Pitching mode is more crucial than heaving mode in assessing floating offshore wind turbine (FOWT) motion characteristics, especially the operation of the SPAR substructure. The aim of this paper is ...to develop an experimental method for improving the SPAR substructure to minimize unnecessary pitch motion. Toward this end, three vertical plate configurations based on the novel SPAR are being developed, known as the 3VP, 4VP, and 5VP models. In consideration of 0⁰, 30⁰, 60⁰, 90⁰-incidence, the pitch response characteristics of the proposed novel SPAR models are comprehensively evaluated in terms of submerged volume ratio, wave-induced motion, non-dimensional damping coefficient, and percentage of motion reduction. The model test results indicate that the 4VP model outperforms the other novel models with respect to dynamic response, particularly the incidence of 0⁰ and 90⁰. This study implies that the novel SPAR development is both feasible and effective in the modification of SPAR-type FOWT substructures.
The Hybrid Cell-Truss Spar Buoy Platform, a relatively new technology for floating structures, is studied for the Andaman Sea, that has deeper water and fault line on the seabed, despite the dominant ...shallow water in Southeast Asian region. This innovative Spar Buoy Platform offers many advantages, such as lower construction cost (CAPEX), a reuse option after service life, lower decommissioning costs and is suitable for use in marginal fields. This research studies three prototype models: Mono Cell-Truss Spar, Three- and Four-Cells-Truss Spar Platforms for water depths of 200m, 400m and 600m, which are subjected to a 10-year and 100-year return period sea-states. The study is focused on hydrostatic stability for stationary keeping systems; while mooring analysis, hydrodynamic analysis and analysis of the structural strength of the platform are conducted as usual in design stage. The dynamic response analyses are conducted in time domain for assessing the serviceability performance of the models. Conclusively, all prototype Spar Platforms are suitable for operation in the Andaman Sea. Nevertheless, the Hybrid Cell-Truss Spar Platforms with three cells-trusses and four cells-trusses will perform with more stability and with lower dynamic responses than that of the Mono Cell-Truss Spar Buoy Platform.
•This paper introduces the innovative Hybrid Cell-truss Spar buoy platform to improve platform dynamic stability performance.•These kinds of floating structures were investigatedon their suitability for application in moderate water depthat Andaman Sea which is not longer economical for on-bottom founded platforms.•All prototype Hybrid Cell-truss Spar buoy platforms meet the design code requirements.•The four cell truss spar shows its superior performance to other two Spar buoy platforms.
As one of the most important reasons of irreparable losses at work, human error is still a significant problem in spite of the rapid technological advancement and reduced role of humans in the ...systems set up and control. Therefore, with the aim of reducing human error, this study presents a new method to improve human reliability using the hybrid approach of SPAR‐H and DSM. For this purpose, the number of 53 tasks was specified for the terminal conductor using Hierarchical Task Analysis (HTA). Then, the error related to each task was calculated utilizing the Standardized Plant Analysis‐Risk Human (SPAR‐H) method, and based on the expert team's opinion. Next, the terminal conductor's tasks were entered into the DSM along with the error numbers and dependencies between tasks, and the most optimal arrangement of tasks was obtained by coding in MATLAB software. Finally, by using the SPAR‐H method, the error of the terminal conductor was calculated based on the new tasks arrangement and compared with the primary state. Based on the obtained results, the 30% increase in reliability shows the significant contribution of the optimal arrangement of tasks in reducing human error. The proposed method of this study helps managers to reviewing the task structure in high‐risk processes as an effective strategy to reduce human error.
Stability of the platform is the most fundamental guarantee for floating offshore wind turbines. In order to explore hydrodynamics of floating wind turbine Spar platform under the coupling effect of ...wind and wave, whole model of floating wind turbine is established based on the OC3-Hywind Spar Buoy platform and the NREL 5 MW wind turbine. Taking the research experiences of traditional marine engineering, this work proposed the structural design method of installing heave plate on main body of Spar. Based on the Bladed Element Momentum theory, this paper adopts FORTRAN language to accomplish the secondary development of hydrodynamic software AQWA to establish the coupled aerodynamic - hydrodynamic - mooring line system model. The amplitude-frequency curves of the added mass, radiation damping, wave exciting force and response amplitude operators (RAO) were obtained based on radiation/diffraction theory to investigate the hydrodynamic performance of floating wind turbine Spar platform in frequency domain. In the time-domain analysis, the three kinds of working conditions include wave-only, non-coupling effect of wind-wave and coupling effect of wind-wave were conducted comparatively to verify the importance of wind load and wind - wave interaction. In addition, the actual motions of original Spar and Spar with heave plates were analyzed to explore the effects of the heave plate and its installation position on the nonlinear dynamic response characteristics of Spar under the coupling effect of wind and wave. The research results indicated that the installation position of the heave plate has little influence on the surge response. In view of the actual heave motion, the heave plate can play a positive effect no matter where the heave plate is installed. When the heave plate is located on the upper part of the platform, the pitch response and the intensity of the fluctuation of the platform will be greatly reduced. Finally, time domain mooring analysis for Spar platform with and without heave plate is performed to illustrate the feasibility of the present approach for mooring modeling.
•A coupled aerodynamic - hydrodynamic - mooring line system model was established based on a secondary development of AQWA.•The coupling effect of wind and wave was considered and its importance was verified.•The effects of heave plate and its installation position on the dynamic response of floating wind turbine were investigated.
In this paper, a contribution to the analysis of electromagnetic ac to dc interactions in complex ac/dc hybrid overhead lines was made. For accurate calculation of such coupling, standard ...transformations like the symmetrical components cannot be used. Therefore, a method based on adjusted modal decomposition was presented, which allows analysis of untransposed and partly transposed configurations in arbitrary switching states. The method was applied to the case of dc fault clearing using single-pole auto reclosing (dc SPAR), where parallel ac circuits could induce a secondary arc in the dc line. The magnitude of the secondary arc current was examined, which allows evaluating the necessary dead time of the dc SPAR. The influence of parameters like line configuration, load flow, and fault location was discussed. After that, a realistic study case hybrid line was analyzed. In particular, the comparison to secondary arcs in ac lines and the behavior as a function of fault location in the context of changing ac systems and line configurations along the hybrid dc corridor provide new insights into a relevant phenomenon.
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.
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