Search Results (14)

The wave period is a wave parameter that is significantly influenced by factors such as wind speed and bottom topography. Previous research on wave period parameterization has primarily focused on wind-dominated sea areas and may not be applicable to certain regions, such as the equatorial calm or coastal areas dominated by swell waves. To address this limitation, this paper utilizes the third-generation wave numerical model SWAN to perform wave numerical simulations for a portion of the Northwest Pacific Ocean. The simulation incorporates observational data from nearshore stations, buoys, and satellite altimeters for error analysis. To develop a new wave parameterization scheme (WS-23), we employ extensive NDBC buoy data and incorporate the exponential rate and wave age characteristics that were previously established by predecessors. Our scheme introduces a judgement mechanism to distinguish between wind waves, swell waves, and mixed waves. The resulting ocean wave factor enhances the mean wave period values calculated using the model and other parameterization schemes. The experimental results demonstrate that our new parameterization scheme effectively improves the abnormal peak of the fitting data. Comparing the output values of the mean wave period element output of the SWAN model with our new parameterization scheme, we observe a reduction in the mean values of $E_a$, $E_c$, and $RMSE$ by 0.231, 1.94%, and 0.162, respectively, while increasing the average $r$ by 0.05. Full article

Marine buoys need to operate in high sea areas far from land for a long time. Therefore, how to provide a long-term power supply for the buoy system is critical to be addressed. Photovoltaic (PV) power supply systems are the most commonly used power supply method for marine buoys. Due to the limitations of the buoy structure and considering the rotation of the buoy in the ocean, most of the PV modules are placed in a four-sided enclosure. The output performance of the PV power supply system in this placement is affected by the tilt angle produced by waves. However, there are few relevant studies on the actual power generation performance of PV power supply systems for marine buoys, and there is a lack of methods for power generation performance analysis. In order to meet the power requirements of the marine buoy, a large design margin must be left. It increases the cost of marine buoys. In this paper, second-order Stokes waves are used to simulate waves of different levels by varying the wave height and frequency. The motion characteristics of the marine buoy are analyzed using ANSYS-AQWA under calm-rippled, smooth, slight, and moderate conditions. Combined with the tilted surface irradiance calculation model to get the variation law of solar radiation of PV modules under dynamic conditions, the effect of different tilt angle PV modules on the output of PV system under dynamic conditions was also studied. The experiments show that for every 5° increase in the tilt angle of the PV modules the output power of the system decreases by 3% on average. As the tilt angle of the PV modules increases, the impact on the system output performance is more pronounced. The output power decreased by 69.5% when the PV modules were tilted at an angle of 90°, and the PV system electrical parameters were similarly affected. By comparing the influence of different tilt angles on the power supply performance of PV modules, we optimize the design of the PV power supply system of the buoy. This enables the designers to maximize the use of limited area and space while reducing the cost and extending the power supply time and service life of the buoy. Full article

The offshore waters of China are a typical monsoon−affected area where the significant wave height (SWH) is strongly influenced by the different seasonal mean flow in winter and summer. However, limited in situ validations of the SWH have been performed on the China–France Oceanography Satellite (CFOSAT) in these waters. This study focused on validating CFOSAT nadir SWH data with SWH data from in situ buoy observations for China’s offshore waters and the Haiyang−2B (HY−2B) satellite, from July 2019 to December 2021. The validation against the buoy data showed that the relative absolute error has a seasonal cycle, varying in a narrow range near 35%. The RMSE of the CFOSAT nadir SWH was 0.29 m when compared against in situ observations, and CFOSAT was found to be more likely to overestimate the SWH under calm sea conditions. The sea−surface winds play a key role in calm sea conditions. The spatial distributions of the CFOSAT and HY−2B seasonal SWHs were similar, with a two−year mean SWH−field correlation coefficient of 0.98. Moreover, the coherence between the two satellites’ SWH variance increased with SWH magnitude. Our study indicates that, in such typical monsoon−influenced waters, attention should be given to the influence of sea conditions on the accuracy of CFOSAT SWH, particularly in studies that combine data from multiple, long−duration space−based sensors. Full article

This study introduces an alternative to the existing methods for measuring ocean currents based on a recently developed technology. The SailBuoy is an unmanned surface vehicle powered by wind and solar panels that can navigate autonomously to predefined waypoints and record velocity profiles using an integrated downward-looking acoustic Doppler current profiler (ADCP). Data collected on two validation campaigns show a satisfactory correlation between the SailBuoy current records and traditional observation techniques such as bottom-mounted and moored current profilers and moored single-point current meter. While the highest correlations were found in tidal signals, strong current, and calm weather conditions, low current speeds and varying high wave and wind conditions reduced correlation considerably. Filtering out some events with the high sea surface roughness associated with high wind and wave conditions may increase the SailBuoy ADCP listening quality and lead to better correlations. Not yet resolved is a systematic offset between the measurements obtained by the SailBuoy and the reference instruments of ±0.03 m/s. Possible reasons are discussed to be the differences between instruments (various products) as well as changes in background noise levels due to environmental conditions. Full article

In this paper, fatigue analysis of oil offloading lines (OOLs) in the floating production storage and offloading (FPSO) catenary anchor leg mooring (CALM) buoy offloading system under wave and current loads in the West Africa Sea area is carried out by the numerical simulation method. The hydrodynamic coupling response is calculated, and fatigue damage is analyzed. Firstly, the numerical model is verified by comparison with the experimental results. Then, according to the environmental statistics in West Africa, the influence of various parameters on the fatigue damage of OOLs is analyzed, including tension characteristics, wave parameters, and structural parameters. Additionally, the effect of current load is studied. Results show that accumulated fatigue damage mainly occurs near the CALM buoy and is mainly caused by the 0° wind wave. Appropriately reducing the cover length of buoyancy material and increasing the wall thickness can reduce fatigue damage. Moreover, the effect of the shuttle tanker can increase the fatigue damage of the OOL near the CALM buoy by about 1.5 times, and the effect of vortex-induced vibration can increase the fatigue damage of the OOL in the middle part by up to 5–10 times. Full article

Floating offshore structures (FOS) must be designed to be stable, to float, and to be able to support other structures for which they were designed. These FOS are needed for different transfer operations in oil terminals. However, water waves affect the motion response of floating buoys. Under normal sea states, the free-floating buoy presents stable periodic responses. However, when moored, they are kept in position. Mooring configurations used to moor buoys in single point mooring (SPM) terminals could require systems such as Catenary Anchor Leg Moorings (CALM) and Single Anchor Leg Moorings (SALM). The CALM buoys are one of the most commonly-utilised type of offshore loading terminal. Due to the wider application of CALM buoy systems, it is necessary to investigate the fluid structure interaction (FSI) and vortex effect on the buoy. In this study, a numerical investigation is presented on a CALM buoy model conducted using Computational Fluid Dynamics (CFD) in ANSYS Fluent version R2 2020. Some hydrodynamic definitions and governing equations were presented to introduce the model. The results presented visualize and evaluate specific motion characteristics of the CALM buoy with emphasis on the vortex effect. The results of the CFD study present a better understanding of the hydrodynamic parameters, reaction characteristics and fluid-structure interaction under random waves. Full article

The application of marine bonded hoses has increased in recent times, due to the need for more flexible conduits and flexible applications in the offshore industry. These marine structures include Catenary Anchor Leg Moorings (CALM) buoys and ocean monitoring buoys. Their attachments include floating hoses, submarine hoses and submarine cables. However, the structural performance challenges of a CALM buoy system from its hydrodynamics water waves and other global loadings, have led to the need for this investigation. In this study, a detailed presentation on the motion characterisation of the CALM buoy hose system is presented. The CALM buoy is a structure with six degrees of freedom (6DoF). A well-detailed experimental presentation on the CALM buoy hose model conducted in Lancaster University Wave Tank is presented using three novel techniques, which are: a digital image captured using Imetrum systems, using an Akaso 4K underwater camera, using wave gauges arranged in a unique pattern and using underwater Bluetooth sensors. The buoy model was also found to respond uniquely for each motion investigated under water waves. The results showed that the higher the profile, the higher the response of the buoy. Thus, this study confirms the existence of flow patterns of the CALM buoy while floating on the water body. Full article

There is an increase in the utilization of the floating offshore structure (FOS) called Catenary Anchor Leg Mooring (CALM) buoys and the attached marine hoses due to the increasing demand for oil and gas products. These hoses are flexible and easier to use but have a short service life of about 25 years. They are adaptable in ocean locations of shallow, intermediate and deep waters. In this research, a numerical model was developed using a coupling method modeled by utilizing ANSYS AQWA and Orcaflex (Orcina Ltd., Ulverston, UK) dynamic models of the CALM buoy hoses. Two cases were comparatively studied: Lazy-S and Chinese-lantern configurations, under ocean waves and current. Comparisons were also made between coupled and uncoupled models. This research presents the hydrodynamic characteristics with a sensitivity analysis on the influence of waves, current attack angle, soil gradient, soil stiffness and environmental conditions that influence the performance of marine hoses. The study comparatively looked at the configurations from dynamic amplification factors (DAF) on marine hoses. The results show that marine hoses can be easily configured to suit the designer’s need, seabed soil type, seabed topography and the profiles that are useful for manufacturers. The sensitivity analysis also shows the effect of hose parameters on its hydrodynamic behavior from the wave–current interaction (WCI). Full article

Due to the demand for oil production in varying water depth regions, the advantage of flexible buoyant conduits has led to an increase in bonded marine hoses for fluid transfer and (un)loading operations. The fluid transfer system for bonded marine hoses is dependent on floating offshore structures (FOS). This paper presents an overview of different systems for sustainable fluid transfer and (un)loading operations via FOS, such as Single Point Mooring (SPM) systems. SPMs are component aspects of the techno-economic design and FOS operation. This review aims to present sustainable fluid transfer technologies while addressing the subject of bonded marine hoses based on application, configuration, test models, hose selection criteria, hose-mooring configurations and operational views. This paper also includes an overview of the hose dynamics, with the loading and unloading (or discharging) techniques for sustainable fluid transfer via marine bonded hoses, based on operational challenges encountered. To dynamically present the hose performance in this review, an overview of the test methods’ guidance as specified in available industry standards was conducted. The pros and cons of marine hose application were also presented. Finally, this study presents different marine hose types and novel design configurations applied in implementing hose-mooring systems. Some concluding remarks with recommended solutions on the technology were presented in this review. Full article

The application of mathematical analysis has been an essential tool applied on Catenary Anchor Leg Mooring (CALM) buoys, Wave Energy Converters (WEC), point absorber buoys, and various single point mooring (SPM) systems. This enables having mathematical models for bonded marine hoses on SPM systems with application with CALM buoys, which are obviously a requisite for the techno-economic design and operation of these floating structures. Hose models (HM) and mooring models (MM) are utilized on a variety of applications such as SPARs, Semisubmersibles, WECs and CALM buoys. CALM buoys are an application of SPM systems. The goal of this review is to address the subject of marine hoses from mathematical modeling and operational views. To correctly reproduce the behavior of bonded marine hoses, including nonlinear dynamics, and to study their performance, accurate mathematical models are required. The paper gives an overview of the statics and dynamics of offshore/marine hoses. The reviews on marine hose behavior are conducted based on theoretical, numerical, and experimental investigations. The review also covers challenges encountered in hose installation, connection, and hang-off operations. State-of-the-art, developments and recent innovations in mooring applications for SURP (subsea umbilicals, risers, and pipelines) are presented. Finally, this study details the relevant materials that are utilized in hoses and mooring implementations. Some conclusions and recommendations are presented based on this review. Full article

Recent design challenges in ocean observations, energy storage, offloading/discharging, and loading operations in both the offshore-renewable industry have led to advances in the application of catenary anchor leg moorings (CALM) buoys. Due to different seabed profiles, soil stiffness and environmental conditions, there is the need for numerical assessment to investigate the behaviour of the submarine hoses, based on the structural and hydrodynamic behaviour. In this study, experimental and numerical investigations are carried out on the dynamic behaviour of the submarine hoses attached to a CALM buoy in Lazy-S configuration. Six mooring lines are attached to the CALM buoy with a water depth of 100 m in the numerical model. A hydrodynamic model utilising ANSYS AQWA was developed then coupled unto the dynamic model in Orcina’s Orcaflex. The studies were carried out to study the effect of flow angles, wave height, soil stiffness and hydrodynamic loads on the structural behaviour of the submarine hoses. Waves at different angles to the submarine hose affected the effective tension more where the hose bends due to the floats attached. Parametric studies were carried out on both linear and nonlinear seabed models, and recommendations were made from the investigations on the submarine hose models. Full article

This paper presents the design and analysis of a mooring buoy and its mooring systems to moor a floating platform mounting an arrayed Wave Energy Converters (WECs). The mooring buoy allows the WEC platform to weathervane around the mooring buoy freely by the prevailing environment directions, which enables consistent power generation. The WEC platform is connected to the buoy with synthetic hawsers, while station-keeping of the buoy is maintained with catenary mooring lines of chains tied to the buoy keel. The buoy also accommodates a power cable to transfer the electricity from the WEC platform to the shore. The WEC platform is designed to produce a total of 1.0 MW with multiple WECs installed in an array. Fully coupled time-domain analyses are conducted under the site sea states, including extreme 50 y and survival 100 y conditions. The buoy motions, mooring tensions and other design parameters are evaluated. Strength and fatigue designs of the mooring systems are validated with requirements according to industry standards. Global and local structural designs of the mooring buoy are carried out and confirm the design compliances. Full article

Mooring systems are among the most critical sub-systems for floating marine energy converters (MEC). In particular, the occurrence of peak mooring loads on MEC mooring systems must be carefully evaluated in order to ensure a robust and efficient mooring design. This understanding can be gained through long-term field test measurement campaigns, providing mooring and environmental data for a wide range of conditions. This paper draws on mooring tensions and environmental conditions that have been recorded (1) for several months during the demonstration of an MEC device and (2) over a period of 18 months at a mooring test facility. Both systems were installed in a shallow water depth (45 m and 30 m, respectively) using compliant multi-leg catenary mooring systems. A methodology has been developed to detect peak mooring loads and to relate them to the associated sea states for further investigation. Results indicate that peak mooring loads did not occur for the sea states on the external contour line of the measured sea states, but for the sea states inside the scatter diagram. This result is attributed to the short-term variability associated with the maximum mooring load for the given sea state parameters. During the identified sea states, MEC devices may not be in survival mode, and thus, the power take-off (PTO) and ancillary systems may be prone to damage. In addition, repeated high peak loads will significantly contribute to mooring line fatigue. Consequently, considering sea states inside the scatter diagram during the MEC mooring design potentially yields a more cost-effective mooring system. As such, the presented methodology contributes to the continuous development of specific MEC mooring systems. Full article

Previous studies have suggested that the accuracy of temperature measurements by surface-moored buoys may be affected by distortions of the near-surface temperature structure by the buoy hull on calm, sunny days. We obtained the first definite observational evidence that the temperature near the hull was not horizontally homogeneous at the same nominal depth. We observed large temperature differences of 1.0 K or more between thermometers at 0.2 m depth. The distortion of the surface temperature field yielded an error in estimates of daytime net surface heat flux up to more than 30 Wm^–2. Full article