Adaptive Tracking Controller for Real-Time Hybrid Simulation

Real-time hybrid simulation (RTHS) is a versatile and cost-effective testing method for studying the performance of structures subjected to dynamic loading. RTHS decomposes a structure into partitioned physical and numerical sub-structures that are coupled together through actuation systems. The sub-structuring approach is particularly attractive for studying large-scale problems since it allows for setting up large-scale structures with thousands of degrees of freedom in numerical simulations while specific components can be studied experimentally.The actuator dynamics generate an inevitable time delay in the overall system that affects the accuracy and stability of the simulation. Therefore, developing robust tracking control methodologies are necessary to mitigate these adverse effects. This research presents a state of the art review of tracking controllers for RTHS, and proposes a Conditional Adaptive Time Series (CATS) compensator based on the principles of the Adaptive Time Series compensator (ATS). The accuracy of the proposed controller is evaluated with a benchmark problem of a three-story building with a single degree of freedom (SDOF) in a realistic virtual RTHS (vRTHS). In addition, the accuracy of the proposed method is evaluated for seven numerical integration algorithms suitable for RTHS

Robust model predictive control for dynamics compensation in real-time hybrid simulation

Hybrid simulation is an efficient method to obtain the response of an emulated system subjected to dynamic excitation by combining loading-rate-sensitive numerical and physical substructures. In such simulations, the interfaces between physical and numerical substructures are usually implemented using transfer systems, i.e., an arrangement of actuators. To guarantee high fidelity of the simulation outcome, conducting hybrid simulation in hard real-time is required. Albeit attractive, real-time hybrid simulation comes with numerous challenges, such as the inherent dynamics of the transfer system used, along with communication interrupts between numerical and physical substructures, that introduce time delays to the overall hybrid model altering the dynamic response of the system under consideration. Hence, implementation of adequate control techniques to compensate for such delays is necessary. In this study, a novel control strategy is proposed for time delay compensation of actuator dynamics in hard real-time hybrid simulation applications. The method is based on designing a transfer system controller consisting of a robust model predictive controller along with a polynomial extrapolation algorithm and a Kalman filter. This paper presents a proposed tracking controller first, followed by two virtual real-time hybrid simulation parametric case studies, which serve to validate the performance and robustness of the novel control strategy. Real-time hybrid simulation using the proposed control scheme is demonstrated to be effective for structural performance assessment

Distributed real-time hybrid simulation: Modeling, development and experimental validation

Real-time hybrid simulation (RTHS) has become a recognized methodology for isolating and evaluating performance of critical structural components under potentially catastrophic events such as earthquakes. Although RTHS is efficient in its utilization of equipment and space compared to traditional testing methods such as shake table testing, laboratory resources may not always be available in one location to conduct appropriate large-scale experiments. Consequently, distributed systems, capable of connecting multiple RTHS setups located at numerous geographically distributed facilities through information exchange, become essential. This dissertation focuses on the development, evaluation and validation of a new distributed RTHS (dRTHS) platform enabling integration of physical and numerical components of RTHS in geographically distributed locations over the Internet.^ One significant challenge for conducting successful dRTHS over the Internet is sustaining real-time communication between test sites. The network is not consistent and variations in the Quality of Service (QoS) are expected. Since dRTHS is delay-sensitive by nature, a fixed transmission rate with minimum jitter and latency in the network traffic should be maintained during an experiment. A Smith predictor can compensate network delays, but requires use of a known dead time for optimal operation. The platform proposed herein is developed to mitigate the aforementioned challenge. An easily programmable environment is provided based on MATLAB/xPC. In this method, (i) a buffer is added to the simulation loop to minimize network jitter and stabilize the transmission rate, and (ii) a routine is implemented to estimate the network time delay on-the-fly for the optimal operation of the Smith predictor.^ The performance of the proposed platform is investigated through a series of numerical and experimental studies. An illustrative demonstration is conducted using a three story structure equipped with an MR damper. The structure is tested on the shake table and its global responses are compared to RTHS and dRTHS configurations where the physical MR damper and numerical structural model are tested in local and geographically distributed laboratories.^ The main contributions of this research are twofold: (1) dRTHS is validated as a feasible testing methodology, alternative to traditional and modern testing techniques such as shake table testing and RTHS, and (ii) the proposed platform serves as a viable environment for researchers to develop, evaluate and validate their own tools, investigate new methods to conduct dRTHS and advance the research in this area to the limits

A state-space partitioned time integration algorithm for real-time hybrid simulation with nonlinear numerical subdomains

This paper describes a state-space partitioned algorithm for real-time hybrid simulation. The state-space modeling is proposed to represent nonlinear numerical substructures. The effectiveness of the proposed method is demonstrated for a virtual bridge case study equipped with seismic isolation devices

Real-time simulation of the TF30-P-3 turbofan engine using a hybrid computer

A real-time, hybrid-computer simulation of the TF30-P-3 turbofan engine was developed. The simulation was primarily analog in nature but used the digital portion of the hybrid computer to perform bivariate function generation associated with the performance of the engine's rotating components. FORTRAN listings and analog patching diagrams are provided. The hybrid simulation was controlled by a digital computer programmed to simulate the engine's standard hydromechanical control. Both steady-state and dynamic data obtained from the digitally controlled engine simulation are presented. Hybrid simulation data are compared with data obtained from a digital simulation provided by the engine manufacturer. The comparisons indicate that the real-time hybrid simulation adequately matches the baseline digital simulation

Real-time-hybrid-simulation of Multi-degree-of-freedom Systems with Multiple Time Steps

Computational simulation and physical experiments are both widely used in testing the response of a structure under earthquake loadings, but physical experiments can be expensive for large problems and numerical may result in the loss of important structural behavior caused by a large amount of assumptions. Real-time hybrid simulation (RTHS) is a combination of these two approaches, which uses both a numerical and physical substructures that interact in real time to simulate structural behavior. The numerical and physical substructures are connected using a transfer system that enforces compatibility between them. The physical substructure needs to be run at a very high frequency (usually 1024 Hz) to ensure stability. This necessitates the numerical substructure be also computed at a correspondingly small time-step (1 millisecond). This research develops a method to speed up the numerical computation and enables the use of larger, more realistic numerical models within RTHS. The numerical substructure is split into multiple parts each solved at a different time-step, then coupled back together to obtain the global RTHS response. The portion closest to the experimental substructure is solved at a smaller time-step that meets the 1-millisecond limit, and the remaining portion is solved at a larger time-step. Multi-time-step RTHS is compared with single-time-step RTHS, in terms of the numerical error and computational time. This approach is shown to preserve accuracy of the computed result while meeting real-time constraint for RTHS computation. The current approach enhances our ability to study important structural dynamics with advanced numerical models

Fluid Structure Interaction for Cascading Seismic and Tsunami Events using Real-Time Hybrid Simulation

While real-time hybrid simulation has been utilized for structures subjected to seismic events for decades, its use in fluid-structure interaction problems is still a novel endeavor. Gathering data for cascading seismic and tsunami events is difficult due to space constraints in existing experimental facilities, complications regarding the application of scaling laws for both the fluid and structure, and limitations of computational software in simulating multiple hazards within the same analysis. To alleviate these constraints, this study demonstrates the feasibility of a real-time hybrid simulation testing method to enhance fluid-structure interaction simulations. A cylindrical bridge pier specimen and three-dimensional numerical bridge model were subjected to cascading seismic and tsunami events within a three-tier real-time hybrid simulation architecture. The domain was partitioned such that the wave-structure interaction was physically simulated and coupled to a numerical model of the remaining bridge. To simulate existing damage, seismic loading was applied in the structural model prior to the wave loading. Textbook short pulse response was exhibited by the specimen, and the results illustrate that a real-time hybrid simulation approach is both feasible and economical for future investigations using this method

NDM-555: EXPERIMENTAL INVESTIGATIONS OF LARGE SCALE TLD-STRUCTURE INTERACTION VIA REAL-TIME HYBRID SIMULATION

In real-time hybrid simulation (RTHS), as a cost-effective experimental testing technique, computer simulations are coupled with physical testing. RTHS divides the test structure into analytical and experimental substructures, and synchronizes them as the equations of motion are being solved in real-time. When conducted properly, the load-rate dependent characteristics of the test structure could be accurately captured by the RTHS. This paper presents real-time hybrid simulation of a three story structure equipped with a large scale tuned liquid damper (TLD) using a recently developed computational/control platform at University of Toronto. TLDs are cost effective and low maintenance vibration absorbers that can be utilized to suppress structural vibrations under dynamic excitation. They dampen energy through liquid boundary layer friction, the free surface contamination, and wave breaking. However, highly nonlinear and velocity dependent behaviour of these devices makes it difficult to establish representative analytical models for TLDs that are accurate for a wide range of operation. In this study, by employing RTHS the TLD will be tested physically as the experimental substructure and the remaining structure will be modeled analytically as the analytical substructure. This will facilitate the investigation of TLD-structure interaction for a wide range of influential parameters while using a user-programmable computational/control platform to carry out the real-time hybrid simulations