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1.
In order to meet the demand of large scale boiler design and operating optimization, this paper establishes the dynamic mathematic model for domestic 600MW subcritical pressure boiler. MMS software is adopted in the whole process from modeling to simulation. This software make process simple and quick. This model is based on modulariza- tion and the comprehensive physical and chemical process in boiler is considered. Simulation result shows that the re- sponses of this model under different disturbance are coincident to mechanics analysis. The simulation result under ste Pdisturbance can be used to analyze unit changes and provide some guide and it also can supply performance reference data to boiler design. 相似文献
2.
Models for Predicting Consequences of LNG Releases 总被引：1，自引：0，他引：1
The growth of LNG trades has grown dramatically around the world year by year. It has become one of the primary energy sources in imports of China, followed oil. Then, it comes to an important problem that how to use it safely. To resolve the potential releases of LNG and other problems involved in safety during storage and transport, computer models based CFD, such as MTB, DEGADIS, FEM3A are applied. By using small scale physical experiments for verification, economical and perfect results can be achieved, and the problems is avoided that traditional physical modeling on spot is hard to control and very expensive. Based the summary about the difficulties that the physical experiments contain, it is proposed that solving method is using ULS wind tunnel in the research of the new model FEM3A for more complex obstacle arrays and non-uniform terrain. A higher order turbulence closure model is given. 相似文献
3.
持续性温强和土壤水分对玉米发育进程的影响及其模拟 总被引：3，自引：0，他引：3
作物的发育进程对产量形成有重要影响,在作物生长模型中也起着时间指针的重要作用。但目前逐日累积温度的发育模式无法解释作物播期不同而成熟期差距很小或基本相同的现象;目前对土壤湿度影响作物发育进程的规律也不十分清楚,多数作物生长模型也未予考虑。本研究以华北夏玉米为研究对象,首先对几种常用的作物发育模式进行稳定性比较,然后再分别探讨持续性温度强度和土壤湿度对夏玉米发育进程的影响规律,并构造相关模式。结果表明,积温(TSUM)、发育单位(CHU)和热量单位(THU)等发育模式中以THU的稳定性最高。夏玉米发育进程不仅由累积温度或热量单位决定,而且受持续性温度强度（某一发育阶段的平均温度）的明显影响。平均温度较高时,完成该发育进程需要累积更多的温度。据此建立的模式对夏玉米分期播种的发育进程模拟有明显改善。土壤水分对夏玉米发育进程有明显影响,水分增加将促使夏玉米营养生长阶段的发育加速,导致抽雄期提前。由此建立的模式对区域上夏玉米发育进程的模拟有一定改善。 相似文献
4.
WANG Ke zhong 《保鲜与加工》2008,(5):42-46
Based on the large scale conceptual model theory of similar material, a physical model of metro station tunnel excavation was simulated. The excavation process of metro station tunnel between existing double tubes also was simulated. Ground settling, soil deformation and displacement of specific points around tunnels were studied. The influence of a cast in place pile on reducing soil displacement was simulated. The dynamic mechanical behavior and deformation laws of the soil were obtained along with some useful conclusions. The conclusions are beneficial for guiding the construction and expanded excavation of metro station spaces between existing double tubes. 相似文献
5.
We have proposed a new interpretation of fruit softening. This was accomplished by generating a hypothesis that probabilities of decay of fruit structure obey the Weibull probabilistic model that has been used in the field of reliability engineering. The elasticity of individual kiwifruit after harvest was continually and nondestructively measured until decomposition by using a laser Doppler vibrometer. The obtained decreasing pattern of elasticity of individual fruit was complex, diverse, and inhomogeneous. Nonetheless, it was satisfactorily explained by a tandem combination of 2 Weibull models involving 4 types of parameters: “shape” related to probability; “scale,” to velocity of decay; “location,” to time lag; and “mixing ratio,” to contribution of the 2 models. Averages of location, shape, and mixing ratio parameters obtained by the measurement of 33 fruit were significantly different between the 2 models, but the scale parameter was not. The results suggested that the complex softening patterns of individual kiwifruit could be described using the tandem model of Weibull distribution, and that the softening process of kiwifruit consisted of at least 2 independent decay phases that are characterized by 2 of 5 parameters: location and mixing ratio. Commencement of the first decay phase could be caused by ethylene treatment after harvest, and the second one spontaneously triggered after a certain time lag. 相似文献
6.
《Netherlands Journal of Sea Research》1995,33(3-4):271-299
The rationale is given of how the gross physical features of the circulation and the stratification of the North Sea have been aggregated for inclusion in the ecosystem box model ERSEM. As the ecosystem dynamics are to a large extent determined by small-scale physical events, the ecosystem model is forced with the circulation of a specific year rather than using the long-term mean circulation field. Especially the vertical exchange processes have been explicitly included, because the primary production strongly depends on them. Simulations with a general circulation model (GCM), forced by three-hourly meteorological fields, have been utilized to derive daily horizontal transport values driving ERSEM on boxes of sizes of a few 100 km. The daily vertical transports across a fixed 30-m interface provide the necessary short-term event character of the vertical exchange.For the years 1988 and 1989 the properties of the hydrodynamic flow fields are presented in terms of trajectories of the flow, thermocline depths, of water budgets, flushing times and diffusion rates. The results of the standard simulation with ERSEM show that the daily variability of the circulation, being smoothed by the box integration procedure, is transferred to the chemical and biological state variables to a very limited degree only. 相似文献
7.
作物气孔导度模型研究进展及应用现状 总被引：1，自引：0，他引：1
旨在为作物耗水和碳水交换相关研究的模型选择提供理论指导,本研究归纳了气孔导度对单一和综合环境因子的响应情况;对现有气孔导度模型进行了分类和比较,包括基于Jarvis模型建立和改进的经验模型、基于BWB模型建立和改进的半经验模型、基于ABA调控建立和改进的模型、基于保卫细胞膨压控制理论建立和改进的模型;并概述了气孔导度模型在作物水分利用研究领域的应用,以叶片气孔导度和冠层导度的定量关系为切入点建立多尺度联合的机理模型将是未来作物耗水尺度拓展研究的热点。 相似文献
8.
This paper mainly analyzes the theory of light-rail. A few optimal fare-pricing models is established based on different objects. The authors combine the benefits of Society, Orbit company and the passengers to establish an AHP model for assessing the fare-pricing models. Finally, they establish an optimal fare-pricing scheme with light-rail. This model is applied to light-rail line 2 in Chongqing. A scale ticket price scheme of this object is given. 相似文献
9.
总结归纳江苏养殖粪污处理典型模式,为区域尺度发展种养结合循环农业,实现农业废弃物资源化统筹协调高效利用,提供模式参考及案件借鉴。以政府主导型的武进区农业废弃物综合治理中心（礼嘉站）为例,介绍种养结合模式背景及构架,分析关键技术组成,剖析经济、生态及社会效益,阐明运行机制。结果表明：收集分散服务体系建设形成了养殖业、种植业、第三方服务组织、政府及社会群众之间的利益共同体,破解了小型养殖粪污无害化处理与资源化利用的瓶颈难题,促进了“乡村振兴”的“环境美、农民富”进程。江苏探索的政府主导型养殖粪污集中处理模式,对构建和发展区域尺度种养结合循环农业更具代表性及示范价值。 相似文献
10.
This paper presents a fading memory based least squares identification method. Compared with the traditional system identification method applied on small scale unmanned helicopter, this method can reduce processing load and improve processing stability during identification. ARMAX model and MIMO model of small scale unmanned helicopter are sonstructed in this way and then do simulation on the models. The result shows that model of MIMO is more precise on representing the helicopter system. 相似文献
11.
Resources for crop production are often scarce in smallholder farming systems in the tropics, particularly in sub-Saharan Africa (SSA). Decisions on the allocation of such resources are often made at farm rather than at field plot scale. To handle the uncertainty caused by both lack of data and imperfect knowledge inherent to these agricultural systems, we developed a dynamic summary model of the soil–crop system that captures essential interactions determining the short- and long-term crop productivity, while keeping a degree of simplicity that allows its parameterisation, use and dissemination in the tropics. Generic, summary functions describing crop productivity may suffice for addressing questions concerning trade-offs on resource allocation at farm scale. Such functions can be derived from empirical (historical) data or, when they involve potential or water-limited crop yields, can be generated using process-based, detailed crop simulation models. This paper describes the approach to simulating crop productivity implemented in the model FIELD (Field-scale Interactions, use Efficiencies and Long-Term soil fertility Development), based on the availability of light, water, nitrogen, phosphorus and potassium, and the interactions between these factors. We describe how these interactions are simulated and use examples from case studies in African farming systems to illustrate the use of detailed crop models to generate summary functions and the ability of FIELD to capture long-term trends in soil C and crop yields, crop responses to applied nutrients across heterogeneous smallholder farms and the implications of overlooking the effects of intra-seasonal rainfall variability in the model. An example is presented that evaluates the sensitivity of the model to resource allocation decisions when operating (linked to livestock and household models) at farm scale. Further, we discuss the assessment of model performance, going beyond the calculation of simple statistics to compare simulated and observed results to include broader criteria such as model applicability. In data-scarce environments such as SSA, uncertainty in parameter values constrains the performance of detailed process-based models, often forcing model users to ‘guess’ (or set to default values) parameters that are seldom measured in practice. The choice of model depends on its suitability and appropriateness to analyse the relevant scale for the question addressed. Simpler yet dynamic models of the various subsystems (crop, soil, livestock, manure) may prove more robust than detailed, process-based models when analysing farm scale questions on system design and resource allocation in SSA. 相似文献
12.
1/20 scale model test and full scale field test were carried out to study the critical velocity for fire ventilation in horizontal tunnels. Combined with the test results, small scale test results by Jae and full scale test and simulation by Hu, a semi empirical model was developed to predict the longitudinal critical velocity for tunnel fire ventilation. Compared with the predictions of the proposed model and other models using air as fire source, it was found that the predictions by Wu and Barker was underestimates. 相似文献
13.
Based on electro-hydraulic power pulsed technology and the characteristic of plasma piston expansion theory, the mathematical model of plasma piston is established and the hydrodynamic equations of fluid in discharge channel are induced. The nondimensional differential equations of hydrodynamic characteristics in cylindrical sym-metry discharge channel are analyzed. The relationships between the discharge time and hydrodynamic characteristics of discharge channel, the electricity parameters of discharge circuit is found by solving the differential equations, which predict the pressure, radius, and ratio of expansion in discharge channel. 相似文献
14.
《European Journal of Agronomy》2009,30(4):175-183
The ability to deliver wheat grain with a specific protein content is a major determinant of the profitability of wheat grain production. Various crop models have been developed to predict yield and grain protein content on a field scale. They can be used to predict each year, before harvest, the yields and grain protein contents of the different fields in a collecting area, leading to an optimization of the grading process into low and high protein standards. Indicators have been developed for nitrogen management at the field scale. They can be used to predict grain quality because grain protein content depends strongly on the crop nitrogen uptake during the vegetative growth of the wheat crop. The aim of this study was to evaluate the accuracy of two indicators, nitrogen nutrition index and chlorophyll content of leaves (in SPAD units), and of two models for categorizing fields according to their grain protein contents. A data set including field measurements over 3 years was used to estimate the sensitivity and specificity of the models and indicators using the receiver operating characteristic evaluation procedure. High values of sensitivity and specificity were obtained for the two indicators, and decision thresholds leading to low false negative and false positive proportions were identified. Nitrogen nutrition index showed the best results for the three grain protein content thresholds considered. Conversely, sensitivity and specificity values obtained for the two models were low. Combining model predictions and indicator values did not give better discrimination than the use of a single indicator. 相似文献
15.
Some schemes that are used to improve the digging machine are introduced in this paper.The merits and faults and the feasibility of these schemes are compared.The scheme with three hydrodynamic shockers and three steel beams to improve the digging machine is discussed.This scheme can solve the problems that probably occur in the digging process.An example is introduced to explain how to determine the parameter of the hydrodynamic shocker.In this paper a new and effective scheme to improve the digging machine is presented. 相似文献
16.
Several previous general lumped parameter model of radioisotope concentration field in groundwater systems, such as EM, PM and EPM model, are introduced, and the ambiguous physical meaning of response functions within these models are pointed out.And then, based on the radioactive decay principles and mass conservation principle, assuming that 1)the fluid system is in steady state, 2)infiltration rate is constant, and 3)the horizontal transport of water flow rate is constant, a general lumped parameter model of radioisotope concentration-fluid coupled field in groundwater systems is deduced under these conditions, that is, Panel model.Compared with the above mentioned models, this new model is built on a clear physical basis with a definite physical meaning of each parameter, so that it could make accurate interpretations on radioisotope data of the relevant water flow system, and provide more precise mathematical foundation on quantitative analysis and simulation of radioisotope concentration. 相似文献
17.
作物蒸散不同时空尺度模型及尺度转换方法研究进展 总被引：1，自引：1，他引：0
为了通过比较经济的成本灵活获取不同尺度的蒸散量,回顾了作物蒸散研究的历史发展,重点评述了作物蒸散不同时空尺度模型及尺度转换方法研究现状,在此基础上,预测了作物蒸散的发展趋势：以精确的点尺度作物蒸散模型为基础,结合遥感数据、数字高程模型和GIS技术建立新颖的空间插值方法,从而实现作物蒸散的空间尺度转换;通过建立精确的基于遥感数据的作物系数模型,利用基于作物系数的时间尺度转换方法,实现作物蒸散时间尺度扩展;基于上述时空尺度转换方法,建立综合性的,面向业务化运行的系统作物蒸散模型。 相似文献
18.
国内众多专家学者对确定城市合理用地规模的方法上进行了多角度探索,本研究有益借鉴这些成果,采用多元线性回归分析和BP神经网络2种较成熟的预测模型,选取城市建设用地面积、地区生产总值、固定资产投资、城市人口数、年末道路面积、城市园林绿地面积、商品房平均售价为观测指标,分析预测河北省邢台市的建设用地规模。结果表明,预测结果并不理想,预测值与实际值的误差始终存在,并随时间推移不断扩大,深入分析预测结果产生偏差的原因,即忽视了非理性因素对城市建设用地规模的影响。建议引入行为金融学理论,将研究对象具化到个人,研究土地市场管理者和投资者在决策过程中的认知、行为偏差,分析城市建设用地面积持续蔓延的非理性动力,应用行为组合理论和资产定价模型对传统研究范式进行有益补充和修正,进而更科学地把握城市用地空间形成机制及演变规律。 相似文献
19.
基于江西省双季稻区10个县30个乡镇农户、合作社以及农机大市场的调查数据,通过对合作社的两种典型模式（合作模式和服务模式）的研究及合作社农户和散户的对比分析,探索合作社对江西双季稻机插推广的促进作用。研究结果表明:合作社农户的成本要低于散户,收益要高于散户,合作社的生产效果比散户的要好;合作社农户的年龄比散户的年龄要低,文化、土地规模、资金要高于散户;合作社农户的机插比例高于散户;目前江西合作社机插典型模式中比较受欢迎的模式是农机大户和种田大户合作模式及“订单式”服务模式;未来种田大户、农机大户和养殖大户是发展江西农民合作生产的主要对象,重点发展的模式是合作社提供水稻生产全程社会化服务模式。 相似文献
20.
随着经济的发展和消费者需求的增加,养殖业从传统的养殖模式逐步过渡到现代的规模养殖。养殖业技术不断进步,养殖规模不断壮大,这给养殖业的投资者带来了发展的机遇,但是同样也带来了一定的风险,怎么使得养殖企业的风险最小是当今研究的一个重点。文章首先对养殖业的风险类型以及产生的原因进行研究,然后提出规模养殖的贝叶斯决策模型,阐述模型的建立和运用过程,利用贝叶斯理论对于规模养殖存在的风险进行定性和定量的分析,进而运用一个决策案例来阐述贝叶斯模型决策的过程。案例的结果表明贝叶斯决策模型可以很好地解决决策风险问题,对于是否需要获取补充信息也做出了明确的判断,同时对于预测情形下的各种方案也做出了风险计算,从而直观地反映决策方案是否符合风险最小,收益最大原则。文中案例是规模养殖业决策风险中的一个问题,类似风险决策问题可以根据决策模型来解决。文章最后对各种风险问题提出决策建议,以期为养殖业的风险决策提供一个有效的方法。 相似文献