Tuned Mass Damper Investigation for Apache Struts RAM 8 Workshop November 3 & 4, 2015 Paul Riehle Roush Industries paul.riehle@roush.com

Overview Tuned Mass Damper (TMD) Background Apache MRGB Strut Dynamics MRGB Strut TMD Application

Rubber Applications for NVH Control Isolation Systems Tuned Mass Dampers Free Layer Damping Constrained Layer Damping Damping Links from RAM 5 Workshop - October, 2012

Rubber Applications for NVH Control Tuned Mass Dampers mass ratio is important stiffness and damping are important frequency tuning is critical rubber elements typically used for TMD damping and stiffness TMD Base System

Tuned Mass Damper Examples Large Torsional Damper Planer Dampers Tuned to Two Frequencies Transfer Case Tuned Damper Heaven!! Tuned Damper

Mounting bracket resonance issue controlled with TMD Transmission Mount Bracket TMD Mounting bracket resonance issue controlled with TMD Gear Whine due to Bracket Resonance

Rubber Property Nonlinearities Temperature Frequency Static preload Dynamic strain amplitude Important Rubber property nonlinearities will cause TMD performance nonlinearities.

Roush TMD Design Process

Apache MRGB Strut TMD Application Objectives Reduce noise and vibration that passes from the main rotor gearbox (MRGB) through the gearbox mounting struts to the Apache airframe resulting in improved component durability and reduced aircrew fatigue. Approach Use modeling, component testing, and rig testing to develop concept TMDs for MRGB struts.

Apache MRGB Strut Dynamics Testing by Roush on a “Blue Rig” identified the MRGB mounting resonance frequencies, damping, and mode shapes. Results indicated that strut structural dynamics create amplifications of MRGB operating vibration and forces. Important resonances groupings occur in the 130-326 Hz and the 450-738 Hz frequency range where the struts exhibit 1st and 2nd bending modes, respectively. Apache MRGB primary gear mesh excitation forces align with 2nd bending modes. “Blue Rig” Test Stand Struts MRGB

Strut Bending Modes 1st Bending Modes 130 – 326 Hz 2nd Bending Modes

Modal Testing Measurement Locations Single Strut Test Fixture Modal Testing Measurement Locations Strut:14 Strut:11 All individual strut testing was performed using a bedplate fixture that was designed to mimic the Blue Rig approximation. Initial modal testing was performed using the measurement locations shown to the right. This was done to attain a correlation between the physical test and FE model. Strut:3

TMD Simulation – Lateral Mode Tuning Strut Point 3 - Lateral Figure 3 Performed curve fit on FRF data for 408 Hz Lateral Mode Participating Inertia of strut is ~3 Kg. Very low damping indicates that tuned damper will be very effective. ~22 dB Figure 4 Damper simulation with 0.1 kg (~¼ Lb) inertia mass shows high attenuation of the response peak

FE: Single Strut – TMD 18 dB 8 dB The TMD proved successful in damping the chosen mode by 18 dB in the lateral direction and subsequently reducing the vertical second order mode by 8 dB

Testing: Single Strut TMD ~20 dB ~5 dB Baseline Strut (No TMD) Strut with Second TMD Tuning Strut with Large Ring TMD Tuning

FE : Blue Rig TMDs

FE: Blue Rig – TMD Global Z Direction Significant response reduction in the frequency ranges of the 2nd strut bending Reduction of response amplitude for the second order bending modes (400-800 Hz) is up to 18 dB

Testing: Blue Rig – TMD Installation Blue Rig Measurement Locations Blue Rig TMD Installation Locations* Impact FRF measurements were made with and without the TMDs installed. The TMD installation locations were chosen based on the individual strut testing installation location. The TMDs were installed using the same local coordinate system that was used for the individual strut testing.

Testing: TMD Results, Blue Rig Struts Base Point 6 Excitation Bedplate: 4 Response X Response Direction ~20-25dB of FRF amplitude reduction are seen at ~450-550Hz. Y Response Direction Z Response Direction Baseline TMDs on All Struts

Testing: TMD Results, Blue Rig Struts Based on testing Frequency response of the Blue Rig system was damped very well It was seen that similar benefits could be achieved using fewer dampers that are strategically placed

Summary TMDs can be very effective at controlling structural resonant and forced responses. It is critical to optimize the TMD mass, damping ratio and tuning to maximize the performance for a given application. Rubber materials are recommended to provide the required TMD damping and stiffness. Material selection criteria should consider the environment and operating conditions such as frequency, temperature, dynamic strain, and static pre-strain. The nonlinear behavior of the TMD must be understood. TMDs were designed for the Apache MRGB mounting struts to reduce the amplification of gear mesh vibration transmitted to the airframe. The TMD development process required the use of several analysis tools and test setups. The TMDs produced a 10 to 20 dB drop in MRGB strut forced response levels.

Questions?