| 1. |
- Carlson, Johan, et al.
(författare)
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Measurement of methane content in upgraded biogas using pulse-echo ultrasound
- 2008
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Ingår i: Proceedings of the International Congress on Ultrasonics.
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Konferensbidrag (refereegranskat)abstract
- In this paper we present an ultrasonic pulseecho technique for estimating the methane (CH4) content in binary mixtures of CH4 and carbon dioxide (CO2). The method is based on parametric estimation of phase velocity and frequency dependent attenuation in combination with Partial Least-Squares Regression (PLSR). The technique is verified using experiments on mixtures with a volume fraction of CO2 in the range of 0 % -10 %. The experiments show that the CH4 content can be accurately estimated with high repeatability.
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| 2. |
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| 3. |
- Johansson, Gustav, et al.
(författare)
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Simulation of post-ADC digital beamforming for large aperture array radars
- 2010
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 45:RS3001
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents simulations and methods developed to investigate the feasibility of using a Fractional-Sample-Delay (FSD) system in the planned EISCAT_3D incoherent scatter radar. Key requirements include a frequency-independent beam direction over a 30 MHz band centered around 220 MHz, with correct reconstruction of pulse lengths down to 200 ns. The clock jitter from sample to sample must be extremely low for the integer sample delays. The FSD must also be able to delay the 30 MHz wide signal band by 1/1024th of a sample without introducing phase shifts, and it must operate entirely in baseband. An extensive simulation system based on mathematical models has been developed, with inclusion of performance-degrading aspects such as noise, timing error, and bandwidth. Finite Impulse Response (FIR) filters in the baseband of a band-pass-sampled signal have been used to apply true time delay beamforming. It has been confirmed that such use is both possible and well behaved. The target beam-pointing accuracy of 0.06° is achievable using optimized FIR filters with lengths of 36 taps and an 18 bit coefficient resolution. Even though the minimum fractional delay step necessary for beamforming is ∼13.1 ps, the maximum sampling timing error allowed in the array is found to be σ ≤ 120 ps if the errors are close to statistically independent.
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| 4. |
- Johansson, Jonny, et al.
(författare)
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Project: EISCAT 3D
- 2007
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Annan publikation (populärvet., debatt m.m.)
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| 5. |
- Lundberg, Angela, et al.
(författare)
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Teaching community in sustainable development : aim, realization and evaluation. Final report from project "Teaching communities" (självförbättrande lärartem)
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A model for the educational development of university teachers (a type of teaching community) has been tested. University staff from different faculties worked and reflected together over the teaching and learning practice in a couple of courses. The community was supervised by an educational developer with a doctoral degree in psychology, and they worked in close collaboration with both undergraduate students and PhD students. The teaching staff that participated improved their teaching skills, extended their repertoire of learning tools, and experienced increased self-reliance. Their motivation and enthusiasm for teaching increased, and today they act as "missionaries" for good teaching and learning practices at the University. It was not obvious, however, that this educational development promoted their academic careers. New project ideas emerged from the teaching community.
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| 6. |
- Lundberg, Jan, et al.
(författare)
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Measurements of friction coefficients between rails lubricated with a friction modifier and the wheels of an IORE locomotive during real working conditions
- 2015
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 324-325, s. 109-117
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Tidskriftsartikel (refereegranskat)abstract
- The real friction coefficients between the rails and the wheels on a 360. t and 10,800. kW IORE locomotive were measured using the locomotive׳s in-built traction force measurement system. The locomotive consisted of two pair-connected locomotives had a CoCo+CoCo bogie configuration, and hauled a fully loaded set of 68 ore wagons (120. t/wagon). The measurements were performed both on rails in a dry condition and on rails lubricated with a water-based top-of-rail (ToR) friction modifier on the Iron Ore Line between the cities of Kiruna and Narvik in Northern Sweden and Norway, respectively. Since full-scale measurements like these are costly, the friction coefficients were also measured at the same time and place using a conventional hand-operated tribometer, with and without the ToR friction modifier. The most important results are that the real friction coefficient is definitely not constant and is surprisingly low (0.10-0.25) when the ToR friction modifier is used, and that it is also significantly dependent on the amount of ToR friction modifier. A large amount will reduce the friction coefficient. Furthermore, it is concluded that the real friction coefficients are in general lower than the friction coefficients measured with the hand-operated tribometer. A final remark is thus that the use of a water-based ToR friction modifier can give excessively low friction, which can result in unacceptably long braking distances.
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| 7. |
- Näsman, Mattias, 1989-, et al.
(författare)
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A promised land? : First summary of the research program
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This document lays out the background for the research program “A promised land? Drivers, challenges and opportunities related to the (green) industrialization of Northern Sweden,” (nr. M22-0029) awarded by the Swedish Riksbankens Jubileumsfond’s in 2022. The document summarizes work in progress and may therefore be updated and republished in different versions according to the requirements of the program. This interdisciplinary program aims to understand the economic, social, and political challenges and opportunities of the ongoing industrial transformation in northern Sweden. A key element of the program is to identify drivers, obstacles, and preconditions in a historical, present, and forward-looking process-perspective.
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| 8. |
- Saari, Juhamatti, et al.
(författare)
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Selection of features for fault diagnosis on rotating machines using random forest and wavelet analysis
- 2018
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Ingår i: Insight. - : British Institute of Non-Destructive Testing. - 1354-2575 .- 1754-4904. ; 60:8, s. 434-442
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Tidskriftsartikel (refereegranskat)abstract
- Identification of component faults using automated condition monitoring methods has a huge potential to improve the prediction of machine failures. The ongoing development of the Internet of Things (IoT) will support and benefit feature selection and improve preventative maintenance decision making. However, there may be problems with the selection of features that best describe a specific fault and remain valid even when the operation mode is changing (for example different levels of load). In this study, features were extracted from vibration signals using wavelet analysis; a feature subset was selected using the random forest ensemble technique. Three different datasets were created where the load of the system was changing while the rotational speed remained the same. The tests were repeated five times by first recording the nominal condition and then introducing four faults: angular misalignment; offset misalignment; partially broken gear tooth failure; and macro-pitting of the gear. To improve previous feature selection techniques, a method is proposed where, before training a classifier, the most promising features are compared at different degrees of torsional load. The results indicate that the proposed method of using random forests to select top variables can help to choose good features that may not have been considered in manual feature selection or in individual load zones.
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| 9. |
- Saari, Juhamatti, 1985-, et al.
(författare)
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Using wavelet transform analysis and the support vector machine to detect angular misalignment of a rubber coupling
- 2015
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Ingår i: Maintenance, Condition Monitoring and DiagnosticsMaintenance Performance Measurement and Management. ; , s. 117-126
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Shaft misalignment is a common problem for many types of rotating systems. It can cause machine breakdowns due to the premature failure of bearings or other components. Common diagnostic approaches rely on detecting increasing vibration response spectra at multiples of the shaft speed. However, in many time-variant systems, such as wind turbines, the speed and load vary considerably, which can make spectrum analysis insufficient. In this paper, a method for detecting shaft misalignment by using wavelet analysis is proposed. The method was experimentally evaluated in a laboratory test rig for four different operating conditions by varying the rotational speed and load. An angular misalignment was introduced between a hydraulic pump (load) and a medium-sized industrial gearbox connected with a rubber coupling. Vibration data were collected by using two accelerometers mounted in an axial and a radial direction directly on the gearbox casing. The features extracted from wavelet representation were classified by using a support vector machine algorithm. The detection of misalignment and the sensitivity of the proposed method are presented using validation data and confusion matrices. The final results of the confusion matrices clearly indicate that this method can detect misalignment even when the speed and load vary. The proposed method can be used for systems which are connected with shafts and there are many similar systems (comprising an electric motor, a gearbox and a centrifugal pump) working under the same circumstances.
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| 10. |
- Siergieiev, Dmytro, et al.
(författare)
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Flow regulation effects on the hydrogeochemistry of the hyporheic zone in boreal rivers
- 2014
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 499, s. 424-436
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Tidskriftsartikel (refereegranskat)abstract
- River-aquifer interfaces are essential for ecosystem functioning in terms of nutrient exchange and biological habitat, but are greatly threatened world-wide. This study examined geochemical aspects of river-aquifer interaction in one regulated and one unregulated boreal river in Northern Sweden to determine whether the geochemical functioning of the hyporheic zone is affected by hydrological alterations, e.g. regulated river discharge and river-aquifer connectivity. In the unregulated Kalix River, the hyporheic pore water was well-oxygenated with orthogonal fluxes (≈0.6-0.7 m d-1) and acted as a sink for Fe, Mn, Al, NH4, and Ca, with fractional losses of 95%, 92%, 45%, 31%, and 15%, respectively. A corresponding elevation in the concentrations of these elements in the hyporheic sediment was observed, with higher saturation indices of Fe-, Mn-, and Al-bearing secondary minerals in hyporheic waters. In the regulated Lule River, hydraulic connectivity at the river-aquifer interface was altered by the presence of a clogging layer (0.04 m d–1). In addition, the river discharge oscillated daily, severely reducing exchange flows across the riverbed (<0.01 m d-1). As a result, the hyporheic pore water was suboxic, with elevated concentrations of filtered Fe and Mn (fractional increase of ≈3700% and ≈2500%, respectively) and other solutes (NH4, Si, S, Ca). A conceptual model revealed functional differences between geochemical features of the hyporheic zone of regulated and unregulated rivers. Overall, the results showed that hyporheic processes are altered along regulated rivers, with resulting impacts on the geochemistry of riverine, riparian and related marine ecosystems.
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