Experimental results for deep surge in a small single-stage centrifugal compressor are compared to predictions based on the lumped parameter Greitzer model developed for axial compressors. Both negative and positive flow branches of the steady characteristic, being essential for the model, were measured. Predictions are in fair agreement with data when using a relaxation time smaller than the one proposed for axial compressors. The stability limit of the model equations have been studied for finite amplitude disturbances.

No abstract

Two large trawl models, at a one-quarter scale, were designed, produced and tested in a flume tank in Hirtshals (Denmark). A traditional trawl, typical for the commercially bottom fisheries in Italy, was selected as a basic design for the development of a new trawl. Characteristics of the new design should include larger meshes in the net areas, where no negative effect on catching power is foreseen, high bosom height, good bottom contact and low towing resistance. The geometry and towing resistance of both the traditional and the experimental trawl models were initially measured in the flume tank for different riggings. Based on the results from detailed flume tank tests, two fullscale trawls were designed and produced. Engineering sea trials have been made on a research vessel to measure the performance of the full-scale trawls and to verify the findings from the flume tank tests. The comparison between sea trials and flume tank tests shows that it is very difficult to accurately model, in the flume tank, trawl sections where the highly elastic Rachel netting made from polyamide is used.

No abstract

No abstract