Traditionally, torsional vibration analysis (TVA) programs operating in frequency domain, consider only one 2- or 4-stroke engine cycle to simulate a steady-state dynamics of the powertrain. There are, however, some phenomena which cannot be revealed during a single-cycle simulation. First such case is related to propeller drives. If the transmission ratio between internal combustion engine and propeller shaft is not synchronized with the number of propeller blades, then low-frequency fluctuations of vibration magnitude (beats) are induced, which can only be seen if multiple engine cycles are analyzed. Second case refers to simulation of random misfiring. Although an isolated event, it has an influence on the system dynamics beyond the engine cycle where it happens, and therefore requires considering multiple cycles. The paper shows how these two cases are dealt with, using AVL software EXCITE Designer.

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