Experimental Investigation of Rossiter Modes for an Open Box Cavity With Adjustable Depth

2021 ◽  
Author(s):  
Steffen Hammer ◽  
Jens Fridh ◽  
Mattias Billson
Keyword(s):  
Prediction Models ◽  
Acoustic Resonance ◽  
Mode Shift ◽  
Project Study ◽  
Shift Pattern ◽  
Long Time ◽  
Shallow Cavity ◽  
Organ Pipe ◽  
Aero Engines ◽  
Operational Range

Abstract Resonance in aerospace is a phenomenon that engineers have been trying to predict and avoid for a long time. Acoustic resonance is only a part in this field. When it was previously studied, it was mostly in connection with long slender gaps at the fuselage of aircrafts. Lately it has become a focus in the development of highly efficient aero engines. Bleed systems in the compressor part of engines are needed but not easy to place aerodynamically. Additionally, these bleed systems have complex geometries. These geometries coupled with the operational range of modern aircraft from low to high subsonic Mach numbers can create unwanted acoustic resonances. This paper is part of project study of these resonances. Here the bleed geometry is simplified to an open box cavity that is studied experimentally in order to measure its acoustic behavior in low to high subsonic flow. The experimental data is compared to theoretical prediction models to create a baseline for future studies. The results show a good agreement between Rossiter prediction and experiments for a shallow cavity of L/D = 4. Deeper cavities with a length to depth ratio of one and 0.5 represent more organ pipe resonance phenomena. This is especially governed by the geometry of the cavity itself and the height of the test section. All cavities experience a shift in modes depending on the operating point. This mode shift pattern is similar for deeper cavities. However, the operating range can be divided into four sections in which a mode shift occurs for all cavities.

scholarly journals Water vapour foreign-continuum absorption in near-infrared windows from laboratory measurements

2012 ◽  
Vol 370 (1968) ◽  
pp. 2557-2577 ◽  
Author(s):  
Igor V. Ptashnik ◽  
Robert A. McPheat ◽  
Keith P. Shine ◽  
Kevin M. Smith ◽  
R. Gary Williams
Keyword(s):  
Water Vapour ◽  
Near Infrared ◽  
Prediction Models ◽  
Weather Prediction ◽  
Pair Interaction ◽  
Atmospheric Conditions ◽  
Laboratory Measurements ◽  
Atmospheric Absorption ◽  
Clear Sky ◽  
Long Time

For a long time, it has been believed that atmospheric absorption of radiation within wavelength regions of relatively high infrared transmittance (so-called ‘windows’) was dominated by the water vapour self-continuum, that is, spectrally smooth absorption caused by H 2 O−H 2 O pair interaction. Absorption due to the foreign continuum (i.e. caused mostly by H 2 O−N 2 bimolecular absorption in the Earth's atmosphere) was considered to be negligible in the windows. We report new retrievals of the water vapour foreign continuum from high-resolution laboratory measurements at temperatures between 350 and 430 K in four near-infrared windows between 1.1 and 5 μm (9000–2000 cm −1 ). Our results indicate that the foreign continuum in these windows has a very weak temperature dependence and is typically between one and two orders of magnitude stronger than that given in representations of the continuum currently used in many climate and weather prediction models. This indicates that absorption owing to the foreign continuum may be comparable to the self-continuum under atmospheric conditions in the investigated windows. The calculated global-average clear-sky atmospheric absorption of solar radiation is increased by approximately 0.46 W m −2 (or 0.6% of the total clear-sky absorption) by using these new measurements when compared with calculations applying the widely used MTCKD (Mlawer–Tobin–Clough–Kneizys–Davies) foreign-continuum model.

New Model for Concrete Creep and Shrinkage Prediction and its Application

2016 ◽  
Vol 249 ◽  
pp. 125-130 ◽  
Author(s):  
Vojtěch Kolínský ◽  
Jan L. Vítek
Keyword(s):  
Prediction Models ◽  
Concrete Strength ◽  
Autogenous Shrinkage ◽  
High Strength ◽  
New Model ◽  
Software Products ◽  
Internal Parameters ◽  
Environment Temperature ◽  
Long Time ◽  
Creep And Shrinkage

At the beginning of this year prof. Z. P. Bažant and his team published a new numerical model for predicting creep and shrinkage in concrete structures. Model, named B4, is conceptually based on the previous version B3. While early prediction models were based mostly on classical concrete composition, the new model allows for observation the variability of modern concrete compositions, i.e. the effects of admixtures, various aggregate types and increasing concrete strength. The model also captures the effects of environment temperature, multi-decade prediction and autogenous shrinkage. This is important for concretes that are produced in Czech Republic and have higher, but not high strength (about 50 MPa). The model also allows to determine internal parameters according to experimental measurements on laboratory specimens or structural members. Therefore it is possible to refine the prediction of the behavior of structures made of this concrete in the long time periods. However, the increased number of input parameters leads to a higher complexity and it is necessary to have computational tools for practical model application. To provide the model to wider engineering community open structure computational program (in MATLAB environment) was created. Software is freely available for download on the internet. Description of the innovations of the model B4 and demonstration of its relatively simple applications using newly developed software products is a subject of this paper.

scholarly journals Graph-Based Prediction of Meeting Participation

2019 ◽  
Vol 3 (3) ◽  
pp. 54
Author(s):  
Gabriel Murray
Keyword(s):  
Predictive Models ◽  
Prediction Models ◽  
Group Discussion ◽  
Activity Level ◽  
Multiple Time ◽  
Time Lags ◽  
Activity Levels ◽  
Linguistic Features ◽  
Long Time ◽  
Short Time

Given a meeting participant’s turn-taking dynamics during one segment of a meeting, and their contribution to the group discussion up to that point, our aim is to automatically predict their activity level at a later point of the meeting. The predictive models use verbal and nonverbal features derived from social network representations of each small group interaction. The best automatic prediction models consistently outperform two baseline models at multiple time-lags. We analyze which interaction features are most predictive of later meeting activity levels, and investigate the efficacy of the verbal vs. nonverbal feature classes for this prediction task. At long time-lags, linguistic features become more crucial, but performance degrades compared with prediction at short time-lags.

A Model with Back-Propagation Algorithm for the Estimation of Irreducible Water Saturation

2011 ◽  
Vol 361-363 ◽  
pp. 445-450 ◽  
Author(s):  
Ping Hua Ma ◽  
Hong Fu Fan ◽  
Ke Li
Keyword(s):  
Prediction Models ◽  
Water Saturation ◽  
Back Propagation ◽  
Superior Performance ◽  
Back Propagation Algorithm ◽  
Irreducible Water Saturation ◽  
Long Time ◽  
Multi Phase Flow ◽  
Conventional Models ◽  
Hidden Layer

As one of the most important reservoir parameters, irreducible water saturation, Swir, is a key parameter in evaluating multi-phase flow, as well as its importance in defining oil in-place. Residual oil saturation, the target of tertiary recovery, is also a function of Swir. In traditionally, Swir is determined by conducting capillary pressure experiments, requiring considerable resources and long time periods, with the consequence of a limited number of core plug evaluations for a particular reservoir. Thus, the estimation of Swir with mathematical models is developed in recent years. The study reported in this paper uses artificial neural network to determine Swir. The optimal model is chosen among 25 simulations, subtilizing different combinations of hidden layer nodes and activation functions for the hidden and output layers. Its performance is compared with other conventional models, demonstrating the superior performance of the proposed Swir prediction models.

Effect of Cavity Volume on the Flow-Excited Acoustic Resonance of a Shallow Cavity in a Pipe-Line

2015 ◽  
Author(s):  
S. Mohamed ◽  
S. Ziada
Keyword(s):  
Strouhal Number ◽  
Pipe Flow ◽  
Acoustic Resonance ◽  
Black Box ◽  
Cavity Volume ◽  
Maximum Value ◽  
Pipe Line ◽  
Shallow Cavities ◽  
Shallow Cavity ◽  
Flow Through

The effect of cavity volume on the aeroacoustic source generated by fully developed pipe flow through an axisymmetric shallow cavity is investigated experimentally. Nine cavity sizes are studied in three different groups of length, L, to depth, H, ratios (L/H = 1, 2 and 3) with three different cavity volumes for each group of L/H. The Sound Wave Method (SWM) is used to measure the aeroacoustic sources as function of the Strouhal number. This methodology does not require knowledge of the details of the unsteady flow-sound interaction in the cavity region because it considers the cavity as a black box with a dipole sound source or sink. The aeroacoustic source strength and the Strouhal number corresponding to its maximum value are found to increase in a systematic manner as the cavity volume is increased for the same L/H ratio. These results indicate that the aeroacoustic sources of shallow cavities are affected not only by the ratio L/H, but also by the cavity volume.

scholarly journals Internal-Tide Spectroscopy and Prediction in the Timor Sea

2015 ◽  
Vol 45 (1) ◽  
pp. 64-83 ◽  
Author(s):  
Samuel M. Kelly ◽  
Nicole L. Jones ◽  
Gregory N. Ivey ◽  
Ryan J. Lowe
Keyword(s):  
Time Scales ◽  
Prediction Models ◽  
Internal Tide ◽  
Surface Displacement ◽  
Internal Tides ◽  
Sea Surface ◽  
Mean Flow ◽  
Long Time ◽  
Timor Sea ◽  
Response Method

AbstractSpectral analyses of two 3.5-yr mooring records from the Timor Sea quantified the coherence of mode-0 (surface) and mode-1 (internal) tides with the astronomical tidal potential. The noncoherent tides had well-defined variance and were most accurately quantified for tidal species (as opposed to constituents) in long records (>6 months). On the continental slope (465 m), the semidiurnal mode-0 and mode-1 velocity and mode-1 pressure variance were 95%, 68%, and 56% coherent, respectively. On the continental shelf (145 m), the semidiurnal mode-0 and mode-1 velocity and mode-1 pressure variance were 98%, 34%, and 42% coherent, respectively. The response method produced time series of the semidiurnal coherent and noncoherent tides. The spectra and decorrelation time scales of the semidiurnal tidal amplitudes were similar to those of the barotropic mean flow and mode-1 eigenspeed (~4 days), suggesting local mesoscale variability shapes noncoherent tidal variability. Over long time scales (>30 days), mode-1 sea surface displacement amplitudes were positively correlated with mode-1 eigenspeed on the shelf. At both moorings, internal tides were likely modulated during both generation and propagation. Self-prediction using the response method enabled about 75% of semidiurnal mode-1 sea surface displacement to be predicted 2.5 days in advance. Improved prediction models will require realistic tide–topography coupling and background variability with both short and long time scales.

Measurement of the Excitation Source of an Axisymmetric Shallow Cavity Shear Layer

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
S. Mohamed ◽  
H. R. Graf ◽  
S. Ziada
Keyword(s):  
Shear Layer ◽  
Sound Field ◽  
Acoustic Resonance ◽  
Acoustic Mode ◽  
Turbulent Pipe Flow ◽  
The Self ◽  
Free Shear Layer ◽  
Axisymmetric Cavity ◽  
Shallow Cavity ◽  
High Reynolds

The interaction of a cavity shear layer with the sound field of an acoustic mode can generate an aeroacoustic source which is capable of initiating and sustaining acoustic resonances in the duct housing the cavity. This aeroacoustic source is determined experimentally for an internal axisymmetric cavity exposed to high Reynolds number, fully developed turbulent pipe flow without the need to resolve the details of neither the unsteady flow field nor the flow-sound interaction process at the cavity. The experimental technique, referred to here as the standing wave method (SWM), employs six microphones distributed upstream and downstream of the cavity to evaluate the fluctuating pressure difference generated by the oscillating cavity shear layer in the presence of an externally imposed sound wave. The results of the aeroacoustic source are in good agreement with the concepts of free shear layer instability and the fluid-resonant oscillation behavior. The accuracy of the measurement technique is evaluated by means of sensitivity tests. In addition, the measured source is used to predict the self-excited acoustic resonance of a shallow cavity in a pipeline. Comparison of the predicted and measured results shows excellent prediction of the self-excited acoustic resonance, including the resonance frequency, the lock-in velocity range, and the amplitude of the self-generated acoustic resonance.

scholarly journals Fast Numerical Wind Turbine Candidate Site Evaluation

2021 ◽  
Vol 11 (7) ◽  
pp. 2953
Author(s):  
Matija Perne ◽  
Primož Mlakar ◽  
Boštjan Grašič ◽  
Marija Zlata Božnar ◽  
Juš Kocijan
Keyword(s):  
Wind Turbine ◽  
Prediction Models ◽  
Weather Prediction ◽  
Measurement Data ◽  
Experimental Modelling ◽  
Numerical Weather ◽  
Nonlinear Regression Models ◽  
Wind Speeds ◽  
Long Time

A long-term measured wind speed time series from the location is typically used when deciding on placing a small wind turbine at a particular location. These data take a long time to collect. The presented novel method of measuring for a shorter time, using the measurement data for training an experimental model, and predicting the wind in a longer time period enables one to avoid most of the wait for the data collection. As the model inputs, the available long-term signals that consist of measurements from the meteorological stations in the vicinity and numerical weather predictions are used. Various possible experimental modelling methods that are based on linear or nonlinear regression models are tested in the field sites. The study area is continental with complex terrain, hilly topography, diverse land use, and no prevailing wind. It is shown that the method gives good results, showing linear regression is most advantageous, and that it is easy enough to use to be practically applicable in small wind projects of limited budget. The method is better suited to small turbines than to big ones because the turbines sited at low heights and in areas with low average wind speeds, where numerical weather prediction models are less accurate, tend to be small.

scholarly journals Raman spectroscopic study of the influence of voltage-time on titania growth-fast anodized nanostructures

2019 ◽  
Vol 65 (5 Sept-Oct) ◽  
pp. 449
Author(s):  
M. Luna Cervantes ◽  
J. Hernández Torres ◽  
L. Zamora Peredo
Keyword(s):  
Tio2 Nanotubes ◽  
Blue Shift ◽  
Time Lapse ◽  
Morphological Characterization ◽  
Electrochemical Anodization ◽  
Mode Shift ◽  
Time Period ◽  
Anodization Process ◽  
Long Time ◽  
Thickness Function

Many studies, focused in TiO2 nanotubes obtained by anodization, uses frequently a NH4F salt concentration from 0.3 – 0.5 wt% and the information about how voltage and time affects to nanotubes morphology, are valid for these concentration, moreover, this range induces a long time of anodized. TiO2 nanotubes were prepared by anodization process of a set of titanium foils in order to study the influence of time and voltage on the morphology of them. The anodization process consists of an organic media of ethylene glycol and 1.2 wt% of NH4F salts, voltage from 5 to 30 V for a time period from 1 to 6 hours, constant potential of 30 V for a time lapse from 10 to 360 minutes and 5 to 480 seconds. All anodized samples are rinsed and annealed to 400 °C by 3 hours to obtain an anatase crystalline structure. The morphological characterization was carried out by Field Emission Scanning Electron Microscopy (FESEM) to verify the presence of the nanostructures: nanopores, nanotubes and nanograss, these nanostructures were identified to appear for a time period from 5 to 480 seconds, 10 to 60 minutes and 1 to 6 hours, respectively. The surface morphology, inner diameter and length of the nanotubes varied with the electrochemical anodization parameters. Raman spectroscopy was used for optical characterization in order to identify the changes in signal intensity and Eg mode Shift and it was observed that intensity suffers an increment and Eg mode suffers a blue shift as a thickness function.

scholarly journals On the long-term aging of S-phase in aluminum alloy 2618A

2021 ◽  
Vol 56 (14) ◽  
pp. 8704-8716
Author(s):  
Christian Rockenhäuser ◽  
Christian Rowolt ◽  
Benjamin Milkereit ◽  
Reza Darvishi Kamachali ◽  
Olaf Kessler ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
Elevated Temperatures ◽  
Prediction Models ◽  
S Phase ◽  
Scanning Calorimetry ◽  
Term Operation ◽  
Transmission Electron ◽  
Long Time ◽  
Engine Components

AbstractThe aluminum alloy 2618A is applied for engine components such as radial compressor wheels which operate for long time at elevated temperatures. This results in coarsening of the hardening precipitates and degradation in mechanical properties during the long-term operation, which is not taken into account in the current lifetime prediction models due to the lack of quantitative microstructural and mechanical data. To address this issue, a quantitative investigation on the evolution of precipitates during long-term aging at 190 °C for up to 25,000 h was conducted. Detailed transmission electron microscopy (TEM) was combined with Brinell hardness measurements and thorough differential scanning calorimetry (DSC) experiments. The results show that GPB zones and S-phase Al2CuMg grow up to < 1,000 h during which the GPB zones dissolve and S-phase precipitates form. For longer aging times, only S-phase precipitates coarsen, which can be well described using the Lifshitz–Slyozov–Wagner theory of ripening. A thorough understanding of the underlying microstructural processes is a prerequisite to enable the integration of aging behavior into the established lifetime models for components manufactured from alloy 2618A.

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