Institute for Systems Research
Permanent URI for this communityhttp://hdl.handle.net/1903/4375
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Item Synthesis and Validation of High-Level Behavior Models for Narrow Waterway Management Systems(2005) Kaisar, Evangelos; Austin, Mark; ISR; SEILThis report formulates a new methodology for the incremental transformation of informal operations concepts for a waterway management system into system-level designs, the latter being formal enough to support automated validation of anticipated component- and system-level behaviors. Scenario specifications and models of behavior are formally modeled as labeled transition systems (LTSs). Each object is the management system is assumed to have behavior that can be defined by a finite state machine; thus, the waterway management system architecture is modeled as a network of communicating finite state machines. Architecture-level behaviors are validated using the Labeled Transition System Analyzer (LTSA). We exercise the methodology by working step by step through the synthesis and validation of a high-level behavior model for a ship passing through a waterway network.Item Phase Analysis of Actuator Response for Sub-Optimal Bang-Bang and Velocity Cancellation Control of Base Isolated Structures(2005) Austin, Mark; Sebastianelli, Robert; ISR; SEILStarting with simplified models of displacement response for a base isolated structure supplemented with sub-optimal bang-bang control, we formulate models of phase analysis of actuator force direction in relation to system displacements and velocities. For the case of steady state displacement response, we prove that the direction of actuator application can neither be perfectly in phase with displacements, nor perfectly in phase with velocities. In practice, however, the actuator force direction is ``almost in phase' with velocities and ``almost orthogonal' to sign changes in displacements. This observation suggests that a very simple velocity cancellation control might be effective in adding value to base isolation system responses. Numerical experiments are conducted to assess improvements in performance due to sub-optimal bang-bang control and velocity cancellation control, and to validate the extent to which the phase analysis predictions hold in linearly elastic and nonlinear time-domain settings.Item Energy- and Power-Balance Assessment of Base Isolated Structures Supplemented with Modified Bang-Bang Control(2005) Sebastianelli, Robert; Austin, Mark; ISR; SEILThis report is the second in series investigating the feasibility of supplementing base isolation with active bang-bang control mechanisms. We formulate discrete approximations to energy- and power-balance equations for a base isolated structure supplemented with constant stiffness bang-bang (CKBB) control. Numerical experiments are conducted to: (1) Identify situations when constant stiffness bang-bang control is most likely to ``add value' to system responses due to base isolation alone, and (2) Quantitatively determine the work done and power required by the actuators. A key observation from the numerical experiments is that ``overall performance' of the actuators is coupled to ``input energy per unit time.'Item Computational Assessment of Suboptimal Bang-Bang Control Strategies for Performance-Based Design of Base Isolated Structures(2005) Sebastianelli, Robert; Austin, Mark; ISR; SEILThis report explores the symbolic solution of the Lyapunov matrix equation as it applies to modified bang-bang control of base isolated structures. We present the Modified Bang-Bang Control strategy for active control of structures. Based on energy concepts, we formulate a rational choice of the ``${ f Q}$" matrix that partitions the amount of potential energy in a base isolated system into two parts: (1) potential energy directed to the main structural system, and (2) potential energy directed to the isolation devices. This symbolic analysis of a 2-DOF system leads to investigating a choice of the ${ f Q}$ matrix that minimizes the entire potential and/or kinetic energy of a emph{n}-DOF structure during an earthquake ground event. Using symbolic analyis procedures, We show that when the entire potential and/or kinetic energy of a emph{n}-DOF structure with uniform mass is minimized, solutions to the Lyapunov matrix equation assume a greatly simplified form. Moreover, this solution to the modified bang-bang control problem is easily calculated without needing to solve the Lyapunov matrix equation. Modified bang-bang control can be easily incorporated into the second-order differential equation of motion for the structure giving intuitive insight as to the effect of active control on the response of the structure. We show that this control strategy is insensititive to localized, nonlinear stiffness changes in the base isolators and therefore is well-suited for this problem area.