Data-driven methods for predicting the representative temperature of bridge cable based on limited measured data

Cable-stayed bridges have been widely used in high-speed railway infrastructure.The accurate determination of cable’s representative temperatures is vital during the intricate processes of design,construction,and maintenance of cable-stayed bridges.However,the representative temperatures of stayed cables are not specified in the existing design codes.To address this issue,this study investigates the distribution of the cable temperature and determinates its representative temperature.First,an experimental investigation,spanning over a period of one year,was carried out near the bridge site to obtain the temperature data.According to the statistical analysis of the measured data,it reveals that the temperature distribution is generally uniform along the cable cross-section without significant temperature gradient.Then,based on the limited data,the Monte Carlo,the gradient boosted regression trees(GBRT),and univariate linear regression(ULR)methods are employed to predict the cable’s representative temperature throughout the service life.These methods effectively overcome the limitations of insufficient monitoring data and accurately predict the representative temperature of the cables.However,each method has its own advantages and limitations in terms of applicability and accuracy.A comprehensive evaluation of the performance of these methods is conducted,and practical recommendations are provided for their application.The proposed methods and representative temperatures provide a good basis for the operation and maintenance of in-service long-span cable-stayed bridges.

简单图像的快速聚焦

为了有效地实现简单图像的快速高精度自动聚焦,提出了一种新的快速聚焦算法。首先在相机进行调焦时自动获取系列零件图像,并记录各图像对应的位置;然后计算每张图像中目标边缘的灰度变化跨度值,从中找到跨度值最小的图像,即为最清晰图像;最后把其所在位置反馈给硬件驱动系统,实现自动聚焦。用新算法分别对不同形状和不同材料的零件,在添加椒盐噪声和没有添加噪声的情况下进行实验,并与计算量小的几种经典最优聚焦函数做了对比试验。结果表明,用新算法对简单图像进行聚焦比常用的最优聚焦函数更敏锐,单峰性更好,抗噪能力更强,而且速度比最快的绝对梯度函数快30%以上。因此,新算法在拍摄简单场景时,鲁棒性好,可以更好地实现快速聚焦。

基于改进TF-IDF算法的情报关键词提取方法

传统的TF-IDF完全基于词频,忽略了词语的其它特征项对关键词的影响。本文提出基于TF-IDF、词位置和词跨度的关键词自动提取的方法。该方法通过在传统的TF-IDF关键词权重计算方法中,加入位置权值及词跨度权值,避免单纯采用TF-IDF算法产生的偏差。实验结果表明,该方法在情报关键词提取中有广泛的应用价值,其准确率、召回率及F1值与传统方法相比有明显提升。

面向不同数据分布的多维直方图算法COCA-Hist

基于代价的RDBMS优化器需要对含有范围查询的合取谓词的结果集基数进行准确的估计,多维直方图对多维数据分布进行模拟,避免在估计结果集基数时采用数据独立性假设,造成估计误差过大,进而导致选择非优化的查询执行计划.在不同的数据分布情况下,传统的多维直方图(如MHist-2)效果有很大不同.数据相关系数和值域密度、值域参数是准确刻画多维数据分布的有效指标,文中提出了根据不同的指标采用不同的动态优化的多维直方图算法COCA-Hist,可以大大改善传统多维直方图在平均情况下的准确性.通过分析传统的多维直方图的最坏情况,COCA-Hist的改进算法可以改进传统的多维直方图在最坏情况下的准确性.实验比较了COCA-Hist和传统的多维直方图MHist-2以及GENHist和STHoles的准确性和时间效率.实验显示无论在平均情况下还是在最坏情况下COCA-Hist的改进算法均优于传统的MHist-2直方图,并且COCA-Hist的准确性和创建时间均比GENHist有极大的改善,在准确性方面COCA-Hist较优于STHoles,而在空间预算有限时STHoles的创建时间比COCA-Hist高两个数量级.

Real edge spans of distance two labelings of graphs

An L（j, k）-labeling of a graph G is an assignment of nonnegative integers to the vertices of G such that adjacent vertices receive integers which are at least j apart, and vertices at distance two receive integers which are at least k apart. Given an L（j, k）-labeling f of G, define the L（j, k） edge span of f, βj,k（G,f） =max{ ｜f（x）-f（y）｜： {x,y}∈E（G）}. The L（j,k） edge span of G, βj,k （G） is min βj,k（ G, f）, where the minimum runs over all L（j, k）-labelings f of G. The real L（.j, k）-labeling of a graph G is a generalization of the L（j, k）-labeling. It is an assignment of nonnegative real numbers to the vertices of G satisfying the same distance one and distance two conditions. The real L（j, k） edge span of a graph G is defined accordingly, and is denoted by βj,k（G）. This paper investigates some properties of the L（j, k） edge span and the real L（j, k） edge span of graphs, and completely determines the edge spans of cycles and complete t-partite graphs.

Deformation mechanism and excavation process of large span intersection within deep soft rock roadway

The FLAC3D software was used to simulate and analyze numerically the displacement, stress and plastic zone distribu-tion characteristics of a large span intersection in a deep soft rock roadway after the surrounding rock was excavated. Our simula-tion results show that there are two kinds of dominating factors affecting roadway stability at points of intersection, one is the angle between horizontal stress and axial direction of the roadway and the other are the angles at the points of intersection. These results are based on a study we carried out as follows: first, we analyzed the failure mechanism of a large span intersection and then we built a mechanical model of a rock pillar at one of the points of intersection. At the end of this analysis, we obtained the failure characteristics of the critical parts on the large span intersection. Given these failure characteristics, we proposed a new supporting method, i.e., a Double-Bolt Control Technology (DBCT). By way of numerical simulation, DBCT can effectively control the deformation of the surrounding rock at the points of intersection in roadways.

Numerical verification of geometry control method of the construction for super-span cable-stayed bridge

Taking Sutong Bridge as the object investigated, the correctness of the geometry control method is verified by numerical simulation analysis. Taking the impact of geometric nonlinearity into account, the impacts of structural geo- metric profile induced by temporary loads and temperature field during the construction procedure are investigated. The simulation results indicate that only the stage state of the structure during construction is affected. Satisfied outcome of construction control can be achieved based on ~eometrv control method.

Safe roof thickness and span of stope under complex filling body

Longhole caving method was used to mine gently inclined thick orebody step by step in a test stope of tin mine under complex filling body. The problem that the complex filling body around the stope affects the stability of roof thickness, chamber and spacer pillar in actual mining was investigated; meanwhile, the formed goaf during mining is so vulnerable that surrounding rock collapses early. Based on this point, elasticity mechanics and limit span theory were used to study separately the roof thickness and the span limit of goaf formed in mining, and then a reasonable roof thickness of 8 m and goaf span of 14 m are proposed. In addition, the stability of roof thickness, chamber and spacer pillar were investigated and analyzed by using numerical analysis method; meanwhile, the field monitoring on the displacement of caving chamber was conducted. The results show that the maximum compressive stress of surrounding rock is 20 MPa, and the maximum tensile stress is 1.2 MPa, which is less than the ultimate tensile strength of 2.4 MPa. Moreover, plastic zone has little influence on stope stability. In addition, the displacement of 11 mm is also smaller. The displacement monitoring results are consistent with the numerical results. Thus, the roof thickness and span of goaf proposed are safe.

Characteristics of wind pressure pulse on large-span flat roofs

The wind pressure pulse events, among the most important characteristics of wind pressure fluctuations on large-span flat roofs, were investigated by wind tunnel tests in this paper. Incorporating the formation mechanism of wind pressure pulse events, the peak over threshold method was employed to study properties of this kind of events. The event duration time, the energy contribution, the number of the pulse events, and the distribution of average peak pressure were calculated. Probability density functions of some typical samples in separation region were also given. Results show that the non-Gaussian roof pressure is strong in the flow separation region owing to the wind pressure pulse events. Evaluations of the extreme peak pressures, which can be determined by the peak over threshold method effectively, are important to the design of building cladding.

Shaking table tests and numerical simulation of dynamic properties of underground structures

It is considered thai the damage of the underground structures caused by earthquakes is minor for a long time. However, the catastrophic damages induced by several recent earthquakes （e. g. Kobe earthquake in 1995 ） revealed that the study on the dynamic properties of the underground structures is indispensable. The dynamic behavior and damage mechanism of underground structure are analyzed by using shaking table tests （ both shallow-and deep-buried） and numerical simulation （3D FEM） including horizontal and vertical input motions, individually and simultaneously. From the results, the underground structure collapsed due to strong horizontal forces although vertical deformation is not negligible. The vertical excitation increases the response of structure, especially the stress and shear stress at the upper section; the soil influenced the property of soilstructure system. In the same excitation, the response in shallow-buried test is larger than deep case. Both overburden and vertical earthquake play important roles in the response of structure and those are two critical aspects in the design of the large-span underground structures, such as subway stations.

Numerical study on the correlation of transonic single-degree-of-freedom flutter and buffet

Transonic single-degree-of-freedom(SDOF) flutter and transonic buffet are the typical and complex aeroelastic phenomena in the transonic flow. In this study, transonic aeroelastic issues of an elastic airfoil are investigated using Unsteady Reynolds-Averaged Navier-Stokes(URANS) equations. The airfoil is free to vibrate in SDOF of pitching. It is found that, the coupling system may be unstable and SDOF self-excited pitching oscillations occur in pre-buffet flow condition, where the free-stream angle of attack(AOA) is lower than the buffet onset of a stationary airfoil. In the theory of classical aeroelasticity, this unstable phenomenon is defined as flutter. However, this transonic SDOF flutter is closely related to transonic buffet(unstable aerodynamic models) due to the following reasons. Firstly, the SDOF flutter occurs only when the free-stream AOA of the spring suspended airfoil is slightly lower than that of buffet onset, and the ratio of the structural characteristic frequency to the buffet frequency is within a limited range. Secondly, the response characteristics show a high correlation between the SDOF flutter and buffet. A similar "lock-in" phenomenon exists, when the coupling frequency follows the structural characteristic frequency. Finally, there is no sudden change of the response characteristics in the vicinity of buffet onset, that is, the curve of response amplitude with the free-stream AOA is nearly smooth. Therefore, transonic SDOF flutter is often interwoven with transonic buffet and shows some complex characteristics of response, which is different from the traditional flutter.

Improvement of the Second Order Approximation of the Smoothed Particle Hydrodynamics

The smoothed particle hydrodynamics (SPH), as a fully Lagrangian particle method, has been suc- cessfully applied to astrophysical problems and extended to elastic dynamics and computational fluid dynamics. High order derivatives have to be approximated when elastic dynamics problems are modeled. However, the approximation errors in SPH could lead to computational failure in the case that the order of derivative is high. A novel method was proposed in order to improve the accuracy of SPH method, which shows the relationship between the selected functions and their SPH approximations. The entire involved system was represented by a finite number of particles that carry individual mass and occupy individual space, and the integral interpo- lation was approximated by a summation interpolation. In addition, error comparison was made between SPH method with and without the present improvement.