无论哪个论坛，都无人解答这个问题。这也不是FDS独有的问题，只要是CFD软件，比如flunt、CFX等，都会出现这个问题。所以火灾模拟中出现这个问题，不用到处问怎么解决，自己看着办吧。我之所以没有把不稳定作为最难的问题，是因为FDS手册上毕竟给出了解决的思路：
It is possible that during an FDS calculation the flow velocity at some location in the domain can increase due to numerical error causing the time step size to decrease to a point where logic in the code decides that the results are unphysical and stops the calculation with an error message in the file CHID.out. In these cases, FDS ends by dumping out one final Plot3D file giving you a hint as to where the error is occurring within the computational domain. Usually, a numerical instability can be identified by fictitiously large velocity vectors emanating from a small region within the domain. Common causes of such instabilities are:
• mesh cells that have an aspect ratio larger than 2 to 1
• high speed flow through a small opening
• a sudden change in the heat release rate
• the removal or creation of an obstruction, like the opening or closing of a door
• a high (>100 g/mol) molecular weight fuel molecule that is not in the FDS database, Table 14.1. In such cases, reduce the molecular weight but maintain the atom ratios.
• long, sealed tunnels, in which pressure fluctuations can cause spurious numerical artifacts. See Section 9 for details.
There are various ways to solve the problem, depending on the situation. Try to diagnose and fix the problem before reporting it. It is difficult for anyone but the originator of the input file to diagnose the problem.
It is possible that during an FDS calculation the flow velocity at some location in the domain can increase due to numerical error causing the time step size to decrease to a point where logic in the code decides that the results are unphysical and stops the calculation with an error message in the file CHID.out. In these cases, FDS ends by dumping out one final Plot3D file giving you a hint as to where the error is occurring within the computational domain. Usually, a numerical instability can be identified by fictitiously large velocity vectors emanating from a small region within the domain. Common causes of such instabilities are:
• mesh cells that have an aspect ratio larger than 2 to 1
• high speed flow through a small opening
• a sudden change in the heat release rate
• the removal or creation of an obstruction, like the opening or closing of a door
• a high (>100 g/mol) molecular weight fuel molecule that is not in the FDS database, Table 14.1. In such cases, reduce the molecular weight but maintain the atom ratios.
• long, sealed tunnels, in which pressure fluctuations can cause spurious numerical artifacts. See Section 9 for details.
There are various ways to solve the problem, depending on the situation. Try to diagnose and fix the problem before reporting it. It is difficult for anyone but the originator of the input file to diagnose the problem.
