Fully coupled hydraulic fracture simulation using the improved element partition method     

Shujun Peng  Zhennan Zhang  Jianye Mou  Bing Zhao  Zhiyuan Liu  Jiading Wang 《国际地质力学数值与分析法杂志》2019,43(1):441-460

The improved element partition method (IEPM) is a newly developed fracture simulation approach. IEPM allows a fracture to run across an element without introducing extra degrees of freedom. It can also simulate any number of fractures in a prescribed mesh without remeshing. In this study, the IEPM is extended to hydraulic fracture simulation. First, the seepage and volumetric storage matrix of a cracked element are derived using virtual nodes (the intersection points of a crack with element edges). Subsequently, the fully coupled hydromechanical equation is derived for this cracked element. To eliminate the extra degrees of freedom (virtual nodal quantities), the water pressure and displacement of the virtual nodes are associated with their adjacent nodes through least squares interpolation. Finally, the fully coupled equation in terms of nodal quantities is obtained. The verification cases validate the method. By using this method, the field-scale hydraulic fracturing process is well simulated. The proposed approach is simple and efficient for field-scale hydraulic fracture simulation.  相似文献   

Hydrodynamic forces on a partially submerged cylinder at high Reynolds number in a steady flow     

《Applied Ocean Research》2019

The hydrodynamic forces on the stationary partially submerged cylinder are investigated through towing test with Reynolds number ranging from 5 × 10⁴ to 9 × 10⁵. Three test groups of partially submerged cylinders with submerged depths of 0.25 D, 0.50 D, and 0.75 D and one validation group of fully submerged cylinders are conducted. During the experiments, the hydrodynamic forces on the cylinders are measured using force sensors. The test results show a considerable difference in the hydrodynamic coefficients for the partially submerged cylinders versus the fully submerged cylinders. A significant mean downward lift force is first observed for the partially submerged cylinders in a steady flow. The maximum of the mean lift coefficients can reach 1.5. Two distinct features are observed due to the effects of overtopping: random distributions in the mean drag coefficients and a clear quadratic relationship between the mean lift coefficients and the Froude number appear in the non-overtopping region. However, the novel phenomenon of a good linear relationship with the Froude number for the mean hydrodynamic coefficients is clearly shown in the overtopping region. In addition, fluctuating hydrodynamic coefficients are further proposed and investigated. These results are helpful to have a better understanding of the problem and to improve related structural designs.  相似文献   

基于分区间泛化Kriging近似模型的船舶局部结构形状优化     

张干锋  王德禹 《海洋工程》2018,36(6):46-57

为提高Kriging近似模型在船舶结构性能多维度响应预测方面的适用性,对常规Kriging近似模型进行分区间泛化改进:一是对设计样本点的各个维度(分量)进行划区,并在每一个分区间内采用最优拉丁超立方(OLhd)取样;二是引入比例系数w1组合高斯与指数型相关函数提高模型对数据的泛化能力,从而在每个划分的区间内建立泛化的Kriging近似模型。通过SCH测试函数,验证了构造的分区间泛化Kriging模型有效性。结合参数化建模和改进Kriging近似模型对某过渡肘板和舱口角隅边界进行形状优化,优化第一阶段由改进的近似模型通过多岛遗传算法得到全局初步的最优解,第二阶段在初步解的基础上缩小优化变量范围,由少量的FEM计算即可在小范围内搜寻到精确的最优设计变量。结果表明:分区间泛化Kriging近似模型在预测多维度响应时较常规Kriging模型预测精度更高;分阶段的形状优化流程在保证极小误差和缩小计算成本的情况下能够得到理想的应力分布和重量优化结果,有助于船舶结构的轻量化研究。  相似文献   

Penetration Depth of Torpedo Anchor in Two-Layered Cohesive Soil Bed by Free Fall     

Cheng Wang  Min-xi Zhang  Guo-liang Yu 《中国海洋工程》2018,32(6):706-717

The penetration depth of torpedo anchor in two-layered soil bed was experimentally investigated. A total of 177 experimental data were obtained in laboratory by varying the undrained shear strength of the two-layered soil and the thickness of the top soil layer. The geometric parameters of the anchor and the soil properties (the liquid limit, plastic limit, specific gravity, undrained shear strength, density, and water content) were measured. Based on the energy analysis and present test data, an empirical formula to predict the penetration depth of torpedo anchor in two-layered soil bed was proposed. The proposed formula was extensively validated by laboratory and field data of previous researchers. The results were in good agreement with those obtained for two-layered and single-layered soil bed. Finally, a sensitivity analysis on the parameters in the formula was performed.  相似文献   

基于HYCOM再分析数据研究琉球海流的形成与起源     

汪敏  刘昭君  朱小华  闫晓梅  张钟哲  赵瑞祥 《海洋学报(英文版)》2019,38(11):1-10

The origin of the Ryukyu Current(RC) and the formation of its subsurface velocity core were investigated using a 23-year(1993–2015) global Hybrid Coordinate Ocean Model(HYCOM) dataset. The volume transport of the RC comes from the Kuroshio eastward branch(KEB) east of Taiwan and part of the North Pacific Subtropical Gyre(pNPSG). From the surface to 2 000 m depth, the KEB(p-NPSG) transport contributes 41.5%(58.5%) to the mean total RC transport. The KEB originally forms the subsurface velocity core of the RC east of Taiwan due to blockage of the subsurface Kuroshio by the Ilan Ridge(sill depth: 700 m). Above 700 m, the Kuroshio can enter the East China Sea(ECS) over the Ilan Ridge, meanwhile, the blocked Kuroshio below 700 m turns to the right and flows along the Ryukyu Islands. With the RC flowing northeastward, the p-NPSG contribution strengthens the subsurface maximum structure of the RC owing to the blockage of the Ryukyu Ridge. In the surface layer, the pNPSG cannot form a stable northeastward current due to frequent disturbance by mesoscale eddies and water exchange through the gaps(with net volume transport into ECS) between the Ryukyu Islands.  相似文献   

超低剂量心脏CT扫描对冠状动脉狭窄分级和量化的价值          下载免费PDF全文

陈安  解学乾  王政  李远  张皓  李念云  孟捷 《CT理论与应用研究》2018,27(6):701-707

目的:在冠状动脉CT成像（CCTA）中，以100 kV扫描为参照，评估70 kV扫描对冠状动脉狭窄程度分级和量化的一致性。方法:选取70名临床怀疑或已知冠心病且适合行CCTA检查的患者，使用256排宽探测器CT，分别用70 kV和100kV管电压进行单心动周期CCTA检查。比较两组扫描的有效辐射剂量（ED）及图像信噪比（SNR）。对冠状动脉的9个节段进行狭窄程度分析。将狭窄程度分为正常（0%）、轻度（1%~49%）、中度（50%~69%）和重度（70%~100%）四个等级。记录狭窄程度一致的冠状动脉节段数目。使用Bland-Altman分析比较冠脉狭窄程度的一致性。结果:70 kV扫描的有效辐射剂量显著低于100 kV扫描的，分别为（0.26±0.08）mSv和（1.07±0.05）mSv （P<0.01），信噪比显著低于100 kV扫描，分别为16.53±5.87和18.19±6.07（P<0.05）。在630个冠状动脉节段中，608个（96.5%）分级一致。Bland-Altman分析显示两组扫描方法评估狭窄程度差异性的95%可信区间约在15%~30%之间。结论:70kV冠状动脉CTA成像可以大幅度降低辐射剂量，对冠脉狭窄程度的分级与常规100kV扫描基本一致。但是对冠状动脉的精确量化测量与常规扫描有一定的差异性。   相似文献   

Numerical study of sand scour with a modified Eulerian model based on incipient motion theory     

Qingqing Yuan  Min Zhao  Tong Ge 《Marine Georesources & Geotechnology》2018,36(7):818-826

Application of the standard Eulerian model to simulations of sand scour results in unrealistic phenomena. Therefore, the present work develops a modified Eulerian model based on sand incipient motion theory. The modified model is applied for simulating a two-dimensional single vertical jet and a moving planar jet. The simulation results generally demonstrate fairly good agreement with published results of scour profiles and the velocity contours of the water and sand phases. In addition, equations to describe self-similar scour profiles for the moving planar jet cases are given. The results demonstrate that the modified model efficiently and accurately simulates the two-dimensional sand scour produced by jets, particularly for the moving jet cases.  相似文献   

风机基础TLP平台在波浪中运动性能的CFD数值分析     

安筱婷  赵伟文  万德成 《海洋工程》2020,38(5):35-49

随着海上风能的开发向深水发展，支撑风机的载体平台越来越受到关注。在经济性与安全性、稳定性的多重要求下，张力腿平台（TLP）在海洋风能资源的开发中体现出了重要地位。采用基于开源平台OpenFOAM开发的计算流体动力学（CFD）水动力学求解器naoe-FOAM-SJTU对一座处于中等水深下的风机基础水下TLP（STLP）的运动响应进行了数值模拟与研究。文中使用弹簧锚链模型模拟STLP的垂向系泊锁链系统，模拟该平台在不同波浪环境下的运动响应情况。首先将STLP单自由度自由衰减CFD模拟结果与已有全耦合时域分析结果进行对比，验证了naoe-FOAM-SJTU求解器及使用弹簧模型模拟STLP系泊系统的准确性与可靠性。随后在考虑非线性波浪载荷的情况下研究极端海况下与一般作业海况下STLP的运动响应情况，计算工况中的风机基础所受弯矩及锚链受力情况，并详细展示流场、速度场信息，分析高阶波浪成分、不同海况等条件对于STLP运动性能的影响。研究结果表明，TLP在中等水深中具有良好的运动性能，naoe-FOAM-SJTU求解器可以有效模拟水中生产平台在波浪环境下的水动力问题，并可以对整个流场进行可视化展示与分析。  相似文献   

Unified numerical study of shallow foundation on structured soft clay under unconsolidated and consolidated-undrained loadings     

Santosh Kumar Yadav  Guan-lin Ye  Usama Khalid 《Marine Georesources & Geotechnology》2020,38(4):400-416

Abstract

Based on a new elasto-plastic constitutive model, this paper presents a soil–water coupled numerical prediction of the bearing capacity for shallow foundation constructed on Ballina soft clay for unconsolidated undrained (UU) and consolidated undrained (CU) conditions. This elasto-plastic constitutive Shanghai model has an advantage of describing the mechanical behaviour of over-consolidated and structured soil under different loading and drainage conditions, by using one set of material parameter. In this paper, the Shanghai model used for both UU and CU conditions has the same initial parameters obtained from laboratory test results. The loading conditions and consolidation stages vary based on construction details. The predicted bearing pressure-settlement responses for UU and CU, approves the field observation. The phenomenon of gaining the bearing capacity due to consolidation is captured and explained by the use of soil–water coupled numerical analysis with a new elasto-plastic model. The stress strain behaviour, stress paths and the decay of the structure of elements at different depths presented in this study, reveal the mechanism for the difference between UU and CU conditions to understand the foundation behaviour. Effect of the initial degree of soil structure on the bearing capacity is also addressed. Overall, this approach provides the integrated solution for the shallow foundation design problems under short and long-term loadings.  相似文献   

A critical CAE analysis of the bottom shape of a multi stepped air cavity planing hull     

《Applied Ocean Research》2019

One of the most important aspects, in the ACS and multi stepped hull design, is the choice of the geometrical shape of the cavity and the steps. In this article a complete experimental and numerical campaign on a multi stepped ACS has been carried out, varying the velocity and the air flow rate under the hull. The experimental tests have been conducted in an ITTC Towing Tank allowing to validate the numerical simulations obtained by means of a CFD U-RANSe (Unesteady Reynolds Averaged Navier-Stokes equations) code. The CFD setup is described in detail. From this campaign a critical analysis of the Froude number influence on the air cushion shape has been argued. The authors identified four different behaviours, from low to very high Froude numbers. The use of CFD has allowed to observe quantities of difficult evaluation by means of traditional experimental test, as e.g. the frictional component of the resistance, the airflow path lines and the volume of fraction in transversal and longitudinal sections. The results have been discussed.  相似文献