TUFLOW 1D Channels and Hydraulic Structures: Difference between revisions
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=Introduction=
The objective of the following pages is to supplement the <u>[https://docs.tuflow.com/classic-hpc/manual/latest/ TUFLOW
=1D Channel Types=
1d_nwk channels represent open channels, hydraulic structures, operational structures and other flow controls. A channel is either digitised as a line or point with the relevant hydraulic properties entered into the appropriate GIS attributes, details for this can be found within the links below or the <u>[https://docs.tuflow.com/classic-hpc/manual/latest/ TUFLOW
==Open Channels==
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Occasionally there are situations where non-standard entrance and exit loss values are needed. A good example is if the approach or departure flow is skewed to the culvert direction. In these situations there may also be a significant bend (energy) loss occurring as the water changes direction entering or leaving the structure. To account for this the modeller may need to increase the entrance and/or exit loss values.<br>
By default, TUFLOW adjusts the entrance and exit losses of 1D structures flowing sub-critical every timestep based on the approach/departure velocities for 1D-1D-1D and with a new feature in the 2020-10-AA build for 2D-1D-2D. The entrance losses are adjusted based on an empirical relationship from flume testing whilst the exit loss equation is theoretically derived as mentioned above -
TUFLOW, by default, allows the losses to reduce to effectively a zero loss coefficient (i.e. 0.0001). A zero loss occurs where the approach and departure velocity is the same as the structure velocity. For example, a clear-spanning bridge over a concrete lined channel with the water level below the bridge deck will experience no energy losses until the bridge deck is surcharged so if your software is applying unadjusted or limited energy loss coefficients there will be an unrealistic energy loss at the structure for flow below the bridge deck. For culverts, in most cases there will be some losses as it is rare that the channel is of identical shape and slope to the culvert with usually the culvert being more constrictive and therefore a higher velocity so the adjusted coefficients are nearly always non-zero. At the other extreme is flow from or into a near still body of water (e.g. a lake or the ocean). In this situation the loss coefficient(s) will not be reduced and the maximum energy loss possible should occur.
If the default adjust losses approach is used (<font color="blue"><tt>Structure Losses</tt></font> <font color="red"><tt>==</tt></font><tt> ADJUST</tt>) the recommendations are to use industry guidelines for the entrance loss coefficient based on the shape/design of the inlet (these coefficients are typically based on a near zero approach velocity), and to use 1.0 for the exit loss coefficient. This applies to 1D culverts connected to 1D channels. The adjusted entrance and exit losses can be viewed over time in the _TSL layer,
Since the 2020-10-AA release, TUFLOW has a new (beta functionality) to have the losses automatically adjusted for linked 1D culverts and other structures connected to 2D domains through SX links (<font color="blue"><tt>Structure Losses SX</tt></font> <font color="red"><tt>==</tt></font><tt> ADJUST</tt>), see Section 6.2 from the <u>[https://downloads.tuflow.com/TUFLOW/Releases/2020-10/TUFLOW%20Release%20Notes.2020-10-AA.pdf 2020-10 Release Notes]</u>.<br>
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==How to represent the hydraulic behavior at the outlet of a pipe, including headwalls and transitions to open channels? ==
In general, pipe outlet headwalls affect the exit loss at the pipe outlet, and this can be modeled by changing the 1d_nwk “ExitC_or_WSb” attribute - exit loss coefficient for outlet controlled flow. The default exit loss coefficient is 1.0, assuming there is no headwall. For more details on these factors, refer to
More guidance on applying entry/loss and contraction coefficients is available [[TUFLOW_1D_Channels_and_Hydraulic_Structures#What_entry.2Fexit_loss_and_contraction_coefficients_should_I_use_for_1D_culverts.3F | here]].
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