共查询到20条相似文献，搜索用时 31 毫秒
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The dynamic finite element model (FEM) of a prestressed concrete continuous girder bridge (PCCGB), named Zhangjiagang river main bridge, was established and updated based on the results of field ambient modal testing using real-coded accelerating genetic algorithm (RAGA), which objective function was defined based on frequency index and correlation coefficient index for evaluating the updated FEM. The dynamic FEM of the bridge was updated based on seven experimental modal parameters. The prediction ability of the updated FEM were evaluated based on three experimental modal parameters. The updated results and prediction ability of updated FEMs indicated that they can reflect adequately the dynamic characteristics of actual PCCGB by using the above objective function and RAGA. 相似文献
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According to the analysis of existing test data, the stress influence coefficient and water-cement ratio influence coefficient in the existing concrete carbonation depth forecasting models are modified and improved. Based on the reliability analysis, the rule of deterioration life is presented. The analysis shows that the rate of carbonation of concrete is accelerated or restricted at the status of tensile or compressive stress, respectively. Especially with the increase of the level of tensile stress, the carbonation rate of concrete will become faster and faster. According to the results of reliability analysis, the relation between probability and reliability of the concrete deterioration is one-to-one corresponsive, meanwhile, the concrete cover thicknesses and stress levels have great influences on the durability life of concrete structures. And with the same reliability, the time of deterioration of concrete decreases with a higher stress levels and a less cover thickness. 相似文献
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Qian Jueshi Meng Zhiliang Zhang Xinyuan 《保鲜与加工》1999,(1):5-9
In order to improve carbonation resistance of high_addition flyash concrete,the grinding of flyash and additon of hydrated_lime in flyash concrete have been studied.It is shown that it is possible to improve the carbonation resistance of high_addition flyash concrete by using these methods without reducing its strength. 相似文献
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The carbonation of the concrete in the air is an unavoidable natural process,Itmakes the volume and strength of the concrete change and the alkality reduce,So the structure in-side concrete and the durability both become worse. The carbonation resistance of the autoclaved sil-icate concrete is tested by the means of speeding up the carbonation artificially and also with the ex-periment of the natural carbonation for 6 years. It is very good for recognizing it correctly andspreading.The carbonation of the new concrete material is discussed. 相似文献
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A radial basis function (RBF) neural network learning algorithm based on immune recognition was proposed to improve the low forecast precision and the slow convergence speed of such networks. In the algorithm, artificial immunity was used to determine the center and width parameters of the Gauss basis function. The recognized data were regarded as antigens and the compression mapping of antigens were taken as antibodies, i.e., the centers of the hidden layer. The recursion least square algorithm (RLS) was employed to determine the output layer weights. The algorithm improved the convergence speed and precision of the RBF neural networks. The model was applied to the blast furnace of a large iron and steel company. The results show that the model has forecast precision far superior to existing models and requires less training time than they do. 相似文献
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《保鲜与加工》2003,(10):156-158
In order to uncover the complex relation in the inventory data and lower the inventory level, based on the idea of black box method, all factors that influence demand are identified firstly. Then an initial forecast model of BP neural networks that adopt LM algorithm is established, and is trained using hospital inventory's history data. The interrelation's information of each factor that influences demand is stored in the link weights matrix W dispersedly. The final forecast model is obtained. We use the model to forecast the demand of medical equipment in Daping hospital. Based on it, the inventory cost is reduced enormously. The theory for the inventory system can be used to make management decision. 相似文献
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海上大风是海洋产业的重大灾害性天气,而延伸期预报是世界性难题。目前,延伸期预报主要分成动力延伸、低频振荡、经验波传播、数理统计、气候扰动分解和集合预报等6种方法,以动力延伸中的数值模式和低频振荡中的MJO监测诊断最为流行。随着大数据时代的到来,基于大数据分析,以数值预报产品为基础的集合预报成为未来业务发展的重点方向。这6种方法都可以用于海上大风等重大灾害性天气预报,许多学者尝试较多的是气候扰动分解、低频振荡中的低频天气图等方法中的溯源技术,通过找到源头,实现重大灾害性天气的延伸期预报。 相似文献
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山西省冬小麦主要病虫害气象等级预报模型 总被引：4，自引：1，他引：3
气象条件是影响农作物病虫害的主要因子,且与作物的发育期密切相关,特别是在特殊年份,如果模型所筛选的因子中较常年有明显的改变,预测结果与实际结果相差较大,因此各预测模型都具有一定的局限性。为提高数理统计预报的实用性,需要采用多年的历史资料,同时在实际工作中应采用尽量多的方法进行预测,以最大限度地获得较高的预测准确率。本文以山西冬小麦的主要病虫害（白粉病、条锈病、麦蜘蛛）为研究对象,研究其发生流行的气象条件预报指标,并建立山西省冬小麦主要病虫害发生的气象条件预测模型,进行山西省冬小麦主要病虫害发生的气象条件预测。通过历史资料进行回测验证,历史拟合准确率达到90%以上,说明应用该方法所建模型在一般年份可以进行冬小麦条锈病、白粉病、麦蜘蛛的预测。 相似文献
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Based on a series of recycle process, waste concrete can be made into fine recycled aggregate which can be used completely or partly to compound concrete as a substitute for natural sand. But the special properties of fine recycled aggregate make the performance of concrete with fine recycled aggregate different from normal concrete. Characteristics of fine recycled aggregate and its influence on physical and mechanical properties of concrete are studied. On this basis, the influence of fine recycled aggregate on gas permeation properties, chloride permeability, and carbonation resistance of concrete are also studied. It is found that fine recycled aggregate produces a lot of defects in crushing preparation. And the compressive strength, the chloride permeability and the carbonation resistance of the concrete with fine recycled aggregate as substitution show difference from that of normal concrete. 相似文献
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Su Zhifeng Yang Wenping Yang Zhenping Du Tianqing Hao Jiaomin Sun Min Gao Zhiqiang 《棉花学报》2015,27(5):435-444
为探求生土地当年最佳施肥方式,快速提高棉花地上部生产力并改良根干物质质量垂直分布,试验连续2年以黄土母质生土为供试土壤,采用根管土柱法,研究不同肥料(N,P,NPK,有机肥,不施肥对照(CK))、不同施肥深度(0~20 cm,40~60 cm,80~100 cm土层)对棉花(Gossypium hirsutum)茎叶干物质质量、棉铃干物质质量及根干物质质量垂直分布的影响。结果表明,所有处理中,以有机肥深施40~60 cm处理的茎叶和棉铃的干物质质量最大,其次为NPK肥深施40~60 cm处理,二者差异显著(P0.05);以含P肥深施40~60 cm处理的根干物质质量较大,且40 cm以下根层的分布比例较大;所有处理均以0~20 cm层的根分布比例最大,约占0~100 cm总根干物质质量的40%~80%。总的来看,当年生土地棉花冠￣根系统的最佳肥料运筹是有机肥深施40~60 cm。 相似文献
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雷暴大风、冰雹天气的预报方法研究 总被引：5，自引：5，他引：0
为了最大限度地减轻雷暴大风、冰雹天气造成的损失,提高这2种灾害性天气的预报预警能力,笔者在统计安徽省2000-2005年4-9月无雷暴、普通雷暴、强对流（雷暴大风、冰雹）样本的基础上,利用1×1格点NCEP资料计算了表征热力、动力、水汽条件的43个参数,对比分析了无雷暴、普通雷暴、强对流（雷暴大风、冰雹）时的物理量极值、归一化平均值等,并基于分析结果选取雷暴大风、冰雹的消空、预报指标,逐月逐时次的确定预报指标的阈值。最后,利用指标叠套法生成安徽省雷暴大风、冰雹天气潜势预报产品。用该方法对2007年的实时运行情况进行检验,2007年6-9月共有28个雷暴大风、冰雹过程,全部报出,空报9个过程,无漏报,过程TS为30.4%。从检验效果来看,指标叠加的数值越大,出现雷暴大风或冰雹的概率也就越大,对农业防灾减灾起到一定积极的作用。 相似文献
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为了给当地政府、农业部门、农户提供准确及时的玉米发育期预报,根据玉米日平均气温稳定通过10℃播种的温度指标,通过分析辽阳市1956—2010年日平均气温稳定通过10℃与5℃初日间隔日数和稳定通过5℃初日的相关性,利用日序与间隔日数建立回归方程,预测日平均气温稳定通过10℃初日,在此基础上做出玉米播种期预报;利用灯塔市农业气象观测站1981—2010年资料,分析玉米从播种到成熟各个发育期发育速度与气象条件的关系,经过对各时段的相关性检验,发现玉米从播种到成熟期间各发育期间隔日数与≥10℃活动积温相关性最好,从出苗到成熟玉米感温性、感光性都比较强,由此建立播种-开花及拔节-成熟的天数预报模型,预报玉米开花及成熟期。经检验,3款预报模型相关系数、复相关系数及F 值均达0.01显著水平,回代与实况值有着比较一致的变化趋势,回代和预报绝对误差(ABSE )和标准误差(RMSE )在2.0~4.3天,可以满足农业气象服务需要,具有推广应用价值。 相似文献
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基于RBF神经网络的蔬菜价格预报研究 总被引：3，自引：2，他引：1
准确预测农产品市场价格对于农户生产决策与政府调控等具有重要意义。针对蔬菜市场价格预报的复杂性,利用RBF神经网络的特性,应用2003-2007年的香菇市场价格数据建立蔬菜价格预报模型,并对RBF神经网络模型的参数选择进行分析。最后应用模型对2008-2009年的香菇市场价格数据进行预报,通过与BP神经网络模型预报结果进行比较,表明RBF神经网络模型具有更高的预报准确度。 相似文献
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为明确枣食芽象甲越冬幼虫的空间分布和抽样技术,为该虫预测预报和综合防治提供理论依据,应用8种聚集度指标、Taylor幂法则和Iwao线性回归分析法,对枣食芽象甲越冬幼虫在枣园土壤中的空间分布型和抽样技术进行研究。结果表明：枣食芽象甲越冬幼虫的空间分布呈聚集分布,种群分布的基本成分是个体群,且聚集是由环境因素或者自身的聚集习性引起的;根据Iwao m*-m关系的序贯抽样决策模型确定了枣食芽象甲越冬幼虫的序贯抽样模型和最适理论抽样公式;当枣食芽象甲幼虫防治阈值为30头/株,10株调查枣树虫口密度大于342头,则需采取措施及时进行防治。本研究建立的序贯抽样模型和最适理论抽样公式可用于该象甲越冬幼虫调查、预测预报和综合防治。 相似文献
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为实现气象预报要向精细化方向发展,为农业生产提供精细化服务的目的,实现为当地政府及农业部门指挥、指导农业生产提供更直观、可靠的细化到乡镇的玉米适宜播种分布情况,通过分析辽阳地区2010—2014 年24 个区域自动站4—5 月逐日平均气温与辽阳本站同期气温的关系,建立24 个回归预报模型,借助于雨量图制作软件利用模型做出的预报,将全地区划分出适宜播种、较适宜播种和不适宜播种3 个区域。经检验,24 个预报模型相关系数均达0.01 显著水平,回代与实况值变化趋势基本一致,回代和预报绝对误差(ABSE)和标准误差(RMSE)在0.2~0.7℃,可以用来预报24 个乡镇的日平均气温。利用雨量图制作软件绘制等值线图,方法简单易掌握,易于推广。 相似文献
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利用盘式吸渗仪确定土壤水力学参数研究进展 总被引：1，自引：0，他引：1
各种农业措施显著影响土壤的物理性质,特别是土壤水力学参数。随着计算机模型广泛用于土壤物质迁移的预测预报,准确确定土壤水力学参数成为一项重要的研究任务。盘式吸渗仪作为一种简便实用的仪器正被广泛用于田间土壤水力学参数的测定。国内外学者研究了稳态、瞬态和反推等方法,利用盘式吸渗仪来确定土壤近饱和导水率、吸渗率和水分特征曲线。同时该仪器可以用于田间测定土壤孔隙分布状况,以及两区模型中的参数。笔者对国内外有关盘式吸渗仪研究从相关理论和应用方面进展进行了综述,并对田间测定操作中注意的问题进行评述,指导田间试验以获得准确的测定数据。盘式吸渗仪在田间测定土壤孔隙,特别是大孔隙流方面有独特的优点,但是其并未在中国不同质地土壤上得以广泛应用。 相似文献
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This paper studies the hydrates and the characteristicsof micro-structure of concrete with gangue cement before and after carbonation under different curing conditions.It is compared with Portlandcement concrete,and the carbonate resistance of concrete with ganguecement is studied too. 相似文献