ISSN  0890-5487 CN 32-1441/P

2022 Vol.36(3)

Display Mode:          |     

Experimental Study on Vortex-Induced Vibration Coupling Wake Interference of Multi-Riser Groups with Sensitive Spacing
Yu WANG, Peng LI, Yu LIU, Xin CHEN, Min LOU, Hai-yan GUO
2022, 36(3): 333-347. doi: 10.1007/s13344-022-0030-y
[Abstract](884) [FullText HTML] (265) [PDF 10742KB](20)
Abstract:
The “riser group−fluid between risers” is taken as the carrier, and the experiment on vortex-induced vibration of tandem riser groups coupling interference effect under sensitive spacing is performed. The least-square method is used to linearly fit the reduced velocity and main frequency, and the rule of Strouhal numbers is analyzed. Each mode is separated based on the mode decomposition theory, and the mode conversion mechanism is also explored. The concept of “interference efficiency” is introduced to study the dynamic characteristics and response evolutions of different riser groups. The results show that the wake shielding effect widely exists in tandem riser groups, and the interference effect of midstream and downstream risers on their upstream risers is significantly lower than that of upstream risers on midstream and downstream risers. The trajectories of midstream and downstream risers lag behind their upstream risers due to multiple shadowing effects, the vibration frequency range of downstream riser is widened and the dominant frequency is extremely unstable. Compared with the isolated riser, wake interference suppresses the vibration displacement of the midstream and downstream risers in the in-line direction, and enhances the displacement of upstream and midstream risers in the cross-flow direction. The interference effect of the fluid between risers at low velocities is stronger than that at higher velocities, and the cross-flow displacements of upstream risers are always in the interference enhancement region. It is urgent to pay attention to the cross-flow displacement of upstream and midstream risers in tandem riser groups considering the safety design.
Study on HOBEM Based on Analytical Panel Integrals Related to Translating-Pulsating Source for Hydrodynamic Responses of Vessels Sailing in Waves
Yun-tao YANG, Ren-chuan ZHU, Yu-long LI
2022, 36(3): 348-362. doi: 10.1007/s13344-022-0031-x
[Abstract](641) [FullText HTML] (199) [PDF 3124KB](5)
Abstract:
A higher-order boundary element method (HOBEM) incorporated with analytical panel integrals related to translating-pulsating source Green’s function is proposed for the hydrodynamic response prediction of ships advancing in waves. In this method, the 9-node bi-quadratic curvilinear elements employed to discretize the mixed-source/dipole boundary integral equation are mapped into the parametric plane through a coordinate transformation. Then in order to ease the numerical instability problem, a novel analytical quadrature is derived to calculate the influence coefficients by changing the integral order and using integration by parts. The singularity caused by infinite discontinuity is analyzed and eliminated by adopting some mathematical techniques. Through the calculations of panel integrals of Green’s function and its x-derivative, the analytical integral method is proved to be always accurate even for field points approaching the free surface, where numerical quadrature is impossible to give reasonable results. Based on this, a higher-order seakeeping program is developed and applied in the motion response prediction of two different types of ships (i.e., a wall-sided ship Wigley III and a non-wall-sided ship S175). By comparing the computed results with the corresponding experimental data and numerical solutions of the translating-pulsating and higher-order Green’s function methods based on traditional Gauss quadrature, it is found that the HOBEM based on analytical quadrature is of better accuracy and stability. For the non-wall-sided ship, only the present method can produce reasonable prediction of motion responses, while obvious oscillatory phenomenon is observed in the results of the other two numerical methods based on Gauss quadrature.
Probabilistic Response and Short-Term Extreme Load Estimation of Offshore Monopile Wind Turbine Towers by Probability Density Evolution Method
Hui ZHANG, Ya-zhou XU
2022, 36(3): 363-371. doi: 10.1007/s13344-022-0032-9
[Abstract](624) [FullText HTML] (232) [PDF 0KB](9)
Abstract:
A new analysis framework based on probability density evolution method (PDEM) and its Chebyshev collocation solution are introduced to predict the dynamic response and short-term extreme load of offshore wind turbine (OWT) towers subjected to random sea state. With regard to the stochastic responses, random function method is employed to generate samples of sea elevation, the probability density evolution equation (PDEE) is solved to calculate time-variant probability density functions of structural responses. For the probabilistic load estimation, a FAST model of NREL 5MW offshore turbine is established to obtain samples of bending moment at the tower base. The equivalent extreme event theory is used to construct a virtual stochastic process (VSP) to assess the short-term extreme load. The results indicate that the proposed approach can predict time-variant probability density functions of the structural responses, and shows good agreement with Monte Carlo simulations. Additionally, the predicted short-term extreme load can capture the fluctuation at the tail of the extreme value distribution, thus is more rational than results from the typical distribution models. Overall, the proposed method shows good adaptation, precision and efficiency for the dynamic response analysis and load estimation of OWT towers.
Modeling and Analyzing Dynamic Response for An Offshore Bottom-Fixed Wind Turbine with Individual Pitch Control
Shuang-yi XIE, Kai-fei ZHANG, Jiao HE, Jian GAO, Cheng-lin ZHANG
2022, 36(3): 372-383. doi: 10.1007/s13344-022-0033-8
[Abstract](638) [FullText HTML] (228) [PDF 4189KB](8)
Abstract:
The asymmetric or periodically varying blade loads resulted by wind shear become more significant as the blade length is increased to capture more wind power. Additionally, compared with the onshore wind turbines, their offshore counterparts are subjected to additional wave loadings in addition to wind loadings within their lifetime. Therefore, vibration control and fatigue load mitigation are crucial for safe operation of large-scale offshore wind turbines. In view of this, a multi-body model of an offshore bottom-fixed wind turbine including a detailed drivetrain is established in this paper. Then, an individual pitch controller (IPC) is designed using disturbance accommodating control. State feedback is used to add damping in flexible modes of concern, and a state estimator is designed to predict unmeasured signals. Continued, a coupled aero-hydro-servo-elastic model is constructed. Based on this coupled model, the load reduction effect of IPC and the dynamic responses of the drivetrain are investigated. The results showed that the designed IPC can effectively reduce the structural loads of the wind turbine while stabilizing the turbine power output. Moreover, it is found that the drivetrain dynamic responses are improved under IPC.
Experimental Study on Wave Attenuation Performance of A New Type of Floating Breakwater with Twin Pontoons and Multi Porous Vertical Plates
Yu-sheng SHEN, Jun-ning PAN, Yi-ren ZHOU, Xing-gang WANG
2022, 36(3): 384-394. doi: 10.1007/s13344-022-0034-7
[Abstract](771) [FullText HTML] (217) [PDF 2660KB](17)
Abstract:
A floating breakwater (FB) has extensive potential applications in the fields of coastal, offshore, and ocean engineering owing to its advantages such as eco-friendliness, low cost, easy and rapid construction, and quick dismantling and reinstallation. An FB composed of twin pontoons and multi-porous vertical plates is proposed to improve the wave attenuation performance. The wave attenuation performance is investigated for different FB structures and vertical plate types under different incident wave heights and periods using 2D wave physical model tests in a wave flume. The results demonstrate that the proposed FB has a better performance than that of the conventional single pontoon-type FB. It reduces the wave transmission due to its enhanced wave reflection and energy loss. The wave transmission coefficient of the proposed FB decreases with an increase in the number of layers and relative draft depth of the vertical plates. However, a further decrease in the wave transmission coefficient is not observed when the number of porous vertical plates is increased from 4 to 5 layers. An equation has been derived to predict the wave transmission of the proposed FB based on the experimental results.
Solitary Wave Simulated by the Water Column Collapsing Method
Jin WANG, Chang-ming DONG, Qing-jun LIU, Qi-hua ZUO
2022, 36(3): 395-402. doi: 10.1007/s13344-022-0035-6
[Abstract](715) [FullText HTML] (214) [PDF 2765KB](5)
Abstract:
Although solitary waves with large ratio of wave height to water depth are difficult to produce in laboratory settings by traditional wave generating methods, a water column collapsing (WCC) method can be employed. This study uses the WCC method to produce large solitary waves and through a series of experiments, an empirical equation is developed that considers wave height and water depth in addition to water column height and depth. Generated solitary waves are studied through wavelet transforms. Results from this analysis demonstrate that the ratios between the initial laboratory-generated solitary wave and its theoretical counterpart range from 0.2−0.8. By using the results, a new solitary wave generating law is derived and can be applied to future solitary wave laboratory studies.
Investigation on Effects of Vertical Degree of Freedom on Gap Resonance Between Two Side-by-Side Boxes Under Wave Actions
Zhi-wei HE, Jun-liang GAO, Hua-bin SHI, Jun ZANG, Hong-zhou CHEN, Qian LIU
2022, 36(3): 403-412. doi: 10.1007/s13344-022-0036-5
[Abstract](595) [FullText HTML] (208) [PDF 2410KB](7)
Abstract:
The possible wave resonance in the narrow gap formed by the parallel arrangement of ships will lead to the sharp increase of wave loads and the rapid growth of motion response. The fluid resonance inside a narrow gap between two side-by-side boxes is investigated numerically based on an open-source CFD package, OpenFOAM. The upstream box remains fixed, while the downstream box is allowed to heave freely under wave actions. This work aims to examine the influence of the motion of the downstream box on the fluid resonant behaviors inside the gap. The hydrodynamic behaviors considered include the wave height inside the gap, the heave displacement, and the reflection, transmission, and energy loss coefficients. Gao et al. (2021) reported the influence of the motion of the upstream box on gap resonant behaviors. For comparative study, some results of Gao et al. (2021) are also presented in this work. It is found that the heave motion of any box in the two-box system leads to a smaller resonant wave height amplification and a larger fluid resonance frequency. The frequency at which the maximum heave displacement of the downstream box occurs is less than the fluid resonant frequency. The heave motion of any box in the two-box system results in a larger reflection coefficient and a smaller energy loss coefficient.
Experimental Study of Overtopping on Sea Dikes and Coastal Flooding Under the Coupled Processes of Tides and Waves
Yan-ting LI, Cheng-jie ZENG, Yi-han Zhao, Po HU, Tian-ting SUN, Yi-jun HOU, Dong-xue MO, Deng-ting WANG
2022, 36(3): 413-426. doi: 10.1007/s13344-022-0037-4
[Abstract](614) [FullText HTML] (218) [PDF 0KB](4)
Abstract:
Storm surges are cataclysmic natural disasters that occur along the coasts and are usually accompanied by large waves. The effects of coupled storm surges and waves can pose a significant threat to coastal security. Previous laboratory studies on the effects of storm surges and waves on coastal structures have typically utilized steady water levels and constant wave elements. An indoor simulation of the coupled processes of tides and waves is developed by adding a tide generation system to an existing laboratory wave basin to model continuous dynamic tide levels so that tide generation and wave-making occur synchronously in the pool. Specific experimental methods are given, which are applied to further study waves overtopping on artificial sea dikes and coastal flooding evolution under the coupled actions of tides and waves. The results of the overtopping discharge obtained by the test with a dynamic water level are compared with those obtained from steady water level tests and the existing empirical formula. In addition, the impacts of ecological coastal shelterbelts and structures on coastal flood processes and distributions are also investigated. The proposed simulation methods provide a new approach for studying the effects of storm surges and waves on coastal areas. The study also aims to provide a reference for coastal protective engineering.
Settlement Mode Analysis for An Immersed Tube Tunnel Considering A Nonuniform Foundation Under Tidal Load
Yan-ning WANG, Huan-zhu ZHOU, Le-chen WANG
2022, 36(3): 427-438. doi: 10.1007/s13344-022-0038-3
[Abstract](528) [FullText HTML] (200) [PDF 4046KB](7)
Abstract:
Immersed tube tunnels are usually placed on soft soil layers in cross-sea tunnelling engineering. Owing to the influence of stratum conditions and slope design, the longitudinal distribution of substratum layers is generally uneven. Thus, the inhomogeneous deformation of the element-joint becomes the key factor in the failure of the immersed tube tunnel. Therefore, a corresponding calculation method for joint deformation is needed to explore the deformation law of immersed tube tunnels. By constructing a three-section immersed tube tunnel analysis model (TTM), the relationship between the two types of deformation of the immersed tube tunnel structure in a longitudinal nonuniform soft soil foundation is described, and the deformation characteristics of the immersed structure under different boundaries are discussed. Based on the mechanical behaviour of the joint and foundation, according to the Timoshenko beam on the Vlasov two-parameter foundation (VTM), considering the tidal cyclic load during the operation and maintenance period, an example analysis is given. Moreover, the deformation characteristics and development trend of the immersed tube tunnel under the influence of different soil layers are discussed. The obtained results have a certain guiding significance for the deformation calculation of immersed tube tunnels.
Influence on the Solid−Liquid Two-Phase Flow from Cross-Section Area of Slurry Pumps for Deep-Sea Mining
Run-kun WANG, Zu-chao ZHU, Xiang-hui SU, Da-sheng TANG, Xing JIN, GRUSZCZYNSKI Maciej
2022, 36(3): 439-450. doi: 10.1007/s13344-022-0039-2
[Abstract](700) [FullText HTML] (204) [PDF 5955KB](6)
Abstract:
To explore the mechanism of solid-liquid two-phase flow in deep-sea mining pumps, this paper investigates the influences of the impeller cross-section area on the multi-phase flow in the slurry pump. Experimental and numerical results are presented for two-phase flow in four impellers with different cross-section areas. They show that the degree of vortex strength and the passing capacity of particles increase as the cross-section area of the impeller. In addition, the correlations between the two-phase flow and cross-section area have been revealed by a mathematical model taking the force of the flow field into account. The simulation results confirm the theoretical analysis, while the experimental pump performances validate the numerical calculation. The influence of the cross-section area on two-phase flow and pump performance could provide theoretical support for the design of high-performance deep-sea mining slurry pumps.
Hydrodynamic Response of A Fully Coupled TLP Hull-TTR System with Detailed Modeling of A Hydraulic Pneumatic Tensioner and Riser Joints
Shuai HAO, Yang YU, Jian-xing YU, Zhi-ming YUAN, Li-xin XU
2022, 36(3): 451-463. doi: 10.1007/s13344-022-0040-9
[Abstract](546) [FullText HTML] (201) [PDF 6282KB](8)
Abstract:
Tension Leg Platform (TLP) in deepwater oil and gas field development usually consists of a hull, tendons, and top tension risers (TTRs). To maintain its top tension, each TTR is connected with a tensioner system to the hull. Owing to the complicated configuration of the tensioners, the hull and TTRs form a strong coupled system. Traditionally, some simplified tensioner models are applied to analyze the TLP structures. There is a large discrepancy between their analysis results and the actual mechanism behaviors of a tensioner. It is very necessary to develop a more detailed tensioner model to consider the coupling effects between TLP and TTRs. In the present study, a fully coupled TLP hull-TTR system for hydrodynamic numerical simulation is established. A specific hydraulic pneumatic tensioner is modeled by considering 4 cylinders. The production TTR model is stacked up by specific riser joints. The simulation is also extended to analyze an array of TTRs. Different regular and irregular waves are considered. The behaviors of different cylinders are presented. The results show that it is important to consider the specific configurations of the tensioner and TTRs, which may lead to obviously different response behaviors, compared with those from a simplified model.
A Prediction Method of Internal Solitary Wave Loads on the Semi- Submersible Platform
Jing-jing ZHANG, Ke CHEN, Yun-xiang YOU, Pan-pan HAN
2022, 36(3): 464-473. doi: 10.1007/s13344-022-0041-8
[Abstract](594) [FullText HTML] (193) [PDF 0KB](5)
Abstract:
An investigation into the prediction method for internal solitary waves (ISWs) loads on the columns and caissons of the semi-submersible platform found on three kinds of internal solitary wave theories and the modified Morison Equation is described. The characteristics of loads exerted on the semi-submersible platform model caused by the ISWs have been observed experimentally, and the inertial and drag coefficients in Morison Equation are determined by analyzing the forces of experiments. From the results, it is of interest to find that Reynolds number, KC number and layer thickness ratio have a considerable influence on the coefficients. The direction of incoming waves, however, is almost devoid of effects on the coefficients. The drag coefficient of columns varies as an exponential function of Reynolds number, and inertia coefficient of columns is a power function related to KC number. Meanwhile, the drag coefficient of caissons is approximately constant in terms of regression analysis of experimental data. The results from different experimental conditions reveal that the inertia coefficient of caissons appears to be exponential correlated with upper layer depths.
Transient Dynamic Analysis of A Variable-Length Rope-Driven Wave Energy System
Wei-cai QUAN, Ding-chao OU, Jing-wei XU, Liang-qing HUO, Yi XI
2022, 36(3): 474-487. doi: 10.1007/s13344-022-0055-2
[Abstract](547) [FullText HTML] (218) [PDF 0KB](7)
Abstract:
A new dynamic model of a variable-length rope, which could be used for the transient analysis of a buoy-rope-generator (BRG) wave energy system, was proposed in this paper. The model started from the basic dynamic equations of variable mass system, and took into account the physical properties such as axial force, shear and bending. According to the principle of D'Alembert-Lagrange, the equivalent integral weak formulation was firstly obtained, and through consistent linearization and isoparametric discretization, the finite element model of the variable-length rope was then derived. The Bathe scheme was employed to solve the model numerically, based on its excellent performance in solving nonlinear dynamic problems, and an automatic time step size algorithm was designed according to the number of iterations of the two substeps of Bathe scheme. The procedures of rope mesh regeneration were also put forward, where only one variable-length element was always located at the top end of the rope, and the rest were all fixed-length elements. The proposed variable-length rope model and solution schemes were verified through comparison with the results of a tank experiment. Finally, the transient dynamics of a kind of BRG system was analyzed and discussed.
Calculation Methods of Added Resistance and Ship Motion Response Based on Potential Flow and Viscous Flow Theory
Qi-ming WU, Bao-ji ZHANG
2022, 36(3): 488-499. doi: 10.1007/s13344-022-0042-7
[Abstract](606) [FullText HTML] (186) [PDF 3819KB](5)
Abstract:
To improve the energy efficiency of ships and to predict ship motion response under actual sea conditions, the far-field theory, strip theory, and Fujii and Takahashi’s modified semi-empirical method are based and studied to calculate the wave-induced added resistance. Firstly, a new modified formula based on the Maruo method is presented to calculate the radiation added resistance for the ship with a complex surface. Meanwhile, some calculation details such as the Green function, the shape of the sections (shape below the still water level or shape below the wave level) in the strip theory, and so on are discussed. Finally, the CFD method is used to simulate the motions of the hull and the added resistance, and the results of the CFD method and those of other numerical methods are analyzed and compared with the experiment results. The modified method in the paper can predict the added resistance in waves for the complex-hull-surface ships well and quickly.
Restoration of Ultimate Strength of Dented Hemispheres Under External Hydrostatic Pressure
Chen HUANG, Jian ZHANG, Fang WANG, Chen-yang DI
2022, 36(3): 500-507. doi: 10.1007/s13344-022-0043-6
[Abstract](645) [FullText HTML] (207) [PDF 5473KB](5)
Abstract:
This study aimed to restore the ultimate strength of dented stainless-steel hemispheres with a radius of 90 mm and a thickness of 0.86 mm. All of the hemispheres were subjected to external hydrostatic pressure. Small stainless-steel stiffened caps were used to eliminate the effect of indention on the ultimate strength. These caps had a radius of 36 mm, a thickness of 0.76 mm, and a height of 10.44 mm. Six hemispherical samples, including two intact hemispheres, two dented hemispheres without stiffening, and two dented hemispheres with stiffening, were prepared. Each hemisphere was geometrically measured for shape and thickness, hydrostatically tested for destruction, and numerically evaluated for comparison. The experimental and numerical data agreed well with each other. As a result, a spherical cap can effectively restore the ultimate strength of dented hemispheres under external hydrostatic pressure. The proposed restoration approach can be used to strengthen underwater pressure hulls with large local geometric imperfections.

水利部交通运输部国家能源局南京水利科学研究院 《中国海洋工程》编辑部 版权所有

Address: 34 Hujuguan, Nanjing 210024, China Pos: 210024 Tel: 025-85829388 E-mail: coe@nhri.cn

Support by Beijing Renhe Information Technology Co. Ltd E-mail: info@rhhz.net

苏ICP备05007122号-5