Three-dimensional finite element simulation and reconstruction of jointed rock models using CT scanning and photogrammetry

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.

An online physical simulation method for enhanced oil recovery by air injection in shale oil

In order to understand the mechanism of air flooding shale oil, an online physical simulation method for enhanced shale oil recovery by air injection was established by integrating CT scanning and nuclear magnetic resonance(NMR). The development effect of shale oil by air flooding under different depletion pressures, the micro-production characteristics of pore throats with different sizes and the mechanism of shale oil recovery by air flooding were analyzed. The effects of air oxygen content, permeability, gas injection pressure, and fractures on the air flooding effect in shale and crude oil production in pores with different sizes were analyzed. The recovery of shale oil can be greatly improved by injecting air into the depleted shale reservoir, but the oil displacement efficiency and the production degree of different levels of pore throats vary with the injection timing. The higher the air oxygen content and the stronger the low-temperature oxidation, the higher the production degree of pores with different sizes and the higher the shale oil recovery. The higher the permeability and the better the pore throat connectivity, the stronger the fluid flow capacity and the higher the shale oil recovery. As the injection pressure increases, the lower limit of the production degree of pore throats decreases, but gas channeling may occur to cause a premature breakthrough;as a result, the recovery increases and then decreases. Fractures can effectively increase the contact area between gas and crude oil, and increase the air sweep coefficient and matrix oil drainage area by supplying oil to fractures through the matrix, which means that a proper fracturing before air injection can help to improve the oil displacement effect under a reasonable production pressure difference.

Modeling and Simulation of a Transmission Line Response to a 400 kV/400V Capacitor Coupled Substation

The access to electricity in rural areas is extremely limited, but it is crucial for all citizens. The population in rural areas of sub-Saharan African (SSA) countries is generally low, making it economically unfeasible to implement traditional rural electrification (CRE) projects due to the high cost of establishing the necessary distribution infrastructure. To address this cost issue, one alternative technology for rural electrification (URE) that can be explored is the Capacitor Coupled Substation (CCS) technology. CCS is a cost-effective solution for supplying electricity to rural areas. The research is necessitated by the need to offer a cost-effective technology for supplying electricity to sparsely populated communities. This paper examines the impact on the transmission network when a 400 kV/400V CCS is connected to it. The system response when a CCS is connected to the network was modeled using MATLAB/Si-mulink. The results, based on the fixed load of 80 kW, showed negligible interference on the transmission line voltage. However, there was minor impact on the parameters downstream of the tapping point. These findings were further supported by introducing a fault condition to the CCS, which showed that interferences with the CCS could affect the overall stability of the transmission network downstream of the tapping node, similar to the behavior of an unstable load.

Computer-Aided Simulation of Mastoidectomy

Objective To establish a three-dimensional model of the temporal bone using CT scan images for study of temporal bone structures and simulation of mastoidectomy procedures. Methods CT scan images from 6 individuals (12 temporal bones) were used to reconstruct the Fallopian canal, internal auditory canal, cochlea, semicircular canals, sigmoid sinus, posterior fossa floor and jugular bulb on a computer platform. Their anatomical relations within the temporal bone were restored in the computed model. The same model was used to simulate mastoidectomy procedures. Results The reconstructed computer model provided accurate and clear three-dimensional images of temporal bone structures. Simulation of mastoidectomy using these images provided procedural experiences closely mimicking the real surgical procedure. Conclusion Computer-aided three dimensional reconstruction of temporal bone structures using CT scan images is a useful tool in surgical simulation and can aid surgical procedure planning.

An analytical simulation technique for cone-beam CT and pinhole SPECT

This study was aimed at developing an efficient simulation technique with an ordinary PC.The work involved derivation of mathematical operators,analytic phantom generations,and effective analytical projectors developing for cone-beam CT and pinhole SPECT imaging.The computer simulations based on the analytical projectors were developed by ray-tracing method for cone-beam CT and voxel-driven method for pinhole SPECT of degrading blurring.The 3D Shepp-Logan,Jaszczak and Defrise phantoms were used for simulation evaluations and image reconstructions.The reconstructed phantom images were of good accuracy with the phantoms.The results showed that the analytical simulation technique is an efficient tool for studying cone-beam CT and pinhole SPECT imaging.

Numerical simulation of asphalt mixture based on three-dimensional heterogeneous specimen

In order to verify the validity of finite element numerical simulation method for asphalt mixture, which consists of aggregates, mastic （where mastic is a kind of fine mixture composed of asphalt binder mixed with fines and fine aggregates） and air voids, based on three-dimensional （3D） heterogeneous specimen, X-ray computerized tomography （X-ray CT） was used to scan the asphalt specimens to obtain the real internal microstrnctures of asphalt mixture. CT images were reconstructed to build up 3D digital specimen, and the viscoelastic properties of mastic were described with Burgers model The uniaxial creep numerical simulations of three different levels of aggregate gradation were conducted. The simulation results agree well with the experimental results. The numerical simulation of asphalt mixture incorporated with real 3D microstructure based on finite element method is a promising application to conduct research of asphalt concrete. Additionally, this method can increase the mechanistic understanding of global viscoelastic properties of asphalt mixtures by linking the real 3D microstructure.

Flow simulation considering adsorption boundary layer based on digital rock and finite element method

Due to the low permeability of tight reservoirs,throats play a significant role in controlling fluid flow.Although many studies have been conducted to investigate fluid flow in throats in the microscale domain,comparatively fewer works have been devoted to study the effect of adsorption boundary layer(ABL)in throats based on the digital rock method.By considering an ABL,we investigate its effects on fluid flow.We build digital rock model based on computed tomography technology.Then,microscopic pore structures are extracted with watershed segmentation and pore geometries are meshed through Delaunay triangulation approach.Finally,using the meshed digital simulation model and finite element method,we investigate the effects of viscosity and thickness of ABL on microscale flow.Our results demonstrate that viscosity and thickness of ABL are major factors that significantly hinder fluid flow in throats.

Study of the numerical simulation of tight sandstone gas molecular diffusion based on digital core technology

Diffusion is an important mass transfer mode of tight sandstone gas. Since nano-pores are extensively developed in the interior of tight sandstone, a considerable body of research indicates that the type of diffusion is mainly molecular diffusion based on Fick＇s law. However, accurate modeling and understanding the physics of gas transport phenomena in nanoporous media is still a challenge for researchers and traditional investigation（analytical and experimental methods） have many limitations in studying the generic behavior. In this paper, we used Nano-CT to observe the pore structures of samples of the tight sandstone of western of Sichuan. Combined with advanced image processing technology, threedimensional distributions of the nanometer-sized pores were reconstructed and a tight sandstone digital core model was built, as well the pore structure parameters were analyzed quantitatively. Based on the digital core model, the diffusion process of methane molecules from a higher concentration area to a lower concentration area was simulated by a finite volume method. Finally, the reservoir＇s concentration evolution was visualized and the intrinsic molecular diffusivity tensor which reflects the diffusion capabilities of this rock was calculated. Through comparisons, we found that our calculated result was in good agreement with other empirical results. This study provides a new research method for tight sandstone digital rock physics. It is a foundation for future tight sandstone gas percolation theory and numerical simulation research.

SPECT-CT虚拟仿真实验教学平台的构建

随着SPECT-CT成为核医学的主流影像诊断设备,人才的缺口也逐渐增大,且传统的教学已无法满足实际需求。为解决教学中存在的理论与实践脱节、设备结构复杂、原理抽象、教学成本较高等问题,本文设计了基于Unity3D的SPECT-CT虚拟仿真实验教学系统,并构建了沉浸式SPECT-CT虚拟实验室场景。结果表明:该系统不仅可弥补学习资源有限、教学重点不突出、教学效率较低等问题,而且能激发学生的学习兴趣。

基于CT图像建模的TATB基PBX超声检测仿真方法

为突破TATB基PBX超声仿真精度的局限,实现结构与性能关联的超声无损检测与表征,提出基于CT图像建模的PBX超声仿真建模方法,利用CT图像中颗粒相与黏结剂相显著的灰度分布差异提取结构形态和特征,通过对CT图像切片降噪、二值化、边界优化等处理,获得了包含造型粉颗粒及边界形态的二维几何结构模型,并将该模型用于超声传播过程的有限元仿真,定量对比了基于CT图像的超声仿真模型与Voronoi模型仿真效果的差异。研究表明,基于CT图像模型可以实现TATB颗粒及边界形态随机复杂结构特征的有效刻画,使得超声仿真结果与实验更趋一致,声速、衰减、频域幅值和表观积分背散射系数的误差分别为0.32%、1.14%、0.92%和1.55%,均在2%以内,相较于Voronoi模型的误差(2.77%、35.93%、20.70%、13.68%)大幅降低,仿真准确性得到显著提升。

基于CT模拟机的治疗等中心计算程序的设计与实现

目的设计可移动式激光灯和CT扫描床的位置计算程序,用于确定放疗患者的治疗等中心。方法使用Spring Boot系统框架,设计治疗等中心计算程序(Therapy Iso-Center Calculation Program,TICP)。操作人员输入可移动式激光灯和CT扫描床的初始位置数据及计划位移数据,TICP能够自动计算治疗等中心对应激光灯和CT扫描床的最终位置。选取36组随机位移数据,使用模体对该程序进行准确性测试。结果TICP实现了治疗等中心对应位置的自动计算、历史记录查看、报表打印以及权限分配等功能。程序测试结果显示,左右(X)及腹背(Z)方向的偏差∆x和∆z均值分别为0.4和0.3 mm,头脚(Y)方向误差∆y≤1 mm;3个方向在偏差等级范围R_(a)内共有65组,R_(b)共有35组,R_(c)共有8组,不同方向上的平移误差等级差异均有统计学意义(P<0.05)。结论使用该程序可有效辅助CT模拟机下确定治疗等中心的工作,提高放疗工作效率。

儿童体部放疗模拟定位CT扫描参数优化

目的:在满足儿童放疗对模拟定位图像质量要求的前提下,通过模体扫描优化模拟定位CT参数设置,以降低放射辐射剂量。方法:使用Cat Phan700模体模拟儿童体部,使用飞利浦24排大孔径螺旋模拟定位CT,在不同毫安秒(mAs)和不同管电压(kV)下扫描模体获取CT图像。mAs范围设置60~400 mAs,每间隔20 mAs进行1次扫描,kV设置80、100、120 kV。图像评价参数包括图像噪声N_(10)和SD均值、均匀性、低对比度分辨率、高对比度分辨率和Air、Acrylic、50%bone、LDPE、20%bone、Teflon、Polystyrene、Delrin^(TM)、Lung、PMP、Water等物质的HU值稳定性。读取模拟定位CT系统自动计算的CTDIVol和DLP以评价辐射剂量。结果:在100 kV条件下,随着mAs增加,CTDI和DLP均呈上涨趋势,数据拟合均为线性关系,斜率分别为0.0345和0.9324。随mAs增加,图像噪声呈非线性下降趋势,mAs从60增加到140 mAs时,N_(10)和SD分别从0.25%和3.74 HU下降到0.14%和2.54 HU,当mAs≥180 mAs,N_(10)在0.10%~0.12%波动,SD均值在2.0~2.5HU波动,下降趋势明显变缓。当mAs从60 mAs增加到200 mAs时,图像低对比度分辨率迅速从0.53降低到0.29。图像均匀性、高对比度分辨率、不同物质HU值,受mAs影响较小。不同管电压扫描结果相比,100 kV、200 mAs的图像质量与120 kV结果相当,80 kV的图像质量无法达到临床要求。结论:为保证辐射剂量尽可能降低,对于模拟直径20 cm的圆柱体,管电压设置为100 kV时,mAs应选择在200 mAs。在实际儿童放疗模拟定位扫描中,可根据该模体结果和儿童的实际体型特征,微调扫描参数设置,以满足辐射防护最优化原则。

PET/CT 虚拟仿真实验平台建设

随着《“健康中国2030”规划纲要》的提出,高端医疗设备成为国家重点支持的领域之一。正电子发射型计算机断层显像技术(PET)和计算机断层扫描技术(CT)是目前世界上很复杂、应用价值很高的医学影像学设备。设备操作复杂、价格昂贵、线下培训成本高等诸多不利因素使得PET/CT仪器的教学培训难以开展。本研究基于虚拟现实技术,开发了一套PET/CT虚拟仿真实验平台,该平台包括虚拟PET/CT科室场景漫游、仪器成像原理、仪器构造及仪器使用考核测评等多个功能。该平台适用于生物医学工程、医学影像学等相关专业的学生。基于该平台学生可随时随地学习PET/CT的相关知识、原理和使用方法,不受时间和空间的限制。该平台特有的交互功能也可以较好地提高学生的参与感和探索欲,达到更理想的教学效果。

一种结合弹性波CT正演模拟与钻孔注水法的防渗墙检测方法研究

防渗墙是水利水电工程项目中的重要部分,随着防渗墙规模的逐渐扩大,常规防渗墙检测方法逐渐减少;为了增加防渗墙的检测手段,研究提出采用弹性波CT正演模拟技术,并与钻孔注水法相结合的方法;在钻孔注水试验时,利用弹性波CT正演模拟技术,检测水流在墙体中的流动情况,从而在检测防渗墙渗透性的同时,完成防渗墙的完整性检测;结果显示,在低速或高速异常速度模型中,走时残差的波动较大,且完全不同;采用围井法,实验深度为15 m时,计算得到的渗透系数为0.14*10~6 cm/s;采用常水头法,深度为15 m时,该方法计算得到的渗透系数为1.88*10~6 cm/s;说明基于弹性波CT正演模拟技术,可以有效地反映防渗墙的状态;而采用围井法检测得到的防渗墙渗透系数,低于采用常水头注水法得到的渗透系数;研究提出的方法可以准确地检测防渗墙的质量。

Experiment of dynamic seepage of tight/shale oil under matrix fracture coupling

A physical simulation method with a combination of dynamic displacement and imbibition was established by integrating nuclear magnetic resonance(NMR)and CT scanning.The microscopic production mechanism of tight/shale oil in pore throat by dynamic imbibition and the influencing factors on the development effect of dynamic imbibition were analyzed.The dynamic seepage process of fracking-soaking-backflow-production integration was simulated,which reveals the dynamic production characteristics at different development stages and their contribution to enhancing oil recovery(EOR).The seepage of tight/shale reservoirs can be divided into three stages:strong displacement and weak imbibition as oil produced rapidly by displacement from macropores and fractures,weak displacement and strong imbibition as oil produced slowly by reverse imbibition from small pores,and weak displacement and weak imbibition at dynamic equilibrium.The greater displacement pressure results in the higher displacement recovery and the lower imbibition recovery.However,if the displacement pressure is too high,the injected water is easy to break through the front and reduce the recovery degree.The higher the permeability,the greater the imbibition and displacement recovery,the shorter the time of imbibition balance,and the higher the final recovery.The fractures can effectively increase the imbibition contact area between matrix and water,reduce the oil-water seepage resistance,promote the oil-water displacement between matrix and fracture,and improve the oil displacement rate and recovery of the matrix.The soaking after fracturing is beneficial to the imbibition replacement and energy storage of the fluid;also,the effective use of the carrying of the backflow fluid and the displacement in the mining stage is the key to enhancing oil recovery.

CT三维重建联合仿真钉道建立在腰椎骨折治疗中的应用价值

目的探讨CT三维重建联合仿真钉道建立在腰椎骨折治疗中的应用价值。方法选取2019年1月—2023年1月收治行椎弓根螺钉内固定术的126例腰椎骨折,采用随机数字表法分为观察组63例和对照组63例,观察组接受CT三维重建联合仿真钉道建立指导手术,对照组接受常规解剖标志法结合C型臂X线透视定位指导手术。观察并比较2组置钉优良率、置钉时间、置钉出血量,手术前后评估患者腰椎Oswestry功能障碍指数(ODI)评分、下腰痛日本骨科协会评分(JOA)、下肢Fugl-Meyer运动功能评定量表(FMA)评分和腰椎功能恢复情况,并观察术后并发症。结果观察组置钉优良率为94.67%(302/319)高于对照组的88.79%(285/321)(P<0.01);观察组置钉时间短于对照组,置钉出血量少于对照组(P<0.01)。术后6个月,观察组ODI、JOA评分低于对照组,FMA评分高于对照组(P<0.05,P<0.01)。观察组术后总并发症发生率低于对照组(P<0.05)。结论利用CT三维重建联合仿真钉道的建立来指导手术,可有效提高腰椎骨折行椎弓根内固定术患者置钉优良率,缩短置钉时间,减少出血量,降低术后并发症发生风险,促进患者术后腰椎功能恢复。

考虑干湿循环影响的残积土μ–CT扫描与渗流模拟

花岗岩残积土广泛分布于中国东南沿海地区,其孔隙结构常因炎热多雨环境引起的干湿循环而发生扩张,改变土体的渗透性能,诱发工程事故。为了揭示干湿循环作用下花岗岩残积土细微观结构与渗透特性的演变规律,对原状样进行0到8次的脱湿–吸湿处理,开展微米计算机层析(μ–CT)扫描试验以获取土体的3维数字化模型,并结合扫描结果与AVIZO软件进行多通道渗流模拟,最后根据试验结果分别从定性和定量角度探究了土体孔隙体积分布与渗透系数的演化规律。结果表明:根据μ–CT扫描的图像结果,花岗岩残积土内部结构被划分为赤铁矿、石英、黏土和孔隙;3维重构模型反映了孔隙结构的扩张与连通模式,孔隙数量和尺寸在干湿循环过程中明显提高,孔隙率和孔隙连通率均与循环次数呈正相关;根据孔隙体积分布曲线可将土中孔隙分为微孔、中孔、大孔和裂隙4种类别,小体积微孔在干湿循环过程中逐渐转化为大体积的连通裂隙;3维渗流模型中的流线数量和分布密度随干湿循环次数增加而明显提高,由渗流模拟计算得到的绝对渗透率和渗透系数也不断增大;渗透系数的计算值总体上与实测值的演化规律相符,说明基于μ–CT扫描结果的渗流模拟可作为评价土体渗透特性的一种辅助手段。研究结果为深入了解花岗岩残积土渗流特性的环境损伤效应提供了重要的参考价值。

CT模拟定位三维适形调强放疗对晚期食管癌患者血清肿瘤标志物及生存质量的影响

目的:探讨CT模拟定位三维适形放疗在晚期食管癌患者中的效果。方法:选取2020年3月至2021年3月该院诊治的72例晚期食管癌患者,按随机数字表法分为两组,各36例。对照组给予常规模拟定位放射治疗,观察组则给予CT模拟定位三维适形调强放疗,5d为1个周期,共放疗5个周期。对比两组临床疗效、血清肿瘤标志物、生存质量。结果:观察组治疗总有效率较对照组高,有统计学差异(P<0.05);治疗后,观察组癌胚抗原(CEA)、人细胞角蛋白21-1片段(CYFRA21-1)、糖类抗原199(CA199)较对照组低,世界卫生组织生存质量测定量表简表(WHOQOL-BREF)内各维度评分较对照组高,有统计学差异(P<0.05)。结论:CT模拟定位三维适形调强放疗在晚期食管癌患者诊治内作用明显,能够下调肿瘤标志物表达,提高其生存质量。

Evaluation of pelvic lymph node coverage of conventional radiotherapy fields based on bony landmarks in Chinese cervical cancer patients using CT simulation

Objective： To evaluate the pelvic lymph node coverage of conventional pelvic fields based on bony landmarks in Chinese patients with cervical cancer by using computed tomography （CT） simulation images to contour pelvic vessels as substitutes for lymph nodes location. Methods： A retrospective review of CT simulation images and conventional pelvic radiation planning data sets was performed in 100 patients with cervical cancer at the International Federation of Gynecology and Obstetrics （FIGO） Stage liB to IIIB in our hospital. Pelvic arteries were contoured on CT simulation images, and the outlines of conventional pelvic fields were drawn as defined by the gynecologic oncology group （GOG） after hiding the contours. The distances between the following vessel contours and field borders were measured： D1, the superior border of the anterior/posterior （AP） field and the bifurcation of abdominal aorta; D2, the ipsilateral border of the AP field and the distal end of external iliac artery; and D3, the anterior border of the lateral （LAT） field and the distal end of the external iliac artery. The distances were recorded as positive values if the measuring point was within the conventional pelvic fields, or they were recorded as negative values. Lymph nodes coverage was considered adequate when D1≥0 mm, D2〉17 mm or D3≥7 mm. Results： All patients had at least 1 inadequate margin, 97 patients （97.0%） had 2, and 22 patients （22.0%） had all the 3. On the AP field, 95 patients （95%） had the measuring point, the bifurcation of the abdominal aorta, out of the field （D1〈0 mm）, and all the patients had a distance less than 17.0 mm between the distal end of the external iliac artery and ipsilateral border （D2〈1 7.0 mm）. On the LAT field, 24 patients （24%） had a distance less than 7.0 mm between the distal end of the external iliac artery and anterior border （D3〈7.0 mm）. Conclusion： We observed that conventional pelvic fields based on bony landmarks provided inadequate coverage of pelvic lymph nodes in our patients with cervical cancer. CT simulation may be a feasible technique for planning pelvic fields optimally and individually.

Construction of a computational MDCT model for simulations of the detector signals

Objective:To develop a computational model of a multi-detector CT scanner(MDCT),which could be used to simulate the signal of each detector element in the MDCT by using the Monte Carlo method.Methods:The CT scanner was modelled,including the X-ray source,the bowtie filter,the collimator,the couch and the detector panel.Under a general scanning condition,the signal in each detector element was simulated based on the model by using the MCNPX code.Both the energy spectra at different tube voltages and energy deposition in the detector panel at different collimations were simulated to test the robustness of the MDCT model built in this study.Furthermore,the simulated signals in each detector element were compared with their recorded signals.The accuracies were evaluated by the relative root mean square error(RRMSE)and the structural similarity(SSIM)for each detector element and the whole detector panel,respectively.Results:The simulated energy spectra before and after passing through the phantom and simulated energy deposition in the detector panel were rational.In the scan range from the apex of lung to pubic symphysis,the RRMSE of the 18 axial projections ranged from 0.02 to 0.17,with an average of 0.08.And the SSIMs were calculated to be 0.979 and 0.976 for projections with the largest peak signal and the smallest peak signal,respectively.Conclusions:The computational model of the MDCT developed in this study is accurate and successful,it is helpful for further accurate simulations of the radiation dose and image quality of the MDCT.