Aerospace carbon fibre-reinforced components are cured under high pressure (7 bar) and temperature in an autoclave. As in an industrial environment, the loading of an autoclave usually changes from cycle to cycle causing different thermal masses and airflow pattern which leads to an inhomogeneous temperature distribution inside the carbon fiber-reinforced plastic part. Finally, the overall process can be delayed and the part quality can be compromised. In this paper, the heat transfer in a small laboratory autoclave has been investigated using calorimeter measurements and a fluid dynamic model. A complex turbulent flow pattern with locally varying heat transfer coefficient has been observed. Especially, the pressure and the inlet fluid velocity have been identified as sensitive process parameters. Further finite element simulations with adjusted boundary conditions provide accurate results of the curing process inside of the components for selective process control. The heat transfer coefficient has been found to be almost stationary during the observed constant pressure autoclave process allowing a separated investigation of the heat transfer coefficient and the curing of the components. The presented method promises therefore a detailed observation of the autoclave process with reduced computational effort.

The bubble curtain is one of the most used measures to reduce underwater pile driving noise. A model of the local distribution of the effective wavenumber was developed. The bubble size distribution was derived from tank measurements. The local distribution of the air fraction was determined by means of an integral method. In a preliminary step, the transfer characteristics of a bubble curtain were studied. The results show a decrease of the transmission coefficient for higher frequencies and additionally for lower water depths. For lower frequencies, λ/2-transmission can be observed. Examining the noise mitigation of a bubble curtain under offshore conditions, a model of the acoustical scenario was developed. Two different offshore measurement sites are described in detail and compared to the modeling results. The distance between bubble curtain and the pile was identified as an important parameter affecting the noise mitigation. The presented approach shows an appropriate representation of the noise mitigation and allows, due to its generic definition, for future investigations of various aspects, e.g., the influence of the soil or the effect of an extra pile near system on the noise mitigation.

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Abstract. Extensive measurements in the area of wind turbines were performed in order to validate a sound propagation model which is based on the Crank–Nicolson parabolic equation method. The measurements were carried out over a flat grass-covered landscape and under various environmental conditions. During the measurements, meteorological and wind turbine performance data were acquired and acoustical data sets were recorded at distances of 178, 535 and 845 m from the wind turbine. By processing and analysing the measurement data, validation cases and input parameters for the sound propagation model were derived. The validation includes five groups that are characterised by different sound propagation directions, i.e. downwind, crosswind and upwind conditions in varying strength. In strong upwind situations, the sound pressure levels at larger distances are overestimated because turbulence is not considered in the modelling. In the other directions, the model reproduces the measured sound propagation losses well in the overall sound pressure level and in the third octave band spectra. As in the recorded measurements, frequency-dependent maxima and minima are identified, and losses generally increase with increasing distance and frequency. The agreement between measured and modelled sound propagation losses decreases with distance. The data sets used in the validation are freely accessible for further research.

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