Experimental Studies on Sloshing Mitigation Using Dual Perforated Floating Plates in A Rectangular Tank

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.     

Optimization of Baffled Rectangular and Prismatic Storage Tank Against the Sloshing Phenomenon

China Ocean Engineering - The fluid motion in partially filled tanks with internal baffles has wide engineering applications. The installation of baffles is expected to reduce the effect of...     

Review on the Progress and Issues in Liquid Tank Sloshing of Ships

With the development of large liquid cargo ships, liquid tank sloshing has gradually become a hot research topic in the area of shipping and ocean Engineering. Liquid tank sloshing, characterized by strong nonlinearity and randomness, not only affects the stability of the ship but also generates a huge impact force on the wall of the tank. To further investigate liquid tank sloshing, a comprehensive review is given on the research process of the most focused subjects of liquid sloshing. Summariz...     

Experimental Study on Sloshing Characteristics in the Elastic Tank Based on Morlet Wavelet Transform

Hydroelastic effect of sloshing is studied through an experimental investigation. Different excitation frequencies are considered with low-fill-depth and large amplitude. Morlet wavelet transform is introduced to analyze the free surface elevations and sloshing pressures. It focuses on variations and distributions of the wavelet energy in elastic tanks. The evolutions of theoretical and experimental wavelet spectra are discussed and the corresponding Fourier spectrums are compared. Afterwards, average values of the wavelet spectra are extracted to do a quantitative study at various points. From the wavelet analysis, sloshing energies are mainly distributed around the external excitation frequency and expanded to high frequencies under violent condition. In resonance, experimental wavelet energy of the elevation in elastic tanks is obviously less than that in the rigid one; for sloshing pressures, the elastic wavelet energy close to the rigid one and conspicuous impulse is observed. It recommends engineers to concern the primary natural frequency and impulsive peak pressures.     

Numerical Simulation of Sloshing Using the MPS-FSI Method with Large Eddy Simulation

A numerical model has been developed to study sloshing of turbulent flow in a tank with elastic baffles. The Moving-Particle Semi-implicit method(MPS) is a kind of meshless Lagrangian calculation method. The large eddy simulation(LES) approach is employed to model the turbulence by using the Smagorinsky Sub-Particle Scale(SPS)closure model. This paper uses MPS-FSI method with LES to simulate the interaction between free surface flow and a thin elastic baffle in sloshing. Then, the numerical model is validated, and the numerical solution has good agreement with experimental data for sloshing in a tank with elastic baffles. Furthermore, under external excitations,the MPS is applied to viscous laminar flow and turbulent flow, with both the deformation of elastic baffles and the wave height of the free surface are compared with each other. Besides, the impact pressure with/without baffles and wave height of free surface are investigated and discussed in detail. Finally, preliminary simulations are carried out in the damage problem of elastic baffles, taking the advantage of the MPS-FSI method in computations of the fluid–structure interaction with large deformation.     

海底散射模型对浅海混响的影响研究

对于混响预报,散射强度是一个相当重要的物理量。在波束位移射线简正波理论的基础上推导了浅海混响模型,仿真比较了负跃层浅海情况四种海底散射模型对应的混响衰减曲线,结果表明海底散射模型对浅海混响的影响较为显著。     

Effects of Topography and Current on Horizontal Irrotational Waves in Shallow Water

Based on the Boussinesq assumption,derived are couple equations of free surface elevationand horizontal velocities for horizontal irrotational flow,and analytical expressions of the correspondingpressure and vertical velocity.After the free surface elevation and horizontal velocity at a certain depth areobtained by numerical method,the pressure and vertical velocity distributions can be obtained by simplecalculation.The dispersion at different depths is the same at the O(ε)approximation.The waveamplitude will decrease with increasing time due to viscosity,but it will increase due to the matching ofviscosity and the bed slope.thus,flow is unstable.Numerical or analytical results show that the waveamplitude.velocity and length will increase as the current increases along the wave direction.but theamplitude will increase.and the wave velocity and length will decrease as the water depth decreases.     

海南岛南部浅海地质灾害调查方法研究

为研究海南岛南部浅海海洋地质灾害和环境地质问题,在研究区域进行了单道地震测量和侧扫声呐测量工作,单道地震剖面显示,在研究区域分布有两条海底埋藏古河道,根据剖面位置,大致确定了研究区域海底埋藏古河道的分布和走向;根据侧扫声呐声图图像,发现在研究区域20m以深海域广泛发育沙脊、沙波地貌。研究结果表明,在研究区域存在潜在的海洋地质灾害因素,研究结果不仅对海南岛海岸带、陆架开发中的环境地质和地质灾害问题的调查具有实际应用价值,而且对于研究海南岛陆架地质环境演变也具有十分重要的意义。     

A New Wetting and Drying Method for Moving Boundary in Shallow Water Flow Models

To deal with the moving boundary hydrodynamic problems of the tidal flats in shallow water flow models, a new wetting and drying (WD) method is proposed. In the new method, a “predicted water depth” is evaluated explicitly based on the simplified shallow water equations and used to determine the status (wet or dry) together with the direction of flow. Compared with previous WD method, besides the water elevation, more factors, such as the flow velocity and the surface shear stress, are taken into account in the new method to determine the moving boundary. In addition, a formula is deduced to determine the threshold, as critical water depth, which needs to be preset before simulations. The new WD method is tested with five cases including three 1D ones and two 2D ones. The results show that the new WD method can simulate the wetting and drying process, in both typical and practical cases, with smooth manner and achieves effective estimation of the retention volume at shallow water body.     

A Model of Wave Spectrum in Shallow Water

By using the shallow water wave data continuously recorded in the Bohai Sea, Huanghai Sea, East China sea and South China Sea. a model of wave spectrum in shallow water is developed with three parameters—average wave height, average period and relative depth—on the basis of the principle of the spectrum pattern simularity and the method of parameterization. The magnitude of frequency index in the high frequency     

A New Wetting and Drying Method for Moving Boundary in Shallow Water Flow Models

To deal with the moving boundary hydrodynamic problems of the tidal flats in shallow water flow models,a new wetting and drying (WD) method is proposed.In the new method,a "predicted water depth" is evaluated explicitly based on the simplified shallow water equations and used to determine the status (wet or dry) together with the direction of flow.Compared with previous WD method,besides the water elevation,more factors,such as the flow velocity and the surface shear stress,are taken into account in the new method to determine the moving boundary.In addition,a formula is deduced to determine the threshold,as critical water depth,which needs to be preset before simulations.The new WD method is tested with five cases including three 1D ones and two 2D ones.The results show that the new WD method can simulate the wetting and drying process,in both typical and practical cases,with smooth manner and achieves effective estimation of the retention volume at shallow water body.     

Experimental Study on A Sloshing Mitigation Concept Using Floating Layers of Solid Foam Elements

A sloshing mitigation concept taking advantage of floating layers of solid foam elements is proposed in the present study. Physical experiments are carried out in a liquid tank to investigate the hydrodynamic mechanism of this concept. Effects of the foam-layer thickness, excitation amplitude, and excitation frequency on the sloshing properties are analyzed in detail. It is found that the floating layers of solid foam elements do not evidently affect the fundamental natural sloshing frequency of the liquid tank evidently among the considered cases. At the resonant condition, the maximum wave height and dynamic pressure are greatly reduced as the foam-layer thickness increases. Higher-order pressure components on the tank side gradually vanish with the increase of the foam-layer thickness. Cases with different excitation amplitudes are also analyzed. The phenomenon is observed when the wave breaking in the tank can be suppressed by solid foam elements.     

Investigation on Touching Sea Bottom by a FPSO in Bohai Oilfield with Shallow Water

As one of the key safety problems, the motion performance and touching sea bottom of a FPSO are paid much attention by the ocean oil companies when the FPSO is exposed to survival storms in the shallow-water working areas. In this paper, timedomain numerical simulations are carried out on a 160 kDWT FPSO with a Yoke mooring system moored in the BZ25-1 oilfield with a water depth of 16.7m. The results are compared with those of the corresponding model tests. Good agreement shows that the time-domain simulations can be used to predict the performance of the FPSO in shallow-water reasonably. It is found that the touch of seabed by a fully loaded FPSO occurred few times under survival storm conditions. Therefore, the FPSO should be less loaded than that in the fully loaded condition under the survival storms.     

浅海海底控制点水平坐标的简化计算方法

提出了一种在声速剖面未知的条件下计算海底控制点水平坐标的方法,根据流体静力学方程将海底应答器的压力值转化为深度值,并以此深度值作为等效声速剖面法的参考深度,基于等效声速剖面法与船底换能器到海底应答器声波的传播时间计算各历元的测距值,通过圆走航利用距离交会法确定海底控制点水平方向的坐标。松花湖的实验表明,这种方法可以获得较高精度的浅海海底控制点水平方向的坐标。     

Shallow Water Effects on Surge Motion and Load of Soft Yoke Moored FPSO

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.     

Simulation of Wetting and Drying Processes in A Depth Integrated Shallow Water Flow Model by Slot Method

A particular porosity method named ＂slot method＂ is implemented in a depth-integrated shallow water flow model （DIVAST） to simulate wetting and drying processes. Discussed is the relationship between the shape factors of the ＂slot＂ and the preset depth used in ＂wetting-drying＂ algorithm. Two typical tests are conducted to examine the performance of the method with the effect of the shape factors of the ＂slot＂ being checked in detail in the first test. Numerical results demonstrate that： 1 ） no additional effort to improve the finite difference scheme is needed to implement ＂slot method＂ in DIVAST, and 2） ＂slot method＂ will simulate wetting and diying processes correctly if the shape factors of the ＂slot＂ being selected properly.     

Model Tests Research on A Float-Over Barge in Shallow Water Under the Undocking Conditions

In this study, the Jinzhou 9-3 CEPD float-over installation project was investigated. During the undocking condition, the water depth of the motion path of the working barge gradually changed from 10.31 m to 9.41 m. The undocking clearance of the HYSY 228 is smaller than 1 m; therefore, the barge shows highly nonlinear hydrodynamic characteristics, and it is difficult to be accurately simulated by numerical analysis. Thus, it is necessary to obtain the hydrodynamic characteristics and laws of the float-over barge at different water depths by using tank model test, to provide some reference and guidance for float-over operations in shallow water.

     

谈浅海油田固定平台应急电站设计

结合埕岛中心二号平台的设计实践,对浅海油田固定平台应急发电机组的选型、布置、辅助系统配置、供电范围等内容进行探讨     

Numerical Investigation on Vortex-Induced Rotations of A Triangular Cylinder Using An Immersed Boundary Method

A numerical study of vortex-induced rotations(VIRs) of an equivalent triangular cylinder, which is free to rotate in the azimuthal direction in a uniform flow, is presented. Based on an immersed boundary method, the numerical model is established, and is verified through the benchmark problem of flow past a freely rotating rectangular body.The computation is performed for a fixed reduced mass of m~*=2.0 and the structural stiffness and damping ratio are set to zero. The effects of Reynolds number(Re=25-180) on the characteristics of VIR are studied. It is found that the dynamic response of the triangular cylinder exhibits four distinct modes with increasing Re: a rest position,periodic rotational oscillation, random rotation and autorotation. For the rotational oscillation mode, the cylinder undergoes a periodic vibration around an equilibrium position with one side facing the incoming flow. Since the rotation effect, the outset of vortex shedding from cylinder shifts to a much lower Reynolds number. Further increase in Re leads to 2 P and P+S vortex shedding modes besides the typical 2 S pattern. Our simulation results also elucidate that the free rotation significantly changes the drag and lift forces. Inspired by these facts, the effect of free rotation on flow-induced vibration of a triangular cylinder in the in-line and transverse directions is investigated. The results show that when the translational vibration is coupled with rotation, the triangular cylinder presents a galloping response instead of vortex-induced vibration(VIV).