离散零空间算法在机织物仿真中的应用

针对机织物卡尔丹角多体模型维数较高,计算效率不理想的问题,提出采用离散零空间算法降低多体动力学方程维数,减少计算复杂度和约束违约所导致的数值漂移.首先结合离散零空间等效变换消去拉格朗日乘子项,然后进行结点参数化,实现两次系统降维,提高机织物仿真速度.通过KES剪切试验与仿真,验证了上述算法应用的可行性.通过仿真计算复杂度及效率特征指标对比,反映出优化方程的降维优势和计算高效,尤其适用于大型织物仿真.     

基于多重网格的地表水文与二维水动力动态双向耦合模型研究

针对流域洪涝模拟模型的计算精度、格式稳定性及计算效率等问题,本文提出基于多重网格技术的地表水文与二维水动力动态双向耦合模型(M-DBCM)。地表水文模型采用非线性水库法模拟降雨产流和径流;二维水动力模型采用浅水方程模拟洪水演进过程。采用不同分辨率的网格划分计算区域,在粗网格区域采用地表水文模型模拟降雨径流过程;在细网格区域采用二维水动力模型模拟洪涝积水区的水流运动。地表水文和二维水动力模型通过内部耦合移动界面(Coupling Moving Interface, CMI)实现无缝连接,保证通过CMI的水量和动量等通量守恒,提高模型的模拟精度。采用时间显式格式同时求解地表水文和水动力模型,在不同区域采用不同的计算时间步长,以提高模型的计算效率。通过典型案例验证本文构建的耦合模型的性能,结果表明本文提出的动态双向耦合模型能够在保证模拟精度的同时提高计算效率。     

斜板沉淀池前配水渠的数值模拟及结构优化

针对配水渠出水优化措施单一、优化效果欠佳的问题,运用CFD软件,采用Realizable k-ε湍流模型对其流速场进行数值模拟,探究了进口宽度（b）和配水渠宽度（B）变化时出水均匀度最优的配水渠长度（L）,并优化了挡墙在双段配水渠中的最佳位置。结果表明：配水渠进口集中主流在池内流域空间的扩散程度是出水均匀度的主要影响因素;当b在1 200~1 600 mm范围时,L取1 750~2 250 mm时的出水均匀度最优,若b大于1 600 mm,最优的L值须适当增加,但不应大于3 000 mm;当B为3 900 mm时,L最佳取值为1 750~2 250 mm,当B为5 300或6 700 mm时,最佳的L值应增加500 mm左右;采用双段配水渠时,挡墙位置应设在进口侧,而不应在配水渠的中间位置。该研究可为配水渠的设计提供一定的理论指导。     

大宁调蓄水库蓄水后生态环境效益分析

南水北调工程的建成通水,改变了北京城市供水格局,给北京带来了巨大的效益,生态环境效益就是其中重要一环。分析北京市南水北调配套工程生态环境效益的组成,科学地计算和评估生态效益,对于未来北京市南水北调配套工程效益的发挥、工程的运行管理、首都水务事业的发展有着重要意义,大宁调蓄水库是北京市南水北调配套工程之一,经计算,大宁调蓄水库蓄水后生态环境总效益为34176.29万元。计算方法也可为类似工程生态环境效益的估算提供参考。     

Effects of expanding zone parameters of vacuum dust suction mouth on flow simulation results

Based on the parametric analysis of the expanding zone of the vacuum dust suction mouth, the flow in the vacuum dust suction mouth was simulated by computational fluid dynamics （CFD） software, Fluent. The effects of the expanding zone parameters on flow simulation were analyzed. The results show that simulation effects depend on threshold values of the expanding zone parameters of the dust suction mouth, and the threshold values of the expanding zone can be obtained according to the different structures of the vacuum dust suction mouth and be selected as the geometric parameters in calculating, and also corners of the expanding zone make unobvious difference in calculation accuracy and in computational efficiency compared with no corner. The simulation results provide practical guidance to the flow simulation on the dust suction mouth.     

广告语言含蓄美——委婉语在广告英语中的应用

在商品经济高度发达的今天,广告已成了我们生活中密不可分的一个重要组成部分。为了能够用有限的篇幅去表达无限的广告内容,同时也避免给消费者带来负面影响,广告商就会绞尽脑汁想尽一切办法去吸引消费者的眼球,在一定程度上追求广告的含蓄美就显得尤为重要,而含蓄美的一个重要变现方式便是委婉语的使用,其婉转、间接的表达方式在很大程度上增添了广告英语的魅力,生动形象,越来越得到大家的认可。     

Molecular dynamics simulations of enantiomeric separations as an interfacial process in HPLC

Since chromatographic separation is a dynamic process, with the interactions between the drug and the chiral stationary phase mediated by the solvent, no single interacting structure, such as could be found by minimizing the energy, could possibly describe and account for the ratio of residence times in the chromatographic column for the enantiomeric pair. We describe the use of explicit-solvent fully atomistic molecular dynamics simulations, permitting all the interactions between the atoms constituting the chiral stationary phase, solvent molecules and the drug molecule. This allows us to better understand the molecular dynamic chiral recognition that provides the discrimination, which results in the separation of enantiomers by high performance liquid chromatography. It also provides a means of predicting, for a given set of conditions, which enantiomer elutes first and an estimate of the expected separation factor. In this review, we consider the use of molecular dynamics toward this understanding and prediction.     

微反应器中费托合成的研究进展

目前费托合成常用的固定床、浆态床和流化床三种反应器存在不同程度的传质和传热问题,同时反应物/产物与催化剂难以分离,而微反应器因其可在接近等温和很小压降条件下进行反应,从而有望改善费托合成的反应性能,提高所用催化剂的活性和选择性。本文首先介绍了微反应器的结构和特性,然后从催化剂种类及其在微反应器中颗粒装填式和器壁涂覆式两种形式简述了微反应器中费托合成的实验研究,并从计算流体力学和动力学研究等方面简述了微反应器中费托合成的模拟计算。     

A computational fluid dynamic analysis of gas and particle flow in flame spraying

The flame spraying process, which is a common industrial thermal spraying application, has been analyzed by means of three-dimensional computational fluid dynamics (CFD) simulations. The process used at the Volvo Aero Corporation for the coating of fan and compressor housings has been modeled. The process uses the Metco 6P torch (Metco, Westbury, NY), which ejects a mixture of acetylene and oxygen at high speed through a ring of 16 orifices to form the flame. A stream of argon gas flowing through an orifice in the center of the ring carries a powder of nickel-covered bentonite through the flame to the spray substrate. The torch is cooled by a flow of air through an outer ring of 9 orifices. The simulation emulated reality closely by including the individual inlets for fuel, cooling air, and injected particles. The gas combustion was simulated as a turbulent, multicomponent chemically reacting flow. The standard, two-equation k-ε turbulence model was used. The chemical reaction rates appeared as source terms in the species transport equations. They were computed from the contributions of the Arrhenius rate expressions and the Magnussen and Hjertager eddy dissipation model. The first simulations included several intermediate chemical substances whose predicted concentration agreed favorably with measurements. Later, more simplified simulations incorporated only the global chemical reaction involving the initial and the final products, with corrections to the thermal properties being made to account for the missing intermediaries. The gas velocity and temperature fields predicted by the later simulations compared satisfactorily to those predicted by the earlier, more elaborate, ones. Therefore, the final simulations, which incorporated injected particles, were conducted employing the simplified model with only the global reaction. An in-house finite difference code was developed to calculate particle properties. Allowance was made for elliptical shapes, phase changes, and internal heat transfer with regard to the composite material. The particle velocities and temperatures predicted by the final simulations compared fairly well with experimental results obtained with the optical DPV2000 system.     

Influence of process parameters on the deposition footprint in plasma-spray coating

This paper presents an investigation of the influence of plasma spray process conditions on the in-flight particle behavior and their cumulative deposition to form a coating on the substrate. Three-dimensional computational fluid dynamics (CFD) analyses were performed to model the in-flight particle behavior in the plasma-spray process and their deposition on the substrate. The plasma spray was modeled as a jet issuing from the torch nozzle through the electrical heating of the arc gas. In the model, particles were injected into the plasma jet where they acquired heat and momentum from the plasma, some got melted and droplets were formed. By means of a droplet splatting model, the particle in-flight data generated by the CFD analyses were further processed to build up an imaginary three-dimensional deposition profile on a flat stationary substrate. It is found that the powder carrier gas flow rate influences the particle distribution on the substrate by imparting an injection momentum to the particles that were directed radially into the plasma jet in a direction perpendicular to the plasma jet. The larger sized particles will acquire higher injection momentum compared with the smaller sized particles. This causes particle distribution at the substrate surface that is elliptical in shape with the major axis of ellipse parallel to the particle injection port axis as illustrated in Fig. 1. Larger particles tend to congregate at the lower part of the ellipse, due to their greater momentum. The distribution of particle size, temperature, velocity, and count distribution at the substrate was analyzed. Further, based on the size and the computed particle temperature, velocity histories, and the impact sites on the substrate, the data were processed to build up a deposition profile with the Pasandideh-Fard model. The shapes of deposition profiles were found to be strongly driven by the segregation effect.