Φ159mm限动芯棒连轧管机组限动速度的确定

芯棒是限动芯棒连轧管机组的主要变形工具之一,限动速度的合理设定有助于减小芯棒磨损,提高产品质量,降低生产成本。采用MPM连轧数模及德国Meer公司的二级控制方法,可推算出与芯棒限动速度有关的参数,再根据生产实际予以修正,可以得到最佳参数。介绍了鞍钢集团新钢铁有限责任公司合理确定限动芯棒连轧管机组芯棒限动速度的方法。

MPM连轧机芯棒限动速度制度的探讨

通过分析芯棒限动速度与预插入行程、芯棒规格和芯棒调头使用之间的关系 ,合理确定芯棒的限动速度 ,以保证连轧工艺的稳定可靠 ,生产出高精度的产品 。

芯棒限动速度对荒管尺寸精度影响的有限元研究

针对限动芯棒连轧管机组荒管尺寸精度控制问题,利用有限元分析软件MSC.SuperForm开展三维模拟,研究芯棒限动速度与荒管尺寸精度及芯棒轴向力的对应关系。研究结果表明:芯棒速度是影响孔型内金属不均匀变形和机架间张/推力的重要因素,提高芯棒速度,荒管尺寸精度和机架间张/推力水平明显改善,但增大了芯棒轴向力。实际生产中,选择芯棒速度时,要综合考虑芯棒轴向力与荒管尺寸精度。

MPM连轧机芯棒限动速度制度的探讨

芯棒是限动芯棒连轧钢管机组中最重要的热变形工具 ,其使用效果决定着钢管生产成本的高低。通过分析限动速度与芯棒预插入行程、芯棒规格和芯棒调头使用之间的关系 ,合理选用芯棒的限动速度 ,以保证连轧工艺的稳定可靠 ,生产出高精度的产品 ,提高芯棒的使用寿命。

芯棒限动速度对金属纵向延伸的影响

本文基于ABAQUS/Explicit操作平台,建立了烟台宝钢尴460mm PQF机组连轧过程的有限元模型,研究了不同芯棒限动速度对金属纵向流动的影响。实验结果表明:随着限动速度的降低,差速轧制效果越明显,可以降低轧制力,减少钢管宽展,利于金属的纵向延伸。

Assel三辊轧管机组芯棒限动速度及循环工艺的探讨

对Assel三辊轧管机组中芯棒的限动速度的选定原则和芯棒循环工艺流程进行了探讨。分析了限动速度与预插入行程、芯棒规格和荒管长度、壁厚的关系,叙述了芯棒循环中冷却与润滑的方法。

φ159mm机组限动齿条超极限事故分析及解决

通过计算机二级监控系统的图表，分析了Ф159mm连轧机组限动齿条超极限事故原因并提出了解决方法。

PQF连轧管机的厚壁超短管轧制工艺技术开发

通过优化PQF连轧管工艺,解决了厚壁超短管轧制时存在的问题,重点介绍了制约生产的关键要素——芯棒限动速度和脱管机轧制速度优化匹配的问题,提出了电气控制增加限动齿条返回延时的措施,实现了脱管机轧制过程扭矩平稳,满足连轧区域的自动化生产。通过现场生产,钢管几何尺寸精度满足标准要求,产品成材率达到机组设计水平。

3D FEM simulation of flow velocity field for 5052 aluminum alloy multi-row sprocket in cold semi-precision forging process

Based on the design of the multi-row sprocket with a new tooth profile,a cold semi-precision forging process for manufacturing 5052 aluminum alloy multi-row sprocket was presented.Through simulating the forging process of 5052 aluminum alloy sprocket billet with 3D rigid-viscoplastic FEM,both the distributions of flow velocity field in axial(U_Z),radial(U_R) and circumferential(U_θ) directions and the curves of velocity component in different deformation regions were respectively obtained.By comparison and analysis of the velocity varying curves,the velocity component relation conditions for filling the die cavity were clarified.It shows that when the die cavity is almost fully filled,the circumferential velocity U_θ increases sharply,implying that U_θplays a key role in fully filling the die cavity.

Upper-bound and finite element analyses of multi-row sprocket during cold semi-precision forging process

The cold semi-precision forging of a multi-row sprocket was investigated using upper-bound （UB） and finite element methods combined with experiments. Based on the design of a new tooth profile for the sprocket, a cold semi-precision forging process and a kinematically admissible velocity field for filling the die cavity were proposed. Using the UB method, the velocity fields of the sprocket billet in the forming process were divided theoretically and calculated. The process of forging a multi-row sprocket was simulated using the FEM package Deform-3D V6.1 to obtain the distributions of the velocity field and the effective stress field in filling the die cavity. Similar to the simulated results, the experiment on cold forging a 5052 aluminum alloy sprocket was successfully performed. By comparing the calculated （UB method）, experimental and simulated load-stroke curves, the calculated and simulated results were basically in accordance with the experimental results. The study provides a theoretical foundation for the development of the precision forging of multi-row sprockets.

Numerical Investigation of Hydrodynamic Flow Over an AUV Moving in the Water-surface Vicinity Considering the Laminar-turbulent Transition

Nowadays, Autonomous Underwater Vehicles(AUVs) are frequently used for exploring the oceans. The hydrodynamics of AUVs moving in the vicinity of the water surface are significantly different at higher depths. In this paper, the hydrodynamic coefficients of an AUV in non-dimensional depths of 0.75, 1, 1.5, 2, and 4D are obtained for movement close to the free-surface. Reynolds Averaged Navier Stokes Equations(RANS) are discretized using the finite volume approach and the water-surface effects modeled using the Volume of Fraction(VOF) method. As the operating speeds of AUVs are usually low, the boundary layer over them is not fully laminar or fully turbulent, so the effect of boundary layer transition from laminar to turbulent flow was considered in the simulations. Two different turbulence/transition models were used: 1) a full-turbulence model, the k-ε model, and 2) a turbulence/transition model, Menter's Transition-SST model. The results show that the Menter's Transition-SST model has a better consistency with experimental results. In addition, the wave-making effects of these bodies are studied at different immersion depths in the sea-surface vicinity or at finite depths. It is observed that the relevant pitch moments and lift coefficients are non-zero for these axi-symmetric bodies when they move close to the sea-surface. This is not expected for greater depths.

Experimental and numerical studies on vibration characteristics of a railway embankment

In order to study the dynamic response of the rail embankment under different speeds and moving load of following vehicles,a model experiment with a ratio of 1:10 is established to test the time history of acceleration and the earth pressure of the embankment at various train speeds.Using the ABAQUS finite element calculation software,a train load is applied through the FORTRAN subroutine,thereby establishing a three-dimensional finite element model with the same size as the model experiment.The data and conclusions of the finite element method model are verified by the model experiment.The model also makes some supplements to the model experiment.The experimental results show that with the increase of speed,the peak acceleration and earth pressure of the embankment also increase.By analyzing the experimental data,it can also be found that the vertical acceleration of the embankment is much greater than the axial acceleration and the lateral acceleration.In addition,the elastic modulus of the soil and the sleeper pitch also have some influence on the acceleration.

Analysis of unsteady supercavitating flow around a wedge

Supercavitating flow around a slender symmetric wedge moving at variable velocity in static fluid has been studied. Singular integral equation for the flow has been founded through distributing the sources and sinks on the symmetrical axis. The supereavity length at each moment is determined by solving the singular integral equation with finite difference method. The supercavity shape at each moment is obtained by solving the partial differential equation with variable coefficient. For the case that the wedge takes the impulse and uniformly variable motion, numerical results of time history of the supercavity length and shape are presented. The calculated results indicate that the shape and the length of the supercavity vary in a similar way to the case that the wedge takes variable motion, and there is a time lag in unsteady supercavitating flow induced by the variation of wedge velocity.

A Note on Fundamental Limit of Quantum Dynamics Rate

The unified bound on the fundamental limit of quantum dynamics rate, as quietly recently obtainedby Levitin and Toffoli [Phys.Rev.Lett.103 (2009) 160502], is improved and refined.The improvement may bearbitrarily large in certain cases.In particular, this puts a limit on the operation rate of quantum gates allowed byquantum mechanics.

Running safety and seismic optimization of a fault-crossing simply-supported girder bridge for high-speed railways based on a train-track-bridge coupling system

Bridges crossing active faults are more likely to suffer serious damage or even collapse due to the wreck capabilities of near-fault pulses and surface ruptures under earthquakes.Taking a high-speed railway simply-supported girder bridge with eight spans crossing an active strike-slip fault as the research object,a refined coupling dynamic model of the high-speed train-CRTS III slab ballastless track-bridge system was established based on ABAQUS.The rationality of the established model was thoroughly discussed.The horizontal ground motions in a fault rupture zone were simulated and transient dynamic analyses of the high-speed train-track-bridge coupling system under 3-dimensional seismic excitations were subsequently performed.The safe running speed limits of a high-speed train under different earthquake levels(frequent occurrence,design and rare occurrence)were assessed based on wheel-rail dynamic(lateral wheel-rail force,derailment coefficient and wheel-load reduction rate)and rail deformation(rail dislocation,parallel turning angle and turning angle)indicators.Parameter optimization was then investigated in terms of the rail fastener stiffness and isolation layer friction coefficient.Results of the wheel-rail dynamic indicators demonstrate the safe running speed limits for the high-speed train to be approximately 200 km/h and 80 km/h under frequent and design earthquakes,while the train is unable to run safely under rare earthquakes.In addition,the rail deformations under frequent,design and rare earthquakes meet the safe running requirements of the high-speed train for the speeds of 250,100 and 50 km/h,respectively.The speed limits determined for the wheel-rail dynamic indicators are lower due to the complex coupling effect of the train-track-bridge system under track irregularity.The running safety of the train was improved by increasing the fastener stiffness and isolation layer friction coefficient.At the rail fastener lateral stiffness of 60 kN/mm and isolation layer friction coefficients of 0.9 and 0.8,respectively,the safe running speed limits of the high-speed train increased to 250 km/h and 100 km/h under frequent and design earthquakes,respectively.

Directivity Effect on PGV Attenuation Relationships in Silakhor Earthquake （2006, Mw6.1）

Rupture directivity effect causes spatial variation in strong ground motion parameters. It causes difference between the strike- normal （V.） and strike-parallel （Vp） components of horizontal ground motion amplitudes. These variations become significant for strong ground motion velocity and the authors have developed a modification to define directivity effect factor to account for the effect of rupture directivity in empirical velocity attenuation relations which are based on modeling Silakhor earthquake, using finite element method by ANSYS. The ground motion parameters that are modified include ratio of Vn/Vp component of horizontal velocity and Vn component to average horizontal velocity （V）. The ratio of Vn to Vp is large in both the forward directivity direction, where velocity is larger, and in the backward directivity direction, where velocity is smaller. Therefore the authors expected that the Vn/Vp was mainly controlled by directivity angle. Also the variation of fault normal velocity to average horizontal velocity ratio by directivity angle （0） is defined from earthquake modeling. It shows Vn/V is controlled by directivity angle, distance between the site, epicenter and rupture length. This ratio has the same trend in Silakhor earthquake strong ground velocity data. In this paper the equation for Vn/Vp variations by directivity angle is recommended. The authors used Somervill et al. （1997） directivity model parameters as （R/L） cos2 ~ to define directivity effect on Vn/V ratio and therefore directivity factor is determined to account in near field empirical strong ground velocity attenuation relationships.

Experimental and Numerical Procedures of a Sonar Platform with a Sound Absorption Wedge

Experiments involving a sonar platform with a sound absorption wedge were carried out for the purpose of obtaining the low frequency acoustic characteristics. Acoustic characteristics of a sonar platform model with a sound absorption wedge were measured, and the effects of different wedge laid areas on platform acoustic characteristic were tested. Vibration acceleration and self-noise caused by model vibration were measured in four conditions: 0%, 36%, 60%, and 100% of wedge laid area when the sonar platform was under a single frequency excitation force. An experiment was performed to validate a corresponding numerical calculation. The numerical vibration characteristics of platform area were calculated by the finite element method, and self-noise caused by the vibration in it was predicted by an experiential formula. The conclusions prove that the numerical calculation method can partially replace the experimental process for obtaining vibration and sound characteristics.

Numerical study on the aerodynamic performance and safe running of high-speed trains in sandstorms

The influence of sandstorms on train aerodynamic performance and safe running was studied in response to the frequent occurrence of sandstorm weather in north China.An Eulerian two-phase model in the computational fluid dynamic (CFD) software FLUENT,validated with published data,was used to solve the gas-solid multiphase flow of a sandstorm around a train.The train aerodynamic performance under different sandstorm levels and no sand conditions was then simulated.Results showed that in sandstorm weather,the drag,lift,side forces and overturning moment increase by variable degrees.Based on a numerical analysis of aerodynamic characteristics,an equation of train stability was also derived using the theory of moment balance from the view of dynamics.A recommended speed limit of a train under different sandstorm levels was calculated based on the stability analysis.

The stress-velocity relationship of twinning partial dislocations and the phonon-based physical interpretation

The dependence of dislocation mobility on stress is the fundamental ingredient for the deformation in crystalline materials. Strength and ductility, the two most important properties characterizing mechanical behavior of crystalline metals, are in general governed by dislocation motion. Recording the position of a moving dislocation in a short time window is still challenging, and direct observations which enable us to deduce the speed-stress relationship of dislocations are still missing. Using large-scale molecular dynamics simulations, we obtain the motion of an obstacle-free twinning partial dislocation in face centred cubic crystals with spatial resolution at the angstrom scale and picosecond temporal information. The dislocation exhibits two limiting speeds: the first is subsonic and occurs when the resolved shear stress is on the order of hundreds of megapascal. While the stress is raised to gigapascal level, an abrupt jump of dislocation velocity occurs, from subsonic to supersonic regime. The two speed limits are governed respectively by the local transverse and longitudinal phonons associated with the stressed dislocation, as the two types of phonons facilitate dislocation gliding at different stress levels.