1,721,216 research outputs found
Influence of Design and Working Parameters on a 2 Dof Manipulator Force-Position Controller
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An Unconventional Method for the Diagnosis and Study of Generator Rotor Thermal Bows
No full textThe rotor thermal sensitivity often affects the dynamic behavior of power unit generators. Owing to this phenomenon, increments of field current and other process parameters that are related to it may cause a shaft thermal bow and significant changes in the synchronous vibration. This symptom can also be caused by many other common malfunctions that affect rotating machines. Therefore, diagnostic techniques aimed at identifying the actual fault are very useful for optimizing maintenance activities. The thermal sensitivity of generator rotors can be deemed as a fault because it is commonly caused by a local deterioration of the winding insulation as well as by jamming phenomena between conductors and rotor slots, caused by friction forces due to the different thermal expansions of these components. This paper shows the results obtained by applying a diagnostic method, based on multiple linear regression models, which has been developed for the analysis of generator vibrations caused by thermal sensitivity. Nevertheless, nonlinear relationships between vibration and process parameters have also been taken into account. The capabilities of this diagnostic technique have been validated using the analysis of experimental data collected in a power plant. The results of this investigation are shown and discussed in the paper
Identification of nonlinear dynamic parameters of thrust bearings in rotating machines: Modelling of axial Sub-Synchronous vibration and experimental verification
Full text linkAxial Sub-Synchronous Vibration (SSV) is an uncommon phenomenon that occurs in turbomachines. Specifically in compressors and large gas turbines equipped with double-sided, oil-lubricated thrust bearings. This phenomenon manifests as high-amplitude vibration which extends throughout the entire machine axial clearance. Consequently, the structural integrity of the machinery can be compromised, as the SSV can lead to detrimental effects such as fatigue cracks, seal abrasion, and fretting on bearings. This vibration develops unpredictably, with sudden amplitude jumps related to operational parameters such as active power, axial clearance adjustments, and lubricating oil temperature. While the literature extensively discusses potential causes, often linking vibration levels to fluid film instabilities on the reverse side of thrust bearings, this theory does not account for all observed cases. To understand the problem, the nonlinear behaviour of the oil film in the thrust bearing is analysed by solving the well-known Reynolds equation. The thrust force on the bearing collar is calculated and used to create a simplified axial model of the machine. Time integration and Harmonic balance methods are used to study the nonlinear dynamics, to identify the bifurcation region, and to perform sensitivity analyses by varying operational parameters. This phenomenon usually amplifies the vibration induced by the coupling between axial-lateral vibration, related to the thrust bearing collar. The proposed model, applied to a well-known example in the literature, offers insights into mitigating the adverse effects of axial SSV and improving the reliability of turbomachines
An Optimal Redundancy Coordination Method for an Haptic Interface
No full textIn this work an optimal method for the solution of the inverse kinematics of a redundant haptic interface is shown. Methods that act on three different spaces are analyzed: at displacements, at velocities and at accelerations levels. For the first two levels features of different criterions for the redundancy coordination, based on kinematic performance indexes will be briefly presented. At the accelerations level it will be presented an original method based on the working frequency of the device. This algorithm automatically switches between two different approaches: at low working frequencies it is preferred a solution that optimizes the dexterity feature of the system, whereas at high frequencies a method that reduces the required motor torques
Influence of the Manipulator Dynamic Properties on the Design of a Force-Position Controller
No full textModeling of the dynamic response of a Francis turbine
Full text linkThe paper presents a detailed numerical model of the dynamic behaviour of a Francis turbine installed in a hydroelectric plant. The model considers in detail the Francis turbine with all the electromechanical subsystems, such as the main speed governor,
the controller and the servo actuator of the turbine distributor, and the electrical generator. In particular, it reproduces the effects of pipeline elasticity in the penstock, the water inertia and the water compressibility on the turbine behaviour. The dynamics of the surge tank on low frequency pressure waves is also modelled together with the main governor speed loop and the position controllers of the distributor actuator and of the hydraulic electrovalve. Model validation has been made by means of experimental data of a 75 MW—470 m hydraulic head—Francis turbine acquired during some starting tests after a partial revamping, which also involved the control system of the
distributor
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