1D Bridges: Difference between revisions
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=Introduction=
The following section looks at bridges using the 1D component of TUFLOW. Reference should also be made to the section on 1D bridges in the <u>[https://downloads.tuflow.com/_archive/TUFLOW/Releases/2018-03/TUFLOW%20Manual.2018-03.pdf 2018 TUFLOW Manual]</u>. For information on bridges in the 2D domain please see the following section on [[TUFLOW_2D_Hydraulic_Structures | 2D hydraulic Structures]] and [[Tutorial_M11#Part_2_-_1D_Open_Channel_with_1D_Bridges_and_Weir_inflow_.282D.29_and_Outflow_.281D.29 | Module 11]]. <br><br>
1D Bridge channels do not require length, Manning's n, divergence or bed slope (so they are effectively zero-length channels in terms of conveyance) and rely on a reasonable estimate of energy losses associated with re-expansion of water after the vena-contracta (often referred to as entrance losses), expansion of water downstream (exit losses), pier losses, bridge deck and guard rail losses. Other factors include accounting for occurrence of bridge deck pressure flow and the effects of bridge skew and multiple bridges (shielding effects of an upstream bridge on a downstream bridge). <br><br>
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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 2020-10-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 2D (adjustment of losses according to approach/departure velocities is the default from 1D to 1D to 1D. This capability was introduced for 2D to 1D to 2D, 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> in Build 2020-10-AA 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
https://www.tuflow.com/Download/Presentations/2012/2012%20Aust%20Workshops%20-%20TUFLOW%20Modelling%20Bends,%20Structures%20and%20Obstructions.pdf
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