International Journal of Lifecycle Performance Engineering (8 papers in press)
Special Issue on: Hybrid Simulation for Multi-Hazard Engineering
Reproduction of Wind and Earthquake Coupling Effect on Wind Turbine Tower by Shaking Table Substructure Test
by Yingpeng Tian, Tao Wang, Huimeng Zhou
Abstract: Wind turbines are being used in increasingly complex working environments that generate coupled wind and earthquake effects. Areas with abundant onshore wind energy in China are concentrated in central and western earthquake-prone regions. Recent projects have tended to construct larger wind turbines to improve efficiency, but this generates more wind-induced vibration. Moreover, different threats are faced by a wind turbine at various stages. During construction, for example, vortex-induced resonance might result in a large lateral displacement of up to 1 meter, making the installation of blades difficult. Meanwhile, during service, the structure of a wind turbine can be damaged by strong gales and sometimes by earthquakes. The present study develops a tuned mass damper, which is designed to mitigate the lateral displacement introduced by vortex-induced resonance. The possibility of reducing the response to a gale and earthquake are then examined. Shaking-table substructure hybrid tests are conducted to verify the performance of the tuned mass damper for different external loads. The experimental results confirm the effectiveness in terms of suppressing vortex-induced resonance, while the mitigation of the response to wind and earthquakes is limited.
Keywords: wind turbine tower; tuned mass damper; wind and earthquake coupled effect; shaking table; substructure test.
Assessing Structural Reliability Using Real-Time Hybrid Substructuring
by Connor Ligeikis, Richard Christenson
Abstract: While numerical simulations can be used to predict the dynamic performance of structural systems, there are some instances where the dynamical behavior and uncertainties of specific system components may be difficult to accurately model. In these instances, structural reliability assessments may be conducted by employing the cyber-physical real-time hybrid substructuring (RTHS) test method. In this approach, a numerical model of a larger structural system, incorporating uncertainty in specific parameters, is coupled with a physical test specimen of a system component to fully capture system-level dynamic interactions and facilitate uncertainty propagation. This paper specifically details a study performed to experimentally validate the previously proposed Adaptive Kriging-Hybrid Simulation (AK-HS) structural reliability method. The AK-HS method combines Kriging metamodeling, an adaptive learning algorithm, Monte Carlo simulation, and RTHS testing to iteratively estimate a structural systems probability of failure given random parameters in the numerical model. The method is validated with a series of bench-scale RTHS tests on a viscous damper connecting two adjacent 6-degree-of-freedom rigid body structures. The AK-HS method is shown to accurately predict probabilities of failure for systems with up to 24 random variables using a reasonable number of RTHS tests.
Keywords: Real-time hybrid substructuring; adaptive kriging-hybrid simulation; structural reliability; metamodeling; vibration control.
Multi-Hazard Real-Time Hybrid Simulation of a Tall Building with Damped Outriggers
by Chinmoy Kolay, Safwan Al-Subaihawi, Thomas Marullo, James Ricles, Spencer Quiel
Abstract: The essence of real-time hybrid simulation (RTHS) is its ability to
combine the benefits of physical testing and computational simulations and
thereby efficiently simulate the dynamic response of a structure. The method is
known to be accurate and more affordable compared to other dynamic testing
techniques. However, the RTHS technique has primarily been applied to simulate
seismic effects in structures. This paper successfully extends its application to
wind response simulation of a 40-storey tall building outfitted with nonlinear
fluid viscous dampers. In the RTHS, the building frame is modelled numerically,
and the dampers are modelled physically. A series of RTHS is performed for
both seismic and wind loadings. This paper presents the RTHS implementation
procedure for multiple hazards, discusses the RTHS results and summarises the
issues and challenges regarding the current implementation. The paper concludes
with some remarks on the essence of RTHS in performance-based engineering
considering multiple hazards.
Keywords: real-time hybrid simulation; seismic response; wind response; tall building; outrigger; damper.
Implementation of real-time hybrid shake table testing using the UCSD large high-performance outdoor shake table (LHPOST)
by Manuel Vega, Andreas Schellenberg, Humberto Caudana, Gilberto Mosqueda
Abstract: Large shake tables can provide extended capabilities to conduct large- and full-scale tests examining the seismic behavior of structural systems that cannot be readily obtained from reduced scale or quasi-static testing conditions. Assessing the behavior of large or complex structural systems introduces challenges such as high cost of full-scale specimens or capacity limitations of currently available shake tables. Some of these limitations may be overcome by employing the real-time hybrid shake table test method that requires only key subassemblies to be evaluated experimentally on the shake table while the remainder of the structure is modeled numerically. As a demonstration of the applicability of this testing method using a large shake table, a series of hybrid shake table tests were conducted on the UCSD Large High-Performance Outdoor Shake Table (LHPOST) with capabilities to test full scale structural models. A physical specimen was coupled with a numerical model using hybrid simulation techniques and shown to reproduce reliable results with adequate mitigation of experimental errors.
Keywords: Hybrid shake table; Midlevel isolation; Substructuring technique; Friction pendulum.
Real-Time Hybrid Simulation Using Analog Electronic Computer Technology
by Michael Harris, Richard Christenson
Abstract: In the field of structural dynamics, Real-Time Hybrid Simulation (RTHS) continues to receive increased interest from researchers conducting component testing incorporating system-level behavior. Increased digital computing power has allowed advances in RTHS. However, limitations in RTHS will persist due to the effects of discrete errors caused by quantization and corresponding numerical integration time step limitations, which can limit the bandwidth and nonlinearities of the system studied. In this paper, an analog electronic computer is constructed to conduct RTHS of a modeled base-isolated structure with a physically tested viscous damping device. The analog computer models a two-degree-of-freedom (2DOF) structure and solves the equations of motion required in RTHS testing. Results of the RTHS tests using the analog computer are compared to RTHS tests implemented with a digital computer in order to validate the proposed analog RTHS method. Further applications of RTHS testing with analog computing including high-frequency dynamic testing are discussed.
Keywords: Real-time Hybrid Simulation; Analog Computer; Base Isolated; Supplemental Damping.
Concept, Experimental Demonstration and Numerical Study of Force-Based Hybrid Simulation
by Bahareh Forouzan, Koushyar Shaloudegi, Narutoshi Nakata
Abstract: Hybrid simulation is an advanced technique for dynamic analysis of structures, combining laboratory testing and numerical models. Many successful applications can be found in the studies for seismic analysis of structures. However, applications to the other hazards such as wind and tsunami have been very limited. One of the challenges is that the conventional hybrid simulation does not strictly ensure force equilibrium conditions at each time step, leaving unbalanced force error. In order to expand applications of hybrid simulation to various types of hazards, the unbalanced force has to be eliminated; it is because motion induced forces in aero and hydrodynamic loads have to be consistent with the structural deformation. This study proposes a force-based hybrid simulation to address the above challenge. The paper introduces a concept of force-based hybrid simulation and presents details of the force-based numerical integration algorithm. Following the description of the structural model and test setup, an experimental demonstration of the force-based hybrid simulation for a linear physical specimen is presented. Furthermore, numerical simulation using Bouc-Wen model is performed for an investigation of the applicability of the force-based hybrid simulation to nonlinear system.
Keywords: Force-based numerical algorithm; Force-control; multi-hazard; dynamic of structure; hybrid simulation; substructuring technique.
Structural Seismic Resilience Evaluation through Real-Time Hybrid Simulation with Online Learning Neural Networks
by Jingzhe Wu, Ruiyang Zhang, Brian Phillips
Abstract: Seismic resilience provides a comprehensive assessment of the ability of a community to withstand and recover from earthquake disturbances. To support the design of seismic resilient structures, quantitative assessment of seismic resilience is needed and requires numerical simulations to be performed under a risk-based context. The associated large uncertainties can lead to large computational costs and limited accuracy in the numerical simulation, especially for structural systems with critical components having complex nonlinearity and rate-dependent behavior. To cope with such uncertainties and address simulation accuracy, a framework integrating real-time hybrid simulation is proposed to ensure the assessment accuracy of the seismic resilience of structures. With real-time hybrid simulation, modeling accuracy under wide range of design scenarios can be improved. To more efficiently develop fragility curves using the results of real-time hybrid simulation, experimental substructure component metamodeling is included through an online learning approach using long-short term memory neural networks. The proposed integration of real-time hybrid simulation and metamodeling in the fragility analysis to support resilience assessment is demonstrated through a proof-of-concept case study on the seismic retrofit of a 6-story building using inter-story isolation.
Keywords: seismic resilience; real-time hybrid simulation; metamodeling; long-short term neural networks; fragility; retrofit; inter-story isolation.
A Hybrid Simulation Approach for Aeroelastic Wind Tunnel Testing: Challenges and Foundational Work
by Azin Ghaffary, Elif Ecem Bas, Mohamed Moustafa
Abstract: Wind tunnel testing is common practice for obtaining realistic design wind loads on specific buildings or optimizing geometric designs. Aeroelastic wind tunnel models are used to account for wind-structure interactions, but not as common as rigid models especially due to required physical simulation of reduced model stiffness and damping. Wind Real-Time Hybrid Simulation (wRTHS) is an evolving approach that can be utilized to improve aeroelastic modeling and current wind tunnel testing approaches. While RTHS has been extensively used for earthquake engineering applications, this paper aims at building on such knowledge and conduct foundational work to assess the performance of a typical RTHS setup for conducting future wRTHS. The main objective is to validate the performance of hardware, computational components, and the transfer system as envisioned for future use in wind tunnels. Four building structures with different breadth to height aspect ratios, one of them controlled by a tuned mass damper are used for this purpose. For sake of trial tests, wind loads form the Tokyo Polytechnic database are used to represent a hypothetical wind tunnel force that are applied to scaled numerical models of the structures in real time to calculate deformed shape of the building and reflect such deformation using hydraulic actuator. The different tests considered various existing RTHS methods but validated it for wind loading using two different computational platforms, namely Simulink and OpenSees. Given the different way of substructuring the equation of motion and frequency content of wind loads versus earthquakes, the test results indicate the validity and efficiency of the proposed hardware, software, and transfer system for future wRTHS.
Keywords: Real-time hybrid simulation; wind loads; computational modeling.