共查询到20条相似文献，搜索用时 15 毫秒
1.
A method to compute wave- and current-induced viscous drift forces and moments on floating platforms in regular and random waves is presented. The relative velocity drag term of Morison's equation is used in conjunction with frequency domain first-order motion transfer functions to compute the drift forces and moments. Mean viscous drift forces and moments in regular waves in all six degrees-of-freedom of a tension leg platform are computed. The relative importance of the free-surface force integration, steady current, wave-current interaction and platform motions on the computed drift forces and moments are discussed. The results from this method, in the frequency domain, are used to compute the drift forces and responses in irregular waves using existing methods developed for potential drift computations. Comparisons with results from time-domain computations are also presented and good agreement between the frequency-domain and time-domain results is found. Some comparisons with experimental data are also made. The frequency-domain method is found to be an efficient and useful tool for the analysis of semi-submersible and tension leg platforms during the preliminary design stage in which extensive parametric studies need to be undertaken. 相似文献
2.
M. Söylemez 《Ocean Engineering》1996,23(5):423-445
This paper presents the derivation of a general method for calculating wave forces on the cylindrical members of offshore structures. By means of the proposed method one can calculate the wave loading on cylindrical members of fixed or floating offshore structures orientated randomly in waves. This method of calculating wave forces is based on the linear Airy wave theory. Calculation procedure of wave force components is presented in great detail on the basis of wave particle kinematic properties obtained from the linear Airy wave theory. In the procedure of calculating wave forces presented, definitions of the wave reference system for propagating wave, the structure reference system for the platform and the member reference system for the tubular members of the structure are first established, and then the calculation of wave forces is given in terms of its components, which are pressure, acceleration and velocity forces, including current forces. At the end of the paper, expressions of total heave, sway and surge forces and total roll, pitch and yaw moments acting on the platform are given as a sum of these forces acting on each member of the platform. The calculation procedure derived in this paper provides a very efficient means of calculating wave forces and moments during the time-domain simulations of a floating platform experiencing large amplitude motion in intact, progressive flooding and damaged conditions. Comparisons of the predictions with the measurements which will be presented elsewhere reveal that the calculation procedure developed can predict large amplitude oscillatory and steady motion characteristics of an intact and damaged platform in waves with an acceptable degree of accuracy. 相似文献
3.
A partly non-linear time-domain numerical model is used for the prediction of parametric roll resonance in regular waves. The ship is assumed to be a system with four degrees of freedom, namely, sway, heave, roll and pitch. The non-linear incident wave and hydrostatic restoring forces/moments are evaluated considering the instantaneous wetted surface whereas the hydrodynamic forces and moments, including diffraction, are expressed in terms of convolution integrals based on the mean wetted surface. The model also accounts for non-potential roll damping expressed in an equivalent linearised form. Finally, the coupled equations of motion are solved in the time-domain referenced to a body fixed axis system.This method is applied to a range of hull forms, a post-Panamax C11 class containership, a transom stern Trawler and the ITTC-A1 containership, all travelling in regular waves. Obtained results are validated by comparison with numerical/experimental data available in the literature. A thorough investigation into the influence of the inclusion of sway motion is conducted. In addition, for the ITTC-A1 containership, an investigation is carried out into the influence of tuning the numerical model by modifying the numerical roll added inertia to match that obtained from roll decay curves. 相似文献
4.
Muhittin Sylemez 《Ocean Engineering》1998,25(4-5)
The purpose of the study was to develop a prediction technique to simulate the motion response of a damaged platform under wave, wind and current forces. The equations of motion were obtained using Newton's second law and the numerical solution technique of non-linear equations of motion is explained for intact and damaged cases. The analysis technique employs large displacement non-linear equations of motion. Solutions were obtained in the time-domain to predict the motion characteristics. In this study, analysis procedures were developed to calculate: (a) wave loading on asymmetrical structural configurations; (b) hydrodynamic reaction forces (inertia or moment of inertia, damping and restoring forces) on asymmetrical shapes. During the damage simulation, change in the mass of the structure as well as wave and hydrodynamic reaction forces, were taken into account. The computer program developed for the time-domain simulation is introduced. In order to avoid slowly decaying transient motions of the structure due to wave excitation forces, an exponential ramp function is used. The application of a ramp function enables a quick convergence in the time-domain solution of equations of motion. Results of a numerical motion simulation program and the experimental studies are also presented in order to make comparisons. Comparison of the test results with the numerical simulations shows good agreement for heave, roll and pitch motions. The formulations and the computational procedures given in this paper provide useful tools for the investigation of the non-linear dynamic stability characteristics of floating structures in waves for intact, damaged and post-flooding conditions in six-degrees of freedom. 相似文献
5.
R.S. Langley 《Ocean Engineering》1984,11(4):381-401
A general method for the dynamic analysis of multi-body offshore structures is presented, being based on a constraint matrix approach. A method of deriving the constraint matrix for a general structure is given, and this is then used to derive the equations of motion of a whole system from those of it's component parts. The response of the system to both first and second order random wave forces is found and then used to calculate the forces and moments in the connecting mechanisms. The structure is assumed to have rigid component parts and a linearised frequency domain analysis method is used, although other methods are discussed. To illustrate it's use, the method is applied to both the SBS and Yoke-CALM design of offshore mooring terminal. 相似文献
6.
为了快速并有效地计算海洋平台等薄壁箱型梁结构的约束扭转极限承载能力,进行了薄壁梁约束扭转极限承载能力简化计算方法研究.基于塑性极限状态分析理论,提出了薄壁梁约束扭转极限状态应力分布假设,将薄壁梁视作为一系列由主要支撑构件和扶强材支撑的板格,推导了薄壁梁约束扭转极限承载能力上限的计算公式.应用非线性有限元方法验证了所提假设和计算公式的精度,将所提方法应用于箱型梁模型和半潜平台的约束扭转极限承载能力的计算分析,并与非线性有限元结果进行了比对,结果表明,本方法具有较高的精度,可用于海洋平台等薄壁梁的扭转极限承载力上限的估算. 相似文献
7.
This paper presents the results of an extensive parametric study to investigate various non-linear aspects of the prediction of the large-amplitude motion responses of a semi-submersible. The main objectives of the parametric studies were to investigate the following aspects, which can non-linearly influence the motion responses and which cannot be studied by linear frequency-domain prediction techniques. These aspects are the effects on the motion responses of flooding time and mass; non-linear wave-exciting and rigid-body induced motion (i.e. added mass and damping) forces; non-linear restoring forces; steady wind and current; variation of GM (transverse metacentric height); and the initial position of the semi-submersible. The investigations were carried out for a particular semi-submersible geometry using a numerical simulation technique in the time domain. The simulations were performed for the model during intact, progressive and post-flooding conditions under the combined loading of regular waves, steady wind and current for two different heading angles. This paper is thus intended to provide some insight into the physical effects of the non-linear terms in the equations of motion which are associated with the wave-excitation forces, rigid-body induced motion forces and restoring forces. Since the resulting motion responses could have a steady component as well as the oscillatory one, the force and motion phenomena were also highlighted through the computation of these components. 相似文献
8.
Li Hongnan Ma Baicun
Professor Shenyang Architectural Civil Engineering Institute Shenyang Assistant Engineer Shenyang Architectural Civil Engineering Institute Shenyang 《中国海洋工程》1997,(2)
An approach to seismic response reduction for offshore platforms by the use of the tuned liq-uid damper is presented in this paper.First of all,the effects of the tuned frequency ratio and excited fre-quency ratio on the seismic response reduction of the platform structure are investigated.Based on the re-sults,a mechanical model and equation of motion for the TLD-platform system are established.And theneffectiveness of the appraoch is verified by numerical calculation. 相似文献
9.
Mu Yang Zhang Shengkun Assistant Dept. of Architecture Ocean Engineering Shanghai Jiao Tong University Shanghai Professor Dept. of Architecture Ocean Engineering Shanghai Jiao Tong University Shanghai 《中国海洋工程》1993,(3)
- A modified space beam element is presented in this paper to consider the local joint flexibility of T, Y tubular joints subjected to axial forces and in- plane bending moments for analysis of platforms. Two numerical examples are shown to verify the efficiency and validity of the method presented here. 相似文献
10.
海上桶基平台基础边界条件的简化方法与结构优化 总被引：2，自引：1，他引：1
海上桶型基础平台采用桶型基础这一新型的基础型式,桶基平台在结构强度校核计算和结构优化中必须考虑其有限元分析模型的基础边界条件简化问题。本文提出了桶基平台有限元分析模型中的基础边界条件简化方法,将桶型基础边界简化为位移弹簧边界元,给出了弹簧刚度的计算方法。通过模型试验与本文提出方法的计算结果的比较,证明本文提出的方法是正确的。同时,将本文提出的方法应用于桶基火炬平台的结构优化,表明该方法是实际可行的并且对于桶基平台的结构强度校核计算与结构优化有重要意义。对于桶基火炬平台的结构优化采用了适合离散变量优化求解的遗传算法,优化的结果有效地降低了结构重量,降低了工程造价。 相似文献
11.
In this study, the seismic response control of offshore platform structures with Shape Memory Alloy (SMA) dampers is investigated. A new SMA damper and its restoring force medel are introduced for the calculation of seismic response reduction. Based on an actual platform structure and its mechanical medel, the parameters which may affect the rate of shock absorption are analyzed, such as the number, position and characteristics of the SMA dampers and the condition of the site where the platform is located. The results show that the SMA damper is an effective control device for offshore platforms and satisfactory control can be achieved by proper selection of the parameters. 相似文献
12.
Unsteady forces, torques and bending moments were predicted for a model podded propulsor unit at various azimuth angles. Predictions in time history include propeller shaft thrust, propulsor unit thrust, normal forces to the propeller shaft bearing, total forces acting on the propulsor unit, propeller shaft torque, blade spindle torque, in-plane and out-of-plane bending moments, and propulsor unit stock shaft torque and bending moments. Analysis was performed for averaged forces and their fluctuations as well. A time-domain unsteady multi-body panel method code, PROPELLA, was further developed for this prediction work. Predictions were compared with a set of time averaged in-house experimental data for a puller-type podded propulsor configuration in the first quadrant operation. Unsteady fluctuations of forces were predicted numerically. Analysis was made for the bending moment on propeller blades, shaft and the propulsor unit stock shaft for azimuth angles from 0° to 45°. It indicates that the magnitude and fluctuation of the forces are significant and they are essential for structural strength and design optimization. The predicted bending moment and global forces on the propulsor unit provide some useful data for ship maneuvering motion and simulation in off-design conditions. 相似文献
13.
The dynamic response of offshore platforms is more serious in hostile sea environment than inshallow sea.In this paper,a hybrid solution combined with analytical and numerical method is proposedto compute the stochastic response of fixed offshore platforms to random waves,considering wave-struc-ture interaction and non-linear drag force.The simulation program includes two steps:the first step is theeigenanalysis aspects associated the structure and the second step is response estimation based on spectralequations.The eigenanalysis could be done through conventional finite element method conveniently andits natural frequency and mode shapes obtained.In the second part of the process,the solution of theoffshore structural response is obtained by iteration of a series of coupled spectral equations.Consideringthe third-order term in the drag force,the evaluation of the three-fold convolution should be demanded fornonlinear stochastic response analysis.To demonstrate this method,a numerical analysis is carrie 相似文献
14.
Passive control of offshore jacket platforms 总被引：3，自引：0，他引：3
The wave-induced dynamic force is one of the most important excitations to be dealt with in the design of offshore structures. In order to perform a reliable design of an offshore structure, it is important to obtain an exact evaluation of its dynamic response but also to examine the ways of reducing the response. This paper presents the response of offshore jacket platforms installed with energy dissipation devices such as viscoelastic, viscous and friction dampers under wave loading. The offshore jacket platforms are modeled as multi-degrees-of-freedom system provided with dampers at each floor location. The wave forces are modeled as per Morison's equation. The governing equations of motion of the jacket platform with dampers are derived and their solution in the frequency domain is presented. The uni-directional random wave loading is expressed by the Pierson-Muskowitz spectrum. The response of the jacket platform with viscoelastic, viscous and friction dampers is compared with the corresponding response without dampers in order to investigate the effectiveness of the passive control systems. It is observed that the additional dampers add substantial damping to structure and thus favorably control the response of platform structure. Among the various energy dissipation devices used for study, the viscoelastic dampers perform better in comparison to the other dampers. This is due to the fact that the added viscoelastic dampers contribute to increased viscous damping as well as lateral stiffness which reduces the response of the offshore jacket platforms significantly. 相似文献
15.
Offshore guyed tower platforms belong to the group of compliant offshore platforms which are most suited for deep water exploration. The basic feature of compliant offshore platforms is that they are designed to move with the waves, in at least some degrees-of-freedom. As far as excitation of wave frequencies is concerned, the system opposes wave forces by inertial effects. The offshore guyed tower derives its stability against lateral movement from its mooring system.In this study, the response of offshore guyed towers to random forces generated by wind and wave is investigated. The exposed portion of the tower is subjected to the action of turbulent wind, while the submerged portion is acted upon by random wave forces. The analysis includes the nonlinearities due to the Morison equation of drag force, the variable submergence effect due to waves, the instantaneous position of the tower and force excursion relation of the mooring lines. A parametric study is conducted to investigate the behaviour of the tower under waves, and the combined effect of wind and wave forces. 相似文献
16.
By extending the linear frequency domain theory, a quasi-non-linear time-domain technique has been developed to investigate the large amplitude motions of catamarans in regular waves. The non-linearity of hydrodynamic forces included in this practical method comes from variations of a ship's submerged portion. These forces are obtained from a database generated by the linear frequency domain method at each time step. The coupled equations, heave and pitch, are solved in the time domain by using the Runge-Kutta method with proper initial values. In order to investigate the non-linear effects of large amplitude motions of the V-1 catamaran in the head-sea condition, numerical results obtained from the linear and non-linear strip methods have been compared with those obtained from a series of experiments carried out in the towing tank of the Hydrodynamics Laboratory at the University of Glasgow. Based on the comparative studies, the numerical results obtained from the time-domain program can provide better predictions for the large amplitude motions of catamarans than the linear frequency domain method. It is concluded that the non-linear effects are significant when the model speeds and wave amplitudes increase. The peak values of large amplitude motions around the resonance frequencies, as obtained from the non-linear time-domain predictions as well as from measurements, are smaller than those obtained from the linear theory. 相似文献
17.
建立了内孤立波作用下Spar平台运动响应的时域数值模型,并利用这一模型计算了内孤立波作用下Spar平台的运动响应。其中根据K-dv方程解出内孤立波的波面及水质点速度表达式,应用Morison公式求出内孤立波对Spar平台的水平作用力;由伯努力方程求解压强,通过在平台底面积分求出内孤立波对Spar平台的垂向作用力;在悬链线理论的基础上,分析锚链对平台的作用力,采用四阶Runge-Kutta方法求解运动方程。数值结果表明,当内孤立波不断接近海洋平台时,Spar平台受到的作用力随之增大,海洋平台会产生远大于表面波作用下的水平位移,从而证实了内孤立波是影响海洋平台稳定的重要因素,在海洋平台的设计和评估中内孤立波的作用是不可忽略的。 相似文献
18.
1 .Introductionanyoffshoreplatformshavebeenbuiltwiththedevelopmentofoceanengineering .However ,mostoffshorearelocatedinseismicregionsandtheplatformsareeasilytobeseriouslydamagedbyearthquakes.Hence ,theanti earthquakedesignhasalwaysbeenamajorpartofresearchonoffshoreplatforms.Theinclusionofvibrationabsorbersintheoffshoreplatformcanbeanattractivemethodofmitigatingseismicresponses .Vibrationabsorberscanbecategorizedintoactiveandpassive .Thetunedmassdamper (TMD)(FujinoandAbe ,1 993) ,eitherpassi… 相似文献
19.
This study considers the coupling effects of ship motion and sloshing. The linear ship motion is solved using an impulse-response-function (IRF) method, while the nonlinear sloshing flow is simulated using a finite-difference method. The IRF method requires the frequency-domain solution prior to conversion to time domain, but the computational effort is much less than that of direct time-domain approaches. The developed scheme is verified by comparing the motion RAOs between the frequency-domain solution and the solution obtained by the IRF method. Furthermore, a soft-spring concept and linear roll damping are implemented to predict more realistic motions of surge, sway, yaw, and roll. For the simulation of sloshing flow in liquid tanks, a physics-based numerical approach adopted by Kim [2001. Numerical simulation of sloshing flows with impact load. Applied Ocean Research 23, 53–62] and Kim et al. [2004. Numerical study on slosh-induced impact pressures on three-dimensional prismatic tanks. Applied Ocean Research 26, 213–226] is applied. In particular, the present method focuses on the simulation of the global motion of sloshing flow, ignoring some local phenomena. The sloshing-induced forces and moments are added to wave-excitation forces and moments, and then the corresponding body motion is obtained. The developed schemes are applied for two problems: the sway motion of a box-type barge with rectangular tanks and the roll motion of a modified S175 hull with rectangular anti-rolling tank. Motion RAOs are compared with existing results, showing fair agreement. It is found that the nonlinearity of sloshing flow is very important in coupling analysis. Due to the nonlinearity of sloshing flow, ship motion shows a strong sensitivity to wave slope. 相似文献
20.
作用在海洋移动式平台上的风倾载荷 总被引：2，自引：0，他引：2
本文在归纳国内外对作用在海洋移动式平台风倾载荷的研究文献的基础上，分析了目前船级社的规范中风载荷计算方法中的几个问题。本文介绍了作者编制的风倾力臂横截曲线计算程序，并给出了计算实例 相似文献