Rough Sea Conditions Research Articles

Innovative multi-tagline anti-swing and positioning system: Dynamic analysis and experimental validation for slender-beam payloads in offshore environments

To address the challenges of low hoisting efficiency, high risk, and difficulty in achieving accurate positioning caused by the double-pendulum phenomenon of slender-beam payload (SBP) under rough sea conditions, a novel Multi-Tagline Anti-swing And Positioning System (MTAPS) is proposed in this study. A three-dimensional double-pendulum dynamic model of the MTAPS is established by using multi-body dynamics and Newton's classical mechanics. Furthermore, a decoupling control method is proposed to suppress the swing of the SBP. Numerous simulations and experiments have proved that the MTAPS can effectively reduce the swing of the SBP in an offshore environment. Under the set working conditions, the MTAPS can effectively reduce the swing of the SBP by more than 85%. The anti-swing device, based on the principles of this system, has been implemented in engineering practices, offering a novel approach for the rapid lifting and precise positioning of SBP in offshore settings.

Incremental robust predictive control for anti-pitching in catamarans with appendage constraints

To solve the problem that high-speed catamarans have excessive amplitude of vertical motion in rough sea conditions, an anti-pitching method based on incremental robust predictive control of catamarans is proposed, which takes into account the model uncertainty and input rate of appendage requirements. Thus, a high-speed catamaran vertical control model is established with T-foils and flaps serving as anti-pitching appendages, and the hydrodynamic coefficient uncertainties is analyzed, which is converted into a state space model with norm-bounded uncertainty to facilitate control system design; moreover, transforming the norm-bounded uncertainty model of a high-speed catamaran into an incremental model, which can increase the integral action to improve the anti-pitching performance. On this basis, the hybrid H2/H∞ robust predictive control method is proposed to achieve wave disturbance resistance capability and robust stability of the catamaran system, taking the rate of input of the anti-pitching appendages as the input constraints, and the linear matrix inequality (LMI) receding-horizon optimization is used to solve the incremental control input of appendages. Ultimately, the effectiveness of the proposed algorithm is verified by digital simulation.

Pitching Stabilization Control for Super Large Ships Based on Double Nonlinear Positive Feedback under Rough Sea Conditions

Due to the rapid development of a global navigation satellite system and the rapid growth of ships, the traditional control algorithms are not suitable; hence, the longitudinal rocking phenomenon generated by external disturbances is more serious when a ship is sailing. This paper takes a mathematical model of the super large oil tanker “KVLCC2”’s longitudinal motion as the controlled plant, establishing a multi-input multi-output instability control system, using the root trajectory shaping method and a weighting matrix to ensure the stability of its transfer function’s mathematical model. An improved closed-loop gain-shaping algorithm is utilized to design a simple robust controller. And a dual nonlinear positive feedback control algorithm is added to the control system to further improve the controller’s pitching stabilization performance and reduce the controller’s output energy. In order to verify that the controller has a consistently strong robustness, simulation experiments are carried out by adding a level 6, 7 and 8 wind wave model and a perturbation link to the control system, respectively. The results show that when the value of the hysteresis constant is taken as 0.25, the output values of the heave displacement and the pitch angle are greatly reduced, and the longitudinal rocking phenomenon is significantly improved. The dual nonlinear positive feedback control algorithm enhances the ship’s pitching stabilization control capability and further reduces the controller’s output energy, which provides technical support for the smooth and efficient sailing of super large ships under changing sea conditions. Combined with a global navigation satellite system, this algorithm provides a new method for pitching stabilization control of super large ships.

Evaluation of operational parameters for vessel's flexible subsea pipelines

AbstractThe operation of offshore vessels is directly related to the use of flexible pipelines. The article describes in detail the analysis of power, geometric, kinematic and technological parameters that affect the main operational characteristics of these pipes during their operation under water, in rough sea conditions and under wind loads. The article describes the degree of dependence between loads on the pipeline and velocity of the oncoming flow, the geometry of the pipe and the distance to the rigid surface of the ship's hull or the seabed. It was determined how the flow velocity during parametric oscillations of the pipeline in unrestricted flow and near the surface of the seabed affects the change in its drag and lift coefficients. An estimate of operational limits of flexible pipeline instability was obtained. On the base of changes in distributed load, specific values for safe lengths of pipelines were formulated. It has been stated that the probability of failure‐free operation of a flexible pipeline at a level of 0.99 is directly determined by the frequency of its oscillation. Its numerical values should always be at a level that does not exceed 3.7% of the frequency of pipe dynamic oscillations.

Rolling Mechanism of Launch Vehicle during the Prelaunch Phase in Sea Launch

During the sea launch of a launch vehicle in low sea state, a rolling phenomenon of the launch vehicle has been observed. In rough sea conditions, launch may failure. This study utilizes dimensionality reduction-driven spatial system projection methods and virtual prototype modeling technology to reveal that the launch vehicle’s rolling is caused by differences in the motion paths of the center of mass. Additionally, during the prelaunch stage, the variation in the trajectory of the launch vehicle’s center of mass caused by the rolling and pitching motions of the transportation vessel has a significant impact on the roll motion of the launch vehicle. The motion in other degrees of freedom has minimal influence on the launch vehicle’s rolling. The minimum rocket rolling occurs when the dynamic coefficient of friction of the launchpad–launch vehicle contact is 0.05, and the dynamic coefficient of friction of the adapters and guideways is 0.4. The conclusions provide a theoretical foundation for optimizing the sea launch system and enhancing the reliability of sea launch in rough sea conditions.

A long sequence time-series forecasting model for ship motion attitude based on informer

Influenced by marine environmental factors, a ship sailing at sea will experience six degrees of freedom oscillating motions. These oscillating motions pose safety risks to ship navigation and maritime operations. Especially in severe weather conditions, these oscillating motions have a significant impact on the takeoff and landing of carrier aircraft, as well as the launch of carrier missiles. Therefore, studying and forecasting the ship motion attitude in wind and waves holds immense significance. This paper presents a sparrow search algorithm (SSA) optimized Informer model based on complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) to forecast the long sequence time-series of ship motion attitude. Firstly, the ship motion attitude time series, as measured by the inertial navigation system, is decomposed using CEEMDAN to obtain several intrinsic mode functions (IMFs) and a residual. Then, the IMFs and residual are fed into SSA-Informer, where SSA is used to optimize the hyperparameter of Informer. Finally, the forecast values of IMFs and residual are superimposed and reconstructed to get the ship motion attitude forecasting result. The forecasting experiment under slight, moderate and rough sea conditions in the East China Sea shows that the proposed model achieves better performance and longer forecasting time compared with other popular methods.

Hydrodynamic Insights on Floating Bubbling Fluidized Beds: Dynamic Solutions for Mitigating Gas Maldistribution

This study examined bubbling fluidized beds as an alternative to fixed-bed dry scrubbers on ships for reducing pollutants from marine fuels. It focused on overcoming the challenges of gas maldistribution/slug formation, especially under rough sea conditions. This research departed from traditional methods by introducing mobile internal elements into the bed emulsion phase and investigating their effectiveness in various settings, such as vertical, inclined, and rolling beds. A specialized hexapod-driven bubbling fluidized bed was developed to mimic marine operating conditions and to study the behavior of shipboard fluidized beds. Techniques such as digital image analysis (DIA) and particle image velocimetry (PIV) were used to observe bubble dynamics and granular phases, measuring local void fractions and particle velocities. A key finding is the effectiveness of moving internals in preventing bubble coalescence, which is critical for avoiding wall slugs, at different inclinations. Three types of packing were used as mobile internals: Super Raschig, Pall, and square rings. Super Raschig rings, which are characterized by high porosity, were the most efficient in reducing bubble coalescence, making them a preferred choice for offshore fluidized bed applications. This research contributes to the advancement of fluidized bed technology in marine applications and provides insight for future improvements.

A Fast In-Motion Alignment Method for INS/DVL in Rough Sea Conditions

A Fast In-Motion Alignment Method for INS/DVL in Rough Sea Conditions

Nezha‐IV: A hybrid aerial underwater vehicle in real ocean environments

AbstractHybrid aerial underwater vehicles (HAUVs) that are capable of autonomously operating in both the aerial and underwater environments with repeated rapid transitions have received great interest in recent years. Current HAUV prototypes cannot fully cope with the unstructured, harsh, and hazardous ocean environments considering the high‐pressure and the strong hydrodynamic perturbations. This work reports on the HAUV, Nezha‐IV, with all basic functions validated in a real ocean environment. Nezha‐IV has four aerial propellers and eight underwater thrusters. It is not only capable of maneuvering delicately during flight and underwater but can also perform dynamic transitions under rough sea conditions. We present the design, construction, control, and oceanic testing of Nezha‐IV and demonstrate reliability and robustness, especially during the transition phases. Performance estimation and results gathered from tests in the South China Sea show that Nezha‐IV can operate at various depths ranging from 0 to 50 m at a velocity of 1 kt for 22 min and hover in the air for 15 min or cruise at a velocity of 10 m/s for 7.2 km in 12 min. This project contributes to the field of HAUV with (i) a HAUV capable of dynamic locomotion with high stability in both media and during transitions; (ii) identification of challenges during water–air transition in harsh sea conditions, and a reliable transition strategy that helps the development of fully autonomous HAUVs; (iii) a modular, foldable, and impact‐resistant HAUV structure; (iv) vehicle's capability proved by extensive tests in dynamic ocean environment.

Offshore floating PV–DC and AC yield analysis considering wave effects

The growing global energy demand increases the need for renewable energy sources. This increase requires land to be occupied, competing with other activities such as agriculture and residency. In such a situation, renewable energy sources expand to other environments like the ocean. However, this new scene poses some challenges, such as the effect of waves on photovoltaic (PV) performance. Consequently, this study aims to evaluate the power output of an Offshore Floating PV (OFPV) system located in the North Sea considering the effect of the waves. A 3D mechanical movement model, which has been validated with data from a real system, is developed for this purpose. A sensitivity analysis is conducted to determine how the size of fluctuations depends on the dimensions of the floater. The main outcome is that a heavy and wide floater aligned with the most common wind direction reduces angle variations. Results from DC power simulations show that sea fluctuations have a negative yet small influence on PV power production. Over the course of the year, these losses amount to just 0.1% of the annual energy yield. However, a hypothetical optimally-tilted PV system placed on water would still generate 14.6% more DC power output than the floating one. On the AC side, laboratory experiments show that these oscillations negatively affect the inverter efficiency during rough sea conditions by a decrease of over 2 percentage points compared to a still system.

Dynamic analysis of the Cable-Driven Anti-swing System for slender payload lifting in the offshore environment

ABSTRACT The slender payload lifting is inefficient and comes with high risk in rough sea conditions. Thus it is not easy to achieve precise assembly. This paper presents a Cable-Driven Anti-swing System (CDAS) for slender payload lifting in the offshore environment. The CDAS for offshore slender payload lifting is simplified as a constrained double-pendulum system with moving base excitations. Further, the dynamic characteristics are simulated and analysed by Matlab/Simulink. The CDAS has a good vibration suppression effect on the first stage pendulum, and it has a specific vibration suppression effect on the second stage pendulum as well under setting conditions. The experimental results show that the simulation curve of the hook and the slender payload is consistent with the experimental results, which verifies the accuracy of the dynamic model. The research results of this paper can provide a theoretical basis for the anti-swing control of the double-pendulum system like slender payload.

The retrofitting of ships by applying retractable bow hydrofoils: a case study

Increasing environmental requirements and a relatively long ship life of 30 years mean more attention is needed to retrofit existing ships. One possibility is using hydrofoils to reduce the ship’s resistance and improve comfort and safety in rough sea conditions. This study investigates the influence of retractable bow hydrofoils on the seakeeping performance and operational conditions of a selected case study vessel (V-shaped bulbous bow). The methods used were full-scale computational fluid dynamics (CFD) simulations and towing tank experiments for validation. The analysis was conducted for bow waves of different lengths and a ship’s operating speed. The most beneficial effect of hydrofoils was observed for wavelengths from λ/LWL = 1.0 to λ/LWL = 1.2. For the wavelength λ/LWL = 1.2, the reduction of heave motion was equal to 33%, pitch motion was equivalent to 28%, and the reduction of wave-added resistance was equal to 25%. The analysis also showed unfavourable conditions for which hydrofoil folding is needed to avoid causing an excessive increase in resistance. A generalized procedure has been developed to assess the potential for resistance and motion reduction by retrofitting existing ships using hydrofoils.

Progressive collapse analysis and ultimate strength estimation of continuous stiffened panel under longitudinal extreme cyclic load and lateral pressure

Stiffened panel is a fundamental member of hull structures which is designed to withstand multiple loads such as revered cyclic load and lateral pressure. At present the ultimate strength of stiffened panel is conventionally determined by the monotonic compression criterion, ignoring the real progressive collapse of ship in rough sea conditions. To provide useful insights for improving the ship design, the present study focuses on dealing with the structural collapse characteristics and ultimate strength estimation of continuous stiffened panel under combined longitudinal extreme cyclic load and lateral pressure. A large number of nonlinear finite element analyses (FEA) are conducted to identify the influences of various factors on the failure mode and ultimate strength including the slenderness ratio of local panel, stiffener type, size and number, sequence and amplitude of the cyclic load, cycle number and lateral pressure. It is found that the ultimate limit state behaviours are governed by the coupling effects of several influential parameters. Based on artificial neural networks (ANN), a prediction model with high accuracy is proposed to evaluate the ultimate strength in different cycles.

Error Analysis and Filtering Methods for Absolute Ocean Gravity Data

The atomic gravimeter has advantages of high accuracy and long-term stability, which is suitable for high-resolution absolute sea-surface and deep-sea gravity measurements. The absolute gravity data measured by the atomic gravimeter are affected by rough sea conditions, with significant non-smooth and non-linear noise signals, which reduce the accuracy of gravity measurements. To eliminate the noises in measured gravity data, this paper analyzed the noise sources and innovatively introduced the Variational Modal Decomposition algorithm according to the noise characteristics. Since the filtering result of Variational Modal Decomposition algorithm is limited by the selection of parameters like modal number K and penalty factor α, a Particle Swarm Optimization algorithm and envelope entropy were introduced to adaptively determine the parameters K and α, obtaining the optimal decomposition solution. To verify the reliability of the method, we processed the ocean gravity data, which were dynamically measured by atomic gravimeter (ZAG-M), by using the Empirical Mode Decomposition algorithm, the Complete Ensemble EMD with Adaptive Noise algorithm, and the PSO-VMD algorithm, respectively. The evaluated external coincidence accuracy acquired by comparing the ZAG-M with the ocean relative gravimeter (KSS-32) deployed on the same ship are 0. 71 mGal, 0.54 mGal and 0.48 mGal, respectively, confirming that the PSO-VMD filtering algorithm has a better filtering performance. Finally, the PSO-VMD was applied to all the lines of this ocean measurement experiment with an internal coincidence accuracy of 0.62mGal, verifying the stability of the ZAG-M atomic absolute gravimeter in ocean dynamic measurements and the effectiveness of the proposed algorithm.

Multi-cable anti-swing system for cranes subject to ship excitation and wind disturbance: Dynamic analysis and application in engineering

Offshore cranes generally have low working efficiency, high operating risk, and low lifting accuracy under rough sea conditions. In this study, a Multi-Cable Anti-Swing System (MCAS) is proposed in terms of a 45-ton crane of a 27,000-ton multipurpose vessel of COSCO Shipping Group as a design prototype, and it is adopted to investigate the dynamic characteristics of the MCAS for cranes within an offshore environment. The MCAS is simplified as a restricted-pendulum with ship-motion excitations, and a wind load is incorporated into the dynamic model of the MCAS. Moreover, the dynamic characteristics of the MCAS are simulated and analyzed using Matlab/Simulink, and the experiments were performed on the laboratory prototype of the crane equipped with the MCAS. As indicated by the crane operation data, the payload swing amplitude was reduced by 85% with the MCAS, which notably increased the lifting efficiency of offshore cranes. The results of this study will contribute to the in-depth optimization and engineering application of the MCAS onboard ships.

Sea Launch Adapter Response in Rough Sea Conditions Considering Strain Rate Effects

The launch vehicle sea launch system is a typical strong nonlinear complex coupled system. There is relative motion between the launch vehicle and the frame-type launcher in the offshore wind and wave environment. The multiple impact loads between the adapters and the guideways are nonlinear and discontinuous. The contact velocities between adapters and guideways are different. The strain rate of polyurethane foam should be considered in the adapter model. Based on the experimental data of polyurethane foam compression, a more accurate modified phenomenology macroscopic model is established. Dynamic models of the sea launch system with and without adapter strain rate effects are established respectively for comparative analysis. The results show that the dynamic effect of adapter strain rate effects on launch vehicle sea launch cannot be ignored.

A conceptual basis for surveying fouling communities at exposed and protected sites at sea: Feasible designs with exchangeable test bodies for in-situ biofouling collection

The enhanced inertia load caused by biofouling on device components, such as the foundations of wind turbines or other structures at sea, modifies the hydrodynamic properties, and increases the stress to structures, predominantly in upper water layers with high impact from wave dynamics. This compromises the stability, functioning, operation as well as the durability of these devices especially in exposed environments. A main challenge is the quantification of the impact of hydrodynamic forces on irregular bodies being overgrown by soft- and hard-bodied biofouling organisms. Therefore, test bodies from the upper 1–5 m water depth and thus exposed to the strongest wave actions close to the surface shall be overgrown by biofouling and used in measurement trials in a wave and current flume. These measurements shall shed light on the varying roughness and its influence on the load bearing capacity of foundation piles. Consequently, the main aims of the present work were the development of two independent test stations as holding devices for artificial test bodies for the collection of biofouling organisms during field studies: a carrying unit floating at the surface in an exposed area (System A) and a sampling device with access from a land-based facility (System B). Both systems are relatively easy to access, exhibit straightforward handling, and are reasonable cost-effective. A Test Body Support Unit (TBSU, System A) was designed and mounted on a spare buoy to carry the test bodies (cylinders), which serve as substrate for the fouling. The system was sufficiently robust to withstand several periods of rough sea conditions over the first two years. This system can only be accessed by vessels. System B (MareLift) provided the robustness and functionality needed for areas exhibiting harsh conditions but can be operated from land. The here used test bodies (steel panels) exhibited a sound basis for the monitoring of succession processes in the biofouling development. System B offered the possibility to analyse two habitats (intertidal and subtidal) and revealed clear differences in the composition and development of their fouling communities.Overall, both systems provide advantages in obtaining standardized biofouling samples compared to previous approaches. Such test stations play an important role in the risk management of marine sectors as they could help characterising biofouling communities over different geographical areas. System A and B provide a sound basis for biofouling research but potentially also for other potential research approaches in exposed areas as they provide space for future developments.

Oil spill remediation by biochar derived from bio-energy industries with a pilot-scale approach during the X-Press Pearl maritime disaster

Most traditional oil spill clean-up techniques are still laboratory based and are expensive and fairly ineffective. This study investigated the capacity of biochars derived from bio-energy industries in oil spill remediation with a pilot-testing. Three different biochars from bio-energy industries, Embilipitya (EBC), Mahiyanganaya (MBC), and Cinnamon Wood Biochar (CWBC) were assessed for the removal of Heavy Fuel Oil (HFO) at three dosages (10, 25, and 50 g L−1). Pilot-scale experiment was conducted with 100 g of biochars separately in the oil slick of X-Press Pearl shipwreck. All adsorbents exhibited rapid oil removal (within 30 min). Isotherm data were well explained by Sips isotherm model (R2 > 0.98). The pilot-scale experiment resulted oil removal for CWBC, EBC and MBC as 0.62, 1.12, and 0.67 g kg−1 respectively, even in rough sea conditions with a limited contact time (>5 min) indicates biochar's capacity in oil spill remediation as a cost-effective material.

Safety evaluation of lashed trailer motions in ferry operations under rough sea conditions

Safety evaluation of a lashed trailer on the cargo deck of ships is essential for ferry operations. Although ferry accidents have occurred worldwide, few studies have focused on the dynamic analysis of trailer motion in irregular sea states. To date, effective counterapproaches have not been established. Thus, first, ferry masters were interviewed to summarize the difficulty in cargo management during rough sea voyages. Second, a modified simulation model of lashed trailer motions was constructed to evaluate the safety of cargo management, considering wave, seakeeping, and trailer motion simulations. Few studies apply the model to the irregular sea state in actual seas, using a combination of three different kinds of models. A simulation was conducted to analyze the collapse of a trailer loaded on a ferry in high waves owing to rapidly developing atmospheric pressures. Essentially, the model can reproduce the collapse of trailers, especially when a shift in the center of gravity is considered when accelerations occur in loaded cargo inside trailers. The model enables the estimation of trailer motions and lashing wire tensions in ferry operations, considering suitable lashing arrangements.

Optimal design of a single-point electromechanical cable subsurface mooring

ABSTRACT Single-point electromechanical (EM) cable subsurface mooring (EMC-SSM) is an innovative subsea structure used to measure several ocean parameters throughout a water column in real time. However, designing an EMC-SSM that can adapt to rough sea conditions is challenging owing to the relative fragility of EM cables. In this study, an optimisation design method based on parameter sensitivity analysis was proposed to improve the responses of EMC-SSM. The unreasonable design and optimisation value were determined by evaluating the slopes of the sensitivity curves of four response parameters: the minimum and maximum tensions, maximum declination angle, and maximum curvature to the net buoyancy of the main float and big sensor package (BSP); drag; added mass coefficient of the BSP; and net weight and hydrodynamic coefficient of small sensor packages. We found that the proposed optimisation design method is effective in identifying and optimising the unreasonable configurations of mooring similar to the EMC-SSM.