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 共查询到19条相似文献,搜索用时 125 毫秒
1.
This paper investigates the bed shear stress based on the condition of the incipient motion of sediment in a uniform-flow flume covered with emergent rigid vegetation,which is represented by arrays of circular cylinders arranged in a regular pattern.A total of 148 tests are performed to observe the influence of the vegetation density,bed slope,flow depth and sediment size on the bed shear stress.The tests reveal that when the sediment is in incipient motion,the resistances acting on the flow passing the rigid vegetation contain the vegetation resistance and the bed shear stress.This shear stress could be divided into two parts:the grain shear stress and the shear stress caused by sand dunes,which are the deformed bedform with the sediment incipient motion.An empirical relationship between the shear stress of the sand dune and vegetation density,the Froude number,the apparent vegetation layer velocity is developed.  相似文献   

2.
A new dual-layer granular bed filter for hot gas cleanup was invented and studied experimentally. Fine sand, 0.5-1 mm grain size and about 1350 kg/m^3 bulk density, was used as the lower layer of the filter. Expanded perlite particles, 2-5 mm grain size and about 70 kg/m^3 bulk density, was used for the upper layer of the filter in this study. It was confirmed that the sizes and densities of these two media matched well; the binary media remained in complete segregation during regeneration by fluidization. Test results show that the filtration of the expanded perlite particle layer was characterized as "deep bed filtration." Filtration of the fine sand layer was "surface cake filtration." The expanded perlite particle layer contributed about 90% to the bed dust capacity, but only about 20% to the total bed pressure drop, which increased the bed dust capacity ten fold compared to a single-layer bed of the same sand and the same total bed pressure drop. The dust cake on the surface of the fine sand layer raised the collection efficiencies to over 99.99%.  相似文献   

3.
In order to utilize solid wastes, ceramic facing brick was made form East-lake sediment and some additives. The strength and freeze-thaw resistance of the samples were tested, and the crystal phases and microstructures were studied by XRD and SEM. The results indicate that the samples have a wide firing temperature range. The main crystal phases are CaAl2Si2O8, α-Al2O3, Fe2O3, which distribute uniformly in the samples. The sample have the best properties in the series ’Ca-Al-Si’, and water absorption (Wa) , porosity (Pa), bulk density (D), bending strength and compressive strength are 7.24%, 15.82%, 2.19 g.cm-3, 45.57 MPa and 56.81 MPa respectively, when the addition amount of East-lake sediment is 80% and the firing temperature is 1 100 ℃. In the series ’K-Al-Si’, the sample with the best properties was obtained when addition amount of East-lake sediment was 70% and firing temperature was 1 060 ℃. The water absorption, porosity, bulk density, bending strength and compressive strength are 7.62%, 16.37%, 2.15 g~cm-3, 39.26 MPa, and 50.81 MPa respectively. They all come up to the national standardization, and meet the needs of manufacturing production.  相似文献   

4.
To lower the costs of wastewater treatment, the submerged hollow fiber ultrafiltration membrane was employed to reuse the filter backwash water and settling tank sludge water. Experimental study indicates that the submerged hollow fiber uhrafihration membrane can condense the concentration of sludge from 0. 1% -0. 3% to 2.5%. At 20 ℃, the system can operate continuously for 80 clays with daily online backwashing with chemical additions only once, and the membrane flux can be recovered up to 97% by using NaClO and NaOH as chemical additions. The results show that the membrane flux is mainly affected by temperature,and has a positive lin- ear relation to temperature with a slope of 0. 368. After treated by submerged hollow fiber uhrafihration membrane, the effluent can reach the National Standard for Drinking Water( GB5749 -85 ) , especially for the sludge water from sedimentation tanks and the backwashing Water from filters in water supply plants.  相似文献   

5.
The Yellow River is well known as a sediment-laden river, which is the main reason that it cannot be controlled as easily as other rivers. Many researchers, such as Qian Ning et al., have found that the sediment load of the Yellow River comes mainly from the sandy and gritty area of the Loess Plateau. Therefore, it is very important to simulate the sediment yield in this area. This paper proposes a method to compute the sediment production in the sandy and gritty area based on the digital watershed model. The suggested model is calibrated and validated in the Chabagou basin, which is a small catchment in the study area. Finally, the model simulates the sediment yield of the sandy and gritty area in 1967, 1978, 1983, 1994 and 1997, which represents a high water and high sediment year, a mean water and mean sediment year, a high water and low sediment year, a low water and high sediment year, and a low water and low sediment year separately. The simulation results, including the runoff depth and erosion modulus, can well explain the "low water and high sediment" phenomena in the Yellow River basin. The total amount of the sediment production and its distribution generated by the model is very useful for water and soil conservation in the sandy and gritty area of the Loess Plateau.  相似文献   

6.
Because of the high momentum of debris flow,when it confluences with the Main River,the water level in the upstream of the conjunction point will increase and a portion of sediment will deposit in the con- junction area.The discharge of downstream will be less then the summation discharge of main river and side channel,and the density of downstream will be difference from both the density of the fluid of main river and tributary.Based on momentum theory,and with the transport coefficient and deposit coefficient,the water ris- ing and sediment depositition characteristic within the conjunction area are studied.An equation that expressed by Froude number is deduced,which can reflect the hydraulic relation and confluence characteristic in the confluence area after the confluence of main river and side channel.The equation is verified with experiment data.The result shows that,if the parameters are used correctly,the calculation value is coincide with the one get from experiment.  相似文献   

7.
This paper presents an analysis of the changes of the longitudinal and lateral profiles in the meander- ing reach of the Lower Wei River over the period from October 1973 to October 1976 during the course of degradation.Analysis results indicated that retrogressive erosion and subsequent downstream erosion occurred in the reach due to the lowering in the Tongguan elevation and the inflowing water carrying low sediment con- centrations.At the end of the degradation,the main channel widths of the majority of sections were increased by 70 to 110 percent,and the elevation differences between the main channel and the floodplain were de- creased slightly by 2 to 45 percent,which caused a decrease in the water stage under the same discharge,the formation of a channd with relatively wide and shallow cross-sectional profiles,and an increase of 50 to 150 percent in the geomorphological coefficients.Therefore,the degradation in this reach was mainly characterized by channel widening,not by channel undercutting.  相似文献   

8.
A formula for the calculation of critical shear stress of non-uniform sediment was developed by on river bed has been established while considering the relative degree expose of grains.The values of the Coeffi- cients in the formula have been obtained.The formula has been verified with prototype observation data, flumes data of both nature and lightweight sand.The computed results fully reflect the characteristics of thresh- old motion of non-uniform sediment.The result have been used in some physical model and mathematical mod- el for study the sediment of TGP reservoir.  相似文献   

9.
A framework of continuum breakage mechanics was used to investigate the dependence of compressibility on grain size distribution(GSD)as well as relative density of sand.Compressibility dependence on GSD was considered by employing a GSD index and relative density dependence was reflected by varying the plastic-breakage coupling angle.Simulations of the experimental results including isotropic compression and one-dimensional compression of sands with different relative densities and GSDs revealed that sand compressibility increased with the increasing GSD index and plastic-breakage coupling angle.The coupling angle decreased with increasing relative density,indicating that grains would break more in sand with comparatively high relative density.  相似文献   

10.
In this paper,the power law of particle size distributions (PSDs) in conventional water treatment processes is developed. After measuring the particle size distributions of raw-water,settled water and filtered water,a mathematical model between particle diameter and the amount of particles was studied. The value of collision frequency factor β in the PSDs model can be used to represent the collision behavior of particles ,and can be used as foundation exponent to choose suitable coagulation to accelerate particles aggregation. At the same time,the relationship between the value of parameter K and the total particles volume V was deduced. K is defined as particle volume exponent,which can represent the total volume of particles. The degression degree of K shows the removal efficiency of potable water treatment units.  相似文献   

11.
基于起动相似选沙的模型沙波相似性的初步试验研究   总被引:1,自引:1,他引:0  
沙波普遍存在于天然河道中,动床模型中沙波运动的相似性是水流运动、泥沙输移及河床冲淤相似的基础。针对动床模型中沙波相似性问题,采用水槽试验的方法,设计满足几何、水流运动、起动相似的沙波实验,分析了沙波波高、沙波组成的相似性。结果表明,对于几何正态模型,在模型沙与原型沙重率相同的情况下,沙波波高基本满足几何相似,平均偏差约在9.2%左右;沙波波高随水流强度的变化规律是相似的, 时开始出现沙波,沙波随着水流强度的增大而逐渐增大,当 接近2.6时,沙波达到最大波高;沙波相同部位的颗粒组成也是相似的。即原型沙与模型沙在重率、形状相同的条件下,考虑起动相似的正态模型沙波是相似的。  相似文献   

12.
以长江天兴洲河段为例,应用平面二维水沙数学模型,采用实测水沙数据进行率定与验证,模拟了不同流量级下采砂区相对分汊口距离不同采砂后分流比、水位和流速变化规律,模拟结果表明,在相同水流条件下,随着采砂区距分汊口距离的增加,采砂后主汊分流比与河段水位和流速变化都呈先增后减的规律.进一步选取2004年作为典型水沙年预测采砂后河段冲淤变化和回淤率,预测结果表明,河段总的冲淤量随着采砂区相对分汊口距离的增加呈先减后增的规律,而采砂区回淤率呈先增后减的规律.模型成果可为本河段采砂的可行性和采砂规划控制提供科学依据.  相似文献   

13.
以城市二级处理出水为试验原水,通过逐渐提高滤速的方式,对停止运行近5个月的O/A两级生物砂滤池进行重新启动。重点研究了反应器的二次启动速度和启动后的脱氮除碳效果,以及C/N比对该工艺脱氮除碳效果的影响。试验结果表明,石英砂表面的生物膜并未死亡,通水运行后能在很短的时间内恢复正常。稳定运行期间,系统对CODCr和NH4+-N的平均去除率分别为45.53%和65.50%,出水CODCr和NH4+-N的平均浓度分别为48.50mg/L和4.12mg/L。当C/N比为5.0时,O/A两级生物砂滤池具有较高的TN脱除效果,TN去除率可达到30%以上,滤池出水TN含量低于15mg/L,均能达到一级A标准的要求。  相似文献   

14.
泥沙补给变化下山区河流河床适应性调整与突变响应   总被引:3,自引:3,他引:0  
针对泥沙运动力学经典理论体系与天然山区河流推移质运动存在显著差异的若干基本问题,开展山区流域沙量补给条件变化下,山区河流河床调整与突变响应机理研究。揭示了泥沙补给条件对非均匀卵石起动、输移的影响特征和卵石沙量补给与山区河流沙波形成、碍航机理;探索了泥沙补给变化下陡坡河道水沙运动奇异特征和宽窄相间漫滩复式航槽河床突变响应现象。采用水沙错峰、水沙分离等集结降阶技术手段调控洪峰时段成灾河段卵石沙量补给条件,是山洪泥沙灾害致灾风险降阶防控的核心。  相似文献   

15.
山区多沙河流漂石河段受水沙条件影响,洲滩发育丰富,改变了漂石河段的水沙运动规律及洲滩演变特征。基于野外调查与室内物理模型试验,探讨了漂石对多沙河段水动力特征及洲滩发育过程的影响。通过都江堰市岷江支流白沙河与龙溪河的野外调查,分析了典型漂石河段床沙组成及漂石河床形态特征。由于山区河流暴雨洪水及挟带的泥沙及河道地形多变等因素,大量上游来沙在漂石河段落淤,河床内洲滩的大量发育。通过系列室内物理模型试验,分析不同泥沙补给条件下漂石河床的洲滩形成过程及河床形态变化与水位响应过程。研究结果表明:暴雨山洪产生丰富的泥沙补给,导致白沙河与龙溪河的粗颗粒平均粒径粗大,存在大量漂石,形成漂石河段。漂石河段水力要素多变,河床形态剧烈调整。当上游泥沙补给时,受漂石周围水流变化影响,漂石河床局部以横向带状溯源淤积为主,下游段两侧淤积突出,极易形成漂石洲滩,从而增大局部河床比降,减缓河道下切。上游来沙不均匀过程显著改变了漂石河床局部水位及泥沙淤积规模。因此,通过野外调查与室内物理模型试验,揭示了水沙条件下的漂石河床形态变化特征,山区河流上游来沙与漂石共同影响洲滩发育过程,表明漂石对山区多沙河流的水沙运动产生突出影响。  相似文献   

16.
生物砂滤池对城市二级出水中氨氮的去除效果研究   总被引:1,自引:1,他引:0       下载免费PDF全文
以城市二级出水为原水,对比了生物砂滤池与普通砂滤池两种过滤方式对其中NH4 -N的去除效果,并对水温、进水NH4 -N浓度以及有机物浓度等影响因素进行了分析。结果表明:水温是影响生物砂滤池除NH4 -N效果的主要因素,水温越高,对NH4 -N的去除效果越好;原水NH4 -N浓度愈高,去除率愈高,原水浓度变化对去除效果影响越小;在常温下,当原水CODCr和NH4 -N浓度均较大时,CODCr大小对NH4 -N去除效果影响显著。普通砂滤池对NH4 -N的去除率大小受原水NH4 -N浓度的影响较大。在中水处理工艺中,生物砂滤池对NH4 -N的去除效果优于普通砂滤池,滤池出水NH4 -N含量低于5mg/L,达到了回用标准要求。  相似文献   

17.
结合滨海滩涂地带火电厂的建设,提出了"塑料排水板+超载预压"处理滨海滩涂深厚淤泥的处理措施,总结了地基处理设计与施工关键技术,以及监测成果,可供类似工程建设参考.  相似文献   

18.
高级氧化组合工艺协同净化微污染水的示范生产实验   总被引:1,自引:1,他引:0  
为考察催化氧化-UV/H_2O_2-生物活性炭(BAC)高级氧化组合联用工艺在实际生产中对微污染水源水的的处理效能,在淮南某水厂示范工程对微污染淮河水进行了生产实验.结果表明,催化臭氧氧化-BAC组合联用工艺对水中的UV_(254)、DOC、氨氮、CODMn及THMFP均有较好的去除效果,且不会带来溴酸盐的问题.催化臭氧氧化工艺对UV_(254)、DOC、CODMn的平均去除率分别为21.8%、8.1%、10.8%.BAC对氨氮有很好的去除效果,最高去除率可达61%;对DOC和COD_(Mn)的平均去除率分别为10.4%和15.3%.催化臭氧氧化接触池对THMFP的平均去除率为34.9%,最高去除率可达53.2%.UV/H_2O_2在示范性生产实验中,对进一步提高有机物的去除能力有限;在实际生产设计中,考虑UV分解剩余臭氧的效用建议采用:催化臭氧氧化-UV-BAC-砂滤是确保饮用水出水安全可靠的高级氧化工艺必要的组合工艺模式.研究结果可为各自来水厂处理低温低浊水、提高出厂水水质以及自来水厂整体工艺的提升改造提供借鉴和参考.  相似文献   

19.
采用平面二维水沙数学模型,依据“92·8”典型洪水情况,对黄河下游夹河滩至高村河段进行了无生产堤条件下的自然漫滩、现状生产堤条件下漫滩及典型滩区分洪淤滩,3种工况条件下的河道冲淤、洪水演进及滩区淹没的数值模拟.模拟成果分析表明,对黄河下游蓄滞洪区进行滞洪沉沙,有效增大了分洪区的削峰滞洪作用,保证和扩大了滩槽泥沙横向交换...  相似文献   

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