1D Bridges: Difference between revisions

Note: Adjustment of losses according to approach/departure velocities is the default from 1D channel to 1D bridge to 1D channel. However, for TUFLOW Builds prior to 2020-10-AA, 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 the 2D. This capability was introduced for 2D channel to 1D bridge to 2D channel in Build 2020-10-AA and onwards, and losses can be automatically adjusted based on the approach/departure 2D velocities across the SX connections by setting "<font color="blue"><tt>Structure Losses SX</tt></font> <font color="red"><tt>==</tt></font><tt> ADJUST</tt>" (see Section 6.2 of the <u>[https://downloads.tuflow.com/TUFLOW/Releases/2020-10/TUFLOW%20Release%20Notes.2020-10-AF.pdf 2020-10 Release Note]</u>). For B bridges the default is not to adjust losses (please refer to the <u>[https://downloadsdocs.tuflow.com/_archiveclassic-hpc/TUFLOWmanual/Releaseslatest/2018-03/TUFLOW%20Manual.2018-03.pdf 2018 TUFLOW Manual]</u> for more information). In the case of 2D connections, refer to the links 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:

Energy loss is caused by the flow contraction due to the expansion of water after the vena-contracta inside a bridge section and the flow expansion downstream of the bridge. The contraction/expansion loss coefficients (or the entry/exit loss coefficients) can be specified for TUFLOW 1D BB bridge using the following attributes:<br>

:* EntryC_or_WSa: the entry loss coefficients (default = 0.5).

:* ExitC_or_WSb: the exit loss coefficients (default = 1.0).

Note that theThe entry/exit loss coefficients are adjusted based on the equations in the figure below, towhich consider the extent of flow contraction/expansion. For example, a clear spanning bridge over a stormwater channel does not cause any contraction/expansion. TheTherefore, the change in approach velocity, structure velocity and the departure velocity are effectively the same, and the loss coefficients can be automatically reduced based on the following equations.:

The entry/exit loss coefficients are not used in the legacy B bridge. Instead, the bridge opening ratio is used to obtain the backwater coefficient Kb value from Figure 6 "Backwater coefficient base curves" of <u>[https://www.fhwa.dot.gov/engineering/hydraulics/pubs/hds1.pdf Hydraulics of Bridge Waterways (Bradley, 1978)]</u>.

PeirPier loss coefficients are treated as a direct energy (form) loss and can be derived from information in publications such as ''Hydraulics of Bridge Waterways'' ([http://www.ciccp.es/ImgWeb/Castilla%20y%20Leon/Documentaci%C3%B3n%20T%C3%A9cnica/Hydraulics%20of%20Bridge%20Waterways%20(1978).pdf FHA, 1978] or [https://austroads.com.au/publications/bridges/agbt08 AUSTROADS, 2019]).

Energy loss estimates from bridge piers (or other obstructions, vertical or horizontal, that do not cause upstream controlled flow regimes like pressure flow), are dependent on the ratio of the obstruction's area perpendicular to the flow direction to the gross flow area of the bridge opening, the shape of the piers or obstruction, and the angularity of the piers/obstruction to the flow direction. For example, using FHABradley (1978) the approach is to:

<li>Calculate the ratio of the water area occupied by piers to the gross water area of the constriction (both based on the normal water surface) and the angularity of the piers. These inputs are used to calculate "J" in the FHA documentation.</li>

<li>Use theFigure FHA7 (1978below) ''Incremental Backwater Coefficient for Piers'' data to calculate "Kp". This is the value that will be entered into the bridge's LC (loss vs height) table as the energy or form loss coefficient. For piers or obstructions that are non-uniform in dimensions or shape the LC table can be used to vary the losses with height accordingly noting that losses will need to be proportioned with depth to reflect the combined effect of the different obstruction shapes/dimensions.<br>

WhenA waterpressure levelflow reachescondition thecan bridgeoccur deckwhen level,the extrawater energylevel loss can be caused byreaches the bridge deck. Itlevel could result into pressure flow condition where(as water is forceforced through a small opening confined by the bridge abutments and the deck), resulting in additional energy losses. As the bridge becomes totally drawndrowned by the water level, itthe condition will switch back to the normal submerged bridge deck flow condition. withTo submergedaccount for this, once water reaches the height of the bridge deck., the TUFLOW BB bridge tests for either the pressure flow condition or drowned flow condition at every timestep by choosing the flow regime that gives the lower flow:

=Irregular shapedShaped bridgesBridges=

In the UK arch shaped bridges can often be seen on waterways, whereas in Australia these types of structures are quite uncommon. Modelling an irregular shaped bridge utilises the hydraulic properties elevation-width (CS/HW) type cross section and an irregular type culvert. <br>

[[File:Irregular_culvert_attribute_details.JPG|border|500px]]<br>

The table below highlights some of the commonly used check files when reviewing 1D bridges. The full list of TUFLOW check files can be found <u>[[TUFLOW_Check_Files | here]]</u>.

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