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xujian (zdp1979)
New member Username: zdp1979
Post Number: 1 Registered: 01-2007
| Posted on Monday, January 22, 2007 - 07:48 am: | |
Hi, every one. i have learned that the " natural boundary conditions" has the meaning of "flux". when i study the sample of version 5.0.8, and find in the example "3d-flowbox",that the inlet hole with the bounadry conditons of "Natural(vx)=0 Natural(vy)=0 Natural(vz)=0 value(p)=pin". i confuse the "Natural(vx)=0 Natural(vy)=0 Natural(vz)=0" because with the calculation results it obviously that the inlet hole has the flow velocity vz, then why it has the boundary of "Natural(vz)=0". i am appreciated for your help. thanx a lot |
Robert G. Nelson (rgnelson)
Moderator Username: rgnelson
Post Number: 740 Registered: 06-2003
| Posted on Monday, January 22, 2007 - 02:13 pm: | |
Natural boundary conditions are discussed in several places in the FlexPDE documentation. See the entries under "natural" in the Help Index. Briefly put, the Natural boundary condition statement supplies the integrand for the surface terms arising from the application of the Divergence theorem to the second order terms of the PDE. In the "3d_flowbox" problem, the second order terms in the velocity equations are the viscous dissipation only. Natural(vz)=0 does not restrict the value of vz at the boundary. It merely says that there is no net transport of energy across the boundary due to viscous forces.
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xujian (zdp1979)
New member Username: zdp1979
Post Number: 2 Registered: 01-2007
| Posted on Monday, January 29, 2007 - 03:33 am: | |
thanx a lot. i will leran again once more.
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