Current Flexible Rotor-Bearing System Balancing Techniques Using Computer Simulation

As the cost of machinery has risen and the need for dependability, safety and increased performance have in a similar manner increased, the needs of industry for viable flexible rotor balancing techniques has no less increased. Various flexible rotor methods have been advocated for supercritical shafting, but few studies or comparisons have appeared in the open literature. Among the procedures for balancing large and/or high speed (supercritical) rotors are the N modal method of Bishop and Gladwell, the N + B modal of Federn, the N and + B simultaneous modal method of Kellenberger, and the influence coefficient method of Lund and Rieger. Each of the aforementioned balancing techniques is examined and explained in detail. The first known modal balancing programs are listed and described. Using these programs as a basis, the influence coefficient method of Lund and Rieger is compared to the modal methods of Bishop and Gladwell, Federn, and Kellenberger. The companies are made with the aid of a Prohl based unbalance response computer program. The rotor systems used for the comparison are flexible shafts, some mounted in damped bearings, and some mounted in undamped bearings. One sample system exhibits rigid body behavior in addition to flexible behavior. These examples form the basis of the first known direct computer based comparison between a current influence balancing technique and the highly developed and distributed modal methods

Predictive Control for Alleviation of Gust Loads on Very Flexible Aircraft

In this work the dynamics of very flexible aircraft are described by a set of non-linear, multi-disciplinary equations of motion. Primary structural components are represented by a geometrically-exact composite beam model which captures the large dynamic deformations of the aircraft and the interaction between rigid-body and elastic degrees-of-freedom. In addition, an implementation of the unsteady vortex-lattice method capable of handling arbitrary kinematics is used to capture the unsteady, three-dimensional flow-eld around the aircraft as it deforms. Linearization of this coupled nonlinear description, which can in general be about a nonlinear reference state, is performed to yield relatively high-order linear time-invariant state-space models. Subsequent reduction of these models using standard balanced truncation results in low-order models suitable for the synthesis of online, optimization-based control schemes that incorporate actuator constraints. Predictive controllers are synthesized using these reduced-order models and applied to nonlinear simulations of the plant dynamics where they are shown to be superior to equivalent optimal linear controllers (LQR) for problems in which constraints are active

The Mode and Timing of Microplate Docking along the Highland Boundary Fault Zone, Scotland

The Highland Boundary Fault Zone is a major crustal fracture with a long and complex structural history, in which brittle deformation was superimposed upon pre-existing fabrics produced by ductile deformation. This thesis describes and interprets the history of HBFZ tectonism, presented in reverse chronological order (youngest events first). Although the HBFZ still experiences small-scale earthquakes, there is evidence to show that significant fault displacement has not occurred since the end of the Carboniferous. Extensional deformation during the Upper Devonian and the Carboniferous was small-scale and localised. Upper crustal deformation in mid-Devonian times, possibly caused by the accretion of the Avalonian terrane with Laurentia, was low in magnitude but widespread in aerial extent. The results and interpretations of a mesofracture analysis are presented to help constrain mid-Devonian brittle deformation across central Scotland. The results show that regional north-south compression caused transpressional reactivation of the pre-existing HBFZ. Because our existing understanding of transpression is incapable of explaining the results of the mesofracture analysis, an alternative transpression model is proposed, in which transpressive strain is "partitioned" into two components; a strike-slip component restricted to the fault zone, and a thrust component deforming the rocks that flank the zone. The "strain-partitioning" model, with some elaboration, helps to explain the mid-Devonian deformation seen in central Scotland. The balance of evidence from the Highland Border, Dalradian, and Midland Valley terranes suggests that ductile deformation along the HBFZ occurred in response to terrane accretion, which probably took place in Ordovician times. A palaeo-tectonic model is presented in which Highland Border and Midland Valley terranes were accreted and laterally displaced, with a sinistrally transpressive sense, onto the Laurentian margin in the Llandeilo and/or Caradoc, and again in the Ashgill and/or Llandovery. The extreme difficulties of postulating the palaeo-tectonic histories of disrupted terranes are discussed in detail

Continuous Modeling of 3D Building Rooftops From Airborne LIDAR and Imagery

In recent years, a number of mega-cities have provided 3D photorealistic virtual models to support the decisions making process for maintaining the cities' infrastructure and environment more effectively. 3D virtual city models are static snap-shots of the environment and represent the status quo at the time of their data acquisition. However, cities are dynamic system that continuously change over time. Accordingly, their virtual representation need to be regularly updated in a timely manner to allow for accurate analysis and simulated results that decisions are based upon. The concept of "continuous city modeling" is to progressively reconstruct city models by accommodating their changes recognized in spatio-temporal domain, while preserving unchanged structures. However, developing a universal intelligent machine enabling continuous modeling still remains a challenging task. Therefore, this thesis proposes a novel research framework for continuously reconstructing 3D building rooftops using multi-sensor data. For achieving this goal, we first proposes a 3D building rooftop modeling method using airborne LiDAR data. The main focus is on the implementation of an implicit regularization method which impose a data-driven building regularity to noisy boundaries of roof planes for reconstructing 3D building rooftop models. The implicit regularization process is implemented in the framework of Minimum Description Length (MDL) combined with Hypothesize and Test (HAT). Secondly, we propose a context-based geometric hashing method to align newly acquired image data with existing building models. The novelty is the use of context features to achieve robust and accurate matching results. Thirdly, the existing building models are refined by newly proposed sequential fusion method. The main advantage of the proposed method is its ability to progressively refine modeling errors frequently observed in LiDAR-driven building models. The refinement process is conducted in the framework of MDL combined with HAT. Markov Chain Monte Carlo (MDMC) coupled with Simulated Annealing (SA) is employed to perform a global optimization. The results demonstrates that the proposed continuous rooftop modeling methods show a promising aspects to support various critical decisions by not only reconstructing 3D rooftop models accurately, but also by updating the models using multi-sensor data

Computational methods and software systems for dynamics and control of large space structures

Two key areas of crucial importance to the computer-based simulation of large space structures are discussed. The first area involves multibody dynamics (MBD) of flexible space structures, with applications directed to deployment, construction, and maneuvering. The second area deals with advanced software systems, with emphasis on parallel processing. The latest research thrust in the second area involves massively parallel computers

Dynamic Balance and Gait Metrics for Robotic Bipeds

For legged robots to be useful in the real world, they must be able to balance and walk reliably. Both of these abilities improve when a system is more effective at moving itself around relative to its contacts (i.e., its feet). Achieving this type of movement depends both on the controller used to perform the motion and the physical properties of the system. Although much work has been done on the development of dynamic controllers for balance and gait, only limited research exists on how to quantify a system’s physical balance capabilities or how to modify the system to improve those capabilities. From the control perspective, there are three strategies for maintaining balance in bipeds: flexing, leaning, and stepping. Both stepping and leaning strategies typically depend on balance points (critical points used for maintaining or regaining balance) to determine whether or not a step is needed, and if so, where to step. Although several balance point estimators exist, the majority of these methods make undesirable assumptions (e.g., ignoring the impact dynamics, assuming massless legs, planar motion, etc.). From the physical design perspective, one promising approach for analyzing system performance is a set of dynamic ratios called velocity and momentum gains, which are dependent only on the (scale-invariant) dynamic parameters and instantaneous configuration of a system, enabling entire classes of mechanisms to be analyzed at the same time. This thesis makes four key contributions towards improving biped balancing capabilities. First, a dynamic bipedal controller is proposed which uses a 3D balance point estimator both to respond to disturbances and produce reliable stepping. Second, a novel balance point estimator is proposed that facilitates stepping while combining and expanding the features of existing 2D and 3D estimators to produce a generalized 3D formulation. Third, the momentum gain formulation is extended to general 2D and 3D systems, then both gains are compared to centroidal momentum via a spatial formulation and incorporated into a generalized gain definition. Finally, the gains are used as a metric in an optimization framework to design parameterized balancing mechanisms within a given configuration space. Effectively, this enables an optimization of how well a system could balance without the need to pre-specify or co-generate controllers and/or trajectories. To validate the control contributions, simulated bipeds are subjected to external disturbances while standing still and walking. For the gain contributions, the framework is used to compare gain-optimized mechanisms to those based on the cost of transport metric. Through the combination of gain-based physical design optimization and the use of predictive, real-time balance point estimators within dynamic controllers, bipeds and other legged systems will soon be able to achieve reliable balance and gait in the real world