兰姆波飞机结冰传感器的最佳工作模态研究

首先建立了兰姆波在覆盖冰层的无限大各向同性板中传播的波速方程。通过数值计算获得了在覆盖不同冰层厚度下薄板中兰姆波的色散曲线。接着绘制了在给定检测频率下兰姆波波速随厚度变化的关系曲线图,进一步提出了兰姆波飞机结冰检测过程中最佳模态的选取方法。研究结果表明冰层厚度与兰姆波波速之间存在对应关系,可以通过判断各阶模态的耦合情况来选取最佳检测模态。     

Fragility assessment of bottom plates in above ground storage tanks during flood events

This study aims to improve the fundamental understanding on the performance of bottom plates in above ground storage tanks (ASTs) during flood events. To this end, fragility models that estimate the probability of material yielding and rupture in the bottom plates were derived. A significant number of ASTs are located in coastal areas and are susceptible to hurricane hazards. Consequently, ASTs have suffered severe damage during past hurricanes resulting in spills with catastrophic environmental and social impacts. Therefore, several failure modes such as flotation, buckling, and sliding have been studied in past research. However, the literature lacks studies that consider the failure of bottom plate due to uplift pressure generated during floods and there are no design guidelines to address this issue. To address this gap, fragility functions that provide the probability of failure as a function of tank geometry, material properties, design parameters, and hazard conditions were developed herein. For this purpose, Latin Hypercube Sampling was performed to span the space of these parameters uniformly. For each parameter combination, maximum stresses in bottom plates were determined using analytical formulations for simply supported and clamped boundary conditions and were compared against two different failure thresholds. The results were used to develop a closed form fragility model using step wise logistic regression. Fragility functions were applied to four case study tanks. Sensitivity analysis were performed to understand the impacts of different probability density functions for various variables on the bottom plates’ fragility. The results provided several insights such as ASTs with larger diameter were vulnerable to bottom plate failure. Comparison with other failure modes revealed that the probability of bottom plate failure was higher than flotation failure for anchored ASTs with clamped boundary condition.     

Influence of thermal radiation on layered dust explosions

Multidimensional unsteady numerical simulations were carried out to explore the influence of thermal radiation on the propagation and structure of layered coal dust explosions. The simulation solved the reactive compressible Navier-Stokes equations coupled to an Eulerian kinetic-theory-based granular multiphase model. The radiation heat transfer is modeled by solving the radiation transfer equation using the third-order filtered spherical harmonics approximation. The radiation was assumed to be gray and all boundaries of the domain are black at 300 K. The reaction mechanism is based on global irreversible reactions for each physical process including devolatilization, char burning, moisture vaporization, and methane combustion. The governing equations were solved using a high-order Godunov method. Several simulation configurations were considered: layer volume fractions of 47% and 1%, channel lengths of 10 m and 40 m, and radiative and non-radiative cases. The results show that gray radiation has a significant influence on the propagation and structure of a layered dust explosion. However, radiation can have opposite effects on different scenarios. For example, radiation promotes the propagation of the dust flame when the layer volume fraction was 1% and in the short-channel cases where reflected shock-flame interactions are important. However, radiation enhances quenching for the 47% volume fraction dust layer in the longer channel.     

芒刺-板式电除尘器收尘极板电流密度分布规律研究

在芒刺-板式电除尘器中,板电流密度分布越均匀,越有利于除尘效率提高.因此,知道收尘极板电流密度分布对电除尘器的电极结构设计是重要的.然而,由于处于芒刺正下方的峰值电流不易确定,导致现有的电流密度分布式很难用于实际工程计算.另外,这些计算式不满足高斯通量定理.要使芒刺-板式电除尘器收尘极板电流密度分布满足高斯电通量定理,电流密度分布规律应服从某种特定的分布函数.通过对Warburg单根芒刺-板式电极极板电流密度分布模型的变量分析,发现芒刺-板式电除尘器收尘极板电流密度分布恰是自由度n=4的t分布.根据电流密度的分布特征,建立了由总电流确定极板电流密度的理论计算式.由于总电流很容易通过实测得到,因此,所建立的极板电流密度t分布模型更具实用性.比较研究表明,该理论式与其他研究者的实验结果有很好的一致性.     

Comparison of API650-2008 provisions with FEM analyses for seismic assessment of existing steel oil storage tanks

API650-2008 is one of the prominent codes consisting of seismic specifications to design steel storage tanks for earthquakes resistance. In spite of the code's broad application, there are some failure modes such as slide bottom, elephant-foot buckling, sloshing and uplift needing more evaluation. In this paper, 161 existing tanks in an oil refinery complex have been classified into 24 groups and investigated using both API650-2008 rules and numerical FEM models. Failure modes and dynamic characteristics of studied models have been calculated by numerical FEM analysis and compared with code requirements. The results demonstrate that, in some cases, there are some imperfections in the code requirements that require further investigation.     

Myoelectric manifestation of muscle fatigue in repetitive work detected by means of miniaturized sEMG sensors

Upper limb work-related musculoskeletal disorders have a 12-month prevalence ranging from 12 to 41% worldwide and can be partly caused by handling low loads at high frequency. The association between the myoelectric manifestation of elbow flexor muscle fatigue and occupational physical demand has never been investigated. It was hypothesized that an elbow flexor muscle fatigue index could be a valid risk indicator in handling low loads at high frequency. This study aims to measure the myoelectric manifestation of muscle fatigue of the three elbow flexor muscles during the execution of the work tasks in different risk conditions. Fifteen right-handed healthy adults were screened using a movement analysis laboratory consisting of optoelectronic, dynamometer and surface electromyographic systems. The main result indicates that the fatigue index calculated from the brachioradialis is sensitive to the interaction among risk classes, session and gender, and above all it is sensitive to the risk classes.     

A reliability evaluation method based on the weakest failure modes for side-by-side offloading mooring system of FPSO

Offshore structures are complex systems, and numerous failure modes must be taken into consideration when reliability analysis in different loads and environment conditions are conducted on them. It is difficult to obtain structural system reliability with respect to complicated systems with numerous failure modes and dependency consideration among them. This paper applies the combination of the weakest failure modes theory with structural reliability theory to conduct reliability analysis on of side-by-side offloading mooring system of FPSO. Firstly, the numerical simulation of the system in different conditions is addressed to acquire the statistical data of time-history stress of components including hawsers, fenders and yoke, based on which, the reliability indexes of all the failure modes and correlation coefficient matrix are derived. Then the weakest failure modes, i.e. the representative failure modes that have significant impact on the system, are located through Probability Network Evaluation Technique. The probability of structural system is estimated through the weakest failure modes by considering the system as series. The analysis results indicate that two environment conditions (0°&0°&0° and 0°&30°&45° in combinations of wave, wind and current) are relative dangerous, which is in good correspondence with the practical expertise. The method is verified to be an effective and convenient evaluation approach for structural reliability analysis in terms of complex systems. It is beneficial for the identification of structure indicators from the weakest failure mode group and conduct optimum of structural system configurations in the design stage.     

露采高边坡模型初始地应力场快速生成方法研究

为防止露釆高边坡建模中初始地应力场畸变,采用子模型法和等效应力梯度边界面力法,用等效应力梯度边界面力替代简化部分水平构造应力,施加侧边界条件.以黄山石灰石矿山高边坡为工程实例,建立取至负地形的高边坡整体计算模型和简化子模型,计算对比整体大模型与简化子模型初始地应力场模拟结果.结果表明:整体大模型与简化子模型水平方向和竖...     

Failure mode and effect analysis using regret theory and PROMETHEE under linguistic neutrosophic context

Failure mode and effect analysis (FMEA), which aims to identify and assess potential failure modes in a system, has been widely utilized in diverse areas for improving and enhancing the performance of systems due to it is a powerful and useful risk and reliability assessment instrument. However, the conventional FMEA approach has been suffered several criticisms for it has some shortcomings, such as unable to handle ambiguous and uncertain information, neglect the relative weights of risk criteria, and without considering the psychological behaviors of decision-makers. To ameliorate these limitations, this paper aims at establishing a hybrid risk ranking model of FMEA via combing linguistic neutrosophic numbers, regret theory, and PROMETHEE (Preference ranking organization method for enrichment evaluation) approach. In the presented model, linguistic neutrosophic numbers are adopted to capture decision-makers’ evaluation regarding the failure modes on each risk criterion. A modified PROMETHEE approach based on regret theory is presented to obtain the risk priority of failure modes considering the psychological behaviors of decision-makers. Moreover, a maximizing deviation model and TOPSIS (Technique for order preference similar to ideal solution) are separately applied to derive the weights of risk criteria and decision-makers. Finally, a numerical example relating to the supercritical water gasification system is employed to implement the presented method, and the effectiveness and feasibility of the proposed model are validated by the results derived from a sensitivity and comparison analysis.     

Mitigation of hydrogen fluoride aerosols by dry powders

Fluid bed tests were used to determine overall reaction rates for eight different dry powders of low hazard and toxicity before and after reaction with HF. In flow chamber tests, a representative oxide, hydroxide and carbonate were used to measure the efficiency of mitigation of an HF aerosol cloud. The results show that dry powders provide a valid alternative to water spray mitigation. Powder efficiencies are higher than water efficiencies at constant weight ratio.

At present, no attempt has been made to provide any technical designs or layouts for powder mitigation systems. However, the technology for smaller systems is available through manufacturers of dry powder chemical fire extinguisher equipment. When these powders are kept dry and under nitrogen atmosphere, a shelf life of several years can be expected.     

一种高层建筑楼、电梯疏散模型的模拟研究

通过分析目前楼、电梯疏散的研究成果,提出了新的楼、电梯疏散模型,给出了两种具有可行性的电梯运行方案:(1)电梯停靠某一层完全疏散此层及以上所有人员,此层以下人员使用楼梯疏散;(2)7层以上的各层按一定比例选择使用电梯疏散,剩余人员选用楼梯疏散.进一步阐述了楼、电梯疏散时间的计算公式.通过对新提出的楼、电梯疏散模型的模拟计算可知:两种运行方案均可有效地降低总的疏散时间,相比之下第二种运行方案疏散效果更佳,但考虑到实际情况第一种方案可操作性更强.最后讨论了电梯速度对疏散的影响,得出疏散时最好选用运行速度较高的电梯,可提高疏散效率.     

The multi-energy critical separation distance

Devastating vapour cloud explosions can only develop under appropriate (boundary) conditions. The record of vapour cloud explosion incidents from the past demonstrates that these conditions are readily met by the congestion by process equipment at (petro-) chemical plant sites. Therefore, the possibility of an accidental release of a flammable and a subsequent vapour cloud explosion is a major hazardous scenario considered in any risk assessment with regard to the process industries.If an extended flammable vapour cloud at a chemical plant site extends over more than one process unit, which are separated by lanes of sufficient width, the vapour cloud explosion on ignition develops the same number of separate blasts. If, on the other hand, the separation between the units is insufficient, the vapour cloud explosion develops one big blast. The critical separation distance (SD) is the criterion that allows discriminating in this matter for blast modelling purposes.This paper summarises some major results of an experimental research programme with the objective to develop practical guidelines with regard to the critical SD. To this end, a series of small-scale explosion experiments have been performed with vapour clouds containing two separate configurations of obstacles. Blast overpressures at various stations around have been recorded while the SD between the two configurations of obstacles was varied.The experimental programme resulted in some clear indications for the extent of the critical SD between separate areas of congestion. On the basis of safety and conservatism, these indications have been rendered into a concrete guideline. Application of this guideline would allow a greater accuracy in the modelling of blast from vapour cloud explosions.     

某装药弹振动特性的安全分析

为分析某装药弹的振动特性,并为该弹提供必要的力学数据,建立某装药弹模态方程。采用ANSYS软件对该弹振动特性进行了数值模拟,利用Block Lanczos法求解,得到前10阶振动固有频率和振型。分析结果表明:低阶频率主要以摆动和转动为主,高阶频率主要以弯曲扭动为主,低阶频率对该弹的影响比较小,高阶频率对该弹的影响比较大,尤其是7～10阶频率,该弹的主振频率为1053.8 Hz,为该弹的优化设计提供科学依据,在加工、储存、运输和使用条件下应低于该频率;为验证该方法可信度,采用某小型装药弹进行了实验验证,实验结果和仿真结果偏差小于1%;同时证明该有限元数值分析的方法是经济可靠的。     

Gas dispersion risk analysis of safety gap effect on the innovating FLNG vessel with a cylindrical platform

While the effect of the safety gap on explosions is well known, little has been carried out to evaluate the effect of the safety gap on dispersion of gas releases, this paper evaluates the effect of safety gap on gas dispersion for a cylindrical Floating Liquefied Natural Gas (FLNG) vessel. The realistic ship-shaped and circular FLNG platforms are established and used for the detailed CFD based analysis; rather than the structural and hydrodynamics advantages of mobility, stability and cost efficiency etc., this study aims to investigate the safety of gas dispersion on the cylindrical FLNG and compare the safety gap effects on different configurations. A series of different safety gap configurations are evaluated for gas dispersion occurring in near field for the traditional FLNG while both near field and far field gas dispersion simulations are conducted on the cylindrical one. The overall results indicate that the safety gap is effective in reducing the gas cloud size in both FLNG configurations, however, when it comes to the gas dispersion in the far field against the leakage point, the safety gap increases the gas cloud size in the cylindrical FLNG vessel on the contrary.     

井底冲击压力特性的研究

运用数值模拟的方法研究了单喷嘴射流撞击井底时产生的冲击压力及其分布规律。研究结果表明，井底最大冲击压力梯度所在的位置距撞击中心约０．１１４倍喷距处，井底最大冲击压力梯度和射流喷速成正比，和喷距成反比，本文绘出了其数学表达式。数值计算结果和室内实验数据吻合较为一致。     

混凝土抗爆墙防护性能的改进

借鉴国外模块化钢结构抗爆墙,根据我国当前工程实际情况,提出对传统混凝土抗爆墙进行改进的方案,以提高其安全防护性能。基于GB 50779—2012、SH/T 3160—2009的简支梁计算模型,对传统截面混凝土抗爆墙与新型抗爆墙的抗爆性能进行分析比较。就规范主要检验的变形指标,从理论分析和数值模拟两方面,对新型抗爆墙的抗爆安全性能进行了分析,并用经验公式及离散化求解方法对模拟结果进行了检验,确保了计算结果的可信性。结果表明,该改进方案是可行的,它能有效提高抗爆墙的安全防护性能。改进后的抗爆墙拥有更大的抗弯承载力,能够减小爆炸冲击时所产生的变形。波段高度越大,承载能力越高,刚度越大,跨中位移越小。改进方案具有良好的经济性,在设计承载力相同的情况下,新型抗爆墙消耗材料较少,并能减少因制作木模板而对环境造成的破坏。     

Adsorption Air Cleaning From Ozone

Not much has been written about air cleaning from ozone. The aim of this paper was to demonstrate the possibility of adsorption air cleaning from ozone. The second aim was to investigate the dependence of the efficiency of ozone removal from the air on the height of the adsorber layer and on concentrations of ozone, and to obtain empirical formulas for calculating the efficiency of ozone treatment. Equipment for air cleaning from ozone and nitrogen and sulphur dioxides is suggested.     

高频焊接场所电磁辐射屏蔽与防护研究

焊接过程产生的电磁场对操作人员健康的影响已得到日益广泛的关注,对高频的防护问题,已成为改善劳动条件、保护劳动力的重要课题.在研究焊接生产电磁辐射环境、劳动者健康与安全现状的基础上,通过试验分析了电磁辐射屏蔽效率及导致屏蔽效率差异的因素.通过对不同部门制定的安全限值的比较分析,提出高频焊机安全使用建议.对控制高频焊接场所电磁辐射,尽可能降低从业人员电磁暴露的影响具有重要意义.     

改进的遗传算法在城市污水处理厂区间数优化设计模型中的应用

对于高度非线性的城市污水处理厂区间数优化设计模型(IPODM),若采用传统的方法求解,不仅计算繁琐,且难以有效地寻找全局最优解.本文通过引入遗传算法(GA),与传统的步长搜索法相结合,大大提高了问题的求解效率.本文给出了这种改进算法在某一城市污水处理厂优化设计中的应用实例.结果表明,不仅解的搜索效率有明显的提高,而且目标函数值在原有的基础上改进了20%,有着显著的经济效益;但是由于遗传算法自身的局限性,所求得的解只是一定条件下的最优区间解.     

Next generation guided wave health monitoring for long range inspection of pipes

Shown in this paper are recent accomplishments of robust leading edge technologies in the guided wave technique and the technology transfer to the Gas and Petrochemical Industries. Focusing of guided wave beams is a key for success, compared to conventional axisymmetric excitation. Guided wave scanning and significant sensitivity enhancement are established via the newly implemented focusing scheme. In addition, using both longitudinal and torsional modes is essential to improve sensitivity and reliability in data analysis over the conventional technique based on only longitudinal or torsional. The related theoretical studies and experimental data are also presented along with field test results for confirmation.