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Mechanical torsors

XDN
Garnet
Garnet

Mechanical torsors

Hi

I want to solve a mechanical torsors problem, but I don't know how to go about it with Mathcad

I have a circular platform. on this platforme i have 3 point B1,B2,B3

on each point i have a forces, respectively F1,F2,F3. About it i know directional vector for each forces.

My platform have a spherical joint in this center (point C).

And i have a torsor which define exterior mechanical load applied on platform at C point.

 

1°/ i write mechanical component:

Capture d’écran 2021-04-01 171405.png

obviously expressed respectively at each point

 

 Now, i want to solve it find FB1,FB2,FB3,X,Y,Z

 

 

For this, i want to make a torsors transportation on C point!Capture d’écran 2021-04-01 171743.png

 

And now! i am stuck😥

 

I make a light mc file for add to this post

 

15 REPLIES 15

Re: Mechanical torsors

And after all torsors transportation, i want to solve the system like this example:

Resultant theorem:
/ X : -0,9911.FB1 -0,9911.FB2 -0,9911.FB3 +XO = 0
/ Y : 0,1152.FB2 -0,1152.FB3 +YO = 0
/ Z : -0,1330.FB1 +0,0665.FB2 +0,0665.FB3 +ZO -12000 = 0
resultant moment theorem :
/ X : 0,0669.FB2 -0,0003.FB3 -1115 = 0
/ Y : 188,3112.FB1 -94,1556.FB2 -94,1556.FB3 +66000 = 0
/ Z : 164,0736.FB2 -163,0825.FB3 = 0

 

 

and finally:

FB1 = 16463,46
FB2 = 16763
FB3 = 16864,87
XO = 49646,1
YO = 11,74
ZO = 11953,37

 

 

I can to solve it with pen and paper, but i can't do it with mathcad

I can see that there is a problem with symbolic evaluations

😥

 

Tags (1)

Re: Mechanical torsors

LucMeekes_0-1617292601229.png

 

My answers are different from yours. I may have made an error somewhere...

Anyway, you should be able to do this in Prime.

 

Success!
Luc

 

Re: Mechanical torsors

great! for different value,

it comes from me because the values of the points have changed slightly

Re: Mechanical torsors

It is possible to keep the formalism of mechanical load, because it's clearer for mechanical readers

Re: Mechanical torsors

I rewrite first matrix, in second equation , with correct values

Capture d’écran 2021-04-01 225904.png

 Capture d’écran 2021-04-01 225920.png

 

 

Capture d’écran 2021-04-01 225509.png

 

But i see a problem in first line

if i solve that

Capture d’écran 2021-04-01 225659.png

 the calculation does not converge ...😓

Re: Mechanical torsors

Please attach your worksheet.

 

Success!
Luc

Re: Mechanical torsors

it's strange

if i rewrite the vector value: i modify the red point value

Capture d’écran 2021-04-01 234623.png

 

 

The matrix is now:

Capture d’écran 2021-04-01 234729.png

 

 

And the calculation is done

Capture d’écran 2021-04-01 234819.png

 

Re: Mechanical torsors

 I don't see a compelling reason for these programs of yours. You can just write:

LucMeekes_0-1617314249380.png

and

LucMeekes_1-1617314260616.png

to get the two matrices.

 

Success!
Luc

 

Re: Mechanical torsors

see attached file

 

it's strange, i copy paste in new sheet.

If i switch this matrix

Capture d’écran 2021-04-01 235709.png

 

The calculus run but it's wrong

if i use the matrix as in picture, the calculus is good

if i switch , it's wrong

 

Re: Mechanical torsors

 
Tags (1)

Re: Mechanical torsors

For the upper left matrix, the determinant is 0, it means the matrix is singular, or in other words, it cannot be inverted.

 That means that lsolve cannot find a solution.

For the lower left matrix that's not the sae, and lsolve can find a solution.

 

Success!
Luc

Re: Mechanical torsors

Maybe this helps..?

LucMeekes_0-1617351969379.png

 

Success!
Luc

Re: Mechanical torsors

in fact from a mechanical point of view, this means that the forces go towards infinity in the singular geometric position ?🙄
 
in your new calculation, if i use initial geometrical configuration the result are:
Capture d’écran 2021-04-02 110711.png
obviously this is absurd
 
If i slip a bit the geometrical value, the result are conform to your screenshot in you precedent post.
these values seem correct to me.
For mechanical design, these values do not need to be very precise
 
Perhaps it is possible to evaluate the geometrical parameter just before singularity 🤔
I don't know how to do that
 
in any case thank you very much for your very precious help🙂
and I understand better your first approach
 
 

Re: Mechanical torsors

however there are other things that don't work

If i move the Bpoints the geometrical value was changed.

The calculation run

but key result are curious ?

If i calculate this manually, i find approximately:

FB1 = -202569,41
FB2 = -194324,39
FB3 = -194325,75
XO = 584902,22
YO = 0,16
ZO = 13455,71

 

and the worksheet give

Capture d’écran 2021-04-02 113628.png

 

see attached full worksheet (sorry it is written in french)

 

Re: Mechanical torsors

I have only a vague idea of what your calculations are about.

My responses have been from a(n almost pure) mathematical viewpoint, and knowledge of Mathcad/Prime,

just trying to streamline your calculations and potentially reducing the amount of typing (which is a general source of error).

 

Success!

Luc

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