1,720,967 research outputs found
Rotordynamic Modal Testing via Journal Bearing Lubricant Film - An Experimental Validation
No full textExperimental modal testing is performed in a rotor-bearing system using the journal-bearing lubricant film as an excitation source (shaker). The aerodynamic pressure field between the rotor and the bushing surface is influenced by the pressurized air injection through four orifices orthogonally machined on the bushing surface. The air injections are independently controlled by four piezoelectric stack actuators. Fluid film excitation forces resulting from the aerodynamic pressure variations are dependent on: i) the air supply pressures; ii) the DC amplitudes of the input signals to the piezoelectric actuators, i.e., opening-closing the flow through the orifices; iii) the AC amplitudes of the input signal – a Gaussian-distributed signal – supplied to the piezoelectric actuators; iv) different configuration of active injection orifice; and v) the journal angular velocity. The estimation of damping ratios and natural frequencies is done using a combination of four operational modal analysis (OMA) algorithms. Additionally, classical experimental modal analysis (EMA) is performed using an instrumented impact hammer and the results are used as a benchmark for the validation of the results coming from the novel technique combining the excitation via fluid film with output-only modal analysis algorithms. Good agreements between the two experimental approaches are found. The influence of the amplitudes of the input signal to the piezoelectric actuators, the air supply pressure, the orifice activation layouts, and the rotor angular velocities on the natural frequencies and damping ratios of the rotor-bearing system are investigated using both experimental dynamic testing techniques
A Presentation of Control Theory Applied to the Design of Controllable Segmented Gas Foil Bearings
No full textWith industry diverging away from the use of oil in the hopes of a more environmentally friendly production, the use of Gas Foil Bearings (GFBs) can facilitate an oil-free alternative for high-speed rotating light machinery. Currently, their application is, however, limited by their low load-bearing capability and low vibration damping. Hybridization has the possibility to mitigate these limitations. The system presented in this paper demonstrates the increased system capabilities through passive and active Hybrid Gas Foil Bearings (HGFB) with radial gas injection. The non-linear differential equations comprising the system, pressure states, foil deflections, rotor movements, and actuator position, are solved simultaneously with and without control feedback. The presented results comprise unbalance response waterfall diagrams
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Evaluation of the Finite Journal Bearing Characteristics, Using the Exact Analytical Solution of the Reynolds Equation
No full textA Journal Bearing with Variable Geometry for the Reduction of the Maximum Response Amplitude During Passage Through Resonance
No full textAn analytical solution of the Reynolds Equation for the finite journal bearing and evaluation of the lubricant pressure
No full textThe Reynolds equation for the pressure distribution of the lubricant in a journal bearing with finite length is solved analytically. Using the method of the separation of variables in an additive and in a multiplicative form a set of particular solutions of the Reynolds equation is added in the general solution of the homogenous Reynolds equation and a closed form expression for the definition of the lubricant pressure is presented. The Reynolds equation is split in four linear ordinary differential equations of second order with non constant coefficients and together with the boundary conditions they form four Sturm-Liouville problems with the three of them to have direct forms of solution and one of them to be confronted using the method of power series. In this part of the work, the mathematical procedure is presented up to the point that the application of the boundaries for the pressure distribution yield the final definition of the solution with the calculation of the constants. The distributions of the pressure given from the particular solution and the solution of the homogeneous Reynolds equation are presented together with the resulting pressure. Also, the results of an approximate analytical solution using Bessels functions and linearization of the fluid film thickness function are also presented together with the results of the numerical solution using the finite differences method. Diagrams for the pressure profiles under the current study are compared with those from the approximate analytical and the numerical solution. The locations in which the maximum, the zero, and the minimum pressure are presented are given as a function of eccentricity rate with closed form expressions
Analytical evaluation of the finite journal bearing impedance forces using the exact analytical solution of the Reynolds equation
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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