圆对称模激励圆形介质棒天线反射特性的分析

本文用一种新的思路来分析H(01)或E(01)波激励下圆形介质棒天线的反射特性。与常规的从场源关系出发来分析天线问题不同，本文的方法从求解介质波导结构的色散特性入手，从散射的角度将天线辐射问题转化为表面波和空间波的传输问题，从而使分析过程得到了很大的简化。     

Geometric Hermite interpolation with circular precision

We present several Hermite-type interpolation methods for rational cubics. In case the input data come from a circular arc, the rational cubic will reproduce it.     

Study of the hydraulic properties of the cylindrical crested weirs

Since the cylindrical and circular crested weirs are economical and easily made compared to some other weirs, they can be used to measure the flow velocity, the water discharge and flow surface control structures in the canals and reservoirs. In this paper, the hydraulic properties of the cylindrical and circular crested weirs, such as the discharge coefficient, the depth on the crest of the weir and the energy loss in 18 laboratory models categorized in 5 categories have been investigated. The results of the experiments indicated that in both the cylindrical and circular crested weirs by increasing the total partial head, the discharge coefficient increases and any changes in the upstream wall slope has no effect on the discharge coefficient. Also, the partial energy loss more occurs in the cylindrical weirs than the half shaped cylindrical weirs and by increasing the downstream inclination angle, the partial energy loss increases subsequently. The partial flow depth on the crest of both the cylindrical and half shaped cylindrical weirs is equal to 0.7 and by increasing of the upstream inclination angle, the partial flow depth on the crest in the values greater than 0.6, increases slightly and the downstream inclination angle changes of the partial flow depth has no effect on the crest.     

Axisymmetric alternating direction explicit scheme for efficient coupled simulation of hydro-mechanical interaction in geotechnical engineering—Application to circular footing and deep tunnel in saturated ground

Explicit solution techniques have been widely used in geotechnical engineering for simulating the coupled hydro-mechanical (H-M) interaction of fluid flow and deformation induced by structures built above and under saturated ground, i.e. circular footing and deep tunnel. However, the technique is only conditionally stable and requires small time steps, portending its inefficiency for simulating large-scale H-M problems. To improve its efficiency, the unconditionally stable alternating direction explicit (ADE) scheme could be used to solve the flow problem. The standard ADE scheme, however, is only moderately accurate and is restricted to uniform grids and plane strain flow conditions. This paper aims to remove these drawbacks by developing a novel high-order ADE scheme capable of solving flow problems in non-uniform grids and under axisymmetric conditions. The new scheme is derived by performing a fourth-order finite difference (FD) approximation to the spatial derivatives of the axisymmetric fluid–diffusion equation in a non-uniform grid configuration. The implicit Crank-Nicolson technique is then applied to the resulting approximation, and the subsequent equation is split into two alternating direction sweeps, giving rise to a new axisymmetric ADE scheme. The pore pressure solutions from the new scheme are then sequentially coupled with an existing geomechanical simulator in the computer code fast Lagrangian analysis of continua (FLAC). This coupling procedure is called the sequentially-explicit coupling technique based on the fourth-order axisymmetric ADE scheme or SEA-4-AXI. Application of SEA-4-AXI for solving axisymmetric consolidation of a circular footing and of advancing tunnel in deep saturated ground shows that SEA-4-AXI reduces computer runtime up to 42%–50% that of FLAC's basic scheme without numerical instability. In addition, it produces high numerical accuracy of the H-M solutions with average percentage difference of only 0.5%–1.8%.     

Model testing study on engineering performances of circular helicoid piles during the whole process of installation and bearing in sandy soil

The circular helicoid pile (CH pile) is a new type of special-shaped pile that has been developed in Japan and South Korea in the past decade and has been widely used in the fields of construction, transportation, natural energy and agriculture due to its excellent compressive and pullout bearing performances. Consequently, this new type of pile has good engineering application prospects. However, as an innovative engineering structure, the CH pile is not widely known by geotechnical engineers worldwide. The geometric structure of the CH pile is similar to a circular helicoid in differential geometry. Therefore, the pile-soil interaction problem cannot be reduced to a plane strain problem or an axisymmetric problem in theoretical research. In view of this, dry silica sand was used as the model foundation in this study, and a model test device and method that can effectively reflect the installation process and loading-bearing service state of CH piles were developed. Under different installation methods, pile structures and foundation soil conditions, 90 model tests were carried out to evaluate the engineering performances of CH piles during the whole process of installation and bearing, including the installation performances during the installation process, the compressive bearing performances under axial compressive loading and the pullout bearing performances under axial pullout loading. Compared with steel sheet piles and steel pipe piles, CH piles have better engineering performance and more economic benefits from the aspects of installation, construction, recycling, timeliness of engineering application, and the relative relationship between bearing capacity and pile mass.     

Shear testing on rock tunnel models under constant normal stress conditions

Large shear deformation problems are frequently encountered in geotechnical engineering. To expose the shear failure mechanism of rock tunnels, compression-shear tests for rock models with circular tunnel were carried out, including single tunnel and adjacent double tunnels. The failure process is recorded by the external video and miniature cameras around the tunnel, accompanied by real-time acoustic emission monitoring. The experiments indicate that the shearing processes of rock tunnel can be divided into four steps: (i) cracks appeared around tunnels, (ii) shear cracks and spalling ejection developed, (iii) floor warping occurred, and (iv) shear cracks ran through the tunnel model. Besides, the roughness of the sheared fracture surface decreased with the increase in normal stress. Corresponding numerical simulation indicates that there are tensile stress concentrations and compressive stress concentrations around the tunnel during the shearing process, while the compressive stress concentration areas are under high risk of failure and the existence of adjacent tunnels will increase the degree of stress concentration.     

Evaluation of passive confinement in CFT columns

This paper presents the experimental results of 32 axially loaded concrete-filled steel tubular columns (CFT). The load was introduced only on the concrete core by means of two high strength steel cylinders placed at the column ends to evaluate the passive confinement provided by the steel tube. The columns were filled with structural concretes with compressive strengths of 30, 60, 80 and 100 MPa. The outer diameter (D) of the column was 114.3 mm, and the length/diameter (L/D) ratios considered were 3, 5, 7 and 10. The wall thicknesses of the tubes (t) were 3.35 mm and 6.0 mm, resulting in diameter/thickness (D/t) ratios of 34 and 19, respectively. The force vs. axial strain curves obtained from the tests showed, in general, a good post-peak behavior of the CFT columns, even for those columns filled with high strength concrete. Three analytical models of confinement for short concrete-filled columns found in the literature were used to predict the axial capacity of the columns tested. To apply these models to slender columns, a correction factor was introduced to penalize the calculated results, giving good agreement with the experimental values. Additional results of 63 CFT columns tested by other researchers were also compared to the predictions of the modified analytical models and presented satisfactory results.     

Axial strength of circular concrete-filled steel tube columns — DOE approach

This paper presents the effect of changes in diameter of the steel tube (D), wall thickness of the steel tube (t), strength of in-fill concrete (f_cu), and length of the tube (L) on ultimate axial load (P_ue) and axial shortening at the ultimate point (δ_ue) of circular Concrete Filled steel Tubes (CFT). Taguchi’s approach with an L9 orthogonal array is used to reduce the number of experiments. With the help of initial experiments, linear regression models are developed to predict the axial load and the axial shortening at the ultimate point. A total of 243 circular CFT samples are tested to verify the accuracy of these models at three factors with three levels. The experimental results are analyzed using Analysis Of Variance to investigate the most influencing factor on strength and axial shortening of CFT samples. Comparisons are made with predicted column strengths using the existing design codes, AISC-LRFD-2005 and EC4-1994.     

圆形槽波导-波纹圆形槽波导模式变换器的仿真设计

应用基于有限元方法的仿真软件HFSS,分析和设计了圆形槽波导-波纹圆形槽波导模式变换器。变换器由具有渐变波纹深度的波纹圆形槽波导构成,可实现TE11到HE11的模式转换。分析表明,变换器的长度和第一个波纹的深度是影响其性能的主要因数。在保持变换器优化长度不变的条件下,调整波纹周期、增加波纹数目和波纹宽度对改善变换器的性能效果不明显。所设计的具有5个渐变深度波纹的模式变换器,在中心频率36GHz上回损可达30dB。变换器实测的结果与仿真分析之结论吻合较好。     

密封油对大型储气柜柜体抗震性能的影响分析

在稀油密封储气柜结构中,密封油存储于活塞四周与柜体壁板之间的环形油沟中,在储气压力下与活塞一起悬浮于柜体中。随着储气柜向大容量、高压力方向发展,密封油的重量显著增加。在气柜结构的地震反应计算模型中,如何考虑密封油对气柜柜体抗震性能的影响,鲜有文献介绍。本文依据气柜的实际结构,将密封油视为环形液体阻尼器,建立气柜结构的CLD计算模型。以某30万m~3正多边形气柜为例,选择3条地震波,应用状态空间分析法,利用MATLAB软件实现2种计算模型的地震反应分析。计算结果对比分析表明,密封油对柜体抗震具有明显的减震效果,属于有利影响。