Dynamic Characteristics Of System Research Articles

Dynamic modeling and analysis of two-span rotor-pedestal system with bearing tilt and extended defect: Simulation and experiment

When the rolling bearing raceway is tilted, the contact load of the raceway increases, which may greatly increase the occurrence of raceway defects. However, the evolution law of the raceway defect extension process on the system dynamic characteristics is not clear when the bearing is tilted. In this paper, considering the influence of rough surface caused by the extension of bearing defects, a mathematical model of raceway extension defects which is more consistent with the actual morphology is proposed. The model can be used to evaluate the damage degree of the bearing raceway of rotating machinery. Taking the two-span rotor-bearing-pedestal system of the test rig as the research object, a nonlinear dynamic model of the system is established considering the nonlinear supporting force of bearings and pedestal, shaft coupling looseness and other nonlinear factors. The effectiveness of the bearing fault characterization model and the system dynamics model is verified by experiments. On this basis, the influence of tilt on bearing fault and the change rule of raceway defect extension on bearing contact characteristics and system dynamic characteristics are discussed. The results indicate that raceway tilt aggravates system vibration caused by the bearing defect. With the increase of the defect range, the impact vibration characteristics weaken, and the roughness of the raceway surface in the defect area has a great influence. However, with the increase of defect depth, the influence law is just the opposite. The research results are expected to provide theoretical support for bearing fault diagnosis of rotating machinery systems.

Cyberphysical System Modeled with Complex Networks and Hybrid Automata to Diagnose Multiple and Concurrent Faults in Manufacturing Systems

Cyber–physical systems use digital twins to provide advanced monitoring and control functions, including self-diagnosis. The digital twin is often conceptualized as a 3D model, but mathematical models implemented in numerical simulations are required to reproduce the dynamical and functional characteristics of physical systems. In this work, a cyber–physical system scheme is proposed to monitor and diagnose failures. The virtual system, embedded at the supervisory control level, combines concepts from complex networks and hybrid automata to detect failures in the hardware components and in the execution of the sequential logic control. An automated storage and retrieval system is presented as a case study to show the applicability of the proposed scheme. The functional test and the obtained results validate the implemented system that is shown to be capable of fault diagnosis and location in real time. The online execution of the digital twin present several advantages for diagnosing multiple concurrent failures in sensors, actuators, and the control unit. This approach can be incorporate into diverse manufacturing systems.

Time-varying mechanism of fluid-structure interaction vibration effects and dynamic characteristics of the cross-over pipeline when the medium flows

The time-varying mechanism of fluid-structure interaction (FSI) vibration effects and dynamic characteristics of the cross-over pipeline with the flowing of the crude and natural gas mixture two-phase medium were revealed in this study. An active fluid finite element method (FEM) model was built for the medium that exhibited a volume ratio 1:1 and flowed through the pipeline under a velocity of 2 m/s. The standard turbulence κ-ε model was modified by incorporating the flow velocity and pressure fluctuation changes with the floating of the medium. The pipeline's FSI vibration effects and the pipeline-crossing system's dynamic characteristics were determined and then analyzed. As indicated by the research results, the medium was affected by frictional damping at the pipeline wall and energy transfer losses at the phase interface, such that irregular flow regimes were generated (i.e., slug flow and wavy flow). The flow velocity was further reduced in the 280 s, and the intervals between pressure fluctuations gradually increased. The FSI vibration effects in the middle section of the cross-over pipeline were significant, with a peak displacement response reaching 45.7538 mm while the medium flow. Notable differences and complex changes were identified in the acceleration response among the monitoring sections of the first and second spanning sections. The dynamic properties of the pipeline-crossing system changed significantly with time. The natural frequencies of the 1st to 7th modes decreased with time.In contrast, the natural frequencies of the 8th to 12th modes tended to decline with complex time-varying characteristics more notably. The methods in the respective direction exhibited time-varying characteristics. Specifically, their relative proportions of the effective mass ratio varied with time. As the research concludes, The research concludes that the flowing mechanical behavior can be more accurately expressed by modifying the standard κ-ε turbulence model using the medium's velocity changes and pressure fluctuation curves. This study can lay a theoretical foundation for gaining insights into the time-varying mechanism of the FSI vibration effects and dynamic characteristics in the cross-over pipeline.

Dynamic characteristics of a rod-fastening rotor system with tie rod bolt loosening

Dynamic characteristics of a rod-fastening rotor system with tie rod bolt loosening

Chaos and multi-layer attractors in asymmetric neural networks coupled with discrete fractional memristor

This article introduces a novel model of asymmetric neural networks combined with fractional difference memristors, which has both theoretical and practical implications in the rapidly evolving field of computational intelligence. The proposed model includes two types of fractional difference memristor elements: one with hyperbolic tangent memductance and the other with periodic memductance and memristor state described by sine functions. The authenticity of the constructed memristor is confirmed through fingerprint verification. The research extensively investigates the dynamics of a coupled neural network model, analyzing its stability at equilibrium states, studying bifurcation diagrams, and calculating the largest Lyapunov exponents. The results suggest that when incorporating sine memristors, the model demonstrates coexisting state variables depending on the initial conditions, revealing the emergence of multi-layer attractors. The article further demonstrates how the memristor state shifts through numerical simulations with varying memductance values. Notably, the study emphasizes the crucial role of memductance (synaptic weight) in determining the complex dynamical characteristics of neural network systems. To support the analytical results and demonstrate the chaotic response of state variables, the article includes appropriate numerical simulations. These simulations effectively validate the presented findings and provide concrete evidence of the system’s chaotic behavior.

Application of inertia emulation control strategy with energy storage system in multi-area hydro -thermal system using a novel metaheuristic optimized tilt controller

This article presents the application of a novel artificial hummingbirds’ algorithm (AHA) based tilt-integral second order of double-derivative controller (TIDD2) in a three-area hydro-thermal power system. Also, the inertia emulation control strategy has been incorporated using various energy storage systems (ESS) to established the frequency in interconnected power system. The supremacy of the proposed controller is established by comparing the system dynamic response with some existing controllers, such as proportional-integral-derivative (PID), tilt-integral-derivative (TID) and cascade of IDD - PID controllers. The fruitfulness of proposed AHA has also been evaluated with system dynamic and convergence characteristics comparison over some of existing metaheuristic optimization techniques such as harris hawk's optimization (HHO) and bird swarm algorithm (BSA). Further, effect of random load pattern (RLP), communication time delay (CTD) and variable CTD on the system dynamic is analyzed. The study of inertia emulation control strategy in a multi-area interconnected power system revealed that, when inertia is emulated with superconducting magnetic energy storage (SMES), the system dynamic exhibits better performance over battery energy storage (BES) and ultra-capacitor (UC). Furthermore, the proposed systems are validated in a real-time environment using OPAL-RT lab software. Also, the scalability of the proposed method is evaluated by using eigenvalue analysis.

An infrared stealth spherical target simulation device and its surface temperature control algorithm

This paper presents a simulation device for infrared stealth spherical target and a feedforward temperature compensation algorithm for its surface temperature. A three-dimensional model and a mathematical model based on heat transfer equation are established. Experimental data from three different spherical targets is used to calculate feedforward compensation and obtain a detailed control law. Experiments verify the reliability of the mathematical model and the accuracy of the temperature control algorithm. The algorithm can control the surface temperature of the spherical target within ±2 °C and has good system dynamic characteristics.

Theoretical modeling and experimental test for dynamic characteristics of an air-spring vibration isolation system

Theoretical modeling and experimental test for dynamic characteristics of an air-spring vibration isolation system

Insight on uncertainty of geometrically nonlinear rotor with rub-impact under maneuvering motion

Maneuvering motion inevitably leads to parametric excitations and inertial forces, which greatly aggravates the whirling motion of rotor system and then induces rub-impact fault between rotor and stator. Under this circumstance, rotor dynamic analysis under maneuvering conditions is of considerable importance for safe and efficient functioning of rotating machinery. Furthermore, the uncertainties are inherently present in mechanical systems due to wear, properties variations and working condition evolutions. The main objective of this paper is to investigate the nonlinear characteristics and interval responses of deterministic and uncertain rotor systems under maneuvering motion. Due to whirling motion with large amplitude, the geometrical nonlinearity of shaft and rub-impact nonlinearity are considered in the rotor system. Then the equations of motion of deterministic rotor system with rub-impact under maneuvering motion are theoretically derived according to the Lagrange's equation. On this basis, the parametric uncertainties of disk eccentricity and flight maneuvers involved in the rotor system are described by the Chebyshev interval algorithm. After that the nonlinear dynamic characteristics of deterministic rotor system under maneuvering motion are numerically solved and analyzed in terms of bifurcation diagram, time histories, whirling orbit, Poincaré map and frequency spectrum. Additionally, the interval responses of vibration displacement and impact force at different rotational speeds are further examined.

Effect of Material Damping Characteristics on Dynamic Analysis of Rotor-Bearing Systems

Dynamical behaviour of rotor-bearing systems is significantly influenced by a large number of parameters related to rotor, disk and bearing. However, inherent material damping. parameters of rotor play an important role on dynamic characteristics of rotor-bearing systems. Conventional transfer matrix method is modified by incorporating viscous and hysteretic form of internal damping parameters of rotor in the analysis. A three-disks rotor system mounted on rigid supports as welL as on flexible bearings is taken as a physical model to demonstrate the effects of damping on dynamic characteristics of the system. The viscous damping of the rotor system diminishes the dynamic response where as the hysteretic form of damping always destabilises the system.

Dynamic scaling design strategy of discontinuous bolted rotor systems based on bidirectional parameter mapping

Rods fastened rotor system are widely used in heavy-duty gas turbines. The contact nonlinearity and discontinuity induced by bolted rotor structures, make it difficult to design a scaled rotor system accurately. Thus, a dynamic scaling design strategy for discontinuous bolted rotor systems is proposed in this paper. An improved continuous modeling method considering rods deformation based on equivalent material layer (EML) is introduced to reflect the weakening effect of the rotor stiffness with bolted structure, and the parameter mapping relationships between the continuous and the discontinuous structure are constructed. The scaling factors of each element of the rotor system are derived by the similarity theory. Through this approach, a discontinuous rotor system can be scaled, demonstrating a high level of consistency with the prototype in terms of natural frequencies, critical speeds as well as frequency response. In addition, modal experiments under different preloads and dynamic acceleration experiment are carried out to verify of the proposed modeling method for discontinuous rotor structures. The testing and simulation results prove that the introduced equivalent material layer reflects the contact effect of prototype accurately. Compared with the experimental results, the maximum deviation of the first two natural frequencies is 4.06%, and the maximum deviation of the critical speeds is 1.36%, demonstrating the potential of small size, low-cost scaled models for predicting the complex dynamic characteristics of the prototype rotor system. Overall, the proposed scaling design strategy provides practical guidance for the design and manufacture of the discontinuous scaled rotor systems, which has broad application in testing, fault prediction and dynamic design of prototypes.

A multi-drive aerodynamic load simulator for floating wind turbine model tests: Development, test and application

Accurate simulation of the aerodynamic loads is strictly required in the integrated model test of Floating Wind Turbines (FWTs). In this paper, a Multi-drive Aerodynamic Loading Simulator (MALS) is designed and manufactured dedicatedly for FWT model tests, with high-performance individually-controlled UAV (unmanned aerial vehicle) propellers serving as the force actuators. Extensive performance evaluation tests are carried out, showing that the developed MALS can generate desired aerodynamic thrusts with satisfying accuracy for both steady and unsteady cases. The maximum change rate of the MALS-generated thrust is about 30 N/s, and over 95% of the fluctuation energy of rotor thrust in the dominant frequency band can be accurately reproduced, covering the requirements of practical wind turbines. Afterwards, a hybrid model test system is constructed based on the proposed MALS, helping to study the dynamic characteristics of FWT systems. In addition, an FWT testing system incorporating a tuned mass damper is constructed. The MALS performs well as a highly controllable actuator, contributing to the FWT tests associated with advanced controllers.

Influence of pivot support stiffness on dynamic characteristics of vertical rotor system

The pivot-jewel bearing pair is the only dynamic and static contact component of the flexible vertical rotor system, and its support stiffness directly affects the dynamic response of the rotor system. A non-linear dynamic model of the vertical rotor system is established, and the effect of different elastic pivot stiffnesses on the dynamic behavior of the rotor system is investigated in combination with experiments. The results show that with the increase of rotational speed, the system has the dynamic characteristics of alternating period 1 and quasi period, and when the speed reaches 550 r/s, 1/3 times low frequency whirl occurs and when the speed rises to 675 r/s, the low frequency amplitude is higher than the rotational frequency amplitude. With the increase of the elastic pivot stiffness, the amplitude of the low frequency whirl at the lower end of the rotor decreases continuously but the proportion of the “width” gradually increases. The rotational speed corresponding to the large amplitude quasi periodic motion of the rotor is delayed from 550 r/s to 650 r/s. The research results can provide a theoretical basis for the optimal design of the bearing subsystem of the vertical rotor system.

Quantitative Aeroelastic Stability Prediction of Wings Exhibiting Nonlinear Restoring Forces

In engineering practice, eigen-solution is used to assess the stability of linear dynamical systems. However, the linearity assumption in dynamical systems sometimes implies simplifications, particularly when strong nonlinearities exist. In this case, eigen-analysis requires linerisation of the problem and hence fails to provide a direct stability estimation. For this reason, a more reliable tool should be implemented to predict nonlinear phenomena such as chaos or limit cycle oscillations. One method to overcome this difficulty is the Lyapunov Characteristic Exponents (LCEs), which provide quantitative indications of the stability characteristics of dynamical systems governed by nonlinear time-dependent differential equations. Stability prediction using Lyapunov Characteristic Exponents is compatible with the eigen-solution when the problem is linear. Moreover, LCE estimations do not need a steady or equilibrium solution and they can be calculated as the system response evolves in time. Hence, they provide a generalization of traditional stability analysis using eigenvalues. These properties of Lyapunov Exponents are very useful in aeroelastic problems possessing nonlinear characteristics, which may significantly alter the aeroelastic characteristics, and result in chaotic and limit cycle behaviour. A very common nonlinearity in flexible systems is the nonlinear restoring force such as cubic stiffness, which would substantially benefit from using LCEs in stability assessment. This work presents the quantitative evaluation of aeroelastic stability indicators in the presence of nonlinear restoring force. The method is demonstrated on a two-dimensional aeroelastic problem by comparing the system behaviour and estimated Lyapunov Exponents.

Dynamic modeling and response characteristics of a solar-driven polygeneration system coupled with hydrogen and thermal energy storage

In this paper, a solar-driven polygeneration system integrated with a solid oxide fuel cell, an absorption chiller, hydrogen storage, and thermal energy storage is proposed for maximally utilizing solar energy and addressing the supply–demand mismatch issue on the time scale. The dynamic model and energy management strategy of the proposed system are constructed, and the short- and mid-term dynamic response characteristics against step perturbations are investigated. Based on eco-office load demands during the typical summer and winter solstices, the long-term dynamic response behaviors of the system load-tracking are also studied. The results demonstrate that: the output dynamic response times are less than 1 s for the photovoltaic, 3–22 s for the proton exchange membrane electrolysis cell, and about 25 s for the solid-oxide fuel cell, all demonstrating short-term transient response characteristics in response to step perturbations of external parameters. In contrast, the dynamic response behaviors of the parabolic trough collector and the absorption chiller elapse 10 to 30 min to reach a stable value in response to the step changes, exhibiting typical mid-term dynamic response characteristics. Furthermore, the outputs of the system could fully satisfy the eco-office load demands in summer, while grid electricity is required to supply parts of power or heat for about 11 h in the morning and evening due to the low solar irradiation and short daylight duration in winter.

A new non-axisymmetric 3D model of the pile-soil system for dynamic analysis of large-diameter piles under eccentric excitation load

With the widely application of large-diameter piles for strengthening soft soil and supporting the offshore structures, the three-dimensional (3D) effect of large-diameter piles have been realized. However, most of the existing 3D theoretical models are axisymmetric, which consider the vertical and radical propagation of stress waves in the pile body during the low-strain pile integrity test (LSPIT). But it is difficult to place the excitation hammer accurately at the center point of the large-diameter pile top in the LSPIT, thus, the hammer-pile-soil system is usually non-axisymmetric. In this paper, a new non-axisymmetric 3D theoretical model is proposed to evaluate the dynamic characteristics of the large-diameter pile-soil system under eccentric excitation load, in which the pile and soil are simulated by the 3D continuum model. The rationality of the new non-axisymmetric solution is verified by comparing it with the results calculated by the finite element model (FEM) and the results derived from the existing 3D theoretical models. Finally, the optimal relative positions of the impact point and the test point in the LSPIT are acquired to weaken the high-frequency interference of the large-diameter pile top. The conclusions drawn from this study provide some useful guidance for evaluating the results of LSPIT.

A 3-D finite element modeling method for time-varying rotor-support system based on rotating-fixed coordinates

The asymmetry of rotor systems is sometimes evident, such as keyed shafts, crack rotors, two-pole generator rotors and especially shaft-disk-blade systems. Meanwhile, the coupling vibration problem between rotor and support structure is becoming more and more prominent due to the light weight of aero-engines. The design and analysis method for the dynamic characteristics of time-varying rotor-support system with detailed structure is needed. Therefore, a modeling method is proposed by using 3-D finite element for time-varying rotor-support system based on rotating-fixed coordinates. The rotor is modeled in rotating coordinate system and the support structure is modeled in fixed coordinate system respectively. The force, energy and displacement between rotor and support structure are transmitted by bearing mechanical parameters. Thus, the time-varying characteristics of the system are expressed explicitly by bearing mechanical parameters, and the dynamic equation of time-varying rotor-support system can be obtained. Then, Floquet theory and Hill infinite determinant method are used to analyze quasi-mode frequency characteristics and stability of time-varying rotor-support system. The results of a typical asymmetric rotor-support system got by the proposed method were compared with existed methods, and more coupling vibration characteristics such as the coupling vibration of rotor axial motion and support plate bending, the coupling vibration of shaft bending and support plate torsion were obtained.

A Vibration Reduction Control Method for Tractor Rear Hydraulic Hitch Based on Pressure Feedback

Tractors transporting heavy hitches tend to tilt severely, resulting in significant dynamic loads on the front axle and affecting handling stability. Tractors and rear hitches can be considered vibration systems with two coupled masses. Thus, active damping control strategies between tractors and rear hitches are proposed in this study. The complexity and versatility of tractor hydraulic hitching during tractor transit transport are considered. A method of improving the tractor hydraulic hitch damping ratio with pressure feedback is proposed. The dynamic characteristics of the pressure feedback hydraulic hitch system are analyzed. A dynamic model of the tractor transfer transport unit is established, and a numerical simulation is carried out to verify the effectiveness of the proposed hydraulic hitch vibration reduction control strategy based on pressure feedback. A real test platform for tractor vibration reduction control is built. The test results show that the pressure feedback vibration reduction control method proposed in this paper affects tractor pitching motion suppression. In addition, the proposed control strategy does not require a force pin sensor. Tractor hydraulic hitch damping control costs are reduced. The vibration reduction control strategy proposed in this study has high reliability and can be used as a reference for non-road-vehicle vibration reduction control.

Fine-Gained Recurrence Graph: Graphical Modeling of Vibration Signal for Fault Diagnosis of Wind Turbine

Benefiting from the recent successes of convolutional neural networks (CNNs), many studies have modeled the vibration signal of energy system into a two-dimensional (2D) input graph to amplify and highlight fault features. However, most works seldomly consider the system dynamic characteristics, which may affect the knowledge discovery and diagnosis quality. To address this issue, this paper proposes a novel graphical modeling approach, termed as fine-gained recurrence graph (FRG), to capture dynamic characteristics of vibration signals from the view of nonlinear dynamics. FRG focuses on modeling the temporal correlations and tendencies between state vectors in phase space and then visualizes the characteristics to represent intrinsic dynamic changes of the vibration signals into 2D graphs. The information representation capability of the proposed FRG is verified using different dynamic signals. Based on this finding, an ensemble fault diagnosis model is proposed fusing FRG with deep CNNs. Meanwhile, transfer learning is accompanied to deal with the training difficulties of deep CNNs. Finally, case studies on experimental data and real wind turbine data illustrate its effectiveness and feasibility. Comparisons with four state-of-the-art approaches have confirmed the preferable information representation and diagnosis performance of the proposed approach.

Accounting for the Influence of the Corrector Hysteresis on the Dynamic Characteristics of Adaptive Optics Systems

Accounting for the Influence of the Corrector Hysteresis on the Dynamic Characteristics of Adaptive Optics Systems