一种曲折裂纹尖端单元位移场的构造方法

在扩展有限元的框架内,本文发展了一种构造裂尖单元位移场的方法。整个裂纹沿程两侧的非连续位移场只通过富集变换的阶梯函数表征,在裂尖单元,通过调整形函数使得非连续性严格地消失于裂纹尖端。在避免混合区单元引入不满足单位分解的附加位移项的同时,实现了裂纹尖端单元位移场部分非连续特性的表达。还对裂尖单元的形函数调整原则进行了分析,以平面四节点单元为例提出了两种调整方式。文中裂尖单元中含有曲折裂纹的算例说明了本文方法的有效性和适用性。     

NLCC controller for SEPIC-based micro-wind energy conversion system

The growth of the power industry is gaining greater momentum as the usage of the non-conventional energy sources that include fuel, solar, and wind energies, increases. Wind energy conversion systems (WECSs) are gaining more popularity and are expected to be able to control the power at the output. This paper describes the current control (CC), non-linear carrier charge control (NLCCC), and fuzzy logic control (FLC) applied to the single-ended primary inductor converter (SEPIC)-based WECS. The current controller has an inherent overcurrent protection with better line noise rejection. The pulses for the switch of the SEPIC are obtained by comparing the current flowing through it with the virtual current reference. FLC is also investigated for the micro-wind energy conversion system (μWECS), since it improves the damping characteristics of WECS over a wide range of operating points. This cannot attain the unity power factor rectification. In this paper, NLCCC is proposed for high-power factor rectifier-based SEPIC in continuous conduction mode (CCM) for μWECS. The proposed converter provides an output voltage with low input current ripple due to the presence of the inductor at the input side. By comparing the signal proportional to the integral of switch current with a periodic non-linear carrier wave, the duty ratio of the converter switch is determined for the NLCC controller. By selecting the shape of the periodic non-linear carrier wave the input-line current can be made to follow the input-line voltage. This work employs a parabolic carrier waveform generator. The output voltage is regulated for changes in the wind speed. The results obtained prove the effectiveness of the NLCC controller in improving the power factor.     

从“虚气相即”到“知行合一”—宋明理学“天人合一”主题的展开、落实及其指向

中国文化一直以“天人合一”为至上追求。但在不同的时代,天人合一又有其不同的内涵,比如在理学的开创阶段,天人合一就表现为本然与实然的统一,这种统一正好表现在张载以“虚气相即”为代表的本体论与宇宙论的并建与统一上,理学的本体宇宙论即由此得以确立。到了朱子时代,天人合一又表现为理与气的不即不离;但理和气本然与实然的两属以及“所以然”与“所当然”的不同侧重,又意味着“尊德性”与“道问学”、理本论与气化宇宙论的分裂。到了王阳明,才从官场与学界共同的内外背反现象中发现了知行为二的根源,所以其从身心一致的“知行合一”出发,并通过致良知,从而完成了从知行到身心、主客包括本然与实然两重世界的统一;而从批评程朱未能“定于一”的罗钦顺起始,则又从理与气之不可分割特征入手走向了气学。这样一来,心学与气学,既是中国文化天人合一追求的两种不同走向,同时也代表着中华民族现代化追求的双重资源。     

家国关系：理解近代以来中国基层治理变迁的一个视角

家国关系是理解20世纪中国基层治理逻辑变迁的重要本土视角。在传统社会,由于家国一体与家国同构,维系家族内部的伦理和结构就是维系国家统治的合法性和社会秩序。然而,近代以来,面对巨大的民族危机,国家却必须打破以家族为本位的社会结构,以社会成员的国族意识代替其家族意识,进而汲取更多的社会资源并进行有效的社会动员。随着家国关系由统一走向对立,国家能力实现了增长,但传统乡村以自治与德治为内容的治理模式也被彻底改变。在这种历史发展的基础之上,新时代的乡村治理需要妥善处理好国家能力增长与基层治理活力保持之间的平衡关系,探索基层自治、德治与法治在新的社会条件下的实现形式和有效融合机制。     

基于KAM500采集器的测试系统设计

为了获取关键测试数据,实时监控系统状态,在有限的空间下组件一套高效的测试系统是至关重要的。根据实际工程测试案例,对以KAM500采集器为核心的测试系统的设计及软件裁剪编译方法进行了分析,为KAM500采集器在实际工程中的应用提供借鉴作用。     

混凝土断裂的连续-非连续方法

采用有限元形函数作为单位分解函数,位移间断用富集节点的附加自由度表示,建立了允许在单元内部位移非连续的局部富集公式以表征混凝土的开裂区域.富集基函数由节点形函数和节点形函数与间断函数的乘积的并集构成.非连续位移的扩展路径完全与网格结构无关.不同于以非协调应变为基础的嵌入非连续模型,对单元的类型没有限制而且间断位移可以贯穿单元边界.局部富集思想与扩展有限元类似,但富集点自由度保持节点位移的物理意义不变,使相邻单元无需进行富集运算.在变分公式中引入混凝土粘结本构定律,推导了考虑断裂过程区非线性影响的基本方程.对混凝土粘结裂纹扩展的数值模拟说明了该计算方法的有效性.     

The simulation of dynamic crack propagation using the cohesive segments method

The cohesive segments method is a finite element framework that allows for the simulation of the nucleation, growth and coalescence of multiple cracks in solids. In this framework, cracks are introduced as jumps in the displacement field by employing the partition of unity property of finite element shape functions. The magnitude of these jumps are governed by cohesive constitutive relations. In this paper, the cohesive segments method is extended for the simulation of fast crack propagation in brittle solids. The performance of the method is demonstrated in several examples involving crack growth in linear elastic solids under plane stress conditions: tensile loading of a block; shear loading of a block and crack growth along and near a bi-material interface.     

含裂纹体的单位分解扩展无网格方法

不连续体的数值模拟尤其是动态裂纹的追踪问题一直是工程界研究的热点和难点问题。无网格方法仅仅需要结点信息,非常适合于求解这类问题。基于单位分解思想,在移动最小二乘近似函数(MLS)中根据裂纹面的不连续位移增加一个Heaviside函数,在裂尖则增加四个扩展函数描述渐进裂纹位移场;应用Galerkin方法推导了平衡方程的离散线性方程,并给出了求解裂纹问题应力强度因子的计算公式。与其他类型的扩展无网格相比,在裂尖处近似函数不需要使用可视准则,很容易生成r1/2奇异;另一个优势是影响域并没有因为裂纹的存在而改变,不会降低方程的稀疏性,求解效率较高。数值算例表明,该方法能方便有效地模拟不连续问题,具有十分广阔的应用空间。     

Generalized q-Schur algebras and quantum Frobenius

The quantum Frobenius map and it splitting are shown to descend to maps between generalized q-Schur algebras at a root of unity. We also define analogs of q-Schur algebras for any affine algebra, and prove the corresponding results for them.