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This paper presents an assessment of the efficiency of the Kriging interpolation models as surrogate models for structural reliability problems involving time-consuming numerical models such as nonlinear finite element analysis structural models. The efficiency assessment is performed through a systematic comparison of the accuracy of the failure probability predictions based on the first-order reliability method using the most common first- and second-order polynomial regression models and the Kriging interpolation models as surrogates for the true limit state function. An application problem of practical importance in the field of marine structures that requires the evaluation of a nonlinear finite element structural model is adopted as numerical example. The accuracy of the failure probability predictions is characterised as a function of the number of support points, dispersion of the support points in relation to the so-called design point and order of the Kriging basis functions. It is shown with the application problem considered that the Kriging interpolation models are efficient surrogate models for structural reliability problems and can provide significantly more accurate failure probability predictions as compared with the most common polynomial regression models. 相似文献
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Abstract In this paper, a graphical prediction method is developed to effectively predict the existence of the limit cycles induced by nonlinear friction force in an electro‐hydraulic control system. The friction‐induced nonlinearity is linearized by its corresponding describing function. Then the stability equation method, accompanied by the parameter plane method, provides a useful tool for the establishment of necessary conditions to sustain a limit cycle in the controller coefficient plane. Henceforth, the limit cycles are predicted in a graphical way, and simulations are carried out to verify the accuracy of the prediction method. 相似文献
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S. LORÉN 《Fatigue & Fracture of Engineering Materials & Structures》2003,26(9):757-766
For metallic material one is interested in estimating the fatigue limit although it is impossible to test if a specimen has infinite life. In this paper two models are compared. One model estimates the fatigue limit and another estimates the endurance limit. The model which estimates the endurance limit is a model which only uses the information that a specimen has broken or not broken at a certain stress level. The model which estimates the fatigue limit also uses the information about when the specimen is broken, i.e., after how many cycles the specimen breaks. The two models are compared, both on real and simulated staircase tests. It is shown that it is possible to estimate the distribution of the fatigue limit although the fatigue limit itself is impossible to observe. When the two models give very different estimates it indicates that the chosen run‐out level is too low. 相似文献
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提出了一种基于浮游生物粒径组成和数量分布关系的生物粒径谱研究方法。这一方法可最大限度地将粒径分组,形成近乎连续的谱图,并利用自然海水样品验证了该技术在浮游生物粒径结构研究中的应用效果,表明该技术对于海洋生态群落结构研究和环境监测等具有广阔的应用前景。 相似文献
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Alexander C. Wagenaar 《Accident; analysis and prevention》1990,22(6):571-585
Effective December 1987 and January 1988, the maximum speed limit on rural limited access highways in Michigan was raised from 55 mph to 65 mph. This study examined the effects of the raised limit on injury morbidity and mortality. A multiple time-series design was used, comparing roads where the speed limit was raised with roads where the limit remained unchanged. Data were collected on numbers and rates of automobile crashes, injuries, and deaths from January 1978 through December 1988. Time-series intervention analyses were conducted to estimate effects associated with the speed limit change while controlling for long-term trends, seasonal cycles, and other patterns. Statistical controls were also included for major factors known to influence crash and injury rates. Results revealed significant increases in casualties on roads where the speed limit was raised, including a 19.2% increase in fatalities, a 39.8% increase in serious injuries, and a 25.4% increase in moderate injuries. Fatalities also increased on 55 mph limited access freeways, suggesting that the 65 mph limit may have spillover effects on segments of freeways where the limit was not changed. No significant changes in fatalities or injuries were found on other types of roads. The increased convenience of reduced travel time with the higher speed limit is obtained at a significant cost in terms of injury morbidity and mortality. 相似文献
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The paper presents some results from a continuing study of the marine durability of steel fibre reinforced concrete. The overall
aim of the investigation is to develop the material for marine applications. The results reported here pertain to pre-cracked
specimens of steel fibre reinforced concrete which were exposed to wet-dry cycles of marine spray in the laboratory simulating
tidal zone conditions of exposure. Two types of concrete mixes were used in the investigation—one with standard concrete constituents
and OPC and the second replacing about 26% of cement with pfa. The cement content of the mixes was 590 and 435 kg m−3, respectively. Fibre reinforcement was provided by means of low carbon steel fibres and melt extract steel fibres at a v
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ℓ/d ratio of 100 and 147. Prism specimens were manufactured and these were precracked to induce cracks of width ranging between
0.03 and 1.73 mm. After cracking, both sealed and unsealed specimens were exposed to laboratory marine spray cycles using
sea water. Some control specimens were cured in the laboratory air throughout. Tests were carried out after 650 marine cycles
(450 days) and 1450 marine cycles (900 days). Based on data on flexural strength, energy absorption capacity, stiffness and
state of corrosion of the fibres, recommendations are made regarding suitable permissible crack widths for the design of steel
fibre reinforced concrete for marine applications. The results indicate that a permissible crack width of 0.2 mm is satisfactory
for concrete reinforced with melt extract fibres. A smaller value is recommended for concrete reinforced with low carbon steel
fibres. Complete healing of open cracks of small widths is observed under exposure to marine cycles. 相似文献
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H. Mayer S. Stojanovic C. Ede B. Zettl 《Materialwissenschaft und Werkstofftechnik》2007,38(8):581-590
Contribution of low load cycles to fatigue damage in 0.15 %C steel The S‐N curve of 0.15 %C steel shows an endurance limit. Two‐step variable amplitude loading experiments serve to investigate the influence of numerous cycles below the endurance limit on fatigue damage. If high stress amplitudes of the loading sequences are more than approx. 15 % above the endurance limit, low load cycles contribute significantly to fatigue damage. Investigations of fatigue crack propagation under two‐step variable amplitude loading show accelerated crack growth caused by low load cycles. If high stress amplitudes of the two‐step sequences are less than 15 % above the endurance limit, beneficial influences of numerous low load cycles are found. Under these conditions, the material can sustain far greater numbers of load cycles than predicted by Miner damage accumulation calculation. Fatigue crack growth studies show that under these conditions for the high load numerous low load cycles lead to stop of the crack propagation. 相似文献
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本文研究了Duffing-Van der Pol振子在一类时滞反馈控制下零解的稳定性问题以及极限环的振幅和稳定性问题。依平均法和对时滞反馈控制项泰劳展开的截断得到的平均方程表明,零解的稳定性除与原方程中线性项的系数有关外,只与线性反馈有关,与非线性反馈无关。通过调整线性反馈的增益和时滞,可以使不稳定的零解变得稳定。零解发生Hopf 分岔导致的周期解的振幅除与原方程中非线性项的系数有关外,与线性反馈和非线性反馈均有关。通过调整反馈增益和时滞,不仅可以控制极限环的振幅,还可以抑制极限环的产生。此外,根据平均方程还容易发现反馈时滞对系统动力学行为的影响具有周期性。数值仿真的结果验证了理论分析的正确性。 相似文献
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Y. KONDO C. SAKAE M. KUBOTA K. YANAGIHARA 《Fatigue & Fracture of Engineering Materials & Structures》2005,28(6):501-506
Fretting fatigue fracture of industrial machines is sometimes experienced after a long period of operation. It has been a question whether the fatigue limit which means infinite life really exists in fretting fatigue or not. Fretting fatigue tests in ultra high cycle region up to 109 cycles were performed. Test results showed that the S‐N curve had a knee point around 2 × 107 cycles and a clear fatigue limit was observed in the giga‐cycle regime for partial slip conditions. An electropotential drop technique was applied to detect the crack growth behaviour under the contact pad. The real‐time measurement of crack depth during the fretting fatigue test at the fatigue limit showed that a crack initiated at an early stage and then ceased to grow after 2 × 107 cycles and the crack became a non‐propagating crack. These results indicated that the fatigue limit exists in fretting fatigue and infinite endurance is achieved by the mechanism of forming a non‐propagating crack. 相似文献
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研究了横向定常风荷载作用下轴向运动弦线的非线性自激振动问题。将风荷载模型化为平均风速的非线性函数,建立动力学微分方程。采用Galerkin方法,将运动弦线简化为离散的二维系统并进行线性化,分析弦线平衡构型的稳定性,根据Routh-Hurtwitz判据确定了平衡点的稳定域。确定了多参数下Hopf分岔点及产生稳定极限环的条件。使用增量谐波平衡(IHB)法求解了自激振动的周期响应,按照Floquet理论确定了周期解的稳定性。最后,讨论了运动速度和平均风速稳定性的影响,并给出相应的稳定性条件。 相似文献
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Hemmings JC Srokosz MA Challenor P Fasham MJ 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2003,361(1802):33-39
The effectiveness of ocean-colour data assimilation in providing robust biological-parameter estimates for basin-scale ecosystem models is investigated for a phytoplankton-zooplankton-nutrient model using North Atlantic satellite chlorophyll data. The model is forced by annual cycles of mixed-layer depth, day length, photosynthetically available radiation and a temperature-dependent phytoplankton maximum growth rate. Although ocean-colour data are potentially limited in their ability to constrain model parameters because they provide information about the phytoplankton component only, this limitation is offset by the volume of data available covering the range of possible biogeochemical responses to similar and widely varying physical conditions. The results are improved by applying wintertime nutrient estimates based on in situ observations as an additional constraint. Repeatability of parameter estimates obtained from independent samples is examined. Results obtained using regional and basin-wide sampling strategies for obtaining the optimization dataset are compared and the geographic applicability of the calibrated models is assessed. 相似文献
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确定前轮非线性摆振极限环振幅的一种方法 总被引:1,自引:0,他引:1
用摄动法给出了当前轮减摆阻尼器含有速度平方阻尼时前轮摆振的极限环振幅表达式,并讨论了极限环的稳定性。在确定极限环振幅时,利用非线性系统所对应的线性系统在临界稳定时特征矩阵的特点,通过对特征矩阵进行三角分解,得到了消除摄动解中奇异项的条件,利用此条件,很方便地获得了飞机前轮非线性摆振的摄动解,并改正了有关文献中的错误。 相似文献
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The area theorems, describing propagation of ultrashort pulses of resonant laser radiation in a two-core nonlinear directional
coupler, are formulated for the first time. It is shown that such a system is characterized by a finite, bounded above set
of areas of the stationary propagating pulses. We also predict quantization of the limit cycles and possible existence of
the regime of periodic complete transfer of the radiation energy from one fiber to another. 相似文献
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一类三次系统无穷远点的中心条件与赤道极限环分支 总被引:1,自引:1,他引:0
本文研究了一类三次系统无穷远点的中心条件与赤道极限环分枝问题。通过将实平面系统转化为复系统研究,给出了计算无穷远点奇点量的递推公式,并在计算机上用Mathematica推导出该系统无穷远点前七个无穷远点奇点量,进一步导出了无穷远点成为中心的条件和七阶细焦点的条件,得到了三次系统无穷远点分支出七个极限环的一个实例。 相似文献
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An exothermic chemical reaction with linear feedback control 总被引:1,自引:0,他引:1
This paper investigates the effect of linear control as applied to an exothermic Sal?nikov chemical reaction. It will demonstrate how the control reduces the amplitude of the naturally occurring oscillations in temperature. However, in different parameter regions, this is not the case; that is, the reaction has desirable behaviour without control. A mathematical and numerical analysis of the system will be presented. Steady-state solutions are examined, and the emergence of limit cycles will be shown via the Hopf condition. The conditions under which oscillatory behaviour is not observed will be identified. When oscillatory behaviour is detected, the region to which it is confined will be described. Finally, an example is given of a nonlinear control, which ensures that the system will only portray stable behaviour, and under certain parameter constraints can eliminate oscillations entirely. 相似文献