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991.
导出了线性波浪作用于上部可渗透的直立刚圆柱体上的水动力的解析解,在线性有势流的假定下,用特征函数展开方法求出了内部和外部流场的解,给出了不同波浪要素及结构尺寸参数下的数值结果,由结果可知,可渗透性可以大大减少波浪作用力,。 相似文献
992.
用奇异函数建立克尔地基上中面单向受拉(压)的阶梯式单向矩形薄板自由振动和强迫振动的微分方程并求得其通解,用W算子给出主振型函数的表达式及常见支承条件下板的频率方程,此处导出的各种情况下的影响函数,亦可用于求解相应情况下梁和板的静力弯曲或稳定性问题。 相似文献
993.
Marco Grandis 《Applied Categorical Structures》1997,5(4):363-413
We investigate a structure for an abstract cylinder endofunctor I whichproduces a good basis for homotopical algebra. It essentially consists ofthe usual operations (faces, degeneracies, connections, symmetries, verticalcomposition) together with a transformation w: I2 I2, whichwe call lens collapse after its realisation in the standard topologicalcase. This structure, if somewhat heavy, has the interest of beingcategorically algebraic, i.e., based on operations onfunctors. Consequently, it can be naturally lifted from a category A to itscategories of diagrams AS and its slice categories A\X,A/X.Further, the dual structure, based on a cocylinder (or path) endofunctor Pcan be lifted to the category of A-valued sheaves on a site, wheneverthe path functor P preserves limits, and to the category Mon A of internalmonoids, with respect to any monoidal structure of A consistent with P. 相似文献
994.
强激光加热旋转薄柱壳的参量选择分析 总被引:1,自引:0,他引:1
为了把激光加热静止圆柱壳的实验测量结果应用到旋转圆柱壳的激光参量估计中,研究了旋转圆柱壳的激光加热效率。用积分变换法得到了旋转圆柱壳的温度分布,分析了最大温升点相对激光峰值强度点的滞后现象。基于静止圆柱壳和薄壳假设,导出了旋转圆柱壳激光加热效率及估计辐照时间的表达式。对于旋转金属圆柱壳,最大温升点相对激光峰值强度点的滞后角和激光加热效率取决于无量纲参量DR(柱壳半径R与束斑半径r0之比)、DL(横向热扩散尺度4ατL与束斑半径r0之比)及DM(加热时间τL与柱壳旋转频率fR的乘积)。达到相同的最大温升时,旋转圆柱壳的激光辐照时间和静止圆柱壳的激光辐照时间之间存在与激光功率无关的非线性关系,而激光功率决定了所需的绝对激光辐照时间。 相似文献
995.
不均匀柱形粒子的光散射特性研究对复杂结构粒子参量的反演具有重要意义。基于德拜理论,对在轴高斯波束垂直入射无限长多层圆柱的散射特性进行了讨论。获得了散射系数的德拜级数展开式;并利用该公式分别计算了均匀和双层圆柱的总散射强度角分布,德拜级数单阶散射强度角分布;总散射强度结果与广义米氏理论(GLMT)进行了比较,两者吻合很好。分析表明圆柱散射强度不同散射角区间的值来自德拜级数不同阶的散射强度贡献;双层圆柱各层半径和折射率的值对德拜级数二阶散射强度角分布中峰值的出现起决定作用。当双层圆柱的外层较薄时,在120°~150°之间会出现两个明显峰值,即出现双重一阶彩虹峰值;反之,当外层厚度大于内层时,只有一个峰值存在。 相似文献
996.
Shaoyong Wang Qi Zhu Shanjia Xu 《International Journal of Infrared and Millimeter Waves》2007,28(7):513-519
Design of a novel compact millimeter-wave microstrip antenna with wide bandwidth and broad beamwidth is presented. In the
structure, multiple layers and a parasitic element as well as a coupling aperture are used to achieve wideband, while a conducting
cylinder and the coupling aperture are used to obtain broad beamwidth. Finally, phased array with eight present elements has
been designed as an example. Compared to traditional microstrip antennas and arrays, present antenna and array are of smaller
dimension and broader beamwidth as well as wider bandwidth. 相似文献
997.
998.
塑料类高分子材料甲基丙烯酸甲酯-亚克力(PMMA)圆柱中亚音速Rayleigh波低频隧穿共振可引起反向散射增强,在低频标准散射体设计等领域具有重要应用价值.提出一种微弱形变的规则波纹表面结构,可实现水中PMMA圆柱反向散射低频共振频率的无源调控.利用微扰法推导了水中微弱形变规则波纹圆柱反向散射低频共振频率偏移的近似解,讨论了波纹微扰系数、周期对规则波纹圆柱共振频率偏移的影响规律.基于Rayleigh波相位匹配方法分析了低频共振频率偏移的机理.研究表明:微弱形变规则波纹圆柱中亚音速Rayleigh波沿微弱形变波纹表面传播,与光滑圆柱体相比,传播路径的改变引起Rayleigh波传播相位变化,导致了Rayleigh波低频共振频率发生偏移.最后开展了微弱形变规则波纹圆柱体声散射特性水池实验,获取了其反向散射共振频率,明显观察到了规则波纹圆柱共振频率偏移现象,与理论预报结果吻合较好. 相似文献
999.
Ying Zhao Songjie Du Jianxu Ding Hongzhi Cui Xiaoyuan Zhan Jie Wu 《Crystal Research and Technology》2016,51(9):524-529
The bcc like structure of cubic bismuth phosphate (Bi13.1POδ) crystal, makes (111) facets hardly be exposed according to the Bravais rule. In this paper, we are focusing on the exposure of smooth (111) facets on cubic bismuth phosphate crystal, and particularly on the process of the smooth (111) facets transforming to stepped and coarse (111) facets by varying the growth conditions, such as the Bi: P ratio of the raw materials, pH values, EDTA concentrations, etc. The results revealed that lower Bi: P ratio was beneficial to smooth (111) facets and with a rise of Bi: P ratio, the (111) facets transformed from smooth surface to stepped and coarse surfaces. With a moderate Bi: P ratio and EDTA concentrations, novel facets with high index were derived on the (111) facets, which were deduced as (611) facets. Additionally, the growth mechanism of the process was summarized in terms of the growth units affected by the Bi: P ratio, pH values and the presence of EDTA. 相似文献
1000.
The flow past a cylinder in a channel with the aspect ratio of 2:1 for the upper convected Maxwell (UCM) fluid and the Oldroyd-B fluid with the viscosity ratio of 0.59 is studied by using the Galerkin/Least-square finite element method and a p-adaptive refinement algorithm. A posteriori error estimation indicates that the stress-gradient error dominates the total error. As the Deborah number, De, approaches 0.8 for the UCM fluid and 0.9 for the Oldroyd-B fluid, strong stress boundary layers near the rear stagnation point are forming, which are characterized by jumps of the stress-profiles on the cylinder wall and plane of symmetry, huge stress gradients and rapid decay of the gradients across narrow thicknesses. The origin of the huge stress-gradients can be traced to the purely elongational flow behind the rear stagnation point, where the position at which the elongation rate is of 1/2De approaches the rear stagnation point as the Deborah number approaches the critical values. These observations imply that the cylinder problem for the UCM and Oldroyd-B fluids may have physical limiting Deborah numbers of 0.8 and 0.9, respectively.The project supported by the National Natural Science Foundation of China (50335010 and 20274041) and the MOLDFLOW Comp. Australia. 相似文献