Analysis Of Dynamic Characteristics Research Articles

Dynamic Compensation Optimization and Frequency Characteristic Analysis for Contactless Energy Transfer Under Load Variations in Rotary Ultrasonic Machining

In rotary ultrasonic machining, contactless energy transfer (CET) converts power from an ultrasonic power supply to the ultrasonic transducers. Two-side compensation circuits improve the efficiency of this process, but the addition of secondary compensation causes problems such as dynamic imbalance. Load changes affect the performance of CET system (CETS) with compensation, and dynamic compensation is needed for good CETS performance, such as high transfer efficiency and output power. This article investigates the frequency characteristics of CETS without compensation under different loads. The effects of two-side compensation on CETS under load variations is studied for the dynamic compensation characteristic. The comparison of mathematical model and performance of CETS with dynamic compensation are investigated to propose the optimized dynamic compensation. The model of CETS with optimized dynamic compensation under load variations is developed. The CETS frequency characteristics with optimized dynamic compensation are studied. The experimental results basically agree with the calculated results. The CETS with optimized dynamic compensation at the series resonant frequency can produce high transfer efficiency, high output power, low input impedance range under load variations in the cutting process of RUM, and solves the problems caused by the secondary side compensation.

A novel nonlinear drift control for sharp turn of autonomous vehicles

Under the sharp turn condition, especially on low adhesion coefficient roads, drift motion can improve vehicle agility and ensure safety. During drift motion, the large sideslip angle and rear wheel slip as well as the saturation of lateral tyre force result in the complex nonlinear dynamic behaviour, such as non-unique equilibrium point and unstable vehicle dynamic. Therefore, this paper focuses on the analysis of dynamic characteristics and the design of both the equilibrium point and feedback controller for drift motion. First, a dynamics model, in which the rear wheel slip ratio is treated as a parametric variable and the influence of rear wheel lateral force on the drift motion is explicitly expressed, is established. Then the expression of steady-state yaw rate and the virtual control input is derived, and the error dynamic model is presented furthermore. To design the equilibrium point, in this paper the effect of rear tyre slip angle and slip ratio on the equilibrium point is discussed, and the condition of stable equilibrium point is proposed. In addition, the design of desired rear tyre slip angle by synthesising the cornering performance during drift motion is presented. For the drift controller design, the main idea is to design the stabilisation controller for the nonlinear dynamic system with the stable equilibrium point and to calculate static feedback gain by means of Lyapunov stability theory. To illustrate the characteristics of drift motion, the influence of the vehicle speed and rear wheel slip ratio on the vehicle path and the low damping characteristics of the dynamic system on the control performance are analysed by different simulation conditions. Moreover, the performance and effectiveness of the proposed drift control are verified by simulation.

Selective region medical image encryption algorithm based on cascade chaos and two-dimensional Joseph traversal

Aiming at the problem that medical image information is easy to be stolen, tampered and maliciously destroyed in the transmission process, a selective region medical image encryption algorithm based on cascade chaos is proposed. The encryption algorithm consists of two stages: region of interest (ROI) encryption and full image encryption. First, the Cubic map is cascaded with an improved Cosine map. Through the analysis of dynamic characteristics, the cascade map has better chaotic performance than the traditional chaotic systems. The key sequence is generated by the cascade map and the image. Then edge detection is performed on the image to determine ROI. ROI is divided into multiple image blocks, and a new gradient algorithm is used to label the sub-blocks containing important information. A modified two-dimensional Joseph traversal method is used to scramble the positions of pixels in each sub-block, and further modify their pixel values with a round of diffusion. Finally, we use a block V-shape scrambling method to scramble the entire image. The final encrypted image is obtained through a round of bidirectional diffusion of all pixels using chaotic sequences. Simulation results and security analysis show that the algorithm has large key space and sufficient security. It can effectively resist various malicious attacks.

Experimental and numerical analysis of the static‒dynamic characteristics and vibration fatigue failure mechanism of railway fastening clips

ABSTRACT To study the static‒dynamic characteristics and vibration fatigue failure mechanism of railway fastening clips, the modal characteristics of the clip in free and installed states are obtained via field experiments, and a refined finite element model of the fastening system is established and verified. Then, static‒dynamic analysis and frequency response analysis are carried out based on the numerical model, and the effects of the system excitation with varied amplitudes and frequencies on the vibration fatigue life of the clip and the distribution characteristics of clip fatigue damage peril points (CFDPPs) are investigated. Eventually, method of dividing the clip vibration fatigue sensitive frequency range (CVFSFR) is proposed. The results show that the fatigue life of the clip is significantly affected by resonance, and the resonance at the 2nd-order natural frequency caused by high-frequency excitation is an important reason for the fatigue failure of the fastening clip.

Model and nonlinear dynamic characteristics analysis of screw-nut joint considering coupling effect of wear and vibration

Wear of rolling elements can produce a huge impact on the mechanical properties of screw-nut joint, and is one of primary causes resulting in the accuracy degradation or even failure of kinematic pairs. Many mechanical models have been constructed to investigate the vibration performance of rolling elements. But the wear influence is considered scarcely because of the complicacy of loading status and wear process. In this study, a novel wear prediction model can be proposed for screw-nut joint to overcome the above difficulty. An ultimate stiffness model can be constructed on basis of the wear model. The influences of running distance, external forces, preload, and structural parameters on wear performance are researched. A dynamic model of screw-nut joint with varying stiffness is constructed to carry out a detailed study on its vibration performance, particularly taking into account the coupling effect between wear and vibration. The influences of wear on the axial stiffness and vibration characteristics are studied based on the proposed model. Moreover, the change rules of axial stiffness and dynamic response under variable preloads are researched. The results indicate that the choice of parameters can produce an appreciable impact on the wear rate. The wear can result in the losses of stiffness and critical displacement of screw-nut joint. Although increasing the preload can improve the stiffness and the critical displacement, it also aggravates the wear degree. When the relative displacement between nut and screw is greater than the critical displacement, the balls with preload and axial force in opposite directions will be out of action, and the monotonic property of stiffness will also change. Due to the monotonicity of stiffness is not consistent before and after the critical displacement point, the amplitude-frequency curve presents a jumping phenomenon.

Optimization Design and Dynamic Characteristics Analysis of Multistage Magnetic Gearbox for MW-scale Wind Turbine

Optimization Design and Dynamic Characteristics Analysis of Multistage Magnetic Gearbox for MW-scale Wind Turbine

Dynamic characteristics analysis of a circular vibrating screen

Aiming at the structural reliability and operation stability of the vibrating screen, this study takes the 2460 double-layer circular vibrating screen as the research object, applies Creo to build a three-dimensional model of the vibrating screen, and uses ANSYS Workbench to analyze the dynamic characteristics of the vibrating screen. Through modal analysis, the natural frequencies and vibration modes of the vibrating screen are obtained. Through harmonic response analysis, the displacement and stress distribution of the vibrating screen at its working frequency are achieved. The analysis results show that the vibrating operates stably without transverse swing, the stress distribution of the screen body is uniform, can bear large dynamic loads, and has good structural strength and stiffness. This research provides a reference for the design of the domestic circular vibrating screen.

Modeling and dynamic characteristic analysis of high speed angular contact ball bearing with variable clearance

In this paper, an analytical calculation model based on Jones raceway control hypothesis model was proposed for high-speed ball bearing, clearance, centrifugal displacement and thermal deformation are considered. The validity of the proposed model was verified by comparing with the Jones model, and the fatigue life model of bearing was established. The bearing dynamic characteristics under axial load and combined load are analyzed, and the change rule of each parameter is revealed. In addition, the influence of different clearances on high-speed bearing is studied, and the dynamic characteristics of bearing are further analyzed. The research show that the proposed model can break the limitation of Jones raceway control hypothesis model, and the bearing ball-raceway contact state and fatigue life are greatly affected by the change of working clearance. Therefore, the analytical calculation model in this paper not only meets the dynamic characteristics analysis of ball bearing under different operation conditions, but also has great significance for the design and use of bearing.

Uncertain Dynamic Characteristic Analysis for Structures with Spatially Dependent Random System Parameters.

This work presents a robust non-deterministic free vibration analysis for engineering structures with random field parameters in the frame of stochastic finite element method. For this, considering the randomness and spatial correlation of structural physical parameters, a parameter setting model based on random field theory is proposed to represent the random uncertainty of parameters, and the stochastic dynamic characteristics of different structural systems are then analyzed by incorporating the presented parameter setting model with finite element method. First, Gauss random field theory is used to describe the uncertainty of structural material parameters, the random parameters are then characterized as the standard deviation and correlation length of the random field, and the random field parameters are then discretized with the Karhunen-Loeve expansion method. Moreover, based on the discretized random parameters and finite element method, structural dynamic characteristics analysis is addressed, and the probability distribution density function of the random natural frequency is estimated based on multi-dimensional kernel density estimation method. Finally, the random field parameters of the structures are quantified by using the maximum likelihood estimation method to verify the effectiveness of the proposed method and the applicability of the constructed model. The results indicate that (1) for the perspective of maximum likelihood estimation, the parameter setting at the maximum value point is highly similar to the input parameters; (2) the random field considering more parameters reflects a more realistic structure.

Horizontal dynamic modeling and vibration characteristic analysis for nonlinear coupling systems of high-speed elevators and guide rails

Horizontal dynamic modeling and vibration characteristic analysis for nonlinear coupling systems of high-speed elevators and guide rails

A unified method for parameter optimization and dynamic characteristics analysis of tuned mass damper inerter

To enhance the performance of the tuned mass damper (TMD), an inerter has recently been incorporated into a conventional TMD system to constitute a new type of an inerter-based passive control system, namely, tuned mass damper inerter (TMDI). The present study proposes a unified design idea for the TMDI based on the Kramers–Kronig relations in the complex effective mass. The TMDI is equivalent to a combination of a static mass and a conventional TMD, and the theoretical links between the TMDI and conventional TMD have been established. Based on the proposed method, the performance of the TMDI is investigated combined with the existing dynamic characteristics of the conventional TMD. It is concluded that the proposed design idea is feasible, and the previously reported dynamic characteristics of the TMDI can be well demonstrated. Moreover, the mass ratio of the equivalent TMD can be used to compare the control performance of the TMDI and TMD, and when it is larger than the physical mass ratio, the inerter enhances the control performance of the TMD.

Revisiting the Ramachandran plot based on statistical analysis of static and dynamic characteristics of protein structures

Ramachandran plots, which describe protein structures by plotting the dihedral angle pairs of the backbone on a two-dimensional plane, have played an important role in structural biology over the past few decades. However, despite continued discovery of new protein structures to date, the Ramachandran plot is still constructed by only a small number of data points, and further it cannot reflect the steric information of proteins. Here, we investigated the secondary structure of proteins in terms of static and dynamic characteristics. As for static feature, the Ramachandran plot was revisited for the dataset consisting of 9,148 non-redundant high-resolution protein structures released in the protein data bank until April 1, 2022. By calculating amino acid propensities, it was found that the proportion of secondary structures with respect to residue depth is directly related to their hydrophobicity. As for dynamic feature, normal mode analysis (NMA) based on an elastic network model (ENM) was carried out for the dataset using our KOSMOS web server (http://bioengineering.skku.ac.kr/kosmos/). All ENM-based NMA results were stored in the KOSMOS database, allowing researchers to use them in various ways. In this process, it was commonly found that high B-factors appeared at the edge of the alpha helix region, which was elucidated by introducing residue depth. In addition, by investigating the change in dihedral angle, it was possible to quantitatively survey the contribution of structural change of protein on the Ramachandran plot. In conclusion, our statistical analysis of protein characteristics will provide insight into a range of protein structural studies.

Dynamic characteristics analysis of long stroke reciprocating pump combined crank-linkage with rack-pinion mechanism

Drilling pump is the heart of drilling rig, its core structure is crank-linkage mechanism. However, the drilling pump is criticized for its short stroke and high stroke frequency. Aiming at these defects, a long stroke reciprocating (LSR) pump combined the crank-linkage with a rack-pinion mechanism is proposed, and its dynamic and flow characteristics are researched. The results reveal that the stroke of the LSR pump is extended twice when the crank radius stays the same. The stroke frequency and flow pulsation rate are lowered under the same rated power. A new multi-fulcrum crankshaft is designed to extend its fatigue life, and the reaction forces of each fulcrum are solved by simulation. The influence of the fulcrums position on the crankshaft modal frequency is further investigated. The flexible characteristics of the multi-fulcrum crankshaft are studied by rigid-flexible coupled analysis. The results show that more fulcrums can effectively reduce the stress of crankshaft, and the maximum stress of the multi-fulcrum crankshaft is only 178.6 MPa. The modal frequency of the multi-fulcrum crankshaft is increased due to more fulcrums, which proved its stiffness and stability are improved. The fatigue life of the multi-fulcrum crankshaft is predicted to reach 30,000 h by finite element analysis. This study would provide a theoretical basis for further development of the LSR pump.

Safety assessment of ancient buddhist pagoda induced by underpass metro tunnel blasting vibration

In the blasting excavation project of the subway tunnel in the urban area, ensuring the safety of the surface buildings (structures) above the crossing area is the key concern. This paper is based on the blasting project of the ancient pagoda (Shengxiang Pagoda) under the tunnel between Pengliuyang Road Station and Simenkou Station of Wuhan Metro Line 5. To protect the integrity of the ancient buildings, this paper mainly adopts the numerical simulation method to analyze the dynamic response characteristics of the tower above the subway and realizes the safety assessment of the tower based on the maximum principal stress and vibration velocity control. The results show that the maximum error rate between the measured data and the numerical simulation results is only 11.9 %, which verifies the reliability of the numerical model and parameters. In the process of blasting vibration propagation, the vibration velocity of the tower body is affected by the whiplash effect and the elevation amplification effect. The vibration velocity of the tower bottom is 0.29 cm / s, and the vibration velocity of the tower tip reaches 4.29 cm / s. The vibration velocity of the upper part of the tower is much larger than that of the lower part. The stress distribution of the tower body is accompanied by stress concentration, with the maximum reaching 0.0442 MPa and the minimum only 0.014 MPa. The safety assessment of the ancient pagoda from the aspects of structural strength and vibration velocity can determine that the structure is safe under this condition. The research results are of great significance to the analysis of dynamic response characteristics and safety evaluation of ancient buildings under blasting load in urban complex environments.

Analysis of nonlinear dynamics characteristics of a kind of hinged connection structures

Analysis of nonlinear dynamics characteristics of a kind of hinged connection structures

Design and Dynamic Characteristics Analysis of Novel Support Adjustment Mechanism of Wheeled Downhole Tractor

Conventional design method of the downhole tractor is based on cementing casing, which is only suitable for the smooth wellbore. For the open hole well, the conventional downhole tractor has poor adaptability and even cannot work normally. In order to improve the obstacle surmounting performance of the wheeled downhole tractor (WDR) and expand the application range of the WDR, a double push rod-double spring support adjustment mechanism (DPRDSSAM) is proposed in this paper. Meanwhile, the proposed DPRDSSAM also needs to increase the traction force and the stability of the WDR in the open hole well. Kinematic simulation numerical models of both conventional support adjustment mechanism and the DPRDSSAM are established. The two models comprehensively considere the influence of different obstacle forms and sizes on the obstacle surmounting performance of the tractor. The influence of different obstacle forms on the obstacle surmounting performance of DPRDSSAM and single push rod support adjustment mechanism (SPRSAM) is analyzed. Results show that the DPRDSSAM has better obstacle surmounting performance than the SPRSAM. The DPRDSSAM can effectively promote further research and application of the tractor in the open hole well.

Research on Dynamic Characteristic Analysis and Energy Consumption Modeling of Five-axis CNC Machine Tool Based on Bond Graph

Research on Dynamic Characteristic Analysis and Energy Consumption Modeling of Five-axis CNC Machine Tool Based on Bond Graph

Characteristics and adjustment strategies of reservoir agglomeration driving state in narrow channel sand body

With the continuous growth of economy, we are more and more aware of the importance of energy and its preciousness. In the production of crude oil, the narrow channel is the best location for oil storage, and the underlying sand body often has oil resources. In this paper, the effect of reservoir polymer flooding is taken as the purpose, the principle of polymer flooding technology as the theoretical basis, through the analysis of dynamic change characteristics, in order to improve the adjustment parameters, to achieve reasonable and efficient exploitation of oil Wells. The application of this technology, through the development of practice, has been recognized as an effective method of oil recovery.

Deep solar ALMA neural network estimator for image refinement and estimates of small-scale dynamics

Context. The solar atmosphere is highly dynamic, and observing the small-scale features is valuable for interpretations of the underlying physical processes. The contrasts and magnitude of the observable signatures of small-scale features degrade as angular resolution decreases. Aims. The estimates of the degradation associated with the observational angular resolution allows a more accurate analysis of the data. Methods. High-cadence time-series of synthetic observable maps at λ = 1.25 mm were produced from three-dimensional magnetohydrodynamic Bifrost simulations of the solar atmosphere and degraded to the angular resolution corresponding to observational data with the Atacama Large Millimeter/sub-millimeter Array (ALMA). The deep solar ALMA neural network estimator (Deep-SANNE) is an artificial neural network trained to improve the resolution and contrast of solar observations. This is done by recognizing dynamic patterns in both the spatial and temporal domains of small-scale features at an angular resolution corresponding to observational data and correlated them to highly resolved nondegraded data from the magnetohydrodynamic simulations. A second simulation, previously never seen by Deep-SANNE, was used to validate the performance. Results. Deep-SANNE provides maps of the estimated degradation of the brightness temperature across the field of view, which can be used to filter for locations that most probably show a high accuracy and as correction factors in order to construct refined images that show higher contrast and more accurate brightness temperatures than at the observational resolution. Deep-SANNE reveals more small-scale features in the data and achieves a good performance in estimating the excess temperature of brightening events with an average of 94.0% relative to the highly resolved data, compared to 43.7% at the observational resolution. By using the additional information of the temporal domain, Deep-SANNE can restore high contrasts better than a standard two-dimensional deconvolver technique. In addition, Deep-SANNE is applied on observational solar ALMA data, for which it also reveals eventual artifacts that were introduced during the image reconstruction process, in addition to improving the contrast. It is important to account for eventual artifacts in the analysis. Conclusions. The Deep-SANNE estimates and refined images are useful for an analysis of small-scale and dynamic features. They can identify locations in the data with high accuracy for an in-depth analysis and allow a more meaningful interpretation of solar observations.

Eksperimentalna i CFD analiza potisnog ležaja od folije podmazanog gasom za različite konfiguracije folije

Thrust foil bearings operating at hydrodynamic conditions are self-acting (aerodynamic) bearings that support high-speed shafts at mild loading conditions with air as a lubricant and are generally used in low-power gas turbines. This paper presents an experimental study and a detailed computational analysis of dynamic characteristics of the foil thrust bearing (FTB) in terms of load-carrying capabilities as a function of thrust runner speed and gap between the bearing assembly and the runner by considering the effect of bearing parameters such as number of foils, shape of the foils, and assembly of foils on the bearing pad. The parametric study was conducted on a newly conceptualized bearing test rig capable of rotating up to 45,000 rpm speeds that measured the axial loads of the air foil thrust bearings (AFTB). The computational model of the foil thrust bearings for various configurations with top foils is simulated using multiphysics software for foil deflections and pressure distributions on the foil surface. The numerical results were compared with the experimental values, while the air foil thrust bearings with multilayered foils called cascaded foils (patented) had higher load capability in comparison to other conventional bearing models.