報告書番号

U89005

タイトル（和文）

水理実験における波の方向スペクトルの測定法

タイトル（英文）

MEASUREMENT OF DIRECTIONAL WAVE SPECTRA IN ALABORATORY BASIN

概要 （図表や脚注は「報告書全文」に掲載しております）

実験室内において方向スペクトルを有する不規則波を再現しようとする試みが最近なされている。本研究は，流速計と波高計の同時観測記録から方向スペクトルを推定する手法を対象とし，実験室内でのデータ測定およびスペクトル推定法に関する知見を得ることを目的とする。本，研究では，まず静水中において電磁流速計を一定の周期で動かすことにより流速計の特性試験を行った。ついで，回折波および越波伝達波の平面実験を行い，流速・波高の同時観測記録からクロススペクトルおよび方向スペクトルの解析を行った。それらの結果，電磁流速計の測定流速値および出力値の位相に問題があることを明らかにすると共に方向スペクトルの推定に当ってそれらをどのように解析すればよいかを示した。また，妥当な方向スペクトル推定値を得るための方法について検討した。

概要 （英文）

RECENTLY, DIRECTIONAL IRREGULAR WAVE GENERATORS HAVE BEEN INSTALLED AT SEVERAL LABORATORIES. THE PRESENT PAPER IS TO DEVELOP AND TEST THE MEASUREMENT AND ANALYSIS TECHNIQUES OF THE DIRECTIONAL WAVE SPECTRA IN A LABORATORY. FIRSTLY,PERFORMANCE TESTS OF THE TWO KINDS OF ELECTROMAGNETIC CURRENT METERS WERE PERFORMED. WE VIBRATED THE CURRENT METERS SINUSOIDALLY IN THE STILL WATER. IT IS REVEALED THATTHESE CURRENT METERS DO NOT SHOW TRUE VELOCITY,ONE OVERESTIMATES AND THE OTHER HAS A FREQUENCY DEPENDENCE. AND IT WAS FOUND THAT THERE IS A TIME DELAY BETWEEN OUTPUT VELOCITY OF THESE CURRENT METERS AND TRUE VELOCITY. SECONDLY,LABORATORY EXPERIMENTS OF THE IRREGULAR WAVE DIFFRACTIONAND THE WAVE TRANSMISSION OVER BREAKWATERS WERE PERFORMED. WAVE PROFILE AND CURRENT VELOCITY OF THE TWO HORIZONTAL COMPONENT WERE MEASURED ATTHE SAME HORIZONTAL POSITION. THE FOLLOWING RESULTS ARE REVEALED FROM CROSS-SPECTRUM ANALYSIS AND DIRECTIONAL SPECTRUM ESTIMATE: (1)MEAN TIMEDELAY OCCARRED BETWEEN THE WAVE PROFILE AND CURRENT VELOCITY IS ABOUT 0.12 SECOND. TO REMOVE THIS TIME DELAY BIAS ERROR,THE SIGNALS OF THE CURRENT METER SHOULD BE SHIFTED IN TIME(2)MAGNITUDE OF THE RESPONSE FUNCTION BETWEEN THE WAVE PROFILE AND CURRENT VELOCITY WERE UNDERESTIMATED. THEN,A RESPONSE FUNCTION ESTIMATED FROM MEASURED DATA SHOULD BE USED RATHER THAN FROM LINEAR WAVE THEORY. (3)IN ORDER TO CALCULATE THE REASONABLE DIRECTIONAL SPECTRUM,IT IS NECESSARY TO USE A FINAL SMOOTH CROSS-SPECTRA ESTIMATE RATHER THAN RAW ESTIMATE. (4)THERE IS NO SIGNIFICANTDIFFERENCE IN THE ESTIMATED DIRECTIONAL SPECTRA WHETHER TIME DELAY OF THE CURRENT METER IS CONSIDERED OR NOT. THIS RESULT IS CHARACTERISTIC OF 3 COMPONENT ARRAY WHICH ARE SETTLED AT THE SAME PLACE. AT THE CASE OFA GENERAL ARRAY,WE MUST CONSIDER THE INFLUENCE OF THIS TIME DELAY ON THE RESPONSE FUNCTION OR AT THE STAGE OF THE TIME HISTORY.

報告者

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