基地周辺における航空機騒音予測コンターの作成手法

抄録

Prediction of noise distribution in the surrounding of airports is very important for the adequate measures of aircraft noise control in these areas. We made a large-scale survey of noise in the surrounding areas of air bases in Japan mainly caused by F-104J, F-4EJ, and F-86F, that is, the main fighters of the Japanese Air Force, and on the basis of the results obtained, the basic data on noise were arranged by the relation between the peak noise level and the distance to aircraft i. e. slant distance (Fig. 7), and the relation between the peak noise level and the duration of noise (Fig. 10). In this paper, we discuss the procedures of drawing out forecast contours for WECPNL in the surrounding areas of air bases by use of the basic data on noise. Here, we drew out a contour in the following order. (1) The surrounding area of the air base was divided into 500-m meshes with the runway as the center and expressed by the coordinate system. (2) Flying courses were set up by referring to the standard course diagrams, etc. (Figs. 12 and 13). The sectional shapes of the flying courses in the distant areas could be almost approximated to be elliptical. Several typical flying courses were selected in the section set up in this way, and projected on a plane expressed by the coordinate system. The location (X, Y, Z) of the aircraft in an arbitrary space was expressed by taking the distance (D) moving on the plane along their respective flying courses from their respective reference points (take-off or landing points) as parameter. (3) The shortest distance from the flying course numerically expressed for each flying pattern to the intersecting points on the mesh was calculated (Fig. 14). As for the sides and rear of the runway at the time of take-off, the slant distance was obtained as the distance from the take-off point. (4) Then, peak noise levels at all intersecting points on the meshes were calculated from the slant distances obtained in this way and by use of the formulas of regression ((1)〜(7)) corresponding to the basic data on noise. (5) The duration of noise was calculated from the peak noise levels calculated as above by use of the formulas of regression ((12)〜(17)) corresponding to them. There are big differences in the number of daily flights in air bases ; there are 10 days or so in a month when there is no flight (Refer to Fig. 16). We calculated the number of flights per day, excepting the days in which there was no flight or only several aircrafts took off and landed. The contour obtained by calculation in this way showed a good agreement with the actual contour with a slight allowance of ±1〜2 dB (Fig. 17 and 18). It is considered that this good agreement is attributable to the following three reasons : (1) The basic data on noise were obtained from our tests on many aircrafts and therefore have a high reliability. (2) We expressed the flying courses of aircraft as of an elliptical section taking variations in flying courses into consideration, and in consequence could reproduce the actual flying condition more accurately. (3) As for the take-off noise on the sides and at the rear of the runway, we considered that the noise of aircraft at a position where it can be confirmed by eyes has an effect, and from this viewpoint calculated the slant distance by choosing the taking-off point (not taking-off run starting point) as reference point.