# Nodal velocity calculation on a RICHARDS flow constant pressure head boundary

Dear OGS community,
I'm modeling dynamic subsurface pipe leakage using the RICHARDS equation
and I face a little problem.

I conduct the leakage (water flow through pipe defect) by assigning a
constant pressure head BC to the lower part of the pipe. After
computation, the nodal velocities directly on this boundary stay
constant throughout a scenario with a changing pressure gradient.

Can anyone tell me how (or refer to anyone who might know) OGS does the
calculation of nodal velocities on nodes of a constant pressure head
boundary? In my model, these velocities seem to be only gravity and not

You'll find the model as well as a .pvd attached.

Thanks a lot and
best regards.
Aaron

cmp_2.7z (3.72 MB)

OGS calculates the Darcy velocity of fluid at Gauss points of each element, and extrapolates the Gauss point velocity to nodes for output if keywords
VELOCITY_X1, VELOCITY_Y1, VELOCITY_Z1 are given in .out file.

···

On 03/04/2015 04:16 PM, Aaron Peche wrote:

Dear OGS community,
I'm modeling dynamic subsurface pipe leakage using the RICHARDS equation
and I face a little problem.

I conduct the leakage (water flow through pipe defect) by assigning a
constant pressure head BC to the lower part of the pipe. After
computation, the nodal velocities directly on this boundary stay
constant throughout a scenario with a changing pressure gradient.

Can anyone tell me how (or refer to anyone who might know) OGS does the
calculation of nodal velocities on nodes of a constant pressure head
boundary? In my model, these velocities seem to be only gravity and not

You'll find the model as well as a .pvd attached.

Thanks a lot and
best regards.
Aaron

All right. The model works. There was a conceptual error.
Thank you Wenqing.

···

Am 3/9/2015 um 12:08 PM schrieb Wenqing Wang:

OGS calculates the Darcy velocity of fluid at Gauss points of each element, and extrapolates the Gauss point velocity to nodes for output if keywords
VELOCITY_X1, VELOCITY_Y1, VELOCITY_Z1 are given in .out file.

On 03/04/2015 04:16 PM, Aaron Peche wrote:

Dear OGS community,
I'm modeling dynamic subsurface pipe leakage using the RICHARDS equation
and I face a little problem.

I conduct the leakage (water flow through pipe defect) by assigning a
constant pressure head BC to the lower part of the pipe. After
computation, the nodal velocities directly on this boundary stay
constant throughout a scenario with a changing pressure gradient.

Can anyone tell me how (or refer to anyone who might know) OGS does the
calculation of nodal velocities on nodes of a constant pressure head
boundary? In my model, these velocities seem to be only gravity and not

You'll find the model as well as a .pvd attached.

Thanks a lot and
best regards.
Aaron

--
Aaron Peche (M.Sc.)
PhD Student
Institute of Fluid Mechanics and Environmental Physics
Leibniz-Universität Hannover
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