Stability Problem Research Articles

On the asymptotic analysis of pulsating planar Poiseuille flow instabilities

The linear stability analysis of a pulsating flow between parallel plates at finite amplitudes and different frequencies demonstrates the presence of instability with a different nature to that initially reported in earlier studies at W o < 25 . The time-dependent stability problem is formulated using a Floquet expansion of the perturbation and solved in a matrix approach. At higher pulsation frequencies (i.e. W o > 30 ), pulsation amplitudes and sufficiently large Reynolds numbers, the time-dependent baseflow displays multiple inflexion points throughout the entire duration of the pulsation. A scaling analysis of the temporal growth rate reveals that the instability is of inviscid type and scales with R e − 1 . Freezing the time-dependent baseflow for a particular set of parameters, the growth rate is simultaneously controlled by viscosity solely acting on the perturbation, and the pulsating frequency coupling the harmonics. In the asymptotic limit ( R e → + ∞ ), we demonstrate that the temporal problem simplifies to a set of steady stability analyses dependent on the phase of the pulsation. In particular, we show that in this limit, Rayleigh and Fjørtoft’s criteria for instability become valid again, that sub-harmonic periodic orbits can be used to estimate the inviscid growth rate and match with the asymptotic values predicted from the viscous stability analysis.

Delay-dependent stability criteria for LFC systems with electric vehicles: A delay-interval-based piecewise Lyapunov functional approach

This paper studies the delay-dependent stability problem of single-area load frequency control (LFC) systems with electric vehicles. A novel Lyapunov-Krasovskii functional (LKF), called the delay-interval-based piecewise Lyapunov functional, is introduced. This innovative LKF approach allows for the construction of distinct LKFs within specific delay intervals, relaxing the requirement that a single LKF must exist for the entire delay interval. By incorporating the zero equation method, less conservatism delay-dependent stability criteria for LFC systems are obtained. Simulations are performed to illustrate the effectiveness and superiority of the presented methods.

Pinning control design for the output regulation of Boolean networks

In previous studies, the output regulation problem (ORP) of Boolean networks (BNs) is usually studied by the augmented system method, however, the state transition matrix dimension of augmented system is growing exponentially as the number of network nodes increases. To reduce the computational complexity, a new method to solve the ORP is adopted in this paper. Firstly, the relationship among the attractors of two BNs and their augmented system is studied, based on which, the ORP is converted into the set stabilisation problem of the original BN, and some necessary and sufficient conditions are given to detect the solvability of the ORP. Secondly, a pinning control for the ORP is considered according to the attractors of the original BNs, and an algorithm to design this kind of controls is provided. Finally, a practical example of signal transduction network is given to illustrate the effectiveness of the method in this paper.

The finite presentation problem for Noetherian algebras

We prove that there exists an affine Noetherian algebra over a field of characteristic zero which is not finitely presented. Specifically, we prove that the Medvedev–Passman–Resco–Small algebra, recently shown to form a counterexample to the stability problem for Noetherian algebras, is not finitely presented. This answers a question due to Bergman and Irving in characteristic zero, a case explicitly left open by Resco and Small in 1993, who gave a counterexample to this question in positive characteristic.

Fractional impulsive controller design of fractional-order fuzzy systems with average dwell-time strategy and its application to wind energy systems

In this study, the issue of adaptive impulsive control of a permanent magnet synchronous generator (PMSG)-based wind energy system (WES) with an average dwell-time strategy is investigated using a Takagi–Sugeno (T-S) fuzzy model described by fractional-order differential equations. A T-S fuzzy model is employed to describe the nonlinear fractional-order PMSG (FOPMSG) model, an average dwell time, an average impulsive condition, a Lyapunov function, and a less conservative algebraic inequality criterion that guarantees stabilization for the considered nonlinear system. First, the mathematical model of the FOPMSG in the n−m reference frame is transformed into a dimensionless chaotic system through affine transformation and time scale transformation. Then, the stabilization problem of the nonlinear chaotic FOPMSG model is considered to validate the proposed sufficient conditions, leading to the derivation of a new stability criterion for the FOPMSG model, instead of addressing the general problem to validate the proposed result. Subsequently, the desired control gains can be obtained to ensure the stabilization of the addressed closed-loop system. By combining adaptive and impulsive control, the model under consideration can be stabilized for any target dynamics. Finally, we demonstrate the efficiency and feasibility of the suggested approach through numerical simulations and comparative results.

A Review of Convex Clustering From Multiple Perspectives: Models, Optimizations, Statistical Properties, Applications, and Connections.

Traditional partition-based clustering is very sensitive to the initialized centroids, which are easily stuck in the local minimum due to their nonconvex objectives. To this end, convex clustering is proposed by relaxing K -means clustering or hierarchical clustering. As an emerging and excellent clustering technology, convex clustering can solve the instability problems of partition-based clustering methods. Generally, convex clustering objective consists of the fidelity and the shrinkage terms. The fidelity term encourages the cluster centroids to estimate the observations and the shrinkage term shrinks the cluster centroids matrix so that their observations share the same cluster centroid in the same category. Regularized by the lpn -norm ( pn ∈ {1,2,+∞} ), the convex objective guarantees the global optimal solution of the cluster centroids. This survey conducts a comprehensive review of convex clustering. It starts with the convex clustering as well as its nonconvex variants and then concentrates on the optimization algorithms and the hyperparameters setting. In particular, the statistical properties, the applications, and the connections of convex clustering with other methods are reviewed and discussed thoroughly for a better understanding the convex clustering. Finally, we briefly summarize the development of convex clustering and present some potential directions for future research.

Resolving subgrid-scale structures for multiphase flows using a filament moment-of-fluid method

Multiphase flows are present in many industrial and engineering applications as well as in some physical phenomena. Capturing the interface between the phases for complex flows is challenging and requires an accurate method, especially to resolve fine-scale structures. The moment-of-fluid (MOF) method improves drastically the accuracy of interface reconstruction compared to previous geometrical methods. Instead of refining the mesh to capture increased levels of detail, the MOF method, which uses zeroth and first moments as well as a conglomeration algorithm, enables subgrid structures such as filaments to be captured at a small extra cost. Coupled to a finite volume Navier–Stokes solver, the MOF method has been tested on a fixed grid and validated using well-known benchmark problems such as the dam break flows, the Rayleigh–Taylor and Kelvin–Helmholtz instability problems, and a rising bubble. The ability of the novel filament MOF method to capture the filamentary structures that eventually form for the Rayleigh–Taylor instability and rising bubble problems is assessed. Good agreement has been found with other numerical results and experimental measurements available in the literature.

Path Optimization of Two-Posture Manipulator of Apple Packing Robots

Automated packing is urgently needed in apple production. This paper proposes an improved genetic algorithm fused with an optimal parameter selection algorithm to optimize the two-posture manipulator working path of packing robots. First, the structure and working principle of the packing robot were designed. Second, the kinematics and packing paths of the two-posture manipulator were analyzed. Finally, the path optimization method for the two-posture manipulator was introduced. The method was based on the improved genetic algorithm by using a two-level coding and region crossover operator. The parameter values can be automatically determined by the optimal parameter selection algorithm. Ten repeated comparative tests show that the total packing time is 23.86 s under the working conditions of four grasping points and fourteen placing points. The optimal performance of the proposed algorithm is better than that of the traditional genetic algorithm, and the average optimization amplitudes are 14.63%, 15.42%, 16.24%, and 13.82% for 9-groove, 12-groove, 14-groove, and 16-groove trays, respectively. The proposed algorithm can effectively prevent the premature convergence problem of the traditional genetic algorithm and the optimization process instability problem, improve the range of optimization, and reduce the manipulator working time during packing.

Electromechanical processes in electric power steering system based on permanent magnet synchronous motor

Relevance. Electric power steering of vehicles successfully competes with hydraulic boosters of similar purposes, showing high efficiency, energy saving and environmental friendliness. Aim. To study and research electromechanical processes of electric power steering system based on permanent magnet synchronous motor. Methods. Mathematical and numerical modeling using the Matlab/Simulink software package. Results. The article discusses the operating modes of an electric power steering based on an electric motor with permanent magnets. The authors analyzed two classic schemes for constructing steering systems with electric power steering – with the electric motor placed on the steering column and on the steering rack. Block diagrams of the mechanical and electrical parts of the steering system have been developed. Based on mathematical dependencies characterizing the operating modes of the steering system, a complete dynamic simulation model of the electric power amplifier was obtained on the MATLAB/Simulink platform. Based on a preliminary analysis of control methods and algorithms in the system to solve the problem of control stability, PI controllers with low-pass filters are implemented to regulate the current and voltage of the electric motor depending on the speed of the vehicle and the angle of rotation of the steering wheels. The simulation results were used to design a real electric power steering for a specific vehicle. Conclusions. The complete simulation model of an electric booster based on a synchronous motor with permanent magnets in a car steering system obtained by the authors adequately reflects the dynamic control processes and can be used in the design of automotive vehicles.

Collaborative design and construction analysis of building structure and foundation of subway overlying complex

With the acceleration of urbanization, land resources are becoming more and more precious, especially in densely populated urban centers. As an efficient land use model, the subway overlying complex can not only optimize the urban spatial layout, but also promote the integration of public transportation and urban development. This paper aims to discuss the collaborative design and construction technology of the building structure and foundation of the subway overcover complex, in order to provide theoretical support and technical guidance for the practice in related fields. Based on the literature review of domestic and foreign subway overcover development projects, this paper reviews the research status and development trend in this field, and identifies the main problems in structural safety, foundation stability and construction efficiency. On this basis, the paper puts forward the design principle of the subway overcover complex, and emphasizes the key role of the synergistic relationship between the structure and the foundation to the success of the whole project. The paper further analyzes the construction technology of subway overcover complex, including specific construction technology, reasonable construction sequence and project management measures. Through comparative analysis of success and failure cases, it reveals the problems that may be encountered in the actual operation and its coping strategies.

«5+1» COOPERATION FORMATS IN THE CENTRAL ASIAN REGION: ANALYSIS OF ECONOMIC INTERACTION WITH JAPAN

The article analyzes Japan’s economic interaction with Central Asia within the framework of the «5+1» format, which is a unique mechanism of multilateral cooperation that has attracted the attention of leading world powers in recent years due to the strategic importance of the region in the context of energy resources and transit routes. The research is based on a comprehensive analysis of investment, trade and economic relations between the countries of Central Asia and Japan. The main purpose was to identify key trends and factors that determine the dynamics of economic interaction and analyze the interrelations of economies. The hypotheses were tested using comparative statistics, dynamic analysis and graphical method, as well as using statistical methods, including calculation of correlation coefficients and multiple regression. Limitations of the study include the lack of data for some countries and periods. The analysis showed a moderate positive correlation between the GDP (Gross domestic product) of the countries of Central Asia and Japan, indicating economic interdependence. Japan’s investment activity is manifested in significant investments in Kazakhstan and Kyrgyzstan, with recent growth in Tajikistan. Trade turnover between the countries fluctuates due to global and regional factors. Despite the positive correlation of economies, Central Asia's influence on Japan remains limited. Japanese investment plays a key role in the region's development, but political instability and domestic problems in the countries reduce their effectiveness. Trade also faces challenges, including customs barriers and infrastructure limitations.

Discrete time stability of augmented Lagrangian formalism based underactuated inverse dynamics control method

Stability problems of robotic systems arise sometimes suddenly, seemingly for no reason. The digital time sampling is often the main cause of these instabilities. Discrete models, which are capable of the prediction of stability, are available for low-degree-of-freedom template models of linear position and force control. However, for the inverse dynamics control of underactuated systems, the literature has a lack of generally applicable results related to the effect of time discretization. Several control approaches are available in the literature out of which a widely used one, the augmented Lagrangian formalism and its stability properties are analysed in this work. Theoretical stability properties are obtained for a generally usable, linear, underactuated, two-degree-of-freedom constrained template model. The actuator dynamics, the finite difference approximation of the feedback velocity and the filtering of the feedback data are considered in the model. These phenomena strongly affects the stability properties. The theoretically obtained stability maps are experimentally validated on an underactuated crane-like indoor robot. The position and orientation accuracy of the robot were assessed: the absolute position error was below 30 mm and the orientation error was below 3°.

Green Synthesis of Boric Acid Modified Bismuth Based Non-Toxic Perovskite Quantum Dots for Highly Sensitive Detection of Oxytetracycline.

In recent years, perovskite quantum dots (PQDs) have successfully attracted widespread attention due to their excellent optical properties. However, the instability and toxicity problems of perovskite quantum dots are the main obstacles limiting their applications. In this work, bismuth-based perovskite quantum dots were synthesized by a ligand-assisted reprecipitation method, based on which a novel boric acid-functionalized bismuth-based non-toxic perovskite quantum dots fluorescent sensor (Cs3Bi2Br9-APBA) that can be stabilized in the ethanol phase was prepared by a boron affinity technique. Based on the covalent binding interaction of Cs3Bi2Br9-APBA with oxytetracycline (OTC), a highly selective and sensitive method for the detection of OTC was developed, which effectively solved the problems of poor stability and toxicity in the application of perovskite quantum dots. Under the optimal conditions, the fluorescence intensity of the synthesized Cs3Bi2Br9-APBA was linear with the concentration range of 0.1 ∼ 18 µM OTC, and the detection limit could reach 0.0802 µM. The fluorescence detection mechanism was explored and analyzed by spectral overlap analysis, suppression efficiency study of observed and corrected fluorescence, and fluorescence lifetime decay curve fitting, the mechanism of OTC detection by Cs3Bi2Br9-APBA was identified as the inner filter effect (IFE). In addition, the sensor successfully realized the quantitative detection of trace OTC in the environment, and our study provides a new idea for the preparation of green perovskite materials with high stability and selectivity.

Evaluation of Cobalt, Nickel, and Palladium Complexes as Catalysts for the Hydrogenation and Improvement of Oxidative Stability of Biodiesel

Developing effective catalysts that can selectively hydrogenate C=C bonds in biodiesel samples is vital as it tackles the major problem of oxidative stability, which greatly limits the utilization of biodiesel as an alternative fuel. In this work, Co, Ni, and Pd catalysts stabilized with the bidentate nitrogen ligands N-(3-(triethoxysilyl)propyl)pyridin-2-ylmethylimine and N-(3-(triethoxysilyl)propyl)picolinamide were synthesized, characterized, and used as pre-catalysts in the transfer hydrogenation of C=C bonds in fatty acid methyl esters. The active catalysts from the Co, Ni, and Pd complexes sequentially hydrogenate the C18:2 chains to C18:1, which is further converted to C18:0 in the FAMEs of both methyl linoleate and jatropha biodiesel. The hydrogenation process was kinetically controlled, and after 3 h it yielded a biodiesel sample that contained 25.83% C16:0, 12.52% C18:2, 41.54% C18:1, 14.47% C18:0 and 3.0% C18:2 isomers. The un-hydrogenated jatropha diesel, hydrogenated jatropha diesel, and a B20 blend of jatropha were tested for susceptibility to oxidation reactions using the Rancimat method and FTIR spectroscopy, and the partial hydrogenation had improved the induction period by 3 h.

Application of improved fish school algorithm in variable frequency speed control system

In order to solve the problems of long adjustment time and poor stability of the commonly used speed current variable frequency negative feedback speed control system in engineering, the author proposes an improved fish school algorithm application method in variable frequency speed control systems. A fish swarm algorithm optimized based on the arena method is applied to a variable frequency speed control system, and the optimization algorithm is applied to the speed control system to screen the PI parameters that meet the requirements of the speed control system. The simulation results show that compared with manual parameter tuning, the controller parameters optimized by the improved fish school algorithm have better control performance. In the absence of overshoot starting, the starting time was shortened by 0.21s, and the system response speed was improved. When a sudden load of 6 N m is applied, the speed drop is reduced by 3 r · min−1, and the recovery time is shortened by 0.15 s, resulting in stronger anti-interference performance of the system. Conclusion: The new algorithm shortens the control time and improves the robustness of the system.

GAN-based image generation

Generative Adversarial Networks (GANs), as a deep learning model, have made significant progress in the field of image generation and style migration. This study aims to methodically investigate GAN-based image generation methods. First, this paper outlines the basic principles of GAN and its application in image generation, focusing on analyzing the structure and performance of representative models such as DCGAN, ProGAN and StyleGAN. This paper summarizes the improvement methods such as WGAN and LSGAN, and evaluates their efficacy in improving the stability of the model and the quality of the generated images in view of the problems of pattern collapse and instability faced by GANs in the training process. Finally, this paper discusses the limitations of current techniques and possible future directions, and suggests research prospects in the field of multimodal fusion and 3D image generation. The research in this paper provides a theoretical framework and useful suggestions for enhancing the application of GAN methods in image generation.

Nonplanar Nanographene: A Hydrocarbon Hole-Transporting Material That Competes with Triarylamines.

Hole-transporting materials (HTMs) are essential for optoelectronic devices, such as organic light-emitting diodes (OLEDs), dye-sensitized solar cells, and perovskite solar cells. Triarylamines have been employed as HTMs since they were introduced in 1987. However, heteroatoms or side chains embedded in the core skeleton of triarylamines can cause thermal and chemical stability problems. Herein, we report that hexabenzo[a,c,fg,j,l,op]tetracene (HBT), a small nonplanar nanographene, functions as a hydrocarbon HTM with hole transport properties that match those of triarylamine-based HTMs. X-ray structural analysis and theoretical calculations revealed effective multidirectional orbital interactions and transfer integrals for HBT. In-depth experimental and theoretical analyses revealed that the nonplanarity-inducing annulative π-extension can achieve not only a stable amorphous state in bulk films, but also a higher increase in the highest occupied molecular orbital level than conventional linear or cyclic π-extension. Furthermore, an in-house manufactured HBT-based OLED exhibited excellent performance, featuring superior curves for current density-voltage, external quantum efficiency-luminance, and lifetime compared to those of representative triarylamine-based OLEDs. A notable improvement in device lifetime was observed for the HBT-based OLED, highlighting the advantages of the hydrocarbon HTM. This study demonstrates the immense potential of small nonplanar nanographenes for optoelectronic device applications.

Nonplanar Nanographene: A Hydrocarbon Hole‐Transporting Material That Competes with Triarylamines

AbstractHole‐transporting materials (HTMs) are essential for optoelectronic devices, such as organic light‐emitting diodes (OLEDs), dye‐sensitized solar cells, and perovskite solar cells. Triarylamines have been employed as HTMs since they were introduced in 1987. However, heteroatoms or side chains embedded in the core skeleton of triarylamines can cause thermal and chemical stability problems. Herein, we report that hexabenzo[a,c,fg,j,l,op]tetracene (HBT), a small nonplanar nanographene, functions as a hydrocarbon HTM with hole transport properties that match those of triarylamine‐based HTMs. X‐ray structural analysis and theoretical calculations revealed effective multidirectional orbital interactions and transfer integrals for HBT. In‐depth experimental and theoretical analyses revealed that the nonplanarity‐inducing annulative π‐extension can achieve not only a stable amorphous state in bulk films, but also a higher increase in the highest occupied molecular orbital level than conventional linear or cyclic π‐extension. Furthermore, an in‐house manufactured HBT‐based OLED exhibited excellent performance, featuring superior curves for current density–voltage, external quantum efficiency–luminance, and lifetime compared to those of representative triarylamine‐based OLEDs. A notable improvement in device lifetime was observed for the HBT‐based OLED, highlighting the advantages of the hydrocarbon HTM. This study demonstrates the immense potential of small nonplanar nanographenes for optoelectronic device applications.

Multi-constrained predictive optimal control for spacecraft attitude stabilization and tracking with performance guarantees

This paper investigates a novel predictive control approach for spacecraft attitude stabilization and tracking problems with consideration of performance constraints, angular velocity limitation and control saturation. First, the prescribed performance control (PPC) structure and barrier Lyapunov function (BLF) are utilized to design the cost function of optimal control problem. Subsequently, a multi-constrained predictive optimal controller for spacecraft attitude stabilization and tracking with performance guarantees is devised via exploiting an explicit receding horizon optimization control strategy under actuator saturation. Compared with the existing methods, the major merit of the proposed one lies in the semi-analytic solving scheme of optimal control problems with high computing efficiency and simultaneous handling of multiple constraints without increasing computational burden. Finally, two illustrative examples are employed to validate the effectiveness of the proposed control method.

DUAL LOOP VOLTAGE DROOP REGULATED CONTROLLER FOR DC MICROGRID USING HYBRID PSO AND GGO ALGORITHMS

Abstract DC microgrids are effectively employed in distribution network integration with renewable energy sources. The droop control technique is commonly utilized for DC microgrid regulation during load sharing. It minimizes the potential instability caused by disturbances such as input voltage changes, uncertainty parameters, and constant power load (CPL). Nevertheless, conventional droop control is inadequate in achieving precise current and satisfactory voltage regulation distribution for load sharing. The proposed approach comprises two separate loops for the DC bus voltage regulation and load current distribution, delivering a CVL and CPL to overcome the single optimization voltage controller technique. The primary loop uses the PSO algorithm to precisely manage the current load sharing among two parallel converters. Due to this the instability problems arising from disturbances, and it mitigated by the proposed topology. The multiobjective optimization technique provides notable resilience, rapid dynamic response, and robust stability over considerable variations in load. The secondary loop utilises the GGO algorithm to optimize the parameter to minimize the DC bus voltage regulation, voltage management, reasonable distribution of load power, and suitable reliability. The performance of the voltage regulation enhance & settling time for output voltage has been mitigated more than 31ms times through the proposed controller compared to conventional controller under the variation of CVL, CPL, and input voltage disturbance demonstrated in simulation results.