Tension leg platform(TLP)is a typical compliant offshore structure for oil/gas resources exploitation.In the design process,the prediction of the free surface elevation is of great importance for the determination of ...Tension leg platform(TLP)is a typical compliant offshore structure for oil/gas resources exploitation.In the design process,the prediction of the free surface elevation is of great importance for the determination of the air gap.So far,the existing researches for predicting the air gap of the TLPs focus on the supporting columns while pay little attention to the horizontal pontoons.For the second order diffraction problem or long incident wave condition,the velocity potential decays slowly with water depth and the effect of pontoons should not be neglected.Herein the effect of pontoons on the diffracted wave field in the vicinity of a TLP platform is investigated in this study.The diffraction of regular waves by a square array of truncated cylinders and a whole TLP structure is studied in detail by using both the linear and the second-order diffraction theory.Numerical calculation is performed for the free surface elevation and wave run up.Numerical results show that the near-trapping phenomenon can occur inside the TLP and leads to significantly increased wave height.To study the effect of pontoons on the free surface elevation comparisons are carried out between the results of these two structures with and without pontoons.It is found that pontoons have an appreciable effect on the diffracted wave field for long incident regular waves and increase the largest response notably when the near-trapping phenomenon occurs at the second-order.展开更多
Hydroelastic effect of sloshing is studied through an experimental investigation. Different excitation frequencies are considered with low-fill-depth and large amplitude. Morlet wavelet transform is introduced to anal...Hydroelastic effect of sloshing is studied through an experimental investigation. Different excitation frequencies are considered with low-fill-depth and large amplitude. Morlet wavelet transform is introduced to analyze the free surface elevations and sloshing pressures. It focuses on variations and distributions of the wavelet energy in elastic tanks. The evolutions of theoretical and experimental wavelet spectra are discussed and the corresponding Fourier spectrums are compared. Afterwards, average values of the wavelet spectra are extracted to do a quantitative study at various points. From the wavelet analysis, sloshing energies are mainly distributed around the external excitation frequency and expanded to high frequencies under violent condition. In resonance, experimental wavelet energy of the elevation in elastic tanks is obviously less than that in the rigid one; for sloshing pressures, the elastic wavelet energy close to the rigid one and conspicuous impulse is observed. It recommends engineers to concern the primary natural frequency and impulsive peak pressures.展开更多
Moonpools are openings right through the hull from continuous deck to bottom of the ship,allowing equipment or mini-submarines to be put into the water at a location on the vessel with minimum ship motion.Open moonpoo...Moonpools are openings right through the hull from continuous deck to bottom of the ship,allowing equipment or mini-submarines to be put into the water at a location on the vessel with minimum ship motion.Open moonpools in a drillship are causing additional resistance when the ship is in forward speed.It was shown that the water inside the moonpool started to oscillate at forward speed.The water mass in the moonpool is subjected to sloshing and piston modes.The vertical motion is piston mode and the longitudinal one is called as sloshing mode.This water particle motion inside the moonpool is mainly depended on the geometry,moonpool depth,and encountered wave frequency.Out of this,moonpool geometry is one of the key factors for the performance of the moonpool.The varying cross-section geometry is one of the practically possible and economically feasible solutions to reduce the oscillation to a considerable level is attempted in this paper.Also the resistance caused by the moonpool and the free surface generated around the hull is investigated with the use of computer simulation.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.11072052,51221961)the National Basic Research Program of China("973"Project)(Grant No.2011CB013703)
文摘Tension leg platform(TLP)is a typical compliant offshore structure for oil/gas resources exploitation.In the design process,the prediction of the free surface elevation is of great importance for the determination of the air gap.So far,the existing researches for predicting the air gap of the TLPs focus on the supporting columns while pay little attention to the horizontal pontoons.For the second order diffraction problem or long incident wave condition,the velocity potential decays slowly with water depth and the effect of pontoons should not be neglected.Herein the effect of pontoons on the diffracted wave field in the vicinity of a TLP platform is investigated in this study.The diffraction of regular waves by a square array of truncated cylinders and a whole TLP structure is studied in detail by using both the linear and the second-order diffraction theory.Numerical calculation is performed for the free surface elevation and wave run up.Numerical results show that the near-trapping phenomenon can occur inside the TLP and leads to significantly increased wave height.To study the effect of pontoons on the free surface elevation comparisons are carried out between the results of these two structures with and without pontoons.It is found that pontoons have an appreciable effect on the diffracted wave field for long incident regular waves and increase the largest response notably when the near-trapping phenomenon occurs at the second-order.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51609168 and 51239008)the Open Fund of State Key Laboratory of Coastal and Offshore Engineering(Grant No.LP1608)the National Key Basic Research Program of China(Grant No.2014CB046804)
文摘Hydroelastic effect of sloshing is studied through an experimental investigation. Different excitation frequencies are considered with low-fill-depth and large amplitude. Morlet wavelet transform is introduced to analyze the free surface elevations and sloshing pressures. It focuses on variations and distributions of the wavelet energy in elastic tanks. The evolutions of theoretical and experimental wavelet spectra are discussed and the corresponding Fourier spectrums are compared. Afterwards, average values of the wavelet spectra are extracted to do a quantitative study at various points. From the wavelet analysis, sloshing energies are mainly distributed around the external excitation frequency and expanded to high frequencies under violent condition. In resonance, experimental wavelet energy of the elevation in elastic tanks is obviously less than that in the rigid one; for sloshing pressures, the elastic wavelet energy close to the rigid one and conspicuous impulse is observed. It recommends engineers to concern the primary natural frequency and impulsive peak pressures.
文摘Moonpools are openings right through the hull from continuous deck to bottom of the ship,allowing equipment or mini-submarines to be put into the water at a location on the vessel with minimum ship motion.Open moonpools in a drillship are causing additional resistance when the ship is in forward speed.It was shown that the water inside the moonpool started to oscillate at forward speed.The water mass in the moonpool is subjected to sloshing and piston modes.The vertical motion is piston mode and the longitudinal one is called as sloshing mode.This water particle motion inside the moonpool is mainly depended on the geometry,moonpool depth,and encountered wave frequency.Out of this,moonpool geometry is one of the key factors for the performance of the moonpool.The varying cross-section geometry is one of the practically possible and economically feasible solutions to reduce the oscillation to a considerable level is attempted in this paper.Also the resistance caused by the moonpool and the free surface generated around the hull is investigated with the use of computer simulation.
