On Tue, 30 Sep 2003 06:13:26 -0700, Pierce Nichols <[EMAIL PROTECTED]> wrote:
> Oh, I would, but for another reason. The 6DOF equations in >Simulink are written with the assumption that mass properties are constant. >That means I would have to, instead of modeling the torques, model the >changing level of propellant... and its sloshing. I might just be able to >get away with modeling it as a pendulum, but that will be pushing it.
Sloshing? Slosh will be a PITA to model, yes. And the purist will want to include it. But...
Where will the slosh come from? Isn't all of the acceleration along the vertical axis of the vehicle? Seems to me the only way you could get slosh is a) if an engine quit, b) if you get hit by a strong gust of wind (POGO will have a pretty high cross sectional density, so will not be greatly affected by wind), or c) if you're flying horizontally at speed and you suddenly pitch back to level. If a) happens, you won't care about slosh. To prevent b), don't fly in strong gusts. To prevent c), don't do that.
Yes?
No. Relatively small perturbations, including relatively slow pitch changes, could start a little bit of slosh going. If the slosh frequency is resonant with the lag in the control system, then it could quickly become a lot of slosh. Mostly what I need to confirm is that the control system won't reinforce sloshing at any propellant level, or that if it will, the range of propellant levels at which this can occur is relatively narrow, and will pass quickly in normal operation.
-p
"No science without fancy, no art without facts" - Vladimir Nabokov
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