Boundary Conditions

For Gmsh meshes, boundary conditions are set by naming Physical Groups in the .geo file. Tolosa-sw matches the Physical Group name against the known BC types listed below.

See also the Boundary Conditions page for the complete BC reference including tidal and time-varying types.

BC Types Reference

BC Type	Syntax	Description
Rigid wall	wall	No-normal-flow (reflection)
Neumann	neumann	Zero normal gradient
Tidal harmonics	tide	All constituents from tide.list
Tidal harmonics (N first)	tide#N	Only the first N tidal constituents
Constant discharge	q#X	Constant discharge X (m³/s)
Discharge from file	q	Reads tabulated file bc_q.txt
Discharge from user function	q#user	Calls bc_user() in m_user_data.f90
Constant SSH	ssh#X	Constant sea surface height X (m)
SSH from file	ssh	Reads tabulated file bc_ssh.txt
SSH from user function	ssh#user	Calls bc_user() in m_user_data.f90
Constant depth	h#X	Constant water depth X (m)
Depth from file	h	Reads tabulated file bc_h.txt
Depth from user function	h#user	Calls bc_user() in m_user_data.f90
Rating curve	ratcurve	Stage–discharge table from bc_<name>.txt

Examples

Wall + Discharge + Tide (Gironde test case)

Physical Curve("wall", 5)    = {1, 3};   ! bank boundaries
Physical Curve("q#1000", 6)  = {2};      ! river head: 1000 m³/s
Physical Curve("tide#15", 7) = {4};      ! ocean: 15 tidal constituents

Time-Varying Discharge

Use BC name q (without #value) and provide a bc_q.txt file:

Physical Curve("q", 6) = {2};

bc_q.txt format (time in seconds, discharge in m³/s):

$ q(t)
0.      800.
3600.   1000.
7200.   1200.
86400.  1000.

Constant SSH at Open Boundary

Physical Curve("ssh#0.5", 7) = {4};   ! constant SSH of 0.5 m

User-Defined SSH (time-varying via bc_user)

Physical Curve("ssh#user", 7) = {4};

Then implement in m_user_data.f90:

MODULE real(rp) FUNCTION bc_user( tag )
   character(len=*), intent(in) :: tag
   select case( tag )
      case('ssh')
         bc_user = 0.5_rp * sin( 2._rp * pi / 44712._rp * tc )
      case default
         call end_program('unknown bc tag: '//tag)
   end select
END FUNCTION bc_user