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Based on vortex theory, we experimentally and directly predict sound sources distributing in the flow field and determine the sound pressure level as a result of the spatial integration of sound sources. In employing this direct evaluation method for the aeroacoustic sound, the problem is that a large integration area is required to minimize errors caused by the sudden truncation of the integration area; we overcome it by adopting and applying a modified formula that neglects the quadrupole sound under the condition that the dipole sound is dominant at a low Mach number. Through the flow field measurement using a time-resolved particle image velocimetry (TR-PIV) technique, we will clearly demonstrate the feasibility of our method and the distribution of dipole sound sources in the vicinity of a body even if a comparatively small integration area must be taken. In this basic study, a circular cylinder with a diameter of 6.0 mm is used; the spatially integrated sound pressure is compared with the actual sound pressure which is measured with a microphone. Further, the sound sources evaluated using only the flow field are determined, which give us detailed information about the amplitude and phase of the sound source structure. This direct evaluation method for the dipole sound is applicable to a more complex body.

Cathodic protection is being applied to buried steel pipelines and polarized potential of pipelines is kept less noble than the protection potential criterion,-0.85 V vs. Cu/CuSO 4. However, instantaneous anodic current has been infrequently observed in some fields even though polarized potential of pipelines is kept less noble than the protection potential criterion. In this study, the influence of instantaneous anodic current on corrosion protection of buried steel pipelines under cathodic protection was evaluated and the oxidation reaction causing anodic current was investigated to some extent. As a result, it was found that most of the anodic current was not attributed to corrosion reaction and the maximum value of corrosion rate of steel was as little as 1.8 m/year. Therefore, it was considered that there was no matter on buried steel pipelines even though the instantaneous anodic current occurred under the protection potential criterion. It was estimated that some part of the anodic current was attributed to the oxidation reactions of components in soil and of rust on the steel surface.

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There is a possibility that alternating current will cause corrosion in a defect of the coating on buried steel pipeline. In this research, we developed an evaluating method with which we could evaluate alternating current corrosion of the steel in a short time compared with conventional evaluating method by mesuring corrosion weight loss. The results of this research showed that alternating current corrosion of buried steel under catholic protection could be estimated by measuring the IR-drop-free potential, especially peak (maximum) potential of the steel using IR-dropfree probe. It was also found that corrosion protection of the steel could be achieved when peak potential of the steel was over 100mV less noble than free corrosion potential of the steel.