两关节压力驱动柔性仿生机器鱼的设计与仿真

为研究设计一种柔软度高、环境适应性强的新型仿生机器鱼, 模仿鲨鱼外形及鲔科鱼类的游动姿态, 设计了一种采用液压柔性驱动结构的仿生机器鱼. 针对单关节液压驱动柔性机器鱼存在其C型摆动姿态不符合鲔科鱼类摆动规律的问题, 采用两关节液压柔性驱动模拟鱼类S型摆动, 并根据液压柔性驱动器原理设计仿生鱼的内部结构. 依据理论波动方程确定机器鱼的摆动幅值, 借助数值模拟计算施加在柔性驱动器内部的压强载荷大小, 并分析计算液压柔性驱动器的驱动效率. 应用有限元分析软件模拟仿生鱼在流体中的自主游动过程, 并将两关节机器鱼与单关节机器鱼的自主巡游过程进行对比仿真, 获得两种机器鱼在流体中自主巡游时的运动姿态、游动速度及流场情况. 结果表明, 在相同的频率与尾鳍摆幅下, 两关节柔性机器鱼的巡游平均速度为0.29 BL/s (BL为鱼体体长), 高于单关节机器鱼巡游平均速度0.15 BL/s, 且由速度矢量图可得出两关节仿生鱼的S型摆动姿态更接近真实鱼类摆动规律, 并在运动过程中会产生一系列离散的反向卡门涡街, 推进效率高.      

On the Dynamic Behavior of Servo-Hydraulic Drives

A servo-hydraulic drive for position control with a flapper-nozzle type servo-valve is described by a 10th-order, non-linear system of ODEs. This system is partially singularly perturbed. The perturbation stems from the compressibility of the hydraulic fluid and the fast dynamics of some sub-systems of the valve. Center manifold theory in the version due to Fenichel is used to study the behavior of the drive system in the case of periodic motions. The insufficient differentiability properties of the system prevent the direct application of Fenichel's theorems. Thus, phase space is decomposed into sub-spaces each with sufficient differentiability properties. There, limit sets of the system can be given as the solution of the reduced problem. Approximate analytical solutions are derived for that. At the boundaries of adjacent sub-spaces transition layers occur which connect these limit set trajectories of adjacent sub-spaces. The order of magnitude of these transition layers is estimated by asymptotic expansions. Further, a comment is given on the stability properties. Stability is strongly affected by the small perturbation parameters and is most critical in the resting position of the drive. Theoretical results are compared with numerical computations and experiments.     

粒状材料中水力劈裂的认识

水力劈裂在岩土工程、环境工程和石油工程中已得到很好地应用,但另一方面又会造成大坝渗漏破坏、浆液流失以及石油行业中经常遇到的浅水流动等严重后果。连续固体材料（如岩石）中的水力劈裂理论是建立在抗拉强度基础之上,对此,国内外的研究已经比较深入。而对于粒状材料中的研究尚处于起步阶段,仅有少数的试验和数值研究。本文综述了粒状材料中水力劈裂室内试验、现场试验、解析分析和数值模拟的研究成果,分析了当前研究中对这一现象认识的不足,并对今后可能的研究方向进行了预测。     

Hydraulic radius and transport in reconstructed model three-dimensional porous media

Methods for reconstructing three-dimensional porous media from two-dimensional cross sections are evaluated in terms of the transport properties of the reconstructed systems. Two-dimensional slices are selected at random from model three-dimensional microstructures, based on penetrable spheres, and processed to create a reconstructed representation of the original system. Permeability, conductivity, and a critial pore diameter are computed for the original and reconstructed microstructures to assess the validity of the reconstruction technique. A surface curvature algorithm is utilized to further modify the reconstructed systems by matching the hydraulic radius of the reconstructed three-dimensional system to that of the two-dimensional slice. While having only minor effects on conductivity, this modification significantly improves the agreement between permeabilities and critical diameters of the original and reconstructed systems for porosities in the range of 25–40%. For lower porosities, critical pore diameter is unaffected by the curvature modification so that little improvement between original and reconstructed permeabilities is obtained by matching hydraulic radii.     

卧式离心铸造过程数值模拟与水力学试验研究

建立了卧式离心铸造情况下液体充型及凝固过程的数学模型.基于该模型对卧式离心铸造轧辊离心阶段的温度场、流场进行了数值模拟.采用水力学模拟试验与数值模拟进行对比,结果表明数学模型准确可靠.通过对卧式离心铸造充型过程中金属液运动规律的分析,发现卧式离心情况下金属液按螺旋形轨迹充填型腔.随着转速的增加,金属液更易于均匀铺满型腔.这对采用卧式离心铸造轧辊的实际生产具有一定的指导作用. 关键词： 卧式离心铸造 数学模型 数值模拟 水力学试验     

Numerical Simulation of Hydraulic Fractures Intersecting Natural Fractures in Shale With Plastic Deformation北大核心CSCD

The plastic deformation and numerous natural joints of shale pose a great challenge for the predic⁃ tion of the hydraulic fracture geometry extension. Based on the finite element method, a fully coupled numeri⁃ cal model for elastoplastic hydraulic fractures was established with natural fractures and bedding planes consid⁃ ered. The numerical model was validated with the KGD analytical solution and Blanton’s curve. The numerical results show that, compared with the numerical model solution of linear elasticity, the hydraulic fractures are prone to enter the natural weak interface due to the rock plastic deformation. The rock plastic deformation area mainly lies in the reservoir layer during the fracture propagation. In the case of rock ductile damage, the hy⁃ draulic fracture is more likely to penetrate the bedding plane. Hydraulic fractures can directly penetrate natural fractures and bedding planes at high injection rates due to large driving forces. The study provides new insights in terms of hydraulic fracture extension in elastoplastic formations. © 2023 Editorial Office of Applied Mathematics and Mechanics. All rights reserved.     

多翼裂缝压裂偏心井半解析模型及其渗流特征

考虑压裂多翼裂缝偏心井的实际情况,建立了多翼裂缝偏心井的数学模型.采用Laplace变换和压降叠加原理得到Laplace空间多翼裂缝压裂偏心井井底压力的半解析解.采用非均匀流量法,对井底压力的半解析解进行离散.结合Stehfest数值反演获得实空间井底压力的数值解和产量分布.借助SAPHIR试井分析软件建立了储层的数值试井模型并进行了数值离散计算.将计算结果与该文的半解析模型计算结果进行了对比,验证了该文模型的正确性.结果表明,多翼裂缝压裂偏心井井底压力变化可划分为8个主要流动阶段.最后讨论了裂缝的无因次导流能力、裂缝的不对称因子和井的偏心距对井底压力变化和产量分布特征的影响.     

井下光纤微地震监测系统设计及应用

为满足油气开发中微地震监测的需求,基于时分复用方案设计了一种新型井下3分量光纤微地震监测系统。结合室内测试,该系统本底噪声小于−101 dB,动态范围大于120 dB,级间串扰小于−67 dB,满足微地震信号探测的需求。该系统已成功应用于新疆油田水力压裂微地震现场探测。监测结果表明:该系统可清晰捕捉微地震的P波、S波信号,较好地揭示了水力压裂微地震信号的特征信息,为微地震事件的空间定位和裂缝特征参数解释建立了良好基础。