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杂谈 
As I defined a moment load at the free end of a tube, an error
occured describing the following message
***ERROR: DEGREE OF FREEDOM 6 IS NOT ACTIVE ON
NODE 12 INSTANCE OUTERTUBE1 
THIS
LOADING IS NOT VALID
***NOTE: DUE TO AN INPUT ERROR THE ANALYSIS
PREPROCESSOR HAS BEEN UNABLE TO
INTERPRET
SOME DATA. SUBSEQUENT ERRORS MAY
BE CAUSED BY THIS OMISSION
***ERROR: DEGREE OF FREEDOM 6 IS NOT ACTIVE ON
NODE 12 INSTANCE OUTERTUBE1 
THIS
LOADING IS NOT VALID
***ERROR: 1 nodes have inactive dof on which
boundary conditions are
specified.
The nodes have been identified in node
set
ErrNodeBCInactiveDof
This was a simplified model. The cross section of the tube lies in the XY plane. I added a moment at one node at the free end of the tube with value of CM3. The cross section surface at another end was constrained in Z direction and one node on the surface was constrained in X and Y direction to avoid the rigid body motion. The boundary condtion of XY plane rotation on this surface was also added.
Node 12 in the error message is the node where the moment load added. I am sure that there were no overconstraints. so I am confused with this situation. Is it the problem degree of freedom of element? The linear brick element C3D8 was utilized.
This was a simplified model. The cross section of the tube lies in the XY plane. I added a moment at one node at the free end of the tube with value of CM3. The cross section surface at another end was constrained in Z direction and one node on the surface was constrained in X and Y direction to avoid the rigid body motion. The boundary condtion of XY plane rotation on this surface was also added.
Node 12 in the error message is the node where the moment load added. I am sure that there were no overconstraints. so I am confused with this situation. Is it the problem degree of freedom of element? The linear brick element C3D8 was utilized.
C3D8 doesn't have degree of freedom 6, hence the error. You can
only apply a direct load in directions 1 to 3. For a moment load it
should be in the direction perpendicular to the
axis.
Thanks for your information. I noticed this problem later. But only
solid elements C3D... or axissymetric elements CAX... are supported
by the postprocessor that I used. In this case, There seems to be
two ways that I can follow, one is to develop new element within
ABAQUS, and the second one is to modify the postprocessor program,
istn't it? However they are both a
big job.
Are there any easier ways for the simulation?
Axisymmetric elements won't be much use if you're applying a moment
at the top unless it's a moment only about the theta direction to
cause the edge to curl.
For solid elements a moment can be applied by applying two forces (a couple) in equal and opposite directions at an equidistance away from the bending axis. As the saying goes: Every couple have their moment.
For solid elements a moment can be applied by applying two forces (a couple) in equal and opposite directions at an equidistance away from the bending axis. As the saying goes: Every couple have their moment.
I am appreciated for your help. The further problem is how to
assign a linear distributed moments(in this case, it is transfered
to forces) along with the tube. This is another problem in this
project that makes me headache.
Using *AMPLITUDE command? But it is described in the manual as following:
Complex time or frequencydependent boundary conditions, loads, and predefined fields can be specified by using the AMPLITUDE parameter on the prescribed condition option to refer to an amplitude curve.
I tried with user subroutine, but the definition of CLOAD is not provided in it.
What else can I do? If *AMPLITUDE is suggested, I wish you can give the tips with a little bit more detail.
Using *AMPLITUDE command? But it is described in the manual as following:
Complex time or frequencydependent boundary conditions, loads, and predefined fields can be specified by using the AMPLITUDE parameter on the prescribed condition option to refer to an amplitude curve.
I tried with user subroutine, but the definition of CLOAD is not provided in it.
What else can I do? If *AMPLITUDE is suggested, I wish you can give the tips with a little bit more detail.
If it says that *Amplitude is for applying a time based dependancy
then it means that.
If you're applying a variable force along the length of the tube to apply your moment then it's probably easier just to edit the input file manually. Alternatively you could apply a variable pressure along the length equivalent to your forces in a similar way to applying a hydrostatic pressure distribution.
If you're applying a variable force along the length of the tube to apply your moment then it's probably easier just to edit the input file manually. Alternatively you could apply a variable pressure along the length equivalent to your forces in a similar way to applying a hydrostatic pressure distribution.
What corus said is correct and should produce a moment  this
method will work perfectly well ***according to the way in which
you describe your model**. A pressure normal to the (axial) surface
of a tube will produce a moment (m) equivalent to m=PAl, where P is
the applied pressure, A is the area over which it is applied and l
the perpendicular length between the applied centroid of pressure
to the centroid of the support. Also be aware of the fact that
applying a pressure in this way will also give you shear, whereas a
pure moment will not  is this how you expect your load to be
applied? We could do with a drawing of your model to see exactly
what's going on. Is it like this:
P
R E S S U R E
<
fixed translations
<
fixed translations
global axes
Y


 Z
pressure applied in ve Y direction?
global axes
Y


 Z
pressure applied in ve Y direction?
If the pressure is applied around the whole circumference then
it won't produce a moment. What I was referring to was applying a
pressure along a narrow strip down one side of the tube. As drej
implies, it's unclear as to what the loading is.
I described the load in the first poster, but I am sorry that it
was not clear. Now I quote it in the first poster:
"The cross section of the tube lies in the XY plane. I added a moment at one node at the free end of the tube with value of CM3. "
In ABAQUS CAE, CM3 refers to the value of the moment in the third direction, i.e. Z direction. So I meant the load was applied in the term of torsion, and the moment should be in the XY plane.

.

. >>M(torsion
moment in the direction
 according
to righthand system)
.
global coordinate system
Y


 Z
In this case, any pressure normal to the outside surface of the tube produces no moment to Zaxis, and this moment is what I expect.
"The cross section of the tube lies in the XY plane. I added a moment at one node at the free end of the tube with value of CM3. "
In ABAQUS CAE, CM3 refers to the value of the moment in the third direction, i.e. Z direction. So I meant the load was applied in the term of torsion, and the moment should be in the XY plane.

.

.

.
global coordinate system
Y


 Z
In this case, any pressure normal to the outside surface of the tube produces no moment to Zaxis, and this moment is what I expect.
去VIEW里面看,通常node set
ErrNodeBCInactiveDof被自动定义成一个集合,这样可以在VISUALIATION中很容易看到.
问题原因有几中,如在某节点的某个自由度被限制的情况下,还施加了边界条件,就会导致这样的情况,检查边界条件,和那些问题节点的自由度情况,特别注意如*EQUATION,*MPC等容易被忽略的命令.
问题原因有几中,如在某节点的某个自由度被限制的情况下,还施加了边界条件,就会导致这样的情况,检查边界条件,和那些问题节点的自由度情况,特别注意如*EQUATION,*MPC等容易被忽略的命令.