Positive Position Research Articles

Experiment-in-the-Loop system for fast and effective tuning of active vibration controllers

Tuning active controllers is one of the main challenges in the field of active vibration control (AVC). To address this challenge, this study introduces a novel approach called Experiment in the Loop (EITL). The EITL method, unlike traditional techniques, automates the tuning process through an algorithm based on Particle Swarm Optimization (PSO). This algorithm carries out numerous experimental tests on a structure and, at each test, tries a new configuration of the controller, evaluates its performance, and iteratively improves the control parameters. The EITL's innovation lies in its ability to achieve fast and efficient tuning without any numerical model, making it a significant advancement in AVC technology. The EITL approach is validated by tuning five Multiple-Input Multiple-Output (MIMO) Positive Position Feedback (PPF) active vibration controllers on a composite beam equipped with three piezoelectric sensors and three piezoelectric actuators. Experimental results show that the ‖H‖∞ norm of the composite beam is reduced up to 96.1% on certain modes, and an average reduction of 74.7% is achieved in a frequency range from 0 to 200 Hz with minimal spillover effects. The developed EITL opens the avenue to a fast and effective tuning of AVC without numerical models.

Stability and Control of Car Dynamics with a Quarter Model via a Novel Simple Harmonic Hump under External Force

Effects of the road, such as speed bumps, can significantly affect a car’s stability. This study focuses on how a quarter-car model is affected by a basic harmonic speed hump and how Cubic Negative Velocity Control (CNVC) is used to control the amplitude of disturbances. This study differs from earlier research in considering various control and force kinds that impact the system. The external forces in this context are a component of a non-linear dynamic system. Two-degree-of-freedom (2DOF) differential coupled equations describe the system’s equation. Numerous numerical experiments have been conducted, including proportional derivative (PD), negative derivative feedback (NDF), positive position feedback (PPF), linear negative velocity control (LNVC), and CNVC; the results show that when the hump is represented as a simple harmonic hump, CNVC has the best effect and can regulate vibrations more precisely than the other approaches on this system. Subsequently, the vibration value of the system was numerically analyzed both before and after the control was implemented. Using the frequency response equation and phase plane approaches in conjunction with the Runge–Kutta fourth order method (RK-4) in the context of resonance situation analysis, the stability of the numerical solution has been evaluated.

Digital Literacy in Saudi Tertiary EFL Context: Perspectives of Students and Potentials for Listening Skills

Technology is regarded as a vital aspect in modern society, revolutionising various fields. Consequently, evolutionary knowledge and skills raise in this paradigm, referred to as digital literacy. The necessity to reveal the influence in EFL, English as a foreign language, context is fundamental. The exploration seeks to examine digital literacy perspectives of 117 Saudi undergraduate EFL learners enrolled in English Language and Translation bachelor’s programme at a Saudi university. It also scrutinises the prospects for improving English listening skills. To achieve the exploration objectives, mixed-method approach is integrated via adopted questionnaires from scholarly work (Mudra, 2020; Najmi & Navaee Lavasani, 2021; Ng; 2012a; Ng; 2012b; Yukselir & Yuvayapan, 2019) with minor adjustments. Findings demonstrate EFL learners’ confidence to their digital literacy skills. They reveal high confidence to solving technical difficulties; conversely, the least positive positioning denotes towards literacy to web relevant activities. Findings advocate for the benefits of listening skills, especially for pronunciation and vocabulary improvement, authentic materials for learning, language learning motivation, and access to entertaining educational materials. The exploration serves endeavour to subsequent academic and pedagogical implementations.

KGB Agents: their Types, Functions and Objectives

KGB agents are one of its pillars and sources of power since on the basis of the information they provided, the operative work was organized, which ensured that the atmosphere of fear and obedience pervade society. The goal of this research is to name and define the types of agents, the tasks they had to carry out, the goals to be achieved as well as in what segments of the population they were most active. The definition of an agent in KGB documents is a Soviet citizen, a foreign country national (subordinate) or an individual who has no citizenship, who collaborated secretly with the KGB organs and fulfilled its tasks ensuring internal security in the USSR. The committee’s apparatus consisted of agents, residents, owners of apartments for secret meetings, and owners of conspiracy apartments who were not on the staff of the agency. KGB secret agents are divided into certain types by the nature of their activities and the tasks they were to carry out. Agents infiltrated into the clergy controlled the Church and seminaries’ activities, attempted to exert influence on anti-Soviet priests as well as to form a positive position of the Vatican and the community of the devout that was in favour of the Soviet regime. Among the émigré communities their goal was to harm the organisations of the diaspora and discredit the cause of Lithuania’s liberation for which they fought. The objective of the agents who were in charge of monitoring resistance activities was to uncover anti-Soviet schemes, especially the ways and organizers of samizdat. They aimed to influence people so that they avoided resistance, and those who got involved would abandon it. Agents using various instruments such as spreading disinformation about individuals, compromising them, trying to “reeducate” them took efforts to discredit non-conformists in the eyes of the public. The role of agents was particularly important for explaining the activities of resistance both in Lithuania and the West. After 1953, requirements for agents were more demanding than before. However, constant search for secret collaborators demonstrates that the work was complicated and the results could not satisfy the KGB although separate individuals suffered harm.

The Role of H. L. A. Hart’s «Rule of Recognition» in Contemporary Anglo-American Legal Positivism

The article explores the role of the theory of «rules of recognition» by Oxford professor H.L.A. Hart in the contemporary theory of Anglo-American legal positivism, introduced by him in his central work «The Concept of Law» (1961), which has a significant influence on contemporary legal theory and philosophy. The authors reveal the content and meaning of the concept of «rules of recognition» as part of the secondary rules – «rules about rules» or «procedural rules» which determine the criteria for the validity of law along with the «rules of change» and the «rules of adjudication» in H.L.A. Hart’s terminology. The authors demonstrate the correlation with the «Grundnorm» of German legal philosophter H. Kelsen, which is more common in the Ukrainian legal theory, and which justifies the existence of constitutional norms as fundamental ones which determine the recognition of law by society and its individuals. The authors analyze the main positions of H.L.A. Hart’s followers – J. Raz, M. Kramer, B. Bix, S. Shapiro and others – regarding this theory and highlights the criticism of its individual provisions. The authors highlight how H.L.A. Hart tried to explain by the «rules of recognition» how law at the fundamental level is a matter of social convention (agreement between people inside the inhabited society), defending one of the components of legal positivism – the thesis of social fact (social sources of law thesis). The authors examine the interdependence between law and coercion by the State, the role of social practice in society’s subordination to law, the role of moral norms in the formation of law, in particular, the «rule of recognition», the correlation between the concepts of «rule of recognition» and «legal validity», and the problem of law enforcement by judges and governmental officials of the «rule of recognition». The authors summarize how H.L.A. Hart eliminates morality from the content of law in motivating judges and governmental officials to apply the rules of law, clarifies the position of legal positivism on the issue of the grounds for society’s submission to law, and demonstrates how the «empirical» theory of recognition prevails over the «analytical» theory, using R. Alexy terminology.

Large-scale magnetic target state estimation using model parameter optimization

Abstract Aiming at the problem of non-negligible target scale in the state estimation of magnetic targets, a state estimation method that requires only the measurement data of a single three-axis magnetic sensor and is insensitive to the initial value is proposed. Firstly, the state estimation model of a single three-component magnetic sensor is established based on a magnetic dipole array. A signal preprocessing method is designed to reject useless signals and keep the waveform intact. Five swarm intelligent optimization algorithms such as Particle Swarm Optimization (PSO), Artificial Hummingbird Algorithm (AHA), Artificial Rabbits Optimization (ARO), Grey Wolf Optimizer (GWO), and Improved GWO (IGWO) are introduced to perform state optimization, and two methods, such as Conjugate Gradient Least Squares (CGLS), and Stepwise Regression (SR), are introduced to calculate the magnetic moment parameters, and PSO-CGLS, AHA-CGLS, AHA-CGLS, ARO-CGLS, ARO-CGLS, ARO-CGLS, ARO-CGLS, ARO-CGLS, ARO-CGLS, ARO-CGLS, ARO-CGLS, and ARO-CGLS are designed in combination. CGLS, ARO-CGLS, GWO-CGLS, IGWO-SR, IGWO-CGLS, and six state estimation methods. In order to address the problem that the parameter optimization range is too large, the state to be estimated is adjusted from the initial state to the state at the moment of the maximum value of the magnetic field modulus, and the method of positive transverse distance estimation is used to narrow the range of positive transverse position optimization. Finally, numerical simulation tests and ship model tests are used for verification, and the results show that the proposed methods are accurate and can meet the needs of precise target state estimation.

Landscape positioning of Neolithic mustatil stone structures along the margins of the Nefud Desert, Saudi Arabia

Monumental rectangular stone structures called mustatils are an important emerging feature of the Holocene archaeological record of northwestern Arabia. To date, few have been excavated, with available radiocarbon dates suggesting an age range of ca. 5400–4200 BC. Here we present a rigorous spatial analysis to identify the patterning and landscape context of 169 mustatils in the southern and western margins of the Nefud Desert. This included: (1) a systematic survey of satellite imagery to identify mustatils; (2) viewshed analysis to examine location and landscape visibility; (3) a point process model to understand how diverse environmental and landscape variables affect mustatil locations; (4) mark correlation function to assess spatial patterning of mustatils based on their size. Results indicate that mustatil locations are determined most by proximity to water (likely locations of enhanced surface water occurrence under the enhanced humidity of the Mid-Holocene), on east facing slopes, close to rocky areas, at elevations between 880 and 950 masl, and on or near topographic ridges (positive topographic position index). Viewshed analysis showed that mustatils are preferentially located in areas that have good views, but not the best that are available, indicating complex landscape positioning that balances a range of topographic and behavioural factors. Using a rank permutation method with size (length) of mustatils as a proxy for labour mobilization we show that mustatils within clusters are not arranged hierarchically based on size, and were likely built by non-stratified groups of people. Our analyses show that people were choosing multiple factors when deciding where to build mustatils, and that the distribution of mustatils may relate to different groups of people resulting in the construction of complex ritual landscapes. As one of the earliest examples of large-scale monumental stone structure construction in global prehistory, understanding mustatils can enlighten us on human-environment interaction during the Neolithic.

The Impact of the Nonlinear Integral Positive Position Feedback (NIPPF) Controller on the Forced and Self-Excited Nonlinear Beam Flutter Phenomenon

This article presents a novel approach to impact regulation of nonlinear vibrational responses in a beam flutter system subjected to harmonic excitation. This study introduces the use of a Nonlinear Integral Positive Position Feedback (NIPPF) controller for this purpose. This technique models the system as a three-degree-of-freedom nonlinear system representing the beam flutter, coupled with a first-order and a second-order filter representing the NIPPF controller. By applying perturbation analysis to the linearized system model, the authors obtain analytical solutions for the autonomous system with the controller. This study aims to reduce vibration amplitudes in a nonlinear dynamic system, specifically when 1:1 internal resonance occurs. The Routh–Hurwitz criterion is utilized to evaluate the system’s stability. Furthermore, the frequency–response curves (FRCs) exhibit symmetry across a range of parameter values. The findings highlight that the effectiveness of vibration suppression is directly related to the product of the NIPPF control signal after comparing with different controllers. Numerical simulations, conducted using the fourth-order Runge–Kutta method, validate the analytical solutions and demonstrate the system’s amplitude response. The strong correlation between the analytical and numerical results highlights the accuracy and dependability of the proposed method.

Controlling the Generator in a Series of Hybrid Electric Vehicles Using a Positive Position Feedback Controller

Controlling the Generator in a Series of Hybrid Electric Vehicles Using a Positive Position Feedback Controller

One Case of Solar Dermatitis Treated with Umbilical Needle "Four Positions" Combined with Body Acupuncture

Solar dermatitis is a kind of hypersensitive skin disease, the main clinical manifestations are redness, swelling, itching and burning. A case of solar dermatitis treated with umbilical acupuncture "four positive positions" combined with body acupuncture by Professor Chen Chaoming is introduced, which provides a new way of thinking for the treatment of solar dermatitis by clinical Chinese medicine external therapy.

Advanced vibrant controller results of an energetic framework structure

Abstract This research shows the influence of a new active controller technique on a parametrically energized cantilever beam (PECB) with a tip mass model. This article remains primarily concerned with regulating the system’s response using a novel control mechanism. This study describes a novel control mechanism called the nonlinear proportional-derivative cubic velocity feedback controller (NPDCVFC). The motivation of this article is to design a novel control algorithm in order to mitigate the nonlinear vibrations of a parametrically energized cantilever beam with a tip mass model. The proposed controller NPDCVFC incorporates nonlinearly second- and first-order filters into the system. The system is governed by one nonlinear differential equation having both quadratic and cubic nonlinearities within the parametric force. The controller’s efficiency in reducing framework vibrations, managing nonlinear bifurcations, and calming unstable motion is evaluated using numerical simulations of instantaneous vibrations. The perturbation technique is beneficial for solving the current model under the proposed worst resonance case ( Ω ˆ p = 2 ω ˆ 0 ) \text{(}{\hat{{\Omega }}}_{\text{p}}=2{\hat{{\omega }}}_{0}) . In order to choose the optimal controller, we have also added three more controller approaches to the configuration. Integral resonant control, positive position feedback, and nonlinear integral positive position feedback are the three controller approaches that are applied to the structure under consideration. We determine that the NPDCVFC as a new controller is the most effective for lowering the high vibration amplitudes. Over the investigated model, all numerical results were performed using the MATLAB 18.0 programmer software. The stability analysis and the effects of various elements on the controlled structure have been investigated. A comparison with recently published works of a comparable model has also been prepared. Experiment capacities for a PECB with a tip mass are obtainable to validate the results, and they demonstrate good agreement with analytical and numerical results.

Experimental Study on Shear Lag Effect of Long-Span Wide Prestressed Concrete Cable-Stayed Bridge Box Girder under Eccentric Load

Based on the engineering background of the wide-width single cable-stayed bridge, the shear lag effects of the cross-section of these bridge box girders under the action of the eccentric load were experimentally studied. The behavior of shear lag effects in the horizontal and longitudinal bridge directions under eccentric load in the operational stage of a single cable-stayed bridge was analyzed by a model testing method and a finite element (FE) analytical method. The results showed that the plane stress calculation under unidirectional live load was similar to the results from spatial FE analysis and structural calculations performed according to the effective flange width described in the design specification. At the position of the main beam near the cable force point of action, the positive stress at its upper wing edge was greatest. At a distance from the cable tension point, the maximum positive stress position trend showed that from the center of the top flange to the junction of the top flange and the middle web to the junction of the top flange and the middle web and the side web. Under eccentric load, the positive and negative shear lag effects on the end fulcrum existed at the same time, and the shear lag coefficient on the web plate was larger than the shear lag coefficient on the unforced side. Due to the influence of constraint at the middle fulcrum near the middle pivot point, positive and negative shear lag effects were significant, and the coefficient variation range was large, resulting in large tensile stress on the roof plate in this area. According to FE analytical results, stress and shear forces of a single box three-chamber box girder under eccentric load were theoretically analyzed, the bending load decomposed into the accumulation of bending moment and axial force, using the bar simulation method, and the overall shear lag effect coefficient λ was obtained and verified.

An experimental approach to multi-input multi-output nonlinear active vibration control of a clamped sandwich beam

Large amplitude vibrations are often associated with geometric nonlinearity. These nonlinear systems are usually controlled using linear controllers, such as positive position feedback (PPF). Nonlinear control has also often been limited to single-input single-output (SISO) architectures. The present study develops a nonlinear PPF controller implemented with both a SISO and a multiple-input multiple-output (MIMO) architecture on a real experimental set-up, consisting of a clamped composite sandwich beam. The controller aimed to reduce the vibration amplitude observed when the structure was subject to a stepped-sine excitation in the frequency neighborhood of the first natural frequency for different force excitation levels. The developed nonlinear controller is based on a linear PPF controller to which a cubic term was added since the system under study is of hardening type. The control parameters were selected by optimization of the reduction of the vibration at low excitation amplitude. The nonlinear MIMO and SISO versions of the controller were compared to linear MIMO and SISO versions, which omitted the cubic term but maintained the other parameters. The nonlinear controllers were found to outperform the linear ones, and the MIMO versions of each controller also outperformed the SISO ones. Overall, the experimental evidence shows that a nonlinear MIMO PPF controller should be preferred for the application under study.

Unlocking sustainability: the dynamic nexus of organizational support, identification, and green HRM practices in cultivating pro-environmental excellence

PurposeThere is a growing need to promote and practice sustainable HRM to foster greener organizations with trained employees who have an attitude and behavior to preserve depleting resources. The purpose of this study is to highlight the importance of sustainable green human resource management (Green HRM) practices along with organizational identification (OI) as a mediating factor and perceived organizational support (POS) as a moderating factor.Design/methodology/approachQuantitative methodology was used, and the data were collected from 311 employees working in telecommunication organizations located in the twin cities of Rawalpindi and Islamabad, Pakistan. Results of the study are based on the structural equation modeling technique using Smart-PLS.FindingsFindings revealed that OI proved to be a significant positive mediator between Green HRM and organizational citizenship behaviors for the environment. POS also proved to be a significant moderator on the relationship between Green HRM and OI.Research limitations/implicationsThe study is limited to the two cities of Pakistan; future studies can focus on more cities so that the results can be more generalized.Practical implicationsThis study will especially be useful for HR practitioners to develop mechanisms to initiate and encourage sustainable HR practices.Social implicationsOrganizations’ positive position is established through the inculcation of green activities among their employees. Thus, a sense of responsibility and attachment among employees toward green behavior makes them good citizens. It also works well for their organization as well as for the environment. Moreover, it preserves environmental resources and helps ensure sustainability.Originality/valueThe research paper was aimed at exploring the importance of sustainable Green HRM practices in a developing country like Pakistan.

Assessment of compaction quality of highway subgrade via roller-integrated positive maximum velocity detection technique

ABSTRACT Quality control of compaction is vital for the long-term performance of highways. Specifically, the assessment of subgrade compaction quality is a key factor. Currently, compaction quality is primarily controlled by parameters set during compaction and subsequent random sampling tests post-construction. However, the impact of human factors and limitations of these sampling tests fall short of meeting the standards of large-scale precision construction. This study introduces a real-time monitoring index to characterise the compaction quality of silt subgrades: the maximum velocity compaction value (MVCV). This index is derived using a combination of the roller-integrated positive maximum velocity detection system and real-time kinematic Beidou positioning system (RTK-BDS). Furthermore, the Green spline interpolation method allows for estimating compaction quality values at any point. A case study from the Hengyong Highway project in China reveals a strong linear relationship between compaction parameters and compactness. This suggests the suitability of this method for characterising the compaction quality of such silt. This assessment approach facilitates a detailed evaluation of compaction quality across the entire construction zone. Hence, it aids in effectively minimising compaction defects, reducing unnecessary rework, and enhancing the overall compaction quality and efficiency of highway construction.

Socialinių pedagogų ir socialinių darbuotojų patirtis realizuojant vaiko dalyvavimo teisę vaikų dienos centruose

The objective of the study is to reveal the realities of the realisation of the right of the child to participate in children’s day care centres based on the experience of social pedagogues and social workers. Qualitative research was chosen for the study by using the method of semi-structured interview. 11 professionals, who work in children’s day care centres in different Lithuanian regions, participated in the study. The study identified the expression of the realisation of the right of the child to participate in children’s day care centres. The expression of the right of the child to participate in children’s day care centres is associated with a positive position of the professionals in the practice of the child’s right to participation, their cooperation with the child, their mutual cooperation, their cooperation with the child’s parents/guardians and other institutions when realising the right of the child to participation. The positive position of the professionals is expressed through the understanding of the importance of this right and inclination to realise it, the acknowledgement of the child as an active participant in decision-making, openness to the opinion of the child and nonsuppression of their opinion. The cooperation of the professionals with the child is expressed through the creation of the relationships, which are based on mutual trust, the informing of the child that his opinion is important, that he can express it and be heard, the provision of information to the child in a way that is understandable to him while empowering him to participate in decision-making, the listening to the child and his support, the taking into account the child’s opinion while responding to his best interests, the analysis of situations and the discussion of various solutions with the child in a way understandable to him, assistance when taking decisions related to him, the involvement of the child and the taking into account his needs and interests when planning and organising socio-educational activities, the encouragement of the child to assume his obligations and responsibilities. The cooperation of children’s day care centres professionals is expressed though their favourable and unified approach towards this right, their involvement in the realisation of this right and the sharing of the experience when realising this right. The cooperation with the child’s parents/guardians is expressed through the assistance to them in understanding the importance and expression of this right, their consulting and assistance while creating conditions for this right to be expressed at home. The cooperation with other institutions is expressed through the sharing of information and insights on the positive aspects of the realisation of this right and the discussion of arising difficulties and possibilities to overcome them.

INNOVATIVE DEVELOPMENT OF HOSPITALITY ENTERPRISES

The article studies the main directions and stages of development of the strategy of innovative development of hotel enterprises. It is substantiated that the development and implementation of innovations is the most important condition for the progressive development of both a separate enterprise, an entrepreneurial structure, and the entire economy as a whole. Innovative processes are now becoming increasingly important, their main task is to achieve competitive advantages for enterprises and more fully meet consumer demand for high-quality services. At present, this can only be achieved through innovations that need to be widely implemented and used in modern economic conditions.
 Innovation drives the emergence of in the market for new or improved products and services. Innovative activities can lead a hotel company to qualitative changes in all processes activities. They are aimed at achieving results - increasing the speed and quality of the visitor service process.
 Innovation process at the enterprise hotel industry consists of a list of actions to introduce services with new properties, new technological processes, the use of new methods and methods of logistics.
 Innovative development in the hotel business allows you to win as many visitors as possible and in the best way satisfy their needs while maintaining a market segment. This development strategy hotel determines its recognition on competitive service markets.
 The best way to achieve good results is to plan a hotel enterprise development strategy based on a systematic analysis of competitors, consumers, and the hotel's technological profile.
 It should not be forgotten that for any hotel, the most important role in the process of innovative development is played by the staff. After all, the human factor certainly affects the positioning of the service and can lead to its positive and negative position

Nonlinear vibrations and control of PFG-GR laminated composite cantilever rectangular variable cross-section plate with NPPF controller

This paper studies the nonlinear vibrations and control of the piezoelectric functionally graded graphene-reinforced laminated composite cantilever rectangular (PFG-GRLCCR) variable cross-section plate with the NPPF controller under the simultaneous resonant cases. The nonlinear dynamic governing equations of motion for the PFG-GRLCCR variable cross-section plate are obtained by using the extended Halpin-Tsai mode, linear constitutive equations of the piezoelectric materials, classical laminated plate theory, von Karman large deformation theory, and Hamilton principle. Considering Galerkin method, the nonlinear ordinary differential governing equations are obtained. The nonlinear positive position feedback (NPPF) controllers are designed according to the similarity principle. The multiple scale method is used to investigate the nonlinear vibration characteristics of the stable motion for the PFG-GRLCCR variable cross-section plate with the NPPF controllers. The amplitude-frequency response curves, force-amplitude response curves, time histories, phase portraits, and bifurcation diagrams are given to investigate the nonlinear dynamic characteristics of the PFG-GRLCCR variable cross-section plate with the NPPF controller. The results demonstrate that the NPPF controller can suppress the nonlinear vibrations of the structure well, and the effectiveness of the controllers is best when the NPPF controller has a similar nonlinear characteristic with the structure. The complex nonlinear vibration characteristics appear for the PFG-GRLCCR variable cross-section plate with the NPPF controller.

Extremal statistics for first-passage trajectories of drifted Brownian motion under stochastic resetting

We study the extreme value statistics of first-passage trajectories generated from a one-dimensional drifted Brownian motion subject to stochastic resetting to the starting point with a constant rate r. Each stochastic trajectory starts from a positive position x 0 and terminates whenever the particle hits the origin for the first time. We obtain an exact expression for the marginal distribution Pr(M|x0) of the maximum displacement M. We find that stochastic resetting has a profound impact on Pr(M|x0) and the expected value ⟨M⟩ of M. Depending on the drift velocity v, ⟨M⟩ shows three distinct trends of change with r. For v⩾0 , ⟨M⟩ decreases monotonically with r, and tends to 2x0 as r→∞ . For vc<v<0 , ⟨M⟩ shows a nonmonotonic dependence on r, in which a minimum ⟨M⟩ exists for an intermediate level of r. For v⩽vc , ⟨M⟩ increases monotonically with r. Moreover, by deriving the propagator and using a path decomposition technique, we obtain, in the Laplace domain, the joint distribution of M and the time tm at which the maximum M is reached. Interestingly, the dependence of the expected value ⟨tm⟩ of tm on r is either monotonic or nonmonotonic, depending on the value of v. For v>vm , there is a nonzero resetting rate at which ⟨tm⟩ attains its minimum. Otherwise, ⟨tm⟩ increases monotonically with r. We provide an analytical determination of two critical values of v, vc≈−1.69415D/x0 and vm≈−1.66102D/x0 , where D is the diffusion constant. Finally, numerical simulations are performed to support our theoretical results.

Design of anti-unwinding attitude coupling controller for flexible spacecraft using positive position feedback control

Flexible vibration has a great impact on flexible spacecraft attitude control, which will reduce the pointing accuracy of the spacecraft platform and bring severe challenges to the design of a high-precision attitude control system for flexible spacecraft. Aiming at the problem of attitude and vibration coupling control of flexible spacecraft, an anti-unwinding attitude coupling controller using the positive position feedback (PPF) control is proposed in this paper. The model compensation control term is constructed based on the prior information to improve the tracking performance. The proposed attitude coupling control method can effectively suppress the flexible vibration while achieving more accurate attitude control. The obtained closed-loop system under the proposed control scheme is asymptotically stable, which is proved by the Lyapunov stability theory. The numerical simulation illustrates that the proposed method can effectively improve the attitude control accuracy of the flexible spacecraft and is capable of large-angle attitude maneuver control because of its prominent performance in attitude tracking and its unwinding-free performance.