Environmental Implication of Subaqueous Lava Flows from A Continental Large Igneous Province: Examples from the Moroccan Central Atlantic Magmatic Province(CAMP)

The Early Jurassic volcanic sequence of the Central Atlantic Magmatic Province(CAMP)of Morocco is classically subdivided into four stratigraphic units:the Lower,Middle,Upper and Recurrent Formations separated

LARGE-EDDY SIMULATION OF STRATIFIED CHANNEL FLOW

An investigation of large-eddy simulation(LES) for turbulent channel flow with buoyancy effects was performed by solving the resolved incompressible Navier-Stokes equations under the Boussinesq approximation. The Smagorinsky eddy-viscosity model and Yoshizawa eddy-viscosity model were used to describe the unresolved subgrid scale (SGS) fluctuations respectively After some numerical testing, the latter was further simplified so that if can be used in the dynamic model closure. A LES code was developed for parallel computations by using the parallel technique, and aas run on the Dawn-1000 parallel computer. To demonstrate the viability and accuracy of the code, our results are compared with and found in good agreement with available LES results.

An improved large eddy simulation of two-phase flows in a pump impeller

An improved large eddy simulation using a dynamic second-order sub-grid-scale （SGS） stress model has been developed to model the governing equations of dense turbulent particle-liquid two-phase flows in a rotating coordinate system, and continuity is conserved by a mass-weighted method to solve the filtered governing equations. In the cur- rent second-order SGS model, the SGS stress is a function of both the resolved strain-rate and rotation-rate tensors, and the model parameters are obtained from the dimensional consistency and the invariants of the strain-rate and the rotation-rate tensors. In the numerical calculation, the finite volume method is used to discretize the governing equations with a staggered grid system. The SIMPLEC algorithm is applied for the solution of the discretized governing equations. Body- fitted coordinates are used to simulate the two-phase flows in complex geometries. Finally the second-order dynamic SGS model is successfully applied to simulate the dense turbu-lent particle-liquid two-phase flows in a centrifugal impeller. The predicted pressure and velocity distributions are in good agreement with experimental results.

A LARGE EDDY SIMULATION OF THE NEAR WAKE OF A CIRCULAR CYLINDER

Viscous flow around a circular cylinder at a subcritical Reynolds number is investigated using a large eddy simulation (LES) coupled with the Smagorinsky subgrid-scale (SGS) model. A fractional-step method with a second-order in time and a combined finite-difference/spectral approximations are used to solve the filtered three-dimensional incompressible Navier-Stokes equations. Calculations have been performed with and without the SGS model. Turbulence statistical behaviors and flow structures in the near wake of the cylinder are studied. Some calculated results, including the lift and drag coefficients, shedding frequency, peak Reynolds stresses, and time-average velocity profile, are in good agreement with the experimental and computational data, which shows that the Smagorinsky model can reasonably predict the global features of the flow and some turbulent statistical behaviors.

A Nonlinear Sub-grid Scale Model for Compressible Turbulent Flow

The governing equations for large eddy simulation （LES） are obtained by filtering the Navier-Stokes （N-S） equations with standard （non-Favre filtering） spatial filter function. The filtered scale stress due to the standard filtering is then reconstructed by using the Taylor series expansion. The loss of information due to truncating the expansion up to the first derivative term is modeled by a dynamic nonlinear model （DNM）, which is free from any empirical constant and wall damping function. The DNM avoids the singularity of the model and shows good local stability. Unlike the conventional dynamic Smagorinsky model （DSM）, the DNM does not require the plane averaging and reduces the computational cost. The turbulent flow over a double ellipsoid for Reynolds number of 4.25 × 10^6 and Mach number of 8.02 is simulated numerically to validate the proposed approach. The results are compared with experiment data, as well as the data of Reynolds averaged numerical simulation （RANS）.

Environmental impacts of a large-scale incinerator with mixed MSW of high water content from a LCA perspective

Large-scale incinerators are applied widely as a result of the heavy burden of municipal solid waste（MSW） generated, while strong opposition is arising from the public living nearby. A large-scale working incineration plant of 1500 ton/day was chosen for evaluation using life cycle assessment. It was found that the corresponding human toxicity impacts via soil（HTs）, human toxicity impacts via water（HTw） and human toxicity impacts via air（HTa）categories are 0.213, 2.171, and 0.012 personal equivalents（PE）, and global warming（GW100）and nutrient enrichment（NE） impacts are 0.002 and 0.001 PE per ton of waste burned for this plant. Heavy metals in flue gas, such as Hg and Pb, are the two dominant contributors to the toxicity impact categories, and energy recovery could reduce the GW100 and NE greatly. The corresponding HTs, HTw and HTa decrease to 0.087, 0.911 and 0.008 PE, and GW100 turns into savings of- 0.007 PE due to the increase of the heating value from 3935 to5811 k J/kg, if a trommel screener of 40 mm mesh size is used to pre-separate MSW. MSW sorting and the reduction of water content by physical pressure might be two promising pre-treatment methods to improve the combustion performance, and the application of stricter standards for leachate discharge and the flue gas purification process are two critical factors for improvement of the environmental profile identified in this work.

DAFT:一种OpenFlow大规模流表区分存储与加速查找架构

软件定义网络作为一种数据转发与逻辑控制相解耦的创新网络范式,当采用OpenFlow协议进行大规模部署时,其数据平面的流表规模急剧增大,对OpenFlow交换机的流表存储资源和分组转发性能提出了严峻的挑战.对此,本文构建了一种OpenFlow大规模流表区分存储与加速查找架构DAFT.该架构根据流量分布特性将OpenFlow网络流区分为重要流和次要流,进而采用TCAM和SRAM分别存储其标识字段,并采用DRAM单独存储其内容字段,有效缓解OpenFlow流表存储资源紧张问题.针对重要流/次要流区分问题,在分析传统大象流/老鼠流区分方法的基础上,基于OpenFlow网络流的包成批特性,提出活跃流/空闲流区分方法,以提高TCAM命中率.针对SRAM流表查找性能瓶颈,利用掩码访问不均匀的特点,采用"往前移1"启发法自适应调整掩码顺序,以减少后续数据包的掩码失败探测次数;利用掩码探测多数会失败的特点,借助计数型布鲁姆过滤器预测元组查找失败结果,从而绕过对应的子流表遍历过程.最后,借助骨干网络流量样本,对本文所提DAFT流表架构的查找性能进行实验评估.实验结果表明:DAFT流表架构的TCAM命中率、SRAM平均查找长度和平均流表访问时间均明显优于传统的大象流/老鼠流架构,且稳定性强,有效提升了OpenFlow交换机的分组转发性能.

Mercury flows in large-scale gold production and implications for Hg pollution control

Large-scale gold production（LSGP） is one of the five convention-related atmospheric mercury（Hg） emission sources in the Minamata Convention on Mercury. However, field experiments on Hg flows of the whole process of LSGP are limited. To identify the atmospheric Hg emission points and understand Hg emission characteristics of LSGP, Hg flows in two gold smelters were studied. Overall atmospheric Hg emissions accounted for 10%–17% of total Hg outputs and the Hg emission factors for all processes were 7.6–9.6 kg/ton. There were three dominant atmospheric Hg emission points in the studied gold smelters, including the exhaust gas of the roasting process, exhaust gas from the environmental fog collection stack and exhaust gas from the converter of the refining process. Atmospheric Hg emissions from the roasting process only accounted for 16%–29% of total emissions and the rest were emitted from the refining process. The overall Hg speciation profile（gaseous elemental Hg/gaseous oxidized Hg/particulate-bound Hg） for LSGP was 34.1/57.1/8.8. The dominant Hg output byproducts included waste acid, sulfuric acid and cyanide leaching residue. Total Hg outputs from these three byproducts were 80% in smelter A and 84% in smelter B. Our study indicated that previous atmospheric Hg emissions from large-scale gold production might have been overestimated.Hg emission control in LSGP is not especially urgent in China compared to other significant emission sources（e.g., cement plants）. Instead, LSGP is a potential Hg release source due to the high Hg output proportions to acid and sludge.

Effects of the computational domain on the secondary flow in turbulent plane Couette flow

A series of direct numerical simulations of the fully developed plane Couette flow at a Reynolds number of 6000（based on the relative wall speed and half the channel height h） with different streamwise and spanwise lengths are conducted to investigate the effects of the computational box sizes on the secondary flow（SF）. Our focuses are the number of counter-rotating vortex pairs and its relationship to the statistics of the mean flow and the SF in the small and moderate computational box sizes. Our results show that the number of vortex pairs is sensitive to the computational box size, and so are the slope parameter, the rate of the turbulent kinetic energy contributed by the SF, and the ratio of the kinetic energy of the SF to the total kinetic energy. However, the averaged spanwise width of each counter-rotating vortex pair in the plane Couette flow is found, for the first time, within 4（1 ± 0.25）h despite the domain sizes.

LES prediction of space-time correlations in turbulent shear flows

We compare the space-time correlations calculated from direct numerical simulation （DNS） and large-eddy simulation （LES） of turbulent channel flows. It is found from the comparisons that the LES with an eddy-viscosity subgrid scale （SGS） model over-predicts the space-time corre- lations than the DNS. The overpredictions are further quantified by the integral scales of directional correlations and convection velocities. A physical argument for the overpre- diction is provided that the eddy-viscosity SGS model alone does not includes the backscatter effects although it correctly represents the energy dissipations of SGS motions. This argument is confirmed by the recently developed elliptic model for space-time correlations in turbulent shear flows. It suggests that enstrophy is crucial to the LES prediction of spacetime correlations. The random forcing models and stochastic SGS models are proposed to overcome the overpredictions on space-time correlations.

Moldflow软件在汽车大型注塑模设计中的应用

针对大型注塑模的结构特点,以某汽车仪表板注塑件为例,应用Moldflow软件,模拟分析阀式控制的流动过程,优化浇注系统设计和成型工艺参数,为注塑模具设计和试模时工艺参数的设定提供了依据,并获得了高质量的产品。

Multi-layer Tectonic Model for Intraplate Deformation and Plastic-Flow Network in the Asian Continental Lithosphere

In a large area of the east—central Asian continent there is a unified seismic network system composed of two families of large—seismic belts that intersect conjugately. Such a seismic network in the middle—upper crust is actually a response to the plastic flow network in the lower lithosphere including the lower crust and lithospheric mantle. The existence of the unified plastic flow system confirms that the driving force for intraplate tectonic deformation results mainly from the compression of the India plate, while the long-range transmission of the force is carried out chiefly by means of plastic flow. The plastic flow network has a control over the intraplate tectonic deformation.

Probabilistic load flow method considering large-scale wind power integration

The increasing penetration of wind power brings great uncertainties into power systems,which poses challenges to system planning and operation.This paper proposes a novel probabilistic load flow(PLF)method based on clustering technique to handle large fluctuations from large-scale wind power integration.The traditional cumulant method(CM)for PLF is based on the linearization of load flow equations around the operation point,therefore resulting in significant errors when input random variables have large fluctuations.In the proposed method,the samples of wind power and loads are first generated by the inverse Nataf transformation and then clustered using an improved K-means algorithm to obtain input variable samples with small variances in each cluster.With such pre-processing,the cumulant method can be applied within each cluster to calculate cumulants of output random variables with improved accuracy.The results obtained in each cluster are combined according to the law of total probability to calculate the final cumulants of output random variables for the whole samples.The proposed method is validated on modified IEEE 9-bus and 118-bus test achieve a better performance with the consideration of both traditional CM,2 m+1 point estimate method(PEM),Monte Carlo simulation(MCS)and Latin hypercube sampling(LHS)based MCS,the proposed method can achieve a better performance with the consideration of bothcomputational efficiency and accuracy.

A numerical study on flame and large-scale flow structures in bluff-body stabilized flames

Large Eddy Simulations(LES) in conjunction with the Flamelet Progress Variable(FPV) approach have been performed to investigate the flame and large-scale flow structures in the bluff-body stabilized non-premixed flames, HM1 and HM3. The validity of the numerical methods is first verified by comparing the predicted velocity and composition fields with experimental measurements. Then the evolution of the flame and large-scale flow structures is analyzed when the flames approach blow-off. The analysis of instantaneous and statistical data indicates that there exists a shift of the control mechanism in the recirculation zone in the two flames. In the recirculation zone, HM1 flame is mainly controlled by the mixing effect and ignition mainly occurs in the outer shear layer. In HM3 flame, both the chemical reactions and mixing are important in the recirculation zone. The Proper Orthogonal Decomposition(POD) results show that the fluctuations in the outer shear layer are more intense in HM1, while the flow structures are more obvious in the outer vortex structure in HM3, due to the different control mechanism in the recirculation zone.It further shows that the flow structures in HM1 spread larger in the intense mixing zone due to higher temperature and less extinction.

An improved dynamic subgrid-scale model and its application to large eddy simulation of rotating channel flows

A new dynamic subgrid-scale (SGS) model, which is proved to satisfy the principle of asymptotic material frame indifference (AMFI) for rotating turbulence, is proposed based on physical and mathematical analysis. Comparison with direct numerical simulation (DNS) results verifies that the new SGS model is effective for large eddy simulation (LES) on rotating turbulent flow. The SGS model is then applied to the LES of the spanwise rotating turbulent channel flow to investigate the rotation effect on turbulence characteristics, budget terms in the transport equations of resolved Reynolds stresses, and flow structures near the wall regions of the rotating channel.

NUMERICAL STUDY OF AN OSCILLATORY TURBULENT FLOW OVER A FLAT PLATE

Oscillatory turbulent flow over a flat plate was studied by using large eddy simulation (LES) and Reynolds-average Navier-Stokes (RANS) methods. A dynamic subgrid-scale model was employed in LES and Saffman's turbulence model was used in RANS. The flow behaviors were discussed for the accelerating and decelerating phases during the oscillating cycle. The friction force on the wall and its phase shift from laminar to turbulent regime were also investigated for different Reynolds numbers. (Edited author abstract) 11 Refs.

Generalized Mean-Flow Theory of Wave-Current-BottomInteractions

The interaction between waves, currents and bottoms in estuarine and coastal regions is ubiquitious, in particular the dynamic mechanism of waves on large-scale slowly varying currents. The wave action concept may be extended and applicated to the study of the mechanism. Considering the effects of moving bottoms and starting from the Navier-Stokes equation of motion of a vinous fluid including the Coriolis force, a generalized mean-flow medel theory for the nearshore region, that is, a set of mean-flow equations and their generalized wave action equation involving the three new kinds of actions termed respectively as the current wave action, the bottom wave action and the dissipative wave action which can be applied to arbitrary depth over moving bottoms and ambient currents with a typical vertical structure, is developed by vertical integration and time-averaglng over a wave peried, thus extending the classical concept, wave action, from the ideal averaged flow conservative system to the real averaged flow dissipative dynamical system, and having a large range of application.

LES Investigation of Drag-Reducing Mechanism of Turbulent Channel Flow with Surfactant Additives

In this work,the drag-reducing mechanism of high-Reynoldsnumber turbulent channel flow with surfactant additives is investigated by using large eddy simulation(LES)method.An N-parallel finitely extensible nonlinear elastic model with Peterlin’s approximation(FENE-P)is used to describe the rheological behaviors of non-Newtonian fluid with surfactant.To close the filtered LES equations,a hybrid subgrid scale(SGS)model coupling the spatial filter and temporal filter is applied to compute the subgrid stress and other subfilter terms.The finite difference method and projection algorithm are adopted to solve the LES governing equations.To validate the correctness of our LES method and in-house code,the particle image velocimetry(PIV)experiment is carried out and representative measured results are compared with LES results in detail.Then the flow characteristics and drag-reducing mechanism of turbulent channel flow with surfactant are investigated from the perspective of drag reduction rate,mean velocity,fluctuation of deformation rate,shear stress,transport and dissipation of turbulent kinetic energy,and turbulent coherent structures.This research can shed a light on the application of turbulent drag reduction technique in district heating,petroleum transport,etc.

A STUDY ON PHYSICAL MECHANISM OF INTERANNUAL VARIATIONS OF LARGE-SCALE FLOW PATTERNS

The thermal forcings of annual and interannual periodic variations are introduced into the barotropic vorticity equation,by using low order spectral model of the equation,more than 40 numerical experiments whose integration time is larger than 100 model years are performed in order to investigate variations of large-scale flow patterns arising from both external interannual thermal forcing and internal dynamical processes.In certain parametric range,when the fre- quency of the forcing term with interannual period equals to the frequency which is created by the internal dynamical processes alone,the amplitude of interannual variations of flow patterns increases obviously,and the period becomes double.In other parametric range,the amplitude of interannual variations of flow patterns shows abrupt changes and other nonlinear behavior,along with gradual changes of interannual forcing parameters.

An improved dynamic subgrid-scale model and its application to large eddy simulation of stratified channel flows

In the present paper, a new dynamic subgrid-scale (SGS) model of turbulent stress and heat flux for stratified shear flow is proposed. Based on our calculated results of stratified channel flow, the dynamic subgrid-scale model developed in this paper is shown to be effective for large eddy simulation (LES) of stratified turbulent shear flows. The new SGS model is then applied to the LES of the stratified turbulent channel flow to investigate the coupled shear and buoyancy effects on the behavior of turbulent statistics, turbulent heat transfer and flow structures at different Richardson numbers.