Vanderbilt University Vibro-Acoustics Laboratory 1 Decentralized Structural Acoustic Control of a Launch Vehicle Payload Fairing Kenneth D Frampton Dept. of Mechanical Engineering Vanderbilt University

Vibro-Acoustics Laboratory Objectives Develop decentralized control systems for launch vehicle payload fairings Control of fairing vibro-acoustic response based on group management middleware services – Groups assigned by modal sensitivity – Groups assigned geographically Investigate the effects of networked embedded systems constraints on control performance

Vanderbilt University Vibro-Acoustics Laboratory Launch Vehicle Payload Fairing Initial efforts focus on a 1/3 scale model Study of a 40 mode finite element model Modes 8,9,13,14,15,16 are known to be the most efficient radiators High noise levels in launch vehicles cause damage to payloads Reduction in noise levels will save in payload deployment costs

Vanderbilt University Vibro-Acoustics Laboratory Decentralized Control Control of large scale systems with networked embedded processors Each “node” consists of an inexpensive, small, computationally limited processor with sensors, actuators and network communications Large numbers of nodes distributed throughout the system Robustness to failures and scalability are critical issues A 11 A 12 A 13 A 14 A 15 A 16 A 17 A 18 Disturbance Vibrating Beam Sensors & Actuators Decentralized Control

Vanderbilt University Vibro-Acoustics Laboratory Control based on Group Management Middleware Assuming that groups can be defined and managed – How well can specific modes be targeted? – At what cost is this type of control achieved? – What information exchange among group members offers the best advantage? – What type of grouping yields the best performance? Two types of locally optimal control design – Each node receives sensor signals from all group members to produce local control signal – Each node uses it’s local sensor signal to command actuators of all group members Grouping based on structural modes or geographic neighbors

Vanderbilt University Vibro-Acoustics Laboratory Two-Port Control Design Objective is to minimize Disturbance to Performance path with sensor/control closed loop – Performance Targeted Modes: 8, 9, 13, 14, 15, 16 – Modal Groups: 15 sensors most sensitive to each mode We can design compensators that are locally, but not globally, optimal Plant Compensator Disturbance Performance Control Sensor

Vanderbilt University Vibro-Acoustics Laboratory Sensor Data Exchange Modal Grouping Control Effort norm = Open Loop norm = Closed Loop norm = Without control With control Frequency, Hz Disturbance to Sensor Singular Values

Vanderbilt University Vibro-Acoustics Laboratory Actuation Data Exchange Modal Grouping Control Effort norm = Open Loop norm = Closed Loop norm = Fairing Modal Control by Modal Groups, Actuator Comm. Without control With control Frequency, Hz Disturbance to Sensor Singular Values

Vanderbilt University Vibro-Acoustics Laboratory Sensor Data Exchange Geographic Grouping, Reach Control Effort norm = Open Loop norm = Closed Loop norm = Frequency, Hz Disturbance to Sensor Singular Values Without control With control

Vanderbilt University Vibro-Acoustics Laboratory Effects of Communication Delay Effects established through SIESTA simulations of beam vibration control Control system sampling rate of 2 kHz 100 node system Delays accumulate as signals are passed from node to node

Vanderbilt University Vibro-Acoustics Laboratory Effects of Delay: Bandwidth 750 Hz, Reach 5

Vanderbilt University Vibro-Acoustics Laboratory Effects of Delay: Bandwidth 750 Hz, Reach Freq=750Hz, Share=5 Frequency(Hz) Transfer function estimate(dB) No feedback Delay 10 Delay 200 Delay 800

Vanderbilt University Vibro-Acoustics Laboratory Conclusions Fairing Control – Specific modes can be targeted for control – Control effort and spillover are not a problem – Sensor data exchange among nodes is not necessarily the best approach. Exchanging control signals or a mixed approach may be preferable. – Geographic grouping may be as good as modal grouping IF you have a good model and good design tools Effects of Delay – For a system with a bandwidth in the hundreds of Hz and a sampling rate of 2 kHz, delays on the order of hundreds of microseconds can result in significant degradation in performance. – The reach of the system is affects the impact due to accumulated delays