Evaluation of thermal gradients and thermosiphon in dual channel cable-in-conduit conductors

In an effort to optimize superconductor cryogenics of large coils, dual channel cable-in-conduit conductors (CICC) have been designed. The qualitative and economic rationale of the conductor central channel is here justified but brings high complexity to the conductor cooling characteristics. Temperature gradients in the cable must be quantified to guarantee conductor temperature margin during coil operation under heat disturbance and set adequate inlet temperature. A simple one-dimensional thermal model, with neither fluid nor strand or jacket conduction, allows to better understand and quantify the steady state behavior of CICC central and annular channels. This thermohydraulic model with homogeneous central and annular temperatures and no jacket conduction is summarized with explicit thermal coupling equations. Local convection coefficients chosen proportional to friction factors lead to a model of global interchannel heat exchange coefficient serving the bithermal model. A first stationary experimental evaluation of the internal heat transfer coefficient using the interchannel heat exchange space constant at various heat loads and mass flow rates is illustrated on two full size samples tested at cryogenic temperatures. Annular heaters experiments with low distributed power achieve pertinent model correlation. Discrepancy between model and experimental data may be linked to the simplistic homogeneous annular temperature hypothesis, to the estimate of CICC mass flow distribution among channels, and to gravitational effects at high heat loads. Perturbation due to the thermosiphon generated between the two channels is considered since neither the experiments nor the expected applications are free of gravity.     

登陆作战海军水雷破障建模与应用

扫除抗登陆方水雷障碍，既是登陆作战的重要环节，也是保障三军联合破除敌抗登陆水际障碍的前提条件．根据抗登陆方水雷情况想定，研究三军联合破障中海军扫雷兵力的运用，创新性地提出了将水雷分为3种类型分别进行分析量化处理的方法，并以此建立了切合实际的海军扫雷模型．根据该模型研制的海军水雷破障辅助决策系统，可以完成已知扫雷时间、扫雷兵力和扫雷率这3个最主要扫雷参数之间的互相求解问题，为指挥员决策提供了定量的客观依据．     

Free and forced vibration analysis of laminated composite plates and shells using a 9-node assumed strain shell element

The natural frequencies of isotropic and composite laminates are presented. The forced vibration analysis of laminated composite plates and shells subjected to arbitrary loading is investigated. In order to overcome membrane and shear locking phenomena, the assumed natural strain method is used. To develop a laminated shell element for free and forced vibration analysis, the equivalent constitutive equation that makes the computation of composite structures efficient was applied. The Mindlin-Reissner theory which allows the shear deformation and rotary inertia effect to be considered is adopted for development of nine-node assumed strain shell element. The present shell element offers significant advantages since it consistently uses the natural co-ordinate system. Results of the present theory show good agreement with the 3-D elasticity and analytical solutions. In addition the effect of damping is investigated on the forced vibration analysis of laminated composite plates and shells.     

高炉炉料落点的确定

在实际装料时,不同密度、粒径及形状系数的颗粒在料面上的落点也各不相同。目前,文献在计算料流轨迹时存在忽略煤气曳力、密度选择不当或曳力公式使用有误等问题,与实际计算常有很大偏差。为此,针对目前料流轨迹计算存在的问题,准确考虑了颗粒在空区下落中所受重力、浮力及煤气曳力的作用,建立数学模型计算炉料颗粒在空区下落的运动轨迹。通过对不同炉料在其粒径范围内的布料半径变化及煤气对其曳力大小的讨论,正确考虑料流轨迹计算时煤气曳力的影响,为准确实现合理布料奠定基础。     

基于CCD的CDT电子束着屏误差自动测试系统

利用CCD图像传感器和图像采集处理技术,实现了电子束着屏误差二维自动测量。在荧光屏的前端附加垂直和水平两组微偏转线圈,通过控制微偏转线圈的电流,改变着屏点附近的磁场,使电子束着屏点的位置在一个粉点范围内精确连续可调。标准光栅的测试验证,系统绝对误差小于5m,表明该系统稳定可靠,一致性好。     

基于DEM的无钟高炉布料料流轨迹研究

离散单元仿真技术被广泛用于研究高炉布料过程中炉料运动的规律,其计算散料运动的方法得到了国内外专家的认可.利用SOLIDWORKS和EDEM的Geometry建立无钟炉顶高炉几何模型,基于DEM结合炉料物理参数进行数学模拟,研究了溜槽倾角、料线深度和溜槽结构对料流轨迹的影响.结果表明:焦炭落点半径随溜槽倾角的增大而增大,...     

Fractional order model parameters for the respiratory input impedance in healthy and in asthmatic children

This paper provides an evaluation of a fractional order model for the respiratory input impedance, using two groups of subjects, respectively healthy and asthmatic children. The purpose is to verify if the model is able to deliver statistically meaningful parameter values in order to classify the two groups. The data are gathered with the non-invasive lung function test of forced oscillations technique, by means of a multisine signal within the 4-48 Hz frequency range. Based on our previous work, a fractional order model for this range of frequencies is obtained. Additional parameters are proposed to evaluate the two groups. The results indicate that the model was unable to detect significant changes between the asthmatic children with normal spirometry results (as result of medication) and the healthy children. Due to medication intake during the hours prior to the exam, bronchial challenge did not modify substantially the respiratory parameters. Our findings correspond to similar studies reported in the specialized literature. Combined model parameters, such as the tissue damping and the tissue elastance were significantly different in the two groups (p < 0.01). Two extra indexes are introduced: the quality factor and the power factor, providing significantly different results between the two groups (p ? 0.01). We conclude that the model can be used in the respective frequency range to characterize the two groups efficiently.     

具有强迫射流的大型腔体中的速度场和热分层实验分析(英文)

本文介绍在模拟实际非能动安全壳冷却系统及接近实际安全壳分隔区域尺寸的条件下,大型矩形腔体中由强迫射流所造成的速度场和热分层现象。推导了强迫射流动量何时打破分层现象的判断准则。分析了射流对混合与分层的影响。基于测量结果讨论了大型腔体中因射流与自然对流传热所造成的速度场。     

Adaptive Pinpoint and Fuel Efficient Mars Landing Using Reinforcement Learning

Future unconstrained and science-driven missions to Mars will require advanced guidance algorithms that are able to adapt to more demanding mission requirements, e.g. landing on selected locales with pinpoint accuracy while autonomously flying fuel-efficient trajectories. In this paper, a novel guidance algorithm designed by applying the principles of reinforcement learning (RL) theory is presented. The goal is to devise an adaptive guidance algorithm that enables robust, fuel efficient, and accurate landing without the need for off line trajectory generation and real-time tracking. Results from a Monte Carlo simulation campaign show that the algorithm is capable of autonomously following trajectories that are close to the optimal minimum-fuel solutions with an accuracy that surpasses that of past and future Mars missions. The proposed RL-based guidance algorithm exhibits a high degree of flexibility and can easily accommodate autonomous retargeting while maintaining accuracy and fuel efficiency. Although reinforcement learning and other similar machine learning techniques have been previously applied to aerospace guidance and control problems (e.g., autonomous helicopter control), this appears, to the best of the authors knowledge, to be the first application of reinforcement learning to the problem of autonomous planetary landing.      

Forced oscillation to reduce zero flow error and thermal drift for non-reciprocal operating liquid ultrasonic flow meters

A new method using forced oscillation excitation for transit-time difference (TTD) measurement is proposed to improve the accuracy and stability in ultrasonic flow metering under non-reciprocal operating conditions. Forced oscillation guarantees the frequencies of the received signals in both directions constant and known, thus the TTD can be measured as the phase difference. Choosing the driving frequency slightly off the resonance of the transducers can considerably decrease the long-term drift of the TTD results caused by temperature variations, and minimize the zero flow error. In the simulations and experiments, the proposed method showed good performance in the non-reciprocal metering system, the zero flow error and the thermal drift on the TTD measurement results were reduced.