Fluid sloshing thermo-mechanical characteristic in a cryogenic fuel storage tank under different gravity acceleration levels

Fluid sloshing usually causes serious safety issues on the dynamic stability and propellant thermal management during the powered-flight phase of launch vehicle. With the wide using of cryogenic propellants, the coupled thermo-mechanical performance during fluid sloshing becomes more prominent. In the present study, one numerical model is established to simulate fluid sloshing by using the VOF method coupled with the mesh motion treatment. The phase change occurring within the tank is considered. Both the experimental validation and mesh sensitivity analysis are made. It shows that present numerical model is acceptable. Based on the developed numerical model, the effect of different super gravity accelerations on fluid sloshing hydrodynamic characteristic is numerically researched. The fluid pressure variation, the sloshing force and sloshing moment, the interface dynamic response and the interface shape variation are investigated, respectively. It shows that the gravity acceleration has caused obvious influences on fluid sloshing characteristic. When the gravity acceleration is higher than 4g₀, fluid sloshing becomes more obvious and must be paid enough attention. With some valuable conclusions obtained, the present work is of great significance for in-depth understanding of fluid sloshing mechanism.     

基于双声表面波器件的引信加速度传感器

In view of the shortcomings of silicon micro acceleration sensor based on piezoresistive effect and capacitance principle, such as temperature drift, low resolution and poor anti-interference ability, a fuze acceleration sensor based on dual SAW devices is proposed. The sensor adopts a dual saw device structure, one is coated with a sensitive film for measurement, the other is an uncoat- ed reference channel for compensation of environmental temperature, pressure, humidity and other factors. The experimental results show that the maximum linear error is only 1.6%, the sensitivity is 54.3Hz/g, and the maximum hysteresis error is less than 1%. Compared with piezoresistive accelerometer and capacitive accelerometer, the linear error of the accelerometer is small, the sensitivi- ty is high, and it has strong anti-interference ability.     

风洞模型加速度负反馈振动主动控制方法研究

针对尾撑式风洞模型强方向性振动问题,基于异位配置加速度负反馈控制器对风洞模型振动主动控制方法进行研究。首先,通过模态分析得到系统低阶模态振动的强方向性并基于系统特性设计了具有结构耦合性的内嵌压电陶瓷作动器的风洞模型振动主动控制系统。然后,基于异位配置NAF控制器分别设计了针对第二阶模态和前两阶模态的单模态NAF控制算法和双模态NAF控制算法。最后,进行了实验验证,结果表明:双模态NAF控制算法控制效果较好,前两阶模态阻尼比分别提高近13倍和近40倍,镇定时间分别缩短近11s和近26s。     

考虑关节角加速度约束的仿人机器人偏摆力矩控制方法

针对仿人机器人步行过程中存在的机器人关节角加速度约束影响控制性能的问题，提出一种考虑关节角加速度约束的仿人机器人偏摆力矩控制方法.该方法充分考虑了双臂在摆动过程中对偏摆力矩的影响，根据力矩平衡条件得到需要抵消的偏摆力矩的大小与方向，将偏摆力矩的控制问题转化为带约束条件的二次规划问题，并设计了一种在线变步长迭代算法计算得到优化后的双臂摆动轨迹.实验表明，该方法能有效抵消机器人步行中产生的偏摆力矩，避免控制过程中的"削峰"现象，有效提高机器人的步行稳定性.     

圆形截面柱的振动台试验及分析

进行了圆柱振动台试验,对模型的加速度反应数据进行获取。试验表明,随着地震的加速度峰值的不断增加,圆柱顶部加速度极值不断增加。柱顶的加速度响应有着增大的趋势,且极值比输入的加速度的极值有一定的放大。     

The flame propagation characteristics and detonation parameters of ammonia/oxygen in a large-scale horizontal tube: As a carbon-free fuel and hydrogen-energy carrier

As a carbon-free fuel and a hydrogen-energy carrier, ammonia is a potential candidate for future energy utilization. Therefore, in order to promote the application of ammonia in detonation engines and to evaluate the safety of ammonia related industrial process, DDT experiments for ammonia/oxygen mixtures with different ERs were carried out in a large-scale horizontal tube. Moreover, pressure transducers and self-developed temperature sensors were applied to record the overpressure and the instantaneous flame temperature during DDT process. The results show that the DDT process in ammonia/oxygen mixtures contains four stages: Slow propagation stage, Flame and pressure wave acceleration stage, Fast propagation and detonation wave formation stage, Detonation wave self-sustained propagation stage. For stoichiometric ammonia/oxygen mixtures, flame front and the leading shock wave propagate one after another with different velocity, until they closely coupled and propagated together with one steady velocity. At the same time, it is found that an interesting retonation wave propagates backward. The peak overpressure, detonation velocity, and flame temperature of the self-sustained detonation are 2 MPa, 2000 m/s and 3500 K, respectively. With the ER increased from 0.6 to 1.6, the detonation velocities and peak overpressures ranged from 2310 m/s to 2480 m/s and 25.6 bar–28.7 bar, respectively. In addition, the detonation parameters of ammonia were compared with those of methane and hydrogen to evaluate the detonation performance and destructiveness of ammonia.     

GPU加速MOC输运计算性能分析研究

特征线方法（MOC）在求解堆芯规模中子输运方程时面临计算时间长的问题，加速和并行算法是目前研究的热点。基于MOC在特征线和能群层面的并行特性，采用统一计算设备构架（CUDA）编程规范，实现了基于图形处理器（GPU）的并行二维MOC算法。测试了菱形差分和步特征线法分别在双精度、混合精度及单精度浮点运算下的计算精度、效率及GPU加速效果。采用性能分析工具对GPU程序性能进行了分析，识别了程序性能瓶颈。结果表明：菱形差分和步特征线法在不同浮点运算精度下均表现出良好的计算精度；相比于CPU单线程计算，GPU加速效果在双精度和单精度情况下分别达到35倍和100倍以上。     

Position-varying surface roughness prediction method considering compensated acceleration in milling of thin-walled workpiece

Machined surface roughness will affect parts’ service performance. Thus, predicting it in the machining is important to avoid rejects. Surface roughness will be affected by system position dependent vibration even under constant parameter with certain toolpath processing in the finishing. Aiming at surface roughness prediction in the machining process, this paper proposes a position-varying surface roughness prediction method based on compensated acceleration by using regression analysis. To reduce the stochastic error of measuring the machined surface profile height, the surface area is repeatedly measured three times, and Pauta criterion is adopted to eliminate abnormal points. The actual vibration state at any processing position is obtained through the single-point monitoring acceleration compensation model. Seven acceleration features are extracted, and valley, which has the highest R-square proving the effectiveness of the filtering features, is selected as the input of the prediction model by mutual information coefficients. Finally, by comparing the measured and predicted surface roughness curves, they have the same trends, with the average error of 16.28% and the minimum error of 0.16%. Moreover, the prediction curve matches and agrees well with the actual surface state, which verifies the accuracy and reliability of the model.     

中子平衡节块离散纵标法及CMFD加速技术研究

本文基于横向积分离散纵标方程,解析得到横向积分通量中出射通量与入射通量的关系,并根据类似于扩散方程节块展开法的输运节块中子平衡方程形式,得到了一种高效的节块离散纵标法数值迭代策略。数值结果表明,本文提出的方法可行且数值结果正确。此外,粗网有限差分(CMFD)加速技术在节块离散纵标法中也取得了非常好的应用效果。     

Laser induced fast ignition made realistic by relativistic velocities-dream or reality?

Due to the recent developments in high power lasers it is suggested to accelerate a micro-foil by the laser pressure to relativistic velocities. The time dependent velocity of this micro-foil is calculated analytically for pulsed constant laser intensity. The accelerated foil collides with a target creating a shock wave on impact. The shock wave parameters are calculated within the context of relativistic fluid dynamics.It is suggested to use the energy of the relativistic micro-foil to ignite a pre-compressed target with a density relevant for fusion ignition. The equations are written and solved for the collision between the micro-foil and the very dense target. The criteria for shock wave ignition and heat wave ignition are used to show that one needs significantly less laser energy for heat wave ignition.The present scheme shows that nuclear fast ignition by micro-foil impact could be attained in the near future with lasers that are currently under construction.