Application of homogenization techniques for inflow transport approximation on light water reactor analysis

The transport cross-section based on inflow transport approximation can significantly improve the accuracy of light water reactor(LWR)analysis,especially for the treatment of the anisotropic scattering effect.The previous inflow transport approximation is based on the moderator cross-section and normalized fission source,which is approximated using transport theory.Although the accuracy of reactivity is increased,the P0 flux moment has a large error in the Monte Carlo code.In this study,an improved inflow transport approximation was introduced with homogenization techniques,applying the homogenized cross-section and accurate fission source.The numerical results indicated that the improved inflow transport approximation can increase the P0 flux moment accuracy and maintain the reactivity calculation precision with the previous inflow transport approximation in typical LWR cases.In addition to this investigation,the improved inflow transport approximation is related to the temperature factors.The improved inflow transport approximation is flexible and accurate in the treatment of the anisotropic scattering effect,which can be directly used in the temperature-dependent nuclear data library.

Strength criterion of porous media: Application of homogenization techniques

The present paper aims at giving some general ideas concerning the micromechanical approach of the strength of a porous material. It is shown that its determination theoretically amounts to solving a nonlinear boundary value problem defined on a representative elementary volume(REV). The principle of nonlinear homogenization is illustrated based on the case of a solid phase having a Green’s strength criterion. An original refinement of the so-called secant method(based on two reference strains) is also provided. The paper also describes the main feature of the Gurson’s model which implements the principle of limit analysis on a conceptual model of hollow sphere. The last part of the paper gives some ideas concerning poromechanical couplings.

Novel stability criteria for fuzzy Hopfield neural networks based on an improved homogeneous matrix polynomials technique

The global stability problem of Takagi-Sugeno（T-S） fuzzy Hopfield neural networks（FHNNs） with time delays is investigated.Novel LMI-based stability criteria are obtained by using Lyapunov functional theory to guarantee the asymptotic stability of the FHNNs with less conservatism.Firstly,using both Finsler＇s lemma and an improved homogeneous matrix polynomial technique,and applying an affine parameter-dependent Lyapunov-Krasovskii functional,we obtain the convergent LMI-based stability criteria.Algebraic properties of the fuzzy membership functions in the unit simplex are considered in the process of stability analysis via the homogeneous matrix polynomials technique.Secondly,to further reduce the conservatism,a new right-hand-side slack variables introducing technique is also proposed in terms of LMIs,which is suitable to the homogeneous matrix polynomials setting.Finally,two illustrative examples are given to show the efficiency of the proposed approaches.

Two-step homogenization for the effective thermal conductivities of twisted multi-filamentary superconducting strand

For the accurate prediction of the effective thermal conductivities of the twisted multi-filamentary superconducting strand,a two-step homogenization method is adopted.Based on the distribution of filaments,the superconducting strand can be decomposed into a set of concentric cylinder layers.Each layer is a two-phase composite composed of the twisted filaments and copper matrix.In the first step of homogenization,the representative volume element(RVE)based finite element(FE)homogenization method with the periodic boundary condition(PBC)is adopted to evaluate the effective thermal conductivities of each layer.In the second step of homogenization,the generalized self-consistent method is used to obtain the effective thermal conductivities of all the concentric cylinder layers.The accuracy of the developed model is validated by comparing with the local and full-field FE simulation.Finally,the effects of the twist pitch on the effective thermal conductivities of twisted multi-filamentary superconducting strand are studied.

Enhancing mechanical properties and corrosion performance of AA6063 aluminum alloys through constrained groove pressing technique

The use of a constrained groove pressing(CGP) method to plastically deform AA6063 aluminum alloy led to the improved surface properties. It was found that hardness magnitude is dramatically improved and its uniformity is considerably decreased after the first pass, while subsequent passes result in better hardness behavior for the processed material. Also, the elongated grains formed in the first pass of the CGP are gradually converted to the equiaxed counterparts by adding pass numbers. Eventually, higher corrosion resistance of the sample by imposing the CGP process is related to the quick formation of passivation film and the change in the morphology of the second phase and precipitates which hinder their electrochemical reactions and decrease the potential localized attack sites.

Prediction of Austenitization and Homogenization of Q235 Plain Carbon Steel during Reheating Process

In this paper, the austenitization and homogenization process of Q235 plain carbon steel during reheating is predicted using a two-dimensional model which has been developed for the prediction of diffusive phase transformation (e.g. α to γ). The diffusion equations are solved within each phase (α and γ) and an explicit finite volume technique formulated for a regular hexagonal grid are used. The discrete interface is represented by special volume elements α/γ, an volume element a undergoes a transition to an interface state before it becomes γ. The procedure allows us to handle the displacement of the interface while respecting the flux condition at the interface. The simulated microstructure shows the dissolution of ferrite particles in the austenite matrix is presented at different stages of the phase transformation. Specifically, the influence of the microstructure scale and the heating rate on the phase transformation kinetics has been investigated. The experimental results agree well with the simulated ones.

Seismic Retrofitting Techniques for Existing Masonry Buildings

In many seismically active regions of the world there are large numbers of masonry buildings. Most of these buildings have not been designed for seismic loads. Recent earthquakes have shown that many of these buildings are seismically vulnerable and should be considered for retrofitting. Different conventional and unconventional retrofitting techniques are available to increase the strength and/or ductility of unreinforced masonry （URM） walls. This paper reviews and discusses seismic retrofitting of masonry walls with emphasis on the conventional techniques. Retrofitting procedures are discussed with regard to a case study： a stone masonry building in lrpinia region, damaged by the 1980 earthquake. The interventions are evaluated by means of finite elements with a macroelement obtained with a homogenization technique. Linear and nonlinear procedures are compared, and peculiarities of each procedure are shown.

Two-Step Efficient Deterministic Secure Quantum Communication Using Three-Qubit W State

A two-step deterministic secure quantum communication （DSQC） scheme using blocks of three-qubit W state is proposed. In this scheme, the secret messages can be encoded by employing four two-particle unitary operations and directly decoded by utilizing the corresponding measurements in Bell basis or single-particle basis. Comparing with most previous DSQC protocols, the present scheme has a high total efficiency, which comes up to 50%. Apart from this, it has still the advantages of high capacity as each W state can carry two bits of secret information, and high intrinsic efficiency because almost all the instances are useful. Furthermore, the security of this communication can be ensured by the decoy particle checking technique and the two-step transmitting idea.

Diffusion Process of High Concentration Spikes in a Quasi-Homogeneous Turbulent Flow

When a mass spreads in a turbulent flow, areas with obviously high concentration of the mass compared with surrounding areas are formed by organized structures of turbulence. In this study, we extract the high concentration areas and investigate their diffusion process. For this purpose, a combination of Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV) techniques was employed to obtain simultaneously the two fields of the concentration of injected dye and of the velocity in a water turbulent channel flow. With focusing on a quasi-homogeneous turbulence in the channel central region, a series of PLIF and PIV images were acquired at several different downstream positions. We applied a conditional sampling technique to the PLIF images to extract the high concentration areas, or spikes, and calculated the conditional-averaged statistics of the extracted areas such as length scale, mean concentration, and turbulent diffusion coefficient. We found that the averaged length scale was constant with downstream distance from the diffusion source and was smaller than integral scale of the turbulent eddies. The spanwise distribution of the mean concentration was basically Gaussian, and the spanwise width of the spikes increased linearly with downstream distance from the diffusion source. Moreover, the turbulent diffusion coefficient was found to increase in proportion to the spanwise distance from the source. These results reveal aspects different from those of regular mass diffusion and let us conclude that the diffusion process of the spikes differs from that of regular mass diffusion.

Performance Improvement of Two-Phase Steam Ejector based on CFD Techniques,Response Surface Methodology and Genetic Algorithm

The steam ejector is a crucial component in the waste heat recovery system.Its performance determines the amount of recovered heat and system efficiency.However,poor ejector performance has always been the main bottleneck for system applications.Therefore,this study proposes an optimization methodology to improve the steam ejector's performance by utilizing computational fluid dynamics(CFD) techniques,response surface methodology(RSM),and genetic algorithm(GA).Firstly,a homogeneous equilibrium model(HEM) was established to simulate the two-phase flow in the steam ejector.Then,the orthogonal test was presented to the screening of the key decision variables that have a significant impact on the entrainment ratio(ER).Next,the RSM was used to fit a response surface regression model(RSRM).Meanwhile,the effect of the interaction of geometric parameters on the performance of the steam ejector was revealed.Finally,GA was employed to solve the RSRM's global optimal ER value.The results show that the RSRM exhibits a good fit for ER(R^(2)=0.997).After RSM and GA optimization,the maximum ejector efficiency is 27.94%,which is 48.38% higher than the initial ejector of 18.83%.Furthermore,the optimized ejector efficiency is increased by 46.4% on average under off-design conditions.Overall,the results reveal that the combination of CFD,RSM,and GA presents excellent reliability and feasibility in the optimization design of a two-phase steam ejector.

基于BEAVRS基准题的三维堆芯建模计算及不同均匀化方案比较分析

两步法作为反应堆数值计算中的主流方法,因其受制于组件均匀化计算和堆芯扩散近似计算中引入的简化假设,对于精细化模型的计算可靠性需要进一步研究。基于DRAGON/DONJON计算BEAVRS 2.02(Benchmark for Evaluation And Validation of Reactor Simulations Rev.2.0.2)基准题在热态零功率状态下的各项参数,先对组件进行输运计算,获得均匀化少群常数;再使用少群常数完成全堆芯扩散计算,最后比较了传统均匀化、一次多区均匀化和多次多区均匀化三种方案的计算误差。结果表明:本文计算结果与基准值相比吻合良好,临界硼浓度的误差在5×10^(-5)以内,控制棒价值的误差在5×10^(-4)以内。进一步对比裂变率发现,采用一次多区均匀化方案能将非对称燃料组件及相邻组件的平均误差从5.62%降低至3.345%,检验了两步法在精细化模型计算中的适用性。

科学标识设计去同质化的方法研究

科学标识的设计容易产生元素同质化的问题,对色彩要素中色相和彩度进行分析,采用5种设计手法试寻找科学标识设计去同质化问题的手法和路径,以实现科学标识的差异化设计。

Improvement of thickness uniformity and elements distribution homogeneity for multicomponent films prepared by coaxial scanning pulsed laser deposition technique

In conventional pulsed laser deposition （PLD） technique, plume deflection and composition distribution change with the laser incident direction and pulse energy, then causing uneven film thickness and composition distribution for a multicomponent film and eventually leading to low device quality and low rate of final products. We present a novel method based on PLD for depositing large CIGS films with uni- form thickness and stoichiometry. By oscillating a mirror placed coaxially with the incident laser beam, the laser＇s focus is scanned across the rotating target surface. This arrangement maintains a constant re- flectance and optical distance, ensuring that a consistent energy density is delivered to the target surface by each laser pulse. Scanning the laser spot across the target suppresses the formation of micro-columns, and thus the plume deflection effect that reduces film uniformity in conventional PLD technique is eliminated. This coaxial scanning PLD method is used to deposit a CIGS film, 500 nm thick, with thickness uniformity exceeding ±3% within a 5 cm diameter, and exhibiting a highly homogeneous elemental distribution.

沥青混合料均匀性评价新方法的探讨

基于数字图像处理技术,首次对沥青混合料中集料的分布状态,即沥青混合料均匀性进行了直接研究.研究结 果表明:从沥青混合料中集料的分布位置和分布数量两方面综合考虑,沥青混合料的均匀性能够定量地进行评价.

均匀沉淀法制备SnO_2-石墨复合粉及其电化学性能

以SnCl4为原料,尿素为沉淀剂,采用均匀沉淀法制备了SnO2石墨复合粉,用XRD、SEM、TGDTA以及电化学方法对复合粉进行了表征。结果表明由于SnO2和石墨表面上不可避免的电化学还原,导致复合粉的首次循环具有较大的不可逆容量,经600℃煅烧4h的复合粉具有较高的可逆容量和循环性能;含30%SnO2的复合粉在0.1C的电流倍率下进行充放电,其初始容量达到520.0mA·h/g,经30次循环后平均每次循环的容量衰减率为0.6%,表明SnO2石墨复合粉是一种具有发展前途的锂离子电池负极材料。

现有刨花板生产线生产麦秸均质板工艺设备适应性评价

对现有刨花板生产线进行改造 ,生产以麦秸为原料的麦秸均质板 ,是解决刨花板厂原料供应不足的有效途径之一。本文分析了我国目前刨花板厂的原料供应状况 ,对利用现有刨花板生产线生产麦秸均质板的工艺设备适应性进行了综合评价 ,并提出了设备改造方案。

蜂窝夹层结构等效弹性常数的多步三维均匀化数值计算分析

基于三维均匀化方法并结合有限元技术,计算三维蜂窝夹层板的等效弹性常数。首先把三维蜂窝夹芯看成由实体与空洞两相材料组成的复合材料结构,建立单胞有限元模型,计算宏观等效弹性常数,通过与其它计算方法相比较,验证了三维均匀化方法的有效性;在此基础上考虑上下面板,运用直接、二次及多步均匀化方法计算三维蜂窝夹层板的整体等效弹性常数,并与工程计算方法比较,结果表明三维均匀化方法的可靠性。

SVD方法在场分析和预测中的应用

由预报场与因子场的奇异值分解(SVD),可找到影响预报场的主要物理因子,能提取两个场相互作用的主要耦合信号。借助最优化技术,可实现由因子场对预报场的客观预报。以华中汛期降水场为左场,4月北半球500 hPa高度场、海平面气压场、北太平洋海温场组成右场,进行SVD分析和预报试验,其结果令人满意。

粗脂肪标准物质的制备及均匀性和稳定性研究

用全麦粉作为粗脂肪标准物质的基体,对粗脂肪标准物质的制备程序和工艺以及标准物质的均匀性和稳定性进行了研究。采用粉碎、混匀、干燥、分装、Co-60辐照灭活(辐照量为2.5Mrad)全麦粉粗脂肪标准物质的制备工艺。粗脂肪标准物质样品的均匀性检验结果经F检验以及14个月稳定性监测结果经t检验表明,单元内和单元间均匀程度以及标准物质样品的稳定性均达到国家一级标准物质的制备要求。

混凝土材料冲击压缩试验中的一些问题

本文简要介绍了在大直径(Φ74mm)直锥变截面式SHPB实验装置上进行混凝土试件冲击压缩实验方法,以及实验过程中出现的试件应力均匀性问题.对于由方波加载造成的试件内应力波反射次数不够,导致应力分布不均匀的问题,我们提出了波形整形的思想,将矩形波改造成三角波,增加试件破坏前的应力作用时间以获得应力均匀;对于由杆与试件接触不平引起的应力分布不均,我们设计了万向头加以消除.在此基础上进行了一系列试验并得出了一些结论.