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1.
《中国海洋工程》2020,(4)
The hydroelastic responses of a submerged horizontal solid/porous plate attached at the front of a very large rectangular floating structure(VLFS) under wave action has been investigated in the context of linear water wave theory. Darcy's law is adopted to represent energy dissipation in pores. It is assumed that the porous plates are made of material with very fine pores so that the normal velocity across the perforated porous is linearly associated with the pressure drop. In the analytic method, the eigenfunction expansion-matching method(EEMM) for multiple domains is applied to solve the hydrodynamic problem and the elastic equation of motion is solved by the modal expansion method. The performance of the proposed submerged horizontal solid/porous plate can be significantly enhanced by selecting optimal design parameters, such as plate length, horizontal position, submerged depth and porosity. It is concluded that good damping effect can be achieved through installation of solid and porous plate.Porous plate has better damping effect at low frequencies, while solid plate has better damping effect at high frequencies. The optimal ratio of plate length to water depth is 0.25-0.375, and the optimal ratio of submerged depth to water depth is 0.09-0.181. 相似文献
2.
Hydroelastic analysis of pontoon-type circular VLFS with an attached submerged plate 总被引：2，自引：0，他引：2
This paper is concerned with the hydroelastic analysis of a pontoon-type, circular, very large floating structure (VLFS) with a horizontal submerged annular plate attached around its perimeter. The coupled fluid–structure interaction problem may be solved by using the modal expansion method in the frequency domain. It involves, firstly, the decomposition of the deflection of a circular Mindlin plate with free edges into vibration modes that are obtained analytically. Then the hydrodynamic diffraction and radiation forces are evaluated by using the eigenfunction expansion matching method which can also be done in an exact manner. The hydroelastic equation of motion is solved by the Rayleigh–Ritz method for the modal amplitudes, and then the modal responses are summed up to obtain the total response. The effectiveness of the attached submerged annular plate in reducing the motion of VLFS has been confirmed by the analysis. 相似文献
3.
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
4.
1 .IntroductionIntheexploitationofoceanresourcesandintheutilizationofoceanspaces,verylargefloatingstructures (VLFS)suchasMega FloatinJapan (Isobe ,1 999)andMobileOffshoreBase (MOB)inUSA (Remmers ,1 999)playasignificantrole .However,owingtotheirlargesizesandrelativelylowbendingrigidities ,theirhydroelasticresponsesinwavesareofthemostconcern .ManystudieshavebeencarriedoutforthepredictionofthehydroelasticresponsesofVLFS′s (Kashiwagi,2 0 0 0 ;Cui,2 0 0 2 ) .However,inalmostallofthesestu… 相似文献
5.
Perforated plates, relevant for several marine applications, are experimentally and numerically investigated. The numerical investigations are performed using a presently developed Navier–Stokes solver. Several comparison and sensitivity studies are presented, in order to validate and verify the solver. Forced heave experiments are performed on two perforated plates with perforation ratios 19% and 28%. Amplitude-dependent added mass and damping coefficients are presented. Good agreement is obtained between the solver and the present experiments. Consistent with existing data, the results show that the hydrodynamic coefficients of perforated plates are highly amplitude dependent. The damping force is found to dominate over added mass force. The damping force dominance increases with increasing perforation ratio. It is highlighted that plate-end flow separation has an important effect on the damping coefficient. The developed numerical solver is two-dimensional, but is found to yield reasonable estimates of hydrodynamic force coefficients when compared with a previous three-dimensional experimental investigation. This could indicate that three-dimensional effects are not dominant for the hydrodynamic forces of perforated plates, and that a two-dimensional viscous flow solver could have relevance as a tool for estimating hydrodynamic forces on three-dimensional perforated structures. 相似文献
6.
The hydroelastic responses of a very-long floating structure (VLFS) in waves connected to a floating oscillating-water-column (OWC) breakwater system by a pin are analyzed by making use of the modal expansion method in two dimensions. The Bernoulli–Euler beam equation for the VLFS is coupled with the equations of motions of the breakwater taking account of the geometric and dynamic boundary conditions at the pin. The Legendre polynomials are employed as admissible functions representing the assumed modes of the VLFS with pinned-free-boundary conditions. It has been shown numerically that the deflections, bending moments and shear forces of the VLFS in waves can be reduced significantly by a pin-connected OWC breakwater. The time-mean horizontal drift forces of the VLFS equipped with the breakwater calculated by the near-field method are also presented. 相似文献
7.
Time Domain Simulation of Transient Responses of Very Large Floating Structures Under Unsteady External Loads 总被引：2，自引：0，他引：2
A time domain finite element method （FEM） for the analysis of transient elastic response of a very large floating structure （VLFS） subjected to arbitrary time-dependent external loads is presented. This method is developed directly in time domain and the hydrodynamic problem is formulated based on linear, inviscid and slightly compressible fluid theory and the structural response is analyzed on the thin plate assumption. The time domain finite element procedure herein is validated by comparing numerical results with available experimental data. Finally, the transient elastic response of a pontoon-type VLFS under the landing of an airplane is computed by the proposed time domain FEM. The time histories of the applied force and the position and velocity of an airplane during landing are modeled with data from a Boeing 747-400 jumbo jet. 相似文献
8.
A ring-shaped spar-type Very Large Floating Structure (VLFS) is proposed as an intermediate base for supporting deepwater resource exploitation far away from the coast line. The proposed VLFS is composed of eight rigidly connected deep-draft spar-type modules and an inside harbor. A double-layered perforated-wall breakwater is vertically attached to the VLFS and pierces through the water surface to attenuate the wave energy in the inside harbor. The hydrodynamic performance characteristics of the ring-shaped VLFS was experimentally evaluated in the present study, focusing on the motion responses, wave elevations, and wave run-ups. The natural periods of the motions in vertical plane were determined to be larger than 40 s, which is much larger than common wave periods. This enhanced the motion performance in vertical plane and afforded favorable habitation and operation condition on the VLFS. A large surge damping was induced by the vertical breakwater, which tended to significantly affect the surge and pitch motions, but had a negligible effect on the heave motion. The component frequencies of the wave elevations in the inside harbor and the wave run-ups were identical with those of the incident waves. The wave attenuation was frequency-dependent and effective for the common wave frequencies, with a smaller loss coefficient observed in higher sea state. The wave attenuation and wave run-ups tended to improve in the absence of the leeward walls. 相似文献
9.
YU Yue-min 《中国海洋工程》2021,35(2):301-307
The performance of dual perforated floating plates in a rectangular tank is investigated based on the model tests under different external excitations for different filling rates.It is found that dual perforated floating plates in the tank can remarkably mitigate violent resonant sloshing responses compared with the clean tank,especially when the external excitation frequency is in the vicinity of the first-order resonant frequency.Next,the parametric studies based on different filling rates and external excitation amplitudes are performed for the first-order resonant frequencies.The presence of dual perforated floating plates seldom shifts the sloshing natural frequencies.Further,dual perforated floating plates change the sloshing modes from the standing-wave mode in the clean tank to the Utube mode,which can arise from the sloshing reduction to some extent. 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.
本文基于雷诺平均的Navier-Stokes方程和k-ε模型求解湍流流动,采用流体体积法(Volume of Fluid,VOF)追踪自由表面运动,建立无反射波浪数值水槽,对多消浪室开孔沉箱的消浪特性进行数值模拟研究。将单消浪室和多消浪室开孔沉箱反射系数和结构前波面分布的数值分析结果与物理模型试验结果进行对比验证,两者符合良好。利用数值算例,研究多消浪室开孔沉箱的反射特性以及开孔结构附近的速度场和湍流强度分布。分析结果表明:波浪与开孔沉箱相互作用时,涡旋和湍动主要分布在开孔墙和消浪室内部自由表面附近;与单消浪室开孔沉箱相比,多消浪室开孔沉箱可以更有效的耗散波浪能量,降低结构的反射系数。本文分析结果可为开孔沉箱结构的工程设计提供参考依据。 相似文献
12.
The hydroelastic responses of a very-long floating structure (VLFS) placed behind a reverse T-shape freely floating breakwater with a built-in oscillating water column (OWC) chamber are analyzed in two dimensions. The Bernoulli–Euler beam equation is coupled with the equations of rigid and elastic motions of the breakwater and the VLFS. The interaction of waves between the floating rigid breakwater and the elastic VLFS is formulated in a consistent manner. It has been shown numerically that the structural deflections of the VLFS can be reduced significantly by a suitably designed reverse T-shape floating breakwater. 相似文献
13.
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
14.
用直接法分析超大型浮体的水弹性响应 总被引：4，自引：2，他引：2
探讨了浮舟桥型超大型浮体结构的水弹性响应分析问题。将超大型浮体结构简化成弹性平板模型,用压力分布法计算流体压力,用直接法计算流体-结构系统,给出了它们的数学计算模型。计算表明本计算方法和程序是正确的,并能保证充分的精度,进而计算了更大尺度的超大型浮体,分析了波长、波向等对响应振幅的影响。 相似文献
15.
This paper numerically and experimentally investigates the hydrodynamic interaction between two semi-submersible type VLFS modules in the frequency domain. Model tests were conducted to investigate the relationship between interactions and wave headings. Numerical studies were performed by solving the radiation-diffraction problem and were validated against the experimental results. Motion Response Amplitude Operators (RAOs) were obtained from numerical and experimental studies. The dependency of the hydrodynamic interaction effect on wave headings is clarified. The influence of different wave periods on the motion responses of two-module VLFS and wave elevations in the gap is studied. The results indicate that the hydrodynamic interactions of the two modules are directly related to the wave headings and the periods of the incident wave. The shielding effect plays an important role in short wave, and the influence decreases with the increase of the incident wavelength. The numerical results based on the diffraction-radiation code can give a relatively good estimation to the responses in short wave while for long wave, it would over-predict the response. 相似文献
16.
超大型浮体在海洋资源开发和海洋空间利用方面有重要应用前景.非均匀海洋环境中的水弹性响应是其应用中的一个重要问题.在近海中最典型的非均匀海洋环境当属由于底部变化引起的非均匀现象.本文分别采用多重尺度法（零阶近似）和常规的有限水深势流格林函数边界积分法,对底部呈二维缓变情况下超大型浮体的水弹性响应问题进行了研究和对比,并与实验工况进行了对照.两种方法与试验结果吻合较好,证明非均匀海洋环境确实对超大型浮体的水弹性响应具有一定的影响. 相似文献
17.
Numerical Solution of Membrane Forces for A Free-Free Floating Plate with Large Deflection 总被引：1，自引：0，他引：1
1 .IntroductionVerylargefloatingstructures (VLFS)haveattractedconsiderableattentionrecentlyduetoitspo tentialuseintheexploitationofoceanresourcesandintheutilizationofoceanspaces (Cui,2 0 0 2 ) .Owingtoitslargesizeandrelativelysmallthickness ,theinfluenceofelasticdeformationonthehydro dynamicresponseisimportant.Thisisknownashydroelasticity .Threedimensionallinear (Wu ,1 984;PriceandWu ,1 985)andnonlinear (Chenetal.,2 0 0 3)hydroelasticityiswellappliedtotheanalysisofthreedimensionalshipsando… 相似文献
18.
19.
《中国海洋工程》2020,(4)
A conceptual design of using novel telescopic piles to position a multi-modular very large floating structure(VLFS),which is supposed to be severed as a movable floating airport, is proposed. The telescopic piles can automatically plug in the soil to resist the environmental loads and pull out from the soil to evacuate or move on to the next operational sea. The feasibility demonstration of the conceptual design includes two parts: function verification and structure design. In the latter part of the conceptual design, a time-domain structural analysis is firstly conducted by using Abaqus software. The simulation results suggest that the preliminary structure scheme is not optimum due to the insufficient structure utilization, although both structure safety of the piles and positioning accuracy are guaranteed. To realize a cost reduction of construction and installation, a Genetic Algorithm-Finite Element Analysis(GA-FEA) method is employed to perform structural optimization. After optimization, 31 percent of the weight of each pile is reduced and higher structure utilization is maintained. The difference of the self-weight and allowable buoyancy of a single module(SMOD) of a semisubmersible-type VLFS is much larger than the weight of the piles.Combined with the function verification in our previous work, the conceptual design of using the novel telescopic pile to position VLFS is demonstrated to be feasible. 相似文献
20.
Experimental and Theoretical Investigation of Wave Forces on A Partially-Perforated Caisson Breakwater with A Rock-Filled Core 总被引：2，自引：0，他引：2
1.IntroductionVertical breakwaters are widely used for harbor and coastline protection in coastal engineering.Recently,perforated breakwaters have been often used in practice as they can effectively reduce thewaveforces actingon,the wave reflectionfromand… 相似文献