Improved Stability Using Environmental Adaptive Yaw Control for Autonomous Unmanned Helicopter and Bifurcation of Maneuvering in Turning

2011 ◽  
Vol 23 (6) ◽  
pp. 1091-1099 ◽  
Author(s):  
Hiroaki Nakanishi ◽  
◽  
Sayaka Kanata ◽  
Tetsuo Sawaragi ◽  
Keyword(s):  
Feedback Loop ◽  
Environmental Changes ◽  
Angular Rate ◽  
Unmanned Helicopter ◽  
Yaw Control ◽  
Heading Control ◽  
Improved Stability ◽  
The Stability ◽  
Turning Maneuver ◽  
Autonomous Helicopter

Adaptation to environmental changes, such as wind, plays a very important role in improving the reliability of autonomous unmanned helicopters. Adaptive yaw (heading) control for an autonomous helicopter is discussed in this paper. The control structure is based on a hierarchal scheme that utilizes an inner yaw feedback control loop plus an outer feedback loop. The outer loop estimates the direction of the airspeed using roll angle and roll angular rate. Stable coupling in yaw and roll motion is induced by the proposed controller to improve the stability of the helicopter’s flight. Turning utilizing the proposed adaptive control system is discussed in particular. Results of flight experiments show that bifurcation of the helicopter’smaneuvering in turning occurs depending on airspeed. The results indicate that the autonomous unmanned helicopter can select a turning maneuver that is suitable for the environmental conditions, thus stabilizing its flight.

scholarly journals Improved Stability Criteria of Static Recurrent Neural Networks with a Time-Varying Delay

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Lei Ding ◽  
Hong-Bing Zeng ◽  
Wei Wang ◽  
Fei Yu
Keyword(s):  
Neural Networks ◽  
Recurrent Neural Networks ◽  
Linear Matrix ◽  
Time Varying ◽  
Time Varying Delay ◽  
Improved Stability ◽  
The Stability ◽  
Delay Dependent ◽  
Delay Dependent Stability ◽  
Varying Delay

This paper investigates the stability of static recurrent neural networks (SRNNs) with a time-varying delay. Based on the complete delay-decomposing approach and quadratic separation framework, a novel Lyapunov-Krasovskii functional is constructed. By employing a reciprocally convex technique to consider the relationship between the time-varying delay and its varying interval, some improved delay-dependent stability conditions are presented in terms of linear matrix inequalities (LMIs). Finally, a numerical example is provided to show the merits and the effectiveness of the proposed methods.

Functional diversity alters the effects of a pulse perturbation on the dynamics of tritrophic food webs

2021 ◽  
Author(s):  
Ruben Ceulemans ◽  
Laurie Anne Myriam Wojcik ◽  
Ursula Gaedke
Keyword(s):  
Food Web ◽  
Food Webs ◽  
Functional Diversity ◽  
Feedback Loop ◽  
Environmental Changes ◽  
Biodiversity Loss ◽  
Trophic Levels ◽  
Nutrient Pulse ◽  
Trade Offs ◽  
Food Web Model

Biodiversity decline causes a loss of functional diversity, which threatens ecosystems through a dangerous feedback loop: this loss may hamper ecosystems' ability to buffer environmental changes, leading to further biodiversity losses. In this context, the increasing frequency of climate and human-induced excessive loading of nutrients causes major problems in aquatic systems. Previous studies investigating how functional diversity influences the response of food webs to disturbances have mainly considered systems with at most two functionally diverse trophic levels. Here, we investigate the effects of a nutrient pulse on the resistance, resilience and elasticity of a tritrophic---and thus more realistic---plankton food web model depending on its functional diversity. We compare a non-adaptive food chain with no diversity to a highly diverse food web with three adaptive trophic levels. The species fitness differences are balanced through trade-offs between defense/growth rate for prey and selectivity/half-saturation constant for predators. We showed that the resistance, resilience and elasticity of tritrophic food webs decreased with larger perturbation sizes and depended on the state of the system when the perturbation occured. Importantly, we found that a more diverse food web was generally more resistant, resilient, and elastic. Particularly, functional diversity dampened the probability of a regime shift towards a non-desirable alternative state. In addition, despite the complex influence of the shape and type of the dynamical attractors, the basal-intermediate interaction determined the robustness against a nutrient pulse. This relationship was strongly influenced by the diversity present and the third trophic level. Overall, using a food web model of realistic complexity, this study confirms the destructive potential of the positive feedback loop between biodiversity loss and robustness, by uncovering mechanisms leading to a decrease in resistance, resilience and elasticity as functional diversity declines.

scholarly journals Stabilizing immature breathing patterns of preterm infants using stochastic mechanosensory stimulation

2009 ◽  
Vol 107 (4) ◽  
pp. 1017-1027 ◽  
Author(s):  
Elisabeth Bloch-Salisbury ◽  
Premananda Indic ◽  
Frank Bednarek ◽  
David Paydarfar
Keyword(s):  
Preterm Infants ◽  
Respiratory Control ◽  
Behavioral State ◽  
Mean Square ◽  
Breathing Patterns ◽  
Nonlinear Properties ◽  
Improved Stability ◽  
Postconceptional Age ◽  
The Stability ◽  
Large Improvement

Breathing patterns in preterm infants consist of highly variable interbreath intervals (IBIs) that might originate from nonlinear properties of the respiratory oscillator and its input-output responses to peripheral and central signals. Here, we explore a property of nonlinear control, the potential for large improvement in the stability of breathing using low-level exogenous stochastic stimulation. Stimulation was administered to 10 preterm infants (postconceptional age: mean 33.3 wk, SD 1.7) using a mattress with embedded actuators that delivered small stochastic displacements (0.021 mm root mean square, 0.090 mm maximum, 30–60 Hz); this stimulus was subthreshold for causing arousal from sleep to wakefulness or other detectable changes in the behavioral state evaluated with polysomnography. We used a test-retest protocol with multiple 10-min intervals of stimulation, each paired with 10-min intervals of no stimulation. Stimulation induced an ∼50% reduction ( P = 0.003) in the variance of IBIs and an ∼50% reduction ( P = 0.002) in the incidence of IBIs > 5 s. The improved stability of eupneic breathing was associated with an ∼65% reduction ( P = 0.04) in the duration of O2 desaturation. Our findings suggest that nonlinear properties of the immature respiratory control system can be harnessed using afferent stimuli to stabilize eupneic breathing, thereby potentially reducing the incidence of apnea and hypoxia.

Amplifier Performance in Terms of Two-Port Parameters

1998 ◽  
Vol 35 (1) ◽  
pp. 47-70
Author(s):  
Jack Willis
Keyword(s):  
Feedback Loop ◽  
High Frequencies ◽  
Feedback Amplifier ◽  
Alternative Means ◽  
The Stability

At high frequencies the complexity of the circuit representing a feedback amplifier is such that the concept of a feedback loop becomes meaningless, and an alternative means of checking the stability of the amplifier is needed. Representing the network as a two-port realises such a solution.

scholarly journals Tailoring capping-layer composition for improved stability of mixed-halide perovskites

2022 ◽  
Author(s):  
Noor Titan Putri Hartono ◽  
Marie-Hélène Tremblay ◽  
Sarah Wieghold ◽  
Benjia Dou ◽  
Janak Thapa ◽  
...  
Keyword(s):  
Solar Cells ◽  
Perovskite Solar Cells ◽  
Capping Layer ◽  
Improved Stability ◽  
Halide Perovskites ◽  
The Stability ◽  
Low Dimensional ◽  
Layer Composition

Incorporating a low dimensional (LD) perovskite capping layer on top of perovskite absorber, improves the stability of perovskite solar cells (PSCs). However, in the case of mixed-halide perovskites, which can...

Improved stability of salvianolic acid B from Radix Salviae miltiorrhizae in deep eutectic solvents

2016 ◽  
Vol 8 (11) ◽  
pp. 2502-2509 ◽  
Author(s):  
Jue Chen ◽  
Shi-fei Li ◽  
Zhi-feng Yao ◽  
Da-wei Yang ◽  
Li-wei Zhang
Keyword(s):  
Environmentally Friendly ◽  
Deep Eutectic Solvents ◽  
Salvianolic Acid B ◽  
Radix Salviae Miltiorrhizae ◽  
Salvianolic Acid ◽  
Salviae Miltiorrhizae ◽  
Improved Stability ◽  
The Stability

Environmentally friendly deep eutectic solvents were developed for enhancing the stability of salvianolic acid B from Radix Salviae miltiorrhizae.

The Role of Internal Irreversibilities in the Performance and Stability of Power Plant Models Working at Maximum ϵ-Ecological Function

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Gabriel Valencia-Ortega ◽  
Sergio Levario-Medina ◽  
Marco Antonio Barranco-Jiménez
Keyword(s):  
Power Plants ◽  
Heat Engine ◽  
Combined Cycle ◽  
Ecological Function ◽  
Operating Conditions ◽  
Maximum Efficiency ◽  
Working Fluid ◽  
Engine Model ◽  
Improved Stability ◽  
The Stability

Abstract The proposal of models that account for the irreversibilities within the core engine has been the topic of interest to quantify the useful energy available during its conversion. In this work, we analyze the energetic optimization and stability (local and global) of three power plants, nuclear, combined-cycle, and simple-cycle ones, by means of the Curzon–Ahlborn heat engine model which considers a linear heat transfer law. The internal irreversibilities of the working fluid measured through the r-parameter are associated with the so-called “uncompensated Clausius heat.” In addition, the generalization of the ecological function is used to find operating conditions in three different zones, which allows to carry out a numerical analysis focused on the stability of power plants in each operation zone. We noted that not all power plants reveal stability in all the operation zones when irreversibilities are considered through the r-parameter on real-world power plants. However, an improved stability is shown in the zone limited by the maximum power output and maximum efficiency regimes.

An Analytical Design Method for Milling Cutters With Non-Constant Pitch to Increase Stability

2000 ◽  
Author(s):  
Erhan Budak
Keyword(s):  
Surface Finish ◽  
Design Method ◽  
Stability Limit ◽  
Analytical Stability ◽  
Chatter Vibrations ◽  
Constant Pitch ◽  
Improved Stability ◽  
Limited Frequency ◽  
The Stability ◽  
Explicit Relation

Abstract Chatter vibrations result in reduced productivity, poor surface finish and decreased cutting tool life. Milling cutters with non-constant pitch angles can be very effective in improving the stability of the process against chatter. In this paper, an analytical stability model and a design method are presented for non-constant pitch cutters. An explicit relation is obtained between the stability limit and the pitch variation which leads to a simple equation for optimal pitch angles. A certain pitch variation is effective for limited frequency and speed ranges which are also predicted by the model. The improved stability, productivity and surface finish are demonstrated by several examples.

scholarly journals A Precise and GNSS-Free Landing System on Moving Platforms for Rotary-Wing UAVs

Sensors ◽  
2019 ◽  
Vol 19 (4) ◽  
pp. 886 ◽  
Author(s):  
Francisco Alarcón ◽  
Manuel García ◽  
Ivan Maza ◽  
Antidio Viguria ◽  
Aníbal Ollero
Keyword(s):  
Relative Position ◽  
Unmanned Helicopter ◽  
Landing Position ◽  
Moving Platforms ◽  
Landing Platform ◽  
Aerial Vehicle ◽  
The Stability ◽  
Novel Concept ◽  
High Level ◽  
Rotary Wing

This article presents a precise landing system that allows rotary-wing UAVs to approach and land safely on moving platforms, without using GNSS at any stage of the landing maneuver, and with a centimeter level accuracy and high level of robustness. This system implements a novel concept where the relative position and velocity between the aerial vehicle and the landing platform are calculated from the angles of a cable that physically connects the UAV and the landing platform. The use of a cable also incorporates a number of extra benefits, such as increasing the precision in the control of the UAV altitude. It also facilitates centering the UAV right on top of the expected landing position, and increases the stability of the UAV just after contacting the landing platform. The system was implemented in an unmanned helicopter and many tests were carried out under different conditions for measuring the accuracy and the robustness of the proposed solution. Results show that the developed system allowed landing with centimeter accuracy by using only local sensors and that the helicopter could follow the landing platform in multiple trajectories at different velocities.

scholarly journals Experimental Study on Dynamic Resilient Modulus of Lime-Treated Expansive Soil

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Zheng Lu ◽  
Yang Zhao ◽  
Shaohua Xian ◽  
Hailin Yao
Keyword(s):  
Moisture Content ◽  
Environmental Changes ◽  
Resilient Modulus ◽  
Expansive Soils ◽  
Expansive Soil ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
The Stability ◽  
Compaction Degree

Dynamic resilient modulus is the design index of highway subgrade design code in China, which is significantly affected by the traffic loads and environmental changes. In this study, dynamic triaxial tests were conducted to investigate the influence of moisture content, compaction degree, cyclic deviator stress, and confining pressure on lime-treated expansive soil. The suitability of UT-Austin model to lime-treated expansive soils was verified. The results indicate that the dynamic resilient modulus of lime-treated expansive soils increases nonlinearly with the increase of compaction degree, while decreases nonlinearly with the increase of dynamic stress level. The dynamic resilient modulus decreases linearly with the increase of moisture content and increases linearly with the increase of confining pressure. Moreover, the moisture content has a more significant effect on the dynamic resilient modulus of lime-treated expansive soil. Therefore, it is necessary to ensure the stability of soil humidity state and its excellent mechanical properties under long-term cyclic loading for the course of subgrade filling and service. Finally, the calculated results of the UT-Austin model for dynamic resilient modulus show a good agreement with the test results.

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