High Oscillations in 6DOF Aircraft Dynamic Simulation

Question

George 2023-7-6

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https://ww2.mathworks.cn/matlabcentral/answers/1992713-high-oscillations-in-6dof-aircraft-dynamic-simulation

回答： Corey Slick 2023-7-14

Output.jpg

I am using Simulink to model 6DOF Aircraft Dynamics, and I have confirmed that the dynamics, attitude and environment work correctly by plotting an orbit with no aerodynamic forces and moments. When I introduce the aerodynamic force and moment calculations that come from this source: https://ntrs.nasa.gov/api/citations/20040110310/downloads/20040110310.pdf I start to get incredibly fast oscillations in my states as shown in the image.

I have modelled the F-16 aerodynamics a couple of times and yield the same coefficients, so I am not certain what the cause of this oscillation is.

The integration method used is ode4 with fixed timestep of 0.01.

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John D'Errico 2023-7-6

So, you changed the problem, by adding extra forcing terms, and suddenly, things go to hell? The probem is now probably stiff, and you will need either a solver that can handle a stiff system, or a significantly shorter time step. That presumes you implemented those foring terms correctly.

What solver you should be using, I have no clue, since I'm not a Simulink user. But I would start looking there, at least after you carefully verify how those terms were put into the model.

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Answer 1

Corey Slick 2023-7-14

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We had a similar problem recently and realized that the order of our damping terms did not match the order of the output angular velocity terms from the 6DoF block.