A numerical study of the motion of a wave running up a beach

The main difficulty for the numerical calculation of the wave running up a beach is the treatment of its moving water boundary. In this paper a scheme of turning the free boundary problem into a fixed boundary problem is designed. The calculated run-up height is consistent with the experiments. Some interesting wave phenomena are also found.     

大跨度脊谷式膜屋盖风载分布的实验研究

基于台州某风雨操场脊谷式张拉膜屋盖缩尺模型风洞试验的数据结果,选取典型测点,研究了屋面迎风前缘、过渡区及中轴区的平均风压和脉动风压系数的分布特性。同时,鉴于屋盖的不规则曲面造型,表面风压梯度变化较大,采用单一体型系数反映屋面风载已不能满足要求。文中在结合屋盖自身复杂体型和风压分布特征基础上,按各榀各边片将屋面划分为不同区域,对5个不利风向角下的区域体型系数进行统计分析,并给出各区域体型系数建议取值。最后,针对这类体型屋盖特点和风压分布特性,得出一些结论和建议,为进一步研究该类屋盖的风荷载特性和结构抗风设计提供了依据。     

Shock tunnel flow visualization using planar laser-induced fluorescence imaging of NO and OH

Temporal sequences of planar laser-induced fluorescence (PLIF) images of several high-speed, transient flowfields created in a reflection-type shock tunnel facility were acquired. In each case, the test gas contained either nitric oxide or the hydroxyl radical, the fluorescent species. The processes of shock reflection from an endwall with a converging nozzle and of underexpanded free jet formation were examined. A comparison was also made between PLIF imaging and shadow photography. The investigation demonstrated some of the capabilities of PLIF imaging diagnostics in complex, transient, hypersonic flowfields, including those with combustion.Nomenclature A spontaneous emission rate - A _las cross sectional area of laser sheet - B laser absorption rate - C _opt constant dependent on optical arrangement, collection efficiency, etc. - D nozzle throat diameter - E _p laser pulse energy - f _J Boltzmann fraction of absorbing state - g spectral convolution of laser and absorption lineshapes - k Boltzmann constant - M _s incident shock Mach number - N noise, root-mean-square signal fluctuation - P static pressure - P ₁ initial pressure of test gas in shock tube - P _a free jet ambient pressure - P _s stagnation pressure - Q electronic quenching rate of excited state - S PLIF signal - t time between shock reflection and image acquisition - T static temperature - T _s stagnation temperature - _a mole fraction of absorbing species     

考虑剪切变形的复合材料多层板壳加权残数解

本文在文献[1]的基础上,将加权残数法用于复合材料多层板壳分析,并推导出相应的关系式。文中给出了算例,并与解析解进行了比较,结果表明,本文方法精度较高,用于复合材料多层板壳分析是有效的。     

饱和土体中压力隧洞衬砌-土相互作用解析研究

基于Biot理论，采用渗流一力学耦合模型研究分析了内水压力作用下饱和土体中压力隧洞衬砌一土的相互作用问题。假定衬砌和土体均为饱和多孔介质，且衬砌和土体完全接触。运用积分变换理论，在hplace变换域中得到了衬砌和土体中的应力、位移和孔隙水压力解答，并利用bplace数值逆变换得到时域中的解。文末的算例分析结果表明：(1)采用渗流一力学耦合模型能较好地反映隧洞衬砌与土体相互作用中应力和变形的随时间变化过程；(2)衬砌和土体的相对刚度对隧洞的计算结果有很大影响。     

Experimental investigation on tunnel sonic boom

Upon the entrance of a high-speed train into a relatively long train tunnel, compression waves are generated in front of the train. These compression waves subsequently coalesce into a weak shock wave so that a unpleasant sonic boom is emitted from the tunnel exit. In order to investigate the generation of the weak shock wave in train tunnels and the emission of the resulting sonic boom from the train tunnel exit and to search for methods for the reduction of these sonic booms, a 1300 scaled train tunnel simulator was constructed and simulation experiments were carried out using this facility.In the train tunnel simulator, an 18 mm dia. and 200 mm long plastic piston moves along a 40 mm dia. and 25 m long test section with speed ranging from 60 to 100 m/s. The tunnel simulator was tilted 8° to the floor so that the attenuation of the piston speed was not more than 10 % of its entrance speed. Pressure measurements along the tunnel simulator and holographic interferometric optical flow visualization of weak shock waves in the tunnel simulator clearly showed that compression waves, with propagation, coalesced into a weak shock wave. Although, for reduction of the sonic boom in prototype train tunnels, the installation of a hood at the entrance of the tunnels was known to be useful for their suppression, this effect was confirmed in the present experiment and found to be effective particularly for low piston speeds. The installation of a partially perforated wall at the exit of the tunnel simulator was found to smear pressure gradients at the shock. This effect is significant for higher piston speeds. Throughout the series of train tunnel simulator experiments, the combination of both the entrance hood and the perforated wall significantly reduces shock overpressures for piston speeds ofu _p ranging from 60 to 100 m/s. These experimental findings were then applied to a real train tunnel and good agreement was obtained between the tunnel simulator result and the real tunnel measurements.     

尖顶弯折三角翼气动特性研究

 对75°后掠三角翼在40%根弦处弯折引起的升阻特性及俯仰特性的 变化进行了低速风洞实验研究，初步分析了尖顶弯折对三角翼气动特性 的影响趋势. 得出尖顶弯折在低速大攻角下，可以使升力系数Cy增大、升阻比提高，并推迟失速攻角amax，从而说明顶部弯折对三角翼气动特 性的改善作用是显著的.     

冲击荷载下土中浅埋箱形结构反应的模型试验研究

本文叙述了土中浅埋箱形结构模型动力试验结果。试验的目的是检验我们在文献[8、9]中,所提出的地表冲击波荷载作用下,土中箱形结构动力反应分析的两步法。试验有两种情况:一是利用室内模爆器进行的小模型(模型尺寸与实际结构之比约为1:40)试验;另一种是利用室外试验坑中进行的模拟平面波加载下的中等模型(尺寸缩比约为1:10)试验。试验的箱形结构有单孔与双孔两种。根据埋深与超压的不同,共进行了20炮次试验,试验对自由场中应力、结构周边压力、结构应变、结构运动等参数进行了测量。试验结果表明,所提出的两步分析法中关于土中结构内力分析的准静态法是可行的。     

Nonlinear stability of large k-value shallow spherical shells with a symmetrically distributed line load

In this paper, we treat the nonlinear stability problem of shallow spherical shells with large values ofk(k=12(1–v) · 2f/h,f = shell rise,h = shell thickness) under the action of uniformly distributed line load along a circle concentric with the shell boundary. Load-deflection curves are computed at successive increments of uniformly distributed line loads by using both cubic B-spline approximations and iterative techniques. Our algorithm yields fairly good convergent results for values ofk as large as 400. The limiting case in which shells are loaded along a circle of small radius has been specially investigated and the computed critical loads are compared with those obtained with central point loads by other authors.     

退火对IrMn基磁隧道结多层膜热稳定性的影响

采用磁控溅射方法制备了结构为IrMn/CoFe/AlO_x/CoFe的磁性隧道结多层膜,样品置于真空磁场中进行退火处理. 将在不同温度退火的磁隧道结结构多层膜置于负饱和场中等待,研究退火温度对样品热稳定性的影响. 结果表明:退火提高了多层膜反铁磁层的单轴各向异性能,增加了样品的交换偏置;随着负饱和场等待时间的延长,被钉扎层的磁滞回线向正场偏移,交换偏置单调减小,但退火减弱了这种趋势. 关键词： 磁隧道结 交换偏置 磁化反转