ISSN  0890-5487 CN 32-1441/P

2021 Vol.35(1)

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A Few Frontier Issues in Ocean Engineering Mechanics
Jia-chun LI, Bing-chuan NIE
2021, 35(1): 1-11. doi: 10.1007/s13344-021-0001-8
[Abstract](1243) [FullText HTML] (336) [PDF 1280KB](41)
Abstract:
In this review, we primarily address the present state of the arts and latest progresses in a few frontier issues mostly relevant to free surface/interface in ocean engineering. They include TC (tropical cyclone) induced extreme surface wave, sloshing of LNG (liquefied natural gas), cavitation/bubble dynamics and VIM (vortex-induced motion) and VIV (vortex-induced vibration). In addition to general description, we mainly focus on the recent advances and challenging aspects of above-mentioned topics. Inspired by the achievements in the previous 70 years, mankind starts a new round of ocean exploration activities. Then, we can find obvious trends: the realm of ocean engineering is expanding from sea surface to deep sea, from low and middle latitude to polar region and from fossil to renewable energy in near future.
Investigation and Discussion on the Beach Morphodynamic Response Under Storm Events Based on A Three-Dimensional Numerical Model
Ming-xiao XIE, Shan LI, Chi ZHANG, Zhi-wen YANG, Zhi-qiang HOU, Hua-qing ZHANG
2021, 35(1): 12-25. doi: 10.1007/s13344-021-0002-7
[Abstract](1064) [FullText HTML] (284) [PDF 8058KB](17)
Abstract:
A well-established 3D phase-averaged beach morphodynamic model was applied to investigate the morphodynamics of a typical artificial beach, and a series of discussions were made on the surfzone hydro-sedimentological processes under calm and storm events. Model results revealed that the nearshore wave-induced current presents a significant 3D structure under stormy waves, where the undertow and longshore currents exist simultaneously, forming a spiral-like circulation system in the surfzone. Continuous longshore sediment transport would shorten the sediment supply in the cross-shore direction, subsequently suppress the formation of sandbars, showing that a typical recovery profile under calm waves does not necessarily develop, but with a competing process of onshore drift, undertow and longshore currents. Sediment transport rate during storms reaches several hundreds of times as those under calm waves, and two storm events contribute approximately 60% to the beach erosion. Sediment transport pattern under calm waves is mainly bed load, but as the fine sands underneath begin to expose, the contribution of suspended load becomes significant.
Fully Coupled Simulation of Interactions Among Waves, Permeable Breakwaters and Seabeds Based on N−S Equations
Yan-ting LI, Deng-ting WANG, Tian-ting SUN, Zhe HUANG, Qing-jun LIU
2021, 35(1): 26-35. doi: 10.1007/s13344-021-0003-6
[Abstract](985) [FullText HTML] (291) [PDF 6638KB](19)
Abstract:
Interstitial flows in breakwater cores and seabeds are a key consideration in coastal and marine engineering designs and have a direct impact on their structural safety. In this paper, a unified fully coupled model for wave−permeable breakwater−porous seabed interactions is built based on an improved N−S equation. A numerical wave flume is constructed, and numerical studies are carried out by applying the finite difference method. In combination with a physical model test, the accuracy of the numerical simulation results is verified by comparing the calculated and measured values of wave height at measurement points and the seepage pressure within the breakwater and seabed. On this basis, the characteristics of the surrounding wave field and the internal flow field of the pore structure, as well as the evolution process of the fluctuating pore water pressure inside the breakwater and seabed, are further analyzed. The spatial distribution of the maximum fluctuating pore water pressure in the breakwater is compared between two cases by considering whether the seabed is permeable, and then the effect of seabed permeability on the dynamic pore water pressure in the breakwater is clarified. This study attempts to provide a reference for breakwater design and the protection of nearby seabeds.
Effect of the Coefficient on the Performance of A Two-Layer Boussinesq-Type Model
Jia-wen SUN, Zhong-bo LIU, Xing-gang WANG, Ke-zhao FANG, Xin-yuan DU, Ping WANG
2021, 35(1): 36-47. doi: 10.1007/s13344-021-0004-5
[Abstract](824) [FullText HTML] (291) [PDF 20923KB](12)
Abstract:
The coefficients embodied in a Boussinesq-type model are very important since they are determined to optimize the linear and nonlinear properties. In most conventional Boussinesq-type models, these coefficients are assigned the specific values. As for the multi-layer Boussinesq-type models with the inclusion of the vertical velocity, however, the effect of the different values of these coefficients on linear and nonlinear performances has never been investigated yet. The present study focuses on a two-layer Boussinesq-type model with the highest spatial derivatives being 2 and theoretically and numerically examines the effect of the coefficient \begin{document}${\textit{α}} $\end{document} on model performance. Theoretical analysis show that different values for \begin{document}${\textit{α}} $\end{document} (0.13≤\begin{document}${\textit{α}} $\end{document}≤0.25) do not have great effects on the high accuracy of the linear shoaling, linear phase celerity and even third-order nonlinearity for water depth range of 0<kh≤10 (k is wave number and h is water depth). The corresponding errors using different \begin{document}${\textit{α}} $\end{document} values are restricted within 0.1%, 0.1% and 1% for the linear shoaling amplitude, dispersion and nonlinear harmonics, respectively. Numerical tests including regular wave shoaling over mildly varying slope from deep to shallow water, regular wave propagation over submerged bar, bichromatic wave group and focusing wave propagation over deep water are conducted. The comparison between numerical results using different values of \begin{document}${\textit{α}} $\end{document}, experimental data and analytical solutions confirm the theoretical analysis. The flexibility and consistency of the two-layer Boussinesq-type model is therefore demonstrated theoretically and numerically.
Numerical Simulation of Water Entry of Wedges in Waves Using A CIP-Based Model
Zi-jun HU, Xi-zeng ZHAO, Meng-yu LI, Xin ZHAO, Wen-wei YAO, Jie SHAO
2021, 35(1): 48-60. doi: 10.1007/s13344-021-0005-4
[Abstract](898) [FullText HTML] (283) [PDF 15530KB](13)
Abstract:
In this study, the water entry of wedges in regular waves is numerically investigated by a two-dimensional in-house numerical code. The numerical model based on the viscous Navier−Stokes (N−S) equations employs a high-order different method—the constrained interpolation profile (CIP) method to discretize the convection term. A Volume of Fluid (VOF)-type method, the tangent of hyperbola for interface capturing/slope weighting (THINC/SW) is employed to capture the free surface/interface, and an immersed boundary method is adopted to treat the motion of wedges. The momentum source function derived from the Boussinesq equation is applied as an internal wavemaker to generate regular waves. The accuracy of the numerical model is validated in comparison with experimental results in the literature. The results of water entry in waves are provided in terms of the impact force of wedge, velocity and pressure distributions of fluid. Considerable attention is paid to the effects of wave parameters and the position of wedge impacting the water surface. It is found that the existence of waves significantly influences the velocity and pressure field of fluid and impact force on the wedges.
Extreme Wave Simulation with Iterative Adaptive Approach in Numerical Wave Flume
Dian-yong LIU
2021, 35(1): 61-71. doi: 10.1007/s13344-021-0006-3
[Abstract](896) [FullText HTML] (281) [PDF 14579KB](7)
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Extreme wave is highly nonlinear and may occur due to diverse reasons unexpectedly. The simulated results of extreme wave based on wave focusing, which were generated using high order spectrum method, are presented. The influences of the steepness, frequency bandwidth as well as frequency spectrum on focusing position shift were examined, showing that they can affect the wave focusing significantly. Hence, controlled accurate generation of extreme wave at a predefined position in wave flume is a difficult but important task. In this paper, an iterative adaptive approach is applied using linear dispersion theory to optimize the control signal of the wavemaker. The performance of the proposed approach is numerically investigated for a wide variety of scenarios. The results demonstrate that this approach can reproduce accurate wave focusing effectively.
Effect of Wave Headings on the Dynamic Response of the Continuous Mating Operation of Floatover Installation
Xiao-dong BAI, Han-bing LUO, Peng XIE
2021, 35(1): 72-83. doi: 10.1007/s13344-021-0007-2
[Abstract](690) [FullText HTML] (272) [PDF 13883KB](6)
Abstract:
The topside floatover installation is always a great challenge and is sensitive to environmental conditions. In this study, experimental analysis on the mating operation of the floatover installation in different wave headings is presented. The continuous mating operation using the rapid transfer technique was experimentally simulated with the assistance of the jacking system and the ballast system. In the continuous transfer modeling, the topsides loads were transferred onto the jacket by several consecutive steps, including the first rapid jack-down for the 30% loads, continuous 30%−70% load transfer and the second repaid jack-down for the remaining 30% loads. Motions of the barge and the topsides as well as loads on the Deck Support Unite (DSU) and the Leg Mating Unite (LMU) in different wave headings were measured. Experimental results illustrated the complex motion behavior and load characteristics of the continuous transfer operation. Results indicate that the rapid jack-down operations will lead to impact loads and larger lateral DSU loads. The bow quartering seas are much more dangerous as it gives rise to the larger motions and loads. Comparisons with the traditional steady-state modeling indicate that the continuous transfer modeling has greater advantages over the steady-state modeling on predicting the loads.
Dynamic Analysis of Semi-Submersible Production Platform Under the Failure of Mooring Lines
Zhen-ju CHUANG, She-wen LIU, Chun-zheng LI, Yu LU, Xin CHANG
2021, 35(1): 84-95. doi: 10.1007/s13344-021-0008-1
[Abstract](925) [FullText HTML] (286) [PDF 33143KB](23)
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This paper quantitatively studies the transient dynamic response of a semi-submersible production platform with the loss of one or several positioning mooring lines. A semi-submersible platform, production risers, and positioning mooring lines are all included in the numerical simulation. Increased motion of the semi-submersible platform, tension variation of the remaining mooring lines/risers and the risk of mooring line or riser clashing are all investigated through fully coupled time-domain analysis. Combined environmental loads are selected from irregular waves and the steady current varying from very rough to extreme sea conditions. Three dimension radiation/ diffraction theories and Morison’s equation are applied to calculate first-order wave force and second-order mean drift force of floating semi-submersible platform. Nonlinear time-domain finite element methods are employed to analyze the behavior of mooring lines and risers. Results show that the failure of mooring lines seriously reduce the platform’s stability performance. The tension of the rest lines is also increased accordingly. Remaining lines which are closer to the failed lines will have larger tension increase to compensate. Line-Line distance provides practical information for the risk of clashing investigation.
Structural Model Updating of Jacket Platform by Control Theory Using Vibration Measurement Approach
HOSSEINLOU Farhad
2021, 35(1): 96-106. doi: 10.1007/s13344-021-0009-0
[Abstract](707) [FullText HTML] (284) [PDF 13178KB](9)
Abstract:
The identification of variations in the dynamic behavior of structures is an important subject in structural integrity assessment. Improvement and servicing of offshore platforms in the marine environment with constant changing, requires understanding the real behavior of these structures to prevent possible failure. In this work, empirical and numerical models of jacket structure are investigated. A test on experimental modal analysis is accomplished to acquire the response of structure and a mathematical model of the jacket structure is also performed. Then, based on the control theory using developed reduction system, the matrices of the platform model is calibrated and updated. The current methodology can be applied to prepare the finite element model to be more adaptable to the empirical model. Calibrated results with the proposed approach in this paper are very close to those of the actual model and also this technique leads to a reduction in the amount of calculations and expenses. The research clearly confirms that the dynamic behavior of fixed marine structures should be designed and assessed considering the calibrated analytical models for the safety of these structures.
Impact of Wind on Tide-Induced Advective Salt Transport in A Well-Mixed Estuary
Wei-lun CHEN, Yu-liang ZHU, Jun KONG, Ao CHU, Wei-sheng ZHANG
2021, 35(1): 107-122. doi: 10.1007/s13344-021-0010-7
[Abstract](655) [FullText HTML] (265) [PDF 14866KB](10)
Abstract:
The tide-induced net advective salt flux in well-mixed estuaries consists of five terms according to the method from Kjerfve. The term resulted from the vertical variation in salinity can be negligible in well-mixed estuaries with four tide-induced salt flux terms, known as F1F4. To explore the effects of wind on these salt fluxes, the current-salinity analytical model combined with the perturbation analysis is extended by including wind. Analytical expressions for the four salt fluxes are derived separately in the present model. Under the assumption that only the M2 tidal component is accounted for and the salt flux generated by diffusion is not studied, the tide-induced net advective salt flux Qsx is in the seaward direction without the wind effect. By applying the Western Scheldt estuary case, the wind influence on the tidal advection salt flux (TASF) distribution in the F4 term was investigated. The phase difference between zero-order velocity and first-order salinity (Δφ) at the surface layer of the estuary is larger than 90° and smaller than 90° at the bottom layer, which leads to landward TASF in the surface layer and seaward TASF in the bottom layer. The distribution of Δφ is not uniform in the horizontal direction with wind included, which differs from the result without wind. In the case of seaward wind with the speed of 18 m/s, the decrease in the zeroth-order velocity phase (φu) at the surface layer is larger than that of the first-order salinity phase (φs) downstream, which leads to an abnormal seaward TASF in this region. Owing to the surface stress caused by wind, the Stokes compensation flow in the middle and lower reaches increases/decreases with the increase of the landward/seaward wind, while the upstream situation is opposite. Thus, the first-order velocity in the middle and lower reaches increases/decreases with the increase of the landward/seaward wind, while the upstream situation is also opposite. The first-order salinity also increases/decreases with the increase of landward/seaward wind, while the upstream salinity tends to zero. Therefore, the tide-induced net advective salt flux Qsx increases/decreases with the increase of the landward/seaward wind, which is contrary to the usual recognition.
Study on Seepage Characteristics of Composite Bucket Foundation Under Eccentric Load
Qing-shan CHEN, Pu-yang ZHANG, Hong-yan DING, Cong-huan LE, Yun-long XU
2021, 35(1): 123-134. doi: 10.1007/s13344-021-0011-6
[Abstract](638) [FullText HTML] (269) [PDF 7508KB](10)
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Under the effect of eccentric loads, when the suction pressure of the composite bucket foundation is leveled, the seepage failure is very easy to occur. The seepage failure occurrence causes the foundation to settle unevenly and impairs the bearing performance. This study uses ABAQUS finite element software to establish a composite bucket foundation model for finite element analysis. The model simulates the seepage of the foundation penetrating process under eccentric load to reveal the induced seepage characteristics of the bucket foundation. The most vulnerable position of seepage failure under the eccentric loading is elucidated. Critical suction formulas for different offset eccentric moment strategies are derived and compared with existing literature formulas. Then the derived formula is supplemented and corrected according to the pressure difference between adjacent cabins. Conclusions can be drawn: (1) Under eccentric loads, the critical suction decreases about 7%−10%. (2) The pressure difference between adjacent cabins impacts significantly on the seepage field, and the critical suction, at most, can be reduced by 17.56%. (3) the offset strategies have little effect on the seepage field. Efficient and appropriate strategies can be selected to meet the requirement of leveling in engineering project.
Cyclic Bearing Mechanism of Suction Caissons Supporting Offshore Wind Turbines in Clay
Teng WANG, Shi-wen YU, Wen-long LIU, Xing-xian BAO, Jun-wei LIU
2021, 35(1): 135-144. doi: 10.1007/s13344-021-0012-5
[Abstract](806) [FullText HTML] (272) [PDF 7900KB](15)
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The bearing behavior of suction caissons supporting offshore wind turbines under two-way cyclic lateral loading and dead load in clay was investigated with consideration of soil strength degradation and adhesive interface friction between caisson walls and heterogeneous clay using the finite-element package ABAQUS. An ABAQUS built-in user subroutine was programmed to calculate the adhesive interface friction between clay and caisson walls. The results of parametric studies showed that the degradation of bearing capacity could be aggravated by the decrease of the aspect ratio. The offset between the rotation point of the soil inside the caisson and the central axis of the caisson increased with the increasing vertical load and number of cycles. The linearly increasing strength profile and adhesive interface led to the formation of an inverted spoon failure zone inside the caisson. The settlement-rotation curves in each cycle moved downwards with increasing number of cycles due to the soil strength degradation.
Time-Dependent Tsunami Source Following the 2018 Anak Krakatau Volcano Eruption Inferred from Nearby Tsunami Recordings
Yi-fan ZHU, Chao AN, Teng WANG, Hua LIU
2021, 35(1): 145-152. doi: 10.1007/s13344-021-0013-4
[Abstract](644) [FullText HTML] (275) [PDF 4370KB](7)
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The eruption of the Anak Krakatau volcano, Indonesia, on 22 December 2018 induced a destructive tsunami (the Sunda Strait tsunami), which was recorded by four nearby tidal gauges. In this study we invert the tsunami records and recover the tsunami generation process. Two tsunami sources are obtained, a static one of instant initial water elevation and a time-dependent one accounting for the continuous evolution of water height. The time-dependent results are found to reproduce the tsunami recordings more satisfactorily. The complete tsunami generation process lasts approximately 9 min and features a two-stage evolution with similar intensity. Each stage lasts about 3.5 min and elevates a water volume of about 0.13 km3. The time, duration and volume of the volcano eruption in general agree with seismic records and geomorphological interpretations. We also test different sizes of the potential source region, which lead to different maximum wave height in the source area, but all the results of time-dependent tsunami sources show the robust feature of two stages of wave generation. Our results imply a time-dependent and complex process of tsunami generation during the volcano eruption.
Optimization Design of Fairings for VIV Suppression Based on Data-Driven Models and Genetic Algorithm
Xiu-quan LIU, Yong JIANG, Fu-lai LIU, Zhao-wei LIU, Yuan-jiang CHANG, Guo-ming CHEN
2021, 35(1): 153-158. doi: 10.1007/s13344-021-0014-3
[Abstract](671) [FullText HTML] (273) [PDF 4126KB](9)
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Vortex induced vibration (VIV) is a challenge in ocean engineering. Several devices including fairings have been designed to suppress VIV. However, how to optimize the design of suppression devices is still a problem to be solved. In this paper, an optimization design methodology is presented based on data-driven models and genetic algorithm (GA). Data-driven models are introduced to substitute complex physics-based equations. GA is used to rapidly search for the optimal suppression device from all possible solutions. Taking fairings as example, VIV response database for different fairings is established based on parameterized models in which model sections of fairings are controlled by several control points and Bezier curves. Then a data-driven model, which can predict the VIV response of fairings with different sections accurately and efficiently, is trained through BP neural network. Finally, a comprehensive optimization method and process is proposed based on GA and the data-driven model. The proposed method is demonstrated by its application to a case. It turns out that the proposed method can perform the optimization design of fairings effectively. VIV can be reduced obviously through the optimization design.
Retraction to: Experimental Study on Crescent Waves Diffracted by A Circular Cylinder [China Ocean Engineering, 2018, 32(5), 624–632. https://doi.org/10.1007/s13344-018-0064-3]
Kai YAN, Liang-duo SHEN, Jin-wei SHANG, Liang MA, Zhi-li ZOU
2021, 35(1): 159-159. doi: 10.1007/s13344-021-0029-9
[Abstract](552) [FullText HTML] (257) [PDF 0KB](13)
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