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Line 9: Care must be taken when choosing the approach to modelling the bridge and setting appropriate loss values. TUFLOW offers two 1D bridge channels, B and BB. BB channels were introduced for Build 2016-03-AA and are a more advanced solution than B channels, which are retained for legacy models. By default, BB channels are superior to B channels as they: (a) adjust the entrance and exit losses every timestep according the approach and departure velocities (in the same manner as for other structures such as culverts); (b) automatically simulates pressure flow conditions. The only loss coefficients required to be specified for BB channels are those due to any piers, and the bridge deck when it is submerged and not under pressure flow. Note: For TUFLOW Builds prior to 2020-01-AC, if the BB bridge is linked directly to a 2D domain (typically via a SX link), there is no adjustment of entrance / exit losses on the sides connected to 2D -(adjustment ~~this~~of ~~capability~~losses according to approach/departure velocities is ~~currently~~the ~~under-development~~default ~~and~~from ~~due~~1D to 1D to 1D. This capability was introduced for ~~release~~2D ~~during~~to 1D to 2D, losses can be automatically adjusted based on the approach/departure 2D velocities across the SX connections by setting "???????????????" in Build 2020-01-AC onwards. In the case of 2D connections, refer to the links from the TUFLOW Library below for a discussion on the intricacies and challenges of taking into account contraction and expansion losses for 1D structures connected directly to 2D domains. For B bridges the default is not to adjust losses (please refer to the manual for more information). https://www.tuflow.com/Download/Presentations/2012/2012%20Aust%20Workshops%20-%20TUFLOW%20Modelling%20Bends,%20Structures%20and%20Obstructions.pdf Line 33: =Loss Theory= ~~Details on how the default loss coefficient of 1.56 was derived can be found [http://www.tuflow.com/forum/index.php?/topic/1419-1d-loss-coefficients-for-bridge-deck-surcharging/#comment-3673 here].~~ ==Pier Losses== <br>▼ ''under construction'' <br> ==~~Pier~~Deck Losses and Pressure Flow== For the legacy B channels, the deck loss coefficient was fixed at a value of 1.5625, which is derived from the discharge coefficient in Hydraulics of Bridge Waterways of 0.8 (1.56 = 1/0.8^2) to approximate pressure flow conditions. Whilst this is reasonable when the bridge deck experiences pressure flow, it will over-estimate the losses once the bridge deck starts to drown out and flow returns fully to downstream controlled. Further details on how the value of 1.56 was derived can be found [http://www.tuflow.com/forum/index.php?/topic/1419-1d-loss-coefficients-for-bridge-deck-surcharging/#comment-3673 here]. ▲<br> Due to the above limitation of B channels, BB channels were developed to automatically switch into and out of pressure flow conditions. For pressure flow, a default discharge coefficient of 0.8 is used which the user can modify using the 1d_nwk HConF_or_WC attribute. Once water commences to surcharge the bridge deck, TUFLOW tests for pressure flow or drowned flow every timestep by choosing the flow regime that gives the lower flow. For drowned bridge flow the 1d_nwk WConF_or_WEx attribute (default = 0.5) can be used to set the energy loss due to the bridge deck/rails if no LC (energy loss versus height) table is specified. When pressure flow occurs a flow regime of "P" is reported in the _TSF layer. For more information on theory and options for B and BB bridges see Section 5.7.2 in the TUFLOW Manual. ''under construction'' <br>

1D Bridges: Difference between revisions