Three-dimensional(3D)parametric measurements of individual gravels in the Gobi region using point cloud technique

Gobi spans a large area of China,surpassing the combined expanse of mobile dunes and semi-fixed dunes.Its presence significantly influences the movement of sand and dust.However,the complex origins and diverse materials constituting the Gobi result in notable differences in saltation processes across various Gobi surfaces.It is challenging to describe these processes according to a uniform morphology.Therefore,it becomes imperative to articulate surface characteristics through parameters such as the three-dimensional(3D)size and shape of gravel.Collecting morphology information for Gobi gravels is essential for studying its genesis and sand saltation.To enhance the efficiency and information yield of gravel parameter measurements,this study conducted field experiments in the Gobi region across Dunhuang City,Guazhou County,and Yumen City(administrated by Jiuquan City),Gansu Province,China in March 2023.A research framework and methodology for measuring 3D parameters of gravel using point cloud were developed,alongside improved calculation formulas for 3D parameters including gravel grain size,volume,flatness,roundness,sphericity,and equivalent grain size.Leveraging multi-view geometry technology for 3D reconstruction allowed for establishing an optimal data acquisition scheme characterized by high point cloud reconstruction efficiency and clear quality.Additionally,the proposed methodology incorporated point cloud clustering,segmentation,and filtering techniques to isolate individual gravel point clouds.Advanced point cloud algorithms,including the Oriented Bounding Box(OBB),point cloud slicing method,and point cloud triangulation,were then deployed to calculate the 3D parameters of individual gravels.These systematic processes allow precise and detailed characterization of individual gravels.For gravel grain size and volume,the correlation coefficients between point cloud and manual measurements all exceeded 0.9000,confirming the feasibility of the proposed methodology for measuring 3D parameters of individual gravels.The proposed workflow yields accurate calculations of relevant parameters for Gobi gravels,providing essential data support for subsequent studies on Gobi environments.

Experimental study of freak waves due to three-dimensional island terrain in random wave

An experimental study is carried out for waves passing an isolated reef terrain in a wave tank. A three-dimensional model of a representative and isolated reef terrain in the West Pacific is built. Random wave trains with various periods and wave heights are generated by a wave maker using the improved JONSWAP spectrum. It is observed that there are different kinds of generation processes and waveforms of freak waves. The freak wave factor Hm/Hs (where Hm is the maximum wave height of wave series, and Hs is significant wave height) is analyzed in detail, in terms of the skewness, kurtosis and water depth, as well as the relationship between freak wave height H& and skewness. The freak wave factor Hm/Hs is found to be in positive correlation with the kurtosis, while larger H[x tends to be related with bigger skewness. The rapid variation of water depth, such as slope and seamount, contributes to the occurrence probability of freak waves.

Three-Dimensional Simulations of RESET Operation in Phase-Change Random Access Memory with Blade-Type Like Phase Change Layer by Finite Element Modeling

An optimized device structure for reducing the RESET current of phase-change random access memory （PCRAM） with blade-type like （BTL） phase change layer is proposed. The electrical thermal analysis of the BTL cell and the blade heater contactor structure by three-dimensional finite element modeling are compared with each other during RESET operation. The simulation results show that the programming region of the phase change layer in the BTL cell is much smaller, and thermal electrical distributions of the BTL cell are more concentrated on the TiN/GST interface. The results indicate that the BTL cell has the superiorities of increasing the heating efficiency, decreasing the power consumption and reducing the RESET current from 0.67mA to 0.32mA. Therefore, the BTL cell will be appropriate for high performance PCRAM device with lower power consumption and lower RESET current.

Three-dimensional stochastic seepage field for embankment engineering

Owing to the complexity of geo-engineering seepage problems influenced by different random factors, three-dimensional simulation and analysis of the stochastic seepage field plays an important role in engineering applications. A three-dimensional anisotropic heterogeneous steady random seepage model was developed on the basis of the finite element method. A statistical analysis of the distribution characteristics of soil parameters sampled from the main embankment of the Yangtze River in the Southern Jingzhou zone of China was conducted. The Kolomogorov-Smirnov test verified the statistical hypothesis that the permeability coefficient tensor has a Gaussian distribution. With the help of numerical analysis of the stochastic seepage field using the developed model, various statistical and random characteristics of the stochastic seepage field of the main embankment of the Yangtze River in the Southern Jingzhou zone of China were investigated. The model was also examined with statistical testing. Through the introduction of random variation of the upstream and downstream water levels into the model, the effects of the boundary randomness due to variation of the downstream and upstream water levels on the variation of simulated results presented with a vector series of the random seepage field were analyzed. Furthermore, the combined influence of the variation of the soil permeability coefficient and such seepage resistance measures as the cut-off wall and relief ditch on the hydraulic head distribution was analyzed and compared with the results obtained by determinate analysis. Meanwhile, sensitivities of the hydraulic gradient and downstream exit height to the variation of boundary water level were studied. The validity of the simulated results was verified by stochastic testing and measured data. The developed model provides more detail and a full stochastic algorithm to characterize and analyze three-dimensional stochastic seepage field problems.

Land use and cover change and influencing factor analysis in the Shiyang River Basin,China

Land use and cover change(LUCC)is the most direct manifestation of the interaction between anthropological activities and the natural environment on Earth's surface,with significant impacts on the environment and social economy.Rapid economic development and climate change have resulted in significant changes in land use and cover.The Shiyang River Basin,located in the eastern part of the Hexi Corridor in China,has undergone significant climate change and LUCC over the past few decades.In this study,we used the random forest classification to obtain the land use and cover datasets of the Shiyang River Basin in 1991,1995,2000,2005,2010,2015,and 2020 based on Landsat images.We validated the land use and cover data in 2015 from the random forest classification results(this study),the high-resolution dataset of annual global land cover from 2000 to 2015(AGLC-2000-2015),the global 30 m land cover classification with a fine classification system(GLC_FCS30),and the first Landsat-derived annual China Land Cover Dataset(CLCD)against ground-truth classification results to evaluate the accuracy of the classification results in this study.Furthermore,we explored and compared the spatiotemporal patterns of LUCC in the upper,middle,and lower reaches of the Shiyang River Basin over the past 30 years,and employed the random forest importance ranking method to analyze the influencing factors of LUCC based on natural(evapotranspiration,precipitation,temperature,and surface soil moisture)and anthropogenic(nighttime light,gross domestic product(GDP),and population)factors.The results indicated that the random forest classification results for land use and cover in the Shiyang River Basin in 2015 outperformed the AGLC-2000-2015,GLC_FCS30,and CLCD datasets in both overall and partial validations.Moreover,the classification results in this study exhibited a high level of agreement with the ground truth features.From 1991 to 2020,the area of bare land exhibited a decreasing trend,with changes primarily occurring in the middle and lower reaches of the basin.The area of grassland initially decreased and then increased,with changes occurring mainly in the upper and middle reaches of the basin.In contrast,the area of cropland initially increased and then decreased,with changes occurring in the middle and lower reaches.The LUCC was influenced by both natural and anthropogenic factors.Climatic factors and population contributed significantly to LUCC,and the importance values of evapotranspiration,precipitation,temperature,and population were 22.12%,32.41%,21.89%,and 19.65%,respectively.Moreover,policy interventions also played an important role.Land use and cover in the Shiyang River Basin exhibited fluctuating changes over the past 30 years,with the ecological environment improving in the last 10 years.This suggests that governance efforts in the study area have had some effects,and the government can continue to move in this direction in the future.The findings can provide crucial insights for related research and regional sustainable development in the Shiyang River Basin and other similar arid and semi-arid areas.

Micromorphological characterization and random reconstruction of 3D particles based on spherical harmonic analysis

The microscopic characteristics of skeletal particles in rock and soil media have important effects on macroscopic mechanical properties. A mathematical procedure called spherical harmonic function analysis was here developed to characterize micromorphology of particles and determine the meso effects in a discrete manner. This method has strong mathematical properties with respect to orthogonality and rotating invariance. It was used here to characterize and reconstruct particle micromorphology in three-dimensional space. The applicability and accuracy of the method were assessed through comparison of basic geometric properties such as volume and surface area. The results show that the micromorphological characteristics of reproduced particles become more and more readily distinguishable as the reproduced order number of spherical harmonic function increases, and the error can be brought below 5% when the order number reaches 10. This level of precision is sharp enough to distinguish the characteristics of real particles. Reconstructed particles of the same size but different reconstructed orders were used to form cylindrical samples, and the stress-strain curves of these samples filled with different-order particles which have their mutual morphological features were compared using PFC3D. Results show that the higher the spherical harmonic order of reconstructed particles, the lower the initial compression modulus and the larger the strain at peak intensity. However, peak strength shows only a random relationship to spherical harmonic order. Microstructure reconstruction was here shown to be an efficient means of numerically simulating of multi-scale rock and soil media and studying the mechanical properties of soil samples.

Three-dimensional image authentication using binarized images in double random phase integral imaging

We proposed a three-dimensional (3D) image authentication method using binarized phase images in double random phase integral imaging (Ini). Two-dimensional (2D) element images obtained from Ini are encoded using a double random phase encryption (DRPE) algorithm. Only part of the phase information is used in the proposed method rather than using all of the amplitude and phase information, which can make the final data sparse and beneficial to data compression, storage, and transmission. Experimental results verified the method and successfully proved the developed 3D authentication process using a nonlinear cross correlation method.

Stochastic analysis of excavation-induced wall deflection and box culvert settlement considering spatial variability of soil stiffness

In this study, a three-dimensional (3D) finite element modelling (FEM) analysis is carried out to investigate the effects of soil spatial variability on the response of retaining walls and an adjacent box culvert due to a braced excavation. The spatial variability of soil stiffness is modelled using a variogram and calibrated by high-quality experimental data. Multiple random field samples (RFSs) of soil stiffness are generated using geostatistical analysis and mapped onto a finite element mesh for stochastic analysis of excavation-induced structural responses by Monte Carlo simulation. It is found that the spatial variability of soil stiffness can be described by an exponential variogram, and the associated vertical correlation length is varied from 1.3 m to 1.6 m. It also reveals that the spatial variability of soil stiffness has a significant effect on the variations of retaining wall deflections and box culvert settlements. The ignorance of spatial variability in 3D FEM can result in an underestimation of lateral wall deflections and culvert settlements. Thus, the stochastic structural responses obtained from the 3D analysis could serve as an effective aid for probabilistic design and analysis of excavations.

A THREE-DIMENSIONAL RANDOM DISPERSION MODEL WITHIN SURFACE LAYER

Taking advantage of the relation of lateral Lagrangian time scale T_(LY) with the stability and height, we establish a three-dimensional random dispersion model and simulate the dispersing process of a ground source within the surface layer. The results calculated show that under the condition of stable stratifica- tion our model is obviously better improved than those obtained by assuming T_(LY) to be constant, while under unstable condition, not much improved.

混凝土随机多面体骨料模型的生成方法

为三维混凝土细观力学行为研究提供一种简便有效的混凝土骨料的生成方法,通过对椭球体的方程进行改造,在其中加入三个随机变量和两个控制参数,从而将其变为不规则多面体以模拟混凝土骨料。采用两个参数对骨料的不规则性进行控制,同时利用椭球体的性质对骨料的外形及尖锐程度进行控制。通过投放实例表明提出的多面体骨料模型能够模拟实际工程中各种级配的混凝土骨料,并通过混凝土三相模型的材料不均质计算说明了该算法的有效性。

基于凸多面体碰撞检测的虚拟砂轮建模研究

虚拟砂轮建模时大多采用包围球对磨粒进行碰撞检测,而包围球相互接触时凸多面体磨粒之间仍存在间隙,导致虚拟砂轮表面与实际砂轮表面差异较大,影响后续磨削过程仿真的准确性。针对这一问题,提出了一种基于凸多面体碰撞检测的虚拟砂轮建模方法。推导了砂轮表面磨粒随机位置的数学模型,基于凸多面体碰撞检测判断磨粒干涉状况,最终生成虚拟砂轮。对基于凸多面体和包围球碰撞检测方法生成的虚拟砂轮表面进行对比分析,发现前者的磨粒位置更具随机性,且可以生成磨粒率为60%的虚拟砂轮,后者则不能生成磨粒率大于50%的虚拟砂轮。最后将虚拟砂轮与真实砂轮进行对比分析,结果表明虚拟砂轮与真实砂轮的表面特征一致,证明了该方法的优越性。

CFD Simulation of the Filtration Performance of Fibrous Filter Considering Fiber Electric Potential Field

Aiming at disclosing the quantitative e ects of Coulomb forces on the ltration e ciency of aerosol particles, a three- dimensional random ber model was established to describe the microstructure of brous lters. Then, computational mod- els including the ow model, particle model, and electric eld model were constructed to estimate the ltration e ciency using the Fluent custom user-de ned function program, neglecting the non-uniformity of the ber potential and the particle charge distribution. The simulation results using the established models agreed with the data in the literature. In particular, the electric eld force was found to be one of the important factors required to improve the ltration e ciency estimation accuracy for the ultra ne particles. Moreover, the variation tendencies of the ltration e ciency and the pressure drop of brous lters were studied based on the in uence factors of the ber potential, particle charge-to-mass ratio, solid volume fraction, ber diameter, and face velocity. The established models and estimated results will provide important guidance on the design of high-e ciency particulate air lters for aerosol particles.

耐火材料微观分析中的随机多面体颗粒模型构建方法

为了建立耐火材料微观结构随机多面体颗粒模型,基于MATLAB和ABAQUS二次开发,充分利用MATLAB快速而精准的制图能力和ABAQUS强大的二次开发功能,将计算分析获得的多面体颗粒点、线、面信息导入ABAQUS,构建了颗粒增强陶瓷材料的精确微观模型。凸型随机多面体颗粒模型能够较好地模拟耐火材料的实际细观结构,为进一步的微观力学分析提供了依据。本工作中提出的随机多面体建模方法对陶瓷、岩土等材料的微观分析具有一定借鉴价值。

三维凸型混凝土骨料随机投放算法

为了提供三维混凝土细观强度研究的数值模型,进行了三维混凝土随机骨料的投放算法研究。以体积为标度建立了一般多面体和凸型多面体两种形状骨料的侵入判别准则。并以凸多面体为研究对象建立了凸型骨料的生长模式和骨料"凸性"条件,给出相应的随机投放算法。该算法中,投放骨料初始形状为任意空间八面体,并始终在最长边上不断生长。在整个生长和投放过程中,骨料始终保持"凸"型。投放实例表明,与球形骨料假定建立的数值混凝土模型相比,凸多面体随机骨料模型能够更广泛地模拟混凝土材料结构。简单的算例说明了该模型可用于混凝土不均质性研究。

三维随机多面体骨料生成和投放技术

提出了一种高效的随机多面体骨料生成和投放技术.通过对基三角形的延拓生成系列多面体,并采用凹凸控制和尖锐判断进行筛选,根据给定级配曲线循环生成不同粒径的骨料,然后在规定的投放区域等概率投放,借助ANSYS的布尔分割运算避免骨料重叠,实现给定级配多面体颗粒复合材料的几何建模.最后给出了两个实例.该技术特别适合带有给定级配和高骨料含量的混凝土和沥青混合料的三维几何建模.

基于LS-DYNA的混凝土三维随机凹凸型骨料数值建模

提出了三维随机凹凸型碎石骨料生成方法,利用ANSYS/LS-DYNA有限元软件进行数值骨料投放模拟,得到了混凝土三维随机凹凸型碎石骨料几何模型。采用"基本单元模型"在投放区域生成立方体网格单元,结合新的空间点与随机多面体空间相对位置判定方法,判定出各单元材料属性,最后生成混凝土三维随机凹凸型碎石骨料有限元模型。以上混凝土细观有限元模型生成方法较好地控制了骨料粒径、数量和级配,生成的数值模型中骨料体积率在55%左右,处于真实混凝土骨料体积率的范围中。生成的数值骨料与真实碎石骨料形状接近。提出的细观混凝土有限元模型为对混凝土力学性能进行细观数值研究奠定了基础。