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An approach for the reproduction of friction induced vibrations in shift gearboxes in audible frequency range is presented. The research's core is given by follower forces, which arise out of the sliding clutch and gear contact. Firstly, a multi-body dynamic system with few degrees of freedom is presented, which is extended step-by-step. Besides the pure analysis of the stationary solution's stability, dynamic solutions are presented and discussed.

reibungserregte Schwingungen --- friction induced vibrations --- Antriebsstrang --- Vibrationsanalyse --- drivetrain --- vibration analysis

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In turbomachinery, the expected new generation of rotors consists of a monobloc bladed disk, called blisk, with better performances and allowing to achieve higher pressure ratios. These structures have a cyclic symmetry and well-defined modes, characterized by a sinusoidal deformation along the circumference of the blisk, which allocate the deformation amplitude uniformly over the blades. In reality, blades have small randomly distributed variations, known as mistuning. In operation, these deviations can cause a localized forced response, leading to unexpected failures due to high cycle fatigue. Moreover, under nominal conditions, the air flow encounters some obstacles, periodically distributed in the turbomachinery, which leads to a periodic pressure variation along the blisk. Due to the rotating structure, the rotor is submitted to a traveling wave excitation of a certain order, whose shape coincides with the eigenmodes of the blisk, then likely to be excited. In addition to this, industrial blisks often have a high spectral density, which makes the identification of individual modes extremely complex with a classical base excitation. 

To simulate engine order excitation, to perform modal appropriation, and to determine experimentally the mistuning, this work aims to design and implement a test bench that generates standing and traveling wave excitation of the desired order, on a compressor blisk. The solution proposed consists of an acoustic excitation system, exciting the structure in a non-intrusive way. This test bench is made up of multiple speakers driven by a voltage module, controlled by a software developed at V2i. One speaker is placed under each blade, which allows exciting the dedicated blade with a desired amplitude and phase. Then, the response of the blisk is measured with a laser Doppler vibrometer, placed on a robot arm. 

In a first instance, a numerical study of the blisk is performed to identify its modal properties. In parallel with this, an experimental mistuning identification method, named the Component Mode Mistuning method, is presented and implemented. This method allows both to compute the mistuned modal properties of the investigated blisk for a given mistuning pattern and inversely, to identify the mistuning from experimental measures. Thirdly, the excitation system is developed, from the choice of the tools to the assembly. Thereafter, to excite each blade with the same amplitude, an accurate process of calibration is conducted. Finally, some tests are performed with the developed test bench: a classical modal analysis by acoustic excitation is made first, and then traveling and standing wave excitations are applied.

Blisk --- Vibration analysis --- Mistuning --- Traveling wave excitation --- Ingénierie, informatique & technologie > Ingénierie aérospatiale

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This report is done as a part of my thesis work concerning development and application of different advanced data processing methods for blade tip timing experimental data. Initial work involves understanding the basics behind blade tip timing measurement method, critical issues affecting the implementation of these methods and the challenges faced in data processing. Then, the existing auto-regressive, sine fitting and spectral data processing methods are applied to an industrial test case to investigate the implementation of these advanced methods and to examine their feasibility towards industrial data. Operation of these different methods are studied and the frequencies/engine orders computed from each method are compared with the Campbell data (FEM) for validation. Feasibility and limitations of different methods are analyzed and discussed. 
Then, different windowing techniques are applied to the basic spectral methods such as non-uniform Fourier transform and Lomb-Scargle periodogram to study the effects of windowing the data on frequency spectrum results. Cross spectrum is applied to non-uniform Fourier transform and Lomb-Scargle periodogram to study its impact on identifying true frequencies in case of severe corruption of replicas. Next, sine fitting method is developed for two frequency identification i.e. to detect simultaneous resonances. This method is tested and validated using the data generated from multi-mode tip timing simulator which is updated from the existing blade tip timing simulator. Finally, the feasibility of this methods is analyzed and discussed.

non-intrusive stress measurement system --- blade tip timing --- turbomachinery --- Under-sampled signal --- Synchronous Vibrations --- blade vibration --- vibration analysis --- sine fitting --- Ingénierie, informatique & technologie > Ingénierie aérospatiale

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Shock (Mechanics) --- Vibration --- Choc (Mécanique) --- Periodicals. --- Périodiques --- #TS:TWER --- 621 --- Mechanical engineering in general. Nuclear technology. Electrical engineering. Machinery --- Periodicals --- Engineering --- Physics --- Architecture --- Civil Engineering --- Acoustics --- Thermodynamics and Heat Transfer --- 621 Mechanical engineering in general. Nuclear technology. Electrical engineering. Machinery --- Vibration control --- Vibration analysis --- Vibration levels --- Shock waves --- Shock absorbers --- Shock and vibration --- Mechanical shock --- Damping (Mechanics) --- Impact --- Mechanics --- Strains and stresses --- shock absorbers --- shock waves --- vibration control --- vibration analysis --- 621 Algemene mechanische bouwkunde. Nucleaire technologie. Electronica. Machinebouw --- Algemene mechanische bouwkunde. Nucleaire technologie. Electronica. Machinebouw --- Vibration.

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This Special Issue highlights the latest enhancements in the abatement of noise and vibrations in aerospace and automotive systems. The reduction of acoustic emissions and the improvement of interior cabin comfort desired by all major transportation industries, as these areas have a direct impact on customer satisfaction and, consequently, the commercial success of new products. Topics covered in this Special Issue deal with computational approaches, instrumentation and data analysis related to noise and vibrations of fixed-wing aircraft, satellites, spacecraft, automobiles, and trains, covering aerodynamically generated noise, engine noise, sound absorption, cabin acoustic treatments, duct acoustics, and vibroacoustic properties of materials. This Special Issue also focuses on industrial aspects. Existing procedures and algorithms that are useful in reaching the abovementioned objectives in the most efficient way are illustrated in the collected papers.

History of engineering & technology --- flexible spacecraft --- periodic disturbance compensation --- compensate torque design --- vibration attenuation --- reaction wheel. --- vibration analysis --- FEM --- multibody simulations --- Plasma flow control --- multichannel discharge --- plasma synthetic actuator --- actuator array --- analytic model --- centrifugal fan --- unsteady flow --- vibroacoustics --- fluid-structure-acoustic coupling --- optimization --- high-speed train --- pantograph --- aerodynamic noise --- large eddy simulation --- acoustic finite element method --- transonic buffet --- tangential slot --- steady and periodic blowing --- postpone of buffet onset --- buffet load alleviation --- component mode synthesis --- petrol engine --- NVH --- FRF --- leakage location --- Lamb wave --- beamforming --- spacecraft in orbit --- vibro-acoustics --- MDO --- aircraft fuselage --- aeroacoustics --- acoustics --- noise --- vibration --- aeronautics --- automotive