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Introduction: The axisymmetric vector nozzle is an important mechanism to realize thrust vectoring technology, which is a complex spatial multilink mechanism, consisting of multi-stage linkage driven by multiple actuators. Under the action of the actuator load, there is resistance between all levels of linkage, which is prone to phenomena such as stagnation and poor adjustment accuracy, and thus affects the reliability of the aero-engine. Materials and methods: A single-link dynamics model of the vector nozzle regulating mechanism is constructed by using Lagrange equations of the first kind. According to the above whole chain vector nozzle adjustment mechanism, three actuators are evenly distributed on one side of the ring, and 12 branch chains are evenly distributed on the right side, and the whole machine model of the vector nozzle adjustment mechanism is constructed. Due to the fact that all branched chains have the same structure and working principle, only four branched chains are analyzed in this paper. Results: The correctness of the dynamic model is verified by comparing the ADAMS simulation results with the numerical simulation results. The simulation results show that the presence or absence of clearance in the single-chain structure has the greatest influence on the motion joint 3. The force on the four joints is almost the same when the mechanism is doing the retracting and expanding motion, and the collision force on joint C is the largest when it is doing the deflecting motion, followed by A, B and D are almost the same with the smallest force. The effect of changing the joint clearance on the retardation force of the three actuators when doing retracting and deflecting motions is also considered. At last, the results show that the clearance will produce wear, and the larger the clearance, the greater the depth of wear and the more intense the degree of wear. Conclusion: The results show that the model presented in this paper can simulate the vector nozzle regulating mechanism well. [ABSTRACT FROM AUTHOR]

Loose coupling exists in the full ceramic bearing-pedestal-foundation system within wide temperature ranges, which brings difficulties to the status monitoring and fault identification. In response to this problem, a dynamic model including the coupling effects in the system is established considering thermal-related fit clearance and pedestal looseness clearance within wide temperature ranges. The numerical integration method is applied in the simulation of system dynamic responses with the loose faults, and the relationship between the loosening impact force and peak values in vibrations is set up. The coupling mechanism between the two faults is thereby revealed, and the results are verified through experiments. Results show that the occurrences of outer ring looseness and pedestal looseness lead to new frequency components in dynamic responses, and the amplitudes of corresponding frequencies increase with the looseness clearances. The real-time running status of the system can be obtained by identifying the amplitude of the fault feature frequencies. This study reveals the fault coupling mechanism in full ceramic bearing-pedestal-foundation system within wide temperature ranges and provides theoretical basis and technical support for the safe and reliable operations for related equipment. [ABSTRACT FROM AUTHOR]

As a high-precision motion mechanism, the kinematics and dynamics of cascade thrust reverser are sensitive to the changes of nonlinear factors which are rarely considered in traditional dynamic modeling and optimization. In order to study the effect of nonlinear factors on the dynamics behavior of cascade thrust reverser mechanism, the dynamic model considering joint clearance and flexible component is established. Lankarani–Nikravesh and modified-Coulomb model are used to establish the contact force at the clearance, and the flexible component in the mechanism is modeled by the absolute node coordinate method. The effects of joint clearance value, clearance position, flexible component, and driving speed on the dynamic response of the mechanism are studied. Specifically, the nonlinear characteristics of the mechanism increase with the clearance value, and the joint clearance near the mobile fairing has greater influence on the kinematics and dynamics of blocker door. For the mechanical system with clearances, the flexible component can partially reduce the vibration of the system. The analysis of the motion synchronization of the thrust reverser actuators indicates that the asynchronous movement of actuators may increase the driving forces of actuators especially for the middle actuator. [ABSTRACT FROM AUTHOR]

The rigid-flexible coupling cable system under large deformation is studied, and the beam element from absolute node coordinate formulation is used to establish flexible cable body of the system. Different numerical integral algorithms are discussed for solving the rigid-flexible cable system and an integration strategy which combines Implicit Euler with Minimum Residual Method (MINRES) is proposed. The influence of the position and number of rigid components and different the lengths of the flexible elements on the system dynamics are analyzed. With constant total mass of the system, higher number of rigid components and their uniform distribution contribute to stabilization of the swing of the flexible cable body. When the total length of the cable is constant, increasing the number of beam elements enhances the nonlinear characteristics of the swing motion and damages the stability. The influence of different factors on the movement of large deformation flexible cable body is obtained through modeling and simulation of the rigid-flexible coupling cable system. [ABSTRACT FROM AUTHOR]

This article presents a novel system identification method for the dynamic parametrical model of the rotor-bearing system based on the Nonlinear Auto-Regressive with exogenous inputs (NARX) model, where the physical parameter of the system appears as coefficients in the model. Customarily, the NARX model-based modeling techniques require random signals as input, which leads to the rotor-bearing system that cannot be modeled using such techniques. To solve this issue, an improved system identification method, defined as the frequency sweep system identification approach is proposed in this paper. Firstly, the frequency domain version modeling framework with a physical parameter is derived based on the traditional modeling framework of the dynamic parametrical model. And then, the candidate model term dictionary corresponding to the frequency domain version modeling framework is derived. The Predicted Residual Sums of Squares based Extended Forward Orthogonal Regression algorithm is applied to identify the dynamic parametrical model of the rotor system. The model obtained by using the proposed method is validated based on the Model Predicted Output method. Finally, an experimental case of the rotor-bearing test rig is demonstrated to show the feasibility of the proposed method for real-world scenarios. Both the numerical and experimental studies illustrating the feasibility of the proposed modeling method, which provides a reliable model for time-domain response prediction and dynamic analysis of the rotor system. [ABSTRACT FROM AUTHOR]

A similarity method for rotating composite blades in thermal environment is developed for the problems of difficulty, time consumption, high cost, and risk in the dynamic test under a high-temperature environment. Within this study, a set of scaling laws are derived for thin-walled composite plates based on their dynamic models and the applicability of the scaling laws is demonstrated in the similitude design of composite blades. The present dynamic model takes into account thermal stress and centrifugal stiffening effect. Analytical calculations show that the scaled models at relatively low temperatures can well reproduce the dynamic characteristics of their corresponding prototypes at high temperatures when taking into account the scaling of temperature change and rotational speed. • Thermal stress and centrifugal stiffening effect are considered in the dynamic model. • The scaling laws for temperature change, rotational speed, natural frequency, and acceleration response are deduced. • Models at low temperatures are used to predict prototypes in high-temperature operating environments. • The scaling laws for thin-walled composite plates are applicable to the prediction of composite blades. [ABSTRACT FROM AUTHOR]

• A unified approach for modeling of the rotor with a bolted-disk joint is proposed. • Effect of tangential stiffness and transition point of bending stiffness are evaluated. • The dynamic model of the bolted-disk joint is presented with two-nodes. • Nonlinear properties of the rotor-bearing system with bolted-disk joint are investigated. • Present work provided a method to detect the change of bolted-joint performance. In large rotating machines, the rotor system involves multistage disks, where bolted joints are the basic form to connect the adjacent disks. Those bolted joints, subjected to unbalanced forces and moments during normal operation, influencing the rotor dynamics and giving rise to different motion states, which are of interest for investigations focusing on vibration signatures and dynamic stability. However, little research has been done on the rotor vibration characteristics considering dynamic parameters of bolted-disk joints. Thus, the bolted-disk joint element with two nodes is proposed by characterizing the mechanical relationship between the adjacent disks in this paper. Then, in terms of the proposed joint element and lumped mass modeling method, the dynamic model for the rotor system with a bolted-disk joint is established. After that, the responses of the system are solved numerically using the Newmark-β method, and bifurcation diagram, three-dimensional spectral plots, Poincare maps as well as spectral plots are used to analyze the dynamic behaviors under different tangential stiffness and transition point of bending stiffness of the bolted joint. Additionally, the influences of the bending stiffness of bolted-disk joint on system response are also examined. Finally, utilizing the rotor dynamic responses experiment performed at a bolted-joint rotor-bearing test rig with an electric tightening wrench, some of the results from the simulation study are verified. The present work provides a theoretical basis for detecting the performance of the bolted joint of the rotor-bearing system, and prevent failure caused by changes in the stiffness of the bolted joint. [ABSTRACT FROM AUTHOR]

• A dynamic model is proposed to solve the vibration response of an L-shaped pipeline under base harmonic and random excitations. • The proposed model is verified by comparing the natural frequencies and mode shapes of experiments. • The vibration response of L-shaped pipeline under random excitation is tested and compared by simulation. The aero-engine pipeline is inevitably subjected to base harmonic and random excitations during operation, but the vibration response analysis of the aero-engine pipeline under base random excitation has been rarely incorporated in the open research. Therefore, a dynamic model of an L-shaped pipeline combining the transfer matrix method (TMM) and lumped parameter method is proposed to solve the vibration response of the aero-engine pipeline under base harmonic and random excitations, and the natural and response characteristics of the pipeline are investigated by simulation and experiment. Firstly, the transfer matrix of the L-shaped pipeline is derived, and the natural frequencies and the corresponding mode shape vectors are obtained. Then, combined with the lumped parameter method, the transfer matrix of the L-shaped pipeline under base harmonic excitation is reconstructed and its frequency domain response is solved. On this basis, the virtual excitation method is introduced to address the dynamic responses of pipelines under base random excitation. Finally, the vibration test system for the L-shaped pipeline subjected to base excitation is built, and the vibration response solution method is verified through the comparison of simulation and experimental results. The work can provide an effective solution for the vibration response analysis of aero-engine pipelines under base harmonic and random excitations. [ABSTRACT FROM AUTHOR]

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

This study aims to investigate the nonlinear vibration properties of a rotor-bearing system carrying a multi-disk bolted joint with a fixed-point rubbing fault. For this purpose, a mathematical model of a multi-disk bolted joint rotor system is explored to determine the effect of rotor-stator rub-impact and rub-impact positions on the nonlinear dynamics of a certain type of aero-engine compressor. First, the dynamics of the rotor system with a rubbing fault are examined numerically. Then, the effect of the rub-impact position in the multi-disk bolted joint on the nonlinear dynamics is studied. The shaft is modeled using a massless shaft, where the stiffness matrix of the shaft is determined based on the flexibility influence coefficient method. The governing equation of the multi-disk bolted joint is deduced considering both the lateral and bending stiffness between the adjacent disks. The dynamic model of the overall system can then be obtained by combining the shaft and multi-disk bolted joint. The resultant governing equations of motion are solved using direct numerical integration. The numerical results obtained from the established model are compared with those of a similar structure in other literature to verify the accuracy of the method used in this study. Then, the dynamic behavior of the rotor system and the mechanical properties of the multi-disk bolted joint under a rubbing fault are presented. Finally, the chaotic response with the rub-impact force acting on different positions of the multi-disk bolted joint is investigated through numerical simulations. • A unified approach for modeling of the multi-disk bolted joint rotor system is proposed. • Mechanical properties of multi-disk bolted joint under rubbing fault are evaluated. • Dynamic properties of the multi-disk bolted joint rotor system with rubbing fault are studied. • Effect of rubbing position in the multi-disk bolted joint on rotor dynamics was demonstrated. [ABSTRACT FROM AUTHOR]

Bolted joint structure is widely utilized in the aeroengine compress rotor systems with convenience in assembly and maintenance. Due to the inherent structure discontinuity and stick-slip behavior at the mating interface, stiffness softening and frictional energy dissipation would be generated at the mating interface, resulting in complex vibration features of the rotor system. In this work, to describe the stick-slip behavior at the mating interface of the rotor system, an Iwan-based model is introduced to describe the contact state of asperities at the multi-scale level. The corresponding model identification method is proposed based on the partial hysteresis curve of the bolted joint. After that, a dynamic model of the bolted joint rotor system is established, and its dynamic response is obtained using the Runge–Kutta method. The effect of preload and friction coefficient on the nonlinear vibration of the bolted joint rotor is evaluated in detail based on the dynamic model. The result indicates that the stiffness softening would lead to the critical speed decreasing and aggravating the vibration response of the rotor system, while the frictional energy dissipation would restrain the response amplitude and induce the self-excited vibration within the super-critical speed range. The higher preload or friction coefficient has little effect on the motion state of the rotor system within the sub-critical speed range and makes system vibration stable between the 1st- and 2nd-order critical speed while unstable at the super-critical speed range. This research helps understand the vibration features of bolted joint rotor systems under the condition of stick-slip behaviors at the mating interface. • A dynamic model of a bolted joint rotor considering mating interface contact is established. • A simplified model of bolted joint to simulate the contact behaviors is proposed. • Dynamic properties of the bolted joint rotor with multi contact state are studied. • Effect of preload and friction coefficient at mating interface on rotor dynamics are investigated. [ABSTRACT FROM AUTHOR]

• A method for calculating stiffness of bearings in gear-rotor systems is proposed. • The proposed method considers the effects of the raceway rib. • It also considers the gear pair meshing, spline connection, and shaft flexibility. • The effects of stiffness on vibration behaviors of the system are analyzed. The raceway misalignment of deep groove ball bearings is a typical engineering problem that dramatically influences the supporting stiffness and vibration behaviors of gear transmission systems. Considering the influences of meshing of the spur gear pair, the connection of the spline, and the flexibility of the shaft in the practical transmission system, a method for calculating the stiffness of bearings with raceway misalignment is proposed. The effects of misalignment angle, input torque and rotational speed on radial, axial and coupling stiffness are analyzed. Subsequently, the dynamic model of the gear-rotor-bearing system is established, and the influences of the time-varying and coupling characteristics of bearing stiffness on the vibration of the system are analyzed. The results show that the raceway misalignment enhances the radial and axial coupling characteristics of the bearing stiffness and aggravates the axial vibration of the system, which is mainly manifested in the increase of the amplitude of the axial meshing frequency. The vibration amplitude of the system is easily affected by high-order resonance in the case of raceway misalignment. [ABSTRACT FROM AUTHOR]

• A dynamic model of bearing-rotor systems with inner ring misalignment is proposed. • A nested iteration method for solving the dynamic model of the system is proposed. • Nonlinearities due to ball-raceway contact and 3D clearance are well considered. • Vibration characteristics of the system with inner ring misalignment are analyzed. The inner ring dynamic misalignment of deep groove ball bearings (DGBBs), as a possible error type in practical engineering, has significant influences on the service performance of the rotor system. A novel dynamic model of the bearing-rotor system with inner ring dynamic misalignment and a model solving method based on the Newton-Raphson and Newmark- β nested iterations are proposed in this paper. This method perfectly integrates the quasi-static model of the ball bearing with the dynamic model of the rotor system. In addition, the proposed model can better consider the nonlinearity caused by the ball-raceway contact and the three-dimensional (3D) clearance inside the bearing. By comparing with the experiment, the accuracy of the proposed model is verified. On this basis, the effects of misalignment angle, radial clearance, and rotational speed on the dynamic characteristics of the system are analyzed. The results show that the inner ring dynamic misalignment introduces additional bearing force excitation and increases the vibration of the system. In addition, the inner ring dynamic misalignment cancels out the radial clearance, enhances the axial restraint of the system, and changes the axial vibration characteristics from soften-type to hardening-type nonlinearity. [Display omitted] [ABSTRACT FROM AUTHOR]