Simulation of fluctuation effect on dendrite growth by phase field method

The dendrite growth process was simulated with the phase field model coupling with the fluctuation.The effect of fluctuation intensity on the dendrite morphology and that of the thermal fluctuation together with the phase field fluctuation on the forming of side branches were investigated.The results indicate that with the decrease of thermal fluctuation amplitude,the furcation of dendrite tip also decreases,transverse dendrites become stronger,longitudinal dendrites become degenerated,Doublon structure disappears,and a quite symmetrical dendrite structure appears finally.Thermal fluctuation can result in the unsteadiness of dendrites side branches,and it is also the main reason for forming side branches.The phase field fluctuation has a little contribution to the side branches,and it is usually ignored in calculation.When the thermal fluctuation amplitude(F_u) is appropriate,the thermal noise can result in the side branches,but cannot change the steady behavior of the dendrites tip.

Fluctuating hydrodynamic methods for fluid-structure interactions in confined channel geometries

We develop computational teractions subject to thermal fluctuations geometry. The methods take into account methods for the study of fluid-structure in- when confined within channels with slit-like the hydrodynamic coupling and diffusivity of microstructures when influenced by their proximity to no-slip walls. We develop stochas- tic numerical methods subject to no-slip boundary conditions using a staggered finite volume discretization. We introduce techniques for discretizing stochastic systems in a manner that ensures results consistent with statistical mechanics. We show how an exact fluctuation-dissipation condition can be used for this purpose to discretize the stochastic driving fields and combined with an exact projection method to enforce incompressibil- ity. We demonstrate our computational methods by investigating how the proximity of ellipsoidal colloids to the channel wall affects their active hydrodynamic responses and passive diffusivity. We also study for a large number of interacting particles collective drift-diffusion dynamics and associated correlation h/actions. We expect the introduced stochastic computational methods to be broadly applicable to applications in which con- finement effects play an important role in the dynamics of microstructures subject to hydrodynamic coupling and thermal fluctuations.

Initial fluctuation effect on elliptic flow in Au+Au collision at 1 GeV/A

How the initial fluctuation affects on the elliptic flow is investigated by investigating the rapidity, transverse 4-velocity, centrality dependencies of elliptic flow for Au+Au at 1 GeV/A with the help of an Isospin Quantum Molecular Dynamics (IQMD). In addition, we compare the flow calculated with respect to participant plane created by the initial geometry in coordinate space with the flow reconstructed by the experimental event-plane method, and compare the flow with the experimental data of the FOPI collaboration. It shows that there exists some discrepancy between the flows reconstructed by the above two methods.

A Hybrid Immersed Boundary/Coarse-Graining Method for Modeling Inextensible Semi-Flexible Filaments in Thermally Fluctuating Fluids Dedicated to Professor Karl Stark Pister for his 95th birthday

A new and computationally efficient version of the immersed boundary method,which is combined with the coarse-graining method,is introduced for modeling inextensible filaments immersed in low-Reynolds number flows.This is used to represent actin biopolymers,which are constituent elements of the cytoskeleton,a complex network-like structure that plays a fundamental role in shape morphology.An extension of the traditional immersed boundary method to include a stochastic stress tensor is also proposed in order to model the thermal fluctuations in the fluid at smaller scales.By way of validation,the response of a single,massless,inextensible semiflexible filament immersed in a thermally fluctuating fluid is obtained using the suggested numerical scheme and the resulting time-averaged contraction of the filament is compared to the theoretical value obtained from the worm-like chain model.

Influence Characteristics of Laser Transmission Amplitude Fluctuation Based on Turbulent Medium

In order to study the transmission characteristics of laser in atmospheric turbulent medium and understand the influence degree of various factors on amplitude fluctuation, by means of smooth perturbation method, this paper establishes a theory model of amplitude fluctuation of laser propagation in turbulent medium by using the smooth perturbation method and reflects the amplitude fluctuation degree, carries out specific discussion on each influence factor. The results show that the larger the wavelength, the more stable the amplitude fluctuation. With the increase of laser section radius, the amplitude fluctuates sharply and then decreases slowly after reaching the peak. Transmission distance is the main influence factor of amplitude fluctuation. With the increase of transmission distance, the amplitude fluctuation will become more obvious. The amplitude acquisition can be comprehensively modulated in a specific transmission distance by wavelength and section ra-dius, so as to ensure the stability of the received laser and provide a theoretical basis for the interferometry technology.

重解中国经济波动——概念、特征与内涵

本文对中国经济波动研究中的重要概念进行了重新阐述与区分:冲击是经济波动的来源,而对经济均衡造成扭曲的“楔子”则是冲击传播的机制,二者并不等同,更不能割裂。在厘清相关概念基础上,从产出、劳动、投资和消费四个角度对中国经济波动的特征和影响因素进行核算,结果表明:效率楔子及经由其传播的冲击是理解中国经济波动的首要因素;劳动楔子对解释中国劳动力市场波动和疫情以来的经济运行特征有重要价值;投资的下滑并非是投资楔子恶化带来的,而是与经济基本面高度相关,但投资楔子对理解中国“低消费”特征有重要意义;不同楔子对经济波动的贡献是动态变化的。本研究利用相应市场楔子对现实中摩擦进行概括测算的思想,对指导在结构模型中如何引入摩擦有重要价值,相关结论对宏观政策取向有一定启发。

基于QC方法减少长距离高起伏输水管线设计工日

针对近年来长距离、高起伏复杂输水管线出现频率日益增多的情况,为有效减少设计工日,QC小组通过现状调查分析确定了“输水管道布置设计耗时多”为主要症结。根据主要症结并兼顾其他因素,设定了活动目标,通过因果分析找出了6项末端因素。运用调查分析法确认了“水锤模拟分析过程复杂”和“管线路径决策流程不完善”2项要因。针对这2项要因,小组成员按照“5W1H”的方法进行了分析讨论,并制定了相应的对策。这些对策得到了有效落实,实现并超越了目标值,设计工日稳中有降,经济效益显著,具有一定的推广应用价值。

猪肉收储政策对我国生猪市场价格波动的影响

猪肉收储政策作为民生商品储备体系的重要组成部分,是做好生猪和猪肉市场保供稳价工作的重要政策工具,对缓解我国生猪市场价格波动具有重要意义。文章基于我国2007—2022年30个省份数据,构建双重差分模型评估自2009年颁布《防止生猪价格过度下跌调控预案(暂行)》及之后一系列猪肉收储政策对我国生猪市场价格波动的影响。结果表明,在控制其他因素后,猪肉收储政策对我国生猪市场价格波动具有显著抑制作用,其作用程度约为0.041;猪肉收储政策对我国生猪市场价格波动的影响具有明显区域异质性,在东部地区该政策效果最强。文章主要考察了猪肉收储政策对生猪市场价格波动的影响,以期为合理控制生猪市场价格提供参考。

电炉变电站集控中心告警信息远程聚合方法研究

电炉变电站集控中心的告警信息远程聚合可以帮助集中监控和管理多个电炉变电站的设备,识别潜在风险或故障,及时采取预防或修复措施。由于不同类型的电炉变电站设备采用的远程监控系统存在较大差异,产生的告警信息具有不同的格式、结构和语义,导致告警信息具有异构性,缺少衡量异构性信息的统一特征。为此,提出一种基于关联度特征的电炉变电站集控告警信息远程聚合方法。根据关联关系度量标准计算异构数据之间的直接关联关系度。通过计算不同告警信息的关联度,联合时间变异系数分析告警信息时间波动特征,根据告警数据的这两种属性将其划分为时间约束属性和相似度约束属性,实现电炉变电站集控告警信息远程聚合。实验结果表明:所提方法能够有效提升告警信息量,且能够显著优化远程获取告警信息的聚合率。

基于栖息地法的水库变动回水区鱼类产卵场生态流量及调控策略研究

揭示水库变动回水区鱼类产卵场栖息地适宜性变化的规律,确定水库变动回水区鱼类产卵场栖息地生态流量阈值及保护调控的方法,为鱼类产卵场栖息地保护提供参考与借鉴。以三峡变动回水区的广阳-石沱江段为研究区域,选取四大家鱼、铜鱼、长鳍吻鮈、圆筒吻鮈和中华金沙鳅等8种产漂流性卵鱼类为研究对象,通过鱼类产卵场栖息地模拟,在耦合8种鱼类生态需求的基础上计算生态流量阈值,并制定相应的调控策略。结果表明,三峡水库在145、150、155、160、165 m和天然情形下变动回水区最小生态流量分别为:6543、7130、9943、13713、17603、6106 m^(3)/s;最大生态流量分别为:17028、17526、23110、28291、29858、15753 m^(3)/s;最适生态流量分别为10002、10916、14479、18810、23226、9365 m^(3)/s,上、下阈值分别为13515、14221、18794、23550、26542、12559 m^(3)/s;8272、9023、12211、16262、20414、7736 m^(3)/s。流量较小时,一定流量范围内,降低水位有利于增加加权可利用面积(AWU);流量较大时,流量增加到一定值后,增加水位有利于增加AWU;而流量在两者之间时,可参考研究结果中的水位及生态流量阈值进行调控决策。

新型数字反应性仪主要性能测试

在实验室及零功率堆上,对新研制的高性能数字反应性仪进行测量精度、连续性和稳定性等主要性能测试。测试结果表明:所研制的反应性仪满足研制技术指标的要求,主要指标均优于反应堆物理试验对反应性仪的使用要求,适用于各类反应堆物理启动试验对反应性的测量。

线性和非线性去趋势化对土性波动范围影响分析

文章基于合肥市黏土层静力触探(cone penetration test,CPT)数据建立土性剖面随机场模型,探究线性和非线性去趋势化对土性波动范围计算结果的影响。利用线性和非线性去趋势方法对原始CPT数据进行去趋势化处理,对得到的波动分量进行平稳性和遍历性检验,采取相关函数法和空间递推法计算波动分量对应的土性波动范围,并讨论计算方法和取样间距对不同去趋势化方法的敏感性。结果表明:对于具有非线性趋势的数据,采用线性去趋势来处理会使得到的波动分量平稳性变差,导致最终计算得到的波动范围均值、标准差和变异系数增大,计算结果稳定性明显变差;相比于线性去趋势,非线性去趋势的适应性更强;此外相关函数法对不同去趋势化方法的敏感性要大于空间递推法,而取样间距不会影响数据整体的趋势性及对去趋势化处理方法的选择。

随机脉动风场作用下输电塔线体系的动力响应分析

输电杆塔及塔线体系(简称塔线体系)是整个电力系统中输电环节的核心部分,沿海地区的强风对塔线体系有着重要影响。为研究在随机脉动风场作用下塔线体系的动力响应特性,文中以广东某地区的1W2C9型鼓型自立式输电杆塔为研究对象,建立输电杆塔的单塔及一塔两线的塔线耦联有限元模型,结合Davenport风速谱与四阶自回归法模拟具有空间相关性的单塔9节点及塔线体系49节点的脉动风场,研究在此脉动风场下的单塔及塔线体系的动力响应,并探究不同风向角对其动力响应的影响。研究结果表明:单塔及塔线体系的动力响应最大值大于其拟静力响应;由于塔线耦联效应的存在,输电线会增加塔线体系的稳定性,降低其动力响应;90°是输电杆塔单塔及塔线体系动力响应的最不利风向角。

高扬程多起伏输水管道停泵水锤防护优化

为兼顾可靠性和经济性,对高扬程、多起伏输水管道停泵水锤防护设备参数进行优化,构建BP神经网络模拟水力过渡过程,以空气阀和单向调压塔参数为决策变量,协同多目标遗传算法(NSGA-Ⅱ)进行优化得到Pareto最优解集,采用熵权-TOPSIS法进行决策确定最佳方案。将该方法应用于工程实例,结果表明,相比初始方案,优化方案以低于92.06%的单向调压塔容积提供相近的正压防护效果,管道沿线最低负压提升49.28%,与无防护措施相比,在满足管材耐压能力的同时,管道沿线最大、最小压力与屈服能力上、下限的最大差距分别减小84.02%和65.00%。该方法可实现停泵水锤防护计算与智能优化算法有效链接,确定可靠且经济的停泵水锤防护设备参数。

Improving mathematical model of burden distribution and correcting chute angle to cope with fluctuation of stock line

Accurate evaluations of the burden distribution are of critical importance to stabilize the operation of blast furnace.The mathematical model and discrete element method(DEM)are two attractive methods for predicting burden distribution.Based on DEM,the initial velocities of the pellet,sinter,and coke were calculated,and the velocity attenuations of the above three particles between the burden and the chute were analyzed.The initial velocity and velocity attenuation were applied to a mathematical model for improving the accuracy.Additionally,based on the improved model,a scheme for rectifying the chute angles was proposed to address the fluctuation of the stock line and maintain a stable burden distribution.The validity of the scheme was confirmed via a stable burden distribution under different stock lines.The mathematical model has been successfully applied to evaluate the online burden distribution and cope with the fluctuation of the stock line.

考虑圆度误差的角接触球轴承温升特性研究

以往有关于轴承温升特性的研究多注重轴承温升以及圆度误差对轴承振动的影响,其中圆度误差对轴承温升影响的文献较少,且研究对象多针对的是低速、轻载轴承的温升。为此,建立了考虑圆度误差、轴承预紧力、离心效应、热力耦合等影响的角接触球轴承热-力耦合模型,研究了轴承沟道圆度误差对轴承温升的影响规律。首先,以轴承拟动力学、弹流润滑理论、传热学理论和基尔霍夫能量守恒定律为基础,建立了考虑圆度误差、轴承预紧力、离心效应、热力耦合等影响的角接触球轴承热-力耦合模型;然后,利用模型分析了不同工况条件、圆度误差对轴承温升特性影响;最后,将模型计算结果与试验结果进行了比较,验证了角接触球轴承热-力耦合模型的合理性。研究结果表明:模型计算结果和实验结果相比,最大相对误差为5.37%;随着圆度误差阶次的增加,轴承温度呈现波动性变化,且随着转速的增加,波动趋势愈加显著;随着润滑油温度的升高,温度波动逐渐减小;当圆度误差的阶次等于球数n/2±2(n=1,2,3…)时,轴承外圈温度比不考虑圆度误差时要低,因此将圆度误差控制在特定阶次内能有效降低轴承温升,从而提高工作效率;轴承外圈温度的波动性与外圈圆度误差的幅值成正比,为轴承设计提供了重要参考;外圈温度与沟道圆度误差阶次之间呈周期性变化,并与钢球的个数形成映射关系,当圆度误差阶次等于球数的(2 n-1)/4倍(n=1,2,3…)时,轴承外圈温度达到最高;当圆度误差阶次等于球数的n/2倍(n=1,2,3…)时,轴承外圈温度最低,这一规律可为轴承的优化提供具体参考方向。

基于弹性波动理论的北关闸底板脱空检测分析

在河道内长期有水情况下,在不损坏工程现状土建结构的前提下,基于弹性波动原理,采用水下冲击映像法检测仪对北关闸的底板脱空进行检测,以确定水闸的安全状态,排除安全隐患。本文主要阐述了水下冲击映像法的基本原理、实现方法和数据处理等,介绍了北关闸底板脱空检测的过程,分析了检测结果,即北关拦河闸1~7号闸底板检测均未发现明显脱空病害缺陷,部分水闸底板存在疏松缺陷。最后针对检测结果提出了相关建议。

考虑风速波动性的海上风电渗透率极限评估方法

大规模具有间歇性、波动性且难以预测的风电接入电网后会给电网的电压和频率稳定性带来一系列挑战,因此如何评估已有区域电网的最大风电极限渗透功率成为了一个重要问题。现有研究大多分析了不同风电渗透率对电网电压和频率稳定性的影响,而缺乏对海上风电渗透率极限的评估。为此,考虑风速波动性的影响,提出了一种针对已有区域电网的海上风电渗透率极限评估方法。首先,通过研究海上风电场静态模型分析海上风电场功率输出特性;然后,通过构建含海上风电场和同步发电机的电网等效模型分析不同风电渗透率下并网点(Point of Common Coupling, PCC)电压与频率特性;最后,针对风速波动引起的电网电压和频率波动,提出考虑风速波动性的海上风电渗透率极限评估方法,并通过算例验证所提方法的有效性。随着海上风电渗透率增加,PCC电压降低速度和幅度也增大,加剧了有功波动对PCC电压的不利影响。此外,高渗透率条件下,电力系统可能面临有功功率缺额问题,造成频率偏差加剧。电压闪变和电压偏差在高渗透率时也随之增加,导致电能质量下降,频率合格率降低。

比率低频振幅技术在延年九转法治疗慢性疲劳综合征伴焦虑抑郁中的应用价值

目的比较延年九转法与认知行为治疗后,慢性疲劳综合征(chronic fatigue syndrome,CFS)伴焦虑与抑郁症状患者的大脑静息态下功能MRI(functional MRI,fMRI)比率低频振幅(fractional amplitude of low-frequency fluctuations,fALFF)的脑区差异改变情况。材料与方法将30例CFS患者随机分为延年九转法组和认知行为组,治疗12周后进行fMRI检测,采用Pearson相关分析探索fALFF变化与焦虑抑郁量表(Hospital Anxiety and Depression Scale,HADS)的线性相关性。结果与认知行为组相比,延年九转法组fALFF减弱的脑区有左侧梭状回、左侧枕上回、左侧角回;增强的脑区有右侧颞中回。焦虑症状分值与梭状回(r=0.525,P=0.044)和枕上回(r=0.559,P=0.030)的fALFF平均值呈正相关,抑郁症状分值与梭状回(r=0.542,P=0.037)的fALFF平均值呈正相关(P<0.05)。结论延年九转法可能通过梭状回、枕上回、角回、颞中回神经活动水平强弱客观反映CFS患者焦虑与抑郁症状。

A Cell Screening Algorithm Integrating Genetic and Numerical Differentiation

The consistency of the cell has a significant impact on battery capacity,endurance,overall performance,safety,and service life extension.However,it is challenging to identify cells with high consistency and no loss of battery energy.This paper presents a cell screening algorithm that integrates genetic and numerical differentiation techniques.Initially,a mathematical model for battery consistency is established,and a multi-step charging strategy is proposed to satisfy the demands of fast charging technology.Subsequently,the genetic algorithm simulates biological evolution to efficiently search for superior cell combinations within a short time while evaluating capacity,voltage consistency,and charge/discharge efficiency.Finally,through experimental validation and comparative analysis with similar algorithms,our proposed method demonstrates notable advantages in terms of both search efficiency and performance.