Strength Design Method for Tubing Hanger of Subsea Christmas Tree Against Big Temperature Difference

The tubing hanger is an important component of the subsea Christmas tree, experiencing big temperature difference which will lead to very high thermal stresses. On the basis of API 17D/ISO 13628-4 and ASME VIII-1, and by comprehensively considering the erosion of oil and the gravity load of the tubing, a calculation model is established by regarding design pressure and thermal stress, and the method for designing the tubing hanger of the horizontal Christmas tree under big temperature difference condition is developed from the fourth strength theory. The proposed theory for strength design of the tubing hanger in big temperature difference is verified by numerical results from ABAQUS.

First-principles investigation on ideal strength of B2 NiAl and NiTi alloys

For B2 NiAl and NiTi intermetallic compounds, the ideal stress–strain image is lack from the perspective of elastic constants. We use first-principles calculation to investigate the ideal strength and elastic behavior under the tensile and shear loads. The relation between the ideal strength and elastic constants is found. The uniaxial tension of NiAl and NiTi along <001> crystal direction leads to the change from tetragonal path to orthogonal path, which is driven by the vanishing of the shear constant C(66). The shear failure under {110}{111} shear deformation occurring in process of tension may result in a small ideal tensile strength(~ 2 GPa) for NiTi. The unlikeness in the ideal strength of Ni Al and Ni Ti alloys is discussed based on the charge density difference.

Unified elastoplastic finite difference and its application

Two elastoplastic constitutive models based on the unified strength the- ory （UST） are established and implemented in an explicit finite difference code, fast Lagrangian analysis of continua （FLAC/FLAC3D）, which includes an associated/non- associated flow rule, strain-hardening/softening, and solutions of singularities. Those two constitutive models are appropriate for metallic and strength-different （SD） materials, respectively. Two verification examples are used to compare the computation results and test data using the two-dimensional finite difference code FLAC and the finite element code ANSYS, and the two constitutive models proposed in this paper are verified. Two application examples, the large deformation of a prismatic bar and the strain-softening be- havior of soft rock under a complex stress state, are analyzed using the three-dimensional code FLAC3D. The two new elastoplastic constitutive models proposed in this paper can be used in bearing capacity evaluation or stability analysis of structures built of metallic or SD materials. The effect of the intermediate principal stress on metallic or SD mate- rial structures under complex stress states, including large deformation, three-dimensional and non-association problems, can be analyzed easily using the two constitutive models proposed in this paper.

Susceptibility-weighted imaging is suitable for evaluating signal strength in different brain regions of a rabbit model of acute hemorrhagic anemia

Acute hemorrhagic anemia can decrease blood flow and oxygen supply to brain, and affect its physiological function. While detecting changes in brain function in patients with acute hemorrhagic anemia is helpful for preventing neurological complications and evaluating therapeutic effects, clinical changes in the nervous systems of these patients have not received much attention. In part, this is because current techniques can only indirectly detect changes in brain function following onset of anemia, which leads to lags between real changes in brain function and their detection.

Investigation into Effects of Buildings near Broadcasting Antenna on Far Fields Using a Finite-Difference Method

A steady state finite difference method is used to calculate EM fields generated by an MW broadcasting antenna. The effects of buildings on the wave propagation is studied based on the numerical results and field measurements. Both the algorithm and results are useful in the design of broadcasting antennas, as well as in the selection of transmitting sites.

Inlet flow disturbance effects on direct numerical simulation of incompressible round jet at Reynolds number 2500

This letter reports inlet flow disturbance effects on direct numerical simulation of incompressible round jet at Reynolds number 2500.The simulation employs an accurate projection method in which a sixth order biased upwind difference scheme is used for spatial discretization of nonlinear convective terms,with a fourth order central difference scheme used in the discretization of the divergence of intermediate velocity.Carefully identifying reveals that the inlet flow disturbance has some influences on the distribution pattern of mean factor of swirling strength intermittency.With the increase of inlet disturbance magnitude jet core cone slightly shortens,observable differences occur in the centerline velocity and its fluctuations,despite the negligible impacts on the least square fitted centerline velocity decay constant(B_u)and distribution parameter(K_u)for velocity profile in self-similar region.

Accuracy Analysis of Position Estimation Based on Measurements of Received Signal Strength Difference

The performance of a cellular location system based on received signal strength difference （RSSD） is investigated. In the cellular location system, each mobile station needs to measure the signal strength transmitted by surrounding base stations, and sends its measurements to the service base station. Using the strength difference between the service base station and neighboring base stations, the position of a mobile station is estimated. The related Cramer-Rao lower bound （CRLB） on the location error of this method was derived, and numerical simulations are made to discuss the influences of the number of base stations, correlation coefficient of shadowing attenuation, and cell radius on CRLB. The results show that the CRLB is positively correlated with the standard deviation of shadowing attenuation and cell radius, but negatively correlated with the number of base stations and the correlation coefficient of shadowing attenuation. In addition, the CRLB results obtained in this paper were compared with those of the cellular location system based on received signal strength （RSS） measurements, which reveals that the former is more tight.

成纱段摩擦应力对亚麻棉混纺纱线质量的影响

针对如何有效经济地提升亚麻棉混纺纱线质量问题,提出了物理集聚纱体表面有害毛羽的方法。通过在成纱段设计和安装旋转式沟槽专件,对纱体施加摩擦应力,增强对纤维的控制力,达到提升纱线质量的目的。理论模型分析可知,摩擦应力的介入导致纱线的捻度传递出现梯度差异,随着摩擦应力的增加,梯度差异增加。在摩擦力和扭转力的协同作用下,纱体表面纤维被捕捉和加捻,达到集聚纤维须条的目的,从而减少毛羽。实验结果证实:随着摩擦应力的增加,纱线毛羽降低的幅度越高,有害毛羽最多可降低35.5%。然而,过大的摩擦应力会恶化条干,最高为1.6%。其中粗节上升7.3%,棉结上升4.8%,而强力没有明显变化。通过计算优化施加的摩擦应力,协同捻度差效应,达到提升纱线质量的目的。

考虑局部损伤区变化的能量平衡尺寸效应模型

尽管研究者已经提出各种各样的尺寸效应模型,但是建立能描述不同类型尺寸效应规律的模型依旧是力学和材料学中最具挑战性的问题之一.首先通过系统深入分析局部损伤区(localized damage zone,LDZ)随试件尺寸的变化规律,提出能够准确地描述LDZ非线性尺寸效应的理论模型并验证.在此基础上,建立考虑LDZ随尺寸变化的能量平衡尺寸效应模型.考虑LDZ变化的能量平衡尺寸效应模型能体现5种不同类型的尺寸效应规律.随着尺寸增大,类型1:名义抗压强度逐渐减小,最终趋于单轴压缩弹性极限;类型2:名义抗压强度先在一定尺寸范围内为真实抗压强度,然后逐渐减小,最终趋于单轴压缩弹性极限;类型3:名义抗压强度先增加,然后逐渐减小,最终趋于单轴压缩弹性极限;类型4:名义抗压强度先逐渐增加到真实抗压强度,然后在一定尺寸范围恒为真实抗压强度,再逐渐减小,最终趋于单轴压缩弹性极限;类型5:名义抗压强度不随尺寸变化.文章模型首次理论预测类型4尺寸效应存在,并证实微纳尺度钛合金尺寸效应试验中存在这一规律.对考虑LDZ变化的能量平衡尺寸效应模型分析表明:LDZ尺寸与试件尺寸相对变化率之间的竞争是本文尺寸效应模型能体现5种类型的尺寸效应的原因.由于笔者先前已经证明能量平衡尺寸效应模型能很好预测类型1,2和5尺寸效应,但其不能体现类型3和4尺寸效应.因此,文章应用考虑LDZ变化的能量平衡尺寸效应模型和IUSEL(improved unified size-effect law)预测类型3和4尺寸效应试验数据,结果表明:考虑LDZ变化的能量平衡尺寸效应模型能很好预测各种材料类型3和4尺寸效应试验数据变化规律,而IUSEL不能描述类型4尺寸效应数据变化规律.考虑LDZ变化的能量平衡尺寸效应模型和IUSEL预测所有尺寸效应数据的总平均确定系数接近.

基于拉压差异的沥青混合料强度与疲劳特性

【目的】探究沥青混合料的拉压差异力学特性。【方法】开展了典型沥青混合料直接拉伸和四点弯曲强度及疲劳试验,基于材料拉压模量差异特性推导并得到了区别于传统四点弯曲梁的真实四点弯曲强度计算公式,分析了传统四点弯曲、真实四点弯曲及直接拉伸应力状态下强度、疲劳寿命及模量衰变规律。【结果】真实四点弯曲强度约为传统四点弯曲强度的80%,在相同加载速率下,不同应力状态强度中直接拉伸强度最小,且其对加载速率的敏感性亦最低;在相同应力水平下,直接拉伸疲劳寿命最小,但在相同真实应力比下直接拉伸疲劳寿命最大,真实四点弯曲疲劳寿命约为传统四点弯曲疲劳寿命的46%;真实四点弯曲疲劳试验的模量衰变速率远小于直接拉伸模量衰变速率,且破坏时前者的模量衰减幅度更小。【结论】材料的拉压差异特性对其力学参数的测试结果及变化规律影响显著,研究成果可为考虑拉压差异的沥青路面结构设计参数取值提供参考。

基于非靶向代谢组学研究邻苯二甲酸二丁酯对菜心代谢产物组成的影响

为研究邻苯二甲酸二丁酯(di-n-butyl phthalate,DBP)胁迫对菜心代谢产物组成的影响,本文基于非靶向代谢组学,通过主成分分析、偏最小二乘判别分析等多元统计分析方法,对DBP胁迫下菜心不同组织代谢产物的差异及其关键通路进行研究。结果发现:不同DBP浓度胁迫下菜心不同组织存在明显差异的代谢产物有105种,主要分布在36条代谢途径中。P<0.05的代谢途径有3条,即色氨酸代谢(Tryptophan metabolism)、苯丙氨酸代谢(Phenylalanine metabolism)和丁酸代谢(Butanoate metabolism)。研究表明,基于非靶向代谢组学可直观反映DBP对菜心代谢产物组成的影响,为后续开发农作物关键通路上的靶向化学调控剂提供科学依据。

双向近场地震下结构性软黏土震陷特性研究

软黏土的震陷效应与土体的结构性有着密切联系,但目前关于土体的结构强度对震陷影响的研究还较少。自然界中很难获取到物质成分相同而结构性质不同的土,为了对P波和S波耦合作用下结构性软黏土的震陷特性进行深入研究,人工制备了物质成分相近而结构强度不同的软黏土,通过开展两组动态围压下的动三轴试验,探讨结构强度、双向动荷载和P波与S波的相位差对其震陷特性的影响规律。试验结果表明:双向激振下,轴向动荷载与结构屈服应力比值越大,双向动荷载的耦合对轴向残余应变积累速度的加速作用越明显;相位差对轴向残余应变的影响则取决于土体结构强度,结构强度越小,影响越大。双向近场地震中,径向动荷载一般会加速震陷的发展,加速作用的大小与土体结构强度大小有关,结构强度越小,加速作用越明显,但轴向动荷载的剪切作用对结构性软黏土的残余应变积累仍起主导作用。研究结果可为软土地区综合防灾提供有益参考。

高结合力工模具TiN涂层的制备

本文分析了电弧离子镀TiN涂层各工艺参数的相互关系,提出了以镀膜温度为主控参数的工艺设计思路;探讨了TiN涂层膜/基结合强度与涂层组织结构的关系和制备高结合力涂层的技术方法。

西北大温差环境下温度对硫铝酸盐水泥砂浆抗压强度的影响

为研究西北大温差环境下温度对硫铝酸盐水泥砂浆作为浅层病害混凝土修补材料的抗压强度影响规律,设计了改性前后三个不同配合比、三个温度梯度(-25、25和80℃)和三个时间长度(6、12和24 h)的试验,测试了试样的抗压强度,采用扫描电子显微镜(SEM)和X射线衍射(XRD)的方法测试了试样的微观性能。结果表明,改性后的试样破坏模式均优于未改性试样。-25℃时,随着时间延长,改性后试样的抗压强度增大幅度均大于未改性试样;25℃时,三个配合比试样抗压强度变化规律相似,均轻微下降;80℃时,掺入0.3%(质量分数)水玻璃、0.1%(质量分数)聚丙烯纤维和0.4%(质量分数)膨胀剂试样的抗压强度下降幅度最小。同时,本文还建立了该配合比试样在不同温度下,随时间延长的相对抗压强度变化率计算公式,可为西北大温差环境下硫铝酸盐水泥砂浆作为浅层病害混凝土修补材料提供参考。

新钢2500 m^(3)高炉“低压差+低燃耗”管控实践

对新钢2500 m^(3)高炉自大修投产后操作技术进行了分析和总结。高炉以坚持长期稳定顺行为主线,以实现现代高炉“高效、低耗”为目标,不断克服入炉有害元素高、品位低、渣量大、操作炉型不稳定等不利影响。在炉况稳定顺行的基础上,通过持续改善原燃料质量,增强排锌、排碱能力、改善料柱透气性、控制合理渣系、活跃炉缸等技术措施,突破了长期高压差、高燃料比操作技术难题,形成了与自身原燃料条件相适应的“低压差+低燃耗”管控技术。

绿地暴露与学龄儿童情绪行为问题的关联研究

目的探索绿地暴露与学龄儿童情绪与行为问题之间的关联。方法采用分层整群随机抽样方法于2019年选取广州市5所小学的2802名6~12岁小学生作为研究对象,学龄儿童的情绪行为问题通过父母版长处与困难问卷(Strength and Difficulties Questionnaire,SDQ)评估,采用归一化植被指数(normalized difference vegetation index,NDVI)结合学龄儿童日常活动模式综合评估个体绿地暴露水平,采用广义线性混合模型分析个体绿地暴露水平与SDQ得分以及情绪行为问题的关系。结果学龄儿童困难总分、情绪症状、品行问题、多动行为、同伴交往以及亲社会行为异常检出率分别为7.7%、5.1%、10.1%、13.5%、13.2%和10.2%。调整混杂因素后,300、500和1000 m缓冲区NDVI每增加一个四分位间距(interquartile range,IQR),学龄儿童的多动行为得分下降0.11~0.18分。此外,1000 m缓冲区NDVI每增加一个IQR,学龄儿童的亲社会行为得分增加0.11(β=0.11,95%CI:0.02~0.21)、外化行为得分下降0.14(β=-0.14,95%CI:-0.29~-0.01)。300 m缓冲区ND-VI每增加一个IQR,外化行为的OR值为0.78(95%CI:0.61~1.00)。未发现个体特征(性别、年龄、家庭人均月收入、父母文化程度以及户外运动时间)对绿地暴露与学龄儿童情绪行为问题之间的关系存在修饰作用。结论绿地暴露增加与学龄儿童较低的情绪行为问题风险相关。

不同假人动态试验安全带力值对比

安全带零部件强度满足动态试验不失效是研究安全带约束性能的重要前提。在车型设计初期应注意不同假人和不同配置下强度设计值需求,以满足动态试验要求。而在使用第95百分位男性假人和紧急锁止卷收器配置时,对安全带强度要求更加严格。文章针对GB14166-2013刚性座椅动态试验进行仿真分析,采用不同百分位假人以及不同卷收器配置仿真计算,进行安全带力值对比,为安全带零件强度设计提供参考。

RSSI/TDOA/DV-Distance组合定位算法

由于目前单一定位算法具有各自的优缺点及适用范围,大规模复杂无线传感器网络则需采用多种定位技术。针对实际应用需求,提出了一种基于接收信号强度指示(RSSI)、到达时间差(TDOA)和矢量距离(DV-Distance)的组合定位算法。该算法扩大了TDOA算法的覆盖范围,提高了成功率,并修正了DV-Distance算法中定位节点与信标节点间有效距离信息。试验表明,该算法满足了复杂定位系统的差异化需求,提高了大规模无线传感器网络的整体定位精度和稳定性。

信息瀑布和连接强度视角下从众信息转发行为感知差异比较研究

[目的/意义]旨在探索从众信息转发行为的感知影响因素,为有效引导用户从众信息转发行为、规范社会化媒体信息传播秩序提出建议。[研究设计/方法]基于信息瀑布和连接强度理论,以个体感知差异为切入点,使用问卷调查法搜集有效样本数据352份。采用偏最小二乘结构方程模型方法进行量表有效性检验,利用独立样本T检验、单因素方差分析和双因素方差分析进行数据分析。[结论/发现]社会化媒体用户因个体差异而对强连接、弱连接、无连接、从众信息转发行为等变量的感知存在显著影响。不同类型连接强度水平越高,用户对从众信息转发行为感知程度越高。用户个体差异与从众信息转发行为之间的关系因连接强度程度不同而存在不同程度影响,强连接与性别、弱连接与学科对从众信息转发行为具有显著的交互作用。[创新/价值]为从众行为和信息转发行为研究提供新的理论视角,以丰富和深化从众行为和信息转发行为领域的已有研究。