
C. Ocampo-Mart´ınez, V . Puig, G. Cembrano, and J. Quevedo, “Application of predictive control strategies to the management of complex networks in the urban water cycle,”IEEE Control Systems Magazine, vol. 33, no. 1, pp. 15–41, 2013
work page 2013
-
[21]
Control of tree water networks: A geometric programming approach,
L. Sela Perelman and S. Amin, “Control of tree water networks: A geometric programming approach,”W ater Resources Research, vol. 51, no. 10, pp. 8409–8430, 2015
work page 2015
-
[22]
Receding horizon con- trol for drinking water networks: The case for geometric programming,
S. Wang, A. F. Taha, N. Gatsis, and M. H. Giacomoni, “Receding horizon con- trol for drinking water networks: The case for geometric programming,”IEEE Transactions on Control of Network Systems, vol. 7, no. 3, pp. 1151–1163, 2020
work page 2020
-
[23]
Non-linear economic model predictive control of water distribution networks,
Y . Wang, V . Puig, and G. Cembrano, “Non-linear economic model predictive control of water distribution networks,”Journal of Process Control, vol. 56, pp. 23–34, 2017
work page 2017
-
[24]
Geometric programming-based control for nonlinear, DAE-constrained water distribution networks,
S. Wang, A. F. Taha, N. Gatsis, and M. H. Giacomoni, “Geometric programming-based control for nonlinear, DAE-constrained water distribution networks,” inProceedings of the American Control Conference, Philadelphia, PA, USA, 2019, pp. 1470–1475
work page 2019
-
[25]
Optimal scheduling of water distribution systems,
M. K. Singh and V . Kekatos, “Optimal scheduling of water distribution systems,”IEEE Transactions on Control of Network Systems, vol. 7, no. 2, pp. 711–723, 2020
work page 2020
-
[26]
GPU- accelerated stochastic predictive control of drinking water networks,
A. K. Sampathirao, P . Sopasakis, A. Bemporad, and P . P . Patrinos, “GPU- accelerated stochastic predictive control of drinking water networks,”IEEE Transactions on Control Systems T echnology, vol. 26, no. 2, pp. 551–562, 2018
work page 2018
-
[27]
Optimal pump control for water distribution networks via data-based distributional robustness,
Y . Guo, S. Wang, A. F. Taha, and T. H. Summers, “Optimal pump control for water distribution networks via data-based distributional robustness,”IEEE Transactions on Control Systems T echnology, vol. 31, no. 1, pp. 114–129, 2023
work page 2023
-
[28]
G. Galuppini, E. Creaco, and L. Magni, “Real-time pressure control in water distribution networks: Stability guarantees via gain-scheduled internal model control,”IEEE Transactions on Control Systems T echnology, vol. 32, no. 3, pp. 731–743, 2024
work page 2024
-
[29]
J. J. V an Gemert, V . Breschi, D. R. Yntema, K. J. Keesman, and M. Lazar, “Exploiting structural observability and graph colorability for optimal sensor placement in water distribution networks,” in2025 European Control Conference (ECC). IEEE, 2025, pp. 546–551
work page 2025
-
[30]
O. Piller, S. Elhay, J. Deuerlein, and A. Simpson, “Local sensitivity of pressure-driven modeling and demand-driven modeling steady-state solutions to variations in parameters,”Journal of W ater Resources Planning and Management, vol. 143, no. 2, p. 04016074, 2017
work page 2017
-
[31]
P . R. Bhave and R. Gupta,Analysis of water distribution networks. Alpha Science Int’l Ltd., 2006
work page 2006
-
[32]
T. M. Walski, D. V . Chase, and D. A. Savic,W ater Distribution Modeling. Waterbury, CT: Haestad Press, 2001
work page 2001
-
[33]
Modelling techniques in dynamic control of water distribution systems,
B. Coulbeck and M. J. H. Sterling, “Modelling techniques in dynamic control of water distribution systems,”Measurement and Control, vol. 11, no. 10, pp. 385–389, 1978
work page 1978
-
[34]
Dynamic simulation of water distribution systems,
B. Coulbeck, “Dynamic simulation of water distribution systems,”Mathematics and Computers in Simulation, vol. 22, no. 3, pp. 222–230, 1980
work page 1980
-
[35]
Dynamical stability of water distribution networks,
N. Masuda and F. Meng, “Dynamical stability of water distribution networks,” Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol. 475, no. 2230, p. 20190291, 2019
work page 2019
-
[36]
P . Dai and P . Li, “Optimal localization of pressure reducing valves in water distribution systems by a reformulation approach,”W ater Resources Management, vol. 28, no. 10, pp. 3057–3074, 2014
work page 2014
-
[37]
L. Hien, B. De Schutter, and F. Logist, “A new mathematical program with com- plementarity constraints for optimal localization of pressure reducing valves in water distribution systems,”Applied W ater Science, vol. 11, no. 10, p. 166, 2021
work page 2021
-
[38]
An efficient algorithm for solving piecewise- smooth dynamical systems,
N. Guglielmi and E. Hairer, “An efficient algorithm for solving piecewise- smooth dynamical systems,”Numerical Algorithms, vol. 89, pp. 1311–1334, 2022
work page 2022
-
[39]
Extended-period analysis with a transient model,
Y . R. Filion and B. W. Karney, “Extended-period analysis with a transient model,”Journal of Hydraulic Engineering, vol. 128, no. 6, pp. 616–624, 2002
work page 2002
-
[40]
Quadratic head loss approximations for optimisation problems in water supply networks,
F. Pecci, E. Abraham, and I. Stoianov, “Quadratic head loss approximations for optimisation problems in water supply networks,”Journal of Hydroinformatics, vol. 19, no. 4, pp. 493–506, 2017
work page 2017
-
[41]
Real-time quintic hermite interpolation for robot trajectory execution,
M. Lind, “Real-time quintic hermite interpolation for robot trajectory execution,” P eerJ Computer Science, vol. 6, p. e304, 2020
work page 2020
-
[42]
EP ANET -Benchmarks: A collection of several benchmark water networks,
KIOS Research and Innovation Center of Excellence, “EP ANET -Benchmarks: A collection of several benchmark water networks,” https://github.com/ KIOS-Research/EPANET-Benchmarks, 2026, accessed April 30, 2026
work page 2026
-
[43]
The impacts of spatially variable demand patterns on water distribution system design and operation,
K. Diao, R. Sitzenfrei, and W. Rauch, “The impacts of spatially variable demand patterns on water distribution system design and operation,”W ater, vol. 11, no. 3, p. 567, 2019
work page 2019
-
[44]
Calibration of design models for leakage management of water distribution networks,
L. Berardi and O. Giustolisi, “Calibration of design models for leakage management of water distribution networks,”W ater Resources Management, vol. 35, pp. 2537–2551, 2021. 13
work page 2021
-
[45]
Teschl,Ordinary Differential Equations and Dynamical Systems, ser
G. Teschl,Ordinary Differential Equations and Dynamical Systems, ser. Graduate Studies in Mathematics. Providence, RI: American Mathematical Society, 2012, vol. 140
work page 2012
-
[46]
P . Kunkel and V . Mehrmann,Differential-Algebraic Equations: Analysis and Numerical Solution, ser. EMS Textbooks in Mathematics. Z ¨urich, Switzerland: European Mathematical Society, 2006, vol. 2
work page 2006
-
[47]
E. Hairer and G. Wanner,Solving Ordinary Differential Equations II: Stiff and Differential-Algebraic Problems, 2nd ed., ser. Springer Series in Computational Mathematics. Berlin, Germany: Springer, 1996, vol. 14
work page 1996
-
[48]
C. Godsil and G. Royle,Algebraic Graph Theory, ser. Graduate Texts in Mathematics. New Y ork: Springer, 2001, vol. 207
work page 2001
-
[49]
H. K. Khalil,Nonlinear Systems, 3rd ed. Upper Saddle River, NJ: Prentice Hall, 2002
work page 2002
-
[50]
R. A. Horn and C. R. Johnson,Matrix Analysis, 2nd ed. Cambridge, UK: Cambridge University Press, 2013. APPENDIXA NDAE MODEL FOR ASIMPLENETWORK This appendix writes the full DAE of Section III for the Threenodesbenchmark shown in Fig. 13. The goal is not to introduce a new model, but to make the general construction concrete by displaying the incidence blo...
work page 2013
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