The coupled motion responses between the lifting topsides and the crane vessel are quite complex in the offshore platform installation. To ensure the safety of lifting operations, achieving precise positioning of the crane vessel and restraining the motions of the lifting topsides is still a challenging task. In this study, the offshore topsides lifted by a dynamic positioning (DP) crane vessel are experimentally and numerically modeled. In the numerical model, a time-domain model of the vessel-topsides system based on the coupled stiffness matrix method is established. For the DP system, a fuzzy Proportional-Integral-Differential (PID)/genetic algorithm-based DP control system is developed in both the numerical and experimental models. The fuzzy control theory is applied to improve the control ability of the PID controller. An improved genetic algorithm is used to solve the thrust distribution problem. In the model tests, vessel and topsides motions, as well as the thrust of the DP system, are experimentally measured. The coupled motions of the vessel-topsides system and the DP system performance in different environmental conditions are evaluated. Good agreements between numerical and experimental results are achieved, demonstrating the feasibility of the coupled motion model and the robustness of the DP system. The experimental and numerical motion results are further statistically analyzed to evaluate the DP capability and lifting safety based on the guidelines. The proposed approach can serve as an effective and accurate way to simulate the coupled motions in the topsides lifting process for practical engineering.

The semi-submersible aquacultural platform has attracted increasing attention in recent years. The semi-submersible aquacultural platform comprises multiple rearing tanks separated by fish nets, and the flow field characteristics within these tanks are of significant importance to fish welfare and pollutant dispersion. This study proposed a numerical model based on the mesh-free Smoothed Particle Hydrodynamics (SPH) method to investigate the flow field of the semi-submersible aquacultural platform under currents. The proposed model represents fish nets with numerous nodes through a simplified system of spheres and springs. Numerical results for both rigid and flexible nets are validated against experimental data, demonstrating that the proposed method provides a reliable and effective approach for simulating fish nets. The maximum displacement of the platform is only 0.009m, indicating that its deformation is negligible. Replacing flexible nets with rigid ones in simulations can improve computational efficiency by approximately 50%. Numerical results show that nets significantly decrease the velocity in the three rearing tanks with velocity reductions ranging from 64% in the upstream tank to 86% in the downstream tank. Velocity variations along the horizontal and vertical directions inside those tanks are discussed in detail. Drag forces on each component are evaluated, with the platform frame accounting for approximately 69% of the total fluid loads, while the nets contribute about 17% and should therefore not be neglected in structural design. The proposed SPH model serves as a powerful tool for simulating complex fluid-structure interactions in the aquacultural platform.

This paper investigates the hydrodynamic performance of a pool-type cylindrical Floating Production Storage and Offloading (FPSO) unit equipped with a bottom damping plate designed to mitigate heave motion. Using a semi-analytical approach, we developed a three-dimensional model based on linear potential flow theory to conduct a comprehensive hydrodynamic analysis of the floating structure. The methodology integrates the eigenfunction matching method with significant nonlinear boundary conditions. We systematically evaluate the wave load and heave motion characteristics of both the entire device and the damping plate, considering various dissipation coefficients and geometric parameters of the damping plate. To validate the accuracy of the proposed semi-analytical model, we compare the results with experimental data and numerical simulations. The calculated results reveal a strong positive correlation between wave loads and different damping plate geometries, with subtle variations in specific directions within the high-frequency domain. Incorporating dissipation coefficients into the potential calculation significantly mitigates abrupt fluctuations in hydrodynamic coefficients at resonant frequencies, enhancing the stability and reliability of the computational results. Additionally, optimizing the geometric parameters of the damping plate substantially influences the hydrodynamic coefficients, particularly for the heave motion of the device. The forces acting on the damping plate under various conditions in irregular incident waves underscore the critical impact of the damping plate on structural safety. The findings identify an optimal damping plate design for a pool-type FPSO to enhance anti-heave effectiveness, providing valuable insights for engineering design.

The structural damage and biomass loss of the aquaculture net cage almost happen every year in China. It is of practical relevance and importance to study the dynamic response of the net cage in extreme offshore conditions. This study carries out comprehensive research on motions and mooring loads of floating fish cage in multidirectional random and focused waves. The multi-directional random waves are simulated by the spreading function and the random wave spectral, while multi-directional focused waves are generated at the predefined instant and locations. The net cage is modeled by the validated lumped-mass point method and Morison equations. Results indicate that surge motions increase and sway motion decrease with the increase of the wave directionality index. While the heave motion of the fish cage is insensitive to the wave directionality. The wave directionality leads to the unsymmetric mooring loads, indicating all mooring lines should be paid attention in multi-directional waves rather than the upwind moorings. Results demonstrate that the snap load of the mooring line is displayed and the net volume significantly decreases under the multi-directional focused wave. The multidirectional trough-focused wave leads to greater motions and slightly smaller mooring forces than the multidirectional crest-focused wave.

The vessel-shaped semi-submersible aquacultural platform gains increasing attention in the aquacultural industry due to the high biomass production and structural strength. Understanding the dynamic characteristics is essential for structural optimization and operational efficiency. This study presents numerical and experimental analyses of the hydrodynamic responses of the vessel-shaped semi-submersible aquacultural platform under wave actions. In the experiments, the vessel-shaped semi-submersible aquacultural platform was modeled with a scale ratio of 1:32. Both regular and random wave tests are carried out in head seas and beam seas. The numerical simulation model of the vessel-shaped semi-submersible aquacultural platform is developed to investigate motion and mooring load characteristics. The time-domain model is formulated based on the potential theory for floating structures, the screen model for nets and the lumped-mass point for mooring lines. The aquacultural platform motions and mooring forces are numerically simulated and compared with the experimental results. The response time-series, spectra, and the statistics are compared, indicating that the proposed numerical model successfully predicts motions and mooring forces. Experimental and numerical results from both regular and random wave tests suggest that the platform experiences slight rotation motions. Different nets with different solidities are utilized to analyze the effect of the nets. The nets have limited influence on the motions of the aquacultural platform.

The twin-barge floatover installation involves complex hydrodynamic and mechanical interactions among multiple floating bodies and mating units. Accurate prediction of multi-body motions and mating unit loads, along with comprehensive operational assessments, is essential to ensure the feasibility and safety of the float-over installation. In this study, a numerical model is developed to simulate the 0 %, 50 %, and 100 % mating phases of an elastically connected twin-barge floatover system. The operability of the system at each stage is evaluated using the proposed multi-body coupled time-domain motion algorithm. This model incorporates the multi-body dynamic interactions and the influence of mating units, including Deck Support Units (DSUs) and Leg Mating Units (LMUs). Numerical results for coupled motions and DSU/LMU mating loads are validated against experimental data. Comparisons of the time-series, spectral, and statistical results across different load transfer stages show good agreement. The operational feasibility during the installation of twin-barge floatover installation is assessed based on the relative motions of the mating points and impact loads on DSUs/LMUs. Results suggest that both the motions and mating loads escalate markedly with increasing the wave height. The recommended operational wave period should not exceed 9 s.

Accurate forecasting of motion and mooring loads in fish cages is vital for efficient field monitoring and numerical simulations. This research introduces an innovative hybrid model that leverages Bidirectional Stateful Long Short-Term Memory (Bi-SLSTM) neural networks to predict the dynamic behavior of fish cages. By incorporating bidirectional data flow and state-preserving mechanisms, the model enhances the accuracy of multi-step predictions. Performance is assessed through the Root Mean Square Error (RMSE) and the Trapezoidal-based Integral Similarity Index (Rtrapz). Results show that Bi-SLSTM outperforms Long Short-Term Memory (LSTM), Gated Recurrent Unit (GRU), and Bidirectional Long Short-Term Memory (BiLSTM) models, achieving Rtrapz values above 0.85 in large multi-step predictions. Further analysis reveals that combining wave and motion data as inputs improves prediction accuracy, with surge and heave predictions reaching 91 % and 98 %, respectively. The hybrid strategy combining motion response and load data provides the best performance for mooring load prediction, with Rtrapz values exceeding 0.85 across different output steps. The Bi-SLSTM model demonstrates strong prediction capability and robustness in forecasting cage dynamics.

The twin-barge floatover installation method is an efficient method for the mega topsides installation for the offshore platform because of the large capacity and the gap-free for the substructures. This paper develops the dedicated software TBF-TJU (Twin-Barge Floatover by TJU) for dynamic response analysis of the twin-barge floatover installation system. A numerical model of the elastically-connected twin-barge floatover installation system was developed to analyze the coupled dynamic response of topsides and barges. The motion equations of the twin-barge and the topsides with consideration of the mechanical connections and the hydrodynamic interactions are derived and then solved in the time domain. The loads on mating units DSU(Deck Support Unit) in head and beam seas are numerically and experimentally investigated in detail. The numerical results are compared to the results of the corresponding tests in regular and random waves. Time-series and statistical comparisons of the motions and loads indicate that the numerical model can provide a reasonable estimation of the dynamic response of the twin barges and the topsides. The motion of the upwind barge is significantly larger than that of the leeward barge in beam sea due to the shielding effect and the hydrodynamic interactions.

The twin-barge floatover method can efficiently utilize two barges to install the mega topside installation. However, the twin-barge floatover system involves hydrodynamic and structural interactions of multiple bodies. In this study, a numerical model is developed for predicting motions and loads of the twin-barge floatover system in beam waves during load transfers. The effects of multibody hydrodynamic interaction and mating loads on various connections and constraint components are considered. The motion equations of the multiple bodies, together with the coupled stiffness matrix, are derived. The numerical results are compared with the experimental results in beam waves. Results indicate that the proposed numerical model can provide accurate and reasonable predictions of the twin-barge floatover installation.

The hydrodynamic performance of an integrated oscillating water column (OWC) combined with a cylindrical caisson type breakwater was investigated. A three-dimensional numerical wave tank was established to simulate the overall energy conversion performance and hydrodynamics of the integrated system with the software StarCCM+. The developed Computational Fluid Dynamics (CFD) model was initially verified with the published physical results and numerical results derived from an analytical solution. The effects of the structural geometry and the pneumatic damping of the PTO system on the wave absorption and power conversion efficiency of the proposed device were investigated using this developed model. Based on this proposed numerical model, the velocity of the air flow, the corresponding air pressure characteristics in the air turbine nozzle and chamber zone were discussed. The results indicate that this proposed half-open land based OWC is adapted to absorb shorter nearshore waves, characterized by dimensionless wave number kd approaching 1.49. Furthermore, a larger opening inlet zone for this proposed OWC would shift the resonant corresponding kd to higher wave frequencies, while lowering the opening inlet could help to increase the power extraction efficiency for long waves. The peak hydrodynamic efficiency is observed at a ratio of OWC inlet width to diameter B/D of 0.97, which is approximately six times larger than that at B/D = 0.5. The inclusion of an impulse turbine yields a more uniform pressure distribution within the central chamber and effectively mitigates wave reflection for smaller incident waves, with maximum efficiency achieved using 37 blades. The property of the efficiency mitigation with insufficient certain intake depth of the wave chamber should be avoided for system design.

双船浮托安装海洋平台时,驳船与平台上部组块、下部结构的连接形式复杂,存在多浮体相互干扰、多体耦合运动和载荷转移.考虑多浮体相互干扰以及甲板支撑单元(DSU)、桩腿对接单元(LMU)、系泊、护舷等影响,提出双驳船与上部组块多体耦合运动算法,推导双驳船与上部组件的耦合刚度矩阵,对载荷转移过程中多体耦合运动及载荷响应进行数值模拟.典型横浪工况下数值模拟结果与水池模型试验吻合较好.

The present paper investigates a hybrid breakwater-oscillating water column (OWC) system by integrating a heaving floater wave energy converter (WEC). Both the water oscillating of the OWC and the wave-induced relative motion of the floater hinged in front of the OWC device are employed to extract wave energy. A three-dimensional wave tank is numerically modelled by Star-CCM + Computational Fluid Dynamics (CFD) software to investigate the hydrodynamic performance of the hybrid system. The hydrodynamic characteristics of symmetric and asymmetric floaters in terms of wave attenuation and energy extraction performance are examined. Four floaters with different bottom shapes are considered. The results indicate that the asymmetric floaters lead to a higher capture width ratio (CWR) and better wave attenuation performance, such that CWR of the hybrid system integrated with the Berkley Wedge bottom shape can reach up to 81.2%. The effects of the radius ratio, the submerged opening height, and the distance between the oscillating buoy (OB) and OWC device are further analyzed. The findings of this paper reveal that the geometrical parameters of the hybrid system have significant effects on wave energy absorption efficiency and hydrodynamic performance. The results provide advice on the design of wave energy devices.

The twin-barge floatover method is a promising approach in the topsides installation of the offshore platform. However, the topsides transfer onto the twin-barge is a challenging task and is seldom investigated. This study focuses on the floatover load transfer operation of the topsides onto the twin-barge by a T-shaped barge and investigates the dynamic responses of the three proximate barges in the operation. The floatover mating process was experimentally simulated by three representative intermediate stages, including 0%, 50%, and 100% stages. The barge and topsides motions, the relative motions of mating points, the contact loads on mating units, tether forces, and mooring forces at various environmental conditions were analyzed. The three floating barges experienced large surge drift motions as well as the sway and yaw drift motions in head seas because of the unsymmetrical configurations. Although a relative radial distance between mating points occurred and exceeded the capture radius of the mating unit at limited instants, the relative motions were to a great extent within the capture radius, indicating the feasibility of the twin-barge floatover method. Comparisons of the loads at the three stages show that the mating units and the tether lines were subjected to larger impact impulse loads at the 0% stage than the 100% stage.

The floatover installation method is one of the two installation methods of the offshore platform topsides and is a much safe and efficient method for the mega integrated topsides. This paper presents a literature review on the research and technical challenges of floatover installations. Various floatover installation methods and concepts for the fixed and floating substructures with passive and active load transfer systems are reviewed, including the conventional single barge floatover installation, the T-barge floatover installation, the twin/dual floater floatover installation, and the dynamically positioning floatover installation. The exclusive mating units including the deck/leg mating units and the related guidelines are discussed. Investigations in respect of the in-site measurements, numerical modeling, and physical model tests are presented, following challenges and gaps between the practices and the research. Finally, further developing and refining modeling techniques are envisioned. This review aims to provide suggestions on research and development activities of floatover installation.

Offshore aquacultural farms are world widely booming in recent years. The bottom-fixed aquacultural farm gains more and more attention because of the large volume and great strength. This study numerically investigates the fluid velocity distribution characteristic around the bottom-fixed aquacultural farm, which is of great importance for fish welfare and pollutant diffusion. The numerical model is developed based on the porous media model for the nets and the rigid walls for the fixed frame. The k-omega turbulence model and the finite volume method are employed to solve the Navier-Stokes equations. The flow velocity distributions around and inside the farm in the varied current velocity are analyzed. The vertical and horizontal flow velocity distributions in various current directions with different net solidities are investigated in detail. Results demonstrated that the configurations of trusses, vertical and horizontal columns of the farm and the interaction with the nets result in complex velocity distributions inside and around the farm. The velocity attenuations at different depths are quite different in uniform and non-uniform currents. The velocity distributions in different attack angles of the flow provide valuable suggestions on the arrangement and layout of the multiple farms.

对一种新型可移动式水下张紧系泊浮筒型油气外输终端系统进行模型试验,详细研究该水下浮筒系统的动力响应和张紧式系泊的受力特性,发现水下系泊浮筒在顶浪时除纵摇运动外还存在垂直于波浪方向的横向运动,张紧式系泊受力呈现脉冲载荷特性.研究为张紧式浮筒外输终端系统的设计提供理论依据.

采用数值模拟和物理模型试验,对比顶浪下蓝疆号系泊起重船吊物系统的运动特性.分析吊物运动对周期和波高变化的敏感性.依据Noble Denton浮式起重船操作规范,结合我国东海海况,对蓝疆号起重船吊装1000 t和3000 t组块的适用性进行分析,为蓝疆号起重船在海上作业的适用性提供理论依据.

Extreme waves with large wave heights may cause the biomass loss and catastrophic damage to the offshore fish cage. This study investigates the hydrodynamic response of fish cage under extreme waves. Focused waves based on the NewWave theory are simulated to represent such extreme waves in this study. Based on the lumped-mass model, the fish cage is numerically simulated to analyze the motion and load characteristics in extreme waves. The results indicate that the fish cage volume dramatically decreases in extreme waves. The extreme wave results in large motions and mooring loads. Different extreme wave crest locations give rise to different net cage responses. The fish cage attacked at the leeward side suffers from larger motions and mooring loads than the upwind side. With the increase of the steepness, surge motions and mooring loads sharply increase. The preceding waves before the highest crest greatly influence the peak values of motions and loads. Results imply that not only the crest location but also the load histories should be carefully examined when investigating the extreme response.

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.