Finite element-rod elements what is the pde

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Discussion Overview

The discussion revolves around the application of finite element analysis (FEA) to structures using rod elements, specifically focusing on identifying the partial differential equations (PDEs) that govern such systems. The scope includes theoretical aspects of FEA, mathematical reasoning, and the derivation of governing equations from physical principles.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • Some participants note that the PDE depends on the specific problem being analyzed, indicating variability based on the structure involved.
  • One participant provides an example involving three rods with different cross-sectional areas and lengths, seeking the PDE that would lead to the stiffness matrix and displacements when solved using FEA.
  • Another participant suggests that Hooke's Law can provide the governing equation for a simple 1D rod, leading to finite element equations.
  • It is mentioned that finite element equations can be interpreted through Galerkin's method, which may allow for deriving the PDE using integration techniques.
  • One participant states that in structural analysis using FEM, the differential equation is often related to the equation of virtual work or can be derived from potential energy considerations.

Areas of Agreement / Disagreement

Participants express differing views on the specific form of the PDEs applicable to various structures, indicating that multiple competing perspectives exist regarding the governing equations in finite element analysis.

Contextual Notes

The discussion highlights the dependence of the PDE on the specific characteristics of the structures being analyzed, as well as the potential for different approaches to derive these equations, which may not be universally applicable.

chandran
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case 1)in finite element analysis of structures using simple rod elements we do the stiffness matrix and then find the displacements from loads and constraints


case 2)finite element method is a technique for solving partial differential equations. In the case1 what is the partial differential equation and what it looks like?
 
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?? The partial differential equation depends on exactly what the problem is. There are many different "structures" that will give different differential equations.
 
i have an example. There are three rods of different cross sectional areas
A1,A2,A3. with lengths L1,L2,L3 connected in series. What will be the pde
which when tried to solve by fem will give the stiffness matrix and force,displacements
 
For your simple 1D rod example, the simple relationship for Hooke's Law will provide the governing equation you require.

Stress = E* strain (from d(stress)/dx = 0)

You can then build the finite element equations from that point. Reference to any reasonably simple FEM textbook will assist you to solve those fundamentals.
 
If you've your FE equations, you can interpret FE as an application of Galerkin's method and work your way backward to the PDE with a suitable application of Gauss' theorem, integration by parts etc. Kind of like deriving BEM.
 
In most cases of structural analysis FEM, the differential equation is the equation of virtual work. Or, you can apply an energetic approach and derive potential energy equations.
 

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