Optimal stochastic control theory applied to interplanetary guidance
Optimal control of nonlinear dynamic system in presence of noise
NOISE REDUCTION↗
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Results for “Dynamic optimization”
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Dynamic programming and Pontryagin's maximum principle
Dynamic programming and Pontryagin maximum principle
DYNAMIC PROGRAMMING↗
Optimal stochastic control.
Optimal stochastic control, discussing dynamic mathematical models described by differential equations
Wonham, W. M.↗
A separation theorem for nonlinear measurements.
Separation theorem for arbitrary nonlinear measurements to find optimal stochastic control without dynamic programming
Curry, R. E.↗
A hybrid NASAP module for direct design of linear dynamic circuits
Hybrid NASAP program module for direct design of linear dynamic circuits using simple optimization without sophisticated computer programming
Beck, C. H.↗
Routh's algorithm - A centennial survey
One hundred years have passed since the publication of Routh's fundamental work on determining the stability of constant linear systems. The paper presents an outline of the algorithm and considers such aspects of it as the distribution of zeros and applications of it that relate to the greatest common divisor, the abscissa of stability, continued fractions, canonical forms, the nonnegativity of polynomials and polynomial matrices, the absolute stability, optimality and passivity of dynamic systems, and the stability of two-dimensional circuits.
Barnett, S.↗
Optimal nodal point distribution for improved accuracy in computational fluid dynamics
In applying finite-difference techniques to flow field problems, the accuracy attained for a fixed number of node points can be improved using unequally-spaced node points. The distribution of these node points is chosen here by minimizing a measure of local truncation error with respect to the parameters which define a transformation between the computational space of equally-spaced node points and the physical space of unequally-spaced node points. The problem then becomes a nonlinear programming problem. Numerical results are presented for two one-dimensional test problems: the Blasius boundary layer problem and the inviscid Burgers' equation.
Pierson, B. L.↗
Prospects for TLRS baseline accuracies in the western USA
One of the main goals of the LAGEOS satellite mission is the detection of regional geotectonic movements. A parametric study with the intention to obtain the optimal baseline precision from dynamic solutions of laser ranging to LAGEOS is presented. The varied parameters are: length of reduced arc, number of tracking stations, data noise and rate, biases, refraction errors, system efficiency, gravity model errors in the value of GM. The baseline precisions are 1-10 cm depending upon the set of parameters adopted. General principles obtained are also presented.
Christodoulidis, D.↗
Optimal output feedback design of systems with ill-conditioned dynamics
Singular perturbation concepts are exploited to develop a procedure for designing a constant gain, output feedback control system. It is assumed that the original system is ill-conditioned in the sense that the plant contains widely separated dynamics, and that an accurate description for the high frequency behavior may not be available. The design procedure attempts to stabilize the system by minimizing a quadratic cost function made up of the control and states associated with a reduced order (low frequency) model for the plant, and a measure of stability for the neglected fast dynamics. The resulting design procedure does not require knowledge of the fast dynamics.
Calise, A. J.↗
Static aeroelastic analysis and tailoring of missile control fins
A concept for enhancing the design of control fins for supersonic tactical missiles is described. The concept makes use of aeroelastic tailoring to create fin designs (for given planforms) that limit the variations in hinge moments that can occur during maneuvers involving high load factors and high angles of attack. It combines supersonic nonlinear aerodynamic load calculations with finite-element structural modeling, static and dynamic structural analysis, and optimization. The problem definition is illustrated. The fin is at least partly made up of a composite material. The layup is fixed, and the orientations of the material principal axes are allowed to vary; these are the design variables. The objective is the magnitude of the difference between the chordwise location of the center of pressure and its desired location, calculated for a given flight condition. Three types of constraints can be imposed: upper bounds on static displacements for a given set of load conditions, lower bounds on specified natural frequencies, and upper bounds on the critical flutter damping parameter at a given set of flight speeds and altitudes. The idea is to seek designs that reduce variations in hinge moments that would otherwise occur. The block diagram describes the operation of the computer program that accomplishes these tasks. There is an option for a single analysis in addition to the optimization.
Mcintosh, S. C., Jr.↗
Randomly Sampled-Data Control Systems
The purpose is to solve the Linear Quadratic Regulator (LQR) problem with random time sampling. Such a sampling scheme may arise from imperfect instrumentation as in the case of sampling jitter. It can also model the stochastic information exchange among decentralized controllers to name just a few. A practical suboptimal controller is proposed with the nice property of mean square stability. The proposed controller is suboptimal in the sense that the control structure is limited to be linear. Because of i. i. d. assumption, this does not seem unreasonable. Once the control structure is fixed, the stochastic discrete optimal control problem is transformed into an equivalent deterministic optimal control problem with dynamics described by the matrix difference equation. The N-horizon control problem is solved using the Lagrange's multiplier method. The infinite horizon control problem is formulated as a classical minimization problem. Assuming existence of solution to the minimization problem, the total system is shown to be mean square stable under certain observability conditions. Computer simulations are performed to illustrate these conditions.
Han, Kuoruey↗
Air-breathing hypersonic vehicle guidance and control studies; An integrated trajectory/control analysis methodology: Phase 1
A tool which generates optimal trajectory/control histories in an integrated manner is generically adapted to the treatment of single-stage-to-orbit air-breathing hypersonic vehicles. The methodology is implemented as a two point boundary value problem solution technique. Its use permits an assessment of an entire near-minimum-fuel trajectory and desired control strategy from takeoff to orbit while satisfying physically derived inequality constraints and while achieving efficient propulsive mode phasing. A simpler analysis strategy that partitions the trajectory into several boundary condition matched segments is also included to construct preliminary trajectory and control history representations with less computational burden than is required for the overall flight profile assessment. A demonstration was accomplished using a tabulated example (winged-cone accelerator) vehicle model that is combined with a newly developed multidimensional cubic spline data smoothing routine. A constrained near-fuel-optimal trajectory, imposing a dynamic pressure limit of 1000 psf, was developed from horizontal takeoff to 20,000 ft/sec relative air speed while aiming for a polar orbit. Previously unspecified propulsive discontinuities were located. Flight regimes demanding rapid attitude changes were identified, dictating control effector and closed-loop controller authority was ascertained after evaluating effector use for vehicle trim. Also, inadequacies in vehicle model representations and specific subsystem models with insufficient fidelity were determined based on unusual control characteristics and/or excessive sensitivity to uncertainty.
Hattis, Philip D.↗
Autonomous vehicle motion control, approximate maps, and fuzzy logic
Progress on research on the control of actions of autonomous mobile agents using fuzzy logic is presented. The innovations described encompass theoretical and applied developments. At the theoretical level, results of research leading to the combined utilization of conventional artificial planning techniques with fuzzy logic approaches for the control of local motion and perception actions are presented. Also formulations of dynamic programming approaches to optimal control in the context of the analysis of approximate models of the real world are examined. Also a new approach to goal conflict resolution that does not require specification of numerical values representing relative goal importance is reviewed. Applied developments include the introduction of the notion of approximate map. A fuzzy relational database structure for the representation of vague and imprecise information about the robot's environment is proposed. Also the central notions of control point and control structure are discussed.
Ruspini, Enrique H.↗
The emulsion chamber technology experiment
Photographic emulsion has the unique property of recording tracks of ionizing particles with a spatial precision of 1 micron, while also being capable of deployment over detector areas of square meters or 10's of square meters. Detectors are passive, their cost to fly in Space is a fraction of that of instruments of similar collecting. A major problem in their continued use has been the labor intensiveness of data retrieval by traditional microscope methods. Two factors changing the acceptability of emulsion technology in space are the astronomical costs of flying large electronic instruments such as ionization calorimeters in Space, and the power and low cost of computers, a small revolution in the laboratory microscope data-taking. Our group at UAH made measurements of the high energy composition and spectra of cosmic rays. The Marshall group has also specialized in space radiation dosimetry. Ionization calorimeters, using alternating layers of lead and photographic emulsion, to measure particle energies up to 10(exp 15) eV were developed. Ten balloon flights were performed with them. No such calorimeters have ever flown in orbit. In the ECT program, a small emulsion chamber was developed and will be flown on the Shuttle mission OAST-2 to resolve the principal technological questions concerning space exposures. These include assessments of: (1) pre-flight and orbital exposure to background radiation, including both self-shielding and secondary particle generation; the practical limit to exposure time in space can then be determined; (2) dynamics of stack to optimize design for launch and weightlessness; and (3) thermal and vacuum constraints on emulsion performance. All these effects are cumulative and affect our ability to perform scientific measurements but cannot be adequately predicted by available methods.
Gregory, John C.↗
Laser scattering in a hanging drop vapor diffusion apparatus for protein crystal growth in a microgravity environment
One type of hardware used to grow protein crystals in the microgravity environment aboard the U.S. Space Shuttle is a hanging drop vapor diffusion apparatus (HDVDA). In order to optimize crystal growth conditions, dynamic control of the HDVDA is desirable. A critical component in the dynamically controlled system is a detector for protein nucleation. We have constructed a laser scattering detector for the HDVDA capable of detecting the nucleation stage. The detector was successfully tested for several scatterers differing in size using dynamic light scattering techniques. In addition, the ability to detect protein nucleation using the HDVDA was demonstrated for lysozyme.
Casay, G. A.↗
On th meridional surface profile of the Gulf Stream at 55 deg W
Nine-month records from nine inverted echo sounders (IESs) are analyzed to describe the mean baroclinic Gulf Stream at 55 deg W. IES acoustic travel times are converted to thermocline depth which is optimally interpolated. Kinematic and dynamic parameters (Gulf Stream meridional position, velocity, and vorticity) are calculated. Primary Gulf Stream variabiltiy is attributed to meandering and and changes in direction. A mean, stream-coordinate (relative to Gulf Stream instantaneous position and direction) meridional profile is derived and compared with results presented by other investigators. The mean velocity is estimated at 0.84 m/s directed 14 deg to the right eastward, and the thermocline (12 c) drops 657 m (north to south), corresponding to a baroclinic rise of the surface of 0.87 m. The effect of Gulf Stream curvature on temporal mean profiles is found to be unimportant and of minimal importance overall. The derived, downstream current profile is well represented by a Gaussian function and is about 190 km wide where it crosses zero. Surface baroclinic transport is estimated to be 8.5 x 10(exp 4) sq m/s, and maximum shear (flanking the maximum) is 1.2 x 10(exp -5). Results compare well with other in situ observational results from the same time period. On the other hand, analyses (by others) of concurrent satellite altimetry (Geosat) suggest a considerable narrower, more intense mean Gulf Stream.
Hallock, Zachariah R.↗
High-Performance Monitoring Architecture for Large-Scale Distributed Systems Using Event Filtering
Monitoring is an essential process to observe and improve the reliability and the performance of large-scale distributed (LSD) systems. In an LSD environment, a large number of events is generated by the system components during its execution or interaction with external objects (e.g. users or processes). Monitoring such events is necessary for observing the run-time behavior of LSD systems and providing status information required for debugging, tuning and managing such applications. However, correlated events are generated concurrently and could be distributed in various locations in the applications environment which complicates the management decisions process and thereby makes monitoring LSD systems an intricate task. We propose a scalable high-performance monitoring architecture for LSD systems to detect and classify interesting local and global events and disseminate the monitoring information to the corresponding end- points management applications such as debugging and reactive control tools to improve the application performance and reliability. A large volume of events may be generated due to the extensive demands of the monitoring applications and the high interaction of LSD systems. The monitoring architecture employs a high-performance event filtering mechanism to efficiently process the large volume of event traffic generated by LSD systems and minimize the intrusiveness of the monitoring process by reducing the event traffic flow in the system and distributing the monitoring computation. Our architecture also supports dynamic and flexible reconfiguration of the monitoring mechanism via its Instrumentation and subscription components. As a case study, we show how our monitoring architecture can be utilized to improve the reliability and the performance of the Interactive Remote Instruction (IRI) system which is a large-scale distributed system for collaborative distance learning. The filtering mechanism represents an Intrinsic component integrated with the monitoring architecture to reduce the volume of event traffic flow in the system, and thereby reduce the intrusiveness of the monitoring process. We are developing an event filtering architecture to efficiently process the large volume of event traffic generated by LSD systems (such as distributed interactive applications). This filtering architecture is used to monitor collaborative distance learning application for obtaining debugging and feedback information. Our architecture supports the dynamic (re)configuration and optimization of event filters in large-scale distributed systems. Our work represents a major contribution by (1) survey and evaluating existing event filtering mechanisms In supporting monitoring LSD systems and (2) devising an integrated scalable high- performance architecture of event filtering that spans several kev application domains, presenting techniques to improve the functionality, performance and scalability. This paper describes the primary characteristics and challenges of developing high-performance event filtering for monitoring LSD systems. We survey existing event filtering mechanisms and explain key characteristics for each technique. In addition, we discuss limitations with existing event filtering mechanisms and outline how our architecture will improve key aspects of event filtering.
Maly, K.↗
An Atomistic Simulation of Crack Propagation in a Nickel Single Crystal
The main objective of this paper is to determine mechanisms of crack propagation in a nickel single crystal. Motivation for selecting nickel as a case study is because we believe that its physical properties are very close to that of nickel-base super alloy. We are directed in identifying some generic trends that would lead a single crystalline material to failure. We believe that the results obtained here would be of interest to the experimentalists in guiding them to a more optimized experimental strategy. The dynamic crack propagation experiments are very difficult to do. We are partially motivated to fill the gap by generating the simulation results in lieu of the experimental ones for the cases where experiment can not be done or when the data is not available.
Majid Karimi↗