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本文推导了随机载荷下的疲劳损伤计算公式。数值计算结果表明：Ｐ．Ｈ．Ｗｉｒｓｃｈｉｎｇ给出的公式在宽带情况下与实际情况不符；Ｇ．Ｃｈａｕｄｈｕｒｙ给出的公式在窄带情况下与实际不符；本文绘出的公式不仅适合于窄带，也适合于具有各种不同带宽的宽带随机载荷。 相似文献
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随机波浪作用下海洋平台主动控制的时滞补偿研究 总被引：1，自引：0，他引：1
基于预测控制理论，研究了适用于海洋平台的时滞补偿控制算法。该方法借助于随机波浪力的近似公式和卡尔曼滤波原理，推导出了随机波浪力向前一步预测公式，同时采用卡尔曼滤波方程，实现了对状态向量向前一步预测。利用随机波浪力及状态向量的实时在线预测公式，推导出最优控制力向前一步预测的表达式。在此基础上，发展了不仅适用于反馈控制系统而且适用于前馈-反馈控制系统的时滞补偿算法。采用一典型海洋平台为数值算例，计算结果表明，该方法在一定时滞范围内对海洋平台主动控制中时滞的补偿效果是显著的。 相似文献
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本文在线性波理论下，从计算孤立小桩柱上随机波浪力的Ｍｏｒｉｓｏｎ公式出发，通过对波浪力的概率密度的推导和分析，提出了一个新的线性化的Ｍｏｒｉｓｏｎ公式，该公式与已在工程上广泛使用的Ｂｏｒｇｍａｎ１９６７年提出的线性化的Ｍｏｒｉｓｏｎ公式在对照力的线性化上略有不同，由这个公式计算的小桩柱上的阻力是按Ｂｏｒｇｍａｎ线性化的Ｍｏｒｉｓｏｎ公式进行计算所得结果的１．０８倍，但按这个新的线性化的Ｍｏｒｉｓｏ 相似文献
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本文基于实际金融问题,提出并进一步研究一类不确定模型下的倒向双重随机递归最优控制问题。首先提出在该模型中,代价泛函由sup■定义,其中■是由一组双重倒向随机微分方程的解组成的集合,再利用先验估计、线性化方法、It■公式等方法,推导出该最优控制问题的最大值原理,进而最终给出该问题最优控制的必要条件和充分条件。 相似文献
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海杂波具有非线性、非平稳和时变特性,多重分形测度分析是对物理系统局部奇异性的一个完整描述。本文根据海杂波电磁散射的经典模型——随机游走模型,利用随机微分理论对海杂波的物理特性进行了系统地建模分析。建立了描述海杂波电磁散射时变特性的随机微分方程,利用Itô公式得到了海杂波散射信号幅度和相位的扩散过程模型,并利用多重分形谱分析了该模型的奇异性。为了验证其准确性,与加拿大McMaster大学IPIX雷达实测海杂波数据的多重分形谱进行对比,实验结果表明两者完全一致,从而表明基于随机游走的随机微分模型是描述海杂波动力学机理的有效算法。 相似文献
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目的：研究川芎对D-半乳糖衰老模型小鼠抗衰老的作用机制。方法：将50只小鼠随机分为正常对照组10只和造模组40只,采用颈背部皮下注射D-半乳糖溶液的方法建立小鼠衰老模型,再将其分为衰老模型组及川芎低、中、高剂量组,每组各10只。药物干预50 d后检测小鼠脑组织中的超氧化物歧化酶（SOD）、谷胱甘肽过氧化物酶（GSH-Px）、丙二醛（MDA）、单胺氧化酶（MAO）。结果：与正常对照组比较,衰老模型组脑组织中SOD、GSH-Px含量降低,MDA、MAO含量升高,差异均有统计学意义（P＜0.05）;与衰老模型组比较,川芎低、中、高剂量组SOD、GSH-Px含量增加,MDA、MAO含量降低,差异均有统计学意义（P＜0.05）。结论：川芎可增加脑组织中SOD、GSH-Px含量,降低MDA、MAO含量,具有良好的延缓衰老的作用。 相似文献
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计算孤立小桩柱上随机波浪力的一个线性化的Morison公式 总被引：2，自引：0，他引：2
本文在线性波理论下，从计算孤立小桩柱上随机波浪力的Ｍｏｒｉｓｏｎ公式出发，通过对波浪力的概率密度的推导和分析，提出了一个新的线性化的Ｍｏｒｉｓｏｎ公嵤健８霉接胍言诠こ躺瞎惴菏褂玫模拢铮颍纾恚幔睿保梗叮纺晏岢龅南咝曰模停铮颍椋螅铮罟綅在对阻力的线性化上略有不同，由这个公式计算的小桩柱上的阻力是按Ｂｏｒｇｍａｎ线嵭曰模停铮颍椋螅铮罟浇屑扑闼媒峁模保埃副叮凑飧鲂碌南咝曰模停铮颍椋螅铮顛公式计算的随机波浪力的方差与直接利用Ｍｏｒｉｓｏｎ公式进行计算的结果是完全相同嵉模闹懈龅睦砺鄯治龊褪导扑憬峁砻鳎旱弊枇ο灾保晌颐翘岢龅募埃拢铮颍纾恚幔罡龅南咝曰模停铮颍椋螅铮罟降玫降男∽闲±刍怕氏碌乃婊ɡ藣力，均比直接由Ｍｏｒｉｓｏｎ公式进行计算得到的结果偏小，但按我们给出的线牲化的崳停铮颍椋螅铮罟降玫降慕峁劝矗拢铮颍纾恚幔畹南咝曰模停铮颍椋螅铮罟降玫降慕峁鼚接近于直接由Ｍｏｒｉｓｏｎ公式给出的结果。 相似文献
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本文研究了一类有脉冲影响的随机Nicholson果蝇模型,应用Lyapunov泛函、It■公式及某些不等式技巧给出了描述该模型方程的全局均方指数最终有界的充分性条件,并估计了指数收敛率和最终的一个界。进一步,给出了实例及仿真模拟,说明了本文所得结论的有效性。 相似文献
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目的：观察血府逐瘀汤加减治疗小儿过敏性紫癜的临床疗效。方法：将96例过敏性紫癜患儿随机分为治疗组和对照组，每组各48例。对照组采用常规西药治疗，治疗组在对照组治疗基础上加用血府逐瘀汤加减治疗。结果：总有效率治疗组为87.50%，对照组为70.84%，组间比较，差异有统计学意义（P＜0.05）；2组主要症状缓解率比较，差异有统计学意义（P＜0.05）；治疗组D-二聚体水平下降优于对照组（P＜0.05）。结论：在西药常规治疗基础上联用血府逐瘀汤治疗小儿过敏性紫癜疗效优于单纯西药治疗。 相似文献
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准确预测波浪作用下沿岸输沙率是沙质海岸研究领域的重要科学问题。根据数十年来国内外沿岸输沙率公式的研究进展,按研究方法对各项成果进行分类,并兼顾时间逻辑,回顾了各研究方法的发展历程及其代表性成果。对各项成果的理论基础、考虑因素、资料来源等方面进行了探讨,并采用现场原型沙、室内原型沙和室内轻质沙等实测资料,对国内外常用公式的预测准确性进行了检验。结果表明,孙林云公式与各项实测资料的吻合程度最高,在众多沿岸输沙率公式中具有明显的先进性。在此基础上,对未来可进一步深化研究的方向作出了展望。 相似文献
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Paul C. Liu 《Ocean Engineering》1987,14(1)
This paper presents an objective assessment of three published wave spectrum formulas for the shallow sea. It compares wave spectra estimated by these formulas with those calculated from actual field measurements made in Lake Erie during 1981 in depths ranging from 1.4 to 14.0 m. The results show that the models each have various degrees of effectiveness and applicability. The choice of which model to use may depend upon the availability of input parameters, and is still basically subjective. The models specifically developed for the shallow depth are found to be less effective. The form of spectral representation may remain similar at all depths, with depth affecting only the wave parameters that characterize the spectrum form. 相似文献
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When a ship model test is performed in a tank, particularly when the tank is small and the ship model is relatively large, the blockage effect will inevitably occur. With increased ship model scale and speed, the blockage effect becomes more obvious and must be corrected. In this study, the KRISO 3600 TEU Container Ship(KCS) is taken as a model and computational fluid dynamics techniques and ship resistance tests are applied to explore the mechanism and correction method of the blockage effect. By considering the degrees of freedom of the sinkage and trim, the resistance of the ship model is calculated in the infinite domain and for blockage ratios of 1.5%, 1.8%, 2.2%, and3.0%. Through analysis of the free surface, pressure distribution, and flow field around the ship model, the action law of the blockage effect is studied. The Scott formula and mean flow correction formula based on the average cross sectional area are recommended as the main correction methods, and these formulas are improved using a factor for the return flow velocity correction based on comparison of the modified results given by different formulas. This modification method is verified by resistance test data obtained from three ship models with different scale ratios. 相似文献
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Numerical experiments are used to assess the potential benefit of the assimilation of tropospheric and stratospheric observations on mesospheric prediction. A simulated atmosphere, taken as truth, is created using the Canadian Middle Atmosphere Model (CMAM). The truth is sampled at the locations of the measurements from the actual observing system to produce observations, which are then assimilated with the CMAM-DAS (Data Assimilation System). Obtained forecasts are compared with the truth, and error statistics are calculated. An assessment based on predictability shows that upward propagation of information resulting from the assimilation of tropospheric and stratospheric observations improves the mesosphere in the largest scales (with horizontal wavenumbers less than approximately 10). At the same time, the principal inability of the system to predict mesospheric small scales is demonstrated. 相似文献
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Derivation of unified wave overtopping formulas for seawalls with smooth,impermeable surfaces based on selected CLASH datasets 总被引：1，自引：0，他引：1
A set of unified formulas for prediction of the mean rate of wave overtopping at coastal structures with smooth, impermeable surfaces have been derived through the analysis of the selected CLASH datasets. The mean wave overtopping rate is expressed as the function of the significant wave height at the structural toe and the relative freeboard. The formulas are applicable for both vertical walls and inclined seawalls with smooth transition between them. The formulas are simple but cover the full range of water depth from the shoreline to deep water. The effects of the toe depth and the seabed slope on wave overtopping rate are duly incorporated in the formulas. Prediction performance of the new formulas is better than the EurOtop formulas for both vertical walls and inclined seawalls. 相似文献
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Predicting the stability of armor blocks of breakwaters and revetments is a very important issue in coastal and ocean engineering. Recently, soft computing tools such as artificial neural networks and fuzzy logic have been used to predict the stability number of armor blocks. However, these tools are not as transparent as empirical formulas. This study presents another soft computing approach, i.e. model trees for predicting the stability number of armor blocks. The main advantage of model trees is that, unlike the other data learning tools, they are easier to use and more importantly they represent understandable mathematical rules. A total of 579 experimental test data from Van der Meer 1988 are used for developing the model. The conventional governing parameters were selected as the input variables and the obtained results were compared with those of measurements, empirical and soft computing models. Using statistical measures, it was shown that the developed models are more accurate than previous empirical and soft computing models. Furthermore, some simple rules are given for armor blocks’ design. 相似文献
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Jin Weiliang Zhu Yuming Li Linpu Associate Professor Dr. -Eng. Zhejiang University Hangzhou
Engineer Metallurgical Building Design Research Institute Beijing
Associate Professor Dalian University of Technology Dalian 《中国海洋工程》1993,(4)
- Based on the Mohr-Coulomb failure principle and Rankine's theory, the laterally loaded pile ultimate resistance formulas of sand and soft clay proposed by Reese and Matlock respectively are discussed in this paper. The authors put forward the modified ultimate resistance formulas on the basis of which the ultimate resistance formula is developed for horizontally loaded pile in multi-layer soil in consideration of the effect of the overburden soil pressure on the calculation of soil layer. It is significant to the correct application of the ultimate resistance formulas in API and ZCS Rules into offshore engineering. 相似文献