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# Angle of Nodestring and Flow Direction

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I have got three basic question: The angle in the angle of the nodestring in the status windows is measured from which axes? East an ccw does not fit and there is no descrition in the SMS manual...or  I am not able to find it.

The second question: the direction of the nodestring maybe reversed, but actually it is just reversing the arrows at both sides of the nodestring. The angle is not changed. But reversing the direction of creation, both angle and arrows are turned. In my understanding that would be actually reversing the direction.

The last question: What function may the arrows have? For my understanding they may e.g. indicate the assumed flow direction, depending on the software used. Taking the conflict between angle and arrows into account, there now may be a conflict between angle and flow direction.

To explain the backround of my question: I was instructed creating the nodestrings for the inflow boundary conidtion of a hydrodynamic model (Hydro_AS-2d) always in such a way, that the arrows are directed into the opposite direction of the flow. The angle in the status window is then written into the boundary condition as initial flow direction. While this all may be correct, I would simply take the assumed angle of flow direction. The angle of the nodestring may be a help, but actually may be totally wrong (e.g. reversed direction, non-linear nodestring).

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Thank you for your question. It sounds like there could be some confusion due to multiple "directions" associated with a nodestring.

1. Nodestrings have a direction as part of their attributes. This direction is identified by two arrows--one on each end of the nodestring. This direction is typically utilized when computing flow across a cross section.

2. Some Nodestring Boundary Conditions can have a direction assigned to them. For a flowrate boundary condition with a specified direction, the direction is normally measured in degrees counter-clockwise from the positive X-Axis.

You mentioned that you are using Hydro_AS-2D. Which boundary condition type are you using?

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Usually the boundary condition is "zulauf" (inflow). The angle of flow direction is required.

1. "directions as part of their attributes":

• Those attributes are stored in the 2dm and actually stored by the order of nodes(?). An actual angle is not saved in the attributes. Is that correct? How and where is the the direction saved, if I reverse the direction of the nodestring?

2. "direction is identified by two arrows"

• If I reverse the direction of the nodestring the angle of the nodestring (status window) is still the same (see both attached pics). That just makes sense to me if that angle indicates the angle of the nodestring or actually nodestring-section (based on the creation order of nodes), not the angle of the arrows. To what exactly refers the angle in the status window?

3. "direction is normally measured in degrees counter-clockwise from the positive X-Axis"

• the angle (see attached Picture "nodestring.jpg") in the status window, if the positive X-Axis is east, neither fits to the arrows nor the nodestring - in special if the angle is constant even changing the direction
• the angle in the status window is actually the angle of the line where the black-square-marker is located -so it may differ depending on the the length and orientation of sections within my nodestring.

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