How to Modelize Column Buckling with Coupled Differential Equations?

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Discussion Overview

The discussion revolves around modeling the buckling of a column using a system of coupled differential equations. Participants explore the challenges associated with variable coefficients and non-linear terms, as well as potential methods for solving the equations both analytically and numerically.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents a system of coupled differential equations for modeling column buckling, noting that the coefficients are not constants.
  • Another participant points out that the presence of the term \(\theta \theta'\) makes the equations non-linear, complicating the use of matrix methods.
  • A suggestion is made to consider the Peano-Baker method for solving linear differential equations, although its applicability is questioned due to the non-linearity.
  • Participants discuss the nature of \(\theta\), with one confirming it is a known function representing a small slope angle.
  • One participant advocates for solving the equations numerically first, arguing that numerical methods are valid for real-world applications, while another insists on the necessity of finding an analytical solution first.
  • A later reply proposes that if \(\theta(x)\) is known, the system may not be non-linear, suggesting a reformulation of the equations for numerical solutions.

Areas of Agreement / Disagreement

Participants express differing views on whether to pursue numerical or analytical solutions first, and there is no consensus on the classification of the system as linear or non-linear based on the known function \(\theta\).

Contextual Notes

Participants note the complexity introduced by variable coefficients and non-linear terms, which may affect the choice of solution methods. The discussion includes uncertainty regarding the nature of the function \(\theta\) and its implications for the equations.

tdcaupv
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Hi,
I have to modelize the buckling of a column and I've come up with this system:
[tex]N'(x) + N(x) \theta ' (x) \theta (x) - Q \theta ' (x) + f = 0[/tex]
[tex]Q'(x) + N(x) \theta ' (x) + Q \theta ' (x) \theta (x) = 0[/tex]

with f a constant

The coefficients (thetas) are not constants.
I've written it as X' = A X + f But I don't know how to diagonalize A since coefficients are not constants.

Thank You for helping me.
 
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Actually, it's worse than that. Not only are the coefficients variable, but the second equation includes [itex]\theta \theta'[/itex] so the equations are non-linear and matrix methods cannot be used at all.
 
edit
 
θ is a known function right?
 
Yes.
 
How complicated is θ?
 
Well, i don't know, I am a bit lost.
Actually, theta is my slope angle which is very small.
 
May I ask why you just don't solve it numerically? I mean really, he didn't say nothing about analytic solution else I'd keep my mouth shut. You know, numerical methods are perfectly fine for the real-world.

So if I may be the practical voice in here: work it first numerically even if you need an analytic solution just to get a handle on it, then do it analytically if you have to.
 
  • #10
First I need to solve it analytically. Maybe equations are not good. Maybe I should get simplier equations, i don't know ...
 
  • #11
No you don't even if you have to solve it analytically. You know if you're going to drive your truck in the dark without lights, it's a good idea to first walk the path with a flash light to see if there are any holes and stuf.

I'm tellin' you the right way to approach this: solve it first numerically even if you have to just dream-up initial conditions. Get a handle on it, then attempt to solve it analytically.

Also, I do not believe this is a non-linear system if [itex]\theta(x)[/itex] is known. You effectively have:

[tex]\frac{dN}{dx}=-Ngh+Qh-f[/tex]

[tex]\frac{dQ}{dx}=-Nh+Qhg[/tex]

where g=g(x) and h=h(x) are known functions. Well there you go: I'm dreamin' up g and h, N(0) and Q(0) too, bingo-bango: Numeric solution in hand.
 
Last edited:

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