涵道螺旋桨气动特性数值模拟

以某涵道螺旋桨为研究对象,利用动量理论分析了孤立螺旋桨和涵道螺旋桨产生不同拉力的原因;同时利用SST k-ω湍流模型,采用三维Navier-Stokes方程,利用滑移网格模型,通过数值模拟分别计算了孤立螺旋桨与涵道螺旋桨的复杂流动,分析它们在不同转速下,拉力系数、功率系数和效率的差异。分析表明,加上涵道以后,有效抑制了螺旋桨桨尖涡,减少了能量损失。在相同转速下,总拉力系数增加23%,涵道螺旋桨的拉力系数与功率系数的比值比孤立螺旋桨的高出40%,效率显著提高,同时需用功率系数也略有增加,约0.05,结果与理论分析相吻合。     

Sr2FeNbO6的晶体结构

系统地研究了Sr2FeNbO6的晶体结构,并利用步进扫描的X光数据成功地确定了Sr2FeNbO6的晶体结构,利用Rietveld方法精修出Sr2FeNbO6是空间群为Pnma(62)的正交结构,其中,晶胞参数分别为a=5.616 1A,b=7.971 7A,c=5.613 0A.     

Numerical investigation of dynamic interaction with projectile and harmonic behaviour for T-finned machine gun barrels

Machine gun barrels differ from their rifle counterparts in terms of profile. To support high rates of sustained fire, machine gun barrels are made thicker in order to dissipate more heat and maintain their flexural rigidity and thus accuracy, but on other hand they also contribute in weight addition to weapon. This investigation deals with comparison between a conventional machine gun barrel and an improved innovative design having T-fins, both having same weight and chambered in 5.56 × 45 NATO ammunition, to compare their structural and harmonic characteristics which were parameterized by factors such as modal spectrum, directional deformation at muzzle ends during a single shot fire and harmonic behaviour at corresponding range of exciting frequencies. The solid models of both the barrels having same weight, were created using Solidworks. The continuous input data functions were generated by MATLAB using the field tested discreet data points. The generated velocity-distance functions were converted into time dependent functions using integration algorithms to calculate transient parameters such as time steps, excitation frequency range, angle of rotation of projectile and its angular velocity. The dynamic condition simulated the varying nature of forces due to eccentricity in projectile and this data was fed to a time step study using ANSYS transient structural work bench followed by modal and harmonic analysis. The results showed a significant reduction in muzzle end deformation which thus proved that the T-finned barrel, although had same weight as that of the conventional one, but had better structural and harmonic characteristics, and hence it would inherit better firing accuracy.     

螺栓法兰连接结构有限元模型参数确定方法

螺栓法兰连接广泛用于各种工业结构中,为准确预测该连接在实际工作中发挥的作用,需要建立准确高效的有限元模型。针对有限元建模过程中模型各种参数的确定问题,综合使用数值仿真手段和试验手段分别对模型网格参数和接触参数的确定开展研究。参数确定后的螺栓法兰连接结构有限元模型在保证计算精度的前提下,计算效率得到显著提高。     

基于滑移网格的潜艇旋臂试验数值模拟?

潜艇水动力系数对潜艇操纵性研究具有重要意义。为了获取较高精度的潜艇旋转导数，以分区结构化网格为基础，采用基于固定坐标系的滑移网格方法，对SUBOFF潜艇进行旋臂试验数值仿真。并对比两种不同的湍流模型下仿真结果，误差均在8％以内，满足工程要求，验证了方法的可行性。     

Effect of silicon carbide and wire-mesh reinforcements in dissimilar grade aluminium explosive clad composites

Aluminium composites are inevitable in the manufacture of aircraft structural elements owing to less weight, superior corrosion resistance and higher specific properties. These composites reduce the weight of the aircraft, improve the fuel efficiency and enhance the maintenance duration. This study proposes the development of dissimilar grade aluminium (aluminium 1100-aluminium 5052) composites with different reinforcement’s viz., stainless steel wire-mesh, silicon carbide (SiC) powders and SiC powder interspersed wire-mesh, by explosive cladding technique. Wire-mesh enhances the friction and restricts the movement of flyer plate to craft a defect free clad, while SiC particles form a band on the interface. Highest strength is obtained when SiC powder interspersed wire mesh is employed as reinforcement. The dissimilar aluminium explosive clad with SiC particle reinforcement results in lower strength, which is higher than that of the weaker parent alloy and that of the conventional dissimilar aluminium explosive clads without any reinforcement.