Multi-dimensional Simulation of Phase Change by a 0D-2D Model Coupling via Stefan Condition

Considering phase changes associated with a high-temperature molten material cooled down from the outside,this work presents an improvement of the modelling and the numerical simulation of such processes for an application pertaining to the safety of light water nuclear reactors.Postulating a core meltdown accident,the behaviour of the core melt(aka corium)into a steel vessel is of tremendous importance when evaluating the vessel integrity.Evaluating correctly the heat fluxes requires the numerical simulation of the interaction between the liquid material and its solid counterpart which forms during the solidification process,but also may melt back.To simulate this configuration,encoun-tered in various industrial applications,one considers a bi-phase model constituted by a liquid phase in contact and interaction with its solid phase.The liquid phase may solidify in presence of low energetic source,while the solid phase may melt due to an intense heat flux from the high-temperature liquid.In the frame of the in-house legacy code,several simplifying assumptions(0D multi-layer discretization,instantaneous heat transfer via a quadratic temperature profile in solids)are made for the modelling of such phase changes.In the present work,these shortcomings are illustrated and further overcome by solving a 2D heat conduction model in the solid by a mixed Raviart-Thomas finite element method coupled to the liquid phase due to heat and mass exchanges through Stefan condition.The liquid phase is modeled with a 0D multi-layer approach.The 0D-liquid and 2D-solid mod-els are coupled by a Stefan like phase change interface model.Several sanity checks are performed to assess the validity of the approach on 1D and 2D academical configurations for which exact or reference solutions are available.Then more advanced situations(genu-ine multi-dimensional phase changes and an"industrial-like scenario")are simulated to verify the appropriate behavior of the obtained coupled simulation scheme.

3D seismic forward modeling from the multiphysical inversion at the Ketzin CO_(2) storage site

From June 2008 to August 2013,approximately 67 kt of CO_(2) was injected into a deep saline formation at the Ketzin pilot CO_(2) storage site.During injection,3D seismic surveys have been performed to monitor the migration of sequestered CO_(2).Seismic monitoring results are limited by the acquisition and signal-to-noise ratio of the acquired data.The multiphysical reservoir simulation provides information regarding the CO_(2) fluid behavior,and the approximated model should be calibrated with the monitoring results.In this work,property models are delivered from the multiphysical model during 3D repeated seismic surveys.The simulated seismic data based on the models are compared with the real data,and the results validate the effectiveness of the multiphysical inversion method.Time-lapse analysis shows the trend of CO_(2) migration during and after injection.

Novel Sum-of-Sinusoids Simulation Channel Modeling for 6G Multiple-Input Multiple-Output Vehicle-to-Everything Communications

In this paper,a statistical cluster-based simulation channel model with a finite number of sinusoids is proposed for depicting the multiple-input multiple-output(MIMO)communications in vehicleto-everything(V2X)environments.In the proposed sum-of-sinusoids(SoS)channel model,the waves that emerge from the transmitter undergo line-of-sight(LoS)and non-line-of-sight(NLoS)propagation to the receiver,which makes the model suitable for describing numerous V2X wireless communication scenarios for sixth-generation(6G).We derive expressions for the real and imaginary parts of the complex channel impulse response(CIR),which characterize the physical propagation characteristics of V2X wireless channels.The statistical properties of the real and imaginary parts of the complex CIRs,i.e.,autocorrelation functions(ACFs),Doppler power spectral densities(PSDs),cross-correlation functions(CCFs),and variances of ACFs and CCFs,are derived and discussed.Simulation results are generated and match those predicted by the underlying theory,demonstrating the accuracy of our derivation and analysis.The proposed framework and underlying theory arise as an efficient tool to investigate the statistical properties of 6G MIMO V2X communication systems.

非均质多孔介质超临界CO_(2)非混相驱替特征及机理研究

为深入理解超临界CO_(2)在非均质储层中的非混相驱替过程,探索其流动特性及对多孔介质流体动力学的影响,为CO_(2)增强油气采收率和地质碳储存技术提供科学依据,采用基于Navier-Stokes方程与Cahn-Hilliard方程耦合的微观两相流模型,结合Voronoi多边形构造技术建立了具有真实孔隙结构特征的非均质多孔介质模型。通过模拟计算,详细描述了不同条件下CO_(2)驱替过程中的流体动力学行为和界面特征,研究了流体界面形态的演变和驱替效率的影响因素。结果表明:超临界CO_(2)注入后,不同模型内均出现了指进特征和复杂的非混相界面;孔道结构特征决定了毛细力大小,影响CO_(2)驱替前缘的稳定性,大孔道易形成指进现象,而狭窄孔道受毛细阻力与黏滞力影响,促使CO_(2)渗流路径转向或分叉,并导致孔隙压力不均匀分布;孔道内的黏滞力阻碍CO_(2)推进,适度调节CO_(2)的黏度和密度有助于提高驱替效率;高毛管数条件下,驱替压力导致流体相界面变得不稳定,CO_(2)优势渗流通道数量增多,指进渗流通道宽度拓宽,在黏滞力作用下出现了非连续的卡断现象;长时间的驱替过程显著提高CO_(2)饱和度,但伴随高能耗损失,驱替效率在CO_(2)突破后期逐渐下降。因此,调控超临界CO_(2)的物理性质、优化控制注入速率,能有效改善CO_(2)在地层中的分布和驱替路径,是提高CO_(2)驱替效率和优化地层开发的重要手段。

Geomechanics model test and numerical simulation of 2G-NPR bolt support effect in an active fault tunnel

Active faults are a common adverse geological phenomenon that can occur during tunnel excavation and has a very negative impact on the construction and operation of the tunnel.In this paper,the grade IV rock surrounding the cross-fault tunnel with poor geological conditions has been chosen for the study.The support capacity of 2^(nd) Generation-Negative Poisson’s Ratio(2G-NPR)bolt in an active fault tunnel has been carried out on the basis of relevant results obtained from the geomechanical model test and numerical investigations of failure model for existing unsupported fault tunnel.The investigation shows that surrounding rock of the tunnel is prone to shear deformation and crack formation along the fault,as a result,the rock mass on the upper part of the fault slips as a whole.Furthermore,small-scale deformation and loss of blocks are observed around the tunnel;however,the 2G-NPR bolt support is found to be helpful in keeping the overall tunnel intact without any damage and instability.Due to the blocking effect of fault,the stress of the surrounding rock on the upper and lower parts of the fault is significantly different,and the stress at the left shoulder of the tunnel is greater than that at the right shoulder.The asymmetrical arrangement of 2G-NPR bolts can effectively control the asymmetric deformation and instability of the surrounding rock.The present numerical scheme is in good agreement with the model test results,and can reasonably reflect the stress and displacement characteristics of the surrounding rock of the tunnel.In comparison to unsupported and ordinary PR(Poisson’s Ratio)bolt support,2G-NPR bolt can effectively limit the fault slip and control the stability of the surrounding rock of the fault tunnel.The research findings may serve as a guideline for the use of 2G-NPR bolts in fault tunnel support engineering.

Measurement and Scenario Simulation of Effect of Urbanisation on Regional CO_2 Emissions Based on UEC-SD Model:A Case Study in Liaoning Province,China

Based on the logical causal relationship and taking Liaoning Province, China, which is the Chinese traditional industrial base and is in the stage of accelerated urbanisation, as a case study, this study builds the ＇Urbanisation-Energy Consumption-COn Emissions System Dynamics （UEC-SD）＇ model using a system dynamics method. The UEC-SD model is applied to analyse the effect of the ar- banisation process on the regional energy structure and CO2 emissions, followed by simulation of future production and living energy consumption structure as well as the evolutionary trend of CO2 emissions of three urbanisation scenarios （low speed, intermediate speed and high speed） under the assumed boundary conditions in urban and rural areas of Liaoning Province, China. The results show that the urbanisation process can alter production and the living energy consumption structure and thereby change regional CO2 emissions. An increase in the urbanisation rate in case area will lead to regional COz emissions rising in the short term, but when the urbanisation rate approaches 80%, CO2 emissions will reach a peak value and then decrease. Comparison of different urbanisation rates showed that pro- duction and living energy consumption exhibit different directions of change and rules in urban and rural areas. The effect of urbanisa- tion on CO2 emissions and energy structure is not direct, and urbanisation can increase the differences in energy and CO2 emissions between urban and rural areas caused by the industrial structure, technical level and other factors.

Debris flow simulation 2D(DFS 2D):Numerical modelling of debris flows and calibration of friction parameters

Debris flows are rapid mass movements with a mixture of rock,soil and water.High-intensity rainfall events have triggered multiple debris flows around the globe,making it an important concern from the disaster management perspective.This study presents a numerical model called debris flow simulation 2D(DFS 2D)and applicability of the proposed model is investigated through the values of the model parameters used for the reproduction of an occurred debris flow at Yindongzi gully in China on 13 August 2010.The model can be used to simulate debris flows using three different rheologies and has a userfriendly interface for providing the inputs.Using DFS 2D,flow parameters can be estimated with respect to space and time.The values of the flow resistance parameters of model,dry-Coulomb and turbulent friction,were calibrated through the back analysis and the values obtained are 0.1 and 1000 m/s^(2),respectively.Two new methods of calibration are proposed in this study,considering the crosssectional area of flow and topographical changes induced by the debris flow.The proposed methods of calibration provide an effective solution to the cumulative errors induced by coarse-resolution digital elevation models(DEMs)in numerical modelling of debris flows.The statistical indices such as Willmott's index of agreement,mean-absolute-error,and normalized-root-mean-square-error of the calibrated model are 0.5,1.02 and 1.44,respectively.The comparison between simulated and observed values of topographic changes indicates that DFS 2D provides satisfactory results and can be used for dynamic modelling of debris flows.

A 2-D Non-local Closure Model for Atmospheric Boundary Layer Simulations

In this paper a new approach for PBL simulation, the non-local closure scheme based on the transient turbulence theory has been used. It was set up as an alternative to local closure schemes which physical concept is reasonable and distinct. A 2-D non-local closure model was developed in order to study the PBL structure and simulatesome interesting atmospheric processes over non-ulliform underlying surface, especially under the convective and unique weather conditions, such as sea-land circulation and the TIBL structure. The modelled results show good agreement with field measurement.

A new simulation model and its application in CO_2 short-circuiting transfer welding

A new simulation model of CO 2 short circuiting transfer welding may be employed to develop a new pattern of welding machine and to predict welding process parameters to obtain the optimum welding technology properties. In this paper, a new simulating model is developed according to the AWP (adapting welding physics process) waveform control method. Good agreement is shown between the predicted and experimentally determined results. The model will make an important promotion in the development of CO 2 arc welding technique.

AN INTEGRATION METHOD WITH FITTING CUBIC SPLINE FUNCTIONS TO A NUMERICAL MODEL OF 2ND-ORDER SPACE-TIME DIFFERENTIAL REMAINDER——FOR AN IDEAL GLOBAL SIMULATION CASE WITH PRIMITIVE ATMOSPHERIC EQUATIONS

In this paper,the forecasting equations of a 2nd-order space-time differential remainder are deduced from the Navier-Stokes primitive equations and Eulerian operator by Taylor-series expansion.Here we introduce a cubic spline numerical model(Spline Model for short),which is with a quasi-Lagrangian time-split integration scheme of fitting cubic spline/bicubic surface to all physical variable fields in the atmospheric equations on spherical discrete latitude-longitude mesh.A new algorithm of"fitting cubic spline—time step integration—fitting cubic spline—……"is developed to determine their first-and2nd-order derivatives and their upstream points for time discrete integral to the governing equations in Spline Model.And the cubic spline function and its mathematical polarities are also discussed to understand the Spline Model’s mathematical foundation of numerical analysis.It is pointed out that the Spline Model has mathematical laws of"convergence"of the cubic spline functions contracting to the original functions as well as its 1st-order and 2nd-order derivatives.The"optimality"of the 2nd-order derivative of the cubic spline functions is optimal approximation to that of the original functions.In addition,a Hermite bicubic patch is equivalent to operate on a grid for a 2nd-order derivative variable field.Besides,the slopes and curvatures of a central difference are identified respectively,with a smoothing coefficient of 1/3,three-point smoothing of that of a cubic spline.Then the slopes and curvatures of a central difference are calculated from the smoothing coefficient 1/3 and three-point smoothing of that of a cubic spline,respectively.Furthermore,a global simulation case of adiabatic,non-frictional and"incompressible"model atmosphere is shown with the quasi-Lagrangian time integration by using a global Spline Model,whose initial condition comes from the NCEP reanalysis data,along with quasi-uniform latitude-longitude grids and the so-called"shallow atmosphere"Navier-Stokes primitive equations in the spherical coordinates.The Spline Model,which adopted the Navier-Stokes primitive equations and quasi-Lagrangian time-split integration scheme,provides an initial ideal case of global atmospheric circulation.In addition,considering the essentially non-linear atmospheric motions,the Spline Model could judge reasonably well simple points of any smoothed variable field according to its fitting spline curvatures that must conform to its physical interpretation.

鄂尔多斯盆地铁边城地区长2油层组剩余油模拟

为了实现油田增储上产及老井挖潜的目标,提升剩余油资源开发潜力,通过岩心、薄片、电镜、物性、模拟方法系统的研究了鄂尔多斯盆地西北部姬塬油田铁边城地区长2段主力油层的剩余油分布特征。研究显示,长2_(1)^(3-2)和长2_(1)^(3-3)小层为主力产油层,平均厚度分别为12.2 m及11.1 m。目的层砂岩储层的孔隙度通常介于12%~18%,渗透率则通常低于8 mD。根据相控原则,建立了主力产层的物理属性模型及流体模型;进而,开展了剩余油分布数值模拟研究。通过基于实测产水及产油量约束的历史生产曲线拟合,获得了剩余油的纵横向分布结果。研究显示,剩余油分布受砂体边界、物性差异及注采关系的影响。剩余油整体上成片分布;但是,受油藏物性差异的影响,注水多呈不均匀受效,因而造成局部剩余油富集。剩余油主要分布在砂体边界处,这些区域无井网控制,因而水驱程度低,剩余油分布较多。受长期注采的影响,井间会形成高渗区,这些其余类似高速通道,会发生快速水淹,其周边则形成剩余油滞留区。可见,剩余油富集明显受微相、物性、注水及井网因素的控制。

O_(2)/CO_(2)气氛下催化裂化烟气循环再生系统模型

富氧燃烧和烟气循环再生技术可实现催化裂化(FCC)再生烟气中CO_(2)的富集。根据采用烟气循环再生的FCC单段再生、并列式两段再生和重叠式两段再生系统型式,基于烧焦动力学模型和充分烧焦设定,分别建立了再生系统模型,并对3种再生系统进行了模拟。结果表明,通过优化O_(2)流量、烟气循环流量等操作条件,单段再生系统烟气、重叠式两段再生系统烟气和并列式两段再生系统第二再生器烟气中CO_(2)体积分数可富集至95%以上,但并列式两段再生系统第一再生器烟气中CO_(2)体积分数难以富集至95%以上。通过再生系统模型可优化再生器操作,在达到较好再生效果的同时,实现CO_(2)的富集。

基于欧拉-欧拉方法的CO_(2)电解池水气传输特性

为研究CO_(2)电解还原过程中的水-气传输特性,基于欧拉-欧拉方法,建立CO_(2)电解池中多相传质过程与电化学相耦合的计算模型,搭建CO_(2)电解池试验测试平台,基于试验数据对仿真模型进行验证;在此基础上分别基于单通道模型和大尺寸单蛇形流场模型对电解池工作特性进行模拟分析。仿真结果表明:较大的水流速度可以加快生成气体的排出,利于催化层电化学反应进行;在大尺寸流场中,由于水排出不及时,有相当一部分水通过质子交换膜传递到阴极侧,导致阴极发生水淹,降低阴极侧液态水含量可在一定程度上改善阴极侧的气体传输;为避免阴极水量过多,应合理设计流场结构和供水供气策略。

Spatial Inhomogeneity of Atmospheric CO_(2) Concentration and Its Uncertainty in CMIP6 Earth System Models

This paper provides a systematic evaluation of the ability of 12 Earth System Models(ESMs)participating in the Coupled Model Intercomparison Project Phase 6(CMIP6)to simulate the spatial inhomogeneity of the atmospheric carbon dioxide(CO_(2))concentration.The multi-model ensemble mean(MME)can reasonably simulate the increasing trend of CO_(2) concentration from 1850 to 2014,compared with the observation data from the Scripps CO_(2) Program and CMIP6 prescribed data,and improves upon the CMIP5 MME CO_(2) concentration(which is overestimated after 1950).The growth rate of CO_(2) concentration in the northern hemisphere(NH)is higher than that in the southern hemisphere(SH),with the highest growth rate in the mid-latitudes of the NH.The MME can also reasonably simulate the seasonal amplitude of CO_(2) concentration,which is larger in the NH than in the SH and grows in amplitude after the 1950s(especially in the NH).Although the results of the MME are reasonable,there is a large spread among ESMs,and the difference between the ESMs increases with time.The MME results show that regions with relatively large CO_(2) concentrations(such as northern Russia,eastern China,Southeast Asia,the eastern United States,northern South America,and southern Africa)have greater seasonal variability and also exhibit a larger inter-model spread.Compared with CMIP5,the CMIP6 MME simulates an average spatial distribution of CO_(2) concentration that is much closer to the site observations,but the CMIP6-inter-model spread is larger.The inter-model differences of the annual means and seasonal cycles of atmospheric CO_(2) concentration are both attributed to the differences in natural sources and sinks of CO_(2) between the simulations.

Using TOUGH2 numerical simulation to analyse the geothermal formation in Guide basin,China

The Guide sedimentary basin is located in the northeastern part of Qinghai-Xizang Plateau,which is rich in geothermal resources.However,exploitation of the geothermal resources has so far been limited,because of limited understanding of the resources quantity and storage gained from scientific researches.In this study,using a typical cross section across the basin and taking into account its geothermal and geological conditions,a new waterheat coupled model was built and associated modelling was done by the software TOUGH2.During modelling process,the accuracy and applicability of the model was confirmed through the calibration of relevant parameters for modelling the heat and water transport and the formation of geothermal reservoir across the basin,with particular focus on the Neogene geothermal field.Results show that the groundwater that flows from the basin margins to the center is heated by the Neogene and Paleogene sedimentary rocks with high geothermal gradients.Since the east-west extending fault F1 is conductive,it acts as preferential flow paths which on one hand provide additional and rapid flows to the thermal reservoir;and on the other hand,cool down the thermal water to a certain extent due to the infiltration of shallower water sources in the vicinity of the fault.Furthermore,the estimated geothermal resources quantity is close to that of previous studies.In comparison with the Paleogene rock formations,the Neogene geothermal reservoir shows a better nature in terms of water content,aquifer permeability and resources exploitability,although the resource quantity of the Paleogene reservoir is considerable.

Two Improvements on Numerical Simulation of 2-DOF Vortex-Induced Vibration with Low Mass Ratio

Till now, there have been lots of researches on numerical simulation of vortex-induced vibration. Acceptable results have been obtained for fixed cylinders with low Reynolds number. However, for responses of 2-DOF vortex-induced vibration with low mass ratio, the accuracy is not satisfactory, especially for the maximum amplitudes. In Jauvtis and Williamson＇s work, the maximum amplitude of the cylinder with low mass ratio m＊=2.6 can reach as large as 1.5D to be called as the ＂super-upper branch＂, but from current literatures, few simulation results can achieve such value, even fail to capture the upper branch. Besides, it is found that the amplitude decays too fast in the lower branch with the RANS-based turbulence model. The reason is likely to be the defects of the turbulence model itself in the prediction of unsteady separated flows as well as the unreasonable setting of the numerical simulation parameters. Aiming at above issues, a modified turbulence model is proposed in this paper, and the effect of the acceleration of flow field on the response of vortex-induced vibration is studied based on OpenFOAM. By analyzing the responses of amplitude, phase and trajectory, frequency and vortex mode, it is proved that the vortex-induced vibration can be predicted accurately with the modified turbulence model under appropriate flow field acceleration.

Magnetic properties of La2CuMnO6 double perovskite ceramic investigated by Monte Carlo simulations

We present a theoretical study of the magnetic properties of the lanthanum copper manganate double perovskite La2CuMnO6 ceramic,using Monte Carlo simulations.We analyze and discuss the ground state phase diagrams in different planes to show the effect of every physical parameter.Based on the Monte Carlo simulations,which combine Metropolis algorithm and Ising model,we explore the thermal behavior of the total magnetization and susceptibility.We also present and discuss the influence of physical parameters such as the external magnetic field,the exchange coupling interactions between magnetic atoms,and the exchange magnetic field on the magnetization of the system.Moreover,the critical temperature of the system is about Tc=70 K,in agreement with the experimental value.Finally,the hysteresis loops of La2CuMnO6 are discussed.

压缩机透平分轴布置的超临界CO_(2)简单回热循环动态特性

超临界CO_(2)布雷顿循环发电系统配合高温颗粒储热系统,被认为是新一代光热发电机组的重要技术路线之一。深入研究超临界CO_(2)布雷顿循环动态特性,是实现新一代光热发电机组高效、灵活设计和运行的重要基础。该文以西安热工研究院有限公司耦合颗粒换热器的超临界CO_(2)布雷顿循环机组为对象,构建了动态仿真模型,并进行动态仿真计算。该机组采用透平压缩机分轴布置的形式。结果显示:相对于颗粒/循环冷却水入口温度阶跃变化的工况,系统在颗粒/循环冷却水流量阶跃变化工况中响应更快、能够更快地达到新的稳定状态。压缩机转速扰动对系统流量影响迅速且明显,压缩机转速调节可以作为系统流量控制的重要手段。透平在不同流量下最优转速不同,当透平转速变化后更接近最优转速时机组循环净效率增高,反之降低。

百年尺度不同区域地表气温对CO_(2)浓度非均匀动态分布敏感度的研究

地球系统模式结果表明大气CO_(2)浓度的快速增加是气候变化重要的原因之一。卫星资料分析结果表明,大气CO_(2)浓度并非均一的,而是有明显的区域差异,以人类活动为主的碳排放会影响这一区域差异。这种空间差异如何影响区域地表气温对CO_(2)的敏感度,需要进一步深入系统的研究,利用地球系统模式BNU-ESM(Earth System Model of Beijing Normal University)进行数值模拟,并与观测数据进行比较,结果表明:在试验模拟结果2°C阈值内,非均匀CO_(2)浓度试验的CO_(2)浓度增加阈值范围小于均匀CO_(2)浓度试验结果,偏少约为4.3 ppm(106)。在区域尺度上,中国地表气温对CO_(2)敏感度普遍低于美国、欧洲以及北半球平均水平,这表明CO_(2)浓度空间差异对地表气温的敏感度的影响存在明显区域差异,很可能是CO_(2)浓度辐射效应与气候系统反馈过程的共同作用结果,这需要进一步研究。非均匀CO_(2)浓度对地表气温敏感度影响将会对碳中和目标下未来碳汇潜力精准估算提供科学支持。

基于SMP2的导弹攻防对抗仿真系统研究

指出了当前基于HLA进行攻防对抗仿真系统开发存在的不足,提出了基于仿真模型可移植性标准(SMP2)标准进行攻防对抗仿真系统开发的思路。简要介绍了SMP2标准的顶层架构以及SMP2仿真系统的运行结构和开发过程。针对战略导弹突防仿真的应用需求,搭建了基于SMP2的战略导弹突防仿真系统软件体系结构,讨论了系统的模型框架以及关键功能的设计与实现。