- #1
Sean Powell
- 7
- 0
Hello,
This is not a homework problem, but an engineering office problem.
I’m looking to replace a steel compression spring with a gas cylinder. The spring is presently designed to absorb a known amount of kinetic energy which it ideally converts to potential energy (neglecting friction, yadda yadda) and compression is solvable by a simple formula. PE = ½*K*dL assuming the spring was fully relaxed to start.
When I impact a closed gas cylinder the force response is governed by PV=nRT and we can generally assume no major temperature changes during impact. That means force doubles at half stroke, quadruples at ¾ stroke, is 10 times at 90% stroke etc. I know enough to subtract ambient air pressure to get a correct baseline. My problem is the force is so low for the first half of the stroke and climbs so rapidly for the last 20% or so that I’m having a tough time predicting the response of stopping a rolling vehicle impact.
Ideally I need a formula for potential energy in a compressed gas cylinder if I know: Diameter, L1 (usually free length), P1 (usually atmospheric), L2 (new compressed length) and some basic assumptions like human breathable atmosphere not too far from sea level.
From here I think I can calculate peak force so I know how to design the ratchet mechanism so the car isn’t rebounded. Yes, I know I could probably do this better with a dampened spring but there are other design issues (and patents to get around).
Thanks in advance,
Sean
This is not a homework problem, but an engineering office problem.
I’m looking to replace a steel compression spring with a gas cylinder. The spring is presently designed to absorb a known amount of kinetic energy which it ideally converts to potential energy (neglecting friction, yadda yadda) and compression is solvable by a simple formula. PE = ½*K*dL assuming the spring was fully relaxed to start.
When I impact a closed gas cylinder the force response is governed by PV=nRT and we can generally assume no major temperature changes during impact. That means force doubles at half stroke, quadruples at ¾ stroke, is 10 times at 90% stroke etc. I know enough to subtract ambient air pressure to get a correct baseline. My problem is the force is so low for the first half of the stroke and climbs so rapidly for the last 20% or so that I’m having a tough time predicting the response of stopping a rolling vehicle impact.
Ideally I need a formula for potential energy in a compressed gas cylinder if I know: Diameter, L1 (usually free length), P1 (usually atmospheric), L2 (new compressed length) and some basic assumptions like human breathable atmosphere not too far from sea level.
From here I think I can calculate peak force so I know how to design the ratchet mechanism so the car isn’t rebounded. Yes, I know I could probably do this better with a dampened spring but there are other design issues (and patents to get around).
Thanks in advance,
Sean