Dynamic Response
Zhinong Li; Fang Qiao; Yunlong Li; Shiyao Chen; Shijian Zhou; Fei Wang
Abstract
Currently, the existing study on rotor system with disk-shaft clearance primarily focus on analyzing factors such as interference force and friction coefficient, while neglecting the vibration characteristics during the rotational states. Therefore, a finite element model is established by taking rotor ...
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Currently, the existing study on rotor system with disk-shaft clearance primarily focus on analyzing factors such as interference force and friction coefficient, while neglecting the vibration characteristics during the rotational states. Therefore, a finite element model is established by taking rotor systems with disk-shaft clearance as the research object. The vibration characteristics of rotor systems under different clearances or rotation speeds are analyzed. Increasing clearance leads to gradual fluctuations in the speed difference of shaft to disk, accompanied by an increasing periodicity of these fluctuations. In the time domain diagram, beat vibration characteristic become evident, and its period undergoes noticeable changes. The amplitude of rotation frequency increases, while that of multiple frequency decreases gradually and tends to a constant value. The presence of clearance causes the orbit of the disk center to become an irregular circle, and the shape of 8 appears. Additionally, collision and friction of shaft to disk result in apparent serrations in the orbit. As the rotational speed increases, the speed difference initially increases but eventually reaches a stable value. The beat vibration characteristic disappears due to the small speed difference, leading to a small amplitude of the multiple frequency. The orbit of the disk center tends to become circular, and the serrated phenomenon weakens and disappears. Finally, the experiments of rotor systems with disk-shaft clearance are carried out. The results are in good agreement with the simulations, which verifies the correctness of the dynamic model. The research results can provide a theoretical basis for understanding rotor systems with disk-shaft clearance.
Dynamic Response
Yonghui Park
Abstract
A hydraulically driven mold oscillator is challenging to estimate the dynamic state variables precisely. Significantly, the additional stiffness effect of hydraulic oil is variable according to operating conditions, and it is hard to formulate it as a mathematical expression. This study investigates ...
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A hydraulically driven mold oscillator is challenging to estimate the dynamic state variables precisely. Significantly, the additional stiffness effect of hydraulic oil is variable according to operating conditions, and it is hard to formulate it as a mathematical expression. This study investigates the dynamic characteristics of a mold oscillator operated by two hydraulic cylinders with other springs and dampers to determine the non-linear effect and estimate exact dynamic state variables to improve the accuracy control. The mold oscillator was excited in either step oscillation or sine-sweeping oscillation to measure its dynamic behaviors, including mold displacement and hydraulic cylinder pressure. Due to non-linear properties, the dynamic behaviors change according to excitation conditions during sine-sweeping oscillation. Primarily, peak frequencies around 50 Hz are founded from experimental pressure-displacement data in the frequency domain. To identify the oscillating mechanisms, equivalent 1-DOF and 2-DOF mass-damper-spring models for the mold oscillator are established. The fundamental system property is derived by experiment and a Finite Element multi-body dynamics model. In addition, inverse dynamics and numerical analysis were applied to derive the unknown force from the hydraulic servo system and structural characteristics. The unknown force is related to a friction problem and an elastic deflection by relative components near the mold. For high accuracy control, the unknown force model by an additional mass-spring model that causes high-frequency vibrations at 49, 48, 47, 46, or 45 Hz was suggested to formulate the equation of motion with the additional vibrations without any arbitrary modeling process.
Dynamic Response
J. Akbari; H. Valaei; M. F. Sepahvand
Abstract
Finite-element modeling of structures using elements without rotational degrees of freedom (DOFs) is usually stiffer than their physical behavior. Therefore, the stiffness of a structural system will be smoothed by adding rotational DOFs in the numerical model. In the traditional displacement-based finite-element ...
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Finite-element modeling of structures using elements without rotational degrees of freedom (DOFs) is usually stiffer than their physical behavior. Therefore, the stiffness of a structural system will be smoothed by adding rotational DOFs in the numerical model. In the traditional displacement-based finite-element method, adding drilling rotations is not easy. The main contribution of this paper is performing dynamic analyses using the finite strip element with added drilling rotations to the elements. For this purpose, any quadrilateral area is divided into two independent sets of orthogonal strips comprising truss and Bernoulli-Euler beam elements. Then by using new shape functions, mass, damping, stiffness matrices, and equivalent nodal forces are derived. Finally, time history analysis for plane stress or strain type problems for direct earthquake records is performed using the developed formulations. The numerical studies show that the results of the finite strip method using coarse meshes are competitive with the results of the finite-element method using fine meshes. This advantage is valuable in time-consuming computational problems, e.g., dynamic or nonlinear analyses.
Dynamic Response
Chandan Kumar; Vikas Rastogi Rastogi
Abstract
This work deals with effects of asymmetric stiffness on the dynamic behaviour of the rotor system. The analysis is presented through an extended Lagrangian Hamiltonian mechanics on the asymmetric rotor system, where symmetries are broken in terms of the rotor stiffness. The complete dynamics of asymmetries ...
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This work deals with effects of asymmetric stiffness on the dynamic behaviour of the rotor system. The analysis is presented through an extended Lagrangian Hamiltonian mechanics on the asymmetric rotor system, where symmetries are broken in terms of the rotor stiffness. The complete dynamics of asymmetries of rotor system is investigated with a case study. In this work, a mathematical model is developed considering symmetry breaking of a finite rotor due to stiffness. The natural frequency and amplitude of the rotor are obtained analytically through extended Lagrangian formulation. The asymmetries in rotor are also modeled through bond graph modeling technique for the computational analysis. The simulation result shows a considerable agreement with the analytical results. The limiting dynamics of rotor is shown and analyzed through simulation.
