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Articulated Joint for substructure
How to define articulated joint for substructure.
Hi,
Could you clarify your question?
In the substructure, the SUBCONSTRAINTS table allows you to constrain individual degrees of freedom (DOFs) of a joint to one another, either rigidly or via nonlinear springs and dampers. However, it is not possible to directly articulate the movement between joints. That said, you could apply external forces to the model to induce a form of articulated motion.
Best regards,
David
Quote from David on 18. November 2025, 13:33Hi,
Could you clarify your question?
In the substructure, the SUBCONSTRAINTS table allows you to constrain individual degrees of freedom (DOFs) of a joint to one another, either rigidly or via nonlinear springs and dampers. However, it is not possible to directly articulate the movement between joints. That said, you could apply external forces to the model to induce a form of articulated motion.
Best regards,
Hi David,
Please how can I add some stiffness so the following joint does not rotate freely about Z axis:
SUBCONSTRAINTS
ID JntID Jnt2ID TrP Fixed Spring DoF_tX DoF_tY DoF_tZ DoF_rX DoF_rY DoF_rZ
1 1 0 1 0 0 1 1 1 1 1 0
Regards
Salem
Hi Salem,
you can do this by defining a spring, and then assigning the spring to the DOF’s directly in the constraint table.
So in your example you would define a 2nd constraint which assigns the spring to DoF_rZ, which is left unconstrained by the constraint with ID=1.
See: https://docs.qblade.org/src/user/turbine/substructure.html#nonlinear-spring-and-damper-constraints
Best regards,
David
Hi David,
I am not sure I understand correctly. This is what I did:
NLSPRINGDAMPERS
ElemID Type Coefficient & Displacement/Velocity Sets (for NL springs, dampers)
100 spring 1.000 4E+12.0
SUBCONSTRAINTS
ID JntID Jnt2ID TrP Fixed Spring DoF_tX DoF_tY DoF_tZ DoF_rX DoF_rY DoF_rZ
1 1 0 1 0 1 1 1 1 1 1 0
100 1 0 1 0 100 1 1 1 1 1 0
I get
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Hi,
if you want to assign a rigid constraint in the SUBCONSTRAINTS table, between a joint and the TP, you should set column 6 to zero, since you dont want to use a spring stiffness, but define a rigid constraint. In this case your DOFs 1-5 would be rigidly constrained between JNT1 and the TP.
Now to assign the spring to DOF 6 you should set column 6 to 100 (which is your spring ID) but then assign this spring only to DOF 6, so your SUBCONSTRAINTS would look like this:
SUBCONSTRAINTS CstID JntID JntCon TpCon GrdCon Spring DoF_X DoF_Y DoF_Z DoF_rX DoF_rY DoF_rZ 1 1 0 1 0 0 1 1 1 1 1 0 2 1 0 1 0 100 0 0 0 0 0 1
Best regards,
David
Quote from David on 10. June 2026, 13:36Hi,
if you want to assign a rigid constraint in the SUBCONSTRAINTS table, between a joint and the TP, you should set column 6 to zero, since you dont want to use a spring stiffness, but define a rigid constraint. In this case your DOFs 1-5 would be rigidly constrained between JNT1 and the TP.
Now to assign the spring to DOF 6 you should set column 6 to 100 (which is your spring ID) but then assign this spring only to DOF 6, so your SUBCONSTRAINTS would look like this:
SUBCONSTRAINTS CstID JntID JntCon TpCon GrdCon Spring DoF_X DoF_Y DoF_Z DoF_rX DoF_rY DoF_rZ 1 1 0 1 0 0 1 1 1 1 1 0 2 1 0 1 0 100 0 0 0 0 0 1Best regards,
David
Hi David,
Thanks very much. To test the spring works as expected, I increased the defined stiffness to a vey high value to see if it will behave as though it were rigid (100 spring 1.000 4E+40.0), but I still get rotations, any insight?
Regards,
Salem
Hi,
your numeric stiffness values are not recognized as a valid number string:
For example, 4E+40.0 cannot be read correctly. Use 4E+40 instead, since the exponent must be an integer and cannot contain a decimal point.
BR,
David
Hi David,
Sorry, I just seem not to get it to work, it keeps moving in DoFs I want constraint. Say I want the transition piece connection to be fixed in all DoFs apart from DoF_rZ, I tried the following:
10 spring 1.000 141968844.0
SUBCONSTRAINTS
ID JntID Jnt2ID TrP Fixed Spring DoF_tX DoF_tY DoF_tZ DoF_rX DoF_rY DoF_rZ
1 1 0 1 1 10 0 0 0 0 0 1
I just need what this TrP joint should be defined as to achieve this.
Hello again,
as mentioned before, consider the following example:
SUBCONSTRAINTS CstID JntID JntCon TpCon GrdCon Spring DoF_X DoF_Y DoF_Z DoF_rX DoF_rY DoF_rZ 1 1 0 1 0 0 1 1 1 1 1 0 2 1 0 1 0 100 0 0 0 0 0 1
Here, CstID = 1 rigidly constrains the DOFs DoF_X, DoF_Y, DoF_Z, DoF_rX, and DoF_rY between JntID = 1 and the TP.
CstID = 2 then creates a rotational spring between JntID = 1 and the TP along DoF_rZ.
As a result, all DOFs between JntID = 1 and the TP are rigidly constrained, except for DoF_rZ, where the rotational spring introduces compliance.
Also, make sure that you correctly define the table for the springs, see this template:
NLSPRINGDAMPERS ElemID Type Coefficient & Displacement/Velocity Sets (for NL springs, dampers) 1 spring 1.000 1.160E+06 2.000 2.21E+06
Best,
David
