Fluid Flow and Solidification Simulation in Beam Blank Continuous Casting Process With 3D Coupled Model

Based on turbulent theory, a 3D coupled model of fluid flow and solidification was built using finite difference method and used to study the influence of superheating degree and casting speed on fluid flow and solidification, analyze the interaction between shell and molten steel, and compare the temperature distribution under different technological conditions. The results indicate that high superheating degree can lengthen the liquid-core depth and make the crack and breakout possible, so suitable superheating should be controlled within 35℃ according to the simulation results. Casting speed which is one of the most important technological parameters of improving production rate, should be controlled between 0. 85 m/min and 1.05 m/min and the caster has great potential in the improvement of blank quality.

Numerical analysis on flow field of weld pool during deep penetration electron beam welding of titanium alloy

Flow field of weld pool during deep penetration electron beam welding of TA 15 titanium alloy was numerically and experimentally studied using a hybrid heat source of Gaussian surface heat source and rotational paraboloidal body heat source. And the formation mechanism of the weld pool flow field was analyzed. The results showed that the movement of the liquid metal in the top weld pool was the fiercest and weakened gradually in the middle and bottom of the weld pool. The maximum flow velocity of the liquid metal was about 0. 295 m/s in the top surface of weld pool. The primary driving forces of the movement of liquid metal in the weld pool were the recoil pressure of metal vapor and the surface tension.

MECHANICAL VIBRATIONAL POWER FLOW IN BEAM-PLATE ASSEMBLIES

The vibrational power flow in the beam-plate assemblies and then with the isolators is investigated using analytical ' power flow' approach based on the some concepts of mechanical mo- bility and structural dynamics. Theoretical expressions of the power flow in the structures are given and examined. The numerical results of the expressions are good agreements with the measuring re- sults obtained by the technique of vibration intensity. On the basis of these results, possible ways of reducing the vibrational power flow in the structures are suggested .

Analysis of the Pipe Heat Loss of the Water Flow Calorimetry System in EAST Neutral Beam Injector

Neutral beam injection heating is one of the main auxiliary heating methods in controllable nuclear fusion research. In the EAST neutral beam injector, a water flow calorimetry （WFC） system is applied to measure the heat load on the electrode system of the ion source and the heat loading components of the beamline. Due to the heat loss in the return water pipe, there are some measuring errors for the current WFC system. In this paper, the errors were measured experimentally and analyzed theoretically, which lay a basis for the exact calculation of beam power deposition distribution and neutralization efficiency.

EFFECT OF SUBMERGED ENTRY NOZZLE (SEN) PARAMETERS AND SHAPE ON 3-D FLUID FLOW IN MOULD FOR BEAM BLANK CONTINUOUS CASTING

According to turbulent theory and characteristics of beam blank continuous casting, 3-D model to represent the flow of beam blank mould is established. The predicted results indicate that the exit obliquity of up 15°(+15°) should be adopted, which will benefit the floatation of non-metallic inclusion and purification of the molten steel. When the nozzle angle is 120°, the flow pattern is reasonable. Proper nozzle depth can be 200mm. Turbulent kinetic of meniscus can be reduced by adopting the square nozzle and suitable area of side outlet when casting speed increases. The results are consistent with those of water model experiment, so the model is exact and reasonable. The model can provide important information for design of SEN and defining of immersion depth.

Nonparaxial propagation properties of the chirped Airy Gaussian vortex beams in uniaxial crystals orthogonal to the optical axis

In this article, we investigate the nonparaxial propagation properties of the chirped Airy Gaussian vortex（CAiGV）beams in uniaxial crystals orthogonal to the optical axis analytically and numerically. We discuss how the linear chirp parameters, the quadratic chirp parameters, and the Gaussian factors influence the nonparaxial propagation dynamics of the CAiGV beams. The intensity, the energy flow, the beam center, and the angular momentum of the CAiGV beams are deeply investigated. It is shown that the Gaussian factors have a great effect on the intensity and the centroid positions of the CAiGV beams. With the Gaussian factors increasing, the intensity of CAiGV beams decreases rapidly. The main lobes of the transverse intensity distribution of the CAiGV beams are similar to triangles.

Numerical analysis of thermal fluid transportation during electron beam welding of 2219 aluminum alloy plate and experimental validation

A three-dimensional mathematical model using volume-of-fluid method is developed to investigate the heat transfer, fluid flow and keyhole dynamics during electron beam welding of 2219 aluminum alloy plate. In the model, an adaptive heat source is employed to simulate the heating process of electron beam. Fluid flow is mainly driven by surface tension, thermo-capillary force, recoil pressure, hydrostatic pressure and thermal buoyancy. The thermal-fluid transport behaviors of welding pool during the drilling and backfilling stages of keyhole and the formation reason of the nail-shaped weld with an arc crater are systematically analyzed. Finally, all calculation results are validated by experiments and show good agreements.

Space-charge limiting currents for magnetically focused intense relativistic electron beams

The self-consistent differential equations, which describe a laminar-flow equilibrium state in a magnetically focused intense relativistic electron beam propagating inside a conducting waveguide, are presented. The canonical angular momentum, Pe, defined under the conditions at the source, uniquely determines the possible solutions of these equations. By numerically solving these equations, the space-charge limited current and the externally applied magnetic field are obtained in a solid beam and a hollow beam in two cases of Pθ= 0 （magnetically shielded source） and Pθ= const. （immersed source） separately. It is shown that the hollow beam is more beneficial to the propagation of the intense relativistic beam through a drift tube than the solid beam.

Effect of H_2 dilution on the structure and properties of nc-CrC/a-C:H coatings deposited by a hybrid beams system

Nanocomposite Cr C/hydrogenated amorphous carbon(nc-CrC/a-C:H) coatings were deposited by a hybrid beams system comprised of a hollow cathode ion source and a cathodic arc ion-plating unit with varying H_2 flow rates. The influences of H_2 flow rates on the morphologies, microstructures, and properties of the coatings were systematically studied. The morphologies and microstructures of the coatings were characterized by SEM, AFM, XPS, Raman spectroscopy, GIXRD, and HRTEM. The mechanical and tribological properties were measured by a nano-indenter, scratch tester, and ball-ondisk tribometer. The wear tracks were evaluated using 3D profilometer, optical microscope, and EDS analysis. It has been found that a moderate H_2 flow rate can effectively smooth the surface, enlarge the fraction of a sp^3 bond, and improve the properties. The coating exhibits the highest hardness and elastic modulus at the H_2 flow rate of 40 sccm. A superior combination of adhesion strength,friction coefficient, and wear resistance can be achieved at the H_2 flow rate of 80 sccm.

EXPERIMENTAL INVESTIGATION ON THE CHAOTIC PHENOMENA IN THE WAKE OF A NATURAL THERMAL CONVECTION FLOW

Chaotic phenomena in the wake of thermal convection flow fields above a heating flat plate were investigated experimentally. A newly developed electron beam fluorescence technique (EBF) was used to simultaneously measure density fluctuation at 7 points in a cross section above the plate. Correlation dimensions, intermittence coefficients, Fourier spectrum have been obtained for different Grashof numbers. Spatial distribution of correlation dimensions are presented. The experimental result shows that there is a certain relationship between the density fluctuation and the Gr number. And time-spacial characteristic of chaos evolution is also given.

Achievement of 1000 s plasma generation of RF source for neutral beam injector

A radio frequency(RF) ion source was developed for neutral beam injector in Institute of Plasma Physics, Chinese Academy of Sciences(ASIPP). A cylindrical driver based RF plasma source was tested and optimized for long pulse operation. Recently, the plasma source achieved 1000 s stable plasma discharge with RF power of 35 k W and source pressure of 0.7 Pa for the first time.The heat loading on each of driver components such as the Faraday shield(FS), RF coil and expansion chamber was measured by the water flow calorimeter system. The experiment results showed that FS is the component with highest heat loading and the heat loading on FS was about 65.8% of total heat loading on source. The details of the long pulse operation of RF plasma source are presented in this paper.

基于动态模态分解的Π形梁涡振流场特征分析

为探索Π形桥梁断面的涡振机理及气动措施的抑振原理,采用动态模态分解方法,结合计算流体动力学数值模拟,对某Π形桥的不同工况进行流场解耦和对比分析.结果表明,主梁下表面方腔内的不稳定涡是导致Π形梁涡激振动的重要因素,增设2道四分点下稳定板将空腔分割成3个较小的区域,可减少下缘分离涡的形成空间并降低空腔内涡的强度和尺度,从而有效抑制涡振.第2阶分解模态与结构振动同频,是引起涡激振动的主导模态;此模态能够直观揭示流场中主涡的形成和发展,简化流场分析的复杂性.第3、4分解阶模态与结构的涡振频率存在明显的倍频关系,能够精确捕获涡激力中的高频成分,有利于深入理解涡激振动的瞬时变化特性,制定更为精细的抑振措施.

Pulsed Gas Jets for Formation of High-Intensity Cluster Beams

The possibility of using of pulsed supersonic gas jets for the formation of high intensity cluster ion beams are discusses. The results of experimental investigations of pulsed gases expansion are generalized in terms of dimensionless similarity parameters. The results of the experimental study of formation of an high-intensity cluster beam of argon are presented. The fundamental phenomenon influences on the main parameters of cluster beam (cluster size, intensity ect.) are considered.

地下连续工字钢接头混凝土绕流机理研究

在地下连续墙施工过程中,由于工字钢与槽壁之间存在较大的空隙,混凝土的浇筑容易绕流至地连墙两侧工字钢处,在工字钢表面形成凝结块,影响下一幅地连墙的施工质量,导致接缝位置发生渗漏,不利于施工安全。本文以广州市某地铁车站工程为例,采用有限元方法模拟分析富水条件下地下连续墙在不同接头箱情况下的绕流机理,为地下连续墙的安全施工提供理论指导,并将含翼缘接头箱进行工程应用,提高了施工质量,减少混凝土绕流。

智慧梁厂预制箱梁生产线及系统工艺研究

随着预制装配式桥梁建设的不断发展,预制施工技术将成为桥梁施工中的一个主流技术。为解决传统箱梁预制过程中的一些质量缺陷问题,本文以高速公路项目智慧梁厂预制箱梁施工项目为依托,提出了一种“纵移式底模台车+固定式液压侧模+智能蒸汽养护”的环形生产流水线施工工艺,将智能生产设备、信息化管控等高新技术集成到智慧梁厂预制结构建设中来,实现预制箱梁生产智能化。与传统预制结构施工相比,智慧梁厂的流水线施工工艺,极大的提高了预制梁体施工质量,减少生产周期。

板-梁耦合结构振动功率流与声辐射特性研究

针对车身低频结构噪声控制问题,首先以车身典型板-梁耦合结构简化模型为研究对象,推导出一种以CBAR焊点单元轴向位移响应和速度响应为计算参数的净功率流简化计算公式。然后以振动净功率流和等效辐射声功率(ERP)为评价参数,研究了板-梁耦合结构振动辐射噪声产生机理,从中可知不可忽视焊点对板、梁之间功率流传递的影响,而且合理设计焊点布局有利于提高辐射噪声水平。最后,基于净功率流简化计算公式,提出了一种焊点布局拓扑优化方法,结合板-梁耦合结构振动辐射噪声控制算例验证了其有效性。上述研究成果可为车身NVH品质的提高提供一种新的思路和方法,具有良好的工程实用价值和应用前景。

激光内送粉变姿态熔覆非水平熔池流场的数值模拟

目的提高激光内送粉变姿态熔覆层成形质量,对变姿态熔覆时非水平熔池流场随基板倾斜角的演变规律进行研究。方法首先,利用FLUENT软件中离散相模型对喷嘴流场进行模拟,获取粉末频次的分布规律。其次,采用流体体积法耦合熔化/凝固模型对熔池流场进行计算。通过施加质量源项引入同步送粉,施加能量源项模拟激光热输入,选取姿态角为30°、60°、90°进行计算,对熔池流场及熔覆层界面进行追踪分析。最后,基于激光内送粉熔覆工艺进行实验测定。结果粉斑内粉末量呈“中间均匀,两端密集”的分布规律。熔池流动为“双环流”分布特征,但流动方向受重力影响,产生偏转。取3种姿态角计算时间同为0.3 s时,熔池中心处流体的偏转角分别为2°、4°、6°,并且随着倾斜角的增大,熔覆层高度分别增加了0.28%、0.83%、1.45%,熔覆层宽度减小了1.19%、1.28%、1.73%,熔覆层顶点偏移量增大到48.08、86.54、105.76μm。最后结合实验测定,数值计算与实验结果一致。结论Marangoni应力使得激光内送粉熔覆熔池流体产生由中心向边界流动的“双环流”分布特征,非水平熔池流动方向受重力影响产生偏转。随着基板倾斜角增大,熔覆层截面高度增加、宽度降低、顶点偏移量增加。为提高不便摆平非水平基面的激光内送粉变姿态熔覆再制造成形质量提供了指导。

一种用于水下闸门启闭电磁挂脱梁研究

水利水电工程广泛使用的自动挂脱梁主要分为机械和液压两大类。机械自动挂脱梁易出现误操作;液压自动挂脱梁可能出现梁销轴卡阻、穿退销不到位、电缆拉断、电缆和泵站进水等故障。针对上述问题,结合乌东德水电站分层取水叠梁门启闭条件,研究试制了一种无线控制的新型电磁自动挂脱梁,先后在制造厂和水电站叠梁门工作现场进行了水上水下启闭门试验和水下密封试验,验证了在动水条件下操作闸门可行。

大型污水泵站进水流态优化设计研究

污水泵站在城市排水系统中,承担传输城市污水的功能,是保证城市排水系统安全稳定的重要设施。由于污水泵站建设容易受用地条件、市政管网布置条件等因素制约,容易引发泵站进水流态紊乱、池体水量分布不匀等问题。以上海市浦东新区灶东污水泵站扩建工程为例,在进水闸门井中采用交错式组合梁和导流墩的组合形式优化进水分布,同时在前池中采用八字形导流墩和组合式横梁的组合形式优化入流,能够有效改善前池进水流态,优化各泵组进水条件,从而保障大型污水泵站运行的安全稳定,也为其它相似工程的优化设计提供思路。

三期双流法在CT肺动脉造影的可行性和安全性评价

目的 评价三期双流法在CT肺动脉造影(CTPA)中的可行性和安全性。方法 纳入2022年2—12月可疑肺动脉栓塞患者80例,根据注射对比剂的不同方式分为传统双流组和三期双流组各40例,进行能谱CT扫描。测量或计算2组图像的各级肺动脉、右肺肺静脉和主动脉CT值、肺动脉信噪比和对比噪声比、射束硬化伪影(BHA)指数。采用3分法对图像质量和安全性进行主观评分。比较2组图像的主客观结果。结果 客观评价方面,三期双流组在左肺动脉干、左肺上叶、左肺叶间、左肺下叶、右肺动脉干和右肺下叶基底段动脉CT值均高于传统双流组(P<0.05),其动静脉分离程度、BHA值亦显著优于传统双流组,差别有统计学意义(P<0.05)。主观质量评价方面,三期双流组的平均上腔静脉BHA、动静脉分离均大于传统双流组(P<0.05);主观安全性上,三期双流组的患者主观感受优于传统双流组,差别有统计学意义(P=0.042)。结论 三期双流法CT肺动脉造影在临床上具有良好的可行性和安全性,在CT肺动脉造影中能有效提升动静脉分离效果并减少BHA。