三维自适应FE-SPH耦合算法在多层间隔金属靶侵彻问题中的应用

鉴于有限元算法不能有效地模拟侵彻过程所产生的金属碎片, 本文中基于三维自适应FE-SPH耦合算法的基本理论, 自主开发了模拟多层间隔金属靶侵彻问题的三维FE-SPH耦合计算程序。该程序采用四面体单元对多层间隔金属靶侵彻模型进行初始离散, 计算过程中, 当四面体单元等效塑性应变超过某一设定值时, 单元自动转化为SPH粒子, 并引入有限单元-粒子接触算法和耦合算法, 实现大变形和破碎区域采用SPH方法计算, 克服有限元法单元畸变存在的问题。多层间隔靶侵彻算例分析表明, 三维FE-SPH耦合计算程序采用等效塑性应变作为转化判据计算结果较稳定, 并且能够有效地再现侵彻过程中所产生的碎片, 能够模拟侵彻碎片对后层靶的毁伤效应。     

基于SPH-FEM耦合方法的柔性导爆索分离装置爆炸分离过程数值模拟

为深入研究柔性导爆索在爆炸分离装置中的作用过程和机理,提出一种改进的光滑粒子流体动力学方法（smoothed particle hydrodynamics, SPH）与有限单元法（ finite element method, FEM）耦合算法。新方法中不仅包含导爆索模拟的SPH方法与分离装置模拟的FEM方法之间的接触算法,同时将完全损伤失效后的单元采用转化算法动态转化成SPH粒子继续参与计算,转化后的粒子与未转化的有限单元之间采用接触算法计算。采用该方法对环型和平板型两种爆炸分离结构的分离过程进行了数值模拟,验证了新方法的准确性与问题适用性;分析了分离板的变形断裂及损伤碎片的飞溅过程,得到了分离装置表面不同时刻的应力分布、损伤因子的变化趋势、von Mises应力的变化趋势;探讨了炸药在不同比内能情况下单元的屈服损伤速度、碎片的飞溅位移速度。     

高速碰撞数值计算中的SPH自适应粒子分布法

针对传统光滑粒子法在计算高速碰撞问题时会出现近邻粒子逸出核函数影响域而产生数值破坏这一缺陷,提出了一种根据粒子间距变化自动添加、合并粒子的SPH自适应粒子分布算法。采用该方法对Taylor碰撞和超高速碰撞问题进行了数值模拟,结果表明,该方法可以有效地消除计算中出现的数值破坏,提高计算精度。     

一种新型SPH-FEM耦合算法及其在冲击动力学问题中的应用

为了充分发挥光滑粒子流体动力学方法(smoothed particle hydrodynamics,SPH)在处理大变形和有限元(finite element method,FEM)问题时计算精度高的优势,提出了一种新型SPH-FEM耦合算法.该耦合算法在大变形区域使用SPH粒子离散,其余区域使用有限元离散.在耦合界面...     

SPH-FEM接触算法在冲击动力学数值计算中的应用

为了充分发挥光滑粒子流体动力学方法(Smoothed Particle Hydrodynamics,SPH)易于处理大变形以及有限元(Finite Element Method,FEM)计算精度和效率高的优势,论文基于无网格粒子接触算法,在有限元节点处设置背景粒子,通过接触力的方式计算SPH粒子和有限单元之间的接触问题...     

关于弹体冲击和贯穿混凝土的三维数值模拟

利用FEM和SPH算法相结合给出弹体冲击和贯穿混凝土的三维数值模拟。将弹体划分为四面体有限元网格,混凝土划分为光滑粒子。为形成单元方便,将弹体划分成三个独立的模块并且这三个独立的模块具有拼凑功能。给出光滑粒子-有限元界面的滑移面算法。为了提高计算效率,在程序的前处理中预设界面的从属点和每个光滑粒子的关联点。计算结果与实验结果对比表明,FEM和SPH算法相结合及编制的程序能有效模拟弹体对混凝土的三维冲击和贯穿过程。同时给出在垂直冲击中二维计算与三维计算的差别。     

光滑粒子法与有限元的耦合算法及其在冲击动力学中的应用

扼要讨论了光滑粒子法的离散思想,充分利用光滑粒子法和有限元方法各自的优点,提出了一种初始时刻用有限元建模,计算过程中大变形单元自动转换为光滑粒子的耦合算法。高速碰撞的系列算例说明,耦合算法不但适宜于计算大变形冲击动力学问题,而且由于集两种方法的优点于一身,可以更高效地模拟一些高速碰撞问题,提高计算效率。     

基于耦合算法的三维复杂结构冲击动力学特性

光滑粒子流体动力学-有限元耦合算法（SPH-FEM）较好地结合了SPH和FEM的优势,近年来逐渐被引入冲击动力学相关问题研究中。然而早期的研究对象多为单一材料的简单结构,所取得的研究成果距离实际工程应用仍有一定差距。为此,在总结前人工作的基础上,对SPH-FEM耦合算法进行适当改进,通过引入复合材料损伤模型,对复合材料蒙皮结构飞行器舱段结构进行建模计算,分析其在爆炸冲击激励下的冲击动力学特性。将数值计算结果与试验结果进行对比分析,验证该算法和模型的有效性和准确性,初步实现SPH-FEM的工程实际应用。最后总结了复合材料蒙皮结构飞行器在爆炸冲击激励下的一系列结构动态响应规律,以期为航天飞行器结构设计与防护提供参考。     

SPH方法在聚能装药射流三维数值模拟中的应用

采用有限元软件LS-DYNA中的SPH算法实现聚能装药射流形成过程的三维数值模拟.将SPH方法和FEM方法与理论计算结果相比较.研究结果表明:SPH数值模拟计算过程十分稳定,避免了有限元数值模拟过程中的网格扭曲、缠绕和物质穿透等问题,而且计算精度比有限元方法更高;采用SPH方法计算的射流速度、射流长度与有限元计算结果和...     

DEM与FEM动态耦合算法研究

离散单元法作为一种有效的数值分析方法,能够模拟脆性材料的裂纹扩展及碎片飞散等破坏特性,但是无法从根本上克服计算效率低下的诟病;传统有限单元法具有计算高效稳定的优点,却难以描述脆性材料冲击破坏过程中连续体向非连续体的转化。本文首先提出一种基于罚函数法的改进型离散单元和有限单元耦合方法,以提高耦合分析精度。在此基础上提出了动态耦合算法:即在初始阶段,模型全部为有限单元,当局部即将发生破坏时,仅使即将发生破坏的有限单元及相邻单元自动转化为离散单元,在离散单元区域研究破坏问题。这种算法充分利用有限单元法计算高效的优点,同时最大限度克服了离散单元法计算效率的不足。最后,通过两个简单算例验证了改进型耦合算法和动态耦合算法的有效性。     

流变学研究的若干问题

本文综述了1988年8月第10届国际流变学会议部分大会邀请报告及分组报告的下列几个领域内容:①分子动力学;②光学流变测量;⑧血液的动态测量;④数值仿真;⑤钻探油井;⑥强化采油;⑦减阻;⑧聚合物挤压成形加工;⑨食品流变学.     

(Q)SAR modelling of nanomaterial toxicity: A critical review

There is increasing recognition that some nanomaterials may pose a risk to human health and the environment. Moreover, the industrial use of the novel engineered nanomaterials (ENMs) increases at a higher rate than data generation for hazard assessment; consequently, many of them remain untested. The large number of nanomaterials and their variants (e.g., different sizes and coatings) requiring testing and the ethical pressure towards nonanimal testing means that in a first instance, expensive animal bioassays are precluded, and the use of (quantitative) structure–activity relationships ((Q)SARs) models as an alternative source of (screening) hazard information should be explored. (Q)SAR modelling can be applied to contribute towards filling important knowledge gaps by making best use of existing data, prioritizing the physicochemical parameters driving toxicity, and providing practical solutions for the risk assessment problems caused by the diversity of ENMs. This paper covers the core components required for successful application of (Q)SAR methods to ENM toxicity prediction, summarizes the published nano-(Q)SAR studies, and outlines the challenges ahead for nano-(Q)SAR modelling. It provides a critical review of (1) the present availability of ENM characterization/toxicity data, (2) the characterization of nanostructures that meet the requirements for (Q)SAR analysis, (3) published nano-(Q)SAR studies and their limitations, (4) in silico tools for (Q)SAR screening of nanotoxicity, and (5) prospective directions for the development of nano-(Q)SAR models.     

On the boundedness and the stability properties of solution of certain fourth order differential equations

This paper investigates equation(1)in two cases:(i)P≡0,(ii)P(≠O)satisfies|P(t,x,y,z,ω)|≤(A |y| |z| |ω|)q(t),where q(t)is a nonnegative function of t.For case(i)the asymptotic stability in the large of the trivial solution x=0 is investigatedand for case(ii)the boundedness result is obtained for solutions of equation(1).Theseresults improve and include several well-known results.     

国内非牛顿流体力学进展

非牛顿流体;;本构方程;;流变测量;;流动稳定性;;收缩流动;;聚合物加工;;石油工业;;生物流体力学     

Overview of Identification Methods of Mechanical Parameters Based on Full-field Measurements

This article reviews recently developed methods for constitutive parameter identification based on kinematic full-field measurements, namely the finite element model updating method (FEMU), the constitutive equation gap method (CEGM), the virtual fields method (VFM), the equilibrium gap method (EGM) and the reciprocity gap method (RGM). Their formulation and underlying principles are presented and discussed. These identification techniques are then applied to full-field experimental data obtained on four different experiments, namely (i) a tensile test, (ii) the Brazilian test, (iii) a shear-flexural test, and (iv) a biaxial test. Test (iv) features a non-uniform damage field, and hence non-uniform equivalent elastic properties, while tests (i), (ii) and (iii) deal with the identification of uniform anisotropic elastic properties. Tests (ii), (iii) and (iv) involve non-uniform strain fields in the region of interest. Working group “Identification” of the French CNRS research network (GDR 2519) “Mesures de champs et identification en Mécanique des Solides / Full-field Measurements and Identification in Solid Mechanics”.     

Synthesis of submicron-sized composite particles with unique morphology by emulsifier-free seeded emulsion copolymerization

Polystyrene （PSt） microspheres with diameter of 375 nm to be used as the seeds for seeded emulsion polymerization were prepared via emulsion polymerization using potassium persulfate （KPS） as initiator in ethanol-water mixed solvents. Emulsifier-free seeded emulsion copolymerization of styrene （St） with acrylonitrile （AN） was carried out in the presence of poly（ethylene glycol） monomethoxymonomethacrylate （PEGm） macromonomer as reactive stabilizer and 2,2＇-azobisisobutyronitrile （AIBN） as initiator to obtain submicron-sized PEGm graft poly（styrene-coacrylonitrile） （PEGm-g-PSAN） composite particles with unique morphology. Scanning electron microscopy （SEM） indicated that St and AN together contributed to forming the unusual morphology. The concentration of St and AN, total monomer concentration, initiator type and the monomer adding method remarkably affected the morphology of the composite polymer particles.     

On (g, f)-factorizations of graphs

I.IntroductionLetGbeafinitegraph(withoutloops),V(G)andE(G)bethevenicessetandedgesset,respectively.Foreachxos(G),wedenotebydo(x)thedegreeofxinG.Letg,fbetwononnegativeinteger-valuedfunctionsdefinedonV(G)andg相似文献   

Improving control effects of absence seizures using single-pulse alternately resetting stimulation(SARS) of corticothalamic circuit

Presently, we develop a simplified corticothalamic(SCT) model and propose a single-pulse alternately resetting stimulation(SARS) with sequentially applying anodic(A, "+") or cathodic(C, "-") phase pulses to the thalamic reticular(RE) nuclei,thalamus-cortex(TC) relay nuclei, and cortical excitatory(EX) neurons, respectively.Abatement effects of ACC-SARS of RE, TC, and EX for the 2 Hz–4 Hz spike and wave discharges(SWD) of absence seizures are then concerned. The m∶n on-off ACC-SARS protocol is shown to effectively reduce the SWD with the least current consumption. In particular, when its frequency is out of the 2 Hz–4 Hz SWD dominant rhythm, the desired seizure abatements can be obtained, which can be further improved by our proposed directional steering(DS) stimulation. The dynamical explanations for the SARS induced seizure abatements are lastly given by calculating the averaged mean firing rate(AMFR)of neurons and triggering averaged mean firing rates(TAMFRs) of 2 Hz–4 Hz SWD.     

Computerized Developments in Design,Generation, Simulation of Meshing,and Stress Analysis of Gear Drives

The paper represents new computerized developments in design, generation, simulation of meshing, and stress analysis of gear drives. The main contents of the paper are: (i) application of a predesigned parabolic function of transmission errors for reduction of noise, (ii) computerized simulation of noise caused by transmission errors, (iii) modification of the basic algorithm of tooth contact analysis, and (iv) application of approaches developed for enhanced design and simulation of meshing of the following gear drives: (a) spiral bevel gear drives, (b) face-gear drives (including an approach for grinding), and (c) modified helical gear drives. The developed theory is illustrated with numerical examples.     

Comment on “Analysing flow and heat transfer of a viscoelastic fluid over a semi-infinite horizontal moving flat plate, IJNLM, 43 (2008) 772”

In this report we make corrections to a paper by Rafael Cortell (IJNLM, 43 (2008) 772). In this paper (IJNLM, 43 (2008) 772) the author considered an incorrect equation (by including a wrong term instead of correct term) for his considered flow and heat transfer problem and reported unrealistic results as a consequence. In this communication we have considered the correct equation (replacing the incorrect term by correct one) and solved it analytically. Our analysis shows that the unrealistic behavior as observed by Cortell (IJNLM, 43 (2008) 772) persists no more if one considers the correct term.