Dynamic Characteristics Of System Research Articles

Long‐term building safety assessment from a series of earthquake excitations

AbstractStructural health monitoring is conducted to ensure the structural integrity of a building during earthquakes. This study aimed to improve our understanding of the dynamic response of buildings subjected to a series of earthquake excitations, focusing on interpreting structural dynamic characteristics and identifying potential seismic damage subjected to a series of earthquake excitations. To this end, a series of seismic response data of a 13‐story reinforced‐concrete/steel building were collected through long‐term monitoring over 2 years. A systematic approach for monitoring the health of the building was established by integrating several algorithms for vibration‐based (both output‐only and input–output parametric nonparametric feature‐discrimination algorithms) and model‐based feature extraction techniques. Furthermore, the time‐varying dynamic characteristics of the building were determined, including its modal frequency, mode shape, and stiffness, as extracted from features obtained over the monitoring period of 2 years. Safety assessment of this newly compound high‐rise building is investigated to explore the system dynamic characteristics through long‐term seismic monitoring.

Research on dynamic calibration and compensation method of strain-gauge type force sensor

Purpose This paper aims to propose an effective dynamic calibration and compensation method to solve the problem that the statically calibrated force sensor would produce large dynamic errors when measuring dynamic signals. Design/methodology/approach The dynamic characteristics of the force sensor are analyzed by modal analysis and negative step dynamic force calibration test, and the dynamic mathematical model of the force sensor is identified based on a generalized least squares method with a special whitening filter. Then, a compensation unit is constructed to compensate the dynamic characteristics of the force measurement system, and the compensation effect is verified based on the step and knock excitation signals. Findings The dynamic characteristics of the force sensor obtained by modal analysis and dynamic calibration test are consistent, and the time and frequency domain characteristics of the identified dynamic mathematical model agree well with the actual measurement results. After dynamic compensation, the dynamic characteristics of the force sensor in the frequency domain are obviously improved, and the effective operating frequency band is widened from 500 Hz to 1,560 Hz. In addition, in the time domain, the rise time of the step response signal is reduced from 0.29 ms to 0.17 ms, and the overshoot decreases from 26.6% to 9.8%. Originality/value An effective dynamic calibration and compensation method is proposed in this paper, which can be used to improve the dynamic performance of the strain-gauge-type force sensor and reduce the dynamic measurement error of the force measurement system.

A parametric study of a bolted joint rotor-bearing system with an unbalanced offset disk

The turbine disk is the core component of an aero-engine whose position and unbalanced force seriously affect the vibration stability of the rotor system. Ignoring the influence of the offset disk may result in discrepancies between real-world scenarios and numerical simulation results. The present work aims to explore the nonlinear dynamic characteristics of rotor systems under the coupling of bolted joint and offset disk effect, as well as the influence of offset disk position and its unbalanced force on the system dynamic behavior and bending stiffness of bolted joint also investigated. The governing equations of a bolted joint rotor-bearing system with an offset disk were established based on the finite element method and derived as a dimensionless expression in the first. Then, the Newmark method was employed for the numerical solution of the motion equations, and then a bifurcation analysis of the rotor system and the evolution of bending stiffness for the bolted joint was studied. Next, by comparing the frequency-amplitude diagrams, bifurcation diagrams, time history, shaft obits, and bending stiffness diagrams of the bolted joint, the effect of the offset disk position and its unbalanced force on the nonlinear system dynamic was revealed. Finally, an experimental study was carried out to verify the numerical result using the bolted joint rotor test rig with an offset disk. The analysis result of the present work can provide theoretical guidance for structure design and stability analysis on the aero-engine.

Vibration behavior and power transmission of coupled plate structures with embedded acoustic black holes joined at an arbitrary angle

The Acoustic Black Hole (ABH) technology is widely recognized for its passive vibration and noise attenuation capabilities, characterized by lightweight and high efficiency. Exploring the dynamic behavior and energy transmission characteristics of the ABH coupled-plate system is a novel endeavor that provides a theoretical foundation for applying ABH structures in complex coupled systems. In this work, a semi-analytical dynamic model for the ABH coupled-plate system (comprising an ABH plate and a uniform plate) with an arbitrary connection angle is proposed by using the Rayleigh-Ritz framework. To ensure the continuity of high-order spatial derivatives at the edges, the modified version of the Fourier series is employed to describe the vibration displacement fields for transverse and in-plane vibration components. This enables the proposed model to determine the necessary derivatives of relevant quantities, namely the structural intensity and power flow, which facilitates the description of energy transmission behaviors in the ABH coupled-plate structure. Firstly, the convergence characteristics of the model are studied and the accuracy of modal information and dynamic response is verified through the comparison of those calculated from the finite element method (FEM), additionally, the experiment is carried out to verify the proposed model. Subsequently, several numerical examples are presented to study the vibrational characteristics of the ABH coupled-plate system and the good vibration attenuation of the ABH coupled-plate is observed as well. Finally, the vibrational energy transmission results are obtained and the influence of some important system parameters such as coupling angles on energy transmission characteristics in such systems are investigated. This work can shed some new light on ABH structures with potential application to such complex coupled-plate structures.

Incommensurate fractional-order analysis of a chaotic system based on interaction between dark matter and dark energy with engineering applications

Chaotic systems, characterized by their sensitivity to initial conditions and the presence of deterministic unpredictability, have garnered significant attention in various fields of science and engineering. Researchers have demonstrated a growing interest in recent years in identifying various physical systems as chaotic system, including but not limited to fluid dynamics, electrical circuits, and biological oscillators. In this study, a cosmological chaotic system that portrays the interaction between dark matter and dark energy is examined using incommensurate fractional-order analysis. The effects of incommensurate fractional orders are evaluated by means of phase portraits, bifurcation diagrams and Lyapunov exponents spectra. It is dedicated that wider chaotic regions are observed once the values of these incommensurate fractional orders are changed. Meanwhile, a hidden attractor is found based on the stability analysis and basin of attraction in the incommensurate fractional-order dark matter and dark energy (IFODMDE) chaotic system. These findings highlight the richer dynamic characteristics of the IFODMDE chaotic system. Furthermore, the identified hidden attractor is effectively employed in this study for various engineering applications, including chaos control, random number generator (RNG) design, and image encryption. The analytical results offer a more accurate description of real-world physical phenomena, thanks to the inclusion of incommensurate fractional orders. The application results prove the good randomness of the IFODMDE chaotic system.

Dynamic behavior of high damping rubber bearings and lead rubber bearings under near-fault earthquakes

Civil engineering structures are susceptible to natural calamities such as earthquakes, floods, and strong winds. Base isolation is a proven method for protecting structures during earthquakes. It involves inserting a flexible layer between the foundation and superstructure to isolate the structure from earthquakes, thereby changing the system's dynamic characteristics. The present study compares the dynamic performance of passive base isolators, specifically High Damping Rubber Bearings (HDRBs) and Lead Rubber Bearings (LRBs), under near-fault ground motion conditions to assess their effectiveness in reducing seismic impact on structures. The isolator is first analyzed using a static general approach and validated against existing literature before undergoing dynamic analysis. In this research, the LRB isolation system is analyzed using a dynamic explicit approach in ABAQUS, while the HDRB is analyzed using a dynamic implicit approach. The behavior of these isolators is studied under seismic events such as those from the Imperial Valley, Managua, Loma Prieta, Northridge, and Kocaeli ground motions. The results indicate that LRBs significantly reduce acceleration at the top of the bearing compared to HDRBs. The maximum reductions in response are 68.42% for the Kocaeli earthquake in case of LRBs and 61.80% for the Northridge earthquake in case of HDRBs. The LRB shows a minimum acceleration response reduction of 57.24%, while for HDRB, it is 24.47% for the Imperial Valley records in both cases.

ON THE THEORY OF FRICTION SYSTEMS WITH HEREDITARY TYPE FRICTION

The work is devoted to the study of the nonlinear dynamics of frictional vibration systems, which take into account, when developing mathematical models of vibration systems, an essentially nonlinear function that describes the work of friction forces with memory. The problem considered in the work combines two well-known Painleve? problems and the problem of studying the friction forces of hereditary friction. In both cases, we are talking about the idealization of real elastic bodies and flexible bonds with ideal absolutely hard and rigid ones. Using the well-known experimentally proven hypothesis of A.Yu. Ishlinsky and I.V. Kragelsky about the hereditary dependence of the coefficient of friction of relative rest at low speeds of movement of bodies, the dynamic system under study is transformed from autonomous to non-autonomous, in which new types of movements that have not previously been observed in the study of vibration systems appear. In particular, taking into account the Painleve? paradox entails the previously unexpected possibility of the occurrence of instability and self-oscillations, and taking into account the heredity of the friction coefficient leads to the appearance of chaotic movements of bodies. A numerical and analytical method has been developed for studying the behavior of the dynamic characteristics of friction vibration systems depending on the chosen model of the relative static friction coefficient. Based on the main parameters, the new bifurcation diagrams presented in this work demonstrate the presence of arbitrarily complex periodic regimes of body motion, including chaotic ones. It has been established that the transition to chaotic modes of motion occurs according to the well-known period doubling scenario. Analytical relations are given for point mappings of Poincare? surfaces, which made it possible to obtain succession functions illustrating arbitrarily complex modes of body motion, including chaotic ones. It is noted that such body movements were not found during the study of such vibration systems.

Analysis of electromechanical coupling modal and dynamic response characteristics of permanent magnet gear transmission system considering variable load condition

In order to study the influence of electromagnetic (EM) effect and load change on the modal characteristics and dynamic response of gear transmission system driven by permanent magnet synchronous motor (PMSM), a electromechanical coupling dynamic model is established. The composite air gap permeability coefficient is introduced, and the formula of permanent magnet flux linkage under the influence of space harmonic and cogging effect is derived. The variation laws of gear meshing stiffness and bearing support stiffness under the influence of load change are simulated and analyzed. The natural frequency and vibration modal under different load, flux linkage and PI controller gain are revealed. On this basis, the influence of EM effect and load change on the resonance domain is analyzed through frequency sweep analysis and time domain simulation. Results indicate that the 1st order natural frequency and resonance amplitude will increase with the load, and the influence of PMSM EM excitation will gradually dominate. The increase of the flux linkage and speed loop controller gain Kpω will reduce the 1st order natural frequency. When Kpω =123, a new mode appears, and there is a modal transition between the new mode and mode 1 when Kpω =161. The research results can provide theoretical guidance for improving the transmission performance and structure optimization design of the permanent magnet gear transmission system.

Analysis of the approaches used for calculating involute splined couplings and the methods of considering their influence on the dynamic behavior of systems

Spline couplings, due to their high reliability and strength parameters, are widespread not only in mechanical engineering. The ability to transmit high torque with a sufficiently long service life has led to the extensive use of these couplings in the aircraft industry. Since this unit is under heavy loads in aircraft gas turbine engines, much attention is paid not only to strength characteristics, but also to the influence on the dynamic parameters of the rotor system. To mitigate the risks of destruction and the occurrence of defects, a large number of studies are carried out allowing us to evaluate the rotor system operation with splines and make a forecast of its behavior in the event of various factors leading to a change in the operation of splines. This paper provides a review of various methods, techniques and models of involute spline couplings used in the analysis of the dynamic behavior of rotor systems. The analytical models that allow us to take into account the coupling in various systems as well as finite element models that demonstrate the description of various processes in splines. The publications, devoted to the comparison of finite element models with analytical ones confirming the results associated with the dynamic characteristics of systems with an increase in radial and angular swashes, have been considered. The results of comparing the above models and their results with experimental research to verify and confirm various effects are also presented. The given research of rotor systems with swash allows for a conclusion about a significant spline influence, since they can cause a change in the coupling rigidity, redistribution of contact, increased loads in meshing, increased vibration amplitudes, change in the spectrum of excited frequencies and self-oscillatory processes due to various factors.

Investigation on the Impact of Excitation Amplitude on AFM-TM Microcantilever Beam System's Dynamic Characteristics and Implementation of an Equivalent Circuit.

Alterations in the dynamical properties of an atomic force microscope microcantilever beam system in tapping mode can appreciably impact its measurement precision. Understanding the influence mechanism of dynamic parameter changes on the system's motion characteristics is vital to improve the accuracy of the atomic force microscope in tapping mode (AFM-TM). In this study, we categorize the mathematical model of the AFM-TM microcantilever beam system into systems 1 and 2 based on actual working conditions. Then, we analyze the alterations in the dynamic properties of both systems due to external excitation variations using bifurcation diagrams, phase trajectories, Lyapunov indices, and attraction domains. The numerical simulation results show that when the dimensionless external excitation g < 0.183, the motion state of system 2 is period 1. When g < 0.9, the motion state of system 1 is period 1 motion. Finally, we develop the equivalent circuit model of the AFM-TM microcantilever beam and perform related software simulations, along with practical circuit experiments. Our experimental results indicate that the constructed equivalent circuit can effectively analyze the dynamic characteristics of the AFM-TM microcantilever beam system in the presence of complex external environmental factors. It is observed that the practical circuit simulation attenuates high-frequency signals, resulting in a 31.4% reduction in excitation amplitude compared to numerical simulation results. This provides an essential theoretical foundation for selecting external excitation parameters for AFM-TM cantilever beams and offers a novel method for analyzing the dynamics of micro- and nanomechanical systems, as well as other nonlinear systems.

Dynamic characteristics analysis of a rotor system with loose support considering internal friction in couplings

Along with the rotating machinery advances toward high speeds, the significance of the excitation force of the seal fluid in the rotor system is growing, which can cause serious accidents. Most of the previous research on rotors in rotating machinery has predominantly focused on the effects of misalignment in couplings. In this article, a novel model is proposed, introducing an analytical approach that combines both internal friction in couplings and loosening support faults. Additionally, an analysis and discussion of the vibration characteristics of the rotating system under the influence of internal friction are presented. This method allows for a more comprehensive assessment of the performance of rotors in engineering applications. Assuming that the left support of the rotor is loose, this model focused on how various factors such as rotor speeds, eccentricity, seal disc mass, and left-end support mass affect the labyrinth seal rotor system's dynamic characteristics. Based on the findings, The emergence of internal friction forces advances the chaos of the rotor. It seems that as the rotating speed increases, there will be a small frequency range, resulting in fluid oscillation, and the system stability will be reduced at this time. The improvement in the seal disc's quality has minimal impact on the stability of the left journal, but it will reduce the stability of the seal disc. The increase in the mass of the left end support will increase the stability of the movement at the left journal and reduce the stability of the movement at the seal disc.

Power Management Strategy of Hybrid Fuel Cell Drones for Flight Performance Improvement Based on Various Algorithms

In recent years, there has been a growing demand for multipurpose drones that can handle surveillance, environmental monitoring, and urgent deliveries. This trend has spurred the need for increased power and longer flight times for drones. Hence, many researchers introduced various hybrid systems to enhance endurance. In particular, a hybrid system that integrates solar cells, fuel cells, and batteries can substantially enhance a drone’s endurance. However, linking multiple power sources necessitates a control strategy that prioritizes safety and durability. It is also essential to analyze the control characteristics of each component as the dynamic behavior of individual components, coupled with environmental factors, significantly impacts the overall dynamic characteristics of drone systems. This study introduces a PEMFC–battery drone model. The model’s dynamic characteristics can be evaluated based on changes in environmental conditions and the control strategies of primary components. The validity of this model is confirmed by analyzing the dynamic characteristics of drone systems. As a result, the MRAC logic applied to the flight-level control and thrust motor of the drone was found to amplify the characteristics of the underlying PI and IP controllers. These control characteristics can lead to the development of control strategies for improving the flight performance or power durability of the aircraft by being properly applied to the flight environment of the drone.

Dynamics and Soliton Propagation in a Modified Oskolkov Equation: Phase Plot Insights

This study explores the modified Oskolkov equation, which depicts the behavior of the incompressible viscoelastic Kelvin–Voigt fluid. The primary focus of this research lies in several key areas. Firstly, the Lie symmetries of the considered equation are identified. These symmetries are utilized to transform the discussed model into an ordinary differential equation. Analytical solutions are subsequently derived using the new auxiliary equation technique. Next, a comprehensive analysis of the equation’s dynamic nature is undertaken from multiple aspects. Bifurcation is carried out at fixed points within the system, and chaotic behavior is unveiled by introducing an external force to the dynamic system. Various tools, including 3D and 2D phase plots, time series, Poincaré maps, and multistability analysis, are employed to identify the chaotic nature of the system. Furthermore, the sensitivity of the model is explored across diverse initial conditions. In general, comprehending the dynamic characteristics of systems holds immense significance in forecasting outcomes and innovating new technologies.

Dynamic characteristics of a novel liquid air energy storage system coupled with solar heat and waste heat recovery

Liquid air energy storage (LAES) is a promising energy storage technology for its high energy storage density, free from geographical conditions and small impacts on the environment. In this paper, a novel LAES system coupled with solar heat and absorption chillers (LAES-S-A) is proposed and dynamically modeled. A power-speed control system is established for this system. Two operating control strategies are developed for the solar heat collection process. The transient characteristics of the novel system during the start-up, load-up process and encountering different disturbances are investigated. Besides, the dynamic responses when the waste heat is used for producing heating energy are also studied. The results indicate that the power-speed control system can guarantee a very short equilibrium time and a very small overshoot. The energy efficiency of the LAES-S-A system is 65.84 %, while that is 75.32 % when the waste heat is used for producing heating supply. When a disturbance occurs, the equilibrium times of the absorption chiller, air turbines and heating device are 1500 s, 40 s and 38 s, respectively. Compared with the absorption chiller, the heating device can better cooperate with the air turbines. The results can provide a reference for future studies.

Deep learning-assisted multi-objective optimization of coke dry quenching system efficiency

Coke dry quenching is a promising technology for energy saving and environmental protection in the industrial sectors. Prediction of system efficiency index (SEI) and dynamic adjustment of operating parameters are essential to ensure high system efficiency. In this study, a deep learning-assisted multi-objective optimization framework was proposed to improve coke quenching efficiency and steam production simultaneously. Firstly, numerous on-site process parameters were collected as the data basis for subsequent model construction, and a system-level heat balance model was established and validated for real-time calculation of coke burning loss rate. Then, an attention-based one-dimensional convolutional neural network was developed as a data-driven surrogate model to establish the mapping relationship between the operating parameters and SEI. Finally, the Non-dominated Sorting Genetic Algorithm II was combined with the Technique for Order of Preference by Similarity to Ideal Solution to rapidly identify the optimal operating parameters under different loads. The optimization results also provided a new insight into the system dynamic characteristics. The results show that the surrogate model can swiftly and precisely predict SEI, with R2 exceeding 0.9. Compared with initial operating conditions, the optimal decision scheme has improved SEI by 82 %, with the optimal coke burning loss rate and main steam flow rate of 0.56 % and 83.6 t/h, respectively. This work will provide valuable decision aids for technicians to reach the desired system efficiency.

Dynamic Characteristics of Three-Body Braking System Considering Tire-Road Friction

Abstract With the significant increase in vehicle ownership in our country, urban traffic conditions have become increasingly congested. Low-speed driving has become more prevalent, leading to more frequent instances of starting and braking. Consequently, the issue of low-speed braking flutter has become increasingly prominent. While the brake is in an open environment, the dust and particles in the air and the debris generated by the brake itself will have an impact on the braking behavior. In addition, according to the theory of modal coupling, the braking stability of the vehicle is also affected by other components. In this paper, different dynamic torsional models of braking system are established according to different braking conditions. Through numerical calculation, the influence of tire parameters, road conditions, and particles on the friction dynamics characteristics of braking system pairs is explored. The results show that the instability of the brake pair system often occurs at low speed. Different tire slip ratios, tire offset factors, and road conditions will lead to different relative motions of the braking system, but the existence of particles in the brake lining-disk interface can enhance the motion stability of the system.

Analysis of vibration characteristics of face gear powering-split transmission system

A nonlinear dynamic model of the face gear powering-split transmission system was established, and the nonlinear dynamic characteristics of the face gear powering-split transmission system were studied by considering various factors such as support stiffness, time-varying meshing stiffness, lateral clearance of teeth, comprehensive transmission error and bearing stiffness. The Runge–Kutta integral method is used to solve the differential dynamics of the system. The nonlinear behavior of the system is described by the phase plane diagram, time history diagram, frequency domain diagram, and Poincare section diagram. The influence of external excitation frequency on the nonlinear behavior of the system is described by the bifurcation diagram. In addition, the multi-scale method is used to analyze the superharmonic resonance of the system and determine the stability conditions of the superharmonic resonance of the system. The influence of meshing damping, time-varying meshing stiffness, and time-delay control parameters on the amplitude-frequency characteristics of the system is studied by numerical analysis of the superharmonic resonance. The results show that the system will show periodic chaotic alternating motion characteristics under external excitation. Selecting meshing damping, meshing stiffness, and time delay control parameters in a reasonable range can effectively reduce the superharmonic co-amplitude and keep the system in a stable state.

Simulation and experimental study on impact dynamic characteristics of the spline rotor system

The development of accurate impact dynamics models in rotating machinery with spline couplings is a challenging problem that demands special attention. The dynamic behavior of the system is highly dependent on the spline coupling stiffness, which is nonlinear under different loads. To address this challenge, rotor dynamics models that incorporate spline couplings have been developed. In this paper, firstly, the mechanical model of spline coupling considering large deformation under different loads is established and verified by finite element software. Furthermore, a spline rotor dynamics model considering nonlinear stiffness is established, and the influence of different impact loads on the vibration response of the system is emphatically analyzed. Finally, the proposed model is experimentally verified to accurately predict the impact dynamics of the rotor system, which provides a certain theoretical reference for the impact resistance design of the spline rotor system.

Dynamic security region of natural gas systems in integrated electricity-gas systems

In an integrated electricity-gas system (IEGS), gas-fired units with flexibility response capabilities address the uncertainty associated with renewable energy by swiftly adapting their output, which may result in uncertain fluctuations in the gas withdrawal of gas-fired units, potentially posing risks to the security of IEGS. Hence, it is necessary to efficiently evaluate the dynamic security region (DSR) of natural gas systems in IEGS by considering the real-time dynamic characteristics of natural gas systems, which are not satisfactorily handled in state-of-the-art works. To bridge this gap, this paper first conceptionally verifies the necessity of the DSR and establishes its mathematical model. Then, a dimensionality reduction method is proposed for the efficient solution and visualization of the high-dimensional DSR evaluation model. A fast evaluation (FE) algorithm is developed to address the difficulties of the nonconvex dynamic constraints in the reduced DSR model. Finally, the necessity and notable advantages of the proposed DSR model and FE are verified based on small and relatively large test systems in comparison with common security region models and algorithms. To the best of our knowledge, this is the first paper that comprehensively presents models and efficient algorithms regarding the DSR of natural gas systems in IEGS.

Dynamic characteristics of spur gear system with tooth root crack considering gearbox flexibility

Considering the calculation efficiency and accuracy of meshing characteristics of gear pair with tooth root crack fault, the parametric model of cracked spur gear is established by simplifying the crack propagation path. LTCA method is used to calculate the time-varying meshing stiffness (TVMS) and transmission error (TE) of the cracked gear pair, and is verified by finite element (FE) method. The crack area share index is proposed to measure the degree of crack fault and the application range of simplified crack propagation path is obtained. The gearbox is introduced into the calculation as the condensation model, and the dynamic model of gear system with root crack fault considering gearbox flexibility is established. The effects of gearbox flexibility, rotational speed, crack degree and gear torque on the vibration response fault characteristics of gear system are analyzed. Compared with the simulation results without considering gearbox flexibility, the simulation results considering gearbox flexibility are smaller in amplitude and closer to the experimental results. The fault shock degree in acceleration waveform and fault frequency modulation in FFT spectrum are more obvious considering gearbox flexibility. The fault characteristics of vibration response are more obviously affected by the reduction of gearbox flexibility and the increase of fault degree than the change of rotational speed and gear torque. The research results provide theoretical and technical support for fault diagnosis and health monitoring of gear systems.