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RSS2023 Vol. 10, No. 1
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2023, 10(1): 1-12.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.001
Abstract:
Introduction Most of the completed offshore wind farms in the world are located in shallow water (water depth < 30 m), mainly based on fixed foundations such as monopiles. With the increasingly mature wind power technology, offshore wind power gradually shifts towards the trend of large unit, and the foundation diameter of single-pile offshore wind turbines will also increase as the wind turbine become larger. The environmental loads and soil conditions are becoming more and more stringent. The study on pile-soil interaction of large-diameter monopile offshore wind turbines has become one of the key technical issues of offshore wind power technology. Method The impact of different pile-soil models on the dynamic response of large monopile offshore wind turbines in shallow water areas with 10 MW large offshore wind turbines was studied. Result The results show that the macro element method considers the nonlinear stiffness and plasticity, thus the sum of power spectral density near the characteristic frequency of the macro element method is large, which demonstrates the great advantages of the macro element method over other traditional pile-soil models. Conclusion The study of this paper has far-reaching theoretical value and engineering application prospects for the overall safe operation of wind turbine.
2023, 10(1): 13-20.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.002
Abstract:
Introduction Offshore wind power has become a research hotspot in the development of global wind power. China's offshore wind power is still in its infancy, the current operation mode is not conducive to the large-scale centralized transmission of offshore wind power and cannot adapt to the long-term development under the new situation. Moreover, the subsidy policies of European countries for offshore wind power conflict with China's development ideas, so they cannot be used for reference, and there are still some disadvantages in the European modes. Therefore, it is necessary to explore a new mode suitable for the development of offshore wind power in China's offshore deep-water areas. Method Firstly, the development status of offshore wind power in European countries was analyzed and the current transmission modes of offshore wind power were summarized. Secondly, four application scenarios of offshore wind power transmission technology were given. Finally, the feasibility of offshore wind power business model was analyzed. Result The results show that the connection to grid at an equal price is expected to be achieved in Guangdong during the 14th Five-Year Plan period after the separation of offshore wind power generation and transmission side links. The centralized development of offshore wind power in deep-water areas is more feasible for economy and environmental intensive utilization compared with the decentralized development. Conclusion The research conclusion can provide technical support for the scheme design and construction mode of the follow-up large-scale offshore wind power centralized transmission project and has a good demonstration application prospect.
2023, 10(1): 21-28.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.003
Abstract:
Introduction The purpose of this paper is to study the influence of real "wake effect" of adjacent offshore wind farms on generation loss. Method The method is established with the wake scene classification based on the actual arrangement of wind farms under different wind direction and the real wake power loss of adjacent wind farms (with a spacing of more than 20D) in operation are analyzed, based on the actual SCADA data of wind turbines in large offshore wind farms and the measured wind data of LIDAR in the same period. Result The results show that: for the large-scale offshore wind farms with regular arrangement, the power generation normalization of the actual SCADA data can better reflect the distribution characteristics of offshore wind energy resources and the difference of power generation capacity; Under the condition of highly centralized wind direction, the adjacent wind farms in the downwind are obviously affected by the "wake effect" of the upwind wind farm; The buffer zones with different distances of adjacent wind farms have an obvious effect on the recovery of wind speed which affected the power generating capacity. The power generating capacity can be improved but if the buffer zone can reach enough distance; In different scenes of this case, the buffer zone distance is between 23D and 44D, and the power loss of wake decreases by 27%~4%. Conclusion This work can provide guidance for the planning of offshore wind power base and the optimization design of large offshore wind frams.
2023, 10(1): 29-38.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.004
Abstract:
Introduction In order to accurately forecast the wind direction in the next 4 hours, a very short-term wind direction multistep forecast algorithm based on VMD-LSTM（Variational Mode Decomposition-Long Short-Term Memory） is proposed. Method Wind direction sequence was collected from 3 wind turbines of a wind farm of Mingyang Smart Energy Group for preprocessing and analysis. The correlation of wind direction in different periods was calculated using the autocorrelation function (ACF) to select the characteristic length of wind direction sequence. Based on variational mode decomposition (VMD), the wind direction sequence was decomposed into relatively intrinsic mode functions, the number of which was determined by minimum sample entropy. Models were build for each intrinsic mode function to make very short-term wind direction 24-step forecast. Finally, the wind direction sequence was reconstructed from the forecasted intrinsic mode functions. Result The results obtained demonstrate that the average MAE（Mean Absolute Error）, RMSE（Root Mean Square Error） and MAPE（Mean Absolute Percentage Error） of the 24-step wind direction forecast based on VMD-LSTM in 4 quarters are 8.430°, 16.870° and 9.155, respectively. The algorithm performs better than other common data modeling methods regarding each error evaluation index at different time scales in each quarter. Conclusion The proposed algorithm can optimize the control yaw angle in the actual production of wind farms.
2023, 10(1): 39-47.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.005
Abstract:
Introduction To reduce fossil energy consumption and mitigate environmental pollution, offshore wind power is one of the effective ways to solve the problem. However, there are some problems in offshore wind power, such as strong intermittency, large volatility and bidirectional peak shaving. Therefore, it is of great significance to study the output characteristic curve of offshore wind power. Method In this paper, a Gaussian Mixture Model (GMM) based on Bayesian Information Criterion was proposed. The original output curve of offshore wind power was classified and the characteristic curve was extracted. Result The characteristic curve of offshore wind power which can reflect the characteristics of different wind areas is obtained, and it is applied to the calculation of electric quantity balance of offshore wind power output. Conclusion At last, the effectiveness of the proposed method is verified by taking the original offshore wind power output curves of different sea wind areas under the installed capacity of 15 GW of offshore wind power in a coastal province as the research object.
2023, 10(1): 48-56.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.006
Abstract:
Introduction The spudcan foundation is the key structure of the mobile jack-up platform, which displaces surrounding soil during its penetrating installation. In order to ensure the safety in the application of mobile jack-up platform to the offshore wind power installation works, it is particularly important to research the evolution of surrounding soil flow mechanism during spudcan penetration, and to evaluate the penetration resistance of spudcan reliably. Method The coupling Euler-Lagrange (CEL) method was used in this research to simualte the process of spudcan penetration under several typical seabed geological conditions (homogeneous and heterogeneous clay, sand, "clay-sand-clay" and "clay (hard)-sand (soft) and clay (hard)"), and to analyze the differences of penetration mechanisms. Result The simulation results show that in the process of spudcan penetration, the soil flow mechanism and penetration resistance of spudcan are closely related to the strength characteristics of seabed soil, while the friction coefficient of the interface between spudcan and seabed soil has little effect on the penetration mechanism and resistance. Conclusion From comparision with the results calculated in accordance current design specifications, the method combining large deformation finite element analysis and industry code design should be recommended to be applied in engineering design practice, as to provide a better basis for the assessment of punch-through risk and the prediction of penetrating depth in the process of spudcan penetration.
2023, 10(1): 57-63.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.007
Abstract:
Introduction The connection between offshore wind turbine foundation and superstructure is usually made by grouting. It is crucial to ensure the safety of the grouted connections, and the study of grouted connections is always a key and difficult point. Methods A review of relevant mechanical studies on grouted connections of offshore wind turbines was conducted. The basic mechanical properties of grouted materials for offshore wind turbines were described. The force mechanism of grouted connections and the factors affecting the bearing capacity were summarized, and the existing code design and future research directions were described. Result The grouted connection has severe requirements for the use of grouting materials. Therefore, the high-strength grout needs to be used. Under axial compression, the grouted connections usually exhibit a ductile damage mode of the compression struts. The bearing capacity of grouted connections is mainly influenced by the radial stiffness of grouted connections, the height-to-spacing ratio of shear keys, the shape of shear keys, the length-to-diameter ratio of grouted connections and the strength of grouting materials. The relevant design codes have clear design methods for the design of ultimate bearing capacity, but there are few studies and imperfections in fatigue design. Conclusion Therefore, it is necessary to further research the fatigue performance of grouted connections submerged in water. Moreover, it is necessary to use full-scale or small-scale specimens in future experimental studies, and refined numerical models need to be used for analysis in numerical studies.
2023, 10(1): 64-71.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.008
Abstract:
Introduction This paper adoptes the methods based on parametric study and CPT in-situ test for analysis and calculation, the preliminary analysis is carried out according to the actual construction data. By doing this, the self-weight penetration of monopiles can be better and faster predicted and the risks in monopile installation are significantly reduced. Method Modified the design input parameters by API recommended pile capacity theory, combined with error analysis, the predicted self-weight penetration was compared to the real data on site. Result The analysis results show that there is a great difference in prediction of self-weight penetration due to the different reduction strength coefficient \begin{document}$ {S}_{\mathrm{r}} $\end{document} ![]()
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Conclusion Through comparative analysis, the value range of clay strength reduction coefficient \begin{document}$ {S}_{\mathrm{r}} $\end{document} ![]()
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2023, 10(1): 72-80.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.009
Abstract:
Introduction Under the wave-current combinations during the service period of offshore wind turbine, local scour inevitably occurs around pile foundation, which threatens the overall stability and safety of offshore wind turbine. Method In this paper, the normal physical model test at a scale of 1∶30 was carried out for the wind power foundation with a diameter of 8.0 m to study the scour depth, sand cover, solidified soil protection range, and protection effect. Result The results show that due to the good hydrodynamic conditions considered in this test, the maximum scour depth is 0.133 cm. In this case, the 1 cm-thick sand cover with a splicing size of 1.0 m×1.0 m can meet the stability requirements. When solidified soil is adopted for protection, the protection range shall not be less than 5 times the pile diameter, and block stones shall be laid at the edge of solidified soil to avoid scouring at the lower part of solidified soil. Conclusion The test results can provide reference for scouring test and engineering design of similar projects.
2023, 10(1): 81-87.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.010
Abstract:
Introduction Scouring around pile foundation is an important technical problem in the construction and maintenance of offshore wind power plants. The scour hole developed under the environmental load like wave, current, etc. would reduce the stability of pile-soil structure and cause a non-negligible impact on the safety of the whole structure. Method In this paper, CFD technique combined with sand transport model were employed, scour around cylinder pile in sandy seabed under steady current was numerically simulated and studied by solving the nonlinear coupling equations of flow and scour, the development process of scour hole around pile was observed, and the time-varying curve of scour depth was obtained. Result The computing results show that the scour depth increases rapidly at the beginning of scouring, and then the process slows down gradually. In the calculation time of 16 minutes, the scour depth grows to 0.81 times the pile diameter. Conclusion According to the development of scour depth, it is suggested that for the wind farm located in sandy seabed aera, scour protection should be considered during the construction period, and the methods such as increasing the protective structures are recommended to prevent scour forming and extending.
2023, 10(1): 88-97.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.011
Abstract:
Introduction The purpose is to study the influence of tidal current and wave on the sub-aqueous foundation of wind turbine in offshore wind farm. Method Through two seabed topography surveys, the changes of seabed topography were compared. Result The study shows that the erosion of the foundation of offshore wind turbines mainly occur in the direction of local tides. In the early stage of construction, a deep scour pit will be formed, and scour troughs will appear after two years, and siltation will appear around the foundation after the scour troughs are formed. Conclusion Long-term monitoring of the foundation erosion of offshore wind turbines is helpful to understand the changes in the extent and depth of erosion. Hydrological surveys will help to establish ocean hydrodynamic models to predict the foundation erosion of wind turbines. Measures such as rock dumping and solidified soil should be carried out for erosion filling to delay the occurrence of erosion.
2023, 10(1): 98-104.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.012
Abstract:
Introduction The present, design and construction technology of suction bucket foundation is not mature, and there is lack of the normative guidance documents, the special research on the key technology of the construction process control of the suction bucket was implemented. Method Taking an offshore wind farm project as the background, based on the measured data of orientation platform foundations, statistical analysis, data mining, process back in the inversion method and technology was used. Result The constitution and function of the complete set of installation equipment of suction bucket foundation and the intelligent and digital control system are described in detail. The control parameters and control standards in the construction process of suction bucket foundation of guide frame platform are discussed. The feasibility analysis and calculation method and parameter value method of suction bucket penetration/jacking are summarized. The key points and control methods of each link in the whole process of suction bucket from penetration to jacking and recovery are put forward. Conclusion Finally, according to the measured construction data of seven four-pile guide frame platform suction bucket foundation, the variation characteristics of control parameters and the control effect during the construction of suction bucket foundation are illustrated. It can be used for reference in the design and construction of similar suction bucket platform foundation.
2023, 10(1): 105-111.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.013
Abstract:
Introduction In recent years, China has put into operation a large number of offshore booster stations and accumulated rich experience in the construction and operation of offshore booster stations. Based on these experiences, it is found that the current design of offshore booster stations has certain problems, such as relatively simple analysis of operation mode, general load of air conditioning power supply in important equipment rooms, the "unattended" design concept of offshore booster stations does not conform to reality, and inadequate consideration of environmental protection requirements. The design of offshore booster station still has new optimization space. Method The experience feedback of several offshore wind farms in the construction and operation stage in recent years were analyzed and the relevant of standards at home and abroad was studied. Result Design optimization suggestions are put forward for the operation mode, HVAC load classification of important equipment rooms, personnel duty form of offshore booster station. Conclusion The design optimization suggestions of offshore booster station summarized in this paper can be used as a reference for subsequent design of new offshore booster station.
2023, 10(1): 112-117.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.014
Abstract:
Introduction With the development of Marine economy, more and more projects of offshore wind power transmission, offshore oil and gas platform power supply and island network power supply involve laying submarine cables. At present, the main laying protection method is direct burial laying, but the buried depth design without considering the economy is obviously unreasonable. In order to effectively protect the submarine cable and reasonably control the investment, it is necessary to determine the reasonable burial depth of the submarine cable in the project development stage. Therefore, in the absence of sufficient design input data, this paper proposes a simplified calculation method for the depth of anchor penetration, which provides a basis for determining the laying protection scheme in the early stage of the project. Method In this paper, the anchor penetration process was divided into three stages to establish mathematical models, and a series of boundary conditions were assumed for the anchor penetration process. On this basis, based on the energy method, we analyzed and deduced the mechanical model of the anchor movement process at each stage, and proposed a simplified calculation method of the anchor penetration depth considering the shear damage of the seabed substrate. By conducting a comparative analysis of the calculated values of the method and measured values under different situations, we explored the applicability and scope of the calculation method. Result The comparison between the calculated value of this simplified method and the measured result shows that this calculation method is suitable for calculating the depth of anchor penetration in the case of clay with shear strength greater than 20 kPa, and the calculation error of this method is within the acceptable range. Conclusion From the comparative analysis of the calculation results in this paper, it can be seen that the simplified calculation method has guiding significance for the application in engineering practice, but the method still needs to accumulate different measured data in practice for verification and fitting correction, and combine the empirical method and probabilistic method for further analyses, to provide design basis for submarine cable laying protection.
2023, 10(1): 118-123.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.015
Abstract:
Introduction Based on an offshore wind farm construction project in Qidong, Jiangsu Province, the numerical simulation study on mechanical characteristics of submarine cable during laying process was carried out and the local stress distribution of the suspension span of submarine cables under different trenching depths was analyzed. Method A numerical model of submarine cable laying based on ABAQUS numerical simulation software was established. Result Results show that the stress of the lifting point at the trailing edge of the submarine cable increases significantly during the burial process compared with that before the burial operation. This is the most dangerous position as the cable at this position has the largest stress during the whole burial process. The trenching depth has a significant effect on the stress at the lifting point at the trailing edge of the cable. With the increase of the trenching depth, the stress at the lifting point at the trailing edge increases correspondingly. Conclusion The selection of cable material at the lifting point should be protected in the cable laying operation, and the yield stress parameters of the cable should be mainly based on the stress analysis results of the cable in the burial operation. The research results can provide a reference for submarine cable laying operation.
2023, 10(1): 124-132.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.016
Abstract:
Introduction The current marine geological exploration, particularly the geotechnical investigation, often follows traditional experiences without a clear objective, and lacks the evaluations of soil sample disturbance and test results. Therefore, it is necessary to conduct in-depth research on marine geotechnical investigation technology. Method Based on the domestic and international research on marine geological exploration technology and multi-year working experience in different sea areas, we developed a new accurate marine geological exploration technology with emphasis on the principle of consistency. The geotechnical investigation part of the new method included two basic aspects: (1) comprehensive evaluation of soil sample disturbance; (2) comprehensive evaluation of consistency of soil strength test results. Result The three-dimensional cross-consistency analysis of geotechnical, geophysical, and geological models has established an accurate geological exploration system. Several examples of marine engineering projects showed that the new technology can screen good acquisition methods and data through comprehensive evaluation of clay soil sample disturbance, and conduct consistency analysis of various data by combining the laboratory geotechnical tests with in-situ tests and the routine geotechnical tests with advanced geotechnical tests to obtain richer and more continuous data at the borehole. Compared with the traditional single geotechnical test, our new technology demonstrated the improved reliability and accuracy of the data, and the missing data between the sampling points are compensated. Conclusion The proposed new method can reinforce the application of geological exploration data, reduce investigation costs, and provide more geotechnical parameters that are more reliable for marine engineering projects including offshore wind power.
2023, 10(1): 133-138.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.017
Abstract:
Introduction The paper aims to study the cost composition and cost level of the offshore flexible DC delivery system and provide beneficial exploration for the cost control of the offshore flexible DC delivery system. Method By collecting the design and cost quantities of the offshore flexible DC delivery system, we analyzed the costs of offshore flexible DC delivery system by using statistical analysis method, cost composition method and comparative analysis method. Result The unit capacity investment level and investment composition of typical schemes of offshore flexible DC delivery system are given, and the key factors of cost level control of offshore flexible DC delivery system are put forward. Conclusion The unit capacity investment of offshore flexible DC delivery system is 3,750~4,600 yuan/kW, and the costs, according to their component ratio (from high to low), are equipment procurement cost, construction cost, other cost and installation cost, and the systems, according to their component ratio (from high to low), are: marine converter station, sea cable, onshore converter station and other parts. Compared with the onshore flexible DC delivery system, the overall difference is about 1.3~1.6 times.
2023, 10(1): 139-145.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.018
Abstract:
Introduction In order to respond to the national initiative of intensive sea use, develop clean energy, and contribute to carbon neutralization, a preliminary analysis was conducted on the multi-energy integration mode of offshore wind power and wave energy devices, and the WEC was optimized to achieve higher power output. Method Based on potential flow theory, the floating fan platform - WEC array was simulated to analyze the influence of the dimension and the inherent period of the WEC on the output power of the WEC. Result The simulation results show that under the same inherent period, the flatter the WEC is, the greater the total power of the WEC array is, and the economic difference of the WEC is small. For sea conditions, the economic difference of WEC array under different inherent periods is great, so it should be considered comprehensively. Conclusion In the known sea conditions, the inherent period and the dimenson of WECs can be optimized to achieve higher power output and increase energy output per unit sea area.
2023, 10(1): 146-153.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.019
Abstract:
Introduction In order to improve the flexible fault ride through (FFRT) capability of semi-direct drive wind power system, this paper proposes an improved grid-side control strategy with reactive power priority. Method Based on the analysis of the traditional grid side control strategy, reactive power priority control was added to the traditional grid side control according to the latest test rules of fault voltage ride through capability, and reactive current was injected into the grid to support the voltage recovery during the transient faults of the grid. According to the improved grid-side control strategy, the FFRT simulation operation of wind turbine was realized by using chopper circuits combined with the improved grid-side control strategy when the deep sag and rise of the grid was realized. Combined with the 6 MW semi-direct drive wind turbine of a certain project, the fault voltage ride field test was carried out by using mobile FFRT test equipment. Results The test and simulation results show that the improved grid-side control strategy can improve FFRT operation of semi-direct drive wind power system and stable control of reactive current. Conclusion The improved grid-side control strategy can give priority to injecting the corresponding stable reactive current into the grid under various symmetric low voltage/high voltage fault conditions and asymmetric high voltage fault conditions, which can assist the voltage recovery of the grid and improve the FFRT capacity of the semi-direct drive wind power system.
2023, 10(1): 154-159.
doi: 10.16516/j.gedi.issn2095-8676.2023.01.020
Abstract:
Introduction In view of the irregular geometric shape, complex load and heavy weight of the nacelle of a permanent magnet direct drive wind turbine, it is necessary to optimize the analysis and design. Method Based on the finite element analysis of the geometric parameters of the nacelle and the calculation results of the shape of the elbow, the finite element analysis was established. Result After optimization, the maximum von Mises stress of the nacelle is reduced from 181 MPa to 173 MPa, and the stress is reduced by 4.4%, which meets the strength requirements. The weight of the nacelle is reduced by 14.2% from 52.7 tons to 45.2 tons. Conclusion The research shows that the optimization effect is obvious, which provides a reference for the design and optimization method of such nacelle of wind turbine.
