可调行程式无缓冲增力气缸的设计与应用

介绍了带脚架可调行程式无缓冲增力气缸的技术参数、工作原理、结构特点及应用场合等,为进一步改善其性能以满足使用要求提供参考。

运载火箭牵制释放发射研究

为提高发射可靠性,运载火箭采用牵制释放系统。以连杆式牵制释放机构和套筒-缓释销型减载缓释放机构组成的牵制释放系统为例,运用Adams多体动力学软件和Abaqus有限元软件,研究运载火箭牵制释放发射时牵制力的特性,对比连杆之间角度不同时气缸力的变化,仿真缓释销从套筒内拔出的过程并得到缓释力曲线,比较有无减载缓释放机构时火箭起飞的运动规律。研究表明,连杆机构能大大减小气缸力的设计要求,连杆之间的夹角对气缸力有较大的影响,减载缓释放机构能为火箭提供递减的缓释力,减小突然释放时对箭体的冲击。研究结果对运载火箭牵制释放发射具有一定的参考价值。

气动爬缆机器人气压分析与试验

针对索径变化较大、表面情况恶劣的缆索 ,提出了一种采用铰链结构的气动蠕动式爬缆机器人结构模型 ,建立了该机器人气缸受力与高空气压损失等理论模型 ,并对样机研制实例进行了验算 .研制了工程样机并在上海徐浦大桥上成功地进行了现场试验 .仿真和试验表明 ,机器人气体压力损失与施工距离、高度、系统耗气量、气管倾斜度等成正比例非线性变化 ;机器人下降时速度较上升时均匀性好 ,能在斜拉桥缆索上安全。

Mechanism and optimization of fuel injection parameters on combustion noise of DI diesel engine

Combustion noise takes large proportion in diesel engine noise and the studies of its influence factors play an important role in noise reduction. Engine noise and cylinder pressure measurement experiments were carried out. And the improved attenuation curves were obtained, by which the engine noise was predicted. The effect of fuel injection parameters in combustion noise was investigated during the combustion process. At last, the method combining single variable optimization and multivariate combination was introduced to online optimize the combustion noise. The results show that injection parameters can affect the cylinder pressure rise rate and heat release rate, and consequently affect the cylinder pressure load and pressure oscillation to influence the combustion noise. Among these parameters, main injection advance angle has the greatest influence on the combustion noise, while the pilot injection interval time takes the second place, and the pilot injection quantity is of minimal impact. After the optimal design of the combustion noise, the average sound pressure level of the engine is distinctly reduced by 1.0 d B(A) generally. Meanwhile, the power, emission and economy performances are ensured.

Reaction thrust characteristics of high-pressure submerged water jet of cylinder nozzles

The shapes and geometrical parameters of nozzles are key factors for fluidics. The relationship among the reaction thrust, flow rate pressure, diameter do and length L of a cylinder nozzle is analyzed theoretically. The simulation of the flow field characteristics was conducted via the FLUENT computational fluid dynamics package. Effects of the inlet conditions and the nozzle dimensions on the reaction thrust of a water jet were addressed particularly. The reaction thrust experiments were performed on a custom-designed test apparatus. The experimental results reveal that a） the nozzle diameter and the inlet conditions exert great influence on the water jet reaction thrust; and b） for L≤4d0, where the nozzle is treated as a thin plate-orifice, the reaction thrust is independent of nozzle length; for L〉4d0, where the nozzle is treated as a long orifice, the reaction thrust can reach maximum under the condition of a certain flow rate. These findings lay a theoretical foundation for the design of nozzles and have significant value, especially for the future development of high-oressure water-let orooulsion technology.

Numerical Simulation of Two-Dimensional Flow over Three Cylinders by Lattice Boltzmann Method

The numerical simulation using the multiple relaxation time lattice Boltzmann method （MRT-LBM） is carried out for the purpose of investigating the two-dimensional flow around three circular cylinders. Among these three circular cylinders, one of the three cylinders on which a forced in-line vibrating is used to do this research and attempt to find out the effects of the moving cylinder and the other two rigid cylinders on the wake characteristics and vortex formation. As a benchmark problem to discuss the problem of lift coefficient r.m.s for these cylinders with spacing ratios T/ D between other rigid side-by-side cylinders, and the calculation is carried out with two compared cases at Reynolds number of 100, two of the cylinders are rigid and the other one is an in-line vibrated cylinder lying downstream, in addition, forced vibrating amplitude and frequency are A/D = 0.5 and fv= 0.4 （where A is the forced amplitude, D is the cylinder diameter, and fv stands for the vibrating frequency, respectively）. The calculated results not only indicate that the spacing ratios T/D （T is the center-to-center spacing between the two upstream cylinders） have influence on the wake patterns and the formation of vortex shedding, but also analyze the lift coefficient r.m.s for the three cylinders with the spacing ratios S/D （where S is the center-to-center spacing between the center of upstream two side-by-side cylinders and downstream cylinder）.

Base Stress of the Opened Bottom Cylinder Structures

The base stress of the opened bottom cylinder structure differs greatly from that of the structure with a closed bottom. By investigating the inner soil pressure on the cylinder wall and the base stress of the cylinder base, which were obtained from the model experiments, the interactions among the filler inside the cylinder, subsoil and cylinder are analyzed. The adjusting mechanism of frictional resistance between the inner filler and the wall of the cylinder during the overturning of the cylinder is discussed. Based on the experimental study, a method for calculating the base stress of the opened bottom cylinder structure is proposed. Meanwhile, the formulas for calculating the effective anti-overturning ratio of the opened bottom cylinder are derived.

Grain refinement of gravity die cast secondary AlSi7Cu3Mg alloys for automotive cylinder heads

The effects of AITi5B1 grain refinement and cooling rate on the microstructure and mechanical properties of a secondary AlSi7Cu3Mg alloy were reported. Metallographic and image analysis techniques have been used to quantitatively examine the macrostructural and microstructural changes occurring with the addition of grain-refining agent at different cooling rates by using a step casting die. The results indicate that the addition of AlTi5B1 produces a fine and uniform grain structure throughout the casting and this effect is more pronounced in the slowly solidified regions. Increasing the cooling rate, lower amount of grain refiner is necessary to produce a uniform grain size throughout the casting. On the other hand, the initial contents of Ti and B, present as impurity elements in the supplied secondary alloy, are not sufficient to produce an effective grain refinement. The results from the step casting geometry were applied to investigate a gasoline 16V cylinder head, which was produced by gravity semi-permanent mould technology. The grain refinement improves the plastic behaviour of the alloy and increases the reliability of the casting, as evidenced by the Weibull statistics.