Long-term operation optimization of circulating cooling water systems under fouling conditions

Fouling caused by excess metal ions in hard water can negatively impact the performance of the circulating cooling water system(CCWS)by depositing ions on the heat exchanger's surface.Currently,the operation optimization of CCWS often prioritizes short-term flow velocity optimization for minimizing power consumption,without considering fouling.However,low flow velocity promotes fouling.Therefore,it's crucial to balance fouling and energy/water conservation for optimal CCWS long-term operation.This study proposes a mixed-integer nonlinear programming(MINLP)model to achieve this goal.The model considers fouling in the pipeline,dynamic concentration cycle,and variable frequency drive to optimize the synergy between heat transfer,pressure drop,and fouling.By optimizing the concentration cycle of the CCWS,water conservation and fouling control can be achieved.The model can obtain the optimal operating parameters for different operation intervals,including the number of pumps,frequency,and valve local resistance coefficient.Sensitivity experiments on cycle and environmental temperature reveal that as the cycle increases,the marginal benefits of energy/water conservation decrease.In periods with minimal impact on fouling rate,energy/water conservation can be achieved by increasing the cycle while maintaining a low fouling rate.Overall,the proposed model has significant energy/water saving effects and can comprehensively optimize the CCWS through its incorporation of fouling and cycle optimization.

Development Trend of Water Supply and Drainage Engineering Based on Life Cycle Assessment and Building Information Model

With the rapid development of construction engineering and municipal engineering in recent years, water supply and drainage technology has gradually matured. Building water supply and drainage design contains the design of rainwater drainage, sewage drainage design, water supply design and fire water supply design. At present, the research on the life cycle assessment of urban drainage system is mainly focused on the sewage treatment plant, therefore in this paper we introduce the theoretical basis of life cycle assessment. In the era of information network, building information model（BIM） technology is widely applied to the design of building water supply and drainage, which and effectively improves the design effi ciency, and makes up for the traditional water supply and drainage design of a lot of problems. In this paper, we analyze the development trend of water supply and drainage engineering based on life cycle assessment and building information model.

Responses of the circulation and water mass in the Beibu Gulf to the seasonal forcing regimes

In the past 20 a, the gulf-scale circulation in the Beibu Gulf has been commonly accepted to be driven by a wind stress or density gradient. However, using three sensitive experiments based on a three-dimensional baroclinic model that was verified by observations, the formation mechanisms were revealed： the circula- tion in the northern Beibu Gulf was triggered by the monsoon wind throughout a year; whereas the southern gulf circulation was driven by the monsoon wind and South China Sea （SCS） circulation in winter and sum- mer, respectively. The force of heat flux and tidal harmonics had a strong effect on the circulation strength and range, as well as the local circulation structures, but these factors did not influence the major circulation structure in the Beibu Gulf. On the other hand, the Beibu Gulf Cold Water Mass （BGCWM） would disappear without the force of heat flux because the seasonal thermocline layer was generated by the input of heat so that the vertical mixing between the upper hot water and lower cold water was blocked. In addition, the wind-induced cyclonic gyre in the northern gulf was favorable to the existence of the BGCWM. However, the coverage area of the BGCWM was increased slightly without the force of the tidal harmonics. When the model was driven by the monthly averaged surface forcing, the circulation structure was changed to some extent, and the coverage area of the BGCWM almost extended outwards 100%, implying the circulation and water mass in the Beibu Gulf had strong responses to the temporal resolution of the surface forces.

A two-time-level split-explicit ocean circulation model (MASNUM) and its validation

A two-time-level, three-dimensional numerical ocean circulation model（named MASNUM） was established with a two-level, single-step Eulerian forward-backward time-differencing scheme. A mathematical model of large-scale oceanic motions was based on the terrain-following coordinated, Boussinesq, Reynolds-averaged primitive equations of ocean dynamics. A simple but very practical Eulerian forward-backward method was adopted to replace the most preferred leapfrog scheme as the time-differencing method for both barotropic and baroclinic modes. The forward-backward method is of second-order of accuracy, computationally efficient by requiring only one function evaluation per time step, and free of the computational mode inherent in the three-level schemes. This method is superior to the leapfrog scheme in that the maximum time step of stability is twice as large as that of the leapfrog scheme in staggered meshes thus the computational efficiency could be doubled. A spatial smoothing method was introduced to control the nonlinear instability in the numerical integration. An ideal numerical experiment simulating the propagation of the equatorial Rossby soliton was performed to test the amplitude and phase error of this new model. The performance of this circulation model was further verified with a regional（northwest Pacific） and a quasi-global（global ocean simulation with the Arctic Ocean excluded） simulation experiments. These two numerical experiments show fairly good agreement with the observations. The maximum time step of stability in these two experiments were also investigated and compared between this model and that model which adopts the leapfrog scheme.

Physical Modeling of the Vacuum Circulation Refining Process of Molten Steel

The available studies in the literature on physical modeling of the vacuum circulation (RH, i.e. Ruhrstahl Heraeus) refining process of molten steel have briefly been reviewed. The latest advances made by the author with his research group have been summarized. Water modeling was employed to investigate the flow and mixing characteristics of molten steel under the RH and RH KTB (Kawasaki top blowing) conditions and the mass transfer features between molten steel and powder particles in the RH PTB (powder top blowing) refining. The geometric similarity ratio between the model and its prototype (a multifunction RH degasser of 90 t capacity) was 1:5. The effects of the related technological and structural factors were considered. These latest studies have revealed the flow and mixing characteristics of molten steel and the mass transfer features between molten steel and powder particles in these processes, and have provided a better understanding of the refining processes of molten steel.

A Two-Dimensional Zonally Averaged Ocean Carbon Cycle Model

An ocean carbon cycle model driven by a constant flow field produced by a two-dimensional thermohaline circulation model is developed. Assuming that the biogenic carbon in the oceans is in a dynamic equilibrium, the inorganic carbon cycle is investigated. Before the oceanic uptake of CO_2 is carried out, the investigation of 14C distributions in the oceans, including natural and bomb-produced 14C,is conducted by using different values of the exchange coefficient of CO_2for different flow fields (different vertical diffusivities) to test the performance of the model. The suitable values of the exchange coefficient and vertical diffusivities are chosen for the carbon cycle model. Under the forcing of given preindustrial atmospheric CO_2 concentration of 280 ppmv, the carbon cycle model is integrated for seven thousand years to reach a steady state. For the human perturbation, two methods including the prescribed atmospheric pCO_2 and prescribed industrial emissions are used in this work. The results from the prescribed atmospheric pCO_2 show that the oceans take up 36% of carbon dioxide released by human activities for the period of 1980-1989, while the results from the prescribed industrial emission rates show that the oceans take up 34% of carbon dioxide emitted by industrial sources for the same period. By using the simple method of subtracting industrial emission rate from the total atmosphere+ocean accumulating rate, it can be deduced that before industrial revolution a non-industrial source exists, while after 1940 an extra sink is needed, and that a total non-industrial source of 45 GtC is obtained for the period of 1790-1990.

Water migration in subgrade soil under seasonal freeze-thaw cycles in an alpine meadow on the Qinghai-Tibet Plateau

Highway frost heave and thawing settlement caused by water migration towards the freezing front and ice lens development is widespread in the alpine meadow area of the southeast QinghaiTibet Plateau(QTP). A laboratory experiment on a highway reconstruction and expansion project in the QTP was carried out in this work to analyze the effects of fine particle content, initial water content, and the number of freeze-thaw cycles(FTCs) on frost depth, temperature gradient(Grad T), total water intake, and water intake flux. Based on the results of the laboratory experiment, a modified model of migration potential related to fine particle content, freeze-thaw history, and freezing time was established. The results show that, with the increase of fine particle content, the frost depth of soil decreases, the curve of total water intake over time is transformed from an Sshape to an arch, and the curve of water intake flux over time is transformed from a peak shape to descending shape. The variation trend of migration potential with freezing time and the freeze-thaw history is the same as that of water intake flux with freezing time and freeze-thaw history. The variation trend of soil intake flux can be used as a reference to determine the variation trend of soil migration potential. This study provides a reference for the design and construction of highway subgrade in the alpine meadow area of the QTP.

Hydrological Structure, Circulation and Water Mass Transport in the Gulf of Cadiz

Hydrological and LADCP data from four experiments at sea (Semane 1999, 2000/1 2000/3, 2001) are used to describe the structure and circulation of Mediterranean Water in the Gulf of Cadiz. These data were gathered on meridional sections along 8?20′W and 6?15′W and between these longitudes on a zonal section along 35?50′N. The mesoscale and the submesoscale structures (Mediterranean Water Undercurrents, meddies, cyclones) observed along these sections are characterized in terms of thermohaline properties and of velocity. The transports of mass and salt in each class of density (North Atlantic Central Water, Mediterranean Water, North Atlantic Deep Water) are computed with an inverse model. The model indicates a general eastward flux in the Central Water layer, and a westward flux in the Mediterranean Water layer, but there is also a horizontal recirculation and entrainment in these two layers, as well as strong transports associated with the meddy and cyclone found during Semane 1999.

A Numerical Study of Water Circulation in A Thermally Stratified Embayment

Princeton Ocean Model is used to study the response of Jervis Bay, NSW, Australia, to the local wind and remote shelf coastal trapped wave (CTW) forcings in summer seasons when the water column is stratified by the water temperature.The study has revealed that the response of bay to the wind forcing is the generation of the wind driven currents and the internal Kelvin waves (IKW). However, both temperature and flow sub-inertial oscillations in the bay are weaker than those from the observations and the correlation between the modeled and observed low frequency currents is low. In response to the forcing of CTWs on the adjacent shelf, IKWs are also established in the bay and amplitudes of sub-inertial oscillations of temperature and currents agree better with the observations. It can be concluded that sub-inertial baroclinic flows in the bay is dominantly forced by remote CTW on the shelf adjacent to Jervis Bay during thermally stratified summer seasons.

Pressure fluctuation and its influencing factors in circulating water pump

In order to investigate the effect of sampling frequency and time on pressure fluctuations, the three-dimensional unsteady numerical simulations were conducted in a circulating water pump. Through comparison of turbulence models with hydraulic performance experiment, SST k-co model was confirmed to study the rational determination of sampling frequency and time better. The Fast Fourier Transform （FFT） technology was then adopted to process those fluctuating pressure signals obtained. On these bases, the characteristics of pressure fluctuations acting on the tongue were discussed. It is found that aliasing errors decrease at higher sampling frequency of 17 640 Hz, but not at a lower sampling frequency of 1 764 Hz. Correspondingly, an output frequency range ten-times wider is obtained at 17 640 Hz. Compared with 8R, when the sampling time is shorter, the amplitudes may be overvalued, and the frequencies and amplitudes of low-frequency fluctuations can not be well predicted. The frequencies at the tongue are in good agreement with the values calculated by formula and the frequency compositions less than the blade passing frequency are accurately predicted.

A Lagrangian mean theory on coastal sea circulation with inter-tidal transports Ⅱ. Numerical Experiments

The results of the new concept of coastal sea circulation are demonstrated by numerical simulations for the first time.The numerical experiments in three types of rectangular model seas illustrate the dependence of circulation on tidal phases due to the convectively nonlinear effect which is estimated by a newly defined drift dispersion index.Then,the present theory is applied in the Bohai Sea of China.At the Bohai Straits and the Huanghe River mouth area the circulation direction even reverses owing to different initial tidal phases which shows that the theory copes with nonlinearity well.The calculated M2 tide-induced residual circulation shows that a clockwise gyre exists in the center of an anticlockwise gyre in the central Bohai Sea due to the topographic features.In the Bohai Gulf the tide induced circulation shows a 3D structure with outflow at the surface and the inflow at the bottom which can partly explains the spread of the Huanghe River fresh water out of the Bohai Gulf and the inflow of the sediment from the Huanghe River.

陆地高分辨率水文—生物地球化学过程CNMM-DNDC三维模型的研发及应用进展

CNMM-DNDC模型是本文作者团队研发的陆地高分辨率水文—生物地球化学过程三维模型。本文系统介绍了建模背景和理念、核心过程和模型特点、模拟功能和观测验证、多尺度区域或流域初步应用以及未来发展展望。自2018年刊发首个版本以来,该模型经过了多方面科学过程改进和模拟功能扩展,在元素化学反应、物质相变和机械迁移等基本物理、化学、生物过程层面,完成了对陆地表层系统碳氮磷水循环全耦合的精细刻画。迄今开展的观测验证表明,CNMM-DNDC模型基本普适于不同生物气候带(从热带到寒区多年冻土地带)的流域或区域长时间序列“三高”(时间、空间和过程高分辨率)综合模拟,实现对陆地生态系统的碳、氮、磷、水三维运移、水土流失、水力驱动溶解态和颗粒态碳氮磷横向迁移、碳氮温室气体和污染气体排放、生态系统生产力、水分蒸散发和水分能量平衡等众多可持续发展目标表征变量的预测。该模型广泛推广应用于多尺度区域或流域的复杂过程虚拟科学试验研究和服务于面向生态环境建设与减污降碳的优化调控决策,可望为协同落实联合国多个可持续发展目标提供先进的数值模拟技术支撑。

循环水槽船模阻力修正方法

在循环水槽中开展船模阻力测量是船型优劣分析的常规试验之一,因此对循环水槽阻力修正方法进行研究是十分必要的。以集装箱船标模(KCS)为研究对象在循环水槽中开展模型阻力和流场测量试验,根据循环水槽自身流动特性并结合拖曳水池已有的修正方法,分析并总结适用于水槽船模阻力与阻塞效应的修正方法。由总结的修正公式与修正流程可知,循环水槽中2.5~3.5 m尺寸模型试验与大模型试验结果阻力换算偏差在1%左右,设计航速点阻力换算偏差小于1%。结果表明,有必要对循环水槽中阻力进行自由面倾斜度修正,采用Tamura公式进行阻塞效应修正能得到更为精确的阻力试验结果。

水循环关键要素遥感反演研究进展

水循环是地球系统中至关重要的过程,对水资源管理、气候变化应对和生态环境保护有着深远的影响。遥感是大尺度监测水循环关键要素的主要手段,过去几十年已经取得诸多进展。梳理了当前蒸散发和降水等水循环关键通量要素及土壤水和水储量等水循环关键储量要素的遥感反演技术研究进展,指出了当前精细化监测的发展方向,提出技术创新方向以及亟待解决的科学问题,以期为提升水循环遥感学科发展和应用的深度与广度提供参考。

变化环境下汉江流域水循环要素响应规律

汉江是长江第一大支流,也是南水北调中线工程和引汉济渭工程的水源地,具有重要的战略地位,科学评估气候变化和人类活动等变化环境下其水循环的响应,对流域水资源的可持续利用和制定适宜的管理政策有着重要意义。本文以汉江流域为研究区域构建了校准后的VIC分布式水文模型,随后基于降尺度后的全球气候模式数据和不同时期土地覆盖遥感数据设置不同情景的模拟,全面分析变化环境下流域水循环要素响应规律,并量化了气候变化和土地利用对径流变化的贡献率。结果表明:不同气候变化情景下,年均降水中上游增加显著,年内降水更加集中于夏秋季节丰水期,各月实际蒸散发整体增加且年内分布更加均匀化;丹江口入库流量和流域出口断面流量在RCP8.5情景呈显著增加趋势,流域年内枯水期流量减少,丰水期流量全年占比最大增加了8.51%,未来月流量更加集中于丰水期,发生干旱和洪涝灾害的概率将会增加。汉江流域的部分稀树草原和有林地在21世纪以来转化为郁闭度更高的落叶阔叶林,土地利用的变化没有使得流量的年际变化趋势有较大改变,但使得流量整体降低了。不同时期气候变化和土地利用对丹江口入库流量变化的贡献率分别为80%~88%和12%~20%,对流域出口断面流量变化的贡献率分别为72%~88%和12%~28%,气候变化是汉江流域径流变化的主要驱动力。

不同时间尺度BEPS模型模拟差异分析

生态过程模型已经被广泛用于模拟总初级生产力(Gross Primary Productivity,GPP)和蒸散发(Evapotranspiration,ET)。本研究使用BEPS(Biosphere-atmosphere Exchange Process Simulator)模型两个不同时间尺度的版本,即日步长(BEPS-Daily)和小时步长(BEPS-Hourly),比较两种模型模拟结果的差异,并分析误差来源。结果表明:1)叶面积指数(Leaf Area Index,LAI)是驱动陆地生态系统模型的重要植被结构参数。BEPS-Daily模拟的阳叶LAI会大于BEPS-Hourly,而模拟的阴叶LAI会更小;2)植被的气孔控制着CO 2和水汽的交换,气孔导度表征气孔对环境因子的响应程度。BEPS-Daily计算的气孔导度对环境因子的敏感度高于BEPS-Hourly。因此,当受到辐射、气温以及土壤水分等环境因子的限制时,BEPS-Daily模型计算得到的气孔导度会出现低估的情况,这会导致BEPS-Daily模拟的GPP和蒸腾也出现了低估的模拟值;3)总体来说,两模型的模拟精度差别不大,BEPS-Hourly的模拟精度略高,而BEPS-Daily则具备更高的运算效率,因此,在应用中可根据实际需求选择模型。

温度影响的吸力循环过程GMZ膨润土持水特征

为揭示核废料深地质处置库多重屏障系统运营过程中膨润土持水性能随水-热耦合作用的周期性变化规律,通过温控气相平衡法和PEG渗析法进行了一系列单次吸力循环及多次吸力循环试验,研究了在自由膨胀条件下吸力循环和温度对膨润土持水性的影响。基于试验所得数据对膨润土持水曲线预测模型Van Genuchten模型进行了修正及验证。研究结果显示:单次吸力循环试验中,膨润土在脱湿路径下的含水率始终高于吸湿路径,表现出回滞现象;随着温度的升高,膨润土的持水能力及回滞现象均呈减弱趋势;而随着吸力或循环次数的增加,回滞现象和温度对持水能力的影响均减弱;在多次循环试验中,每次循环中试样均可累积含水率,但多次脱湿-吸湿循环相比于多次吸湿-脱湿循环表现出更强的累积能力,且每次循环含水率的累积随温度升高或循环次数增加而减少。修正后的Van Genuchten模型同时考虑了温度效应和吸湿或脱湿路径的影响,并且该模型预测结果与试验数据误差在5%以内,证实了其可靠性。

干湿循环作用下原状黄土渗透性及其对土-水特征曲线的影响

为评估干湿循环作用对原状黄土水力特性的劣化效应,对甘肃Q 3黄土进行了4组不同干湿循环路径下的饱和渗透试验与土-水特征测试,分析土体饱和渗透系数和土-水特征曲线随干湿循环次数、循环幅度和下限含水率的变化规律。结果表明:原状黄土饱和渗透系数劣化度与干湿循环次数间关系可采用双曲线函数进行描述,6次循环后劣化度变化趋于稳定;土体饱和渗透系数劣化度随循环幅度增大而线性增大,随下限含水率增大而线性减小。V-G模型对干湿循环下黄土的土-水特征曲线拟合效果良好,模型参数θs、α、n变化幅度较小,而参数θr随循环次数增加呈指数下降趋势。依据试验结果建立了考虑干湿循环3参数的饱和渗透系数劣化模型与土-水特征曲线模型,并对土体非饱和渗透系数进行了预测分析。

气候变化对HBV水文模型参数敏感性和不确定性的影响

阐明气候变化对流域水文模型参数的影响是分析参数可移植性、预估未来水量平衡组分的基础科学问题。基于CMIP6框架下3种数据来源(CNRM、IPSL和MRI)的气象信息,驱动HBV水文模型模拟赣江流域2015—2100年的月径流变化,量化并评估气候变化下控制径流模拟过程典型参数的敏感性和不确定性。研究结果表明:①未来降水增多或减少比持平情况下模型参数敏感性整体更高,其中土壤模块(计算土壤蒸散发和含水量)参数敏感性最高;②区分年内丰枯期与全年平均结果相比,响应模块(划分各径流组分)参数敏感性更高、未来增幅更大,且未来降水增多或减少均会使枯水期土壤模块和响应模块参数的敏感性增高,表明降水量及其年内分配会影响模型参数敏感性;③随机扰动响应模块参数导致的径流不确定性最大(贡献超50%),特别是未来降水增多情景下(超70%),因此,若未来气候变化使径流组分(快速、慢速流比例)大幅变化,需重点关注该模块参数。

基于水代谢和水循环理论的石羊河流域水资源承载力评价

基于水代谢和水循环理论,构建了包含输入、消耗、活力、调节、输出5个子系统的水资源承载力评价指标体系,采用最小二乘法组合网络层次分析法和熵权法确定权重,基于可变模糊集模型综合评价了石羊河流域2011—2020年水资源承载力,耦合高斯混合回归模型和3种可解释性机器学习方法量化了各评价指标对承载力的影响,从全局和局部尺度探究了其与水资源承载力的关系。结果表明:2011—2020年流域水资源承载力总体呈波动向好态势,但仍处于濒临超载的状态,评分值由2011年的3.79增长到2013年的4.18,之后下降到2020年的3.23;高斯混合回归模型能够较好地处理高维、小样本的水资源承载力指标数据;单位面积农业灌溉用水量、污水处理回用率、生态环境用水率、水资源开发利用率、产水模数和地下水开采率是该流域水资源承载力的主要影响因素;从全局看,水资源承载力与主要影响因素呈非线性关系,并随其非单调变化,从局部看,2011—2015年主要影响因素多表现为对水资源承载力的抑制作用,2016—2020年逐步转为促进作用;流域水资源承载力虽有提高,但仍需加强水资源开发利用管理,降低地下水开采率。