Conservative Conditions Research Articles

Prediction and suppression of chaos following flutter in wind turbines

Chaotic motion in a fluttering wind turbine blade is investigated by the development of an efficient analytical predictive model that is then used to suppress the phenomenon. Flutter is a dynamic instability of an elastic structure in a fluid, such as an airfoil section of a wind turbine blade. It is presently modelled using generalised two degree of freedom coupled modes of a blade airfoil section (pitch and plunge) combined with local unsteady aerodynamics, based on flutter derivatives and a continuous bilinear lift curve under damping. The mode coupling causes instability and limit cycle flutter due to a Hopf bifurcation. Following the critical flutter speed, the response can transition to chaos through successive other bifurcations like period doubling. New closed-form conservative analytical conditions for chaos following blade flutter are identified and discussed for the wind turbine section taking into account the blade geometry and optimal design of the wind turbine. These predictions are numerically verified for a range of conditions including stall slope and damping. The results confirm that chaos following blade flutter can occur due to nonlinearities in the aerodynamics, i.e. due to a bilinear lift law. This phenomenon is then suppressed to unrealistically high wind speeds and/or eliminated by quantified variation of system parameters using the predictive model. The results show that small changes in tip speed ratio (−15%), and stall slope factor (−17%) can eliminate or suppress chaos following flutter, while, in general, larger magnitude changes in dynamic parameters (i.e. mass, inertia > 81%, stiffness > 97%, damping > 100%) are required to achieve the same, by detuning the coupled plunge and pitch natural frequencies or damping out overlapping parametric resonances. These results also highlight that the analytical predictions can remarkably be generalized to any parameter set and provide almost instantaneous calculations representing many thousands of numerical simulations from many bifurcation diagrams (computational acceleration factor of 107 times). General insight is also provided into the occurrence and suppression of airfoil chaos following flutter in aeroelastic structures like wind turbines.

Topological slow light enhanced second harmonic generation in double-resonant topological photonic crystal

Generally, the second-harmonic generation and slow light of multi-band topological edge states (TESs) have been studied separately. Therefore, the influence of simultaneous slow light and topology protection on second-harmonic generation (SHG) is deficient. Here, we propose a high-efficiency SHG using dual-frequency TESs in topological photonic crystals (TPCs) with slow-light conditions. The wave vector matching condition and energy conservation condition (frequency doubling) can be achieved by adequately adjusting the overall structural parameters of TPCs. The double-resonant nonlinear interaction between two TESs is enabled using a square lattice TPC. Due to the topological localization of the TES and the long interaction time of slow-light effect, the energy densities of the fundamental wave and SHG are significantly increased. Consequently, the high intrinsic efficiency of SHG can be obtained in the order of 7.40 × 10−4. Our work opens new avenues for using topological protected and slow light enhanced nonlinear frequency conversion in a TPC system.

Аналіз логістичних витрат підприємства

The article examines the problems of the operation of the enterprise's logistics system, which are relevant and require immediate resolution by optimizing logistics costs and improving the operation of this system as a whole. The connection between the optimization of logistics costs and the strengthening of the company's competitive advantages due to the successful selection of contractors, optimal product distribution channels, modeling of logistics systems and chains, and the creation of conditions for resource conservation is substantiated. The quality of logistics processes is reflected in the effective indicators of the transport company's activity, as costs aimed at the use of labor, means and labor items are minimized.
 The logistics system of a modern company is increasingly becoming the subject of scientific research and development as a key form of automation, integration, optimization and management of material resources and information flows circulating in business units. The issue of optimization of logistics costs of production enterprises is characterized by incompleteness and requires further scientific research.
 The quality of logistics processes is reflected in the effective indicators of the enterprise's activity due to the minimization of costs for the use of labor, funds and labor items. The main types of logistics costs were analyzed in the article. And also the need to determine the presence of hidden types of logistics costs was noted. It was outlined that the complexity of determining logistics costs is caused by the influence of internal and external environmental factors. Changes in the structure of logistics costs were analyzed based on the data of the investigated enterprise. The impact of labor costs on logistics workers of the selected enterprise was considered and the dynamics of costs associated with the provision of logistics services on the total amount of logistics costs was analyzed. It was determined that the relationship between the total logistics costs and the set of their factor characteristics is a close direct one. Correlation-regression analysis to identify influencing factors on the behavior of logistics costs of the analyzed enterprise was performed.
 It was substantiated that the definition of factors and their influence on logistics costs make it possible to influence the costs of the enterprise and ensure the attractiveness of the product for consumers. The influence of logistics levers on the profitability of the enterprise was schematically displayed. The indicators of logistics cost management assessment, which provide an opportunity to form a qualitative description of the state of the enterprise's logistics system, were given in the article.

A novel variational inequality approach for modeling the optimal equilibrium in multi-tiered supply chain networks

We present a novel variational inequality model (VIM) to capture the complex real decision-making process in multi-tiered supply chain networks (MSCN) without strictly limiting the features of related functions. The VIM is formulated with the equilibrium conditions on links as the optimization goal and the flow conservation condition as the main constraints. We transform the VIM into a series of equivalent Non-Linear Programming Models (NLPMs) to solve. To address this challenge, we propose a novel population-based heuristic algorithm called the Multiscale Model Learning Algorithm (MMLA). The MMLA is inspired by the learning behavior of individuals in a group and can converge to an optimal equilibrium state of the MSCN. The MMLA has two key operations: zooming in on the search field and learning search in a learning stage. The excellent performers, called medalists, are imitated by other learners. With the increase in learning stages, the learning efficiency is improved, and the searching energy is concentrated in a more promising area. We employ sixteen benchmark optimization problems and two supply chain networks to demonstrate the effectiveness of the MMLA and the rationality of the equilibrium models. The results obtained by MMLA for the NLPM show that the MMLA can solve the equilibrium model effectively, and multiple optimal equilibrium states may exist for an MSCN. The flexibility of the NLPM makes it possible to consider more complicated decision-making mechanisms in the model.

The impact of farm size on sustainability of beef cattle farms: A case study of the Samsun province, Turkey

ABSTRACTMany global agricultural problems, such as the decline of agricultural land, soil pollution, climate change, water scarcity, and rural poverty threaten the sustainability of agricultural production systems. This study aimed to (i) develop a methodology to measure the sustainability of beef cattle farms, (ii) measure economic, social and environmental sustainability, and (iii) determine the impact of farm size on the sustainability of beef cattle farming. The study data were collected from 155 beef cattle sample farms via face-to-face surveys in Samsun Province, Turkey. A multi-stage process was employed to measure sustainability. The most important factors contributing to sustainability were determined as the debt-asset ratio, beef yield, and production cost for economic sustainability; the adequacy of educational institutions in the village or district and misunderstanding with neighbours for social sustainability; paying attention to meteorological conditions for pesticide use and nature conservation for environmental sustainability. The composite sustainability index was determined as 0.43 in small farms, 0.51 in medium farms and 0.61 in large farms. It has been found that an increase in the farm size had a positive impact on economic, social, and environmental sustainability of beef cattle farming. The methodology and indicators developed can be used to ensure the sustainability of different agricultural sectors.

Phytoecological study of a Biosphere Reserve in arid climate in Tunisia

Anthropic effects and global change threaten biodiversity and genetic resources. Thus, their conservation becomes a primary necessity. This work aims to assess the conservation conditions for vegetation and causes that limit the progressive dynamics of the vegetation cover after a long period of defense. Using the quadrat point method, his work was conducted in two fenced zones and an unfenced zone of the Biosphere Reserve of BouHedma in a Tunisian arid climate. A total of 66 transects were investigated. In each transect species richness and, α and β indices were determined. The α and β diversity showed a low similarity in family and species composition in the studied zones. The Poaceae and Asteraceae families were the most representative in the studied zones and the most used for grazing. These results highlight that long-term conservation contributes to minimizing the reduction of biodiversity in the reserve. It is necessary to minimize razing and deforestation, especially in the unfenced zone. Thus, the setup of barriers and fences is highly recommended to retain the soil. In addition, finding an effective communication plan with the local population and visitors seems to be crucial.

Data analysis techniques for the visualization and classification of historical vehicle engines’ health status using data-driven solutions

In the field of cultural heritage, the use of non-destructive techniques to determine the state of conservation of an artifact is of the utmost importance, to avoid damage to the object itself. In this paper, we present a data pipeline and several machine learning techniques for the visualization, analysis and characterization of engines in historical vehicles. The paper investigates the use of vibro-acoustic signals acquired from the engines in different states of conservation and working conditions to train machine learning solutions. Data are classified according to their state of health and the presence of anomalies. The t-SNE algorithm is used for dimensionality reduction for data visualization. The machine learning algorithms tested showed encouraging performance in associating acoustic emission data with the engine signature, the type of anomaly and the working conditions. Nevertheless, a larger dataset would allow us to improve and strengthen the results.

Caputo−Wirtinger integral inequality and its application to stability analysis of fractional-order systems with mixed time-varying delays

Various techniques of integral inequality are widely used to establish the delay-dependent conditions for the dynamics of differential systems so that the conservatism of conditions can be reduced. In the integer-order systems, the integral term of ∫τωp˙T(s)Sp˙(s)ds often appears in the derivative of Lyapunov−Krasovskii functional, and how to scale down this term to obtain less conservative condition is a key problem. Similarly, the integral term of ∫τω(Dsα0Cp(s))TS0CDsαp(s)ds with fractional derivative may also be encountered in the analysis of dynamical behaviors for fractional-order systems. In view of this, the paper intends to construct several novel fractional Wirtinger integral inequalities under the sense of Caputo derivative, and to investigate the stability of fractional-order systems with mixed time-varying delays based on the constructed Caputo−Wirtinger integral inequalities. Meanwhile, in order to analyze the stability for our concerned models by the new inequalities, two new theorems of generalized fractional-order Lyapunov direct method are given. Finally, a numerical example is designed to validate the correctness and practicability of the obtained results.

Decentralized QFT Controller Design Based on the Equivalent Subsystems Method

Since the 1970s various decentralized control methodologies have been developed to deal with the challenge of controlling complex and/or spatially distributed systems with multiple inputs and multiple outputs (MIMO), e.g., chemical plants, power systems, water systems, etc. In general, the use of distributed information and control structures requires the synthesis of control laws in a constrained (decentralized) information structure. The article presents a novel frequency domain robust decentralized controller design method that is appropriate for uncertain dynamic MIMO systems with equal numbers of input and output variables, which consist of interconnected physical subsystems and are given as a set of square transfer function matrices. The main framework of the proposed method provides the Equivalent Subsystems Method (ESM), whereby the overall closed-loop system under a decentralized controller is stable if, and only if, all the individual closed-loop equivalent subsystems are stable. By generating equivalent subsystems for all transfer matrices, which describe the uncertain MIMO system, the individual uncertain equivalent subsystems are obtained as sets of respective frequency responses. Such representation allows the application of the QFT (quantitative feedback theory) approach to independently design local single-input single-output (SISO) robust controllers which constitute the resulting decentralized controller implemented in real subsystems. The designed controller ensures robust stability of the overall closed-loop system and the required performance as specified by the standard QFT performance specification types in both the equivalent subsystems and the overall closed-loop system. Compared to the existing method and references therein, the proposed method reduces the conservatism of the robust stability conditions and enables the exploitation of the benefits by the SISO QFT approach in the independent design of the robust decentralized controller. The developed design procedure is verified and illustrated in a case study on the robust decentralized level controller design of the quadruple tank process.

Extended dissipative analysis of affine transformed IT2 fuzzy control systems with time delay and disturbances

This paper focuses on the problem of stability and stabilization for interval type-2 (IT2) fuzzy systems with time-varying delays and external disturbances using the extended dissipative theory. In particular, our approach is to develop a new type of IT2 fuzzy controller that uses affine parameter-based weighting variables. Based on appropriate augmented Lyapunov-Krasovskii functionals and recently developed integral inequalities, some less conservative sufficient conditions are derived in the existence of the zeros equations. Specifically, the required conditions for co-design of affine matched membership functions-based IT2 fuzzy control law are provided such that the generalized performance index, the L2−L∞, H∞, passivity and (Q,S,R)−γ-dissipative problems are investigated. Finally, four examples are represented to verify the advantages of the developed method by comparing it with some existing results.

Robust dynamic output feedback predictive control for discrete uncertain systems with time-varying delays

A robust dynamic output feedback predictive control approach is developed for a discrete system with time-varying delays, unknown external disturbances, and unmeasurable states. First, the discrete system is transformed into an incremental state deviation model. Based on this model, a novel tracking deviation feedback model is established by extending the output tracking error. Then, a robust predictive control law, possessing more degrees of freedom, is designed. The closed-loop model is further given in conjunction with the feedback model. Second, by using the linear matrix inequality (LMI) method, relaxation technique, and variable transformation method, a less conservative stability condition is given in LMI form, which allows the controller to tolerate a greater range of time-varying delays. The gains of the control law are acquired by solving the stability condition, and the control performance can be significantly enhanced. Finally, by utilizing the TTS20 water tank as a simulation case, the viability and effectiveness of the proposed method are demonstrated.

Thermal Behavior Modeling of Lithium-Ion Batteries: A Comprehensive Review

To enhance our understanding of the thermal characteristics of lithium-ion batteries and gain valuable insights into the thermal impacts of battery thermal management systems (BTMSs), it is crucial to develop precise thermal models for lithium-ion batteries that enable numerical simulations. The primary objective of creating a battery thermal model is to define equations related to heat generation, energy conservation, and boundary conditions. However, a standalone thermal model often lacks the necessary accuracy to effectively anticipate thermal behavior. Consequently, the thermal model is commonly integrated with an electrochemical model or an equivalent circuit model. This article provides a comprehensive review of the thermal behavior and modeling of lithium-ion batteries. It highlights the critical role of temperature in affecting battery performance, safety, and lifespan. The study explores the challenges posed by temperature variations, both too low and too high, and their impact on the battery’s electrical and thermal balance. Various thermal analysis approaches, including experimental measurements and simulation-based modeling, are described to comprehend the thermal characteristics of lithium-ion batteries under different operating conditions. The accurate modeling of batteries involves explaining the electrochemical model and the thermal model as well as methods for coupling electrochemical, electrical, and thermal aspects, along with an equivalent circuit model. Additionally, this review comprehensively outlines the advancements made in understanding the thermal behavior of lithium-ion batteries. In summary, there is a strong desire for a battery model that is efficient, highly accurate, and accompanied by an effective thermal management system. Furthermore, it is crucial to prioritize the enhancement of current thermal models to improve the overall performance and safety of lithium-ion batteries.

Dynamic Sensorless Control Approach for Markovian Switching Systems Applied to PWM DC-DC Converters with Time-Delay and Partial Input Saturation.

This paper provides a detailed analysis of the output voltage/current tracking control of a PWM DCDC converter that has been modeled as a Markov jump system. In order to achieve that, a dynamic sensorless strategy is proposed to perform active disturbance rejection control. As a convex optimization problem, a novel reformulation of the problem is provided to compute optimal control. Accordingly, necessary less conservative conditions are established via Linear Matrix Inequalities. First, a sensorless active disturbance rejection design is proposed. Then, to carry out the control process, a robust dynamic observer-predictive controller approach is introduced. Meanwhile, the PWM DC-DC switching power converters are examined as discrete-time Markovian switching systems. Considering that the system is subject to modeling uncertainties, time delays, and load variations as external disturbances, and by taking partial input saturation into account, the Lyapunov-Krasovskii function is used to construct the required feasibility frame and less conservative stability conditions. As a result, the proposed design provides an efficient control strategy with disturbance rejection and time-delay compensation capabilities and maintains robust performance with respect to constraints. Finally, a PWM DC-DC power converter simulation study is performed in different scenarios, and the obtained results are illustrated in detail to demonstrate the effectiveness of the proposed approach.

Scattering at Temporal Interfaces: An overview from an antennas and propagation engineering perspective

Recent years have witnessed a surge of interest in exotic electromagnetic (EM) wave propagation in time-varying systems. An interesting concept is the one of a temporal interface, the time-analogue of a spatial interface, formed by an abrupt and uniform change of the EM properties of the host medium in time. A time interface scatters the incident wave in a dual fashion compared to its spatial counterpart, conserving momentum but transforming frequency and exchanging energy with the wave. This article provides an overview of the wave-scattering features induced by time interfaces from an antennas and propagation engineering perspective. We first discuss the dualities of wave propagation across spatial and temporal interfaces, by recasting the telegrapher equations in a linear time-variant (LTV) transmission line (TL). Then, we introduce the scattering matrix to describe temporal scattering processes, and derive the conditions for reciprocity and momentum conservation. Understanding temporal scattering through the lens of conventional microwave engineering theory may facilitate the analysis and implementation of next-generation metamaterials encompassing temporal degrees of freedom.

Stability analysis of sampled-data systems via affine canonical Bessel-Legendre inequalities

The looped-functional approach has been extensively used for stability analysis of sampled-data systems. For this approach, this paper introduces two new functionals to minimise the conservatism of stability conditions. The first one is called a non-negative integral functional (NIF) that is added to the derivative of a common Lyapunov functional. The second one is a general looped-functional (GLF), whose values at sampling instants are traditionally not well-defined, and are defined here in terms of their limits. Leveraging further affine canonical Bessel-Legendre inequalities expressed by simplified polynomials, a polynomial-based NIF, a polynomial-based GLF, and a polynomial-based zero equality are tailored for obtaining hierarchical types of stability conditions in the form of linear matrix inequalities. Finally, numerical examples show that: (i) the proposed functionals lead to less conservatism when compared with several state-of-the-art methods; and, (ii) the resulting stability conditions exhibit a hierarchical characteristic in the sense that the higher level of hierarchy, the less conservatism of the criteria.

Generalized dissipativity dynamic output feedback control for coronary artery system

This work addresses the problem of synchronizing pathological changes in a patient with coronary artery obstruction to the corresponding nominal coronary artery system (CAS) model. The CAS model is characterized by nonlinear terms, so the synchronization problem is transformed into an equivalent time-varying delay T-S fuzzy framework using the sector of nonlinearity approach. New bilinear matrix inequalities (BMIs) conditions for robust stability analysis and dynamic output feedback gain synthesis are derived based on a less conservative condition for stability assessment of T-S fuzzy systems. A simple change of coordinate is used to solve the cross terms of the bilinearities, allowing the problem to be formulated in terms of linear matrix inequalities (LMIs) and solved using standard semi-definite programming. The effectiveness of the controller design approach is demonstrated through extensive simulations under diverse performance criterion that the controller can achieve.

Diversity and bioactivity of sediment-associated fungi from a mangrove forest in Mexico with different conservation conditions

The biological importance of rhizosphere sediment-associated fungi in mangroves is poorly understood, especially when they are affected by high salinity and anaerobiosis in disturbed areas. This study evaluated the fungal diversity in the rhizosphere sediments of three mangrove species associated with three conservation conditions of mangrove forests in preserved, semi-preserved, and deteriorated areas. In addition, fungal bioactivity was correlated to the fungal diversity found in mangrove species from each area. We isolated 50 fungal strains belonging to three phyla, seven classes, and 10 orders. The fungal diversity was higher in the preserved area (H' = 2.22) than in the semi-preserved (H' = 1.73) and deteriorated areas (H' = 1.68); the redundancy analysis showed a tendency of fungal accumulation towards the rhizosphere of Rhizophora mangle and Avicennia germinans in the preserved and semi-preserved areas. In addition, the redundancy analysis showed that 10 bioactive fungi genera tended to accumulate on the rhizosphere of R. mangle and A. germinans in the preserved and semi-preserved areas. The preserved area is related to the semi-preserved area, with a 28% Jaccard similarity coefficient. The diversity and bioactivity of the isolated fungi encourage the need to conserve and restore mangrove ecosystems considering their current and potential services, such as bioprospecting new pharmacological compounds.

Обоснование безопасных расстояний по отношению к окружающим объектам при проведении камуфлетных взрывов в горных породах

Introduction. Despite the simplicity and accessibility of camouflage blasting, the issues of ensuring the safe conduct of such work are important. A camouflage explosion eliminates the occurrence of an air shock wave and the harmful effects of the explosion products on the environment, but leads to strong seismic vibrations. The impact of seismic loads on nearby objects can lead to the loss of their carrying capacity, damage and destruction, therefore, when choosing a place for installing camouflage charges, the task arises of assessing the field of environmental velocities during an explosion and determining the distances at which the velocities do not exceed the maximum allowable values established for objects under consideration. The aim of the study is to solve the problem of determining the velocity field in a continuous elastic-plastic medium during a camouflage explosion. Research methodology. The solution of the central symmetric problem of the propagation of explosive disturbances in solid media is based on the assumption that a deep spherical charge of a certain radius is placed in an unbounded half-space, which instantly turns into a high-pressure gas without changing the volume. It is assumed that the pressure in the cavity decreases according to a power law, and the relationship of pressure with the radius, velocity and acceleration of the expanding cavity is determined by the camouflage equation , whose constants A, B and C are functions of the parameters of rocks and soils. The perturbed state of the medium caused by the expanding cavity is also characterized by densities ρ0 and ρ respectively, in the elastic and plastic regions of its deformation, and the transition from the elastic state to the plastic state is accompanied by an instantaneous change in the density of the medium from ρ0 to ρ, introduced to approximately take into account the actual compressibility. Results. The determination of the velocity field in the medium surrounding the charge during the explosion is reduced to solving the ordinary differential equation of motion of a spherical cavity expanding due to internal pressure. It is shown that the unknown constant included in the obtained relation can be determined from the condition of conservation of the energy released during the explosion in the entire elastoplastic region of the medium motion. Discussion. The novelty of the result obtained lies in the substantiation of the possibility of using the assumptions about the vibrationless nature of the movement of the camouflage cavity and the incompressibility of the medium in the plastic and elastic regions to determine the velocity field that forms in a continuous medium during the explosion of a camouflage charge. Conclusion. Under the assumption of the vibrationless nature of the motion and the incompressibility of the medium in the plastic and elastic regions, a solution is obtained for the centrally symmetric problem of determining the velocity field in a continuous elastoplastic medium during a camouflage explosion. The solution obtained makes it possible to estimate the sizes of expansion zones, plastic deformation of the medium, and the impact of explosive disturbances on various objects.

A two‐way coupling 2D‐3D hybrid finite element numerical model using overlapping method for tsunami simulation

AbstractThis paper describes a 2D‐3D hybrid model for tsunami simulations that uses an overlapping method based on an arbitrary grid. A 2D model is used to simulate wave propagation from the source area to the offshore area, and a 3D model is then used to simulate the free surface flow around structures in coastal areas. An overlapping method that satisfies the conservation and compatibility conditions is developed to couple the two models. The shallow water equations are applied for the 2D model, and the Navier‐Stokes equations and continuity equations are applied for the flow field of the 3D model. The Allen‐Cahn equation is applied for the interface‐capturing method of the 3D model. The stabilized finite element method is applied for the spatial discretization and the Crank‐Nicolson method is used for the temporal discretization of the governing equations. The model is verified and validated through several numerical analysis examples.

Conservation of Dong Minority Wooden Structures: In Situ Material Investigation of the Yashang Drum Tower in Hunan, China

ABSTRACT The Dong Minority Drum Tower is an essential element of Chinese wooden structural heritage. Although its historical and cultural context has been frequently discussed, the material characteristics remain virtually unexplored. This study focuses on Yashang Drum Tower as a representative Dong Minority wooden structure and aims to understand the current conservation condition of this piece of vernacular heritage today. This study presents the first technical results of an in situ material investigation wherein the wood species and the physical and mechanical properties of two samples were identified. A macroscopic inspection and visual classification were conducted, and the moisture content and the internal qualities of the wooden structures were detected via non-/minor-destructive tests. The preliminary conclusions with regard to three critical issues include the wood species of this particular indigenous material, a visual classification of the wooden structure, and the condition of the wood material in terms of conservation.