報告書番号

383034

タイトル（和文）

不規則波に対する屈折計算法の適用性

タイトル（英文）

STUDY OF REFRACTION OF IRREGULAR WAVES BASEDON THE CONSERVATION EQUATION OF ENERGY FLUX

概要 （図表や脚注は「報告書全文」に掲載しております）

浅海域での波浪変形を精度良く推定することは，構造物の耐波浪設計あるいは海浜変形予測にとって重要な課題である。本研究では，方向スペクトルを持つ不規則の屈折変形計算法としてエネルギー平衡方程式に基づく方法を取り上げ，その適用性と問題点について検討した。主な研究成果は以下の通りである。１．エネルギー平衡方程式に基づく屈折計算法は，波向線法による規則波の屈折計算結果を線形的に合成する方法（成分波法）と等価な方法であることを理論的に明らかにした。２．リアス式湾を対象とした不規則波の実験結果と数値計算結果との比較より，この方法の適用性が確認された。３．一方，球面浅瀬の水理実験との比較より，波向交差の著しい領域への適用性は不十分であることが分かった。今後，現地波浪に対するこの方法の適用性を検討するとともに，砕波変形を計算に取り入れ，推定精度の向上を図る必要がある。

概要 （英文）

IN THE PREDICTION OF BEACH CHANGES WITH NUMERICAL MODELS,IT IS OF FUNDAMENTAL IMPORTANCE TO ESTIMATE THE WAVE HEIGHT DISTRIBUTION NEAR THE SURFZONE.FOR CALCULATION OF REFRACTED WAVES,BOTH THE WAVE RAY METHOD OF GEOMETRICAL OPTICS AND A METHOD BASED ON THE CONSERVATION EQUATION OF ENERGY FLUX ARE FREQUENTLY EMPLOYED.IN ADDITIONTO THESE TWO METHODS,A CONSERVATION EQUATION FOR THE ENERGY FLUX OF IRREGULAR OCEAN WAVES WITH CONTINUOUS DIRECTIONAL SPECTRA HAS BEEN PRESENTED BY KARLSSON. ONE IS AT A LOSS AS TO WHICH METHOD TO CHOOSE BECAUSE DIFFERENCES BETWEEN THE THREE METHODS HAVE NOT BEEN CLEARLY DELINEATED.THEREFORE,IN THE PRESENT INVESTIGATION THE FORMULATIONS OF EACH METHOD WERE THEORETICALLY EXAMINED.IT IS SHOWN THAT THE WAVE RAY METHOD AND THE CONSERVATION EQUATION OF ENERGY FLUX METHOD ARE EQUIVALENT AND ARE RELATED THROUGH A COORDINATE TRANSFORMATION.IT IS ALSO SHOWN THAT KARLSSON S METHOD FOR OBTAINING OCEANWAVE SPECTRA IS EQUIVALENT TO SUPERPOSED SOLUTIONS OF SINUSOIDAL WAVES CALCULATED BY THE WAVE RAY METHOD. TWO EXPERIMENTS WERE PERFORMED TO EXAMINE THE APPLICABILITY OF THE ABOVE-MENTIONED CALCULATION PROCEDURES.BOTH REFRACTION AND SHOALING PREDICTION WERE EXAMINED.A BAY MODEL AND CIRCULAR SHOAL WERE USED,AND THE INCIDENT WAVE CONSISTED OF IRREGULAR WAVES WITH FREQUENCY SPECTRA. BY COMPARISON BETWEEN EXPERIMENTAL AND CALCULATED RESULTS,IT IS CONCLUDED THAT KARLSSON S METHOD IS USEFUL EXCEPT NEAR A CAUSTIC,SUCH AS THAT WHICH IS FORMED AROUND A CIRCULAR SHOAL.THE ADVANTAGES OF THIS METHOD ARE THAT THE WAVE DIRECTION,WAVE HEIGHT AND DIRECTIONAL SPECTRA CAN BE CALCULATED SIMULTANEOUSLY AND THAT THE CALCULATION PROCESS IS MORE COMPACT AS COMPAREDTO THE SUPERPOSITION OF SINUSOIDAL WAVES IN THE WAVE RAY METHOD.

報告者

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