Effect of droplet characteristics on liquid-phase distribution in spray zone of internal mixing air-mist nozzle

In continuous casting production,droplet characteristics are important parameters for evaluating the nozzle atomization quality,and have a significant impact on the secondary cooling effect and the slab quality.In order to study the behavior of atomized droplets after reaching the slab surface and to optimize the spray cooling effect,the influence of droplet diameter and droplet velocity on the migration behavior of droplets in the secondary cooling zone was analyzed by FLUENT software.Results show that the droplets in the spray zone and on the slab surface are mainly concentrated in the center,thus,the liquid volume fraction in the center is higher than that of either side.As the droplet diameter increases,the region of high liquid volume fraction on the slab surface becomes wider,and the liquid phase distribution in the slab width direction becomes uneven.Although increasing the droplet velocity at the nozzle exit has little effect on droplet diffusion in the spray zone,the distribution becomes more uneven due to more liquid reaches the slab surface per unit time.A prediction formula of the maximum water flow rate on the slab surface for specific droplet characteristics was proposed based on dimensionless analysis and validated by simulated data.A nozzle spacing of 210 mm was recommended under the working conditions in this study,which ensures effective coverage of the spray water over the slab surface and enhances the distribution uniformity of water flow rate in the transverse direction.

Parameterization for the Depth of the Entrainment Zone above the Convectively Mixed Layer

It has been noted that when the convective Richardson number Ri* is used to characterize the depth of the entrainment zone, various parameterization schemes can be obtained. This situation is often attributed to the invalidity of parcel theory. However, evidence shows that the convective Richardson number Ri* might be an improper characteristic scaling parameter for the entrainment process. An attempt to use an innovative parameter to parameterize the entrainment-zone thickness has been made in this paper. Based on the examination of the data of water-tank experiments and atmospheric measurements, it is found that the total lapse rate of potential temperature across the entrainment zone is proportional to that of the capping inversion layer. Inserting this relationship into the so-called parcel theory, it thus gives a new parameterization scheme for the depth of the entrainment zone. This scheme includes the lapse rate of the capping inversion layer that plays an important role in the entrainment process. Its physical representation is reasonable. The new scheme gives a better ordering of the data measured in both water-tank and atmosphere as compared with the traditional method using Ri*. These indicate that the parcel theory can describe the entrainment process suitably and that the new parameter is better than Ri*.

Impact of tropical cyclone Matmo on mixed zone of the Yellow and Bohai Seas

The Bohai Sea is a low-lying semi-enclosed sea area that is linked to the Yellow Sea via the Bohai straits(mixed zone). Its of fshore seabed is shallow, which makes it vulnerable to serious marine meteorological disasters associated with the northward passage of Pacific tropical cyclones. Analyses on data of remote sensing and buoy of the mixed zone of the Yellow and Bohai seas indicate that all the wind speed, significant wave height, and salinity(SAL) increased, sea surface temperature decreased, and wind energy density changed considerably during the passage of tropical cyclone Matmo on July 25, 2014. It was found that the SAL inversion layer in the mixed zone of the Yellow and Bohai Seas was caused by the tropical cyclone. Furthermore, it was found that the tropical cyclone transported the northern Yellow Sea cold water mass(NYSCWM) into the mixed zone of the Yellow and Bohai Seas. The NYSCWM has direct influence on both the aquaculture and the ecological environment of the region. Therefore, further research is needed to establish the mechanism behind the formation of the SAL inversion layer in the mixed zone, and to determine the influence of tropical cyclones on the NYSCWM.

基于联合熵隐私保护的自适应动态Mix-zone方案

针对车联网中Mix-zone方案灵活性低以及隐私保护程度对用户缺乏透明度的问题,提出一种交通自适应的动态Mix-zone创建方法,可以根据道路交通状况为车辆动态创建Mix-zone,随时随地为车辆创建Mix-zone进行假名更换,建立基于身份和位置的隐私保护;提出对Mix-zone进行隐私分级的联合熵度量模型,可通过归一化的定量计算结果度量Mix-zone达到当前区域车辆隐私需求的程度。使用深圳市某区的出租车辆的轨迹数据验证了联合熵隐私度量模型及基于该模型的Mix-zone创建方案,实验结果表明,该联合熵模型能刻画交通场景中参数与隐私保护程度的正比关系,在联合熵所表示的无序性指标上,所提Mix-zone创建方案相较其他方案,具有更好的隐私保护效果。

车联网中Mix-zone的隐私保护机制研究

车联网在通过位置服务中解决道路安全问题、为驾乘者提供便捷服务的同时,也带来了相应的隐私保护问题。文章总结了隐私保护内容,重点分析了车联网的假名隐私保护技术,假名方案分为基于特殊地形、基于安静时段、加密Mixzone。不同的假名方案在不同的道路特征下会有特定的应用场景。继而针对隐私保护水平的高低,着重分析了特殊地形的Mix-zone的性能。

Uncertainty and Sensitivity Analyses of the Simulated Seawater—Freshwater Mixing Zones in Steady-State Coastal Aquifers

The uncertainty and sensitivity of predicted positions and thicknesses of seawater-freshwater mixing zones with respect to uncertainties of saturated hydraulic conductivity, porosity, molecular diffusivity, longitudinal and transverse dispersivities were investigated in both head-control and flux-control inland boundary systems. It shows that uncertainties and sensitivities of predicted results vary in different boundary systems. With the same designed matrix of uncertain factors in simulation experiments, the variance of predicted positions and thickness in the flux-control system is much larger than that predicted in the head-control system. In a head-control system, the most sensitive factors for the predicted position of the mixing zone are inland freshwater head and transverse dispersivity. However, the predicted position of the mixing zone is more sensitive to saturated hydraulic conductivity in a flux-control system. In a head-control system, the most sensitive factors for the predicted thickness of the mixing zone include transverse dispersivity, molecular diffusivity, porosity, and longitudinal dispersivity, but the predicted thickness is more sensitive to the saturated hydraulic conductivity in a flux-control system. These findings improve our understandings for the development of seawater-freshwater mixing zone during seawater intrusion processes, and give technical support for groundwater resource management in coastal aquifers.

Privacy Protection with Dynamic Pseudonym-Based Multiple Mix-Zones Over Road Networks

In this research we proposed a strategy for location privacy protection which addresses the issues related with existing location privacy protection techniques. Mix-Zones and pseudonyms are considered as the basic building blocks for location privacy; however, continuously changing pseudonyms process at multiple locations can enhance user privacy. It has been revealed that changing pseudonym at improper time and location may threat to user's privacy. Moreover, certain methods related to pseudonym change have been proposed to attain desirable location privacy and most of these solutions are based upon velocity, GPS position and direction of angle. We analyzed existing methods related to location privacy with mix zones, such as RPCLP, EPCS and MODP, where it has been observed that these methods are not adequate to attain desired level of location privacy and suffered from large number of pseudonym changes. By analyzing limitations of existing methods, we proposed Dynamic Pseudonym based multiple mix zone(DPMM) technique, which ensures highest level of accuracy and privacy. We simulate our data by using SUMO application and analysis results has revealed that DPMM outperformed existing pseudonym change techniques and achieved better results in terms of acquiring high privacy with small number of pseudonym change.

Sedimentation in the Submarine Outfall and in the Mixing Zones （Avoiding, Diagnosis and Remediation）

Some practical design tips and important recommendations are given to minimize the negative effect of discharge of wastewater laden with solid particles via submarine outfall. This study emphasizes the role of respecting the hydraulic conditions in the outfall to prevent sedimentation in the outfall or their accumulation in adjacent areas; also it includes the ways used to improve the outfall hydraulic capacity that decreases with time. The diagnostics and remediation procedures of mixing zones are discussed, especially in the case of previous toxic discharge that results in toxic sediments at the bed load. A literature review of techniques used to assess sediment quality near discharge points and locate effluent-affected sediment deposit is presented that include using acoustic profiles and images, chemical analysis, toxicity tests and multivariate indicators.

Mixing Zone Guidelines Application in a Smelter in Northern Sweden with Discharge to the Baltic Sea

This pilot study intended to investigate the application of Mixing Zone Guidelines in northern Sweden. The EC （European Commission）-Mixing Zone Guidelines were applied to seven effluent discharges. The effluents were from industrial processes used in the Ronnskar smelter, in northern Sweden. Each outlet in the smelter area discharges water into the Bothnian bay of the Baltic Sea. Cadmium （Cd）, mercury （Hg）, nickel （Ni） and lead （Pb） were the primary substances present in the effluents. A ＂Tiered Approach＂ was followed for mixing zone assessments in each of the discharge points. Discharge Test was used at Tier 2 and CORMIX （Cornell Mixing Zone Expert System model）, version 7, at Tier 3. At each discharge point, the AA-EQS （annual average-environmental quality standard） for each metal was met within a distance of 500 m from the outfalls. This distance was exceeded to meet the MAC-EQS （maximum allowable concentration-environmental quality standard） criteria at points 1 and 3 for total Hg concentrations. However, for the proper application of Mixing Zone Guidelines, a version of the Discharge Test for coastal waters should be developed and used. The decision at which tier the dissolved metal concentration should be compared with EQS values could depend on the effluent characteristics. For Swedish coastal waters, some consideration should be given to the background concentration of metals.

支持虚拟车辆辅助假名更新的混合区位置隐私保护方案

在车载通信系统中,车辆的位置信息泄露会危及驾驶员的隐私安全,而基于混合区中,车辆的假名更新是实现位置隐私保护的一种有效方法。然而,现有的一些混合区方案忽略了车辆密度变化对位置隐私保护效果的影响。针对此问题,提出了一种支持虚拟车辆辅助假名更新的混合区位置隐私保护方案。该方案旨在根据周围合作车辆的密度不同来动态调整生成所需的虚拟车辆,并广播它们的踪迹,使攻击者无法区分虚拟车辆和真实车辆,从而实现车辆的位置隐私保护。仿真实验结果表明,该方案通过引入虚拟车辆信息,使攻击者无法区分虚拟车辆和真实车辆,有效降低了车辆真实位置或轨迹泄露的可能性,同时提高了交通密度较低情况下的位置隐私保护效果。

W火焰锅炉SCR脱硝超低排放技术及应用

截至2021年底,全国已有超过95%的燃煤火电机组实现了氮氧化物超低排放,剩余均为燃用无烟煤的W火焰锅炉,其产生的氮氧化物质量浓度高达750~1200 mg/m^(3),实现超低排放难度大,是我国实现超低排放政策的“最后一公里”。目前,选择性催化还原(SCR)脱硝流场技术主要有“SCR分区混合动态调平技术”“全烟道断面混合流场技术”“常规精准喷氨技术”等。以某设计脱硝效率需高达95%的W火焰锅炉为例,通过计算流体力学(CFD)模拟的方式对比3种技术的性能指标,“SCR分区混合动态调平技术”的各项指标明显优于其他技术。工程改造后,在脱硝系统入口氮氧化物质量浓度为1000 mg/m^(3),出口低于50 mg/m^(3)时,可实时保持氨逃逸量小于3μL/L,远超常规SCR脱硝系统最高设计效率(93%),为W火焰锅炉氮氧化物超低排放提供了新的技术路线。

公路隧道入口区域驾驶人吸睛效应综合评价

为全面和系统评价公路隧道入口区域视觉吸引对驾驶人吸睛效应视觉表现的影响,本文招募30名被试开展自然驾驶实验,采集驾驶人在公路隧道入口区域不同视觉吸引条件下的眼动数据,基于因子分析法选取驾驶人吸睛效应敏感评价指标,并分别构建线性混合效应模型和数据包络分析模型,识别和探究公路隧道入口区域视觉吸引对驾驶人吸睛效应视觉表现的影响特征和作用机理。结果表明:因子分析结果显示,驾驶人吸睛效应敏感视觉指标为注视持续时间、瞳孔直径、扫视持续时间和扫视幅度;公路隧道入口区域不同视觉吸引条件对驾驶人吸睛效应的视觉表现和综合效率有显著影响,且受驾驶人年龄和驾驶经验的个体特质因素影响显著,而性别因素对其没有显著性影响;视觉吸引的存在均会不同程度地损害驾驶人的正常视觉绩效,降低其合理有效性;提示标语视觉吸引条件下,驾驶人的视觉注意水平最差,视觉认知负荷程度最高,吸睛效应的负面影响最大,广告牌条件次之。

二氧化碳作天然气地下储气库垫层气的可行性

CO_(2)用作天然气地下储气库垫层气,在储气库运行过程中,注采参数等因素不合理导致CO_(2)与天然气之间过渡混合和天然气采收率低等问题。开展了CO_(2)和CH_(4)物性对比及混气实验,论证了CO_(2)作垫层气的可行性;建立储气库二维模型,模拟CO_(2)作垫层气注采过程,对影响CO_(2)-CH_(4)混合程度的地层参数和运行参数进行分析。研究结果表明:CO_(2)垫层气比例不超过20%,采出气中CO_(2)摩尔含量不高于3%,CO_(2)-CH_(4)混合程度、储层平均压力下降幅度较小。渗透率越大,工作气回采携带CO_(2)垫层气量越多,实际CO_(2)垫层气量占比减小,CO_(2)垫层气量不足以为工作气开采提供“助力”。孔隙度对CO_(2)-CH_(4)混合程度几乎没有影响。合理控制采气速度能有效抑制混合带发展,即在用气高峰适当提高采气速度,用气低谷减小采气速度保证最低用气标准。研究结果为CO_(2)作天然气地下储气库垫层气的工程实践提供理论指导。

基于适宜性和空间功能值的德兴市矿粮复合区“三生”空间优化研究

[目的]深入开展“三生”功能评价与空间调控优化,协调重构不合理的空间布局与结构,缓解矿粮空间冲突,为国土空间治理和区域高质量发展提供参考。[方法]以德兴市矿粮复合区为例,结合空间适宜性评价、功能值测算与空间自相关分析,基于AVC“三力”理论对研究区进行“三生”空间优化研究。[结果](1)农业、工业生产空间分别集中于西南部和北部,生活空间集中度自西北向东南递减,而生态空间分布广泛且整体均衡;(2)生产、生态空间多呈现聚集态势,而生活空间功能聚集性较弱,呈零星分布,且矿区对其空间适宜性、功能值及聚集度有负面影响;(3)空间重构后,生活、生态空间功能值分别从1.948 6亿元、90.755 0亿元提升至1.951 8亿元、90.778 9亿元。[结论]综合考虑适宜性、空间功能值与集中度进行空间优化与重构,研究区生活与生态空间功能值有所提高,各类空间分布趋于集聚态势,缓解了矿区对于人们生活与粮食生产的负面影响。未来应针对各类空间进行系统治理与管控,并严格控制矿区开发,以保障生产、生活与生态功能。

机械搅拌驱动下固液混沌混合特性数值模拟

混沌搅拌对于理解复杂系统行为、改善混合过程的效率和质量以及推动科学和技术的发展具有重要意义。通过数值模拟计算,从搅拌迹线和流场揭示了混沌搅拌的搅拌效果优于普通匀速搅拌。通过流场迹线分析,得出混沌搅拌强化搅拌效果的根本原因是混沌搅拌打破了搅拌的隔离死区。同时混沌搅拌所产生的整个流场的紊乱程度要远远大于普通匀速搅拌。

矿粮复合区“三生”空间冲突诊断及演化特征分析——以大冶市陈贵镇为例

[目的]促进乡镇级矿粮复合区空间结构协调稳定,为国土空间规划的合理布局及实施提供科学参考。[方法]以矿粮复合区陈贵镇为例,基于生命周期法选取1986—2020年的5个研究时间节点,通过空间现状图和转移矩阵解释空间格局变化,构建改进的空间冲突测度模型,利用ArcGIS 10.2结合Fragstats 4.2软件分析空间冲突演化特征,使用Google Earth历史影像验证了冲突结果。[结果]农业生产空间和生态空间是转入和转出面积最大的两类空间类型,“耕地—林地”互转成为最显著的土地转换方式;1986—2020年,陈贵镇“三生”空间冲突整体有上升的趋势,在矿业衰退期,较弱、中等和强空间冲突空间单元占比分别减少3.2%,3.09%,0.22%,较强空间冲突占比增加6.51%;“三生”空间的冲突等级除了生活空间,均集中在较弱空间冲突和中等空间冲突等级,两者面积占比超过70%;借助Google Earth历史影像进行对比验证,发现“三生”空间冲突结果与空间现状较吻合。[结论]矿粮复合区受城市化和工业化的影响较大,空间冲突特征明显,参考空间冲突诊断结果,可针对性地实施空间冲突缓解措施,促进地区的可持续发展。

基于潜标观测的黑潮-亲潮混合区近惯性能量季节变化特征研究

近惯性内波广泛存在于全球海洋,是维持深层海洋跨等密度面湍流混合及海洋层结的重要能量来源。基于黑潮-亲潮混合区的多年深海潜标数据,分析了:(1)该海域近惯性内波及其能量的季节变化特征与影响因素,(2)上层和深层近惯性运动的频率、波数谱及垂向分布等特征。结果表明,该海域存在丰富的近惯性动能,无论海洋上层还是深层均呈现显著的冬季强、夏季弱的季节变化特征,冬季(12~2月)上层的近惯性能量可占全年能量的41%,深层近惯性信号同样显著,同潮汐信号相当。平板模型分析表明,该区域近惯性动能的季节循环特征主要受风场的季节变化所主导,同时受到黑潮延伸体流轴的摆动调制。

关井阶段CO_(2)作储气库垫层气的动态影响规律

目的为应对地下储气库中的垫层气损失,采用经济气体CO_(2)作为垫层气,目前,CO_(2)作垫层气在实际应用中存在各种条件限制,且对其在关井阶段的应用研究较少,有必要对在关井阶段CO_(2)作垫层气对天然气储气库的运行影响因素进行研究。方法利用有限元模拟CO_(2)作储气库垫层气时,研究关井阶段储气库动态参数(注气压力、注气速率和CO_(2)垫层气比例)对混气带的影响规律。结果注气压力对混气带的影响不大,将其控制在12 MPa左右最为合理,此时混气带占储气面积的比例为23.7315%;混气带面积占比随注气速率的增大而减小,但是在注气口附近会出现混合区域,导致回采天然气时出现大量的混合气体,所以注气速率控制在0.7×10^(8) m^(3)/d时最为合理,这时混气带面积占比为18.3246%;CO_(2)作垫层气的比例对天然气-CO_(2)之间的混合影响明显,当CO_(2)垫层气比例为20%时,混气带面积占比为7.2365%。结论根据实验结果设计针对混气带的控制措施,当注气压力控制为12 MPa时,注气速率为0.7×10^(8) m^(3)/d,当CO_(2)垫层气比例为20%时,能让储气库的运作更为经济,实验结果可为实际储气库的建设提供参考。

Seasonal Variation of the Sea Surface Temperature Growth Rate of ENSO

El Ni?o–Southern Oscillation(ENSO) exhibits a distinctive phase-locking characteristic, first expressed during its onset in boreal spring, developing during summer and autumn, reaching its peak towards winter, and decaying over the next spring. Several studies have demonstrated that this feature arises as a result of seasonal variation in the growth rate of ENSO as expressed by the sea surface temperature(SST). The bias towards simulating the phase locking of ENSO by many state-of-the-art climate models is also attributed to the unrealistic depiction of the growth rate. In this study, the seasonal variation of SST growth rate in the Ni?o-3.4 region(5°S–5°N, 120°–170°W) is estimated in detail based on the mixed layer heat budget equation and recharge oscillator model during 1981–2020. It is suggested that the consideration of a variable mixed layer depth is essential to its diagnostic process. The estimated growth rate has a remarkable seasonal cycle with minimum rates occurring in spring and maximum rates evident in autumn. More specifically, the growth rate derived from the meridional advection(surface heat flux) is positive(negative) throughout the year. Vertical diffusion generally makes a negative contribution to the evolution of growth rate and the magnitude of vertical entrainment represents the smallest contributor. Analysis indicates that the zonal advective feedback is regulated by the meridional immigration of the intertropical convergence zone, which approaches its southernmost extent in February and progresses to its northernmost location in September, and dominates the seasonal variation of the SST growth rate.

基于响应面法的机制砂路面混凝土配合比优化及其性能研究

为实现多目标性能机制砂混凝土配合比设计,本文采用Box-Behnken响应面法进行试验设计,探究了石粉掺量、浆体体积分数及水胶比对机制砂路面混凝土性能(坍落度、28 d抗压强度和磨损量)的影响,并结合SEM和XRD对硬化浆体的微观结构进行了分析。结果表明,通过响应面法建立的回归模型能够精确预测各因素与性能之间的关系,精度达95%以上。在各因素中,水胶比对坍落度和抗压强度的影响最显著,而对磨损量的影响较小。经优化,得到最佳的机制砂路面混凝土配合比:水胶比0.36,浆体体积分数25%,石粉掺量10%(质量分数)。此外,掺量不超过10%的石粉改善了界面过渡区,有助于提升混凝土的力学性能。