An Earth-independent permanent extraterrestrial habitat system must function as intended under continuous disruptive conditions, and with significantly limited Earth support and extended uncrewed periods. Designing for the demands that extreme environments such as wild temperature fluctuations, galactic cosmic rays, destructive dust, meteoroid impacts (direct or indirect), vibrations, and solar particle events, will place on long-term deep space habitats represents one of the greatest challenges in this endeavor. This context necessitates that we establish the know-how and technologies to build habitat systems that are resilient. Resilience is not simply robustness or redundancy: it is a system property that accounts for both anticipated and unanticipated disruptions via the design choices and maintenance processes, and adapts to them in operation. We currently lack the frameworks and technologies needed to achieve a high level of resilience in a habitat system. The Resilient ExtraTerrestrial Habitats Institute (RETHi) has the mission of leveraging existing novel technologies to provide situational awareness and autonomy to enable the design of habitats that are able to adapt, absorb and rapidly recover from expected and unexpected disruptions. We are establishing both fully virtual and coupled physical-virtual simulation capabilities that will enable us to explore a wide range of potential deep space SmartHab configurations and operating modes.
Over the past few decades, considerable attention has been given to structural control systems to mitigate structural vibration under natural hazards such as earthquakes and extreme weather conditions. Traditional wired structural control systems often employ a large amount of cables for communication among sensors, controllers and actuators. In such systems, implementation of wired sensors is usually quite complicated and expensive, especially on large scale structures such as bridges and buildings. To reduce the laborious installation and maintenance cost, wireless control systems (WCSs) are considered as a novel approach for structural vibration control. In this work, a WCS is developed based on the open source Arduino platform. Low cost, low power wireless sensing and communication components are built on the Arduino platform. Structural control algorithms are embedded within the wireless sensor board for feedback control. The developed WCS is first validated through a series of tests. Next, numerical simulations are performed simulating wireless control of a 3-story shear structure equipped with a semi-active control device (MR damper). Finally, experimental studies are carried out implementing the WCS on the 3-story shear structure in the Intelligent Infrastructure Systems Lab (IISL). A hydraulic shake table is used to generate seismic ground motions. The control performance is evaluated with the impact of modeling uncertainties, measurement noises as well as time delay and data loss induced by the wireless network. The developed WCS is shown to be effective in controlling structural vibrations under several historical earthquake ground motions.
KEYWORDS: Sensors, Monte Carlo methods, Data acquisition, Data modeling, Distributed computing, Computer simulations, Matrices, Signal to noise ratio, Civil engineering, Algorithm development
In this paper two modal identification approaches appropriate for use in a distributed computing environment are applied
to a full-scale, complex structure. The natural excitation technique (NExT) is used in conjunction with a condensed
eigensystem realization algorithm (ERA), and the frequency domain decomposition with peak-picking (FDD-PP) are
both applied to sensor data acquired from a 57.5-ft, 10 bay highway sign truss structure. Monte-Carlo simulations are
performed on a numerical example to investigate the statistical properties and sensitivity to noise of the two distributed
algorithms. Experimental results are provided and discussed.
Identification of the changes in the properties of a structure are a potential indication of damage in that structure. In
nonlinear systems, hysteretic models are often used to represent structural deterioration as well. Thus, the updating of
such nonlinear hysteretic models using measured responses from a monitoring system is one approach to identify
structural properties and thus damage. Nonlinear observer theory provides the tools to update such models, potentially
online and in real-time. This paper examines several nonlinear observers that can be applied as online hysteretic model
updating tools, and compares the results by using a Bouc-Wen model updating case. The online updating feature also
demonstrates the potential application in providing state feedback to nonlinear structural control.
Civil engineering structural systems exhibit hysteretic behavior when under extreme loading conditions as well as when
energy dissipation devices are employed. To investigate the optimal control strategy for reducing the system response
under random excitations (earthquakes, wind gust or sea waves), a general control solution is proposed in this paper.
The approach considers the solution of the Hamilton-Jacobi-Bellman equation for general nonlinear stochastic systems,
under the assumption that the evolution of the state of the stochastic system can be described by a Markov diffusion
process. Several numerical examples are provided to verify the efficacy of the optimal control solution obtained from the
proposed method. First, a linear oscillator is used to verify that the obtained solution is indeed the optimal solution by
comparing it to the closed form solution. Then the proposed method is applied to several nonlinear systems including
Van der Pol and Duffing oscillators and a Bouc-Wen system. In each case, optimality is demonstrated by comparing the
system responses and costs under optimal control with the ones obtained using linearized optimal control.
KEYWORDS: Control systems, Control systems design, Earthquakes, Systems modeling, Electroluminescence, Actuators, Instrument modeling, Smart structures, Civil engineering, Performance modeling
This paper discusses the results of expanded study of series simulations conducted to compare the effectiveness of various control systems for earthquake hazard mitigation. A systematic comparison of the performance of different control systems will be useful for the designer in selecting the most effective control system for a structure. Ideal passive, active and semi-active control systems are employed in this study. For determining the control action, an H2/LQG control algorithm was selected for the active system and a clipped optimal control algorithm was selected for the semi- active system. In both cases the control algorithm was based on acceleration measurements for determination of the control action. To evaluate and compare the controllers, the structural responses of various 3, 6, and 10-story buildings are examined. An El Centro earthquake and pulse excitation are used as the ground excitations. The mass is held constant while the stiffness of the structure is varied to examine structures with a range of natural frequencies.
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