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An extended unresolved CFD-DEM coupling method for simulation of fluid and non-spherical particles

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Particuology 2022年第9期20卷 1-12页

作者： Liping He zhengxian liu Yongzhi Zhao Department of Mechanics School of Mechanical EngineeringTianjin UniversityTianjin 300350China Institute of Process Equipment College of Energy EngineeringZhejiang UniversityHangzhou 310027China

This study develops an extended unresolved CFD-DEM coupling method for simulation of the fluid-solid flow with non-spherical *** limitation of fluid grid size is discussed,by simulating the settling of a cylinder in a Newtonian fluid based on the resolved and unresolved CFD-DEM coupling ***,the calculation of porosity and the fluid-particle relative velocity based on the particle shape enlarge-ment method for simulation of non-spherical particles is *** availability of the particle shape enlargement method for the simulation of non-spherical particles with different sphericity is discussed in this work,by comparing it with the results from the equivalent diameter enlargement *** lim-itation of the equivalent diameter enlargement method for non-spherical particles is revealed from the simulation *** typical cases are employed to elaborate and verify the extended unresolved CFD-DEM method based on particle shape enlargement method,by presenting a good consistency with the experimental *** proves that the extended unresolved CFD-DEM method is suitable for differ-ent CFD grid size ratios,and consolidates that it is a universal calculation method for CFD-DEM coupling simulation.

关键词： CFD-DEM Unresolved method Fluid-solid flow Non-spherical particle Rod

Exact Bayesian and Fiducial Limits for the Mean of Lognormal Distribution

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Journal of Systems Engineering and Electronics 1994年第2期5卷 41-46页

作者： Zhou, Yuanquan Weng, Zhaoxi liu, zhengxian Beijing Inst of Structure and Environment Beijing China

In this paper, the exact Bayesian limits, taking conjugate and noninformative prior distribution, and the exact fiducial limits for the mean of the lognormal distribution are presented. They can be found iteratively by one-dimension integral on a finite interval. The new algorithm is very convenient and with high accuracy. It can meet the practical engineering need excellently. However, the primitive algorithm is rather cumbersome. By the way, the very close approximate limits with a simple algorithm are derived. They can be applied immediately to engineering. Otherwise, they can also be used as a search interval to find the root of equation for the exact limits.

关键词： Algorithms Approximation theory Engineering research Failure analysis Integral equations Integration Iterative methods Materials testing Reliability theory Service life Statistical tests

On the nature of tip clearance flow in subsonic centrifugal impellers

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Science China(Technological Sciences) 2013年第9期56卷 2170-2177页

作者： liu zhengxian PING Yan ZANGENEH Mehrdad School of Mechanical Engineering Tianjin University State Key Laboratory of Engines Tianjin University Department of Mechanical Engineering University College London

Increasing demand for downsizing of engines to improve CO2 emissions has resulted in renewed efforts to improve the efficiency and expend the stable operating range of the centrifugal compressors used in petro-chemical equipment and turbochargers. The losses in these compressors are dominated by tip clearance flow. In this paper, the tip clearance flow in the subsonic impeller is numerically investigated. The nature of the tip clearance in inducer, axial to radial bend and exducer are studied in detail at design and off-design conditions by examining the detailed flow field through the clearance and the interaction of the clearance flow with the shear effect with the endwalls. The correlation between blade loading and span wise geometry and clearance flow at different locations are presented.

关键词： centrifugal impeller tip clearance subsonic flow numerical simulation blade loading

Influences of Leading-Edge Tubercle Amplitude on Airfoil Flow Field

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Journal of Thermal Science 2023年第4期32卷 1335-1344页

作者： ZHAO Ming WEI Tong ZHAO Yijia liu zhengxian Department of Mechanics School of Mechanical EngineeringTianjin UniversityTianjin300350China Tianjin Key Laboratory of Modern Engineering Mechanics Tianjin UniversityTianjin300350China

The influences of leading-edge tubercle amplitude on airfoil flow field have been analyzed at high angle of *** accuracy of a large eddy simulation(LES)research is validated through quantitative comparisons with corresponding experimental ***,a proper orthogonal decomposition(POD)analysis has been carried out based on the unsteady flow field and the fluid mechanisms of corresponding POD modes have been ***,the influences of leading-edge tubercle amplitude have been *** the streamwise vorticity is larger than that of small amplitude cases,the momentum transfer process at peaks is more obvious for large amplitude,leading to delayed flow *** amplitude and wavelength play important roles in the generation of laminar separation bubble(LSB)at ***,the Karman vortex shedding process takes place at specific trough sections as pairs of periodic spatial structures exist in the dominant POD *** destruction of Karman vortex shedding process is strengthened along with the increase of amplitude.

关键词： leading-edge tubercle airfoil flow field proper orthogonal decomposition

Dynamic Coupling Correlation of Gas Film in Dry Gas Seal with Spiral Groove

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Chinese Journal of Mechanical Engineering 2014年第4期27卷 853-859页

作者： liu zhengxian WANG Musu ZHOU Yue WU Ningning School of Mechanical Engineering Tianjin University State Key Laboratory of Engines Tianjin University

In working state, the dynamic performance of dry gas seal, generated by the rotating end face with spiral grooves, is determined by the open force of gas film and leakage flow rate. Generally, the open force and the leakage flow rate can be obtained by finite element method, computational fluid dynamics method and experimental measurement method. However, it will take much time to carry out the above measurements and calculations. In this paper, the approximate model of parallel grooves based on the narrow groove theory is used to establish the dynamic equations of the gas film for the purpose of obtaining the dynamic parameters of gas film. The nonlinear differential equations of gas film model are solved by Runge-Kutta method and shooting method. The numerical values of the pressure profiles, leakage flux and opening force on the seal surface are integrated, and then compared to experimental data for the reliability of the numerical simulation. The results show that the numerical simulation curves are in good agreement with experimental values. Furthermore, the opening force and the leakage flux are proved to be strongly correlated with the operating parameters. Then, the function-coupling method is introduced to analyze the numerical results to obtain the correlation formulae of the opening force and leakage flux respectively with the operating parameters, i.e., the inlet pressure and the rotating speed. This study intends to provide an effective way to predict the aerodynamic performance for designing and optimizing the groove styles in dry gas seal rapidly and accurately.

关键词： dry gas seal spiral groove gas film dynamic data fitting method coupling function

Mechanical properties and shape memory behavior of 4D printed functionally graded cellular structures

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Science China(Technological Sciences) 2023年第12期66卷 3522-3533页

作者： ZENG ChengJun liu LiWu ZHAO Wei liu zhengxian XIN XiaoZhou liu YanJu LENG JinSong Department of Astronautical Science and Mechanics Harbin Institute of TechnologyHarbin 150001China Center for Composite Materials and Structures Harbin Institute of TechnologyHarbin 150080China

The properties of functionally graded(FG) cellular structures vary spatially, and the varying properties can meet the requirements of different working environments. In this study, we fabricated FG cellular structures with shape memory effect by 4D printing and evaluated the compressive performance and shape memory behavior of these structures with temperature through experimental analysis and finite element simulations. The results show that the maximum energy absorption gradually decreases but the compressive modulus gradually increases with increasing gradient parameters. Moreover, the finite element simulations also show that the compressive deformation mode of the structure shifts from uniform to non-uniform deformation with increasing gradient parameters. The compressive modulus and compressive strength of 4D printed FG structures decrease with increasing temperature due to the influence of the shape memory polymer, and they exhibit outstanding shape recovery capability under high-temperature stimulus. The proposed 4D printed FG structures with such responsiveness to stimulus shed light on the design of intelligent energy-absorbing devices that meet specific functional requirements.

关键词： functionally graded structures 4D printing shape memory polymers energy absorption cellular structures

World’s first spaceflight on-orbit demonstration of a flexible solar array system based on shape memory polymer composites

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Science China(Technological Sciences) 2020年第8期63卷 1436-1451页

作者： LAN Xin liu LiWu ZHANG FengHua liu zhengxian WANG LinLin LI QiFeng PENG Fan HAO SiDa DAI WenXu WAN Xue TANG Yong WANG Mian HAO YanYan YANG Yang YANG Cheng liu YanJu LENG JinSong Center for Composite Materials and Structures Harbin Institute of TechnologyHarbin 150080China Department of Aerospace Science and Mechanics Harbin Institute of TechnologyHarbin 150001China Institute of Telecommunication Satellite China Academy of Space TechnologyBeijing 100094China State Key Laboratory of Space Power-Sources Technology Shanghai Institute of Space Power-SourcesShanghai 200245China

With a 10%reversible compressive strain in more than 10 deformation cycles,the shape memory polymer composites(SMPCs)could be used for deployable structure and releasing *** this paper,without traditional electro-explosive devices or motors/controllers,the deployable SMPC flexible solar array system(SMPC-FSAS)is studied,developed,ground-based tested,and finally on-orbit *** epoxy-based SMPC is used for the rolling-out variable-stiffness beams as a structural frame as well as an actuator for the flexible blanket solar *** releasing mechanism is primarily made of the cyanate-based SMPC,which has a high locking stiffness to withstand 50 g gravitational acceleration and a large unlocking displacement of 10 *** systematical mechanical and thermal qualification tests of the SMPC-FSAS flight hardware were performed,including sinusoidal sweeping vibration,shocking,acceleration,thermal equilibrium,thermal vacuum cycling,and thermal cycling *** locking function of the SMPC releasing mechanisms was in normal when launching aboard the SJ20 Geostationary Satellite on 27 Dec.,*** SMPC-FSAS flight hardware successfully unlocked and deployed on 5 Jan.,2020 on geostationary *** triggering signal of limit switches returned to ground at the 139 s upon heating,which indicated the successful unlocking function of SMPC releasing mechanisms.A pair of epoxy-based SMPC rolled variable-stiffness tubes,which clapped the flexible blanket solar array,slowly deployed and finally approached an approximate 100%shape recovery ratio within 60 s upon *** study and on-orbit successful validation of the SMPC-FSAS flight hardware could accelerate the related study and associated productions to be used for the next-generation releasing mechanisms as well as space deployable structures,such as new releasing mechanisms with low-shocking,testability and reusability,and ultra-large space deployable solar arrays.

关键词： shape memory polymer composite releasing mechanism shape memory polymer composite tubes flexible solar array

有效性与正当性:作为国家课程的公民科——基于对英格兰公民科国家课程危机的考察

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外国教育研究 2015年第1期42卷 80-88页

作者：刘争先北京师范大学公民与道德教育研究中心北京100875

2011年英格兰新一轮国家课程改革引发了公民科国家课程危机。由于未能明晰公民科作为国家课程的有效性和正当性的区分及其逻辑,忽视了公民科作为国家课程的特殊性,使得围绕公民科作为国家课程的论争陷入了实用主义的逻辑。公民教育与国... 详细信息

2011年英格兰新一轮国家课程改革引发了公民科国家课程危机。由于未能明晰公民科作为国家课程的有效性和正当性的区分及其逻辑,忽视了公民科作为国家课程的特殊性,使得围绕公民科作为国家课程的论争陷入了实用主义的逻辑。公民教育与国家建构的特殊关系奠定了公民科作为国家课程的正当性基础,也使得公民科并非仅仅是增设的一门新课程,而且是一种新的特殊类型的课程。对于英格兰公民科国家课程危机的讨论和反思,有助于我们理解公民科以及国家课程的本质属性。

关键词：公民科有效性正当性国家课程英格兰

On Tip Clearance Vortex Cavitation Noise

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On Tip Clearance Vortex Cavitation Noise