User Forum of Software BASEMENT

anamenja

User

Registered: 2020-03-11

Posts: 4

Weir boundary is a sink

Hi

I tried do model a simple weir situation in a river and had the following problems

1. The amount of water entering the inner boundary weir is not the same as coming out of the inner boundary (balance of string_name1 is not equal to balance of string_name2). Over 10% of the water amount (konstant discharge) disappers in the inner boundary! Same sink can be observed for type hqralation!

2. It seems that the weir level contained in the separate file is not taken into account for the model calculation properly. I had to lower the weir level in the separate file for about 2.0m to get the water level I wanted to have at the weir boundary!

Is there a problem / some restrictions to the inner boundary (weir, hqrelation)?

Thanks

anamenja

User

Registered: 2020-03-11

Posts: 4

Re: Weir boundary is a sink

I found the solution to the problems:

Problem 1: The two strings string_name1 and string_name2 have to be of the exact same lengt. In case string_name2 is shorter than string_name2 the weir boundary condition acts as a sink!

In my model I had different string lentghs and got the following wrong result:
length of string_name1 = 17.68m
length of string_name2 = 14.57m
Q entering weir condition = 48.7m3/s
Q downstream weir condition = 40.1m3/s
=> Only 82% of the discharge entering the weir boundary appers downstream of the boundary condition. That is exactly the relation between length2 and lenght1.

at developpers: this is a bug that should be fixed or at least be explicitly written in the Documentation of Tag 'type'.

Problem 2: The difference in weir level and water level is due to filling behind the weir. I checked the difference with Poleny and the model seems to works correctly. Sorry about the confusion.

Last edited by anamenja (2020-03-19 07:53:31)

Matthias Bürgler

Developer

From: Zürich

Registered: 2019-04-04

Posts: 150

Re: Weir boundary is a sink

Hi anamenja

Thanks for pointing out this hidden behaviour of the weir boundary condition. We will consider changing the boundary condition to be always mass conservative or at least explicitly warn about this behaviour.

Best
Matthias

anamenja

User

Registered: 2020-03-11

Posts: 4

Re: Weir boundary is a sink

Thanks! If somehow possible mass conservation has to be given for this boundary condition.