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1.
Hybrid model testing technique is widely used in verification of a deepwater floating structure and its mooring system,but the design of the truncated mooring systems which can reproduce both static and dynamic response same as the full-depth mooring system is still a big challenge,especially for the mooting systems with large truncation.A Cell-Tress Spar operated in 1500 m water depth is verified in a wave basin with 4 m water depth.A large truncation factor arises even though a small model scale 1:100 is adopted.Computer program modules for analyzing the static and frequency domain dynamic response of mooting line are combined with multi-objective genetic algorithm NSGA-II to optimize the truncared mooting system.Considering the asymmetry of layout of mooring hnes,two different truncated mooring systems are respectively designed for both directions in which the restoring forces of the.mooting system are quite,different.Not only the static characteristics of the mooting systems are calibrated,but also the dynamic responses of the single truncated mooting line are evaluated through time domain numerical simulation and model tests.The model test results of 100-year storm in the GOM are reconstructed and extrapolated to a full depth.It is found that the experimental and numerical resuits of Spar wave frequency motion agree well,and the dynamic responses of the full-depth mooring lines are better reproduced,but the low frequency surge motion is overestimated due to the smaller mooring-induced damping.It is a feasible method adopting different truncated mooring systems for different directions in which the restoring force characteristics are quite different and cannot be simulated by one truncated mooring system.Hybrid verification of a deepwater platform in wave basin with shallow water depth is still feasible if the truncated mooring systems are properly designed,and numerical extrapolation is necessary. 相似文献
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由于聚酯缆绳具备优异的力学性能,促使以其为主体系缆的绷紧式系泊系统得以广泛应用和发展。但聚酯系缆具有复杂的黏弹性和黏塑性,且由于在安装和使用过程中可能产生不同程度的损伤,使得聚酯系缆的动刚度特性发生演变,从而对系泊系统的动力响应产生直接影响。以一系泊于1 020 m水深的Spar平台为例,运用ABAQUS软件建立了由聚酯缆绳组成的系泊系统有限元模型,并利用ABAQUS子程序将损伤缆绳动刚度经验公式进行导入计算,以更好地反映系缆真实的动刚度变化。基于该有限元模型,计算了在相同水流、波浪工况下,不同损伤度、不同损伤系缆的系缆张力历程和平台的横荡、纵荡位移响应,分析了不同损伤度、不同损伤系缆对系缆张力及平台位移的影响。这些成果对把握绷紧式系泊系统在聚酯系缆有损伤情况下的非线性动力响应及其安全应用具有重要的参考价值。 相似文献
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Xiaohong Chen Yu Ding Jun Zhang Pierre Liagre John Niedzwecki Per Teigen 《Ocean Engineering》2006,33(1):93-117
The dynamically coupled interaction between the hull of a floating platform and its risers and tendons plays an important role in the global motions of the platform and the tension loads in the tendons and risers. This is an especially critical design issue in the frequency ranges outside the wave frequencies of significant energy content. This study examines the importance of this coupled dynamic interaction and the effectiveness of different approaches for their prediction. A numerical code, named COUPLE, has been developed for computing the motions and tensions pertaining to a moored floating structure positioned and restrained by its mooring/tendon and riser systems. In this study the experimentally measured motions of a mini-TLP are compared with those computed using COUPLE and alternative predictions based upon quasi-static analysis. The comparisons confirm that COUPLE is able to predict the dynamic interaction between the hull and its tendon and riser systems while the related quasi-static analysis fails. The comparisons also show that wave loads on the mini-TLP can be accurately predicted using the Morison equation provided that the wavelength of incident waves is much longer than the diameters of the columns and pontoons and that the wave kinematics used are sufficiently accurate. Although these findings are based upon the case of a mini-TLP, they are expected to be relevant to a wide range of floating or compliant deepwater structures. 相似文献
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Accurate prediction of the offshore structure motion response and associate mooring line tension is important in both technical applications and scientific research. In our study, a truss spar platform, operated in Gulf of Mexico, is numerically simulated and analyzed by an in-house numerical code ‘COUPLE'. Both the platform motion responses and associated mooring line tension are calculated and investigated through a time domain nonlinear coupled dynamic analysis. Satisfactory agreement between the simulation and corresponding field measurements is in general reached, indicating that the numerical code can be used to conduct the time-domain analysis of a truss spar interacting with its mooring and riser system. Based on the comparison between linear and nonlinear results, the relative importance of nonlinearity in predicting the platform motion response and mooring line tensions is assessed and presented. Through the coupled and quasi-static analysis, the importance of the dynamic coupling effect between the platform hull and the mooring/riser system in predicting the mooring line tension and platform motions is quantified. These results may provide essential information pertaining to facilitate the numerical simulation and design of the large scale offshore structures. 相似文献
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Dynamics of large-truncated mooring systems coupled with a catenary moored semi-submersible 总被引：2，自引：2，他引：0
With the floating structures pushing their activities to the ultra-deep water,model tests have presented a challenge due to the limitation of the existing wave basins.Therefore,the concept of truncated mooring system is implemented to replace the full depth mooring system in the model tests,which aims to have the same dynamic responses as the full depth system.The truncated mooring system plays such a significant role that extra attention should be paid to the mooring systems with large truncation factor.Three different types of large truncation factor mooring system are being employed in the simulations,including the homogenously truncated mooring system,non-homogenously truncated mooring system and simplified truncated mooring system.A catenary moored semi-submersible operating at 1000 m water depth is presented.In addition,truncated mooring systems are proposed at the truncated water depth of 200 m.In order to explore the applicability of these truncated mooring systems,numerical simulations of the platform’s surge free decay interacting with three different styles of truncated mooring systems are studied in calm water.Furthermore,the mooring-induced damping of the truncated mooring systems is simulated in the regular wave.Finally,the platform motion responses and mooring line dynamics are simulated in irregular wave.All these simulations are implemented by employing full time domain coupled dynamic analysis,and the results are compared with those of the full depth simulations in the same cases.The results show that the mooring-induced damping plays a significant role in platform motion responses,and all truncated mooring systems are suitable for model tests with appropriate truncated mooring line diameters.However,a large diameter is needed for simplified truncated mooring lines.The suggestions are given to the selection of truncated mooring system for different situations as well as to the truncated mooring design criteria. 相似文献
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Based on the lumped-mass method and rigid-body kinematics theory, a mathematical model of a gravity cage system attacked by irregular waves is developed to simulate the hydrodynamic response of cage system, including the maximum tension of mooring lines and the motion of float collar. The normalized response amplitudes (response amplitude operators) are calculated for the cage motion response in heave and surge, and the mooring line tension response, in regular waves. In addition, a statistical approach is taken to determine the motion and tension transfer functions in irregular waves. In order to validate the numerical model of a gravity cage attacked by irregular waves, numerical predictions have been compared with the experimental observations in the time and frequency domain. The effect of wave incident angle on the float collar motion, mooring line tension and net volume reduction of the gravity cage system in irregular waves is also investigated. The results show that at high frequencies, the cage system has no significant heave motion. It tends to contour itself to longer waves. The variation amplitude of mooring line forces decreases as the wave frequency increases. With the increasing of wave incident angle, the horizontal displacement of the float collar increases. 相似文献
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A.K. AgarwalA.K. Jain 《Ocean Engineering》2003,30(4):487-516
Many innovative floating offshore structures have been proposed for cost effectiveness of oil and gas exploration and production in water depths exceeding one thousand meters in recent years. One such type of platform is the offshore floating Spar platform. The Spar platform is modelled as a rigid body with six degrees-of-freedom, connected to the sea floor by multi-component catenary mooring lines, which are attached to the Spar platform at the fairleads. The response dependent stiffness matrix consists of two parts (a) the hydrostatics provide restoring force in heave, roll and pitch, (b) the mooring lines provide the restoring force which are represented here by nonlinear horizontal springs. A unidirectional regular wave model is used for computing the incident wave kinematics by Airy’s wave theory and force by Morison’s equation. The response analysis is performed in time domain to solve the dynamic behavior of the moored Spar platform as an integrated system using the iterative incremental Newmark’s Beta approach. Numerical studies are conducted for sea state conditions with and without coupling of degrees-of-freedom. 相似文献
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Many innovative floating offshore structures have been proposed for cost effectiveness of oil and gas exploration and production in water depths exceeding one thousand meters in recent years. One such type of platform is the offshore floating Spar platform. The Spar platform is modelled as a rigid body with six degrees-of-freedom, connected to the sea floor by multi-component catenary mooring lines, which are attached to the Spar platform at the fairleads. The response dependent stiffness matrix consists of two parts (a) the hydrostatics provide restoring force in heave, roll and pitch, (b) the mooring lines provide the restoring force which are represented here by nonlinear horizontal springs. A unidirectional regular wave model is used for computing the incident wave kinematics by Airy’s wave theory and force by Morison’s equation. The response analysis is performed in time domain to solve the dynamic behavior of the moored Spar platform as an integrated system using the iterative incremental Newmark’s Beta approach. Numerical studies are conducted for sea state conditions with and without coupling of degrees-of-freedom. 相似文献
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针对目前小油田早期生产中存在的不足,提出一种适用于浅水海域的新型张力腿式储油处理平台,该平台主要由储油箱、浮箱、吸力桩、系泊链和甲板结构构成,具备原油处理和储存功能。应用非线性时域耦合分析法,研究了有义波高、平均波周期、水深对该平台的运动响应和系泊链张力的影响。计算结果表明,波高对平台动力响应有较大影响,有义波高每增加0.4 m,平台水平位移相应增加0.408 m,而系泊链力随有义波高的增加呈准线性增大;波周期对平台水平运动影响显著,平均波周期从6.5 s逐级变化至8.5 s时,最大水平位移自3.760 m渐增至5.467 m,而波周期对系泊链力影响较小,变化率一般小于10%;该新型平台对水深大于20 m的浅水海域有良好的动力特性,而对水深小于20 m的海域却表现异常。因此,该新型张力腿式平台能满足水深不小于20 m浅海区的油田早期生产需要。 相似文献
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Both numerical calculation and model test are important techniques to study and forecast the dynamic responses of the floating offshore wind turbine (FOWT). However, both the methods have their own limitations at present. In this study, the dynamic responses of a 5 MW OC3 spar-type floating wind turbine designed for a water depth of 200 m are numerically investigated and validated by a 1:50 scaled model test. Moreover, the discrepancies between the numerical calculations and model tests are obtained and discussed. According to the discussions, it is found that the surge and pitch are coupled with the mooring tensions, but the heave is independent of them. Surge and pitch are mainly induced by wave under wind wave conditions. Wind and current will induce the low-frequency average responses, while wave will induce the fluctuation ranges of the responses. In addition, wave will induce the wavefrequency responses but wind and current will restrain the ranges of the responses. 相似文献
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《Applied Ocean Research》2007,29(1-2):45-54
Catenary mooring lines are typically subjected to bimodal loads, comprising of a wave frequency (WF) component due to the first-order wave forces and a low frequency (LF) component induced by the second-order wave forces. For moored vessels, the LF forces due to current and wind also play a role. Only dynamic wave loads are considered herein, while current and wind loads are modeled as constant forces. Because of the nonlinearities of the mooring line characteristics, the dynamic line tension and the second-order responses, both the WF and LF line tensions are in principle nonGaussian. These facts make it difficult to estimate the combined fatigue damage of mooring lines in the frequency domain. A fatigue combination rule based on the Jiao and Moan’s theory has been extended to cover the nonGaussian case. The purpose of this paper is to improve and validate the frequency-domain method by time-domain analysis based on a simplified, but accurate mechanical model of the dynamic line tension. Improvements on the LF and combined fatigue damage estimation have been made by considering the nonsymmetrical property of the LF line tension distribution. Both the WF and LF mooring line tensions due to wave loading have been simulated in the time domain for different sea states and the combined fatigue damage has been estimated by using the rainflow cycle counting algorithm. The accuracy of the frequency-domain method for estimating the bimodal nonGaussian fatigue damage of mooring lines has been verified by the time-domain simulations and is considered to be acceptable. 相似文献
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O.A. Montasir 《Ocean Engineering》2011,38(13):1417-1429
Spar platform has been regarded as a competitive floating structure for deep and ultra deep water oil and gas production. In this paper, an efficient methodology has been developed to determine the slow motion responses of slender floating offshore structures due to wave forces. Based on this methodology, a MATLAB program named ‘TRSPAR’ was developed to predict the dynamic responses in time domain and it was used in this study to obtain the numerical results of a typical truss spar platform connected to sea bed using nine taut mooring lines. The difference frequency forces were calculated using the principles of the extension of Morison equation for an inclined cylinder and the wave kinematics were predicted using hyperbolic extrapolation. Mooring lines were modelled as nonlinear springs and their stiffness was obtained by conducting the static offset simulation. Because of the lack of detailed calculations in literature, most of the equations used were derived and presented in this paper. The effects of the different sources of the second order difference frequency forces were compared for inertia and drag forces in terms of response spectra. To validate the TRSPAR code, its results were compared to results of a typical truss spar model test. 相似文献
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This paper quantitatively studies the transient dynamic response of a semi-submersible production platform with the loss of one or several positioning mooring lines.A semi-submersible platform,production risers,and positioning mooring lines are all included in the numerical simulation.Increased motion of the semi-submersible platform,tension variation of the remaining mooring lines/risers and the risk of mooring line or riser clashing are all investigated through fully coupled time-domain analysis.Combined environmental loads are selected from irregular waves and the steady current varying from very rough to extreme sea conditions.Three dimension radiation/diffraction theories and Morison’s equation are applied to calculate first-order wave force and second-order mean drift force of floating semi-submersible platform.Nonlinear time-domain finite element methods are employed to analyze the behavior of mooring lines and risers.Results show that the failure of mooring lines seriously reduce the platform’s stability performance.The tension of the rest lines is also increased accordingly.Remaining lines which are closer to the failed lines will have larger tension increase to compensate.Line-Line distance provides practical information for the risk of clashing investigation. 相似文献
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Much attention should be paid to a large FPSO moored permanently in an oil field with water depth of only about 20 m, since shallow water effects on the hydrodynamics may bring about collision and damage. A 160kDWT FPSO with a permanent soft yoke mooring system is investigated with various shallow water depths and focuses are the low frequency surge motion and mooring load. Computation for the FPSO system is made based on linear 3-D potential fluid theory and time-domain numerical simulation method. Corresponding model test is carried out in the ocean engineering basin of Shanghai Jiao Tong University. It is shown that, in the surge natural period, low frequency surge motion and mooring force increase remarkably with the decrease of water depth. Especially, the smaller the ratio of water depth and draught is, the quicker the increase is. The shallow water effects should be taken into account carefully for determining the design load of a single point mooring system. 相似文献
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A two-degree freedom model for an ALT-tanker system is established corresponding to the pitch of the ALT and the surge of the tanker.Tension in the mooring cable between the ALT and the tanker is represented by an unsymmetrical,piecewise-nonlinear function.Wave load on the tower is evaluated by use of the Morison equation.The first order wave load acting on the tanker is calculated by the linear diffraction theory based on the 2-D Helmholtz equation,and the near field approach of Pinkster is used to evaluate the second order drift force.The dynamic equation of motion is established based on the principle of D'lembert.Dynamic response and cable tension of a mooring system composed of an 88.4 m ALT and a 100000 t grade tanker are calculated.The influence of wave frequency,wave excitation amplitude,wind and current force on ALT-tanker motion and cable tension is discussed. 相似文献
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《Applied Ocean Research》2005,27(4-5):187-208
In the present paper, the performance of a moored floating breakwater under the action of normal incident waves is investigated in the frequency domain. A three-dimensional hydrodynamic model of the floating body is coupled with a static and dynamic model of the mooring lines, using an iterative procedure. The stiffness coefficients of the mooring lines in six degrees of freedom of the floating breakwater are derived based on the differential changes of mooring lines' tensions caused by the static motions of the floating body. The model of the moored floating system is compared with experimental and numerical results of other investigators. An extensive parametric study is performed to investigate the effect of different configurations (length of mooring lines and draft) on the performance of the moored floating breakwater. The draft of the floating breakwater is changed through the appropriate modification of mooring lines' length. Numerical results demonstrate the effects of the wave characteristics and mooring lines' conditions (slack-taut). The existence of ‘optimum’ configuration of the moored floating breakwater in terms of wave elevation coefficients and mooring lines' forces is clearly demonstrated, through a decision framework. 相似文献
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以Spar型浮式风机为研究对象,研究涡激力对于浮式风机系统运动的影响。对多体动力学软件FAST进行二次开发,加入涡激力的计算接口,实现了在平台涡激、波激、空气动力载荷及系泊联合作用下的Spar浮式风机系统的运动响应的计算。计算了在风、浪、流联合作用下,频率锁定现象发生时,Spar基础的运动响应,分析了风浪下Spar风机运动响应的涡激运动特性,并研究了不同的入流角度的影响。结果表明:考虑涡激力后,Spar基础的横荡运动明显增大;风浪流同向时,风浪的存在会抑制流载荷引起的横荡在涡泄频率的运动;在流与风浪垂直时,会激发Spar基础的更大的纵荡运动响应。 相似文献