6 Replies Latest reply on Dec 4, 2014 7:04 PM by David Grigg

    URES result in Simulation

    David Grigg

      General question here about URES result in a simple Static Analysis.

      I'm not sure what the displacement results are based upon.

      Are the displacement results computed to some fraction of Yield Strength?

      For example, if I simply apply a force on the end of a simply supported beam, the resulting URES value is based upon what material condition?

       

      Sorry for the simple question, it just isn't obvious initially.

       

      Thanks

        • Re: URES result in Simulation
          Mike Pogue

          The results are based on Hook's law. As shown on the Wikipedia page, it relates a force vector to a stress displacement vector via a stiffness tensor for some differential unit of volume. This equation is discretized using Galerkins method into a linear system of equations which the computer can solve. The property most closely related to displacement is the Young's modulus, a measure of the stiffness of the material, with second order effects from Poisson's ratio. From these two properties, you can compute any elastic property for an orthotropic material.

           

          The math behind FEA is very, very complicated. You can conceptualize Hooke's law by it's most common, high school form: F = K*x, where F is the applied force, K is the spring constant (a function of the Young's modulus and the geometry), and x is the resultant displacement (Ures, the diagonal of the vector displacement). The solution is x = K*F^-1, which, in some sense, is the matrix equation that every FEA solver solves. This means that if you pull on a spring of stiffness K with a force F, you get a displacement x = K/F when it settles down.

          • Re: URES result in Simulation
            Jared Conway

            most common questions relative to ures

            1. what is it? sqrt (x^2+y^2+z^2)

            2. does it include displacement from strain only or also displacement from "moving". > both

            3. how is it calculated, as mike noted, F=kx

             

            i'm not sure what you mean about stiffness calculations and static matching frequency? the stiffness matrix is the same regardless of the type of analysis so yes, it should be the same, but displacements have no meaning in frequency.