Experimental study of vertical and batter pile groups in saturated sand using a centrifuge shaking table

To study the dynamic response of vertical and batter pile groups in saturated sand,dynamic tests of these pile groups in saturated sand were carried out using the ZJU400 geotechnical centrifuge at Zhejiang University.The following results were obtained.(1)As the motion intensity increased,the peak acceleration in soil layers at different depths significantly decreased,indicating that the soil stiffness was significantly reduced.(2)During the motion process,the instantaneous bending moment of the vertical and batter pile groups at different depths changed continuously,which had a strong relationship with the saturated sand liquefaction.In the process of sand liquefaction,the residual bending moment generated by the batter pile was more obvious than that of the vertical pile.(3)With the liquefaction of the saturated sand,the distribution of the maximum bending moment of the vertical pile group changed,and the bending moment near the pile cap of the vertical and batter pile groups was always large.(4)In certain cases,the horizontal acceleration and dynamic displacement of the vertical pile cap were amplified.When the motion intensity was large,residual displacement of the batter pile cap occurred.

Filling mode and regularity of vertical centrifugal casting process of titanium alloy in thin-walled cylinder cavity

The mold filling process of titanium alloy in a thin-walled cylinder cavity under vertical centrifugal casting process was studied by means of the hydraulic simulation experiments. Results show that the filling mode of the melt in the cylinder cavity varies with casting wall-thickness. When the casting wall-thickness is less than or equal to the thickness of the first layer during the filling process, the melts fill the cavity from the bottom to the top.When the casting wall-thickness is greater than the thickness of the first layer during the filling process, the melts first fill the largest radius parts of the cavity with a certain thickness of the first layer from the bottom to the top of the cavity, and then they fill the cavity from the larger radius part to the smaller radius part. The melt filling ability increases with the increment of the mold rotational speed and the pouring temperature. In another aspect, the melt filling ability rises with the decrement of the melt viscosity, and the melt with the better filling ability is prone to fill the cylinder cavity layer by layer.

Solidified structure of thin-walled titanium parts by vertical centrifugal casting

The solidified structure of the thin-walled and complicated Ti-6AI-4V castings produced by the vertical centrifugal casting process was studied in the present work. The results show that the wall thickness of the section is featured with homogeneously distributed fine equiaxial grains, compared with the microstructure of the thick-walled section. The grain size of the castings has a tendency to decrease gradually with the increasing of the centrifugal radius. The inter-lamellar space in thick-walled casting parts is bigger than that of the thin-walled parts, and the profile of inter-lamellar space is not susceptible to the centrifugal radius.

Centrifugal model test and numerical simulation of vertical earth pressure on soft foundation box culvert

To obtain the vertical earth pressure on a soft foundation box culvert and investigate the interaction of the soil-culvert-foundation system, both a centrifugal model test and a numerical simulation were conducted and the comparisons with the current methods to determine the load on a culvert were completed. The results of the model test and numerical analysis are in satisfactory agreement, which shows that the direction of the shear stress between the culvert and the adjacent embankment depends on the differential settlement between them. A vertical earth pressure concentration appears on the culvert with a rigid piles foundation because of a downward shear stress. The ratio of the load on a soft foundation culvert and the overburden pressure above the culvert raises first and then decreases as the backfill height increases. In order to reduce the load on a culvert, it is suggested to limit the stiffness difference of the foundations under the culvert and embankment and to use a light backfill over the culvert.

Numerical Simulation of Bubble Migration in Liquid Titanium Alloy Melt During Vertical Centrifugal Casting Process

The bubble migration in liquid titanium alloy melt during vertical centrifugal casting process has been predicted. The effects of different parameters, such as the initial bubble location, the mold rotational speed and the mold rotational direction on the bubble in the migration process are investigated. The results show that the bubble migration can be divided into the radial movement to the mould rotation axis and the circular movement to the mould wall opposite to rotational direction of the casting mould. The casting mould wall has an impeditive effect on the circular movement of the bubble during its migration process. And the bubble finally migrates like a straight line along the mould wall located at the opposite direction of the rotational casting mould whether it rotates clockwise or anti-clockwise. The bubbles at the position near the mould wall located at the opposite direction of the rotational casting mould are much easier to migrate in a straight line. The instantaneous speed of the gas bubble increases with the increment of the mould rotational speed. However the mould rotational speed is high or low, the moving speed of the gas bubble increases slightly at the primary stage, and then decreases gradually like a ladder.

Numerical simulation and experimental investigation of two filling methods in vertical centrifugal casting

A mathematical model of the centrifugal filling process was established. The calculated results show that the centrifugal field has an important influence on the filling process. Moreover, the process of liquid flow and the location of free surface in sprue were simulated based on the Solution Algorithm-Volume of Fraction (SOLA-VOF) technique. In order to verify the mathematical model and computational results, hydraulic simulation experiment was carried out. The results of experiments and numerical simulation indicate the accuracy of mathematical model. Two kinds of filling methods were investigated and the results show that the bottom filling is better than the top filling that can achieve stable filling and reduce defects.

不同灌浆效果下黏土海床导管架桩基础的竖向承载特性离心试验

在40~60 m水深海域,海上风力发电机多使用导管架基础作为主要支撑结构.导管架通过水下高强灌浆与桩基础顶部连接,形成顶端密封段,共同承载竖向荷载.针对桩基顶部灌浆正常、灌浆不足、灌浆不良存在通孔3种不同灌浆效果开展离心模型试验,分析极限状态下基础的竖向承载力及灌浆段与桩身段的承载力分担比,并与现有理论计算方法进行对比.结果表明,灌浆密封顶盖的承载力取决于密封效果.对于灌浆密封顶盖灌浆正常和灌浆不足的基础,灌浆密封顶盖的承载力约占基础总承载力的25%~30%;灌浆不良存在通孔时,基础灌浆段承载力发挥较早且很快达到极限,其分担比远低于其他两者承载力.试验结果可为导管架桩基础设计中的灌浆段承载力计算提供参考依据.

磨床生产中常见液压件的铸造技术

在磨床生产中最为常见的盘盖类、平板类、方块及短圆柱类液压件外形结构简单,但其截面厚度大、技术要求高,铸造废品率偏高(30%~40%)。在盘盖类液压件生产中应用离心式集渣包,解决了除渣、补缩问题;在平板类液压件生产中采用“平做立浇”工艺满足了铸件两大平面的高质量要求;在方块及短圆柱类液压件生产中采用一坯多件连铸、“平做立浇”工艺,并通过适当的成分选择与控制,保证了厚大截面液压件铸造的成品率及工艺出品率。引入模数的概念,通过计算、比较各几何体的模数,为准确控制铸件的冷却速度提供了依据。

零流量工况下立式离心泵振动特性试验研究

离心泵在启动时一般为关阀启动,即为零流量工况。立式离心泵在长距离调水和大型灌溉工程中应用日益广泛。为探究立式离心泵零流量工况下振动特性,在水泵底座布置了1个三向振动传感器,在水泵进、出口法兰盘顶部各布置1个轴向振动传感器以及在水泵出口管道顶部布置1个压力脉动传感器,测试了零流量工况下额定转速(1.0 nr)以及1.2 nr、0.8 nr、0.6 nr、0.4 nr等5个不同转速下的水泵振动和压力脉动。结果表明:零流量工况下立式离心泵进口轴向、出口轴向和底座轴向上的振动均较大;升速至1.2倍额定转速,底座轴向上的振动强度增至额定转速振动强度的1.6倍,降速至0.8倍额定转速,振动强度降至额定转速振动强度的1/4倍,降低转速启动,能大幅度降低水泵的振动强度;叶片频率是水泵进口、出口和底座轴向方向振动的主要频率,压力脉动是零流量工况下立式离心泵振动的一个重要激励源。研究结果可为同类大型立式离心泵的设计以及泵站建成后的运行管理提供参考。

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。

立式离心浇注精密铸造技术研究进展

离心铸造是将金属液注入高速旋转的铸型内,使其做离心运动充满铸型形成铸件的技术。根据转轴位置的不同,可将其划分为卧式和立式离心铸造。通过离心铸造的方式生产中空筒形和环形铸件及铸管等,生产效率高、成本低,且铸件组织细密。按照旋转轴位置分类,离心铸造可以分为水平(或卧式)离心铸造和立式离心铸造。立式离心铸造相较于卧式离心铸造占地小、操作方便、材料适用性好、工艺灵活性高,已有几十年的历史,最早用于生产火炮弹壳等军事产品。随着立式离心铸造技术的不断发展,已被广泛应用于民用领域。本文从关键技术、数值模拟、典型铸件3个方面,简述了国内外近几年立式离心铸造技术的研究进展,介绍了可铸金属的选择、铸造工艺设计、铸型选择与设计、离心铸造涂料、离心铸造机等的研究成果,呈现了光滑粒子流体动力学(SPH)法、粒子跟踪测速(PTV)法、夹杂物运动规律等方法在立式离心铸造数值模拟方面的应用,列举了双金属复合轧辊、锥段转鼓、大口径厚壁变径管等立式离心铸造技术的典型铸件案例。

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.

煤用离心脱水机发展历程与展望

煤炭脱水是湿法选煤不可缺少的一个环节,而离心脱水机是煤炭脱水的常用设备。文章简述了离心脱水机的分类,并重点介绍了立式刮刀卸料离心脱水机、卧式振动卸料离心脱水机、卧式刮刀卸料离心脱水机和卧式沉降过滤式离心脱水机的发展历程。立式刮刀卸料离心脱水机主要用于13~0.5mm末煤脱水和<3mm粗煤泥脱水,目前最大机型筛篮直径为1400mm,以其煤质适应性强、脱水效果好、可靠性高等优点,是诸多选煤厂的首选机型;针对易损件多且使用寿命短的问题,近几年研究主要集中在提高易损件的寿命、降低使用成本和智能监控方面。卧式振动卸料离心脱水机主要用于选煤厂50~0.5mm块末煤脱水,易损件少、处理能力大,该机已由单质体振动发展为双质体振动,最大机型筛篮直径为1600mm,设备稳定可靠,彻底解决了漏油、开裂等问题;自主研发的卧式振动卸料离心脱水机智能监控系统已实现了设备状态实时监测和故障预警。卧式刮刀卸料离心脱水机主要用于<3mm粗煤泥脱水,目前最大机型为WLL1300,采用新型的结构形式,易损件更换简便,排料顺畅,大幅提升了单机处理能力。卧式沉降过滤式离心脱水机主要用于<0.5mm细煤泥脱水,发展至今单机处理能力最大的机型为WLG1600×2400,该机通过改进排料系统的结构,解决了脱水产物溜槽易堵塞等问题,延长了螺旋和筛网寿命,提高了差速器可靠性。最后,对国产离心脱水机未来的发展提出了展望:研制大型的卧式振动离心脱水机和立式刮刀卸料离心脱水机,顺应选煤厂日益大型化的需求;着力发展立式刮刀卸料离心脱水机,增大处理能力,提高运行可靠性;重点发展兼具沉降和过滤的卧式沉降过滤式离心脱水机,解决易损件更换和维修困难等问题;提高离心脱水机智能化水平,实现无人值守。

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。

Melt flow,solidification structures,and defects in 316 L steel strips produced by vertical centrifugal casting

Vertical centrifugal casting can significantly enhance the filling capability of molten metals,enabling the production of complex thin-walled castings at near-rapid cooling rates.In this study,the melt flow,solidification structures,and defects in 316 L steel cast strips with a geometry of 80 mm×60 mm×2.5 mm produced by vertical centrifugal casting were numerically and experimentally analyzed under different rotation speeds.With gradually increasing the rotation speed from 150 r/min to 900 r/min,the simulated results showed the shortest filling time and minimum porosity volume in the cast strip at a rotation speed of 600 r/min.Since a strong turbulent flow was generated by the rotation of the mold cavity during the filling process,experimental results showed that a“non-dendritic”structure was obtained in 316 L cast strip when centrifugal force was involved,whereas the typical dendritic structure was observed in the reference sample without rotation.Most areas of the cast strip exhibited one-dimensional cooling,but three-sided cooling appeared near the side of the cast strip.Moreover,the pores and cracks in the 316 L strips were detected by computed tomography scanning and analyzed with the corresponding numerical simulations.Results indicated the existence of an optimal rotational speed for producing cast strips with minimal casting defects.This study provides a better understanding of the filling and solidification processes of strips produced by vertical centrifugal casting.

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.

BIM技术在超大型单级单吸立式离心水泵组装工程中的应用

针对超大型单级单吸立式离心水泵装配过程中因二维设计导致的偏心度高问题,文章以蜀山泵站工程中的水泵机组为研究对象,提出基于BIM技术的超大型单级单吸立式离心水泵组装工程施工技术。通过将水泵结构划分为多个模块并建立三维仿真模型,精确描述复杂构件位置,预先对关键部件进行预装配加工。现场利用吊车和地坦克运输材料,按序组装,并基于运行数据微调。施工结果表明,在设计水流量25m^(3)/s、转速7000r/min条件下,水泵扬程达221.5m,满足泵站运行要求。本研究为超大型水泵的高效组装提供了新方法,确保了工程质量和效率。

卧式振动离心机与立式刮刀离心机比较及故障分析

目前卧式振动离心机和立式刮刀离心机是选煤厂常用的末煤离心脱水机。介绍了2种离心脱水机的工作原理、结构与性能。分析2种离心机在使用过程中常见故障,提出了解决问题的方法。

立式离心场下钛合金熔体充填及凝固过程研究(英文)

研究立式离心场下不同铸造工艺参数对钛合金熔体的充填及凝固缺陷形成的影响。结果显示,立式离心场下得到的钛合金铸件质量优于重力场下的铸件。立式离心场下,合金熔体由于受离心力和科氏力的作用,沿着与旋转方向相对的型壁进行充填,且熔体的截面面积随充填长度的增加而逐渐减小,但是在内浇口处由于速度降低导致截面面积有所回升。此外,铸型的旋转方向,旋转半径及旋转速度直接影响铸件缺陷的形成。旋转方向直接影响合金熔体的充填顺序,进而影响合金熔体的凝固顺序及缺陷位置。实验结果显示,旋转半径及旋转速度的增加有利于减少铸件的缺陷体积。

立式离心铸造过程中熔体横截面的变化规律

对Ti合金立式离心铸件的充填和凝固过程进行研究。结果发现,在离心场下,柯氏力对熔体运动方向的改变影响非常大,熔体沿着与旋转方向相对的型壁进行正向加速充填,当达到最远端后反向充填。在正向充填过程中,对没有内浇道的铸型,熔体在横浇道内的截面面积随充填长度的增加而逐渐减小,当横浇道侧壁存在内浇道时,熔体通过内浇道进入型腔,导致熔体在内浇道入口处产生速度降,熔体横截面面积在该处有所回升,然后随充填长度的增加而减少。同时,旋转方向对有内浇道铸型的充填顺序影响非常大。