The present paper deals with acoustic resonance in tube bundles which occurred in actual boiler plants. A practical method to suppress the resonant noise is proposed based on scale model tests. In those experiments, besides the transverse modes which are relatively well-known, longitudinal modes which are known to be difficult to suppress, were realized. The relation of both kinds of acoustic modes to vortex shedding frequency was clarified. In the following step, a design method of the acoustic energy absorbers is proposed based on the feedback system stability theory. According to this theory, acoustic energy absorbers were equipped in the duct of the test model, and remarkable increase of the critical flow velocity was confirmed for both types of resonant mode. Based on these results, this method was applied to the actual boiler plants and it was confirmed that the proposed method is the effective countermeasure for both types of acoustic resonant modes.

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Two types of vectorized programs of the discrete variational Xα method with the basis set of Slater-type orbitals have been developed. The first type calculates a basis function every time that it is used and the second type reads a basis function from outside memories.They are examined for the most efficient way of performing calculations with the HITAC S-810/20 supercomputer (630 MFLOPS at peak) and its available outside memory devices. The acceleration factor of computation by the first type of program over scalar processing is more than 12. The second type of program has no advantage over the first in small electron systems of atomic clusters with primitive basis functions. But in larger systems such as Si 2 O 7 H 6 with complex basis functions, the second type of program, used with semiconductor memories, results in 11 times less CPU time than the first type of program.

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The effects of microstructural factors on irradiation growth of zirconium-base alloys have been evaluated on the basis of a growth model in which point defects parameters obtained by molecular dynamics are used. Comparison of experimental data on specimens with well-defined microstructures and the calculated results of these data have confirmed predictive capability of the model. The calculated results show that irradiation growth could be reduced by the factors such as (1) an increase of the grain size, (2) a reduction of the grain aspect ratio, or (3) a decrease of the dislocation density.