A sub-grid scale model for Burgers turbulence based on the artificial neural network method

The present study proposes a sub-grid scale model for the one-dimensional Burgers turbulence based on the neuralnetwork and deep learning method.The filtered data of the direct numerical simulation is used to establish thetraining data set,the validation data set,and the test data set.The artificial neural network(ANN)methodand Back Propagation method are employed to train parameters in the ANN.The developed ANN is applied toconstruct the sub-grid scale model for the large eddy simulation of the Burgers turbulence in the one-dimensionalspace.The proposed model well predicts the time correlation and the space correlation of the Burgers turbulence.

Mechanical and numerical models for sea ice dynamics on small-meso scale

On small-meso scale, the sea ice dynamic characteristics are quite different from that on large scale. To model the sea ice dynamics on small-meso scale, a new elastic-viscous-plastic （EVP） constitutive model and a hybrid Lagrangian- Eulerian （HLE） numerical method are developed based on continuum theory. While a modified discrete element model （DEM） is introduced to model the ice cover at discrete state. With the EVP constitutive model, the numerical simulation for ice ridging in an idealized rectangular basin is carried out and the results are comparable with the analytical solution of jam theory. Adopting the HLE numerical model, the sea ice dynamic process is simulated in a vortex wind field. The furthering application of DEM is discussed in details for modeling the discrete distribution of sea ice. With this study, the mechanical and numerical models for sea ice dynamics can be improved with high precision and computational efficiency.

A SECOND-ORDER DYNAMIC SUBGRID-SCALE STRESS MODEL

A second-order dynamic model based on the general relation between the subgrid-scale stress and the velocity gradient tensors was proposed. A priori test of the second-order model was made using moderate resolution direct numerical simulation date at high Reynolds number ( Taylor microscale Reynolds number R-lambda = 102 similar to 216) for homogeneous, isotropic forced flow, decaying flow, and homogeneous rotating flow. Numerical testing shows that the second-order dynamic model significantly improves the correlation coefficient when compared to the first-order dynamic models.

Evaluation of Subgrid-scale Models in Large-eddy Simulations of Turbulent Flow in a Centrifugal Pump Impeller

The current research of large eddy simulation （LES） of turbulent flow in pumps mainly concentrates in applying conventional subgrid-scale （SGS） model to simulate turbulent flow, which aims at obtaining the flow field in pump. The selection of SGS model is usually not considered seriously, so the accuracy and efficiency of the simulation cannot be ensured. Three SGS models including Smagorinsky-Lilly model, dynamic Smagorinsky model and dynamic mixed model are comparably studied by using the commercial CFD code Fluent combined with its user define function. The simulations are performed for the turbulent flow in a centrifugal pump impeller. The simulation results indicate that the mean flows predicted by the three SGS models agree well with the experimental data obtained from the test that detailed measurements of the flow inside the rotating passages of a six-bladed shrouded centrifugal pump impeller performed using particle image velocimetry （PIV） and laser Doppler velocimetry （LDV）. The comparable results show that dynamic mixed model gives the most accurate results for mean flow in the centrifugal pump impeller. The SGS stress of dynamic mixed model is decompose into the scale similar part and the eddy viscous part. The scale similar part of SGS stress plays a significant role in high curvature regions, such as the leading edge and training edge of pump blade. It is also found that the dynamic mixed model is more adaptive to compute turbulence in the pump impeller. The research results presented is useful to improve the computational accuracy and efficiency of LES for centrifugal pumps, and provide important reference for carrying out simulation in similar fluid machineries.

Gap models across micro-to mega-scales of time and space:examples of Tansley’s ecosystem concept

Background:Gap models are individual-based models for forests.They simulate dynamic multispecies assemblages over multiple tree-generations and predict forest responses to altered environmental conditions.Their development emphases designation of the significant biological and ecological processes at appropriate time/space scales.Conceptually,they are with consistent with A.G.Tansley’s original definition of"the ecosystem".Results:An example microscale application inspects feedbacks among terrestrial vegetation change,air-quality changes from the vegetation’s release of volatile organic compounds(VOC),and climate change effects on ecosystem production of VOC’s.Gap models can allocate canopy photosynthate to the individual trees whose leaves form the vertical leaf-area profiles.VOC release depends strongly on leaf physiology by species of these trees.Leaf-level VOC emissions increase with climate-warming.Species composition change lowers the abundance of VOC-emitting taxa.In interactions among ecosystem functions and biosphere/atmosphere exchanges,community composition responses can outweigh physiological responses.This contradicts previous studies that emphasize the warming-induced impacts on leaf function.As a mesoscale example,the changes in climate(warming)on forests including pest-insect dynamics demonstrates changes on the both the tree and the insect populations.This is but one of many cases that involve using a gap model to simulate changes in spatial units typical of sampling plots and scaling these to landscape and regional levels.As this is the typical application scale for gap models,other examples are identified.The insect/climatechange can be scaled to regional consequences by simulating survey plots across a continental or subcontinental zone.Forest inventories at these scales are often conducted using independent survey plots distributed across a region.Model construction that mimics this sample design avoids the difficulties in modelling spatial interactions,but we also discuss simulation at these scales with contagion effects.Conclusions:At the global-scale,successful simulations to date have used functional types of plants,rather than tree species.In a final application,the fine-scale predictions of a gap model are compared with data from micrometeorological eddy-covariance towers and then scaled-up to produce maps of global patterns of evapotranspiration,net primary production,gross primary production and respiration.New active-remote-sensing instruments provide opportunities to test these global predictions.

IMPROVED SUBGRID SCALE MODEL FOR DENSE TURBULENT SOLID-LIQUID TWO-PHASE FLOWS

The dense solid-phase governing equations for two-phase flows are obtained by using the kinetic theory of gas molecules.Assuming that the solid-phase velocity distributions obey the Maxwell equations,the collision term for particles under dense two-phase flow conditions is also derived. In comparison with the governing equations of a dilute two-phase flow,the solid-particle's governing equations are developed for a dense turbulent solid-liquid flow by adopting some relevant terms from the dilute two-phase governing equations.Based on Cauchy-Helmholtz theorem and Smagorinsky model, a second-order dynamic sub-grid-scale(SGS)model,in which the sub-grid-scale stress is a function of both the strain-rate tensor and the rotation-rate tensor,is proposed to model the two-phase governing equations by applying dimension analyses.Applying the SIMPLEC algorithm and staggering grid system to the two-phase discretized governing equations and employing the slip boundary conditions on the walls,the velocity and pressure fields,and the volumetric concentration are calculated.The simulation results are in a fairly good agreement with experimental data in two operating cases in a conduit with a rectangular cross-section and these comparisons imply that these models are practical.

Numerical study of anomalous dynamic scaling behaviour of (1+1)-dimensional Das Sarma-Tamborenea model

In order to discuss the finite-size effect and the anomalous dynamic scaling behaviour of Das Sarma-Tamborenea growth model, the （1＋1）-dimensional Das Sarma-Tamborenea model is simulated on a large length scale by using the kinetic Monte-Carlo method. In the simulation, noise reduction technique is used in order to eliminate the crossover effect. Our results show that due to the existence of the finite-size effect, the effective global roughness exponent of the （1＋1）-dimensional Das Sarma-Tamborenea model systematically decreases with system size L increasing when L 〉 256. This finding proves the conjecture by Aarao Reis[Aarao Reis F D A 2004 Phys. Rev. E 70 031607]. In addition, our simulation results also show that the Das Sarma-Tamborenea model in 1＋1 dimensions indeed exhibits intrinsic anomalous scaling behaviour.

Macroscopic damping model for structural dynamics with random polycrystalline configurations

In this paper the macroscopic damping model for dynamical behavior of the structures with random polycrystalline configurations at micro-nano scales is established. First, the global motion equation of a crystal is decomposed into a set of motion equations with independent single degree of freedom （SDOF） along normal discrete modes, and then damping behavior is introduced into each SDOF motion. Through the interpolation of discrete modes, the continuous representation of damping effects for the crystal is obtained. Second, from energy conservation law the expression of the damping coefficient is derived, and the approximate formula of damping coefficient is given. Next, the continuous damping coefficient for polycrystalline cluster is expressed, the continuous dynamical equation with damping term is obtained, and then the concrete damping coefficients for a polycrystalline Cu sample are shown. Finally, by using statistical two-scale homogenization method, the macroscopic homogenized dynamical equation containing damping term for the structures with random polycrystalline configurations at micro-nano scales is set up.

ARMA Modelling of Benue River Flow Dynamics: Comparative Study of PAR Model

The seemingly complex nature of river flow and the significant variability it exhibits in both time and space, have largely led to the development and application of the stochastic process concept for its modelling, forecasting, and other ancillary purposes. Towards this end, in this study, attempt was made at stochastic modelling of the daily streamflow process of the Benue River. In this regard, Autoregressive Moving Average (ARMA) models and its derivative, the Periodic Autoregressive (PAR) model were developed and used for forecasting. Comparative forecast performances of the different models indicate that despite the shortcomings associated with univariate time series, reliable forecasts can be obtained for lead times, 1 to 5 day-ahead. The forecast results also showed that the traditional ARMA model could not robustly simulate high flow regimes unlike the periodic AR (PAR). Thus, for proper understanding of the dynamics of the river flow and its management, especially, flood defense, in the light of this study, the traditional ARMA models may not be suitable since they do not allow for real-time appraisal. To account for seasonal variations, PAR models should be used in forecasting the streamflow processes of the Benue River. However, since almost all mechanisms involved in the river flow processes present some degree of nonlinearity thus, how appropriate the stochastic process might be for every flow series may be called to question.

3-D Modelling of the Confederation Bridge Using Data of Full Scale Tests

Long-span bridges are special structures that require advanced analysis techniques to examine their performance. This paper presents a procedure developed to model the Confederation Bridge using 3-D beam elements. The model was validated using the data collected before the opening of the bridge to the public. The bridge was instrumented to conduct fullscale static and dynamic tests. The static tests were to measure the deflection of the bridge pier while the dynamic tests to measure the free vibrations of the pier due to a sudden release of the static load. Confederation Bridge is one of the longest reinforced concrete bridges in the world. It connects the province of Prince Edward Island and the province of New Brunswick in Canada. Due to its strategic location and vital role as a transportation link between these two provinces, it was designed using higher safety factors than those for typical highway bridges. After validating the present numerical model, a procedure was developed to evaluate the performance of similar bridges subjected to traffic and seismic loads. It is of interest to note that the foundation stiffness and the modulus of elasticity of the concrete have significant effects on the structural responses of the Confederation Bridge.

Particle Modeling Based on Interatomic Potential and Crystal Structure: A Multi-Scale Simulation of Elastic-Plastic Deformation of Metallic Material

We formulate a macroscopic particle modeling analysis of metallic materials (aluminum and copper, etc.) based on theoretical energy and atomic geometries derivable from their interatomic potential. In fact, particles in this framework are presenting a large mass composed of huge collection of atoms and are interacting with each other. We can start from cohesive energy of metallic atoms and basic crystalline unit (e.g. face-centered cubic). Then, we can reach to interparticle (macroscopic) potential function which is presented by the analytical equation with terms of exponent of inter-particle distance, like a Lennard-Jones potential usually used in molecular dynamics simulation. Equation of motion for these macroscopic particles has dissipative term and fluctuation term, as well as the conservative term above, in order to express finite temperature condition. First, we determine the parameters needed in macroscopic potential function and check the reproduction of mechanical behavior in elastic regime. By using the present framework, we are able to carry out uniaxial loading simulation of aluminum rod. The method can also reproduce Young’s modulus and Poisson’s ratio as elastic behavior, though the result shows the dependency on division number of particles. Then, we proceed to try to include plasticity in this multi-scale framework. As a result, a realistic curve of stress-strain relation can be obtained for tensile and compressive loading and this new and simple framework of materials modeling has been confirmed to have certain effectiveness to be used in materials simulations. We also assess the effect of the order of loadings in opposite directions including yield and plastic states and find that an irreversible behavior depends on different response of the particle system between tensile and compressive loadings.

空间异形拱桥振动台试验设计

振动台试验是研究大型结构复杂动力特性和地震响应的有效手段,由于振动台尺寸和载重的限制,合理设计缩尺模型结构是振动台试验成功的关键。基于量纲相似法及弹性相似律,取1∶20的几何相似比,以某空间异形拱桥为原型,开展了其关键参数动力缩尺模型设计。首先,通过有限元数值分析,分析了动力作用下原桥模型与缩尺桥模型的动力特性、关键部位内力与位移等响应,以验证缩尺模型的合理性;并在选取合理地震动作用下,开展了结构时程响应分析。研究结果表明:缩尺模型桥与原型桥前10阶模态完全吻合且频率误差小于7%,关键截面内力、位移和加速度等响应误差未超过10%,缩尺模型桥可较好地反映原桥动力特性和响应特点。研究成果可为空间异形拱桥振动台抗震设计提供技术支撑并为同类桥梁振动台试验提供参考。

我国青贮玉米生产的集聚演变及其作用机制——基于动态空间杜宾模型

为观测青贮玉米生产的动态变化,研究基于2001—2021年我国30个省面板数据,选用重心模型分析青贮玉米生产集聚区域变动。在此基础上,借助动态空间杜宾模型剖析要素投入、社会经济、政策支持对中国青贮玉米生产区域变动的影响。结果表明,我国青贮玉米存在空间聚集现象,即2001—2021年间我国青贮玉米生产量的莫兰指数总体上呈“先降再升再降再升”的发展态势。生产重心演变轨迹结果显示,我国青贮玉米生产区域重心呈现“先东北后西北、西南”的演变趋势。机制结果表明,粮食优势、财政扶持、务工收入增加是推进青贮玉米生产的主要驱动因素;生产基础设备、化肥施用、农业收益对本省份青贮玉米生产具有正向影响,但对相邻省份青贮玉米生产的影响不显著。

Understanding the Dynamics Location of Very Large Populations Interacted with Service Points

This paper offers preliminary work on system dynamics and Data mining tools. It tries to understand the dynamics of carrying out large-scale events, such as Hajj. The study looks at a large, recurring problem as a variable to consider, such as how the flow of people changes over time as well as how location interacts with placement. The predicted data is analyzed using Vensim PLE 32 modeling software, GIS Arc Map 10.2.1, and AnyLogic 7.3.1 software regarding the potential placement of temporal service points, taking into consideration the three dynamic constraints and behavioral aspects: a large population, limitation in time, and space. This research proposes appropriate data analyses to ensure the optimal positioning of the service points with limited time and space for large-scale events. The conceptual framework would be the output of this study. Knowledge may be added to the insights based on the technique.

新型波形钢腹板组合箱梁桥动力性能分析

对一种新型波形钢腹板组合箱梁桥结构开展了动力特性及抗震性能分析;以鄄城黄河大桥跨中箱梁段为例,建立组合箱梁桥的多尺度有限元模型,并与实测值进行了对比,验证了多尺度模型的有效性;基于此设计了该新型波形钢腹板组合箱梁的截面参数,采用多尺度建模方法研究了各参数变化对箱梁动力特性的影响规律,通过地震反应谱法分析了该结构在各向地震作用下的结构响应。结果表明:箱梁横隔板的数量和厚度是结构动力特性的敏感参数,对结构的扭转刚度影响很大;增大波形钢腹板厚度可有效提高结构刚度,且刚度增大对频率的影响程度大于质量增大对频率的影响,建议腹板厚度宜设为20~30 mm;槽形钢板可有效提高截面的抗弯刚度,尤其对结构竖向弯曲模态影响较大;横向地震作用对混凝土顶板和横隔板应力的影响最大,纵向地震力对波形钢腹板应力的影响最大,竖向地震力对混凝土底板和槽形钢板的应力影响较大。

基于模型预测控制的高比例可再生能源电力系统多时间尺度动态可靠优化调度

提出基于模型预测控制的高比例可再生能源电力系统多时间尺度动态可靠优化调度方法,通过日前优化调度、日内滚动优化、运行风险计算及反馈校正几个环节,对可再生能源发电和系统内可调资源进行最优调度。日内实时调度阶段,基于日前调度计划和实时运行状况,采用回归预测算法,自适应选择重要变量预测系统未来运行状态,通过吉布斯抽样得到关键变量的概率密度,快速量化系统下一时刻的运行风险,并将风险反馈至日内滚动优化阶段,重复进行可靠优化调度。仿真算例结果验证所提方法的适应性和可行性。

重力坝地震断裂的多边形比例边界有限元模型研究

为研究重力坝的地震断裂破坏机理,基于线弹性断裂力学和多边形比例边界有限元法(Polygon SBFEM)提出一种全自动的重力坝动态断裂分析模型。该模型继承了SBFEM在断裂分析中高精度和高效率的优势,通过建立多边形比例边界有限单元广义动态应力强度因子的时域分析方法实现任意时刻断裂参数的求解,并结合裂缝扩展准则可实时判定裂缝稳定性;对达到临界状态的裂缝采用多边形网格局部重剖分技术,开发了考虑裂缝张开-闭合行为的动态接触模拟算法,进而实现了裂缝动态扩展高效自动化模拟。以Koyna重力坝为研究对象,考虑大坝库水动力相互作用,模拟了地震作用下坝体裂缝扩展过程,获得了断裂路径,验证了模型的正确性。其后,进一步探讨了数值模型中网格密度和裂缝扩展步长等因素的影响,结果显示仅用粗网格即可获得满意的计算结果,且三种裂缝扩展步长模拟的大坝裂缝扩展轨迹接近,但随着裂缝扩展步长增大,大坝更早失效破坏。研究成果可为混凝土坝的地震断裂分析提供有力的技术手段。

爆炸载荷下水下隧道的压力分布和动力响应

为了研究隧道结构在水中爆炸冲击下的荷载分布和动力响应,设计并制作了1/10缩尺隧道模型,进行了3次水下爆炸试验,对隧道模型的压力、冲量和位移进行了研究。研究结果表明:冲击波在浅水区会产生明显的水面截断效应,该效应会使近水面的冲量减小;自由场冲击波峰值压力的试验值与理论值吻合良好,误差在20%以内;圆形截面隧道迎爆面峰值压力为自由场峰值压力的1.626~1.716倍,顶面峰值压力为自由场峰值压力的54.3%~65.2%,背爆面峰值压力为自由场峰值压力的25.5%~31.3%;水中爆炸作用下的冲量时程曲线呈明显的阶梯状,每一次的气泡脉动都伴随着相应的冲量增加;水下爆炸会引起隧道结构产生振动,其振动过程可分为结构急速变形、结构大幅振动和结构颤振3个阶段,隧道结构的最大位移发生在结构大幅振动阶段。

耕地“三位一体”保护视角下中国省域休耕规模与空间布局

实施土地休耕是落实“藏粮于地”战略的关键,目前宏观尺度的全国休耕空间布局尚未确定,该研究探究了粮食安全约束下的全国范围内最大休耕规模以及中国省域休耕空间优化布局。以耕地数量、质量和生态“三位一体”保护为研究视角,该研究通过系统动力学、灰色预测模型等方法构建最大休耕规模预测模型,并结合“压力-状态-响应”模型构建休耕迫切度评价体系,依据评价结果分配各省休耕规模,从而得到中国省域休耕空间布局。结果表明:1)预计在90%、95%、100%的粮食自给率下,到2030年中国最大休耕规模分别为3237.310万、2678.970万和2120.640万hm^(2);2)省域之间的休耕迫切度水平存在差异,上海、内蒙古等地休耕迫切度较高,四川、广西等地休耕迫切度较低;3)在耕地三位一体保护的约束条件下,地区之间休耕规模差异较大,内蒙古、甘肃等地休耕规模较大,北京、上海等地休耕规模较小。该研究将数量、质量和生态多元目标融合进休耕空间分区研究,能够为未来休耕制度的全面建立以及精准落地提供思路与方法参考。

大型渡槽动水压力离心模型试验研究

以引江济淮工程淠河总干渠渡槽为参考研究对象,采用离心机振动台对刚性渡槽在简谐荷载激励下的动水压力进行了试验研究,并将试验结果与常用的简化模型的计算结果进行了对比分析。试验结果表明:动水压力与加速度幅值呈线性相关,与加载频率、水深呈非线性相关;离心模型试验可以准确的模拟动水压力及流固耦合作用,可以为水弹性问题的研究提供新的分析方法。