An innovative fully submersible floating offshore wind turbine (FOWT) concept, which is realized by fully submerging a conventional semi-submersible platform, is presented and assessed through fully coupled aerohydro-servo-elastic analysis using the DTU 10 MW reference wind turbine. This study investigates whether fully submersible FOWTs can mitigate wave-induced responses and assesses their technical feasibility. A methodology is proposed to determine the appropriate submergence depth for the fully submersible FOWT. Dynamic responses of the fully submersible FOWT at this submergence depth are compared with the conventional semisubmersible FOWT under typical sea conditions. The results indicate that for the novel fully submersible FOWT, the absolute submergence depth is 35 m, and the relative submergence depth (the ratio of the absolute submergence depth to the wavelength) is 0.115. Compared to the semi-submersible baseline, the fully submersible FOWT can effectively suppress wave-frequency motion responses under extreme survival conditions, with mean surge motions reduced by a factor of 3.64, maximum of heave motions 2.27 times lower, and maximum and standard deviation of pitch motions reduced by 42.51% and 35.88%, respectively. However, it exhibits inferior tower structural performance, along with significantly elevated dynamic mooring tensions under extreme survival conditions. Notably, both configurations achieve comparable power output.

Marine aquaculture plays a vital role in global food production. Trestle-netting enclosure aquaculture facilities (TNEAFs) address certain limitations of traditional nearshore farming but still face challenges such as internal flow attenuation, which can lead to waste accumulation and reduced water quality. To address these issues, this study proposes a novel composite enclosure aquaculture facility (CEAF) that integrates the flow-modulating functions of artificial reefs with the structural robustness of TNEAF. The flow characteristics around the CEAF module (CEAFM) are systematically investigated using particle image velocimetry. The effects of slope angle (35 degrees-55 degrees), relative water depth (0.37-0.55), and inflow velocity (0.10-0.30 m/s) are quantitatively assessed, with emphasis on upwelling and wake dynamics. Results demonstrate that the CEAFM effectively modifies the local flow to enhance ecological functionality. Increasing the slope angle reduces both dimensionless upwelling area (by 34.12%-50.07%) and wake area (by 34.44%-55.21%). A 35 degrees slope optimizes upwelling area, maximum upwelling velocity, and wake area, whereas a 50 degrees slope minimizes mean wake velocity, revealing a design tradeoff between water exchange efficiency and habitat tranquility. Relative water depth exerts a dominant influence, causing linear reductions in dimensionless upwelling height (29.18%-30.68%) and area (46.26%-58.57%), together with a parabolic increase in dimensionless maximum upwelling velocity (19.43%-23.24%). As inflow velocity increases, dimensionless upwelling height and area decrease (by 6.27%-9.22% and 9.68%-26.10%, respectively), whereas dimensionless maximum upwelling velocity increases (8.60%-11.01%). These findings offer practical insights for optimizing the eco-hydrodynamic performance of aquaculture systems. The CEAFM represents an innovative step toward sustainable marine aquaculture through engineered flow-field management.

Experimental measurements are carried out for ship motion responses coupling with fluidized washed kaolin slurry flow. In the laboratory test, the washed kaolin slurry flow in tanks keeps on suspended states under wave actions. Coupling actions of fluidized washed kaolin slurry flow can generate the significant effect on roll motion responses. The typical anti-rolling behavior can be observed in beam sea, where the variation of roll motion amplitudes with incident periods shows the two-peak characteristics in such cases. With the increase of water contents, the variation tendency of coupling ship roll response deviates more from the results of empty ship. The increased filling depths can increased and decreased the peak values of roll amplitudes around the long-period and short-period ranges, respectively. The influence of fluidized washed kaolin slurry flow on sway motion responses are non-negligible at short-period range; while it is insignificant on heave motion responses. The motivation of this work is providing an experimental verification of the coupling effect between fluidized kaolin slurry and ship motion.

The coupling actions between the sway and roll motion responses of a ship with sloshing inside are investigated according to experimental measurements and numerical simulations. The increased coupling actions between sway and sway motion responses can be observed after considering the internal sloshing flow actions. When the ship is empty, only the sway motion response around the roll resonant periods can be affected by the roll motion coupling actions, while the sway motion coupling actions cannot affect the roll motion response. After considering the internal sloshing flow, the discrepancy between the sway-roll system and individual roll or sway system can be observed not only around the sloshing natural periods but also around the resonant sway and roll resonant periods and sloshing natural periods. It includes both the sway and roll motion responses. Finally, the influence of incident wave amplitudes and filling conditions are also discussed in this study.

Experimental measurements for the motion responses of the moored barge alongside a bottom-mounted platform in beam sea are carried out, by which the behavior of motion responses of the barge and the forces on hawsers and fenders are considered. The sway and roll motions are the most important responses in six degrees-of-freedom. The seaward motion responses are mainly held by the hawsers; while the landward motion responses are mainly astricted by the fenders. Correspondingly, the variation tendencies between the tension forces on the hawsers, the compressed deformation and forces of the fenders, and the sway and roll motion responses of the barge generally have the similar behavior. The nonlinear characteristic in this work is mainly from the force-deformation relationship of fenders. With the increase of incident wave amplitudes, the generally decreased normalized amplitudes can be observed, including the tension forces of hawsers, the compressed deformation and the forces of the fenders. More relative kinetic energy is absorbed by the fenders under larger incident wave amplitudes, which is the essential reason for this phenomenon. The dependence of normalized sway/roll motion responses with incident wave amplitudes is more complex. The normalized sway and roll motion amplitudes around the natural roll periods significantly increase with the increase of incident wave amplitudes. This might be the most noteworthy phenomenon in practical engineering.

This paper investigates the stability issues of the Unmanned Surface Vehicle (USV)–Unmanned Underwater Vehicle (ROV) system induced by cable loads under real marine conditions and high-speed operation. This study focuses on the dynamic coupling characteristics of cable forces affecting the unmanned platform and outlines the variation patterns of these forces under different operational scenarios. By developing the dynamic models of the USV, UC, and UUV, a comprehensive system model for the unmanned marine platform is constructed. The accuracy of the cable model is validated through experimental results, and the coupling interference effects of the cable during collaborative operations are systematically analyzed from multiple perspectives. Additionally, the cable tension and force behaviors under high-speed cruising conditions are thoroughly examined. The results provide a solid foundation for the development of cable load prediction models for collaborative marine unmanned platforms, and offer both theoretical and numerical insights for dynamic control strategies based on cable force adjustments.

Potential analysis for coupling effect of ship motion and liquid sloshing is considered. A three-dimensional FPSO ship with three partially-filled prismatic tanks are carried out for the global ship response. It is found that the coupling effects are dominant in beam waves. The roll RAOs show typical anti-rolling effect, so that the roll motion decreases dramatically near ship motion resonance and double peaks at sloshing motion resonant frequencies can be observed. The filling mass, that is, the number of filling tank in this work, has significant effect on the ship rolling RAOs, especially at around the ship motion natural frequency.

Semi-submersible floating offshore wind turbines (FOWTs) present a promising solution for deep-sea wind energy. However, their hydrodynamic behavior under wave-current interactions remains poorly understood. This study examines the dynamic responses of three representative semi-submersible FOWTs-Braceless, DeepCwind, and V-shaped-under regular waves, uniform currents, and combined wave-current conditions. A fully coupled computational fluid dynamics (CFD) model is developed, incorporating the overset mesh and volume of fluid (VOF) method, to capture platform motions and flow field evolution. The results indicate that structural parameters-including column diameter, spacing, waterline area, and restoring stiffness-govern the natural periods, resonance behavior, and susceptibility to wave slamming and vortex-induced motion (VIM). Flow field analysis reveals that liquid-solid relative motion is the primary contributor to viscous damping. Wave-current interactions induce nonlinear amplification, particularly in surge and pitch responses. In some cases, surge motion increases by more than 3 m. Platforms with asymmetric layouts or low restoring stiffness are especially susceptible to amplified responses. The findings indicate that increasing column diameter alone is insufficient to suppress VIM or wave slamming. Instead, optimizing geometric configurations and implementing passive flow control strategies provide more effective solutions.

The motion responses, mooring tensions, and submergence depth are the dominant factors for the arrangement of the Submerged Floating Tunnel (SFT) subjected to waves. Generally, the maximum values of motion responses, mooring tensions, and absolute submergence depth are mainly focused on. In the present study, experiments are implemented to measure the motion responses and mooring tensions of the SFT with different mooring patterns and submergence depths under waves with different characteristic wave heights and periods. In order to evaluate the arrangement of the SFT more effectively and comprehensively, besides the maximum values, several new characteristic parameters are introduced. Such parameters account for the motion responses in the frequency domain, the uniformity of the tension distribution, the length of time during which the cable reaches a relaxed condition during wave action, the KC number, the dimensionless period, the wave height, and the submergence depth. The results from the optimization analysis show the following: according to the characteristic values of motion responses and mooring tensions, the pattern of diagonal cables is better than that of diagonal cables + vertical cables; and within the range of the present experiments, there are optimal dimensionless parameters—the dimensionless submergence depth d0/LP ≥ 0.15, the KC number ≤ 0.8, or the dimensionless wave height Hs/d0 ≤ 0.10—for the condition of which the dynamic responses and mooring tensions vary slightly.

This study performed experimental investigation on the dynamic response of an in-place floating offshore wind turbine (FOWT) under freak wave actions. Based on the method of wave profile modulation, various freak wave profiles embedded in unidirectional Gaussian seas were generated in wave basin and the action of these waves on the FOWT was measured and analyzed, which has not been done before. The motions of FOWT were analyzed in time domain as well as time-frequency domain. The effect of freak wave parameters on FOWT motions was addressed, i.e., freak wave height, freak wave period, large crest, and deep trough. The dynamic response of FOWT was observed as a spike at the occurrence of freak wave in a conventional random wave, where the impact of freak wave can last for 17 spectral peak periods of wave. Data analysis shows that the motions of FOWT increased linearly with the freak wave height. In addition, the occurrence of freak wave induced the coupled effect on surge and pith, which was strengthen with the increase of freak wave height and wave period. Compared to a large crest, a deep trough of freak wave led to stronger motions and was supposed to be a key concern on the safety of the FOWT. The novel findings in this study provided a reference for the design of survival load on a FOWT and benchmarks for validating numerical models.

Floating offshore wind turbines (FOWTs) are at high risk being attacked by freak waves with profiles of large crest or deep trough, which could damage the structures or weaken the efficiency of power generation. This study developed a numerical model to address the dynamic response of an in-place FOWT under the action of freak waves with large crest and deep trough. Based on the modulation method of freak wave profiles, various random wave trains embedded freak waves were firstly generated in the numerical wave tank. Noted that these waves generated match Gaussian seas. Then, the effect of freak waves was investigated extensively through the FOWT motions, axial acceleration on nacelle, tether forces as well as wave loads and wave fields in time domain and time-frequency domain. The results show that the occurrence of freak waves significantly amplified the dynamic response of FOWT and the impact lasted for approximately 20 spectral peak periods. Under freak waves, the effect of quadratic phase coupling on nacelle acceleration was first observed. The large crest led to a larger horizontal excursion. While the deep trough caused a larger pitch inducing a larger axial acceleration on nacelle. In addition, the nonlinear interaction (between FOWT and freak waves) caused by the large crest was stronger than that caused by deep trough.

在以往的关于畸形波作用时刻结构物所受波浪荷载的教学实验中,大多采用不同类型的传感器分别采集浪高和波压力荷载,并由多人协同进行人工同步的采集方式来进行,此方法受人为因素影响明显,特别是在复杂极端波浪作用下,能够实现单一波浪作用时刻下结构物所受到的瞬时荷载的精确采集十分重要.自研浪高—压力同步采集系统,从根本上实现了波浪及其压力在采集时的完全同步.特别在该系统投入到教学实验之后,对阐明诸如结构物在单一波浪作用下的动力响应特征问题的机理性研究起到了关键性作用.

More and more attentions have been paid on freak wave since it leads to serious damages on marine structures. The conventional method is to conduct linear superposition in frequency domain to obtain freak waves. In this study, the expected freak wave is firstly embedded in an irregular wave train and then transformed into frequency domain by Fast Fourier Transform (FFT). Because of the visualization and maneuverability in time domain, the profile of freak wave can be modulated conveniently. Therefore, special freak wave cases such as Three Sisters Wave (TSW), can also be obtained by this method. The correction on wave spectrum for freak wave train is firstly presented. It was then validated in experiments. The results show that the method is efficient to generate freak waves and TSW, and has good agreements in both time domain and frequency domain. The advantage of the proposed method is that the other waves can be maintained very well when modulating the profile of freak wave. The novel method is helpful to investigate the mechanism of freak wave-structures interaction in deep.

Fluid resonance within a narrow gap formed by a box in close proximity to a plane wall under cnoidal wave action is investigated using the Computational Fluid Dynamics (CFD) package OpenFOAM®. Fluid resonance behavior excited by the second-order harmonic component of the incident cnoidal waves is concerned. Numerical simulations show the large second-order induced wave height in the gap which increases as the incident wave height gets larger or the water depth gets shallower. The large double-frequency component of the cnodial waves is the major reason for the phenomenon. Harmonic analysis indicates that the CFD results can be represented well by a second-order approximation, and the free surface nonlinearity is an indispensable factor in the action of the cnoidal incident wave. Similar phenomenon is also found in the horizontal wave force. However, the second-order induced resonance within the gap has insignificant effect on the vertical wave force.

"我有一个关于加快发展东北水网经济、改善生态环境的建议,供中央领导参阅."2019年7月1日上午, 89岁高龄的邱大洪院士把一份建议书亲手递交到正在大连参加夏季达沃斯会议的李克强总理手中.建议书是邱大洪听说李克强总理来大连而连夜赶写出来的.这份心系东北振兴的情怀与担当让人为之敬仰.

Previous studies have shown that the twin-plate breakwater has good performance in wave dissipation, in particular under deep water conditions. The performance of twin-plate breakwater is subjected to several parameters and some of these parameters are coupled to the others. Thus far, there was no simple and effective method to calculate the dissipation coefficient of the twin-plate breakwater. The objective of the present study is to address the mechanism of wave dissipation and apply the developed RN number to evaluate the dissipating performance on the twin-plate breakwater. The experimental results showed that the transmission, reflection and dissipation coefficients were strongly depending on the developed RN number. Based on various data fitting, an optimal empirical equation is obtained to predict the dissipation of the twin-plate breakwater through the developed RN number. The empirical equation has been verified by the Chi-square test and hence can be used for bulk estimation for transmission coefficient under normal and oblique waves.

The twin-plate breakwater, a novel permeable breakwater, was studied experimentally in the State Key Laboratory of Coastal and Offshore Engineering in Dalian, China. The dual horizontal plates were placed in parallel with the upper one at the still water level. This study is to investigate the distribution of dynamic wave pressures and wave loads on the twin-plate breakwater under the conditions of regular waves (with the relative plate width B/L = 0.28 similar to 4.43 and relative wave height H/d = 0.1 similar to 0.4) and random waves (with the relative plate width B/L = 0.2 similar to 0.66 and relative wave height H-s/d = 0.1 similar to 0.35). Effects of the relative plate width, relative wave height, and wave steepness have been addressed. The experimental results demonstrate that the effect of the relative plate width is dominant among the above parameters. For the purpose of bulk estimation in engineering applications, we overlooked the effects of the relative plate width, relative wave height, and wave steepness and obtained the best-fitting equation to predict the maximum dynamic wave pressure and wave force on the twin-plate breakwater.

The hydrodynamic behavior of box-systems with and without narrow gaps is investigated by employing a numerical wave flume based on OpenFOAM® package. After the validation with available experimental data and simulating results in the literature, the related phenomena induced by the large-amplitude free surface oscillation in narrow gaps are examined. Numerical comparisons between the single- and two-box systems suggest that the fluid resonance in the narrow gap can significantly affect the behavior of box-system, including wave responses, hydrodynamic coefficients, and vertical wave forces of the box-system. Analogous phenomena can also be observed in three-box system at the fundamental natural frequency, which is generated by the in-phase free surface oscillations in narrow gaps. At the second natural frequency, only a little discrepancy in the results of wave responses, hydrodynamic coefficients, and total wave forces can be observed between two- and three-box systems. The wave forces on each box in three-box system are significantly affected by the wave resonance in two gaps, including the fundamental and second resonant frequencies.

The present study investigates experimentally the wave-dissipating performance of twin-plate breakwater under oblique random waves. Through extensive model tests, the effects of the relative plate width and relative wave height on the dissipating performance are investigated under various incident wave angles. The results show that the dissipating performance changes insignificantly within the measured range of 15 degrees similar to 60 degrees incident angles. The transmission coefficient kt under oblique waves fluctuates around the value under normal waves. In addition, the transmission was directly affected by the relative plate width, i.e., the transmission was 0.1 < kt < 0.15 for B/L < 0.5 and 0.5 < kt < 0.10 for B/L >= 0.5. In particular, under oblique waves the wave patterns after the twin-plate breakwater exhibited significant three-dimensional characteristics, which were different from those under normal incident waves. To validate the present experimental results, the measured transmission coefficients are compared to those of Neelamani and Gayathri (2006) under normal incident waves, and the comparison shows good agreement.