Project ForgeTheory of Machines
Governors & Flywheels
GATE 2021
Medium
Consider a reciprocating engine with crank radius R and connecting rod of length L. The secondary unbalance force for this case is equivalent to the primary unbalance force due to a virtual crank of
- Aradius L²/4R rotating at half the engine speed
- Bradius R/4 rotating at half the engine speed
- radius R²/4L rotating at twice the engine speed
- Dradius L/2 rotating at twice the engine speed
Explanation
The reciprocating inertia force is F=mRω²[cosθ + (R/L)cos2θ]. The primary term mRω²cosθ is a crank of radius R at speed ω; the secondary term mRω²(R/L)cos2θ = m(R²/4L)(2ω)²cos2θ is equivalent to a virtual crank of radius R²/4L rotating at 2ω.
Source: GATE ME 2021 Session 1 (ME-1) (2021)
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