Long-period Gratings in-situ Sensing for Flow Monitoring in Liquid Composite Molding

Liquid composite moulding (LCM) processes are used to manufacture high quality and complex-shaped composite parts in the automotive, marine, aerospace and civil industries. On-line sensing plays an important role in controlling the quality of the final product in the LCM manufacturing environment. The long-period fiber grating (LPG) technology, a new real-time fiber optic sensor system, was developed to monitor the flow front progression. The sensor operation and characterization under various process conditions were discussed in detail. The experimental results showed that LPG sensors were robust and reliable to detect the arrival of resin at pre-selected locations in structures with low-medium fiber volume fraction; however were limited at different depths in structures with high fiber volume fraction.

Shear flow induced vibrations of long slender cylinders with a wake oscillator model

A time domain model is presented to study the vibrations of long slender cylinders placed in shear flow. Long slender cylinders such as risers and tension legs are widely used in the field of ocean engineering. They are subjected to vortex-induced vibrations（VIV） when placed within a transverse incident flow. A three dimensional model coupled with wake oscillators is formulated to describe the response of the slender cylinder in cross-flow and in-line directions. The wake oscillators are distributed along the cylinder and the vortex-shedding frequency is derived from the local current velocity. A non-linear fiuid force model is accounted for the coupled effect between cross-flow and in-line vibrations. The comparisons with the published experimental data show that the dynamic features of VIV of long slender cylinder placed in shear flow can be obtained by the proposed model,such as the spanwise average displacement,vibration frequency,dominant mode and the combination of standing and traveling waves. The simulation in a uniform flow is also conducted and the result is compared with the case of nonuniform flow. It is concluded that the flow shear characteristic has significantly changed the cylinder vibration behavior.

OPTICAL TELEPHONE CORD PASSING THROUGH LONG PIPE WITH SPIRAL FLOW

A new effective technique, useful in telecommunications industry for passing an optical telephone cord attached to a connector through pipeline,has been developed using the spiral flow. Using this technique, the cord could be passed through a straight pipeline 150 meters long and a roll of vinyl tube 50 meters long. However, under the same condition, the cord could not pass through when using the turbulent flow. To obtain a high speed stable spiral flow, a nozzle with an annular slit connected to a conical cylinder was used. A pressurized fluid with no tangential flow was supplied through this slit and the fluid, passing through the conical cylinder, was deformed into spiral flow with the steeper axial velocity distribution compared to that of turbulence pipe flow due to Coanda effect and instability. As a result, the cord was attracted to the axis area of the pipe, which effectively increased the ability for the work of cord passing. This high ability for cord passing is attributed mainly to the reduction of the friction made between the cord and the pipe wall, caused by the deformation to spiral flow.

Vortex-Induced Vibrations of A Long Flexible Cylinder in Linear and Exponential Shear Flows

A numerical study based on a wake oscillator model was conducted to determine the response performance of vortex-induced vibration(VIV) on a long flexible cylinder with pinned-pinned boundary conditions subjected to linear and exponential shear flows. The coupling equations of a structural vibration model and wake oscillator model were solved using a standard central finite difference method of the second order. The VIV response characteristics including the structural displacement, structural frequency, structural wavenumber, standing wave behavior,travelling wave behavior, structural velocity, lift force coefficient and transferred energy from the fluid to the structure with different flow profiles were compared. The numerical results show that the VIV displacement is a combination of standing waves and travelling waves. For linear shear flow, standing waves and travelling waves dominate the VIV response within the low-velocity and high-velocity zones, respectively. The negative values of the transferred energy only occur within the low-velocity zone. However, for exponential shear flow, travelling waves dominate the VIV response and the negative energy occurs along the entire length of the cylinder.

The axisymmetric long-wave interfacial stability of core-annular flow of power-law fluid with surfactant

The long wave stability of core-annular flow of power-law fluids with an axial pressure gradient is investigated at low Reynolds number. The interface between the two fluids is populated with an insoluble surfactant. The analytic solution for the growth rate of perturbation is obtained with long wave approximation. We are mainly concerned with the effects of shear-thinning/thickening property and interfacial surfactant on the flow stability. The results show that the influence of shear-thinning/thickening property accounts to the change of the capillary number. For a clean interface, the shear-thinning property enhances the capillary instability when the interface is close to the pipe wall. The converse is true when the interface is close to the pipe centerline. For shear-thickening fluids, the situation is reversed. When the interface is close to the pipe centerline, the capillary instability can be restrained due to the influence of surfactant. A parameter set can be found under which the flow is linearly stable.

Bifurcation and Chaos of Gear Pair System Supported by Long Journal Bearings Based on Turbulent Flow Effect and Nonlinear Suspension Effect

A systematic analysis of the dynamic behavior of a gear-bearing system with nonlinear suspension, turbulent flow effect, long journal bearing approximation, nonlinear oil-film force and nonlinear gear mesh force is performed in the present study. The dynamic orbits of the system are observed by bifurcation diagrams plotted using the dimensionless unbalance coefficient and the dimensionless rotational speed ratio as control parameters. The onset of chaotic motion is identified from the phase diagrams, power spectra, Poincaré maps, Lyapunov exponents and fractal dimension of the gearbearing system. The numerical results reveal that the system exhibits a diverse range of periodic, sub-harmonic, quasiperiodic and chaotic behaviors. The results presented in this study provide some useful insights into the design and development of a gear-bearing system for rotating machinery that operates in highly rotational speed and highly nonlinear regimes.

移动信道Markov模型的Stateflow仿真技术

针对具有长突发误码特性的无线信道特征,根据移动通信系统的仿真要求,基于简单分群马尔科夫(Markov)信道模型,提出了利用stateflow技术的信道仿真方法,并生成移动信道的差错序列。仿真结果表明,该信道模型能够有效地描述无线移动信道的统计特性,并具有可视化、流程化和层次化的特点,在无线移动通信系统的软件仿真中具有实用性。

The effect of stochastic acceleration and delay probability on the velocity and the gap between vehicles in traffic flow

This paper proposes a new combined cellular automaton （CA） model considering the driver behavior of stochastic acceleration and delay with the velocity of the preceding vehicle and the gap between the successive vehicles based on the WWH model and the noise-first NaSch model. It introduces the delay probability varying with the gap, adds the anticipation headway and increases the acceleration with a certain probability. Through these simulations, not only can the metastable state and start-stop wave be obtained but also the synchronized flow which the wide moving jam results in. Moreover, the effect of stochastic acceleration and delay on traffic flow is discussed by analyzing the correlation of traffic data. This indicates that synchronized flow easily emerges in the critical area between free flow and synchronized flow when acceleration and delay are synchronized or their probability is close to 0.5.

基于多维可预知特征的TCN-LSTM城轨短期客流预测

地铁客流量波动受众多因素影响,准确的客流预测数据有利于制定更高效的行车控制方案和客流管控方案。为提高客流预测精度,提出一种基于多维可预知特征的时序卷积神经网络-长短期记忆神经网络模型(TCNLSTM)地铁短期客流预测方法。考虑外部因素的影响,引入Spearman相关系数分析并提取日期、天气等可预知特征及其状态集,以提升预测精度,缩小特征空间,克服了冗余特征数据导致的模型过于复杂问题;通过融合时序卷积神经网络(TCN)提取的客流时间序列特征和可预知特征状态集构建了长短期记忆神经网络(LSTM)层输入,组合模型学习客流与外部影响因素的长短期依赖,从而实现常规日、节假日、不同天气等多场景下的短期客流预测。基于某西南城市地铁刷卡交易数据,对比差分整合移动平均自回归模型(ARIMA)、TCN、LSTM及TCN-LSTM模型的短期客流预测结果,得出组合模型的总体平均绝对误差(MAE)值比其他方法低27%~48%,均方误差(MSE)值低13%~35%,平均绝对百分比误差(MAPE)值低2.8%~6.7%,上述3项指标均表明TCN-LSTM模型的客流预测效果更好。此外,对比实验表明通过融入提取的可预知特征数据,TCN-LSTM模型在测试集上的预测误差评价指标明显降低,所提方法能有效提高地铁短期客流预测精度。

Long-term phenotypic characterization of human bone marrow and adipose tissue derived mesenchymal stromal cells

We present methods to characterize mesenchymal stromal cells (MSC) over long time periods in vitro. The methods entail passaging cells multiple times and performing differentiation studies with the cells at each passage. Using an array of surface markers and flow cytometric quantification, the data can be correlated to traditional measures of differentiation such as PCR and staining. Using these methods to quantify the amount of differentiation, we concluded that many common MSC markers do not specifically define MSCs with true stem cell properties. Additionally, adipose-derived as opposed to bone marrow-derived MSCs show long-term CD34+ labeling. The methods described can be used to help identify stem cell markers and to characterize the state of stem cells in vitro. Compiling these data from multiple laboratories would be helpful to determine source, extraction and culture methods needed to obtain high yields of useful stem cells.

全产业链贯通布局下钒液流电池长时储能发展思考

清洁能源的发展和“双碳”目标的实施推动了能源结构调整和电网系统升级,这必将催生巨大的万亿长时储能需求,麦肯锡预测2030年全球可再生能源占比将升至60%~70%,长时储能比2025年增加5~10倍(预计2025年30~40 GW)。全钒液流电池相比其他电化学储能具有安全长寿、灵活可靠、资源丰富等优点,2018~2023年国家和地方发布了多项清洁能源储能配置标准的政策性文件,在此背景下钒储能电池行业企业持续高速增长,行业集中度提升,宏观领域表现为我国钒储能产业正处在加速发展期。目前,钒储能电池总体成本较高,主要原因是钒原料价格高,降低成本的核心环节是钒资源提取成本和电解液生产制造成本。中国恩菲研发的短流程制备钒电解液技术相对于传统钒电解液制备技术具有流程短、钒利用率高的特点,制造成本降低了30%~50%,后期随着钒资源开发和新工艺的研发成功,钒储能产业降本优势将愈发突出。在国家政策支持下,钒液流电池储能系统有望在短期内实现规模化、商业化应用,成为储能领域的重要选择。未来,钒液流电池储能系统仍需从多方面进行优化,如重视技术创新和研发、健全回收利用体系等,以实现钒液流电池长时储能产业的可持续发展。

“流空间-场所空间”视角下长征国家文化公园区域文化景观体系构建

【目的】构建区域文化景观体系,并探讨旅游流空间与场所空间的相互作用关系,以指导长征国家文化公园区域主题展示区的空间组织模式优化。【方法】通过“流空间-场所空间”视角,提出区域文化景观体系的空间结构要素,并运用社会网络分析识别区域旅游流网络结构特征。【结果】旅游流空间为场所空间提供感知需求,而场所空间为旅游流提供行为目标,这种相互作用关系体现了区域文化景观体系的空间结构的功能与价值两大特征;可通过“流—网—链—域—场—点”6个空间结构要素构建区域文化景观体系,并应用“斑块—廊道—节点”模式划定区域主题展示区;长征国家文化公园延安段可划分出6个主题展示区,其中甘泉县包含1个重点展示园、1条集中展示带和2个特色展示点。【结论】在“流空间-场所空间”视角下,区域文化景观体系构建要进一步挖掘区域性特征,而区域主题展示区的空间组织模式应综合考虑供需两侧的现实需求。这些发现为区域文化景观空间功能的研究提供了理论视角与体系结构,可对长征国家文化公园的具体建设提供直接支持。

考虑延误特征的航站楼离港聚集客流预测方法

为满足航班延误下航站楼内资源规划与旅客管理对聚集客流预测所提出的高精度和高效率要求,本文提出一种融合延误特征的离港聚集客流预测方法。通过引入航班延误特征量化表征航站楼离港聚集客流的波动情况,探究航班延误下离港聚集客流波动规律和分布特征,构建基于自适应噪声完全集合经验模态分解(CEEMDAN)、排列熵算法(PE)以及鲸鱼优化算法(WOA)优化的长短期记忆神经网络(LSTM)的短期航站楼聚集客流预测模型。首先,应用CEEMDAN将聚集客流数据序列分解为若干模态分量(Intrinsic Mode Function, IMF)和残差量(Residual, Res),降低原序列中数据的复杂性和非平稳性影响;其次,为减小模型计算规模,同时提高预测效率和精度,采用PE算法对IMF分量进行熵值重构;最后,建立WOA-LSTM聚集客流预测模型,利用鲸鱼优化算法优化LSTM超参数,叠加重构分量的预测结果,得到最终的聚集客流预测值。将模型应用于长三角某枢纽机场进行实例验证。结果表明:CEEMDAN-PE-WOA-LSTM预测模型性能最优,相较单一的LSTM模型,候机大厅聚集客流预测的均方根误差、平均绝对误差以及百分比误差分别降低42.78%、44.00%及45.62%;相较CEEMDAN-WOA-LSTM模型,预测效率提高41.64%。本文所提模型能够有效拟合存在显著非线性和非平稳性特征的候机大厅聚集客流,具有较高的预测精度和运算效率。

氩气环境对激光诱导击穿光谱法检测钢中C、P、S元素的影响研究

激光诱导击穿光谱技术在实现钢水成分在线分析上展现了强大的应用潜力。然而,在测量钢中非常重要的C、P、S组成元素时,由于其有效的发射谱线无法在空气中远距离传输,这些元素的探测一直是个挑战。该论文工作研究了在1.5 m长探枪下,探枪中氩气环境对检测钢中C、P、S元素的影响规律,发现氩气流量过大或过小都不利于光谱测量,在气流量设置为11 L·min^(-1)时,获得的光谱最稳定且谱线强度最大。使用14个标准钢样本,在最优气流量下对C、P、S三种元素实现了明显检出以及定量分析。通过内标标定后,三种元素获得的检出限(LOD)分别为0.009%、0.04%、0.015%,相对标准偏差(RSD)分别为2.34%、1.05%、1.01%,相关系数(R)分别为0.998、0.997、0.987,均方根误差(RMSE)分别为0.02%、0.02%、0.03%。该论文研究成果验证了该探枪设计的有效性,为实现钢水成分中C、P、S在线分析提供了重要的设计依据。

煤炭超临界水制氢反应器内多相流场智能滚动预测研究

煤炭超临界水制氢技术在高温高压条件下利用超临界水充分气化煤炭,实现了高效低排放的转化和制氢过程。为解决因反应器内复杂多相流行为导致的仿真耗时问题,以及常见代理模型时序预测时间短、精度下降快等问题,提出基于本征正交分解(proper orthogonal decomposition,POD)和Koopman理论的深度学习模型POD-Koopman,用于捕捉和学习反应器内复杂流场的长时时空演变特征,实现数据驱动的长时滚动预测。测试结果表明其能在较小计算开销下准确滚动预测反应器内多相流场时变行为,助力下游制氢反应器工业化设计及优化任务。

舟曲虎家崖滑坡直接转化泥石流的特征、过程与机理研究

滑坡直接转化而成的泥石流通常比滑坡本身运移距离更远,波及范围更广,危害也更严重,但目前相关转化机制及其影响因素的研究较少。2020年10月20日位于白龙江左岸、甘肃省舟曲县的虎家崖暴发小型泥石流,侵入省道313,威胁毗邻村庄。通过现场调查、室内岩土试验、遥感解译和降雨资料分析,本文对虎家崖泥石流形成的地质环境条件、运移及堆积特征等进行了调查,研究了浅层滑坡失稳并直接转化为泥石流的主要特征、过程、影响因素及其形成机理,探讨其未来发展趋势。研究表明:(1)虎家崖上游狭长沟道堆积体受到长达19 d、累计98.5 mm的持续性降雨的激发而发生慢速滑坡,区域强震造成的坡体结构损伤对滑坡发育也有贡献。(2)滑坡后段与滑坡前缘的剪出部分在运动过程中直接转化为泥石流,但中段滑坡体则维持剪切滑动。(3)转化过程受滑坡前缘剪出土体饱水程度、沟道坡度与落差以及地表径流等因素的影响。(4)虎家崖狭长沟道后缘可能因毗邻泄流坡滑坡活动牵引而破坏,同时上游沟道残余滑坡体与灰岩崩塌体、出口右侧残余滑坡体可能受降雨、地震等激发而失稳,再次转化为泥石流,威胁沟道下方虎家崖村和省道S313。

基于CNN-BiLSTM的油田注水流量预测

针对深度学习中的RNN(Recurrent Neural Networks)常用于时间序列预测,但其存在难以对历史序列进行特征提取、以及无法突出关键信息的影响且时间序列过长时早期信息易丢失等问题,提出一种基于双重注意力机制CNN(Convolutional Neural Networks)-BiLSTM(Bi-directional Long Short-Term Memory)的油田注水流量预测方法。该方法以油田历史注水数据为输入,利用CNN层提取历史注水数据特征,并引入特征注意力机制层,通过计算权重值的方式为特征赋予相应权重,使关键特征更容易得到较大权重,进而对预测结果产生影响;BiLSTM层对数据进行时序建模,并引入时间步注意力机制,通过选取关键时间步并突出该时间步的隐藏状态表达,使早期隐藏状态不会随时间消失,能提升模型对长时间序列的预测效果,最后完成流量预测。以公开数据集和中国南部某地区油田注水数据为算例,并与MLP(Multilayer Perceptron)、GRU(Gate Recurrent Unit)、LSTM(Long Short-Term Memory)、BiLSTM,CNN进行对比,证明该方法在油田注水流量预测中精度更高,可帮助油田制定生产计划、减少资源浪费以及提高注采率,具有一定的实际工程应用价值。

环境驱动无人船大洋长航程路径规划研究

环境驱动无人船,如波浪滑翔机、saildrone等,由于自身低航速性、欠驱动性和弱机动性,导致其在大洋航行时受洋流干扰显著,甚至在部分强洋流海域出现失控的情况。本文基于先验已知的动态流场,通过B样条控制点随机生成无人船路径,并计算每一条路径在动态流场中考虑路径距离、航行速度以及路径光滑度的综合代价函数,使用遗传算法迭代搜索最优控制点组合。此外,考虑到大洋长航程路径规划中时间跨度长的特点,将出发时间作为路径优化参数,对比分析不同出发时间对行程用时的影响。仿真表明,所提出的路径规划策略能够有效提升大范围动态流场中欠驱动无人船的平均航速,缩短目标抵达时间。同时,在大范围长时序航行中,选择适当的出发时间可以进一步缩短行程用时。

HL-2A装置上刮削层丝状结构时空特征的实验研究

在HL-2A装置上,采用环向相距2100mm的组合探针阵列研究了刮削层涨落谱特征和阵发性丝状结构(blob)动力学过程。实验结果表明,沿磁力线方向静电涨落具有强的环向长程相关性,平行波数接近0,符合交换模的特征。电子回旋共振加热(ECRH)期间,在最后闭合磁面外侧形成径向宽度约1.0cm的E×B剪切层,它对经过该区域的blob具有一定的拉伸作用。条件平均方法分析指出,ECRH期间相比于欧姆加热条件下blob极向尺寸仅增加了20%~30%,但blob内部电势差增大了约40%~60%,暗示了blob内部电势差增加是导致blob径向速度增加的主要原因。这些实验结果为ECRH期间观察到blob阵发性输运的增加提供了一种解释,对理解blob径向速度定标律以及控制blob对流输运具有重要的意义。

狭小空间大管径超长溜管浇筑超大底板施工技术分析

为提升狭小空间下深基坑超大底板的施工质量,文中依托某超高层建筑项目施工实践,对该项目超长溜管单侧浇筑方案及施工技术进行分析,并评估大体积混凝土温控效果。结果表明,溜管浇筑工艺的最快浇筑速度达到了650 m^(3)/h,是常规汽车泵浇筑速度的8倍,节省造价58万元,具有较好的社会效益和经济效益;所有条件下的温度监测数据均满足设计要求,表明蓄水保温法对混凝土的温度控制具有良好的应用效果。