Matrix swelling effect will cause the change of microstructure of coal reservoir and its permeability,which is the key factor affecting the engineering effect of CO_(2)-ECBM technology.The Sihe and Yuwu collieries are...Matrix swelling effect will cause the change of microstructure of coal reservoir and its permeability,which is the key factor affecting the engineering effect of CO_(2)-ECBM technology.The Sihe and Yuwu collieries are taken as research objects.Firstly,visualization reconstruction of coal reservoir is realized.Secondly,the evolution of the pore/fracture structures under different swelling contents is discussed.Then,the influence of matrix phase with different swelling contents on permeability is discussed.Finally,the mechanism of swelling effect during the CO_(2)-ECBM process is further discussed.The results show that the intra-matrix pores and matrix-edge fractures are the focus of this study,and the contacting area between matrix and pore/fracture is the core area of matrix swelling.The number of matrix particles decreases with the increase of size,and the distribution of which is isolated with small size and interconnected with large size.The swelling effect of matrix particles with larger size has a great influence on the pore/fracture structures.The number of connected pores/fractures is limited and only interconnected in a certain direction.With the increase of matrix swelling content,the number,porosity,width,fractal dimension,surface area and volume of pores/fractures decrease,and their negative contribution to absolute permeability increases from 0.368% to 0.633% and 0.868%-1.404%,respectively.With the increase of swelling content,the number of intra-matrix pores gradually decreases and the pore radius becomes shorter during the CO_(2)-ECBM process.The matrix continuously expands to the connected fractures,and the width of connected fractures gradually shorten.Under the influence of matrix swelling,the bending degree of fluid flow increases gradually,so the resistance of fluid migration increases and the permeability gradually decreases.This study shows that the matrix swelling effect is the key factor affecting CBM recovery,and the application of this effect in CO_(2)-ECBM process can be discussed.展开更多
To improve spectral X-ray CT reconstructed image quality, the energy-weighted reconstructed image xbins^W and the separable paraboloidal surrogates（SPS） algorithm are proposed for the prior image constrained compres...To improve spectral X-ray CT reconstructed image quality, the energy-weighted reconstructed image xbins^W and the separable paraboloidal surrogates（SPS） algorithm are proposed for the prior image constrained compressed sensing（PICCS）-based spectral X-ray CT image reconstruction. The PICCS-based image reconstruction takes advantage of the compressed sensing theory, a prior image and an optimization algorithm to improve the image quality of CT reconstructions.To evaluate the performance of the proposed method, three optimization algorithms and three prior images are employed and compared in terms of reconstruction accuracy and noise characteristics of the reconstructed images in each energy bin.The experimental simulation results show that the image xbins^W is the best as the prior image in general with respect to the three optimization algorithms; and the SPS algorithm offers the best performance for the simulated phantom with respect to the three prior images. Compared with filtered back-projection（FBP）, the PICCS via the SPS algorithm and xbins^W as the prior image can offer the noise reduction in the reconstructed images up to 80. 46%, 82. 51%, 88. 08% in each energy bin,respectively. M eanwhile, the root-mean-squared error in each energy bin is decreased by 15. 02%, 18. 15%, 34. 11% and the correlation coefficient is increased by 9. 98%, 11. 38%,15. 94%, respectively.展开更多
The main objective of this paper is to evaluate the effects of asphalt concrete types on the microstructural characteristics at high-temperature. Suspend-dense structure and Skeleton-dense structure were selected to i...The main objective of this paper is to evaluate the effects of asphalt concrete types on the microstructural characteristics at high-temperature. Suspend-dense structure and Skeleton-dense structure were selected to investigate the deformation of pavement at meso-scale. The internal microstructures of typical asphalt concretes, AC, SUP and SMA, were scanned by X-ray CT device, and microstructural changes before and after high-temperature damage were researched by digital image processing. Adaptive threshold segmentation algorithm（ATSA） based on image radius was developed and utilized to obtain the binary images of aggregates, air-voids and asphalt mastic. Then the shape and distribution of air-voids and aggregates were analyzed. The results show that the ATSA can distinguish the target and background effectively. Gradation and coarse aggregate size of asphalt mixtures have an obvious influence on the distribution of air-voids. The movements of aggregate particles are complex and aggregates with elliptic sharp show great rotation. The effect of gradation on microstructure during high-temperature damage promotes the research about the failure mechanism of asphalt concrete pavement.展开更多
In this paper a series of digital image processing methods were adopted for getting separated coarse aggregates from asphalt mixture specimen using high-resolution X-ray Computed Tomography (CT) images.The existing th...In this paper a series of digital image processing methods were adopted for getting separated coarse aggregates from asphalt mixture specimen using high-resolution X-ray Computed Tomography (CT) images.The existing three dimensional (3D) particles matching methods based on two dimensional (2D) continuous cross-sections were analyzed and a new 'overlap area method' was presented.After the 3D particles were extracted one by one successfully,the basic parameters of each aggregate:perimeter,area,surface area,and volume were calculated by chain code method.Finally,the 3D mass center coordinates and the sphericity index were introduced.展开更多
Utilizing lightweight Al alloys in various industrial applications requires achieving precise pressure tightness and leak requirements.Vacuum pressure impregnation(VPI)with thermosetting polymers is commonly used to a...Utilizing lightweight Al alloys in various industrial applications requires achieving precise pressure tightness and leak requirements.Vacuum pressure impregnation(VPI)with thermosetting polymers is commonly used to address leakage defects in die-cast Al alloys.In this study,the efficacy of the VPI technique in sealing alloy parts was investigated using a combination of nondestructive micro X-ray computed tomography(micro XCT)and a standard leak test.The results demonstrate that the commonly used water leak test is insufficient for determining the sealing performance.Instead,micro XCT shows distinct advantages by enabling more comprehensive analysis.It reveals the presence of a low atomic number impregnates sealant within casting defects,which has low grey contrast and allows for visualizing primary leakage paths in 3D.The effective atomic number of impregnated resin is 6.75 and that of Al alloy is 13.69 by dual-energy X-ray CT.This research findings will contribute to enhancing the standard VPI process parameters and the properties of impregnating sealants to improve quality assurance for impregnation in industrial metals.展开更多
Different sedimentary zones in coral reefs lead to significant anisotropy in the pore structure of coral reef limestone(CRL),making it difficult to study mechanical behaviors.With X-ray computed tomography(CT),112 CRL...Different sedimentary zones in coral reefs lead to significant anisotropy in the pore structure of coral reef limestone(CRL),making it difficult to study mechanical behaviors.With X-ray computed tomography(CT),112 CRL samples were utilized for training the support vector machine(SVM)-,random forest(RF)-,and back propagation neural network(BPNN)-based models,respectively.Simultaneously,the machine learning model was embedded into genetic algorithm(GA)for parameter optimization to effectively predict uniaxial compressive strength(UCS)of CRL.Results indicate that the BPNN model with five hidden layers presents the best training effect in the data set of CRL.The SVM-based model shows a tendency to overfitting in the training set and poor generalization ability in the testing set.The RF-based model is suitable for training CRL samples with large data.Analysis of Pearson correlation coefficient matrix and the percentage increment method of performance metrics shows that the dry density,pore structure,and porosity of CRL are strongly correlated to UCS.However,the P-wave velocity is almost uncorrelated to the UCS,which is significantly distinct from the law for homogenous geomaterials.In addition,the pore tensor proposed in this paper can effectively reflect the pore structure of coral framework limestone(CFL)and coral boulder limestone(CBL),realizing the quantitative characterization of the heterogeneity and anisotropy of pore.The pore tensor provides a feasible idea to establish the relationship between pore structure and mechanical behavior of CRL.展开更多
X-ray CT scanners,due to the transmissive nature of X-rays,have enabled the non-destructive evaluation of industrial products,even inside their bodies.In light of its effectiveness,this study introduces a new approach...X-ray CT scanners,due to the transmissive nature of X-rays,have enabled the non-destructive evaluation of industrial products,even inside their bodies.In light of its effectiveness,this study introduces a new approach to accelerate the inspection of many mechanical parts with the same shape in a bin.The input to this problem is a volumetric image(i.e.,CT volume)of many parts obtained by a single CT scan.We need to segment the parts in the volume to inspect each of them;however,random postures and dense contacts of the parts prohibit part segmentation using traditional template matching.To address this problem,we convert both the scanned volumetric images of the template and the binned parts to simpler graph structures and solve a subgraph matching problem to segment the parts.We perform a distance transform to convert the CT volume into a distance field.Then,we construct a graph based on Morse theory,in which graph nodes are located at the extremum points of the distance field.The experimental evaluation demonstrates that our fully automatic approach can detect target parts appropriately,even for a heap of 50 parts.Moreover,the overall computation can be performed in approximately 30 min for a large CT volume of approximately 2000×2000×1000 voxels.展开更多
The geometry of joints has a significant influence on the mechanical properties of rocks.To simplify the curved joint shapes in rocks,the joint shape is usually treated as straight lines or planes in most laboratory e...The geometry of joints has a significant influence on the mechanical properties of rocks.To simplify the curved joint shapes in rocks,the joint shape is usually treated as straight lines or planes in most laboratory experiments and numerical simulations.In this study,the computerized tomography (CT) scanning and photogrammetry were employed to obtain the internal and surface joint structures of a limestone sample,respectively.To describe the joint geometry,the edge detection algorithms and a three-dimensional (3D) matrix mapping method were applied to reconstruct CT-based and photogrammetry-based jointed rock models.For comparison tests,the numerical uniaxial compression tests were conducted on an intact rock sample and a sample with a joint simplified to a plane using the parallel computing method.The results indicate that the mechanical characteristics and failure process of jointed rocks are significantly affected by the geometry of joints.The presence of joints reduces the uniaxial compressive strength (UCS),elastic modulus,and released acoustic emission (AE) energy of rocks by 37%–67%,21%–24%,and 52%–90%,respectively.Compared to the simplified joint sample,the proposed photogrammetry-based numerical model makes the most of the limited geometry information of joints.The UCS,accumulative released AE energy,and elastic modulus of the photogrammetry-based sample were found to be very close to those of the CT-based sample.The UCS value of the simplified joint sample (i.e.38.5 MPa) is much lower than that of the CT-based sample (i.e.72.3 MPa).Additionally,the accumulative released AE energy observed in the simplified joint sample is 3.899 times lower than that observed in the CT-based sample.CT scanning provides a reliable means to visualize the joints in rocks,which can be used to verify the reliability of photogrammetry techniques.The application of the photogrammetry-based sample enables detailed analysis for estimating the mechanical properties of jointed rocks.展开更多
X-ray CT （computed tomography） was used to scan asphalt mixture specimen to ob- tain high resolution continuous cross-section images and the meso-structure. According to the theory of three-dimensional （3D） recons...X-ray CT （computed tomography） was used to scan asphalt mixture specimen to ob- tain high resolution continuous cross-section images and the meso-structure. According to the theory of three-dimensional （3D） reconstruction, the 3D reconstruction algorithm was investi- gated in this paper. The key to the reconstruction technique is the acquisition of the voxel posi- tions and the relationship between the pixel element and node. Three-dimensional numerical model of asphalt mixture specimen was created by a self-developed program. A splitting test was conducted to predict the stress distributions of the asphalt mixture and verify the rationality of the 3D model.展开更多
The ground subsidence on the underground pipe often is caused with the reduction of the effective stress and the loss of suction in the base course and then,soil drainage into the pipe.The final formation of the cavit...The ground subsidence on the underground pipe often is caused with the reduction of the effective stress and the loss of suction in the base course and then,soil drainage into the pipe.The final formation of the cavity growth in the ground was observed as the ground subsidence.Authors focused this problem and hence performed model tests with water-inflow and drainage cycle in the model ground.The mechanism of cavity generation in the model ground was observed using an X-ray Computed Tomography(CT)scanner.In those studies,water was supplied into the model grounds from the defected underground pipe model in case of the change of relative density and grain size distribution.As results,it was observed that the loosening area was generated from the defected part with water-inflow and some of the soil particles in the ground were drained into the underground pipe through the defected part.And afterward,the cavity was generated just above the defected part of the model pipe in the ground.Based on this observation,it might be said that the bulk density of soil around the defected pipe played one of key factor to generate the cavity in the ground.Moreover,the dimension of the defected part should be related to the magnification of the ground subsidence,in particular,crack width on a sewerage pipe and particle size would be the quantitative factor to evaluate the magnification of the ground subsidence.In this paper,it was concluded that the low relative density of soil would become the critical factor to cause the fatal failure of model ground if the maximum grain size was close to the dimension of crack width of defective part.The fatal collapse of the ground with high relative density more than 80%would be avoided in a few cycles of water inflow and soil drainage.展开更多
Pore scale variables(e.g.,porosity,grain size)are important indexes to predict the hydraulic properties of porous geomaterials.X-ray images from ten types of intact sandstones and another type of sandstone samples sub...Pore scale variables(e.g.,porosity,grain size)are important indexes to predict the hydraulic properties of porous geomaterials.X-ray images from ten types of intact sandstones and another type of sandstone samples subjected to triaxial compression are used to investigate the permeability and fracture characteristics.A novel double threshold segmentation algorithm is proposed to segment cracks,pores and grains,and pore scale variables are defined and extracted from these X-ray CT images to study the geometric characteristics of microstructures of porous geomaterials.Moreover,novel relations among these pore scale variables for permeability prediction are established,and the evolution process of cracks is investigated.The results indicate that the porescale permeability is prominently improved by cracks.In addition,excellent agreements are found between the measured and the estimated pore scale variables and permeability.The established correlations can be employed to effectively identify the hydraulic properties of porous geomaterials.展开更多
The microstructure characteristics and meso-defect volume changes of hardened cement paste before and after carbonation were investigated by three-dimensional （3D） X-ray computed tomograpby （XCT）, where three type...The microstructure characteristics and meso-defect volume changes of hardened cement paste before and after carbonation were investigated by three-dimensional （3D） X-ray computed tomograpby （XCT）, where three types water-to-cement ratio of 0.53, 0.35 and 0.23 were considered. The high-resolution 3D images of microstructure and filtered defects were reconstructed by an XCT VG Studio MAX 2.0 software, The meso- defect volume fractions and size distribution were analyzed based on 3D images through add-on modules of 3D defect analysis. The 3D meso-defects volume fractions before carbonation were 0.79%, 0.38% and 0.05% corresponding to w/c ratio=0.53, 0.35 and 0.23, respectively. The 3D meso-defects volume fractions after carbonation were 2.44%, 0.91% and 0.14% corresponding to w/c ratio=0.53, 0.35 and 0.23, respectively. The experimental results suggest that 3D meso-defects volume fractions after carbonation for above three w/c ratio increased significantly. At the same time, meso-cracks distribution of the carbonation shrinkage and gray values changes of the different w/c ratio and carbonation reactions were also investigated.展开更多
The objective of this paper is to propose a new quality evaluation method for asphalt concrete mixture using X-ray CT scanner.To achieve this aim,asphalt mixtures should be subjected to the X-ray CT scanning and its c...The objective of this paper is to propose a new quality evaluation method for asphalt concrete mixture using X-ray CT scanner.To achieve this aim,asphalt mixtures should be subjected to the X-ray CT scanning and its characteristics should be clarified.The approach employed in this study was as follows:1)Coarse aggregate,fine aggregate,filler and bitumen were prepared;2)dense-graded,coarse-graded and porous asphalt mixtures were made;3)materials and mixtures were subjected to the X-ray CT scanning;4)frequency of CT-value,threshold value,average slice CT-value,average segment CT-value were computed.In the material examination,CT-value of aggregate becomes smaller in the order of coarse aggregate,fine aggregate and filler and CT image of bitumen was nearly homogeneous.In the mixture examination,histograms of CT-value and four segmentation images made from CT images expressed the material and mixture characterization such as particle size and the difference in bitumen content and mixture type visibly and the bitumen content varies with the threshold values.In addition,the average segment CT-value without threshold value by dividing the fine aggregate from the coarse aggregate and average CT-value of the coarse aggregate,especially is highly correlated with average CT-value of the bitumen.展开更多
Representative elementary volume(REV)is the key to study the heterogeneity of digital coal and characterize its macroscopic and microscopic properties.The permeability evolution law of digital coal based on REV analys...Representative elementary volume(REV)is the key to study the heterogeneity of digital coal and characterize its macroscopic and microscopic properties.The permeability evolution law of digital coal based on REV analysis can provide theoretical support for the application of permeability prediction model in multi-scale reservoirs.This study takes typical coal samples from Bofang and Sihe coal mines in Qinshui Basin as research object.First,the nondestructive information of two samples is scanned and visualized.Secondly,the calculation methods of two-dimensional(2D)and threedimensional(3D)fractal dimensions of pores and fractures are illustrated.Then,the determination methods of REV based on porosity and fractal dimension are compared.Finally,the distribution pattern of fractal dimension and porosity curves is studied,the relationship between 2D and 3D fractal dimension is characterized,and the application of fractal permeability model in permeability analysis of multi-scale reservoir is further discussed.The REV size varies greatly in different vertex directions of the same sample and between samples,so REV analysis can only be performed in specific directions.When the REV based on fractal dimension is determined,the porosity curve continues to maintain a downward trend and then tends to be stable.The 2D fractal dimension has a positive linear correlation with the 3D fractal dimension,and the porosity can be expressed as a linear function of the fractal dimension.The permeability through REV analysis domain is mainly affected by fractal dimension,dip angle,azimuth angle and maximum fracture length,which is of great significance for exploring permeability evolution law of coal reservoir at different scales.This study is of great significance for enriching the determination methods of REV in digital coal and exploring the permeability evolution law of multi-scale reservoirs.展开更多
基金This work was financially supported by the National Natural Science Foundation of China(No.42102217)the University Synergy Innovation Program of Anhui Province(No.GXXT-2021-018)+3 种基金the Natural Science Research Project of Anhui University(No.KJ2020A0315No.KJ2020A0317)the Natural Science Foundation of Anhui Province(No.2108085MD134)the Foundation of State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing(No.PRP/open-2005).
文摘Matrix swelling effect will cause the change of microstructure of coal reservoir and its permeability,which is the key factor affecting the engineering effect of CO_(2)-ECBM technology.The Sihe and Yuwu collieries are taken as research objects.Firstly,visualization reconstruction of coal reservoir is realized.Secondly,the evolution of the pore/fracture structures under different swelling contents is discussed.Then,the influence of matrix phase with different swelling contents on permeability is discussed.Finally,the mechanism of swelling effect during the CO_(2)-ECBM process is further discussed.The results show that the intra-matrix pores and matrix-edge fractures are the focus of this study,and the contacting area between matrix and pore/fracture is the core area of matrix swelling.The number of matrix particles decreases with the increase of size,and the distribution of which is isolated with small size and interconnected with large size.The swelling effect of matrix particles with larger size has a great influence on the pore/fracture structures.The number of connected pores/fractures is limited and only interconnected in a certain direction.With the increase of matrix swelling content,the number,porosity,width,fractal dimension,surface area and volume of pores/fractures decrease,and their negative contribution to absolute permeability increases from 0.368% to 0.633% and 0.868%-1.404%,respectively.With the increase of swelling content,the number of intra-matrix pores gradually decreases and the pore radius becomes shorter during the CO_(2)-ECBM process.The matrix continuously expands to the connected fractures,and the width of connected fractures gradually shorten.Under the influence of matrix swelling,the bending degree of fluid flow increases gradually,so the resistance of fluid migration increases and the permeability gradually decreases.This study shows that the matrix swelling effect is the key factor affecting CBM recovery,and the application of this effect in CO_(2)-ECBM process can be discussed.
基金The National Natural Science Foundation of China(No.51575256)the Fundamental Research Funds for the Central Universities(No.NP2015101,XZA16003)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘To improve spectral X-ray CT reconstructed image quality, the energy-weighted reconstructed image xbins^W and the separable paraboloidal surrogates（SPS） algorithm are proposed for the prior image constrained compressed sensing（PICCS）-based spectral X-ray CT image reconstruction. The PICCS-based image reconstruction takes advantage of the compressed sensing theory, a prior image and an optimization algorithm to improve the image quality of CT reconstructions.To evaluate the performance of the proposed method, three optimization algorithms and three prior images are employed and compared in terms of reconstruction accuracy and noise characteristics of the reconstructed images in each energy bin.The experimental simulation results show that the image xbins^W is the best as the prior image in general with respect to the three optimization algorithms; and the SPS algorithm offers the best performance for the simulated phantom with respect to the three prior images. Compared with filtered back-projection（FBP）, the PICCS via the SPS algorithm and xbins^W as the prior image can offer the noise reduction in the reconstructed images up to 80. 46%, 82. 51%, 88. 08% in each energy bin,respectively. M eanwhile, the root-mean-squared error in each energy bin is decreased by 15. 02%, 18. 15%, 34. 11% and the correlation coefficient is increased by 9. 98%, 11. 38%,15. 94%, respectively.
基金Funded by National Natural Science Foundation of China(No.51178114)the Fundamental Research Funds for the Central Universities(No.CXLX12_0117)the Scientific Research Foundation of Graduate School of Southeast University(No.YBJJ1318)
文摘The main objective of this paper is to evaluate the effects of asphalt concrete types on the microstructural characteristics at high-temperature. Suspend-dense structure and Skeleton-dense structure were selected to investigate the deformation of pavement at meso-scale. The internal microstructures of typical asphalt concretes, AC, SUP and SMA, were scanned by X-ray CT device, and microstructural changes before and after high-temperature damage were researched by digital image processing. Adaptive threshold segmentation algorithm（ATSA） based on image radius was developed and utilized to obtain the binary images of aggregates, air-voids and asphalt mastic. Then the shape and distribution of air-voids and aggregates were analyzed. The results show that the ATSA can distinguish the target and background effectively. Gradation and coarse aggregate size of asphalt mixtures have an obvious influence on the distribution of air-voids. The movements of aggregate particles are complex and aggregates with elliptic sharp show great rotation. The effect of gradation on microstructure during high-temperature damage promotes the research about the failure mechanism of asphalt concrete pavement.
基金Sponsored by the Key Projects of National Natural Science Foundation of China (Grant No.51038004)the Western China Communications Construction and Technology Project (Grant No.2009318000078)
文摘In this paper a series of digital image processing methods were adopted for getting separated coarse aggregates from asphalt mixture specimen using high-resolution X-ray Computed Tomography (CT) images.The existing three dimensional (3D) particles matching methods based on two dimensional (2D) continuous cross-sections were analyzed and a new 'overlap area method' was presented.After the 3D particles were extracted one by one successfully,the basic parameters of each aggregate:perimeter,area,surface area,and volume were calculated by chain code method.Finally,the 3D mass center coordinates and the sphericity index were introduced.
文摘Utilizing lightweight Al alloys in various industrial applications requires achieving precise pressure tightness and leak requirements.Vacuum pressure impregnation(VPI)with thermosetting polymers is commonly used to address leakage defects in die-cast Al alloys.In this study,the efficacy of the VPI technique in sealing alloy parts was investigated using a combination of nondestructive micro X-ray computed tomography(micro XCT)and a standard leak test.The results demonstrate that the commonly used water leak test is insufficient for determining the sealing performance.Instead,micro XCT shows distinct advantages by enabling more comprehensive analysis.It reveals the presence of a low atomic number impregnates sealant within casting defects,which has low grey contrast and allows for visualizing primary leakage paths in 3D.The effective atomic number of impregnated resin is 6.75 and that of Al alloy is 13.69 by dual-energy X-ray CT.This research findings will contribute to enhancing the standard VPI process parameters and the properties of impregnating sealants to improve quality assurance for impregnation in industrial metals.
基金supported by the National Natural Science Foundation of China(Grant Nos.41877267 and 41877260)the Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA13010201).
文摘Different sedimentary zones in coral reefs lead to significant anisotropy in the pore structure of coral reef limestone(CRL),making it difficult to study mechanical behaviors.With X-ray computed tomography(CT),112 CRL samples were utilized for training the support vector machine(SVM)-,random forest(RF)-,and back propagation neural network(BPNN)-based models,respectively.Simultaneously,the machine learning model was embedded into genetic algorithm(GA)for parameter optimization to effectively predict uniaxial compressive strength(UCS)of CRL.Results indicate that the BPNN model with five hidden layers presents the best training effect in the data set of CRL.The SVM-based model shows a tendency to overfitting in the training set and poor generalization ability in the testing set.The RF-based model is suitable for training CRL samples with large data.Analysis of Pearson correlation coefficient matrix and the percentage increment method of performance metrics shows that the dry density,pore structure,and porosity of CRL are strongly correlated to UCS.However,the P-wave velocity is almost uncorrelated to the UCS,which is significantly distinct from the law for homogenous geomaterials.In addition,the pore tensor proposed in this paper can effectively reflect the pore structure of coral framework limestone(CFL)and coral boulder limestone(CBL),realizing the quantitative characterization of the heterogeneity and anisotropy of pore.The pore tensor provides a feasible idea to establish the relationship between pore structure and mechanical behavior of CRL.
文摘X-ray CT scanners,due to the transmissive nature of X-rays,have enabled the non-destructive evaluation of industrial products,even inside their bodies.In light of its effectiveness,this study introduces a new approach to accelerate the inspection of many mechanical parts with the same shape in a bin.The input to this problem is a volumetric image(i.e.,CT volume)of many parts obtained by a single CT scan.We need to segment the parts in the volume to inspect each of them;however,random postures and dense contacts of the parts prohibit part segmentation using traditional template matching.To address this problem,we convert both the scanned volumetric images of the template and the binned parts to simpler graph structures and solve a subgraph matching problem to segment the parts.We perform a distance transform to convert the CT volume into a distance field.Then,we construct a graph based on Morse theory,in which graph nodes are located at the extremum points of the distance field.The experimental evaluation demonstrates that our fully automatic approach can detect target parts appropriately,even for a heap of 50 parts.Moreover,the overall computation can be performed in approximately 30 min for a large CT volume of approximately 2000×2000×1000 voxels.
基金supported by the National Natural Science Foundation of China(Grant Nos.42277150,41977219)Henan Provincial Science and Technology Research Project(Grant No.222102320271).
文摘The geometry of joints has a significant influence on the mechanical properties of rocks.To simplify the curved joint shapes in rocks,the joint shape is usually treated as straight lines or planes in most laboratory experiments and numerical simulations.In this study,the computerized tomography (CT) scanning and photogrammetry were employed to obtain the internal and surface joint structures of a limestone sample,respectively.To describe the joint geometry,the edge detection algorithms and a three-dimensional (3D) matrix mapping method were applied to reconstruct CT-based and photogrammetry-based jointed rock models.For comparison tests,the numerical uniaxial compression tests were conducted on an intact rock sample and a sample with a joint simplified to a plane using the parallel computing method.The results indicate that the mechanical characteristics and failure process of jointed rocks are significantly affected by the geometry of joints.The presence of joints reduces the uniaxial compressive strength (UCS),elastic modulus,and released acoustic emission (AE) energy of rocks by 37%–67%,21%–24%,and 52%–90%,respectively.Compared to the simplified joint sample,the proposed photogrammetry-based numerical model makes the most of the limited geometry information of joints.The UCS,accumulative released AE energy,and elastic modulus of the photogrammetry-based sample were found to be very close to those of the CT-based sample.The UCS value of the simplified joint sample (i.e.38.5 MPa) is much lower than that of the CT-based sample (i.e.72.3 MPa).Additionally,the accumulative released AE energy observed in the simplified joint sample is 3.899 times lower than that observed in the CT-based sample.CT scanning provides a reliable means to visualize the joints in rocks,which can be used to verify the reliability of photogrammetry techniques.The application of the photogrammetry-based sample enables detailed analysis for estimating the mechanical properties of jointed rocks.
基金supported by National Natural Science Foundation of China(NSFC)(No.51178056)Fundamental and Applied Research Project of Chinese National Transportation Department(No.2013319812010)the Special Fund for Basic Scientific Research of Central Colleges,Chang'an University(No.CHD2013G3212003)
文摘X-ray CT （computed tomography） was used to scan asphalt mixture specimen to ob- tain high resolution continuous cross-section images and the meso-structure. According to the theory of three-dimensional （3D） reconstruction, the 3D reconstruction algorithm was investi- gated in this paper. The key to the reconstruction technique is the acquisition of the voxel posi- tions and the relationship between the pixel element and node. Three-dimensional numerical model of asphalt mixture specimen was created by a self-developed program. A splitting test was conducted to predict the stress distributions of the asphalt mixture and verify the rationality of the 3D model.
文摘The ground subsidence on the underground pipe often is caused with the reduction of the effective stress and the loss of suction in the base course and then,soil drainage into the pipe.The final formation of the cavity growth in the ground was observed as the ground subsidence.Authors focused this problem and hence performed model tests with water-inflow and drainage cycle in the model ground.The mechanism of cavity generation in the model ground was observed using an X-ray Computed Tomography(CT)scanner.In those studies,water was supplied into the model grounds from the defected underground pipe model in case of the change of relative density and grain size distribution.As results,it was observed that the loosening area was generated from the defected part with water-inflow and some of the soil particles in the ground were drained into the underground pipe through the defected part.And afterward,the cavity was generated just above the defected part of the model pipe in the ground.Based on this observation,it might be said that the bulk density of soil around the defected pipe played one of key factor to generate the cavity in the ground.Moreover,the dimension of the defected part should be related to the magnification of the ground subsidence,in particular,crack width on a sewerage pipe and particle size would be the quantitative factor to evaluate the magnification of the ground subsidence.In this paper,it was concluded that the low relative density of soil would become the critical factor to cause the fatal failure of model ground if the maximum grain size was close to the dimension of crack width of defective part.The fatal collapse of the ground with high relative density more than 80%would be avoided in a few cycles of water inflow and soil drainage.
基金supported by the National Natural Science Foundation of China(Grant Nos.51839009 and 51679017)the Graduate Research and Innovation Foundation of Chongqing,China(Grant No.CYB18037).
文摘Pore scale variables(e.g.,porosity,grain size)are important indexes to predict the hydraulic properties of porous geomaterials.X-ray images from ten types of intact sandstones and another type of sandstone samples subjected to triaxial compression are used to investigate the permeability and fracture characteristics.A novel double threshold segmentation algorithm is proposed to segment cracks,pores and grains,and pore scale variables are defined and extracted from these X-ray CT images to study the geometric characteristics of microstructures of porous geomaterials.Moreover,novel relations among these pore scale variables for permeability prediction are established,and the evolution process of cracks is investigated.The results indicate that the porescale permeability is prominently improved by cracks.In addition,excellent agreements are found between the measured and the estimated pore scale variables and permeability.The established correlations can be employed to effectively identify the hydraulic properties of porous geomaterials.
基金Funded by the Scientific Research Foundation of the Graduate School of Southeast University (YBJJ1113)the National Basic Research Program of China (No.2009CB623200)the National Natural Science Foundation of China (No.51178103)
文摘The microstructure characteristics and meso-defect volume changes of hardened cement paste before and after carbonation were investigated by three-dimensional （3D） X-ray computed tomograpby （XCT）, where three types water-to-cement ratio of 0.53, 0.35 and 0.23 were considered. The high-resolution 3D images of microstructure and filtered defects were reconstructed by an XCT VG Studio MAX 2.0 software, The meso- defect volume fractions and size distribution were analyzed based on 3D images through add-on modules of 3D defect analysis. The 3D meso-defects volume fractions before carbonation were 0.79%, 0.38% and 0.05% corresponding to w/c ratio=0.53, 0.35 and 0.23, respectively. The 3D meso-defects volume fractions after carbonation were 2.44%, 0.91% and 0.14% corresponding to w/c ratio=0.53, 0.35 and 0.23, respectively. The experimental results suggest that 3D meso-defects volume fractions after carbonation for above three w/c ratio increased significantly. At the same time, meso-cracks distribution of the carbonation shrinkage and gray values changes of the different w/c ratio and carbonation reactions were also investigated.
文摘The objective of this paper is to propose a new quality evaluation method for asphalt concrete mixture using X-ray CT scanner.To achieve this aim,asphalt mixtures should be subjected to the X-ray CT scanning and its characteristics should be clarified.The approach employed in this study was as follows:1)Coarse aggregate,fine aggregate,filler and bitumen were prepared;2)dense-graded,coarse-graded and porous asphalt mixtures were made;3)materials and mixtures were subjected to the X-ray CT scanning;4)frequency of CT-value,threshold value,average slice CT-value,average segment CT-value were computed.In the material examination,CT-value of aggregate becomes smaller in the order of coarse aggregate,fine aggregate and filler and CT image of bitumen was nearly homogeneous.In the mixture examination,histograms of CT-value and four segmentation images made from CT images expressed the material and mixture characterization such as particle size and the difference in bitumen content and mixture type visibly and the bitumen content varies with the threshold values.In addition,the average segment CT-value without threshold value by dividing the fine aggregate from the coarse aggregate and average CT-value of the coarse aggregate,especially is highly correlated with average CT-value of the bitumen.
基金supported by the National Natural Science Foundation of China(Grant No.42102217)the University Synergy Innovation Program of Anhui Province(No.GXXT-2021-018)+2 种基金the Natural Science Research Project of Anhui University(Nos.KJ2020A0315 and KJ2020A0317)the Natural Science Foundation of Anhui Province(No.2108085MD134)the Foundation of State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing(No.PRP/open-2005).
文摘Representative elementary volume(REV)is the key to study the heterogeneity of digital coal and characterize its macroscopic and microscopic properties.The permeability evolution law of digital coal based on REV analysis can provide theoretical support for the application of permeability prediction model in multi-scale reservoirs.This study takes typical coal samples from Bofang and Sihe coal mines in Qinshui Basin as research object.First,the nondestructive information of two samples is scanned and visualized.Secondly,the calculation methods of two-dimensional(2D)and threedimensional(3D)fractal dimensions of pores and fractures are illustrated.Then,the determination methods of REV based on porosity and fractal dimension are compared.Finally,the distribution pattern of fractal dimension and porosity curves is studied,the relationship between 2D and 3D fractal dimension is characterized,and the application of fractal permeability model in permeability analysis of multi-scale reservoir is further discussed.The REV size varies greatly in different vertex directions of the same sample and between samples,so REV analysis can only be performed in specific directions.When the REV based on fractal dimension is determined,the porosity curve continues to maintain a downward trend and then tends to be stable.The 2D fractal dimension has a positive linear correlation with the 3D fractal dimension,and the porosity can be expressed as a linear function of the fractal dimension.The permeability through REV analysis domain is mainly affected by fractal dimension,dip angle,azimuth angle and maximum fracture length,which is of great significance for exploring permeability evolution law of coal reservoir at different scales.This study is of great significance for enriching the determination methods of REV in digital coal and exploring the permeability evolution law of multi-scale reservoirs.
