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Micro-curved panels with moving micro/nanoparticles included are essential microstructures in the engineering field. So, improving its stability for use in various situations is an essential key for biomechanical engineers. There is potential for using graphene nanoplatelets (GPLs)-reinforced epoxy as the matrix phase in a fiber composite as it has been shown that GPLs successfully improve the properties of epoxy materials when compared to clean epoxy. So, in the current work, dynamic deflection of the axially reinforced thick micro-curved panel under a moving load is presented. Optimizing the geometry of composite materials is essential in structural design if you want to achieve the highest possible levels of strength or stability. In the present study, we use the genetic algorithm and particle swarm optimization to find the optimal radius ratio for lowering the displacement fields. For modeling the micro-size structure, modified couple stress theory with one length scale parameter is presented. The displacement fields are modeled using Taylor's series higher-order terms considering strain in the thickness direction. Using forced vibration analysis, the space and time-dependent equations are solved via double Fourier series and state-space method, respectively. It is shown that reinforcing a microstructure with GPLs in the axial direction has lower deflection than in other directions. The results show that velocity and external loading of moving micro/nanoparticle, geometry properties, and length scale parameters have an important role in the time-dependent deflections of the axially reinforced thick micro-curved panel under moving micro/nanoparticles. The current outputs can be used in the biomechanical engineering field for modeling a micro-curved panel under moving micro/nanoparticles. [ABSTRACT FROM AUTHOR]

In this paper, a three-dimensional (3D) solution of static behavior of simply supported doubly curved functionally graded multilayered (FGM) magneto-electro-elastic shells subjected to mechanical, electric displacement, magnetic flux, electric potential and magnetic potential loads is presented. A coupling procedure based on the state space and the Runge–Kutta methods is elaborated for the 3D magneto-electro-elastic governing equations. An efficient semi-analytical approach is resulted for arbitrary functionally graded shells in thickness direction. The proposed mathematical modeling has been validated by several numerical tests. The obtained results are in good agreement with the available ones given by the three-dimensional asymptotic approach, the state space approach and a meshless collocation method. It has been revealed that, the loading conditions, the materials properties gradient index, the span-to-thickness ratio and the radius-to-thickness ratio remarkably influence the static response of FGM shells. [ABSTRACT FROM AUTHOR]

The high-damping viscoelastic (VE) materials are widely used to reduce unwanted vibrations in civil structures. However, the significant frequency and temperature dependences from high-damping VE materials cause a challenge in efficiently analyzing the structural dynamic behaviors. The aim of this study is to propose a generalized dynamic analysis method for the linear structural system with VE elements. The implementation steps and advantages of the dynamic analysis method are presented. In this method, the frequency-dependent matrices and non-proportional damping induced by VE elements are fully considered in modal coordinates, and then the state-space representation converted from the modal-based transfer function is adopted to implement the time-domain simulation. Any popular VE constitutive models which accurately describe frequency-dependent matrices can be applied to the method. The number of the state-space representation can be adjusted according to the interested frequency range. Numerical applications performed on a viscoelastically damped structure, a VE base-isolated structure, and a structure with a VE tuned mass damper (TMD) demonstrate the numerical accuracy, efficiency, and generality of the proposed dynamic analysis method. [ABSTRACT FROM AUTHOR]

The increasing penetration of power‐electronics interfaced resources brings new challenges regarding the small‐signal stability of power systems. To address this issue, grid‐forming (GFM) controlled converters have emerged as an alternative to their conventional grid‐following counterparts. This paper investigates the mechanisms behind converters driven stability and quantifies the stabilizing effect of GFM controls. The linearized state‐space model of different combinations of control strategies is analysed in a multi‐infeed system considering various operating points. Through a parametric sensitivity study and an examination of the participation factors of key eigenvalues of the linearized models, it is confirmed that GFM controls contribute to system stabilization. Moreover, this paper demonstrates that this stabilizing effect varies significantly depending on the specific GFM control implemented: whether a current control loop is used or not notably impacts stability. The article studies the stabilizing impact of grid‐forming (GFM) in power systems. All things being equal (inertia, damping, and tuning), the presence of a current control in the GFM scheme significantly reduces the stabilizing impact. This phenomenon is highlighted under different setups and is explained using the analysis of participation factors. [ABSTRACT FROM AUTHOR]

A common type of nonlinear system in the field of process industry is asymmetrical heating and cooling processes. These systems have two operating modes, heating and cooling, each with a particular dynamic feature. This study deals with identifying and controlling such processes. The relay feedback identification method based on the state-space approach, which results in exact estimates, is used in the identification procedure to achieve two first-order plus dead time (FOPDT) process models. Following process identification, two sets of PI-PD controller parameters are acquired in line with the user-defined gain and phase margin specifications, and the system is controlled using a gain-scheduled PI-PD control method. Some simulation examples are provided to demonstrate the use and profitability of the suggested identification and control approaches. Comparisons with a similar study are provided for both identification and control approaches to clearly demonstrate the benefits of the suggested procedures. [ABSTRACT FROM AUTHOR]

Crime prediction based on reliable data and sound statistical methodologies can provide valuable input for tactical deployment of police resources in so-called crime hot spots and effective planning of police operations. In Rio de Janeiro, the Public Safety Secretariat uses criminal activity forecasts to detect crime patterns and evaluate police performance. This paper evaluates the impact of reconciliation on the forecasts of 271 series of registered criminal occurrences in the city of Rio de Janeiro on a monthly basis from January 2003 to December 2019. We verify that reconciliation improves crime count forecasts, especially on the most disaggregated series. [ABSTRACT FROM AUTHOR]

Due to its unique features, the flyback converter is widely used to convert DC to DC power. This converter has a non‐minimum phase (NMP) dynamic behavior, which is one of its most significant disadvantages. By changing the topology of the flyback converter to a forward‐flyback (FF) converter, the dynamic behavior of the converter can be minimum phase (MP) while the main advantages of the flyback converter such as isolation of the output from the input and simple topology are maintained. This article proposes an innovative FF converter topology by doubling the forward path and adding only one diode and one capacitor. In addition to better dynamic behavior, the proposed double FF (DFF) converter has the same advantages as the conventional FF converter. A new method is used to obtain the transfer function of the output voltage to the duty cycle of the proposed converter. The converter is designed in continuous conduction mode (CCM) with minimum phase dynamics. Finally, simulation and experimental results of both conventional FF and the proposed DFF converters are obtained and compared to validate the superiority of the proposed converter. [ABSTRACT FROM AUTHOR]

In this article, an exact analytical method for the free vibration analysis of functionally graded (FG) graphene platelet (GPL)-reinforced composite (GPLRC) sector cylindrical shells is presented by considering Levy-type boundary conditions for the first time. The analysis relies on the use of the Halpin–Tsai micro-mechanical model for evaluating the material properties of the graded layers of the shell with three different grading patterns. Mathematical modeling of the Levy-type cylindrical shell is based on the Hamilton principle and the Sanders first-order shear deformation theory (FSDT). The governing equations of the composite shell are analytically solved using the state-space method. The validity of the proposed analytical method is demonstrated by the excellent agreement between the obtained results of the exact analytical solution and the results available in the literature. Furthermore, some parametric studies are conducted to reveal the effects of variations in boundary conditions, GPL distribution patterns, GPL weight fraction, and geometrical parameters such as shallowness angle, length-to-radius ratio, and thickness on the free vibration behavior of the shell structure. Natural frequencies and mode switching are reported for different mode numbers. [ABSTRACT FROM AUTHOR]

In this paper, a state-space method for double-beam systems with variable cross sections is developed, making it possible to calculate the transverse vibration of the double-beams accurately and effectively. Due to the variability in the double-beam cross sections with the viscoelastic interlayer in between, the governing equations of vibration for the systems become highly coupled partial differential equations, making the problem difficult to solve. A basic double-beam system is introduced to modify the original governing equations to two inhomogeneous differential equations. Given the separation of variables, several mode-shape coefficients and a state variable are defined to construct the state-space equations. The coupling terms and variables are transferred into the constant coefficient matrix of the state-space equations, decoupling them. Numerical procedures are presented to solve the state-space equations to obtain homogenous and inhomogeneous solutions, including the natural frequencies and mode shapes in free vibration and the dynamic responses in forced vibration, respectively. The method has substantial advantages in decoupling high-order partial differential equations and can be further extended to solve complex structural systems. Numerical results also demonstrate that the method is accurate and efficient. Finally, an engineering application with a rail-bridge with a floating slab track is discussed in detail with the method. [ABSTRACT FROM AUTHOR]

Room impulse responses (RIRs) between static loudspeaker and microphone locations can be estimated using a number of well-established measurement and inference procedures. While these procedures assume a time-invariant acoustic system, time variations need to be considered for the case of spatially dynamic scenarios where loudspeakers and microphones are subject to movement. If the RIR is modeled using image sources, then movement implies that the distance to each image source varies over time, making the estimation of the spatially dynamic RIR particularly challenging. In this paper, we propose a procedure to estimate the early part of the spatially dynamic RIR between a stationary source and a microphone moving on a linear trajectory at constant velocity. The procedure is built upon a state-space model, where the state to be estimated represents the early RIR, the observation corresponds to a microphone recording in a spatially dynamic scenario, and time-varying distances to the image sources are incorporated into the state transition matrix obtained from static RIRs at the start and end points of the trajectory. The performance of the proposed approach is evaluated against state-of-the-art RIR interpolation and state-space estimation methods using simulations, demonstrating the potential of the proposed statespace model. [ABSTRACT FROM AUTHOR]

The improvement of information sciences promotes the utilization of data for process monitoring. As the core of modern automation, time-stamped signals are used to estimate the system state and construct the data-driven model. Many recent studies claimed that the effectiveness of data-driven methods relies greatly on data quality. Considering the complexity of the operating environment, process data will inevitably be affected. This poses big challenges to estimating faults from data and delivers feasible strategies for electrical systems of industry. This paper addresses the missing data problem commonly in traction systems by designing a martingale posterior-based data generation method for the state-space model. Then, a data-driven approach is proposed for fault detection and estimation via the subspace identification technique. It is a general scheme using the Bayesian framework, in which the Dirichlet process plays a crucial role. The data-driven method is applied to a pilot-scale traction motor platform. Experimental results show that the method has good estimation performance. [ABSTRACT FROM AUTHOR]

Driven by the versatility and adaptability of next-generation soft robotic devices, investigating the vibrational behavior under fluid-electromechanical coupling represented by a soft dielectric elastomer actuator (DEA) tube filled with fluid evokes much attention. Here, we investigate the axisymmetric vibration of an inviscid compressible fluid-filled thin DEA tube by using the Gent model to define the behavior of the tube under multi-fields. We consider the effect of the fluid by exploiting the relation of the radial fluid pressure at the fluid-solid interface. Following the general incremental theory of nonlinear electro-elasticity, we formulate the incremental governing and constitutive equations needed for vibration analysis and solve them numerically using the state-space method (SSM). The results demonstrate the influence of the applied voltage, overcritical circumferential stretch, higher frequency modes, and phase velocity modes on the early development of axisymmetric instability and dielectric breakdown. The existence of the fluid contributes to more reduction in the frequency and phase velocity compared to the fluid-free case due to the added mass effect. Moreover, the results show the role of fluid in the partial self-healing of the soft DEA. A parametric study on specific variables deduces that increasing the thickness of the soft DEA tube reduces the frequency effectively, whereas applying higher voltages causes a thinning in the thickness, leading to the need for thicker tubes. [ABSTRACT FROM AUTHOR]

The mechanical behaviors of the clamped laminated arch with temperature-dependent material properties under the thermal and mechanical loadings are studied in this paper. An analytical method based on the theory of thermoelasticity is proposed for predicting the exact solutions of stresses and displacements in the arch with arbitrary thickness and layer numbers. The clamped support is equivalent to a simply support with a support reaction with the unit pulse function and the Dirac function. The space state method is utilized to establish the state equation by employing the displacements and stresses as the state variables. A slice model is introduced to simplify the coefficient matrix. Based on the continuities at the interfaces, the displacement and stress relationships between the internal and external surfaces of the laminated arch are derived with the transfer matrix method. Exact solutions for the displacements and stresses can be obtained according to the stress boundary conditions on the surfaces of the laminated arch. Finally, convergence and comparison studies demonstrate the excellent efficiency and accuracy of the present method. The influences of material dependency with temperature, thermal load, and thickness-to-radius ratio on the distributions of displacements and stresses are discussed in detail. [ABSTRACT FROM AUTHOR]

An approach to estimate the dynamic characteristic of multilayered three-dimensional cubic quasicrystal cylindrical shells, annular plates, and truncated conical shells with different boundary conditions is presented. These investigated structures can be in a vacuum, totally filled with quiescent fluid, and subjected to internal flowing fluid where the fluid is incompressible and inviscid. The velocity potential, Bernoulli's equation, and the impermeability condition have been applied to the shell–fluid interface to obtain an explicit expression, from which the fluid pressure can be converted into the coupled differential equations in terms of displacement functions. The state-space method is formulated to quasicrystal linear elastic theory to derive the state equations for the three structures along the radial direction. The mixed supported boundary conditions are represented by means of the differential quadrature technique and Fourier series expansions. A global propagator matrix, which connects the field variables at the internal interface to those at the external interface for the whole structure, is further completed by joint coupling matrices to overcome the numerical instabilities. Numerical examples show the correctness of the proposed method and the influence of the semi-vertical angle, different boundary conditions, and the fluid debit on the natural frequencies and mode shapes for various geometries and boundary conditions. [ABSTRACT FROM AUTHOR]

Abstract The increasing penetration of power‐electronics interfaced resources brings new challenges regarding the small‐signal stability of power systems. To address this issue, grid‐forming (GFM) controlled converters have emerged as an alternative to their conventional grid‐following counterparts. This paper investigates the mechanisms behind converters driven stability and quantifies the stabilizing effect of GFM controls. The linearized state‐space model of different combinations of control strategies is analysed in a multi‐infeed system considering various operating points. Through a parametric sensitivity study and an examination of the participation factors of key eigenvalues of the linearized models, it is confirmed that GFM controls contribute to system stabilization. Moreover, this paper demonstrates that this stabilizing effect varies significantly depending on the specific GFM control implemented: whether a current control loop is used or not notably impacts stability.

Abstract Due to its unique features, the flyback converter is widely used to convert DC to DC power. This converter has a non‐minimum phase (NMP) dynamic behavior, which is one of its most significant disadvantages. By changing the topology of the flyback converter to a forward‐flyback (FF) converter, the dynamic behavior of the converter can be minimum phase (MP) while the main advantages of the flyback converter such as isolation of the output from the input and simple topology are maintained. This article proposes an innovative FF converter topology by doubling the forward path and adding only one diode and one capacitor. In addition to better dynamic behavior, the proposed double FF (DFF) converter has the same advantages as the conventional FF converter. A new method is used to obtain the transfer function of the output voltage to the duty cycle of the proposed converter. The converter is designed in continuous conduction mode (CCM) with minimum phase dynamics. Finally, simulation and experimental results of both conventional FF and the proposed DFF converters are obtained and compared to validate the superiority of the proposed converter.

Rapid launching is a crucial technology for the digitalization and regularization of space transportation systems. This paper focuses on the fast trajectory prediction of the launch-vehicle boost phase. A high-precision and high-efficiency analytical solution of the whole boost phase dynamics model of the rocket is obtained by adopting one of the regular perturbation methods called the state-space perturbation method in the launch rotated coordinate system. An analytical framework known as the perturbation expansion framework is proposed by first figuring out the correlation with the state variables/independent variables and then performing the approximate expansion. This framework can successfully address the issue of analytically solving the transfer matrix and integral term caused by the coupling and time-varying properties among state variables of the affine equations of the boost phase. The analytical solution developed in this paper has great fidelity and takes into account the combined effects of various factors, including thrust, aerodynamic force, Earth's gravity, oblateness, and rotation. It can serve as a theoretical guide for the rapid launch requirements and iterative design processes for early rocket demonstrations in engineering. [ABSTRACT FROM AUTHOR]

Due to the assumption of acceleration variation in traditional step-by-step integration methods such as Newmark, sufficiently small time steps are required to ensure numerical stability and accuracy in dynamic systems. In contrast, the state-space approach, based on piecewise interpolation of discrete load functions, does not rely on predetermined acceleration assumptions and has demonstrated high efficiency in terms of stability and accuracy. The original state-space method requires the calculation of the inverse of the structural mass in the transition matrix. However, when a lumped mass matrix is used, this computation renders the entire mass matrix singular, resulting in an invalid solution expression. To address this issue, this study proposes an improved state-space approach for the transient analysis of large-scale structural systems with local nonlinearities. In this approach, a nonlinear force corrector is introduced as an external force term applied to the linear elastic system to account for the nonlinear behavior of locally yielding components. Consequently, the original nonlinear dynamic system can be transformed into an equivalent linear elastic transient system. Furthermore, based on the lumped mass matrix, a first-order ordinary differential state-space equation for such an equivalent linear elastic transient system is derived. Simulation results from three transient system examples show that the state-space approach outperforms the Newmark method in terms of accuracy and stability for dynamic systems characterized by high frequency and low damping. The prediction results show that the state-space approach appears to be insignificantly affected by the choice of the consistent or lumped mass matrix. The numerical results show that the root-mean-square errors between the consistent and lumped matrices in the top displacement time histories of a 15-storey plane frame under various seismic intensities are all less than 1%, and in the base reaction time histories responses the discrepancies are only about 0.5%, indicating that the use of lumped mass matrices is quite reliable. When many nodes or degrees of freedom have no assigned mass, the dimensionality of the state-space equation can be significantly reduced using the lumped mass approach. Therefore, the simulation of large-scale systems can be simplified by employing the improved state-space approach with lumped mass matrices, yielding results nearly identical to those obtained using traditional methods. In conclusion, the improved state-space approach has great potential for the simulation of transient behavior in large-scale systems with local nonlinearities. [ABSTRACT FROM AUTHOR]

Purpose: Multilayer composite liner structures are the primary structural form of hydraulic tunnels. However, the bearing mechanism of multilayer composite liners has not been investigated thoroughly. Many existing design schemes do not properly achieve a balance between structural safety, anti-seepage capacity, and cost effectiveness. Thus, a new composite liner structure type and its theoretical model was proposed. Design/methodology/approach: A novel hydraulic tunnel composite liner structure with a polyurea spray coating interlayer was proposed in this study. A theoretical model based on the state-space method was developed and verified using FEM models and existing theoretical models. Parametric analysis was conducted based on the theoretical model to investigate the influence of various variables, including interfacial shear stiffness, inner liner thickness, and outer liner elastic modulus. Findings: It was concluded that the proposed theoretical model can be used successfully to calculate multilayer composite liner structures with high calculation efficiency. The overall deformation stiffness of the composite liner system increased with the interfacial shear stiffness. The sprayed coating interlayer significantly affects the residual force distribution between the outer and inner liners, which can also be affected by the adjustment of the thickness of the outer and inner liners. Thus, attention should be paid to these factors in the rational design of the proposed composite liner system. Originality/value: With the development of China's water conservancy projects, complex geological conditions, high surrounding rock stress, high internal and external water pressures, and other unique application scenarios have gradually increased. This places higher requirements on the bearing performance and impermeability of hydraulic tunnel lining structures. On the other hand, conventional hydraulic tunnel lining structures can hardly achieve a satisfactory balance between economy, structural safety, and impermeability. Thus, the proposed structure has the potential to be used in a wide range of applications. [ABSTRACT FROM AUTHOR]

• Semi-analytical solution of damping fluid-conveying pipe systems are obtained. • The concepts of the original system and the adjoint system are introduced for research. • The eigenvalues and eigenfunctions of the original system and the adjoint system are obtained. • The orthogonality condition of damped gyroscopic system is obtained in state space. • It is proved that the original system and the adjoint system of the system with free boundary are not orthogonal. In this paper, the response solutions of the damped fluid-conveying pipe system with elastic torsion constraints at both ends are analyzed. The pipe system considering gyroscopic effect induced by internal flow and damping effect is a typical damped gyroscopic system. This system cannot be decoupled in the modal space by the traditional modal analysis, and then the semi-analytical response solutions cannot be obtained by the classical modal superposition method. In order to remedy this problem, this paper proposes a new method based on complex modal superposition method and state-space method to give the semi-analytical response solutions of the damped fluid-conveying pipe system. The adjoint system is introduced through the concept of adjoint operator, and the orthogonality conditions of the damped fluid-conveying pipe system are derived in the state-space by using the eigenvalue relationship between the original system and the adjoint system. The Laplace transformation method is used to solve the eigenvalue problems of the original system and the adjoint system, and the implicit function equations about the eigenvalues and analytical eigenfunctions are obtained. According to the obtained orthogonality conditions, the semi-analytical response solutions of the system under arbitrary initial conditions and excitations are given, and the obtained solutions include transient and steady-state response solutions. In the numerical discussion part, the reliability and accuracy of the present method are verified. This research has positive significance for the dynamic analysis of fluid-conveying pipe systems, and the obtained orthogonality conditions have potential value for the nonlinear dynamics research. [ABSTRACT FROM AUTHOR]

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Abstract In biological systems, impulses are often used to model mutations in gene expression. In order to describe the instantaneity of the impulse, this paper employs a hybrid‐index model of impulsive Boolean networks with state‐triggered impulses. Based on this model, the time‐domain output controllability is investigated. Using the quotient mapping method, the hybrid‐domain solutions of this model are mapped to the time‐domain solutions, mathematically. Then a necessary and sufficient condition for output controllability in the time domain is presented. Finally, an example is given to demonstrate the correctness and effectiveness of the obtained results.

This paper presents a high-performance, multilevel inverter with symmetry and simplification. This inverter is a single-phase, seven-level symmetric switched-capacitor inverter based on the concept of the double voltage clamping circuit connected to the half-bridge circuit. Above all, only a single DC power supply is used to achieve a single-phase inverter with seven levels and a voltage gain of three. In addition to analyzing the operating principle of the proposed switched-capacitor multilevel inverter in detail, the stability analysis and controller design are carried out by the state-space averaging method. The feasibility and effectiveness of the proposed structure are validated by some simulated results based on the PSIM simulation tool and by some experiments using FPGA as a control kernel, respectively. However, in this study, the switches were implemented by MOSFETs to meet a high switching frequency. These MOSFETs can be replaced by IGBTs in the motor drive applications so that the used switching frequency can be reduced. [ABSTRACT FROM AUTHOR]

In this paper we present a framework for the construction and implementation of general virtual element spaces based on projections built from constrained least squares problems. Building on the triples used for finite element spaces, we introduce the concept of a virtual element method (VEM) tuple which encodes the necessary building blocks to construct these projections. Using this approach, a wide range of virtual element spaces can be defined. We discuss Hk-conforming spaces for k = 1, 2 as well as divergence and curl free spaces. This general framework has the advantage of being easily integrated into any existing finite element package, and we demonstrate this within the open source software package Dune. [ABSTRACT FROM AUTHOR]

In biological systems, impulses are often used to model mutations in gene expression. In order to describe the instantaneity of the impulse, this paper employs a hybrid‐index model of impulsive Boolean networks with state‐triggered impulses. Based on this model, the time‐domain output controllability is investigated. Using the quotient mapping method, the hybrid‐domain solutions of this model are mapped to the time‐domain solutions, mathematically. Then a necessary and sufficient condition for output controllability in the time domain is presented. Finally, an example is given to demonstrate the correctness and effectiveness of the obtained results. [ABSTRACT FROM AUTHOR]

Goal: Poor arousal management may lead to reduced cognitive performance. Specifying a model and decoder to infer the cognitive arousal and performance contributes to arousal regulation via non-invasive actuators such as music. Methods: We employ a Bayesian filtering approach within an expectation-maximization framework to track the hidden states during the $n$-back task in the presence of calming and exciting music. We decode the arousal and performance states from the skin conductance and behavioral signals, respectively. We derive an arousal-performance model based on the Yerkes—Dodson law. We design a performance-based arousal decoder by considering the corresponding performance and skin conductance as the observation. Results: The quantified arousal and performance are presented. The existence of Yerkes—Dodson law can be interpreted from the arousal-performance relationship. Findings display higher matrices of performance within the exciting music. Conclusions: The performance-based arousal decoder has a better agreement with the Yerkes—Dodson law. Our study can be implemented in designing non-invasive closed-loop systems.

Modern transducers and actuators may have functional layers with multi-field coupling and some elastic layers. This paper considers a tubular bilayer system consisting of a thin dielectric tube coated with a thick elastic layer. We study the nonlinear electromechanical response and the linear axisymmetric vibration of the system subject to different applied voltages and inner/outer pressures within the framework of the general nonlinear theory of electro-elasticity, the related linear incremental theory, and by considering the continuity conditions at the interface. We investigate instability behaviour using the same basic formulae. The state-space method provides efficient and accurate free vibration analysis, considering the dynamic response at the lowest frequencies, so we can neglect the viscous and damping effects, which is well suited to this problem. New results indicate that the bilayer system improves its frequency capability and stability compared to the monolayer dielectric tube. The thick outer elastic layer stiffens the bilayer system against axisymmetric bifurcation, bulging and necking instabilities. It also performs better in front of axisymmetric instability, increasing the system's capability to receive or produce higher voltages, especially for long waves.This work thoroughly explains bilayer functional systems' behaviour when exposed to extreme environments such as high voltage or pressure. [ABSTRACT FROM AUTHOR]

Linear models, seasonal autoregressive integrated moving average (SARIMA) models, and state-space models have been widely adopted to model and forecast economic data. While modeling using linear models and SARIMA models is well established in the literature, modeling using state-space models has been extended with the proposal of alternative estimation methods to the maximum likelihood. However, maximum likelihood estimation assumes, as a rule, that the errors are normal. This paper suggests implementing the bootstrap methodology, utilizing the model's innovation representation, to derive distribution-free estimates—both point and interval—of the parameters in the time-varying state-space model. Additionally, it aims to estimate the standard errors of these parameters through the bootstrap methodology. The simulation study demonstrated that the distribution-free estimation, coupled with the bootstrap methodology, yields point forecasts with a lower mean-squared error, particularly for small time series or when dealing with smaller values of the autoregressive parameter in the state equation of state-space models. In this context, distribution-free estimation with the bootstrap methodology serves as an alternative to maximum likelihood estimation, eliminating the need for distributional assumptions. The application of this methodology to real data showed that it performed well when compared to the usual maximum likelihood estimation and even produced prediction intervals with a similar amplitude for the same level of confidence without any distributional assumptions about the errors. [ABSTRACT FROM AUTHOR]

Polymerization products are indispensable for our daily life, and the relevant modeling process plays a vital role in improving product quality. However, the model identification of the related process is a difficult point in industry due multivariate, nonlinear and time-varying characteristics. As for the conventional offline subspace identification methods, the identification accuracy may be not satisfying. To handle such a problem, an enhanced on-line recursive subspace identification method is presented on the basis of principal component analysis and sliding window (RSIMPCA-SW) in this paper to obtain the state space model for polymerization. In the proposed on-line subspace identification approach, the initial L-factor is acquired by the LQ decomposition of the sampled historical data, firstly, and then it is updated recursively through the bona fide method after the new data have been handled by the sliding window rule. Subsequently, principal component analysis (PCA) is introduced to calculate the extended observation matrix, and finally the on-line model parameters are extracted. Compared with the traditional subspace schemes, smaller computation complexity and higher identification precision are anticipated in the proposed method. A case study on the modeling of the ethylene polymerization verifies the effectiveness of the developed approach, in which the related statistical indexes of the obtained identification model are better. [ABSTRACT FROM AUTHOR]

This research proposes the effect of micropolar-Cosserat (MC) parameters (length-scale parameters and Cosserat shear modulus) on the dispersion characteristics of propagating wave modes in periodic composite panels (PCPs). These inbuilt parameters are due to the assumption of the length-scale boundary conditions that allow for capturing the micro-rotational (MR) wave mode along with the flexural ones. A significant contribution of this study is the transformation of the two-dimensional (2-D) periodic composite problem into a series of one-dimensional (1-D) ones using the MC continuum theory. The analysis employs the transfer matrix method in the framework of the state-space approach to investigate periodic systems in the eigenvalue domain. Additionally, Bloch–Floquet's periodic boundary conditions (PBCs) are applied to the unit cell to ensure the periodicity of the system. The main innovation lies in observing veering, locking, and coupling phenomena, which occur due to alterations in lamina orientation and MC parameters. Moreover, the presence of inbuilt parameters renders the dispersion characteristics highly sensitive to even minor coefficient variations, with a mere 1% change significantly impacting eigenmode fluctuations. The sudden bandgap (BG) disappearing nature could be used to identify the accurate value of the coefficient for designing and analyzing PCPs. [ABSTRACT FROM AUTHOR]

Summary: It is well known that all practical control systems are subject to external disturbances. Therefore, a feedback controller should be designed so that the closed‐loop system has some desired properties such as stability, good tracking performance, at the same time, the impact of external disturbances on the performance of the closed‐loop system is attenuated to some degree. On the other hand, almost all models for real fully actuated systems, which are derived based on the physical laws, are described by a set of high order differential equations. The traditional method for controlling these fully actuated systems is to convert the high order differential equations to first order differential equations, which are called the state equations, and then to design feedback controllers by using the state‐space design methods. Such conversion causes some inconveniences. To overcome such inconveniences, a high‐order fully actuated (HOFA) design method has been proposed to control HOFA systems. The main goal of this paper is to design a weak disturbance decoupling controller for HOFA nonlinear systems to guarantee the stability and desired output tracking performance of the closed‐loop system and to attenuate the impact of disturbances. [ABSTRACT FROM AUTHOR]

To design and optimize the thermal management of metal hydride (MH) tank, high-fidelity model (HFM) composed of numerous partial differential equations, is often adopted to capture the spatial evolution of key parameters accurately. However, computational difficulties raise in dealing with such nonlinear interconnections for system-level simulation. Therefore, the model reduction of MH system has drawn much attention aiming at the trade-off between accuracy and computational cost. In this paper, a hybrid modeling method which integrates advantages of the state-space model (SSM) and HFM, is proposed and applied for the model reduction of MH tank. In particular, four data-driven matrices are introduced to improve the model accuracy. The results show that the root mean square errors of the average temperature between hybrid reduced model (HRM) and HFM are 0.0399 K and 0.1989 K respectively for the cases without and with thermal management. In addition, the HRM is able to capture dynamic characteristic under perturbed input variables with a relative error of temperature within 0.4%, indicating great potential for system-level simulation. What's more, the analysis of predominant pole derived from the state matrices of different thermal managements, reveals that the expanded graphite has superior effect on the adjustment time extension compared with fins, while the fins have distinct advantages in heat transfer enhancement at the cost of volumetric hydrogen storage density. • A hybrid modeling method combining state-space model and data-driven correction is proposed. • The reduced model of MH tank shows great agreement with HFM under various operation parameters. • The accuracy of reduced model has also been verified for the MH tank with thermal management and perturbed variables. • The effect of thermal management on the dynamic characteristic of MH tank is summarized. [ABSTRACT FROM AUTHOR]

With this paper, we purpose to introduce and characterized some generalized classes of completely monotone functions on some types of white noise spaces [ABSTRACT FROM AUTHOR]

Abstract The voltage source converter (VSC) interlinking AC and DC power networks is a core equipment in AC/DC hybrid power systems. To analyze the stability of this system based on the impedance method, it is necessary to establish the hybrid AC/DC admittance model of interlinking VSC. This paper presents a unified and systematic AC/DC hybrid admittance modelling framework which is widely applicable to different control methods of interlinking VSCs. The hybrid admittance models for interlinking VSCs under PQ control, VdcIq control, and Vf control are explicitly formulated, with their elements individually reflecting the dynamics of the AC side, DC side, and the interaction between them. Subsequently, the impedance network model of interlinking VSC systems is formulated based on the hybrid admittance, and furthermore the frequency‐domain modal analysis is performed to analyze the system oscillation stability. Finally, frequency scanning and time‐domain simulation results in MATLAB/Simulink are provided to validate the effectiveness of the modelling and oscillation stability analysis method.

The voltage source converter (VSC) interlinking AC and DC power networks is a core equipment in AC/DC hybrid power systems. To analyze the stability of this system based on the impedance method, it is necessary to establish the hybrid AC/DC admittance model of interlinking VSC. This paper presents a unified and systematic AC/DC hybrid admittance modelling framework which is widely applicable to different control methods of interlinking VSCs. The hybrid admittance models for interlinking VSCs under PQ control, VdcIq control, and Vf control are explicitly formulated, with their elements individually reflecting the dynamics of the AC side, DC side, and the interaction between them. Subsequently, the impedance network model of interlinking VSC systems is formulated based on the hybrid admittance, and furthermore the frequency‐domain modal analysis is performed to analyze the system oscillation stability. Finally, frequency scanning and time‐domain simulation results in MATLAB/Simulink are provided to validate the effectiveness of the modelling and oscillation stability analysis method. [ABSTRACT FROM AUTHOR]

With the expansion of electronics in recent decades, it is notorious to observe that embedded systems are increasingly necessary to improve people's quality of life and to facilitate the diagnosis of systems in general, ranging from pacemakers to control systems. The increased use of electronic components for technological support, such as telemetry systems, electronic injection, and automotive diagnostic scanners, enhances the perspective of data analysis through an embedded system aimed at vehicular systems. Thus, this work aims to design and implement an embedded data acquisition system for the analysis of vehicle vertical dynamics. The methodology for this study was structured into several stages: mathematical modeling of a motorcycle's mass-spring-damper system, coding for the Arduino microcontroller, computational data analysis supported by MATLAB software version 9.6, electronic prototyping of the embedded system, implementation on the vehicle, and the analysis of motorcycle vertical dynamics parameters. In addition, a mathematical modeling of the mass-spring-damper system was performed using the state-space method. The system was implemented on the Arduino microcontroller platform, enabling real-time data transfer from a motorcycle. The experimental results have successfully validated the proposed data acquisition system. [ABSTRACT FROM AUTHOR]

We consider general nonlinear function‐on‐scalar (FOS) regression models, where the functional response depends on multiple scalar predictors in a general unknown nonlinear form. Existing methods either assume specific model forms (e.g., additive models) or directly estimate the nonlinear function in a space with dimension equal to the number of scalar predictors, which can only be applied to models with a few scalar predictors. To overcome these shortcomings, motivated by the classic universal approximation theorem used in neural networks, we develop a functional universal approximation theorem which can be used to approximate general nonlinear FOS maps and can be easily adopted into the framework of functional data analysis. With this theorem and utilizing smoothness regularity, we develop a novel method to fit the general nonlinear FOS regression model and make predictions. Our new method does not make any specific assumption on the model forms, and it avoids the direct estimation of nonlinear functions in a space with dimension equal to the number of scalar predictors. By estimating a sequence of bivariate functions, our method can be applied to models with a relatively large number of scalar predictors. The good performance of the proposed method is demonstrated by empirical studies on various simulated and real datasets. [ABSTRACT FROM AUTHOR]

Causal inference in complex systems has been largely promoted by the proposal of some advanced temporal causation models. However, temporal models have serious limitations when time series data are not available or present insignificant variations, which causes a common challenge for earth system science. Meanwhile, there are few spatial causation models for fully exploring the rich spatial cross-sectional data in Earth systems. The generalized embedding theorem proves that observations can be combined together to construct the state space of the dynamic system, and if two variables are from the same dynamic system, they are causally linked. Inspired by this, here we show a Geographical Convergent Cross Mapping (GCCM) model for spatial causal inference with spatial cross-sectional data-based cross-mapping prediction in reconstructed state space. Three typical cases, where clearly existing causations cannot be measured through temporal models, demonstrate that GCCM could detect weak-moderate causations when the correlation is not significant. When the coupling between two variables is significant and strong, GCCM is advantageous in identifying the primary causation direction and better revealing the bidirectional asymmetric causation, overcoming the mirroring effect. Temporal causation models perform poorly in causal inference for variables with limited temporal variations. This paper establishes a causal inference model, which can reveal the nonlinear complex casual associations based on cross-sectional Earth System data. [ABSTRACT FROM AUTHOR]

Thin-walled open section composite beams (TWOSCB) used extensively in aerospace structures exhibit several non-classical effects such as torsional warping, warping shear, material coupling, and shear deformation. Arbitrary cross-section and material coupling make the governing equations highly coupled and difficult to solve analytically. In this paper, a unified coupled-field formulation is developed to analyze TWOSCB accommodating all non-classical effects. Using the state-space method to derive analytical expressions for displacements and forces, Vlasov solutions of isotropic beams are recovered. Results obtained for arbitrarily laminated mono-symmetric composite channel and I-section beams subjected to bending and torsion loads show excellent agreement with available results in the literature. [ABSTRACT FROM AUTHOR]

• State-space method improves solving efficiency of lumped-parametric models of blisks • Traveling wake excitation is derived by aerodynamic load fitting of blade surface • The modular expression of three-blade blisk model can be extended to the multi-blade blisk model. • Dimensions of state space is two times of degrees of freedom for the blisk models • Stiffness mistuning is independent of the steady-state response of the tuned blade In order to improve the solution efficiency of vibration characteristics for the mistuned blisk, a modular method combined with state-space method based on lumped-parametric model is developed for the first attempt, which provides a general modeling framework which can be employed to conveniently construct the lumped-parametric models of bladed disk systems with multiple mistuning and variable blade number. It is noteworthy that a pressure fit in the axial-span-pressure space is performed to obtain the continuous equations of aerodynamic forces according to the aerodynamic loads acting on the blade surface. The function of traveling wake excitation is established by considering the rotational velocity. Subsequently, 1N-degree-of-freedom (1N-DOF) and 2N-DOF lumped-parametirc models are respectively used to construct the mistuned blisk. A modular solution method of multiple mistuned lumped-parametirc model is derived from the controllable canonical form and minimum realisation, which reveals that the minimum dimension of the state space is two times of its DOF. The correctness of the present method is varified by several comparisions. Vibration localization is found in the transient response and steady-state response of the blisk. The effects of the mistuning on the blades and the disk are discussed, respectively. [ABSTRACT FROM AUTHOR]

• A continuous system load identification algorithm based on SSM and Newmark-β is proposed for the first time. • Combination of modal truncation order and sensor layout optimization by modal strain energy. • The proposed algorithm has better accuracy and noise immunity than SSM and GKFM. • For continuous systems, the proposed algorithm has a solution time of 0.38s and is insensitive to the time step. • The proposed algorithm has good accuracy in experimental validation. Dynamic load identification based on structural responses is an important problem in the field of engineering and plays an important role in the condition assessment of mechanical structures. Current popular load identification methods such as the state-space method (SSM) and the Green's kernel function method (GKFM) are implemented on discrete systems with outstanding performance, but when dealing with complex continuous systems, there are some limitations such as low efficiency and inaccuracy. In this paper, a continuous system load identification algorithm based on SSM and Newmark-β is proposed for the first time. Using modal coordinate transformation and modal truncation methods, the number of infinite vibration differential equations of a continuous system in physical space are converted to a finite number of vibration differential equations in modal space, where the modal truncation order and the optimal layout of the sensors are combined by modal strain energy. The Newmark-β method in modal space is derived and thus combined with SSM to obtain a load identification model Y =HF called SSM-Newmark-β method, which reduces the size of the transfer matrix H. The solution time of the proposed algorithm is 0.38 s for continuous systems, which is rather shorter than that for discrete systems. Furthermore, the simulations show that it has better accuracy and noise immunity than SSM and GKFM in the identification of sinusoidal load, impact load, and random load. The effect of time step is also discussed which reveals that the larger time step has less effect on the proposed algorithm. An experimental study is carried out on a cantilever beam system. The result verifies that the SSM-Newmark-β algorithm has better accuracy in load identification for the continuous system. This research provides a new sight for the real-time identification of dynamic loads for complex structures. [ABSTRACT FROM AUTHOR]

The aim of this work is the design of a current control by means of state feedback, based on linear matrix inequalities (LMI), and it is applied in a DC-DC coupled inductors Buck-Boost modular converter, which has been widely used in distributed generation systems with renewable energy sources. This method considers constraints on the location of poles defined in the complex plane called d-stability. The closed-loop control system is implemented in Matlab® Simulink and validated under different test scenarios, where better dynamic performance is obtained, its operating range is extended, with shorter settling times and a better time-response, in contrast with the classical PI control technique. [ABSTRACT FROM AUTHOR]

Purpose: The main aim of this work is to investigate the free vibration of functionally graded rotating nanotubes using the Euler–Bernoulli beam theory under the assumptions of Eringen's nonlocal elasticity theory, which gets close to the nanostructure's behaviors. The material properties are assumed to be graded in the nanotube thickness direction according to the power-law distribution. Methods: Hamilton's principle is used to derive equations of motion and boundary conditions, which are uncoupled and solved analytically using the state-space method. The gyroscopic effect is considered in the equations of motion and, unprecedentedly, in the boundary conditions. Results: The effects of rotating speed, mode number, material power-law index, and geometrical and nonlocal parameters on both critical speeds and natural frequencies under various boundary conditions for functionally graded rotating nanotubes are plotted and investigated for the first time. Conclusion: The current formulation of the rotating FG-NT is expected to serve as a standard for assessing the accuracy of designing various nanomotors, whether experimental, numerical, or analytical. [ABSTRACT FROM AUTHOR]

Piezoelectric quasicrystals have attracted extensive attention due to their unique physical and mechanical properties. This paper studies the dynamic response of multilayered two-dimensional decagonal piezoelectric quasicrystal sector plates with imperfect interfaces. Based on the quasicrystal linear elasticity, partial differential state equations along the thickness direction are derived by using the state-space method. Then, by virtue of the differential quadrature method and the Fourier series expansions, this boundary-value problem with mixed boundary conditions and imperfect interfaces is solved. In addition, via the joint coupling matrix, the field quantities in the interior of the structure are connected to those on the external surfaces with numerical instability. Finally, parameter studies on the effects of angular spans, imperfect interfaces, and mixed boundary conditions are numerically investigated where the dimensionless frequencies and modes are exhibited. [ABSTRACT FROM AUTHOR]

ARIMA is seldom used in supply chains in practice. There are several reasons, not the least of which is the small sample size of available data, which restricts the usage of the model. Keeping in mind this restriction, we discuss in this paper a state-space ARIMA model with a single source of error and show how it can be efficiently used in the supply-chain context, especially in cases when only two seasonal cycles of data are available. We propose a new order selection algorithm for the model and compare its performance with the conventional ARIMA on real data. We show that the proposed model performs well in terms of both accuracy and computational time in comparison with other ARIMA implementations, which makes it efficient in the supply-chain context. [ABSTRACT FROM AUTHOR]

Two state–space representations, also known as state–space models (SSMs), are proposed to estimate dynamic spatial relationships from time series data. At each time step, the weight matrix, which captures the latent state, is updated in the context of a spatial autoregressive process. Specifically, two types of SSMs are considered: the first one identifies the spatial effects in the form of multivariate regression, where the higher orders of the spatial matrix are introduced to the regression coefficient, while the second one updates the spatial matrix taking advantage of the likelihood function of a spatial autoregressive (SAR) model. Different filtering algorithms are proposed to estimate the latent state. The simulation results show that the first state–space representation performs better in both lower-dimensional and higher-dimensional cases, while the performance of the second representation is sensitive to the state dimension. In a real-world case study, the time-varying weight matrices are estimated with weekly credit default swap (CDS) data for 16 banks, and the results show that the methods can identify communities that are consistent with the country-driven partition. [ABSTRACT FROM AUTHOR]

Approximate analytical solutions are presented for the transient thermoelastic problem of rectangular plates with time-dependent convection and radiation boundaries. To include the nonlinear radiation boundary, the whole heating process is divided into several time steps, and a linearized approximation is used to simplify the radiation term for each step. The one-dimensional transient temperature along the thickness direction is solved using the technique of the separation of variables. The displacement and stress solutions are obtained by applying the state-space method to the three-dimensional thermoelasticity equations. The accuracy of the present solutions is demonstrated by comparison with the reported results in the open literature and the finite element solutions. In the numerical examples, two kinds of thermal boundaries, namely, time-independent convection boundaries and time-dependent convection and radiation boundaries, are considered to show the availability of the present solutions. [ABSTRACT FROM AUTHOR]

This study aims to analyze the physical-mechanical properties and dynamic models of tissue-simulating hydrogels, specifically the photoacoustic (PA) response signals, by varying the concentrations of polyvinyl alcohol (PVA) and molecular weight (MW). A state-space model (SSM) is proposed to study the PVA hydrogels to retrieve the PA-related signal's damping ratio and natural frequency. Nine box-shaped PVA hydrogels containing saline solution were used, with five concentrations of PVA (7, 9, 12, 15, 20%) for MW1 and four for MW2. The results indicated that the concentration of PVA and MW played an important role in the PA wave's amplitude, arrival time, and speed of sound over the hydrogels. The SSM parameters showed that increasing PVA and MW concentrations improved the hydrogels' ability to absorb and transfer energy under the PA effect. These parameters were also found to be correlated with density and modulus of elasticity. Additionally, the concentrations of PVA and MW affected the absorption and optical scattering coefficients. The physical-mechanical properties, including porosity, density, and modulus of elasticity, improved as the concentration of PVA and MW increased. The ultimate goal of this study is to develop hydrogels as phantoms that can be used for tissue simulation and imaging. [ABSTRACT FROM AUTHOR]

Due to the nonlinear behavior of grid-connected cascaded multilevel inverters (GCCMI), the use of nonlinear controllers can guarantee system stability over a wide range of operation. Therefore, state-space modeling is required to design nonlinear controllers. In this manuscript, a comprehensive method is proposed for the general state-space modeling of an n-level GCCMI with LCL coupling. To validate the accuracy of obtained state-space model, an experimental setup of a cascaded multilevel inverter including two H-bridges has been implemented. The outputs of the state-space model are compared with the simulation and experimental results of the GCCMI. This shows that the proposed model is compatible with a real closed-loop system. The simulations were performed using EMTDC/PSCAD software. In the following, the designed general model is used to develop a nonlinear controller based on the Lyapunov stability criteria for a multilevel shunt active power filter (SAPF). Results show that the designed controller is stable and robust in a wide range of operating point changes. [ABSTRACT FROM AUTHOR]

This paper proposes an effective VAR source established as a cascaded H-bridge (CHB) static compensator (STATCOM), which is based on the flux cancellation method. The conventional CHB-STATCOM uses a low-frequency large capacitor as a source. The required capacitance value of the capacitor increases as a function of the amount of VAR produced to compensate the power system. The proposed topology is based on flux cancellation. Therefore, the source of VAR in this case is not limited by the capacitors or the power decoupling transformer size. The sub-module (SM) of the proposed topology comprises of a CHB module with power decoupling circuits. The double-frequency ripple powers on the sub-module (SM) capacitors, which have a phase shift of 120° with respect to each other. The ripple powers are derived from each of the three phases toward a common magnetic core to cancel each other out. An isolated bidirectional triple port dual half-bridge converter is utilized for the flux cancellation process. In this converter, the main challenges are leakage inductances and the high voltage insulation among the three windings of the high-frequency transformer. An αβ-frame-based model is proposed, using the generalized state-space averaging method, for the flux cancellation circuit. Furthermore, the size is significantly reduced by the proposed method, since a small sub-module capacitance of a few microfarads is sufficient to operate the CHB-STATCOM. The analysis and the controller design process are presented, followed by simulation and hardware validations. [ABSTRACT FROM AUTHOR]