Research on Eddy Current Testing System of the Carburized Layer Depth of 20CrMnTi Steel

In this paper the carbon distribution in the carburized layer of 20CrMnTi steel was studied. The relationship between the depth of a carburized layer and the surface carbon distribution was established. Eddy current testing system of the case depth of this carburized steel was built by using ANSYS software as second development platform.

Hybrid Model Testing Technique for Deep-Sea Platforms Based on Equivalent Water Depth Truncation

In this paper, an inner turret moored FPSO which works in the water of 320 m depth, is selected to study the socalled ＂passively-truncated ＋ numerical-simulation＂ type of hybrid model testing technique while the tnmcated water depth is 160 m and the model scale ）, = 80. During the investigation, the optimization design of the equivalent-depth truncated system is performed by using the similarity of the static characteristics between the truncated system and the full depth one as the objective function. According to the truncated system, the corresponding physical test model is made. By adopting the coupling time domain simulation method, the tnmcated system model test is numerically reconstructed to carefully verify the computer simulation software and to adjust the corresponding hydrodynamic parameters. Based on the above work, the numerical extrapolation to the full depth system is performed by using the verified computer software and the adjusted hydrodyrmmic parameters. The full depth system model test is then performed in the basin and the results are compared with those from the numerical extrapolation. At last, the implementation procedure and the key technique of the hybrid model testing of the deep-sea platforms are summarized and printed. Through the above investigations, some beneficial conclusions are presented.

Round robin using the depth of penetration test method on an armour grade alumina

The depth of penetration(DOP)method is a well-known ballistic test method for characterisation and ranking of ceramic armour materials.The ceramic tile is bonded to a backing material of semi-infinite thickness,and the penetration depth of the projectile gives a measure of the performance of the ceramic.There is,however,an inherent variability in the results from this test method.In this work,the accuracy and the variability of the DOP method has been investigated in a round robin exercise.Six ballistic test centres took part in the exercise.A test protocol was developed,in which the threat type(projectile and impact conditions)and a procedure on how to prepare the targets were specified.The targets consisted of alumina tiles of two different thicknesses that were bonded to polycarbonate backing cubes.Two different 7.62 mm armour piercing projectiles were employed;one with a hard steel core and one with a tungsten carbide core.The projectiles and the other materials all came from single material batches in order to avoid batch-to-batch variations in material properties.These materials were distributed between the ballistic test centres.The test results of the different ballistic test facilities were collected and compared.There was not a lot of variation between the average DOP values obtained at each laboratory,but the variation in penetration depth between shots was high.The consequence of this variation may be less confidence in the test results,and a statistical method was used to evaluate the required number of tests that are sufficient to obtain an average result with high confidence.In most cases,the required number of tests is much higher than what is practically feasible.This work was conducted as part of the European Defence Agency-project CERAMBALL.

Anchoring Depth Research of Anti-Slide Piles of Anchor Bar in Soil

The model test result of earth force in the side of anti-slide pile of anchor bars was introduced.There are three groups of the tests.The loads were on the back side of the slope in two groups.The other one was loaded just behind the pile by the jack.In order to get the force of the soil,some earth-pressure boxes were used to get the earth pressure on the side of the piles.The part of the max pressure and the earth pressure was mainly focused under the slip line

Mathematical model for abrasive suspension jet cutting based on orthogonal test design

This paper describes the application of orthogonal test design coupled with non-linear regression analysis to optimize abrasive suspension jet （AS J） cutting process and construct its cutting model. Orthogonal test design is applied to cutting stainless steel. Through range analysis on experiment results, the optimal process conditions for the cutting depth and the kerr ratio of the bottom width to the top width can be determined. In addition, the analysis of ranges and variances are all employed to identify various factors： traverse rate, working pressure, nozzle diameter, standoff distance which denote the importance order of the cutting parameters affecting cutting depth and the kerf ratio of the bottom width to the top width. ~rthermore, non-linear regression analysis is used to establish the mathematical models of the cutting parameters based on the cutting depth and the kerr ratio. Finally, the verification experiments of cutting parameters＇ effect on cutting performance, which show that optimized cutting parameters and cutting model can significantly improve the prediction of the cutting ability and quality of ASJ.

An Experimental Study on the Effect of Foundation Depth, Size and Shape on Subgrade Reaction of Cohessionless Soil

The modulus of subgrade reaction ks depends on several factors such as the size and shape of the foundation as well as the embedment depth of the foundation. The present study is an experimental analysis using plate load test to determine the effect of foundation depth, size as well as the shape on the modulus of subgrade reaction (ks) of cohesionless soils. It was carried out by using nine rigid steel plates with different sizes and shapes (circular, square and retangular). The tests were carried out on cohessionless soil with different relative densities under different applied pressures. The settlement has been measured at the surface of the plate for different depths of footings. The ultimate bearing capacity [qu] has been determined from the stress-settlement relationships. The allowable bearing capacity (qa) was determined by dividing the ultimate bearing capacity (qu) by F.S. = 3.0, after which the corresponding settlement (Sa) has been obtained. However, ks was calculated based on dividing the allowable bearing capacity (qa) by the corresponding settlement (Sa). From the present study it is concluded that the subgrade reaction ks of cohessionless soil increases with increasing foundation depth as well as foundation size. In addition, subgrade reaction ks of cohessionless soil under rectangular footing is higher than that under square and that under circular one with same equivalent area. An empirical formula is presented to calculate the subgrade reaction ks of cohessionless soil under square foundation taking into consideration foundation depth. Fair agreement has been obtained between values of ks from the empirical formula at depth of footing = 0.00 B and Biot (1937) as well as Meyerhof and Baike (1965).

Numerical Analysis on the Effects of Submerged Depth of the Grid and Direction of Incident Wave on Gravity Cage

In this paper, the numerical model of the net cage with the grid mooring system in waves is set up by the lumped mass method and rigid kinematics theory, and then the motion equations of floating system, net system, mooring system, and floaters are solved by the Runge-Kutta fifth-order method. For the verification of the numerical model, a series of physical model tests have been carried out. According to the comparisons between the simulated and experimental results, it can be found that the simulated and experimental results agree well in each condition. Then, the effects of submerged depth of grid and direction of incident wave propagation on hydrodynamic behaviors of the net cage are analyzed. According to the simulated results, it can be found that with the increase of submerged depth of grid, the forces acting on mooring lines and bridle lines increase, while the forces on grid lines decrease; the horizontal motion amplitudes of floating collar decrease obviously, while the vertical motion amplitudes of floating collar change little. When the direction of incident wave propagation changes, forces on mooring lines and motion of net cage also change accordingly. When the propagation direction of incident wave changes from 0° to 45°, forces on the main ropes and bridle ropes increase, while the forces on the grid ropes decrease. With the increasing propagation direction of incident wave, the horizontal amplitude of the forces collar decreases, while the vertical amplitude of the floating collar has little variation.

Optimal Design of Equivalent Water Depth Truncated Mooring System Based on Baton Pattern Simulated Annealing Algorithm

The highest similarity degree of static characteristics including both horizontal and vertical restoring force-displacement characteristics of total mooring system, as well as the tension-displacement characteristics of the representative single mooring line between the truncated and full depth system are obtained by annealing simulation algorithm for hybrid discrete variables （ASFHDV, in short）. A“baton” optimization approach is proposed by utilizing ASFHDV. After each baton of optimization, if a few dimensional variables reach the upper or lower limit, the boundary of certain dimensional variables shall be expanded. In consideration of the experimental requirements, the length of the upper mooring line should not be smaller than 8 m, and the diameter of the anchor chain on the bottom should be larger than 0.03 m. A 100000 t turret mooring FPSO in the water depth of 304 m, with the truncated water depth being 76 m, is taken as an example of equivalent water depth truncated mooring system optimal design and calculation, and is performed to obtain the conformation parameters of the truncated mooring system. The numerical results indicate that the present truncated mooring system design is successful and effective.

Effective depth of dynamic compaction in embankment built with soils and rocks

Effective depth of dynamic compaction was summarized, and the advantages of dynamic compaction technology of effective depth were analyzed elaborately. The formula determining the reinforcement depth was deduced by using dimensional analysis method. The influential factors of hammer weight, hammer area, dry density of filling materials and filling materials types were comprehensively investigated. The formula of effective depth was established based on the definition of the dimensions analysis. Based on experimental results of in-situ dynamic compaction, the technology was applied to highway embankment filled with soils and rocks. From the comparison between the theoretical calculations and the experimental results, it is found that the theoretical results using the developed formula are close to experimental results.

Can MODIS Detect Trends in Aerosol Optical Depth over Land?

The Moderate Resolution Imaging Spectroradiometer （MODIS） sensor onboard NASA＇s Aqua satellite has been collect- ing valuable data about the Earth system for more than 14 years, and one of the benefits of this is that it has made it possible to detect the long-term variation in aerosol loading across the globe. However, the long-term aerosol optical depth （AOD） trends derived from MODIS need careful validation and assessment, especially over land. Using AOD products with at least 70 months＇ worth of measurements collected during 2002-15 at 53 Aerosol Robotic Network （AERONET） sites over land, Mann-Kendall （MK） trends in AOD were derived and taken as the ground truth data for evaluating the corresponding results from MOD｜S onboard Aqua. The results showed that the AERONET AOD trends over all sites in Europe and North Amer- ica, as well as most sites in Africa and Asia, can be reproduced by MODIS/Aqua. However, disagreement in AOD trends between MODIS and AERONET was found at a few sites in Australia and South America. The AOD trends calculated from AERONET instantaneous data at the MODIS overpass times were consistent with those from AERONET daily data, which suggests that the AOD trends derived from satellite measurements of 1-2 overpasses may be representative of those from daily measurements.

某600MW亚临界机组20%深度调峰技术方案应用探讨

新型电力系统中煤电将是最重要的调节性电源,越来越多的煤电机组将参与深度调峰。现有机组普遍面临低负荷时锅炉稳燃、受热面超温、脱硝投入、汽机安全性等问题不能实现深度调峰。对国内某600 MW亚临界机组进行了深度调峰摸底试验,得到了制约机组实现20%负荷深度调峰的瓶颈。针对瓶颈,为实现20%深度调峰,提出了锅炉侧燃烧器优化、磨煤机分离器改造、送风机改造、水平烟道吹灰优化,汽机侧辅助蒸汽系统改造,控制侧逻辑优化等技术方案。

不同嵌岩深度下抗拔桩承载特性研究

以广东省江门市某工程为例,通过有限元分析软件ABAQUS,结合地勘报告及现场对桩基进行抗拔静载试验得出的荷载–位移曲线图,建立抗拔桩三维有限元模型进行数值模拟计算分析,研究不同嵌岩深度增量下抗拔桩的承载特性。研究成果表明:增加嵌岩深度可在一定程度上提高桩基抗拔承载力,但二者之间并非呈线性增长关系。当嵌岩深度增量为3D时,相较于原试桩的桩顶位移量减小54.2%,抗拔承载力提高105.2%,对桩基抗拔承载力的提高效果尤为显著。

叶轮中心淹没深度对特低扬程下立式泵装置流道水力性能的影响

为提高特低扬程泵站立式轴流泵装置的水力性能,该研究对叶轮直径为3.0、2.5、2.0、1.5 m的立式轴流泵装置在不同叶轮中心淹没深度下的进、出水流道流场分别进行了三维湍流流动数值计算,并对流道流场和水头损失进行了分析比较;对某特低扬程泵站在叶轮中心淹没深度为3.08、2.38、1.68 m下的立式轴流泵装置水力性能分别进行了数值计算及比较,并进行了泵装置模型试验验证。研究结果表明:叶轮中心淹没深度对肘形进水流道的水流流态及水头损失的影响很小,但对虹吸式出水流道的流态和水头损失影响较大;随着叶轮中心淹没深度的增大,虹吸式出水流道内的流态逐渐改善,流道水头损失基本呈下降趋势,泵装置效率逐渐增大,特低扬程工况下泵装置模型试验最优工况点的效率达75.92%,泵装置能量性能数值模拟结果与模型试验结果基本一致。研究结果可为特低扬程泵站采用立式泵装置的设计提供一定参考依据。

黄土盾构隧道开挖围岩扰动特性模型试验研究

为了探究不同含水率和埋深等工况下的黄土盾构隧道开挖对围岩的扰动作用特征,采用相似模型试验,首先通过三轴试验测定了不同含水率下原状黄土物理参数及强度指标,通过大量试配得到了不同含水率下与原状黄土强度指标参数相似的试验用土。其后,考虑盾构隧道盾尾间隙特征,开展不同含水率及埋深等组合工况下盾构开挖模拟试验,通过微型土压力传感器、百分表等监测元件以及数字图像技术等手段,分析了不同工况下地层变形、地表沉降和围岩应力的变化规律。研究发现:含水率较低时,围岩的自稳能力强;含水率越高,埋深越大,开挖对地层的扰动作用也越大;地表最大沉降值与含水率呈正相关,与埋深呈负相关;围岩剩余应力随含水率和埋深的增大而增大,但当含水率增大至一定值(26.6%)时,围岩剩余应力骤减;基于不同含水率下的围岩应力及变形发展规律,可将黄土含水率分为自稳、形变以及松动含水率,基于含水率和埋深引起的围岩松动情况,可将不同工况下的黄土盾构隧道围岩压力作用模式按照形变压力和松动压力计算,以更加适应黄土地层的特性。

弱胶结砂岩地基承载力深度修正系数k2试验研究

为探究弱胶结砂岩深度修正合理性及修正系数取值,依托南京龙潭长江大桥北锚碇大型块体基础,对25 m埋深的弱胶结砂岩持力层分别开展基岩深层和浅层平板载荷试验,得到持力层深度修正前后的地基承载力特征值,研究深度修正规律,研究结论:修正浅层载荷试验地基承载力的修正系数k2t取3.3、修正规范法地基承载力的修正系数k2c取8.0,保守考虑时可不区分未修正的承载力特征值获得途径,k2统一取3.3;深度修正后地基承载力有较大提升,说明本工程中对弱胶结砂岩承载力进行深度修正是很有必要的;对比现有规范中土质地基k2的取值规律,弱胶结砂岩的k_(2t)和k_(2c)取值较为保守,该值可为类似地质条件下的工程提供参考。

施工凿毛对铰缝抗剪性能影响研究

为研究空心板梁桥不同凿毛情况对铰缝受力性能的影响及其破坏机理,通过混凝土试块剪切流变试验和利用ABAQUS数值分析软件建立二维内聚力单元模型,分析了铰缝处受力情况和损伤破坏机理,并建立了凿毛界面混凝土抗剪本构关系,以此研究了凿毛深度和凿毛率对空心板梁桥铰缝抗剪性能的影响。研究结果表明:凿毛深度变化不能改变铰缝的受力模式,混凝土铰缝的薄弱面仍在交界面上;随着凿毛深度的增加,凿毛产生的齿状混凝土被剪断,铰缝抗剪强度大大提升;结合试验和有限元数值模拟,得出最佳凿毛深度为15 mm,高于施工规范建议的8 mm,此时铰缝抗剪强度相比凿毛深度为8 mm时提高了44.3%,且凿毛面积取最大凿毛率时,抗剪能力可进一步提高。

Flexural Bond Behavior of Rebar in Ultra-High Performance Concrete Beams Considering Lap-Splice Length and Cover Depth

This study intends to find out the correlation between the cover depth and the bond characteristics of UHPC through pull-out tests of UHPC specimens with different cover depths and bond tests of rebar using flexural members. In this experimental study, specimens are fabricated with the lap-splice length as test variable in relation with the calculation of the lap-splice length for 180- MPa UHPC. Moreover, specimens are also fabricated with the cover depth as test variable to evaluate the effect of the cover depth on the UHPC flexural members. The load-displacement curves are analyzed for each of these test variables to compute the lap-splice length proposed in the K-UHPC structural design guideline and to evaluate the influence of the cover depth on the flexural members. As a result, the stability of the structural behavior can be significantly enhanced by increasing slightly the cover depth specification of the current UHPC Structure Design Guideline from the maximum value between 1.5 times of rebar diameter and 20 mm to the maximum value between 1.5 times of rebar diameter and 25 mm.

埋深和水土含量对松散岩堆抗剪强度的影响

针对松散岩堆剪切力弱会引起滑坡、崩塌等严重自然灾害的问题,运用相似理论,以石英砂为基本岩块、黏性土为填充土,配置相似材料,分别控制不同填充土含量和含水率并进行三轴试验,研究不同埋深下填充土的含量和含水率对松散岩堆抗剪强度的影响。结果表明:填充土的含量和含水率是松散岩堆咬合力和内摩擦角的关键影响因素,咬合力受影响程度更大;填土中的水对于松散岩堆的剪切力起着削弱作用;岩堆剪切力随着埋深的增加而增加,不同埋深处岩堆有相同的最佳填充土含量和含水率;在恒定岩堆土重度情况下,抗剪强度和埋深呈线性关系。

不同埋深条件下盾构施工扰动试验研究

随着城市地下空间开发规模不断扩大,盾构施工诱发的地层扰动对地下既有建(构)筑物及周边环境的安全产生了重要的影响。通过自主研发盾构掘进试验装置,实现了不同地层应力水平的加载,分析了不同埋深条件下盾构施工地层扰动的变化规律及影响范围。研究结果表明:隧道周围地层中土压力变化率随着距隧道水平距离的增大而逐渐递减;盾构掘进完毕后土压力相对于初始土压力减少了约20%~40%;埋深比变化对拱顶、拱底处的土体应力路径影响较小;定义了基于土压力力变化的地层扰动度,随埋深比的增大,地层扰动度逐渐减小,说明深埋条件会降低盾构开挖对地层的扰动作用;盾构掘进完毕后,扰动作用的竖向影响范围高度介于隧道上下0.5D~0.8D(D为隧道直径)之间,当盾构到达监测断面时水平扰动范围宽度约为0.5D,盾构穿越远离后近似为1.2D~1.5D。

海上风电桩基“抛石+”复合防护方法试验研究

针对现有海上风电基础冲刷防护措施的失效机理及薄弱之处,利用扰流环的驻涡原理降低了水流对抛石层的沉陷破坏、利用套筒固定抛石层从而减弱了抛石层的边缘破坏、利用仿生水草垫阻碍下潜水流及侧向来流的功能有效减弱了抛石层的剪切破坏,由此分别提出了“抛石+扰流环”“抛石+套筒”“抛石+仿生水草”三种新型复合防护方法,并按照3类复合防护措施的布置方式提出10种具体的复合防护设计。进一步开展物理模型试验,评估不同复合防护方法的防护效果。试验结果表明,海流作用下3类复合防护的防护效果均较好且明显优于抛石单独防护,防护效率均在66%以上。当抛石铺设范围为3倍单桩直径、抛石厚度为2倍的中值粒径,扰流环内部直径设置为2倍单桩直径、距离抛石层0.5倍桩径时,扰流环能够更好地发挥作用,使得到达抛石层以及周围泥沙的水流分散并且流速减缓,此种复合防护方法的防护效率为82.2%,能够达到理想的防护效果。