A comprehensive study on spar with curved neck profile with a heave plate near the surface is made to assess the effect of geometry and location of heave plate on heave damping. A CFD-based approach ...is adopted to extract the damping and added mass by tracing the heave decay, and the results are validated with those from experiments. Free heave decay tests are conducted on scaled spar models (1:100 scale) in calm water and the results compare reasonably well with that obtained from the numerical model. The experiments conducted for heave motion response indicate a reduction in heave response at resonance. In addition, the effects of heave plate diameter ratio (1-2) and heave plate position to draft ratio (0-0.9) on the heave damping of buoy form spar have been studied numerically to identify the most favorable configuration in terms of heave damping.
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Understanding the complex and dynamic nature of calcite surfaces under ambient conditions is important for optimizing industrial applications. It is essential to identify processes, ...their reversibility, and the relevant properties of CaCO3 solid-liquid and solid-gas interfaces under different environmental conditions, such as at increased relative humidity (RH). This work elucidates changes in surface properties on freshly cleaved calcite (topography, wettability and surface forces) as a function of time (≤28 h) at controlled humidity (≤3–95 %RH) and temperature (25.5 °C), evaluated with atomic force microscopy (AFM) and contact angle techniques. In the presence of humidity, the wettability decreased, liquid water capillary forces dominated over van der Waals forces, and surface domains, such as hillocks, height about 7.0 Å, and trenches, depth about −3.5 Å, appeared and grew primarily in lateral dimensions. Hillocks demonstrated lower adhesion and higher deformation in AFM experiments. We propose that the growing surface domains were formed by ion dissolution and diffusion followed by formation of hydrated salt of CaCO3. Upon drying, the height of the hillocks decreased by about 50% suggesting their alteration into dehydrated or less hydrated CaCO3. However, the process was not entirely reversible and crystallization of new domains continued at a reduced rate.
Currently, there is a rapid demand for the development of floating offshore wind turbines (FOWTs) for deployment in sites with deep water depths. FOWTs are highly complex structures that are ...subjected to combined loading from wind, hydrodynamic, hydrostatic, and mooring loads, and these loads have a significant influence on their dynamic behavior. The complexity of such a multi-body system makes the dynamic analysis considerably challenging and demands an efficient model to capture the physical characteristics of the system accurately. This paper proposes a novel framework for modeling floating offshore wind turbines (FOWTs) based on the vector form intrinsic finite element (VFIFE) method. In this framework, the multi-body dynamics (MBD) is used to handle the rigid body motion, and the analysis of structural deformation and the solution of governing equation of motions (EOMs) is implemented based on the VFIFE method. The methodology considers the FOWT as two rigid bodies: (a) the tower, which is a structural assembly of platform and nacelle; and (b) the rotor that can mechanically rotate relative to the nacelle. Further, a dynamic and flexible model of the mooring system is included, and their axial extension, inertia, and hydrodynamic loads are considered. The EOMs of the FOWT and mooring system are derived by the Newton-Euler (NE) and Newton's second law, respectively and the central difference scheme is implemented to solve the EOMs. Finally, the developed model is subjected to different load cases under the combined action of wind and waves, and the responses of platform motion and the axial tension of the mooring system are calculated and verified against the FAST. After thorough verification of the VFIFE model which showed excellent agreement with FAST results, the proposed model is used (a) to highlight the variations caused by neglecting the dynamic of the mooring system where the results are compared with the quasi-static mooring model developed using the MAP++ module in FAST, and (b) reveal the coupled mechanism of the platform pitch and yaw motion when the rotor is spinning.
•A novel framework was proposed for modeling FOWTs using the vector form intrinsic finite element (VFIFE) method.•The multibody dynamics (MBD) and the VFIFE method were used to handle the rigid body motion and the structural deformation.•The mooring dynamics was considered, and the mooring tension calculated by VFIFE model was found in good agreement with FAST results.•The gyroscopic moments from rotor spin were considered, and the coupled mechanism of platform pitch and yaw was revealed.
•A floating absorber is devised for floating wind turbine pitch mitigation.•The floating absorber does not cause dead load on the wind turbine.•The mass of the floating absorber may be chosen ...suitably large.•The floating absorber is tuned by a fixed point theory adapted to MDOF absorbers.•Pitch reductions of almost 30% are achieved for some load conditions in time domain.
This paper proposes the innovative concept of floating absorber for motion mitigation in floating wind turbines on spar supports. The floating absorber consists in a spar floater coupled with the floating wind turbine by an elastic spring and a viscous damper in parallel. It is conceived to act as a resonant mass tuned to the pitch frequency of the floating wind turbine and, for this purpose, its parameters are calibrated based on the well-established fixed point tuning procedure typically applied for tuned mass dampers. For validation, extensive time-domain numerical simulations are performed on a multi-degree-of-freedom computational model of the coupled system, considering thirty-six different configurations of the floating absorber and fifteen different combinations of wind-wave conditions. The results demonstrate a considerable effectiveness of the floating absorber in reducing the pitch motion of the floating wind turbine. A main advantage over conventional tuned mass devices is that the absorber is not housed in the nacelle of the wind turbine but floats close to the floating wind turbine. This not only ensures reduced costs of installation and maintenance of the floating absorber but allows, also, to increase its mass without causing extra weight on the floating wind turbine, exploiting hydrodynamic added mass as well, with consequent benefits in terms of motion mitigation in the floating wind turbine. Another relevant result is that, for a given mass of the floating absorber and a given attachment point of the parallel spring-dashpot, the performances of the floating absorber do not vary significantly with its geometry. This is important to facilitate design and manufacturing of the floating absorber, confirming the robustness of the proposed concept and its great potential for motion mitigation in floating wind turbines.
Emergency preparedness is of paramount importance in successful emergency responses at sea. Therefore, emergency drills are regularly conducted to maintain acceptable levels of emergency ...preparedness. However, it needs to be considered that emergency drill operations themselves include significant risks, and there is no evidence that these risks are appropriately considered when planning emergency drill operations. Human error is one of the main contributors of accidents during emergency drill procedures. The main question posed is how overall risk, including human errors, during an emergency drill can be correctly evaluated. This paper introduces a new hybrid approach based on the Standardised Plant Analysis Risk Human Reliability Analysis (SPAR-H) method with a fuzzy multiple attributive group decision-making method. The method provides a framework for evaluating specific scenarios associated with human errors and identifies contributors that affect human performance. Estimated human errors are utilised to assess human reliability using a new approach based on a system reliability block diagram. The rescue boat drill procedure for a man overboard is selected to illustrate the method. The findings of this research show each human error probability and its contributing factors per task. As a result, overall reliability of 6.06E-01 was obtained for rescue boat drill operation.
•This method provides the SPAR-H based framework to assess human reliability with a scenario-oriented approach.•This paper proposes a new approach for human reliability which is assessed through a customised reliability block diagram.•This method enables to evaluate the impact of specific characteristics of maritime operations on human performance.•This method elicits the possibility of quantitative human failure through the input of qualitative multiple experts.
Applications including the offshore aquaculture, remotely operated vehicles, data acquisition systems, and desalination can be either supplemented or completely powered by renewable energy. The ...spar-buoy oscillating-water-column wave energy converter concept, typically studied for large scale wave energy production, can be re-designed to meet the power requirements of such applications, which results in a much smaller device working outside resonance conditions under typical sea states, and therefore with a smaller energy conversion efficiency. Experimental results are presented for a 1:10th scale model of a spar-buoy oscillating-water-column, undertaken in a wave channel. Calibrated orifice plates were used to model the flow characteristic of an impulse turbine, which will be used in the full-scale system. The system performance is examined for regular and irregular wave conditions. The results show the presence of non-linear effects, caused by viscous flow and turbine damping. A capture width ratio matrix is generated through stochastic modelling using regular-wave data and the performance of the device is assessed for two locations with different wave energy resource. The device presents an annual-averaged power of approximately 1kW for an Atlantic wave climate, and an annual-averaged power of approximately 0.4kW for a Mediterranean wave climate, which makes it adequate for the supply of specific oceanographic equipment in the first location, while for the second location a larger buoy should be considered.
•A wave energy converter model for low-power applications was tested experimentally.•Power matrix generated using a stochastic model and regular-wave experimental data.•The performance of the device was assessed for two sites with different resource.•The studied device can power oceanographic equipment in the Atlantic Ocean.
As the siting of wind turbines increasingly transitions from shallow water to offshore deep-water locations, improving the platform stability of floating offshore wind turbines is becoming a growing ...concern. By coupling a porous shell commonly used in traditional marine structures, with a FOWT (floating wind turbine platform), a new spar-buoy with a porous shell was designed. A numerical model investigating the coupling effect of the aero-hydro-mooring system is developed, and the results of the motion response are compared with the OC3-Hywind spar. The motion response of the two platforms was simulated in the time-domain with the incident wave period varied in the range of 5~22 s. The exciting wave force with added mass and radiation damping of the spar with the porous shell is compared with the OC3-Hywind spar. The results demonstrate that the motion response amplitude of the spar with the porous shell decreases in all three main motion freedoms (i.e., surge, heave and pitch, etc.), among which the heave motions are most significantly attenuated. The study shows that the coupling of porous shells with a floating platform to achieve the reduced motion responses is feasible and can be an innovative structure for the development of deep-sea offshore floating wind turbines.
Networks of coordinated alternative splicing (AS) events play critical roles in development and disease. However, a comprehensive knowledge of the factors that regulate these networks is lacking. We ...describe a high-throughput system for systematically linking trans-acting factors to endogenous RNA regulatory events. Using this system, we identify hundreds of factors associated with diverse regulatory layers that positively or negatively control AS events linked to cell fate. Remarkably, more than one-third of the regulators are transcription factors. Further analyses of the zinc finger protein Zfp871 and BTB/POZ domain transcription factor Nacc1, which regulate neural and stem cell AS programs, respectively, reveal roles in controlling the expression of specific splicing regulators. Surprisingly, these proteins also appear to regulate target AS programs via binding RNA. Our results thus uncover a large “missing cache” of splicing regulators among annotated transcription factors, some of which dually regulate AS through direct and indirect mechanisms.
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•SPAR-seq is a versatile method for elucidating endogenous RNA regulatory networks•Hundreds of trans-acting factors control ES and neural splicing networks•SPAR-seq defines positive and negative functional and physical interrelationships•Transcription factors have dual direct and indirect roles in splicing regulation
Han, Braunschweig et al. describe SPAR-seq, a strategy for the systematic elucidation of endogenous RNA regulatory networks. Hundreds of factors controlling cell-fate-associated splicing networks are defined, among which are transcription factors that have dual direct and indirect regulatory roles.
•Dynamic modeling of a fault arc burning in air occurring on overhead transmission lines and its numerical simulation in time-domain using an electromagnetic transients program.•Determination of the ...secondary arc duration in case of a single-phase autoreclosure on EHV transmission systems.•Influence of various factors on mixed transmission lines consisting of several overhead line and underground cable sections compensated by shunt reactors.
The transmission system expansion plan of Germany foresees several new EHV (Extra High Voltage) transmission lines to transmit bulk power generated by wind farms in the north of Germany to the South. Some of these EHV lines will be so called "mixed lines" consisting of several underground cable and overhead line sections. The high charging current of XLPE cables has to be compensated by shunt reactors. A planned double-circuit 380 kV transmission line with total length of ca. 110 km is of interest for the analysis of SPAR (single-phase autoreclosure) operation in this paper, where a cable section along the line has a length of 5.5 km. By means of electromagnetic transients simulations the maximum secondary arc duration will be determined for the mixed line under various operating conditions.
The quest for exploiting the ocean resources and understanding its behaviour has been a challenge with increasing needs for innovation and technology. Model testing is an essential step in offshore ...renewable energy technology development. It involves challenges that require experience and guidance. Costly mistakes might arise with the subsequent waste of time and resources. This paper presents the model design and testing processes as part of wave energy projects and the results of experimental testing of two types of oscillating-water-column (OWC) wave energy converters (WEC). The model design aims at the creation of a reduced-scale model to simulate the physical phenomena found in full-scale devices. It is a process that requires several skills and an adequate compromise among all variables. This design involves several approaches as different physical phenomena do not follow the same similarity conditions, requiring adjustments in scale, materials, and other relevant properties. Besides, the model testing process comprises the necessary planning and actions to execute the tests and post-processing of data. This process is addressed here through model design and testing of two WECs: the coaxial-duct and the spar-buoy OWCs. The configurations have been designed and studied for large-scale energy production and small-scale power in oceanographic applications. Although the devices are both OWCs, the designs exhibit significant differences. The development process of the models and results are presented for the two OWC devices. Free-decay tests, hydrodynamic performance and mooring tension results are presented and discussed. These may serve as guidelines and numerical modelling validation.
•Wave energy converters model design and testing processes are addressed.•Physical model conception and verification are discussed.•The methodology is illustrated with two floating oscillating-water-columns devices.•Experimental results were obtained for regular and irregular waves.•Mooring loads were measured under survivability testing conditions.
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