Analysis Of Dynamic Characteristics Research Articles

Bus-impedance-based stability improvement of DC power distribution system considering dynamic performance

A direct-current (DC) power distribution system (PDS) enjoys the benefits of flexibility and efficiency. However, increasing stability issues occur due to the interaction among feedback-controlled converters in PDS. For ensuring stability, various impedance-based method is discussed by scholars. Unlike the traditional analysis method based on minor-loop-gain (MLG), Passivity-Based Stability Criteria (PBSC) is a novel bus-impedance-based method. Although PBSC is a promising measure of stability analysis for the distribution system, the difficulty of stability margin calculation and dynamic characteristic analysis limits its application. Therefore, the relative stability margin (RSM) is proposed to assess the damping levels. Based on RSM, the dynamic performance optimization algorithm (DPOA) is presented to optimize the proposed MMC impedance reshaping (MIR) control. Compared with the past stability analysis, dynamic behaviour is considered in this paper when stability improvement is implemented. By means of the MIR and DPOA, the stability and dynamic performance of the distribution system are enhanced. Simulation results confirm the validity of the proposed viewpoints and method.

Experiment and simulation analysis of tribological and dynamic characteristics in aeroengine hybrid ceramic bearing

Purpose This paper aims to research the tribological and dynamic characteristics of aeroengine hybrid ceramic bearings through wear experiments and simulation analysis. Design/methodology/approach First, the authors carried out wear experiments on Si3N4–GCr15 and GCr15–GCr15 friction pairs through the ball-disc wear test rig to explore the tribological properties of their materials. Second, using ANSYS/LS-DYNA simulation software, the dynamic simulation analysis of hybrid bearings was carried out under certain working conditions, and the dynamic contact stress of all-steel bearings of the same size was simulated and compared. Finally, the change of the maximum contact stress of the main bearing under the change of load and rotation speed was studied. Findings The results show that the Si3N4–GCr15 pair has better tribological performance. At the same time, under the conditions of high speed and heavy load, the simulation analysis shows that the contact stress between the ceramic ball and the raceway of the ring is smaller than the steel ball. That is, hybrid bearings have better transient mechanical properties than all-steel bearings. With the speed increasing to 12,000 r/min, the maximum stress point will shift in the inner and outer rings. Originality/value In this study, the tribological and transient mechanical properties of Si3N4 material were comprehensively analyzed through wear experiments and dynamic simulation analysis, which provided a reference for the design of hybrid bearings for next-generation aeroengines.

Multivariate joint order recurrence networks for characterization of multi-lead ECG time series from healthy and pathological heartbeat dynamics.

Analysis of nonlinear dynamic characteristics of cardiac systems has been a hot topic of clinical research, and the recurrence plots have earned much attention as an effective tool for it. In this paper, we propose a novel method of multivariate joint order recurrence networks (MJORNs) to evaluate the multi-lead electrocardiography (ECG) time series with healthy and psychological heart states. The similarity between time series is studied by quantifying the structure in a joint order pattern recurrence plot. We take the time series that corresponds to each of the 12-lead ECG signals as a node in the network and use the entropy of diagonal line length that describes the complex structure of joint order pattern recurrence plot as the weight to construct MJORN. The analysis of network topology reveals differences in nonlinear complexity for healthy and heart diseased heartbeat systems. Experimental outcomes show that the values of average weighted path length are reduced in MJORN constructed from crowds with heart diseases, compared to those from healthy individuals, and the results of the average weighted clustering coefficient are the opposite. Due to the impaired cardiac fractal-like structures, the similarity between different leads of ECG is reduced, leading to a decrease in the nonlinear complexity of the cardiac system. The topological changes of MJORN reflect, to some extent, modifications in the nonlinear dynamics of the cardiac system from healthy to diseased conditions. Compared to multivariate cross recurrence networks and multivariate joint recurrence networks, our results suggest that MJORN performs better in discriminating healthy and pathological heartbeat dynamics.

The Water Problems and Treatment Strategies of Volcanic Gas Reservoir in Daqing

In order to realize the development strategy of “stabilizing oil and increasing gas and simultaneously boosting oil and gas”, Daqing Oilfield has continuously strengthened the exploration and development of deep natural gas resources since the discovery of Xushen gas Field. The volcanic gas reservoir is the main gas producing area of Songliao Basin. Through “internal excavation and external expansion”, natural gas production has maintained a trend of growth for 12 consecutive years. However, due to the development of fractures and bottom water in volcanic gas reservoir, the development contradiction caused by gas well water is increasingly prominent as the gas field development enters the end of stable production stage. Therefore, on the basis of the understanding of four types of effluent water in volcanic rock reservoir, this paper carries out the analysis of the production dynamic characteristics of typical gas wells, and identifies the difficulties faced by gas wells with different types of effluent water. Through field tests, economic and feasible treatment measures are explored, including continuous circulation gas lift of strong water breakthrough gas well in fracture vertical direction, intelligent foam drainage gas production of weak water breakthrough gas well in fracture vertical direction, and deep water unlocking of gas well in pore vertical water cone and gas reservoir with high water saturation gas reservoir effluent water, which provides technical support for the sustainable and efficient development of volcanic gas reservoir.

Dynamic Characteristics Analysis of the First-Stage Fixed-Axis Gear Pair with Wear Fault for a Wind Turbine Gearbox Considering Different Friction States

Dynamic Characteristics Analysis of the First-Stage Fixed-Axis Gear Pair with Wear Fault for a Wind Turbine Gearbox Considering Different Friction States

An improved time-varying mesh stiffness calculation method and dynamic characteristic analysis for helical gears under variable torque conditions

Based on the slice theory and numerical calculation methods, the time varying meshing stiffness (TVMS) calculation method of the gear pair was constructed for the helical gear pair of a electric continuously variable transmission (ECVT), and the TVMS of the helical gear were calculated under different constant and time-varying torque in this study. The obtained stiffness values were introduced into the established dynamics model of helical gear system, and the influence of changed TVMS, resulting from the variable speed and torque, on the nonlinear dynamic characteristics of gear pair was analyzed using the Runge-Kutta method. The results show that the proposed TVMS calculation method is very effective in computing the TVMS of helical gear pair under time-varying condition. The TVMS and dynamic transmission error (DTE) increase as the torque increase, and vice versa. Meanwhile, the system exhibits a diverse range of periodic, sub-harmonic, and chaotic behaviors at high speed and at low speed when torque is low, whereas not appear at steady high torque under low speed range. This study offers a method for gaining the TVMS of helical gear pair to analyze the dynamic characteristics of gear pair under actual working condition, and the influence of torque that change with the speed ratio on the dynamic performance of a gear system should be considered in the industrial applications.

A Study on the Dynamic Characteristics Analysis of Octacopters Equipped with 2 kg EOTS

A Study on the Dynamic Characteristics Analysis of Octacopters Equipped with 2 kg EOTS

Dynamic feature analysis of handwritten electronic signatures based on Fourier transform.

The utilization of handwritten electronic signatures has expanded in various application scenarios, leading to an increased demand for identification. Unlike handwriting signatures, handwritten electronic signatures offer the advantage of extracting dynamic feature data, including writing pressure, velocity, and acceleration. In this study, the Fourier transform was employed to extract 18 characteristics from the time domain and frequency domain of writing pressure, velocity, and acceleration. The experimental findings revealed distinguishable differences between genuine signatures and random forgeries in writing pressure. However, no statistically significant differences were observed in writing velocity and writing acceleration. Moreover, significant differences were detected in most characteristics when comparing genuine signatures with freehand imitation forgeries and tracing imitation forgeries. The canonical discriminant analysis was performed between the genuine and Non-genuine signatures; the cross-validation estimated the discriminating powerof these characteristics with a satisfactory result. The study proposed a new approach to analyzing handwritten electronic signatures using time-domain and frequency-domain characteristics and demonstrated its effectiveness in the examination.

Macro and micro analyses of static and dynamic shear characteristics of geogrid and rubber–sand mixture interface

A rubber–sand mixture (RSM) can be used as a novel type of geotechnical material in reinforced roadbeds and other projects owing to its being elastic and environment friendly. To explore the static and dynamic shear characteristics of the geogrid and RSM interface, monotonic direct shear (MDS), cyclic direct shear (CDS), and post-cyclic monotonic direct shear (PCDS) experiments were performed in this study. The effects of rubber content (χ) and particle size ratio (r) on the interface shear characteristics were studied. A dynamic model of the rubber–sand mixture was established using PFC3D, and mesoscopic analysis of the cyclic shear process was conducted. The results of the CDS experiments indicated that the peak shear stress with χ = 10 % was the largest. The peak strength and residual strength of PCDS were larger than those of MDS under the same χ and r. After cyclic shearing, the interface apparent cohesion of various rubber contents and particle size ratios increased by 78 % ∼ 172 %. During cyclic shearing, the porosity and particle energy in the shear box changed periodically, and the porosity near the interface was slightly higher than that in the other areas. The kinetic energy of the particles was closely related to the shear displacement.

Analysis of Dynamic Characteristics of Tristable Exponential Section of Piezoelectric Energy Harvester

Variable-cross-section beams have better mass and strength distribution compared with constant cross-section beams, which can optimize the harvesting power of piezoelectric vibration energy harvesters, which are widely used in self-supplied and low-power electronic devices, providing more convenience and innovation for the development of micromechanical intelligence and portable mobile devices. This paper proposes a piezoelectric energy harvester with a tristable-exponential-decay cross section, which optimizes the strain distribution of the cantilever beam through exponential decay changes to improve the harvesting efficiency of the harvester in low-frequency environments. First, the nonlinear magnetic force is obtained based on the magnetic dipole, and the dynamic model is established by using the Euler–Bernoulli beam theory and Lagrangian equation. The influence of the structural parameters of the harvester on the system dynamics and output characteristics is analyzed in the two dimensions of time and frequency, and the influence of the exponential decay coefficient on the system dynamic response and output power is deeply studied. The research shows that the exponential decay section can reduce the first natural frequency of the cantilever beam; by changing the amplitude, frequency, d and dg of the excitation acceleration, the switching of the monostable, tristable and bistable states of the system can be realized. With a decrease in the exponential decay coefficient, under a low-frequency excitation of 0–7 Hz, the output power of the cantilever beam per unit volume is significantly improved, and under a 4 Hz low-frequency excitation, the acquisition output power per unit volume of the cantilever beam is increased by 7 times, thus realizing low-frequency, high-efficiency energy harvesting.

Dynamic characteristics analysis of an aeroengine rotor system subjected to aerodynamic excitation

This paper aims to investigate the dynamic characteristics of an aeroengine rotor subjected to aerodynamic excitation. Firstly, the dynamic model of the turbo-shaft engine rotor system is established by means of finite element (FE) method, taking into account the blade-tip clearance-induced aerodynamic force and oil-film force induced by squeeze film damper. Next, the critical speeds and mode shapes of the rotor are achieved by calculation, simulation and experiment to illustrate the validity of the established model. Then, using bifurcation diagram, rotating orbit and time-domain waveform, the dynamic responses of the turbo-shaft engine high-pressure (HP) rotor with aerodynamic excitation are analyzed, and the effects of blade-tip clearance, inlet and outlet angles on the dynamic responses of the rotor are discussed, respectively. The numerical results reveal that the system maintains a stable-periodic motion at low-speed region. In contrast, at high-speed region, there is a noticeable appearance of instability. Besides, the magnitude of the response decreases with the growth of the blade-tip clearance. The growth of the inlet angle will result in an increase of the magnitude of the response, and the magnitude of the response reduces with the growth of the outlet angle. The aerodynamic force at resonance is greater than that at non-resonance. The research results can assist in understanding the dynamic characteristics of the rotor subjected to aerodynamic excitation, and provide theoretical guidance for the structural design of an aeroengine rotor system.

Discrete element analysis of dynamic characteristics and earthquake collapse of solid structure ancient masonry pagoda

In order to investigate the seismic damage and collapse mechanism of ancient masonry pagodas, a numerical model of the Tang Dynasty masonry pagoda (Xuanzang Pagoda) located at Xingjiao Temple was established using the discrete element software 3DEC, and non-linear mechanical parameters of the contact surfaces between rigid blocks were defined. Dynamic characteristics were analyzed, and the seismic response of the ancient pagoda was calculated by inputting El-Centro waves, Tianjin waves, and Lanzhou artificial waves with different intensities in three directions. The study analyzed the damage failure process of the pagoda, identified vulnerable areas, and obtained its collapse.The results show that the ancient pagoda behaves as an elastic–plastic system at intensity 7 degree seismic action. The acceleration response of the floors increases along the height, and the displacement angle between floors appears as an inflection point at the second floor. The middle floors are especially vulnerable to damage due to low cohesion and strong movements of the internal soil fill. As the intensity increases, significant damage occurs, with rapid floor displacement response and upward extension of cracks. The top floor of the ancient pagoda collapses first with stair-shaped oblique cracks, followed by a floor-by-floor destruction from top to bottom. The collapse of floors with different hole locations also vary. These findings provide valuable insights for predicting the vulnerable areas and collapse of Xuanzang Pagoda under seismic action.

Analysis of Dynamic Features of Gear–Bearing Systems with Bearing Raceway Failures

Analysis of Dynamic Features of Gear–Bearing Systems with Bearing Raceway Failures

Dynamics Solution and Characteristics Analysis of a 6-SPS Passive Vibration Isolator Based on MS-DT-TMM

Dynamics Solution and Characteristics Analysis of a 6-SPS Passive Vibration Isolator Based on MS-DT-TMM

Dynamic Feature Identification of Carbon-Fiber-Reinforced Polymer Laminates Based on Fiber Bragg Grating Sensing Technology

Carbon-fiber-reinforced polymer (CFRP) composites have many advantages, and have been widely used in aerospace structures, buildings, bridges, etc. The analysis of dynamic response characteristics of CFRP composite structures is of great significance for promoting the development of smart composite structures. For this reason, vibration experiments of CFRP laminates with surface-attached fiber Bragg grating (FBG) sensors under various dynamic loading conditions were carried out. Time- and frequency-domain analyses were conducted on the FBG testing signals to check the dynamic characteristics of the CFRP structure and the sensing performance of the installed sensors. The results show that the FBG sensors attached to the surface of the CFRP laminates can accurately measure the dynamic response and determine the excited position of the CFRP laminates, as well as invert the strain distribution of the CFRP laminates through the FBG sensors at different positions. By performing Fourier transform, short-time Fourier transform, and frequency domain decomposition (FDD) on the FBG sensing signals, the time–frequency information and the first eight modal frequencies of the excited CFRP structure can be obtained. The modal frequencies obtained by different excitation types are similar, which can be used for structural damage identification. The research in this paper clarifies the effectiveness and accuracy of FBG sensors in sensing the dynamic characteristics of CFRP structures, which can be used for performance evaluation of CFRP structures and will effectively promote the design and development of intelligent composite material structures.

Обзор существующих методов обнаружения дубликатов исходного кода

This work is devoted to solving the identifying software duplicates problem. To do this, a short survey of existing search methods is made, consisting of the following: textual, lexical, syntactic, metric, semantic. Then a comparative analysis of the methods is carried out according to the following criteria: accuracy, completeness, speed, resource efficiency, scope of implementation; the comparison results are given in tabular form. Also, promising approaches for searching for duplicates are considered, namely, the following: machine learning, graph analysis, syntax tree analysis, dynamic characteristics analysis, spatial characteristics analysis, abstract syntax analysis. Ways to continue investigation are indicated.

A new dynamic 2D fusion model and output characteristic analysis of floating photovoltaic modules considering motion and environmental factors

As a new application form, floating photovoltaic power generation is a green and sustainable energy source with immense development potential. However, built on marine or riverine surface, the floating photovoltaic system not only faces challenges from environment factors that land-based photovoltaic system meets, but also faces challenges from the motion of the floating bodies which are caused by the continuous external forces of wind and waves. Modelling and analyzing the output characteristics of floating photovoltaic modules is desirable and useful to improve power generation efficiency. This paper presents a new dynamic 2D fusion model and analysis method for analyzing the dynamic characteristics of floating photovoltaic modules under continuous changes in motion, irradiance, and temperature caused by actual wind and waves conditions. To achieve accurate measurement of floating photovoltaic modules, the coupling relationship between the motion state and the environmental factors is established. Then the motion state modeling of floating photovoltaic modules based on multi-sensors information fusion is established to acquire the absolute attitude angle with the continuous superposition of high and low frequency motion in the geographical coordinate system. On this basis, a new dynamic 2D fusion model of floating photovoltaic modules is set up to obtain the dynamic output characteristics, which integrates mechanical motion state information with the electrical parameters. Finally, the proposed modelling and analyzing method is evaluated with experimental data. The experimental and analytical results show that the accuracy of the 2D fusion model is higher than 98.7%, the output efficiency of floating photovoltaic modules is only 94.2% compared to the static state, and power generation efficiency can be increased by 2.5% by using the proposed method. The new modelling method proposed in the paper can accurately obtain the output characteristics of the floating photovoltaic system under actual operating conditions, which can effectively improve the efficiency of power generation.

Research on Scheme Design and Structure Optimization of High Speed and High Precision Vehicle Contour Detection Platform

To improve road traffic safety and reduce the incidence of unauthorized vehicle modifications, overloading, and oversizing, this study proposed a detection platform structure to support the quick measurement of key dimensions and high-precision reconstruction of local features using the automotive contour size system. Using CAE technology, static and dynamic characteristic analysis was performed on the platform structure, and optimization design was conducted on the column frame and gantry frame separately. The optimized column frame's first-order modal frequency increased by 243% from 5.16 Hz to 17.65 Hz, with an average optimization ratio of 187% for the first six modal frequencies. For the optimized gantry frame, the average optimization ratio of the key node displacement exceeded 46%, with the first-order modal frequency increasing by 13% from 36.43 Hz to 41.33 Hz, and an average optimization ratio of 21% for the first six modal frequencies. Ultimately, the optimized detection platform's key nodes achieved an average optimization ratio of nearly 60%, with the first-order modal frequency increasing by 240% from 5.16 Hz to 17.57 Hz and an average optimization ratio of 185% for the first six modal frequencies. The optimized platform structure provides robust support for the high-speed and high-precision vehicle contour detection system's implementation.

A hybrid modeling method of metal hydride tank and dynamic characteristic analysis

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

Breakthrough Curve Modeling and Analysis for Lysozyme Adsorption by Tris(hydroxymethyl)aminomethane Affinity Nanofiber Membrane.

In this study, a polyacrylonitrile nanofiber membrane was first hydrolyzed and then functionalized with tris(hydroxymethyl)aminomethane (P-Tris), then used as an affinity nanofiber membrane for lysozyme adsorption in membrane chromatography. The dynamic adsorption behavior of lysozyme was investigated in a flow system under various operating parameters, including adsorption pHs, initial feed lysozyme concentration, loading flow rate, and the number of stacked membrane layers. Four different kinetic models, pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion kinetic models, were applied to experimental data from breakthrough curves of lysozyme. The results showed that the dynamic adsorption results were fitted well with the pseudo-second-order kinetic model. The breakthrough curve experimental results show significant differences in the breakthrough time, the dynamic binding capacity, the length of the mass transfer zone, and the utilization rate of the membrane bed under different operating parameters. Four dynamic adsorption models (i.e., Bohart-Adams, Thomas, Yoon-Nelson, and BDST models) were used to analyze the breakthrough curve characteristics of the dynamic adsorption experiments. Among them, the Yoon-Nelson model was the best model to fit the breakthrough curve. However, some of the theoretical results based on the Thomas and Bohart-Adams model analyses of the breakthrough curve fit well with the experimental data, with an error percentage of <5%. The Bohart-Adams model has the largest difference from the experimental results; hence it is not suitable for breakthrough curve analysis. These results significantly impact dynamic kinetics studies and breakthrough curve characteristic analysis in membrane bed chromatography.