From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Page discussing fundamental expressions for friction damper energy dissipation and engine vibration calculations.
| Identifier | ExFiles\Box 132\2\ scan0204 | |
| Date | 17th February 1941 | |
| Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}4/ST.17.2.41 - 4 - The two fundamental expressions are as follows. The maximum energy dissipated per cycle by a constant friction damper is 1.273 Jd{J. Draper - Frames} ω² α² in lb/cycle. and the corresponding optimum friction torque setting is Td = 0.45 Jd{J. Draper - Frames} ω² α lb in. where Jd{J. Draper - Frames} = mom. of inertia of damper inertia member in lb.in.sec² ω = natural frequency of engine system α = max. vibration amplitude at the free end of the crank-shaft in radians. is obtained by equating harmonic input energy to maximum energy dissipated. Input energy = π Te α in lb. per cycle where Te = resultant harmonic torque for the engine in lb.inches. = TN ΣAR Therefore π TN ΣAR α = 1.273 Jd{J. Draper - Frames} ω² α² and the optimum friction torque setting = Td = 0.45 Jd{J. Draper - Frames} ω² α = (0.45 TN ΣAR) / 1.273 = 1.11 Σα TN AR. C. You were, of course, quite correct in stating that there are no odd order vibrations on a 180° bank engine having two lines of reciprocating parts to each crank. Calculations for this unwholesome engine were made as an afterthought and should never really have been included. It seems that changing from 4 stroke to 2 stroke and firing two cylinders at a time proved just too much for our phase diagrams. All the other vibrations, including the 6th order which is the same as for the 4 stroke engine, remain unchanged. | ||