Large-angle slewing maneuvers for flexible spacecraft

A new class of closed-form solutions for finite-time linear-quadratic optimal control problems is presented. The solutions involve Potter's solution for the differential matrix Riccati equation, which assumes the form of a steady-state plus transient term. Illustrative examples are presented which show that the new solutions are more computationally efficient than alternative solutions based on the state transition matrix. As an application of the closed-form solutions, the neighboring extremal path problem is presented for a spacecraft retargeting maneuver where a perturbed plant with off-nominal boundary conditions now follows a neighboring optimal trajectory. The perturbation feedback approach is further applied to three-dimensional slewing maneuvers of large flexible spacecraft. For this problem, the nominal solution is the optimal three-dimensional rigid body slew. The perturbation feedback then limits the deviations from this nominal solution due to the flexible body effects. The use of frequency shaping in both the nominal and perturbation feedback formulations reduces the excitation of high-frequency unmodeled modes. A modified Kalman filter is presented for estimating the plant states

Evolution of hairpin vortices in a shear flow

Recent experimental studies suggest that the hairpin vortex plays an important (and perhaps dominant) role in the dynamics of turbulent flows near walls. In this study a numerical procedure is developed to allow the accurate computation of the trajectory of a 3-D vortex having a small core radius. For hairpin vortices which are convected in a shear flow above a wall, the calculated results show that a 2-D vortex containing a small 3-D disturbance distorts into a complex shape with subsidiary hairpin vortices forming outboard of the original hairpin vortex. As the vortex moves above the wall, it induces unsteady motion in the viscous flow near the wall: numerical solutions suggest that the boundary-layer flow near the wall will ultimately erupt in response to the motion of the hairpin vortex and in the process a secondary hairpin vortex will be created. The computer results agree with recent experimental investigations

Transform methods for precision continuum and control models of flexible space structures

An open loop optimal control algorithm is developed for general flexible structures, based on Laplace transform methods. A distributed parameter model of the structure is first presented, followed by a derivation of the optimal control algorithm. The control inputs are expressed in terms of their Fourier series expansions, so that a numerical solution can be easily obtained. The algorithm deals directly with the transcendental transfer functions from control inputs to outputs of interest, and structural deformation penalties, as well as penalties on control effort, are included in the formulation. The algorithm is applied to several structures of increasing complexity to show its generality

Why Don’t Judges Case Manage?

The problems of cost and delay experienced by parties seeking civil justice have been the subject of complaints for nearly one hundred years, going back to the days of Roscoe Pound. In the past few years, court leadership across the country has emphasized judicial case management as a significant tool for delivery of cost-effective, fair, and timely civil justice. The declining civil caseload has brought new urgency to these problems as evidence grows that litigants are deserting the civil justice system. Calls for case management to contain cost and delay have come from the Chief Justice of the United States, the Conference of Chief Justices, state bar and Supreme Court commissions, and the American Bar Association. The continuing demand for case management in virtually every lawyer survey, state bar commission, task force, and civil justice report over recent years evidences that judicial case management is not occurring on a day-to-day basis in today’s civil courtrooms. Notwithstanding broad calls for judicial case management, most judges still don’t case manage—if they did, calls for case management would not be persistent and relentless. If court leaders are going to rely on civil case management as a critical tool in improving civil justice, it is critical to understand how judges in everyday courtrooms view civil case management and how to best encourage its utilization. This thesis reports the results of an empirical investigation by survey into judicial attitudes among Florida circuit civil trial judges regarding utilization of case management in the handling of civil disputes in courts of general jurisdiction. The results of surveying Florida circuit judges demonstrate that the lack of widespread civil case management is less a deliberate choice due to resistance or philosophical objection than it is a product of the lack of a definition of what “civil case management” means and the scope of that task, a perceived lack of time and support, and a failure to incentivize its adoption through data sharing and performance measures. Through this research, I hope to provide one state’s perspective on this challenge to provide guidance to my state and others in implementing this cultural shift across civil justice