Real-time Hybrid Testing Research Articles

Shaking‐table substructure test using a MDOF boundary‐coordinating device

AbstractBoundary coordination is necessary for a shaking‐table substructure test (STST), which includes transferring forces and displacements between the tested and numerical substructures. Unlike other real‐time hybrid tests (RTHTs), the physical substructure is mounted on a shaking table and excited by the inertial force, which naturally requires a force control for boundary coordination. However, the natural velocity feedback in hydraulic actuators and high‐frequency noise in the force feedback signals makes it difficult to achieve force control. To solve these difficulties, in this study, a multi‐degree‐of‐freedom (MDOF) boundary‐coordinating device (BCD) is developed to simultaneously implement the boundary shear force and bending moment by the inertial force generated from shaking masses that are uniaxially driven by electromagnetic actuators. An STST framework was developed based on the BCD. The bottom two stories of a four‐story steel moment frame were selected as the physical substructure. A hydraulic shaking table was employed for ground excitation, and the BCD was used as the boundary coordinator for the numerical substructure, that is, the top two stories of the frame. To trace high‐frequency force signals, an enhanced three‐variable control (ETVC) method is proposed. Furthermore, an error‐response negative‐feedback compensation (ENC) method was developed to reduce the adverse effects of loading errors. Several rounds of STST tests demonstrated that the boundary commands were effectively traced by the BCD, so that the STST framework could consistently reproduce the seismic behavior of engineering structures.

Constrained Mode–Damping Solvent Extraction Combined Method for the Soil Incorporation into a Real-Time Hybrid Test of the Soil–Structure System

The real-time hybrid test is an effective testing method for soil–structure interaction research. Due to the data interaction time requirement and formula derivation method, the traditional real-time hybrid test of soil–structure interaction mostly employs a simple numerical substructure model. This study investigated the model construction and numerical simulation of a finite element soil substructure with high simulation accuracy and calculation efficiency. The soil was subdivided into near-field and far-field zones. A constrained mode–damping solvent extraction combined method was applied to the latter zone, reducing the soil’s computational scale and simulating the far-field energy dissipation effect. Then, the basic formula of the near-field zone–structure system was derived using the branch mode method, and the motion equation of the soil–structure system applied to real-time hybrid test was obtained. The soil’s numerical model was realized by the joint application of ANSYS and MATLAB software packages and verified through the real-time hybrid test of the soil–structure system. The results show that the proposed constrained mode–damping solvent extraction combined method had high calculation efficiency and good accuracy. It satisfied the requirements of the soil numerical substructure in real-time hybrid tests.

Experimental study on ice-structure interaction phenomena of vertically sided structures

This study analyses the results from basin tests with a vertically sided cylindrical pile loaded by ice failing in crushing. Tests were performed with a ‘rigid’ structure and with structural models representing a series of single-degree-of-freedom (SDOF) oscillators covering a wide range of mass, frequency, and damping values. The structural models were represented by a real-time hybrid test setup, which combined physical and numerical components to measure real ice forces, apply the forces to a numerical structural model, and simulate the dynamics of the tested structural models in real-time. The test results are analysed and simple numerical simulations are performed to assess the relevance of several ice force characteristics observed from the ‘rigid’ structure tests to the ice-induced vibrations in the SDOF oscillators. The results from the rigid structure tests show that the median ice forcing frequency is linearly related to the ice drift speed. The mean and standard deviation of the ice forces on the rigid structure show a negative force-velocity gradient at low ice drift speeds and indications of a positive force-velocity gradient at higher ice drift speeds. The comparison of experimental results to the simulations of the single-degree-of-freedom oscillator tests shows that the positive force-velocity gradient at higher ice drift speeds allows to best capture the dynamics during continuous brittle crushing as observed in the experiments. Furthermore, the comparison shows that frequency lock-in initiation is primarily driven by the velocity-independent spatial frequency spectrum of the ice force signal. The added damping caused by the positive force-velocity gradient must be considered to capture the frequency lock-in initiation speeds measured in the constant deceleration experiments. The consideration of the negative force-velocity gradient at low relative velocities is not needed to capture these frequency lock-in initiation speeds as observed in the experiments. However, once frequency lock-in is initiated, the negative gradient is needed to correctly capture the dynamics during frequency lock-in. Analysis of the results shows that the peak forces during intermittent crushing at the end of the load build-up phase have a dependence on relative velocity equal to the load dependence on velocity of rigid structures at low speed. This indicates that intermittent crushing is not a purely brittle type of interaction.

High-Bandwidth Mechanical Hardware-In-The-Loop Emulation of Structural Dynamics for More Efficient NVH Development and Testing

<div class="section abstract"><div class="htmlview paragraph">Numerical simulations offer a wide range of benefits. Therefore, they are widely used in research and development. One of the biggest benefits is the possibility of automated parameter variation. This allows testing different scenarios very quickly. Nevertheless, physical experiments in the laboratory or on a test rig are still, and will remain, necessary. Physical experiments offer benefits, e.g., for very complex and/or nonlinear systems and are required for the validation of numerical models. To enhance the quality of experimental NVH investigations and to make use of the benefits of numerical simulation during experimental investigations at the same time, numerical models can be integrated into physical test rigs using the mechanical hardware-in-the-loop (mHIL) method (also referred to as real-time dynamic substructuring, hybrid testing or active control of impedance). During experimental NVH testing, the device under test (DUT) is connected to a mHIL interface which in turn actively emulates the structural dynamics of the boundary condition based on a numerical target impedance model. The goal is to have realistic contact forces instead of blocked forces at the mounting points of the DUT.</div><div class="htmlview paragraph">This paper illustrates the development and characterization of a modular mHIL interface with high bandwidth for NVH testing of a vehicle’s front axle. The physical emulation of structural dynamics based on a target impedance model is demonstrated for synthetic test cases (e.g., emulation of different stiffness settings, or multi-resonant behavior) up to 1 kHz. Furthermore, emulation of the vehicle chassis’ structural dynamics in a single spatial direction is shown for an NVH investigation on a single-axis chassis dynamometer.</div></div>

An innovative aerodynamic design methodology of wind turbine blade models for wind tunnel real-time hybrid tests based on genetic algorithm

The physical model tests of floating offshore wind turbines (FOWTs) in wave basins cannot simulate the aerodynamic loads accurately. The real-time hybrid model test in wind tunnel provided a better solution to this problem, especially for the simulation of unsteady aerodynamic behaviors. The key to wind tunnel test is the design of aerodynamic thrust-matched blade model. In this paper, an innovative methodology was proposed to design the wind turbine blade models for the wind tunnel tests, based on the genetic algorithm. The design was focused on the aerodynamic thrust performance of blade model to achieve equivalent aerodynamic thrust under different wind speeds. To prove the applicability of this methodology, the DTU 10 MW and NREL 5 MW wind turbine were used for case study and the low-Reynolds airfoil SD7032 was chosen for the aerodynamic design. During the design process, three shape control methods were employed for the twist angles and chords of blades and the effects of these three methods were also compared. The aerodynamic performances of blade models were verified using Aerodyn of FAST, compared to the prototypes. According to the results, the aerodynamic thrust performances of blade models reached good agreement with prototypes in the full wind speed range.

Nonlinear behavior simulation of soil-structure interaction system via real-time hybrid testing

Nonlinear behavior simulation of soil-structure interaction system via real-time hybrid testing

A Novel Moving Load Integration Method for Real-Time Hybrid Shaking Table Test of High-Speed Maglev Vehicle–Bridge Interaction System

Real-time hybrid shaking table test for high-speed maglev vehicle–bridge interaction (VBI) system is an important method to study dynamic response of the system. Numerical experiments are usually conducted in advance to guarantee the test performed smoothly. This paper presents a novel moving load integration method combined with a truncated bridge model for fast calculation of bridge responses, and presents a framework for performing numerical experiment of a real-time hybrid test of VBI system. A realistic numerical experiment is conducted on a real-time simulator, i.e. xPC Target, integrating three commercial software, i.e. SIMPACK, ANSYS, and MATLAB-Simulink[Formula: see text], to model a real TR08 single-carriage maglev train, a 5-spans bridge and 28 shaking tables, respectively. The driving speed is 400–600[Formula: see text]km/h and the time step size in the test is 1/256[Formula: see text]s. The accuracy of moving load integration method with truncated bridge model is verified, the effects of speed on the dynamic responses of VBI systems are studied, the time delay of shaking tables and compensation algorithm is investigated, and the effects of local nonlinearity of the bridge on system responses are studied. This paper provides a practical method and valuable reference for the real-time hybrid shaking table test of vehicle–bridge coupled systems.

Reproduction of seismic responses of wind turbine tower by hybrid tests considering shear and bending coupled boundary control

The dynamic responses of wind turbine towers subjected to earthquakes and winds are very complex and might cause significant damages. However, the reproduction of the dynamic response in a laboratory is not easy because the specimen shall be scaled very small to meet the space limits of wind tunnels and shaking tables. Real-time hybrid testing (RTHT) is an appealing option to solve this difficulty, which takes part of a structure as the specimen, while treats the rest numerically so that large scale specimen could be used. However, the application of RTHT to a wind turbine tower requires more complex boundary coordination to reproduce the coupled shear and bending behavior. This paper proposes a shaking-table substructure testing framework, where the lower part of the tower is fixed on the shaking table at the bottom and the top of the specimen is simultaneously loaded by a two-degree-of-freedom loading device. The loading facilities communicate in real time with the numerical substructure, and the superstructure including the wind turbine and blades is numerically simulated under the external excitations. Displacements and forces at the boundary are transferred between the numerical and physical substructures to realize boundary compatibility and equilibrium. A novel boundary loading device controls two masses to realize bending and shear equilibrium at the same boundary surface. Enhanced three-variable control is proposed to improve the performance of boundary coordination and the error-response negative feedback compensation method is proposed to reduce error transmission in RTHT, as demonstrated and introduced in a series of simulations and conceptual study.

Study on the Stabilities of RTH Tests Using the CDM Method considering Two Kinds of Systematic Errors

Real-time hybrid (RTH) test is a promising test method to investigate seismic responses of structures and is essentially a time history analysis. Therefore, an in-depth understanding of the control algorithm, such as a central difference method (CDM), is important for this method. In this paper, stabilities of the CDM considering two kinds of errors are investigated theoretically and experimentally. It turns out that the convergence criterion of the CDM cannot be changed by constant errors but can be changed by proportional errors. The lowest structural natural period to keep the results stable increases with the increase of the ratio of the displacement error to the interface displacement and the integration time step. At last, the theoretical result of the stability of the CDM considering two kinds of systematic errors are confirmed by the proposed test system with a natural rubber bearing.

On Real-Time Hybrid Testing of Ocean Wave Energy Conversion Systems: An Experimental Study

The growing wave energy sector requires an efficient and flexible testing process for the development phase of wave energy systems. Real-time hybrid testing is a promising technique for the accelerated testing of wave energy conversion systems. This article presents an experimental study on developing a hybrid testing platform for wave energy systems at the Wallace Energy System and Renewables Facility (WESRF) at Oregon State University. The wave energy conversion system is broken down into numeric (i.e., virtual) and physical (i.e., hardware) components. The numeric component involves software components such as the control algorithm for Wave Energy Converter (WEC) and controller for the power electronic converters and numerical models for the WEC device hydrodynamics. The hardware involves an ocean wave emulator testbed, Power Take-Off (PTO) mechanism, power electronics, and instrumentation. The numeric components are implemented in a real-time target machine and are interfaced with the experimental system. A case study implementation of Nonlinear Model Predictive Control (NMPC) is presented for a single degree of freedom heaving nonlinear WEC model with a Permanent Magnet Synchronous Generator (PMSG) as a PTO system. A Field-Oriented Control (FOC) algorithm controls the PMSG-PTO generation using a three-phase Integrated Intelligent Power (IIP) module converter. A demonstration of the proposed hybrid testing setup is provided.

Frequency domain analysis method of tuned liquid damper controlled multi-degree of freedoms system subject to earthquake excitation

Tuned liquid damper (TLD) is a typical passive device to control structural response under wind and earthquake excitation. At present, TLD is often used to control single-mode of structure. Hence, the design theory of TLD is often based on single-degree of freedom (SDOF) system in frequency domain, which is hard to accurately evaluate seismic performance of TLD-installed multi-degree of freedoms (MDOFs) with consideration of higher mode. In this work, a frequency domain transfer function for TLD controlled MDOFs system is established through the concept of substructure to evaluate overall seismic performance of TLD-installed MDOFs. The accuracy of the transfer function is verified by real-time hybrid testing. Using this transfer function, the effect of TLD on the seismic performance of MDOFs was discussed in frequency domain by parametric analysis. The analytical results indicated that, based on the design theory for single-mode, the TLD with large mass ratio cannot enhance the seismic performance effectively comparing with small mass ratio. In order to improve the control efficiency of relatively large mass TLD, a design method for multi-mode control is established based on the developed frequency domain transfer function. The simulation results showed that, with same TLD mass, the multi-mode method performed smaller structural acceleration response and similar displacement response relative to the single mode method.

Real-time hybrid testing for efficiency assessment of magnetorheological dampers to mitigate train-induced vibrations in bridges

ABSTRACT The dynamic response of railway bridges is important to consider, as the high velocity loading from the trains increases the risk of resonance. Increasing train speeds and loads result in a need for adaptable properties for railway bridges. One solution is to install magnetorheological dampers, as the response of the structure originating from moving loads could be controlled by alternating the input current to the damper. However, the complexity of such devices results in difficulties to accurately model their behaviour. From this context, real-time hybrid simulations, consisting of a numerical bridge model and a full-scale physical magnetorheological damper in a test frame, are presented in this paper. The novelty of the present paper is the application of RTHS in railway bridge engineering and the substructure combination with magnetorheological dampers. The results from the real-time hybrid simulations show that the bridge deck responses can be reduced to permissible levels.

Real-time hybrid test of a LNG storage tank with a variable curvature friction pendulum system

Real-time hybrid test of a LNG storage tank with a variable curvature friction pendulum system

Real-Time Hybrid Test Using Two-Individual Actuators to Evaluate Seismic Performance of RC Frame Model Controlled by AMD

Seismic responses of a single-story RC frame building model under control using an active mass damper (AMD) are demonstrated through a real-time hybrid simulation (RTHS) method. In this study, the RTHS test is carried out by using a hydraulic actuator and a shaking table under a synchronization. Most parts of the target RC frame model are provided as an analytical model for an online computer simulation, and the only single column of the first story is prepared as an experimental substructure. A hydraulic actuator deforms the actual RC column, and uncertainty or nonlinearity of the RC column’s behavior is focused on this RTHS test. At the same time, a control device of AMD is actually tested under a situation of installing it on the target building's floor. The floor response of the target building model is generated using a shaking table. A control motion of the AMD is manipulated based on an online simulation of the entire RC building model. Firstly, a time delay compensation of the hydraulic actuator is considered. Time delay parameters are identified using a combination model of a time lag and a first-order delay. A PID controller and a time series compensator (TSC) are applied to improve actuator performances. Next, the reproducibility of the RTHS test using two-individual actuators is evaluated. The tracking of a restoring force and deformation of the actual RC column specimen generated by the hydraulic actuator and floor motion responses reproduced on the shaking table are investigated. To improve the online numerical simulation based on the measured force responses of the RC column specimen, a high-pass filter (HPF) is applied for a force correction to utilize its phase-lead property. The effect of this HPF force correction is evaluated in both a linear region and a strong nonlinear region of the actual RC column specimen. Finally, the RTHS test results are compared to fully-numerical simulations, and the control effect of the AMD to increase the damping effect for the target RC building model is also investigated.

Passivity control for nonlinear real-time hybrid tests

In real-time hybrid testing, systems are separated into a numerically simulated substructure and a physically tested substructure, coupled in real time using actuators and force sensors. Actuators tend to introduce spurious dynamics to the system which can result in inaccuracy or even instability. Conventional means of mitigating these dynamics can be ineffective in the presence of nonlinearity in the physical substructure or transfer system. This article presents the first experimental tests of a novel passivity-based controller for hybrid testing. Passivity control was found to stabilize a real-time hybrid test which would otherwise exhibit instability due to the combination of actuator lag and a stiff physical substructure. Limit cycle behaviour caused by nonlinear friction in the actuator was also reduced by 95% with passivity control, compared to only 64% for contemporary methods. The combination of passivity control with conventional methods is shown to reduce actuator lag from 35.3° to 13.7°. A big advantage of passivity control is its simplicity compared with model-based compensators, making it an attractive choice in a wide range of contexts.

Passivity-based adaptive delay compensation for real-time hybrid tests

This article presents a novel passivity-based adaptive delay compensation scheme for cancelling actuator dynamics in real-time hybrid testing. This scheme uses the energy added to the system by actuation hardware, to quantify a variable delay, which is subsequently used for delay compensation. It offers the advantage of correcting for tracking errors and instability in hybrid tests and can be implemented without any information of the actuator’s dynamics. Thus, it offers an advantage over most conventional actuator dynamics mitigation schemes which require an accurate model of the actuator prior to testing. Experimental results compare the performance of passivity-based adaptive delay compensation with that of a state-of-the-art adaptive delay compensation scheme based on position. It was found that passivity-based adaptive delay compensation continuously updates the delay estimate while the position-based scheme only updates the delay when the system crosses zero. The performance of both schemes was found to be similar for sinusoidal inputs, mitigating phase lags of up to 35.6° at 10 Hz in the hybrid system tested. Passivity-based adaptive delay compensation requires no extra hardware as it can be run on the same hardware used to drive the actuator, enabling an affordable solution applicable to a wide range of hybrid tests.

Performance extension of shaking table‐based real‐time dynamic hybrid testing through full state control via simulation

Real-time dynamic hybrid testing (RTDHT) is a state-of-the-art experimental technique for evaluating the performance of a structural system subjected to time-varying loads. Because of the superiority of shaking table for testing rate-dependent and inertial effect existing in structural system, shaking table-based RTDHT is an important branch in RTDHT family, in which shaking table is used to impose inertial forces on physical substructure. Owing to the mass of the seismic platform, shaking table has a relatively narrow testing bandwidth akin to a stand-alone actuator RTDHT system. Furthermore, structure–table interaction confines the physical substructure to a very small mass and linear stage, such that shaking table-based RTDHT is unable to test the structural performance with consideration of high frequency input or non-linearity using large-scale physical substructure. Actually, this is why we develop RTDHT. In this work, a control strategy named full state control via simulation (FSCS) was proposed to extend the testing capacity of shaking table-based RTDHT. The efficiency of FSCS-controlled RTDHT for testing high frequency and non-linear structural performance was verified by a small- and large-scale shaking table-based RTDHT, respectively.

Verification of Optimized Real-time Hybrid Control System for Prediction of Nonlinear Materials Behavior with 3-DOF Dynamic Test

Real-time hybrid method is an economical and efficient test method to evaluate the dynamic behavior. The purpose of this study is to develop the computational algorithm and to prove the reliability of a real-time hybrid control system. For performing the multi-direction dynamic test, three dynamic actuators and the optimized real-time hybrid system with new hybrid simulation program (FEAPH) and a simplified inter-communication were optimized. To verify the reliability and applicability of the real-time hybrid control system, 3-DOF (3 Degrees of Freedom) non-linear dynamic tests with physical model were conducted on a steel and concrete frame structure. As a ground acceleration, El Centro and Northridge earthquake waves were applied. As a result, the maximum error of numerical analysis is 13% compared with the result of shaking table test. However, the result of real-time hybrid test shows good agreement with the shaking table test. The real-time hybrid test using FEAPH can make good progress on the total testing time and errors. Therefore, this test method using FEAPH can be effectively and cheaply used to evaluate the dynamic performance of the full-scale structure, instead of shaking table and full-scale test.

Power-Flow-Based Stabilization for Adaptive Feedforward Filters in Hybrid Testing

Real-time hybrid testing is a technology which allows the coupling of simulations and component tests in order to simulate complex system dynamics. Delays and time lags caused by actuator dynamics and signal processing deteriorate the stability of the tests in many cases. The application of adaptive feedforward filters to hybrid testing enables circumventing this problem. The stability of the filter itself, however, can be affected by the choice of the algorithm parameters or changes in dynamics of the system being tested. Test safety requirements and practical considerations require a failsafe implementation. In this paper, we propose a method for adjusting the parameters of the adaptive feedforward filter based on power-flows in the test setup. The objective is to maintain a passive behavior of the actuation and control system. The stabilization acts on the leakage factor and the adaptation gain of a least-mean-squares adaptation law. A simple numerical system is used to investigate the effect of the algorithm parameters on the stabilization. The method was applied to an experimental setup including a nonlinear stiffness. Several originally unstable configurations were stabilized, the adaptation process could be continued and interface synchronization was achieved in all test cases.

Passivity control with adaptive feed-forward filtering for real-time hybrid tests

Real-time hybrid testing combines the reliability of experimental testing with the convenience of numerical simulation. The system to be tested is split into a physical substructure and a real-time numerical simulation which are coupled using actuators and sensors to transfer data at the interface in real-time. In order to achieve stable and accurate hybrid testing representative of the true system, high fidelity control is required at the substructure interface. However, actuators have a response lag which results in tracking errors and potential instability in hybrid tests. This paper investigates the effectiveness of a combined compensation strategy based on passivity control and adaptive feedforward filtering to improve stability, robustness and tracking performance in real-time hybrid testing. The combined strategy is adaptive and requires no prior information of the actuator dynamics unlike conventional transfer dynamics compensators in real-time hybrid testing. Moreover, the scheme requires no extra hardware making it inexpensive and applicable to a wide range of systems. Experimental results on a single degree of freedom nonlinear real-time hybrid test show the potency of the scheme in synchronizing​ substructure displacements while improving stability. The scheme was also found to restore stability of hybrid tests inherently unstable due to actuator delay whilst phase lags of up to 58 degrees have been successfully mitigated in a lumped parameter mechanical oscillator system.