IMECH-IR中国科学院力学研究所http://dspace.imech.ac.cn:802020-05-25T13:28:10Z2020-05-25T13:28:10ZPIMOL: The Finite Difference Method of Lines Based on the Precise Integration Method for an Arbitrary Irregular DomainXu YJ(徐永君)http://dspace.imech.ac.cn:80/handle/311007/819102020-05-18T02:59:06Z2020-05-18T02:11:33ZTitle: PIMOL: The Finite Difference Method of Lines Based on the Precise Integration Method for an Arbitrary Irregular Domain
Authors: Xu YJ(徐永君)
Description: <p>The aim of this paper is to introduce a new semi-analytical method named precise integration method of lines (PIMOL), which is developed and used to solve the ordinary differential equation (ODE) systems based on the finite difference method of lines and the precise integration method. The irregular domain problem is mainly discussed in this paper. Three classical examples of Poisson's equation problems are given, including one regular and two irregular domain examples. The PIMOL reduces a semi-discrete ODE problem to a linear algebraic matrix equation and does not require domain mapping for treating the irregular domain problem. Numerical results show that the PIMOL is a powerful method.</p>2020-05-18T02:11:33ZAtomic-level structural identification for prediction of localized shear deformation in metallic glasses史荣豪肖攀杨荣白以龙http://dspace.imech.ac.cn:80/handle/311007/819072020-05-19T01:13:10Z2020-05-18T02:11:32ZTitle: Atomic-level structural identification for prediction of localized shear deformation in metallic glasses
Authors: 史荣豪; 肖攀; 杨荣; 白以龙
Description: Unlike obviously topological defects in crystals, "defect" identification in metallic glasses (MGs) is still controversial and under investigation. Based on molecular simulations and analysis of MG samples, a structural parameter related to the Laplacian of local equivalent stiffness is proposed for prediction of localized shear deformation in MGs. It is found that local regions with the parameter of positive and relatively large value represent several particular modes of "stiffness valleys" in initial configuration which will strengthen local shear deformation and lead to the formation of shear transformation zones (STZs). More than 80% of the locations where STZs are formed in six types of MG samples under athermal quasi-static shear deformation match well with the regions predicted by the parameter calculated from initial configuration of the samples. The parameter not only reveals the relationship among local heterogeneity, nonaffine displacement, and shear localization, but also provides an efficient way for predicting the activation of STZs in MGs. (C) 2020 Elsevier Ltd. All rights reserved.2020-05-18T02:11:32ZNumerical study on reflection of an oblique detonation wave on an outward turning wall王宽亮张子健杨鹏飞滕宏辉http://dspace.imech.ac.cn:80/handle/311007/819042020-05-19T01:13:12Z2020-05-18T02:11:29ZTitle: Numerical study on reflection of an oblique detonation wave on an outward turning wall
Authors: 王宽亮; 张子健; 杨鹏飞; 滕宏辉
Description: Oblique detonation waves (ODWs) have been studied widely as the basis of detonation-based hypersonic engines, but there are few studies on ODWs in a confined space. This study simulates ODW reflection on a solid wall before an outward turning corner for a simplified combustor-nozzle flow based on a two-step kinetic model. Numerical results reveal three types of ODW structures: stable, critical, and unstable. When the reflection occurs at the turning point, the stable ODW structure remains almost the same as before reflection. When the wave reflects at the wall before the turning point, either the critical structure or the unstable structure arises, which has never been investigated before. Both structures have the same initial two-section detonation surface: but the critical one becomes stationary at a certain position, while the unstable one keeps traveling upstream. By adjusting the location of the expansion wave and degree of the turning angle, the difference of the two structures is attributed to the thermal choking appearing only in the unstable structure. The thermal choking is achieved by the merging of subsonic zones, whose dependence on the various parameters is discussed.2020-05-18T02:11:29ZSteady state response of an infinite beam on a viscoelastic foundation with moving distributed mass and loadZhang Y(张吟)http://dspace.imech.ac.cn:80/handle/311007/819012020-05-18T02:59:50Z2020-05-18T02:11:28ZTitle: Steady state response of an infinite beam on a viscoelastic foundation with moving distributed mass and load
Authors: Zhang Y(张吟)
Description: <p>Compared with the moving concentrated load model, it is more realistic and proper to use the moving distributed mass and load model to simulate the dynamics of a train moving along a railway track. In the problem of a moving concentrated load, there is only one critical velocity, which divides the load moving velocity into two categories: subcritical and supercritical. The locus of a concentrated load demarcates the space into two parts: the waves in these two domains are called the front and rear waves, respectively. In comparison, in the problem of moving distributed mass and load, there are two critical velocities, which results in three categories of the distributed mass moving velocity. Due to the presence of the distributed mass and load, the space is divided into three domains, in which three different waves exist. Much richer and different variation patterns of wave shapes arise in the problem of the moving distributed mass and load. The mechanisms responsible for these variation patterns are systematically studied. A semi-analytical solution to the steady-state is also obtained, which recovers that of the classical problem of a moving concentrated load when the length of the distributed mass and load approaches zero.</p>2020-05-18T02:11:28ZA Method to Determine Material Length Scale Parameters in Elastic Strain Gradient Theory宋晶如魏悦广http://dspace.imech.ac.cn:80/handle/311007/818982020-05-19T01:13:13Z2020-05-18T02:11:26ZTitle: A Method to Determine Material Length Scale Parameters in Elastic Strain Gradient Theory
Authors: 宋晶如; 魏悦广
Description: With specimen size decrease for advanced structural materials, the measured mechanics behaviors display the strong size effects. In order to characterize the size effects, several higher-order theories have been presented in the past several decades, such as the strain gradient theories and the micro-polar theories, etc. However, in each higher-order theory, there are several length scale parameters included, which are usually taken as the material parameters and are determined by using the corresponding theoretical predictions to fit experimental results. Since such kind of experimental approaches needs high techniques, it is very difficult to be performed; therefore, the obtained experimental results are very few until now; in addition, the physical meanings of the parameters still need to be investigated. In the present research, an equivalent linkage method is used to simply determine the elastic length parameters appeared in the elastic strain gradient theory for a series of typical metal materials. We use both the elastic strain gradient theory and the higher-order Cauchy-Born rule to model the materials mechanics behaviors by means of a spherical expanding model and then make a linkage for both kinds of results according to the equivalence of strain energy densities. The values of the materials length parameters are obtained for a series of typical metal systems, such as the face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close-packed (HCP) metals.2020-05-18T02:11:26ZHigh-precision laser spot center positioning method for weak light conditions高瑞弘刘河山Zhao Y罗子人靳刚http://dspace.imech.ac.cn:80/handle/311007/818952020-05-19T01:13:15Z2020-05-18T02:11:24ZTitle: High-precision laser spot center positioning method for weak light conditions
Authors: 高瑞弘; 刘河山; Zhao Y; 罗子人; 靳刚
Description: In the acquisition stage of many space applications, such as the Taiji program, the spot center of weak laser light must be accurately determined. Underweak light conditions, the precision of most traditional positioning methods is greatly affected. In this paper, we present a high-precision laser spot center positioning method based on the theoretical analysis of influence factors of precision. It is shown through experimental study that the method's precision can fulfill the requirement of the Taiji program. (C) 2020 Optical Society of America2020-05-18T02:11:24ZExperimental investigation of a hypersonic I-shaped configuration with a waverider compression surface李广利崔凯徐应洲王浩祥杨靖许先贵ihttp://dspace.imech.ac.cn:80/handle/311007/818922020-05-19T01:13:16Z2020-05-18T02:11:22ZTitle: Experimental investigation of a hypersonic I-shaped configuration with a waverider compression surface
Authors: 李广利; 崔凯; 徐应洲; 王浩祥; 杨靖; 许先贵i2020-05-18T02:11:22ZNon-premixed turbulent combustion modeling based on the filtered turbulent flamelet equation张健Wang LPGuo YQhttp://dspace.imech.ac.cn:80/handle/311007/818892020-05-19T01:13:17Z2020-05-18T02:11:21ZTitle: Non-premixed turbulent combustion modeling based on the filtered turbulent flamelet equation
Authors: 张健; Wang LP; Guo YQ
Description: In turbulent combustion simulations, the flow structure at the unresolved scale level needs to be reasonably modeled. Following the idea of turbulent flamelet equation for the non-premixed flame case, which was derived based on the filtered governing equations (L. Wang, Combust. Flame 175, 259 (2017)), the scalar dissipation term for tabulation can be directly computed from the resolved flowing quantities, instead of solving species transport equations. Therefore, the challenging source term closure for the scalar dissipation or any assumed probability density functions can be avoided; meanwhile the chemical sources are closed by scaling relations. The general principles are discussed in the context of large eddy simulation with case validation. The new model predictions of the bluff-body flame show sufficiently improved results, compared with these from the classic progress-variable approach.2020-05-18T02:11:21ZWinding-Locked Carbon Nanotubes/Polymer Nanofibers Helical Yarn for Ultrastretchable Conductor and Strain SensorGao YGuo FYCao PLiu JCLi DMWu JWang N苏业旺Zhao Yhttp://dspace.imech.ac.cn:80/handle/311007/818862020-05-19T01:13:18Z2020-05-18T02:08:58ZTitle: Winding-Locked Carbon Nanotubes/Polymer Nanofibers Helical Yarn for Ultrastretchable Conductor and Strain Sensor
Authors: Gao Y; Guo FY; Cao P; Liu JC; Li DM; Wu J; Wang N; 苏业旺; Zhao Y
Description: Wearable and stretchable electronics including various conductors and sensors are featured with their lightweight, high flexibility, and easy integration into functional devices or textiles. However, most flexible electronic materials are still unsatisfactory due to their poor recoverability under large strain. Herein, we fabricated a carbon nanotubes (CNTs) and polyurethane (PU) nanofibers composite helical yarn with electrical conductivity, ultrastretchability, and high stretch sensitivity. The synergy of elastic PU molecules and springlike microgeometry enable the helical yarn excellent stretchability, while CNTs are stably winding-locked into the yarn through a simple twisting strategy, making good conductivity. By virtue of the interlaced conductive network of CNTs in microlevel and the helical structure in macrolevel, the CNTs/PU helical yarn achieves good recoverability within 900% and maximum tensile elongation up to 1700%. With these features, it can be used as a superelastic and highly stable conductive wire. Moreover, it also can monitor the human motion as a rapid-response strain sensor by adjusting the content of the CNTs simply. This general and low-cost strategy is of great promise for ultrastretchable wearable electronics and multifunctional devices.2020-05-18T02:08:58ZInfluences of Morphology Parameters on the Contact Behavior of a Steel InterfaceFan LFZhao L刘小明http://dspace.imech.ac.cn:80/handle/311007/818832020-05-19T01:13:19Z2020-05-18T02:08:56ZTitle: Influences of Morphology Parameters on the Contact Behavior of a Steel Interface
Authors: Fan LF; Zhao L; 刘小明
Description: The surface roughness induced by geometric irregularities (asperities) has substantial influence on the contact stiffness, which further affects the working performance and service life of mechanical equipment. In this study, an elastic-plastic contact law between a sinusoidal asperity and a rigid smooth flat is first studied, which is then applied on a statistical model to simulate the contact behavior of a pair of 18CrMo4 steel surfaces to investigate the influences of morphology parameters on the contact stiffness. The analysis shows that smaller shape ratios xi and larger wavelengths lambda induce larger normal contact stiffness K-n for surfaces with identical roughness, wherein the roughness is defined by the mean value of asperity heights R-a and the standard deviation of asperity heights R-q. The normal contact stiffness increases as R-a decreases under the same loading conditions, while the normal contact stiffness increases as R-q decreases for surfaces with a fixed R-a. Besides, the normal pressure and normal contact, stiffness derived from the proposed contact model are validated. The results demonstrate the potential of the proposed model in contact design due to its ability of establishing the relations between the normal contact stiffness and surface morphology parameters.2020-05-18T02:08:56Z