Search

Migration of colloidal particles induced by temperature gradients is commonly referred to as thermodiffusion, thermal diffusion, or the (Ludwig-)Soret effect. The thermophoretic force experienced by a colloidal particle that drives thermodiffusion consists of two distinct contributions: a contribution resulting from internal degrees of freedom of single colloidal particles, and a contribution due to the interactions between the colloids. We present an irreversible thermodynamics based theory for the latter collective contribution to the thermophoretic force. The present theory leads to a novel "thermophoretic interaction force" (for uncharged colloids), which has not been identified in earlier approaches. In addition, an N -particle Smoluchowski equation including temperature gradients is proposed, which complies with the irreversible thermodynamics approach. A comparison with experiments on colloids with a temperature dependent attractive interaction potential over a large concentration and temperature range is presented. The comparison shows that the novel thermophoretic interaction force is essential to describe data on the Soret coefficient and the thermodiffusion coefficient. • An irreversible thermodynamics based theory is presented leading to a novel "thermophoretic interaction force" on colloidal particles that originates from their mutual interactions. • Explicit microscopic expressions are found for the Soret coefficient and the thermodiffusion coefficient in terms of the (equilibrium) pair-correlation function. • The novel thermophoretic interaction force is essential to be able to describe the experimental data. [ABSTRACT FROM AUTHOR]

In this paper, we consider a restricted (N + 1) -body problem on surfaces M κ 2 , where the constant κ ≠ 0 is the Gaussian curvature, which by means of a rescaling can be reduced to κ = ± 1. This problem consists in the study of the dynamics of an infinitesimal mass particle attracted by N primaries of identical masses describing elliptic relative equilibria of the N -body problem on M κ 2 , i.e., a solution where the primaries are rotating uniformly with constant angular velocity ω on a fixed parallel of S 2 or H 2 and placed at the vertices of a regular polygon. In a rotating frame, this problem yields a two degrees of freedom Hamiltonian system. The goal of this paper is to describe analytically some dynamics features for κ = ± 1. Precisely, we study the relative location of equilibria, obtaining, in particular, that the poles of S 2 and vertex of H 2 represent equilibrium points for any value of the parameters. Thus, analysis of the nonlinear stability of these equilibria is carried out, as well as two types of bifurcations are detected: Hamiltonian-Hopf and N -bifurcation. Additionally, we prove the existence of a family of Hill's orbits and a family of periodic orbits when the primaries are located near the poles of S 2 or the vertex of H 2. Finally we prove the existence of KAM 2-tori related to these periodic orbits. [ABSTRACT FROM AUTHOR]

[Display omitted] The compound eyes of the dragonfly, Pantala flavescens Fabricius, are covered by micro-scaled ocelli capable of sensing polarized light, an attractive property for radar stealth and counterreconnaissance. In this work, we fabricated biomimetic electromagnetic wave absorption materials (EAMs) by analyzing the covert information identifications of biological systems and focusing on the design of metastructures and microstructures. Several bionic metasurfaces with anisotropic double-V meta atoms made up of (FeCoNiSi 8.9 Al 8.9)C 0.2 high-entropy-alloy (HEA) ribbons for multiple-degrees-of-freedom recognition and broadband absorption are presented. The covert phase, amplitude, and angular momentum of electromagnetic waves were controlled and recognized as information by manipulating the rotation angle θ of meta atoms. A vortex wave with a topological charge of 1 was generated to recognize linearly polarization and left- and right-handed circular polarization. In addition, the polarization conversion enhanced absorption. The hierarchical nanostructures of HEA ribbons give rise to suitable electromagnetic loss and a superior impedance match. Finally, inspired by the structure of compound eyes, the designed multilayer metamaterials realized effective absorption (reflection loss (RL) ≤ − 10 dB) within the 4.5–18 GHz regime under 2.8 mm thickness. These materials provide evidence for a new way for integrated EAMs and metamaterials. [ABSTRACT FROM AUTHOR]

A central challenge in physics is to describe non-equilibrium systems driven by randomness, such as a randomly growing interface, or fluids subject to random fluctuations that account e.g. for local stresses and heat fluxes in the fluid which are not related to the velocity and temperature gradients. For deterministic systems with infinitely many degrees of freedom, normal form and center manifold theory have shown a prodigious efficiency to often completely characterize how the onset of linear instability translates into the emergence of nonlinear patterns, associated with genuine physical regimes. However, in presence of random fluctuations, the underlying reduction principle to the center manifold is seriously challenged due to large excursions caused by the noise, and the approach needs to be revisited. In this study, we present an alternative framework to cope with these difficulties exploiting the approximation theory of stochastic invariant manifolds, on one hand, and energy estimates measuring the defect of parameterization of the high-modes, on the other. To operate for fluid problems subject to stochastic stirring forces, these error estimates are derived under assumptions regarding dissipation effects brought by the high-modes in order to suitably counterbalance the loss of regularity due to the nonlinear terms. As a result, the approach enables us to predict, from reduced equations of the stochastic fluid problem, the occurrence in large probability of a stochastic analogue to the pitchfork bifurcation, as long as the noise's intensity and the eigenvalue's magnitude of the mildly unstable mode scale accordingly. In the case of SPDEs forced by a multiplicative noise in the orthogonal subspace of e.g. its mildly unstable mode, our parameterization formulas show that the noise gets transmitted to this mode via non-Markovian coefficients, and that the reduced equation is only stochastically driven by the latter. These coefficients depend explicitly on the noise path's history, and their memory content is self-consistently determined by the intensity of the random force and its interaction through the SPDE's nonlinear terms. Applications to a stochastic Rayleigh-Bénard problem are detailed, for which conditions for a stochastic pitchfork bifurcation (in large probability) to occur, are clarified. [ABSTRACT FROM AUTHOR]

Constraints can be used to eliminate quickly fluctuating degrees of freedom in dynamical systems enabling solutions that resolve the behavior of the system with fewer time steps over long time scales. In Brownian dynamics models, these constraints lead to linear equations which represent saddle point problems describing the velocity tangent to the constraint manifold and the forces resulting from imposition of the constraint on the dynamics. Simulations of these constrained systems must solve these saddle point problems, which are often ill-conditioned and require clever preconditioning in order to facilitate large scale simulation using iterative methods like GMRES. In this work, we show that the projected conjugate gradient (PrCG) method, which applies conjugate gradients projected onto the tangent space of the constraint manifold, has certain advantages compared to preconditioned iterative methods like GMRES, without the need to devise and compute a preconditioner. Specifically, for simulations of beads interacting hydrodynamically with commonly encountered holonomic constraints, PrCG exhibits linear scaling with the number of beads similar to GMRES. However, because PrCG does not require a preconditioner it often requires less precomputational effort both in terms of computational complexity and storage, depending on the nature of the constraints. Furthermore, PrCG produces iterates which are always feasible, allowing for independent tuning of the error tolerance on the bead velocities from the error tolerance on the constraint equations. We demonstrate PrCG's efficiency by solving several example low Reynolds number systems involving rigid bodies, freely jointed chains, and immobile particles, as well as a mixed constraint problem with both a rigid body and immobile particles, comparing to GMRES and analytical solutions, when available. [ABSTRACT FROM AUTHOR]

We present a component-based model order reduction procedure to efficiently and accurately solve parameterized incompressible flows governed by the Navier-Stokes equations. Our approach leverages a non-overlapping optimization-based domain decomposition technique to determine the control variable that minimizes jumps across the interfaces between sub-domains. To solve the resulting constrained optimization problem, we propose both Gauss-Newton and sequential quadratic programming methods, which effectively transform the constrained problem into an unconstrained formulation. Furthermore, we integrate model order reduction techniques into the optimization framework, to speed up computations. In particular, we incorporate localized training and adaptive enrichment to reduce the burden associated with the training of the local reduced-order models. Numerical results are presented to demonstrate the validity and effectiveness of the overall methodology. • Component-based model reduction to incompressible flows in repetitive geometries. • Application of optimization-based formulation to non-overlapping domain decomposition. • Static condensation of local degrees of freedom improves efficiency and modularity. • Refinement of the local bases based on global reduced solves improves performance. [ABSTRACT FROM AUTHOR]

We present a new framework towards the objective of learning coarse-grained models based on the maximum entropy principle. We show that existing methods for assigning clusters using the maximum entropy approach are heuristic or sub-optimal. We propose a machine learning framework informed by rate-distortion theory to learn optimal cluster assignments, aiming to improve the effectiveness of the coarse-graining process. Our approach involves transforming the discrete optimization problem into a probabilistic and continuous form. Our inverse modeling approach involves the development of a fully differentiable, adjoint-driven dynamics solver for use with gradient-based optimization techniques. The entire framework is end-to-end differentiable, facilitating backward pass gradient computation to flow through the ODE solve and probabilistic coarse-graining to train a classifier. We demonstrate application in the evolution of particle quantum states in non-equilibrium conditions. The high dimensionality of these equations poses a significant challenge for efficient and accurate computations, even for seemingly simple chemical systems. Training is performed using a loss function informed by rate-distortion theory to cluster the rovibrational states of some molecule, effectively forming a reduced order model of the master equations. We also introduce variable transformations along with several ways of improving the tractability of the training process. These allow the framework to process the extremely high-dimensional discrete optimization problem successfully. Our method is general, and to demonstrate the effectiveness in a controlled setting, we apply it to a one-dimensional Gaussian source quantization problem for which an analytical solution is known, followed by the problem of isothermal relaxation of a ▪ system with O (10 4) degrees of freedom. • Information theoretic approach to develop coarse grained models of non-equilibrium physics. • High degree of flexibility in choosing the system to drive the clustering process. • End-to-end differentiable and model-consistent approach to clustering. • Several enhancements to promote tractability of implementation. • Potential for enhancing interpretability of the selected physics. [ABSTRACT FROM AUTHOR]

• A novel beam-spring 2-DOF magnetically coupled bistable energy harvester is proposed. • The operating bandwidth is improved by approximately 60 % compared with a CBEH. • The subharmonic responses are characterized by the coexistence of two coupling modes. • Reasonable spring stiffness design is helpful to further enhance the bandwidth. • The excitation threshold peak effect of the 2-DOF coupled system is studied. Introducing the magnetic coupling effect with multiple degrees of freedom to a conventional bistable energy harvester is helpful to further enhance its operating bandwidth. However, it is not straightforward to design due to its extremely complicated dynamic characteristics, meanwhile, some underlying mechanisms also need to be explored ulteriorly. This paper proposes a novel beam-spring two-degree-of-freedom magnetically coupled bistable energy harvester, combining the advantages of multistable and multimodal harvesters. Based on the theoretical model validated by experiments, the complex nonlinear dynamic behaviors of the system are investigated in detail, as well as the effects of key parameters on power generation capacity. It is found that the working bandwidth is improved by more than 60 % because of the additional contribution from the 2nd resonance region. And there are abundant interwell ultraharmonic and subharmonic responses characterized by the coexistence of out-of-phase and in-phase coupling modes. Under appropriate spring stiffness or certain initial conditions, the snap-through motion can be successfully triggered to enter a high-energy orbit. The parameter study shows that the magnet distance and spring stiffness significantly affect the effective bandwidth. Furthermore, the excitation threshold peak effect that hinders the connection of the two resonant frequency bands is also observed. Fortunately, it can be eliminated by the reasonable design of the 1st and 2nd natural frequencies to achieve a consecutive and broad effective bandwidth. This research provides a theoretical case for designing and developing wide-band and low-threshold bistable energy harvester. [Display omitted] [ABSTRACT FROM AUTHOR]

The Hamiltonian analysis for the linearized λ R gravity around the Minkowski background is performed. The first-class and second-class constraints for arbitrary values of λ are presented, and two physical degrees of freedom are reported. In addition, we remove the second-class constraints, and the generalized Dirac brackets are constructed; then, the equivalence between General Relativity and the λ R theory is shown. • The canonical analysis for the Horava-like theory is performed. • The constraints for λ = 1 3 and λ ≠ 1 3 were obtained. • The Dirac brackets are constructed. • The gauge fixing yields the same Dirac's brackets. • The equivalence between G R and λ R model is shown. [ABSTRACT FROM AUTHOR]

Many modern engineering structures exhibit nonlinear vibration. Characterizing such vibrations efficiently is critical to optimizing designs for reliability and performance. For linear systems, steady-state vibration occurs only at the forcing frequencies. However, nonlinearities (e.g., contact, friction, large deformation, etc.) can result in nonlinear vibration behavior including superharmonics — responses at integer multiples of the forcing frequency. When the forcing frequency is near an integer fraction of the natural frequency, superharmonic resonance occurs, and the magnitude of the superharmonics can exceed that of the fundamental harmonic that is externally forced. Characterizing such superharmonic resonances is critical to improving engineering designs. The present work extends the concept of phase resonance nonlinear modes (PRNM) to be applicable to general nonlinearities, and is demonstrated for eight different nonlinear forces. The considered forces include stiffening, softening, contact, damping, and frictional nonlinearities that have not been previously considered with PRNM. The proposed variable phase resonance nonlinear modes (VPRNM) method can accurately track superharmonic resonances for hysteretic nonlinearities that exhibit amplitude dependent phase resonance conditions that cannot be captured by PRNM. The proposed method allows for characterization of superharmonic resonances without constructing a full frequency response curve at every force level with the harmonic balance method. Thus, the present method allows for analysis of potential failures due to large amplitudes near the superharmonic resonance with reduced computational cost. The consideration of single degree of freedom systems in the present paper provides insights into superharmonic resonances and a basis for understanding internal resonances for multiple degree of freedom systems. • A new method for tracking superharmonic resonances across forcing levels is proposed. • Variable phase resonance nonlinear modes (VPRNM) is needed for the present tracking. • Key features are identified at significantly lower cost than using harmonic balance. • Superharmonic resonances are analyzed for eight nonlinear forces. • Hysteretic nonlinearities show superharmonic resonances over a limited force range. [ABSTRACT FROM AUTHOR]

The importance of fluidelastic forces in flow-excited vibrations is crucial, in view of their damaging potential. Flow-coupling coefficients are often experimentally obtained from vibration experiments, performed within a limited experimental frequency range. For any given flow velocity, these coefficients are typically frequency-dependent, as amply documented in the literature since the seminal work of Tanaka and Takahara. Such frequency dependence, which seems quite natural in view of the flows intricacies, not only is awkward for attempting physical interpretations, but also leads to numerical difficulties when performing time-domain computations. In this work, we address this problem by assuming that the measured fluidelastic forces encapsulate "hidden" (non-measured) dynamics of the coupled flow. This leads to the possibility of modelling the flow-structure coupled dynamics through conventional ordinary differential equations with constant parameters. The substructure analysis of such a model, augmented with a set of "hidden" flow variables, readily highlights an inevitability of the frequency-dependence found in the measured flow forces, when these are condensed at the measurement degrees of freedom. The formulation thus obtained clearly suggests the mathematical structure of the measured fluidelastic forces, in particular providing the formal justification for a modelling approach often used in unsteady aeroelasticity. Then, inspired by previous work in the fields of viscoelasticity and soil-structure interaction, we proceed by identifying adequate frequency-independent second-order flow-coupling matrices from the frequency-dependent experimental data, which is a challenging identification problem, even for the specific case of symmetric coupling detailed here. Finally, the developed concepts and procedures are applied to experimental results obtained at CEA-Saclay (France), for the fluidelastic interaction forces acting on a flexible tube within a rigid bundle, although the problem addressed embraces a much wider range of applications. The proposed flow modelling and identification approach shows significant potential in practical applications, with many definite advantages. [ABSTRACT FROM AUTHOR]

• Displacement feedback is used to control friction-induced stick-slip oscillation. • The linear stability analysis of the controlled system is carried out. • Optimization of control parameters is performed by pole-crossover design. • The effect time delay on the control is investigated. • Averaging method is used to study the dynamics of nonlinear system. The present work utilizes a displacement feedback control strategy to mitigate the friction driven stick-slip vibration of a mechanical system with single degree of freedom. The stick-slip vibration is primarily caused by the decrease in friction force due to the changes in velocity of the moving surface. This phenomenon, also known as Stribeck effect, can have a negative impact on the system's performance. A mass on a moving belt is considered as the primary system for stick-slip vibration. The dynamics of stick slip oscillation is represented by the polynomial model. Prior to being sent to the system, the displacement signal of the mass undergoes processing via a filter to effectively control the friction induced instability. Eigenvalue analysis of the linearized controlled system is carried out to obtain the boundary line at which the static equilibrium switches its stability. To conduct the nonlinear analysis, the method of averaging is utilized and the resulting outcomes are then verified through simulation results. The bifurcation analysis shows that the controller has the capability to eliminate undesired oscillations and stabilize the system. In order to optimize the filter parameters, the pole crossover method is utilized. The amplitude of the vibration is seen to be reduced significantly by applying the proposed control. Finally, theoretical study of the nonlinear behavior of the controlled system is carried out while taking into account the existence of time delay. [ABSTRACT FROM AUTHOR]

In earthquake-prone areas, seismic isolation systems are designed to preserve structural safety and prevent occupants' injury and properties' damage. However, seismically isolated structures can be subject to large displacements relative to the ground under earthquakes, which lead to define two problems, the first problem concerns to excessive displacements, whereas the second problem relates to excessive accelerations that occur when the displacements are limited by an obstacle with high relative stiffness. An arrangement that favors the solution of these problems is an appropriate interposition between the isolated structure and the obstacle of the shock absorbers or bumpers. The aim of this paper is to investigate, via numerical parametric analyses, the possibility to exploit the occurrence of impact in a two-sided vibro-impact isolated single-degree-of-freedom (SDOF) system under harmonic base excitation with beneficial effects. Through the analysis of the response scenarios which can occur varying the obstacles' parameters, that is the width of the gap and the mechanical (stiffness and damping) properties, the target is to reduce both the maximum value of the displacement and of the acceleration of the mass, compared to the free flight condition, without possibly reducing the vibration isolation frequency range. This research path leads to the definition of vibro-impacting control systems and to the free and constrained single and multi-objective optimal design of the control system consisting of the integrated assembly of the isolation system, bumpers and gaps. The main results obtained consist in having (i) found a unique optimality condition, (ii) calculated the dissipated energy and given an energetic interpretation to the optimality condition (iii) built maps, that allow to advance behavior predictions, provide indications on the design and allow to make evaluations of the performance of the vibro-impacting system as a function of the stiffness and damping parameters and of the width of the gap. The stiffness ratio and the damping ratio, which define the mechanical properties of the bumpers, are such that the dimensionless relaxation time is about 1, (iv) finally the results are compared to multi-objective optimal design. Ultimately, the advantages of this new isolation system are: (1) provide a physical limit switch to the isolation system in order to limit the maximum displacement of the mass; (2) reduce the effects of amplification dynamics in the resonance zone; (3) reduce the static displacement, all without possibly modifying the dynamic response in the isolation zone. • A new Vibro-Impact Control System integrating isolation, bumper and gap is defined. • Properly selecting parameters allows to beneficially exploit the occurrence of impact. • The study of the response scenarios is functional to identify optimal parameters. • The minimum acceleration criterion is proposed to select optimal parameters. [ABSTRACT FROM AUTHOR]

New technologies, such as additive manufacturing combined with topology optimisation or bio-inspired design, can produce lightweight structures with better dynamical properties but more complex geometries. Analysing these components with the finite element method can become time-consuming because of fine 3D meshes. By exploiting the node-dependent kinematic approach of Carrera's unified formulation and using Lagrange expanding functions, this work presents the implementation of adaptive finite elements for the free-vibration analysis of plates with an arbitrary thickness variation through the in-plane domain. In other words, the kinematics of the 2D model on which the element is based can be adapted to the geometry of the plate. The formulation is mainly based on the 3D integration of the approximating functions and computation of a 3D Jacobian matrix inside the element for the derivation of stiffness and mass matrices; substantially, the resulting elements are 3D elements in which the order of expansion through the thickness can be different from that in the plane of the plate. The free vibration analysis of some plates with different thickness variations is performed. The results demonstrate that the present elements allow us to accurately study these innovative 2D structures by employing much fewer degrees of freedom with respect to classical 3D finite elements. • Introduces a new class of 2D finite elements, the Adaptive finite elements. • These elements can study any type of variable thickness plate. • Validation of these new elements is performed. • Degrees of Freedom reduction is demonstrated. [ABSTRACT FROM AUTHOR]

Lamb wave-based structural health monitoring requires fast and accurate simulation tools for guided wave propagation in structures. In this article, a computationally efficient multiphysics time-domain spectral element (TDSE) model is presented for actuation, propagation, and sensing of Lamb waves in laminated composite strips (beams and panels) integrated with surface-bonded or embedded patch piezoelectric actuators and sensors. The transducers are physically modelled using an electromechanically coupled formulation, which combines an efficient layerwise zigzag theory for kinematics with a layerwise distribution for the electric potential field. The high-order TDSE has n physical nodes containing mechanical and electric degrees of freedom (DOFs) and a separate virtual electric node for modelling the transducers' equipotential surfaces with significantly reduced DOFs. The continuity of the displacement fields at the intersections (patch fronts) of the hybrid laminate integrated with patch transducers with the host laminate is maintained using the advanced hybrid point-least squares continuity model. The present guided wave predictions show excellent agreement with experimental measurements as well as continuum-based finite element solutions for isotropic and composite strips with surface-bonded piezo patches. The patch front continuity is shown to have a significant effect on the accuracy. The model is used to study the interaction of guided waves with the notch-type damage. The results establish the superiority of the proposed TDSE model over its standard two-node counterpart in terms of accuracy and efficiency. On the other hand, the equivalent single-layer theory-based model with the same number of DOFs yields highly erroneous predictions. • Presents an efficient multiphysics spectral element for smart composite strips. • First electromechanical spectral element based on an efficient layerwise theory. • Enforces continuity of nonlinear displacement field at piezo patch intersection. • Employs virtual electric node to satisfy equipotential conditions on piezo surfaces. • Enables fast, accurate simulation for Lamb wave-based structural health monitoring. [ABSTRACT FROM AUTHOR]

Quasi-zero-stiffness (QZS) isolators have shown great promise for low-frequency vibration isolation, thus outperforming conventional linear isolators. However, the hardening behavior typically exhibited in QZS isolators can deteriorate the isolation performance at high excitation amplitudes. To tackle this problem, utilizations of inherent material damping in soft resin offer a feasible way to counteract the hardening effect. This paper proposes a continuous QZS isolator, which can be readily fabricated by three-dimensional (3D) printing using soft resin. QZS properties are achieved by combining the snap-through behavior of inclined beams and the support of folded beams, acting as negative-stiffness (NS) and positive-stiffness (PS) elements, respectively. Analytical methods are developed for predicting the stiffness of the NS and PS elements of the design, whose efficacy is demonstrated numerically and experimentally through examining the static behavior. To evaluate the vibration isolation performance of the QZS isolator, a nonlinear single-degree-of-freedom (SDOF) model is proposed. The model incorporates cubic nonlinear damping in addition to classical viscous damping. The harmonic balance method (HBM) and the Runge-Kutta algorithm are employed to solve the equation of motion and to predict the velocity transmissibility. Parametric analyses are conducted to assess the effect of the excitation amplitude on isolation performance. The results show that an increased excitation level entails a down-shifting of the peak frequency in the transmissibility curve and that of the starting frequency of the effective isolation zone, resulting in enhanced isolation performance at large amplitudes. Numerical findings are further supported by dynamic experiments with varying excitation levels, demonstrating the validity of the proposed numerical model. [ABSTRACT FROM AUTHOR]

In this work, an adaptive shape optimization is developed using Geometry Independent Field approximaTion (GIFT) for 3D acoustics problems. The geometry-independent field approximation, using Non-uniform Rational B-splines (NURBS) to model the geometry, and Polynomial-splines over Hierarchical T-meshes (PHT-splines) to model the field space, are employed for 3D shape optimization problems in the context of time-harmonic acoustics. The adaptive optimization scheme proposed in this work combines a gradient-based optimization method with a local refinement algorithm. In this case, two types of local refinement algorithms are tested: a recovery-based and a residual-based algorithm. Single and multi-patch examples are studied, and it is shown that the proposed adaptive shape optimization scheme can lead to the same results as the uniform optimization, but using less time and fewer degrees of freedom. • Geometry Independent Field approximation (GIFT) is proposed for 3D shape optimization Helmholtz acoustic problems. • Geometry is modeled by NURBS while the physical domain is modeled by PHT-splines. • The proposed optimization scheme combines a gradient-based method with adaptive optimization. • Two different types of marking algorithms for the adaptive-refinement are tested: recovery-based and residual-based. • Shape optimization is performed over NURBS control points on the boundary. [ABSTRACT FROM AUTHOR]

• A computationally efficient method for obtaining coupled vibrations of a serpentine belt accessory drive system. • Harmonic balance method with alternating frequency/time domain technique together with hysteretic tensioner model. • A dimensionality reduction method for the dynamic matrix of accessory drive system equations. Serpentine belt accessory drive system (SBADS) is a typical coupled vibration system with rigid body vibrations and continuum vibrations. Vibration behaviors of a SBADS consist of rotational vibrations of pulleys and tensioner arm and transverse vibrations of belt spans. In modeling of a SBADS, transverse vibration of a belt span consisting of time and space coordinates is discretized into multiple degrees of freedom with only time variable. As a result, number of degrees of freedom of a SBADS is large, and computational efficiency of dynamic responses of a SBADS is low. To solve this issue, a calculation method for nonlinear dynamic characteristics of a SBADS is proposed based on the harmonic balance method with alternating frequency/time domain technique in the paper. An engine front end accessory drive system is taken as a study example, the coupling vibration model of the SBADS is established, and hysteretic behavior of the tensioner is considered in the model. In addition, a dimensionality reduction method for the dynamic matrix is proposed based on local nonlinearity of the model. A calculation method for nonlinear dynamic responses of the SBADS is subsequently developed by combining the harmonic balance method and alternating frequency/time domain technique. Nonlinear dynamic responses estimated by the proposed method are validated by comparing with numerical simulations. Finally, amplitude-frequency responses of the SBADS are calculated using arc-length continuation method, and influences of nonlinear tensioner on frequency domain responses and internal resonance phenomena of the SBADS are analyzed. [ABSTRACT FROM AUTHOR]

Digital technologies can be used to gather accurate information about the behavior of structural components for improving systems design, as well as for enabling advanced Structural Health Monitoring (SHM) strategies. New avenues for achieving automated and continuous structural assessment are opened up via development of virtualization approaches delivering so-called Digital Twins (DTs), i.e., digital mirrored representations of physical systems relying on fusion of simulation models and real-time monitoring data. In this framework, the main motivation of the work presented in this paper stems from the existing challenges in the implementation and deployment of a real-time predictive framework for virtualization of dynamic systems. Kalman-based filters are usually employed in this context to address the task of joint input-state prediction in structural dynamics. A Gaussian Process Latent Force Model (GPLFM) approach is exploited in this work to construct flexible data-driven a priori models for the unknown inputs, which are then coupled with a combined deterministic-stochastic state-space model of the structural component under study for Kalman-based input-state estimation. The use of Gaussian Process (GP) regression for this task overcomes the limitations of the conventionally adopted random-walk model, thus limiting the necessity of offline user-dependent calibration of this type of data assimilation methods. This paper proposes the use of alternative covariance functions for GP regression in structural dynamics. A theoretical analysis of the GPLFMs linked to the investigated covariance functions is offered. The outcome of this study provides insights into the applicability of each covariance type for GP-based input-state estimation. The proposed framework is validated via an illustrative simulated example, namely a 3 Degrees of Freedom (DOF) system subjected to an array of different loading scenarios. Additionally, the performance of the method is experimentally assessed on the task of joint input-state estimation during testing of a 3D-printed scaled Wind Turbine (WT) blade. [ABSTRACT FROM AUTHOR]

6-DoF grasp estimation methods based on point clouds have long been a challenge in robotics due to the limitations of single data input, which hinder the robot's perception of real-world scenarios, thus reducing its robustness. In this work, we propose a 6-DoF grasp pose estimation method based on RGB-D data, which leverages ResNet to extract color image features, utilizes the PointNet++ network to extract geometric information features, and employs an external attention mechanism to fuse both features. Our method is an end-to-end design, and we validate its performance through benchmark tests on a large-scale dataset and evaluations in a simulated robot environment. Our method outperforms previous state-of-the-art methods on public datasets, achieving 47.75mAP and 40.08mAP for seen and unseen objects, respectively. We also test our grasp pose estimation method on multiple objects in a simulated robot environment, demonstrating that our approach exhibits higher grasp accuracy and robustness than previous methods. [ABSTRACT FROM AUTHOR]

Given the current context of changes in aeronautics to reduce emissions, it is also necessary to modernise the computation methods to anticipate future cases where disciplines which are now calculated separately (i.e. manoeuvers and gusts) should be computed at the same time including flexible effects and using a time-domain approach. In this work, a static aeroelasticity formulation is adapted to compute wind gust loads. This static method uses aerodynamic matrices to calculate an effective angle of attack (used to recover the local pressure coefficients) from a structural deformation. The approach has been to define this deformation including unsteady effects influence in order to use the same formulation as the static case. Three gust cases (two unsteady and one quasi-steady) have been tested in a rectangular wing, and the proposed method has been compared to the aeroelastic high-fidelity solution and to an uncorrected version of the Doublet Lattice Method (Nastran Solution 146). The proposed solution benefits from the use of the lookup tables to accurately estimate the peak lift coefficient value (maximum error of 6.7%) at least 2.5 times faster than the Doublet Lattice Method. Nevertheless, using a limited model with only two degrees of freedom prevents the proposed method from capturing complex dynamics coming from highly unsteady gust excitation or from aerodynamic instabilities. [ABSTRACT FROM AUTHOR]

[Display omitted] The dynamics of colloidal suspension confined within porous materials strongly differs from that in the bulk. In particular, within porous materials, the presence of boundaries with complex shapes entangles the longitudinal and transverse degrees of freedom inducing a coupling between the transport of the suspension and the density inhomogeneities induced by the walls. Colloidal suspension confined within model porous media are characterized by means of active microrheology where a net force is applied on a single colloid (tracer particle) whose transport properties are then studied. The trajectories provided by active microrheology are exploited to determine the local transport coefficients. In order to asses the role of the colloid-colloid interactions we compare the case of a tracer embedded in a colloidal suspension to the case of a tracer suspended in an ideal bath. Our results show that the friction coefficient increases and the passage time distribution widens upon increasing the corrugation of the channel. These features are obtained for a tracer suspended in a (thermalized) colloidal bath as well as for the case of an ideal thermal bath. These results highlight the relevance of the confinement on the transport and show a mild dependence on the colloidal/thermal bath. Finally, we rationalize our numerical results with a semi-analytical model. Interestingly, the predictions of the model are quantitatively reliable for mild external forces, hence providing a reliable tool for predicting the transport across porous materials. [ABSTRACT FROM AUTHOR]

Active vibration isolation systems (AVISs) equipped with Lorentz actuators are utilized in diverse sectors to minimize vibrations transmitted to delicate payloads by offering controlled stiffness and damping. Traditional actuators in AVISs, however, are confined to a single degree of freedom (DOF). This implies that a higher number of these types of actuators is necessary to achieve vibration isolation across all six DOF in an AVIS. Consequently, this can amplify assembly errors and prolong response times, thereby compromising system performance. They also present challenges related to thrust, weight, and heat dissipation. This paper delves into the design, modeling, optimization, and validation of an innovative 6-DOF AVIS which can apply various payloads to generate various displacements and performs consistently over a range of payloads. The main feature of the proposed system is its two-axis Lorentz actuator (TALA). With identical configurations for both axes, the TALA facilitates 2-DOF in-plane motion with mutual decoupling, a novel feature in AVISs, to the best of our knowledge. Moreover, through a parametric design strategy and multi-objective optimization, it achieves a superior force constant, reduced coil weight, and minimized heat dissipation. Results from the proposed AVIS underscore its promise as a versatile tool for ultraprecision measurement instruments, including atomic force microscopes, scanning probe microscopes, and optical payloads. [ABSTRACT FROM AUTHOR]

• This article introduced the stiffness characteristics of the joint surface between the mechanical connection structures of the spindle-tool holder, tool holder-spring clamp, and spring clamp-tool of the spindle system in the robot machining system into the prediction of machining stability. • This paper proposed a method for establishing a tool tip frequency response prediction model for robot milling systems, which improves the accuracy of theoretical prediction of the tool tip dynamic characteristics of robot milling systems under different postures, Compared to the method of obtaining tool tip frequency response of robot milling system through experiments to support milling stability prediction, the method proposed in this paper effectively improves the efficiency of robot milling stability prediction. • The prediction results of the proposed tool tip frequency response prediction model were imported, and a two-degree-of-freedom chatter prediction model considering the regenerative effect is established, and the robot milling chatter is predicted considering redundant degrees of freedom. The accuracy of prediction results is verified by milling experiment. The change of tool tip frequency response caused by the posture dependence of robot dynamic is one of the key problems that make it difficult to accurately predict the milling stability of robot. In this paper, a tool tip frequency response prediction method considering the interface stiffness characteristics of spindle-tool system is proposed for stability prediction of robotic milling under the condition of posture variation. Firstly, the interface stiffness models of spindle-toolholder, toolholder-spring clip and spring clip-tool are established based on Yoshimura's unit area method. Then, The dynamics model for the robot body and the interface stiffness models for spindle-tool system are imported into the finite element analysis model of the spindle system, so that the prediction of the tool tip frequency response is realized by harmonic response analysis. Compared with the experimental results, the maximum error of the natural frequency was not more than 2 %, and the maximum error of the amplitude was not more than 12 %. Finally, the 2 DOF robot milling stability prediction model is established. Then the robot milling chatter is predicted considering redundant degrees of freedom from the perspective of regenerative chatter prediction theory, and the accuracy of prediction results is verified by milling experiment. [ABSTRACT FROM AUTHOR]

A high-order, degree-adaptive hybridizable discontinuous Galerkin (HDG) method is presented for two-fluid incompressible Stokes flows, with boundaries and interfaces described using NURBS. The NURBS curves are embedded in a fixed Cartesian grid, yielding an unfitted HDG scheme capable of treating the exact geometry of the boundaries/interfaces, circumventing the need for fitted, high-order, curved meshes. The framework of the NURBS-enhanced finite element method (NEFEM) is employed for accurate quadrature along immersed NURBS and in elements cut by NURBS curves. A Nitsche's formulation is used to enforce Dirichlet conditions on embedded surfaces, yielding unknowns only on the mesh skeleton as in standard HDG, without introducing any additional degree of freedom on non-matching boundaries/interfaces. The resulting unfitted HDG-NEFEM method combines non-conforming meshes, exact NURBS geometry and high-order approximations to provide high-fidelity results on coarse meshes, independent of the geometric features of the domain. Numerical examples illustrate the optimal accuracy and robustness of the method, even in the presence of badly cut cells or faces, and its suitability to simulate microfluidic systems from CAD geometries. • High-order HDG method with immersed NURBS surfaces. • No additional unknowns introduced on non-matching boundaries/interfaces. • Suitability of coarse meshes independent of the geometric features of the domain. • Optimal convergence and robustness even in the presence of badly cut cells or faces. • Application to incompressible one-fluid and two-fluid Stokes flows. [ABSTRACT FROM AUTHOR]

In experimental dynamic substructuring, coupling of substructures sharing a line- or surface-like interface proves to be a challenge due to the difficulties in interface modelling. Modelling a high number of degrees of freedom at the common interface can be too stringent when imposing compatibility and equilibrium conditions, thereby causing redundancy and ill-conditioning. To mitigate the effects of overdetermination and experimental errors, that can lead to a high error amplification, several techniques have been developed, proposing different reduction spaces to weaken the interface conditions. This work investigates reduction space definitions in dynamic substructuring for coupling continuous interfaces. In particular, a comparative investigation of three established techniques, namely the frequency-based modal constraints for fixture and subsystem, singular vector transformation, and virtual point transformation, is conducted within the frequency domain. The feasibility of all approaches is supported by an experimental case study, which can guide practitioners in selecting a suitable approach for their specific needs. [Display omitted] • Dynamic coupling of line- or surface-like interfaces is investigated. • Various reduction bases are compared based on the experimental case study. • Guidelines are provided that guide practitioners in selecting a suitable reduction basis. [ABSTRACT FROM AUTHOR]

To understand the changes in moisture state, wheat gluten (WG) structure and oil penetration during deep-fat frying, batter-breaded fish nuggets (BBFNs) were prepared using the batter with a wheat starch and WG blend at a ratio of 11:1 (w/w), then fried at different temperatures (150–190 °C) and times (30–150 s). As the increase of frying temperature and the prolongation of frying time, a significant portion of bound water in the BBFNs converted to the free water, the fluorescence intensity decreased significantly and the secondary structure of WG changed from disorder to order, while the opposite trend was presented for the 190 °C and 150 s, respectively. The increase of frying temperature significantly reduced the surface hydrophobicity. In addition, the pores and cracks in the crust gradually grew larger, causing the surface oil content of fried BBFNs decreased first and then increased, accompanying with an increased content of penetrated oil and the expanded Sudan Red B dyeing area. This study indicated that frying temperature and frying time significantly changed the moisture state and WG structure in the crust, thereby affecting the oil penetration. The results could be used to provide a scientific guidance for the large-scale production of low-fat fried BBFNs. [Display omitted] • Frying decreased the freedom degree of water in the crust. • Change in moisture state affected wheat gluten structure. • Stable wheat gluten structure inhibited oil penetration of fried breaded fish nuggets. [ABSTRACT FROM AUTHOR]

Analysis of structural vibrations presents challenges due to the coupling between different degrees of freedom, often preventing the derivation of analytical expressions for quantities such as poles, vibration amplitude, etc. While numerical methods are commonly employed to tackle such challenges, their purely numerical nature prevents achieving a comprehensive understanding of the system behaviour. This paper builds on a novel recursive transfer function formulation recently proposed by the authors to analytically characterise the dynamics of generic undamped mass-chain systems. This approach provides fundamental properties and analytical insights that cannot be obtained through current numerical approaches, representing a significant breakthrough in the understanding of vibrations and offering valuable insights for analysing complex vibrating systems. These results presented in this paper allow for a rapid assessment of the minimum phase nature of the vibration system through straightforward stability assessment, and present analytical expressions for sums and multiplications of natural frequencies squared by induction and Vieta's formulas. Furthermore, it derives conditions for existence of repeated roots using direct analytical derivation of the characteristics equations, including purely imaginary roots and repeated roots at the origin, showing that repeated roots can only occur when some forms of spatial symmetries exist, and confirms bounds for the arithmetic mean of natural frequencies by using inequalities between geometric, arithmetic and quadratic means. Additionally, analytical conditions are established for systems with different degrees of freedom to share the same roots, providing a theoretical foundation for eigenvalue assignment in the time domain or pole placement in the frequency domain. This foundation enables the determination of desired natural frequencies from scratch using transparent analytical conditions, without relying on complex algorithms typically required by current inverse methodologies involving passive structural modifications or active controllers. Moreover, this paper also explores the relationship between independent and coupled vibrations, providing insights for comparing natural frequencies. Overall, this paper contributes to a deeper understanding of structural vibrations through analytical exploration and offers practical guidance for eigenvalue assignment and natural frequency analysis. [ABSTRACT FROM AUTHOR]

We present a new high-order accurate discretisation on unstructured meshes of quadrilateral elements. Our Face Upwinded Spectral Element (FUSE) method uses the same node distribution as a high-order continuous Galerkin (CG) method, but with a particular choice of node locations within each element and an upwinded stencil on the face nodes. This results in a number of benefits, including fewer degrees of freedom and straight-forward integration with CG. We present the derivation of the scheme and the analysis of its properties, in particular showing stability using von Neumann analysis. We show numerical evidence for its accuracy and efficiency on multiple classes of problems including convection-dominated flows, Poisson's equation, and the incompressible Navier-Stokes equations. • A new stabilised spectral element method based on continuous solutions and face upwinding. • Using a special set of local nodes, the scheme is stable for arbitrary polynomial degrees. • For the special case of constant coefficient 1D problems, the scheme can be written as a Spectral Difference method. • In general, the method can be understood as a nodally-integrated Petrov-Galerkin scheme. • Some benefits over the popular Discontinuous Galerkin method include fewer degrees of freedom, sparser Jacobian matrices, and better CFL condition. [ABSTRACT FROM AUTHOR]

This work focuses on deriving guidelines for choosing structural theories for composite shells using Convolutional Neural Networks (CNN). The Axiomatic/Asymptotic Method (AAM) is used to evaluate higher-order structural theories' accuracy and computational efficiency based on polynomial expansions. AAM exploits the Carrera Unified Formulation to derive the finite element matrices and obtain natural frequencies. The outcomes of AAM concerning the accuracy and computational cost are used to train CNN for various composite shell configurations. The trained network can then be used as a substitute for finite element models to estimate the accuracy of a given structural theory. The results are provided via Best Theory Diagrams (BTD), in which the set of generalized displacement variables to retain the best accuracy can be read for a given amount of nodal degrees of freedom. Verification is carried out using results from FEM. The results proved the computational efficiency of CNN and highlighted the influence of the shell thickness for the proper choice of the structural theory. Third-order terms and transverse stretching are often necessary to obtain acceptable accuracy. • The accuracy of a structural theory is problem-dependent. • The selection process for the optimal modeling strategy can be a challenging task. • The synergistic use of machine learning and Carrera Unified Formulation can reduce the complexity of the selection process. [ABSTRACT FROM AUTHOR]

We use a perturbative approach to evaluate transition amplitudes corresponding to quantum friction, for a scalar model describing an atom which moves at a constant velocity, close to a material plane. In particular, we present results on the probability density per unit time of exciting degrees of freedom on specific regions of the plane. This allows one to know spatial features of the effect which could have practical relevance, for instance, for the design of nanodevices. We show that the result of integrating out the probability density agrees with previous results for the same system. We also study the effect of including higher order terms in the perturbative calculation of the probability amplitude for quantum friction, and show that they do not alter the picture obtained from the first non-trivial order, in particular, the velocity threshold for the phenomenon to occur. • We investigate quantum friction between moving media, focusing on implications for nanodevices. • We use perturbative analysis to calculate quantum friction, examining spatial effects and probability densities. • We identify a velocity threshold for quantum friction, consistent across perturbative orders. • Higher order terms do not change the fundamental understanding of quantum friction. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study on the implementation of a self-tuning vibration absorber for tonal vibration control. The study considers a tuneable vibration absorber, composed by a spring-mass-damper system with variable stiffness and damping components, which is attached to a single degree of freedom mechanical system subjected to a harmonic excitation. The online tuning of the absorber stiffness and damping parameters is performed using an extremum seeking algorithm set to minimise the vibration kinetic energy of the hosting system. The paper proposes a two-paths tuning approach, which, starting from initial estimates of the stiffness and damping parameters of the absorber, searches for their optimal values along constant-damping and constant-stiffness paths respectively. The study presents a comprehensive analysis on the implementation of the algorithm at off-resonance and at resonance frequencies of the hosting system. Also, it investigates how the intrinsic parameters of the algorithm influence the convergence to the optimal stiffness and damping values. The proposed tuning methodology does not require a reference signal for the tonal excitation and, thus, can be suitably implemented both for fixed and time-varying tonal disturbances. [ABSTRACT FROM AUTHOR]

• A vibrating system with four reverse internal-driving degrees of freedom is proposed. • Self-balancing characteristics and stability are studied. • Stable states and the motion types in the different resonant regions are analyzed. • Test bench is designed to verify the correctness of the theory and analysis results. For self-synchronous vibrating systems, the large dynamic loads are usually transmitted by the system to the foundation, resulting in the problems of noise pollution, damaging the foundation, and exacerbating components and parts wear and tear, etc. In the current study, from the perspectives of mechanics and mechanism, we have discovered the principle of self-balancing based on self-synchronization theory, which can effectively solve these problems. First, a dynamical model with four internal degrees of freedom driven by four reverse-rotating exciters is proposed to study its synchronization, stability, and self-balancing characteristics. Then, in theory, the equations of motion, the criteria of synchronization and stability of the system are deduced using Lagrange's methods, the average method, and Routh–Hurwitz stability criterion, respectively. Based on the principle that the dynamic load transmitted to the foundation when the system realizes self-balancing is theoretically zero, the self-balancing conditions of the system are further provided. Based on these conditions, the stability and self-balancing characteristics of the system in different resonant regions are qualitatively analyzed numerically, including the stable phase differences among exciters, stability ability of the system, amplitudes of rigid frames, and motion characteristics. Finally, the simulations and experiments are further carried out to examine the correctness of the theoretical results and numerical analysis results. It's shown that the reasonable working point in engineering should be selected in the first sub-resonant region of the vibrating system. The present work can provide theoretical guidance for designing some new types of vibrating systems with the function of self-balancing. [ABSTRACT FROM AUTHOR]

The classic finite difference shock-capturing methods, such as the WENO-JS scheme, are currently perceived as having limited small-scale capture capabilities due to excessive dissipation. A typical technique for enhancing the performance of a scheme in higher wavenumber regions is spectrum optimization. However, this approach compromises accuracy since it requires degrees of freedom to optimize dispersion and dissipation characteristics. In order to maintain accuracy while simultaneously enhancing spectral properties and significantly raising the maximum resolved bandwidth of a scheme, this study proposes a piecewise spectrum optimization method (PSOM) that employs schemes with different dispersion and dissipation properties in different wavenumber regions. A new scale sensor with improved resolving efficiency and more stable performance is developed to detect local wavenumbers more precisely after thoroughly investigating the scale sensor algorithm. The above method is applied to the 6th-order TENO scheme that can completely distinguish between discontinuous and smooth regions, the threshold value C T is redesigned in different wavenumber regions to meet the dissipation requirements in various scale spaces, and a scale-adaptive scheme called TENO-SA is proposed. The potential advantages of the TENO-SA scheme in terms of spectral properties are demonstrated through the ADR and NSA methods. The accuracy analysis also indicates that the scheme can maintain optimal accuracy at low wavenumber regions. Numerous multi-scale benchmarks are introduced to validate the effectiveness of the PSOM and the new scale sensor, as well as the more effective and accurate simulation ability of the TENO-SA scheme for small-scale structures in broadband problems. • A piecewise spectrum optimization strategy is given to maximize the resolved bandwidth. • Different CT values are used at various wavenumbers to minimize dissipation error. • A scale sensor with both high resolvable wavenumber and steady performance is proposed. • The designed new approaches are applied in TENO to construct a scale-adaptive scheme. • Proposed scheme exhibits notable spectral properties for better simulating complex flows. [ABSTRACT FROM AUTHOR]

• A novel CMS method is proposed for the non-proportionally damped nonlinear systems. • Regarding the nonlinear interface forces as additional unknowns simplifies the synthesis procedure. • This method can preserve the intrinsic properties of nonlinear interface forces as much as possible. Engineering structures are generally designed based on linear elasticity assumptions. However, it is difficult to describe the connected structures using a simple linear system, due to factors such as sliding and friction at interfaces, and variations in contact areas during vibration processes. Therefore, it is necessary to develop an approach to tackle such systems with interface nonlinearities. In this paper, we proposed an extended free-interface component mode synthesis method. According to the proposed method, the substructures are separated at the nonlinear interfaces. Then the component mode synthesis procedure is carried out. By reasonably neglecting the contributions of higher order modes to the damping and inertia terms, it is demonstrated that the nonlinear interface forces and their time derivatives can be expressed as functions of themselves, as well as modal displacements and velocities. This characteristic facilitates the synthesis of the reduced order models for substructures in the state space. Also owing to this operation, the original properties of nonlinear interface forces can be preserved as much as possible, without any linearization. This method is suitable for non-proportionally damped structures with local nonlinearities such as mechanical structures with nonlinear spring and dashpot connections, rotor-bearing systems and so on. It also may be an alternative for the dynamic analysis of jointed structures with contact nonlinearities. Two numerical examples are presented to demonstrate the capability of the proposed method: (1) an eighteen degrees of freedom spring-dashpot-mass system with cubic spring and cubic dashpot interface connections is studied and (2) a more complex mechanical structure: a dual-rotor system with deep-groove ball bearing inter-shaft support. The numerical simulation results indicate that the dynamic responses of the reduced order model match very well with that of the full model, revealing the high accuracy of the proposed method with low computational costs. [ABSTRACT FROM AUTHOR]

• Constructing fractional-order foundation model for hydrogenerator unit. • Deriving nonlinear broadband dynamic equations for CSFS. • Discussing differences between CSFS and traditional single shaft system. • Analyzing the coupled dynamic performances of CSFS. The analysis of the coupled shaft-foundation system (CSFS) of a water turbine generator set is an extremely complicated task owing to its structural complexity and inherent nonlinear broadband dynamic characteristics. Thus, the coupling relationships of the CSFS remain unclear. The broadband vibration of the foundation subsystem has an evident influence on the vibration of the shaft subsystem of the unit; however, for the analysis of the dynamic characteristics of the water turbine generator, an overly complicated foundation can be reasonably simplified. To this end, this paper reports the development of novel energy-equivalent broadband modeling approaches to investigate the nonlinear vibration characteristics of CSFS. First, a relatively traditional integer-order lumped parameter model of the foundation subsystem was constructed, and its parameters were determined by fitting the response spectra obtained from an accurate hydropower house model. To improve the narrow-frequency limitation of the integer-order model and account for random disturbances, a novel fractional-order broadband modeling method is proposed. The advantage of the proposed fractional-order equivalent foundation model is that it can simultaneously reveal the broadband characteristics of complex structures at low frequencies of less than 1 Hz to high frequencies of hundreds of Hz with a single degree of freedom. Finally, coupled dynamic equations for the fractional-order CSFS model were derived and solved by considering the actions of various nonlinear factors and hydraulic pulsation excitation. A comparison of the dynamic responses of the CSFS with field test data demonstrated the effectiveness and practicability of the proposed modeling approaches. The results of the integer- and fractional-order CSFS models provide insights into the abundant dynamic laws and inner mechanisms of the nonlinear coupled dynamic system. Furthermore, they provided a reliable theory for the design and stability analysis of a hydropower unit, considering the varied vibrations of the coupled foundation. [ABSTRACT FROM AUTHOR]

• A method for estimating full set of amplitude-dependent FDs at the whole wind speed regime from free vibration wind tunnel tests is proposed and validated. • The evolution characteristics of the nonlinear coupled and uncoupled aerodynamic damping with wind speed and vibration amplitude were revealed. • The influence of structural parameters on the post-flutter performance were investigated based on the developed 2D nonlinear flutter analysis method. • The influences of vertical DOF (mode) and 3D effects on nonlinear flutter response were revealed based on the developed 3D nonlinear flutter analysis method. To estimate nonlinear flutter response of long-span bridges, this study established a method for identifying full set of amplitude-dependent flutter derivatives (FDs) from free vibration wind tunnel tests. Taking a typical double-deck truss bridge as a Case study, the amplitude-dependent FDs of the bridge deck at the whole wind speed regime are identified and cross-validated based on large-amplitude free vibration wind tunnel tests of its single degree of freedom (SDOF) torsional and 2DOF vertical-torsional section models. The influential mechanism of vertical DOF on nonlinear flutter was revealed by quantitatively comparing the nonlinear aerodynamic damping of the SDOF and 2DOF systems. The amplitude-dependent FDs are then used to calculate the nonlinear flutter responses of the 2D bridge section and a prototype long-span suspension bridge (1650m) with four main cables based on developed 2D and 3D nonlinear flutter analysis methods. Finally, the influence of structural parameters and 3D effects on nonlinear flutter are quantified and discussed. The results show that the 2DOF system has a lower critical wind speed and higher torsional stable amplitudes compared with the SDOF system since the participation of vertical DOF introduces the negative coupled aerodynamic damping to the system. The aerodynamic nonlinearity becomes stronger and stronger as the wind speed increases and it mainly leads to the significant amplitude dependence of the uncoupled aerodynamic damping, which is the key factor to cause the limit cycle oscillation (LCO)-type of flutter. While the coupled aerodynamic damping appears to be a relatively linear damping with weak amplitude-dependence within the studied wind speed and it mainly plays the role of reducing the stability of the system. The 3D effects of the vibrating bridge deck will reduce the system stability mainly by increasing the negative uncoupled aerodynamic damping. Therefore, the amplitudes of nonlinear flutter will be seriously underestimated if the 3D effects are ignored. [ABSTRACT FROM AUTHOR]

The effects of unsteady motions of flapping flat plates and corrugated structures in different parameters are studied using fluid–solid coupling and overlapping grid methods. Based on the dragonfly's right forewing and right hindwing model, these actions include sweeping and pitching, take-off acceleration, and tandem wings cruising in the reverse phase at 180 °. The results show that when the advance ratio J = 0. 36 , the "inflow deflection" improves the aerodynamic force in two degrees of freedom compared to simple flapping. When considering only the impact of flexibility, the aerodynamic forces of flexible flat plates and corrugated structures are better than those of the rigid wing models. Considering the effect of corrugated structures, the lift of flexible corrugated wings diminishes, but more thrust is generated. From the perspective of vortex street, vortex rings materialize only in the downstroke stage, while the attachment effect of leading-edge vortices is noticeable in several models. In the same phase flapping, the two wings combine to form a giant wing, which generates significant forward flight momentum. In out-of-phase flapping mode, the series wings generate two lifts and two or three thrust peaks to attain the required forward flight speed while sustaining a high lift. [Display omitted] • Explore the aerodynamics of the flexible corrugate structure dragonfly wing. [ABSTRACT FROM AUTHOR]

This paper presents a novel projection-based embedded discrete fracture model (pEDFM) applicable to general two-phase flow simulation in anisotropic reservoirs for the first time. The novel pEDFM is developed based on hybrid two-point flux approximation and mimetic finite difference (TPFA-MFD) methods, which retains the basic features of two-point flux approximation (TPFA) based generic pEDFM workflow and incorporates new features of mimetic finite difference (MFD) to handle full-tensor permeabilities. This is achieved by introducing the concept of effective connection, formulating additional pressure degrees of freedom for effective connections, assigning effective matrix-matrix (m-m) and matrix-fracture (m-f) connections to the corresponding sides of matrix-cell interfaces, presenting methods corresponding to different types of connections to handle low-conductivity fractures, and further deriving formulas of numerical fluxes for effective connections. The resulting global equation system is solved by a Newton-Raphson nonlinear solver with the temporary discretization of the implicit backward Euler scheme. The 2D and 2.5D numerical examples show the novel pEDFM could achieve the same level of computation accuracy and convergence as the reference discrete fracture model (DFM), while avoiding the gridding difficulty of complex fracture networks. It also significantly outperforms classical EDFM based on MFD and generic pEDFM workflow in the computational accuracy for cases with anisotropic full tensor permeabilities. The novel pEDFM, to our best knowledge, is for the first time proposed and developed for general anisotropic two-phase flow simulation and maybe the numerical simulation framework for multi-phase flow in fractured reservoirs with the best comprehensive performance so far. [ABSTRACT FROM AUTHOR]

The macroscopic forcing method (MFM) of Mani and Park [1] and similar methods for obtaining turbulence closure operators, such as the Green's function-based approach of Hamba [2] , recover reduced solution operators from repeated direct numerical simulations (DNS). MFM has already been used to successfully quantify Reynolds-averaged Navier–Stokes (RANS)-like operators for homogeneous isotropic turbulence and turbulent channel flows. Standard algorithms for MFM force each coarse-scale degree of freedom (i.e., degree of freedom in the RANS space) and conduct a corresponding fine-scale simulation (i.e., DNS), which is expensive. We combine this method with an approach recently proposed by Schäfer and Owhadi [3] to recover elliptic integral operators from a polylogarithmic number of matrix–vector products. The resulting Fast MFM introduced in this work applies sparse reconstruction to expose local features in the closure operator and reconstructs this coarse-grained differential operator in only a few matrix–vector products and correspondingly, a few MFM simulations. For flows with significant nonlocality, the algorithm first "peels" long-range effects with dense matrix–vector products to expose a more local operator. We demonstrate the algorithm's performance for the eddy diffusivity and eddy viscosity operators, which correspond to the unclosed parts of the ensemble-averaged transport equations, excluding the analytically known, closed parts of such equations. However, the algorithm can also be applied to the full operators. We focus on scalar transport in a laminar channel flow and momentum transport in a turbulent channel flow. For these problems, we recover eddy diffusivity- and eddy viscosity-like operators, respectively, at 1% of the cost of computing the exact operator via a brute-force approach for the laminar channel flow problem and 13% for the turbulent one. Applying these operators to compute the averaged fields of interest has visually indistinguishable behavior from the exact solution. Our results show that a similar number of simulations are required to reconstruct the operators to the same accuracy under grid refinement. Thus, the accuracy corresponds to the physics of the problem, not the numerics, so long as the grid is sufficiently refined. We glean that for problems in which the RANS space is reducible to one dimension, eddy diffusivity, and eddy viscosity operators can be reconstructed with reasonable accuracy using only a few simulations, regardless of simulation resolution or degrees of freedom. • Fast Macroscopic Forcing Method analyzes closure operators for fluid flows. • The new method has cost complexity improvements over existing methods. • Cost improvements mean only few full resolution simulations required for flow closures. • Examples provided for RANS-like turbulence closures. • Can construct closure operators for other PDEs with hard-to-resolve scales. [ABSTRACT FROM AUTHOR]

Vegetation restoration has significant impacts on ecosystems, and a comprehensive understanding of microbial environmental adaptability could facilitate coping with ecological challenges such as environmental change and biodiversity loss. Here, abundant and rare soil bacterial and fungal communities were characterized along a 15−45-year chronosequence of forest vegetation restoration in the Loess Plateau region. Phylogenetic-bin-based null model analysis (iCAMP), niche breadth index, and co-occurrence network analysis were used to assess microbial community assembly and environmental adaptation of a Robinia pseudoacacia plantation under long-term vegetation restoration. The drift process governed community assembly of abundant and rare soil fungi and bacteria. With increasing soil total phosphorus content, the relative importance of drift increased, while dispersal limitation and heterogeneous selection exhibited opposite trends for abundant and rare fungi. Rare soil fungal composition dissimilarities were dominated by species replacement processes. Abundant microbial taxa had higher ecological niche width and contribution to ecosystem multifunctionality than rare taxa. Node property values (e.g., degree and betweenness) of abundant microbial taxa were substantially higher than those of rare microbial taxa, indicating abundant species occupied a central position in the network. This study provides insights into the diversity and stability of microbial communities during vegetation restoration in Loess Plateau. The findings highlight that abundant soil fungi and bacteria have broad environmental adaptation and major implications for soil multifunctionality under long-term vegetation restoration. • Drift processes governed abundant and rare subcommunities assembly. • Species replacement dominate rare subcommunity dissimilarity. • Average variance degree of rare taxa was higher than abundant taxa. [ABSTRACT FROM AUTHOR]

In this paper, a selective discontinuous Galerkin (SDG) method and a polynomial preserving recovery (PPR) method are developed and integrated with the immersed-finite-element particle-in-cell (IFE-PIC) method, in order to carry out the plasma-material interaction simulation on adaptive Cartesian meshes (ACM). To significantly save the computational cost in practice, the PIC simulation often needs to use Cartesian meshes for the whole domain and the ACM for some focused regions in the plasma-material interaction problems. Therefore, we utilize the SDG method with immersed finite elements for the field solver of the IFE-PIC method, as the key technique to allow the local Cartesian mesh refinement which will generate hanging nodes. To minimize the degree of freedom of the SDG on the ACM and reduce the computational cost, a new selective technique of the discontinuous global basis functions is proposed for the SDG. Various types of nodes in the ACM are discussed for the implementation of this selective technique, including the hanging nodes. Meanwhile, the gathering and scattering steps of the PIC simulation also need to be appropriately performed on the ACM. The PPR method is a generic gradient recovery technique to be incorporated into the IFE-PIC method for more accurate force deposition on the ACM. In addition, two other algorithmic structures of the traditional IFE-PIC method have been modified to accommodate the ACM in the simulation, including a new mapping array structure for the particle positioning and a new charge deposition with some special particle positions in the ACM. As a result, the integrated immersed-selective-discontinuous-Galerkin particle-in-cell (ISDG-PIC) method can efficiently perform the plasma-material interactions simulation on the Cartesian meshes with local mesh refinement independent of the interface. Several numerical experiments are performed to demonstrate the convergence, efficiency, and applicability of the proposed ISDG-PIC method. • Immersed-selective-discontinuous-Galerkin particle-in-cell (ISDG-PIC) method. • Polynomial preserving recovery (PPR) method. • A new mapping array structure for the particle positioning. • A new charge deposition with some special particle positions in the adaptive Cartesian meshes. • A series of numerical examples for validation. [ABSTRACT FROM AUTHOR]

[Display omitted] • An implicit solvent/implicit surface model parameterization for gold surface. • Adsorption free energy calculation for amino acids using molecular dynamics (MD). • In silico evaluation of free energy of adsorption for the set of peptides and gold. • Comparison and discussion of results obtained with experimental data. The interaction of proteins and peptides with inorganic surfaces is relevant in a wide array of technological applications. A rational approach to design peptides for specific surfaces would build on amino-acid and surface specific interaction models, which are difficult to characterize experimentally or by modeling. Even with such a model at hand, the large number of possible sequences and the large conformation space of peptides make comparative simulations challenging. Here we present a computational protocol, the effective implicit surface model (EISM), for efficient in silico evaluation of the binding affinity trends of peptides on parameterized surface, with a specific application to the widely studied gold surface. In EISM the peptide surface interactions are modeled with an amino-acid and surface specific implicit solvent model, which permits rapid exploration of the peptide conformational degrees of freedom. We demonstrate the parametrization of the model and compare the results with all-atom simulations and experimental results for specific peptides. [ABSTRACT FROM AUTHOR]

[Display omitted] • Al 2 O 3 sites around atomically dispersed Rh functionalized by octylphosphonic acids. • Functionalization decreases CO desorption free energy and promotes hydroformylation. • Eyring analyses suggest influence on kinetics through modified activation entropies. • Altered activation entropies due to lower initial state mobility of Rh(CO) 2 on Al 2 O 3. • Approach allows for deviation from enthalpy-entropy compensation. Oxide supported atomically dispersed late transition metal catalysts exhibit unique catalytic reactivity and selectivity compared to metal clusters. For this class of catalysts, efforts have been devoted to understand how variations in the active site or support composition influence catalytic properties. Here, we examine the influence of phosphonic acid functionalization of γ-Al 2 O 3 surrounding atomically dispersed Rh active sites on their chemical and catalytic reactivity. It was observed that support functionalization modifies the activation entropies of elementary steps (CO desorption) and catalytic cycles (ethylene hydroformylation) on atomically dispersed Rh sites, with minimal influence on reaction enthalpies. Changes in activation entropy were attributed to support functionalization causing a decrease in the translational degrees of freedom associated with mobile atomically dispersed Rh(CO) 2 species on the γ-Al 2 O 3 support. Changes to the activation entropies on functionalized catalysts caused increases in turn over frequencies and selectivity for ethylene hydroformylation in gas phase steady state conditions. The observed breaking of enthalpy–entropy compensation suggests that support functionalization may enable tuning of catalytic reactivity beyond the confines of linear free relationships for catalysts consisting of mobile active sites. [ABSTRACT FROM AUTHOR]

This paper deals with three degrees of freedom Hamiltonian system in the case that the frequencies of the linearization are in 1:2:3 resonance. We obtain the truncated second order normal form expressed with the basic invariants. Also, we identify the coefficients of the terms that remain in normalization procedure. We concentrate on determining the relative equilibria with or without considering a perturbation in frequencies. By a homogeneous structure, all relative equilibria are computed and the linear stability of isolated relative equilibria is investigated. Especially we find some parametric manifold of relative equilibria and a quintic polynomial which determines relative equilibria. [ABSTRACT FROM AUTHOR]

An approximation of a Generalized Langevin equations with small mass and randomly fast oscillation is derived. By some bounded estimates and a diffusion approximation the limiting equation is shown to be stochastic partial differential equations (SPDEs) driven by white noise. [ABSTRACT FROM AUTHOR]

A quantum phase space version of the continuity equation for systems with internal degrees of freedom is derived. The 1-D Dirac equation is introduced and its phase space counterpart is found. The phase space representation of free motion and of scattering in a nonrelativistic and relativistic case for setups with internal degrees of freedom is discussed and illustrated. Properties of Wigner functions of unbound states are analysed. • Discrete phase space quantum mechanics is discussed. • 1-D scattering processes in frames of phase space quantum theory are analysed. • Properties of interference terms between spatially separated components of Wigner function are derived. [ABSTRACT FROM AUTHOR]

Control volume analysis models physics via the exchange of generalized fluxes between subdomains. We introduce a scientific machine learning framework adopting a partition of unity architecture to identify physically-relevant control volumes, with generalized fluxes between subdomains encoded via Whitney forms. The approach provides a differentiable parameterization of geometry which may be trained in an end-to-end fashion to extract reduced models from full field data while exactly preserving physics. The architecture admits a data-driven finite element exterior calculus allowing discovery of mixed finite element spaces with closed form quadrature rules. An equivalence between Whitney forms and graph networks reveals that the geometric problem of control volume learning is equivalent to an unsupervised graph discovery problem. The framework is developed for manifolds in arbitrary dimension, with examples provided for H (div) problems in R 2 establishing convergence and structure preservation properties. Finally, we consider a lithium-ion battery problem where we discover a reduced finite element space encoding transport pathways from high-fidelity microstructure resolved simulations. The approach reduces the 5.89M finite element simulation to 136 elements while reproducing pressure to under 0.1% error and preserving conservation. • Partition of unity architecture learns physically-relevant control volumes from data. • Machine-learned Whitney forms preserve underlying topological structure. • Learned models exhibit algebraic convergence comparable to FEM methods. • Learned models reduce degrees of freedom by 40000x for lithium-ion battery problem. [ABSTRACT FROM AUTHOR]

This paper aims to extend the definition of complexity for a self-gravitating system in f (R , T) theory. We take a static sphere and calculate the corresponding modified field equations as well as the mass function in terms of an effective energy density. The Schwarzschild exterior metric is then taken to determine the junction conditions at the hypersurface. We break the Riemann curvature tensor orthogonally and obtain four scalar functions. We observe that only Y T F involves the key factors which determine the structural complexity, thus we call it the complexity factor. Moreover, the field equations contain extra degrees of freedom, thus we require some constraints to close the system. We take the complexity-free condition along with four constraints leading to different models. A particular model is chosen to analyze physical attributes of the resulting solutions for multiple values of the model parameter. It is concluded that the solutions corresponding to P r = 0 , a polytropic as well as a linear equation of state show stable behavior for particular values of the model parameter. • Extend the definition of complexity for a self-gravitating system in f (R , T) theory. • We break the Riemann curvature tensor orthogonally and obtain four scalar functions. • We take the complexity-free condition along with four constraints leading to different models. • We conclude that solutions corresponding to particular constraints show stable behavior. [ABSTRACT FROM AUTHOR]