Abstract
The fluctuation of an acoustic pressure in a straight pipe is modeled with a linear dynamic system whose state variables are stationary waves of different modes. In our previous report, low order modes of the stationary wave were used to construct an accurate pipe-length on-line measurement system, since high order modes generally disappear faster than lower order ones. But, we found that not only the low order modes but also high order ones are relatively plentifully contained in the fluctuation of the acoustic pressure. These higher order modes have generally a high resolution ability with respect to the pipe-length because of the larger distance between actual and predicted acoustic pressures. This paper presents a criterion to select the optimal modes, using the distance measure “divergence”, to realize a much more accurate pipe length measurement.
