Coupling Dynamic Characteristics Research Articles

Research on the dynamic characteristics of a 3-DOF parallel tool head

PurposeThe purpose of this paper is to describe and evaluate the time-varying and coupling dynamic characteristics of a 3-DOF parallel tool head.Design/methodology/approachFrom the view of control, a new dynamic index of a 3-DOF parallel tool head is proposed based on the dynamic model in the joint space. This index can reflect the time-varying and coupling dynamic characteristics which are the main characteristics of the parallel mechanisms, and its distribution in the whole workspace is also given. Through comparison of the dynamic load (driving current) of each driving shaft, a series of experiments is designed and carried out on a prototype to validate the effectiveness of the dynamic analysis. The tracking error of each driving shaft has also been taken into consideration.FindingsThe simulations of the index have the same variation law with the experimental results. The dynamic load of the driving shaft becomes larger with the increase of the dynamic index, and the dynamic performance becomes worse at the same time.Originality/valueThe main dynamic characteristics of the 3-DOF parallel tool head can be described and evaluated through this work.

Analysis of Dynamic Coupling Characteristics of the Slope Reinforced by Sheet Pile Wall

Large deformation of slope caused by earthquake can lead to the loss of stability of slope and its retaining structures. At present, there have been some research achievements about the slope reinforcement of stabilizing piles. However, due to the complexity of the structural system, the coupling relationship between soil and pile is still not well understood. Hence it is of great necessity to study its dynamic characteristics further. In view of this, a numerical model was established byFLAC3Din this paper, and the deformation and stress nephogram of sheet pile wall in peak ground motion acceleration (PGA) at 0.1 g, 0.2 g, and 0.4 g were obtained. Through the analysis, some conclusions were obtained. Firstly, based on the nephogram of motion characteristics and the positions of the slip surface and the retaining wall, the reinforced slope can be divided into 6 sections approximatively, namely, the sliding body parts of A, B, C, D, and E and the bedrock part F. Secondly, the deformation and stress distributions of slope reinforced by sheet pile wall were carefully studied. Based on the results of deformation calculation from time history analysis, the interaction force between structure and soil can be estimated by the difference of peak horizontal displacements, and the structure-soil coupling law under earthquake can be studied by this approach.

A coupling dynamics analysis method for a multistage planetary gear system

The lumped parameter and finite element methods (FEM) are two relatively common modeling approaches for the coupling vibration analysis of the planetary gear system. In order to overcome the lack of fidelity of the lumped parameter models and the high computational cost of finite element models, and in order to obtain accurate vibration response predictions to understand the coupling vibration mechanism in the planetary gear system, a comprehensive, fully coupled, dynamic modeling method is proposed by applying a virtual equivalent shaft element. The continuous planetary gear transmission system is divided into numerous shafting elements. The dynamic model of the planetary gear system is constructed applying these shafting elements, including the shaft segments and flexible ring gear, and as well as the flexible planet carrier. The proposed method is implemented on a two-stage planetary gear system, and it is verified by comparing the results to the calculations using existing lumped parameter and FEM. The quasi-static and dynamic modeling results are presented to study the dynamic behavior and coupling characteristics in-depth. The proposed method can be used to guide the design of high reliability and low vibration planetary gear systems.

A method for designing control parameters of a 3-DOF parallel tool head

The mechatronic system of a parallel tool head consists of the mechanical subsystem and the control subsystem, and appropriate control parameters have a significant effect on the performance of the parallel tool head. Thus, it is a core issue of how to make the right choice of the control parameters. However, due to the time-varying and coupling dynamic characteristics, there is still not an effective control parameters design method during industrial machining process. In this paper, by taking a 3-DOF parallel tool head with proportional control and velocity feedforward compensation as an object of study, a complete method for designing control parameters is investigated. First, a coupling variable is specified to reflect the dynamic properties between the mechanical subsystem and the control subsystem. Next, a novel dynamic index is proposed to evaluate the dynamic load of each driving shaft in the workspace, and the shaft with maximum dynamic load should be mainly pay attention. Then, based on the typical movement experiments, two design indices are proposed to ensure that the coupling variable has appropriate properties during the motion process. Finally, a parameters design experiment and a cutting experiment of an S-shaped test piece are performed, the results show that compared with the original control parameters used in industry, the tracking error of the driving shaft is much better when using the optimized control parameters, and the test piece meets the accuracy requirement. This design thought can also be applied to other parallel manipulators in industry.

Characterisation of the human-seat coupling in response to vibration

Characterising the coupling between the occupant and vehicle seat is necessary to understand the transmission of vehicle seat vibration to the human body. In this study, the vibration characteristics of the human body coupled with a vehicle seat were identified in frequencies up to 100 Hz. Transmissibilities of three volunteers seated on two different vehicle seats were measured under multi-axial random vibration excitation. The results revealed that the human-seat system vibration was dominated by the human body and foam below 10 Hz. Major coupling between the human body and the vehicle seat-structure was observed in the frequency range of 10–60 Hz. There was local coupling of the system dominated by local resonances of seat frame and seat surface above 60 Hz. Moreover, the transmissibility measured on the seat surface between the human and seat foam is suggested to be a good method of capturing human-seat system resonances rather than that measured on the human body in high frequencies above 10 Hz.Practitioner Summary: The coupling characteristics of the combined human body and vehicle seat system has not yet been fully understood in frequencies of 0.5–100 Hz. This study shows the human-seat system has distinctive dynamic coupling characteristics in three different frequency regions: below 10 Hz, 10–60 Hz, and above 60 Hz.

A parametric model for control integrated design of hypersonic vehicles

Aiming to the complex operation condition and strong coupling dynamic characteristics of hypersonic vehicles, this paper develops a parametric model which is suitable to the control integrated design. First, the necessities and research status of the control integrated design of hypersonic vehicles are discussed. Then, the typical hypersonic waverider shape is geometrically parametrized using the quadratic curve and class/shape function methods. After that, the forces and moments of the hypersonic vehicle are estimated based on the surface element method in combination with the engineering estimation formulas, and the nonlinear dynamic parametrization model is built. Furthermore, the analytical expressions of forces and moments are obtained by means of the sensitive analysis strategies as a result that the complicated nonlinear dynamics model is changed to the iterative design model. Finally, an illustrative example is provided to verify the feasibility of this proposed method, and the according results show that the developed parametrization model enables to meet the requirements of the control integrated design.

Synchronization and coupling dynamic characteristics of a dual-rotors exciter

In this work, some theoretical analyses, numerical simulations and experimental results on synchronization of a dual-rotors exciter are given. The exciter is made up of two rotors with eccentric masses (REMs) respectively driven by two DC motors with common axis. By adjusting the phase difference between two REMs to change the response amplitude, the decoupling between response amplitude and exciting frequency can be realized. The motion equations of the vibration system are established by using Lagrange equation, and the dimensionless coupling equations of that are obtained by applying the average method of small parameter. According to the existence condition of the zero solution of the dimensionless coupling equations, the synchronization condition of the vibration system is obtained. The stability condition of the vibration system implementing synchronization motion is acquired based on the principle of Hamilton. Through the comparison between numerical simulations and experimental results, the validity of theoretical analyses is proved, which helps the design of the dual-rotors exciter.

Drift-off warning limits for deepwater drilling platform/riser coupling system

Abstract The drift-off dynamic model of deepwater drilling platform and riser coupling system was established. An analysis method on drift-off warning limits of deepwater drilling platform and riser coupling system was proposed, and a deepwater drilling platform/riser system was taken for case study. The analysis model of deepwater riser, wellhead and conductor coupling system and the drift-off dynamic model of platform were established respectively. The drift-off dynamic solver of deepwater platform was developed. The coupling dynamic characteristics and coupling effect of the deepwater drilling platform and riser system were analyzed in combination with example, and the analysis method for drift-off warning limits was described. The results show that: the riser load acting on platform plays a driving role in the platform drift-off in the initial drift-off stage, and begins to inhibit the platform drift-off gradually as the drift-off displacement increases; During the platform drift-off, the transient response speed of upper riser parameters is high, while the transient response of lower riser parameters presents an obvious hysteresis effect; As the current speed increases or water depth decreases, the drift-off warning limits of deepwater drilling platform/riser coupling system decrease and the deepwater drilling riser should be disconnected earlier.

Stability analysis in milling of the thin walled part considering multiple variables of manufacturing systems

In order to improve the precision of the milling stability analysis, the more exact milling dynamic model considering multiple variables of manufacturing systems is proposed, and in order to reduce the calculation time for the stability analysis of the milling dynamic model, the fast calculation of the stability analysis is proposed. Firstly, the contact region of the milling cutter and the thin walled part is discretized into many small intervals, the milling dynamic model considering helix angle of the milling cutter, two degrees of freedom of the thin-walled part, and coupling dynamic characteristic of the tool–spindle system is established in a discrete small interval. The dynamic model in the small discrete interval considering multiple variables is transformed into equation of states, and the equation of states is integrated in the range of the milling depth to establish the milling dynamic model considering multiple variables of manufacturing systems. Secondly, in order to enhance the calculation speed of the stability analysis for the established dynamic model considering multiple variables, and to avoid the loss of information, the sampling rule of the delay term is defined based on the sampling rule of Shannon sampling theorem, and the delayed term is reconstructed in the discrete interval by using the Shannon interpolation function, and the validity of the fast calculation of the stability analysis is verified by two degrees of the freedom milling dynamic model. Finally, the validity of the established milling dynamic model considering multiple variables is verified by milling experiment, and the results show that the established dynamic model is effective.

In-situ coupling between kinase activities and protein dynamics within single focal adhesions.

The dynamic activation of oncogenic kinases and regulation of focal adhesions (FAs) are crucial molecular events modulating cell adhesion in cancer metastasis. However, it remains unclear how these events are temporally coordinated at single FA sites. Therefore, we targeted fluorescence resonance energy transfer (FRET)-based biosensors toward subcellular FAs to report local molecular events during cancer cell adhesion. Employing single FA tracking and cross-correlation analysis, we quantified the dynamic coupling characteristics between biochemical kinase activities and structural FA within single FAs. We show that kinase activations and FA assembly are strongly and sequentially correlated, with the concurrent FA assembly and Src activation leading focal adhesion kinase (FAK) activation by 42.6 ± 12.6 sec. Strikingly, the temporal coupling between kinase activation and individual FA assembly reflects the fate of FAs at later stages. The FAs with a tight coupling tend to grow and mature, while the less coupled FAs likely disassemble. During FA disassembly, however, kinase activations lead the disassembly, with FAK being activated earlier than Src. Therefore, by integrating subcellularly targeted FRET biosensors and computational analysis, our study reveals intricate interplays between Src and FAK in regulating the dynamic life of single FAs in cancer cells.

Multi-field Coupling Dynamic Characteristics and Data Fitting Based on Kriging Model

Multi-field Coupling Dynamic Characteristics and Data Fitting Based on Kriging Model

Multi-field coupling dynamic characteristics based on Kriging interpolation method

Multi-field coupling problems are taken more and more attention mainly because of the higher requirement of load, efficiency, and reliability in aero-engine operation. This research takes an aero-engine compressor as the research object, 3D flow field and structural models are established. For the method of cyclic symmetric, single-sector model is selected as the calculation domain. Considering the influence of former stator wakes, compressor flow field is simulated. The article analyzes the distribution law of unsteady aerodynamic load on rotor blade. Based on Kriging model, load transfer of aerodynamic pressure and temperature is achieved from flow field to blade structure. Then the effects of centrifugal force, aerodynamic pressure and temperature load are discussed on compressor vibration characteristic and structural strength. The results show dominant fluctuation frequencies of aerodynamic load on rotor blade are manly at frequency doubling of stator–rotor interaction, especially at one time frequency (1 × f0). Magnitude and pulsation amplitude on pressure surface are far greater than that on suction surface. Load transfer with Kriging model has a higher precision, it can meet the requirement of multi-field coupling dynamic calculation. In multi-field coupling interaction, temperature load makes the natural vibration frequencies decrease obviously, centrifugal force is the main source of deformation and stress. Bending stress induced by aerodynamic pressure and temperature load can counteract part of bending stress induced by centrifugal force. However, temperature load causes the maximum displacement of blade-disk system to increase.

Numerical and experimental investigation on self-synchronization of two eccentric rotors in the vibration system

In this paper, we study the coupling dynamic characteristic of a single mass vibration machine driven by two eccentric rotors rotating oppositely. According to the coordinate of rotor flux, we deduce the electromagnetic torque of an induction motor in the steady state operation. From three ways of numerical analysis, model simulation and experiment, we discuss the coupling dynamic characteristic by using the actual parameters of this vibration machine. The results show that when the synchronization condition is satisfied, not only the vibration synchronization transmission can be achieved, but also the synchronization motion of the two motors with different power supply frequencies also can be achieved. The phase of the bigger mass-radius product lags behind that of the smaller one, the phase of the bigger distance between the rotation center of eccentric rotor and the mass center of the vibration rigid body lags behind that of the smaller one, and the phase difference decreases with increasing the synchronization velocity. We present a new method that adjusting the power supply frequencies of the two motors to make the vibration system with different structure parameters carry out the 0 phase difference, and its feasibility is verified by experiment.

Study on the dynamic coupling characteristics of 3PTT-2R numerical control serial–parallel machine based on singular constraints and position coupling factors

The dynamic coupling problem for the self-designed “3 parallel ∪ 2 series” mixed-type numerical control machine tool is studied based on the singular constraints and position coupling factors in order to ensure that the machine can have better dynamic characteristics and a higher quality of parts during the process of machining complex surface. This article puts forward a method based on singular constraints and the coupling factor. A whole dynamic coupling model of series and parallel mechanism is established and the coupling factors are determined. Numerical and parameter simulations of mechanism are analyzed and the real working space is obtained. And this article takes the simulation of the process of machining complex part and the force of the machine tool. The simulation results show that the established dynamics model is credible and reliable on the basis of considering singular constraints and position coupling factors. It is proved that the simulation data can correspond to the established model and the situation of force and kinematic suits the working mechanism. The cutting experiment of complex surface parts was took and the machine tool was run more smoothly and faster than the conventional machine tools. The velocity of the machine is regular and circular and there are no kinematic singularity data on the machine’s trajectory. The trajectory of the tool is in the working space completely and the accuracy of the part is good. The surface roughness results show that the kinematics accuracy of the machine tool is good. The interference fringe results show that the force of the machine tool is uniform. As there is no singular coupled vibration and collision, it is proved that the theoretical analysis is correct. The dynamics model of 3PTT serial and parallel mechanism is complete in this article. And the working space of the mechanism is obtained on the base of analysis of the singular constraints and position coupling factors. The article has carried out the dynamic simulation and processing experimental verification. Not only the method and process of this article was solved by dynamics coupling problem of 3PTT-2R numerical control machine tool actively, real-time and effectively, but also it was laid a foundation for accurate control of numerical control machine tools.

New Developments in Fault Analysis Based on Dynamical Perspective

ABSTRACTElectric power system essentially belongs to strongly nonlinear complex dynamic system. It has strong coupling and other various dynamic characteristics. In theory, the nonlinear dynamical model associated with complex power system should exist. In this paper, we have discussed two kinds of nonlinear circuits, nonlinear RLC circuit that can be constructed to be Liénard equation model and Chua's circuit. In our research, the superstable periodic parameters of period doubling bifurcations are solved accurately, and it is also the fault characteristic in nonlinear circuits, which may represent the essential attribute of complex electric power system. The research will contribute to solving the blackout problems in real electrical engineering. It is an inevitable request that applying nonlinear dynamical system theory to the research of complex electric power system, which is not only beneficial to the effective solution of power system's own problems, but realizing new breakthroughs in nonlinear dynamical system theory by finding new problems.

Structure Optimization of the Aluminum Alloy Frames of Flight Simulator

Frames are the main components of the flight motion simulator, which are the support for each shaft system, at the same time the rotating load for the external shaft, so the stiffness and dynamic characteristics of the frames in a large extent determines the final accuracy and dynamic performance of the flight motion simulator. For the cast aluminum alloy ZL114A frames of a 3-DOF flight motion simulator, using finite element analysis method, the dynamic characteristics are calculated and analyzed, and then the each order resonance frequency and mode of vibration are obtained. By using of the modal synthesis method and optimization algorithms, the structural dynamics of frames are designed optimally, so as to further reducing the moment of inertia, and improving the stiffness and dynamic characteristics of frames. This method has provided important reference for the reasonable design of the frame structure, and definitively established the foundation to further study the triaxial coupling dynamic characteristics and system mechanical optimization for the flight motion simulator.

Multi-degree-of-freedom coupling dynamic characteristic of TBM disc cutter under shock excitation

When the tunneling boring machine (TBM) cutterhead tunnels, the excessive vibration and damage are a severe engineering problem, thereby the anti-vibration design is a key technology in the disc cutter system. The structure of disc cutter contains many joint interfaces among cutter ring, cutter body, bearings and cutter shaft. On account of the coupling for dynamic contact and the transfer path among joint interface, mechanical behavior of disc cutter becomes extremely complex under the impact of heavy-duty, which puts forward higher requirements for disc cutter design. A multi-degree-of-freedom coupling dynamic model, which contains a cutter ring, a cutter body, two bearings and cutter shaft, is established, considering the external stochastic excitations, bearing nonlinear contact force, multidirectional mutual coupling vibration, etc. Based on the parameters of an actual project and the strong impact external excitations, the modal properties and dynamic responses are analyzed, as well as the cutter shaft and bearings’ loads and load transmission law are obtained. Numerical results indicate the maximum radial and axial cutter ring amplitudes of dynamic responses are 0.568 mm and 0.112 mm; the maximum radial and axial vibration velocities are 41.1 mm/s and 38.9 mm/s; the maximum radial and axial vibration accelerations are 94.7 m/s2 and 58.6 m/s2; the maximum swing angle and angular velocity of cutter ring are 0.007° and 0.0074 rad/s, respectively. Finally, the maximum load of bearing roller is 40.3 kN. The proposed research lays a foundation for structure optimization design of disc cutter and cutter base, as well as model selection, modification and fatigue life of the cutter bearing.

Multi-directional coupling dynamic characteristics analysis of TBM cutterhead system based on tunnelling field test

The core component, TBM cutterhead, bears a multi-directional impact load because of its direct contact with rock during tunneling. Unreasonable cutter design and parameter set lead to severe vibration or abnormal injury during excavation, seriously affecting the efficiency of the TBM tunneling. Therefore, study of cutterhead dynamics response under impact loads is one of the core content of TBM system design. TBM multi-degree-of-freedom coupled dynamic model contains different geological conditions, cutter speed, body mass, time-varying mesh stiffness, transmission error, etc. A method is proposed to solve the problem based on Newmark algorithm, which further improves the solution efficiency. A tunneling field test was conducted, and the results verify the correctness of the model and the simplified cutter system. The simulation results of the Dahuofang project show that: ➀ The calculation process of Newmark is simplified, the calculation speed increased 3-4 orders of magnitude higher than Runge-Kutta method, while the solving time was reduced from 2.6e5 s to 155 s under the same precision; ➁ Compared with the results of two kinds of rock with compressive strength 150 MPa and 95 MPa, the translational vibration amplitude ratio is 3.33 and axial vibration amplitude ratio is 2.08. It indicates that as the rock compressive strength increases, the growth of the cutterhead’s vibration amplitude increase accelerated, rather than proportional increases; ➂ The vibration decreases along with the cutter speed becomes larger and the system becomes stabilized when the cutterhead speed turns into 4r/min. The cutter head speed clearly affects torsional, lateral and longitudinal vibration. The change rate has reached 0.53-0.61. Therefore, TBM should choose the right cutter speed to avoid bearing damage, seal failure and other serious accidents; 4 The translational vibration of components decreases with the components’ mass increase. It has the greatest impact on the horizontal and vertical vibration of the big ring. The vibration changing rate of the big ring reaches 0.31. The big ring has almost no effect on the axial vibration and overturn, but the energy consumed on rock cutting will be reduced as the mass increases. Body weight should be chosen reasonably considering vibration,construction economy and internal excitation of parameters. The above conclusions provide a theoretical basis for TBM dynamics optimization design, vibration control and cutterhead architecture design.

Research on rigid–flexible coupling dynamic characteristics of boom system in concrete pump truck

Concrete pump truck plays an important role in infrastructure construction and national economic development. In recent years, its boom system becomes longer, and its dynamic and control become more complicated. In order to study the dynamic characteristics of boom system, three dynamic models such as multi-rigid-body model, rigid–flexible coupling model, and rigid–flexible coupling model with equivalent hydraulic cylinder were built in this work. Simulation analysis and experimental analysis were done, and they show that we should not only consider the large-range motion but also consider the small flexible deformation to study the dynamic characteristics of boom system precisely. It provides the theoretical basis to vibration control, trajectory prediction, and life assessment for boom system and such structures.

Nonlinear Coupling Characteristics Analysis of Integrated System of Electromagnetic Brake and Frictional Brake of Car

Since theoretical guidance is lacking in the design and control of the integrated system of electromagnetic brake and frictional brake, this paper aims to solve this problem and explores the nonlinear coupling characteristics and dynamic characteristics of the integrated system of electromagnetic brake and frictional brake. This paper uses the power bond graph method to establish nonlinear coupling mathematical model of the integrated system of electromagnetic brake and frictional brake and conducts the contrastive analysis on the dynamic characteristics based on this mathematical model. Meanwhile, the accuracy of the nonlinear coupling mathematical model proposed above is verified on the hardware in the loop simulation platform, and nonlinear coupling characteristics of the integrated system are also analyzed through experiments.