Dynamic Bayesian networks for reliability evaluation of subsea wellhead connector during service life based on Monte Carlo method

The subsea wellhead connector is a critical connection component between subsea Christmas tree and subsea wellhead for preventing the leakage of oil and gas in the subsea production system. Excited by cyclical loadings due to environmental forces and the other support forces, the subsea wellhead connector is prone to the failure, which could lead to the loss of subsea tree or wellhead integrity and even catastrophic accidents. With the Monte Carlo simulation method, this paper presents a reliability analysis approach based on dynamic Bayesian Networks, aiming to assess the failure probability of the subsea wellhead connector during service life. Take the driving ring component of the subsea wellhead connector as an example to demonstrate the reasonability of the proposed model. The generation data is processed by the transform between the numerical value and the state variable. Based on the stress-strength interference theory, the structure reliability of the driving ring with 96.26% is achieved by the proposed model with the consideration the aging of the material strength and the most influential factors are figured out. Meanwhile, the corresponding control measures are proposed effectively reduce the failure risk of the subsea wellhead connector during service life.     

Critical review for the quantification of leachate production: Evaluation example for the “Oum Azza” public landfill in Rabat city,Morocco

The estimation of leachate quantities produced in landfills is necessary to dimension the treatment plants allowing to reduce the polluting load of these effluents and consequently avoid their negative impacts on the environment. Different leachate quantification methods were used in this study to assess the leachate volume produced at the Oum Azza landfill. The water balance method give comparable estimations of leachate production to the Ouled Berjal landfill ratio. The first method showed average values between 487 and 495 m³/day for 2015, 2018, and 2019, and at the same time, the second method gave values between 470 and 477 m³/day for the same years. In contrast, the World Bank ratio showed high values that vary between 2260 and 2295 m³/day for 2015, 2018, and 2019. The on-site data and the statistical analysis showed us that the World Bank ratio is not adapted for the estimation of the leachates produced in Oum Azza landfill, while the water balance and the ratio of Ouled Berjal landfill allowed to give comparable results to reality.     

气相色谱-串联质谱法测定沉积物中多环芳烃

采用ASE法提取沉积物中16种多环芳烃,以固相萃取法净化提取液,用气相色谱-串联质谱法测定。通过优化测定条件,使方法在5.00μg/L~1 600μg/L范围内线性良好,方法检出限为0.15μg/kg~0.66μg/kg。空白石英砂的加标回收率为61.9%~121%,7次测定结果的RSD为2.6%~11.1%。     

考虑岩石抗拉强度受围压影响的地层破裂压模型

预测地层破裂压力是地下流体注入工程中的关键问题，关系到工程的稳定性和安全性。根据地测资料，岩石的抗拉强度会随着围压产生变化，然而目前常见的地层破裂压预测模型均未考虑该因素。基于厚壁圆筒法，针对2种砂岩开展不同围压条件下的砂岩致裂试验，根据试验数据，计算各组试验中试样的抗拉强度，并拟合围压与岩石抗拉强度的关系函数。研究岩石抗拉强度随围压变化的规律，提出能在实际地层中表征该规律的参数，基于该参数对现有的地层破裂压模型进行修正，并结合实测数据验证修正模型的可靠性。研究结果表明:岩石的抗拉强度随着围压的增加呈现明显的线性正相关关系，低围压下，新模型的预测结果与实测数据较为接近。随着围压增加，二者的差异逐渐增大，说明选取的特征参数在低围压下能较好地描述抗拉强度受围压的影响效应，而高围压下参数的取值需进一步研究。     

煤对CO2，N2和CH4的吸附速率经验公式与异同性研究*

为了解决吸附速率拟合公式缺乏而解吸经验公式众多的问题，通过替换解吸参数、定性和对比分析各经验公式对煤吸附CO₂，N₂，CH₄吸附速率的适用性，选取4种不同煤质的煤样在0.5，1.0和2.0 MPa下进行定温吸附实验，分析压力和煤质对吸附速率的影响规律。研究结果表明:时间函数式对3种气体在不同压力和煤质下的吸附速率拟合效果最佳；压力和煤质对3种气体吸附速率的影响既存在共性又具有差异性，气体吸附速率与压力符合指数函数关系，与挥发分呈现出二次函数关系，并且压力升高会导致最低吸附速率趋向于较高变质程度煤样；CH₄和N₂的吸附速率随压力升高而升高，而CO₂的吸附速率因煤样而不同，且在同压下，不同气体的最高和最低吸附速率煤样的变质程度也不同。     

基于响应曲面法的遗煤自燃分析与研究*

为研究高瓦斯易自燃煤层不同供风量、高抽巷抽采流量、低抽巷抽采流量3因素对采空区自燃“三带”分布影响规律，选取阳煤五矿8406工作面为研究对象，在数值模拟研究基础上，采用Design Expert软件进行Box Behnken试验设计，构建采空区氧化升温带宽度在3因素、3水平条件下的二次回归响应曲面模型，并对不同条件下采空区氧化升温带宽度进行预测与分析。结果表明:二次回归方程P值为0.001 6，预测模型显著，模型的失拟项为0.606 3，不显著，回归方程具有统计学意义；当供风量为1 500~2 000 m3/min，低抽流量为450~650 m3/min，高抽流量为100~200 m3/min时，对氧化升温带宽度一次项重要度排序为C（高抽巷抽采流量）>A（供风量）>B（低抽巷抽采流量），二次项重要度排序为AC（供风量和高抽巷抽采流量）>AB（供风量和低抽巷抽采流量）>BC（低抽巷抽采流量和高抽巷抽采流量），且AB,AC,BC之间均无交互作用。     

建筑安全风险因素分级排序的风险矩阵法

为减少风险分级排序时产生的风险结,在引入施工安全事故频率的基础上,采用单元格细化和Borda序值法改进原有的风险矩阵法。改进后的方法使得风险等级数量增加,风险结数量减少。将该方法应用于脚手架工程的风险因素的分级与排序,风险等级分为6级,且实现了12个因素的明确排序。     

液氮泡沫发生器内流动特性研究

低温液氮与泡沫混合液直接接触产生氮气泡沫是一种新型的掺混形式,利用液氮高汽化比的特点,搭建液氮泡沫可视化实验装置,进行氮气-水两相流及液氮泡沫流动特性的研究。结果表明,液氮相变产生大量氮气,其与泡沫液混合产生泡沫,温度有所回升,最终趋于泡沫混合液温度;管路沿程压降较小;液氮射流破碎及流动过程可分为6个区域:低温液氮区、向上循环翻滚区、滞留区、泡沫与泡沫混合液混合区、致密泡沫区、泡沫混合液区。流体向下游流动过程中持续发泡;为防止管路结冰,需合理控制泡沫混合液与液氮流量。     

Experimental research of LNG accidental underwater release and combustion behavior

Evaluating potential hazards caused by accidental LNG release from underwater pipelines or vessels is a significant consideration in marine transportation safety. The aim of this study was to capture the dynamic behavior of LNG jet released under water and to analyze its vapor dispersion characteristics and combustion characteristics on the water surface during different release scenarios. Controlled experiments were conducted where LNG was jet released from a cryogenic storage tank. The dynamic process of LNG being jet released from orifices of different sizes and shapes, as well as the rising plume structure, were captured by a high-speed camera. The leakage flow rate and pipeline pressure were recorded by a flow meter and pressure gauge, respectively. The concentration distribution that emanated from the water surface was measured utilizing methane sensors in different positions with various wind speeds. The flame combustion characteristics of LNG vapor clouds, which immediately ignited upon the enclosed water tank, were also recorded. Additionally, the mass burning rate of the flame on the water surface was evaluated, and a new correlation between the ratio of flame length and width was established. The results indicated a large dimensionless heat release rate (Q*) and a continuous release flow rate in a limited burning area. This study could provide greater understanding of the mechanisms of LNG release and combustion behavior under water.     

燃煤电厂超低排放气态污染物监测技术综述

介绍了燃煤电厂超低排放气态污染物监测系统的采样系统和分析单元,分析了其各自的优缺点。对稀释抽取式、冷干抽取式和热湿抽取式3种采样方法,以及非分散红外吸收法(NDIR)、非分散紫外吸收法(NDUV)、紫外差分吸收法(DOAS)、紫外荧光法(UVF)和化学发光法(CL)5种分析方法进行对比。结果表明,冷干抽取式+紫外差分法以及稀释抽取式+紫外荧光法+化学发光法可以较好地符合燃煤电厂超低排放监测的要求。