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TomWild

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Registered: 04/11/2008

Junctions in culverts
Hi

Please can someone indicate why changes in cross section (i.e. dimensions) are not allowed in any type of conduit node, without using junctions?

Thanks!

02/03/2010 10:30

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adamsk

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Registered: 04/11/2008 Warnings: 0

Tom,
I'll respond why subsequently, but just to clarify the "rules":

Connecting different types (e.g. circular to rectangular) of conduits together (i.e. without a junction or other unit in between) is not allowed anywhere.

Connecting the same type of conduit together, but of different dimensions: this is allowed, and calculated correctly in the timestepping methods (unsteady or steady timestepping), although in the Direct Steady Method the change in shape will not be computed.

If you need to connect different types of conduit together, you must insert a unit (e.g. a junction or a loss unit) in between them.

02/03/2010 10:33

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TomWild

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Many thanks Konrad, very helpful. Look forward to the explanation in due course.

02/03/2010 10:35

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adamsk

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...The reason why the steady direct method doesn't allow a change in dimensions is best explained by how the direct method works.
The steady state momentum equation is solved working from the downstream end to upstream in each reach. It finds the dimensions of the downstream-most conduit node in a reach, and applies this to all sections upstream until it encounters a break (i.e. a non-conduit unit). It also needs to calculate water levels at intermediate "subnodes" between each node pair, for which there is no input data.

In theory, it could obtain the dimensions at the upstream node and interpolate properties (much as it does for river/conduit sections), but I'm not sure if this is appropriate.

Konrad

02/03/2010 11:03

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