•Merged FTA, SPAR-H, and RCM for comprehensive nuclear plant risk assessment.•Applied Fussell-Vesley criterion to pinpoint crucial system events.•Uniquely quantified the effectiveness of risk ...mitigation measures.
Probabilistic Safety Assessment (PSA) provides a systematic and quantitative approach to assess the risk associated with different components and systems within a nuclear power plant. By quantifying the impact of risk mitigation measures, decision-makers can prioritize and implement solutions that have the most significant impact on reducing risk. Fault Tree Analysis (FTA) is employed as a systematic method within PSA, encompassing all modes of failure across equipment and associated support systems, including unavailability due to maintenance (UDM), human errors (HEs), and common cause failures (CCFs). In the present research, the Extra Borating System (EBS) and the Chilled Water Operating Circuit System (CWOCS) of essential loads are modeled in the SAPHIRE code using VVER-1000 design data. Through importance analysis employing the Fussell-Vesley criterion, the most significant basic events for these two systems are identified. Subsequently, the outcomes of the importance analysis are examined using diversity, SPAR-H, and Reliability Centered Maintenance (RCM) techniques. Recommendations such as the enhancement of diversity, increasing staff training, promoting Human Machine Interface (HMI), reduction of maintenance time, and improvement of power supply reliability are proposed for the most crucial basic events. The ensuing impact of these measures on the reliability of the EBS and CWOCS is subsequently assessed. Through a comparison between the new failure probability and the previous, it is determined that improvements in CCFs contribute a 30% effect; HEs have a 14% effect and UDMs have a 5% effect, with a cumulative impact of 35% on the failure probability of the EBS system. Similarly, for the CWOCS system, enhancements in CCFs contribute 20%, UDMs 17%, and improved power supply reliability 19%, with a cumulative impact of 29%.
The crew of a nuclear‐powered submarine under development in Brasil plays an important role in its safety. For this reason, crew members must be trained in procedures against undesired events. ...However, information that would help to accurately decrease human error probability (HEP) on board nuclear‐powered submarines is not available in the literature. Therefore, a methodology is required to obtain this information. This study introduces importance measures to evaluate the contribution of performance shaping factors (PSFs) and their levels to HEP. Importance measures Fussell‐Vesely, risk reduction worth, risk achievement worth, and Birnbaum importance, commonly used in probabilistic safety assessment, are introduced to identify PSFs and PSF levels that contribute the most to HEP. The proposed approach is focused on identifying HEP's main contributors, oriented toward decision‐making. The methodology uses the PSFs established in the Standardized Plant Analysis Risk‐Human Reliability Analysis method and a Bayesian network to quantify HEP. Moreover, the results of an application case demonstrate the method's effectiveness in integrating expert opinions into representative values of HEP and in identifying critical PSFs and PSF levels that should be the object of the decision‐making process to improve human performance.
This study investigated the dynamic behaviour of a spar-type offshore floating wind turbine (OFWT) analysed under various wave loads by conducting an experiment campaign. Both the characteristic of ...the spar platform itself and the spar with realistic moorings have been investigated. A particular focus of the study was the motions of the mooring lines, which were measured at a series of discrete points along one line using an underwater motion capture system, in parallel with tension measurement at the anchor points. The main objective of this study is to provide experimental measured data to validate numerical software on the research of mooring line motions.
A free decay test has been carried out to confirm the spar platform motions natural frequencies and damping characteristics. The platform was then subjected to a range of regular and irregular waves to obtain the motion characteristics of the platform and the mooring lines. For the mooring line motions, which has rarely been discussed in published research, a non-linear snatching phenomenon has been observed at the tank for some wave frequencies. This non-linear behaviour shows that snatching leads to the high instantaneous mooring line tensions and platform accelerations could cause the failure of the mooring lines in the real structure.
•The mooring line motion has been measured at certain locations in the tank tests.•A potentially harmful and highly non-linear “snatching” phenomenon was observed.•The non-linear snatching disappears at the platform heave/pitch natural frequencies.•Dynamic responses of the spar platform are investigated under various wave loads.
This paper discusses a new installation method for floating offshore wind with installation procedure, essential variables, and fender system effects on the dynamic responses. The conventional ...installation method involves mating wind turbines and substructures in calm and protected waters and towing the assembled units to an operating site. Due to geographical, time, and economic disadvantages, this method may be challenging to meet the rapidly surging demand for floating wind power worldwide. The new onsite installation method was introduced as an alternative, using a catamaran to install fully assembled wind turbines at the operation site. The proposed concept can be employed to install and maintain fixed and floating offshore wind turbines in any location. While the conventional installation method consists of a series of installation processes, the proposed installation steps can be performed in parallel, suggesting more flexible operation planning. Fenders and wires were applied as a mechanical coupling system to enable onsite installation in harsh offshore environments. The fender system with pretensions on wires showed reduction effects on the relative horizontal displacement, relative vertical displacement, and relative alignment by approximately 78%, 64%, and 32%, respectively. Therefore, the fender system application can significantly increase the practicality of the onsite installation method.
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•Novel onsite installation concept for floating offshore wind turbines is presented.•Benefits in the scheduling of the new installation procedure are discussed.•Expected challenges during the installation operation are investigated.•Critical responses of the installation concept are identified.•Feasibility and effects of applying the fender system are evaluated.
Risks associated with deepwater drilling are dynamic because of various accident-causing factors such as equipment failures, abnormal processes, and operator errors. All these factors should be ...considered during the implementation of dynamic and quantitative risk assessment (DQRA) for drilling operations. Dynamic Bayesian network (DBN) can graphically present the cause-effect relationships among different types of risk influencing factors (RIFs). Hence, this study developed a four-step DBN model for the DQRA of deepwater drilling. Firstly, multi-type contributing RIFs were identified according to the process flow. Subsequently, a network structure was developed to present the potential accident scenarios and capture the interdependencies among the RIFs. Thereafter, the probabilities of equipment failures, abnormal processes, and operator errors were determined using the probabilistic, data-based, and Standardized Plant Analysis Risk—Human Reliability Analysis (SPAR-H) approach, respectively. Finally, DBN inference was performed to evaluate the probabilistic risk of drilling operations. The model was applied to a case study of DQRA for managed pressure drilling (MPD), where the calculated initial blowout probability was 9.30 × 10−5, whereafter it was updated dynamically. This case study demonstrates the practicability of the proposed approach. This study contributes to a systematic investigation of the role of multisource data in DQRA using a full DBN approach. The assessment results can provide early warnings for practitioners to implement risk elimination or mitigation measures in real time.
•A dynamic Bayesian network model is proposed to quantitatively assess deepwater drilling risks.•Probability distribution function is used to calculate equipment failure probabilities.•Data-based approach is used to deal with abnormal process probabilities.•SPAR-H is used to evaluate operator error probabilities.
The integrated installation method for offshore wind turbines has the characteristics of high efficiency and low economic cost due to the small amount of construction work. However, the complexity of ...the entire system is exacerbated by environmental loads and mechanical couplings. Hence, it is urgent to investigate the dynamic response of OWTs during integrated installation procedures. This work compares the dynamic responses between NREL 5 MW and IEA 15 MW OWT installation systems. The hydrodynamics are calculated using the potential flow theory and the Morison equation, while the aerodynamics under wind turbine parked conditions are computed using the blade element momentum theory. Time domain simulations, considering various wind and wave conditions, are conducted via SIMA. This paper discusses the effects of wind and wave loads on the motion responses of catamaran installation vessel and spar, the relative motion at the mating point, and the sliding gripper forces, respectively. The results reveal that both the surge motions of the catamaran and the spar and the pitch motion of the spar exhibit sensitivity to wind loads. During installation, the motion response of the IEA 15 MW model is more dramatic than that of the NREL 5 MW system. Under wave-only conditions, the radial distances of the mating points for both NREL 5 MW and IEA 15 MW systems reach 1.65 m and 2.51 m, respectively. However, the influences of wind loads and wave incident angle are limited.
•A spar-type foundation is designed for the IEA 15 MW offshore wind turbine.•A numerical model for a floating wind turbine installation process is established.•Dynamic responses of two OWTs during integrated installation process are compared.•The relative motion of the mating point is sensitive to wave height.
•Ash resulting from severe fire episode reduces raindrop impact on soil aggregates.•Management, vegetation regrowth and soil chemistry decrease soil aggregate stability.•Intense rainfall on ...fire-affected soils does not affect soil TN and TC levels.•Intense rainfall increases cations, phosphorous and SPAR in soil solution.
Intense rainfall events after severe wildfires can have an impact on soil properties, above all in the Mediterranean environment. This study seeks to examine the immediate impact and the effect after a year of an intense rainfall event on a Mediterranean forest affected by a high severity wildfire. The work analyses the following soil properties: soil aggregate stability, total nitrogen, total carbon, organic and inorganic carbon, the C/N ratio, carbonates, pH, electrical conductivity, extractable calcium, magnesium, sodium, potassium, available phosphorous and the sodium and potassium adsorption ratio (SPAR). We sampled soils in the burned area before, immediately after and one year after the rainfall event. The results showed that the intense rainfall event did not have an immediate impact on soil aggregate stability, but a significant difference was recorded one year after. The intense precipitation did not result in any significant changes in soil total nitrogen, total carbon, inorganic carbon, the C/N ratio and carbonates during the study period. Differences were only registered in soil organic carbon. The soil organic carbon content was significantly higher after the rainfall than in the other sampling dates. The rainfall event did increase soil pH, electrical conductivity, major cations, available phosphorous and the SPAR. One year after the fire, a significant decrease in soil aggregate stability was observed that can be attributed to high SPAR levels and human intervention, while the reduction in extractable elements can be attributed to soil leaching and vegetation consumption. Overall, the intense rainfall event, other post-fire rainfall events and human intervention did not have a detrimental impact on soil properties in all probability owing to the flat plot topography.
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Several floating wind turbine designs whose hull designs reflect those used in offshore petroleum industry have emerged as leading candidates for the future development of offshore wind farms. This ...article presents the research findings from a model basin test program that investigated the dynamic response of a 1:50 scale model OC3 spar floating wind turbine concept designed for a water depth of 200 m. In this study the rotor was allowed to rotate freely with the wind speed and this approach eliminated some of the undesirable effects of controlling wind turbine rotational speed that were observed in earlier studies. The quality of the wind field developed by an array of fans was investigated as to its uniformity and turbulence intensity. Additional calibration tests were performed to characterize various components that included establishing the baseline wind turbine tower frequencies, stiffness of the delta type mooring system and free decay response behaviour. The assembled system was then studied under a sequence of wind and irregular wave scenarios to reveal the nature of the coupled response behaviour. The wind loads were found to have an obvious influence on the surge, heave and pitch behaviour of the spar wind turbine system. It was observed from the experimental measurements that bending moment at the top of the support tower is dominated by the 1P oscillation component and somewhat influenced by the incoming wave. Further it was determined that the axial rotor thrust and tower-top shear force have similar dynamic characteristics both dominated by tower’s first mode of vibration under wind-only condition while dominated by the incident wave field when experiencing wind-wave loading. The tensions measured in the mooring lines resulting from either wave or wind-wave excitations were influenced by the surge/pitch and heave couplings and the wind loads were found to have a clear influence on the dynamic responses of the mooring system.
•The gyroscopic effects of rotor rotation on yaw motion and the coupled response behaviours of surge, pitch and heave are investigated through model testing method.•The response characteristics of primary turbine loads and the suppression effect of aerodynamic loads on motions are analysed.•The mooring system response behaviours are studied and discussed.
Multi-rotor floating offshore wind turbines have been recently proposed as an innovative technology to further reduce the cost of offshore wind energy. Even though examples of commercial prototypes ...are present, the literature lacks studies on the dynamic performance of such systems. This work presents a comparative analysis of a two-rotor wind turbine concept mounted on spar-type, semi-submersible, and tension-leg platforms. Their short-term performance is assessed by considering six different load cases considering directionally congruent turbulent wind profiles and irregular sea states. The analysis is carried out through an in-house fully-coupled code developed in Modelica. AeroDyn v15 within FAST v8 by NREL is coupled to the Modelica code to achieve blade-element momentum capabilities. Results indicate that platform yaw motion is an important dynamic mode of the systems, particularly for the spar configuration. Stiffer station-keeping lines and longer fairlead distance to the platform centerline reduce significantly yaw motion, as in the case of the semi-submersible and tension-leg configurations. Large tower base bending moment standard deviations and the associated concentration of energy at the platform heave and pitch motion frequencies indicate an increased risk for fatigue damage for the TLP configuration, especially at above-rated wind speeds. Moreover, large tendon loads can pose concerns in terms of fatigue and limit state performance. Large mean platform pitch angle and yaw standard deviation contribute to the reduction of electric power output quality. Extreme storm conditions greatly increase the response standard deviation, especially for the semi-submersible configuration.
•Dynamic analysis of two-rotor wind turbine mounted on spar, semi-submersible, and TLP floating platforms.•Platform yaw motion significant dynamic mode for each system.•Platform yaw motion is particularly high for spar-type floating platforms given lower yaw stiffness and shorter fairlead distance from the centerline.•For TLP platform, large tendon loads and tower base bending moment STD indicate an increased risk for fatigue damage.•Extreme storm conditions increase the response STD, especially for the semi-submersible platform.
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