Feb. 19, 2008 CU-NEES 2008 FHT Workshop 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

Feb. 19, 2008 CU-NEES 2008 FHT Workshop 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

Feb. 19, 2008 CU-NEES 2008 FHT Workshop 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

Feb. 19, 2008 CU-NEES 2008 FHT Workshop Multi-story Building Earthquake Most damage happens here – need better understanding by experimentation Rest of the structure is undamaged – does not have to be physically build in the laboratory

Feb. 19, 2008 CU-NEES 2008 FHT Workshop Wall Specimen Actuators Physical Experiment Computer Model Interact during the experiment to mimic testing the whole building

Feb. 19, 2008 CU-NEES 2008 FHT Workshop 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

Feb. 19, 2008 CU-NEES 2008 FHT Workshop Use of hybrid simulation Laboratory Testing For Qualification For Discovery Develop or calibrate Material/system models 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 not very useful for this purpose Some kind of computation-in- the-loop with geometric reasoning about state-space may be possible Hybrid Simulation is useful for qualification/proof-of-concept testing when the interaction of a component with its surroundings needs to be accurately represented

Feb. 19, 2008 CU-NEES 2008 FHT Workshop 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

Feb. 19, 2008 CU-NEES 2008 FHT Workshop Feedback interaction in reality Substructure 1 Computational Substructure 2 Physical External Input (Eg. Ground Motion) Boundary Condition Work Conjugate Boundary Condition

Feb. 19, 2008 CU-NEES 2008 FHT Workshop In hybrid simulation however … Substructure 1 Computational Substructure 2 Physical External Input (Eg. Ground Motion) Boundary Condition Work Conjugate Boundary Condition Actuator / Transfer Device

Feb. 19, 2008 CU-NEES 2008 FHT Workshop In hybrid simulation however … Substructure 1 Computational Substructure 2 Physical External Input (Eg. Ground Motion) Boundary Condition Work Conjugate Boundary Condition Actuator / Transfer Device Sensor

Feb. 19, 2008 CU-NEES 2008 FHT Workshop In hybrid simulation however … Substructure 1 Computational Substructure 2 Physical External Input (Eg. Ground Motion) Boundary Condition Work Conjugate Boundary Condition Actuator / Transfer Device Sensor Natural Physical Feedback

Feb. 19, 2008 CU-NEES 2008 FHT Workshop In hybrid simulation however … Substructure 1 Computational Substructure 2 Physical External Input (Eg. Ground Motion) Boundary Condition Work Conjugate Boundary Condition Actuator / Transfer Device Sensor Natural Physical Feedback Actuator Feedback

Feb. 19, 2008 CU-NEES 2008 FHT Workshop In hybrid simulation however … Substructure 1 Computational Substructure 2 Physical External Input (Eg. Ground Motion) Boundary Condition Work Conjugate Boundary Condition Actuator / Transfer Device Sensor Natural Physical Feedback Actuator Feedback NEW DYNAMICS

Feb. 19, 2008 CU-NEES 2008 FHT Workshop 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

Feb. 19, 2008 CU-NEES 2008 FHT Workshop 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

Feb. 19, 2008 CU-NEES 2008 FHT Workshop Hybrid Simulation Pseudo-dynamic Dynamic Substructure 1 Computational Substructure 2 Physical External Input (Eg. Ground Motion) Boundary Condition Work Conjugate Boundary Condition Has no inertia effects of interest 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 Substructure 1 Computational Substructure 2 Physical External Input (Eg. Ground Motion) Boundary Condition Work Conjugate Boundary Condition Has significant inertia effects More practical applications necessitate this form of hybrid simulation My research is in this area

Feb. 19, 2008 CU-NEES 2008 FHT Workshop Hybrid Simulation Pseudo-dynamic Dynamic Real-time Slow CU NEES Site Hybrid simulation with Shaking Tables CU NEES Site

Feb. 19, 2008 CU-NEES 2008 FHT Workshop 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

Feb. 19, 2008 CU-NEES 2008 FHT Workshop Recall Substructure 1 Computational Substructure 2 Physical External Input Boundary Condition Work Conjugate Boundary Condition Actuator / Transfer Device Sensor Natural Physical Feedback Actuator Feedback Motivation: Want actuator to behave the same way as Substructure 1

Feb. 19, 2008 CU-NEES 2008 FHT Workshop Introduce a controller Substructure 1 Computational Substructure 2 Physical External Input Boundary Condition Work Conjugate Boundary Condition Actuator / Transfer Device Natural Physical Feedback Actuator Feedback Controller

Feb. 19, 2008 CU-NEES 2008 FHT Workshop Introduce a controller Substructure 1 Computational Substructure 2 Physical External Input Work Conjugate Boundary Condition Actuator / Transfer Device Natural Physical Feedback Actuator Feedback Controller Takes the same input as Substructure 1 Boundary Condition + -  Tries to do the same Thing as Substructure 1 Error

Feb. 19, 2008 CU-NEES 2008 FHT Workshop Model Reference Control Controller designed so that does the same thing as Part implemented in the computer

Feb. 19, 2008 CU-NEES 2008 FHT Workshop Another Approach Internal Model Control - IMC Part implemented in the computer

Feb. 19, 2008 CU-NEES 2008 FHT Workshop 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

Feb. 19, 2008 CU-NEES 2008 FHT Workshop CU FHT Algorithm Computer implementation of IMC Discretize at 10 msDiscretize at 1 ms CU FHT Algorithm !! (Shing et. al., 2005)

Feb. 19, 2008 CU-NEES 2008 FHT Workshop 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

Feb. 19, 2008 CU-NEES 2008 FHT Workshop Hybrid Simulation with a Shaking Table Necessary when physical substructure has distributed mass Masses simulated Physical substructure has no masses of significance, hence no inertia effects (Hence pseudo-dynamic) 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

Feb. 19, 2008 CU-NEES 2008 FHT Workshop 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

Feb. 19, 2008 CU-NEES 2008 FHT Workshop 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 – 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 Physical Substructure Computational Substructure Shaking Table External Actuator Computational Substructure Physical Substructure Response Feedback Reaction Wall Shaking Table Physical Substructure Response Feedback Hybrid Simulation Configurations Combination of Shaking Table and External Actuator Shaking Table Only

Feb. 19, 2008 CU-NEES 2008 FHT Workshop 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