第十八届美国理论与应用力学大会总结

1会议概况2018年6月5—9日,第18届美国理论与应用力学大会(18th U.S. National Congress of Theoretical and Applied Mechanics, USNCTAM2018)在美国芝加哥召开.本次大会由美国力学国家委员会和中国力学学会联合主办,旨在探讨和交流近四年世界范围内在理论和应用力学领域的基础研究、创新技术的最新进展,吸引了来自世界各地的近千名专家学

新疆人口增长预测与可持续发展研究

人口问题是可持续发展的核心问题,在全面建设小康社会的新的历史时期,新疆未来的人口发展状况对区域整个国民经济和社会发展都将起着关键的影响。文中采用《新疆统计年鉴》统计数据对新疆2010年和2020年的人口发展规模做出预测,并在预测的基础上对人口与水资源、耕地资源、矿产和能源资源的可持续发展进行了分析。通过预测分析得到以下结论:新疆未来的人口增长速度依然会相当高;人口增长对于水资源、耕地资源和矿产能源资源的压力不会很大;但是鉴于新疆人口存在的人口文化素质低、人口城镇化水平低以及流动人口数量大等问题,仍然必须制定科学的人口政策,促进人口与经济社会的可持续发展

Effect of plasticity on the coefficient of restitution of an elastoplastic sphere impacting an elastic plate

A sphere impacting a plate is different from impacting a half-space bulk, because energy in the former case can be dissipated in a form of flexural wave propagating on the plate. Such energy loss by the elastic wave can be explained by the Zener model; however, this model is only valid for low-velocity impact with elastic Hertzian contact law. For high-velocity impact with contact plasticity, the Zener model is not valid any ore because energy dissipation by plasticity may take a large fraction, so that the Zener model, which ignores plasticity, will overestimate the coefficient of restitution (COR). In order to study how much the plasticity affects the sphere impacting the plate, we developed a modified Zener model by employing the contact plasticity into the controlling equation. Using the developed model, we firstly presented a thickness-dependent yielding velocity (yielding impact velocity depends on the thickness of the plate), above which the contact plasticity should be taken into account. What is more, we presented a semi-analytical solution to predict the COR over a large range of plate thickness. Meanwhile, finite element simulations were carried out to prove that the present model can give enough accuracy for the high velocity impact. (C) 2021 Elsevier Ltd. All rights reserved

Revisiting the interaction of highly nonlinear solitary wave with wall: From infinite to finite thickness

The classical reflection of a highly nonlinear solitary wave (HNSW) on an elastic wall has been used to determine the material properties of the wall, but does not work on a plate (a wall with finite thickness). In this paper, by coupling sphere-plate contact with chain dynamics, we revealed that: with the same initial velocity, the energy dissipation of multi-sphere plate impact is different from the single sphere plate impact, but the contact force on the plate performs similarly. Based on this fact, we then developed two universal force models considering the dissipative feature of the plate. These force models (reflection force on the chain and contact force on the plate) can universally connect the signals of the HNSW with the dissipative feature of the plate. With the obtained force models, we proposed a non-destructive evaluation method, which can identify both the plate material and thickness by measuring the two forces: the reflection force on the chain and the contact force on the plate. Agreement with finite element simulations suggests that non-destructive evaluation of thin-walled structure can be realized by using HNSW with the proposed method

Effect of plasticity on dynamic impact in a journal-bearing system: A planar case

Plasticity is inevitable during contact with a high load, and thus should be considered when simulating high-load contact. Plasticity during non-conformal contact has been well studied. However, no contact law that considers plasticity during conformal contact has been developed, even though such &quot;plastic conformal contact&quot; commonly occurs in journal-bearing systems under high loads. Herein, we constructed a plastic Winkle model of plastic conformal contact, and integrated it into a contact solver to simulate the impact dynamics of a single journal-bearing system. The plastic contact law was first verified by finite-element simulations, which were in good agreement with the plastic indentation observed during loading and unloading. To study the plasticity during conformal impact, we integrated the contact law into a dynamic-contact model of the single journal-bearing system. The results indicate that the energy dissipation due to plasticity was much greater than that from damping and friction. Ignoring plasticity may result in an unrealistic travel distance of the journal during impact. The developed model was used to construct a velocity map to determine whether or not that plasticity should be considered. (c) 2020 Elsevier Ltd. All rights reserved.</p

Distribution Characteristics of Sea Surface Salinity and Its Relations to Tide in Jiulongjiang Estuary-Xiamen Bay

根据2006~2007年九龙江口-厦门湾海域5个航次的调查结果,分析该海域表层盐度的分布特征及其随潮时的变化.结果表明:河口区,表层盐度分布随潮变化;因受外海高盐水和九龙江冲淡水影响的不同,高潮前1~2 h,河口海域表层盐度北部随时间降低,而南部则随时间略有升高;厦门湾海域存在明显的冲淡水锋面,其位置及强度也随潮变化.According to 5 cruises of observations in the Jiulongjiang Estuary-Xiamen Bay during 2006 and 2007,we analyzed the distribution characteristics of sea surface salinity as well as its variability with tide.The results showed that the sea surface salinity varied with tide in the estuary.Due to the different influence of oceanic water with higher salinity and fresh water from the Jiulongjiang River,the salinity in the southern estuary increased with time at 1～2 hours before high tide.However,the salinity decreased with tide in the northern estuary.Obvious plume fronts were detected in the Xiamen Bay,and their location and strength varied with tide.国家自然科学基金项目(40576015)资

海洋沉积物32Si测年方法研究

天然32Si是宇宙射线成因的,随着降水进入湖泊或海洋,被硅质生物摄取后最终存在于生物硅中。32Si来源单一,生产速率相对恒定,半衰期为150 a,可测年的时间尺度为100～1 000 a,是该时间尺度最合适的测年核素,填补了百年到千年时间尺度测年方法的空白。本文建立了海洋沉积物32Si的测量方法,主要步骤为:（1）样品前处理;（2）生物硅的分离与纯化;（3）生物硅样品中磷的分离与纯化;（4）32P的制样与β计数测量。全程通过硅钼蓝和磷钼蓝分光光度法监测实验过程硅和磷的损失情况,对南沙海域采集的沉积物岩心进行研究,得到南沙海域沉积物岩心32Si的平均活度为16.60 mBq/kg,范围值为8.39～33.34 mBq/kg;32Si在SiO2中的平均比活度为0.356 Bq/kg,32Si的核素丰度平均值为1.29×10-16 (32Si/SiO2);根据岩心32Si活度估算得深水区（水深1 335～1 537 m）和浅水区（121～141 m）岩心的沉积速率分别为0.106 cm/a、0.191 cm/a;根据32Si活度计算32Si的平均沉降通量为2.14×10-6 Bq/（cm2·a）,与参考文献的结果较为吻合。中国地质调查局项目(GZH201500207,GZH201300503,DD20160146

热泵干燥双层干燥室内部气流组织模拟

热泵干燥系统干燥室内气流分布直接影响干燥效果,模拟其内部流场分布规律可为干燥室结构的优化设计提供理论依据。本文建立了双层干燥室数学模型,模拟了干燥室内部气流分布规律,对比了增加进风挡板对各层物料速度分布的影响。结果表明,无进风挡板时下层干燥室风速较大,整体风速在1 m/s以上,上层干燥室风速较小,部分区域不足0.3 m/s,上下差距较大,气流分布较为不均。增设进风挡板后改善了其内部气流分布规律,提高了物料层附近气流分布的均匀性。增设挡板后相同位置的气流不均匀度下降,其中上侧两托盘截面处分别由59.7%下降至27.1%、58.6%下降至36.8%,改善了气流分布及干燥效果

An analysis on temperature and salinity at the surface water of Fujian coast in late August of 2006

通过对福建沿海2006年8月20~24日表层温、盐度的调查资料进行分析,得出以下结果:(1)受九龙江、晋江以及闽江冲淡水的影响,福建沿海存在较强的河口锋.(2)在东山、平潭附近海域存在上升流迹象.(3)在沿岸区,潮汐对海水表层温、盐分布的影响显著.Several phenomena are analyzed according to the temperature and salinity measurements at surface water along the Fujian coast in late August of 2006.The results show that:(1)As affected by the diluted water from the Jiulongjiang River,Jinjiang River and Minjiang River,there exist strong salinity fronts in the estuaries.(2)Upwelling are evident near both Dongshan and Pingtan.(3)Tide has shown effects on the sea surface temperature and salinity along Fujian coast.国家自然科学基金资助项目(40576015、40521003、40331004

Dynamic Impact of High-Density Aluminum Foam

High-density aluminum foam can provide higher stiffness and absorb more energy during the impact Obtaining the constitutive law of such foam requires tri-axial tests with very high pressure, where difficulty may arise because the hydrostatic pressure can reach more than 30MPa. In this paper, instead of using tri-axial tests, we proposed three easier tests-tension, compression and shear to obtain the parameters of constitutive model (the Deshpande-Fleck model). To verify the constitutive model both statically and dynamically, we carried out additional triaxial tests and direct impact tests, respectively. Based on the derived model, we performed finite element simulation to study the impact response of the present foam. By dimensional analysis, we proposed an empirical equation for a non-dimensional impact time (t) over bar (d), the impact time divided by the time required for plastic wave travelling from the impact surface to the bottom surface, to determine the deformation characteristic of the aluminum foam after impact. For the case with (t) over bar (d) 5, the deformation tends to exhibit an upsetting-type characteristic