Uncoupled System Research Articles

Theoretical and experimental analysis of a nonlinear vibro-acoustic energy sink

This study is concerned with the experimental and theoretical analysis of a vibroacoustic nonlinear system devoted to absorption application. Based on the nonlinear energy sink principle, the dynamics of the system is reduced to two coupled degrees of freedom, one of which exhibits nonlinear behavior due to a large displacement mechanism. The set-up allows for precisely characterizing the nonlinear function of the mechanical system, first uncoupled and then coupled with an acoustic and linear resonator. Continuation procedures are performed experimentally and numerically, respectively using a phase-locked loop (PLL) and the asymptotic numerical method implemented in the MANLAB software package. The comparison between theoretical predictions and experimental results obtained on the uncoupled system allows for a parameter identification of the nonlinear resonator. Measurements on the coupled system highlight the energy pumping phenomenon, which can be predicted from numerical predictions in which identified parameters are introduced. The procedure aims at proposing analytical models for achieving efficient level attenuation, and providing design guidelines for sound reduction at high levels in confined spaces.

Investigation of a high-performance control algorithm for a unified chaotic system synchronization control based on parameter adaptive method

With the rapid development of computer technology, parameter adaptive control methods are becoming more and more widely used in nonlinear systems. However, there are still many problems with synchronous controllers with multiple inputs and a single output, uncertainty, and dynamic characteristics. This paper analyzed a synchronization control strategy of uncoupled nonlinear systems based on parameter dynamic factors to adjust the performance of the synchronization controller, and briefly introduced the manifestations of chaotic motion. The characteristics and differences of continuous feedback control methods and transmission and transfer control methods were pointed out. Simple, effective, stable, and feasible synchronous control was analyzed using parameter-adaptive control theory. By analyzing the non-linear relationships between various models at different orders, the fuzzy distribution of the second-order mean and their independent and uncorrelated matrices were obtained, and their corresponding law formulas were established to solve the functional expression between the corresponding state variables and the dynamic characteristics of the system. The error risk test, computational complexity test, synchronization performance score test, and chaos system control effect score test were carried out on the control algorithms of traditional chaos system synchronization methods and chaos system synchronization methods based on parameter adaptive methods. Parameter adaptive methods were found to effectively reduce the error risk of high-performance control algorithms for synchronization of the unified chaos system. The complexity of the calculation process was simplified and the complexity score of the calculation process was reduced by 0.6. The application of parameter adaptive methods could effectively improve the synchronization performance of control algorithms, and the control effectiveness rating of control algorithms was improved. The experimental test results proved the effectiveness of control algorithms, which greatly enriched the field of modern control applications and also drove the vigorous development of nonlinear dynamics research, thus making significant progress in chaos application research.

Coupled Meteo–Hydrodynamic Approach in Semi-Enclosed Basins and Sensitivity Assessment of Wind-Driven Current

A coupled numerical approach that combines the WRF model and the Mike 3 (DHI) hydrodynamic model was developed and applied in two semi-enclosed basins in the Ionian Sea (Italy) to assess the wind-driven current. To gain a better understanding of how the sea current field can vary depending on meteorological data forcing, three different scenario were set up. The sensitivity of the sea current pattern was investigated as a function of the type of meteorological forcing and appreciating the differences in the results. The aims of this study are threefold. Firstly, we wish to define an ad hoc procedure to join the model-computed meteorological parameters in the hydrodynamic model. Secondly, we will investigate the feedback from the Mar Piccolo and Mar Grande basins in the Ionian Sea using fully coupled simulations and an uncoupled system where the atmospheric parameters are derived from a ground station. Finally, we will evaluate the results achieved by applying two scenarios of typical meteorological conditions to the study site. The model results highlighted the variability of sea currents depending on meteorological forcing.

High-fidelity single logical qubit encoding scheme assisted by single-sided quantum dot-cavity systems.

We present an encoding scheme of a single logical qubit with single-sided quantum dot (QD)-cavity systems, which is immune to the collective decoherence. By adjusting the Purcell factor to satisfy the balanced reflection condition, the detrimental effects of unbalanced reflection between the coupled and uncoupled QD-cavity systems can be effectively suppressed. Furthermore, the fidelity of each step can be increased to unity regardless of the strong coupling regime and the weak coupling regime of cavity quantum electrodynamics (QED) with the assistance of waveform correctors. The scheme requires QD-cavity systems and simple linear optical elements, which can be implemented with the currently experimental techniques.

An Analytical Study of Suspension Bridge Collapse Based on the Characteristics of the Eigen Values

This research discusses an analytical approach to suspension bridge accidents focusing on eigenvalue characteristics. This research uses eigenvalue analysis to explore patterns that may contribute to bridge structural failure. The analysis steps include reducing the model to an uncoupled and linear system, as well as determining homogeneous and non-homogeneous solutions, which helps identify accident-prone patterns. The analysis results also reveal significant differences in dynamic characteristics between safe bridges and those that experience accidents. This research highlights the importance of a deep understanding of eigenvalues in designing, maintaining, and managing suspension bridges. The implication of this research is the development of more effective prevention strategies to improve suspension bridge safety in the future. By analyzing eigenvalues, this research provides deep insight into the factors that influence the stability of suspension bridges. These findings provide a strong foundation for developing recommendations for more effective design, maintenance, and management of suspension bridges. The conclusions of this research can help improve the safety and reliability of suspension bridges worldwide and contribute to civil engineering and infrastructure security.

Seismic response analysis of single‐degree‐of‐freedom structure coupled with tuned self‐centering wall

AbstractThis paper investigates the possibility of using self‐centering walls (SCWs) as tuned mass dampers (TMDs) to control the seismic response of structures. The basic characteristics of this system are investigated using a two‐degree‐of‐freedom (2‐DOF) model, representing the main structure as a single‐degree‐of‐freedom (SDOF) oscillator interconnected with an SCW through viscous and elastic devices. The nonlinear equations of motion for the proposed coupled system are derived and then utilized to determine the displacement amplification response. The coupling parameters are optimized to minimize the dynamic response of the oscillator using a numerical method. A simulation study is conducted to investigate the response of the proposed system by considering six recorded earthquakes. Several parameters are studied, including the mass ratio, the influence of prestressing, and the slenderness angle of the wall. The displacement spectra are generated using the optimized parameters and compared to those of the uncoupled system and the traditional coupled system, which features a rigid connection between the structure and the wall. The results reveal that the proposed system effectively suppresses both maximum and root mean square responses of structures, outperforming the traditional coupled system in most cases. Improved performance for the proposed system can be achieved by increasing the wall's mass ratio and decreasing the slenderness angle. Moreover, prestressing has an adverse impact on the system's displacement response. Finally, the influence of wall flexibility is examined using a finite element model, revealing a minimal effect on the system's response.

Nonlinear dynamics of magnetically coupled double beam based piezoelectric energy harvester under galloping excitation

This paper presents a magnetically coupled double cantilever beam-based piezoelectric energy harvester. Two square-shaped bluff bodies are attached to the tip of the beams to induce galloping-based oscillation in the proposed system. Spatio-temporal electro-mechanical equations of motion are developed using the Lagrange principle and discretized to their temporal form using generalized Galerkin’s method. 4th order Runge-Kutta method-based MATLAB solver (ode45) is used to solve these equations of motion and obtain numerical results. A prototype of the system is developed and experimented in a wind tunnel to support the numerical findings. Three wind speed regions (light air, light breeze, and gentle breeze) based on the Beaufort wind force scale are considered for getting a detailed insight into the system dynamics. Periodic, quasi-periodic, and chaotic oscillations are observed depending on different coupling conditions and wind speeds. Typical hopf bifurcation, Torus 3 bifurcations occur in the system due to galloping and magnetic repulsive force. Parametric studies are conducted for each wind speed region considering the load resistances and distance between the permanent magnets. Significant improvement in power output can be found for light air and gentle breeze regions with the magnetically coupled system than the uncoupled system (without magnetic interaction), whereas the uncoupled system performs better in the light breeze region.

Enhanced Temperature Sensing by Multi‐Mode Coupling in an On‐Chip Microcavity System

AbstractThe microcavity is a promising sensor platform, but any perturbation will disturb its linewidth, cause resonance shift or splitting. However, such sensing resolution is limited by the cavity's optical quality factor and mode volume. Here, an on‐chip integrated microcavity system is proposed and demonstrated that the resolution of a self‐referenced sensor can be enhanced with multi‐mode coupling. In experiments, inter‐mode coupling strength is carefully optimized with a pulley waveguide and observed a resolution improvement of nearly 3 times in the frequency domain. While experiencing small refractive index change tuned by temperature, mode‐coupled system shows a 7.2 times sensitivity enhancement that is than the uncoupled system on the same chip and a very significant lineshape contrast ratio change as great reference for minor frequency shifts. This approach will help design microcavity sensors to improve detection sensitivity and resolution under limited manufacture precision.

The dual nature of biomimetic melanin.

Melanin-inspired nanomaterials offer unique photophysical, electronic and radical scavenging properties that are widely explored for health and environmental preservation, or energy conversion and storage. The incorporation of functional melanin building blocks in more complex nanostructures or surfaces is typically achieved via a bottom-up approach starting from a molecular precursor, in most cases dopamine. Here we demonstrate that indeed, the oxidative polymerization of dopamine, for the synthesis of melanin-like polydopamine (PDA), leads to the simultaneous formation of more than one nanosized species with different compositions, morphologies and properties. In particular, a low-density polymeric structure and dense nanoparticles (NP) are simultaneously formed. The two populations could be separated and analyzed in real time using a chromatographic technique free of any stationary phase (flow field fractionation, FFF). The results following the synthesis of melanin-like PDA showed that the NP are formed only during the first 6 hours as a result of a supramolecular self-assembly-driven polymerization, while the formation of the polymer continues for about 36 hours. The two populations were also separated and characterized using TEM, UV-vis absorption spectroscopy, fluorescence and light scattering spectroscopy, DLS, FTIR, ζ-potential measurements, gel electrophoresis and pH titrations. Interestingly, very different properties between the two populations were observed: in particular the polymer contains a higher number of catechol units (8 mmol g-1 -OH) with respect to the NP (1 mmol g-1 -OH) and presents a much higher antioxidant activity. The attenuation of light by NP is more efficient than that by the polymer especially in the Vis-NIR region. Moreover, while the NP scatter light with an efficiency up to 27% they are not fluorescent, and the polymer does not scatter light but shows an excitation wavelength-dependent fluorescence typical of multi-fluorophoric uncoupled systems.

Artificial neural network-based prediction model of elastic floor response spectra incorporating dynamic primary-secondary structure interaction

The evaluation of the Floor Response Spectrum (FRS) holds paramount significance in assessing the seismic behavior of secondary structures. Precise FRS prediction empowers engineers to make informed decisions concerning structural design, retrofitting, and safety precautions. This study aims to scrutinize the impact of dynamic interaction between primary and secondary structures on FRS. Both the elastic primary structure (PS) and elastic secondary structure (SS) employ a single-degree-of-freedom (SDOF) system. Governing motion equations for both coupled (with dynamic interaction) and uncoupled (without dynamic interaction) systems are formulated and solved numerically. The study investigates how variations in the vibration period of PS (Tp), tuning ratio (Tr), mass ratio (μ), and damping ratio (ξs) of SS influence FRS. The FRS impact remains minimal at μ = 0.001 (0.1%); however, with increasing mass ratio, PS-SS dynamic interaction significantly affects SS's spectral acceleration response. Coupled analysis is crucial only for secondary structures tuned to the primary structure's vibration period (0.8≤Tr≤1.2). This study utilizes two-layer feed-forward Artificial Neural Networks (ANNs) for FRS prediction. The Levenberg-Marquardt (LM) backpropagation (BP) algorithm trains the network using a comprehensive dataset. In summary, it is evident that the ANNs, once trained, enable accurate prediction of the FRS, exhibiting a R2 of 99%. Additionally, a design expression is formulated utilizing the ANN model and subsequently compared with the existing formulation.

Comparison of different coupling variants for building and HVAC simulation

Coupled building and HVAC simulations applying the FMI standard promise many advantages in terms of system design and optimisation. In this paper, a systematic analysis of possible options for such couplings is presented. For one of these options, a case study is carried out where a quantitative comparison between the uncoupled reference system and the corresponding coupled system with different communication step sizes is carried out. Based on the simulation results, recommendations and challenges for such couplings are derived. In particular, the correlation between the communication step size of the FMUs and the computing time, as well as the deviations of the simulation results compared to the results of an uncoupled simulation are analysed.

Multivariable non-singular terminal composite sliding mode control of gas-water-coal mixture lifting system

In order to ensure the stability of flow rate and valve pressure difference during gas-water-coal mixture lifting, a multivariable non-singular terminal composite sliding mode (MNTCSM) controller based on accurate feedback linearization is proposed. The multi-input multi-output nonlinear system with time delay and coupling is transformed into a multi-input multi-output uncoupled linear system by using an improved Smith predictor and accurate feedback linearization. At the same time, the MNTCSM controller is designed to make the flow and pressure tracking errors of the decoupling system converge to zero in a finite time. Finally, simulations and experiments are designed for different control methods to verify the feasibility and effectiveness of the proposed scheme.

Polaritonic linewidth asymmetry in the strong and ultrastrong coupling regime.

The intriguing properties of polaritons resulting from strong and ultrastrong light-matter coupling have been extensively investigated. However, most research has focused on spectroscopic characteristics of polaritons, such as their eigenfrequencies and Rabi splitting. Here, we study the decay rates of a plasmon-microcavity system in the strong and ultrastrong coupling regimes experimentally and numerically. We use a classical scattering matrix approach, approximating our plasmonic system with an effective Lorentz model, to obtain the decay rates through the imaginary part of the complex quasinormal mode eigenfrequencies. Our classical model automatically includes all the interaction terms necessary to account for ultrastrong coupling without dealing with the rotating-wave approximation and the diamagnetic term. We find an asymmetry in polaritonic decay rates, which deviate from the expected average of the uncoupled system's decay rates at zero detuning. Although this phenomenon has been previously observed in exciton-polaritons and attributed to their disorder, we observe it even in our homogeneous system. As the coupling strength of the plasmon-microcavity system increases, the asymmetry also increases and can become so significant that the lower (upper) polariton decay rate reduction (increase) goes beyond the uncoupled decay rates, γ - < γ 0,c < γ +. Furthermore, our findings demonstrate that polaritonic linewidth asymmetry is a generic phenomenon that persists even in the case of bulk polaritons.

Fast method for the determination of radiation-relevant eigenmodes of underwater structures when using FEM shell elements (“modal reduction”)

A self-developed code based on the BEM for the determination of the backscattered sound pressure level in the far field was extended so that additional FEM shell elements and thus elastic material properties can be considered. For this purpose, a separate FEM equation system is built up and directly integrated into the system of the BEM via corresponding transformation matrices. A common variant for solving the FEM-specific parts is to use a solver based on eigenvalue calculations, which provides the corresponding eigenfrequencies and eigenvectors of the uncoupled FEM equation system for a given upper cutoff frequency. It can be observed that only a part of the determined modes has a considerable sound radiation efficiency and is therefore relevant for the result. An algorithm determines these modes by a fast post-processing routine considering a given percentage, reduces the size of the eigenvalue equation system accordingly, and thus shortens the solution time. Furthermore, it was investigated whether the condition of the entire system of equations is improved by removing the irrelevant modes when using iterative solution methods and whether the number of iterations can thus be reduced. The paper describes the basics of FEM coupling with BEM, presents the reduction algorithm used and shows the results obtained for corresponding test structures depending on the reduction percentage used.

Quantitative Analyses of Coupling in Hybrid Zones.

In hybrid zones, whether barrier loci experience selection mostly independently or as a unit depends on the ratio of selection to recombination as captured by the coupling coefficient. Theory predicts a sharper transition between an uncoupled and coupled system when more loci affect hybrid fitness. However, the extent of coupling in hybrid zones has rarely been quantified. Here, we use simulations to characterize the relationship between the coupling coefficient and variance in clines across genetic loci. We then reanalyze 25 hybrid zone data sets and find that cline variances and estimated coupling coefficients form a smooth continuum from high variance and weak coupling to low variance and strong coupling. Our results are consistent with low rates of hybridization and a strong genome-wide barrier to gene flow when the coupling coefficient is much greater than 1, but also suggest that this boundary might be approached gradually and at a near constant rate over time.

Wind induced coupling effects of transmission tower-line system at microtopography

The coupled and uncoupled Dynamic Finite Element Models (DFEMs) of the transmission tower-line system consisting of two towers and three spans of conductors and ground wires were built at the windward and crosswind slope of a cosinoidal hill. The acceleration ratios of mean wind profiles of cosinoidal mountains were summarized from previous studies, then the mean wind profile over the windward, crosswind and leeward slopes were revised. The wind loads acting on the transmission tower-line system were calculated based on the revised profile. The wind-induced dynamic responses of the coupled and uncoupled DFEMs were detected, and the coupling effects on reaction force of hanging points, displacements and accelerations at the tower top, axial forces of main rods and wind-induced vibration coefficients were analysed. The results show that due to the lack of the TMD-like effect, the uncoupled system is more sensitive to wind load and has significant wind-induced vibration compared to the coupled system, making the three-dimensional force of the hanging point, displacements and accelerations at the tower top, axial forces of main rods increasing, but the wind-induced vibration coefficients change little. Generally, the coupling effects of the tower-line system are significant. Ignoring it will make the structural design of transmission towers conservative.

(Invited) Coupled Quantum Emitters in Carbon Nanotubes

The development of covalent diazonium functionalization of carbon nanotubes brings unique opportunities in terms of original quantum sources of light. In particular, it should be possible to create a linear ensemble of closely packed single-photon sources along the carbon nanotube backbone. The physical proximity of several dopants would make it possible to couple them simultaneous to a resonant cavity mode and to induce original dynamics and light emission properties. Here, we investigate experimentally the case of a series of four quantum emitters attached to the same carbon nanotube coupled to a high finesse fiber cavity. We explore their properties through PLE, polarization and super-localization measurements and their light emission properties using time-correlation techniques and photo-luminescence decay measurements. We show that two pairs show qualitatively different behaviors in terms of spectral diffusion and luminescence saturation, which we interpret using two models of electronically coupled or uncoupled two-level systems.

Driveline System Effects on Powertrain Mounting Optimization for Vibration Isolation under Actual Vehicle Conditions

&lt;div&gt;Vehicle vibration is the key consideration in the early stage of vehicle development. The most dynamic system in a vehicle is the powertrain system, which is a source of various frequency vibration inputs to the vehicle. Mostly for powertrain mounting system design, only the uncoupled powertrain system is considered. However, in real situations, other subsystems are also attached to the powertrain unit. Thereby, assuming only the powertrain unit ignores the dynamic interactions among the powertrain and other systems. To address this shortcoming, a coupled powertrain and driveline mounting system problem is formulated and examined. This 16 DOF problem is constructed around a case of a front engine-based powertrain unit attached to the driveline system, which as an assembly resting on other systems such as chassis, suspensions, axles, and tires. First, the effect of a driveline on torque roll axis and other rigid body modes decoupling is examined analytically in terms of eigensolutions and frequency responses. It is observed from the analysis that when the optimized uncoupled powertrain system is introduced in real vehicle conditions, the vibration isolation level of the powertrain mountings gets degraded. Then, a new improved approach of considering coupled powertrain and driveline systems in the initial design phase itself is proposed. The mounting system parameters such as mount location, mount orientation angle, and stiffness rate are optimized and redesigned for the proposed system. The results of the redesigned system show that the decoupling of the rigid body mode parameters is improved and consequently powertrain vibration performance is also improved in static and dynamic conditions of the vehicle. Overall, the findings of this study suggest that considering the driveline along with the powertrain as a coupled system at the early phase of the mounting system design itself improves the vibration performance of the vehicle during real-life situations.&lt;/div&gt;

Uncoupling Techniques for Multispecies Diffusion–Reaction Model

We consider the multispecies model described by a coupled system of diffusion–reaction equations, where the coupling and nonlinearity are given in the reaction part. We construct a semi-discrete form using a finite volume approximation by space. The fully implicit scheme is used for approximation by time, which leads to solving the coupled nonlinear system of equations at each time step. This paper presents two uncoupling techniques based on the explicit–implicit scheme and the operator-splitting method. In the explicit–implicit scheme, we take the concentration of one species in coupling term from the previous time layer to obtain a linear uncoupled system of equations. The second approach is based on the operator-splitting technique, where we first solve uncoupled equations with the diffusion operator and then solve the equations with the local reaction operator. The stability estimates are derived for both proposed uncoupling schemes. We present a numerical investigation for the uncoupling techniques with varying time step sizes and different scales of the diffusion coefficient.

Uncoupling system and environment simulation cells for fast-scaling modeling of complex continuum embeddings.

Continuum solvation models are becoming increasingly relevant in condensed matter simulations, allowing to characterize materials interfaces in the presence of wet electrified environments at a reduced computational cost with respect to all atomistic simulations. However, some challenges with the implementation of these models in plane-wave simulation packages still persists, especially when the goal is to simulate complex and heterogeneous environments. Among these challenges is the computational cost associated with large heterogeneous environments, which in plane-wave simulations has a direct effect on the basis-set size and, as a result, on the cost of the electronic structure calculation. Moreover, the use of periodic simulation cells is not well-suited for modeling systems embedded in semi-infinite media, which is often the case in continuum solvation models. To address these challenges, we present the implementation of a double-cell formalism, in which the simulation cell used for the continuum environment is uncoupled from the one used for the electronic-structure simulation of the quantum-mechanical system. This allows for a larger simulation cell to be used for the environment, without significantly increasing computational time. In this work, we show how the double-cell formalism can be used as an effective periodic boundary conditions correction scheme for nonperiodic and partially periodic systems. The accuracy of the double-cell formalism is tested using representative examples with different dimensionalities, both in vacuum and in a homogeneous continuum dielectric environment. Fast convergence and good speedups are observed for all the simulation setups, provided the quantum-mechanical simulation cell is chosen to completely fit the electronic density of the system.