Jump to content
TUFLOW Forum
neildohert10

Bridge Modelling_large Head loss with high velocities

Recommended Posts

Hi,

I’m asking if anyone has had Tuflow report much larger head loss at a bridge crossing then expected when relatively high velocities occur.

I am modelling a river with a bridge crossing and am getting a large head change of approximately 2 m at the location of the bridge, where I estimate the head difference should be less then 1m.

The location I am modelling has relatively high velocities of 2.5 to 3.5 m/s the channel width is 50-150m with a peak flow depth of up to 8m.

I have modelled the bridge pylons as having a 5% blockage and a obvert of 11.5m.

The peak water elevation is leess then the bridge base so I’m not getting effects from the bridge blockage.

Any comments or advice would be much appreciated.

Regards

Neil

Share this post


Link to post
Share on other sites

Hi Neil

I assume you're using 2D flow constrictions or layered flow constrictions. Have you specified form loss coefficients? If so, note that for 2d_fcsh and 2d_lfcsh layers the FLC value is in form loss per metre length in the direction of flow for polygons, while for lines it is the total form loss value. This is done so that these layers are independent of cell size (ie. if you change your cell size, there is no need to change the FLC values). Refer to Table 4.19 in the 2010-10 manual.

Can you please email the relevant GIS layers, the .tlf file and the 2d_uvpt_check layer to support@tuflow.com and we'll cross-check your inputs. Usually, you need to add additional losses for bridge piers, etc, so to be getting a 2m head drop with only 2.5 to 3.5 m/s velocities indicates that something is probably wrong with the inputs.

Cheers

Bill

Share this post


Link to post
Share on other sites

Further to the previous posts, the large head drop was the result of applying a FLC to a layered FC shape polygon as an absolute value, not a per unit length amount. For FC and layered FC shape polygons, the FLC values must be the FLC per unit length in the direction of flow. The flow length (width of polygon) was around 10m, so once the FLC was divided by 10 an appropriate head drop resulted.

Cheers

Bill

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...