43,149 research outputs found
Scaling of solar wind e and the AU, AL and AE indices as seen by WIND
No full textWe apply the finite size scaling technique to quantify the statistical properties of fluctuations in AU, AL and AE indices and in the parameter that represents energy input from the solar wind into the magnetosphere. We find that the exponents needed to rescale the probability density functions (PDF) of the fluctuations are the same to within experimental error for all four quantities. This self-similarity persists for time scales up to ~4 hours for AU, AL and and up to ~2 hours for AE. Fluctuations on shorter time scales than these are found to have similar long-tailed (leptokurtic) PDF, consistent with an underlying turbulent process. These quantitative and model-independent results place important constraints on models for the coupled solar wind-magnetosphere system
aE Journal 2015/2016: aE/INTECTURE innovating architecture
No full textThe graduation studio of Architectural Engineering focuses on the integration of (new) technology in architecture. For this purpose, the name aE/ INTECTURE® was devised, which will be developed further as a brand in the coming years. Students start with a technical fascination and translate this into an architectural concept, finally being able to implement this within the environment in a responsible way. ‘If technology is the answer, what is the question?‘ Under the guidance of a team of enthusiastic (guest) lecturers, students search for the dot on the horizon that is necessary for coming up with solutions that improve the quality of the built environment and make it more sustainable. In addition, either the ‘making‘ (make) or ‘the energy and material flow’ (flow) is used and applied as a basis in different contexts.Architectural Engineerin
An experimental investigation into the correlation between Acoustic Emission (AE) and bubble dynamics
No full textBubble and cavitation effects phenomena can be encountered in two-phase gas-liquid systems in industry. In certain industries, particularly high-risk systems such as a nuclear reactor/plant, the detection of bubble dynamics, and the monitoring and measurement of their characteristics are necessary in controlling temperature. While in the petro-chemical engineering industry, such as oil transportation pipelines, the detection and monitoring of bubbles/cavitation phenomena are necessary to minimise surface erosion in fluid carrying components or downstream facilities. The high sensitivity of Acoustic Emission (AE) technology is feasible for the detection and monitoring of bubble phenomena in a two phase gas-liquid system and is practical for application within the industry.
Underwater measurement of bubble oscillations has been widely studied using hydrophones and employing acoustic techniques in the audible range. However, the application of Acoustic Emission (AE) technology to monitor bubble size has hitherto not been attempted. This thesis presents an experimental investigation aimed at exploring AEs from gas bubble formation, motion and destruction. AE in this particular investigation covers the frequency range of between 100 kHz to 1000 kHz.
The AE waveform analysis showed that the AE parameter from single bubble inception and burst events, i.e. AE amplitude, AE duration and AE energy, increased with the increase of bubble size and liquid viscosity. This finding significantly extends the potential use of AE technology for detecting the presence of bubbles in two-phase flow.
It is concluded that bubble activity can be detected and monitored by AE technology both intrusively and non-intrusively. Furthermore, the bubble size can be determined by measurement of the AE and this forms the significant contribution of this thesis
An investigation on the diagnostics and prognostic capabilities of acoustic emission (AE) on a spur gearbox
No full textThe aim of this research project is to explore a new technique, Acoustic Emission (AE),
on both the diagnostic and prognostic capabilities in monitoring gear teeth degradation
(pitting), and compare with the more widely used techniques such as vibration
monitoring and Spectrometric Oil Analysis (SOA). Furthermore, by employing the
experimental results and past literature, a model in predicting the amount of gear surface
pitting wear using AE activity level was proposed. The successful forinulation of this
proposed model may be able to predict the remaining life of the gear after pitting has
been detected, thereby allowing timely replacement to be carried out without the risk of
catastrophic failure.
A series of experimental tests which include seeded defect simulations, study on the
effect of operating parameters over AE (under isothermal conditions), AE source
determination tests and accelerated gear fatigue tests have been performed to investigate
the diagnostics and prognostics capabilities of AE via a back-to-back gearbox set up. The
experimental results achieved have highlighted some significant findings: (a) The
variation in rotating speeds, change the AE levels in a much significant amount as
compared to the same variation in applied load. (b) The prime source of AE was
postulated to be asperity contact under rolling and sliding of the meshing gear teeth
surfaces. (c) AE technique has a far better degradation (pitting) monitoring capability
compared to vibration and SOA techniques.
These findings have made a vast contribution in condition monitoring of gearbox using
AE technique and the proposed model has also offered opportunity to make AE a
potentially viable and effective tool in diagnosis and prognosis of gearbox or even other
rotating machinery defects
An Investigation of Acoustic Emission Responses of a Self Aligning Spherical Journal Bearing
No full textHigh power industrial machinery such as steam turbines and large pumps use journal bearings as rotor supports because this type of bearing is a high load carrying capacity. However, abnormal operating conditions in the journal bearings will degrade machine performance, shorten life time and increase the risk of operation. Bearing condition monitoring can detect faults at early stage and hence minimise the occurrence of catastrophic failures. Vibration measurement from an accelerometer is an effective method for monitoring journal bearing. However, due to frequency limitation, it cannot give accurate monitoring results when the bearing produces high frequency excitations such as asperity contacts. For overcoming the limits, acoustic emission (AE) is required for detecting early faults in self aligning journal bearings in high frequency ranges. AE source in journal bearings may originate from sliding friction. The friction in sliding bearings depends on lubricated regions which are influenced by load, speed, lubricant viscosity and bearing conditions. When bearing is operated in boundary lubricated region more asperity contact occurs and generates large AE responses. Hydrodynamic lubrication means that the bearing surfaces are completely separated by oil film, almost there is not severity contact and hence creates very small AE signal. Mixed lubrication occurs between boundary and hydrodynamic lubrication range and creates medium of AE value. The result of AE experiment for self-aligning spherical journal bearing indicates that AE can detect bearing fault in high frequency range till 15000 Hz. For addition there is a positive correlation between speed, load and AE RMS value. For lubricant, if the lubricant has higher viscosity, it generates smaller AE amplitude. The AE characteristic also shows that AE RMS value relates to the friction curve
Strain rate and temperature dependence of Omori law scaling constants of AE data: Implications for earthquake foreshock-aftershock sequences
No full textLittle is known about the temperature and strain rate dependence of acoustic emission AE activity (AE). Hence, we carried out a preliminary series of flow-through triaxial compression tests on porous sandstones at different temperatures and strain rates. The AE data exhibits clear foreshock and aftershock sequences with respect to the dynamic failure of the test specimen. Significant AE activity starts less than 5 min before sample failure irrespective of the strain rate. The increase in the AE event rate is steeper and the foreshock exponent p′ is smaller in the slow strain rate tests. It could be the reason why there are no easily recognisable foreshock sequences for most individual earthquakes. The aftershock decay parameter p is a linear function of test temperature as it has also been inferred for natural seismicity. The seismic b-value decreases systematically with increasing deformation rate suggesting a greater proportion of small cracks in the slow strain rate tests. Hence, the AE activity is a function of both strain rate and temperature
Scaling in long term data sets of geomagnetic indices and solar wind ϵ as seen by WIND spacecraft
No full textWe study scaling in fluctuations of the geomagnetic indices (AE, AU, and AL) that provide a measure of magnetospheric activity and of the ε parameter which is a measure of the solar wind driver. Generalized structure function (GSF) analysis shows that fluctuations exhibit self-similar scaling up to about 1 hour for the AU index and about 2 hours for AL, AE and ε when the most extreme fluctuations over 10 standard deviations are excluded. The scaling exponents of the GSF are found to be similar for the three AE indices, and to differ significantly from that of ε. This is corroborated by direct comparison of their rescaled probability density functions
Condition Monitoring of Helical Gears Using Acoustic Emission (AE) Technology
No full textTechniques such as vibration monitoring, thermal analysis and oil analysis are well
established as means to have been used to improve reliability of gearboxes and extend
time-to-failure. In this area Acoustic Emission (AE) technology is still in its infancy but
the attention shown by researchers towards this method has increased dramatically
because several studies have shown the AE offers the important advantage of improved
sensitivity over more conventional monitoring tools for the early detection and
prediction of gear failure.
Helical gear lubrication is critically important for maintaining the integrity of operating
gears and the oil also prevents asperity contact at the gear mesh thereby protecting the
gears from a deterioration process and surface failures. In gear systems, there are three
types of lubrication regimes: Dry Running, Boundary Lubrication (BL), Hydrodynamic
Lubrication (HL) and Elastohydro-dynamic Lubrication (EHL). The last regime is
associated with the normal operating running condition of gears.
Acoustic emissions were acquired from gears and analysed for different lubrication
regimes (dry, BL, HL and EHL regimes at different temperatures), and corresponding
specific film thicknesses (λ) levels. The results showed an inverse relationship between
AE signal levels and specific film thickness (λ) of the oil. This relation was used to
determine the lubrication regime from the measured AE signals. For instance, dry
running had the highest AE levels which were attributed to the metal-to-metal contact of
the gear mesh. The BL regime had relatively high AE levels which also attributed to the
level of asperity contact is greater than the oil film thickness. The HL regime was
characterized by the lowest AE levels due to the lubricant oil completely separating the
teeth during gear meshing. Finally, the EHL regime showed intermediate AE levels
compared to the BL and HL regimes because the oil film was less than for the HL
regime but greater than for the BL regime.
It is shown that the application of advanced signal processing methods is necessary for
monitoring helical gears; Kurtosis and Spectral Kurtosis were used to investigate the
AE signatures and found to be effective in de-noising (spectral kurtosis) acquired
signals. Acoustic Emission proved to be a powerful tool to detect the oil regime for both
defective and non-defective conditions.
It is concluded that the experimental findings of this research programme will provide
the foundations for significant advancement in the application of AE for the
determining the lubrication regime present within a helical gearbox and for the detection
of developing gear faults. This should give a new impetus in the field of maintenance
and prevention of human and material catastrophes.
Several papers presenting the findings of this research have been published in
international journals and given at conferences
The embedded population around Herbig Ae/Be stars
No full textHerbig Ae/Be stars are intermediate mass young stars in the pre-main sequence phase of evolution. There are only few stars of this type known so far, and all of them seem to be relatively isolated, in contrast to their low mass counterparts, the T Tauri stars. A possible explanation of this fact is that other young stars formed near the known YSO are deeply embedded in the molecular cloud environment and are not detectable at optical wavelengths. We used the new ARcetri Near Infrared CAmera (ARNICA) to survey in the J, H and K bands the regions of sky around Herbig stars. The aim of this work is to identify embedded YSO and investigate the clustering properties of these young stars
aE Journal 2017/2018: aE/Intecture innovating architecture
No full textDriven by the need to think differently about resources, energy, power generation, the choice of materials, and user involvement, we see the built environment in a new perspective. The program, Architectural Engineering, seeks for innovative and inspiring architectural solutions for social and environmental issues throughout all scales.To achieve this, innovation of the architectural challenge is high on our agenda. Innovation is more than just a technical improvement. How do you implement new current issues in modern architecture? We anticipate new energy, materials, and circularity. We also use the current environment of the metropolis and the countryside. We add new buildings, strengthen existing stock, and work on new components of buildings. From high to low tech. From digital to traditional, looking carefully to the context.Architectural Engineerin
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