Solve block for 3-D moments

[ptc-1700862]

I am trying to solve a linear set of equations.

I have the following criteria

sum of forces = 0
sum of moments about a point=0
sum of moments about another point = 0
etc.

By equating all of these, the reaction force at each point can be created.

I have tried to solve this quickly using a solve-block, but it won't converge to the same value and often has an error that is not equal to zero.

Also, it is not possible to get the solve block to work when I set up the solver to be linear.

Anybody know of a solution?

[ptc-1368288]

You first have to make sure there is a common solution instead of random solutions. You may have to constrain more than just equate to 0. If you wish, you may "save as" 11 or lower for a much larger audience and just in case some version solves . Reading your description, your attempt looks underspecified for the solver.

jmG

[ValeryOchkov]

On 7/3/2009 8:55:09 AM, ViestursSondors wrote:
>I am trying to solve a linear
>set of equations.
>
>I have the following criteria
>
>sum of forces = 0
>sum of moments about a point=0
>sum of moments about another
>point = 0
>etc.
>
>By equating all of these, the
>reaction force at each point
>can be created.
>
>I have tried to solve this
>quickly using a solve-block,
>but it won't converge to the
>same value and often has an
>error that is not equal to
>zero.
>
>Also, it is not possible to
>get the solve block to work
>when I set up the solver to be
>linear.
>
>Anybody know of a solution?

May be the MAS-solution help you:
http://twt.mpei.ac.ru/MCS/Worksheets/SelBeam/BeamModEng.xmcd

Val
http://twt.mpei.ac.ru/ochkov/v_ochkov.htm

[TomGutman]

You have both too many and too few equations. Your equations are not linearly independent. Torques can be balanced around any point, if they balance around one point they balance around all. Thus you have redundant equations (causing the failure of the linear algorithm) and not enough independent constraints to define a unique solution.
__________________
� � � � Tom Gutman

[RichardJ]

In addition to Tom's comments, the lhs of your equations produce a 3 element vector. Even if all the elements in that vector are 0, the vector is not equal to 0. Your rhs needs to be a 3 element vector of 0s.

Richard

[TomGutman]

Actually the equating of the vectors to zero is OK. While the equality predicate does not consider a scalar zero equal to a vector of zeros, as a constraint the equating of a vector to a scalar results in constraints equating each element of the vector to the scalar. = is an overloaded operator, and its use as a predicate is not quite the same as its use as a constraint.
__________________
� � � � Tom Gutman

[RichardJ]

An interesting observation. I'm not sure I like that behavior though. I would prefer consistency of behavior (in this case that means that a vector should never be taken to be equal to a scalar).

Richard

[ptc-1368288]

>I am trying to solve a linear set of equations.<<br> _____ you mean:

"a set of linear equations" ?

Past two chevron Mathcaders, if you save in version 8 (for instance), a much greater community will look at it, even collabs not versed in your stuff. Just a suggestion. Dressing a solver is sometimes quite an art, as it reads in this thread.

jmG