CU-NEES 2008 FHT Workshop1
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
Hybrid Testing;Benchmarks and Validation
Gary Haussmann
Eric Stauffer
CU-NEES 2008 FHT Workshop2
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
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 Workshop3
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
Validation Process
• Well Understood Model
• Predict Analytical Response
• Compare With FHT Test Results
CU-NEES 2008 FHT Workshop4
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
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 Workshop5
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
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 Workshop6
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
Validation: Results
CU-NEES 2008 FHT Workshop7
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
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 Workshop8
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
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 Workshop9
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
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 Workshop10
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
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 Workshop11
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
When Real-Time Matters• A Simple Hybrid Test With MR Damper
• Try Various Real-Time Methods and Compare
CU-NEES 2008 FHT WorkshopNEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
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 Workshop13
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
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 Workshop14
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
Real-Time Test Results
• Slower Tests Reduce Damper Effect
• Hard To See The Difference
CU-NEES 2008 FHT Workshop15
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
Real-Time Test Results
• Slower Tests Reduce Damper Effect
• Hard To See The Difference
CU-NEES 2008 FHT Workshop16
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
Real-Time Results
• Exaggerate The Differences
• Assign Hard Real-Time = 100%
• Assign No Damper = 0%
• Scale The Rest Appropriately
CU-NEES 2008 FHT Workshop17
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
Real-Time Results
CU-NEES 2008 FHT Workshop18
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
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 Workshop19
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
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 Workshop20
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
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 Workshop21
NEES at CU Boulder
The George E Brown, Jr. Network for Earthquake Engineering Simulation
01000110 01001000 01010100
Feb. 19, 2008
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