Introducing Inertia with Rigid Groups in Altair RADIOSS Posted November 30, 2016 · Report reply Hi, I tried giving the additional mass and inertia to the global rigid body. However, during the RIGID BODY INITIALIZATION of the global rigid body (in _0000.out), the added mass and inertia are ignored and only the slave node mass is considered. Is there any workaround where I can add mass and inertia externally? Also, I am facing another problem with global rigid body: The model is initially off the ground, so the global rigid body is activated. Once it reaches the ground after free fall phase, the global rigid body is turned off and the computation is carried out as expected (with a lower time step and all elements active) for 30 ms. Beyond that, the error (which is -5% at this point) starts increasing and reaches +99% at which point the dynamics become nonphysical. i.e. the kinetic energy of the system increases to 10,000 J even though the initial total energy of the system is 460 J. Is there any reason for this sort of instability?