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431.
This paper aims to assess the uncertainty on the extreme mooring loads of floating system considering short-term variability. Two environmental contour approaches based on the inverse First and Second Order Reliability Methods are employed to identify critical sea states that may give rise to extreme loads. The uncertainty related to the construction of environmental contours is addressed including significant differences due to marginal distribution fitting, parameter estimation methods and joint models. Three measured datasets are analysed using a known conditional joint distribution and proposed mixed copula model. 3-h time domain numerical simulation for each sea state is conducted and the characteristic extreme responses of mooring lines subjected to design loads are assessed. The uncertainties due to various statistical models including the average conditional exceedance rate method as well as global maxima, peak-over-threshold method combined with Gumbel distribution, Generalized Extreme Value distribution, Generalized Pareto distribution and 3-parameter Weibull distribution are investigated and quantified. It is observed that marginal distributions, joint models and parameters estimation methods have apparent effect on design loads estimation, and the extreme tensions of the semi-submersible platform shows significant difference using various probabilistic models. The results indicate that those epistemic uncertainties should be account for in the reliability analysis or safety factor calibration for mooring systems. 相似文献
432.
A method based on a Bi-fidelity Kriging model is proposed for structural reliability analysis. It is based on adding low-fidelity data samples to the model to predict high-fidelity values, thus saving computational effort. Distance Correlation develops the correlation between the low and high-fidelity functions, initially proposed to assess the correlation between two variables. The bi-fidelity Kriging response surface model's efficiency as a surrogate model will be assessed for structural reliability problems that demand high computational costs, such as nonlinear finite element analysis structural models. The efficiency assessment is performed by comparing the accuracy of the failure probability predictions based on the Subset Simulation and First-order reliability method using the Bi-fidelity Kriging model as a surrogate for the performance function. The idea is illustrated by considering a representative component of marine structures analyzed by finite element analysis to create bi-fidelity scenarios to assess structural reliability with many variables. The results show that the proposed multi-fidelity method can provide an accurate failure probability estimation with less computational cost. 相似文献
433.
The paper analyzes Russian and European emission and dispersion models aimed at the estimation of road transport related air pollution on street and regional scale as exemplified with St. Petersburg, Russia. It demonstrates the results of model calculations of peak concentrations of main harmful substances (NОX, CO and PM10) along the St. Petersburg Ring Road at high traffic volume and adverse meteorological conditions (calm, temperature inversion) executed by means of a Russian street pollution model, and it evaluates the computed results against the measurements from monitoring stations. The paper also examines the ways of adaptation of the COPERT IV model – a software tool for calculation of air pollutant and greenhouse gas emissions from road transport on regional or country scale – to the inventory conditions of the Russian Federation, compares the COPERT IV numerical estimates with the national inventory data. It also reveals the obstacles and possibilities in the harmonization of the Russian and European approaches. 相似文献
434.
435.
This paper presents a study on the numerical calculation of the friction resistance coefficient of an infinitely thin plate
as a function of the Reynolds number. Seven eddy-viscosity models have been selected: the one-equation turbulence models of
Menter and Spalart–Allmaras; the k-ω two-equation model proposed by Wilcox and its TNT, BSL and SST variants and the two-equation model. The flow has been computed at 14 Reynolds numbers in sets of seven geometrically similar Cartesian grids
to allow a reliable estimation of the numerical uncertainty. The effect of the computational domain size has been reduced
to negligible levels (below the numerical uncertainty). And the same holds for the iterative and round-off errors. In the
finest grids of each set, the numerical uncertainty of the friction resistance coefficient is always below 1%. Special attention
has further been given to the solution behaviour in the laminar-to-turbulent transition region. Curve fits have been applied
to the data obtained at the 14 Reynolds numbers and the numerical friction lines are compared with four proposals from the
open literature: the 1957 ITTC line, the Schoenherr line and the lines suggested by Grigson and Katsui et al. The differences
between the numerical friction lines obtained with the seven turbulence models are smaller than the differences between the
four lines proposed in the open literature. 相似文献
436.
讨论了在工程项目索赔中因生产率降低所造成损失的索赔问题。利用时间序列指平滑原理方法和模糊数学理论,给出了因生产率降低所造成损的计算中成本的模糊估测方法, 相似文献
437.
铁道车辆液压锚定机械手 总被引:1,自引:0,他引:1
针对铁道车辆在港口、厂矿等装卸时需要固定的要求,研制出铁道车辆液压锚定机械手。机械手最大锚定力为450 kN,在非工作状态时设备最高点不高出轨面。机械手采用液压驱动,由升降臂、伸缩臂和末端手爪组成。升降臂采用双杆结构的四连杆机构,并对伸缩缸、支撑杆等关键部件进行强度校核。液压系统采用节能设计,并利用液压锁实现机械手的位置锁定。采用程序互锁和行程时间联合冗余控制,以保障系统的可靠性。现场使用表明,机械手在1.5 m水平距离内可实现车辆空间位置自动寻找、自动摘挂车钩、定位和位置锁定,达到设计目标,可实现安全高效生产。 相似文献
438.
为减小列车由直线进入曲线时车轮对轨道产生的横向冲击力,对曲线入口的结构性晃车问题进行了分析,进而对轮轨游间及相关技术标准进行了讨论,从机车车辆和线路2个方面提出了建议。 相似文献
439.
440.
Yusuke Tahara Robert V. Wilson Pablo M. Carrica Frederick Stern 《Journal of Marine Science and Technology》2006,11(4):209-228
Steady flow simulations for the Korean Research Institute for Ships and Ocean Engineering (KRISO) container ship (KCS) were
performed for towing and self-propulsion. The main focus in the present article is on the evaluation of computational fluid
dynamics (CFD) as a tool for hull form design along with application of state-of-the-art technology in the flow simulations.
Two Reynolds-averaged Navier-Stokes (RANS) equation solvers were employed, namely CFDShip-Iowa version 4 and Flowpack version
2004e, for the towing and self-propulsion cases, respectively. The new features of CFDShip-Iowa version 4 include a single-phase
level-set method to model the free surface and an overset gridding capability to increase resolution in the flow and wave
fields. The new features of Flowpack version 2004e are related to a self-propulsion scheme in which the RANS solver is coupled
with a propeller performance program based on the infinitely bladed propeller theory. The present work is based on a close
interaction between IIHR-Hydroscience and Engineering of the University of Iowa and Osaka Prefecture University. In the following
article, overviews are given of the present numerical methods and results are presented and discussed for the KCS in towing
and self-propulsion modes, including comparison with available experimental fluid dynamics (EFD) data. Additional evaluation
is provided through discussion of the recent CFD Workshop Tokyo 2005, where both methods appeared to yield very promising
results. 相似文献