AIFlow fabric directionality
Posted: 15 Apr 2016, 13:27
Hello,
I have been trying to use the AIFlow solver and I've run into a wall about understanding how the fabric inputs relate to the output velocity. In the papers (e.g., Ma et al., 2010, p. 807) and the Elmer/Ice documentation, it seems that the fabric factors a11, a22, a33 describe the orientation of the c-axes. Therefore, for a tight single pole fabric at e.g., the bottom of an ice core, we would expect something like a11=a22<<a33= approx 0.9. However, this doesn't seem to agree with the velocity patterns returned by the AIFlow solver. I have tried multiple geometries, but I'll explain one here. Take a simple vertical cylinder filled with ice (z defines the axis of the cylinder), which will exhibit Poiseuille flow in the negative vertical direction. One would expect that if the c-axes are vertical, the velocity would be lower than if the c-axes are horizontal. However, using the AIFlow solver with
Fabric 1 = Real 0.0
Fabric 2 = Real 0.0
in the sif file results in z velocities two orders of magnitude higher than with
Fabric 1 = Real 0.0
Fabric 2 = Real 1.0
or
Fabric 1 = Real 1.0
Fabric 2 = Real 0.0
in the sif file. (The latter two yield similar velocity magnitudes.) All models produce the expected flow pattern, but with the reverse of the expected velocity relationship (i.e., when c-axes are horizontal, flow is slower than when c-axes are vertical). This suggests that the Fabric factor is defining an ease-of-slip direction rather than the normal to the ease-of-slip plane (=c-axes). I do not incorporate any fabric evolution in this test case, so the prescribed Fabric factors are constant. I have tried several different viscosity models, with the most recent being 010010010.Va. Any suggestions as to what I am missing? Happy to provide the sif and geometry if it would be useful.
Thanks,
Chris
I have been trying to use the AIFlow solver and I've run into a wall about understanding how the fabric inputs relate to the output velocity. In the papers (e.g., Ma et al., 2010, p. 807) and the Elmer/Ice documentation, it seems that the fabric factors a11, a22, a33 describe the orientation of the c-axes. Therefore, for a tight single pole fabric at e.g., the bottom of an ice core, we would expect something like a11=a22<<a33= approx 0.9. However, this doesn't seem to agree with the velocity patterns returned by the AIFlow solver. I have tried multiple geometries, but I'll explain one here. Take a simple vertical cylinder filled with ice (z defines the axis of the cylinder), which will exhibit Poiseuille flow in the negative vertical direction. One would expect that if the c-axes are vertical, the velocity would be lower than if the c-axes are horizontal. However, using the AIFlow solver with
Fabric 1 = Real 0.0
Fabric 2 = Real 0.0
in the sif file results in z velocities two orders of magnitude higher than with
Fabric 1 = Real 0.0
Fabric 2 = Real 1.0
or
Fabric 1 = Real 1.0
Fabric 2 = Real 0.0
in the sif file. (The latter two yield similar velocity magnitudes.) All models produce the expected flow pattern, but with the reverse of the expected velocity relationship (i.e., when c-axes are horizontal, flow is slower than when c-axes are vertical). This suggests that the Fabric factor is defining an ease-of-slip direction rather than the normal to the ease-of-slip plane (=c-axes). I do not incorporate any fabric evolution in this test case, so the prescribed Fabric factors are constant. I have tried several different viscosity models, with the most recent being 010010010.Va. Any suggestions as to what I am missing? Happy to provide the sif and geometry if it would be useful.
Thanks,
Chris