A selective smoothed finite element method with visco-hyperelastic constitutive model for analysis of biomechanical responses of brain tissues

Brain tissues are known for exhibiting complex nonlinear and time-dependent properties, which require visco-hyperelastic constitutive models for proper simulation. In this paper, a Total Lagrangian Explicit Selective Smoothed Finite Element Method (Selective S-FEM) is formulated to analyze the dynamic behavior of incompressible brain tissues undergoing extremely large deformation. The proposed Selective S-FEM deals with three-dimensional problems using four-node tetrahedron elements that can be automatically generated for geometrically complex soft tissues. It consists of the three key ingredients. (i) A visco-hyperelastic constitutive model is developed within the framework of S-FEM in the first time, allowing adequate modeling of the dynamic brain tissue behavior. (ii) Selective S-FEM strategy is used for overcome the mesh distortion and the volumetric locking that often occurs in soft tissues. (iii) Total Lagrangian formulation is used in an explicit algorithm allowing rigorous simulation of extreme large deformation. (iv) A combined implementation of Selective S-FEM with the visco-hyperelastic constitutive model for dynamic simulations. The shear deformation is calculated by Face/Edge-based S-FEM, and the volume deformation is calculated by NS-FEM. Numerical experiments show that Selective S-FEM is a robust solver with good accuracy, and excellent ability to reduce element distortion effects in simulate time-dependence behavior of bio-tissues.     

一种太阳能电池MPPT控制器实现及测试方法的研究

本文根据太阳能电池的特性,设计了一种基于"电压扰动法"的太阳能电池最大功率点跟踪(MPPT)控制器,并提出了一种简单、实用的模拟太阳能电池对控制器进行测试的方法,理论证明该方法是可行的,并得到实际验证.在此实验方法下,对设计的MPPT控制器进行测试,结果表明它有较好的跟踪性能.     

聚丙烯大分子表面改性剂PP-g-PMMA的制备及应用

以马来酸酐为桥联剂,通过其与含端羟基PMMA的偶合反应,合成了新型大分子表面改性剂PP-g-PMMA,用IR、NMR、TG、DSC对接枝物进行表征,并通过共混研究了接枝物对聚丙烯的表面改性。结果表明,PP-g-PMMA的热稳定性随着PMMA侧链的含量增加及分子量的增大而略有下降,PMMA侧链的存在降低了PP主链的结晶能力,阻碍其形成较为完整的β晶相;所合成的接枝物具有表面外迁性,可富集于共混物薄膜的表面,有望作为PP的大分子长效表面改性剂使用。     

单兵空调系统研究

在炎热环境中单兵空调系统可以对士兵的身体进行冷热调节,制造一种微气候环境。通过试验研究的方法,采用强化传热措施及轻质材料来减小微型制冷系统的质量及体积,研制了一种微型蒸汽压缩制冷系统作为单兵空调的冷源,微型制冷系统的制冷量为300 W,质量为2.85 kg,几何尺寸为270 mm×260 mm×120 mm．此微型制冷系统提供的制冷量能够保证一个士兵在40℃环境温度下作战时感觉舒适,不会产生热应激。所研制的微型制冷系统为我国士兵的个体热防护提供了一种轻便、易于携带的装备。     

Characterization and applications of a new tabletop confocal micro X-ray fluorescence setup

A tabletop confocal three-dimensional micro X-ray fluorescence (3D micro-XRF) setup was designed, based on polycapillary X-ray optics and a micro-focus X-ray source. This confocal setup consists of a polycapillary full lens to focus the incident beam and a polycapillary half lens to collect the X-ray fluorescence. The confocal volume was proved to be ellipsoidal. The full-width at half maximum (FWHM) of the confocal volume in three directions were measured with a “knife edge” scan method to obtain the spatial resolution of the confocal setup. The structure of multilayer samples was studied using the depth scan technique.     

Hybrid method for quantification of stress states in shotcrete tunnel shells: combination of 3D in situ displacement measurements and thermochemoplastic material law

A hybrid method for quantification of the loading of shotcrete tunnel shells, combining thermochemomechanical material modeling of shotcrete with 3D in situ displacement measurements in the framework of the non-linear finite element method, is presented. Histories of displacement fields, determined from in situ measurements by suitable interpolation functions, are prescribed on the outer boundary of a part of the tunnel, discretized in 2D or 3D. The main goal is the determination of fields of safety degrees, amounting to 0% for the unloaded shell and to 100% for the material loaded up (locally) to the compressive strength. A comprehensive investigation of the significance of the individual material characteristics of shotcrete as well as that of the third dimension in space on the structural behavior is performed. The Sieberg tunnel in Lower Austria, constituting a part of the high capacity railway line between Vienna and Salzburg, is used as the vehicle for this investigation. This tunnel was very recently completed.     

一种基于提升小波变换的音频无损编解码方法

提出了一种基于整型提升小波技术的无损音频编解码方法,该方法在AVS（Audio Video Coding Standards）无损编码基线系统提案RM0框架基础上,通过增加整型小波提升模块,对音频信号进行分带处理,增强了带内信号的相关性,提高了信号的压缩比。最后通过与AVS无损编码基线系统RM0的对比,验证了该技术的有效性。     

化工有机废液流化床焚烧处理的结焦结渣问题研究

化工有机废液流化床焚烧过程中,碱金属盐类在炉膛受热面沉积,造成炉膛的结焦结渣:熔融的碱金属盐类沿炉壁流到床层,在床温条件下形成低熔点共晶体,引起床料的粘结、破坏流化,最终导致床层严重结焦结渣。论述了有机废液流化床焚烧炉结焦结渣的形成机理、影响因索及其抑制措施。     

薄壁叶片精密加工装夹方案设计与优化

针对航空发动机薄壁叶片刚性弱、加工工艺性差、加工过程中易发生弹性变形等问题,提出了无预载荷、有轴向拉压载荷的装夹方案,分析了3种装夹方案中的弯曲和扭转变形,建立了叶片的弯扭组合变形数学模型。通过对叶片弯扭组合变形数学模型的分析,得出了3种装夹方案下叶片几何尺寸与叶片加工变形位置的关系,以及拉压载荷对叶片加工变形的影响规律。