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POLI di MI tecnicolanotecnicolano LOAD REDUCTION IN LEAD-LAG DAMPERS BY SPEED-SCHEDULED APERTURE AND MODULATED CONTROL OF A BY-PASS VALVE C.L. Bottasso,

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Presentation on theme: "POLI di MI tecnicolanotecnicolano LOAD REDUCTION IN LEAD-LAG DAMPERS BY SPEED-SCHEDULED APERTURE AND MODULATED CONTROL OF A BY-PASS VALVE C.L. Bottasso,"— Presentation transcript:

1 POLI di MI tecnicolanotecnicolano LOAD REDUCTION IN LEAD-LAG DAMPERS BY SPEED-SCHEDULED APERTURE AND MODULATED CONTROL OF A BY-PASS VALVE C.L. Bottasso, S. Cacciola, A. Croce, L. Dozio Politecnico di Milano, Italy American Helicopter Society 66th Annual Forum and Technology Display Phoenix, AZ, USA, May 11-13, 2010

2 Adaptive Lead-Lag Damping POLITECNICO di MILANO Outline Introduction and motivation Approach and methods - Damper model - Rotor-vehicle multibody model - Control laws Results Conclusions and outlook

3 Adaptive Lead-Lag Damping POLITECNICO di MILANO Introduction and Motivation purely passive Lead-lag dampers are typically purely passive devices adaptive smart dampers The idea of using adaptive smart dampers has been around for a long time: Reed, US Patent 1972 Mechanical-hydraulic device for selective damping of lag frequency Bauchau et al., SBIR I & II, Active modulation of by-pass valve aperture for selective damping of lag frequency Gandhi at al., Aeronautical Journal 2003 HHC modulation of by-pass valve for reduction of vibratory hub loads …

4 Adaptive Lead-Lag Damping POLITECNICO di MILANO Introduction and Motivation Motivation Motivation: high operating and maintenance costs of dampers and their interfaces to rotor system The main dilemma in damper design The main dilemma in damper design: Different damping levels are required for different flight conditions High damping required for very small range of the flight envelope (ground resonance, high-g turns, …) Much lower damping appropriate for all other flight regimes

5 Adaptive Lead-Lag Damping POLITECNICO di MILANO Introduction and Motivation By-pass valve By-pass valve: relatively straightforward way of changing damping (and hence loads) in a damper Focus of present work Focus of present work: reduce loadsdecrease in the damping to lower but still safe values 1.Can we significantly reduce loads if we allow for a decrease in the damping to lower but still safe values? speed-scheduled aperturemodulating control 2.Can load reductions be achieved with a simple speed-scheduled aperture of the by-pass valve or do we need a modulating control law (valve aperture as a function of blade motion)?

6 Adaptive Lead-Lag Damping POLITECNICO di MILANO Outline Introduction and motivation Approach and method - Damper model - Rotor-vehicle multibody model - Control laws Results Conclusions and outlook

7 Adaptive Lead-Lag Damping POLITECNICO di MILANO Damper Model Physics-based Physics-based mathematical model of hydraulic damper: set of stiff non-linear ordinary differential equations Coupled set of stiff non-linear ordinary differential equations (solved with time-adaptive modified Rosenbrok 2 nd order integrator) Compressible fluid Compressible fluid state equations in the two chambers orifice Fluid flow through orifice relief valves Flow through pressure relief valves dynamics Piston and relief valve dynamics: - Friction - Contact-impact Actuated by-pass valve Actuated by-pass valve

8 Adaptive Lead-Lag Damping POLITECNICO di MILANO Damper Model Characteristic load-speed curves by-pass valve aperture Characteristic load-speed curves for varying by-pass valve aperture Δ byp = A byp /A or Low speed: relief valves closed Low speed: relief valves closed High speed: relief valves open High speed: relief valves open Knee: transition region Knee: transition region Knee moves to higher speed for increased by-pass aperture Standard passive damper Standard passive damper: Tuned to experimental data by identifying: - Orifice and relief valve discharge coefficients - Relief valve pre-load Standard passive damper Standard passive damper: Tuned to experimental data by identifying: - Orifice and relief valve discharge coefficients - Relief valve pre-load Adaptive damper with by-pass Adaptive damper with by-pass: Effect of by-pass aperture on characteristic curve Adaptive damper with by-pass Adaptive damper with by-pass: Effect of by-pass aperture on characteristic curve

9 Adaptive Lead-Lag Damping POLITECNICO di MILANO Rotor-Vehicle Multibody Model Detailed multibody model rigid fuselage Detailed multibody model of rotor coupled to rigid fuselage (A109E helicopter): Elastic blades Kinematically accurate: - Control linkages - Damper and damper linkages Peters-He dynamic inflow Rotor-damper couplingdirect coupling Rotor-damper coupling: avoid direct coupling of models due to wildly different time scales –Damper characteristic curveslook-up table –Damper characteristic curves stored in a look-up table –Used at run time during multibody simulation trimmed at various flight conditions Vehicle model trimmed at various flight conditions Validation Validation using experimental data (see paper)

10 Adaptive Lead-Lag Damping POLITECNICO di MILANO Control Laws Damping criterion Damping criterion (provided by helicopter manufacturer): 30% of damping For each flight condition, ensure 30% of damping of conventional passive damper

11 Adaptive Lead-Lag Damping POLITECNICO di MILANO Control Laws

12 Adaptive Lead-Lag Damping POLITECNICO di MILANO Estimation of Damping Modified Pronys method Modified Pronys method to account for periodic nature of problem (Bottasso et al., EWEC 2010) LTP LTP system: x · = A(ψ)x + B(ψ)u u where u = exogenous inputs (speed, collective and cyclic pitch), constant in steady trimmed conditions Fourier reformulation (Bittanti & Colaneri 2000): A(ψ) = A 0 +Σ i (A is sin(i ψ)+A ic cos(i ψ)) B(ψ) = B 0 +Σi(B is sin(i ψ)+B ic cos(i ψ)) 1.Approximate A(ψ) A 0 1.Approximate state matrix: A(ψ) A 0 2.Transfer periodicity to inputs term LTI Obtain linear time invariant (LTI) system: x · = A 0 x + Ub(ψ) b(ψ) periodic where b(ψ) = exogenous periodic dummy inputs

13 Adaptive Lead-Lag Damping POLITECNICO di MILANO Estimation of Damping Estimation process: 1.Trim helicopter and perturb with impulsive torque input at lag hinge ARX model harmonic inputs 2.Identify discrete-time ARX model (using Least Squares or Output Error method) with harmonic inputs 3.Compute discrete poles, and transform to continuous time (Tustin transformation) 4.Obtain frequencies and damping factors LTI Given reformulated LTI system x. = A 0 x + Ub(ψ) Pronys method use standard Pronys method (Hauer 1990; Trudnowski 1999) Frequency domain Frequency domain verification of correct identification Frequency domain Frequency domain verification of correct identification Time domain Time domain verification of correct identification Time domain Time domain verification of correct identification

14 Adaptive Lead-Lag Damping POLITECNICO di MILANO Outline Introduction and motivation Approach and method - Damper model - Rotor-vehicle multibody model - Control laws Results Conclusions and outlook

15 Adaptive Lead-Lag Damping POLITECNICO di MILANO Results SSA control law: Δ byp = A byp /A or Maximum loads Maximum loads Damping factors Damping factors Substantial reductions in damper loads (-37% ÷ -70%) 30% damping constraint Significant valve apertures

16 Adaptive Lead-Lag Damping POLITECNICO di MILANO Results Valve aperture Valve aperture Damper loads Damper loads HHC control law: Further reductions in damper loads peaks Max SSA aperture: Δ byp = 38 Max HHC aperture: Δ byp = 68

17 Adaptive Lead-Lag Damping POLITECNICO di MILANO Results Small maximum allowed by-pass aperture Small maximum allowed by-pass aperture: -Valve opening is not enough to prevent activation of pressure relief valves -Small load reduction Larger maximum allowed by-pass aperture Larger maximum allowed by-pass aperture: -Pressure relief valves remain closed -Damper operates in the parabolic region -Larger load reduction

18 Adaptive Lead-Lag Damping POLITECNICO di MILANO Results Summary Summary: SSA vs. HHC Maximum loads Maximum loads Damping factors Damping factors Negligible effect of HHC on lag damping

19 Adaptive Lead-Lag Damping POLITECNICO di MILANO Outline Introduction and motivation Approach and method - Damper model - Rotor-vehicle multibody model - Control laws Results Conclusions and outlook

20 Adaptive Lead-Lag Damping POLITECNICO di MILANO Conclusions damper loadsby-pass valve Investigated reductions in damper loads achieved using a by-pass valve SSAHHC modulation Two control laws: simple SSA and HHC modulation 30% safe damping margin Results have shown that the 30% safe damping margin is achieved with: Significant reduction Significant reduction of loads wrt passive damper (SSA: 37-68% HHC: 74-81%) (SSA: 37-68%; HHC: 74-81%) Acceptable Acceptable valve openings (SSA: A or HHC: 70 A or ) (SSA: A or ; HHC: 70 A or ) selective not necessary It appears that additional control loops aimed at selective increase in damping of lag mode are not necessary

21 Adaptive Lead-Lag Damping POLITECNICO di MILANO Outlook minimum damping requirement Perform more detailed investigation of the minimum damping requirement (air-resonance, high-g turns, damping-critical flight conditions) extended life of damperinterfaces Translate load reductions computed here in extended life of damper and of its interfaces to the rotor system experimental facility Develop an experimental facility comprising modified hydraulic damper with by-pass valve and damper test bench trade-offs increased system complexity More fully understand trade-offs between improved performance of HHC wrt simple SSA and increased system complexity (is it worth it?)

22 Adaptive Lead-Lag Damping POLITECNICO di MILANO Acknowledgements MECAER Meccanica Aeronautica SpA Italian Ministry of Defense Research funded by MECAER Meccanica Aeronautica SpA and the Italian Ministry of Defense AgustaWestland Thanks to AgustaWestland for modeling and validation data of the A109E helicopter, and for valuable feedback


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