what's the meaning of" natural bounda... Log Out | Topics | Search
Moderators | Register | Edit Profile

FlexPDE User's Forum » User Postings » what's the meaning of" natural boundary conditions" « Previous Next »

Author Message
Top of pagePrevious messageNext messageBottom of page Link to this message

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
Top of pagePrevious messageNext messageBottom of page Link to this message

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.
Top of pagePrevious messageNext messageBottom of page Link to this message

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.

Add Your Message Here
Post:
Username: Posting Information:
This is a private posting area. Only registered users and moderators may post messages here.
Password:
Options: Enable HTML code in message
Automatically activate URLs in message
Action:

Topics | Last Day | Last Week | Tree View | Search | Help/Instructions | Program Credits Administration