This paper presents the results from a numerical study on the nonlinear dynamic behaviors including bifurcation and chaos of a truss spar platform. In view of the mutual influences between the heave and the pitch mode...This paper presents the results from a numerical study on the nonlinear dynamic behaviors including bifurcation and chaos of a truss spar platform. In view of the mutual influences between the heave and the pitch modes, the coupled heave and pitch motion equations of the spar platform hull were established in the regular waves. In order to analyze the nonlinear motions of the platform, three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs were constructed, the Poincare maps and the power spectrums of the platform response were calculated. It was found that the platform motions are sensitive to wave fre- quency. With changing wave frequency, the platform undergoes complicated nonlinear motions, including 1/2 sub-harmonic motion, quasi-periodic motion and chaotic motion. When the wave frequency approaches the natural frequency of the heave mode of the platform, the platform moves with quasi-periodic motion and chaotic motional temately. For a certain range of wave frequencies, the platform moves with totally chaotic motion. The range of wave frequencies which leads to chaotic motion of the platform increases with increasing wave height. The three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs reveal the nonlinear motions of the spar platform under different wave conditions.展开更多
This paper presents the heave responses and the moonpool water motions of a truss Spar platform with semi-closed moonpool in random waves. A 2-DOF（degree of freedom） coupling dynamical equations of the platform heav...This paper presents the heave responses and the moonpool water motions of a truss Spar platform with semi-closed moonpool in random waves. A 2-DOF（degree of freedom） coupling dynamical equations of the platform heave and vertical motions of the moonpool water are derived. The linear wave theory is used to simulate the random waves. The response statistical values and the power spectrums are calculated to analyze the mutual influences between the platform heave and the moonpool water motions for different opening ratios of the moonpool. The effect of coupling parameters on the platform heave and the moonpool water motions are analyzed. The results show that motions of the moonpool water significantly affected the platform heave when the characteristic wave period is far away from the natural period of the platform heave, and different moonpool opening ratios lead to different heave amplitudes of the platform. In the actual design, an optimized moonpool opening ratio can be designed to reduce heave motions of the platform.展开更多
Spar technology has been applied to the deep-sea oil and gas exploitation for several years. From the first generation of classic spar, the spar platform has developed into the second generation of truss spar and the ...Spar technology has been applied to the deep-sea oil and gas exploitation for several years. From the first generation of classic spar, the spar platform has developed into the second generation of truss spar and the latest cell spar. Owing to its favorable adaptability to wide range of water depth and benign motion performances, spar has aroused quite a lot of interests from oil companies, universities and research institutes. In the present paper, a new cell-truss spar concept, put forward by the State Key Laboratory of Ocean Engineering （SKLOE） at Shanghai Jiao Tong University, is studied both numerically and experimentally. The numerical simulation was conducted by means of nonlinear time-domain fully coupled analysis, and its results were compared to the experimental data. Whereafter, detailed analysis was carried out to obtain the global performances of＇ the new spar concept. Proposals for the improvement of numerical calculation and experimental technique were tabled meanwhile.展开更多
Considering the static stability and the change of the displacement volume, including the influences of higher order nonlinear terms and the instantaneous wave surface, the nonlinear coupled heave-pitch motion was est...Considering the static stability and the change of the displacement volume, including the influences of higher order nonlinear terms and the instantaneous wave surface, the nonlinear coupled heave-pitch motion was established in stochastic waves. The responses of heave-pitch coupling motion for the Truss Spar platform were investigated. It was found that, when the characteristic frequency of a stochastic wave is close to the natural heave frequency, the large amplitude pitch motion is induced under the parametric-forced excitation, which is called the Mathieu instability. It was observed that the heave mode energy is transferred to pitch mode when the heave motion amplitude exceeds a certain extent. In addition, the probability of internal resonant heave-pitch motion is greatly reduced while the characteristic wave frequency is away from the natural heave frequency.展开更多
The research purpose of this paper is to estimate the impacts of the parameters of the guide plate on the vertical motion characteristics of the moonpool fluid. With the volume of fluid(VOF) method, three-dimensional ...The research purpose of this paper is to estimate the impacts of the parameters of the guide plate on the vertical motion characteristics of the moonpool fluid. With the volume of fluid(VOF) method, three-dimensional models of the moonpool fluid motions of the truss spar platform are established. Simulation results are then presented for the moonpool forced oscillation by employing the dynamic mesh method and user-defined functions in FLUENT. The motions of the moonpool fluid and the loads on the guide plates are obtained for both cases of square-ring and crisscross. The results show that the shape and area of the guide plate at the bottom of the moonpool have a significant impact on the physical parameters of the moonpool, including the load on the moonpool guide plate, motion form of the moonpool fluid and the mass flow rate.展开更多
基金supported by the National Natural Science Foundation of China under Grant No.51179125the Innovation Foundation of Tianjin University under Approving No.1301
文摘This paper presents the results from a numerical study on the nonlinear dynamic behaviors including bifurcation and chaos of a truss spar platform. In view of the mutual influences between the heave and the pitch modes, the coupled heave and pitch motion equations of the spar platform hull were established in the regular waves. In order to analyze the nonlinear motions of the platform, three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs were constructed, the Poincare maps and the power spectrums of the platform response were calculated. It was found that the platform motions are sensitive to wave fre- quency. With changing wave frequency, the platform undergoes complicated nonlinear motions, including 1/2 sub-harmonic motion, quasi-periodic motion and chaotic motion. When the wave frequency approaches the natural frequency of the heave mode of the platform, the platform moves with quasi-periodic motion and chaotic motional temately. For a certain range of wave frequencies, the platform moves with totally chaotic motion. The range of wave frequencies which leads to chaotic motion of the platform increases with increasing wave height. The three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs reveal the nonlinear motions of the spar platform under different wave conditions.
基金financially supported by the National Natural Science Foundation of China(Grant No.51179125)the Innovation Foundation of Tianjin University(Grant No.1301)
文摘This paper presents the heave responses and the moonpool water motions of a truss Spar platform with semi-closed moonpool in random waves. A 2-DOF（degree of freedom） coupling dynamical equations of the platform heave and vertical motions of the moonpool water are derived. The linear wave theory is used to simulate the random waves. The response statistical values and the power spectrums are calculated to analyze the mutual influences between the platform heave and the moonpool water motions for different opening ratios of the moonpool. The effect of coupling parameters on the platform heave and the moonpool water motions are analyzed. The results show that motions of the moonpool water significantly affected the platform heave when the characteristic wave period is far away from the natural period of the platform heave, and different moonpool opening ratios lead to different heave amplitudes of the platform. In the actual design, an optimized moonpool opening ratio can be designed to reduce heave motions of the platform.
基金This workis financially supported by the Major Fundamental Research Program of ScienceTechnology Commission of Shanghai Municipality(Grant No.05DJ14001)National High Technology Research and Development Programof China(863Program,Grant No.2006AA09A107).
文摘Spar technology has been applied to the deep-sea oil and gas exploitation for several years. From the first generation of classic spar, the spar platform has developed into the second generation of truss spar and the latest cell spar. Owing to its favorable adaptability to wide range of water depth and benign motion performances, spar has aroused quite a lot of interests from oil companies, universities and research institutes. In the present paper, a new cell-truss spar concept, put forward by the State Key Laboratory of Ocean Engineering （SKLOE） at Shanghai Jiao Tong University, is studied both numerically and experimentally. The numerical simulation was conducted by means of nonlinear time-domain fully coupled analysis, and its results were compared to the experimental data. Whereafter, detailed analysis was carried out to obtain the global performances of＇ the new spar concept. Proposals for the improvement of numerical calculation and experimental technique were tabled meanwhile.
基金Supported by the National Natural Science Foundation of China(No. 51079097, 50879057)
文摘Considering the static stability and the change of the displacement volume, including the influences of higher order nonlinear terms and the instantaneous wave surface, the nonlinear coupled heave-pitch motion was established in stochastic waves. The responses of heave-pitch coupling motion for the Truss Spar platform were investigated. It was found that, when the characteristic frequency of a stochastic wave is close to the natural heave frequency, the large amplitude pitch motion is induced under the parametric-forced excitation, which is called the Mathieu instability. It was observed that the heave mode energy is transferred to pitch mode when the heave motion amplitude exceeds a certain extent. In addition, the probability of internal resonant heave-pitch motion is greatly reduced while the characteristic wave frequency is away from the natural heave frequency.
基金Supported by the National Natural Science Foundation of China under Grant No.51179125 and No.51279130
文摘The research purpose of this paper is to estimate the impacts of the parameters of the guide plate on the vertical motion characteristics of the moonpool fluid. With the volume of fluid(VOF) method, three-dimensional models of the moonpool fluid motions of the truss spar platform are established. Simulation results are then presented for the moonpool forced oscillation by employing the dynamic mesh method and user-defined functions in FLUENT. The motions of the moonpool fluid and the loads on the guide plates are obtained for both cases of square-ring and crisscross. The results show that the shape and area of the guide plate at the bottom of the moonpool have a significant impact on the physical parameters of the moonpool, including the load on the moonpool guide plate, motion form of the moonpool fluid and the mass flow rate.
