121 research outputs found
Towards acoustic condition monitoring for detection and characterisation of laser induced breakdown in a gas turbine laser ignition system
Acoustic detection and characterisation of laser induced breakdown is an attractive proposition in laser ignition systems in which condition monitoring is necessary but where optical access for monitoring purposes is impractical. Presented is a signal processing method based on wavelet decomposition for the non-invasive detection of acoustic emissions resulting from laser induced breakdown in an atmospheric pressure combustion test rig, representative of a single combustion chamber in a sub 15 MW industrial gas turbine. The probability and consistency of laser induced breakdown is determined from the acoustic signal and used to characterize the operating conditions and identify abrupt and incipient or slowly developing faults
Passive control of the lateral critical speeds of a rotating shaft using eccentric sleeves
Classical techniques for mitigating vibration in rotating structures are divided into three main categories viz. careful design and manufacture, correct installation and effective control strategies. The balancing sleeves analysed in this thesis were developed as a ‘semi active’ method of vibration control to improve the state of balance of dynamically unstable coupling shafts. However, the addition of the balancing sleeves affects the natural dynamics of the shaft, and requires a detailed understanding of their characteristics and the impact on the overall shaft dynamics in order to be useful in practice. As a first approximation, the sleeves are initially modelled as part of a full coupling shaft using the Extended Hamilton’s Principle. The simulation studies show that the flexibility of the sleeves have little impact upon the dynamics of the system and can therefore be neglected. However, when compared to results from the use of computational finite element methods with different sleeve lengths, discrepancies are identified. Experimental validation using a purpose built high speed test facility is used to show that the difference is due to the lack of appropriate modelling of sleeve flexibility characteristics. A full system model using finite element methods is therefore devised. More widely, a study of the impact of sleeve lengths shows that the classical definition of a ‘shaft mode’ does not encompass sufficient fidelity to discriminate between modes that are initially considered as being shaft dominated and those that are considered as sleeve dominated mode shapes, and the sharp transition that occurs between the two. It is notable that the transition between the two dominant modal contributors occurs at sleeve lengths that impart a natural frequency that is close to that corresponding to the shaft. It is concluded that the mechanism of passive control via use of the sleeves is a combination of softening due to the added mass of the sleeves and coherence of the individual modes of the shaft and sleeves. In this way, it is shown that the sleeves act in a manner similar to a tuned mass-damper. By appropriate design therefore, use of balancing sleeves offer the opportunity to increase the critical speed margin in practical applications and reduce unwanted lateral vibrations
On the Importance of Sleeve Flexibility in Passive Control of Critical Speeds of a Rotating Shaft Using Eccentric Sleeves
In this paper, the critical speeds of a rotating shaft fitted with eccentric balance sleeves are identified from a scaled, high speed experimental test facility. The results are compared with the results of dynamic finite element simulations. It is shown that the stiffness of the sleeves must be accommodated when considering passive control characteristics critical speeds of a rotating shaft using eccentric sleeve
Generalised analysis of compensating balancing sleeves with experimental results from a scaled industrial turbine coupling shaft
The paper furthers the analysis of a recently proposed balancing methodology for high-speed,
flexible shafts. This mechanism imparts corrective balancing moments, having the effect of\ud
simulating the fixing moments of equivalent double or single encastre mounted shafts. This
is shown to theoretically eliminate/nullify the 1st lateral critical speed (LCS), and thereby
facilitate safe operation with reduced LCS margins. The paper extends previously reported
research to encompass a more generalised case of multiple, concentrated, residual
imbalances, thereby facilitating analysis of any imbalance distribution along the shaft.
Solutions provide greater insight of the behaviour of the balancing sleeve concept, and the
beneficial implications for engineering design. Specifically: 1) a series of concentrated
imbalances can be regarded as an equivalent level of uniform eccentricity, and balance sleeve
compensation is equally applicable to a generalised unbalanced distribution, 2) compensation
depends on the sum of the applied balancing sleeve moments and can therefore be achieved
using a single balancing sleeve (thereby simulating a single encastre shaft), 3) compensation
of the 2nd critical speed, and to a lesser extent higher orders, is possible by use of two
balancing sleeves, positioned at shaft ends, 4) the concept facilitates on-site commissioning
of trim balance which requires a means of adjustment at only one end of the shaft, 5) the
Reaction Ratio, RR, (simply supported/ encastre), is independent of residual eccentricity, so
that the implied benefits resulting from the ratio (possible reductions in the equivalent level
of eccentricity) are additional to any balancing procedures undertaken prior to encastre
simulation. Analysis shows that equivalent reductions in the order of 1/25th, are possible.
Experimental measurements from a scaled model of a typical drive coupling employed on an
industrial gas turbine package, loaded asymmetrically with a concentrated point of
imbalance, are used to support the analysis and conclusions
Passive control of critical speeds of a rotating shaft using eccentric sleeves: model development (GT2016-58155)
This paper considers the passive control of lateral critical speeds in high-speed rotating shafts through application of eccentric balancing sleeves. Equations of motion for a rotating flexible shaft with eccentric sleeves at the free ends are derived using the extended Hamilton Principle, considering inertial, non-constant rotating speed, Coriolis and centrifugal effects. A detailed analysis of the passive control characteristics of the eccentric sleeve mechanism and its impact on the shaft dynamics, is presented. Results of the analysis are compared with those from three-dimensional finite element simulations for 3 practical case studies. Through a comparison and evaluation of the relative differences in critical speeds from both approaches it is shown that consideration of eccentric sleeve flexibility becomes progressively more important with increasing sleeve length. The study shows that the critical speed of high-speed rotating shafts can be effectively controlled through implementation of variable mass/stiffness eccentric sleeve systems
Report on an all-sky LIGO search for periodic gravitational waves in the S4 data
We report on an all-sky search with the LIGO detectors for periodic
gravitational waves in the frequency range 50-1000 Hz and having a negative
frequency time derivative with magnitude between zero and Hz/s. Data
from the fourth LIGO science run have been used in this search. Three different
semi-coherent methods of summing strain power were applied. Observing no
evidence for periodic gravitational radiation, we report upper limits on strain
amplitude and interpret these limits to constrain radiation from rotating
neutron stars.Comment: 5 pages, 1 figure, presented at Amaldi7, Sydney (July 2007
Searching for stochastic gravitational-wave background with the co-located LIGO interferometers
This paper presents techniques developed by the LIGO Scientific Collaboration
to search for the stochastic gravitational-wave background using the co-located
pair of LIGO interferometers at Hanford, WA. We use correlations between
interferometers and environment monitoring instruments, as well as time-shifts
between two interferometers (described here for the first time) to identify
correlated noise from non-gravitational sources. We veto particularly noisy
frequency bands and assess the level of residual non-gravitational coupling
that exists in the surviving data.Comment: Proceedings paper from the 7th Edoardo Amaldi Conference on
Gravitational Waves, held in Sydney, Australia from 8-14 July 2007. Accepted
to J. Phys.: Conf. Se
Особенности конфликтогенных зон у больных невротическими расстройствами женщин
Представлены данные о различии конфликтогенных зон у женщин и мужчин, страдающих невротическими расстройствами. Показано, что выявленные особенности необходимо учитывать в диагностике и психотерапии невротических расстройств.The authors report the data about the differences in conflectogenic zones among women and men with neurotic disorders. It was shown that the revealed peculiarities should be taken into consideration in diagnosis and psychotherapy of neurotic disorders
Detection Confidence Tests for Burst and Inspiral Candidate Events
The LIGO Scientific Collaboration (LSC) is developing and running analysis
pipelines to search for gravitational-wave transients emitted by astrophysical
events such as compact binary mergers or core-collapse supernovae. However,
because of the non-Gaussian, non-stationary nature of the noise exhibited by
the LIGO detectors, residual false alarms might be found at the end of the
pipelines. A critical aspect of the search is then to assess our confidence for
gravitational waves and to distinguish them from those false alarms. Both the
'Compact Binary Coalescence' and the 'Burst' working groups have been
developing a detection checklist for the validation of candidate-events,
consisting of a series of tests which aim to corroborate a detection or to
eliminate a false alarm. These tests include for example data quality checks,
analysis of the candidate appearance, parameter consistency studies and
coherent analysis. In this paper, the general methodology used for candidate
validation is presented. The method is illustrated with an example of simulated
gravitational-wave signal and a false alarm.Comment: 15 pages, 8 figures, Contribution to 12th Gravitational Wave Data
Analysis Workshop. Version sent to Classical and Quantum Gravity immediately
before publication. It addresses the CQG referee's comment
Effects of heat treatment on the atomic structure and surface energy of rutile and anatase TiO2 nanoparticles under vacuum and water environments
Nanomaterials have become a widely used group of materials in many chemical engineering applications owing to their ability to provide an enhanced level of functional properties compared to their crystalline and bulk counterparts. Here we report fundamental level advancements on how the anatase and rutile phase of TiO2 nanoparticles chemo-thermally respond between room temperature and the melting temperature under both vacuum and water environments. The current study is based on using molecular dynamics (MD) simulations. We present results on the equilibrium crystal morphology of these phases, structural and surface energy of TiO2 nanoparticles in the size range of 2-6 nm under different temperatures. Thermodynamic and structural properties, in the form of potential energy and Radial Distribution Functions (RDF’s) respectively, are calculated for both forms of TiO2 nanoparticles. The temperature associated with the melting transition increased with an increase in the particle size in both the phases. The potential energy change associated with the melting transition for anatase was seen to be less than that for rutile nanoparticles. Also the temperature at which the RDF’s began to stretch and broaden was observed to be lower for the case of anatase than rutile, suggesting that rutile attains the most thermal stable phase for the nano particle sizes considered in this study. Structural changes in anatase and rutile nanoparticles under different temperatures revealed that non-spherical (rod-like) rutile nanoparticles tend to be thermodynamically more stable. Surface energy influences the shape of TiO2 nanoparticles at different temperatures. The increase in the surface energy of nanoparticles under vacuum when compared with that of water environment is higher for the anatase phase than the rutile phase of nanoparticle sizes studied here. The fundamental level simulation results reported here provide a strong platform for potentially accounting for the effects of atomic-scale phase characteristics of TiO2 nanoparticles and surface energy under different temperature fields in nano processing applications and related multi-scale modelling approaches in future
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