Analysis of Engine Dynamics Under Transient Run-Up Conditions 2004-01-1454
The target of dynamic simulation is to investigate complex engine dynamic behavior in the whole speed range under different loading conditions in the most effective way during Engine Development Process (EDP). AVL has developed a method for transient run-up analysis by using the simulation tool AVL EXCITE. The main objective of this new method is the controlled speed increase by defining a speed ramp.
Transient run-up analysis is of interest for different kind of analysis during the EDP, such as crankshaft dynamics and strength, low frequency vibration analysis, bracket strength and durability analysis, acoustic analysis, etc. By using this method the time required for simulations and thus the whole project duration is significantly reduced. Conventionally the speed range is divided in single speed steps and for each speed a separate transient simulation has to be performed. The number of these simulations depends on the required speed resolution. The run-up analysis integrates all these separate simulations in one single EXCITE run. As it is possible to analyze the complete speed range of interest continuously in time domain, all resonances can be detected and the complex engine dynamic behavior can be predicted. In addition to reduced process time a transient run-up analysis can give more detailed answers on how a particular parameter influences a specific dynamic behavior of the engine.
AVL EXCITE is a non-linear flexible multi-body system solver. The components of the power unit are treated as separate flexible parts (subsystems) which perform either only small vibrations (e.g. engine block) or vibrations coupled with big global movements (e.g. crankshaft, connecting rod). The engine components are coupled with forces in the connections by different linear or non-linear joints, considering e.g. the non-linear behavior of the oil film in bearings and piston-liner contacts. Due to the high non-linearities in the system, the analysis is performed in time domain, by using an implicit integration method (Newmark or Hilber-Hughes-Taylor), with step size control.
External loads are created as boundary conditions for a transient run-up analysis based on interpolations between engine stationary operating points according to a predefined run-up ramp. The presented transient run-up methodology does not make limitation for boundary condition definition and also boundary conditions of real transient engine phenomena can be included in engine structural dynamic analysis.