Real-time Hybrid Simulation Results Research Articles

Evaluation of wind-induced response of high-rise structure with TMD system by real-time hybrid simulation test with motor-driven shaking table

Due to the difficulty in constructing the small-scaled model of tuned mass damper (TMD) system to meet the requirement of dynamic similarity law, it is hard to evaluate the vibration control effect of passive TMD system on the wind-induced response of high-rise structure by wind tunnel test. The Real-Time Hybrid Simulation (RTHS) test could provide a suitable solution to this problem by increasing the size of the scaled TMD model to overcome the limitation in dynamic similarity law. A RTHS test system with a linear electric motor-driven shaking table was developed by the interface with model interface toolkit in general real time system operating environment. Taking the Guangzhou New TV Tower with a passive TMD system as an example, the Finite Element (FE) model of Guangzhou New TV Tower was selected as the numerical substructure and TMD system was selected as the experimental substructure, the RTHS test was conducted at a sampling frequency of 250 Hz to estimate the wind-induced response of this high-rise structure with a TMD system in various dynamic wind loading cases. To reduce the time delay effect generated by the nonlinear interaction between motion control system and experimental substructure, the adaptive time series (ATS) compensator for time delay compensation was proposed in the RTHS test. The RTHS results were also compared with the numerical simulation results using the FE model of the investigated object. The RTHS test with additional ATS time delay compensator can obtain more accurate experimental results. The effectiveness of the proposed RTHS test system was testified to be powerful test system to evaluate the wind-induced response of high-rise structures with complex passive TMD system.

Discussion on the accuracy of methods for determining interface force between numerical and physical substructures in shaking table-based real-time hybrid simulation

Real-time hybrid simulation (RTHS) is a developing experimental technology that combines the advantages of numerical simulation and physical test. In RTHS, the interface force is a key physical quantity coupling the dynamic response of physical substructure and numerical substructure. An inaccurate force determination method can distort RTHS results and may cause incorrect estimations of the dynamic performance of structures. This article aims to systematically discuss the impact of possible error in determining the interface force during shaking table-based RTHS. The errors caused by two typical force determination methods, (1) using force sensors and (2) using strain gauges, are comprehensively investigated. These two force determination methods are typically used for (1) performance evaluation of nonlinear damping systems and (2) investigation of soil–structure interaction effects. Virtual hybrid simulation numerical models (in which both physical and numerical substructures are simulated numerically) representing the interface force determination processes are established. The impacts of error on the RTHS results are evaluate quantitatively. The reported findings can assist in developing a deeper understanding of the causes of errors during RTHS and enhance the experimental designs. This, in turn, leads to more accurate and reliable results in RTHS testing.

Real-time hybrid simulation for seismic control performance evaluation of an active inerter damper system

Active structural control has been recognized as an intelligent method to mitigate seismic vibrations of structures by generating superior supplemental damping in structural engineering studies. Recently, active inerter damper (AID) that consists of an inerter and an actuation system has been evolved from active mass damper. AID has advantages of small volume and light weight because of the mechanical properties of inerter that amplify the inertial force by numerous times the mass of the inerter; therefore, installation of an AID system becomes simple in real engineering applications. However, it is difficult to validate seismic control performance of a multi-story specimen with an AID system in structural laboratories limited by capacity of testing facilities. In this study, real-time hybrid simulation (RTHS), which combines experimental testing with numerical simulation is applied to evaluate the control performance of the AID system. A 10-story shear building is numerically simulated as a benchmark building controlled by the AID, which is physically driven in the structural laboratory. A modal linear-quadratic regulator (LQR) with optimized weighting matrices is designed for generating the desired control force for the AID. Meanwhile, a surrogate model of the modal LQR is trained and implemented for comparison purpose. In addition, two force tracking controllers are implemented to reproduce the desired control force through the AID. Furthermore, three approaches for acquiring the achieved force of AID are proposed and employed to feedback the control force to the numerical model for completing the RTHS loop. Finally, mitigation of seismic response is compared and discussed methodically based on the RTHS results. This study suggests the most appropriate RTHS technique for evaluating the control performance of buildings with the AID system.

On the size effects of toroidal tuned liquid column dampers for mitigating wind- and wave-induced vibrations of monopile wind turbines

The toroidal tuned liquid column damper (TTLCD) can be applied in flexible structures to improve the structural dynamic responses. This study focuses on the impact of size effects of TTLCD on the control efficiency. Two types of size effects are experimentally addressed using the real-time hybrid simulation (RTHS) technique: (1) the effects of experimental scale, and (2) the effects of length ratio. A large number of RTHSs are performed, in which a monopile wind turbine is numerically simulated as the numerical substructure, and five TTLCDs with various experimental scales or length ratios are experimentally tested as the physical substructure. The RTHS results show that the effects of experimental scale on the control efficiency and liquid response are insignificant, and a larger length ratio leads to a stronger performance. Besides, the TTLCD is found to be an efficient additional damping device in monopile wind turbines. The comparison between the RTHS results and the simulation results from a theoretical model is made, and it demonstrates that the theoretical model can capture the dynamic interaction process between the structure and TTLCD with good accuracy.

Electrical Submersible Pumps: A System Modeling Approach for Power Quality Analysis With Variable Frequency Drives

This article proposes a high-level engineering guide to develop an integrated system model for power quality analysis in electrical submersible pump (ESP) applications with variable frequency drives (VFDs). Such analyses are troublesome in the industry due to the complexity of these systems. In this article, simple steps to perform system integration analyses of such arrangements, including torsional analysis, are developed. A simplified VFD-ESP model suitable for coupled electrical and mechanical analysis in steady state is proposed in all their configurations of practical interest. Such a model can be easily implemented in common simulation software, significantly reducing engineering efforts for implementation and analysis. The focus of the proposed model is the prediction of ESP failures that might result from a poor power quality caused by VFDs. Analytical expressions of different types of harmonics in these systems, as well as their accurate locations in the frequency domain, including their interharmonics and common-mode harmonics, are derived for this purpose. The effectiveness of the proposed model is verified through offline and real-time hybrid simulation results. Finally, a comparison between simulation results obtained using the proposed model and measurements collected on a down-scale laboratory prototype is carried out to demonstrate the accuracy of the suggested modeling approach.

Real‐time hybrid simulation of a space substructure based on high‐strength steel composite Y‐eccentrically braced frames

Real-time hybrid simulation (RTHS) is a novel structural seismic test method that has good application prospects. The applicability of RTHS for large-scale space frame structures is further investigated in this study based on high-strength steel composite Y-eccentrically braced frames (Y-HSS-EBFs). First, an RTHS system was established, which included OpenSees, OpenFresco, an xPC-Target, and an electrohydraulic servo control system. An adaptive feedforward delay compensator based on displacement prediction was introduced. Then, a shaking table test model of a three-story Y-HSS-EBF was taken as the prototype, the third-story frame with the strongest nonlinear performance was taken as the experimental substructure, and the remaining two stories were taken as the numerical substructure in order to perform the RTHS. The results of the RTHS were compared with those obtained in a purely numerical model and a shaking table test, and the stability of the RTHS system was analyzed. The results indicate that the RTHS results are in good agreement with the numerical simulation results and that RTHS can be used to obtain results similar to the ones obtained using the shaking table. In the typical seismic testing frequencies and the mass distribution ranges of the substructures, the RTHS system displayed good stability and reliability and was able to effectively evaluate the seismic performance of large-scale space frame structures.

Sliding mode control design for the benchmark problem in real-time hybrid simulation

Real-time hybrid simulation (RTHS) is a novel cyber-physical testing technique for investigating especially large or complicated structural systems. Controllers are required to compensate for the dynamics of transfer systems that emulate the interactions between the physical and numerical substructures. Thus, both the stability and accuracy of RTHS testing highly depend on the effectiveness of the control strategy. This paper proposes a robust sliding mode controller (SMC) as a transfer system control strategy in RTHS. A design procedure of the SMC control strategy is presented. The benchmark problem on RTHS control is utilized for demonstration and validation of SMC for this class of problems. Virtual RTHS results show that the SMC strategy significantly improves the performance and robustness of RTHS testing.

Real-time hybrid simulation on high strength steel frame with Y-shaped eccentric braces

In recent years, real-time hybrid simulation (RTHS) has been widely examined by researchers as a new, economical, and reliable seismic testing technology for structural analysis. In this paper, RTHS is applied to the space structure experiment of a high strength steel frame with Y-shaped eccentric braces (HSYE). First, the proposed RTHS method utilized the upper stories of the prototype as the experimental substructure, and the lower stories was taken as the numerical substructure and simulated in finite element software. Then, the OpenFresco test platform and xPC-Target with an adaptive feed-forward delay compensator were used to realize real-time loading. Before conducting the RTHS, the method of adding an adaptive stage before seismic acceleration record was proposed to compensate the initial delay. On this basis, the seismic behavior of the HSYE was tested using selected seismic acceleration records. The results indicated that the RTHS results are stable and reliable. Under an earthquake simulated load, the HSYE structure can give full play to the local energy dissipation characteristics of the shear link and ensure the elasticity of the main frame, which has vast engineering application prospects.

Multi-hazard real-time hybrid simulation of a tall building with damped outriggers

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.

A robust linear-quadratic-gaussian controller for the real-time hybrid simulation on a benchmark problem

Abstract During a real-time hybrid simulation (RTHS), inevitable time delay of actuators when responding to a command will reduce the accuracy of test results and sometimes even cause unstable testing. The inner-loop controller of an actuator is generally capable of eliminating the effects due to small time-delays. However, if a test specimen behaves nonlinearly, accuracy of RTHS results will be impaired. In addition to the uncertainty of test specimens and transfer system, measurement noises of the displacement and force sensors also require a robust external controller for RTHS. In this paper, a robust linear-quadratic-gaussian (LQG) controller with a Loop Transfer Recovery (LTR) procedure and a polynomial-based feedforward prediction (FP) algorithm is proposed to compensate the adverse effects due to time delay and uncertainties within the RTHS testing system. The stability and robustness of the proposed controller are analysed in the frequency domain using the Nyquist curve and the Bode diagrams. Numerical simulations are then carried out on the benchmark problem using both the proposed robust and the conventional LQG controllers and their performance is compared using the nine evaluation criteria. It is demonstrated that the robust LQG (RLQG) controller outperforms the conventional LQG controller in terms of compensating the parameter uncertainties in the testing system and achieving accurate RTHS results.

Performance study of sliding mode controller with improved adaptive polynomial-based forward prediction

Abstract Benchmark problem for real-time hybrid simulation (RTHS) is proposed to enable researchers assessing the robustness and performance of various tracking controllers in a uniform setting. In this paper, a controller combining the sliding mode controller (SMC) and an improved adaptive polynomial-based forward prediction (IAFP) algorithm is proposed. The SMC is adopted for its robustness to the uncertainties that may be experienced in an RTHS testing; while the IAFP is employed as a time delay compensator to stabilize RTHS with large time delay and reduce the time delay effects. Numerical simulations and physical experiments of the RTHS on a linear test specimen are conducted utilizing the program available through the benchmark problem. Time history responses obtained from RTHS are compared with those of the reference model and the nine evaluation criteria are computed, from which the robustness of the proposed controller and accurate RTHS results are demonstrated.

Reliability Assessment of Real-time Hybrid Simulation Under Worst-Case Scenarios Using Frequency-Domain Evaluation Indices

Real-time hybrid simulation (RTHS) allows researchers to physically evaluate critical parts of a prototype structure at full scale in the laboratory while the rest is numerically modeled. The reliability of the RTHS experimental results however still remains unsolved in the presence of experimental errors even though a number of methods have been proposed based on the actuator tracking in the time domain. Frequency-domain evaluation indices (FEI) provide a novel and effective technique to evaluate the amplitude and phase errors of the actuator tracking. In this paper, the correlation between the reliability of RTHS results and the FEI indices is explored for the worst-case scenarios of single-degree-of-freedom (SDOF) linear elastic structures. The influence of natural frequency and damping ratio are considered through a suite of ground motions. The relationship between the FEI parameters and the error of RTHS replicating actual structural response is explored and a criterion based on worst-case scenarios is proposed for reliability assessment. Numerical simulations are conducted to demonstrate the effectiveness of the proposed reliability criterion.

Localized evaluation of actuator tracking for real-time hybrid simulation using frequency-domain indices

Accurate actuator tracking plays an important role in real-time hybrid simulation (RTHS) to ensure accurate and reliable experimental results. Frequency-domain evaluation index (FEI) interprets actuator tracking into amplitude and phase errors thus providing a promising tool for quantitative assessment of real-time hybrid simulation results. Previous applications of FEI successfully evaluated actuator tracking over the entire duration of the tests. In this study, FEI with moving window technique is explored to provide post-experiment localized actuator tracking assessment. Both moving window with and without overlap are investigated through computational simulations. The challenge is discussed for Fourier Transform to satisfy both time domain and frequency resolution for selected length of moving window. The required data window length for accuracy is shown to depend on the natural frequency and structural nonlinearity as well as the ground motion input for both moving windows with and without overlap. Moving window without overlap shows better computational efficiency and has potential for future online evaluation. Moving window with overlap however requires much more computational efforts and is more suitable for post-experiment evaluation. Existing RTHS data from Network Earthquake Engineering Simulation (NEES) is utilized to further demonstrate the effectiveness of the proposed approaches. It is demonstrated that with proper window size, FEI with moving window techniques enable accurate localized evaluation of actuator tracking for real-time hybrid simulation.

A rate‐dependent constitutive model of high damping rubber bearings: modeling and experimental verification

SummaryIn this study, a constitutive model of high damping rubber bearings (HDRBs) is developed that allows the accurate representation of the force–displacement relationship including rate‐dependence for shear deformation. The proposed constitutive model consists of two hyperelastic springs and a nonlinear dashpot element and expresses the finite deformation viscoelasticity laws based on the classical Zener model. The Fletcher–Gent effect, manifested as high horizontal stiffness at small strains and caused by the carbon fillers in HDRBs, is accurately expressed through an additional stiffness correction factor α in the novel strain energy function. Several material parameters are used to simulate the responses of high damping rubber at various strain levels, and a nonlinear viscosity coefficient η is introduced to characterize the rate‐dependent property. A parameter identification scheme is applied to the results of the multi‐step relaxation tests and the cyclic shear tests, and a three‐dimensional function of the nonlinear viscosity coefficient η with respect to the strain, and strain rate is thus obtained. Finally, to investigate the accuracy and feasibility of the proposed model for application to the seismic response assessment of bridges equipped with HDRBs, an improved real‐time hybrid simulation (RTHS) test system based on the velocity loading method is developed. A single‐column bridge was used as a test bed and HDRBs was physically tested. Comparing the numerical and RTHS results, advantage of the proposed model in the accuracy of the predicted seismic response over comparable hysteretic models is demonstrated. Copyright © 2016 John Wiley & Sons, Ltd.

Comparison of delay compensation methods for real-time hybrid simulation using frequency-domain evaluation index

The delay compensation method plays an essential role in maintaining the stability and achieving accurate real-time hybrid simulation results. The effectiveness of various compensation methods in different test scenarios, however, needs to be quantitatively evaluated. In this study, four compensation methods (i.e., the polynomial extrapolation, the linear acceleration extrapolation, the inverse compensation and the adaptive inverse compensation) are selected and compared experimentally using a frequency evaluation index (FEI) method. The effectiveness of the FEI method is first verified through comparison with the discrete transfer function approach for compensation methods assuming constant delay. Incomparable advantage is further demonstrated for the FEI method when applied to adaptive compensation methods, where the discrete transfer function approach is difficult to implement. Both numerical simulation and laboratory tests with predefined displacements are conducted using sinusoidal signals and random signals as inputs. Findings from numerical simulation and experimental results demonstrate that the FEI method is an efficient and effective approach to compare the performance of different compensation methods, especially for those requiring adaptation of compensation parameters.