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6DOF F = m a ?

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Old   April 8, 2022, 07:43
Unhappy 6DOF F = m a ?
Will Crawford-Jones
Join Date: Jan 2021
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I'm testing a DFBI contact model in Star-CCM+ and have noticed that if I apply a constant force of 1N to a 1kg mass via a field function and observe the acceleration using a report, I found the acceleration during the first time step is = 0.5 (you'd expect it to be =1). From the 2nd timestep onwards it becomes = to 1, as would be expected. Firstly, what is causing this? I noticed that in the manual it says "For time integration, the 6-DOF solver employs a trapezoidal scheme of second order accuracy", is this the reason? Although, I noticed under Theory > 6-DOF Rigid Body Motion > Equations of Free Motion it gives f = m .dv/dt.

Secondly, is it possible to 'switch' this off, such that a 6DOF body simply moves with f / m = a ?

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