Circulation pumps as structure-borne sound sources: emission to finite pipe systems

In a recent paper, it was shown that the structure-borne sound power from circulation pumps into straight pipes is primarily through the translation components, which generate longitudinal and bending waves. In this paper, the subsequent wave mode conversions at pipe junctions are considered. A central heating system was physically modelled as various combinations of pipes with a radiator. The experimental measurements were of fixed pipe lengths and resonance effects dominated the system response. In addition, small misalignments increased wave mode conversion. In order to consider only the effect of number and orientation of pipe junctions, an idealised pipe system was modelled such that the length of the connecting pipes could be varied stochastically, thereby randomising out resonance effects. For typically domestic pipe systems the mixing of wave types is such that the radiated sound is determined by the largest component of the structure-borne power from the pump into the pipe system, irrespective of the direction.