Just a typo: Of course it should be:
The model may work in some cases even without the T12L1JntReac if this part
is NOT loaded in particular.
From: anyscript@yahoogroups.com [mailto:anyscript@yahoogroups.com] On Behalf
Of Sebastian Dendorfer
Sent: 10. oktober 2008 16:01
To: anyscript@yahoogroups.com
Subject: RE: [AnyScript] AnyReacForce
Hello Thomas,
From a kinetics point of view, the spherical joint provides three reaction:
Forces in X,Y and Z direction, whereas the three rotations are kept “open”.
With the line AnyReacForce T12L1JntReac={AnySphericalJoint &ref=.T12L1Jnt;};
full support is applied to the joint. This means also the rotational degrees
of freedom are supported with infinite strength - three moments are applied
to the rotational degrees of freedom to carry whatever the joint has to
carry.
These rotational degrees of freedom are the kinematic measure I mentioned in
my previous mail. Joints in AnyBody can be understood as kinematic measures
equipped with drivers. For instance, a spherical joint is a
distance between two points on two different segments that is driven to be
zero. So three translational measures are zero, and three rotational
measures have to be specified elsewhere.
The model may work in some cases even without the T12L1JntReac if this part
is loaded in particular. But generally speaking you are right. If the thorax
had all the muscles integrated than the AnyReacforce would not be needed
here.
The moments around the spherical joint would than be balanced by the muscle
forces, the thorax joints itself, as spherical joints cannot carry moments.
I hope this makes things a bit clearer, otherwise please ask again.
Sebastian
From: anyscript@yahoogrou <mailto:anyscript%40yahoogroups.com> ps.com
[mailto:anyscript@yahoogrou <mailto:anyscript%40yahoogroups.com> ps.com] On
Behalf
Of Zander, Thomas
Sent: 10. oktober 2008 15:00
To: anyscript@yahoogrou <mailto:anyscript%40yahoogroups.com> ps.com
Subject: Re: [AnyScript] AnyReacForce
Hello John and Sebastian,
thanks for your answers. Step by step i understand more of the model, but i
have still a more basical question: What does the command
AnyReacForce T12L1JntReac={AnySphericalJoint &ref=.T12L1Jnt;};
cause? The command consists of nothing else than that single line, it refers
to a joint that is defined few lines above, and the joint already generates
forces itself, so what does AnyReacForce do additionally to what the
spherical joint does?
Sebastian, you wrote, “AnyReacForce basically provides all forces and
moments
that are necessary”. Necessary to do what? What or where is the measure, you
mentioned?
When a model works without T12L1JntReac and SacrumPelvisReaction why are the
results different with and without these AnyReacForces (the rotations of the
lumbar segments are the same but the muscle forces are different)?
John, when i understood you correctly, you wrote, that if the thorax had
muscles integrated, the reaction force (moment) would not be necessary. But
how can the thorax transfer moments when the disc can be represented by
spherical joints?
Thank you for your helpfulness,
regards, Thomas
John wrote:
> Just as a follow-up to Sebastian’s message: The reason why the muscles
> do not adequately balance the T12L1 joint is that the thorax part of the
> spine is not modeled. So the muscles that would normally be present in
> the thorax section are not included in our model and therefore the joint
> adjacent to the thoracic section cannot be balanced without the
> additional reaction force.
>
Sebastian wrote:
>
> The AnyReacForce basically provides all forces and moments that are
> necessary. The AnyRecForce behaves just like normal forces in AnyBody
> and takes the form of the kinematic measure, so a linear measure results
in
> a force and a rotational measure results in a moment.
>
> Applying the AnyReacForce to a Spherical Joint will therefore result in
> moments to carry the rotational degrees of freedom.
>
> In your mentioned cases this is necessary because there are no muscles
> that can support the Sacrum/Pelvis connection, so the AnyReacForce has to
> provide the forces. In the T12L1 joint the reaction force is also in some
> cases necessary, in others it may work without. It appears in some
> applications that the muscles are simply not enough to balance the system.
>
Thomas wrote:
>
> the standing model contains 7 lumbar joints for 8 segments (T12, L1,
> L2, L3, L4, L5, Sacrum, and Pelvis) coupled by the spine rythm, but
> only two of them (the outermost, i.e. T12L1 and SacrumPelvis) have an
> additional reference (T12L1JntReac and SacrumPelvisReaction) which is
> used by AnyReacForce.
>
> Although i read the manual for AnyReacForce i don’t understand its
> meaning. It is clear to me that the spherical joints generate forces
> to accomplish the constraints, but AnyReacForce generates moments
> (according to AnyMechOutputFileForceExport). Commenting these two
> AnyReacForce folders out changes the results of the analysis.
>
> Can SomeOne please explain to me, what AnyReacForce in the present
> combination with the reference to a spherical joint does and what it
> physically represents?
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