User Forum of Software BASEMENT

sajjad

User

Registered: 2014-10-01

Posts: 102

1d-2d coupling BC error

Hi, all

i have a cross like model with four channels intersecting at right angle in the centre. I have developed a 1d-2d coupling with the crossing in 2d and the four channels in 1d. the coupling is through the bc 'coupling_hydrograph'. When i run the basement, a fatal error occurs and i receive the following message :
"there is an attempt to couple to a hydrograph as a downstream boundary. This is nonsense. Hydrograph can in a coupled 1d simulations only be used as upstream boundary". Should i change the bc from coupled_hydrograph to some other(which ?). Any other suggestions. Would be gratefully appreciated.

Regards

Stephan Kammerer

Developer

Registered: 2015-03-31

Posts: 67

Re: 1d-2d coupling BC error

Hi Sajjad,

a bc of type 'coupling_hydrograph' can only be used as upstream bc. The time series of the inflow is thereby determined by the corresponding outflow from your upstream sub domain. As downstream bc you have to use 'coupling_hqrelation' or 'coupling_weir/gate' for example. To couple 1d and 2d sub domains via coupling type 'sequential' you will always have to specify which is your upstream and your downstream domain. However you can account for backwater effects of downstream sub domains by using the tag 'two_way_coupling' = 'yes'.

Hope this can solve your problems!
Stephan

sajjad

User

Registered: 2014-10-01

Posts: 102

Re: 1d-2d coupling BC error

Thanks for your kind reply.

I have changed the BC accordingly i.e. at a coupling interface the upstream boundary is coupling_hydrograph while downstream boundary is coupling_hqrelation.
But, now I am getting another 'fatal error', which is:

A fatal error occured
The slope must not be negative=-0.1
in file: BASEchain\BChydrograph.cpp on line 106
Version: R2.5.3 R2396, compiled at oct 20 2015
Basement must be terminated now

Kindly help me decipher this message (it would be good idea to include an explanation of these error messages in basement documentation)

Regards

sajjad

User

Registered: 2014-10-01

Posts: 102

Re: 1d-2d coupling BC error

Hi, all

In continuation of my previous post, I have discovered that the true problem is not the error reported above but the problem is that in 1D the flow hydrograph is pretty modest 3.5 lit/s, and I consistently get the message
'  At the hydrograph boundary all edges are set inactive (not wetted), but
   the inflow is bigger than 0.0. Either the cells in the boundary cross
   section are too big or the inflow is too small to ensure that at least one
   element is wetted.'
Benefiting from an earlier post, I changed the initial condition from 'dry' to 'table', q_out=0.5 to 1 lit/s but still the same message.

Regards
'

Stephan Kammerer

Developer

Registered: 2015-03-31

Posts: 67

Re: 1d-2d coupling BC error

Hey,

possible options to avoid such problems at 2D boundaries can be:

1. avoiding dry starts, use initial type 'continue' with a restart file (*.cgns) or the type 'index_table' where you can define an initial water depth based the MATID = index of your mesh.

2. refine the 2D mesh at the inflow boundary to decrease the element size.

3. reduce the number of nodes in the STRINGDEF of your inflow boundary.

I hope one of these options can solve your problems!

Stephan

Last edited by Stephan Kammerer (2015-11-23 17:21:16)

sajjad

User

Registered: 2014-10-01

Posts: 102

Re: 1d-2d coupling BC error

Dear sir,

referring to your reply, are not the steps 2 and 3 in contradiction to each other? coz when i refine the 2d mesh at the interface, i had to increase the no . of nodes and had to increase nodes at the interface( which is advised to be reduced in step 3).

Regards