3D Model Retrieval Method Based on Affinity Propagation Clustering

In order to improve the accuracy and efficiency of 3D model retrieval,the method based on affinity propagation clustering algorithm is proposed. Firstly,projection ray-based method is proposed to improve the feature extraction efficiency of 3D models. Based on the relationship between model and its projection,the intersection in 3D space is transformed into intersection in 2D space,which reduces the number of intersection and improves the efficiency of the extraction algorithm. In feature extraction,multi-layer spheres method is analyzed. The two-layer spheres method makes the feature vector more accurate and improves retrieval precision. Secondly,Semi-supervised Affinity Propagation ( S-AP) clustering is utilized because it can be applied to different cluster structures. The S-AP algorithm is adopted to find the center models and then the center model collection is built. During retrieval process,the collection is utilized to classify the query model into corresponding model base and then the most similar model is retrieved in the model base. Finally,75 sample models from Princeton library are selected to do the experiment and then 36 models are used for retrieval test. The results validate that the proposed method outperforms the original method and the retrieval precision and recall ratios are improved effectively.

Coping with uncertainties through an automated workflow for 3D reservoir modelling of carbonate reservoirs

Reliable 3D modelling of underground hydrocarbon reservoirs is a challenging task due to the complexity of the underground geological formations and to the availability of different types of data that are typically affected by uncertainties. In the case of geologically complex depositional environments, such as fractured hydrocarbon reservoirs, the uncertainties involved in the modelling process demand accurate analysis and quantification in order to provide a reliable confidence range of volumetric estimations. In the present work, we used a 3D model of a fractured carbonate reservoir and populated it with different lithological and petrophysical properties. The available dataset also included a discrete fracture network(DFN) property that was used to model the fracture distribution. Uncertainties affecting lithological facies, their geometry and absolute positions(related to the fault system), fracture distribution and petrophysical properties were accounted for. We included all different types of uncertainties in an automated approach using tools available in today’s modelling software packages and combining all the uncertain input parameters in a series of statistically representative geological realizations. In particular, we defined a specific workflow for the definition of the absolute permeability according to an equivalent, single porosity approach, taking into account the contribution of both the matrix and the fracture system. The results of the analyses were transferred into a 3D numerical fluid-dynamic simulator to evaluate the propagation of the uncertainties associated to the input data down to the final results, and to assess the dynamic response of the reservoir following a selected development plan. The "integrated approach" presented in this paper can be useful for all technicians involved in the construction and validation of 3D numerical models of hydrocarbon-bearing reservoirs and can potentially become part of the educational training for young geoscientists and engineers, since an integrated and well-constructed workflow is the backbone of any reservoir study.

Saint-Venant and Navier-Stokes Models for Tsunami Simulations

Into the frame of the French TANDEM project (Tsunamis in the Atlantic and the English ChaNnel: Definition of the Effects through numerical Modelling) Principia has been working on the development and qualification of two in-house CFD software: the 2D EOLE-SV (Saint-Venant) model for simulation of large scale tsunami propagation from the source up to coastal scale and the 3D EOLE-NS (Navier-Stokes) model dedicated to tsunami coastal impact modelling. This paper presents a large range of test cases carried out into the frame of the project and dedicated to the validation of numerical codes in various tsunami wave conditions. The main aspects of phenomena such as wave generation, propagation and coastal impact are investigated on academic situations. A real case simulation is concerned as well, the devastating 2011 Tohoku event which is compared with in-situ data.

A three-dimensional solution of hydraulic fracture width for wellbore strengthening applications

Determining the width of an induced hydraulic fracture is the first step for applying wellbore strengthening and hydraulic fracturing techniques. However, current 2-D analytical solutions obtained from the plane strain assumption may have large uncertainties when the fracture height is small. To solve this problem, a 3-D finite element method(FEM) is used to model wellbore strengthening and calculate the fracture width. Comparisons show that the 2-D plane strain solution is the asymptote of the 3-D FEM solution. Therefore, the 2-D solution may overestimate the fracture width. This indicates that the2-D solution may not be applicable in 3-D conditions. Based on the FEM modeling, a new 3-D semi-analytical solution for determining the fracture width is proposed, which accounts for the e ects of 3-D fracture dimensions, stress anisotropy and borehole inclination. Compared to the 2-D solution, this new 3-D semi-analytical solution predicts a smaller fracture width.This implies that the 2-D-based old design for wellbore strengthening may overestimate the fracture width, which can be reduced using the proposed 3-D solution. It also allows an easy way to calculate the fracture width in complex geometrical and geological conditions. This solution has been verified against 3-D finite element calculations for field applications.

通信台站覆盖预测及三维显示

研究通信台站覆盖预测及其优化显示的问题。传统的战场通信台站覆盖预测与地形显示并没有有机结合起来,并且通常是二维显示,不仅信息量少,而且很不直观。为优化覆盖预测与显示,基于战场地形高程等地理数据,实现了战场地形的三维再现。结合台站信息和地理信息数据,利用ITU-R P.1546电波传播模型,进行了台站覆盖预测及在三维地形上的显示。仿真结果表明系统三维效果显著,能够比较客观、形象地反映通信台站覆盖。在战场实际使用过程中,设计的系统可以为指战员呈现逼真、直观的战场通信状况,可大大提高制定作战方案能力和效率。

Lamb波传播特性研究

应用三维弹性理论对Lamb波频散曲线进行理论建模。在Lamb波主动监测系统中,应用Gabor小波变换理论分析Lamb波信号的时延及相位角,获得了板中Lamb波的相群速度频散曲线。比较理论曲线与实验数据,证明了三维弹性理论建模方法的有效性。

基于三维有限元模型对裂纹非对称转子振动及裂纹扩展控制研究

针对裂纹非对称转子的振动问题,运用非线性接触单元法建立了裂纹非对称转子的三维有限元模型,并采用自由界面模态综合法对模型进行降阶来缩短计算时间。通过仿真分析了相关参数的变化对主共振不稳定区域及不同裂纹位置对转子的振动特性变化等的影响,结果表明裂纹的出现会影响转子的共振频率及不稳定区域范围。同时采用模糊PID控制电磁执行器(EMA)实现对该转子系统振动的主动控制。其次,基于转子动力学理论及提出的裂纹开闭映射法研究了转速、不均匀质量和非对称转子的扁平性等参数变化对转子裂纹开闭特性的影响,提出了有效延缓裂纹扩展的方法。通过实验,利用EMA可对裂纹转子的振动及裂纹呼吸效应等均具有抑制效果,验证了控制方法的有效性。

基于圆柱抛物方程的城市环境电波预测模型

提出了一种三维实体重建技术与柱坐标抛物方程结合的城市环境电波传播预测方法。从数字地图中提取城市建筑物高程矢量数据,建立立体光刻文件的拓扑数据结构,将其转化为抛物方程模型对应的扇形栅格数据,实现城市建筑群的三维几何模型重构。同时结合聚类算法并利用城市影像信息对地表环境进行分类,对不同类型的地表媒质赋予不同电磁参数,实现真实城市环境下同时包含建筑物信息和地表媒质参数的一体化电磁建模。最后,采用分步傅里叶圆柱坐标系抛物方程法,对三维城市环境中电波的传播特性进行仿真分析。数值计算结果表明,相较于传统经验模型,该方法能够考虑电波的反射、折射和衍射效应,可准确预测真实城市环境下的电波传播规律,且具有较高计算效率。本模型可为无线网络规划、电磁频谱地图构建等提供指导。

水利工程三维模型试验变形的数码摄影监测

在水利工程隧道三维立体模型观测面设置测量标点,采用数码相机监测模型试验过程,通过数码图像识别监测物体变形前后标记点的变形数据。基于BP神经网路的图像识别,对某隧道施工开挖、加固过程进行三维地质力学模型试验,取得了满意的观测结果,为三维力学模型试验收敛变形观测提供了一种新方法。

三维非平面裂纹扩展参数化模拟方法

发展一种基于有限元方法(FEM)的自动模拟三维非平面裂纹扩展的模拟方法。该方法采用参数化建模的方式建立裂纹体,以镶嵌裂纹体的方式在结构中插入裂纹,然后通过有限元计算得到裂纹扩展参量,自动更新裂纹体从而模拟裂纹的扩展过程。通过模拟三个裂纹扩展算例,计算了裂纹扩展循环数,对比试验结果,误差分别为19.5%、16.1%、2.1%。结果表明:该方法能够模拟三维非平面裂纹的扩展并计算扩展寿命,具有一定的精度和适用性。

A review of multiscale expansion of low permeability reservoir cracks

The study of rock crack propagation by multi-scale method is of great significance to comprehensively and accurately understand the law of rock crack evolution.In this paper,the theoretical,experimental and numerical methods from macroscale,mesoscale and microscale used for crack propagation in recent years are summarized and analyzed.Firstly,the evolution mechanism of the crack and the related research status are analyzed from a single scale.Secondly,multi-scale theory,modeling,meshing algorithm and macro-mesoscopic parameters are reviewed in the multi-scale coupling method.Through the analysis of the results published in recent years,it is considered that the following aspects need to be further studied:the characteristic parameters of the rock are different at different scales,so the extraction of the characteristic parameters under different scales is essential to modeling and coupling;the heterogeneity of rock and the prefabrication of cracks are greatly affected by human factors,so that 3D printing will be a good breakthrough to build the model of crack owing to its accurate control on the distribution and the size of cracks.The internal stress field of the rock is complex and varied,and the generation and expansion of the microcracks in the process of crack propagation are closely related to the surrounding environment.Therefore,it is of great importance to combine theoretical,experimental and numerical research with practical engineering.