A comparison of the performance of N simulation models in the prediction of Nmin on farmers' fields in the spring

The performance of three different models, which simulate changes in the inorganic N content of the soil, was evaluated in respect of their ability to predict N_min content in the spring under cereal crops. The models of British, Dutch and German origin, were tested using data from farmers' fields supplied by 70 farmers over two growing seasons in FRG. The models were run between harvest of the previous crop and spring of the following year, and predictions of N_min in the spring compared to soil measurements. The performance of the models was assessed by counting the number of cases in which predictions agreed within 10 or 20 kg (N) ha^–1 of the measurements. Predictions were less than ± 10 kg (N) ha^–1 of measured values in only 30–44% and 28–55% of cases in 1988 and 1989, respectively. Predictions were less than ± 20 kg (N) ha^–1 of measured values in 62–70% and 68–82% of cases in 1988 and 1989, respectively. Predictions in 1989 were better because the initial N_min content in the autumn was included in the model input. None of the models tested had been designed to use input data of the type available to farmers. It is concluded that, at present, the results are too variable for any of the models to be used with confidence as tools to aid in N fertilizer recommendations.     

Simulation of nitrogen dynamics and biomass production in winter wheat using the Danish simulation model DAISY

A dynamic simulation model for the soil plant system is described. The model includes a number of main modules, viz., a hydrological model including a submodel for soil water dynamics, a soil temperature model, a soil nitrogen model including a submodel for soil organic matter dynamics, and a crop model including a submodel for nitrogen uptake. The soil part of the model has a one-dimensional vertical structure. The soil profile is divided into layers on the basis of physical and chemical soil characteristics. The simulation model was used to simulate soil nitrogen dynamics and biomass production in winter wheat grown at two locations at various levels of nitrogen fertilization. The simulated results were compared to experimental data including concentration of inorganic nitrogen in soil, crop yield, and nitrogen accumulated in the aboveground part of the crop. Based on this validation it is concluded that the overall performance of the model is satisfactory although some minor adjustments of the model may prove to be necessary.     

面向水泥分解炉工况预测的仿真代理 模型构建研究

水泥分解炉在实际运行中存在部分关键工况参数难以通过测量取样直接获取的问题,目前主流的解决方法是直接数值模拟法,该方法存在响应时间长,不能并行计算多工况的缺点。本文提出构建基于Kriging模型的分解炉工况参数仿真代理模型,将分解炉分解率作为预测目标,对影响因子筛选并构建优化拉丁超立方抽样空间,通过有限元仿真计算获取响应值;利用Kriging插值模型对仿真数据进行拟合,得到Kriging仿真代理模型。模型检验结果表明,预测的[R2]达到了0.917 8,代理模型预测结果与有限元仿真结果具有很好的一致性,可以实现对分解炉分解率的在线预测。     

微椭圆孔轴面织构油封密封性能仿真模拟及机理探究

提出轴面微椭圆孔织构油封运行时的理论分析模型,通过仿真模拟得到微孔结构参数对其性能的影响规律。结果表明：微椭圆孔轴面织构的润滑减摩性主要体现在相对运动的过程中微织构会使液膜产生显著的动压润滑效应,致使界面间形成非接触式密封和润滑状态;在研究的工况条件下,密封可靠性在微椭圆孔的方向性方面有所体现,合适的方向性能使流体在孔区流程变长,且其受边界阻挠在孔区一侧动压增强另一侧形成空化区,低压的空化区会快速抽吸即将泄漏出的流体从而提高密封可靠性,故而通过改变织构结构尺寸可控制油封的性能。为提高油封的寿命并降低泄漏率,在研究范围内,选用半轴比γ≥0.8（在面积比固定不变的情况下）、孔深h₁=1.5~4μm和旋转角α₁=0°~45°或175°~215°的轴面微椭圆孔织构较为合适。     

Development of nitrogen fertilizer recommendations for arable crops in the Netherlands in relation to nitrate leaching

In the Netherlands, current nitrogen fertilizer recommendations for arable crops are based on the amount of soil mineral nitrogen in early spring. The larger the amount of soil mineral nitrogen, the lower the recommended application rate of fertilizer nitrogen. A more refined method is to draw up a balance sheet in which the nitrogen requirement of the crop is given on the one side and the contributions of fertilizer nitrogen, soil mineral nitrogen, and the amount of nitrogen mineralized during the growing period on the other. The most refined method of nitrogen fertilizer recommendation is the use of a simulation model that predicts the daily crop nitrogen requirement and nitrogen supply to the crop from various pools during the growing period. A simulation model thus adds the time element to nitrogen fertilizer recommendations. Moreover, in contrast with the other two methods, a simulation model allows identification of environmental side-effects of nitrogen fertilizer application.The current Dutch nitrogen fertilizer recommendations aim at predicting the economically optimum application rate of fertilizer nitrogen. From the environmental point of view it is interesting to know how much soil mineral nitrogen has accumulated in the soil at harvest, because this nitrogen is a potential loss to the environment through nitrate leaching during the subsequent winter period. If the economically optimum application rate of fertilizer nitrogen is applied to arable crops, it is unlikely that soil mineral nitrogen accumulates, except in the case of potatoes. Model calculations have shown that accumulation of soil mineral nitrogen after potatoes can be prevented when the recommended nitrogen application rate is reduced by 25%. In that case tuber yield is reduced by only 2%.     

凝胶型连结料体系黏度模型的参数拟合

采用有机铝型螯合物凝胶剂、松香改性酚醛树脂、亚麻仁油和高沸点煤油制备胶印油墨用连结料,研究了亚麻仁油、高沸点煤油和凝胶剂的用量对连结料流变性能的影响。根据流变实验测定值,准确地拟合出该连结料体系的一系列黏度模型。根据该黏度模型,能够在改变原料配比、温度与剪切速率的条件下,相当精确地描述连结料体系的黏度。因此,若能利用汇编语言设计出连结料的配方计算软件,则可根据连结料体系中各因素变化来直接调节连结料的流变参数,达到快速调整连结料配方、缩短生产工艺时间、稳定连结料质量、适应高速印刷油墨要求的目的。     

动力锂离子电池仿真模型研究进展

锂离子电池作为新能源电动汽车优异的动力来源受到广泛关注,获得高性能的锂离子电池对电动汽车的发展至关重要。数值仿真技术突破了传统实验的限制而极大地促进了锂离子电池的研究工作。高效、实用的仿真模型可以将多种化学反应及物理场相互耦合,预测多种因素对于电池各种性能的影响,使仿真结果尽可能地接近真实情况。本文主要介绍了仿真研究的优势和重要意义,分别从电池热模型、电学特性模型、老化模型等出发,比较了众多仿真模型针对锂离子电池性能的仿真结果,总结不同模型的优势以及存在的薄弱环节,并提出仿真研究以后的发展趋势为：①从机理出发,研究多物理场相互作用关系,实现多场耦合;②从模型和算法入手,扩大模型的研究范围,兼顾简化模型和提高精确度;③从电池本身入手,注重电池材料的性能改善以及成组方式和结构优化。     

马脊梁镜煤有机质大分子模型构建及分子模拟

运用工业分析、元素分析及¹³C核磁共振波谱、X射线光电子能谱和傅里叶变换红外光谱分析,构建了马脊梁镜煤有机质大分子结构模型。在该结构模型中,芳环桥碳与周碳之比为0.24,芳环的类型以蒽、萘为主;脂肪碳原子主要是甲基、亚甲基和次甲基,氧接脂碳含量最少;每个大分子平均含氧原子22个,氧原子存在于酚羟基、羰基、羧基和醚氧中,个数分别为9、4、3和3;氮原子以一个吡啶和一个吡咯的方式存在。该结构模型的平均分子式为C₂₂₂H₁₆₈O₂₂N₂,分子量为3212。对所建分子模型分别进行了核磁共振碳谱、红外光谱及密度的模拟计算,并与测试结果进行对比验证。结果表明,所建模型能够较好地反映马脊梁镜煤有机质的大分子结构特征。     

A structured model for the simulation of bioreactors under transient conditions

Modeling the transient behavior of continuous culture is of primary importance for the scale‐up of biological processes. Spatial heterogeneities increase with the reactor size and micro‐organisms have to cope with a fluctuating environment along their trajectories within the bioreactor. In this article, a structured model for bioreactions expressed in terms of biological extensive variables is proposed. A biological variable is introduced to calculate the growth rate of the population. The value is updated on the basis of the difference between the composition in the liquid and biotic phase. The structured model is able to predict the transient behavior of different continuous cultures subject to various drastic perturbations. This performance is obtained with a minimum increase in the standard unstructured model complexity (one additional time constant). In the final part, the consequences of decoupling the growth rate from the substrate uptake rate are discussed. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

基于多尺度模型的MIP提升管反应历程数值模拟

MIP(maximizing iso-paraffins process)工艺采用两个反应器串联技术,可有效改善汽油质量。MIP反应器的冷态模拟虽能揭示反应器内的流动行为及几何结构的影响,但无法考虑反应引发的变化。为更准确地揭示该反应器中的油气及颗粒运动行为,尝试了三维瞬态反应模拟。模拟采用双流体模型结合十二集总反应动力学模型,并在相间动量传递模型和传热模型中考虑了多尺度结构的影响,然后与基于均匀分布的传统模型作对比。结果表明,相比于传统模型,多尺度模型能较准确预测二反段内的流动结构、颗粒浓度以及温度分布。在预测产率方面,两种模型所得结果类似,都对油浆和柴油的预测较好,对液化气和干气的预测偏差较大。这说明,仅在动量传递及传热模型中考虑多尺度结构的影响是不够的。     

基于优化算法对活性污泥数学模型稳态仿真

活性污泥数学模型No.1(ASM1)涉及的参数多,而且数学模型是非线性的,求解困难.采用非线性优化的方法仿真ASM1,把仿真结果和基准值做了比较.仿真结果证明非线性优化仿真方法可行.     

CFD simulation of the effect of rain on the performance of horizontal wind turbines

Wind turbine power output is influenced by environmental conditions, including rain. Therefore, a better understanding of the effect of rain on the performance of wind turbines is necessary. Our coupled Lagrangian‐Eulerian multiphase computational fluid dynamics model was modified to more accurately simulate the momentum transfer during water film formation on the airfoils of a horizontal‐axis turbine and the performance loss caused by the rainwater film on the National Renewable Energy Laboratory (NREL) turbine performance. To obtain three‐dimensional numerical simulation of the wind turbine in manageable computational time, simplifying assumptions were made and the validity of these assumptions was verified by simulating the flow over the S809 airfoil of the NREL turbine. In a dry environment, simulation of turbine power output agreed well with NREL experimental data. Our multiphase model showed that the rain film accumulation and flow on the surface of the turbine airfoil reduces the power output of the turbine. © 2017 American Institute of Chemical Engineers AIChE J, 63: 5375–5383, 2017     

搅拌釜三维流场的雷诺应力模型数值模拟

引言 近年来,雷诺平均Navier-Stokes方程及其封闭方程组成的湍流模型在应用于搅拌釜复杂湍流现象的模拟上取得了成功,主要是采用标准k-ε[1]、RNG k-ε[2]等模型.     

Some results of nitrogen simulations with the model ANIMO

Simulation of the nitrogen behavior in the soil and the nitrogen uptake by winter wheat was performed using the model ANIMO. As input for the model ANIMO simulations of the hydrological conditions in the soil crop ecosystem were executed with the model SWATRE. Compared with measured data the simulation of nitrogen uptake by the crop was satisfactory. The simulation of mineral nitrogen in the soil agreed reasonably well with measured data for one of the experiments used for the analysis. The agreement was less for experiments with additional fertilizer applications in May and June.     

A molecular thermodynamic approach to the prediction of phase equilibria in reservoir simulation

Highly asymmetric molecules interacting during miscible-gas processes of oil recovery are responsible for the form of the reservoir fluid phase diagrams, from which feasible displacement conditions can be chosen. In order to fit the expermental fluid phase behavior, current reservoir models employ classical equations of state which cannot easily account for the polydisperse and asymmetric nature of such systems. Using a continuous thermodynamics extension of the Simplified Perturbed Hard-Chain Theory (SPHCT) equation of state of Kim et al. (1986), an alternative molecular method for representing these equilibria in reservoir-fluid systems is presented. The approach yields results which compare well with both experimental data and classical calculation procedures.     

基于Euler多相流模型的卧螺离心机速度场数值模拟与分析

应用计算流体力学软件Fluent,基于Euler多相流模型,在多重参考系坐标下,选用RNG k-ε湍流模型,对卧螺离心机内部的三维速度场进行了数值模拟和分析。结果表明：当液体进入转鼓后,对沉降分离起主要作用的周向速度迅速增大,经过较短的距离即可获得稳定的流动状态,且沿转鼓轴向变化较小;轴向速度沿径向的梯度在转鼓柱段较小,而在锥段较大,且在靠近转鼓的区域,锥段的轴向速度比柱段的大;径向速度复杂多变,无明显规律,流动受几何结构的影响很大。     

基于二维Ising模型及Monte - Carlo模拟的锰氧化物Griffiths相研究

在对锰氧化物磁性质实验研究的基础上,利用二维Ising模型及Monte - Carlo方法模拟存在非Ising自旋掺杂系统的磁性质.模拟结果表明,对非Ising自旋系统进行部分掺杂将导致系统的磁性质背离居里外斯定律,出现Griffiths相,通过对非Ising格点紧邻格点自旋大小的统计平均值进行计算,分析了非Ising...     

管道渗流对表层土壤影响的数值模拟

采用有限容积法建立埋地管道泄漏多孔介质流固耦合相变数学模型,对油品管道下侧泄漏进行压力场和体积分数的数值模拟。研究表明管道泄漏后,压力对于表层土的影响极小,可以忽略不计。体积分数经过一定时间后,等值线形成一个正苹果形。由于重力作用y轴比x轴扩散快,之后油品最外层等值线到达表层土下缘,油品开始渗入表层土,密集的等值线继续向上扩散,当等值线前锋到到表层土上缘时外界就会发现有泄漏现象发生,但是最大等值线前锋并没有到达表层土。当表层区域都向表层有油品输出,并且比较密集的等值线前锋已经处在表层土,这时地表应该会出现油品液体的流动。再经过一段时间,外层等值线到达土壤最下缘,这就意味着开始有油品开始污染地下水。