A more accurate hourly prediction of day-ahead wind power can effectively reduce the uncertainty of wind power integration and improve the competitiveness of wind power in power auction markets. ...However, due to the inherent stochastic and intermittent nature of wind energy, it is very difficult to sharply improve the multi-step wind power forecasting (WPF) accuracy. According to theory of direct and recursive multi-step prediction, this study firstly proposes the models of R (recursive)-VMD (variational model decomposition)-LSTM (long short-term memory) and D (direct)-VMD-LSTM for the hourly forecast of day-ahead wind power by using a combination of a novel and in-depth neural network forecasting model called LSTM and the variational model decomposition (VMD) technique. The data from these model tests were obtained from two real-world wind power series from a wind farm located in Henan, China. The experimental results show that LSTM can achieve more precise predictions than traditional neural networks, and that VMD has a good self-adaptive ability to remove the stochastic volatility and retain more adequate data information than empirical mode decomposition (EMD). Secondly, the R-VMD-LSTM and D-VMD-LSTM are comparatively studied to analyze the accuracy of each step. The results verify the effectiveness of the combination of the two models: The R-VMD-LSTM model provides a more accurate prediction at the beginning of a day, while the D-VMD-LSTM model provides a more accurate prediction at the end of a day.
Within recent years, microbial induced calcium carbonate precipitation (MICP) technology has been widely applied to ground improvement. The addition of fiber has a great improvement on properties of ...biocemented sand. This paper studied the influence of three fiber types on properties of biocemented calcareous sand by using MICP technology and discovered the influence mechanism of three fiber types on biocemented calcareous sand. Unconfined compressive strength (UCS) test, tensile strength test, and calcium carbonate content were carried to estimate properties of biocemented calcareous sand. The microstructures of biocemented calcareous sand with fibers and surface of three fiber types were observed under the scanning electron microscope. The test results showed that the ductility, the bridging role, and calcium carbonate content of biocemented calcareous sand with carbon fiber were better, followed by basalt fiber and glass fiber. The UCS, tensile strength, and calcium carbonate content of biocemented calcareous sand increased with the increasing fiber content. The optimum fiber content of biocemented calcareous sand was found to be 1%. Compared with biocemented calcareous sand without fiber, the unconfined compressive strength of biocemented calcareous sand at optimum glass fiber, basalt fiber, and carbon fiber content increased by 458%, 784%, and 1133%, respectively. Meanwhile, the tensile strength of biocemented calcareous sand at optimum basalt fiber, glass fiber, and carbon fiber content increased by 115%, 129%, and 317%, respectively. Therefore, the properties of biocemented calcareous sand with carbon fiber are better than basalt fiber and glass fiber.
Pile foundations in calcareous sand are often applied to bear vertical cyclic loads. Model tests of a single pile bearing vertical cyclic loads were performed in calcareous sand, and the accumulated ...settlement and bearing capacity were measured via sensors using a self-designed experimental device. The influences of the dynamic load and number of cycles on the accumulated settlement and bearing capacity of the pile were analyzed. The results revealed that the accumulated settlement of the pile increased with the number of cycles, it was categorized as either stable, progressive, or destructive. The "threshold effect" was observed once a critical number of cycles had been achieved, the particles breakage hindering the settlement tendency lead to the accumulated settlement rate of the pile gradually decreased and stabilized. During cyclic loading, the proportions of the upper load shared by the pile end and side constantly changed, the pile-side frictional resistance gradually decreased, while the average resistance of pile end slowly increased. After cyclic loading, the bearing capacity of the pile was improved slightly, but the pile-side frictional resistance was greatly reduced, two formulas were presented. The test results can be used for the design of pile foundations in calcareous sand.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Commercial virtual power plants (CVPP) connect the form of renewable energy resource portfolio to the power market and reduce the risk of the unstable operation of a single renewable energy. ...Combining different kinds of large-scale renewable energy in CVPP to provide capacity services like base load, peak shaving, and valley-filling, etc., for the system loads is an urgent problem to be solved. Therefore, it is valuable to analyze the capacity allocation ratio of the CVPP to maximize the utilization of all kinds of energy, especially for the large-scale multi-energy base. This paper proposed a multi-energy coordinated operation framework by considering various load demands, including base load and peak shaving for the capacity allocation of CVPP based on the world’s largest renewable energy resource base on the upstream area of the Yellow River. The main procedures of this framework are as follows: (1) A paratactic model satisfying base load and peak shaving is proposed to determine the ability of the CVPP operation model’s capacity services to meet the different demands of the power system load. (2) A hybrid dimension reduction algorithm with a better convergence rate and optimization effect solves the proposed paratactic model based on the ReliefF and the Adaptive Particle Swarm Optimization (APSO). The results show that the large-scale CVPP with different compositions can achieve both of the goals of a stable base load output and stable residual load under different weather conditions. Compared with the operation on sunny days, the base load fluctuation and residual load fluctuation of CVPP on rainy days are reduced by 14.5% and 21.9%, respectively, proving that CVPP can alleviate renewable energy’s dependence on weather and improve energy utilization.
The reclamation coral sand (CS) layer is the survival environment for island reef vegetation in the South China Sea. The root system within the CS bed draws water necessary for vegetation growth, ...implying that the water-retention capacity of CS plays a pivotal role in determining vegetation viability. Particle size distribution (PSD) significantly influences the water-retention capacity of geomaterials. This study examines the impact of PSD on the water-retention capacity of CS from both macro (soil–water characteristic curve, SWCC) and micro (pore water distribution) perspectives using the pressure plate test and nuclear magnetic resonance technique, and an F&X model was used to analyze the SWCC of CS. The findings indicated that the F&X model aptly describes the SWCC of CS with different PSDs. Both the air entry value and residual water content rise with an increased content of fine grains (d < 0.25 mm), suggesting that the presence of fine grains augments the water-retention capacity of CS. It is considered that a size range of d = 0.075–0.25 mm predominantly impacts the water-retention capacity of CS. The PSD primarily influences the water-retention capacity by affecting the pore size distribution of CS. The volume of small pores swells with the surge of fine-grain content, while the maximum pore size contracts with increasing fine-grain content. Limited pore connectivity in CS means macropores can retain water even under high suction, bolstering the water-retention capacity of CS. These findings offer theoretical guidance for selecting gradation parameters for the planting layer on island reefs.
The Artificial Ground Freezing (AGF) method, which is widely used in tunnel excavations, significantly affects the properties of geotechnical materials in frozen walls under extremely low ...temperatures. In order to simulate the AGF process, the freezing treatment with a temperature of −30°C and thawing treatment temperature of 25°C were performed on natural specimens of granite residual soil (GRS). Subsequently, triaxial (TRX) tests were conducted to evaluate mechanical properties and Nuclear Magnetic Resonance Image (NMRI) tests were applied to detect pore distributions of GRS. To clarify variations of microstructure after freezing-thawing, the relaxation time (T
2
) distribution curves and T
2
-weighted images from NMRI results were thoroughly analyzed from the perspective of quantization and visualization. Results show that the shear strength as well as the cohesion of GRS are reduced sharply by the AGF process, while the internal friction angle decreases gently. The pore size distribution (PSD) converted from the T
2
curve is constituted of two different peaks, corresponding to micro-pores with diameters from 0.1 to 10 µm and macro-pores with diameters from 10 to 1,000 µm. Under the AGF impact, the expansion in macro-pores and shrinkage in micro-pores simultaneously exist in the specimen, which was verified from a visualized perspective by T
2
-weighted images. The frost heaving damage on shear strength is attributed to the microstructural disturbance caused by the presence of large-scale pores and uneven deformations in GRS, which is subjected to the AGF impact under an extremely low temperature.
The permeability coefficient of calcareous sand is an important hydraulic parameter in reef engineering. The loading and permeation tests of calcareous sand and quartz sand under the same conditions ...were carried out by self-developed loadable sand permeability device, and the influencing factors were studied to obtain the calculation formula of the permeability coefficient of calcareous sand under load, containing void ratio e, particle gradation, permeability coefficient Ks and the relative crushing rate Br proposed by Hardin. The results show that under the same load, the permeability coefficient and compressive deformation of calcareous sand decrease more than that of quartz sand, and the relative breakage rate of calcareous sand increases with the increase of load, while there is exponential correlation between its Ks and Br. It can be concluded that the pores of calcareous sand are compacted under load, and the granule breakage leads to gradation change, which affects the permeability coefficient of calcareous sand.
The presence of mica is considered to be why the physical and mechanical properties of micaceous soil differ significantly from those of common clay and sand, such as the difficulty in compacting ...micaceous soil and its high compressibility and resilience. However, despite micaceous residual soil being widespread in transportation engineering, the specific role played by mica in determining its geotechnical properties remains ambiguous, as does the underlying mechanism for doing so. Presented here is a systematic investigation of the compaction, compression, and hydraulic characteristics of residual soil with varying mica content, with scanning electron microscopy used to scrutinize the structural features of mica and the resulting microstructural changes within the soil under different compression stress levels. The findings show that adding mica to residual soil results in coarser gradation, and the distinctive flaky layered structure and interlayer pores of mica particles characterize the residual soil with high compressibility, water retention, swelling potential, and inadequate compaction. The specific effects of particle arrangement between mica and soil particles—such as bridging and ordering—contribute to the high porosity and permeability of soil. Also, the breakdown of the mica stacking structure and the degradation of bridging and ordering effects under high consolidation stresses decrease the resilience and permeability of soil, leading to further compression deformation. This study elucidates the microscopic mechanism whereby mica influences the physical and mechanical properties of micaceous residual soil, thereby contributing to enhanced insights into the compaction, compression, and hydraulic properties of such soils.
Shi, X.; Huang, S.; Huang, Q.; Lei, X.; Li, J.; Li, P., and Yang, M., 2019. Deep-learning-based wind speed forecasting considering spatial–temporal correlations with the adjacent wind turbines. In: ...Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 623-632. Coconut Creek (Florida), ISSN 0749-0208. The accurate prediction of wind speed, which greatly influences the secure and efficient application of wind energy, is still an important issue and a huge challenge. Previous research has largely focused on advanced algorithms, often ignoring the contribution of expanding predictors to predict wind speed. In order to promote the accuracy of forecasting, this study proposes a provisory wind speed forecasting model based on spatial-temporal correlation (SC) theory, in which the target and adjacent wind turbines, as well as the related time-lag characteristics, are examined through Wavelet Coherence Transformation analysis (WCT). Prior to that, the continuous wavelet transforms (CWT) are used to detect the spatial–temporal correlations with adjacent wind turbines. The CWT results show that the adjacent wind turbines which have a strong correlation with the target wind turbine are adopted as important factors of the forecasting model. Moreover, the study focuses on long short term memory (LSTM), a typical deep learning model from the family of deep neural networks, and compares its forecast accuracy to traditional methods with a proven track record of wind speed forecasting. Wind speed series of these model tests are taken from a Buckley City wind farm in Washington State, USA. The results of testing set reveal that (1) the root mean square error (RMSE), mean absolute error (MAE), and mean absolute percentage error (MAPE) of the proposed model (SC-LSTM) are 0.49 m/s, 0.28 m/s and 2.57%, respectively, which are much lower than those of the conventional Back Propagation (BP) model, Extreme Learning Machines (ELM) model, and Support Vector Machine (SVM) model; (2) the proposed model that considers spatial–temporal correlations with adjacent wind turbines based on the WCT can obtain reliable and excellent prediction results, providing an excellent hybrid model for wind speed forecasts.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The existence of shallow gas seriously affects the stability of seabed formations. In the early stage of the construction of the Jiayong Cross-sea High-speed Railway Bridge, during the preliminary ...survey of the west line of Haiyan, the central sea area of the bridge frequently encountered shallow gas. On the basis of exploration, physicochemical test analysis, etc., the hydrogeological conditions, stratigraphic deposition, and shallow gas distribution and origin of the shallow gas-rich area at the bridge site are discussed, and the possible shallow gas disasters and genesis of the bridge construction at various stages are analyzed. corresponding preventive measures. The research shows that the formation water in this area is mainly Quaternary loose rock pore water, and the gas-bearing soil layer is Quaternary Holocene to Lower Pleistocene alluvial clay and sandy soil, of which the sandy soil layer is the main gas storage layer. The gas belongs to the typical primary type early biogenic gas that is not affecte
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