skew 1

[civeng00]

I still have skewing issues with the Hec-Ras?? how can we skew it -ve??

 

[sknight701]

civeng00,

There is no negative skew. Please post more details of the problem.

 

[civeng00]

ok my problem is the when i see my model in perspective view my bridge does not align to the bank and i did try with skewing but as i skew it water surface elevation goes up.

 

[mricks]

By skewing the bridge, wouldn't the WSE go up as a result of reducing the available cross sectional area (multiplying 'x' by cosine of the angle)?

 

[sknight701]

civeng00,

The perspective view doesn't work very well at all unless all the data is georeferenced. Also, mricks is correct that skewing the bridge will raise the water surface elevation. However, you should only skew the bridge if it skewed greater than 30 degrees to the downstream flow direction.

 

[civeng00]

Thanks, Sknight701 so you mean we should not be skewing bridge if skew is less than 30 degree is that correct.
And yes whenever i skew the bridge WSE goes up.

 

[civeng00]

What is georeferenced in HEC-RAS??
would you explain me please.

 

[sknight701]

Civeng00,

Regarding the skew, that is exactly what I mean. The hydraulic reference manual of RAS has a good explanation of doing skew. And I also made a boo-boo. The cutoff for not skewing the bridge is 20 degrees, not 30. Me bad. And yes, skewing a bridge will always decrease its hydraulic efficiency, so your water surface elevations will go up.

Many items can be georeferenced into RAS using various coordinate systems. You can take the coordinates of your stream channel thalweg, bank stations, cross sections, etc. from AutoCAD or MicroStation and input them into the RAS georeference tables, and the program will draw the system for you. Then when you enter the bridge, it will be lined up properly with everything else.

However, it is not required to georeference anything to run a RAS model. Just ignore the perspective view, which will be totally useless.

 

[civeng00]

i got a problem in microstation when i am using my tools, the tool box remain open for about 2sec and then it disappears i tried everything to keep my tool boxes keep open.please anybody knows how to keep my tool boxes remain open while i am working.

 

[civeng00]

i got a problem in microstation when i am using my tools, the tool box remain open for about 2sec and then it disappears i tried everything to keep my tool boxes keep open.please anybody knows how to keep my tool boxes remain open while i am working.