Vertical Migration of Fine-Grained Sediments from Interior to Surface of Seabed Driven by Seepage Flows–‘Sub-Bottom Sediment Pump Action'

A scientific hypothesis is proposed and preliminarily verified in this paper: under the driving of seepage flows, there might be a vertical migration of fine-grained soil particles from interior to surface of seabed, which is defined as ‘sub-bottom sediment pump action' in this paper. Field experiments were performed twice on the intertidal flat of the Yellow River delta to study this process via both trapping the pumped materials and recording the pore pressures in the substrate. Experimental results are quite interesting as we did observe yellow slurry which is mainly composed of fine-grained soil particles appearing on the seabed surface; seepage gradients were also detected in the intertidal flat, under the action of tides and small wind waves. Preliminary conclusions are that ‘sediment pump' occurs when seepage force exceeds a certain threshold: firstly, it is big enough to disconnect the soil particles from the soil skeleton; secondly, the degree of seabed fluidization or bioturbation is big enough to provide preferred paths for the detached materials to migrate upwards. Then they would be firstly pumped from interior to the surface of seabed and then easily re-suspended into overlying water column. Influential factors of ‘sediment pump' are determined as hydrodynamics(wave energy), degree of consolidation, index of bioturbation(permeability) and content of fine-grained materials(sedimentary age). This new perspective of ‘sediment pump' may provide some implications for the mechanism interpretation of several unclear geological phenomena in the Yellow River delta area.

Computational study of fluid-borne noise in vertical inline pump

The objective of present work is to find out the sources of fluid-borne noise in vertical inline pump for various flow rates. The three-dimensional unsteady Reynolds Average Navier Stokes equation was solved using computational fluid dynamics code to predict the acoustic distribution. The pump chosen for study was of low specific speed and the experimental performance characteristic was very well matched with computational head developed. PROUDMAN sound power contour analysis showed the critical zone of noise in inlet pipe,impeller,and volute. Based on this,the variations of acoustic power were depicted over the cross section of inlet pipe,along the mean streamline of inlet pipe,as well along the volute circumference. The result concludes that the predominant flow noise is at tongue region and followed by noise generated due to turbulence in inlet pipe which occurs by the sudden variation in flow passage as well it depends on the operating condition of pump. The frequency analysis gives a glimpse of understanding about the broadband noise distribution due to flow phenomenon over a frequency range.

Vibration Control of Vertical Turbine Pump by Optimization of Vane Pitch Tolerances of an Impeller Using Statistical Techniques

The objective of the study is to find the tolerance on vane pitch dimensions of a Vertical Turbine(VT)pump impeller.For this purpose,the study is divided into two parts viz.to find the critical hydraulic eccentricity of a VT pump impeller by way of numerical simulations and design of experiments to find the vane pitch tolerance using critical hydraulic eccentricity.The effect of impeller vane pitch deviations on hydraulic unbalance is examined for a vertical turbine pump using Design of Experiments(DOE).A suitable orthogonal matrix has been selected with vane pitch at different axial locations of an impeller as the control factors.Hydraulic eccentricity,which is the output of the DOE experiments is analyzed using S/N ratio,ANOM and regression analysis to find the significant control factor effecting the hydraulic unbalance and hence vibrations.The vane pitch deviation at outlet and inlet of impeller shroud geometry are found to be the most critical factor affecting the pump vibrations.

Different vertical distribution of zooplankton community between North Pacific Subtropical Gyre and Western Pacific Warm Pool: its implication to carbon flux

The mesozooplankton in both epipelagic and mesopelagic zones is essentially important for the study of ecosystem and biological carbon pump. Previous studies showed that the diel vertical migration (DVM) pattern of mesozooplankton varied among ecosystems. However, that pattern was largely unknown in the Western Pacific Warm Pool (WPWP). The vertical distribution, DVM and community structure of mesozooplankton from the surface to 1 000 m were compared at Stas JL7K (WPWP) and MA (North Pacific Subtropical Gyre, NPSG). Two sites showed similarly low biomass in both epipelagic and mesopelagic zones, which were in accordance with oligotrophic conditions of these two ecosystems. Stronger DVM (night/day ratio) was found at JL7K (1.31) than that at MA (1.09) on surface 0–100 m, and an obvious night increase of mesopelagic biomass was observed at JL7K, which was probably due to migrators from bathypelagic zone. Active carbon flux by DVM of zooplankton was estimated to be 0.23 mmol/(m2·d) at JL7K and 0.16 mmol/(m2·d) at MA. The community structure analysis showed that calanoid copepods, cnidarians and appendicularians were the main contributors to DVM of mesozooplankton at both sites. We also compared the present result with previous studies of the two ecosystems, and suggested that the DVM of mesozooplankton was more homogeneous within the WPWP and more variable within the NPSG, though both ecosystems showed typically extremely oligotrophic conditions. The different diel vertical migration strength of mesozooplankton between NPSG and WPWP implied different efficiency of carbon pump in these two ecosystems.

Numerical simulation on heat transfer performance of vertical U-tube with different borehole fill materials

Heat exchange performance of vertical U-tube heat exchanger was studied with two different borehole fill materials and CFD software. Borehole surface temperature and water temperature distribution were simulated on the condition of continuous operation for 8 h in winter with inlet water temperature being 10℃. The results show that there is no obvious difference on heat exchanger performance between the two different borehole fill materials.

Analytical modelling of end thermal coupling in a solid-state laser longitudinally bonded by a vertical-cavity top-emitting laser diode

The intrinsic features involving a circularly symmetric beam profile with low divergence, planar geometry as well as the increasingly enhanced power of vertical-cavity surface-emitting lasers （VCSELs） have made the VCSEL a promising pump source in direct end bonding to a solid-state laser medium to form the minimized, on-wafer integrated laser system. This scheme will generate a surface contact pump configuration and thus additional end thermal coupling to the laser medium through the joint interface of both materials, apart from pump beam heating. This paper analytically models temperature distributions in both VCSEL and the laser medium from the end thermal coupling regarding surface contact pump configuration using a top-emitting VCSEL as the pump source for the first time. The analytical solutions are derived by introducing relative temperature and mean temperature expressions. The results show that the end contact heating by the VCSEL could lead to considerable temperature variations associated with thermal phase shift and thermal lensing in the laser medium. However, if the central temperature of the interface is increased by less than 20 K, the end contact heating does not have a significant thermal influence on the laser medium. In this case, the thermal effect should be dominated by pump beam heating. This work provides useful analytical results for further analysis of hybrid thermal effects on those lasers pumped by a direct VCSEL bond.

竖井式进出水口水力特性研究进展

竖井式进出水口是抽水蓄能电站水道系统两端控制水流的常用进出水口型式之一。竖井式进出水口双向过流,水流在短距离内经历两次90°流向转变(水平-竖直-水平),流向变化剧烈,水力条件复杂,深入研究竖井式进出水口水力特性,进而优化其体型结构,对抽水蓄能电站设计及施工具有重要意义。首先,介绍竖井式进出水口应用背景及体型特点,分析竖井式进出水口水力特性存在的问题;其次,对竖井式进出水口孔口流量分配、拦污栅断面流速分布、漩涡和水头损失等方面研究进展进行总结;最后,归纳了竖井式进出水口水力特性研究方法,探讨了今后研究应聚焦的主要方向。

宽式防旋墩环形堰竖井水力特性分析

目前许多拟建抽蓄工程泄洪洞的环形堰竖井入口设置了新型宽式防旋墩,以消除喉口处由不可控漩流引起的呛水等不利流态,而宽式防旋墩环形堰竖井的水气特性与以往采用起旋墩和窄式防旋墩的竖井存在较大差异,业内对其认识尚不清晰。以石台抽水蓄能电站下水库泄洪洞的竖井作为研究对象,采用物理模型试验与数值模拟相结合的手段,分析了流态、流速、压力、消能率等水力指标。研究结果表明:宽式防旋墩引导水流平顺进入竖井形成脱壁流,其尾部可形成顺畅的进气通道,空气经此通道可充分进入竖井以保持井内流态与压力的稳定;新型竖井过流能力满足要求,各部位流速、压力分布正常,总消能率达85%以上;宽式防旋墩可消除不可控漩流导致的呛水现象并引导水流在竖井内形成脱壁流态,使竖井壁面免于空蚀破坏;墩尾通气量足够时,可取消通气管及环形堰与竖井结合部突扩体型,简化工程布置。相关经验可供类似抽蓄电站工程的泄洪洞竖井设计参考。

沙集泵站改造叶轮选型及流道改形研究

针对沙集泵站空化汽蚀较为严重,在工程加固改造时主体结构不变,无法通过降低站房底板增加叶轮淹没深度,从而提高空化性能的实际问题,采用计算流体动力学CFD方法,考虑泵站进口不同水位,对水泵装置全流道内部流动进行数值分析,研究水泵空化和能量特性。小幅降低叶轮中心高程,不仅未能减小空化范围,反而降低了泵装置效率,不宜采用。通过优选水泵水力模型、降速、增径并适当修整流道等方法,在保证泵装置能量性能的前提下,提高水泵空化性能。结果表明,采用方案一:叶轮直径增至1.68 m,转速降至250 r/min,基本消除了叶片进水边附近的附着空化,同时能够满足泵站特征水位组合下的流量和效率。成果也可用于类似泵站的设计和机组的选型。

立式自吸泵前口环几何参数对其自吸性能的影响

为探究立式自吸泵前口环几何参数对其自吸性能的影响,以350WFB-1200-50型外混式无密封立式自吸泵为研究对象,在保证自吸泵其他参数不变的情况下,通过改变前口环间隙δ和前口环长度l的数值大小,共设计20种方案.利用数值计算和试验验证相结合的研究方法,通过定常数值计算得到不同方案外特性曲线图及前口环进出口压差图;通过非定常数值计算得到不同方案不同时刻中间截面气体体积分布云图、不同方案自吸泵出口含气率变化图及不同方案自吸完成时间曲线图来研究立式自吸泵前口环几何参数与其自吸性能的关系.研究发现:前口环间隙δ和前口环长度l对自吸泵自吸性能均有影响,适当减小前口环间隙δ和增大前口环长度l均能提高自吸泵自吸性能,且当前口环间隙δ过大时,其对自吸泵自吸性能的影响大于前口环长度l对自吸泵自吸性能的影响.

大型立式离心泵压力脉动特性研究

大型立式离心泵目前广泛应用于大型水利工程。水泵在运行时所产生的压力脉动可能导致机组产生振动进而影响机组性能。本研究采用数值模拟方法,基于尺度自适应SAS模型,对泵的三维流体域进行了详细的网格划分和边界条件设定,通过网格无关性验证和试验验证,证明了数值模拟方法的可靠性。研究结果表明,吸水室压力脉动的主频幅值随流量增加呈减小趋势,小流量工况下出现了低频脉动。叶轮的压力脉动主要受到两倍转频的影响,而压水室的压力脉动则以叶片通过频率为主。特别是在小流量工况下,压水室的压力脉动幅值显著增大,这一现象与流体动力学特性及蜗道结构特征密切相关。此外,压水室中隔板的存在对压力脉动的传递起到了一定的阻挡作用,但在特定位置如隔舌附近,压力脉动幅值仍然较大。本研究对于理解立式离心泵压力脉动特性及其影响因素具有一定的指导作用。

立式离心泵典型故障复现试验研究

为了给立式离心泵的故障诊断提供试验和理论依据,搭建立式离心泵仿真试验台,进行立式离心泵典型故障的仿真复现试验,分析了转子不平衡、转子不对中和支座连接松动等故障的振动特性及其频谱特征.结果表明:机脚处的振动位移信号对支座连接松动故障的振动特性敏感性更高,轴系的振动信号对转子故障的振动特性敏感性更高;转子不平衡故障和转子不对中故障表现出不同的频谱特征,转子不平衡故障的频谱特征表现为1倍振动主要频率(amplitude power frequency,APF)幅值增大,且随着故障程度的增加,幅值呈现了逐渐减小的趋势,转子不对中故障的频谱特征表现为产生新的振动特征频率2APF,且随着故障程度的增大,信号幅值逐渐增大;支座连接松动故障表现为频谱图中的主频变为3APF,并出现新的2APF和1/2分数谐波频率.

面向双气室铯光泵磁力仪的VCSEL稳频研究

在地磁场测量领域中,自激振荡式碱金属原子光泵磁力仪因为快速响应与高精度成为一项重要技术。其中自激式双气室光泵磁力仪无需考虑移相电路带来的信号误差,电路简单。使用垂直腔面发射激光器作为泵浦光源有效降低了磁力仪功耗和体积。针对使用垂直腔面发射激光器的便携式双气室铯光泵磁力仪激光稳频方法进行设计,设计方案包括激光器温度控制电路,光泵磁力仪信号反馈电路,激光器电流源调制与控制电路。将注入电流调制的稳频方法用于双气室光泵磁力仪结构,减小稳频代价的同时具有较好稳定性,温度控制精度达到0.002℃,10秒内波长稳定度达到4.36×10^(-10),初步探索了自激式双气室光泵磁力仪集成化与小型化的可能性。

船用立式离心泵流噪声特性分析

为了降低舰船在航行时的噪声,对船用立式离心泵内部流动噪声的特性进行研究。基于计算流体动力学(CFD)数值仿真方法计算某型立式离心泵的非定常流场,分析其在不同位置处的脉动压力特性,并通过试验验证流场计算结果的准确性。提取在3种工况下通过非定常流场计算得到的叶片旋转偶极子和蜗壳固定偶极子声源信息,在LMS Virtual lab中进行内部流动噪声计算,并分析其流动噪声特性。研究结果表明:叶轮出口不均匀的射流-尾迹结构和叶轮与隔舌的动静干涉作用是立式离心泵叶轮部位和蜗壳部位产生脉动压力的主要诱因;内场噪声与脉动压力直接相关,噪声频率特性与脉动压力频率特性一致,主要峰值频率集中在叶频和倍频处;固定偶极子声源和旋转偶极子声源均对立式离心泵内场流动噪声有很大贡献,与旋转偶极子声源相比,固定偶极子声源对进出口噪声的影响更大。研究成果可供船用立式离心泵减振降噪和低噪声设计参考。

光泵磁力仪中垂直腔面发射激光器激光波长锁定

针对光泵磁力仪(OPM)对小型化、低功耗以及激光光源波长稳定性的要求,提出一套垂直腔面发射激光器激光波长锁定控制方案.所提基于多普勒吸收的光反馈波长锁定方案以133 Cs原子D1线F_(g)=4→F_(e)=3超精细能级跃迁波长为参考波长,OPM的原子蒸汽气室同时作为波长锁定的工作气室,无需任何额外装置即可将激光波长锁定在该D1线跃迁波长.使用数字比例积分微分控制与模糊控制算法进行激光的温度控制,使温度波动在±0.005℃内;采用基于电流镜的激光电流驱动方案,使电流波动在±50 nA内,为激光波长锁定提供了良好的硬件基础.最后,在实验室环境下实现OPM长达2 h的稳定信号输出.

立式轴流泵装置马鞍区振动特性研究

为分析叶片角度下立式轴流泵在马鞍区工况的振动特性,采用流体计算软件CFX的数值模拟与泵装置试验结合的方法,在验证计算结果准确性的情况下,数值计算了3个叶片角度、4个流量下的泵段形变、振动特性、压力脉动、非周期性力;并通过试验测试了泵段马鞍区振动性能。研究结果表明,泵段在0.30 QBEP至0.60 QBEP之间存在马鞍区,在马鞍区工况内造成泵段振动的主要因素为叶轮-导叶之间动静交界面的干扰作用;为保证泵装置运行过程中的稳定性,最小运行流量应超过本文所定义的强化马鞍区工况流量;泵装置在马鞍区内运行时,叶片安放角越小越稳定。

新型近无泄漏立式柱塞泵的设计及效率研究

针对传统立式柱塞泵在特殊工况下的漏油问题,设计了一种新型立式柱塞泵结构,并对其效率进行研究。以传统凸轮驱动立式柱塞泵为研究对象,在其柱塞端加入直筒型弹性密封构件,泵体与柱塞位置采取倒置方式,凸轮通过滚子轴承与泵体接触作往复直线运动,利用橡胶密封套代替密封圈防止泄漏。在对立式柱塞泵结构和工作原理分析的基础上,计算柱塞泵容积效率及机械效率。计算结果表明,该设计容积效率为98.4%,机械效率为95.2%,性能及效率均有所提高,且无油液污染,可作为一种小型柱塞泵为医用仪器及设备提供动力。

VS6式乙烯输送泵故障分析及改善措施

立式筒袋泵(API610 VS6型式)是输送乙烯的重要设备,在实际运行中,经常出现振动异常、噪声偏大、轴承温度高、机械密封泄漏等问题,分析了立式筒袋泵出现故障的原因,综合考虑泵的使用条件及企业经济效益等因素,建议通过优化工艺操作管理、加强润滑管理、增加降温措施、管路清洁化管理等方法,保障装置安全平稳运行。

基于有限元分析法的双基础立式泵机组减振的研究与改造

采用有限元分析法,基于大型有限元软件ANSYS建立机组与楼板的模型,对大型双基础立式泵机组的振动和电机层楼板的承载能力进行分析评估。旨在经过不断修正获取动力特性与实测值较为吻合的结构有限元模型。通过实践改造,有效降低楼板振动,提高泵站运行的安全可靠性。

Numerical investigations on performance improvement mechanism of a high-power vertical centrifugal pump with special emphasis on hydraulic component matching

The purpose of this paper is to investigate the performance improvement mechanism of a high power vertical centrifugal pump by using numerical calculations.Therefore,a comparative study of energy losses and internal flow characteristics in the original and optimized models was carried out with special attention to the hydraulic component matching.The optimized model(model B)was obtained by optimizing the vaned diffuser and volute based on the original model(model A),mainly the diffuser inlet diameter,diffuser inlet vane angle,volute channel inlet width and volute throat area were changed.Firstly,the comparative results on performance and energy losses of two models showed that the efficiency and head of model B was significantly increased under design and part-load conditions.It is mainly due to the dramatic reduction of energy loss PL in the diffuser and volute.Then,the comparisons of PL and flow patterns in the vaned diffuser showed that the matching optimization between the model B impeller outlet flow angle and diffuser inlet vane angle resulted in a better flow pattern in both the circumferential and axial directions of the diffuser,which leads to the PL3 reduction.The meridian velocity Vm of model B was significantly increased at diffuser inlet regions and resulted in improvements of flow patterns at diffuser middle and outlet regions as well as pressure expansion capacity.Finally,the comparisons of PL and flow characteristics in the volute showed that the turbulence loss reduction in the model B volute was due to the flow pattern improvement at diffuser outlet regions which provided better flow conditions at volute inlet regions.The matching optimization between the diffuser and volute significantly reduced the turbulence loss in volute sections 1–4 and enhanced the pressure expansion capacity in sections 8–10.