Optimal structure of sensor systems composed of nonidentical sensors

The sensor system has two types of contradictory failures; a fail-dangerous failure and a fail-safe failure. A method of obtaining the optimal structure is developed for the sensor system which is composed of general components. The optimal structure minimizes an expected damage, considering all possible boolean structures including noncoherent systems. A simple optimality criterion is obtained and several properties of the optimal structures are derived; a noncoherent structure can be optimal in some cases. A simple systematic search algorithm can be used effectively to determine the optimal system. Analytic solutions are obtained for systems composed of identical components. Illustrative examples are given.     

Flow induced acoustic resonance in in-line tube banks

In the present paper the attention is focused on the relation between vortex shedding phenomena andacoustic resonance which occurred in the two-dimensional model of boiler.There were tube bankswith in-line arrangement for small tube pitch ratio.We measured the sound pressure level,the phasedelay of acoustic pressures,the spectrum of velocity fluctuation and the gap velocity.As a result, wefound two peak frequencies of sound pressure level with different Strouhal numbers S_t,mainly about0.26 and 0.52.The noise of S_t=0.26 was the resonance of transverse mode and S_t=0.52 waslongitudinal mode.The vortex shedding of S_t=0.15 was generated inside the tube banks withoutacoustic resonance. As gap velocity increased, we observed that the peak level of spectrum was weakand broad-banded. The onset velocity of the acoustic resonance of longitudinal mode was lower thanthat of transverse mode.