| 1. |
- Liu, Xianli, et al.
(författare)
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Feature extraction of milling chatter based on optimized variational mode decomposition and multi-scale permutation entropy
- 2021
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer Nature. - 0268-3768 .- 1433-3015. ; 114:9-10, s. 2849-2862
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Tidskriftsartikel (refereegranskat)abstract
- In the milling process, chatter is easy to occur and has a very adverse impact on the quality of the workpiece and the production efficiency. A chatter feature extraction method based on optimized variational mode decomposition (OVMD) and multi-scale permutation entropy (MPE) was proposed to solve the problem that it is difficult to detect the machining chatter state during milling. The methodology presented in this article allows the occurrence of machining chatter to be effectively identified through real-time digital signal processing and analysis. First, in order to solve the problem of variational mode decomposition (VMD) parameter selection, an automatic selection method based on particle swarm optimization (PSO) and the maximum crest factor of the envelope spectrum (CE) was proposed. Then, the decomposed signal was reconstructed based on the energy ratio. In order to solve the problem that the single-scale permutation entropy (PE) cannot detect milling chatter well, the MPE was introduced to detect milling chatter. Finally, experimental verification was carried out, and the MPE of the reconstructed signals at different scales was extracted and analyzed. The results show that using the OVMD algorithm to process the signals can significantly improve the discrimination of MPE. With the increase of the scale factor, the MPE of the milling signals tends to decrease. At the same time, MPE is better than single-scale PE in chatter detection, and the MPE at scale factor of 4 is more conducive to chatter detection.
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| 2. |
- Meng, Boyang, et al.
(författare)
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Uniformity, Periodicity and Symmetry Characteristics of Forces Fluctuation in Helical-Edge Milling Cutter
- 2021
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Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 11:6
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Tidskriftsartikel (refereegranskat)abstract
- Under most processing conditions, the milling force is expected to be stable and not to fluctuate, in order to improve the processing quality. This study focuses on analyzing the force fluctuation characteristics under conditions of different processing and cutter parameters. An original model is proposed to predict the force fluctuation during the milling process of a helical-edge cutter. At the same time, three force fluctuation characteristics related to the axial cutting depth and cutter parameters are determined: uniformity, periodicity and symmetry. The corresponding mathematical derivation and proof method are given for the first time through a force transformation of projecting the superposition chip thickness on a virtual cutting edge. On this basis, a fast estimation method and an accurate simulation method for force fluctuation prediction are established to quantify the intensity of force fluctuations under different parameters. Both two prediction methods and the experimental cutting tests validate the proposed theory effectively. The result shows a high potential of the proposed theory for studying the force behavior under different milling parameters or cutter parameters and at least 75% of the test workload can be reduced.
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| 3. |
- Jiang, Chuanyin, et al.
(författare)
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The Role of In Situ Stress in Organizing Flow Pathways in Natural Fracture Networks at the Percolation Threshold
- 2019
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Ingår i: Geofluids. - : Hindawi Publishing Corporation. - 1468-8115 .- 1468-8123. ; 2019
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the effect of in situ stresses on fluid flow in a natural fracture network. The fracture network model is based on an actual critically connected (i.e., close to the percolation threshold) fracture pattern mapped from a field outcrop. We derive stress-dependent fracture aperture fields using a hybrid finite-discrete element method. We analyze the changes of aperture distribution and fluid flow field with variations of in situ stress orientation and magnitude. Our simulations show that an isotropic stress loading tends to reduce fracture apertures and suppress fluid flow, resulting in a decrease of equivalent permeability of the fractured rock. Anisotropic stresses may cause a significant amount of sliding of fracture walls accompanied with shear-induced dilation along some preferentially oriented fractures, resulting in enhanced flow heterogeneity and channelization. When the differential stress is further elevated, fracture propagation becomes prevailing and creates some new flow paths via linking preexisting natural fractures, which attempts to increase the bulk permeability but attenuates the flow channelization. Comparing to the shear-induced dilation effect, it appears that the propagation of new cracks leads to a more prominent permeability enhancement for the natural fracture system. The results have particularly important implications for predicting the hydraulic responses of fractured rocks to in situ stress fields and may provide useful guidance for the strategy design of geofluid production from naturally fractured reservoirs.
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| 4. |
- Sun, Zhixue, et al.
(författare)
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Joint influence of in-situ stress and fracture network geometry on heat transfer in fractured geothermal reservoirs
- 2020
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier. - 0017-9310 .- 1879-2189. ; 149
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Tidskriftsartikel (refereegranskat)abstract
- We quantitatively investigate the superimposed influence of geometrical properties and geomechanical deformations of two-dimensional fracture networks on heat transfer in fractured geothermal reservoirs. The reservoir model consists of rock matrix with uniform properties and natural fractures following power law length scaling. We model its thermo-hydro-mechanical behavior based on sequentially linked solvers that resolve the solid deformation, fluid flow and heat transport processes. The fracture aperture is spatially variable and dependent on the stress loading conditions, based on which stress-dependent fluid flow is further simulated. Our numerical results show a good correlation between the heat extraction efficiency and the fracture network connectivity. The connectivity seems to be a prerequisite for geomechanical factors to impact heat transfer. Depending on the hydraulic boundary condition, the stress loading may lead to different geothermal responses: under a high hydraulic gradient, an increased stress ratio results in a decrease in the heat extraction efficiency; in contrast, under a low hydraulic gradient, an increased stress ratio corresponds to an enhanced heat production. The observed effects of in-situ stress and fracture network geometry on heat transport are quantitatively characterized by a dimensionless analysis using the fracture-matrix Peclet number, which is defined as the ratio of convection timescale in the fracture to conduction timescale in the matrix. Our research findings have important implications for understanding the heat exchange performance of fractured rocks in geothermal reservoirs naturally subjected to complex in-situ stress conditions.
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