# does "drag" boundary condition can't work with P1DGP2?

Asked by liu chin chi

Hi all,

the manual metions in 8.12.3.11, does it means "drag" boundary condition can't work with P1DGP2?
But 8.16 and 8.16.6 sugguest P1DGP2 and both a type::drag and a type::no normal flow at bottom boundary condition.
I'm a liitle confused.

By the way, dose there any forum for Fluidity model users to communicate ?
Maybe who has some basic questions like me can search the information first before asking.

Please excuse my poor English. Thanks.

8.12.3.11 No normal flow
When using .../control volumes under Pressure .../spatial discretisation or when
using .../integrate continuity by parts with CG Pressure and Velocity this boundary condition
type imposes a weak no normal flow boundary condition on the surfaces specified.

8.16 Configuring ocean simulations
This section contains advice for running a large scale ocean simulation in three dimensions. The
flow domain is characterised by the large aspect ratio between horizontal and vertical length scales.
The following is a set of recommended discretisation options for such simulations. It is based on
the use of the P1DGP2 velocity, pressure element pair [Cotter et al., 2009]. The recommendations are
applicable to both global or ocean-scale domains as well as to smaller, regional or coastal domains.
For the first case, see the additional instructions in section 8.16.8, to solve the equations on the sphere.

8.16.6 Boundary conditions
For the bottom boundary condition, add both a type::drag and a type::no normal flow
boundary condition under Velocity. A typical value for a dimensionless bottom friction coefficientfor the ocean is 0.0025.

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Matthew Piggott
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 Revision history for this message Matthew Piggott (m-d-piggott) said on 2014-02-21: #1

Hi,

You will need to add both a drag BC as well as a no-normal flow BC.

8.12.3.11 isn't saying anything about drag - this is a BC on the tangential
component of velocity, whereas no-normal flow is a BC on the normal
component of velocity.

Best wishes
Matt

On 21 February 2014 07:31, liu chin chi <
<email address hidden>> wrote:

> New question #244332 on Fluidity:
>
> Hi all,
>
> the manual metions in 8.12.3.11, does it means "drag" boundary
> condition can't work with P1DGP2?
> But 8.16 and 8.16.6 sugguest P1DGP2 and both a type::drag and a type::no
> normal flow at bottom boundary condition.
> I'm a liitle confused.
>
> By the way, dose there any forum for Fluidity model users to
> communicate ?
> Maybe who has some basic questions like me can search the information
> first before asking.
>
> Please excuse my poor English. Thanks.
>
> 8.12.3.11 No normal flow
> When using .../control volumes under Pressure .../spatial discretisation
> or when
> using .../integrate continuity by parts with CG Pressure and Velocity
> this boundary condition
> type imposes a weak no normal flow boundary condition on the surfaces
> specified.
>
> 8.16 Configuring ocean simulations
> This section contains advice for running a large scale ocean simulation
> in three dimensions. The
> flow domain is characterised by the large aspect ratio between horizontal
> and vertical length scales.
> The following is a set of recommended discretisation options for such
> simulations. It is based on
> the use of the P1DGP2 velocity, pressure element pair [Cotter et al.,
> 2009]. The recommendations are
> applicable to both global or ocean-scale domains as well as to smaller,
> regional or coastal domains.
> For the first case, see the additional instructions in section 8.16.8, to
> solve the equations on the sphere.
>
> 8.16.6 Boundary conditions
> For the bottom boundary condition, add both a type::drag and a
> type::no normal flow
> boundary condition under Velocity. A typical value for a dimensionless
> bottom friction coefficientfor the ocean is 0.0025.
>
> --
> You received this question notification because you are a member of
> Fluidity Core Team, which is an answer contact for Fluidity.
>

 Revision history for this message liu chin chi (caite8001) said on 2014-02-21: #2

Hi , Matthew

Maybe I misunderstand 8.12.3.11. Dose it means no-normal flow BC under Velocity can be used with P1DGP2 mesh ?

Regards,

ChinChi

 Revision history for this message Jon Hill (jon-hill) said on 2014-02-21: #3

Hi ChinChi,

no_normal_flow can be used with P1DG_P2.

Jon

On 21/02/2014 10:01, liu chin chi wrote:
> Question #244332 on Fluidity changed:
>
> Status: Answered => Open
>
> liu chin chi is still having a problem:
>
> Hi , Matthew
>
> Maybe I misunderstand 8.12.3.11. Dose it means no-normal flow BC
> under Velocity can be used with P1DGP2 mesh ?
>
> Regards,
>
> ChinChi
>

--
Dr Jon Hill
Research Fellow
AMCG, Earth Science and Engineering
Imperial College London
Mob: 07748254812
Phone: +44(0)2075949321

 Revision history for this message Matthew Piggott (m-d-piggott) said on 2014-02-21: #4

Hi ChinChi

Yes, a weak version of the BC is just an implementation issue. It will
still give you no flow
through that boundary.

Best wishes
MAtt

On 21 February 2014 10:01, liu chin chi <
<email address hidden>> wrote:

> Question #244332 on Fluidity changed:
>
> Status: Answered => Open
>
> liu chin chi is still having a problem:
>
> Hi , Matthew
>
> Maybe I misunderstand 8.12.3.11. Dose it means no-normal flow BC
> under Velocity can be used with P1DGP2 mesh ?
>
> Regards,
>
> ChinChi
>
> --
> You received this question notification because you are a member of
> Fluidity Core Team, which is an answer contact for Fluidity.
>

 Revision history for this message liu chin chi (caite8001) said on 2014-02-21: #5

Thanks Matthew Piggott, that solved my question.

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