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A semi-analytical model for coupled flow in stress-sensitive multi-scale shale reservoirs with fractal characteristics 被引量:2
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作者 Qian Zhang Wen-Dong Wang +4 位作者 Yu-Liang Su Wei Chen Zheng-Dong Lei Lei Li Yong-Mao Hao 《Petroleum Science》 SCIE EI CAS CSCD 2024年第1期327-342,共16页
A large number of nanopores and complex fracture structures in shale reservoirs results in multi-scale flow of oil. With the development of shale oil reservoirs, the permeability of multi-scale media undergoes changes... A large number of nanopores and complex fracture structures in shale reservoirs results in multi-scale flow of oil. With the development of shale oil reservoirs, the permeability of multi-scale media undergoes changes due to stress sensitivity, which plays a crucial role in controlling pressure propagation and oil flow. This paper proposes a multi-scale coupled flow mathematical model of matrix nanopores, induced fractures, and hydraulic fractures. In this model, the micro-scale effects of shale oil flow in fractal nanopores, fractal induced fracture network, and stress sensitivity of multi-scale media are considered. We solved the model iteratively using Pedrosa transform, semi-analytic Segmented Bessel function, Laplace transform. The results of this model exhibit good agreement with the numerical solution and field production data, confirming the high accuracy of the model. As well, the influence of stress sensitivity on permeability, pressure and production is analyzed. It is shown that the permeability and production decrease significantly when induced fractures are weakly supported. Closed induced fractures can inhibit interporosity flow in the stimulated reservoir volume (SRV). It has been shown in sensitivity analysis that hydraulic fractures are beneficial to early production, and induced fractures in SRV are beneficial to middle production. The model can characterize multi-scale flow characteristics of shale oil, providing theoretical guidance for rapid productivity evaluation. 展开更多
关键词 Multi-scale coupled flow Stress sensitivity Shale oil Micro-scale effect fractal theory
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Experimental investigation on coal pore-fracture variation and fractal characteristics synergistically affected by solvents for improving clean gas extraction 被引量:1
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作者 Feilin Han Sheng Xue +3 位作者 Chunshan Zheng Zhongwei Chen Guofu Li Bingyou Jiang 《International Journal of Mining Science and Technology》 SCIE EI CAS CSCD 2024年第3期413-425,共13页
Chemical solvents instead of pure water being as hydraulic fracturing fluid could effectively increase permeability and improve clean methane extraction efficiency.However,pore-fracture variation features of lean coal... Chemical solvents instead of pure water being as hydraulic fracturing fluid could effectively increase permeability and improve clean methane extraction efficiency.However,pore-fracture variation features of lean coal synergistically affected by solvents have not been fully understood.Ultrasonic testing,nuclear magnetic resonance analysis,liquid phase mass spectrometry was adopted to comprehensively analyze pore-fracture change characteristics of lean coal treated by combined solvent(NMP and CS_(2)).Meanwhile,quantitative characterization of above changing properties was conducted using geometric fractal theory.Relationship model between permeability,fractal dimension and porosity were established.Results indicate that the end face fractures of coal are well developed after CS2and combined solvent treatments,of which,end face box-counting fractal dimensions range from 1.1227 to 1.4767.Maximum decreases in ultrasonic longitudinal wave velocity of coal affected by NMP,CS_(2)and combined solvent are 2.700%,20.521%,22.454%,respectively.Solvent treatments could lead to increasing amount of both mesopores and macropores.Decrease ratio of fractal dimension Dsis 0.259%–2.159%,while permeability increases ratio of NMR ranges from 0.1904 to 6.4486.Meanwhile,combined solvent could dissolve coal polar and non-polar small molecules and expand flow space.Results could provide reference for solvent selection and parameter optimization of permeability-enhancement technology. 展开更多
关键词 Clean gas extraction Chemical solvent Experimental investigation fractal characteristics Pore fracture
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量化三维网格模型复杂度的Fractal Dimension^(+)方法
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作者 孙鸣 丁展 《金陵科技学院学报》 2024年第2期1-11,73,共12页
对三维网格模型复杂度的评估及应用进行研究,提出基于Fractal Dimension^(+)方法量化三维网格模型复杂度。该方法利用分形几何学的分形维度来确定三维网格模型的不规则性;为了全面量化复杂度并且提高量化的准确性和可信度,在分形维度算... 对三维网格模型复杂度的评估及应用进行研究,提出基于Fractal Dimension^(+)方法量化三维网格模型复杂度。该方法利用分形几何学的分形维度来确定三维网格模型的不规则性;为了全面量化复杂度并且提高量化的准确性和可信度,在分形维度算法中添加孔隙比和亏格数的概念,全面考虑介质内部空间分布和几何结构的连接性以及孔洞分布的信息。对大量三维网格模型进行实验,结果表明Fractal Dimension^(+)方法可以有效计算出准确的复杂度。 展开更多
关键词 三维网格模型 模型复杂度 fractal Dimension^(+) 分形维度 孔隙比 亏格
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A novel box-counting method for quantitative fractal analysis of threedimensional pore characteristics in sandstone
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作者 Huiqing Liu Heping Xie +2 位作者 Fei Wu Cunbao Li Renbo Gao 《International Journal of Mining Science and Technology》 SCIE EI CAS CSCD 2024年第4期479-489,共11页
Fractal theory offers a powerful tool for the precise description and quantification of the complex pore structures in reservoir rocks,crucial for understanding the storage and migration characteristics of media withi... Fractal theory offers a powerful tool for the precise description and quantification of the complex pore structures in reservoir rocks,crucial for understanding the storage and migration characteristics of media within these rocks.Faced with the challenge of calculating the three-dimensional fractal dimensions of rock porosity,this study proposes an innovative computational process that directly calculates the three-dimensional fractal dimensions from a geometric perspective.By employing a composite denoising approach that integrates Fourier transform(FT)and wavelet transform(WT),coupled with multimodal pore extraction techniques such as threshold segmentation,top-hat transformation,and membrane enhancement,we successfully crafted accurate digital rock models.The improved box-counting method was then applied to analyze the voxel data of these digital rocks,accurately calculating the fractal dimensions of the rock pore distribution.Further numerical simulations of permeability experiments were conducted to explore the physical correlations between the rock pore fractal dimensions,porosity,and absolute permeability.The results reveal that rocks with higher fractal dimensions exhibit more complex pore connectivity pathways and a wider,more uneven pore distribution,suggesting that the ideal rock samples should possess lower fractal dimensions and higher effective porosity rates to achieve optimal fluid transmission properties.The methodology and conclusions of this study provide new tools and insights for the quantitative analysis of complex pores in rocks and contribute to the exploration of the fractal transport properties of media within rocks. 展开更多
关键词 3D fractal analysis fractal dimension Rock pore structure Box-counting method Permeability simulation Computational geosciences
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Fractal Study on the Evolution of Micro-Pores in Concrete Under Freeze-Thaw
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作者 孙浩然 邹春霞 +2 位作者 XU Deru GUO Xiaosong HUANG Kun 《Journal of Wuhan University of Technology(Materials Science)》 SCIE EI CAS CSCD 2024年第1期109-117,共9页
After exposure to freeze-thaw cycles, scanning electron microscopy(SEM) and nuclear magnetic resonance(NMR) were used to test the four mixtures. The microstructure is qualitatively analyzed from the 2D SEM image and t... After exposure to freeze-thaw cycles, scanning electron microscopy(SEM) and nuclear magnetic resonance(NMR) were used to test the four mixtures. The microstructure is qualitatively analyzed from the 2D SEM image and the 3D pore distribution curve before and after freezing and thawing. The fractal dimension is utilized to characterize the two-dimensional topography image and the three-dimensional pore distribution, quantitatively. The results reveal that the surface porosity and volume porosity increase as the freeze-thaw action increases. Self-similarity characteristics exist in micro-damage inside the concrete. In the fractal dimension, it is possible to characterize pore evolution quantitatively. The fractal dimension correlates with pore damage evolution. The fractal dimension effectively quantitatively characterizes micro-damage features at various scales from the local to the global level. 展开更多
关键词 fractal dimension freeze-thaw cycle CONCRETE SEM NMR
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Advancements in Numerical Solutions:Fractal Runge-Kutta Approach to Model Time-Dependent MHD Newtonian Fluid with Rescaled Viscosity on Riga Plate
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作者 Muhammad Shoaib Arif Kamaleldin Abodayeh Yasir Nawaz 《Computer Modeling in Engineering & Sciences》 SCIE EI 2024年第11期1213-1241,共29页
Fractal time-dependent issues in fluid dynamics provide a distinct difficulty in numerical analysis due to their complex characteristics,necessitating specialized computing techniques for precise and economical soluti... Fractal time-dependent issues in fluid dynamics provide a distinct difficulty in numerical analysis due to their complex characteristics,necessitating specialized computing techniques for precise and economical solutions.This study presents an innovative computational approach to tackle these difficulties.The main focus is applying the Fractal Runge-Kutta Method to model the time-dependent magnetohydrodynamic(MHD)Newtonian fluid with rescaled viscosity flow on Riga plates.An efficient computational scheme is proposed for handling fractal timedependent problems in flow phenomena.The scheme is comprised of three stages and constructed using three different time levels.The stability of the scheme is shown by employing the Fourier series analysis to solve scalar problems.The scheme’s convergence is guaranteed for a time fractal partial differential equations system.The scheme is applied to the dimensionless fractal heat and mass transfer model of incompressible,unsteady,laminar,Newtonian fluid with rescaled viscosity flow over the flat and oscillatory Riga plates under the effects of spaceand temperature-dependent heat sources.The first-order back differences discretize the continuity equation.The results show that skin friction local Nusselt number declines by raising the coefficient of the temperature-dependent term of heat source and Eckert number.The numerical simulations provide valuable insights into fluid dynamics,explicitly highlighting the influence of the temperature-dependent coefficient of the heat source and the Eckert number on skin friction and local Nusselt number. 展开更多
关键词 fractal scheme stability convergence fractal Newtonian fluid with rescaled viscosity fluid heat generation
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Fractal model of spontaneous imbibition in low-permeability reservoirs coupled with heterogeneity of pore seepage channels and threshold pressure
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作者 Ming-Sheng Zuo Hao Chen +3 位作者 Xi-Liang Liu Hai-Peng Liu Yi Wu Xin-Yu Qi 《Petroleum Science》 SCIE EI CAS CSCD 2024年第2期1002-1017,共16页
Spontaneous imbibition(SI)is an important mechanism for enhancing oil recovery in low-permeability reservoirs.Due to the strong heterogeneity,and the non-Darcy flow,the construction of SI model for lowpermeability res... Spontaneous imbibition(SI)is an important mechanism for enhancing oil recovery in low-permeability reservoirs.Due to the strong heterogeneity,and the non-Darcy flow,the construction of SI model for lowpermeability reservoirs is extremely challenging.Commonly,traditional SI models based on single or averaged capillary tortuosity ignore the influence of heterogeneity of pore seepage channels and the threshold pressure(TP)on imbibition.Therefore,in this work,based on capillary model and fractal theory,a mathematical model of characterizing SI considering heterogeneity of pore seepage channels is established.On this basis,the threshold pressure was introduced to determine the pore radius at which the wetted phase can displace oil.The proposed new SI model was verified by imbibition experimental data.The study shows that for weakly heterogeneous cores with permeability of 0-1 m D,the traditional SI model can characterize the imbibition process relatively accurately,and the new imbibition model can increase the coefficient of determination by 1.05 times.However,traditional model has serious deviations in predicting the imbibition recovery for cores with permeability of 10-50 m D.The new SI model coupling with heterogeneity of pore seepage channels and threshold pressure effectively solves this problem,and the determination coefficient is increased from 0.344 to 0.922,which is increased by2.68 times.For low-permeability reservoirs,the production of the oil in transitional pores(0.01-0.1μm)and mesopores(0.1-1μm)significantly affects the imbibition recovery,as the research shows that when the heterogeneity of pore seepage channels is ignored,the oil recovery in transitional pores and mesopores decreases by 7.54%and 4.26%,respectively.Sensitivity analysis shows that increasing interfacial tension,decreasing contact angle,oil-water viscosity ratio and threshold pressure will increase imbibition recovery.In addition,there are critical values for the influence of these factors on the imbibition recovery,which provides theoretical support for surfactant optimization. 展开更多
关键词 Spontaneous imbibition Low-permeability reservoir fractal model Threshold pressure Capillary tube
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Quasi-static and dynamic compressive behaviour of additively manufactured Menger fractal cube structures
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作者 Damith Mohotti Dakshitha Weerasinghe +3 位作者 Madhusha Bogahawaththa Hongxu Wang Kasun Wijesooriya Paul JHazell 《Defence Technology(防务技术)》 SCIE EI CAS CSCD 2024年第7期39-49,共11页
This paper presents the first-ever investigation of Menger fractal cubes'quasi-static compression and impact behaviour.Menger cubes with different void ratios were 3D printed using polylactic acid(PLA)with dimensi... This paper presents the first-ever investigation of Menger fractal cubes'quasi-static compression and impact behaviour.Menger cubes with different void ratios were 3D printed using polylactic acid(PLA)with dimensions of 40 mm×40 mm×40 mm.Three different orders of Menger cubes with different void ratios were considered,namely M1 with a void ratio of 0.26,M2 with a void ratio of 0.45,and M3with a void ratio of 0.60.Quasi-static Compression tests were conducted using a universal testing machine,while the drop hammer was used to observe the behaviour under impact loading.The fracture mechanism,energy efficiency and force-time histories were studied.With the structured nature of the void formation and predictability of the failure modes,the Menger geometry showed some promise compared to other alternatives,such as foams and honeycombs.With the increasing void ratio,the Menger geometries show force-displacement behaviour similar to hyper-elastic materials such as rubber and polymers.The third-order Menger cubes showed the highest energy absorption efficiency compared to the other two geometries in this study.The findings of the present work reveal the possibility of using additively manufactured Menger geometries as an energy-efficient system capable of reducing the transmitting force in applications such as crash barriers. 展开更多
关键词 Additive manufacturing fractal geometries Menger cube Energy absorption QUASI-STATIC
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Damage Characteristics Analysis and Fractal Study of Shale With Prefabricated Fractures under Thermal-mechanical Coupling
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作者 张辉 邬忠虎 +3 位作者 SONG Huailei WANG Wentao TANG Motian CUI Hengtao 《Journal of Wuhan University of Technology(Materials Science)》 SCIE EI CAS CSCD 2024年第3期570-586,共17页
To study the damage and failure of shale with different fracture inclination angles under uniaxial compression loading,in this work,RFPA2D-Thermal,a two-dimensional real failure process analysis software,was used for ... To study the damage and failure of shale with different fracture inclination angles under uniaxial compression loading,in this work,RFPA2D-Thermal,a two-dimensional real failure process analysis software,was used for numerical simulation.Numerical simulation results show that quartz in shale mainly affects the tensile and compressive strength of shale by increasing rock brittleness.The coupling of temperature and pressure will cause lateral and volume destruction of shale,which enables the shale body to be more easily broken.Fracture inclination is the key factor affecting shale damage patterns.The failure mode of shale with low-and high-angle fractures is mainly shear failure,and the compressive strength does not vary with crack inclination.The damage mode of obliquely intersecting fractured shale is slip damage along the fracture face,the compressive strength decreases and then increases with the fracture inclination,and a minimum value exists.The acoustic emission simulation results of the damage process effectively reflect the accumulated internal damage and macroscopic crack appearance until fracture instability when the prefabricated fractured shale is subjected to uniaxial compressive loading.The crack inclinations of 0°and 120℃ corresponds to the most complex"N"shape damage mode.The crack inclinations of 30°and 60°,and the damage mode is an inverted"λ"shape. 展开更多
关键词 SHALE temperature and pressure numerical simulation fracture dip angle fractal dimension
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Fractal analysis of major faults and fractal dimension of lineaments in the Indo-Gangetic Plain on a regional scale
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作者 Vipin Chauhan Jagabandhu Dixit 《Earthquake Science》 2024年第2期107-121,共15页
The Indo-Gangetic Plain(IGP)is one of the most seismically vulnerable areas due to its proximity to the Himalayas.Geographic information system(GIS)-based seismic characterization of the IGP was performed based on the... The Indo-Gangetic Plain(IGP)is one of the most seismically vulnerable areas due to its proximity to the Himalayas.Geographic information system(GIS)-based seismic characterization of the IGP was performed based on the degree of deformation and fractal dimension.The zone between the Main Boundary Thrust(MBT)and the Main Central Thrust(MCT)in the Himalayan Mountain Range(HMR)experienced large variations in earthquake magnitude,which were identified by Number-Size(NS)fractal modeling.The central IGP zone experienced only moderate to low mainshock levels.Fractal analysis of earthquake epicenters reveals a large scattering of earthquake epicenters in the HMR and central IGP zones.Similarly,the fault fractal analysis identifies the HMR,central IGP,and south-western IGP zones as having more faults.Overall,the seismicity of the study region is strong in the central IGP,south-western IGP,and HMR zones,moderate in the western and southern IGP,and low in the northern,eastern,and south-eastern IGP zones. 展开更多
关键词 geospatial analysis fractal modeling seismicity pattern fractal dimension
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Microstructure Characterization of Bubbles in Gassy Soil Based on the Fractal Theory
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作者 WU Chen LIN Guoqing +3 位作者 LIU Lele LIU Tao LI Chengfeng GUO Zhenqi 《Journal of Ocean University of China》 CAS CSCD 2024年第1期129-137,共9页
The microscopic characterization of isolated bubbles in gassy soil plays an important role in the macroscopic physical properties of sediments and is a key factor in the study of geological hazards in gas-bearing stra... The microscopic characterization of isolated bubbles in gassy soil plays an important role in the macroscopic physical properties of sediments and is a key factor in the study of geological hazards in gas-bearing strata.Based on the box-counting method and the pore fractal features in porous media,a fractal model of bubble microstructure parameters in gassy soil under different gas con-tents and vertical load conditions is established by using an industrial X-ray CT scanning system.The results show that the fractal di-mension of bubbles in the sample is correlated with the volume fraction of bubbles,and it is also restricted by the vertical load.The three-dimensional fractal dimension of the sample is about 1 larger than the average two-dimensional fractal dimension of all the slices from the same sample.The uniform porous media fractal model is used to test the equivalent diameter,and the results show that the variation of the measured pore diameter ratio is jointly restricted by the volume fraction and the vertical load.In addition,the measured self-similarity interval of the bubble area distribution is tested by the porous media fractal capillary bundle model,and the fitting curve of measured pore area ratio in a small loading range is obtained in this paper. 展开更多
关键词 gassy soil bubble microstructure parameters fractal dimension vertical load
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Experimental realization of fractal fretwork metasurface for sound anomalous modulation
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作者 何佳杰 于书萌 +1 位作者 江雪 他得安 《Chinese Physics B》 SCIE EI CAS CSCD 2024年第5期473-478,共6页
Natural creatures and ancient cultures are full of potential sources to provide inspiration for applied sciences.Inspired by the fractal geometry in nature and the fretwork frame in ancient culture,here we design the ... Natural creatures and ancient cultures are full of potential sources to provide inspiration for applied sciences.Inspired by the fractal geometry in nature and the fretwork frame in ancient culture,here we design the acoustic metasurface to realize sound anomalous modulation,which manifests itself as an incident-dependent propagation behavior:sound wave propagating in the forward direction is allowed to transmit with high efficiency while in the backward direction is obviously suppressed.We quantitatively investigate the dependences of asymmetric transmission on the propagation direction,incident angle and operating frequency by calculating sound transmittance and energy contrast.This compact fractal fretwork metasurface for acoustic anomalous modulation would promote the development of integrated acoustic devices and expand versatile applications in acoustic communication and information encryption. 展开更多
关键词 acoustic metasurface fractal geometry sound anomalous modulation
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Flow behavior of a coupled model between horizontal well and fractal reservoir
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作者 Peiqing Lian Jianfang Sun +1 位作者 Jincai Zhang Zhihui Fan 《Energy Geoscience》 EI 2024年第4期267-277,共11页
Many research findings have proven that the system of porous medium reservoirs exhibits different heterogeneous structures at various scales,demonstrating some form of self-similarity with fractal characteristics.In t... Many research findings have proven that the system of porous medium reservoirs exhibits different heterogeneous structures at various scales,demonstrating some form of self-similarity with fractal characteristics.In this paper,fractal theory is incorporated into the reservoir to investigate coupled flow between reservoir and horizontal well.By examining the pore structure of highly heterogeneous reservoirs,the fractal dimension can be determined.Analytical methods are utilized to solve the Green function of a point source in a reservoir with fractal characteristics.Employing Green's function and the principle of spatial superposition,a finite flow model for a horizontal well coupled with a fractal reservoir is developed to calculate the flow rate and flow profile of the horizontal well.The model also accounts for the impact of wellbore friction and is solved numerically.A specific example is used for calculation to analyze the influence of fractal parameters on the production and flow rate of the horizontal well.When considering the fractal characteristics of oil reservoirs,the flow rate of the horizontal well is lower than that in Euclidean space.As the fractal dimension increases,the connectivity of pores in the reservoir improves,making it easier to drive the fluid into the wellbore,and the flow distribution along the wellbore becomes more uniform.Conversely,as the anomalous diffusion index increases,the connectivity between pores deteriorates,thus the distribution of flow rate along the wellbore becomes more uneven. 展开更多
关键词 fractal dimension RESERVOIR Horizontal well Anomalous diffusion index
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A Compact UHF Antenna Based on Hilbert Fractal Elements and a Serpentine Arrangement for Detecting Partial Discharg
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作者 Xiang Lin Jian Fang +4 位作者 Ming Zhang Kuang Yin Yan Tian Yingfei Guo Qianggang Wang 《Energy Engineering》 EI 2024年第5期1127-1141,共15页
Efforts to protect electric power systems from faults have commonly relied on the use of ultra-high frequency(UHF)antennas for detecting partial discharge(PD)as a common precursor to faults.However,the effectiveness o... Efforts to protect electric power systems from faults have commonly relied on the use of ultra-high frequency(UHF)antennas for detecting partial discharge(PD)as a common precursor to faults.However,the effectiveness of existing UHF antennas suffers from a number of challenges such as limited bandwidth,relatively large physical size,and low detection sensitivity.The present study addresses these issues by proposing a compact microstrip patch antenna with fixed dimensions of 100 mm×100 mm×1.6 mm.The results of computations yield an optimized antenna design consisting of 2nd-order Hilbert fractal units positioned within a four-layer serpentine arrangement with a fractal unit connection distance of 3.0 mm.Specifically,the optimized antenna design achieves a detection bandwidth for which the voltage standing wave ratio is less than 2 that is approximately 97.3%of the UHF frequency range(0.3–3 GHz).Finally,a prototype antenna is fabricated using standard printed circuit board technology,and the results of experiments demonstrate that the proposed antenna is capable of detecting PD signals at a distance of 8 m from the discharge source. 展开更多
关键词 Power system fault partial discharge UHF antenna fractal antenna micro-strip antenna
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Computational Quantification of Map Projection Distortion by Fractal Dimension of Coastlines
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作者 Franklin Lee 《Journal of Applied Mathematics and Physics》 2024年第5期1890-1903,共14页
Maps, essential tools for portraying the Earth’s surface, inherently introduce distortions to geographical features. While various quantification methods exist for assessing these distortions, they often fall short w... Maps, essential tools for portraying the Earth’s surface, inherently introduce distortions to geographical features. While various quantification methods exist for assessing these distortions, they often fall short when evaluating actual geographic features. In our study, we took a novel approach by analyzing map projection distortion from a geometric perspective. We computed the fractal dimensions of different stretches of coastline before and after projection using the divide-and-conquer algorithm and image processing. Our findings revealed that map projections, even when preserving basic shapes, inevitably stretch and compress coastlines in diverse directions. This analysis method provides a more realistic and practical way to measure map-induced distortions, with significant implications for cartography, geographic information systems (GIS), and geomorphology. By bridging the gap between theoretical analysis and real-world features, this method greatly enhances accuracy and practicality when evaluating map projections. 展开更多
关键词 Map Projection Distortion COASTLINE fractal Dimension CARTOGRAPHY Geographic Information Systems
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Fractal Analysis on Methane Hydrate Formation in Porous Media
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作者 Xinfang Cao Peizhuo Mo 《Journal of Electronic Research and Application》 2024年第3期207-212,共6页
The study of the hydrate formation process in porous media is of great significance for hydrate application.In this work,the formation process of methane hydrate in porous media was monitored in situ by a low-field ma... The study of the hydrate formation process in porous media is of great significance for hydrate application.In this work,the formation process of methane hydrate in porous media was monitored in situ by a low-field magnetic resonance imaging(MRI)system.The formation characteristics of methane hydrate in porous media and the change of fractal dimension of pore space were studied through the change of residual water saturation and T2 relaxation time distribution.The experimental results show that the hydrate formation process is divided into two stages:fast and slow.During the formation process,the water in the pores is continuously consumed and transformed into hydrate,and the overall T2 distribution gradually shifts to the left.In the formation process of hydrate,the pore space becomes more complex,the change of fractal dimension from top to bottom of the reactor gradually increases,and the hydrate formation rate also gradually increases. 展开更多
关键词 MRI experiment Water saturation fractal dimension
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一种基于Fractal-DenseNet的电磁血管断层图像重建算法
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作者 杨丹 王雨佳 +1 位作者 辛采凝 徐彬 《东北大学学报(自然科学版)》 EI CAS CSCD 北大核心 2023年第7期931-937,共7页
针对电磁血管断层图像重建中存在的欠定性、病态性,提出一种基于Fractal-DenseNet的电磁血管断层图像重建算法.基于血流磁电耦合效应的血管断层图像重建原理,将FractalNet的分形思想与DenseNet的密集紧密连接思想相结合,构建了一种适用... 针对电磁血管断层图像重建中存在的欠定性、病态性,提出一种基于Fractal-DenseNet的电磁血管断层图像重建算法.基于血流磁电耦合效应的血管断层图像重建原理,将FractalNet的分形思想与DenseNet的密集紧密连接思想相结合,构建了一种适用于反演血液流速分布的Fractal-DenseNet网络模型,用于血管断层图像重建.通过人体前臂尺动脉血流磁电耦合测量模型,建立血管断层剖面流速和血流磁电效应引起的电压信号的对应数据对,分别作为网络模型输入和输出;通过监督学习,实现基于血管断层流速分布的血管断层图像重建.结果表明:Fractal-DenseNet重建结果的均方根误差和相关系数分别为0.0078,99.28%;本文算法具有良好的抗噪性,可在复杂边界条件下实现血管断层图像重建. 展开更多
关键词 血管断层图像重建 fractal-DenseNet 血流磁电耦合效应 人体前臂尺动脉 监督学习
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Effect of shear-induced contact area and aperture variations on nonlinear flow behaviors in fractal rock fractures 被引量:5
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作者 Changsheng Wang Richeng Liu +2 位作者 Yujing Jiang Gang Wang Hengjie Luan 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2023年第2期309-322,共14页
This study experimentally analyzes the nonlinear flow characteristics and channelization of fluid through rough-walled fractures during the shear process using a shear-flow-visualization apparatus.A series of fluid fl... This study experimentally analyzes the nonlinear flow characteristics and channelization of fluid through rough-walled fractures during the shear process using a shear-flow-visualization apparatus.A series of fluid flow and visualization tests is performed on four transparent fracture specimens with various shear displacements of 1 mm,3 mm,5 mm,7 mm and 10 mm under a normal stress of 0.5 MPa.Four granite fractures with different roughnesses are selected and quantified using variogram fractal dimensions.The obtained results show that the critical Reynolds number tends to increase with increasing shear displacement but decrease with increasing roughness of fracture surface.The flow paths are more tortuous at the beginning of shear because of the wide distribution of small contact spots.As the shear displacement continues to increase,preferential flow paths are more distinctly observed due to the decrease in the number of contact spots caused by shear dilation;yet the area of single contacts in-creases.Based on the experimental results,an empirical mathematical equation is proposed to quantify the critical Reynolds number using the contact area ratio and fractal dimension. 展开更多
关键词 FRACTURE Shear displacement fractal dimension Nonlinear flow Contact area Flow visualization
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Multi-scale pore fractal characteristics of differently ranked coal and its impact on gas adsorption 被引量:3
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作者 Zhongbei Li Ting Ren +4 位作者 Xiangchun Li Ming Qiao Xiaohan Yang Lihai Tan Baisheng Nie 《International Journal of Mining Science and Technology》 SCIE EI CAS CSCD 2023年第4期389-401,共13页
Well-developed pores and cracks in coal reservoirs are the main venues for gas storage and migration.To investigate the multi-scale pore fractal characteristics,six coal samples of different rankings were studied usin... Well-developed pores and cracks in coal reservoirs are the main venues for gas storage and migration.To investigate the multi-scale pore fractal characteristics,six coal samples of different rankings were studied using high-pressure mercury injection(HPMI),low-pressure nitrogen adsorption(LPGA-N2),and scanning electron microscopy(SEM)test methods.Based on the Frankel,Halsey and Hill(FHH)fractal theory,the Menger sponge model,Pores and Cracks Analysis System(PCAS),pore volume complexity(D_(v)),coal surface irregularity(Ds)and pore distribution heterogeneity(D_(p))were studied and evaluated,respectively.The effect of three fractal dimensions on the gas adsorption ability was also analyzed with high-pressure isothermal gas adsorption experiments.Results show that pore structures within these coal samples have obvious fractal characteristics.A noticeable segmentation effect appears in the Dv1and Dv2fitting process,with the boundary size ranging from 36.00 to 182.95 nm,which helps differentiate diffusion pores and seepage fractures.The D values show an asymmetric U-shaped trend as the coal metamorphism increases,demonstrating that coalification greatly affects the pore fractal dimensions.The three fractal dimensions can characterize the difference in coal microstructure and reflect their influence on gas adsorption ability.Langmuir volume(V_(L))has an evident and positive correlation with Dsvalues,whereas Langmuir pressure(P_(L))is mainly affected by the combined action of Dvand Dp.This study will provide valuable knowledge for the appraisal of coal seam gas reservoirs of differently ranked coals. 展开更多
关键词 Multi-scale pore structure fractal theory fractal characteristics Differently ranked coal Coalbed gas adsorption
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Fractal nature of human gastrointestinal system:Exploring a new era
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作者 Fabio Grizzi Marco Spadaccini +5 位作者 Maurizio Chiriva-Internati Mohamed A A A Hegazi Robert S Bresalier Cesare Hassan Alessandro Repici Silvia Carrara 《World Journal of Gastroenterology》 SCIE CAS 2023年第25期4036-4052,共17页
The morphological complexity of cells and tissues,whether normal or pathological,is characterized by two primary attributes:Irregularity and self-similarity across different scales.When an object exhibits self-similar... The morphological complexity of cells and tissues,whether normal or pathological,is characterized by two primary attributes:Irregularity and self-similarity across different scales.When an object exhibits self-similarity,its shape remains unchanged as the scales of measurement vary because any part of it resembles the whole.On the other hand,the size and geometric characteristics of an irregular object vary as the resolution increases,revealing more intricate details.Despite numerous attempts,a reliable and accurate method for quantifying the morphological features of gastrointestinal organs,tissues,cells,their dynamic changes,and pathological disorders has not yet been established.However,fractal geometry,which studies shapes and patterns that exhibit self-similarity,holds promise in providing a quantitative measure of the irregularly shaped morphologies and their underlying self-similar temporal behaviors.In this context,we explore the fractal nature of the gastrointestinal system and the potential of fractal geometry as a robust descriptor of its complex forms and functions.Additionally,we examine the practical applications of fractal geometry in clinical gastroenterology and hepatology practice. 展开更多
关键词 fractals Geometry GASTROENTEROLOGY ESOPHAGUS STOMACH COLON PANCREAS Liver Time-series Shape Behavior
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