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The feasibility of incorporating semi‐active resettable springs (SRSs) to mitigate torsional response of structures is investigated. The effectiveness and robustness of the SRSs in reducing seismic demand was demonstrated on a spectrum of building properties idealized with one‐story asymmetric structures. The effects of the SRSs on the edge displacements were analyzed and several system parameters were identified that significantly effect the edge displacements. Two approaches based on geometric constraints and modal analysis are proposed to determine the proper distribution of the SRSs to minimize edge displacements. Limitations and guidelines on implementation are also provided. [ABSTRACT FROM AUTHOR]

The transportation sector produces a large portion of greenhouse gas emissions in the United States. Meeting ambitious reductions in greenhouse gasses requires large-scale adoption of battery electric vehicles and has led to several policies and laws aimed at incentivizing their sales. While electric vehicles comprise a small percentage of the overall fleets of vehicles, the expected production of electric vehicles is soon expected to be in the millions. This will create challenges in providing an adequate charging infrastructure, as well as the ensuing management of the overall electricity demand at the grid level. In this work, a novel smart-charging protocol for battery electric vehicle charging at workplace parking structures is proposed. The Octopus Charger-based Mixed Integer Linear Programming protocol allows octopus chargers (i.e., charging stations with multiple cables) to independently schedule charging periods for their assigned vehicles. The proposed protocols can manage a parking structure demand load while reducing the number of installed charging stations. Driving patterns from the National Household Travel Survey were used to perform simulations, to verify and quantify the effectiveness of the proposed protocol. The proposed protocol resulted in improved peak load reductions for all simulated smart-charging scenarios when compared with uncontrolled charging. Critically, the assignment algorithm resulted in a number of required chargers close to the theoretical minimum. [ABSTRACT FROM AUTHOR]

The control system for fuel cell gas turbine hybrid power plants plays an important role in achieving synergistic operation of subsystems, improving reliability of operation, and reducing frequency of maintenance and downtime. In this paper, we discuss development of advanced control algorithms for a system composed of an internally reforming solid oxide fuel cell coupled with an indirectly heated Brayton cycle gas turbine. In high temperature fuel cells it is critical to closely maintain fuel cell temperatures and to provide sufficient electrochemical reacting species to ensure system durability. The control objective explored here is focused on maintaining the system power output, temperature constraints, and target fuel utilization, in the presence of ambient temperature and fuel composition perturbations. The present work details the development of a centralized linear quadratic regulator (LQR) including state estimation via Kalman filtering. The controller is augmented by local turbine speed control and integral system power control. Relative gain array analysis has indicated that independent control loops of the hybrid system are coupled at time scales greater than 1 s. The objective of the paper is to quantify the performance of a centralized LQR in rejecting fuel and ambient temperature disturbances compared with a previously developed decentralized controller. Results indicate that both the LQR and decentralized controller can well maintain the system power to the disturbances. However, the LQR ensures better maintenance of the fuel cell stack voltage and temperature that can improve high temperature fuel cell system durability. [DOI: 10.1115/1.3155007] Keywords: SOFC hybrid, gas turbine, control design, relative gain array, linear quadratic regulator, Kalman filter

This paper addresses control of structural vibrations using semi-active actuators that are capable of manipulating stiffness and/or producing variable stiffness. Usually vibration suppression is achieved using damping devices rather than stiffness ones. However, stiffness devices can produce large forces and have significant advantages for shock isolation purposes. In this work we use a passivity approach to establish the requirements for the control law for a structure equipped with semi-active stiffness devices. We also solve an optimal control problem that demonstrates that our passive, resetting feedback control law approximates the optimal control. Simulation and experimental results are presented in support of the proposed approach. [DOI:10.1115/1.2432360]

Two multiobjective control strategies are presented and applied to the wind-excited benchmark problem. The first strategy, referred to as the energy-to-peak based controller, deals with a class of 'energy-bounded' excitations, whereas the second strategy, referred to as the peak-to-peak based controller, addresses a class of peak-bounded excitations. Both control strategies are derived by minimizing the sum of weighted peak response quantities with the constraints (or penalties) on the peak values of another set of quantities such as the control resources. Both the state feedback and dynamic output feedback controllers are derived and presented. The design syntheses of these two control strategies are developed and formulated within the framework of linear matrix inequalities (LMIs), so that the LMI toolbox in MATLAB can be used effectively and conveniently. These two control strategies are applied to the wind-excited 76-story benchmark building to demonstrate their applicability and control performances. Simulation results illustrate that the proposed control strategies are viable for civil engineering structures, and their performances are excellent in comparison with that of the linear quadratic Gaussian sample controller. CE Database subject headings: Active control; Structural control; Peak values; Bench marks; Wind loads.

This work studies connectivity maintenance of mobile networks. A mobile network of interest consists of two types of nodes, pre-deployed (client) and intermediate nodes. Upon initial deployment of client nodes in a field, multiple stationary intermediate nodes are placed strategically to establish robust network connectivity. We study scenarios in which an initially connected network consisting of pre-deployed and intermediate nodes is exposed to mobility of the former. Two types of node mobility scenarios are investigated. The first scenario analyzes the bounds of mobility when pre-deployed nodes move at small scales. The bounds of node mobility preserving connectivity are derived through analysis and verified by simulations. The second scenario considers the movement of pre-deployed nodes beyond the bounds of the first scenario thereby breaking connected links and partitioning the connected network. This scenario then considers relocating the existing intermediate nodes in order to reestablish connectivity. A general formulation is proposed in the form of an optimization problem. We prove that the general formulation of the problem is NP-hard. Next, we turn our attention to a practical scenario in which the location of nodes is made available using GPS signals. We solve the problem of practical scenario in polynomial time and analyze the complexity of our solution. We also present comprehensive performance evaluation results of our proposed algorithm. [ABSTRACT FROM AUTHOR]

This work investigates the active defense problem wherein a target aircraft launches a defending missile (i.e. a defender) to intercept an attacking missile in three-dimensional (3D) space. The novelty of this work includes: adding a safe distance for the target, which protects the target from being influenced by defensive interception, and designing a new 3D defensive guidance strategy without linearization to meet different guidance requirements. The defensive guidance strategy combines the approach of analyzing 3D pursuit-evasion engagement and the optimal control to obtain the guidance law. The approach derives the analytical solutions of 3D pursuit-evasion engagement, and a fast algorithm to predict the trajectory of attacking missile is proposed based on these analytical solutions. The advantages of this guidance strategy include incorporation of the added safe distance requirement directly without hindering the ability of the optimal guidance law to meet other requirements, and straight-forward extension for advanced scenarios where multi-defenders intercept the attacking missile simultaneously from different directions. The performance of the 3D defensive guidance law is evaluated via simulations. [ABSTRACT FROM AUTHOR]

This paper investigates gain-scheduled control design for linear systems with time-varying state delays subject to actuator saturation and external disturbance. Assuming the disturbance is peak bounded, a sufficient delay-dependent condition is established to guarantee that a family of level sets, corresponding to a novel parameter-dependent Lyapunov–Krasovskii functional, are nested and invariant to the closed-loop system. The invariant sets are then used to obtain nested reachable sets (ellipsoids) to bound the closed-loop states. A family of continuous controllers are designed based on these nested ellipsoids. The controller with the best performance is selected, each time, based on the closed-loop state vector, while complying with the saturation bound, and the resulting closed-loop system is locally input-to-state stable. All conditions are represented in the form of linear matrix inequalities (LMIs) by the linear spline method. Finally, the benefit of the control method is illustrated by two examples. [ABSTRACT FROM AUTHOR]

Semi-active variable stiffness resettable devices can reduce seismic demands and damages in structures. Despite their advantages, variable stiffness resettable devices are under-utilized mainly because of the shortage of fundamental research in quantifying the sensitivity of key seismic response parameters, and losses, in structures that use such systems for seismic hazard mitigation. Within this setting, the research summarized herein measures the effectiveness of semi-active resettable energy dissipating devices in the Single-Degree-of-Freedom domain aiming at quantifying the sensitivity of their seismic response to variation in control parameters and generating the required knowledge to utilize such semi-active devices in the Multi-Degree-of-Freedom domain. The performance (i.e. maximum relative displacement and peak absolute acceleration demands) of Single-Degree-of-Freedom systems with an array of semi-active control logics under various dynamic excitation regimes is studied. Two sets of 40 ground motions representing various seismic loading conditions (i.e. pulse-like and rock-site ground motions) are used, and an efficient control logic for mitigating these seismic demands is proposed. Numerical results show that proposed control logic enables a decrease of 40-60% for both maximum relative displacement and seismic base shear and 15-25% decrease for peak absolute acceleration. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We discuss a variation of dilated matrix inequalities for the conventional Bounded Real matrix inequality and other similarly structured inequalities. Here, system matrices are separated from Lyapunov matrix to allow the use of different Lyapunov matrices in multi-objective and robust problems. The search involves a bounded scalar parameter that enters the problem nonlinearly and is dealt with a line search. To demonstrate the benefits of the new dilated matrix inequalities over the conventional ones, an example of controller synthesis with ℒ2-gain performance measure (ℋ∞ control) for a system with polytopic uncertainty (robust problem) has been studied. It is shown that for the resulting robust problem the performance obtained via the dilated form is at least equal to that of the conventional one. Also, the connection between the proposed dilated form and the Full Block S-procedure is discussed. [ABSTRACT FROM AUTHOR]

SUMMARY We consider the dynamic anti-windup design problem for linear systems with saturating actuators. The basic idea proposed here is to apply anti-windup only when the performance of saturated system faces substantial degradation. We provide synthesis LMIs to obtain the gains of the dynamic anti-windup compensator in a structure that delays the activation of the anti-windup. Benefits of the proposed design method over the immediate activation of the anti-windup are demonstrated using a well-known example. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]