1D Bridges: Difference between revisions
Content deleted Content added
No edit summary |
|||
| (6 intermediate revisions by 2 users not shown) | |||
Line 1:
<br>▼
<br>▼
=Introduction=
The following section looks at bridges using the 1D component of TUFLOW
'''Example of a bridge that could be modelled in 1D'''
Line 20 ⟶ 16:
:*automatically simulates pressure flow conditions. The only loss coefficients required to be specified for BB channels are those due to piers, and the bridge deck when it is submerged and not under pressure flow.
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 (refer to the <u>[https://
:*<u>[https://www.tuflow.com/Download/Presentations/2012/2012%20Aust%20Workshops%20-%20TUFLOW%20Modelling%20Bends,%20Structures%20and%20Obstructions.pdf 1D and 2D Modelling Bends, Structures and Obstructions]</u>
:*<u>[https://www.tuflow.com/Download/Publications/Modelling%20of%20Bends%20and%20Hydraulic%20Structures%20in%20a%202D%20Scheme,%20Syme,%202001.pdf Modelling of Bends and Hydraulic Structures in a Two-Dimensional Scheme]</u>
Line 62 ⟶ 58:
A pressure flow condition can occur when the water level reaches the bridge deck level (as water is forced through a small opening confined by the bridge abutments and the deck), resulting in additional energy losses. As the bridge becomes totally drowned by the water level, the condition will switch back to the normal submerged bridge deck flow condition. To account 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:
:*The pressure flow equation is based on the Section 8.3 of the <u>[https://www.fhwa.dot.gov/engineering/hydraulics/pubs/hds1.pdf Hydraulics of Bridge Waterways (Bradley, 1978)]</u>, with a default deck discharge coefficient of 0.8. This value can be modified using the 1d_nwk HConF_or_WC attribute. Note that the original hydraulic experiment conducted by Liu (1967) used a flume with a pair of bridge abutments and a deck. This means the impact of both abutments and deck are considered in this approach. The entry/exit losses are switched off during the pressure flow calculation to avoid the overestimation of the contraction/expansion losses.
:*For the drowned flow condition, the BB bridge considers extra energy loss caused by the bridge deck/rails using a deck loss coefficient (default = 0.5) in addition to the entry/exit losses. The deck loss coefficient can be adjusted using the WConF_or_WEx attribute or by specifying the LC (energy loss versus height) table. <br>
The _TSF and _TSL layers can be used to find out the regime/form loss values used for BB bridges:
*"P": pressure flow
*"D": ds water level > the soffit level, but it applies normal flow because the normal flow equation predicts smaller velocity
*" ": ds water level < the soffit level, normal 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.<br>
<br>
=Irregular
[[File:Irregular_culvert_1.jpg|border|300px]]▼
[[File:Irregular_culvert_2.jpg|border|400px]]▼
▲<br>
1. Create a 1d_tab HW (height vs width) .csv file for each standard shape (ie. set up a database of the irregular shapes). For the height value you can start at a value of zero so that height becomes depth (this might making the .csv files easier). As the height increases the width changes to reflect the particular irregular shape you are modeling. In the example below, the width at the top of the arch (2.1m) is set to a small value of 0.001m as opposed to zero as the HW becomes NA past the top of the irregular shape. <br>▼
London, UK (pht: Rohan King)<br>▼
To create an irregular shaped bridge:
▲
[[File:HW_arch_example.JPG|border|900px]] <br>
<br>
GIS example set up:<br>
[[File:Irregular_culvert_attribute_details.JPG|border|500px]]<br>
<br>
▲2. Any number of 1d_tab lines can reference the same .csv file, ie. you don't need to have a unique .csv file for every 1d_tab line. <br>
[[File:Arch HW attributes.JPG|border|300px]] <br>
3. One option is to copy and paste the 1d_tab lines across each pipe (if you use a two vertex 1d_tab line there is no requirement that the 1d_tab line is snapped to the 1d_nwk pipe line - they just need to intersect). Each line will need to reference the relevant standard irregular shape HW .csv file (this could be automated using SQL Select if you have an attribute on the pipe to indicate which irregular shape it is). <br>▼
4. The inverts of the pipes should raise or lower the standard irregular shape cross-section to the appropriate height.▼
</ul>▼
<br>
▲
▲
▲[[File:Irregular_culvert_1.jpg|border|300px]]
▲[[File:Irregular_culvert_2.jpg|border|400px]]
▲London, UK (pht: Rohan King)<br>
<br>
=Check Files=
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>.
{| align="left" class="wikitable" width="20%"
Line 119 ⟶ 117:
|}
<br><br><br><br><br><br><br><br><br><br>
<br><br><br><br><br><br><br><br><br>
Any further questions please email TUFLOW support: [mailto:support@tuflow.com?Subject=TUFLOW%201D%20bridges%20help support@tuflow.com]
<br><br>
{{Tips Navigation
|uplink=[[
}}
| |||