| 1. |
- Michelsen, H. A., et al.
(författare)
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Modeling laser-induced incandescence of soot: a summary and comparison of LII models
- 2007
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 87:3, s. 503-521
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Tidskriftsartikel (refereegranskat)abstract
- We have performed a comparison of ten models that predict the temporal behavior of laser-induced incandescence (LII) of soot. In this paper we present a summary of the models and comparisons of calculated temperatures, diameters, signals, and energy-balance terms. The models were run assuming laser heating at 532 nm at fluences of 0.05 and 0.70 J/cm(2) with a laser temporal profile provided. Calculations were performed for a single primary particle with a diameter of 30 nm at an ambient temperature of 1800 K and a pressure of 1 bar. Preliminary calculations were performed with a fully constrained model. The comparison of unconstrained models demonstrates a wide spread in calculated LII signals. Many of the differences can be attributed to the values of a few important parameters, such as the refractive-index function E(m) and thermal and mass accommodation coefficients. Constraining these parameters brings most of the models into much better agreement with each other, particularly for the low-fluence case. Agreement among models is not as good for the high-fluence case, even when selected parameters are constrained. The reason for greater variability in model results at high fluence appears to be related to solution approaches to mass and heat loss by sublimation.
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| 2. |
- Oliveira, M. H. de Andrade, et al.
(författare)
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Soot, PAH and OH measurements in vaporized liquid fuel flames
- 2013
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 112, s. 145-152
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Tidskriftsartikel (refereegranskat)abstract
- Qualitative measurements of both OH and polycyclic aromatic hydrocarbons (PAH) as well as quantitative data of soot volume fraction f(v) have been obtained in vaporized liquid fuels, with the main goal of providing experimental data for combustion models and numerical mechanism validation. Measurements were carried out in a laminar coflow burner which was designed, built and integrated with an evaporation system, enabling the combustion of vaporized liquid fuels at pressures of up to 3.0 MPa to be studied. The fuels n-heptane and n-decane, referred to in the literature as being important surrogate fuels, were selected for measurements at atmospheric pressure that were carried out in the experimental setup described, making use of a combination of the Laser Induced Fluorescence (LIF) and Laser Induced Incandescence (LII) techniques. Partially premixed flames of n-heptane and n-decane showed similar combustion characteristics in the range of 1.9 < phi < 3.7. For both of the fuels the threshold for soot formation was found to be at about phi similar to 3.3. Comparison of the LIF and LII measurements for the n-heptane flames within the range of 3.7 <= phi <= 8.5 indicated the maximum PAH LIF signal to be a good predictor of f(vmax) obtained from LII. Excitation at 266 nm using delayed detection was found to result in the signals obtained showing a close linear correlation with the soot volume fraction obtained from LII when prompt detection at 1064 nm excitation was used. Neither the effects of any additional photo-chemical processes making use of high laser power at 266 nm nor the effects of particle size on the delayed gate times appeared to be of any significance for the flame conditions studied here. (C) 2013 Elsevier Ltd. All rights reserved.
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| 3. |
- Bladh, Henrik, et al.
(författare)
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Influence of Soot Particle Aggregation on Time-Resolved Laser-Induced Incandescence Signals
- 2011
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 104:2, s. 331-341
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Tidskriftsartikel (refereegranskat)abstract
- Laser-induced incandescence (LII) is a versatile technique for quantitative soot measurements in flames and exhausts. When used for particle sizing, the time-resolved signals are analysed as these will show a decay rate dependent on the soot particle size. Such an analysis has traditionally been based on the assumption of isolated primary particles. However, soot particles in flames and exhausts are usually aggregated, which implies loss of surface area, less heat conduction and hence errors in estimated particle sizes. In this work we present an experimental investigation aiming to quantify this effect. A soot generator, based on a propane diffusion flame, was used to produce a stable soot stream and the soot was characterised by transmission electron microscopy (TEM), a scanning mobility particle sizer (SMPS) and an aerosol particle mass analyzer coupled in series after a differential mobility analyzer (DMA-APM). Despite nearly identical primary particle size distributions for three selected operating conditions, LII measurements resulted in signal decays with significant differences in decay rate. However, the three cases were found to have quite different levels of aggregation as shown both in TEM images and mobility size distributions, and the results agree qualitatively with the expected effect of diminished heat conduction from aggregated particles resulting in longer LII signal decays. In an attempt to explain the differences quantitatively, the LII signal dependence on aggregation was modelled using a heat and mass transfer model for LII given the primary particle and aggregate size distribution data as input. Quantitative agreement was not reached and reasons for this discrepancy are discussed.
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| 4. |
- Bladh, Stina, et al.
(författare)
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Psychometric performance of a generic walking scale (Walk-12G) in Multiple Sclerosis and Parkinson's disease
- 2012
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Ingår i: Journal of Neurology. - Heidelberg : Springer Berlin/Heidelberg. - 0340-5354 .- 1432-1459. ; 259:4, s. 729-738
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Tidskriftsartikel (refereegranskat)abstract
- Walking difficulties are common in neurological and other disorders, as well as among the elderly. There is a need for reliable and valid instruments for measuring walking difficulties in everyday life since existing gait tests are clinician rated and focus on situation specific capacity. The Walk-12G was adapted from the 12-item multiple sclerosis walking scale as a generic patient-reported rating scale for walking difficulties in everyday life. The aim of this study is to examine the psychometric properties of the Walk-12G in people with multiple sclerosis (MS) and Parkinson’s disease (PD). The Walk-12G was translated into Swedish and evaluated qualitatively among 25 people with and without various neurological and other conditions. Postal survey (MS, n = 199; PD, n = 189) and clinical (PD, n = 36) data were used to test its psychometric properties. Respondents considered the Walk-12G relevant and easy to use. Mean completion time was 3.5 min. Data completeness was good (<5% missing item responses) and tests of scaling assumptions supported summing item scores to a total score (corrected item-total correlations >0.6). Coefficient alpha and test–retest reliabilities were >0.9, and standard errors of measurement were 2.3–2.8. Construct validity was supported by correlations in accordance with a priori expectations. Results are similar to those with previous Walk-12G versions, indicating that scale adaptation was successful. Data suggest that the Walk-12G meets rating scale criteria for clinical trials, making it a valuable complement to available gait tests. Further studies involving other samples and application of modern psychometric methods are warranted to examine the scale in more detail.
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| 5. |
- Delhay, J., et al.
(författare)
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Soot volume fraction measurements in aero-engine exhausts using extinction-calibrated backward laser-induced incandescence
- 2009
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 95:4, s. 825-838
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Tidskriftsartikel (refereegranskat)abstract
- Control and reduction of soot particle emissions from aeronautic turbines requires a monitoring system suitable for quantification of these emissions. Currently, such emissions are estimated using the technique of smoke number. This is an extractive method, which is not sensitive enough for the low emission levels of modern gas turbines. Within a recent European project, AEROTEST, part of the project aimed at investigating an alternative soot monitoring technique, laser-induced incandescence (LII) as an in-situ optical diagnostic for quantification of soot emissions. For aero-engine applications, especially those involving large-scale turbines, it is necessary to perform the measurements at long distance from the turbine. The LII technique is favourable in this respect as it provides for non-intrusive measurements and, by detecting the isotropic LII signal along the same axis as the incoming laser beam (so called backward LII), both the laser and the detector can be built inside one system located several meters from the turbine. The concept was initiated in the previous European projects, AEROJET I and II. This paper describes the modified version of the system and the procedure developed to achieve reliable and quantitative soot volume fraction measurements in the exhausts of aero-engines. Application of the backward LII technique is demonstrated in the exhaust of a military turbojet engine for different engine speeds.
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| 6. |
- Fruth, Florian, et al.
(författare)
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Unsteady forcing vs. efficiency - The effect of clocking on a transonic industrial compressor
- 2013
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Ingår i: ASME 2013 Fluids Engineering Division Summer Meeting. - : ASME Press. - 9780791855546 ; , s. V01AT02A010-
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Konferensbidrag (refereegranskat)abstract
- A numerical investigation on the impact of clocking on the efficiency and the aerodynamic forcing of the first 1.5 stages of an industrial transonic compressor was conducted. Using unsteady 3D Navier-Stokes equations, seven clocking positions were calculated and analyzed. Efficiency changes due to clocking were up to 0.125%, whereas modal excitation changes up to 31.7%. However, no direct correlation between the parameters of efficiency, stimulus and modal excitation was found as reported by others. It was found that potential forced response risks can be reduced by clocking, resulting only in minor efficiency penalties. Assuming almost sinusoidal behavior of efficiency and stimulus changes, as found in this investigation, both parameters can be set into correlation by using an ellipse interpolation. Direct impact of design changes on efficiency and stimulus through clocking can be deducted from that graph and quick estimations about extrema be made using only 5-6 transient simulations. Results however also stress the importance of considering modal excitation when optimizing for aerodynamic forcing, for which the ellipse interpolation is not necessarily possible. Highest efficiency is achieved with the IGV wake impinging on the stator blade leading edge at mid-span. It was found however that this alone is not a sufficient criteria in case of inclined wakes, as wake impingement at different span positions leads to different efficiencies.
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| 7. |
- Gutierrez Salas, Mauricio, et al.
(författare)
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Forced response analysis of a mistuned compressor blisk comparing three different reduced order model approaches
- 2016
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Ingår i: Proceedings of the ASME Turbo Expo. - : ASME Press. - 9780791849835
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Konferensbidrag (refereegranskat)abstract
- Accurate structural modeling of blisk mistuning is critical for the analysis of forced response in turbomachinery. Apart from intentional mistuning, mistuning can be due to the manufacturing tolerances, corrosion, foreign object damage and in-service wear in general. It has been shown in past studies that mistuning can increase the risk of blade failure due to energy localization. For weak blade to blade coupling, this localization has been shown to be critical and higher amplitudes of vibration are expected in few blades. This paper presents a comparison of three reduced order models for the structural modeling of blisks. Two of the models assume cyclic symmetry while the third model is free of this assumption. The performance of the reduced order models for cases with small and large amount of mistuning will be examined. The benefits and drawbacks of each reduction method will be discussed.
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| 8. |
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| 9. |
- Lebzelter, T., et al.
(författare)
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Comparative modelling of the spectra of cool giants
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 547, s. A108-
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Tidskriftsartikel (refereegranskat)abstract
- Context. Our ability to extract information from the spectra of stars depends on reliable models of stellar atmospheres and appropriate techniques for spectral synthesis. Various model codes and strategies for the analysis of stellar spectra are available today. Aims. We aim to compare the results of deriving stellar parameters using different atmosphere models and different analysis strategies. The focus is set on high-resolution spectroscopy of cool giant stars. Methods. Spectra representing four cool giant stars were made available to various groups and individuals working in the area of spectral synthesis, asking them to derive stellar parameters from the data provided. The results were discussed at a workshop in Vienna in 2010. Most of the major codes currently used in the astronomical community for analyses of stellar spectra were included in this experiment. Results. We present the results from the different groups, as well as an additional experiment comparing the synthetic spectra produced by various codes for a given set of stellar parameters. Similarities and differences of the results are discussed. Conclusions. Several valid approaches to analyze a given spectrum of a star result in quite a wide range of solutions. The main causes for the differences in parameters derived by different groups seem to lie in the physical input data and in the details of the analysis method. This clearly shows how far from a definitive abundance analysis we still are.
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| 10. |
- Nilsson, Maria H, et al.
(författare)
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Fatigue in Parkinson's Disease: Measurement Properties of a Generic and a Condition-specific Rating Scale.
- 2013
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Ingår i: Journal of Pain and Symptom Management. - : Elsevier BV. - 1873-6513 .- 0885-3924. ; 46:5, s. 737-746
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Tidskriftsartikel (refereegranskat)abstract
- CONTEXT: High-quality fatigue rating scales are needed to advance the understanding of fatigue and determine the efficacy of interventions. Several fatigue scales are used in Parkinson's disease, but few have been tested using modern psychometric methodology (Rasch analysis). OBJECTIVES: To examine the measurement properties of the generic Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) scale and the condition-specific 16-item Parkinson Fatigue Scale (PFS-16) using Rasch analysis. METHODS: Postal survey data (n=150; 47% women; mean age 70 years) were Rasch analyzed. The PFS-16 scores were tested according to both the original polytomous and the suggested alternative dichotomized scoring methods. RESULTS: The PFS-16 showed overall Rasch model fit, whereas the FACIT-F showed signs of misfit, which probably was the result of a sleepiness-related item and mixing of positively/negatively worded items. There was no differential item functioning by disease duration but by fatigue status (greater likelihood of needing to sleep or rest during the day among people classified as nonfatigued) in the PFS-16 and FACIT-F. However, this did not impact total score-based estimated person measures. Targeting and reliability (≥0.86) were good, but the dichotomized PFS-16 showed compromised measurement precision. Polytomous and dichotomized PFS-16 and FACIT-F scores identified six, three, and four statistically distinct sample strata, respectively. CONCLUSION: We found general support for the measurement properties of both scales. However, polytomous PFS-16 scores exhibited advantages compared with dichotomous PFS-16 and FACIT-F scores. Dichotomization of item responses compromises measurement precision and the ability to separate people, and should be avoided.
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