MODELING AND SIMULATION METHODS FOR MDOF STRUCTURES AND ROTATING MACHINERY WITH IMPACT DAMPERS

Previously published work on applied impact damping typically relates to SDOF models or simple MDOF models such as the classical cantilever beam. Structural models often require an extremely large number of DOF with mode shapes that are generally very complex. Dynamics simulation of these typically becomes both complicated and time consuming. The n onlinear behavior of impact dampers further complicates such simulatio n in that standard linear solutions are not possible. The primary obje ctive in this research extends previous work by applying impact damper s to MDOF structures that are modeled with general three-dimensional ' 'beam'' finite elements. Modal-based models of the MDOF systems and ef ficient impact damper tracking algorithms were also developed that sig nificantly reduced CPU time for simulation. Significant among the obje ctives was obtaining an impact damper design for the MDOF casing struc ture of the Space Shuttle Main Engine (SSME), High-Pressure Oxygen Tur bo-Pump (HPOTP), subject to pump rotor shaft unbalance, Impact damper performance is based on suppression of vibration at casing critical fr equencies for rotor speed ranges, at rotor full speed, and vert high u nbalance to simulate a defect such as losing an impeller blade fragmen t or a cracked bearing [6]. Simulations show significant reductions in vibration at the casing critical-frequencies and very high unbalance levels while little or no improvement was observed off resonance. Addi tionally, the previous work with an experimental rotor bearing system (RBS) and impact damper was modeled using the developed modal-based me thods. Simulation of the resulting model response shows remarkable agr eement with the experimental. Finally, both the RES and the HPOTP were modeled and simulated as unstable systems with attached impact damper s. The simulations predict that the impact damper is an excellent stab ilizing mechanism for a range of instability driver values. Simulation of the models in this research with the developed modal based algorit hms were accomplished with excellent efficiency, and accurate results.