I am simulating the deflectiopn of a beam with fixed supports at each end with a concentrated load at the middle. The beam dimensions are 200mm long, 10mm wide, 10mm high. The load is 100N. E=2.1e11 N/m^2. The Simulation result with default mesh is .003429mm. The theoretical deflection is .00296mm. +15.8% error. The deflection equation for a centrally loaded beam fixed at both ends is dy=(P*L^3)/(192*E*I).

Hi Jerry: using your equation, I calculate theoretical = 0.0238 mm and ran a Simulation (default, solid mesh) = 0.0244 mm, for a 2.5% difference (compared to theoretical). Can you describe the model setup? I used half a beam, fixed one end. I put a "roller" on the opposite end, and 50 N on that same end perpendicular to the beam axis.