基于自动网格划分与权窗平滑的自适应减方差方法

如何更高效发挥减方差的作用是蒙特卡罗方法在先进核能系统屏蔽分析应用中的研究热点之一。本文发展了一种基于自动网格划分与权窗平滑的自适应减方差方法,在蒙特卡罗和确定论耦合的一致性伴随驱动的重要性抽样方法(Consistent Adjoint Driven Importance Sampling,CADIS)基础上,利用计算机辅助设计(Computer Aided Design,CAD)自动转换和自由程自动划分SN网格,通过确定论方法伴随预计算,实现基于伴随通量的区域权窗参数自动配置,并对伴随通量变化剧烈区域进行权窗平滑处理,保证了粒子在不同区域的有效偏倚,进一步提高计算的效率,从而解决大空间蒙特卡罗计算难以收敛的问题。该方法已初步应用于中国铅基反应堆(China Lead-based Reactor,CLEAR)堆顶盖的屏蔽计算分析,该案例具有结构复杂、屏蔽材料厚重的特点,测试结果表明本方法将计算效率提高近10倍。     

跨高速铁路施工安全防护棚架设计

结合工程实例,对跨高速铁路施工防护棚架的设计和施工方案进行了研究,并对荷载、防护支架结构、防护支架拆除后钢管立柱的稳定性作了计算分析,证明了该防护棚架设计的合理性。     

门式刚架的柱顶位移计算探讨

文章主要对无吊车门式刚架的柱顶位移计算进行探讨,推导出柱顶位移的计算公式,并结合具体实例进行分析,希望对有关门式刚架计算有一定的参考。     

Electronic and magnetic structures and bonding properties of Ce2T2X (T = nd element; X = Mg,Cd, Pb or Sn) intermetallics from first principles

The electronic structure and chemical bonding properties of four families of Ce₂T₂X (T = nd element; X = Mg, Cd, Pb or Sn) intermetallics crystallizing in an ordered U₃Si₂ type structure are shown from density functional theory (DFT) calculations to present electronic and magnetic structure properties arising from their peculiar valence electron count (VEC). Trends of the magnetism are discussed in terms of the characteristics of the Ce(4f) states as well as the energetic position of the transition metal element d states.     

Electronic structure and ferromagnetism of Fe11NiSi4, Fe11CoSi4, Fe11CrSi4 and Fe3Si from first principles

Based on the density functional theory (DFT), the plane-wave pseudopotential method was used to calculate structural stabilities, electronic structures, and ferromagnetism of Fe₃Si, Fe₁₁NiSi₄, Fe₁₁CoSi₄ and Fe₁₁CrSi₄ intermetallic compound. This study showed that the Fe₁₁NiSi₄ and Fe₁₁CrSi₄ phase are more stable than Fe₃Si phase, especially Fe₁₁NiSi₄, but decreased with Fe₁₁CoSi₄ phase. Calculating the density of states and the Mulliken electronic populations showed that Fe₁₁NiSi₄ had the highest structural stability because of its Fermi level, which was close to the bottom of the pseudo-gap. Fe₁₁NiSi₄ also had the largest Mulliken population, which increased the metallic bonding of the alloying system. The total magnetic moments of Fe₁₁NiSi₄, Fe₁₁CoSi₄ and Fe₁₁CrSi₄ were 20.04μ_B, 19.98μ_B, and 18.81μ_B, respectively. These magnetic moments mainly originated from the 3d spin polarization of Fe and those of additional atoms.     

Transient safety evaluation of the heat pipe microreactor – Potential energy source for hydrogen production

Recently, microreactor designs have been receiving significant attention in the nuclear industry due to their potential advantages in certain applications. These nuclear reactor designs have been considered to provide reliable and sustainable power for on-site installation and operation. Microreactors may be utilized to provide heat and power to hydrogen production, remote communities, and industrial facilities such as military installations, disaster relief zones, and are being considered for underwater and deep space operation as well. However, these designs and concepts remain largely untested and unproven in the commercial industry. Further research and development are still required to prove microreactor designs are safe and reliable for commercial use. Different cooling technologies have been taken into consideration for microreactor concepts since the 1960s, mainly for federal space reactor projects such as LEGOLRCS, HOMER, and KRUSTY. This work provides thermal hydraulics and analysis for the Idaho National Laboratory's MAGNET (Micro-reactor Agile Non-nuclear Experimental Testbed) facility. The MAGNET facility is currently being developed to duplicate a microreactor design using heat pipe cooling technology. Our main goal is to examine the response of the test facility under steady-state and transient operation conditions. We constructed our own estimated model of the MAGNET geometry using a software coupling method made up of MOOSE/SAM software systems. The steady state results of this work have been published in a former article. The new results mainly focus on the transient states. By communicating with the Idaho National Laboratories, we upgraded the geometry of MAGNET heat pipes. This not only verifies the design of the facility under such conditions but also benchmarks the modeling capability of the MOOSE/SAM code system that can be potentially used to model other microreactor concepts in the future.     

基于联合节点行为策略的WSN覆盖控制算法

针对无线传感器网络在对移动目标节点覆盖过程中出现网络能量快速消耗问题，提出了一种基于联合节点行为策略的覆盖算法。根据网络模型建立传感器节点与目标节点从属关系，确定覆盖关联模型；利用概率理论求解邻居节点冗余覆盖度，确定最少传感器节点数量；给出了邻居节点覆盖期望值的求解方法；仿真实验表明，该算法与其他算法在网络覆盖率和网络生存周期两个性能指标上均提升了12.39%和15.01%，从而验证了算法的有效性。     

Electronic and structural properties of low-index L12–Al3Zr surfaces by first-principle calculations

The atomic relaxations, electronic properties and surface energies of low index L1₂-Al₃Zr surfaces were studied by using the first-principles method based on the density functional theory. Five low index surfaces with different terminations are studied systematically. The study shows that atomic relaxations occur mainly within the outermost two layers. The stoichiometric (111), non-stoichiometric (110) and (001) surfaces with different terminations are investigated. The (111) surface which has the lowest surface energy and is independent on the chemical potential of Al atom is found to be the most thermodynamically stable surface. For the non-stoichiometric surfaces, the AlZr terminated (001) surface and Al terminated (110) surface are metastable under an Zr-rich and Al-rich condition respectively. These results are in consistant with the results of density of states. The lattice misfit between α-Al and L1₂-Al₃Zr is not more than 1.65% by our calculation, indicating L1₂-Al₃Zr is a potent effective heterogeneous nucleating agent for α-Al.     

ZrB2: Adjusting the phase structure to improve the brittle fracture and electronic properties

Although ZrB₂ is a promising ultrahigh-temperature ceramic, the intrinsic brittleness and low fracture toughness are the main bottlenecks. To solve these key problems, by means of first-principles calculations, we predict ZrB₂ new phases, and investigate the influence of new phase on the mechanical properties and electronic properties of ZrB₂. The calculated results show that two new ZrB₂ phases: RuB₂-type with orthorhombic structure (Pmmn, No.59) and ReB₂-type with hexagonal structure (P63/mmc, No.194) are dynamical stability at the ground state. Although RuB₂-type and ReB₂-type structures weaken the volume deformation resistance and shear deformation resistance of ZrB₂, it results in brittle-to-ductile transition due to the formation of weak Zr-B bond along the shear direction. Importantly, ReB₂-type structure improves the electronic properties of ZrB₂ because of the strong charge overlap between conduction band and the valence band near Fermi level (E_F). Therefore, our work can open up a new clue to improve the ductility and electronic properties of ZrB₂.     

基于FEM的自动变速箱波形弹簧特性研究

波形弹簧是汽车自动变速箱离合器、制动器用的关键元件之一。波形弹簧载荷与变形之间的特性关系是弹簧设计时较为关心的问题。笔者通过公式法、FEM计算了波形弹簧的特性曲线,实验数据证明FEM的结果比公式计算的结果更加准确。同时也讨论了弹簧的耐久寿命。因此,FEM在波形弹簧的设计研究中具有实际意义而且是有效的。