Load Bearing Capacity and Safety Analysis for Strain-hardening Austenitic Stainless Steel Pressure Vessels

By increasing the yield strengths of austenitic stainless steels for pressure vessels with strain hardening techniques,the elastic load bearing capacity of austenitic stainless steel pressure vessels can be significantly improved.Two kinds of strain hardening methods are often used for austenitic stainless steel pressure vessels：Avesta model for ambient temperature applications and Ardeform model for cryogenic temperature applications.Both methods are obtained from conventional design rules based on the linear elastic theory,and only consider the hardening effect from materials.Consequently this limits the applications of strain hardening techniques for austenitic stainless steel pressure vessels because of safety concerns.This paper investigates the effect of strain hardening on the load bearing capacity of austenitic stainless steel pressure vessels under large deformation,based on the elastic-plastic theory.Firstly,to understand the effect of strain hardening on material behavior,the plastic instability loads of a round tensile bar specimen are derived under two different loading paths and validated by experiments.Secondly,to investigate the effect of strain hardening on pressure vessels strength, the plastic instability pressure under strain hardening is derived and further validated by finite element simulations.Further,the safety margin of pressure vessels after strain hardening is analyzed by comparing the safety factor values calculated from bursting tests,finite element analyses,and standards.The researching results show that the load bearing capacity of pressure vessels at ambient temperature is independent of the loading history when the effects of both material strain hardening and structural deformation are considered.Finite element simulations and bursting tests results show that the minimum safety factor of austenitic stainless steel pressure vessels with 5% strain hardening is close to the recommended value for common pressure vessels specified in the European pressure vessel standard.The proposed study also shows that in the strain hardening design of austenitic stainless steel pressure vessels,the calculation for plastic instability pressure could use theoretical formula or finite element analyses based on geometrical dimensions and material property parameters before strain hardening,but a 5%strain should be employed as a design limit.The proposed research can be used for the strain hardening design of austenitic stainless steel pressure vessels safely.

Poor Wheel-Running Exercise Can Decrease Blood Pressure through Hormonal Control and Increase Endurance Exercise Capacity in Middle-Aged Normal Rats

The aim of this study was to examine the effects of voluntary wheel-running (WR) on body weight (BW), waist circumference, mesenteric fat mass (MFM), adipocyte size, circulating cytokines/hormones, blood pressure (BP) and exercise endurance capacity in 11-month-old normal rats. Three-week WR with about 0.2 km of daily running distance caused a gradual loss in BW despite an increased intake of food/water. MFM decreased as daily running distance increased. Moreover, there was a positive correlation between MFM and BW, waist circumference or adipocyte size. On the other hand, WR significantly decreased systolic/diastolic BPs, and increased endurance exercise capacity. WR rat sera contained lower concentrations of angiotensin II, aldosterone, vasopressin and endothelin-1 and higher concentration of brain natriuretic peptide compared with sedentary rat sera. Thus, WR-induced reduction in resting BPs may be accomplished by attenuated vasoconstriction, enhanced vasodilatation and reduction in blood volume. In addition, circulating vascular endothelial growth factor and interleukin-6 were higher in WR rats, suggesting angiogenesis, anti-inflammation and insulin-sensitization. These results support a prevalent idea that daily light-exercise is a potential strategy for preventing metabolic syndrome.

H-M Bearing Capacity of A Modified Suction Caisson Determined by Using Load-/Displacement-Controlled Methods

This paper presents a series of monotonically combined lateral loading tests to investigate the bearing capacity of the MSCs （modified suction caissons） in the saturated marine fine sand. The lateral loads were applied under load- and displacement-controlled methods at the loading eccentricity ratios of 1.5, 2.0 and 2.5. Results show that, in the displacement-controlled test, the deflection-softening behavior of load-deflection curves for MSCs was observed, and the softening degree of the load-deflection response increased with the increasing external skirt length or the decreasing loading eccentricity. It was also found that the rotation center of the MSC at failure determined by the load-controlled method is slightly lower than that by the displacement-controlled method. The calculated MSC capacity based on the rotation center position in serviceability limit state is relatively conservative, compared with the calculated capacity based on the rotation center position in the ultimate limit state. In the limit state, the passive earth pressures opposite the loading direction under load- and displacement-controlled methods decrease by 46% and 74% corresponding to peak values, respectively; however, the passive earth pressures in the loading direction at failure only decrease by approximately 3% and 7%, compared with their peak values.

Characteristic Test Study on Bearing Capacity of Suction Caisson Foundation Under Vertical Load

Suction caisson foundations are often subjected to vertical uplift loads,but there are still no wide and spread engineering specifications on design and calculation method for uplift bearing capacity of suction caisson foundation.So it is important to establish an uplift failure criterion.In order to study the uplift bearing mechanism and failure mode of suction caisson foundation,a series of model tests were carried out considering the effects of aspect ratio,soil permeability and loading mode.Test results indicate that the residual negative pressure at the top of caisson is beneficial to enhance uplift bearing capacity.The smaller the permeability coefficient is,the higher the residual negative pressure will be.And the residual negative pressure is approximately equal to the water head that causes seepage in the caisson.When the load reaches the ultimate bearing capacity,both the top and bottom negative pressures are smaller than Su and both the top and bottom reverse bearing capacity factors are smaller than 1.0 in soft clay.Combined the uplift bearing characteristics of caisson in sandy soil and soft clay,the bearing capacity composition and the calculation method are proposed.It can provide a reference for the engineering design of suction caisson foundation under vertical load.

Negative Pressure Consolidation of Silt Inside Bucket Foundation

A series of model experiments of bucket foundations concerning suction installation and negative pressure consolidation in saturated silt were carried out in a cube steel bin at Tianjin University. The experimental results show that the silt inside the bucket has been strengthened by negative pressure, and the strengthening effect decreases with the increase of the distance from the bucket. A three-dimensional numerical model of the experiments was built by means of finite element software ABAQUS with fluid-solid coupling method. The results show that the bearing capacity of the silt inside the bucket foundation increases significantly at the former stage of negative pressure consolidation, while the increasing trend slows down over time. The rotation centers of the bucket foundation and the inner soil region tend to be closer to each other based on the consolidation. The bearing capacity of the bucket foundation is improved effectively with the increase of soil strength. The effects of negative pressure consolidation on the bearing capacity of bucket foundation were also illustrated by an actual offshore wind power project case.

Combined control of fluid adsorption capacity and initial permeability on coal permeability

The variations of strain and permeability of coal were systematically studied through the physical simulation of N2 and water injection.The effects of fluid adsorption capacity and initial permeability on strain,permeability and the dominant effect of pore pressure were discussed.The adsorption strain and strain rate of coal during water injection are significantly higher than those during N2 injection.An edge of free adsorption exists in the early phase of N2 and water injection,which is related to fluid saturation.Within this boundary,the strain rate and pore pressure are independent.Moreover,the injec-tion time of initial stage accounts for about 20%of the total injection time,but the strain accounts for 70%of the total strain.For water injection,this boundary is about half of water saturation of coal.Besides,the influence of pore pressure on permeability is complex,which is controlled by adsorption capacity and initial permeability of coal.When the initial permeability is large enough,the effect of adsorption strain on permeability is relatively weak,and the promoting effect of pore pressure on fluid migration is dominant.Therefore,the permeability increases with increasing pore pressure.When the initial permeability is relatively low,the pore pressure may have a dominant role in promoting fluid migration for the fluid with weak adsorption capacity.However,for the fluid with strong adsorption capacity,the adsorption strain caused by pore pressure may play a leading role,and the permeability reduces first and then ascends with increasing pore pressure.

Pile end bearing capacity in rock mass using cavity expansion theory

Much empiricism is involved in design of rock-socketed piles in rock masses.In light of this,an analytical solution based on the cavity expansion theory is proposed for calculating the ultimate bearing capacity at the tip of a pile embedded in rock masses obeying the Hoek-Brown failure criterion.The ultimate end bearing capacity is evaluated by assuming that the pressure exerted at the boundaries of a pressure bulb immediately beneath the pile tip is equal to the limit pressure required to expand a spherical cavity.In addition,a relationship is derived to predict the pile load-settlement response.To demonstrate the applicability of the presented solution,the results of this study were compared to those of 91 field tests from technical literature.Despite the limitations,it is found that the end bearing resistance computed by the present work is in good agreement with the field test results.

Spatio-temporal Pattern of Ecosystem Pressure in Countries Along the Belt and Road: Combining Remote Sensing Data and Statistical Data

Building a Green Silk Road by integrating the Sustainable Development Goals(SDGs) is one of the Belt and Road Initiative(BRI) visions, but the BRI faces enormous challenge that is the conflict between economic development and ecological sustainability.Understanding the current scale and trend of the impact of human activities on the ecosystem is the preliminary work to ensure that human activities do not exceed the ecological carrying capacity under the BRI. This study evaluated the ecosystem pressure in countries along the Belt and Road(B&R) from 2000–2017 based on the supply-consumption balance relationship of ecological resources. Net primary productivity(NPP) is taken as the measure of ecological resources, and the supply level and consumption intensity of ecological resources is estimated based on remote sensing data and statistical data, respectively. Results show that thirteen countries with overconsumed ecological resources concentrated in the West Asia/Middle East. Although the intensity of the ecological resource consumption correlated with ecological resource endowments, the ecosystem pressure was determined by social development dependence on the ecological resources at the same ecological resource endowments level. Nearly 80% of countries along the B&R suffered from significantly increased(P < 0.05) ecosystem pressure during 2000–2017, since most of the countries along the B&R were developing countries,and their economic development was highly dependent on ecological resources. Some West Asia/Middle East countries successfully mitigated the ecosystem pressure by importing feed for livestock. Likewise, the Southeast Asian islands benefitted from the import of agricultural products. The results highlight that the BRI should reduce the dependence of social development demands on local ecological resources by international trade for ensuring the increasing ecosystem pressure trend within the ecological carrying capacity.

Vertical drainage capacity of new electrical drainage board on improvement of super soft clayey ground

As an advanced polymer composites electro-kinetic geosynthetics, the electro-osmotic vertical drainage(EVD) board could drain water quickly and accelerate consolidation process. However, the drainage rate was mainly impacted by the vertical drainage capability. Therefore, vertical drainage capability at the top of EVD board was theoretically analyzed. Basic requirements for drainage at the top of the board were summed up, as well as the formula of anode pore pressure when losing the vertical drainage capability. Meanwhile, a contrast test on the top and bottom drainage capacities was conducted. In use of the advanced EVD board, the voltage potential and pore pressure of anode were measured. Moreover, the derived formulas were verified. The result shows that the decrease of electric force gradient had an observable impact on the drainage capability. There was nearly no difference between the energy consumption for the two drainage methods. Although a little less water was discharged, the top drainage method had more advantages, such as high initial drainage velocity, few soil cracks, low anode water content and high soil strength. All of these show that the super soft soil ground could be consolidated quickly in use of the advanced EVD board through the top drainage. The top drainage method could efficiently improve the drainage effect, decrease the energy consumption and speed up the project proceeding.

Numerical simulation and experimental verification of a novel double-layered split die for high-pressure apparatus used for synthesizing superhard materials

Based on the principles of massive support and lateral support, a novel double-layered split die(DLSD) for high-pressure apparatus was designed to achieve a higher pressure-bearing capacity and larger sample cavity. The stress distributions of the DLSDs with different numbers of divided blocks were investigated by the finite element method and compared with the stress distributions of the conventional belt-type die(BTD). The results show that the cylinders and first-layer supporting rings of the DLSDs have dramatically smaller stresses than those of the BTD. In addition, increasing the number of divided blocks from 4 to 10 gradually increases the stress of the cylinder but has minimal influence on the stress of the supporting rings. The pressure-bearing capacities of the DLSDs with different numbers of divided blocks, especially with fewer blocks, are all remarkably higher than the pressure-bearing capacity of the BTD. The contrast experiments were also carried out to verify the simulated results. It is concluded that the pressure-bearing capacities of the DLSDs with 4 and 8 divided blocks are 1.58 and 1.45 times greater than that of the BTD. This work is rewarding for the commercial synthesis of high-quality, large-sized superhard materials using a double-layered split high-pressure die.

ON THE DRIVING BEHAVIOR，VARIABLE－DIAMETEREFFECT AND BEAKING CAPACITY OF DRIVENCAST－IN－SITU PILE WITHFLAT

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A simplified dynamic method for field capacity estimation and its parameter analysis

This paper presents a simplified dynamic method based on the definition of field capacity. Two soil hydraulic characteristics models, the Brooks-Corey （BC） model and the van Genuchten （vG） model, and four soil data groups were used in this study. The relative drainage rate, which is a unique parameter and independent of the soil type in the simplified dynamic method, was analyzed using the pressure-based method with a matric potential of -1/3 bar and the flux-based method with a drainage flux of 0.005 cm/d. As a result, the relative drainage rate of the simplified dynamic method was determined to be 3% per day. This was verified by the similar field capacity results estimated with the three methods for most soils suitable for cultivating plants. In addition, the drainage time calculated with the simplified dynamic method was two to three days, which agrees with the classical definition of field capacity. We recommend the simplified dynamic method with a relative drainage rate of 3% per day due to its simple application and clearly physically-based concept.

Adjustment of Liquid Production in Reservoir with Handling Capacity Constraints

A oilfield was an oil reservoir with strong bottom water in offshore, the water cut was as high as 96%. In the high water cut stage, the most effective way of increasing oil production was to extract liquid and increase oil. The processing capacity of oilfield fluid was limited by the conditions. By using Petrel-RE-2017 software, combining reservoir engineering and percolation mechanics methods, this paper analyzes the effect of large-scale liquid pumping, expand coverage and shut-in coning in oil reservoirs with bottom water, and formulates the adjustment strategy of single well production structure of the whole oilfield. It was confirmed that large-scale liquid production can expand coverage and shutting down well can reduce water cut. It can provide reference and guidance for oil field with strong bottom water when it encounters bottleneck of liquid treatment capacity.

Research on method of pressure grouting piling of driven tube

The pressure grouting pile of driven tube can improve the load bearing capacity of the single pile from the mechanism of pressure grouting pile of driven tube.On the basis of analyzing the mechanism,the authors designed the machines and tools of pressure grouting,determined the operating manufacture and technology parameter on the pressure grouting secondly.The result shows that the pressure grouting pile of driven tube not only changes the pile type but also reduce the length of the pile and its engineering cost,it enhances the load bearing capacity of single pile an the same time.

考虑工作记忆容量和时间压力影响的驾驶绩效分析

随着风险驾驶机理研究的不断完善,外部情境因素和驾驶人内部认知差异逐渐成为当前研究的热点和难点。本文为研究时间压力、工作记忆容量与驾驶绩效之间的关系,采用时间约束和动机等主客观相结合的方法实现时间压力的施加,采用复杂跨度范式测量驾驶人工作记忆容量。基于驾驶模拟器系统构建相关驾驶场景,开展心理学与模拟驾驶行为试验,采集驾驶人心理、操作和车辆运行数据,分别就时间压力、工作记忆容量及其组合对驾驶绩效的影响进行分析。结果表明:时间压力对超速比例、碰撞概率、制动反应时间、左转选择间隙皆有显著的影响效应,且时间压力越高,超速比例越大、碰撞概率越高、制动反应时间越快、左转选择间隙越小的频次越多;工作记忆容量仅对制动反应时间有影响,工作记忆容量越高,制动反应时间越快;时间压力与工作记忆容量对制动反应时间无交互影响,但随着时间压力的增大,高工作记忆容量人群与低工作记忆容量人群在制动反应时间上的差异逐渐变小。这些发现为研究时间压力下的驾驶绩效提供了驾驶人认知方面的新见解。

制造业关联网络承压能力研究:基于投入产出表的特征分析与压力测试

数字经济快速发展对制造业关联网络带来诸多不确定性影响,制造业关联网络承压能力研究尤为重要。为应对这一形势,基于2017年、2018年和2020年投入产出表,借助产业集群三角形化方法识别并构建制造业关联网络,结合最大权树法分析制造业关联网络特征,并测试不同程度冲击对制造业关联网络产生的压力。研究发现:①化学产品是制造业关联网络的核心产业,但其核心地位呈下降趋势;②总体而言,制造业对整个关联网络的后向关联效应较强,非制造业的前向关联效应较强;③随着压力源头产业直接关联产业数量的增加,制造业关联网络所承受的压力呈下降趋势;随着压力源头产业与其它产业关联程度的下降,制造业关联网络承受的压力呈下降趋势。研究结论可为制造企业应对承压状态、促进经济高质量发展提供理论依据与实践参考。

外包薄壁夹心钢-混组合管柱层间作用对其受压承载力的影响

为了研究外包薄壁夹心钢混组合管柱层间作用下的力学性能,建立了组合管柱有限元分析模型,通过库伦摩擦定义层间作用力,改变影响参数值,研究了轴压、偏压作用下组合管柱的力学性能。结果表明:当摩擦系数由0.2增大至0.4时,轴心受压柱与偏心受压柱极限承载力分别提高了1.06%、13.35%,由0.4增大至0.6时,分别提高了0.06%、13.61%;随着内外钢管与混凝土之间外力的增加,层间作用力和机械咬合力也相应地增加,增强层间作用力可以明显提高外包薄钢混凝土偏心受压组合管柱的极限承载力。

渤海某区块浅层气对工程影响的评估

以渤海某区块项目为例,采用保压取样方法获取待评估区域海底土层样品并对所含气体开展组分测定,定性判断浅层气成因。采用静力触探孔压消散试验方法获取地层中超孔隙水压力,定量评估对含浅层气地层承载力的折减效应。结果表明,内浅层气主要组分为甲烷和二氧化碳,气体含量较低。内地层中的浅层气可能属于生物成因气。含浅层气地层的超孔隙水压力相对上覆有效压力比值约3%,承载力折减因数为1.0%~1.1%。所采取的方法能够有效评估浅层气对海上基础设施和生产安全的影响程度,具有推广价值。

CO_(2)-EOR过程中油藏储层构造封存能力的模拟

为应对日益严峻的能源危机和温室效应,CO_(2)提高采收率技术脱颖而出,因此CO_(2)提高采收率后的地质封存安全性和相应的封存能力评估引起了广泛关注。借助数值模拟方法,基于吉林油田某区块油藏的实际储层条件,构建了注入CO_(2)含量为10%~90%的9个模型,分别探究了含水饱和度为30%,50%和90%以及储层压力为10 MPa,20 MPa和30 MPa时油藏各相组分的分布规律;基于前人对封存CO_(2)安全储存状态划分的研究,最终明确了CO_(2)的安全封存量。结果表明:1)当含水饱和度(30%)和压力(10 MPa)一定时,增加CO_(2)含量(10%~90%)可大幅提高CO_(2)的有效封存体积分数(26%~93%);2)压力的提升(10~30 MPa)促进了CO_(2)在油相中的溶解,从而略微降低了储层的封存能力(18%~7%);3)含水饱和度对储层封存CO_(2)的能力的影响微乎其微。该研究旨在阐明不同条件下CO_(2)的构造埋存量,为相关研究提供借鉴。

地基承载力特征值确定土变形模量的探讨

目前我国地基沉降计算主要采用土压缩模量来计算,再用经验系数对计算结果进行修正。这种方法对于一些结构性较强的硬土地基误差较大,主要原因是取样扰动影响。为此,探讨了变形模量与地基承载力特征值的理论联系,在笔者提出的确定变形模量经验方法基础上,总结出依据地基承载力特征值确定变形模量的方法,该方法具有理论依据,可便捷地通过岩土工程勘察报告中常提供的地基承载力特征值确定土的变形模量,能够更为准确计算地基沉降值。采用不同方法(压板试验法、压缩模量推求法、标贯击数法、承载力经验法、依据地基承载力特征值确定变形模量法)计算了若干试验案例,通过对不同方法结果的对比,初步验证了依据地基承载力特征值确定变形模量法是可行的。