1D Bridges: Difference between revisions
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=Introduction=
The following section looks at bridges using the 1D component of TUFLOW
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>
Care must be taken when choosing the approach to modelling the bridge and setting appropriate loss values.
TUFLOW offers two bridge channels, B and BB. BB channels 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: 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 - this capability is currently under-development and due for release during 2020. For B bridges the default is not to adjust losses (refer to the manual for more information).
As a typical rule-of-thumb, if the channel upstream &/or downstream of the bridge is modelled in 1D then the bridge should also be modelled in 1D. Ideally any change in the channel from ESTRY 1D to 2D or vice-versa should also occur at a structure (i.e. bridge, culvert, etc) to facilitate the transition in solution schemes. The images below displays a typical preferred setup, however as is the case with hydraulic modeling your particular model situation may be different and therefore not always conform to these ideals.<br>
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