J. Qian, Lei Zhao, Xiao-juan Li, Wen-qing Li, Zhi-jiang Jin
{"title":"Effect of droplet superficial velocity on mixing efficiency in a microchannel","authors":"J. Qian, Lei Zhao, Xiao-juan Li, Wen-qing Li, Zhi-jiang Jin","doi":"10.1631/jzus.A2200159","DOIUrl":"https://doi.org/10.1631/jzus.A2200159","url":null,"abstract":"In this study, droplet characteristics including droplet length and formation time, and mixing efficiency in droplets were investigated via the volume of fluid (VOF) method coupled with a user defined scalar (UDS) model. A cross-shaped junction with a square cross-section was designed and used for droplet formation. An initial arrangement which differed from that of a conventional operation was adopted. Results show that when the droplet superficial velocity is constant, the exchange between the dispersed phase velocity and the continuous phase velocity has a marginal effect on the droplet formation time. However, the exchange has a great effect on droplet length. These findings provide a valuable guide for future operation of droplet formation. In addition, the results show that the mixing efficiency in the droplet forming stage can be classified into time-dominated and length-dominated regimes according to the droplet superficial velocity. When a droplet flows in a microchannel, a higher droplet superficial velocity increases mixing efficiency due to the faster inner circulation and shorter droplet length.","PeriodicalId":17508,"journal":{"name":"Journal of Zhejiang University-SCIENCE A","volume":"27 1","pages":"783 - 794"},"PeriodicalIF":3.2,"publicationDate":"2022-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83714181","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yang Yang, Yingzhong Lou, Guanzhen Lin, Zhiguo He, Pengcheng Jiao
{"title":"Hydrodynamics of high-speed robots driven by the combustion-enabled transient driving method","authors":"Yang Yang, Yingzhong Lou, Guanzhen Lin, Zhiguo He, Pengcheng Jiao","doi":"10.1631/jzus.A2200331","DOIUrl":"https://doi.org/10.1631/jzus.A2200331","url":null,"abstract":"Underwater vehicles play important roles in underwater observation, ocean resource exploration, and sample collection. Soft robots are a unique type of underwater vehicles due to their good environmental adaptability and motion flexibility, although they are weak in terms of actuation and response ability. The transient driving method (TDM) was developed to resolve these shortcomings. However, the interaction between the robots’ swift motions and flow fields has not yet been fully studied. In this study, a computational fluid dynamic model is developed to simulate the fluid fields disturbed by transient high-speed motions generated by the robots. Focusing on the dependence of robot dynamics on thrust force and eccentricity, typical structures of both flow and turbulence fields around the robots are obtained to quantitatively analyze robot kinematic performance, velocity distribution, vortex systems, surface pressure, and turbulence. The results demonstrate the high-speed regions at the robots’ heads and tails and the vortex systems due to sudden expansion, indicating a negative relationship between the maximum fluid velocity and eccentricity. The reported results provide useful information for studying the environmental interaction abilities of robots during operating acceleration and steering tasks. 目 的 水下航行器在水下观测、 海洋资源勘探和样本采集中发挥着重要作用. 软机器人是一种独特的水下机器人, 具有良好的环境适应性和运动灵活性, 但它们的驱动和响应能力较弱. 同时, 机器人的快速运动与流场之间的相互作用尚未得到充分研究. 为解决这些问题, 本文旨在开发一种计算流体动力学模型, 以模拟由机器人产生的瞬态高速运动所干扰的流场. 创新点 1. 通过流固耦合与动网格技术开发了瞬变速机器人水下运动的数模模型. 2. 基于偏心率和化学放能反应驱动过程, 建立二者与机器人水下运动表现、 压力场、 速度场和湍流结构的关系. 方 法 1. 关注机器人动力学对推力和偏心率的依赖性, 并开发基于流固耦合方法与动网格技术的计算流体力学模型. 2. 获得机器人周围湍流场的典型结构, 并定量分析速度分布、 涡流结构、 压力和湍流特性. 结 论 1. 机器人头部和尾部都会因突然加速而出现高流速区域, 且在推力较高的一侧拐角处出现湍涡; 机器人尾部产生的高 k (湍流动能) 区域随运动向内发展. 2. 本研究揭示了最大流速与偏心率之间的关系. 3. 机器人表面上的最大压力与推力呈正相关, 与偏心率呈负相关; 偏心率使机器人旋转, 会增强流场的扰动, 也会使头部区域的 k 和 ε (湍流耗散率) 降低.","PeriodicalId":17508,"journal":{"name":"Journal of Zhejiang University-SCIENCE A","volume":"44 1","pages":"820-831"},"PeriodicalIF":3.2,"publicationDate":"2022-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86827161","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shang-cheng Xu, Yi Wang, Zhengguo Wang, Xiaoqiang Fan, B. Xiong
{"title":"Effects of bump parameters on hypersonic inlet starting performance","authors":"Shang-cheng Xu, Yi Wang, Zhengguo Wang, Xiaoqiang Fan, B. Xiong","doi":"10.1631/jzus.A2200155","DOIUrl":"https://doi.org/10.1631/jzus.A2200155","url":null,"abstract":"Unstart is an unwanted flow phenomenon in a hypersonic inlet. When an unstart occurs, the captured airflow flowing through the engine significantly decreases with strong unsteady characteristics, which may lead to thrust loss or even combustor flameout. In this study, various bump configurations were designed to be integrated with a hypersonic inlet to improve its starting ability. A bump was defined as an integrated 3D compression surface installed upstream of the inlet entrance. The starting processes of these bump inlets were numerically simulated to investigate the effect laws and flow mechanisms of the bump parameters. Tests on bump height revealed that the starting performance could be significantly improved by increasing bump height, with the starting Mach number decreasing by 0.55 for the inlet with the highest bump. The high bump facilitates the side movement of the subsonic flow in the separation zone, which leads to a small separation bubble, thus accelerating the starting process. Further, the starting ability can be improved by designing a relatively wide bump, which results in a decline in the starting Mach number by 0.44. When the bump has the same or greater width compared with the airflow capture range, a growing spillage along the transverse direction can be formed so that the airflow in the separation bubble can be easily excluded, improving the starting ability.","PeriodicalId":17508,"journal":{"name":"Journal of Zhejiang University-SCIENCE A","volume":"48 1","pages":"807 - 819"},"PeriodicalIF":3.2,"publicationDate":"2022-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84659225","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yong-bin Jin, Shao-wen Cheng, Yan-yan Yuan, Hong-Tao Wang, Wei Yang
{"title":"Anthropomorphic hand based on twisted-string-driven da Vinci’s mechanism for approaching human dexterity and power of grasp","authors":"Yong-bin Jin, Shao-wen Cheng, Yan-yan Yuan, Hong-Tao Wang, Wei Yang","doi":"10.1631/jzus.A2200216","DOIUrl":"https://doi.org/10.1631/jzus.A2200216","url":null,"abstract":"Designing anthropomorphic prosthetic hands that approach human-level performance remains a great challenge. Commercial prosthetics are still inferior to human hands in several important properties, such as weight, size, fingertip force, grasp velocity, and active and passive dexterities. We present a novel design based on the under-actuated da Vinci’s mechanism driven by a flexible twisted string actuator (TSA). The distributed drive scheme allows structural optimization using a motion capture database to reproduce the natural movement of human hands while keeping adaptability to free-form objects. The application of TSA realizes a high conversion from motor torque to tendon contraction force while keeping the structure light, flexible, and compact. Our anthropomorphic prosthetic hand, consisting of six active and 15 passive degrees of freedom, has a weight of 280 g, approximately 70% of that of a human hand. It passed 30 of the 33 Feix grasp tests on objects in daily living and retained a loading capacity of 5 kg. This simple but intelligent mechanism leads to excellent stability and adaptability and renders feasible wide applications in prosthetics and in service robots.","PeriodicalId":17508,"journal":{"name":"Journal of Zhejiang University-SCIENCE A","volume":"36 1","pages":"771 - 782"},"PeriodicalIF":3.2,"publicationDate":"2022-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84721288","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Modeling the optimal compensation capacitance of a giant magnetostrictive ultrasonic transducer with a loosely-coupled contactless power transfer system","authors":"Tian Lan, Pingping Feng, Jianjian Wang, Jianfu Zhang, Huizhong Zhou","doi":"10.1631/jzus.A2200367","DOIUrl":"https://doi.org/10.1631/jzus.A2200367","url":null,"abstract":"The giant magnetostrictive rotary ultrasonic processing system (GMUPS) with a loosely-coupled contactless power transfer (LCCPT) has emerged as a high-performance technique for the processing of hard and brittle materials, owing to its high power density. A capacitive compensation is required to achieve the highest energy efficiency of GMUPS to provide sufficient vibration amplitude when it works in the resonance state. In this study, an accurate model of the optimal compensation capacitance is derived from a new electromechanical equivalent circuit model of the GMUPS with LCCPT, which consists of an equivalent mechanical circuit and an electrical circuit. The phase lag angle between the mechanical and electrical circuits is established, taking into account the non-negligible loss in energy conversion of giant magnetostrictive material at ultrasonic frequency. The change of system impedance characteristics and the effectiveness of the system compensation method under load are analyzed. Both idle vibration experiments and machining tests are conducted to verify the developed model. The results show that the GMUPS with optimal compensation capacitance can achieve the maximum idle vibration amplitude and smallest cutting force. In addition, the effects of magnetic conductive material and driving voltages on the phase lag angle are also evaluated.","PeriodicalId":17508,"journal":{"name":"Journal of Zhejiang University-SCIENCE A","volume":"28 1 1","pages":"757 - 770"},"PeriodicalIF":3.2,"publicationDate":"2022-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77265232","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Three-dimensional flow field mathematical model inside the pilot stage of the deflector jet servo valve","authors":"Shuang Li, Yaochen Yin, Jiang-yang Yuan, Sheng-rong Guo","doi":"10.1631/jzus.A2200030","DOIUrl":"https://doi.org/10.1631/jzus.A2200030","url":null,"abstract":"A new flow field mathematical model is proposed to describe accurately the flow field structure and calculate the static characteristics of the pilot stage in a deflector jet servo valve (DJSV). The flow field is divided into five regions, a 3D turbulent jet is adopted to describe the free jet region, and a velocity distribution expression of the jet is proposed. The jet entrainment model is put forward in the pressure recovery region to describe the coupling relationship between the pressure in the receiving chamber and the jet flow. The static characteristics, including pressure-flow characteristics, pressure characteristics, and flow characteristics of the pilot stage are obtained. The flow field structure and the static characteristics are verified by finite element analysis (FEA) and experiment, respectively, and the mathematical model results are in good agreement with the experimental and simulation results.","PeriodicalId":17508,"journal":{"name":"Journal of Zhejiang University-SCIENCE A","volume":"5 1","pages":"795 - 806"},"PeriodicalIF":3.2,"publicationDate":"2022-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75196212","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pei Wang, Y. Ge, Tuo Wang, Qi-wei Liu, Shun-xiang Song
{"title":"CFD-DEM modelling of suffusion in multi-layer soils with different fines contents and impermeable zones","authors":"Pei Wang, Y. Ge, Tuo Wang, Qi-wei Liu, Shun-xiang Song","doi":"10.1631/jzus.A2200108","DOIUrl":"https://doi.org/10.1631/jzus.A2200108","url":null,"abstract":"目的 不同细颗粒含量及含不透水区域层状土中的潜蚀过程与均质土中的潜蚀过程存在差异。本文旨在探讨非均质土以及复杂边界条件下间断级配土的潜蚀过程。 创新点 1. 建立计算流体动力学-离散元法(CFD-DEM)耦合数值模型, 并通过单颗粒下落速度和Ergun测试进行模型验证, 确认该方法的准确性; 2. 分析不同细颗粒含量层状土对潜蚀量的影响, 从而阐述非均质土中潜蚀的演化过程; 3. 揭示层状土中不同分布的不透水区域对潜蚀的影响。 方法 1. 采用颗粒下落以及Ergun测试对CFD-DEM耦合数值模拟中流体及颗粒参数进行标定(图2); 2. 利用标定参数对具有不同细颗粒含量的层状土试样进行潜蚀模拟(图7); 3. 对含有不透水区域的层状土试样进行潜蚀模拟。 结论 1. 对于层状土样, 累积侵蚀质量主要由底层土层决定; 一般来说, 底层土层的细颗粒含量越多, 累积侵蚀量越大; 此外, 当底层以上的土层细颗粒含量较高时, 潜蚀得到缓解; 反之, 则潜蚀较为严重。2. 对具有不同不透水区域的试样进行的测试表明, 流量在决定累积质量方面起主要作用; 土样内部的不透水区域可以增加周围区域的流速, 有利于细颗粒的迁移, 加剧潜蚀; 但当不透水区域较多时, 由于增加了流动路径的长度, 阻碍细颗粒的迁移, 潜蚀程度则有所降低。 Suffusion in broadly graded granular soils is caused by fluid flow and is a typical cause of geo-hazards. Previous studies of it have mainly focused on suffusion in homogeneous soil specimens. In this study, the coupled discrete element method (DEM) and computational fluid dynamics (CFD) approach is adopted to model suffusion in multi-layered soils with different fines contents, and soils with one or more impermeable zones. The parameters of the CFD-DEM model are first calibrated with the classic Ergun test and a good match with experiment is obtained. Then suffusion in multi-layered soils with different fines contents and impermeable zones is simulated and discussed. The simulation results show that, for soils with multiple layers, the cumulative eroded mass is mainly determined by the fines content of the bottom layer. In general, the higher the fines content of the bottom soil layer, the higher the cumulative eroded mass. In addition, suffusion is more severe if the fines content of the layer above is decreased. Impermeable zones inside soil specimens can increase the flow velocity around those zones, facilitating the migration of fine particles and intensifying suffusion.","PeriodicalId":17508,"journal":{"name":"Journal of Zhejiang University-SCIENCE A","volume":"7 1","pages":"6-19"},"PeriodicalIF":3.2,"publicationDate":"2022-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89648733","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Effect of morphological gene mutation and decay on energy dissipation behaviour of granular soils","authors":"Wei Xiong, Qi-min Zhang, Jian-feng Wang","doi":"10.1631/jzus.A2200226","DOIUrl":"https://doi.org/10.1631/jzus.A2200226","url":null,"abstract":"目的 本文旨在探讨不同尺度颗粒形貌特征对于砂土应力-应变以及能量耗散行为的影响。 方法 1. 通过同步X射线计算断层扫描实验,提取高精度的真实颗粒形貌,并通过三维点云表征;2. 通过基于球谐分析的主成分分析方法,构建不同尺度下颗粒形貌的突变与衰减;3. 通过离散单元法仿真,模拟不同形貌试件的三轴剪切过程,并进一步讨论不同尺度颗粒形貌对于颗粒材料应力-应变以及能量耗散行为的影响。 结论 1. 通过比较较松散和较密实的试件,发现对于较松散试件,颗粒形貌对颗粒材料的初始刚度、应力-应变、体积应变和摩擦能量耗散等响应的影响更为明显;2. 对于不同尺度下的颗粒形貌,局部圆度较长径比对颗粒材料宏观响应的影响更大;3. 颗粒材料的能量耗散行为由颗粒形貌和初始孔隙率共同决定。 In this paper, the X-ray micro-computed tomography (X-ray µCT), spherical harmonical-based principal component analysis (SH-PCA), and discrete element method (DEM) were incorporated to generate virtual samples with morphological gene mutation at different length scales. All samples were subjected to axial compression and constant confining stress. The effects of multiscale particle morphology on the stress-strain and energy storage/dissipation responses of granular soils were investigated. It is found that: (a) the effects of particle morphology on the initial stiffness, stress-strain, volumetric strain, and frictional energy dissipation behaviours are more pronounced for looser samples than for denser ones; (b) among different length scales, the particle morphology at the local roundness-level outperforms the one at the general form-level in dictating the macro-scale responses of granular soils; (c) the energy dissipation of a granular assemblage is a result of competition between particle morphology and initial void ratio.","PeriodicalId":17508,"journal":{"name":"Journal of Zhejiang University-SCIENCE A","volume":"46 1","pages":"303-318"},"PeriodicalIF":3.2,"publicationDate":"2022-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82357415","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}