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  • 1.
    Bordag, Michael
    et al.
    Univ Leipzig, Vor Hospitaltore 1, D-04103 Leipzig, Germany..
    Nikolaev, Vladimir
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS).
    Analytic corrections to the electromagnetic casimir interaction between a sphere and a plate at shortdistances2010Inngår i: International Journal of Modern Physics A, ISSN 0217-751X, E-ISSN 1793-656X, Vol. 25, nr 11, s. 2171-2176Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For the vacuum interaction of a sphere in front of a plane, both obeying conductor boundary conditions, we consider the approximation of small separation. We derive the next-to-leading order of the asymptotic expansion in the separation-to-radius ratio epsilon. This correction is of order epsilon. In opposite to the scalar cases it contains also contributions proportional to logarithms in first and second order, epsilon In epsilon and e(ln epsilon)(2). We compare this result with the available findings of numerical and experimental approaches.

  • 2.
    Bååth, Lars
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Maskinteknisk produktframtagning (MTEK), Fotonik.
    Noise Spectra from Wind Turbines2013Inngår i: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 57, s. 512-519Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents observations of audio noise in frequency range 20e20 000 Hz from wind turbines. The observations were performed around the theoretically calculated 40 dBA noise perimeter around the wind turbine farm at Oxhult, Sweden. This paper describes a newly designed and constructed a field qualified data acquisition system to measure spectra and total noise level of sound from wind turbines. The system has been calibrated at SP Borås. It is shown that it has a flat frequency response and is linear with amplitude and time.

    The total noise level (as integrated 20e20 000 Hz) is shown to be below 35 dBA (below the reference background noise at 36 dBA) at a 10 m altitude wind speed of 4e5 m/s. The measurements were made along the theoretical 40 dBA border at 8 m/s.

    It is concluded that the theoretical 40 dBA border seems reasonable calculated if the manufacturer specifications are used to extrapolate the sound level to correspond to 8 m/s at 10 m. Our data indicate that a simple sound propagation model is sufficient since the sound level is more affected by the nearby environment than the large scale forest structure. Also, the large scale forestry structure is bound to change with time and the error bars of measurements on total sound level are about 1 dBA, which is larger than any fine tuning with a more sophisticated model. More care should be taken to model the reflections from walls and other obstacles close to the microphones.

    The distribution of the spectral noise level around the turbine farm suggests that the noise originates from individual wind turbines closest to the measurement location rather than from the wind turbine farm as a whole. The spectra show narrow band spectral line features which do not contribute signifi-cantly to the total noise at this level. The narrow band features are only detectable at very long inte-gration time and at 1 Hz spectral resolution. The spectral features are typical to originate from mechanical noise.

    The spectral acquisition method described in this paper can be used as a field qualified system for sound measurements in forest areas. The high spectral resolution is a viable remote diagnostic method for mechanical faults in the turbine machinery. Future work will concentrate on these two areas.

  • 3.
    Ivchenko, Alexander
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    Incorporation of OpenFOAM software into Computational Fluid Dynamics process in Volvo Technology2011Independent thesis Advanced level (degree of Master (One Year)), 10 poäng / 15 hpOppgave
    Abstract [en]

    In this thesis work the feasibility of using open source OpenFOAM software as a solver part for Computation Fluid Dynamics in Volvo Technology is studied. Since the structure of the case in OpenFOAM is rather complex, one of the main purposes of this thesis work was also to make the process of using OpenFOAM as user-friendly as possible. The general conclusion that can be drawn from this work is that a very streamlined workflow can be, and has been, designed and created.

  • 4.
    Ottermo, Fredric
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS).
    Möllerström, Erik
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS). Uppsala University, Uppsala, Sweden.
    Nordborg, Anders
    Sound View Instruments, Borrby, Sweden.
    Hylander, Jonny
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS).
    Bernhoff, Hans
    Uppsala University, Uppsala, Sweden.
    Location of aerodynamic noise sources from a 200 kW vertical-axis wind turbine2017Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 400, s. 154-166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Noise levels emitted from a 200 kW H-rotor vertical-axis wind turbine have been measured using a microphone array at four different positions, each at a hub-height distance from the tower. The microphone array, comprising 48 microphones in a spiral pattern, allows for directional mapping of the noise sources in the range of 500 Hz to 4 kHz. The produced images indicate that most of the noise is generated in a narrow azimuth-angle range, compatible with the location where increased turbulence is known to be present in the flow, as a result of the previous passage of a blade and its support arms. It is also shown that a semi-empirical model for inflow-turbulence noise seems to produce noise levels of the correct order of magnitude, based on the amount of turbulence that could be expected from power extraction considerations.

  • 5.
    Pullissery, Mehthab
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Sustainability, Innovation and Management in Building (SIMB).
    Reduction of heat loss for an immersion heater2017Independent thesis Advanced level (degree of Master (One Year)), 10 poäng / 15 hpOppgave
    Abstract [en]

    In this study, an electrical immersion heater mounted on a water tank has been investigated. Themain aim was to reduce heat transfer and to utilize the maximum energy available from heater toheat the water. To observe the effects of essential geometrical and operating parameters on thesystem performance, different computational test cases were run for three different designs.In the first case of simulation, the immersion heater of existing design mounted on a water tankhas been analyzed. The cold-water tank with inlet and outlet and given appropriate boundaryconditions was used to see the temperature contours inside the water tank and temperature of theimmersion layer itself.In the second case, an insulation plate has been introduced in the immersion heater head in orderto reduce heat loss by considering the possible heat leakage through the gap inside the heaterhead by radiation.In the third case, an insulation ring has been introduced in the immersion heater head as asubstitute for the insulation plate which has the same aim as second case.The results obtained from the CFD simulation shows the thermal performance of immersionheater in a water tank for three different cases. The results are helpful in optimizing both heatingelement and immersion heater by introducing different changes to optimize the design. It showsthat the redesigned immersion heater and storage tank can provide improved working conditions.Also, at early design stages, CFD simulations could be used as an effective tool to optimizethermal storage tank parameters, so it may add value to the storage tank and immersion heaterperformance and efficiency, by optimizing the whole thermal heating system design and size.Different materials and geometry design are tested giving the minimum heat losses from thesystem and uniform temperature distribution in the water heater.

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