共查询到20条相似文献，搜索用时 31 毫秒
1.
Real sea conditions are characterized by multidirectional sea waves. However, the prediction of hull load responses in oblique waves is a difficult problem due to numeral divergence. This paper focuses on the investigation of numerical and experimental methods of load responses of ultra-large vessels in oblique regular waves. A three dimensional nonlinear hydroelastic method is proposed. In order to numerically solve the divergence problem of time-domain motion equations in oblique waves, a proportional, integral and derivative (PID) autopilot model is applied. A tank model measurement methodology is used to conduct experiments for hydroelastic responses of a large container ship in oblique regular waves. To implement the tests, a segmented ship model and oblique wave testing system are designed and assembled. Then a series of tests corresponding to various wave headings are carried out to investigate the vibrational characteristics of the model. Finally, time-domain numerical simulations of the ship are carried out. The numerical analysis results by the presented method show good agreement with experimental results. 相似文献
2.
The importance of hydroelastic analysis of large and flexible container ships of today is pointed out. A methodology for investigation of this challenging phenomenon is drawn up and a mathematical model is worked out. It includes definition of ship geometry, mass distribution, structure stiffness, and combines ship hydrostatics, hydrodynamics, wave load, ship motion and vibrations. Based on the presented theory, a computer program is developed and applied for hydroelastic analysis of a flexible segmented barge for which model test results of motion and distortion in waves have been available. A correlation analysis of numerical simulation and measured response shows quite good agreement of the transfer functions for heave, pitch, roll, vertical and horizontal bending and torsion. The tool checked in such a way can be further used for reliable hydroelastic analysis of ship-like structures. 相似文献
3.
开发并验证了一种基于CFD-FEM耦合的弹性浮体水弹性响应计算模拟方法。采用CFD方法建立黏性数值水池模拟非线性波浪，弹性浮板进行有限元离散，并在交界面进行数据交互实现耦合计算；通过与水池试验数据和三维板理论在各种波浪环境下的浮体垂向位移结果对比，证实CFD-FEM耦合方法的有效性。并进一步研究了浮板的厚度、入射波波幅和浮板的三维效应对浮板水弹性响应的影响。结论表明，波幅的增加会加剧弹性浮板的水弹性响应，浮板各点处的垂向位移随波幅的增加而增大；当浮板厚度改变时，不同厚度浮板自由端处的垂向位移差异较小，而在中部等位置处，厚度对浮板的水弹性响应有较大的影响。 相似文献
4.
Evaluation of bending moments and shear forces at unit connections of very large floating structures using hydroelastic and rigid body analyses 总被引：1，自引：0，他引：1
Byoung Wan Kim Sa Young Hong Jo Hyun Kyoung Seok Kyu Cho 《Ocean Engineering》2007,34(11-12):1668-1679
This paper investigates the characteristics of bending moments, shear forces and stresses at unit connections of very large floating structures (VLFS) under wave loads. The responses of VLFS are calculated by solving multi-body motion equation considering hydroelasticity and connection stiffness. Hydroelastic responses are calculated by the direct method. Higher-order boundary element method (HOBEM) is used for fluid analysis and finite element method (FEM) is introduced for structural analysis. The equation of motion is modified to describe the unit connections by employing spring elements. Bending moments and shear forces at the connections are obtained from the dynamic equilibrium condition for pressures and inertia forces. Two types of VLFS units such as tandem arranged units and side-by-side arranged units are considered in the numerical examples. The influences of connection stiffness, wave frequency and heading angle on responses of VLFS are investigated through the numerical examples. Rigid body analysis along with hydroelastic analysis is also carried out in the numerical analysis and comparison of those two approaches is discussed. 相似文献
5.
Comparison of Linear Level I Green-Naghdi Theory with Linear Wave Theory for Prediction of Hydroelastic Responses of VLFS 总被引：4，自引：0，他引：4
Very Large Floating Structures (VLFS) have drawn considerable attention recently due to their potential significance in the exploitation of ocean resources and in the utilization of ocean space. Efficient and accurate estimation of their hydroelastic responses to waves is very important for the design. Recently, an efficient numerical algorithm was developed by Ertekin and Kim (1999). However, in their analysis, the linear Level I Green-Naghdi (GN) theory is employed to describe fluid dynamics instead of the conventional linear wave (LW) theory of finite water depth. They claimed that this linear level I GN theory provided betler predictions of the hydroelastic responses of VLFS than the linear wave theory. In this paper, a detailed derivation is given in the conventional linear wave theory framework with the same quantity as used in the linear level I GN theory framework. This allows a critical comparison between the linear wave theory and the linear level I GN theory. it is found that the linear level 相似文献
6.
By integration of the second-order fluid pressure over the instantaneous wetted surface, the generalized first- and second-order fluid forces used in nonlinear hydroelastic analysis are obtained. The expressions for coefficients of the generalized first- and second-order hydrodynamic forces in irregular waves are also given. The coefficients of the restoring forces of a mooring system acting on a flexible floating body are presented. The linear and nonlinear three-dimensional hydroelastic equations of motion of a moored floating body in frequency domain are established. These equations include the second-order forces, induced by the rigid body rotations of large amplitudes in high waves, the variation of the instantaneous wetted surface and the coupling of the first order wave potentials. The first-order and second-order principal coordinates of the hydrelastic vibration of a moored floating body are calculated. The frequency characteristics of the principal coordinates are discussed. The numerical results indicate that the rigid resonance and the coupling resonance of a moored floating body can occur in low frequency domain while the flexible resonance can occur in high frequency domain. The hydroelastic responses of a moored box-type barge are also given in this paper. The effects of the second-order forces on the modes are investigated in detail. 相似文献
7.
In this study, we develop a numerical method for a 3D linear hydroelastic analysis of floating structures with liquid tanks subjected to surface regular water waves and compare the numerical results with experimental tests. Considering direct couplings among structural motion, sloshing, and water waves, a mathematical formulation and a numerical method extended from a recent work [1] are developed. The finite element method is employed for the floating structure and internal fluid in tanks, and the boundary element method is used for the external fluid. The resulting formulation completely incorporates all the interaction terms including hydrostatic stiffness and the irregular frequency effect is removed by introducing the extended boundary integral equations. Through various numerical tests, we verify the proposed numerical method. We also performed 3D hydroelastic experimental tests of a floating production unit (FPU) model in an ocean basin. The measured dynamic motions are compared with the numerical results obtained using the proposed method. 相似文献
8.
A new hybrid method for the time-domain nonlinear simulation of the hydroelastic load effects and the peak over threshold (POT) method for the calculation of the short-term extreme responses are briefly described and applied to a flexible SL-7 class containership and a flexible liquefied natural gas (LNG) ship. Three stiffness levels, three stiffness distributions and three modal damping ratios are used to study the influence of the hull flexibility and structural damping on the short-term prediction of extreme vertical hydroelastic load effects. The results give justification for some simplified treatment of the first vertical flexible mode in early design stage when structural details are not available. 相似文献
9.
The quasi-steady resonant vibration of a flexible seagoing vessel under resonant wave excitation force, called springing, is studied in this paper. A higher-order B-spline Rankine panel method is used to represent the effects of the fluid motion surrounding this flexible seagoing vessel, and a finite element formulation based on Vlasov beam is employed for structural response. The boundary integral equation and finite element equation, both for fluid and structural domains, are fully coupled with each other using an iterative implicit method in the time domain. Coupling between the two field equations is achieved by relying on fixed-point iteration with relaxation aided by Aitken's δ2 process to maximize convergence speed. The steady-unsteady coupling term or m-term in the linearized body boundary condition derived by Timman and Newman is taken into account for accurate prediction of flexible body motion when forward speed is present. The 2nd derivative of basis potential in the m-term is obtained by modifying Nakos approach, which was originally developed using the Stokes theorem for rigid body ship motion problem. For the solution of the FE equation, instead of conventionally used modal superposition method, a direct integration scheme based on Newmark method is employed. It is believed that this technique is more attractive in the sense that it allows us free from the selection of optimum number of mode-shapes in the computation. 相似文献
10.
This paper presents the use of a modular raft Wave Energy Converter (WEC)-type attachment at the fore edge of a rectangular Very Large Floating Structure (VLFS) for extracting wave energy while reducing hydroelastic responses of the VLFS under wave action. The proposed modular attachment comprises multiple independent auxiliary pontoons (i.e. modules) that are connected to the fore edge of the VLFS with hinges and linear Power Take-Off (PTO) systems. For the hydroelastic analysis, the auxiliary pontoons and the VLFS are modelled by using the Mindlin plate theory while the linear wave theory is used for modelling the fluid motion. The analysis is performed in the frequency domain using the hybrid Finite Element-Boundary Element (FE-BE) method. Parametric studies are carried out to investigate the effects of pontoon length, PTO damping coefficient, gap between auxiliary pontoons, and incident wave angle on the power capture factor as well as reductions in the hydroelastic responses of the VLFS with the modular attachment. It is found that in oblique waves, the modular attachment comprising multiple narrow pontoons outperforms the corresponding rigid attachment that consists of a single wide pontoon with respect to the power capture factor and the reduction in the deflection of the VLFS. In addition, it is possible to have a considerable gap between pontoons without significantly compromising the effectiveness of the modular attachment. 相似文献
11.
针对不规则波浪作用下Wigley型船的运动响应问题进行了系统的研究,采用统计学方法深入探讨了船舶不规则运动幅值和响应周期的分布规律,并通过傅里叶变换对船舶运动响应进行了频谱特征分析。结果表明,船舶横摇方向与升沉和纵摇方向随机运动的响应特征有显著差异。在升沉与纵摇方向,波浪谱峰频率远离自振频率,前十分之一大振幅运动对应周期离散性较小,基本稳定在波浪谱峰周期附近,但小振幅运动周期分布离散性较大,频谱分析指出船舶升沉与纵摇运动响应频谱在波浪谱峰频率附近出现明显峰值。而在横摇方向,波浪谱峰频率与自振频率相耦合,不同振幅的横摇运动响应周期均稳定在自振周期附近,且周期离散性较小,频谱分析也表明横摇运动响应频谱主要集中于船舶运动自振频率附近。 相似文献
12.
羟基杀灭船舶压载水微小生物中试实验研究 总被引：2，自引：0，他引：2
采用羟基处理压载水技术，使用羟基处理设备和管道作为模拟船舶排放压载水的管道。研究了羟基对海产小球藻、游仆虫和异养细菌的杀灭效果，说明羟基能有效杀灭压载水中的微小生物；并模拟船舶排放压载水过程中排放地的海水对处理后压载水的稀释作用，稀释后的水样经过96h的培养，没有发现微小生物复活的情况，证明了羟基杀灭船舶压载水微小生物在长度为4m(接触时间为2s)的接触管道内已经完成。并研究了羟基处理压载水技术对水质情况的影响，结果表明羟基有效杀灭船舶压载水微小生物的同时能改善压载水水质。 相似文献
13.
《Ocean Engineering》2007,34(13):1797-1810
Reliable estimation of the on-site sea state parameters is essential to decision support systems for safe navigation of ships. The wave spectrum can be estimated from procedures based on measured ship responses. The paper deals with two procedures—Bayesian Modelling and Parametric Modelling—which both use complex-valued frequency response functions (FRF) to estimate the wave spectrum. It is therefore interesting to investigate how the filtering aspect, introduced by FRF, affects the final outcome of the estimation procedures. In order to do this, extensive numerical simulations—with known wave parameters—are carried out for a large container vessel. The study shows that filtering has an influence on the estimations, since high-frequency components of the wave excitations are not estimated as accurately as lower frequency components. 相似文献
14.
The purpose of this paper is to optimise the hydroelastic performance of a composite marine propeller to reduce vibration and dynamic stress. A hydroelasticity method based on the finite element method (FEM) coupled with computational fluid dynamics (CFD) is used to simulate the composite marine propeller in a non-uniform wake. Composite blades can be considered as a cantilever-like laminated structure experiencing an unsteady hydrodynamic load and centrifugal force. The objective of the improved design is to minimise the vibratory hub loads. The ply angle and stacking sequence are considered as the design variables. The nonlinear periodic transient responses and vibration hub loads of the composite blade are obtained by solving coupled equations using the Newton–Raphson numerical procedure. Compared to the starting design of the propeller, the optimum solution results in a 49.6–70.6% reduction of the 7/rev hub loads. 相似文献
15.
In this paper, using a second-order steady-state approach and a three-dimensional (3D) pulsating source distribution method derives the nonlinear hydrodynamic forces on a ship advancing in waves. The nonlinear hydrodynamic forces considered here consist of the mean lateral drifting force and the added resistance, which can be expressed as products of the ship-motion responses, the radiation potential, diffraction potential and the incident-wave potential. All related velocity potentials applied in the calculations are in 3D form. The Series 60 and Marine ship hulls are used for numerical calculations and the results are compared with existing experimental data and two-dimensional (2D) solutions. The comparisons show that the results obtained in the paper generally agree with experimental data well. It is also found that the nonlinear hydrodynamic forces obtained based on the present 3D source distribution methods are indeed improved in some calculations compared with the 2D method, especially for the mean lateral drifting force. 相似文献
16.
The present study is employing the equivalent irregular wave approach to predict the wave loads for a ship encountering the worst sea state with respect to the critical dynamic loading parameter. Two different hydrodynamic numerical models, i.e. 3D pulsating source technique and 3D translating pulsating source technique, are applied to calculate the corresponding RAO of the ship moving in waves. Incorporating the RAO of the related physical properties, we can calculate the extreme value for the corresponding ship loading factor, which can be regarded as the worst sea state in the service lifetime of the ship. With the time and period of the occurrence of the corresponding extreme value, we can simulate the time history of the wave load in this period, which is so-called equivalent irregular wave approach. Comparing with the results calculated by the traditional equivalent regular wave approach, we find that the equivalent irregular wave approach can simulate the corresponding wave load more realistic, especially for dynamic pressure. Using the equivalent irregular wave approach can offer the effective and practical base for the ship structural analysis. 相似文献
17.
《Ocean Engineering》2006,33(3-4):350-364
The aim of this paper is to investigate the propagation of ship waves on a sloping coast on the basis of results simulated by a 2D model. The governing equations used for the present model are the improved Boussinesq-type equations. The wave breaking process is parameterized by adding a dissipation term to the depth-integrated momentum equation. To give the boundary conditions at the ship location, the slender-ship approximation is used. It was verified that, although ship waves are essentially transient, the Snell's law can be applied to predict crest orientation of the wake system on a sloping coast. Based on simulated results, an applicable empirical formula to predict the maximum wave height on the slope is introduced. The maximum wave height estimated by the proposed method agrees well with numerical simulation results. 相似文献
18.
Dynamic Response Analysis for Embedded Large-Cylinder Breakwaters Under Wave Excitation 总被引：4，自引：0，他引：4
1 .IntroductionThestaticmethodsarecommonlyusedinthestabilityanalysisofembeddedlarge cylinderbreak waters .Thestaticanalysismodelscanbedividedintotwocategories :simplifiedmodels (Zhouetal.,1 995;WangandZhu ,2 0 0 2 )andfiniteelementmodels (MengandWang ,1 999) .Thesimplifiedmodelsinheritthetraditionalengineeringexperiencesandareconvenienttouseinengineeringprac tice.However,itisdifficultforthesimplifiedmodelstodepictthegeometricandphysicalpropertiesofastructure soilsystemprecisely .Thefiniteel… 相似文献
19.
The application of very large floating structure (VLFS) to the utilization of ocean space and exploitation of ocean resources has become one of the issues of great interest in international ocean engineering field. Owing to the advantage of simplicity in structure and low cost of construction and maintenance, box-type VLFS can be used in the calm water area near the coast as the structure configuration of floating airport. In this paper, a 3D linear hydroelastic theory is used to study the dynamic response of box-type VLFS in sinusoidal regular waves. A beam model and a 3D FEM model are respectively employed to describe the dynamic characteristics of the box-type structure in vacuum. A hydrodynamic model (3D potential theory of flexible body) is applied to investigate the effect of different dry models on the hydroelastic response of box-type structure. Based on the calculation of hydroelastic response in regular waves, the rigid body motion displacement, flexible deflection, and the short term and long 相似文献
20.
系泊船非线性波浪力时域计算: 二维模型 总被引：6，自引：1，他引：6
为找到具有工程实用价值的港口系泊船波浪力的时域计算方法,建立了在港口中存在系泊船时非线性波浪力时域计算的垂直二维耦合模型:用Boussinesq方程计算船的两侧的外域,用欧拉方程计算船底面下的内域,两域在交界面处的连接条件是流量连续和压力相等.将复平面内的边界元方法应用于所研究问题,对耦合模型进行了验证.进行了相关模型实验,实验结果与数值计算结果比较表明这两种数值计算模型都具有满意的精度,但耦合模型的计算效率要远远高于边界元方法的计算效率.本耦合模型的数学处理简单,可适用于工程计算. 相似文献