The current cost of electricity has been preventing the technological progress of wave energy converters. The use of compact wave energy converters arrays is seen as a technological breakthrough for ...reducing these costs. These array configurations aim to maximize the energy extracted per unit area of marine space and to promote the sharing of components and installation, operation and maintenance tasks. Mooring lines are fundamental components in these systems and represent a considerable portion of the project cost. Reducing the number of mooring lines through the application of arrays with inter-body connections has a high potential for cost reduction. In this paper, we present the experimental study of different configurations of a five-device array of spar-buoy oscillating-water-column wave energy converters in a wave basin, focusing on the analysis of the devices motion and the mooring line loads. The study compares the performance of a single isolated device, an array with independently-moored devices and three arrays with inter-body connections, with different levels of connectivity in the mooring arrangement. Tests were carried out for moderate and extreme wave conditions. Results show good performance for all configurations when subjected to moderate sea conditions. Under extreme sea conditions, high peak tensions were observed in the lines of all array configurations. Particularly large values were detected in the inter-body lines, caused by their full extension. Based on these results, guidelines for the design of mooring systems for compact wave energy converter arrays are presented.
•Wave-tank tests of five-device array configurations of spar-buoy OWCs are presented.•Line loads of independently-moored and inter-body connected arrays are evaluated.•Inter-body connected array shows reduction of 58% in line length and 73% in anchors.•Inter-body connected arrays presented the largest tensions under extreme waves.•Longer inter-body lines are expected to avoid high load peaks observed in the tests.
•A bottom-moored Spar-buoy OWC is simulated using a nonlinear Froude-Krylov model.•Drag forces due to real fluid effects are estimated using experimental data.•The numerical model detects the ...occurrence of parametric resonance in pitch & roll.•Numerical results are validated using model-scale experiments in a wave tank.•Parametric resonance shows a reduction in energy conversion efficiency up to 53%.
The wave energy sector has faced enormous technological improvements over the last five decades, however, due to the complexity of the hydrodynamic processes, current numerical models still have limitations in predicting relevant phenomena. In particular, floating spar-type wave energy converters are prone to large undesirable roll and pitch amplitudes caused by a dynamic instability induced by parametric resonance. Detecting this phenomenon accurately is essential as it impacts drastically on power extraction, structural loads and mooring forces. This paper presents the validation of results from a numerical model, capable of detecting parametric resonance, using experimental data. Experiments were carried out for a scaled model of the Spar-buoy OWC (Oscillating Water Column) device at a large ocean basin. The buoy uses a slack-mooring system attached to the basin floor. The scaled turbine damping effect is simulated by a calibrated orifice plate. Two different buoy draft configurations are considered to analyse the effect of different mass distributions. The numerical model considers the nonlinear Froude-Krylov forces, which allows it to capture complex hydrodynamic phenomena associated with the six-degree-of-freedom motion of the buoy. The mooring system is simulated through a quasi-static inelastic line model. Real fluid effects are accounted for through drag forces based on the Morison’s equation and determined from experimental data. The comparison of results from regular-wave tests shows good agreement, including when parametric resonance is detected. Numerical results show that parametric resonance can produce a negative impact on power extraction efficiency up to 53%.
•A fully coupled and efficient model of a spar-buoy floating offshore wind turbine (FOWT) is developed.•The associated aerodynamics, hydrodynamics, and structural dynamics of FOWT are investigated.•A ...bistable track nonlinear energy sink is proposed, designed and incorporated into the developed model to control FOWT responses.
Floating offshore wind turbines (FOWTs) have complex dynamics problems and strong coupling effects within their entire systems, and they are sensitive to winds and sea waves that may cause structural fatigue damages and power production fluctuations. Structural vibration control is a promising way to reduce FOWT responses, but most previous studies focused on linear control strategies with the limitations of requiring large strokes and having narrow effective frequency bandwidth. Nonlinear energy sinks (NESs) have emerged as an alternative to overcome the above limitations of linear control methods. In the present study, an OC3-Hywind spar-buoy FOWT is selected as a prototype structure for developing an in-house model to investigate its associated aerodynamics, hydrodynamics, and structural dynamics. The wind turbine blades and tower are modelled by three-dimensional Euler-Bernoulli beam elements and the floater is assumed as a rigid body. The blades’ pre-twist, pitch, and rotating angles are also considered to develop the system’s time-varying mass, stiffness, and damping matrices. The nonlinear quasi-static model is adopted to calculate the forces generated by the mooring cables. The straightforward and efficient in-house model is validated against FAST. Subsequently, a bistable track NES with a profile combining both negative second-order and positive fourth-order terms is proposed, designed, and incorporated into the model to mitigate FOWT responses under two investigated environmental conditions. Results show that the in-house model is of high accuracy in estimating dynamic characteristics and responses of FOWTs, paving the way for preliminary design and analysis of FOWTs with different platform types. Moreover, the bistable track NES can effectively control the fore-aft displacements at the tower top with practical strokes.
Introduction: Human error plays a significant role in the occurrence of industrial accidents. Displacement and unloading operations are operations in which the occurrence of human error may lead to ...plenty of human and financial losses. The present study aimed to investigate the possibility of human error occurrence in overhead crane operators in a Steel Company in Hormozgan, Iran. Material & Methods: This cross-sectional and descriptive study was conducted using the Standardized Plant Analysis Risk-Human Reliability Analysis (SPAR-H) technique. In this study, the job tasks of overhead crane operators were firstly analyzed using the hierarchical task analysis (HTA) technique. Subsequently, the probability of human error in job tasks was assessed using the SPAR-H technique. (Ethic code: IR.ACECR.JDM.REC.1399.005) Findings: Generally, five main tasks and 16 sub-tasks have been analyzed in this study. The highest probability of error was related to the three sub-tasks of longitudinal motion, transverse motion, and high and low motion (0.3975). The lowest probability of error was under the duty of recording shift reports, transmitting information orally, and writing (0.05). The results of this study clearly showed the effect of interdependence on increasing the probability of error occurrence. Discussion & Conclusion: Based on the results of the present study, some preventive measures were proposed to reduce the possibility of human error, including identifying and controlling job stressors, correcting the ergonomic status of crane cabins, preparing work instructions, as well as training and monitoring their proper implementation.
The OWC spar-buoy is an axisymmetric floating version of an oscillating-water-column (OWC) based device whose power take-off (PTO) system is an air turbine/generator set. Latching has been regarded ...as one of the most promising techniques to improve the efficiency of wave energy converters. In the case of the OWC spar-buoy, latching control is performed by opening/closing a high-speed stop valve installed in series with the turbine. The present paper has three main objectives. Firstly, to assess the performance improvements that can be achieved with a latching control strategy within a receding horizon framework. Secondly, to establish the practical requirements of this type of control by evaluating the sensitivity of the turbine power output to several receding horizon time intervals. Finally, to test and validate experimentally the proposed algorithms in a small-scale PTO test rig. All the experimental tests were performed considering irregular wave conditions.
•An optimal latching control strategy is proposed for an OWC spar-buoy.•The optimal control is implemented within a receding horizon framework.•Significant performance improvements are achieved with latching control.•The practical requirements for the receding horizon time intervals are established.•The control strategy is validated using real-time hardware-in-the-loop tests.
•The coal mine is gradually moving towards an intelligent production mode, which also poses new challenges to the reliability of miners' work.•Based on SPAR-H method, this paper improves the method ...according to the characteristics of human–computer interactive operation in intelligent mines, and develops a human reliability analysis method suitable for intelligent mines.•The optimized SPAR-H method can not only quantify the possibility of human error but also put forward targeted measures to prevent human error by operators.•This study introduces the path weighted value of PSFs, considers the impact of different PSFs on human error, modifies the probability of human error, and improves the conservative problem of the HRA method in the field of HCI.
In order to evaluate the human reliability of human–computer–interaction (HCI) in intelligent mines and prevent the human performance error of the operators, this study base on the SPAR-H method and take the chute monitoring center as the research object to develop a human reliability analysis method suitable for smart mines. First, the basic error probability of human error in the HCI is determined. Second, adjust the judgment standard of performance-shaping factors (PSFs). Then, the analytic hierarchy process and entropy weight evaluation model is constructed to determine the weight of PSFs, calculate the weight path weight value. Finally, the improved spar-h method is obtained, compared with the difference between SPAR-H and CREAM, the difference between the improved SPAR-H method and the two methods is more obvious. After applying the improved SPAR-H method to the chute monitoring operation, it can find that the optimized SPAR-H method can not only quantify the possibility of human error but also put forward targeted measures to prevent human error by operators.
Accurate estimation of the dynamic behavior of Floating Offshore Wind Turbines (FOWTs) under typhoon environment is essential to design and install FOWTs in a prone area of typhoons such as around ...Japan. Up to now, extensive efforts for development of design tools for FOWTs have been made, and nowadays several design tools are available. Needless to say, it is of utmost importance that the engineering design tools have been verified and validated for the real physical phenomena before being applied to real designs/projects with confidence. Much efforts have thus been made as code-to-code comparisons and by validations using model test data. Validations of the design tools using full-scale field data for FOWTs have also been made, but available open literatures are quite limited, particularly for design-driving extreme cases. In this paper, we describe the analysis of the dynamic response of a 2-MW spar-type FOWT at the time of typhoon attack in the actual sea area. The central atmospheric pressure of the typhoon at the closest time was 965 hPa, the maximum instantaneous wind speed at the hub height was 52.2 m/s, and the maximum significant wave height was 6.9 m. The dynamic responses under the typhoon environment are numerically simulated by using the time-series records of the wind speed, the wind direction, the wave height, the wave direction, the current speed, and the current direction which were acquired during the typhoon passing through close to the FOWT. Then the simulated motion responses are compared with the measured motion responses for the same durations. By the comparisons, the numerical simulation tool which was used for the design of the FOWT has been partially validated. It has also been confirmed that the spatial coherence of the wind speed has a significant effect for the platform motions, particularly for yaw motion.
•Dynamic response of a spar-type floating wind turbine during typhoon attack is presented here.•In-site measured values are compared with numerical simulations.•Basically, good agreement is observed except for yaw motion.•The spatial coherence of the wind speeds has a significant effect for the platform motions, particularly for yaw motion.
•Quantitative human reliability analysis is performed under ER extended SPAR-H modelling.•Human reliability is predicted for cargo discharging operations in crude oil tanker.•A comprehensive insight ...into human reliability can be gained by improving operational safety in tanker ships.
Human reliability analysis is essential to predict ship crew performance at the operation level for critical shipboard operations which pose a high risk. Specifically, the crew who are working on tanker ships has to be extra vigilant against the hazardous nature of the cargo. This paper performs a detailed human reliability analysis step by step for cargo discharging operations in crude oil tankers. To achieve this purpose, a Standardised Plant Analysis Risk Human Reliability Analysis (SPAR-H) extended by the Evidential Reasoning (ER) approach is used to systematically predict the probability of human errors. While SPAR-H provides a robust tool to calculate human error probability simultaneously, the ER fuses raters’ opinions in decision-making. The finding of the research shows that the overall human reliability is found at 6.52E-01 for cargo discharging operations in crude oil tankers. Besides its practical contributions to maritime crude oil transportation, the proposed approach presents how a comprehensive insight into human reliability can be gained.
Human error plays a crucial role in maritime transportation risk analysis, as a significant percentage of accidents, including collisions, groundings, capsizing, fires, and explosions, can be ...attributed to human errors. However, obtaining a dataset that quantifies human error probabilities for maritime risk analysis is challenging due to commercial constraints. To address this issue, this paper proposes a conceptual framework that integrates evidential reasoning (ER) and the standardized plant analysis risk-human reliability analysis (SPAR-H) method to quantify human errors, while employing fault tree analysis (FTA) to predict risk. The specific focus of this study is ship collision risk in congested waters, which serves as a demonstration case to showcase the proposed method and illustrate a detailed analysis of collision risk. The findings reveal that “inadequate watchkeeping due to sole lookout”, “improper RADAR monitoring”, and “ineffective execution of COLREG-related actions” are the most significant human errors contributing to collision risk in congested waters. The outcomes of this research provide valuable insights for ship owners, safety professionals, ship masters, inspectors, and researchers in the maritime industry. The findings can assist in minimizing collision risk and improving navigational safety in congested waters.
•A comprehensive risk analysis considering human factors under FTA extended Evidential Reasoning (ER) SPAR-H method is presented.•A novel quantitative risk analysing is performed to provide a detailed structure for human-related failures that lead to ship collision in congested water.•The paper provides insights to maritime stakeholders to reduce collision risks and improve navigational safety in congested waters.
For large-scale exploitation of the offshore wave energy resource, floating wave energy converters should be deployed in arrays with inter-body mooring connections, reducing the number of bottom ...slack-mooring lines needed and consequently the project total cost. The present paper concerns the experimental investigation of the dynamics, energy extraction and mooring system performance of the OWC spar-buoy, deployed isolated and in a triangular array configuration, with inter-body mooring connections. For this purpose, three 1:32 scale models of the device were built and tested at Plymouth University large ocean basin. Pressure variations inside the OWC air chamber, mooring line forces in the buoy fairleads and buoys motion were measured. The turbine damping effect was simulated using a calibrated orifice fixed at the top of the air chamber. Tests were carried out for regular and irregular wave conditions with different wave heights and periods. Several model configurations were tested, including the variation of the mooring lines pre-tension, the structure ballast and the turbine damping. The closure of the air chamber, for turbine protection purposes, was found to be correlated with a large increase of the mooring loads. Results show a comparable performance between the three-device array and isolated device configuration.
•Three OWC spar-buoy 1:32nd scale models were tested in a wave tank.•The devices were tested isolated and in array, under regular and irregular waves.•The motion, energy extraction and mooring system performances were studied.•Comparable power performances were found between array and isolated device scenario.•Closing the air chamber for turbine protection aggravated the loads on the moorings.
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