某型柴油机重大故障原因分析

摘 要：通过对故障柴油机连杆、连杆螺栓、平衡块螺栓、排气阀、排气阀导管、活塞、缸套等失效件的理化分析，故障柴油机气门间隙的检查，连杆受力分析与气阀的动力学分析及疲劳计算，结果表明：故障柴油机的首断件为排气阀，排气阀断裂的原因是气阀间隙过大造成的，在气阀间隙较大的情况下，阀杆受力大大增加，其疲劳安全系数大大降低。以上理论计算和理化分析的结果为正确判断柴油机的故障提供了有力支持。     

Comparing different contour methods with response-based methods for extreme ship response analysis

Environmental contours are often applied in probabilistic structural reliability analysis to identify extreme environmental conditions that may give rise to extreme loads and responses. They facilitate approximate long term analysis of critical structural responses in situations where computationally heavy and time-consuming response calculations makes full long-term analysis infeasible. The environmental contour method identifies extreme environmental conditions that are expected to give rise to extreme structural response of marine structures. The extreme responses can then be estimated by performing response calculations for environmental conditions along the contours.Response-based analysis is an alternative, where extreme value analysis is performed on the actual response rather than on the environmental conditions. For complex structures, this is often not practical due to computationally heavy response calculations. However, by establishing statistical emulators of the response, using machine learning techniques, one may obtain long time-series of the structural response and use this to estimate extreme responses.In this paper, various contour methods will be compared to response-based estimation of extreme vertical bending moment for a tanker. A response emulator based on Gaussian processes regression with adaptive sampling has been established based on response calculations from a hydrodynamic model. Long time-series of sea-state parameters such as significant wave height and wave period are used to construct N-year environmental contours and the extreme N-year response is estimated from numerical calculations for identified sea states. At the same time, the response emulator is applied on the time series to provide long time-series of structural response, in this case vertical bending moment of a tanker. Extreme value analysis is then performed directly on the responses to estimate the N-year extreme response. The results from either method will then be compared, and it is possible to evaluate the accuracy of the environmental contour method in estimating the response. Moreover, different contour methods will be compared.     

Probabilistic fatigue analysis of marine structures using the univariate dimension-reduction method

Probabilistic fatigue analysis of offshore structures requires the numerical simulation of a huge number of loading cases to compute the long-term multi-dimensional integral associated to the fatigue damage assessment. This paper proposes the implementation of the univariate dimension-reduction method developed by Rahman and Xu [1] in order to compute the long-term fatigue damage more efficiently. This method is particularly attractive because it reduces significantly the number of simulations by decomposing the N-dimensional integral associated to expected long-term fatigue damage assessment into the sum of N one-dimensional integrals. In addition, this paper compares the univariate-dimension reduction method with the brute force direct integration methodology and other methods based on Taylor expansions, such as perturbation approach and asymptotic expansion method discussed by Low and Cheung [2]. Two comprehensive examples are included to show the effectiveness of the method. At first, the performance of the univariate dimension-reduction method is evaluated by assessing the fatigue damage of a theoretical structure represented by a single stress response amplitude operator (RAO). Then, in order to show a case of practical application, the fatigue damage is evaluated for a Steel Lazy Wave Riser (SLWR) connected to an FPSO in a water depth of 2200 m.     

大型C型独立液货罐Y型接头疲劳强度评估

随着C型独立液货罐的新技术发展,目前在工业界推出了采用双体罐和三体罐构造形式的新颖大型C型独立液货罐。由于双体罐和三体罐构造的要求,在相邻罐体连接处设有Y型接头。该Y型接头位置处由于结构件交汇,构造复杂、应力集中,在船舶运动、蒸汽压力变化,以及温度变化的动载作用下有可能发生疲劳损伤。本文对新颖大型C型独立液货罐Y型接头疲劳强度评估方法的规范技术要求及制定开展了深入详尽的研究，包括对C型独立液货罐疲劳损伤计算工况择取，液货内部动压力计算公式推导，蒸气压力、温度变化等低周疲劳载荷模式确定等，创新提出一整套基于热点应力的C型独立液货罐Y型接头的疲劳损伤评估方法的规范实施要求。进一步地，还推导了基于一般实际情况假设下的C型独立液货罐Y型接头疲劳评估筛分准则，并应用本文上述研究成果和结论，进行了双体和三体罐Y型接头疲劳评估和筛分准则的应用与验证。     

考虑残余应力效应的深潜器耐压壳体疲劳研究

本文考虑焊接残余应力的影响,给出包含裂纹萌生和裂纹扩展全过程的载人深潜器耐压球壳疲劳寿命预报方法,分别基于局部应力-应变法和能计及负应力比效应的裂纹扩展单一曲线模型预报了耐压球壳的工艺疲劳寿命和使用疲劳寿命,研究焊接残余应力大小对球壳疲劳寿命的影响。结果表明,忽略拉伸残余应力的影响将导致疲劳寿命预测结果偏于危险;耐压球壳整体受压时,拉伸残余应力使得球壳局部区域承受拉-压循环载荷,计算使用疲劳寿命过程中须考虑其影响;降低拉伸残余应力可有效提高耐压球壳的疲劳寿命。     

A copula-based approach for estimating the travel time reliability of urban arterial

Estimating the travel time reliability (TTR) of urban arterial is critical for real-time and reliable route guidance and provides theoretical bases and technical support for sophisticated traffic management and control. The state-of-art procedures for arterial TTR estimation usually assume that path travel time follows a certain distribution, with less consideration about segment correlations. However, the conventional approach is usually unrealistic because an important feature of urban arterial is the dependent structure of travel times on continuous segments. In this study, a copula-based approach that incorporates the stochastic characteristics of segments travel time is proposed to model arterial travel time distribution (TTD), which serves as a basis for TTR quantification. First, segments correlation is empirically analyzed and different types of copula models are examined. Then, fitting marginal distributions for segment TTD is conducted by parametric and non-parametric regression analysis, respectively. Based on the estimated parameters of the models, the best-fitting copula is determined in terms of the goodness-of-fit tests. Last, the model is examined at two study sites with AVI data and NGSIM trajectory data, respectively. The results of path TTD estimation demonstrate the advantage of the proposed copula-based approach, compared with the convolution model without capturing segments correlation and the empirical distribution fitting methods. Furthermore, when considering the segments correlation effect, it was found that the estimated path TTR is more accurate than that by the convolution model.     

液化天然气B型独立液货舱结构低周疲劳研究

基于某B型独立液货舱为研究对象,开展液化天然气(LNG)船码头装卸货工况下的结构应力和温度场热应力分析,重点针对液货舱水平强框处连接节点计算其因装卸货受力和温度变化所引起的疲劳累积损伤。研究结果表明,部分研究疲劳节点由装卸货产生的低周疲劳损伤在整个结构疲劳累积损伤中的占比较大,对结构疲劳损伤起主导作用,需要在液货舱疲劳强度分析中予以重点关注。因此,对此类B型独立液货舱进行结构设计必须考虑低周疲劳的影响。     

海上风机支撑结构的时域和频域疲劳对比研究

对海上风机支撑结构进行动力响应分析,求出结构危险节点的载荷谱和功率谱密度函数,结合疲劳损伤模型和Dirlik概率模型,分别在时域和频域内对支撑结构进行疲劳寿命分析.由于时域法计算疲劳寿命需进行应力循环计数,这一过程需处理的数据庞大,耗时长.频域法省去应力循环计数,代之以概率密度函数,可相对准确、快速地计算结构的疲劳寿命.分析结果表明,采用Dirlik概率模型的频域分析法能较准确地反映海上风机支撑结构在随机载荷作用下的疲劳损伤情况,计算结果误差在可接受范围内.     

基于概率密度演化的斜拉索多级变幅时变疲劳可靠度分析

拉索是斜拉桥的主要受力构件,在车辆、风等交变荷载作用下易发生多级变幅疲劳损伤,而经典可靠度方法预测多级变幅时变疲劳可靠度难度大且计算效率低。针对这一问题,提出一种高效的多级变幅斜拉索时变疲劳可靠度预测方法。基于Miner累积损伤理论,建立同时考虑荷载和材料随机性的变幅疲劳损伤概率演化模型;构建应力幅出现频率指标,解决多级变幅疲劳损伤演化过程中偏微分方程难以确定问题,通过概率密度演化方法精确计算多级变幅时变疲劳可靠度,并采用五级变幅材料试验数据和某桥梁斜拉索的模拟数据验证所提方法的可行性。结果表明:所提方法的计算效率远高于蒙特卡洛方法;在小概率失效时,其计算精度高于蒙特卡洛方法。     

基于KENTRACK的铁路沥青混凝土底砟层疲劳特性评价

重复动载疲劳损伤是沥青混凝土底砟层的破坏形式之一。本文建立了沥青混凝土底砟层的三维有限元分析模型,分析其在列车荷载作用下的受力变形特性。采用KENTRACK设计方法分析了沥青混凝土底砟层的疲劳寿命。结果表明:沥青混凝土底砟层等厚度替代基床表层的路基结构形式在列车荷载作用下基床表层的竖向动变形和振动加速度明显减小;沥青混凝土底砟层的层底拉应变在10×10^-6~90×10^-6,处于较低水平;沥青混凝土底砟层具有良好的疲劳耐久性,可用于工程实践。