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Centrifugal compressors with low and moderate pressure ratio usually have characteristic with a wider stable operating region. Flat speed lines allow substantial reduction of the air mass flow rate with almost constant pressure ratio and without sudden surge occurrence. The surge is typically preceded by a stall or mild surge causing significant and thus quite easily detectable pressure oscillations. The preceding unstable operation is oscillatory yet still quite safe compared to deep surge. Research described in this paper deals with changes in both the engine slow pressures and fast parameters (pressures, noise, vibrations). Parameters were measured along constant speed lines from the operating line point down near to the compressor surge line. The goal was to describe typical changes in engine parameters and to define a stipulated limit of engine safe operation. Newly defined criteria of centrifugal compressor stable run will allow evaluation of engine operability, without the need to drive the engine into the compressor surge repeatedly.

We present a dynamic hair animation method designed for use in real-time virtual environments. Basing on recent research results in elastic rod simulation, we introduce an enhanced physically plausible technique which utilizes specific properties of hair strands to achieve better performance and more stable simulation. Stability is also enhanced by decoupling major sources of dynamic equation stiffness into a separate post-integration step. We also use the same decoupling principle to treat hair-head collisions in a very efficient and robust way. Thanks to this, we can afford to use a fast explicit integration scheme, which, combined with a short time step, allows our method to provide smooth results even in frequency-sensitive areas such as haptics-based hair modelling.

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