韶冶CHGN型刮泥机的改造

介绍总废水处理站预沉池刮泥机的改造及改造后的效果。     

韶冶CHGN型刮泥机的改造

介绍总废水处理站预沉池刮泥机的改造及改造后的效果.     

刮泥机轨道固定装置的改进

本对刮泥机轨道固定装置进行受力分析，并对其主要的压铁块进行改进，同时增加了简单的防松装置。     

φ30m辐射式刮泥机的改进

分析了φ30m辐射式刮泥机在使用维修过程中存在的一些缺点，介绍了相应的改进措施。     

莱钢焦化厂生物脱氮系统优化实践

莱钢焦化厂1#生物脱氮系统在运行过程中存在污泥脱水效果差、加碱成本高、二沉池污泥上浮等问题,通过实施带式浓缩压滤机代替螺压脱水机、液碱代替纯碱、刮泥机改造等技术措施,解决了上述问题。系统优化后运行稳定,沉降比由60%～70%降至20%～40%,加碱成本降低了38%,出水悬浮物由90mg/L降至30mg/L。     

市场需求及小型自动轧管机组的改造

简要介绍了我国无缝钢管生产情况和无缝钢管市场需求情况，指出小型自动轧管机组改造的必要性，提出改造小型自动轧管机组的具体设想，以供小型自动轧管机组实施改造时参考。     

精整线液压系统液位联锁控制的改造

通过对清整线１２个液压系统的现场调查、统计、计算，指出了低液位运行产生的危害，阐述了改造的具体措施，改造后的效果。     

12.5MVA铁合金电炉技术改造的实践

文中比较具体地介绍了将敝口式高烟罩硅铁炉改造成封闭式硅锰炉的实践，电炉运行结果表明。改造是成功的，效果是明显的，并指出了改造后的电炉在运行中存在的某些问题。     

济（源）钢单辊破碎机的改造

就该厂单辊破碎机改造前的状况及技术情况作了详细介绍，并对改造效果进行了分析，指出取消水冷系统是可行的，但仍需进一步完善和改进。     

煤气初终冷轻焦油洗萘工艺的改进

叙述了我厂旧系统焦炉煤气初终冷轻焦油洗萘存在的问题和两次工艺改造的具体方法，指出了改造后工艺的特点、效果及不足，并对改造后工艺指标和经济运行情况进行了统计与分析。     

Stiffness Degradation and Time to Cracking of Cover Concrete in Reinforced Concrete Structures Subject to Corrosion

Corrosion-induced cracks in reinforced concrete (RC) structures degrade the stiffness of the cover concrete. The stiffness degradation is mainly caused by the softening in the stress-strain relation in the cracked concrete. Limited efforts have been made to model the cracking and the corresponding effects on the cover concrete, despite of its importance in assessing and modeling the behavior of RC structures. This paper proposes a stiffness degradation factor to model the stiffness degradation of the cover concrete subject to cracking. The proposed factor is computed in terms of the cracking strain corresponding to the maximum opening of the concrete cracks based on an energy principle applied to a fractured RC structure. The time to cracking of the cover concrete is then determined as the time from the corrosion initiation needed by the crack front to reach the outer surface of the cover concrete. The proposed stiffness degradation factor and the method to compute the time to cracking are illustrated through two numerical examples. The times to cracking of the cover concrete that are predicted using the proposed method are in agreement with the measured values from laboratory experiments.     

Computational Analysis of Masonry Structures with a Funicular Model

This paper presents a computational approach for the assessment of masonry structures based on the well known analogy between the equilibrium of arches and that of hanging strings or cables working in tension. According to the analogy, the hanging strings model the inverted shape of the equilibrium lines (or thrust lines) describing the locus of the equilibrium forces acting across the sections of the arch. The approach proposed combines two developments. First, a new cable element is proposed to numerically model the strings used to describe the equilibrium lines. The formulation proposed, obtained as a modification of the conventional equations for inextensible cables, is based on an exact analytical derivation. Compared to other available numerical approaches, it has the advantage of ensuring the exact equilibrium of the cable net after deformation. Second, complementary algorithms are proposed for the assessment of the strength of masonry structures by the application of the limit theorems of plasticity (static approach). These algorithms are intended to find optimized solutions complying with the so-called safe (or lower-bound) and uniqueness theorems. Two examples of application are described to illustrate the accuracy of the method and its ability to handle masonry structural systems.     

Position‐Force Adaptive Control for Construction Robots

Typical tasks in construction engineering that can be performed by robots include the spraying or cleaning of surfaces. Both applications require that the external force at the end effector of the manipulator be properly controlled. In this paper, the force‐control problem in spraying is analyzed. The paper shows that an unpredictable jet force causes the end effector to diverge from its desired trajectory. The interface between the end effector of the robot and the jet force is modeled as soft contact because both force error and displacement of the end effector are measurable. Therefore, the force‐control problem is simplified to the position‐control problem. The proposed control scheme, using a position‐force adaptive controller, is applied to counterbalancing a jet force. Computer simulation demonstrates that the scheme works well. The maximal position error can be controlled to within 4 mm with the new controller.     

Purging of a Neutrally Buoyant or a Dense Miscible Contaminant from a Rectangular Cavity. I: Case of an Incoming Laminar Boundary Layer

The flow past two-dimensional (2D) channel cavities along with the removal of neutrally buoyant or dense miscible contaminants introduced instantaneously inside the cavity are studied using eddy resolving techniques. In the simulations, the incoming boundary layer is laminar and the flow is observed not to transition to turbulence as it is convected over the cavity. As for these flow conditions the main coherent structures in the separated shear layer over the cavity are quasi-dimensional, 2D simulations are performed. It is found that the mechanism of removal of the contaminant is very different between the neutrally buoyant and buoyant cases. In the neutrally buoyant case the contaminant is purged from the cavity mostly due to the interactions between the vortices shed in the separated shear layer with the main recirculation eddies inside the cavity and with the trailing edge corner. In the simulations in which a dense contaminant is introduced inside the cavity, after the initial stages of the mass exchange process, the main phenomenon is the presence of a large amplitude internal wave motion which interacts with a strong cavity vortex situated near the trailing edge corner in between the shear layer and the density interface. The density variation across this oscillatory interface is strong. Through this interaction wisps of denser contaminant are extracted from the region beneath the density interface, before being ejected from the cavity by the separated shear layer vortices. The values of the global mass exchange coefficients for the different phases of the purging process are estimated from simple dead-zone models. As expected, the purging process is delayed in the case in which the density of the contaminant is larger than the one of the carrying fluid.     

Formation of Secondary Containment Systems Using Permeation of Colloidal Silica

U.S. Environmental Protection Agency (USEPA) regulations require the capture of spills from liquid tanks containing hazardous chemicals by using a secondary containment system. Compacted clay or geomembrane liners are commonly used in secondary containment systems, but they are cumbersome when used in conjunction with existing liquid tanks because of pipeline networks surrounding the tanks. This study evaluates the formation of hydraulic barriers for secondary containment through the permeation of colloidal silica grout. A simplified infiltration model is presented to predict the downward movement of the colloidal silica grout into a soil layer, considering the time-dependent increase in dynamic viscosity of the colloidal silica for different concentrations of an electrolyte accelerator. Because the simplified infiltration model cannot predict the soil-grout interaction or the permeation of the colloidal silica by fingering, its results were calibrated by using the observations from a large-scale column test involving the permeation of colloidal silica into sand. The predicted position of the wetting front was found to match that of the experiment when the parameter governing the change in viscosity of the colloidal silica was increased by a factor of 30. The infiltration model calibrated with observations from column infiltration experiments provides a simple approach to the design of the secondary containment systems using permeation of colloidal silica.     

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.     

Horizontal Injection of Gas–Liquid Mixtures in a Water Tank

Experiments were carried out to investigate the behavior of horizontal gas–liquid injection in a water tank. Measurements of bubble properties and mean liquid flow structure were obtained. The turbulence in the liquid phase appears to help generating bubbles with relatively uniform diameters of 1–4?mm. Both bubble properties and mean liquid flow structure depended on the gas volume fraction and the densimetric Froude number at the nozzle exit. It was found that the bubbles strongly affected the trajectory of the water jet, which behaved similarly to single-phase buoyant jets. However, at gas volume fractions smaller than about 0.15, the water jet completely separated from the bubble core. Bubble slip velocity was also found to be higher than the terminal velocity for isolated bubbles reported in the literature. Dimensionless correlations were proposed to describe bubble characteristics and the trajectory of the bubble plumes and water jets as a function of the gas volume fraction and the densimetric Froude number. Finally, applications of the results for aeration/mixing purposes are presented.     

Failure Analysis of a Bridge Embankment with Cracked Approach Slabs and Leaking Sand

This paper describes a successful failure analysis to determine the causes of loss of backfill sand from a mechanically stabilized earth (MSE) wall, and cracks on the concrete approach slabs on top of it. The Texas Department of Transportation was concerned that the cracks on the approach slabs may be related to the excessive loss of backfill from behind the MSE walls, and that the embankment structure may be unsafe due to potential voids under the concrete slab. Several cubic meters of sugar sand had washed out of the wall and deposited adjacent to the paneled walls. A series of destructive and nondestructive tests were carried out to determine the causes of the problems. It was found that the cracking of the approach slab and the loss of backfill were unrelated. Suggestions for resolving both problems were made based on this study.     

Generalized Model for Geosynthetic-Reinforced Granular Fill-Soft Soil with Stone Columns

This paper pertains to the development of a mechanical model to predict the behavior of a geosynthetic-reinforced granular fill over soft soil improved with stone columns. The saturated soft soil has been idealized by Kelvin–Voight model to represent its consolidation behavior. The stone columns are idealized by stiffer springs. Pasternak shear layer and rough elastic membrane represent the granular fill and geosynthetic reinforcement layer, respectively. The nonlinear behavior of the granular fill and the soft soil is considered. Effect of consolidation of the soft soil due to inclusion of the stone columns has also been included in the model. Plane strain conditions are considered for the loading and reinforced foundation soil system. An iterative finite difference scheme is applied for obtaining the solution, and results are presented in nondimensional form. Comparison between the results from the present study and the analytical solution using theory of elasticity shows reasonable agreement. The advantage of using geosynthetic reinforcement is highlighted. Results indicate that inclusion of the geosynthetic layer effectively reduces the settlement. Nonlinearity in the behavior of the soft soil and the granular fill is reduced due to the use of geosynthetic reinforcement layer.     

Analysis of Arch Dams Using Coupled Trial Load and Block Element Methods

This paper presents the use of the trial load method and the block element method with elastoviscoplastic discontinuities for analysis of arch dams. The arch dam is considered as an arch-cantilever system and the foundation as a block element system. With the displacement compatibility condition at the contact surface of the dam and the foundation (including abutment), the governing equations of the arch dam and foundation are established. These methods are used for the analysis of the double curvature arch dam with complex geology conditions of the Xiaowan Hydroelectric Project in China. The deformation and stress states in both the dam body and the foundation are determined. Furthermore, the stability safety factors of the foundation and the abutment are calculated at the same time, which allows for an optimal design of the arch dam considering the strength, the deformation and the stability of the dam and foundation.