SUMMARYReal-time hybrid simulation combines experimental testing of physical substructure(s) and numerical simulation of analytical substructure(s), and thus enables the complete structural system to be considered during an experiment. Servo-hydraulic actuators are typically used to apply the command displacements to the physical substructure(s). Inaccuracy and instability can occur during a real-time hybrid simulation if the actuator delay due to servo-hydraulic dynamics is not properly compensated. Inverse compensation is a means to negate actuator delay due to inherent servo-hydraulic actuator dynamics during a real-time hybrid simulation. The success of inverse compensation requires the use of a known accurate value for the actuator delay. The actual actuator delay however may not be known before the simulation. An estimation based on previous experience has to be used, possibly leading to inaccurate experimental results. This paper presents a dual compensation scheme to improve the performance of the inverse compensation method when an inaccurately estimated actuator delay is used in the method. The dual compensation scheme modifies the predicted displacement from the inverse compensation procedure using the actuator tracking error. Frequency response analysis shows that the dual compensation scheme enables the inverse compensation method to compensate for actuator delay over a range of frequencies when an inaccurately estimated actuator delay is utilized. Real-time hybrid simulations of a single-degree-of-freedom system with an elastomeric damper are conducted to experimentally demonstrate the effectiveness of the dual compensation scheme. Exceptional experimental results are shown to be achieved using the dual compensation scheme without the knowledge of the actual actuator delay a priori.
Quantum information processing based on Rydberg atoms emerged as a promising direction two decades ago. Recent experimental and theoretical progresses have shined exciting light on this avenue. In this concise review, we will briefly introduce the basics of Rydberg atoms and their recent applications in associated areas of neutral atom quantum computation and simulation. We shall also include related discussions on quantum optics with Rydberg atomic ensembles, which are increasingly used to explore quantum computation and quantum simulation with photons.
Real-time hybrid simulation combines experimental testing and numerical simulation, and thus is a viable experimental technique for evaluating the effectiveness of supplemental damping devices for seismic hazard mitigation. This paper presents an experimental program based on the use of the real-time hybrid simulation method to verify the performance-based seismic design of a two story, four-bay steel moment resisting frame (MRF) equipped with compressed elastomer dampers. The laboratory specimens, referred to as experimental substructures, are two individual compressed elastomer dampers with the remainder of the building modeled as an analytical substructure. The proposed experimental technique enables an ensemble of ground motions to be applied to the building, resulting in various levels of damage, without the need to repair the experimental substructures, since the damage will be within the analytical substructure. Statistical experimental response results incorporating the ground motion variability show that a steel MRF with compressed elastomer dampers can be designed to perform better than conventional steel special moment resisting frames (SMRFs), even when the MRF with dampers is significantly lighter in weight than the conventional MRF.
SUMMARYReal-time hybrid testing is a method that combines experimental substructure(s) representing component(s) of a structure with a numerical model of the remaining part of the structure. These substructures are combined with the integration algorithm for the test and the servo-hydraulic actuator to form the real-time hybrid testing system. The inherent dynamics of the servo-hydraulic actuator used in real-time hybrid testing will give rise to a time delay, which may result in a degradation of accuracy of the test, and possibly render the system to become unstable. To acquire a better understanding of the stability of a real-time hybrid test with actuator delay, a stability analysis procedure for single-degree-of-freedom structures is presented that includes both the actuator delay and an explicit integration algorithm. The actuator delay is modeled by a discrete transfer function and combined with a discrete transfer function representing the integration algorithm to form a closed-loop transfer function for the real-time hybrid testing system. The stability of the system is investigated by examining the poles of the closed-loop transfer function. The effect of actuator delay on the stability of a real-time hybrid test is shown to be dependent on the structural parameters as well as the form of the integration algorithm. The stability analysis results can have a significant difference compared with the solution from the delay differential equation, thereby illustrating the need to include the integration algorithm in the stability analysis of a real-time hybrid testing system.
SUMMARYReal-time hybrid simulation provides a viable method to experimentally evaluate the performance of structural systems subjected to earthquakes. The structural system is divided into substructures, where part of the system is modeled by experimental substructures, whereas the remaining part is modeled analytically. The displacements in a real-time hybrid simulation are imposed by servo-hydraulic actuators to the experimental substructures. Actuator delay compensation has been shown by numerous researchers to vitally achieve reliable real-time hybrid simulation results. Several studies have been performed on servo-hydraulic actuator delay compensation involving single experimental substructure with single actuator. Research on real-time hybrid simulation involving multiple experimental substructures, however, is limited. The effect of actuator delay during a real-time hybrid simulation with multiple experimental substructures presents challenges. The restoring forces from experimental substructures may be coupled to two or more degrees of freedom (DOF) of the structural system, and the delay in each actuator must be adequately compensated. This paper first presents a stability analysis of actuator delay for real-time hybrid simulation of a multiple-DOF linear elastic structure to illustrate the effect of coupled DOFs on the stability of the simulation. An adaptive compensation method then proposed for the stable and accurate control of multiple actuators for a real-time hybrid simulation. Real-time hybrid simulation of a two-story four-bay steel moment-resisting frame with large-scale magneto-rheological dampers in passive-on mode subjected to the design basis earthquake is used to experimentally demonstrate the effectiveness of the compensation method in minimizing actuator delay in multiple experimental substructures.
Real-time hybrid simulation is a viable and economical technique that allows researchers to observe the behavior of critical elements at full scale when an entire structure is subjected to dynamic loading. To ensure reliable experimental results, it is necessary to evaluate the actuator tracking after the test, even when sophisticated compensation methods are used to negate the detrimental effect of servo-hydraulic dynamics. Existing methods for assessment of actuator tracking are often based on time-domain analysis. This paper proposes a frequency-domain-based approach to the assessment of actuator tracking for real-time hybrid simulations. To ensure the accuracy of the proposed frequency response approach, the effects of spectrum leakage are investigated as well as the length and sampling frequency requirements of the signals. Two signal pre-processing techniques (data segmentation and window transform) are also discussed and compared to improve the accuracy of the proposed approach. Finally the effectiveness of the proposed frequency-domain-based approach is demonstrated through both computational analyses and laboratory tests, including real-time tests with predefined displacement and real-time hybrid simulation.
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