My role as 142nd president of the Institution of Civil Engineers is to provide leadership and guidance for the Institution and its members. Like my predecessors, my role is to deliver the Institution\'s strategy. ...
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My role as 142nd president of the Institution of Civil Engineers is to provide leadership and guidance for the Institution and its members. Like my predecessors, my role is to deliver the Institution\'s strategy. Like my predecessors, I am deeply honoured to be elected your president, but also somewhat daunted by the role, bearing in mind those who have gone before. One of these is, of course, our first president, Thomas Telford. On 9 August 2007, we will celebrate the 250th birthday of Thomas Telford. The year is a special year to celebrate civil engineers and their achievements, and it is a special opportunity to recognise our value as civil engineers.
The low-thrust spacecraft trajectory problem can be reduced to only a few parameters using calculus of variations and the well-known primer vector theory. This low dimensionality combined with the extraordinary speed ...
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The low-thrust spacecraft trajectory problem can be reduced to only a few parameters using calculus of variations and the well-known primer vector theory. This low dimensionality combined with the extraordinary speed of modern computers allows for rapid exploration of the parameter space and invites opportunities for global optimization. Accordingly, a general low-thrust trade analysis tool is developed based on a global search for local indirect method solutions. An efficient propagator is implemented with an implicit "bang-bang" thrusting structure that accommodates an a priori unknown number of switching times. An extension to the standard adjoint control transformation is introduced that provides additional physical insight and control over the anticipated evolution of the thrust profile. The uniformly random search enjoys a perfect linear speedup for parallel implementation. The method is applied specifically on multirevolution transfers in the Jupiter-Europa and Earth-moon restricted three body problems. In both cases, thousands of solutions are found in a single parallel run. The result is a global front of Pareto optimal solutions across the competing objectives of flight time and final mass.
An active flow control experiment was conducted on a cropped NACA 0018 airfoil to study 3D effects and maneuverability aspects made possible by a segmented actuation system installed in the airfoil. The 14 piezo-fluid...
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An active flow control experiment was conducted on a cropped NACA 0018 airfoil to study 3D effects and maneuverability aspects made possible by a segmented actuation system installed in the airfoil. The 14 piezo-fluidic actuators were installed at the corner of the cropped region, inclined at 30 degrees to the local surface, facing downstream. Operating all actuators at unison significantly increased lift and generated a pitch-down moment. Operating all actuators at the same magnitude but varying the phase along the span generated larger lift-increment, with respect to the uniform phase excitation. Significant rolling moment can be generated when only half-span of the wing is actuated. The latter effect, as indicated by the 3D pressure distribution, persists to the leading edge even though the excitation was introduced close to the trailing edge. When a pair, out of the possible fourteen actuators is not operating, very little of the control authority is lost. This is an important finding when issues like fault tolerance and robustness of fluidic-piezo actuators are considered.
This paper presents the results of a research effort focused on the modeling, identification, control design, simulation, and flight-testing of YF-22 research aircraft models in closed-loop formation. These models wer...
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This paper presents the results of a research effort focused on the modeling, identification, control design, simulation, and flight-testing of YF-22 research aircraft models in closed-loop formation. These models were designed, manufactured, and instrumented at West Virginia University (WVU). The first phase of flight tests was performed with the goal of exciting all the aircraft dynamic modes. The recorded flight data were then used for a parameter identification study. The output of this Study was a mathematical model of the WVU YF-22 aircraft, which was then used for the design of the formation control laws. The design of the formation control laws is based on an inner/outer loop design with the objective of controlling the forward, lateral, and vertical distances between two aircraft in the formation. The design for the outer loop scheme was based on feedback linearization while a root locus-based approach was used for the design of the inner loop scheme. The paper presents experimental results validating the performance of the formation control laws using a 'virtual leader' configuration. (c) 2007 Elsevier Ltd. All rights reserved.
This article addresses the problem of the choice of the predictors for the multiple linear regression in model output statistics. Rather than devising a selection procedure directly aimed at the minimization of the fi...
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This article addresses the problem of the choice of the predictors for the multiple linear regression in model output statistics. Rather than devising a selection procedure directly aimed at the minimization of the final scores, it is examined whether taking the model equations as a guidance may render the process more rational. To this end a notion of constant fractional errors is introduced. Experimental evidence is provided that they are approximately present in the model and that their impact is sufficiently linear to be corrected by a linear regression. Of particular interest are the forcing terms in the coupling of the physics parameterization to the dynamics of the model. Because such parameterizations are estimates of subgrid processes, they are expected to represent degrees of freedom that are independent of the resolved-scale model variables. To illustrate the value of this approach, it is shown that the temporal accumulation of sensible and latent heat fluxes and net solar and thermal radiation utilized as predictors add a statistically significant improvement to the 2-m temperature scores.
The potential of angles-only navigation for autonomous orbital rendezvous is discussed. Flight algorithms for a proposed rendezvous guidance, navigation, and control system are presented. Emphasis is placed on the ang...
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The potential of angles-only navigation for autonomous orbital rendezvous is discussed. Flight algorithms for a proposed rendezvous guidance, navigation, and control system are presented. Emphasis is placed on the angles-only navigation filter development to determine relative position and attitude between a passive noncooperative target satellite and a maneuvering chaser vehicle. The navigation filter, a 32-state extended Kalman filter, processes angular measurements, from an optical navigation camera along with gyro and star tracker data to estimate the inertial position, velocity, attitude, and angular rates of both vehicles. The filter's performance is evaluated and tested by running a coded prototype in a closed-loop six-degree-of-freedom Monte Carlo simulation containing the various sensors;actuators;guidance, navigation, and control flight algorithms;and dynamics associated with a simple rendezvous scenario. The results include navigation errors, trajectory dispersions, attitude dispersions, and A v usage. The Monte Carlo results are then compared with linear covariance analysis results and the advantages and potential of each approach are discussed.
Optimality properties of synergetic controllers are analyzed using the Euler-Lagrange conditions and the Hamilton-Jacobi-Bellman equation. First, a synergetic control strategy is compared with the variable structure s...
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Optimality properties of synergetic controllers are analyzed using the Euler-Lagrange conditions and the Hamilton-Jacobi-Bellman equation. First, a synergetic control strategy is compared with the variable structure sliding mode control. The connections of synergetic control design methodology and the methods of variable structure sliding mode control are established. In fact, the methods of sliding surface design for the sliding mode control are essential for designing invariant manifolds in the synergetic control approach. It is shown that the synergetic control strategy can be derived using tools from the calculus of variations. The synergetic control laws have a simple structure because they are derived from the associated first-order differential equation. It is also shown that the synergetic controller for a certain class of linear quadratic optimal control problems has the same structure as the one generated using the linear quadratic regulator approach by solving the associated Riccati equation. The synergetic optimal control and sliding mode control methodologies are applied to the nonlinear control of the wing-rock suppression problem. Two different wing-rock dynamic models are used to test the design of the synergetic and sliding mode controllers. The performance of the closed-loop systems driven by these controllers is analyzed and compared.
guidance is provided for geotechnical engineers designing civil engineering works in silty soils. A detailed characterization of two estuarine silt sites in Ireland is performed and the soil properties are linked to t...
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guidance is provided for geotechnical engineers designing civil engineering works in silty soils. A detailed characterization of two estuarine silt sites in Ireland is performed and the soil properties are linked to their geological origin. It was found that these soils are susceptible to densification by conventional and high-quality fixed piston tube sampling and care needs to be taken when using laboratory-derived design parameters, particularly for consolidation and shear strength properties. The 1D consolidation and creep of these silts can be modelled successfully by the well-known Janbu formulation. Settlement predictions from laboratory-derived parameters match measured data reasonably well, but tend to underestimate primary consolidation, consistent with a sampling densification effect. Vane data should be used with caution, as measured strength values may be high, and it seems that more reliable parameters can be derived from cone penetration tests. Conventional techniques for determining soil strength from triaxial tests in silt are inappropriate because of the dilational nature of the material, and more reliable and logical strength estimates can be made from a limiting strain criterion.
Ecologically based landscape units and associated characteristics of natural disturbance (e.g., seral stage and patch size distribution) were recently developed for the northeast corner of British Columbia and used as...
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Ecologically based landscape units and associated characteristics of natural disturbance (e.g., seral stage and patch size distribution) were recently developed for the northeast corner of British Columbia and used as the basis for establishing guidance and policy for natural disturbance-based management for two large timber supply areas. I discuss the development of the landscape units;development of guidance for the units;and implementation of the guidance for old forest, interior old forest, and early seral patch size objectives. This paper demonstrates how natural-disturbance-based management can be successfully implemented.
The IR image real-time generation system is composed of image generation and display computer, Si-bridge MOS resistance array control computer, 128 × 128 MOS resistance array and power, real-time comm
The IR image real-time generation system is composed of image generation and display computer, Si-bridge MOS resistance array control computer, 128 × 128 MOS resistance array and power, real-time comm
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