Hello Pavel
According to your suggestion, I defined the motion in the entire spine with FDK;
AnyKinEqSimpleDriver FDK_Measure = {
…
…
AnyKinLinear L4L5Trans = {
AnyRefNode &L5Node = …HumanModel.BodyModel.Trunk.SegmentsLumbar.L5Seg.L4L5JntNode;
AnyRefNode &L4Node = …HumanModel.BodyModel.Trunk.SegmentsLumbar.L4Seg.L4L5JntNode;
};
AnyKinRotational L4L5Rot = {
Type = RotAxesAngles;
Axis1 = x;
Axis2 = y;
Axis3 = z;
AnyRefNode &L5Node = …HumanModel.BodyModel.Trunk.SegmentsLumbar.L5Seg.L4L5JntNode;
AnyRefNode &L4Node = …HumanModel.BodyModel.Trunk.SegmentsLumbar.L4Seg.L4L5JntNode;
…
…
DriverPos = {0,…}
DriverVel = {0,…}
Reaction.Type ={ Off,Off,On,On,On,Off….}
CType = {ForceDep, ForceDep, Hard, Hard, Hard, ForceDep…}
Between all vertebral bodies is rotational and translational stiffness (Also between L5-Sacrum). Rotation in the lumbar spine is non-linear (according your file), all other stiffness is linear. FDK is considered in 2D; compression and shear (Posterior-Anterior) forces and extension/flexion moment.
In this model the deformation is still unrealistic (too few boundary conditions; only posture Driver T12-Pelvis for motion), thus spine rhythm for rotation in the lumbar and the thoracic spine was reinserted. For translation still FDK. The SacrumPelvis joint in the lumbar spine rhythm was taken out (these dof’s are driven by the SacrumPelvisDriver). In this model I use also the linear stiffness of the IVD’s for the lumbar spine, because the non-linear stiffness combined with the spine rhythm is resulting in too high muscle activity (Psoas, Rectus abdominus, Erector spinae). And this is leading to high compression and shear forces.
To summarize
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The current model possess linear stiffness for rotation and translation between all VB’s (with the values form the literature; Markolf K.L. (1970), PANJAB M.M. (1976), Heuer et al. (2007), Bisschop A. (2011)). The rotational motion is defined with two spine rhythms for the lumbar and thoracic spine. The Translational motion is defined with FDK in the entire spine. I also inserted the lumbar ligaments to gain more stiffness.
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The Buckle is attached on T12.
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Rectus abdominus is attached on T12. When RA is attached on T11 or further above, then psoas major is very active because in this case this muscle has to create the bending of the lumbar section.
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I use the polynomial (3) solver, because this solver has a lower muscle activity (envelope) as the AuxMinMax solver. The motion is a flexion of 30 degree between pelvis and T12 (posture Driver). The motion between T1 and T12 is zero (T12T1 Driver).
What do you think about this model, could anything cause problems in this condition?
I also implemented the thoracic ligaments, but they are not active at the moment, this is only for future proposes when information about the properties is available. Anyway, I saw that the reference (li) in the lumbar ligament definition is not correct for L3L4Ligaments.any und in L4L5Ligaments.any, what is the reason therefor?
I send you my current model and the first results in a separate e-mail.
Thank you for your answer
Regards, Gregor