| 1. |
- Karlsson, Mikael, et al.
(författare)
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Prediction of the onset of sound amplification at shear layers using linear stability analysis
- 2019
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Ingår i: 25th AIAA/CEAS Aeroacoustics Conference, 2019. - Reston, Virginia : American Institute of Aeronautics and Astronautics Inc, AIAA.
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Konferensbidrag (refereegranskat)abstract
- A simple numerical technique for predicting the potentiality of sound amplification by shear layers is presented. The technique applies Howe’s energy corollary to describe the energy exchange between the vortical mode in the shear layer and the acoustic wave incident on the layer. Potential sound amplification by the vortical mode is identified when the net energy gain of the incident acoustic wave is positive. The technique only requires steady flow simulation and linear stability analysis so the computational cost is modest. Numerical results are compared with a measurement on a particle agglomeration pipe and it shows that the sound amplification can be satisfactorily predicted by the simple technique.
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| 2. |
- Svensson, Henrik, 1982, et al.
(författare)
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Influence of Pt on the metal-oxide interface during high temperature oxidation of NiAl bulk materials
- 2009
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Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X. ; 51:3, s. 539-546
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the investigation was to study the mechanisms improving oxide scale adherence in Pt-free and Pt-rich beta-NiAl materials during high temperature oxidation. Theoretical density-functional theory (DFT) calculations were used to calculate the work of separation of the beta-NiAl(111)/alpha-Al(2)O(3)(0001) metal-oxide interfaces, in pure NiAl and Pt-rich NiAl materials. The experimental work was focused on the studies of the metal-oxide interface, its development and morphology. Based on the theoretical and experimental results a complementary picture is presented for a better understanding of the Pt effect on the oxidation and oxide adhesion. It is shown that the interfacial bonding is decreased with addition of Pt to beta-NiAl. The beneficial effect of Pt on the adhesion energy is attributed to the enhancement of contact areas between the oxide and the metal. The influence of Pt on the diffusion of Al and the formation of interfacial voids is also discussed.
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| 3. |
- Du, Lin, et al.
(författare)
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Modelling of Acoustic Resonators Using the Linearized Navier Stokes Equations
- 2016
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Ingår i: SAE Technical Paper Series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- To tune the acoustics of intake systems resonators are often used. A problem with this solution is that the performance of these resonators can be affected a lot by flow. First, for low frequencies (Strouhal-numbers) the acoustic induced vorticity across a resonator inlet opening will create damping, which can reduce the efficiency. Secondly, the vorticity across the opening can also change the end-correction (added mass) for the resonator, which can modify the resonance frequency. However, the largest problem that can occur is whistling. This happens since the vortex-sound interaction across a resonator opening for certain Strouhal-numbers will amplify incoming sound waves. A whistling can then be created if this amplified sound forms a feedback loop, e.g., via reflections from system boundaries or the resonator. To analyse this kind of problem it is necessary to have a model that allows for both sound and vorticity and their interaction. This means using a convected wave equation type of model is not sufficient. A better approach is to apply the linearized Navier Stokes equations, which will give a full model of the vortex-sound effects. In this paper an effort to apply this approach on a set of generic resonators is described. Besides the numerical results comparisons with experiments are also presented.
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| 4. |
- Lai, Y., et al.
(författare)
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Study of Installation Effects on Automotive Cooling Fan Noise
- 2022
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- Vehicle electrification is one of the biggest trends in the automotive industry. Without the presence of combustion engine, which is the main noise source on conventional vehicles, noise from other components becomes more perceivable; among these components, the cooling fan is one of the major noise sources, especially during battery charging. The design of cooling fan modules is usually carried out in the early stage before building prototype vehicles. Therefore, understanding the installation effects of the cooling fan on the radiated sound is essential to secure good customer satisfaction. In this study, three different measurement setups of cooling fans are carried out: free field, wall mounted, and in-vehicle measurement. Four cooling fan prototypes with different fan blade designs are used in each measurement. Correlations of these measurements are investigated through comparisons of the measurement results. The installation effects are identified through spectrum difference between free field and in-vehicle measurement. A spectral decomposition method is implemented to enable the separation of source strength and propagation effect in the results. One variable is introduced to represent the installation effects of vehicles tested in the present study.
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| 5. |
- Sjöberg, Elisabeth, et al.
(författare)
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Social Media and Its Dual Use in Biopreparedness: Communication and Visualization Tools in an Animal Bioterrorism Incident
- 2013
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Ingår i: Biosecurity and Bioterrorism. - : Mary Ann Liebert Inc. - 1538-7135 .- 1557-850X. ; 11:Supplement 1, s. S264-S275
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Tidskriftsartikel (refereegranskat)abstract
- This article focuses on social media and interactive challenges for emergency organizations during a bioterrorism or agroterrorism incident, and it outlines the dual-use dilemma of social media. Attackers or terrorists can use social media as their modus of operandi, and defenders, including emergency organizations in law enforcement and public and animal health, can use it for peaceful purposes. To get a better understanding of the uses of social media in these situations, a workshop was arranged in Stockholm, Sweden, to raise awareness about social media and animal bioterrorism threats. Fifty-six experts and crisis communicators from international and national organizations participated. As a result of the workshop, it was concluded that emergency organizations can collect valuable information and monitor social media before, during, and after an outbreak. In order to make use of interactive communication to obtain collective intelligence from the public, emergency organizations must adapt to social networking technologies, requiring multidisciplinary knowledge in the fields of information, communication, IT, and biopreparedness. Social network messaging during a disease outbreak can be visualized in stream graphs and networks showing clusters of Twitter and Facebook users. The visualization of social media can be an important preparedness tool in the response to bioterrorism and agroterrorism.
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| 6. |
- Sundberg, Mikael, et al.
(författare)
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Fibre-optic array for curvature assessment : application in otitis diagnosis
- 2004
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Ingår i: Medical & Biological Engineering & Computing. - 0140-0118. ; 42:2, s. 245-252
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Tidskriftsartikel (refereegranskat)abstract
- A contact-free sensor consisting of two parallel optical-fibre arrays was designed to assess surface shapes of diffusely scattering media. By sequentially illuminating objects using one fibre array and detecting the diffusely back-scattered photons by the other, a source-detector intensity matrix was formed, where the matrix element (i, j) was the intensity at detector j when light source i was excited. Experimental data from convex and concave polyacetal plastic surfaces were recorded. A mathematical model was used for simulating source-detector intensity matrices for the surfaces analysed in the experiments. Experimental results from the system were compared with the theoretically expected results provided by the mathematical model. The shape and relative amplitude showed similar behaviour in the experiments and simulations. A convex/concave discriminator index D, representing the detected intensity difference between two source-detector separations, was defined. The relative dynamic range of D, defined as the difference between the maximum and the minimum divided by the mean of the index, was 1.37 for convex surfaces and 0.68 for concave surfaces, at a measuring distance of 4.5mm. The index D was positive for convex surfaces and negative for concave surfaces, which showed that the system could distinguish between convex and concave surfaces, an important result for the diagnosis of otitis media.
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| 7. |
- Wollbrant, C. E., et al.
(författare)
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Extrinsic rewards and crowding-out of prosocial behaviour
- 2022
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Ingår i: Nature Human Behaviour. - : Springer Science and Business Media LLC. - 2397-3374. ; 6, s. 774-781
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Tidskriftsartikel (refereegranskat)abstract
- A natural experiment in the environmental domain shows how attempts to increase prosocial behaviours like recycling using monetary rewards can be counter-productive, and how this effect depends on underlying pro-environmental motivation. The law of supply is a fundamental principle of economics and states that any increase in price will increase the quantity supplied. In the case of prosocial behaviour, however, increasing rewards have reduced supply, posing a challenge to standard economic theory. Attempts to study such 'crowding-out' have been limited by their small scale and the inherent difficulties posed by calibration of experimental tests. We analyse a large-scale natural experiment in the environmental domain consisting of 20,370 independent observations derived from aggregation of approximately 27 million individual decisions. We find that aggregate supply of prosocial behaviour is 's-shaped', demonstrating how attempts to increase prosocial behaviour using monetary rewards can be counter-productive. Our study shows that results derived from a small set of data points collected from an underlying s-shaped data-generating process are vulnerable to misinterpretation, and that proxy measures of intrinsic motivation ought to be collected to ensure theoretical advance.
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