163 lines
7.1 KiB
ReStructuredText
163 lines
7.1 KiB
ReStructuredText
======================
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Comparison with Hammer
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======================
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During the development process, we have consistently compared TSNet results with
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Bentley Hammer [HAMMER]_ using different networks and many different transient events.
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In this section, we present the comparison between TSNet and Hammer results.
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The Hammer models used to generate the events is also included
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in the GitHub example directory (https://github.com/glorialulu/TSNet/tree/master/examples/networks)
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for the user's reference.
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Tnet 0
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^^^^^^^^^
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We first show the comparison for a simple network,
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consisting of one reservoir, two pipes, and one valve, as illustrated in :numref:`tnet0_network`.
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The wave speed for both pipes is :math:`1200m/s`, and lengths and diameters are given in the figure.
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The transient event is generated by closing the end-valve at the beginning of the simulation
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during 2s; thus, the flow rate at the end valve decreases linearly from :math:`0.05m^3/s` at :math:`t=0s` to
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:math:`0m^3/s` at :math:`t=2s` and remains zero thereafter.
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:numref:`tnet0_hammer` (a) shows the flow rate through the valve, and
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:numref:`tnet0_hammer` (b) presents the pressure transients generated at node N-1 during 60s simulation period.
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The solid line represents TSNet results and the dashed-dotted line shows Hammer results.
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These results indicate a perfect match between TSNet and Hammer simulation results for this simple network.
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.. _tnet0_network:
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.. figure:: figures/tnet0_network.png
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:width: 500
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:alt: tnet0_network
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Topology of a simple network.
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.. _tnet0_hammer:
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.. figure:: figures/tnet0_calibration.png
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:width: 500
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:alt: tnet0_hammer
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Comparison of TSNet and Hammer results: (a) flow at the valve; (b) pressure head at N-1.
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Tnet 3
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^^^^^^^
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We then show the comparison between TSNet and Hammer results for
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a more complicated network, Tnet3,
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for three different transient events:
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1. Shut down of PUMP-1,
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2. Burst at JUNCTION-73, and
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3. Closure of VALVE-1.
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The results for the three transient-generating events are shown in
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:numref:`pump_hammer`, :numref:`burst_hammer`, and :numref:`valve_hammer`, respectively.
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.. The Hammer model that was used to generate the events is also included
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in the GitHub example directory for the user's reference.
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* We would like to note beforehand that we do not expect to
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obtain the exact same results from TSNet
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as Hammer since different numerical schemes were implemented,
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such as wave speed adjustment, pressure dependent demand, and boundary conditions.
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.. In fact, due to the fact that Hammer is a closed-source software,
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we do not know precisely what numerical schemes are implemented in Hammer,
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which directly motivated us to develop TSNet in the first place.
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Pump shut-down
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~~~~~~~~~~~~~~~~~
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Both TSNet and Hammer are utilized to simulate
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the shut down of PUMP-1.
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The time step is specified as 0.002s in both software.
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:numref:`pump_hammer` reports the pressure change with respect to the nominal pressure
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at multiple junctions, where the solid lines represent TSNet results
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and the dashed lines show Hammer results.
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TSNet and Hammer results are very similar to each other
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in terms of attenuation and phase shift throughout the 20s simulation period,
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despite slight discrepancies, which can be explained by
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the different wave speed adjustment schemes and boundary condition configurations adopted
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by the two software.
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.. _pump_hammer:
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.. figure:: figures/tnet3_pump_hammer_002.png
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:width: 500
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:alt: pump_hammer
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Comparison of pressure transients at multiple junctions generated by shutting down PUMP-1 in TNet3:
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TSNet (solid lines) Hammer (dashed lines) results.
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.. Moreover, we tested the consistency of the solution when altering
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the time step of the simulation in TSNet and Hammer.
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We simulated the pump shut-down event with different time steps, i.e., :math:`dt = \{0.002s, 0.0055, 0.0115s\}`
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and plot the results in :numref:`convergence`.
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The green and purple lines represent the pressure at JUNCTION-30, and JUNCTION-90, respectively,
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and the different line types (solid, dashed, dotted) represent different time steps (see legend).
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:numref:`convergence` (a) represents the results from TSNet, and
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:numref:`convergence` (b) shows the results from Hammer.
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We observe that the pressure transients simulated by TSNet with different time steps, resemble closely
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with each other, and all of pressure traces disclose anticipated level of details about the reflection,
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transmission, propagation, and attenuation of the pressure waves.
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However, the Hammer predicts significantly different and uncharacteristic results with time steps larger than
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0.002s (i.e., :math:`dt =\{0.0055s, 0.0115s\}`), with small transient amplitude, delayed pressure peaks,
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and high attenuation.
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The pressure transients exhibit consistency only when the time step is smaller than 0.002s,
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which is the reason why we chose time step as 0.002s to compare the results from Hammer and TSNet.
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Burst event
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~~~~~~~~~~~
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Aburst event was simulated at Junction-73 using both TSNet and Hammer.
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:numref:`burst_hammer` reports the pressure change with respect to the nominal pressure
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at multiple junctions, where the solid lines represent TSNet results,
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and the dashed lines show Hammer results.
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It can be observed that during the first transient cycle, i.e., around 0-8s,
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TSNet and Hammer results exhibit very good agreement with each other.
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Although the discrepancies increase a bit in terms of attenuation and phase shift during the latter period,
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the overall match is satisfactory considering that different time step and wave speed adjustment schemes
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are adopted in the two software.
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.. _burst_hammer:
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.. figure:: figures/tnet3_burst_hammer.png
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:width: 500
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:alt: burst_hammer
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Comparison of pressure transients at multiple junctions generated by the burst at JUNCTION-73 in Tnet3:
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TSNet (solid lines) Hammer (dashed lines) results.
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Valve closure
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~~~~~~~~~~~~~
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Both TSNet and Hammer are utilized to simulate
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the closure of VALVE-1.
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The comparison of the results is presented in :numref:`valve_hammer`.
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Again, adequate resemblance can be observed between the TSNet (a) and
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Hammer results (b). Considering that pressure transients are of smaller amplitude and
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more chaotic, the results are presented in two separate plots with same scale for clarity.
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.. _valve_hammer:
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.. figure:: figures/tnet3_valve_hammer.png
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:width: 500
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:alt: valve_hammer
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Comparison of pressure transients at multiple junctions generated by closing VALVE-1 in Tnet3:
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(a): TSNet results, (b): Hammer results.
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.. In summary, we are able to show adequate consistency between TSNet and Hammer
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results in two networks undergoing different transient events.
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In the Reservoir-Pipe-Valve network, shown in :numref:`tnet0_network`, TSNet and Hammer predict exact same
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pressure and flow results when a transient event is generated by gradually closing the end-valve.
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In the larger network, TSNet and Hammer results are remarkably similar with each other despite minor discrepancies
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due to the differences in modeling and numerical schemes.
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Moreover, as presented in :numref:`convergence`,
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TSNet performs better with relatively large time step than Hammer. |