Simulation and Control Aspects of FHT

1. Simulation and Control Aspects of FHT M. V. Sivaselvan CO-PI CU-NEES Assistant Professor Dept. of Civil, Environmental and Architectural Eng. University of Colorado at Boulder siva@colorado.edu CU-NEES 2008 FHT Workshop

2. Outline • What is hybrid simulation? • Why do it? • Challenges in implementing a hybrid simulation system • Types of hybrid simulation • Hybrid simulation algorithms – architecture and equivalence • Hybrid testing with shaking tables • Current and planned work, Conclusions CU-NEES 2008 FHT Workshop

3. Outline • What is hybrid simulation? • Why do it? • Challenges in implementing a hybrid simulation system • Types of hybrid simulation • Hybrid simulation algorithms – architecture and equivalence • Hybrid testing with shaking tables • Current and planned work, Conclusions CU-NEES 2008 FHT Workshop

4. Rest of the structure is undamaged – does not have to be physically build in the laboratory Most damage happens here – need better understanding by experimentation Earthquake Multi-story Building CU-NEES 2008 FHT Workshop

5. Interact during the experiment to mimic testing the whole building Computer Model Physical Experiment Actuators Wall Specimen CU-NEES 2008 FHT Workshop

6. Outline • What is hybrid simulation? • Why do it? • Challenges in implementing a hybrid simulation system • Types of hybrid simulation • Hybrid simulation algorithms – architecture and equivalence • Hybrid testing with shaking tables • Current and planned work, Conclusions CU-NEES 2008 FHT Workshop

7. For Discovery For Qualification Develop or calibrate Material/system models Use of hybrid simulation Laboratory Testing • Examine the performance of a component in its host environment • Proof of concept tests • Interaction with surroundings may significantly modify input • Hybrid simulation is useful Hybrid Simulation is useful for qualification/proof-of-concept testing when the interaction of a component with its surroundings needs to be accurately represented • Hybrid simulation not very useful for this purpose • Some kind of computation-in-the-loop with geometric reasoning about state-space may be possible CU-NEES 2008 FHT Workshop

8. Outline • What is hybrid simulation? • Why do it? • Challenges in implementing a hybrid simulation system • Types of hybrid simulation • Hybrid simulation algorithms – architecture and equivalence • Hybrid testing with shaking tables • Current and planned work, Conclusions CU-NEES 2008 FHT Workshop

9. Feedback interaction in reality External Input (Eg. Ground Motion) Substructure 1 Computational Boundary Condition Substructure 2 Physical Work Conjugate Boundary Condition CU-NEES 2008 FHT Workshop

10. In hybrid simulation however … External Input (Eg. Ground Motion) Substructure 1 Computational Boundary Condition Actuator / Transfer Device Substructure 2 Physical Work Conjugate Boundary Condition CU-NEES 2008 FHT Workshop

11. In hybrid simulation however … External Input (Eg. Ground Motion) Substructure 1 Computational Boundary Condition Sensor Actuator / Transfer Device Substructure 2 Physical Work Conjugate Boundary Condition CU-NEES 2008 FHT Workshop

12. In hybrid simulation however … External Input (Eg. Ground Motion) Substructure 1 Computational Boundary Condition Natural Physical Feedback Sensor Actuator / Transfer Device Substructure 2 Physical Work Conjugate Boundary Condition CU-NEES 2008 FHT Workshop

13. In hybrid simulation however … External Input (Eg. Ground Motion) Substructure 1 Computational Boundary Condition Natural Physical Feedback Sensor Actuator / Transfer Device Actuator Feedback Substructure 2 Physical Work Conjugate Boundary Condition CU-NEES 2008 FHT Workshop

14. In hybrid simulation however … External Input (Eg. Ground Motion) Substructure 1 Computational Boundary Condition NEW DYNAMICS Natural Physical Feedback Sensor Actuator / Transfer Device Actuator Feedback Substructure 2 Physical Work Conjugate Boundary Condition CU-NEES 2008 FHT Workshop

15. Challenges • These additional dynamics create significant problems • When the structure to be simulated is lightly damped, almost always renders the system unstable • Need to develop control algorithms to make hybrid simulation possible • Causality → Design of such algorithms requires knowledge about physical substructure (predictive model, implicit integration etc.) → This is a conflict → Robustness of algorithm with respect to modeling of the physical substructure • A numerical algorithm need not be causal, a hybrid simulation algorithm does CU-NEES 2008 FHT Workshop

16. Outline • What is hybrid simulation? • Why do it? • Challenges in implementing a hybrid simulation system • Types of hybrid simulation • Hybrid simulation algorithms – architecture and equivalence • Hybrid testing with shaking tables • Current and planned work, Conclusions CU-NEES 2008 FHT Workshop

17. External Input (Eg. Ground Motion) External Input (Eg. Ground Motion) Boundary Condition Boundary Condition Substructure 1 Computational Substructure 1 Computational Substructure 2 Physical Substructure 2 Physical Work Conjugate Boundary Condition Work Conjugate Boundary Condition Hybrid Simulation • Born from the displacement-based finite element – one of the elements is now physical ! • Algorithms also reflect this • If in addition, there are no frequency-dependent behavior is the physical substructure – can be done as slowly as we want to Pseudo-dynamic Dynamic Has no inertia effects of interest Has significant inertia effects • More practical applications necessitate this form of hybrid simulation • My research is in this area CU-NEES 2008 FHT Workshop

18. Hybrid Simulation Pseudo-dynamic Dynamic Real-time Slow Hybrid simulation with Shaking Tables CU NEES Site CU NEES Site CU-NEES 2008 FHT Workshop

19. Outline • What is hybrid simulation? • Why do it? • Challenges in implementing a hybrid simulation system • Types of hybrid simulation • Hybrid simulation algorithms – architecture and equivalence • Hybrid testing with shaking tables • Current and planned work, Conclusions CU-NEES 2008 FHT Workshop

20. Recall External Input Substructure 1 Computational Boundary Condition Motivation: Want actuator to behave the same way as Substructure 1 Natural Physical Feedback Actuator / Transfer Device Sensor Actuator Feedback Substructure 2 Physical Work Conjugate Boundary Condition CU-NEES 2008 FHT Workshop

21. Introduce a controller External Input Substructure 1 Computational Boundary Condition Controller Natural Physical Feedback Actuator / Transfer Device Actuator Feedback Substructure 2 Physical Work Conjugate Boundary Condition CU-NEES 2008 FHT Workshop

22. + Error S - Tries to do the same Thing as Substructure 1 Takes the same input as Substructure 1 Introduce a controller External Input Substructure 1 Computational Boundary Condition Controller Natural Physical Feedback Actuator / Transfer Device Actuator Feedback Substructure 2 Physical Work Conjugate Boundary Condition CU-NEES 2008 FHT Workshop

23. Model Reference Control • Controller designed so that does the same thing as • Part implemented in the computer CU-NEES 2008 FHT Workshop

24. Part implemented in the computer Another Approach Internal Model Control - IMC CU-NEES 2008 FHT Workshop

25. Equivalence of different approaches • The two approaches can be shown to be shown to be different parametrizations of a 2 DOF controller • Each offers a different perspective • MRC useful in design • IMC useful in robustness analysis CU-NEES 2008 FHT Workshop

26. CU FHT Algorithm • Computer implementation of IMC Discretize at 10 ms Discretize at 1 ms CU FHT Algorithm !! (Shing et. al., 2005) CU-NEES 2008 FHT Workshop

27. Outline • What is hybrid simulation? • Why do it? • Challenges in implementing a hybrid simulation system • Types of hybrid simulation • Hybrid simulation algorithms – architecture and equivalence • Hybrid testing with shaking tables • Current and planned work, Conclusions CU-NEES 2008 FHT Workshop

28. Masses simulated Hybrid Simulation with a Shaking Table • Necessary when physical substructure has distributed mass • In many cases of practical interest for hybrid simulation, mass is distributed and there is no such natural way of lumping the mass for substructuring. • Examples: • Nonstructural components in civil structures • Payloads in aerospace structures • Machine components • Dams, chimneys and other continuum civil structures • Soil / fluid-structure interaction • The interface device must be able to dynamically excited a system with distributed mass – shaking table Physical substructure has no masses of significance, hence no inertia effects (Hence pseudo-dynamic) CU-NEES 2008 FHT Workshop

29. Outline • What is hybrid simulation? • Why do it? • Challenges in implementing a hybrid simulation system • Types of hybrid simulation • Hybrid simulation algorithms – architecture and equivalence • Hybrid testing with shaking tables • Current and planned work, Conclusions CU-NEES 2008 FHT Workshop

30. Hybrid Testing with Shaking Tables • 1.5 m x 1.5 m working area • +/- 200 mm dynamic stroke • Frequency range – 0-50 Hz • Maximum payload – 2000 kg • Maximum Acceleration – 1.0-2.9 g • Maximum Velocity – 1 m/s • Will give CU structures lab capability to perform such hybrid simulations as listed in the previous slide • Collaboration with MTS Systems Hybrid Simulation Configurations Combination of Shaking Table and External Actuator Shaking Table Only Response Feedback Response Feedback Computational Substructure External Actuator Physical Substructure Physical Substructure Physical Substructure Reaction Wall Shaking Table Shaking Table Computational Substructure CU-NEES 2008 FHT Workshop

31. Conclusions • Hybrid simulation – online combination of computation and physical experimentation • Useful for qualification/proof-of-concept testing when the interaction of a component with its surroundings needs to be accurately represented • Challenge – added dynamics and feedback paths created by the transfer system/actuator applying that applied interface conditions between the two substructures. • More difficult in dynamic hybrid simulation where physical substructure has significant inertia (as opposed to pseudo-dynamic) • Algorithms based on a control-systems perspective offer more promise than those motivated by the finite element method CU-NEES 2008 FHT Workshop