Richard Christenson

A fully dynamic magneto-rheological fluid damper model

Control devices can be used to dissipate the energy of a civil structure subjected to dynamic loading, thus reducing structural damage and preventing failure. Semiactive control devices have received significant attention in recent years. The magneto-rheological (MR) fluid damper is a promising type of semiactive device for civil structures due to its mechanical simplicity, inherent stability, high dynamic range, large temperature operating range, robust performance, and low power requirements. The MR damper is intrinsically nonlinear and rate-dependent, both as a function of the displacement across the MR damper and the command current being supplied to the MR damper. As such, to develop control algorithms that take maximum advantage of the unique features of the MR damper, accurate models must be developed to describe its behavior for both displacement and current. In this paper, a new MR damper model that includes a model of the pulse-width modulated (PWM) power amplifier providing current to the damper, a proposed model of the time varying inductance of the large-scale 200 kN MR dampers coils and surrounding MR fluid—a dynamic behavior that is not typically modeled—and a hyperbolic tangent model of the controllable force behavior of the MR damper is presented. Validation experimental tests are conducted with two 200 kN large-scale MR dampers located at the Smart Structures Technology Laboratory (SSTL) at the University of Illinois at Urbana-Champaign and the Lehigh University Network for Earthquake Engineering Simulation (NEES) facility. Comparison with experimental test results for both prescribed motion and current and real-time hybrid simulation of semiactive control of the MR damper shows that the proposed MR damper model can accurately predict the fully dynamic behavior of the large-scale 200 kN MR damper. (Some figures may appear in colour only in the online journal)

Large-Scale Real-Time Hybrid Simulation for Evaluation of Advanced Damping System Performance

AbstractAs magnetorheological (MR) control devices increase in scale for use in real-world civil engineering applications, sophisticated modeling and control techniques may be needed to exploit their unique characteristics. Here, a control algorithm that utilizes overdriving and backdriving current control to increase the efficacy of the control device is experimentally verified and evaluated at large scale. Real-time hybrid simulation (RTHS) is conducted to perform the verification experiments using the nees@Lehigh facility. The physical substructure of the RTHS is a 10-m tall planar steel frame equipped with a large-scale MR damper. Through RTHS, the test configuration is used to represent two code-compliant structures, and is evaluated under seismic excitation. The results from numerical simulation and RTHS are compared to verify the RTHS methodology. The global responses of the full system are used to assess the performance of each control algorithm. In each case, the reduction in peak and root mean s...

System Identification of a 200 kN Magneto-Rheological Fluid Damper for Structural Control in Large-Scale Smart Structures

This paper presents a hyperbolic tangent model to capture the salient dynamic behavior of large-scale 200 kN magneto-rheological (MR) fluid dampers. The damper model will be used for simulation studies of the effectiveness of semiactive control for seismic protection as well as for controller design and diagnostic tests for large-scale real-time testing of the MR dampers at the University of Colorado at Boulder (CU) fast hybrid test (FHT) facility. A series of sinusoidal tests are conducted at the CU FHT facility for varying frequencies, amplitudes, and constant control current levels to determine the parameters of the hyperbolic tangent model as functions of current. Finally, the simulated damper force from the MR damper model is compared to that of the physical MR dampers subjected to random excitation and random control current. The hyperbolic tangent model is observed to predict closely the experimentally obtained MR damper forces over a wide dynamic range and within the constraints of computation time and fixed integration time step required for real-time diagnostic tests utilizing the CU FHT system.

A comparison of 200 kN magneto-rheological damper models for use in real-time hybrid simulation pretesting

Control devices can be used to dissipate the energy of a civil structure subjected to dynamic loading, such as earthquake, wave and wind excitation, thus reducing structural damage and preventing failure. The magneto-rheological (MR) fluid damper is a promising device for use in civil structures due to its mechanical simplicity, inherent stability, high dynamic range, large temperature operating range, robust performance, and low power requirements. The MR damper is intrinsically nonlinear and rate dependent. Thus a challenging aspect of applying this technology is the development of accurate models to describe the behavior of such dampers for control design and evaluation purposes. In particular, a new type of experimental testing called real-time hybrid simulation (RTHS) combines numerical simulation with laboratory testing of physical components. As with any laboratory testing, safety is of critical importance. For RTHS in particular the feedback and dynamic interaction of physical and numerical components can result in potentially unstable behavior. For safety purposes, it is desired to conduct pretest simulations where the physical specimen is replaced with an appropriate numerical model yet the numerical RTHS component is left unchanged. These pretest simulations require a MR damper model that can exhibit stability and convergence at larger fixed integration time steps, and provide computational efficiency, speed of calculation, and accuracy during pretest verification of the experimental setup. Several models for MR dampers have been proposed, including the hyperbolic tangent, Bouc?Wen, viscous plus Dahl and algebraic models. This paper examines the relative performance of four MR damper models of large-scale 200?kN MR dampers as needed for pretest simulations of RTHS. Experimental tests are conducted on two large-scale MR dampers located at two RTHS test facilities at the Smart Structures Technology Laboratory at the University of Illinois at Urbana Champaign and the Lehigh University Network for Earthquake Engineering Simulation facility. It is shown that each of the MR damper models examined has relative merits and the ultimate selection of the particular model is dependent on the specific RTHS being tested.

Experimental evaluation of an adaptive inverse compensation technique for real-time simulation of a large-scale magneto-rheological fluid damper

Magneto-rheological (MR) dampers are semi-active control devices whose characteristics are varied under different current inputs in accordance with semi-active control laws to achieve optimized vibration control of a structural system. Experimental evaluation of the effectiveness of MR dampers for seismic hazard mitigation using selected control laws is necessary to enable performance-based design procedures to be developed and for these devices to become accepted by the practical design community. Real-time hybrid simulation provides an economical and efficient experimental technique which enables both the damper rate dependence and the damper–structure interaction to be accounted for. A successful real-time hybrid simulation requires accurate actuator control to achieve reliable experimental results. A time delay and actuator time lag (referred to hereafter as simply the delay) can be introduced into the actuator response due to state determination, communication, and servo-hydraulic dynamics. The variable current inputs and resulting variable forces induced by semi-active control laws pose additional challenges for actuator control by introducing variable delay in a real-time hybrid simulation. In this paper a newly developed adaptive inverse compensation technique is experimentally evaluated for application in real-time hybrid simulation involving an MR damper subjected to band-limited white noise-generated random displacements and variable current inputs. Actuator control is assessed using different evaluation criteria. The adaptive inverse compensation method is demonstrated to achieve good actuator control and therefore shows good potential for use in real-time hybrid simulation of structural systems with semi-active MR dampers.

On the evaluation of the efficacy of a smart damper: a new equivalent energy-based probabilistic approach

Smart damping technology has been proposed to protect civil structures from dynamic loads. Each application of smart damping control provides varying levels of performance relative to active and passive control strategies. Currently, researchers compare the relative efficacy of smart damping control to active and passive strategies by running numerous simulations. These simulations can require significant computation time and resources. Because of this, it is desirable to develop an approach to assess the applicability of smart damping technology which requires less computation time. This paper discusses and verifies a probabilistic approach to determine the efficacy of smart damping technology based on clipped optimal state feedback control theory.

Real-time hybrid simulation of a complex bridge model with MR dampers using the convolution integral method

Magneto-rheological (MR) fluid dampers can be used to reduce the traffic induced vibration in highway bridges and protect critical structural components from fatigue. Experimental verification is needed to verify the applicability of the MR dampers for this purpose. Real-time hybrid simulation (RTHS), where the MR dampers are physically tested and dynamically linked to a numerical model of the highway bridge and truck traffic, provides an efficient and effective means to experimentally examine the efficacy of MR dampers for fatigue protection of highway bridges. In this paper a complex highway bridge model with 263 178 degrees-of-freedom under truck loading is tested using the proposed convolution integral (CI) method of RTHS for a semiactive structural control strategy employing two large-scale 200 kN MR dampers. The formation of RTHS using the CI method is first presented, followed by details of the various components in the RTHS and a description of the implementation of the CI method for this particular test. The experimental results confirm the practicability of the CI method for conducting RTHS of complex systems.

Real-Time Hybrid Test Validation of a MR Damper Controlled Building with Shake Table Tests

Real-time hybrid testing (RTHTing) is a relatively new form of experimental testing where only the critical components of the system are physically tested while the rest of the structure is simulated. A RTHT can provide a cost-effective means for testing semiactive controlled civil structures. This paper describes the experimental validation of the RTHT facility at the University of Connecticut through comparison of RTHT results with corresponding shake table responses of a Magneto-Rheological (MR) fluid damper controlled test structure. The two-story structure has an MR damper connected between the ground and first story and is excited by ground accelerations. For the shake table tests the fully physical building model and MR damper are tested on a medium-scale shake table. In the RTHT the MR damper alone will be tested physically while the rest of the test structure and ground excitation is simulated in the RTHT control computer. The performance of the RTHT is validated by comparing the building responses and measured damper force with those from the shake table test in both the time and frequency domains.

Experimental Comparison of the Performance and Residual Capacity of CFFT and RC Bridge Columns Subjected to Blasts

AbstractThe blast performance of concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) bridge columns was studied through a two-phase study comprised of blast and residual axial capacity experiments. Two one-fifth-scale CFFT columns and two one-fifth-scale conventional RC columns having comparable flexural capacities were subjected to distinct levels of explosive loading, causing damage but not complete failure. The blast resilience of the damaged columns was quantified by measuring the residual axial capacity of each column. The damaged CFFT columns exhibited superior strength and ductility retention compared with the damaged RC columns. Additionally, the damaged CFFT columns demonstrated a more predictable axial compressive mode of failure because the exterior FRP tube resisted the shear crack initiation observed in the damaged RC columns.

Real-time hybrid simulation using the convolution integral method

This paper proposes a real-time hybrid simulation method that will allow complex systems to be tested within the hybrid test framework by employing the convolution integral (CI) method. The proposed CI method is potentially transformative for real-time hybrid simulation. The CI method can allow real-time hybrid simulation to be conducted regardless of the size and complexity of the numerical model and for numerical stability to be ensured in the presence of high frequency responses in the simulation. This paper presents the general theory behind the proposed CI method and provides experimental verification of the proposed method by comparing the CI method to the current integration time-stepping (ITS) method. Real-time hybrid simulation is conducted in the Advanced Hazard Mitigation Laboratory at the University of Connecticut. A seismically excited two-story shear frame building with a magneto-rheological (MR) fluid damper is selected as the test structure to experimentally validate the proposed method. The building structure is numerically modeled and simulated, while the MR damper is physically tested. Real-time hybrid simulation using the proposed CI method is shown to provide accurate results.