Dynamics of a Gear System with Faults in Meshing Stiffness

Gear box dynamics is characterised by a periodically changing stiffness. In real gear systems, a backlash also exists that can lead to a loss in contact between the teeth. Due to this loss of contact the gear has piecewise linear stiffness characteristics, and the gears can vibrate regularly and chaotically. In this paper we examine the effect of tooth shape imperfections and defects. Using standard methods for nonlinear systems we examine the dynamics of gear systems with various faults in meshing stiffness.Comment: 10 pages, 8 figure

Energy harvesting from a non-linear standing beam–mass system: Two- versus one-mode approximations

We investigate the effect of including the second mode of natural vibration on the computed response of a forced non-linear gravity-loaded beam–mass structure used for non-linear piezoelectric energy harvesting. Using the method of assumed-modes and Lagrange’s equations, we develop the discretized equations of generalized coordinates of the system including the electro-mechanical equation. The equation of motion is further simplified to find the single-mode approximation. The phase-portraits, time-histories, Poincaré sections, and frequency–response curves of the system are computed. It is shown that the number of mode shapes affects the response, and it is required to include higher modes to improve the analytical–computational results. The system shows distinct behavior varying from a linear single-frequency response to a multi-frequency chaotic response. The average power across the load resistor consequently shows a noticeable variation depending on the characteristics of the overall system response

Vibration analysis for anti-symmetric laminated composite plates resting on visco-elastic foundation with temperature effects

In this work, a comprehensive vibrational behavior analysis is performed on anti-symmetric laminated composite plates resting on visco-elastic foundations undergoing thermal effects. Here, the governing equations of motion are developed through Hamilton's principle and Reddy's plate theory as higher-order shear deformation theory (HSDT) is employed to capture high accuracy. Also, the generalized differential quadrature method (GDQM) is used to predict the vibration response and the natural frequencies. The effects of temperature change, Winkler-Pasternak and damping coefficients for the elastic foundation, the elastic ratio, the arrangement of different anti-symmetric laminates, and the aspect and slenderness ratios are observed and discussed in detail. The results are extracted for fully clamped boundary conditions and the effects of other boundary conditions are also illustrated

Mode shape transformation for model error localization with modal strain energy

A modeling error location method based on modal strain energy is presented in this paper. Errors in the design model with shell elements are located by an error indicator which is based on changes between the equivalent modal strain energy and the modal strain energy of the design model. The equivalent modal strain energy is defined as a quadratic form using the stiffness matrix of the design model and the mode shape of the reference coming from the sophisticated and high fidelity finite-element model, called the supermodel, or the full-field measurement. The major obstacle to obtain the equivalent modal strain energy is how to match the mode shapes of a solid element and those of a shell element since each node of the solid element contains only three translation degrees of freedom (dofs) while each node of the shell element has six dofs, including three translation and three rotation components. In order to solve this problem, a mode shape transformation method from the solid element to the shell element is proposed using the shape functions or linear approximation. Using this approach, the errors in the design model can be determined and the updating parameters can be selected so that the updated model has physical meaning and can represent the dynamic characteristics of the real structure. The simulation of a simple plate is used initially to illustrate the effectiveness of the proposed method. Then, a rotor test rig casing is taken as an example for further investigation. A comparison of the updating parameters selected by the proposed method and the traditional sensitivity analysis technique is then undertaken. It is verified that the updating parameters selected based on error location have physical sense and represent the true errors in the design model through the updating results. The advantage of this technique is that only detailed mode shapes from the reference is required. The approach shows potential for further industrial engineering applications

Modal sensitivity of three-dimensional planetary geared rotor systems to planet gear parameters

A parameter study is presented to determine effects of planet gear design parameters on the global modal behaviour of planetary geared rotor systems. The modal sensitivity analysis is conducted using a three-dimensional dynamic model of a planetary geared rotor system for the number of planet gears, planet mistuning, mass of planet gears, gear mesh stiffness and planet gear speed. These parameters have varying impacts on both natural frequencies and mode shapes, therefore the sensitivity of the planetary geared rotor vibration modes to the planet gear parameters is determined by computing the frequency shifts and comparing the mode shapes. The results show that the mass and mesh stiffness of planet gears have a larger influence on the global dynamic response. Torsional modes and coupled torsional-axial modes are more sensitive to gear mesh stiffness whereas lateral vibration modes are more sensitive to gearbox mass. Planet mistuning results in coupling between lateral and torsional vibrations. The planetary gearbox becomes more rigid in the torsional-axial modes and more flexible in the lateral modes with an increase in the number of planet gears. Planet gears are also found to be having significant gyroscopic effects inside the planetary gearbox. The main original findings in this study can be directly used as initial guidelines for planetary geared rotor design

Fixed-time rendezvous control of spacecraft with a tumbling target under loss of actuator effectiveness

This paper investigates the fixed-time fault-tolerant control problem of spacecraft rendezvous and docking with a freely tumbling target in the presence of external disturbance and thruster faults. More specifically, based on the attitude of the target spacecraft, a line-of-sight coordinate frame is defined first, and the dynamical equations relative to the tumbling target are derived to describe the relative position (not six degrees of freedom). Then two fixed-time position controllers are proposed to guarantee that the closed-loop system is stable in finite time in the sense of a fixed-time concept, even in the presence of simultaneous external disturbance and thruster faults. Numerical simulations illustrate that the chaser spacecraft can successfully perform the rendezvous using the proposed controllers

Modeling and design of a class of hybrid bistable symmetric laminates with cantilever boundary configuration

Multistable laminates have been widely analyzed in the recent past for their potential in morphing applications. However, all the analytical models developed up until now have taken into account only the free-free boundary condition. In this work two objectives are met: (a) an analytical model is developed, which extends the previously available models in literature to account for the cantilever boundary condition for a special class of hybrid bistable symmetric laminates (HBSL); (b) the previously proposed HBSL is modified by replacing the aluminum layers with bi-direction glass-epoxy prepregs in the layup. It is observed that the modified layup has a curvature similar to the previously proposed HBSL while maintaining bistability. The analytical model developed here successfully captures the equilibrium shapes and the snap-through behavior for this special class of laminates which is validated against the results obtained using ABAQUS® and experiments. The developed model is then subsequently used to study the design space and bistability characteristics of the HBSL and the proposed modified layup (m-HBSL) in the cantilever boundary condition

Support position optimization with minimum stiffness for plate structures including support mass

The optimum position and minimum restraint stiffness of a flexible point support to raise a natural frequency of a thin bending plate is investigated, with the inclusion of the corresponding additional support mass. First the derivatives of the natural frequencies of the plate structure are derived with respect to the support movement using a finite element model. Second, the minimum support stiffness is analyzed to raise a plate's natural frequency to a target value by solving a characteristic eigenvalue problem. Then the optimal support design is studied to find the optimal attachment point and the associated minimum stiffness. Several typical examples of plate systems are analyzed with addition of the point supports with non-negligible mass. It appears that including the support mass in the plate vibration analysis can significantly increase the minimum support stiffness required to raise a given natural frequency to its target, whereas the optimal support position remains consistent with the massless support design case

On wave propagation in two-dimensional functionally graded porous rotating nano-beams using a general nonlocal higher-order beam model

This paper studies the wave propagation of two-dimensional functionally graded (2D-FG) porous rotating nano-beams for the first time. The rotating nano-beams are made of two different materials, and the material properties of the nano-beams alter both in the thickness and length directions. The general nonlocal theory (GNT) in conjunction with Reddy's beam model are employed to formulate the size-dependent model. The GNT efficiently models the dispersions of acoustic waves when two independent nonlocal fields are modelled for the longitudinal and transverse acoustic waves. The governing equations of motion for the 2D-FG porous rotating nano-beams are established using Hamilton's principle as a function of the axial force due to centrifugal stiffening and displacement. The analytic solution is applied to obtain the results and solve the governing equations. The effect of the features of different parameters such as functionally graded power indexes, porosity, angular velocity, and material variation on the wave propagation characteristics of the rotating nano-beams are discussed in detail