Hybrid Testing; Benchmarks and Validation

Gary Haussmann Eric Stauffer Hybrid Testing;Benchmarks and Validation CU-NEES 2008 FHT Workshop

Outline • Validation: Test vs. Analytical Models • Sources of error • Results and comparison • Capabilities, from PSD to Real-time • When do you need real-time? • The same test at multiple speeds • Limitations • Model size • Velocity, displacement limits CU-NEES 2008 FHT Workshop

Validation Process • Well Understood Model • Predict Analytical Response • Compare With FHT Test Results CU-NEES 2008 FHT Workshop

Validation: Error Sources • Actuator Lag • For a stiff specimen, lag leads to negative “damping” • For a damping specimen, lag leads to negative “mass” • MR Damper Model • Nonlinear Response • Use a Linearized Model • Measurement Error • Instrument Noise CU-NEES 2008 FHT Workshop

Validation: MR Damper • Perform Simple Tests to Characterize Damper • Variety of velocities and displacements • Generate a Damper Model for Analytical Solution CU-NEES 2008 FHT Workshop

Validation: Results CU-NEES 2008 FHT Workshop

Validation: Results • Large amplitude tests match analytical • As amplitude decreases, lag increases in the test results • Primary error source: MR Damper model • Linearized model doesn't match near-zero response of the actual damper • Not noticeable with large signals • Revise Damper Model CU-NEES 2008 FHT Workshop

Capabilities: PSD • Pseudodynamic testing • Time is not a factor • Local or Distributed Testing • No Limits on Model Size • Three Independent or Coordinated Actuators • 12+ Measurement Channels CU-NEES 2008 FHT Workshop

Capabilities: Real-Time • Soft or Hard Real-Time • Limitations: • Local only • Max Model Size • Actuator Velocity Limits • Data Channel Limit (~80) • Pausing “ill-advised” CU-NEES 2008 FHT Workshop

Real-Time Testing? • You don't always need real-time • Stiffness primary phenomenon • Low-frequency excitation • Real-time Situations • Velocity-based components • Rate-dependent forces • Can we model it instead? CU-NEES 2008 FHT Workshop

When Real-Time Matters • A Simple Hybrid Test With MR Damper • Try Various Real-Time Methods and Compare CU-NEES 2008 FHT Workshop

Various Modeling Schemes • Hard Real-Time • Soft Real-Time • “Fake” Soft Real-Time • OpenFresco OS Soft Real-Time • Interpolate/Extrapolate • Ramp-and-Hold • Scaled time: *10, *100 CU-NEES 2008 FHT Workshop

Real-Time vs. Stretched Time • Velocity-based components • Impact is reduced • Slower time leads to less response • Stiffness-based components still valid • Virtual forces can emulate a velocity-based response if no real-time available • Compute velocity-based response in slow test • Requires reasonable damping model CU-NEES 2008 FHT Workshop

Real-Time Test Results • Slower Tests Reduce Damper Effect • Hard To See The Difference CU-NEES 2008 FHT Workshop

Real-Time Results • Exaggerate The Differences • Assign Hard Real-Time = 100% • Assign No Damper = 0% • Scale The Rest Appropriately CU-NEES 2008 FHT Workshop

Real-Time Results CU-NEES 2008 FHT Workshop

Real-Time TestingAnalysis Limitations • Standard update rate: 0.97mS period • 60Hz Monitor: 16mS • Model Size • Degrees-of-freedom: 130 • Ever-increasing • Material Modeling • Complex materials take more time • Elastic Linear easiest CU-NEES 2008 FHT Workshop

Real-Time TestingSpecimen Limitations • Actuator Limitations • Displacement: +-6 inches • Velocity: 10/20 inches/sec • Force: 110 or 220 Kips • Use actuator model to predict these results • Coupled and Multi-DOF test Configuration • Crosstalk and parasitic coupling • Exacerbated in real-time CU-NEES 2008 FHT Workshop

Real-Time TestingBonus Capabilities • MATLAB xPC/Real-time Workshop • Also hooked into SCRAMnet • Additional modeling/analysis during test • PXI Instrument/DAQ Chassis • Analog and Digital I/O • Acquire quantities in real-time over SCRAMnet • Streaming analysis data • Visualize OpenSEES model during test • Debugging, Entertainment CU-NEES 2008 FHT Workshop

Conclusion • Hybrid Test Validation • Compare test and analytical solution • Damper model main source of discrepancy • Real-time vs. slower time • Damping effects are reduced • Slower tests approach no-damping results • Hybrid testing limitations • Model size • Actuator limits CU-NEES 2008 FHT Workshop

Hybrid Testing; Benchmarks and Validation