MOTIONS OF MOORED FLOATING BODY AND DYNAMIC TENSION OF MOORING LINES IN REGULAR WAVES

In this paper, the theoretical and the experimental studies of moored floating cylinder and tension of mooring lines in waves are made. The main conclusions obtained are as follows. (1) Heaving and swaying motion of moored floating cylinder in regular waves can be estimated theoretically. As for roll, the calculated values are noticeably higher than those given by experimental results at resonance frequency. (2) The experimental results of the average tension of mooring line in waves are interpreted theoretically. (3) The experimental results of the tension amplitude of mooring chain due to oscillation of floating cylinder in waves are much larger than calculated results by using static catenary theory. Here is proposed an approximate calculation method in which both an inertia force and hydrodynamic forces acting on the chain are taken into account. The experimental results agree with the calculated results.1. Introduction / 2. Drifting force and motions of free floating cylinder in beam sea / 3. Tension of mooring lines and motions of the moored cylinder in beam sea / 4. Conclusion

水面上で上下揺する柱状体に働く非線型流体力について

三角形断面，ルイスフォーム断面（矩型），船首バルブ断面（深吃水），船首バルブ断面（浅吃水）の四種断面の半没水柱状休を大振福の強制上下揺をさせ，その時柱状体に働く流体力を計測し，その結果をフーリエ変換し， 1st order, 2nd order, 3rd orderの流体力を求め，1st orderの力については線型理論による計算結果と比較した．また同時に進行する発散波の計測を行ない，線型理論による計算結果と比較し，流体力から求めた減衰係数と発散波から求めた減衰係数の差を粘性抗力と結びつけて流体力の解析を行なった．1. 緒言 / 2. 供試模型及び実験装置 / 3. 実験解析およびその結果 / 4. N^^-_zに対する粘性影響 / 5. 結

WAVE FORCES EXERTED ON SUBMERGED CIRCULAR CYLINDERS FIXED IN DEEP WAVES

Wave forces exerted on circular cylinders in deep waves are investigated. The circular cylinders are fixed horizontally below the water surface. Experimental results are compared with values calculated by linear theory and the other data obtained differently. Main conclusions obtained are as follows: 1) In case of small period paramaters, inertia coefficients obtained by experiments show good agreement with theoretical values calculated by linear theory. But for large period parameters, the experimental values are much smaller than the theoretical ones. 2) For large period parameters, Drag coefficients derived in the present investigation approximately coincide with those obtained in experiments on hydrodynamic forces acting on circular cylinders in oscillatory flow. But there is much difference between them in case of not so large period parameters.1. Introduction / 2. Experimental arrangement / 3. Analysis of the experimental results and comparison with the theoretical result / 4. Conclusio

動揺する没水円盤に働く流体力について

浅水域で上下揺する円盤に働く流体力を水底からの距離，上下揺の振幅，周期を変えて計測し，付加質量係数M^^-_z，抵抗係数C_Dを求めた． / また水底，水面の影響がなければレイノルズ数，上下揺周期が変ってもM^^-_Z, C_Dの値は変らないが，上下揺振幅比ε(=Z_a/D/2, Z_a; 上下揺振幅, D; 円盤直径）が大きくなればM^^-_zは大きくなり，C_Dは小さくなることを見いだし，M^^-_z, C_D のεに対する実験式を求めた．さらに水底，水面の影響はM^^-_z, C_D ともに大きくなる方向に現われることを見いだした．1. 緒言 / 2. 模型実験 / 3. 実験結果及びその考察 / 4. 結

NONLINEAR HYDRODYNAMIC FORCES ACTING ON CYLINDERS HEAVING ON THE SURFACE OF A FLUID

1. Introduction / 2. Model Experiments / 3. Analysis of the experimental results and comparison with the theoretical result / 4. Viscous effect on N_z / 5. ConclusionLinear and nonlinear hydrodynamic forces are investigated by using two-dimensional cylinders heaving with large amplitude on a free surface. Sections of the cylinders are circle, Lewis form, bulbous bow form (deep and shallow draft) and triangle. The hydrodynamic forces acting on the cylinders and the concurrent progressive wave heights are measured. First, second and third order forces are obtained from the measured forces by using Fourier analysis. The first order forces and wave heights are compared with values calculated by linear theory. The second-order forces of the circular cylinder are compared with the values calculated by Lee, Parissis and Potash using perturbation method. Also, the influence of viscous drag force upon the damping coefficient is discussed

Development of a Calculation Method for Vortex Induced Vibration of a Long Riser Oscillating at its Upper End

A numerical scheme is developed to simulate three-dimensional dynamics of a flexible riser. Equations of the riser motion are derived based on ‘Hamilton’s Principle’ and solved using the mode expansion method. This scheme was verified by comparing with results of forced oscillation experiments. Finally, to validate the accuracy of this numerical scheme, the numerical and experimental results were compared and showed good agreements

潮流中で振動する係留ライン張力の実験的研究

曳航水槽中で，係留索及び鎖の上端を強制動揺させながら一定速度で走行し，係留反力を計測した．また，ランプドマス法による数値計算を行い，実験と比較した．1. 緒言 / 2. 実験 / 　2.1. 実験結果と数値計算の比較 / 3. 結

上下揺する半没水円柱に働く非線型流体力について

半没水円柱に大振幅の強制上下揺をさせ，その時円柱に働く反力を計測し，その結果をフーリエ解析して1st order, 2nd orderおよび3rd orderの流体力を求め， 1st orderの力については線型理論， 2nd orderの力についてはperturbation methodによる理論計算結果と比較した．さらに流体の粘性に基づく抗力についての考察をも行なった．以上の研究をまとめたものである．1. まえがき / 2. 模型実験 / 3. 実験解析および実験値と理論値との比較 / 4. ^^^-に対する粘性影響の考慮 / 5. 結