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Old 12-23-2006, 02:01 AM   #26
Erick Mead
 
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Re: human structure model discussion

Quote:
David Knowlton wrote:
Heaven's man! Imagine your favorite dog as a child with a chain drooping from his shoulder. Got it? The poor thing would fall over and look at you with baleful eyes - pleading that you would give a more sensible model a chance! Do it for Rover Erick!
A chain of solid spheres having no bending resistance and no cohesion will bear compressive load without buckling if it maintains the funicular (hanging cable) curve for that load. This was Coulomb's proof of the function of the catenary shape.

Under self-weight it is an inverted catenary. Externally the funicular load may appear very different for different loads, but internally it is always the same. If the funicular shape is attained, the load path runs in the precise center of the load member. An intriguing observation for Aikido.

If it runs outside the center, relative bending stress develops -- tension on one side of the limb and compression on the other. If it moves outside the limb in the right way then the side of the limb that is in tension to generate load resistance, comes into compression, and the attacker's push cancels itself out. The limb develops an unopposed rotational moment and tends to rotate and buckle. This is how kokyu tanden ho functions mechanically.
Quote:
David Knowlton wrote:
See a bigger picture than the bones - look at the tensegrity icosahedron and imagine it strung with rubber bands. If I link several of them - then deform them in a spiral movement - then let go - they spring back. I have just extended my (tensegrity) arm in the rowing exercise. ... Your chain hangs limply from my shoulder. Limp is bad Erick, in more ways than one.
Then we do it differently. Flexible motion propagates internal rotations freely, and concentrates (or dissipates) energy with greater efficiency than rigid rotation or translation. I rotate my hips forward which propagates up my spine, through my shoulders and down to my hands throwing them out. No arm muscle involved, They rise without me lifting them without any arm muscle. As a counterexample -- try suriage in a rigid mode. It won't work, or you will overshoot -- you do not generate nearly enough deflection potential in the blade velocity by rigid rotation.

I can accept tensegrity joints hypothetically or not (since you have a few holes to fill), and it does not affect the dynamic structural model I propose. You yourself have illustrated that tensegrity icosahedra are fair approximations of solid spheres. If I understand the premise and the models, then the limbs/ligament assemblies are just stretched icosahedra, and you posit the joints as proper icosahedra. I can even accept, if demonstrated, that tensegrity manipulation may allow for adaptive adjustment of the structure's shaee under load. But it answers none of the other salient points.

Falling chains, whipping and compressive chains are premised on relaxed (i.e. -- not in tension from external load) structure (which tensegrity is NOT), disproportionate manipulation of dynamic energy (which tensegrity does not obviously do), and supercritical responses under load (which tensegrity also does not) (and therefore making reaction or point of load response diffcult to predict and anticipate).

Merely standing quietly is FAR more dynamic, active, chaotic and counterintuitive than your static tensegrity model would suggest.

http://www.pubmedcentral.nih.gov/art...?artid=1456055

The leg muscles and ligaments operate in reverse of the direction of the static model "tension spring" model would have to if they directly provided an uprighting force, which I understand your tensegrity model would also do.

http://www.pubmedcentral.nih.gov/art...?artid=1664994

And having seen the models, actual anatomy is missing a significant class of structural necessity in the model - the little compressive members (bones?) forming the three coordinate planes of the icosahedra around all of the joints ...

Last edited by Erick Mead : 12-23-2006 at 02:13 AM.

Cordially,

Erick Mead
一隻狗可久里馬房但他也不是馬的.
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Old 12-23-2006, 09:07 AM   #27
billybob
 
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Re: human structure model discussion

Erick,

I appreciate the way you answered all relevant points, and were willing to see at least some potential in the tensegrity model. I may not cover all points in my response, but I trust you will bring them back up if they continue to be at issue.

The big 'IF'. Coulomb's spheres are proven mathematically and beyond my skill to dispute, if even understand. But:
Quote:
A chain of solid spheres having no bending resistance and no cohesion will bear compressive load without buckling if it maintains the funicular (hanging cable) curve for that load. This was Coulomb's proof of the function of the catenary shape.
Keeping spheres lined up is pretty darn tricky. It's a big IF.

I would submit that mast rigging and radio towers do not display tensegrity. B. Fuller uses an analogy: Two people dive from opposite ends of a pool, they meet in the middle, turn and push off of one another, and head in opposite directions. No 'ground' is required for tensegrity. He goes on to liken it to 'a balloon':

"The balloon is indeed not only full of holes, but it is in fact utterly discontinuous. It is a net and not a bag. In fact, it is a spherical galaxy of critically neighboring energy events."

"In the geodesic tensegrity sphere, each of the entirely independent, compressional chord struts represents two oppositely directioned and force-paired molecules. The tensegrity compressional chords do not touch one another. They operate independently, trying to escape outwardly from the sphere, but are held in by the spherical-tensional integrity's closed network system of great-circle connectors"

Erick:
Quote:
Flexible motion propagates internal rotations freely, and concentrates (or dissipates) energy with greater efficiency than rigid rotation or translation. I rotate my hips forward which propagates up my spine, through my shoulders and down to my hands throwing them out.
The propagation of energy from turning your hip does NOT propagate up your spine. It propagates through your framework as a coordinated whole. Your spine would experience displacement to the side and blow apart if you tried using it like a rigid member.

Source for Bucky quotes:
(http://www.angelfire.com/mt/marksomers/134c.html)

I liked the reference to 'motion' being necessary to stay standing in a human. My physical therapist said "If you want stability - you'd better be mobile." I had NO idea what the man was talking about. I've disagreed with him before. I like to form my own ideas - to a fault.

Here is a picture of triangles in the human body: http://www.thebodyworker.com/neckmusclesdeep.gif

Going forward, I'll keep reading about statics, and running your ideas past my best friend the engineer and former aikido instructor. He's Real patient about explaining stuff to me.

Dave
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Old 12-23-2006, 01:36 PM   #28
Erick Mead
 
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Re: human structure model discussion

Quote:
David Knowlton wrote:
The big 'IF'. Coulomb's spheres are proven mathematically and beyond my skill to dispute, if even understand. But:
Keeping spheres lined up is pretty darn tricky. It's a big IF.
So is kokyu. That's what makes it so powerful, it can both supprt structure and collapse it without warning. If the connection is sound, and the energy of the attack is accepted, the attacker has borne part of his center into the attack, and therefore the combined structure, and his center must also goes with the collapse of that structure. That's how the unliftable body works. The trick is to maintain that structure in this supercritical (top of the hill) mode until the critical moment when he has committed to a place where there is no place to go but the downhill slide.
Quote:
David Knowlton wrote:
I would submit that mast rigging and radio towers do not display tensegrity. .... No 'ground' is required for tensegrity. He goes on to liken it to 'a balloon':
They don't need ground. I can guy a mast off the ceiling as easily as the ground.
Quote:
David Knowlton wrote:
The propagation of energy from turning your hip does NOT propagate up your spine. It propagates through your framework as a coordinated whole. Your spine would experience displacement to the side and blow apart if you tried using it like a rigid member.
It is not a sideways turn of the hips. It is the rotation of the hips forward in the sagittal plane and then the stop that causes the top-torso to flex forward also, cascading little internal rotations of the vertebral connections delivering a pulse of that internal rotation down the arms, rotating the limbs at progressively smaller radii and with greater effective moment as a result, and up they come.

The spine can transmit both a relatively rigid rotation of the whole under low impulse, and a wave of small internal rotations up or down the chain of vertebrae for larger impulses. In torsion, for the sideways trunk rotation you speak of, the whole torso acts as stressed skin tube.

There, your balloon image actually works. Breathing in makes the structure stronger in torsion by expanding the inertial radius, and statically pretensioning the intercostal ligaments and abdomen fabric, so that it can absorb compression loads in bending or torsional buckling without opposing muscular tension.

Cordially,

Erick Mead
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Old 12-23-2006, 03:17 PM   #29
billybob
 
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Re: human structure model discussion

Reference diagram: http://www.ancient-egypt.de/assets/images/image0041.jpg

You can see that the person represented here has a line drawn down the middle. The spine is Behind that line. What supports the weight of the human? The space in the middle of the 'tube'. Note where Fuller speaks of the 'discontinuity' of the tensegrity structure...'the compression members do not touch'. Compression members are the 'sticks' in the icosahedron model.

Ref: this photo: http://www.uni-kassel.de/fb14/stahlb...ity/tense3.gif

Now, ref this diagram: http://www.bartelby.net/107/Images/small/image409.jpg

Tensegrity structures are like balloons - tension and compression are in balance. They can be represented as spheres, icosahedra, tubes, ad infinitum. They have the advantages of your rigged mast, without needing to be tied down on one side. The structure is independent and whole by itself.

Note this: http://www.fibersource.com/Textile_A...egrity%201.jpg

I'm belaboring this point so you can see that the main 'line' of load bearing power in a tensegrity structure may be Empty Space! It is counterintuitive, and I think it is also not how we are ennervated. In balance we feel very little - off balance and we get alarm bells.

Culturally, we like our work ethic! Fie on a kokyu that feels natural! Calisthenics in football and the Navy - were supposed to hurt. Ouch.

You ask
Quote:
And having seen the models, actual anatomy is missing a significant class of structural necessity in the model - the little compressive members (bones?) forming the three coordinate planes of the icosahedra around all of the joints ...
It's a model. The necessity for finding what was doing the work of supporting the human may have come from the observation of the first diagram I mention - the spine is Behind the central line of a human. What holds us up?

David
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Old 12-23-2006, 05:14 PM   #30
billybob
 
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Re: human structure model discussion

To help in looking at this diagram: http://www.bartelby.net/107/Images/small/image409.jpg

I should mention something. Before plywood was invented, wood frame homes had boards nailed Diagonally, at the corners, to keep the box structure from folding up, like parallelograms do without being made of thick materials to take those forces. With plywood, a light frame structure can be used and then 'sheathed' with plywood. I built a lightweight, but large shed in my yard this way - I only had to sheath the outside of the structure.

So, when you look at this: http://www.bartelby.net/107/Images/small/image409.jpg - see the triangles Contained in the plane of the muscle wrapping. The triangle is Inherent in the plane of the plywood. This isn't 'cheating' on using tensegrity to descrbe the human body, because I'm talking about lines of force, not necessarily about finding tension lines and 'little bone' structures that match one to one with the models we use.

The human body is complex, but seems to be based on some simple structures (echoing an early post in the thread). Pulling these out and thinking in three dimensions is tough for us.

dave
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