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Aiming to the problem that thermal error seriously weakens grinding accuracy, according to the involute property and involute helical gear form-grinding principle, this work proposes a novel thermal error predicting model with the combination of steady-state temperature field working condition and non-steady-state temperature field working condition to optimize machining accuracy, eliminate warm-up time, and improve processing efficiency. In view of the above, the independently developed new type of high-precision horizontal forming CNC gear grinder L300G is taken as research object, and the combination of fuzzy clustering algorithm and mutual information theory is taken to optimize temperature variables, which is also verified with the comprehensive gray correlation; on this basis, L300G thermal error predicting model is established based on the combination of autoregressive time series and BP neural network. Then, the model is given practice tests through temperature field finite element analysis, temperature and thermal error measuring, temperature variables optimizing, thermal error predicting, and involute helical gear form-grinding. Results show that the model is fairly effective in thermal error predicting; what is more, after thermal error real-time compensation, it can eliminate warm-up time of gear grinder about 6000 s, and the Gleason measuring results show that the involute helical gear form-grinding tooth profile accuracy is improved from level 6 to 4, which verifies the correctness. So that it is expected to be widely used in high-precision form-grinding of horizontal gear grinder; besides, it also has significance for high-precision form-grinding research of vertical gear grinder. [ABSTRACT FROM AUTHOR]

A 3D electromagnetic model of the end region of a 1550 MW nuclear generator is set up. The electromagnetic forces on the involute and nose parts of the end winding under a rated operation are obtained through the 3D time-step finite element method. The electromagnetic forces on different coils in the same phase are analyzed. By changing the rotor’s relative length and stator coil’s linear length in the 3D electromagnetic model, the electromagnetic force distributions on the end winding are obtained. The influence of each structure change on the electromagnetic force in different directions is studied in detail. Conclusions that can be helpful in decreasing the electromagnetic forces on the end winding through optimizing the end region design are presented. [ABSTRACT FROM AUTHOR]

Optimizing hydrofracturing schemes for multiple vertical wells is crucial for developing complex fracture networks that facilitates the transport of unconventional hydrocarbon resources in tight reservoirs. The stress shadow effect that occurs between multiple wells has a significant effect on the development of fracture networks. However, the influence of fracturing schemes, including fracturing sequences and well spacing, on stress shadow effects are poorly understood. In this study, a three-dimensional (3D) numerical model based on actual reservoir data was developed to explore these influences. The simulation considers hydromechanical coupling and leak-off effects and employs the adaptive finite element–discrete element method to achieve high-precision solutions and reliable 3D fracture propagation paths. Typical fracturing cases were simulated to address the differences between sequential and simultaneous fracturing, the effects of different well spacing in sequential fracturing, and the optimization of the number of multiple vertical wells required to maximize fracturing efficiency. Our results indicate that the 3D fractured areas produced in simultaneous fracturing are much smaller than those produced in sequential fracturing. For sequential fracturing, the fractured areas of three vertical wells were larger than the fractured areas of five vertical wells. In the sequential fracturing of three wells, the fractured areas were almost unchanged because the well spacing was large enough to sufficiently weaken the stress shadow effect, thus inducing almost constant fractured areas in each fracturing sequence. Using the computed stress difference and fractured areas, we defined an area ratio to quantify the stress shadow effect, which reflects the feasibility of various fracturing schemes. It is easier to induce more microseismic events during simultaneous fracturing than during sequential fracturing, and the cumulative magnitude of simultaneous fracturing is higher; furthermore, the cumulative magnitude of sequential fracturing of the three wells was lower than that of the five wells, reflecting weak stress shadow effects. • Stress shadow effects in hydrofracturing of multiple vertical wells were studied. • 3D adaptive finite element–discrete element models were proposed. • Simulation considered the hydro-mechanical coupling and leak-off effects. • Influences of different fracturing schemes of multiple wells were compared. • Fracturing-induced microseismic events were used to address stress shadow effect. [ABSTRACT FROM AUTHOR]

Tight multilayered hydrocarbon reservoirs are typical in unconventional oil and gas extraction, in which widespread bedded interfaces have crucial effects on hydraulic fracturing propagation behavior. However, because of the complex natural properties of bedded interfaces in natural layers, such as geometric structure, distribution, strength, and contact conditions, their effects on fracture propagation and governing mechanisms are not well understood. In particular, traditional theoretical models are not suitable for characterizing the propagation behavior of hydraulic fractures in multilayered reservoirs and conventional numerical methods cannot effectively simulate the interactions between hydraulic fractures and bedded interfaces. In this study, the adaptive finite element-discrete element method was introduced to probe the effects of bedded interfaces on hydraulic fracture propagation. Different numerical models of five deviation angles of representative bedded interfaces were established based on the geometric and physical parameters of natural multilayered reservoir rocks. Some novel techniques (local remeshing near the fracture tips to guarantee accurate fracture propagation path, mesh coarsening to improve the computation efficiency, characterization technology for bedded interfaces and contacts between layers, and hydro-mechanical coupling between fluid flow in fracture network and porous rock matrix in the fracturing process) were comprehensively utilized. Furthermore, the fracturing-induced microseismic damaged and contact slip events were identified based on the computed moment tensors to detect the interactions between the hydraulic fractures and bedded interfaces. The results of the cases with single and multiple perforations in horizontal wells show that the bedded interfaces disturb the stress continuity, reselect propagation direction of hydraulic fractures in multiple perforations, induce hydraulic fracture growth, and promote the occurrences of fracturing-induced damaged and contact slip events. The offset and deflection of hydraulic fractures increase with increasing deviation angles between hydraulic fractures and bedded interfaces and the offset vanishes when the deviation angle is 0°. • Adaptive finite element-discrete element method was proposed. • The effects of bedded interfaces on hydraulic fracture propagation were studied. • Models of bedded interfaces of multilayered reservoir rocks were developed. • Bedded interfaces disturb the stress continuity and provoke fracture growth. • Bedded interfaces promote fracturing-induced microseismic events. [ABSTRACT FROM AUTHOR]