二甲醚燃料喷射压力对喷雾发展过程的影响

利用定容容器模拟增压发动机缸内高温高压条件,利用高速摄像机观察二甲醚喷雾,探讨了喷射压力对喷雾贯穿距离、喷雾蒸发等喷雾发展过程的影响规律。结果表明:在喷射初期喷雾贯穿距离与喷射时间成正比关系,在喷射后期,环境气体卷入喷雾中,喷雾贯穿距离与喷射时间平方根成正比关系;二甲醚燃料液态喷雾贯穿距离相对于气态来说非常短,DME液态喷雾贯穿距离基本不随时间的增加而增长。     

海利动力打桩公式参数取值试验研究

以深圳港盐田港区西作业区集装箱码头为依托,采用动测试验方法,研究了土体恢复系数(K值)及海利公式中锤击能量的有效传递系数(n值)和桩土体系总的弹性变形(C值)的取值,得到求解1 200 mm和1 000 mm桩基极限承载力的更便捷、准确的计算方法,并利用海利公式确定终锤贯入度e值,为打桩停锤提供控制标准。     

天津港易堵管黏土物理力学指标及应用

基于天津港地区大量的易堵管黏土标准贯入试验和室内土工试验资料,应用数理统计方法,对易堵管黏土标准贯入击数与物理力学指标间的相关关系进行研究分析。结果表明:经验公式的回归系数均在0.8以上,具有较高的可靠性。研究结果经过可靠性分析验证后,为易堵管黏土通过原位测试指标来计算黏土的物理力学指标提供了可行的方法,该方法节约疏浚工程勘察费用,给类似的疏浚工程以借鉴,具有较高的实际应用价值。     

Solving conformal contacts using multi-Hertzian techniques

Recently, publications aiming at wheel–rail contact surveys let readers think that multi-Hertzian methods present severe drawbacks with respect to ‘virtual penetration’ methods. These surveys criticise multi-Hertzian solutions mainly because presenting ‘larger contacts overlaps’ and ‘frequent secondary contacts near the border of the first contact’, both obvious geometric possibilities of which the practical occurrence and eventual inconvenience would remain purely theoretical unless established over definite methods demonstrating poor practical results. Recent surveys all quote Piotrowski–Chollet 2005 survey of wheel–rail contact models that attempted to illustrate defective multi-Hertzian techniques by concentrating on the method initiated by Sauvage in the 1990s and further developed by Pascal. The 2005 paper not only gives no evidence of practical inconveniences of Sauvage’s method but also confuses static geometric contact overlaps with the dynamical overlapping of forces. In reality it mixes Sauvage method up with a quite different technique. Thus a clarification is now necessary by reminding what the proper Sauvage technique really is and by showing some of its practical successful applications. The present paper, focusing on determination of normal contact forces in conformal situations, intends to explain clearly the advantages of the unequivocal localisation of secondary ellipses in that multi-Hertzian method which has been developed in INRETS VOCO codes in the 1990s and successfully used by SNCF and ALSTOM in the INRETS-SNCF code, VOCODYM, and later in Pascal’s online calculation of railway elastic contacts code. It proved its effectiveness for studying freight wagons derailments as well as rail wear and head-check, unrounded wheels wear, high-speed lines’ deformations or TGV comfort. While simulating American ACELA trainsets’ behaviour on the US North-East Corridor tracks, prior to actual tests, as part of the commercial contract. It has been also a major tool for bringing back together French and American Safety Standards.     

Developing travel time estimation methods using sparse GPS data

Existing methods of estimating travel time from GPS data are not able to simultaneously take account of the issues related to uncertainties associated with GPS and spatial road network data. Moreover, they typically depend upon high-frequency data sources from specialist data providers, which can be expensive and are not always readily available. The study reported here therefore sought to better estimate travel time using “readily available” vehicle trajectory data from moving sensors such as buses, taxis, and logistical vehicles equipped with GPS in “near” real time. To do this, accurate locations of vehicles on a link were first map-matched to reduce the positioning errors associated with GPS and digital road maps. Two mathematical methods were then developed to estimate link travel times from map-matched GPS fixes, vehicle speeds, and network connectivity information with a special focus on sampling frequencies, vehicle penetration rates, and time window lengths. Global positioning system (GPS) data from Interstate I-880 (California) for a total of 73 vehicles over 6 h were obtained from the University of California Berkeley's Mobile Century Project, and these were used to evaluate several travel time estimation methods, the results of which were then validated against reference travel time data collected from high resolution video cameras. The results indicate that vehicle penetration rates, data sampling frequencies, vehicle coverage on the links, and time window lengths all influence the accuracy of link travel time estimation. The performance was found to be best in the 5-min time window length and for a GPS sampling frequency of 60 s.     

预制型芯柱嵌岩桩设计与施工若干问题探讨

嵌岩桩作为一种比较特殊的桩基础形式,其施工工艺控制要求对嵌岩桩设计至关重要。结合工程实例经验,针对预制型芯柱嵌岩桩设计与施工过程中关于选取预制桩斜率、控制终锤贯入度、规定孔内沉渣厚度要求、确定泥浆指标等问题,通过列举分析工程实例、试算轴向承载力及分析规范计算公式,得出了预制型嵌岩桩设计过程中关键参数的取值注意要点及建议值,此外还给出了施工常见问题及处理措施。     

高桩码头增加钢管桩沉桩入土深度的施工措施

在丹东港大东港区317~#高桩码头工程中,为增加钢管桩在卵石层中的入土深度,满足桩基嵌固长度要求,通过采用增加外箍的开口桩尖,有效缩减了沉桩过程中卵石层的侧摩阻力,入土深度增加2 m以上,侧模阻力在沉桩后30d逐渐恢复,满足桩基承载力要求。结果表明,增加外箍桩尖能够有效缩减施工过程中卵石的侧摩阻力,增加桩入土深度,满足嵌固长度要求。     

基于CFD模拟的钢管桁主梁气动特性研究

基于计算流体力学方法,以深圳市拟建山谷沟壑处景观桥为研究对象,建立三维仿真节段模型进行气动性能研究。首先研究节段桁架模型在对称边界条件下的合理性,得出可以利用节段模型来代替三维整桥进行数值模拟。然后通过比较三维整桥模拟与国内现行规范中桁架桥气动参数选取方法,做出检验并提出改进建议。以桁架桥结构截面的外轮廓和实面积比作为控制条件建立二维等效模型,采用4种二维圆管桁主梁CFD计算简化模型,并计算了在-5°、-3°、0°、3°、5°攻角情况下的桁架桥梁静力三分力系数。同时基于非定常时程曲线,对4种二维等效模型附近的空间流场结构、涡振性能差异进行了对比。     

单孔主动预燃室火焰射流机理研究

基于单孔主动预燃室,研究了火焰射流的形成机理。在圆形自由紊动射流理论的基础上,提出了单孔主动预燃室点火的火焰射流贯穿距随时间变化的经验公式。该经验公式可以通过射流锥角、预燃室喷口直径和射流在预燃室喷口处的初速度预测射流贯穿距。通过主动预燃室的定容燃烧弹试验和CONVERGE仿真验证,该经验公式所预测的射流贯穿距和反向求得的射流初速度与实测值吻合,最大相对误差分别为6.92%和5.82%。认为此公式能够正确预测单喷孔主动预燃室的射流贯穿距,对于优化预燃室结构以实现更高效地点火,继而提升内燃机的理论热效率具有参考意义。     

Ballistic performance of ultra-high molecular weight polyethylene laminates against fragment-simulating projectiles北大核心CSCD

[目的]旨在探究破片侵彻作用下高强聚乙烯(UHMWPE)纤维增强层合板的毁伤响应过程、失效模式转变和能量吸收特性。[方法]采用有限元软件ANSYS/AUTODYN,建立UHMWPE层合板抗破片侵彻数值模型,分析UHMWPE层合板的失效模式转变和能量吸收特性。[结果]破片侵彻作用下UHMWPE层合板的动态响应过程大致可以分为剪切冲塞阶段和拉伸变形阶段。破片入射速度和靶板厚度会直接影响靶板的能量吸收特性。靶板厚度越大,剪切冲塞模式占比越大。在靶板厚度不变的情况下,随着破片侵彻速度的提高,剪切冲塞模式占比越来越大,最终趋于稳定。在破片弹道极限速度以上初始小范围内,靶板吸能随破片入射速度增大有所减小,随后破片速度继续增加会扩大靶板剪切冲塞破坏范围,导致靶板整体吸能量增加。[结论]基于所建立的数值模型能够较好地模拟破片侵彻作用下UHMWPE层合板的动态响应过程,可以为UHMWPE材料在弹道防护领域的应用提供参考。