226-Lect 11 - 1 W eek 11 1 Week 11 Mech226 The Energy...

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Unformatted text preview: 1 W eek 11 1 Week 11 Mech226 The Energy Approach See section 9.10 in M&R for detail on the Quinns Energy Method W eek 11 2 Story so far Our analysis until this week has been restricted to steady state conditions, (eg constant angular velocities) or to links with known velocities and accelerations. These simplification are appropriate and satisfactory in most cases. When are they not? W eek 11 3 Energy methods For some mechanisms, the nature of the driving energies require an analysis that takes into account both : The kinematic constraints of the linkages and The rate at which energy is applied to the mechanism ie how fast it responds to an input. W eek 11 4 Mechanism Examples Circuit breakers (where the time between the triggering signal and the breaking of contact is critical) Air bag deployment systems Retracting seat belt locking mechanisms Door closer and latches Suspension systems Cat and marsupial traps, rat and mouse traps 2 W eek 11 5 Energy Method Analysing energy flow into and out of the mechanism is an excellent and efficient way of gain insight into these mechanisms Fundamentally based on the first law of thermodynamics the conservation of energy Energy in = change in stored energy + energy taken from the system W eek 11 6 Energy balance mechanical system internal energy energy in energy out W eek 11 7 internal energy Made up of two parts Kinetic 0.5 m V 2 (Linear) & 0.5 I 2 (rotational) Where V is the CG velocity of the link in question Potential m g h Where h is the height of the CG above a datum W eek 11 8 Energy in and out The in and out energy of the mechanism are determined from the external forces and torques inertia forces and torques do not count The particular energy method that will be applied is the Quinns Energy Distribution Method. 3 W eek 11 9 Quinns Energy Distribution Method This method applies to mechanism having RIGID links that do no change in mass or inertia during motion Basic Propositions s Energy in energy out = change in the energy stored in the links themselves ( KE and PE) W eek 11 10 Quinns Energy Method Basic Propositions continued s At any particular PHASE of the mechanism, the SHARE (proportion) of the total kinetic energy stored in the mechanism, held by one link IS FIXED s This proportion is NOT AFFECTED by the actual velocity at which these calculations are made....
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This note was uploaded on 10/27/2009 for the course MECH 226 taught by Professor Weihuali during the Three '09 term at University of Wollongong, Australia.

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226-Lect 11 - 1 W eek 11 1 Week 11 Mech226 The Energy...

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