Author: Robert G. Parker
Publisher:
ISBN:
Category :
Languages : en
Pages : 58

View

Book Description

Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781723138720
Category :
Languages : en
Pages : 166

View

Book Description
The work performed on global dynamic simulation and noise correlation of gear transmission systems at the University of Akron is outlined. The objective is to develop a comprehensive procedure to simulate the dynamics of the gear transmission system coupled with the effects of gear box vibrations. The developed numerical model is benchmarked with results from experimental tests at NASA Lewis Research Center. The modal synthesis approach is used to develop the global transient vibration analysis procedure used in the model. Modal dynamic characteristics of the rotor-gear-bearing system are calculated by the matrix transfer method while those of the gear box are evaluated by the finite element method (NASTRAN). A three-dimensional, axial-lateral coupled bearing model is used to couple the rotor vibrations with the gear box motion. The vibrations between the individual rotor systems are coupled through the nonlinear gear mesh interactions. The global equations of motion are solved in modal coordinates and the transient vibration of the system is evaluated by a variable time-stepping integration scheme. The relationship between housing vibration and resulting noise of the gear transmission system is generated by linear transfer functions using experimental data. A nonlinear relationship of the noise components to the fundamental mesh frequency is developed using the hypercoherence function. The numerically simulated vibrations and predicted noise of the gear transmission system are compared with the experimental results from the gear noise test rig at NASA Lewis Research Center. Results of the comparison indicate that the global dynamic model developed can accurately simulate the dynamics of a gear transmission system. Choy, F. K. and Qian, W. Glenn Research Center DYNAMIC CHARACTERISTICS; GEARS; MATHEMATICAL MODELS; MODAL RESPONSE; STRUCTURAL VIBRATION; TRANSMISSIONS (MACHINE ELEMENTS); DYNAMIC MODELS; DYNAMIC STRUCTURAL ANALYSIS; EQUATIONS OF MOTION; FINITE ELEMENT ME...

Author: Qingkai Han
Publisher: Springer
ISBN: 9789811096952
Category : Technology & Engineering
Languages : en
Pages : 164

View

Book Description
This book explores the dynamics and vibration properties of gearboxes, with a focus on geared rotor systems. It discusses mechanical theories, finite-element based simulations, experimental measurements and vibration signal processing techniques. It introduces the vibration-resonance calculation method for the geared rotor system in wind turbines and load sharing of the planetary gear train, and offers a method for calculating the vibrations of geared rotor systems under either internal excitations from gear sets or external loads transferred from wind loads. It also defines and elaborates on parameter optimization for planetary gear systems based on the torsional dynamics of wind-turbine geared rotor systems. Moreover, it describes experimental measurements of vibrations on the wind-turbine gearbox performed on the test rig and on site, and analyzes the vibration signals of different testing points, showing them in both time and frequency domains. Lastly, it lists the gear coupling frequencies and fault characteristic frequencies from the vibrations of the gearbox housing. The technologies and results presented are valuable resources for use in dynamic design, vibration prediction and analysis of gearboxes and geared rotor systems in wind turbines as well as many other machines.

Author: Shengli Zhang
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages :

View

Book Description
This study presents an effort in system level identification and gear dynamics analysis. The mechanical system usually includes several parts with different mechanisms to achieve a particular job. To simulate the motion of the parts, evaluate the performance, and analyze the vibration of the system, a system level modeling is needed. However, the modeling is challenging because of unknown parameters, nonlinearities, and uncertainties. System identification is one of the key techniques to obtain a reliable dynamic model by appropriately choosing the mathematical model, identifying the unknowns, and reducing the uncertainties. This study illustrates approaches and procedures in building system-level model for an electric impact wrench. Electric impact wrench, whose operation involves dynamic events occurring at vastly different time scales, is an important tool used in manufacturing and maintenance services where high torque is required. A first-principle-based, system-level model is built by incorporating the dynamics of gear transmission, spindle, and impacting components. The nonlinear impact and kinematic constraints are explicitly analyzed, and systematic parametric identification is performed based on a multi-objective optimization approach, i.e. archived multi-objective simulated annealing. The predictions from the model with system identification correlate well with the experimental results. In the system level modeling, it is found that gear transmission is one of the most popular and important sub-system whose dynamics and health conditions affect the system performance significantly. Therefore, this study also presents the effort in the gear dynamics analysis and fault diagnosis. It is well known that the nonlinear characteristics of the gearbox are mainly induced by time-varying mesh stiffness and backlash. To solve this nonlinear system, numeric method is usually employed whose time step has to be carefully controlled and the accuracy suffers from cumulative errors. To overcome the limitations of the numeric method, an approach, integrating Floquet theory with harmonic balance method, is proposed to analytically analyze the dynamics of the gearbox that subjects to parameter excitation and backlash nonlinearity. This approach can not only solve the steady-state system response, as traditional harmonic balance method, but also the transient response of the system. Case study verifies the accuracy of the proposed approach and its efficiency in calculating the frequency response of the system. The proposed method also accurately predicts the nonlinear jump of the gearbox. In the gear fault diagnosis, a fault signature enhancement method, i.e. angle-frequency domain synchronous averaging, is developed. This method is capable of highlighting the fault related features from the nonstationary and noisy vibration signal. Rather than being averaged in time-domain as traditional method, the vibration signal is averaged in angle-frequency domain after being resampled from time domain into angle domain and analyzed by the joint angle-frequency technique so as to solve the phase shift problem. The enhanced results are then analyzed through feature extraction algorithms, i.e. Kernel Principal Component Analysis, Multilinear Principal Component Analysis, and Locally Linear Embedding, to extract the most distinct features for fault classification and identification. Experimental study demonstrates that the proposed method significantly enhances the fault related features and improves the identification rate of support vector machine in identifying multi gear faults.

Author:
Publisher:
ISBN:
Category : Mechanics, Applied
Languages : en
Pages : 400

View

Book Description

Author: Gang Liu
Publisher:
ISBN:
Category : Gearing
Languages : en
Pages : 218

View

Book Description
Abstract: Multi-mesh gear systems are used in a variety of industrial machinery, where noise, quality, and reliability lie in gear vibration. The dynamic gear mesh forces are the source of vibration and result from parametric excitation and contact nonlinearity. The primary goal of this work is to develop mathematical models for multi-mesh gearsets with nonlinear, time-varying elements, to conduct numerical and analytical studies on nonlinear gear dynamic behaviors, such as parametric instabilities, frequency response, contact loss, and profile modification, and to provide guidelines for practical design and troubleshooting. First, a nonlinear analytical model considering dynamic load distribution between individual gear teeth is proposed, including the influence of variable mesh stiffnesses, profile modifications, and contact loss. This model yields better agreement than two existing models when compared against nonlinear gear dynamics from a finite element benchmark. Perturbation analysis finds approximate frequency response solutions for providing guidance for optimizing system parameters. The closed-form solution is validated by numerical integration. Second, the nonlinear, parametrically excited dynamics of idler and counter-shaft gear systems are examined. The periodic steady state solutions are obtained using analytical and numerical approaches. With proper stipulations, the contact loss function and the variable mesh stiffness are reformulated into a form suitable for perturbation. The closed-form solutions from perturbation analysis expose the impact of key parameters on the nonlinear response. The analysis for this strongly nonlinear system compares well to separate harmonic balance/continuation and numerical integration solutions. Finally, this work studies the influences of tooth friction on parametric instabilities and dynamic response of a single-mesh gear pair. A mechanism whereby tooth friction causes gear tooth bending is shown to significantly impact the dynamic response. A dynamic model is developed to consider this mechanism together with the other contributions of tooth friction and mesh stiffness fluctuation. Perturbation analysis finds approximate solutions that predict and explain the parametric instabilities. The effects of time-varying friction moments about the gear centers and friction-induced tooth bending are critical to parametric instabilities and dynamic response. The impacts of friction coefficient, bending effect, contact ratio, and modal damping on the stability boundaries are revealed.

Author: Rhys Gareth Jones
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description
In the mathematical modelling of gear vibrations it is found that there is a gap between the transient models developed in academia and the steady state models frequently used in industry. It is seen that the academic models are adept at modelling the nonlinear phenomena seen during gear contact for system with only a few degrees-of-freedom, whereas the industrial models are capable of solving the linear steady state response of more complex transmission systems. The work presented in this thesis attempts to bridge the gap between the two models, through the development of a transient nonlinear model of a gear pair with increased degrees-of-freedom. An understanding of the gear contact is achieved through the use of advanced static finite element analysis with nonlinear gear contact. Through FEA the effects of gear misalignment on these contact conditions is also investigated. The findings from the FEA are then used in a mathematical model of a single stage spur gear transmission, which is developed as part of the thesis, to determine the system accelerations. The mathematical model includes the time varying mesh stiffness and the time varying and nonlinear bearing stiffness's and frictional forces. The effects of lateral misalignment seen in the FEA results are also included into the model to investigate their effects. The model parameters are then varied to determine their effects and the simulated accelerations are compared against experimental results. It is found from this comparison that although some similarities between the simulated and experimental results are achieved for the aligned case, insufficient corroboration is found for the axially and radially misaligned results to confirm the validity of the mathematical model for modelling misalignment. From this, further experimental results were requested to gain a better con- fidence in the effects of lateral misalignment.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 128

View

Book Description
Planetary gear noise and vibration are primary concerns in their applications in helicopters, automobiles, aircraft engines, heavy machinery, and marine vehicles. Dynamic analysis is essential to the noise and vibration reduction. This work analytically investigates some critical issues and advances the understanding of planetary gear dynamics. A lumped-parameter model is built for the dynamic analysis of general planetary gears. The unique properties of the natural frequency spectra and vibration modes are rigorously characterized. These special structures apply for general planetary gears with cyclic symmetry and, in practically important case, systems with diametrically opposed planets. The special vibration properties are useful for subsequent research. Taking advantage of the derived modal properties, the natural frequency and vibration mode sensitivities to design parameters are investigated. The key parameters include mesh stiffnesses, support/bearing stiffnesses, component masses, moments of inertia, and operating speed. The eigensensitivities are expressed in simple, closed-form formulae associated with modal strain and kinetic energies. As disorders (e.g., mesh stiffness variation, manufacturing and assembling errors) disturb the cyclic symmetry of planetary gears. their effects on the free vibration properties are quantitatively examined. Well-defined veering rules are derived to identify dramatic changes of natural frequencies and vibration modes under parameter variations. The knowledge of free vibration properties, eigensensitivities and veering rules provide important information to effectively tune the natural frequencies and optimize structural design to minimize noise and vibration. Parametric instabilities excited by mesh stiffness variations are analytically studied for multi-mesh gear systems. The discrepancies of previous studies on parametric instability of two-stage gear chains are clarified using perturbation and numerical methods.

Author: Geunho Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 378

View

Book Description

Author: National Aeronautics and Space Adm Nasa
Publisher: Independently Published
ISBN: 9781730827273
Category : Science
Languages : en
Pages : 90

View

Book Description
A review of the available literature on gear housing vibration and noise radiation is presented. Analytical and experimental methodologies used for bearing dynamics, housing vibration and noise, mounts and suspensions, and the overall gear and housing system are discussed. Typical design guidelines, as outlined by various investigators, are also included. Results of this review indicate that although many attempts were made to characterize the dynamics of gearbox system components, no comprehensive set of design criteria currently exist. Moreover, the literature contains conflicting reports concerning relevant design guidelines. Lim, Teik Chin and Singh, Rajendra Unspecified Center...