Numerical simulation of recalescence of 3-dimensional isothermal solidification for binary alloy using phase-field approach

A accelerated arithmetic algorithm of the dynamic computing regions was designed,and 3-dimensional numerical simulation of isothermal solidification for a binary alloy was implemented.The dendritic growth and the recalescence of Ni-Cu binary alloy during the solidification at different cooling rates were investigated.The effects of cooling rate on dendritic patterns and microsegregation patterns were studied.The computed results indicate that,with the increment of the cooling rate,the dendritic growth velocity increases,both the main branch and side-branches become slender,the secondary dendrite arm spacing becomes smaller,the inadequate solute diffusion in solid aggravates,and the severity of microsegregation ahead of interface aggravates.At a higher cooling rate,the binary alloy presents recalescence;while the cooling rate is small,no recalescence occurs.

A phased approach to enable hybrid simulation of complex structures

Hybrid simulation has been shown to be a cost-effective approach for assessing the seismic performance of structures. In hybrid simulation,critical parts of a structure are physically tested,while the remaining portions of the system are concurrently simulated computationally,typically using a finite element model. This combination is realized through a numerical time-integration scheme,which allows for investigation of full system-level responses of a structure in a cost-effective manner. However,conducting hybrid simulation of complex structures within large-scale testing facilities presents significant challenges. For example,the chosen modeling scheme may create numerical inaccuracies or even result in unstable simulations; the displacement and force capacity of the experimental system can be exceeded; and a hybrid test may be terminated due to poor communication between modules(e.g.,loading controllers,data acquisition systems,simulation coordinator). These problems can cause the simulation to stop suddenly,and in some cases can even result in damage to the experimental specimens; the end result can be failure of the entire experiment. This study proposes a phased approach to hybrid simulation that can validate all of the hybrid simulation components and ensure the integrity largescale hybrid simulation. In this approach,a series of hybrid simulations employing numerical components and small-scale experimental components are examined to establish this preparedness for the large-scale experiment. This validation program is incorporated into an existing,mature hybrid simulation framework,which is currently utilized in the Multi-Axial Full-Scale Sub-Structuring Testing and Simulation(MUST-SIM) facility of the George E. Brown Network for Earthquake Engineering Simulation(NEES) equipment site at the University of Illinois at Urbana-Champaign. A hybrid simulation of a four-span curved bridge is presented as an example,in which three piers are experimentally controlled in a total of 18 degrees of freedom(DOFs). This simulation illustrates the effectiveness of the phased approach presented in this paper.

Analytic equation of state for solids with multi-exponential potential based on analytic mean field potential approach and applied to the epsilon phase of solid oxygen

The thermodynamic properties of the ε phase of solid oxygen are studied by using the analytic mean field approach （AMFP）. Analytic expressions for the Helmholtz free energy, internal energy and equation of state of solid oxygen have been derived based on the multi-exponential potential. The formulism for the case of double-exponential （DE） model is applied to the ε phase of solid oxygen. Its four potential parameters are determined through fitting the experimental compression data of the ε phase of solid oxygen. Numerical results of the pressure dependence of the volume calculated by using the AMFP are in good agreement with the original experimental data. This suggests that the AMFP is a useful approach to study the thermodynamic properties of the ε phase of solid oxygen. Furthermore, we predict the variation of the volume, lattice parameters and intermolecular distances with pressure, and some thermodynamic quantities versus volume, at several higher temperatures.

Two-Phase Multi Objective Fuzzy Linear Programming Approach for Sustainable Irrigation Planning

The objective of the present study is to develop the irrigation planning model and to apply the same in the form of Two-Phase Multi Objective Fuzzy Linear Programming (TPMOFLP) approach for crop planning in command area of Jayakwadi Project Stage I, Maharashtra State, India. The development of TPMOFLP model is on the basis of various Linear Programming (LP) models and Multi Objective Fuzzy Linear Programming (MOFLP) models, these models have been applied for maximization of the Net Benefits (NB), Crop production (CP), Employment Generation (EG) and Manure Utilization (MU) respectively. The significant increase in the value of level of satisfaction (λ) has been found from 0.58 to 0.65 by using the TPMOFLP approach as compare to that of MOFLP model based on maxmin approach. The two-phase approach solution provides NB = 1503.56 Million Rupees, CP = 335729.30 Tons, EG = 29.74 Million Man days and MU = 160233.70 Tons respectively. The proposed model will be helpful for the Decision Maker (DM) to take a decision under conflicting situation while planning for different conflicting objectives simultaneously and has potential to find out an integrated irrigation planning with prime consideration for economic, social and environmental issue.

“Top-Down-Approach”降水相态分析法在双流机场一次降雪过程中的应用

选取ERA5再分析资料和常规气象资料等多源数据,运用“Top-Down-Approach”降水相态分析法,分析了2023年1月16日双流机场降雪过程,重点探究了降水相态的预报着眼点。结果表明:(1)湿度超过85%的-12~-16℃温度层有利于枝状雪花的形成,高浓度云中冰相粒子与水相粒子重叠区有利于低融化比雪花的形成,在预报时需重点关注。(2)当湿球0℃温度层偏低时,可降低降雪预报中对地面温度的限制。(3)结合温度廓线分析,微波辐射计液态水廓线产品可以指示冰云层主要分布高度,还能反映出液态水含量在降雪过程开始前显著增强且在降雪趋于结束时提前降低的变化特征,对降雪过程有一定的指示意义。

A high-order target phase approach for the station-keeping of periodic orbits

A novel high-order target phase approach(TPhA)for the station-keeping of periodic orbits is proposed in this work.The key elements of the TPhA method,the phase-angle Poincare map and high-order maneuver map,are constructed using differential algebra(DA)techniques to determine station-keeping epochs and calculate correction maneuvers.A stochastic optimization framework tailored for the TPhA-based station-keeping process is leveraged to search for fuel-optimal and error-robust TPhA parameters.Quasi-satellite orbits(QSOs)around Phobos are investigated to demonstrate the efficacy of TPhA in mutli-fidelity dynamical models.Monte Carlo simulations demonstrated that the baseline QSO of JAXA’s Martian Moons eXploration(MMX)mission could be maintained with a monthly maneuver budget of approximately 1 m/s.

A phase-field study on the oxidation behavior of Ni considering heat conduction

Phase-field modeling approach has been used to study the oxidation behavior of pure Ni when considering heat conduction. In this calculation, the dependence of the coefficient of the Cahn–Hilliard equation Lc on the temperature T was considered. To this end, high-temperature oxidation experiments and phase-field modeling for pure Ni were performed in air under atmospheric pressure at 600,700, and 800？C. The oxidation rate was measured by thermogravimetry and Lc at these temperatures was determined via interactive algorithm. With the Lc-T relationship constructed, oxidation behavior of Ni when considering heat conduction was investigated. The influence of temperature boundaries on the oxidation degree, oxide film thickness, and specific weight gain were discussed. The phase-field modeling approach proposed in this study will give some highlights of the oxidation resistance analysis and cooling measures design of thermal protection materials.

Parameters affecting microsegregation in phase-field simulation

The influence of various material and computational parameters such as interface kinetic coefficient(β), surface energy(σ), anisotropy parameter(γ) and the noise amplitude(α) upon microsegregation patterns during the crystal growth was investigated by using the phase-field model which incorporated the concentration field equations. The computed results indicate that, when the appropriate value is assigned to α, the fluctuant scope of solute composition in the solid is steady, and the influence of α on microsegregation is small; the larger the interface kinetic coefficient β, the more acutely the solute composition in the solid fluctuates, but the severity of microsegregation in the front interface reduces; with the increment of anisotropy parameter γ, the fluctuation of solute composition in the solid becomes more acutely, and the severity of microsegregation in the front interface aggravates; the larger surface energy σ, the smaller the fluctuant scope of solute composition in the solid is, and the smaller the degree of microsegregation is.

A new method of phase measurement based on optimization

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Theoretical Computation of Nonlinear System Equations of Heavier Pellets Movements for Two Phase Flow

This paper presents nonlinear ordinary differential equations (ODES) of the heavier pellets movement for two phase flow, which actually represent a system of equations. The usual methods of solution such as Runge -Kutta method and it's datum results are discussed. This paper solves ODES of general form using variable mesh-length, linearizing the nonlinear terms by finite analysis method, fuilding an iteration sequence, and amending the nonlinear terms by iteration . The conditions of convergent operation of iteration solution is checked. The movement orbit and velocity of the pellets are calculated. Analysis of research results and it's application examples are illustrated.

A simple approach for the estimation of CO_2 penetration depth into a caprock layer

Caprock is a water-saturated formation with a sufficient entry capillary pressure to prevent the upward migration of a buoyant fluid. When the entry capillary pressure of caprock is smaller than the pressure exerted by the buoyant CO2plume, CO2gradually penetrates into the caprock. The CO2penetration depth into a caprock layer can be used to measure the caprock sealing efficiency and becomes the key issue to the assessment of caprock sealing efficiency. On the other hand, our numerical simulations on a caprock layer have revealed that a square root law for time and pore pressure exists for the CO2penetration into the caprock layer. Based on this finding, this study proposes a simple approach to estimate the CO2penetration depth into a caprock layer. This simple approach is initially developed to consider the speed of CO2invading front. It explicitly expresses the penetration depth with pressuring time, pressure difference and pressure magnitude. This simple approach is then used to fit three sets of experimental data and good fittings are observed regardless of pressures, strengths of porous media, and pore fluids(water,hydrochloric acid, and carbonic acid). Finally, theoretical analyses are conducted to explore those factors affecting CO2penetration depth. The effects of capillary pressure, gas sorption induced swelling, and fluid property are then included in this simple approach. These results show that this simple approach can predict the penetration depth into a caprock layer with sufficient accuracy, even if complicated interactions in penetration process are not explicitly expressed in this simple formula.

The Influence of Climate Change and Variability on Aircraft Take-off and Landing Performance;a Case Study of the Abeid Amani Karume International Airport-Zanzibar

Climate change (CC) and variability have been world widely reported to pose number of risks in aviation industry including accidents, astray, and other operational difficulties. The impact of weather on landing and take-off performances has been several times experienced at Abeid Amani Karume International Airport (AAKIA);however, the influence of climate change and variability to the aircraft performance needs to be assessed. Thus, this study investigated the influence of climate change and variability on aircrafts take-off and landing performances. Specifically, the study investigated;i) the influence of climate change on Take-off Distance Required (TODR) and Maximum Take-off Mass (MTOM) for different types of aircraft;ii) the influence of climate variability to the aircraft landing performance on light, medium and heavy aircraft and lastly, iii) the study investigated the seasonal and annual variability on aircraft landing performance due to climate variability. The datasets used in this study include the eight years (2014-2021), aircraft operational records (diversion and missed approach events) and Aviation Routine Weather Reports (METAR) records which were utilized as the indicators for landing performance, the long-term (1990-2020) annual maximum temperatures (Tmax) which was used to determine the TODR and MTOM. Statistical tools including mean, percentage changes, correlations, regression, and the chi-square test were used for analysis and hypotheses testing. The results revealed that light and medium aircraft categories were significantly most affected on diversion events as compared to the heavy categories;however, for the missed approach events the impact was vice versa. Moreover, the seasonal and annual variability on diversion and missed approach events were significantly different (at p ≤ 0.001). As for the take-off performance, results show that the TODR and MTOM were significantly increasing and decreasing (at p ≤ 0.001), based on increasing air temperatures. Therefore, the study concludes that the changing climate has significantly affected aircraft by increasing the TODR and decreasing the MTOM, while the climate variability has significantly affected landing performance by influencing the diversion and missed approach events. Thus, the study recommends (i) further research works including the feasibility study on runway extension for the safety of future aircraft operations at the AAKIA and (ii) proper maintenance and improvement of the Instrumental Landing Systems (ILS) as an adaptation measures to the landing aircraft during bad weather events.

Effects of three-phase-lag on two-temperature generalized thermoelasticity for infinite medium with spherical cavity

The thermoelastic interaction for the three-phase-lag （TPL） heat equation in an isotropic infinite elastic body with a spherical cavity is studied by two-temperature generalized thermoelasticity theory （2TT）. The heat conduction equation in the theory of TPL is a hyperbolic partial differential equation with a fourth-order derivative with respect to time. The medium is assumed to be initially quiescent. By the Laplace trans- formation, the fundamental equations are expressed in the form of a vector-matrix differ- ential equation, which is solved by a state-space approach. The general solution obtained is applied to a specific problem, when the boundary of the cavity is subjected to the ther- mal loading （the thermal shock and the ramp-type heating） and the mechanical loading. The inversion of the Laplace transform is carried out by the Fourier series expansion tech- niques. The numerical values of the physical quantity are computed for the copper like ma- terial. Significant dissimilarities between two models （the two-temperature Green-Naghdi theory with energy dissipation （2TGN-III） and two-temperature TPL model （2T3phase）） are shown graphically. The effects of two-temperature and ramping parameters are also studied.

“产出导向法”在博士研究生学术英语演讲教学中的应用——以促成环节为例

本文将“产出导向法”应用于博士研究生学术英语演讲教学中,帮助研究生将内容艰深的学术论文引言转化为易于非专业观众理解的学术英语演讲开场白演讲稿。本文先展示教学设计方案,然后根据学生及观摩教师访谈、学生作业等数据汇报教学效果。结果表明,在“产出导向法”的“学用一体”理念指导下,本教学实验的促成环节培养了研究生用英语进行学术交流的“关键能力”,提升了教学质量。

基于产出导向“促成”环节的英语写作微课程设计——以How to write a business memo为例

文章概述了产出导向法(production-oriented approach,POA)的基本理论框架以及其中“促成”环节的流程,探讨了基于POA的大学英语写作课程的产出任务及教学流程,并从写作微课程实例出发,分析了“促成”的教学环节与教学安排,从内容促成、语言促成两方面探讨了基于促成环节的英语写作微课设计。

共同富裕理论内涵、指数评价与实践进路探析

共同富裕是社会主义的本质要求,需要立足中国国情探索发展路径。在深刻把握共同富裕理论内涵的基础上,基于人的全面发展视角探索性构建中国共同富裕评价指标体系,初步确定指标阶段性目标,开展四个地区共同富裕指数的动态演进和空间差异研究,对主体性、共享性、发展性、保障性四个维度进行比较评价。研究发现中国共同富裕建设已经取得了一定的成绩,共同富裕水平逐年稳健提升,但是仍面临区域间不均衡、区域内不均衡、增速差异性等挑战。未来,可在主体性、共享性、发展性、保障性四个维度进一步优化实践路径。

两级单相光伏并网系统积分滑模控制

针对典型的两级单相光伏并网系统,为了提高其抗干扰能力,提出了一种基于自适应指数趋近律的积分滑模控制策略,以实现光伏最大功率追踪和并网电流控制。首先,针对前级DC/DC变换器,采用基于扰动观察法的积分滑模控制,使光伏输出电压跟踪其参考电压,从而实现光伏最大功率追踪;其次,针对后级DC/AC变换器,采用基于双环控制的积分滑模控制,不仅保证了直流母线电压恒定,而且确保了并网电流准确、快速地跟踪并网电流参考值。仿真结果表明:所设计的积分滑模控制不仅使光伏并网系统具有良好的动态和稳态性能,而且增强了系统的鲁棒性,降低了系统抖振。

基于改进无源-滑模的MMC抗扰动控制策略研究

传统的PI控制、无源控制因其内部控制结构参数固定,在系统遇到扰动时,同一组参数无法同时保证系统在多种扰动下的响应速度及控制效果。在模块化多电平换流器(MMC)欧拉-拉格朗日模型的基础上引入滑模控制,解决无源控制内部参数固定的问题,提升系统的抗扰动运行能力,并在原有的趋近律上进行优化,降低滑模控制自身存在的抖振,使系统有更好的动态特性。在MATLAB/Simulink平台中搭建MMC仿真模型进行仿真,分别对应用PI控制、无源-滑模控制、改进无源-滑模控制的电流内环进行对比分析,验证了改进无源-滑模控制在相同的仿真条件下具有更强的抗扰动性,响应速度更快,并且在滑模控制的基础上改进趋近律后,有效降低了滑模控制自身存在的抖振问题。

差异化背景下的POA驱动设计问题反馈及建议——以高级汉语口语课为例

以汉语专业留学生高级汉语口语课为例,在产出导向法教学理念的指导下,结合具体的教学实践,分析在驱动环节中所存在的系统性问题,如驱动时机、输入材料、驱动设计与驱动效果等。同时,在差异化背景下,探究其解决路径:寻求合适的驱动时机,扫清驱动中输入材料的障碍,加强对驱动产出的评价反馈,并将差异化转化为有利的教学资源,从而有效提升教学效果。

HAPA理论下分阶段容量管理对老年急性心力衰竭患者心功能、水肿程度及健康信念的影响

目的:探究健康行为过程取向(HAPA)理论下分阶段容量管理对老年急性心力衰竭患者心功能、水肿程度及健康信念的影响。方法:选取2020年1月-2021年12月厦门大学附属第一医院急诊科收治的102例老年急性心力衰竭患者作为研究对象,依据护理方法不同将其分为对照组(n=51,予以常规容量管理)和观察组(n=51,予以HAPA理论下分阶段容量管理),比较两组心功能指标、水肿程度及健康信念水平。结果:干预后,两组心功能相关指标较干预前均改善,且观察组血浆氨基末端脑钠肽前体(NT-proBNP)低于对照组,左心室射血分数(LVEF)高于对照组,差异有统计学意义(P<0.05);观察组干预后水肿程度轻于对照组,差异有统计学意义(P<0.05);干预后,两组个人健康信念、感到有控制力、感到自愿利用、感到威胁、感到有实施力评分均高于干预前,且观察组高于对照组,差异有统计学意义(P<0.05)。结论:老年急性心力衰竭患者应用HAPA理论下分阶段容量管理能有效改善心功能,缓解水肿程度,同时还能提高健康信念。