低速重载轴承的故障诊断

分析了低速重载轴承的故障特点及其诊断方法,分别就内圈故障、外圈故障、滚动体故障、保持架故障的诊断方法以及故障的严重程度的判断进行了讨论,并用此方法对两例轴承故障实例进行了分析。     

汽轮发电机振动故障专家系统诊断方法研究

通过对汽轮发电机振动故障机理、故障特征和故障原因的分析,建立了汽轮发电机振动故障特征表,根据振动故障特征表的知识以决策树的形式构建了汽轮发电机振动故障专家系统知识库,并建立了汽轮发电机振动故障专家系统决策树诊断模型。最后通过发电机振动故障实际案例对汽轮发电机振动故障专家系统诊断方法进行了验证,证明了其准确性和可行性。     

棒线裙板中继故障的解决方法

裙板中继故障是棒材生产线的一种主要故障,发生频繁、故障较难预测,同时处理时间较长,对生产影响较大。文章介绍了描述了八钢2#棒材裙板中继故障的解决办法,较好解决了此故障。     

GK1F型机车柴油机机油压力低故障的分析与处理

分析了GK1F型机车柴油机机油压力低故障的危害,介绍了机油压力低故障产生的原因,针对故障原因提出了运用系统性方法判断处理机油压力低故障。     

逆变器故障处理实践

介绍了石钢小型棒材连轧生产线西门子传动柜3次过流报警故障经过,故障均为F011报警信号,记录波形和现场状况有很大差异。按照事故处理原则,通过分析和试验找出了原因,分别为:触发板故障、控制电源板连线故障和负荷故障。为今后快速查找故障,积累了实践经验。     

一起220kV输电线路故障及保护动作分析

通过对现场设备和线路的检查、故障动作报告、故障录波,分析了一起线路接地故障的类型、过程和产生原因,对故障存在的疑点进行了分析和排查,并对故障中继电保护的动作行为进行了分析,得出了结论及工作改进的方向。     

6kV同步电动机定子绕组故障修复

分析同步电机定子绕组匝间短路故障,采用甩掉故障线圈的局部修理方法对6kV同步电机定子绕组匝间故障进行修复,减少了故障停机时间,取得了良好效果。     

电力系统利用小波奇异性的行波故障测距

高压输电线路故障的准确定位,能够缩短故障修复时间,提高供电可靠性,减少停电损失.对于占绝对多数的瞬时性故障来讲,准确的故障定位可以找出故障的原因,及时发现隐患,防止事故再次发生.基于小波变换的行波故障测距系统将小波变换引入双端行波故障定位,实现了快速可靠的定位和选相.     

20GJ型增压器喷机油故障原因分析及判断

使用20GJ型增压器的柴油机,喷机油故障多,原因多样,判断故障较难.针对增压器各种可能出现的故障及判断方法,进行了分析和论述,为处理故障提供了方便.     

空分设备运行故障原因分析及处理

介绍了空分设备运行故障的种类,分别阐述仪电控故障、机械故障、工艺故障的种类,分析了故障产生的原因,提出了排除故障的措施,使空分设备的运行安全性和稳定性得到提高。     

Drawdown due to Temporally Varying Pumping Discharge: Inversely Estimating Aquifer Parameters

A ramp kernel method is proposed for accurately calculating the drawdown due to any temporal variation in pumping discharge. The use of the ramp kernels assumes the linear variation between the two consecutive measured pumping discharges. The prior studies assume a rectangular variation between the two consecutive measured pumping discharges. In the rectangular variation, a uniform pumping rate is assumed during a time span. An analytical equation for calculating the ramp kernel is derived. An optimization method is used with the proposed ramp kernels for inversely estimating the aquifer parameters from drawdown due to an arbitrary unsteady pumping discharge. Unlike the prior methods, the proposed method accurately identifies the parameters even when the sampling interval for the drawdown and pumping discharge is longer than that needed for assuming a linear variation. The proposed method outperforms the prior method. Application of the proposed method is illustrated using examples.     

New Orleans Levee System Performance during Hurricane Katrina: London Avenue and Orleans Canal South

Hurricane Katrina was one of the worst natural disasters in U.S. history. The effects of the hurricane were particularly devastating in the city of New Orleans. Most of the damage was due to the failure of the levee system that surrounds the city to protect it from flooding. This paper presents the results of centrifuge models conducted at Rensselaer Polytechnic Institute and the U.S. Army Corps of Engineers simulating the behavior of the levees at London Avenue North and South that failed during Hurricane Katrina. Those levees failed without being overtopped by the storm surge. Also included are the results of a centrifuge model of one levee section at Orleans Canal South, which did not fail during the hurricane. The key factor of the failure mechanism of the London Avenue levees was the formation of a gap between the flooded side of the levee and the sheetpile. This gap triggered a reduction of the strength at the foundation of the protected side of the levee. The results are fully consistent with field observations.     

Case Study of Fluvial Modeling of River Responses to Dam Removal

A plan was made to remove Matilija Dam on the Ventura River. With dam removal, the delta in the reservoir and the downstream channel were expected to undergo major changes in morphology. The FLUVIAL-12 model was employed to simulate reservoir and river channel responses after dam removal. As a first step, the model was calibrated using the Ventura River data to establish its validity. In calibration, the model was used to simulate the fluvial processes starting from the time of dam completion. The simulated sediment deposition above the Matilija Dam matches closely with the deposits measured by the U.S. Bureau of Reclamation. A large amount of sediment was stored in the reservoir; some of the stored sediment would be transported downstream after dam removal. An important consequence of dam removal is the major increase of sediment release to the river channel downstream. The sediment supply to the downstream reach is not only from the stored sediment in the reservoir but also from natural sediment inflow from the upstream watershed. Therefore, sediment supply to the downstream reach will exceed the natural sediment flow before the dam presence. This situation tends to overload the downstream reach with sediment, resulting in excessive deposition. The amount of sediment release from the area above the removed dam is closely related to the changes in reservoir morphology. It is necessary to model changes in the channel bed profile and channel width during erosion in order to determine the amount of sediment removal. The amount of sediment release may not be simulated using an erodible-bed model but it may be determined using an erodible boundary model.     

Evaluation, Rehabilitation Planning, and Stay-Cable Replacement Design for the Hale Boggs Bridge in Luling, Louisiana

The Hale Boggs Bridge opened to traffic on October 5, 1983. At the time, it was the first U.S. cable-stayed crossing over the Mississippi River. The PE (polyethylene) protective sheathing was damaged in many of the cables before and during installation, and after the opening of the bridge to traffic. Repairs were attempted to correct the defects in cable sheathing. Many of the repairs performed poorly and failed to protect the main tension element. The condition of 39 out of 72 cables indicated a critical need for repair and timely action was recommended. To address these damages, and to assure the structural integrity of the bridge structure, several strategies involving a range of repair and replacement options were evaluated using life cycle cost analysis. It was concluded that the strategy to replace all cables presents the best value among evaluated alternatives. The design of the complete 72 cable array replacement is the first occasion on which this process is attempted in North America. The final design of the replacement cables is heavily influenced by the geometric restrictions of the existing anchorage locations. The replacement cables are being designed for a 75-year design life and incorporated with the latest advancements in corrosion protection and vibration control. Maintenance of traffic design is an essential part of the project. The bridge is a critical regional link and constitutes a hurricane evacuation route. Traffic maintenance during cable replacement was designed to be as unobtrusive to the public and commerce as practical. This paper describes efforts associated with cable condition assessment, rehabilitation strategy, and design considerations and concepts, undertaken by the writers since 2002 to improve the condition of this major river crossing.     

Below-Average Bidding Method

The low-bid method, typically used for competitive bidding in the United States, may result in a contract with a firm that submits either accidentally or deliberately an unrealistically low-bid price. Such an occurrence hurts both the owner and the contractor by promoting disputes, increased costs, and schedule delays. To address this problem, other countries have adopted bidding methods based on the average of the bids submitted. One such approach is the below-average method where the winning bid is closest to but below the average of all bids. A competitive bidding model for the below-average-bid method is presented and its merits relative to the average-bid method and the low-bid method are explored. The below-average-bid process is investigated analytically and through Monte Carlo simulation. The results of bidding models for the below-average, the average, and the low-bid methods are presented in four easy-to-use nomograms which allow contractors to determine the optimal lump-sum bid price for each method without the need for complicated analysis. A comparison of the three methods provides information and insights to help owners with the difficult choice of a suitable bidding method for the project at hand.     

Reliability-Based Optimal Design of Truss Structures Using Particle Swarm Optimization

In this work, the particle swarm optimization method is employed for the reliability-based optimal design of statically determinate truss structures. Particle swarm optimization is inspired by the social behavior of flocks (swarms) of birds and insects (particles). Every particle’s position represents a specific design. The algorithm searches the design space by adjusting the trajectories of the particles that comprise the swarm. These particles are attracted toward the positions of both their personal best solution and the best solution of the swarm in a stochastic manner. In typical structural optimization problems, safety is dealt with in a yes/no manner fulfilling the set of requirements imposed by codes of practice. Considering uncertainty for the problem parameters offers a measure to quantify safety. This measure provides a rational basis for the estimation of the reliability of the components and of the entire system. Incorporating the reliability into the structural optimization framework one can seek a reliability-based optimal design. For the problems examined herein, the reliability indexes of the structural elements are obtained from analytical expressions. The structure is subsequently analyzed as a series system of correlated elements and the Ditlevsen bounds are used for the calculation of its reliability index. The uncertain-random parameters considered in this work are the load, the yield-critical stress; and the cross sections of the elements. The considered design variables of the optimization problem are the cross-sectional areas of the groups, which control the size of the truss, and the heights and lengths that control the shape of the truss. The results of the optimization are presented for a 25-bar truss and a 30-bar arch and the robustness of the optimization scheme is discussed.     

Bridge Scour and Substructure Deterioration: Case Study

In 1988, the State of Mississippi set up its first statewide underwater bridge inspection program. During this inspection, serious damage was found on the substructure of two parallel bridges on I-10 near Biloxi. Significant scour had occurred, exposing the steel piling. These piles had severe corrosion with cross sections reduced by 50%. Because of the reduced cross section, the web and flanges of the piles had buckled locally. This damage was exacerbated by collisions associated with barge traffic on the waterway. This accumulation of problems resulted in a bridge on the verge of collapse. Two alternatives were used to repair the substructure. The more seriously damaged piles were encased in concrete, and the less seriously damaged ones were dewatered and a concrete seal was placed around the piles. After 10?years, the piers with pile encasements showed no additional scour effects. However, the piers with the large concrete seals had scoured by as much as 3?m (10?ft). Described in this paper is the analysis of damage, design of the repair, and a review of the performance of the two types of repair over a 10-year period.     

Evaluation of Construction Practices That Influence the Bond Strength at the Interface between Pavement Layers

This study investigated the influence of several construction practices on the bond strength at the interface between pavement layers. These practices included the surface treatment, curing time, residual application rate, and equipment tracking. Three tests were performed for estimating the bond strength between an existing hot mix asphalt (HMA) and a newly constructed HMA overlay, namely the Florida Dept. of Transportation shear tester, the University of Texas at El Paso pull off test, and the torque bond test. Testing involved a CSS-1 type emulsion as the tack coat. The results from the three tests were statistically analyzed. Generally, milling provided a significantly better bond at the interface between the existing surface and the new overlay. Curing time had a minimal effect on the bond strength. The results indicated that the absence of tack coat did not significantly affect the bond strength at the interface for the milled sections, whereas it severely decreased the strength for the nonmilled sections. The results also showed that increasing the residual rate of tack coat did not generally affect the bond strength at the interface.     

Bridge Blockage and Overbank Flow Simulations Using HEC–RAS in the Keelung River during the 2001 Nari Typhoon

On September 16, 2001, Typhoon Nari resulted in severe flooding in the Keelung River basin. More than 1,000 shipping containers were swept by the rising water from the floodplain into the river, blocking 14 bridges. A severe overbank flow due to the blockage occurred at the Ba-Tu Railway Bridge. The overbank flow then passed through a railway tunnel and inundated Keelung City, resulting in significant damage. The objective of this study was to determine the influence of the bridge blockage and the Ba-Tu overbank flow on the water stages in the Keelung River during Typhoon Nari. The floating-pier-debris module and the lateral-weir module in the Hydrologic Engineering Center–River Analysis System (HEC-RAS) unsteady-flow routing model were applied to investigate water stage variation due to the bridge blockage and overbank flow. The numerical simulation results provided by this study served as an important reference for authorities who needed to clarify the responsibility of the containers’ owners for the loss of lives and property during this typhoon.     

Influence of the chromium and ytterbium co-doping on the photoluminescence of zinc selenide crystals

The luminescent properties of ZnSe, ZnSe：Cr（0.05 at.% Cr）, ZnSe：Yb（0.03 at.% Yb） and ZnSe：Cr：Yb（0.05 at.% Cr, 0.05 at.% Yb） crystals, doped during the growth process by the chemical vapor transport method, were studied within the temperature interval of 6–300 K. At the 6 K temperature in the visible spectral range 2 bands were observed： a band in the excitonic spectral region and a band of self-activated luminescence. It was shown that co-doping of zinc selenide crystals with the chromium and ytterbium led to the combination of the impurities influence on the photoluminescent properties. At the liquid helium temperature in the middle infrared range of the spectra of the ytterbium and chromium co-doped crystal a band with the maximum localized at 1.7μm was observed, which was overlapped with a complex band in the middle-IR spectral range, characteristic for the chromium doped ZnSe crystals. On the basis of obtained data an interaction mechanism of the chromium and ytterbium co-doping impurities was proposed. Guided by the existent model of the ytterbium ion incorporation in the selenide sublattice of the ZnSe crystals, an assumption about stabilization of single charged chromium ions in the zinc sublattice crystal nodes, by means of formation of the local charge compensating clusters, was made. It was assumed that the resonant energy transfer from one chromium ion to another,which led to the concentration quenching of the IR emission in the ZnSe：Cr PL spectra, would lead to the broadening of the IR emission in the spectra of ytterbium and chromium co-doped zinc selenide crystals.g