Dynamic characterization of a high speed gamma-ray tomograph

A HSGT (High Speed Gamma-ray Tomograph) has been designed and built at the University of Bergen with the objective to monitor rapid changes in multiphase hydrocarbon flow regimes. In order to perform real-time image reconstruction with photon integration times as low as 10 ms, a novel DACS (Data Acquisition and Control System) has been developed. The DACS is based on FPGA (Field-Programmable Gate Array) programming of the CompactRIO module from National Instruments to minimize its data acquisition and control time. The CompactRIO module includes a reconfigurable FPGA, which provides hardware-level data acquisition and control determinism with a time resolution of 25 ns. The data acquisition and control time for the HSGT obtained with the novel DACS interface design is 0.18 ms, which corresponds to a data transmission bandwidth of 1.35 Mbytes/s given that the HSGT data frame consists of 85 channels each comprising a 24 bit resolution. The DACS also facilitates FPGA sensor data pre-processing, i.e. normalization, of the acquired tomograph data to speed up the image reconstruction. Dynamic characterization of the HSGT for rotational and translational movements is presented in this paper, which is based on calculation of the RMSE (Root Mean Square Error) of the acquired tomogram compared to that of the test phantom. The test phantom consists of two spherical holes with different radius in a polypropylene sample. The results of the dynamic characterization show that the HSGT can sustain imaging of a rotational object with angular velocities ～30 rad/s. For translational movement (free fall) the HSGT is able to detect internal cross-sectional structures with velocities up to ～4 m s^?1.     

Researches on two-phase flows around a hydrofoil using Shan-Chen multi-phase LBM model

In this paper, the Shan-Chen-type multiphase lattice Boltzmann model was proposed to investigate two-phase flows around a hydrofoil. In the model, The Shan-Chen force accounts for the attraction force calculated over nearest neighbours of the pseudopotential function, which is employed to mimic the molecular interactions that cause phase segregation. Firstly, the lattice Boltzmann model was validated by the liquid flows around a hydrofoil by means of comparison of drag coefficients and the Shan-Chen model was validated by the Laplace law. And then aiming at various existing bubbles of different radii preplaced above the hydrofoil leading edge, the evolution of gasliquid two-phase flows was successfully reproduced based on heterogeneous cavitation assumption. The shedding bubbles become smaller and smaller downstream the hydrofoil, and finally collapse behind the tailing edge. The inter-particle forces are analyzed based on the two-phase flow density, and then the corresponding pseudo-velocity distribution is predicted near the phase interface. Then the attached cavitating flows is studied based on homogeneous cavitation assumption. It can be concluded that the attached cavitation occurs and evolves under some reasonable conditions. It can be found that that a small change in the velocity or pressure will bring great influence on the bubble size. All the above-analyses demonstrate that Shan-Chen multiphase model can capture well the inter-phase force and can be treated as an alternative potential approach for predicting cavitating flows.     

高速切削技术及高速切削可转位铣刀的研究

高速切削是先进制造技术中最重要的加工工艺之一，而切削刀具是实现这一工艺的关键。论文介绍了高速切削技术，以及高速切削技术要求的高速切削刀具，特别说明的是高速切削铣刀；论述了高速切削的可转位铣刀的特点、切削刀具材料和刀体结构。     

一种高速冷气涡轮的设计计算方法

通过对一种高速冷气涡轮进行研究,结合计算实例,分析了其结构参数对涡轮输出功率以及效率的影响．从而为优化冷气涡轮设计、提高性能参数提供了参考依据。     

Carbody hunting investigation of a high speed passenger car

This paper describes the low frequency carbody hunting problem of a high speed passenger car emerged in the process of tests and service operations. It causes a significant deterioration of lateral comfort. First, the vehicle model is established as a multiple rigid body system. Using root locus analysis, the effect of system parameters on the carbody hunting stability has been studied. It shows that carbody hunting instability has something to do with suspension parameters and wheel/rail conditions. To find the causes of this carbody hunting problem, component tests have been carried out. Based on the theoretical hunting stability analysis and component tests, solutions are proposed and then validated in the field test.     

80MN快锻液压机结构动态特性分析

针对高频次锻造工况下作业的80MN快锻液压机结构动态特性要求高等问题,基于ANSYS动力学分析的原理,并考虑到动力学分析需要占用的计算机资源大,简化了活动横梁装配,忽略了导向架,对活动横梁与立柱接触结合部x方向采用耦合连接,活动横梁底面覆盖一层目标单元,锻件顶面覆盖一层接触单元,形成接触对;活动横梁的初始速度设置为15 mm/s,加速度设置为537 mm/s^2,加速度的加载采用阶梯加载方式,同时考虑结构预紧力对结构分析的影响,建立了其结构动力学分析的有限元模型,进行了结构在动载荷作用下的动力学响应分析计算,获得了液压机结构的动应力分布规律和变形分布规律.研究结果表明,结构动态最大位移值约为最大静态位移值的2倍,结构在动态载荷下的应力也约为静态的2倍,发现了结构刚度薄弱环节,为在设计过程中更加合理地布置结构刚度,提供了理论依据.     

某型直升机大速度下的异常振动分析

某型直升机在大速度飞行时出现短时的抖动现象,采用传统傅立叶变换无法得到这一变化过程的详细信息。采用小波分析和修正的傅立叶级数展开算法对振动信号进行分析,结果显示采用该方法可以有效获取信号中的非稳态变化信息,并进一步分析得到大速度下激起的摆振后退型是直升机抖动的原因。     

高速转子的低速动平衡

介绍了高速转子的分类、低速动平衡的评定标准，分别以压缩机转子和汽轮机转子为例，介绍了高速转子的低速动平衡方法。     

Computation of turbulent flows and radiated sound from axial compressor cascade

The losses at off-design points from a compressor cascade occur due to the deviation from a design incidence angle at the inlet of the cascade. The self-noise from the blade cascade at off-design points comes from a separated boundary layer and vortex sheddings. If the incidence angle to the cascade increases, stalling in blades may occur and the noise level increases significantly. This study applied Large-Eddy Simulations (LES) using deductive and deductive dynamic SGS models to low Mach-number, turbulent flow with each incidence angle to the cascade ranging from −40° to +20°, and compared numerical predictions with measured data. It was observed that the oscillating separation bubbles attached to the suction surface do not modify wake flows dynamically for cases of negative incidence angles. However, an incidence angle greater than 8° caused a separated vortex near the leading edge to be shed downstream and created stalling. The computed performance parameters such as drag coefficient and total pressure loss coefficient showed good agreement with experimental results. Noise from the cascade of the compressor is summarized as sound generated by a structure interacting with unsteady, turbulent flows. The hybrid method using acoustic analogy was observed to closely predict the measured overall sound powers and directivity patterns at design and off-design points of blade cascade.     

A high resolution numerical scheme for a high speed gas-liquid two-phase flow

A high resolution numerical method for solving high speed gas-liquid two-phase flow is proposed and applied to the two-phase shock tube problem. The present method employs a finite-difference 4th-order Runge-Kutta method and Roe’s flux difference splitting approximation with the MUSCL TVD scheme. A homogeneous equilibrium gas-liquid two-phase model that takes account of the compressibility of mixed media is used. Therefore, the present density-based numerical method permits simple treatment of the whole gasliquid two-phase flow field, including wave propagation, large density changes and incompressible flow characteristics at the low Mach number. The speed of sound of above two-phase media has been derived on the basis of thermodynamic relations. By this method, a Riemann problem for the Euler equations of a one-dimensional shock tube was computed. Numerical results such as detailed observations of shock and expansion wave propagations through the gas-liquid two-phase media at thermal and isothermal conditions, and some features related to computational efficiency are made. Comparisons of predicted results with exact solutions are provided and discussed.     

高速高加速堆垛机速度控制曲线研究与优化

将以高速高加速堆垛机作为研究对象,采用动力学分析并利用叠加原理得到立柱动态挠曲变形公式,分析影响立柱变形的因素。提出一种新型速度曲线优化控制方案,当进行长距离作业,堆垛机速度可以到达最大设计速度时选择S型速度控制曲线,当运行短距离作业,堆垛机速度无法达到最大设计速度即需减速制动时选择三角函数型速度控制曲线。此方案使堆垛机速度加速度变化连续平滑,抑制立柱变形而产生摆动,提高堆垛机稳定性。     

高弹性锥体高速刀柄的性能研究

设计一种具有高弹性锥体的双面定位新型高速刀柄,在实心刀柄锥体上开有直、环交错槽,形成多个独立小锥面,增加刀柄锥体的弹性.高弹性锥体能够增大刀柄与主轴的配合过盈量,补偿主轴的高速离心膨胀,提高刀柄的极限转速.借助ANSYS Workbench有限元软件对该高速刀柄的静态和高速性能进行分析,具体研究刀柄锥面与端面的压力分布特点、主轴的膨胀变形规律以及刀柄-主轴联接的径向刚度.结果表明,新型高速刀柄具有较高的极限转速,在高转速下具有可靠的定位精度和联接刚度,特别适合于高速加工.     

高速开关阀在高速带钢纠偏系统中的应用

高速带钢纠偏装置需一种工作稳定可靠 ,响应速度快 ,抗污染能力强 ,并能由计算机直接控制的液压执行器。本文将高速开关阀作为高速带钢纠偏装置的电液转换元件 ,效果很好     

Numerical simulation of flows around axisymmetric inlet with bleed regions

A numerical simulation of flows in an axisymmetric supersonic inlet with bleed regions is performed. An existing code which solves the Reynolds Averaged Navier-Stokes equations and the two-equation turbulence model equations is converted into an axisymmetric code. In addition, a bleed boundary condition model has been applied to the code. In this paper, the modified code is validated by comparing numerical results against experimental data and other computational results for flows on a bump and over an oblique shock with bleed region. Using the code, numerical simulation is performed for the flows in an inlet with multiple bleed regions.     

高速切削技术的发展与展望

结合国内外高速切削技术的研究现状,介绍高速切削的概念、国内外发展动态及其相关技术的发展;探讨高速切削的应用领域;分析高速切削研究现存问题并展望高速切削的发展趋势和未来研究方向。     

一种高速单相无刷直流电机的控制方法研究

Aiming at setting the problem that conventional single-phase BLDCM control method is not able to meet the performance require­ments which is decided by vacuum cleaners, a control method combined with conduction angle control,phrase advance method and free­ wheeling method is presented. Based on a 350 W Single-Phase BLDC motor,a 2-D finite element model and a control system analytical mod­el were established and a field-circuit coupled simulation was used to validate the control method. According to the analysis of simulation results,the influence that how the motor performance was influenced by the different combinations of turn-on angle and turn-off angle was obtained. The optimal control parameters were determined and the feasibility and effectiveness of the proposed control method were explored by experiments. The results indicate that the proposed method could make the motor control system achieve the performances,such as graded adjustable speed,high speed and high efficiency. The simulation results are in consistency with the experimental data demonstrates that the applied Field-circuit coupled simulation approach is of practical meaning. [ABSTRACT FROM AUTHOR]     

物料高速连续抛掷状态下的新模态

振动给料机工作时分为滑行输送、中速抛掷输送及高速抛掷输送几种状态。其工作在哪种状态下由抛掷指数D=λgω2决定,其中λ为给料机振幅,ω为给料机圆频率,g为重力加速度。抛掷指数D=3.3~3.84时为高速抛掷输送的连续抛掷输送状态,即物料抛起后,当它再与给料机的料槽相接触的瞬时,给料机的振动相位处于物料的起抛区域,物料即刻又被抛起,物料前一次抛掷的抛止相位为这次抛掷的抛始相位,这样物料处于连续的抛掷状态。经物料抛掷运动模拟计算,可知在抛掷的初始若干周期,每次两次的抛止相位(或抛始相位)都不相同,但是经过一定次数的抛掷后,从第n…     

Vortical flows over a LEX-delta wing at high angles of attack

The vortical flows over sharp-edged delta wings with and without a leading edge extension have been investigated using a computational method. Three-dimensional compressible Rey-nolds-averaged Navier-Stokes equations are solved to provide an understanding of the effects of the angle of attack and the angle of yaw on the development and interaction of vortices and the aerodynamic characteristics of the delta wing at a freestream velocity of 20 m/s. The present computations provide qualitatively reasonable predictions of vortical flow characteristics, compared with past wind tunnel measurements. In the presence of a leading edge extension, a significant change in the suction pressure peak in the chordwise direction is much reduced at a given angle of attack. The leading edge extension can also stabilize the wing vortex on the windward side at angles of yaw, which dominates the vortical flows over yawed delta wings.     

Vortical flows over a delta wing at high angles of attack

The vortex flow characteristics of a sharp-edged delta wing at high angles of attack were studied using a computational technique. Three dimensional, compressible Reynolds-averaged Navier-Stokes equations were solved to understand the effects of the angle of yaw, angle of attack, and free stream velocity on the development and interaction of vortices and the relationship between suction pressure distributions and vortex flow characteristics. The present computations gave qualitatively reasonable predictions of vortical flows over a delta wing, compared with past wind tunnel measurements. With an increase in the angle of yaw, the symmetry of the pair of leading edge vortices was broken and the vortex strength was decreased on both windward and leeward sides. An increase in the free stream velocity resulted in stronger leading edge vortices with an outboard movement.