Layout Analysis and Optimization of Airships with Thrust-Based Stability Augmentation

Despite offering often significant advantages with respect to other flying machines, especially in terms of flight endurance, airships are typically harder to control. Technological solutions borrowed from the realm of shipbuilding, such as bow thrusters, have been largely experimented with to the extent of increasing maneuverability. More recently, also thrust vectoring has appeared as an effective solution to ameliorate maneuverability. However, with an increasing interest for high-altitude airships (HAAs) and autonomous flight and the ensuing need to reduce weight and lifting performance, design simplicity is a desirable goal. Besides saving weight, it would reduce complexity and increase time between overhauls, in turn enabling longer missions. In this perspective, an airship layout based on a set of non-tilting thrusters, optimally placed to be employed for both propulsion and attitude control, appears particularly interesting. If sufficiently effective, such configurations would reduce the need for control surfaces on aerodynamic empennages and the corresponding actuators. Clearly, from an airship design perspective, the adoption of many smaller thrusters instead of a few larger ones allows a potentially significant departure from more classical airship layouts. Where on one side attractive, this solution unlocks a number of design variables-for instance, the number of thrusters, as well as their positioning in the general layout, mutual tilt angles, etc.-to be set according simultaneously to propulsion and attitude control goals. In this paper, we explore the effect of a set of configuration parameters defining three-thrusters and four-thrusters layout, trying to capture their impact on an aggregated measure of control performance. To this aim, at first a stability augmentation system (SAS) is designed so as to stabilize the airship making use of thrusters instead of aerodynamic surfaces. Then a non-linear model of the airship is employed to test the airship in a set of virtual simulation scenarios. The analysis is carried out in a parameterized fashion, changing the values of configuration parameters pertaining to the thrusters layout so as to understand their respective effects. In a later stage, the choice of the optimal design values (i.e., the optimal layout) related to the thrusters is demanded to an optimizer. The paper is concluded by showing the results on a complete numerical test case, drawing conclusions on the relevance of certain design parameters on the considered performance, and commenting the features of an optimal configuration

Structure of myelin P2 protein from equine spinal cord

Equine P2 protein has been isolated from horse spinal cord and its structure determined to 2.1 Å. Since equine myelin is a viable alternative to bovine tissue for large-scale preparations, characterization of the proteins from equine spinal cord myelin has been initiated. There is an unusually high amount of P2 protein in equine CNS myelin compared with other species. The structure was determined by molecular replacement and subsequently refined to an R value of 0.187 (<sub>free</sub> = 0.233). The structure contains a molecule of the detergent LDAO and HEPES buffer in the binding cavity and is otherwise analogous to other cellular retinol-binding proteins

Optimal Shutdown Management

The paper presents a novel approach for the synthesis of the open-loop pitch profile during emergency shutdowns. The problem is of interest in the design of wind turbines, as such maneuvers often generate design driving loads on some of the machine components. The pitch profile synthesis is formulated as a constrained optimal control problem, solved numerically using a direct single shooting approach. A cost function expressing a compromise between load reduction and rotor overspeed is minimized with respect to the unknown blade pitch profile. Constraints may include a load reduction not-to-exceed the next dominating loads, a not-to-be-exceeded maximum rotor speed, and a maximum achievable blade pitch rate. Cost function and constraints are computed over a possibly large number of operating conditions, defined so as to cover as well as possible the operating situations encountered in the lifetime of the machine. All such conditions are simulated by using a high-fidelity aeroservoelastic model of the wind turbine, ensuring the accuracy of the evaluation of all relevant parameters. The paper demonstrates the capabilities of the novel proposed formulation, by optimizing the pitch profile of a multi-MW wind turbine. Results show that the procedure can reliably identify optimal pitch profiles that reduce design-driving loads, in a fully automated way

Cyclic Pitch Control for the Reduction of Ultimate Loads on Wind Turbines

In this paper we study the use of individual blade pitch control as a way to reduce ultimate loads. This load alleviation strategy exploits the fact that cyclic pitching of the blades induces in general a reduction of the average loading of a wind turbine, at least for some components as the main bearing, the yaw bearing, or the tower. When ultimate loads are generated during shutdowns, the effect of the use of cyclic pitch results in reduced peak loads. In fact, as the machine starts from a less stressed condition, the response to an extreme gust or other event will result in reduced loading on its components. This form of load mitigation can be seen as a preventative load mitigation strategy: the effect on load reduction is obtained without the need to detect and react to an extreme event, but by simply unloading the machine so that, in case an extreme event happens, the result will be less severe. The effect of peak load mitigation by preventative cyclic pitch is investigated with reference to a multi-MW wind turbine, by using high-fidelity aeroelastic simulations in a variety of operating conditions

Herbaceous Vegetation Dynamic after Cut and Burn Shrub Plants in Southern Brazil

A savanna area at Serra do Sudeste in southern Brazil, was studied during four years to evaluate the influence of cutting and burning shrub plants on dynamic of herbaceous vegetation. The cover of each species in 44 permanent quadrats (0,25 m2) and in each area (cut and burned) was evaluated. The results suggested that grasses and legumes were favored by cutting shrub plants. Burning favored forbs in the first years after disturbance and retarded the development of native forage species desirable for grazing

Optimum Filter Synthesis with DPLMS Method for Energy Reconstruction

Optimum filters are granted increasing recognition as valuable tools for parametric estimation in many scientific and technical fields. The DPLMS method, introduced some twenty years ago, is effective among the synthesis algorithms since it derives the optimum filters directly from the experimental signal and noise waveforms. Two new extensions of the DPLMS method are here presented. The first one speeds up the synthesis phase and improves the energy estimation by synthesizing optimum filters with automatically designed flat-top length. The second one improves the quality of parameter estimation in multi-channel systems by taking advantage of the inter-channel noise correlation properties. The theoretical and functional aspects behind the DPLMS method for optimum filter synthesis are first recalled and illustrated in more detail. The two new DPLMS extensions are subsequently introduced from the theoretical viewpoint and more thoroughly considered from the applicative perspective. The DPLMS optimum filters have been applied first to simulated signals with various amounts and characteristics of superimposed noise and then to the experimental waveforms acquired from a solid-state Ge detector. The results obtained are considered from both the absolute viewpoint and in comparison with those of more traditional, suboptimal filters. The results demonstrate the effectiveness of the two new DPLMS extensions. For single-channel energy estimations, the optimum filters provide comparatively better results than the other filters. The DPLMS multi-channel optimum filters further enhance the quality of the estimations, compared to single-channel optimum filters, with non-negligible inter-channel noise correlation. The effectiveness and robustness of the DPLMS method in synthesizing high-quality filters for energy estimation will be tested soon within leading-edge multi-channel physics experiments.Comment: 15 pages, 13 figure

Time-domain Simulation of electronic noises

In this paper, a procedure is proposed to computer simulate the electronic noise of ionizing-radiation spectrometers. The viewpoint of the simulator is the output of the preamplifier, with or without an anti-aliasing filter, just in front of the ADC. Examples are given for the case of segmented high purity Germanium detectors (HPGe). The method makes use of the fractional calculus basics. A software procedure provides the noisy waveform as a function of the fundamental electrical-physical parameters of the system, including: detector capacitance, detector leakage current, feedback resistor, 1/f-noise coefficient of the input transistor, temperature of the preamplifier input devices. The ADC quantization noise is also included in the simulation