非线性微分动力系统稳定域计算的波形松弛方法

非线性微分动力系统稳定域计算是在许多领域具有实际应用的问题。本文对非线性微分动力系统稳定域的计算方法进行了总结,通过对稳定域边界流形的全面分析,提出了用波形松弛方法计算稳定域边界流形的思想,给出了计算稳定域边界流形的波形松弛算法。第一步,找出微分动力系统的所有平衡点,确定渐近稳定平衡点稳定域边界上的平衡点;第二步,用微分动力系统的反方向系统确定原系统渐近稳定平衡点稳定域边界上平衡点的稳定流形;第三步,渐近稳定平衡点稳定域的边界是由边界上平衡点和该平衡点稳定流形的并集构成。最后用例子来说明波形松弛方法在计算稳定域边界流形的有效性。     

混凝土单轴拉伸的应变软化行为及描述

本文将试件和试验机置于一个系统中，对混凝土单轴拉伸试验的稳定性条件进行了分析并得到了单轴拉伸应变软件条件下部分的稳定平衡路径，结果表明，软化曲线的形状不仅与材料性质有关，还与试验机刚度和试件尺寸有关，此时不应将混凝土的软化性质单纯视为材料特性，在不同的软化阶段，应采用不同的模型表达，本文还将理论曲线与试验结果进行了比较，在软化段初上降部分模型结果与实验曲线符合较好。     

液氧输送系统压力异常下降成因分析与数值研究

针对某运载火箭液氧输送系统分支管路压力异常的问题,采用CFD软件对液氧输送系统管路进行了数值模拟,并对压力异常的维持、不同过载条件与不同管路开闭条件下压力响应进行了计算分析。结果表明:随着边界条件与时间不同,液氧输送管路在运行中会形成3种型态各异的流场,造成压力异常的流场是一种稳定平衡的流场;在不同管路开闭条件下,流场会发生旋转等物理形状上的变化,从而对各并联管路的压力造成影响。计算结果阐明了压力异常状况产生的原因,对于维护运载火箭的稳定运行及后期的输送系统改进提供了指导。     

自动电话机稳定平衡回损和回声平衡回损测量结果的不确定度评定

本文介绍了电话机通话状态交流阻抗对应的稳定平衡回损和回声平衡回损测量结果不确定度评定,分析了不确定度主要来源,计算和评定了相应的标准不确定度、合成不确定度和扩展不确定度。     

存在内外质量交换的声空化泡动力学模型

对于空化微气泡的动力学研究多基于气泡内外无质量交换的Rayleigh模型。考虑了气泡内外的物质交换,泡内气体分子数量,即气泡平衡半径成为变量,进而将Rayleigh模型推广到有质量交换的情形。通过数值计算,获得稳定平衡半径,以及它与驱动声压的相关性。结果表明:在低声压驱动下,气泡稳定平衡半径随驱动声压增大而减小;而在高声压下,气泡稳定平衡半径随驱动声压增大而增大,稳定平衡半径-声压曲线存在一个转折点。     

自动电话机稳定平衡回损和回声平衡回损测量结果的不确定度评定

本文介绍了电话机通话状态交流阻抗对应的稳定平衡回损和回声平衡回损测量结果不确定度评定,分析了不确定度主要来源,计算和评定了相应的标准不确定度、合成不确定度和扩展不确定度.     

几率矩阵法计算涡轮分子泵叶列传输几率

本文介绍了用几率矩阵法计算涡轮分子泵叶列传输几率，并对现在的几种计算方法作了相互比较，发现几率矩阵法具有计算速度快，模型简单，且能处理几何形状复杂而其他方法难以解决的问题。     

复杂形状食品冻结时间的几何因子预测法

本文阐述了用于计算复杂形状食品冻结晶解冻时间的几何因子法，给出了大平板冻结和解冻时间及多种复杂状食品形状因子的计算公式。经验证，利用形状因子法计算各种形状食品冻结和解冻时间的精度较高。     

对声辐射模态法的改进

以简支矩形板为例，通过声辐射模态研究结果声辐射问题，从物理和数学意义上对声辐射模态进行了解释，并对声辐射的自由度进行讨论，由于声辐射模态形状是频率的函数，这限制了声辐射模态在噪声控制中的应用。本文提出对声辐射模态算法进行改进，使声辐射模态形状在中、低频时与频率无关。最后进行了数值计算研究，结果表明，这种方法是可行的。     

喷射沉积柱状坯形状模型

通过坐标跟踪法建立了沉积坏形状预测模型。该模型不但考虑沉积坯任何表面点身自位置变化对沉积效果的影响，同时考虑了该点温度和其它表面点位置对该点沉积效果的影响，其计算过程严格按照喷射成形的实际过程执行，可实时计算并记录沉积坯的形貌，并验证了计算效果。本文模型可用于多种工艺下喷射沉积坯的形状预测。     

超声辐照对PP/EPDM共混物在加工过程中微相结构的影响

研究了超声辐照对聚丙烯／三元乙丙橡胶(PP／EPDM)共混物挤出过程及二次加工中微相结构的影响．结果表明随超声功率的增加EPDM相的比表面积增大，界面作用增强．超声辐照使EPDM在PP中形成的良好的分散效果在经过热压二次成型后仍大部分得以保持．动态流变分析显示超声振动使PP／EPDM共混物的内部结构变得更加均匀．Palierne乳液模型计算结果表明，超声辐照使共混物中两相的界面张力降低，这说明超声辐照使两相间形成了良好的界面结构和牢固的界面作用，有效地阻止了EPDM液滴在共混过程以及随后的热压成型加工过程中的合并．     

瓦楞纸板生产线原纸张力自适应模糊PID控制

目的为了解决张力控制不稳定对瓦楞纸板质量和生产效率产生影响的问题。方法对放卷辊进行动力学分析,建立瓦楞纸板的原纸张力数学模型,并分析张力稳定的主要因素。针对传统PID控制不能实现原纸张力控制过程中参数的自适应调整,提出一种变论域自适应模糊PID控制策略,采用变论域模糊控制实现控制参数自整定和控制规则的自调整,并将其应用于原纸张力控制系统中。结果仿真结果表明,该张力控制策略的响应时间约为0.65 s,最大超调量为3%。结论所设计的控制方法与传统的PID控制相比,具有响应速度快、抗干扰能力强、控制输出稳定等优点,能够实现原纸张力的稳定控制。     

Remarks on tension instability of Eulerian and Lagrangian corrected smooth particle hydrodynamics (CSPH) methods

The paper discusses the problem of tension instability of particle‐based methods such as smooth particle hydrodynamics (SPH) or corrected SPH (CSPH). It is shown that tension instability is a property of a continuum where the stress tensor is isotropic and the value of the pressure is a function of the density or volume ratio. The paper will show that, for this material model, the non‐linear continuum equations fail to satisfy the stability condition in the presence of tension. Consequently, any discretization of this continuum will result in negative eigenvalues in the tangent stiffness matrix that will lead to instabilities in the time integration process. An important exception is the 1‐D case where the continuum becomes stable but SPH or CSPH can still exhibit negative eigenvalues. The paper will show that these negative eigenvalues can be eliminated if a Lagrangian formulation is used whereby all derivatives are referred to a fixed reference configuration. The resulting formulation maintains the momentum preservation properties of its Eulerian equivalent. Finally a simple 1‐D wave propagation example will be used to demonstrate that a stable solution can be obtained using Lagrangian CSPH without the need for any artificial viscosity. Copyright © 2001 John Wiley & Sons, Ltd.     

考虑纤维体积含量变化的纤维缠绕厚壁柱形结构的等强度设计

纤维缠绕厚壁柱形管道或容器在缠绕张力作用下会使缠绕纤维层的应力状态不断变化,形成沿壁厚力学性能非均匀的结构。依据缠绕过程中的纤维束应力状态分析和纤维束本构关系,获得了纤维体积含量与所受应力状态的关系。基于正交各向异性本构关系和双层筒模型的离散叠加法,建立了给定缠绕张力确定纤维缠绕厚壁柱形结构剩余张力的计算方法,并计算了等张力缠绕纤维层的纤维体积含量沿壁厚的分布。利用Tsai-Wu失效准则研究了纤维体积含量非均匀的厚壁柱形结构的纤维层强度。研究表明:缠绕工艺使内层纤维体积含量和强度均略高于外层,纤维缠绕厚壁柱形结构的强度分析和设计时应考虑这种影响;利用变化的缠绕张力设计可以实现强度比沿壁厚的均匀分布。     

用于压/拉检测的机器人皮肤柔/弹性传感器阵列设计

基于炭黑/硅橡胶复合材料的压力以及拉伸敏感特性,设计了一种可用于检测机器人皮肤接触压力和拉伸特性的新型传感器阵列。该传感器阵列的弹性电极结构克服了传统传感器不可拉伸的缺点,实现了传感器阵列的柔/弹性;阵列中设计了9个检测压力的传感器单元和2个检测拉伸的传感器单元,通过传感器结构设计和拉/压干扰特性分析以及补偿算法解决了拉伸和压力同时测量时的干扰问题,并构建了求解压力与拉伸的数学模型。实验结果表明:该传感器阵列实现了对压力和拉伸的同步检测,可用于机器人柔性皮肤中关节等部位。     

The Theory of Critical Distances to estimate the static strength of notched samples of Al6082 loaded in combined tension and torsion. Part I: Material cracking behaviour

The present paper is the first of a two-part series reporting an experimental and theoretical study of the fracture of circumferentially notched samples of a commercial aluminium alloy, i.e. Al6082, subjected to tension, torsion and mixed tension/torsion loading. The overall aim of the work was to investigate the use of a particular method of failure prediction, known as the Theory of Critical Distances. This first part reports the experimental data - load-deflection curves and observed material failure modes - and discusses the consequences of these findings for the development of the theory, which is covered in the second part. It was observed that relatively blunt notches loaded in tension failed by a conventional ductile fracture mode similar to plain (unnotched) specimens. However, in tensile specimens containing sharp notches, failure occurred via the initiation, stable propagation and, finally, unstable propagation, of circumferential ring cracks. Under torsional loading, and independent of the notch root radius, static failures of the tested samples always occurred by the formation and stable propagation of ring cracks. Under mixed-mode loading there was a gradual transition between the ductile and brittle modes and between stable and unstable cracking. For all types of loading, it was observed that crack initiation always coincided with peak loading conditions, and that cracks invariably grew on the plane perpendicular to the specimen’s longitudinal axis.     

Surface Tension and Viscosity of Quasicrystal-Forming Ti–Zr–Ni Alloys

Recent X-ray scattering measurements show that icosahedral short-range order in Ti–Zr–Ni alloys is responsible for a change in phase selection from the stable C14 Laves phase to the quasicrystalline icosahedral phase, and that icosahedral short-range order increases at deeper undercoolings. This change in short-range order should be reflected in changes in the thermophysical properties of the melt. The surface tension and viscosity of quasicrystal-forming Ti–Zr–Ni alloys were measured over a range of temperature, including both stable and undercooled liquids, by an electrostatic levitation (ESL) technique. ESL is a containerless technique which allows processing of samples without contact, greatly reducing contamination and increasing access to the metastable undercooled liquid. The measured viscosity is typical of glass-forming alloys of similar composition to the quasicrystal-forming alloys studied here; however, the surface tension shows an anomaly at deep undercoolings.     

Experimental characterization of microstructure development during loading path changes in bcc sheet steels

Interstitial free sheet steels show transient work hardening behavior, i.e., the Bauschinger effect and cross hardening, after changes in the loading path. This behavior affects sheet forming processes and the properties of the final part. The transient work hardening behavior is attributed to changes in the dislocation structure. In this work, the morphology of the dislocation microstructure is investigated for uniaxial and plane strain tension, monotonic and forward to reverse shear, and plane strain tension to shear. Characteristic features such as the thickness of cell walls and the shape of cells are used to distinguish microstructural patterns corresponding to different loading paths. The influence of the crystallographic texture on the dislocation structure is analyzed. Digital image processing is used to create a “library” of schematic representations of the dislocation microstructure. The dislocation microstructures corresponding to uniaxial tension, plane strain tension, monotonic shear, forward to reverse shear, and plane strain tension to shear can be distinguished from each other based on the thickness of cell walls and the shape of cells. A statistical analysis of the wall thickness distribution shows that the wall thickness decreases with increasing deformation and that there are differences between simple shear and uniaxial tension. A change in loading path leads to changes in the dislocation structure. The knowledge of the specific features of the dislocation structure corresponding to a loading path may be used for two purposes: (i) the analysis of the homogeneity of deformation in a test sample and (ii) the analysis of a formed part.     

Hierarchically porous CMC/rGO/CNFs aerogels for leakage-proof mirabilite phase change materials with superior energy thermal storage

As a kind of essential hydrated salt phase change energy storage materials, mirabilite with high energy storage density and mild phase-transition temperature has excellent application potential in the problems of solar time and space mismatch. However, there are some disadvantages such as supercooling, substantial phase stratification and leakage problem, limiting its further applications. In this work, for the preparation of shaped mirabilite phase change materials (MPCMs), graphene (GO), sodium carboxymethyl cellulose (CMC), and carbon nanofibers (CNFs) were used as starting materials to prepare lightweight CMC/rGO/CNFs carbon aerogel (CGCA) as support with stable shape, high specific surface area, and well-arranged hierarchically porous structure. The results show that CGCA has regular layered plentiful pores and stable foam structure, and the pore and sheet interspersed structure in CGCA stabilizes PCMs via capillary force and surface tension. The hydrophilic aerogels supported MPCMs decrease mirabilite leaking and reduce supercooling to around 0.7‒1 °C. The latent heats of melting and crystallization of CGCA-supported mirabilite phase change materials (CGCA-PCMs) are 157.1 and 114.8 J·g⁻¹, respectively. Furthermore, after 1500 solid‒liquid cycles, there is no leakage, and the retention rate of crystallization latent heat is 45.32%, exhibiting remarkable thermal cycling stability.     

Development of a fatigue testing system for thin films

Only a few works on fatigue behavior of thin films under tension–tension loading can be found because of some limitations of a testing system. In this study, a fatigue testing system capable of performing load controlled tension–tension fatigue tests even for ductile thin films was developed by using an electrodynamic actuator. With the system, fatigue testing can be performed over a wide range of loading frequency. Besides, a capacitive displacement gauge was developed to measure the monotonic and cyclic deformation of thin films with high resolution during fatigue testing. As the displacement gauge is stable and its response is so fast, the displacement can be measured instantaneously and continuously during fatigue testing of high frequency.