弹性波层析成像在灌注桩检测中应用

在阐述弹性波层析成像研究历史和现状的基础上,采用弹性波层析成像检测混凝土灌注桩的质量。计算中采用了改进的射线追踪方法和最小二乘QR法,并结合一个工程实例证明了该方法的科学性、可行性和应用效果。     

三维结构下全路径迭代射线追踪方法

基于Fermat原理对三维任意界面情况下的2点间射线追踪问题进行了研究。通过采用一阶Taylor不完全展开等办法,给出了三维情况下全路径迭代射线追踪算法的计算格式,并在几个三维介质模型上进行了射线追踪模拟计算。计算结果表明:它的计算速度相当快,且其计算精度可以根据需要达到任意要求,为三维结构下地震偏移和层析成像提供了一种可行的射线追踪方法。     

超声波层析成像技术在混凝土构件中的应用研究

目前,混凝土构件超声测缺一般都采用超声波透过混凝土的信号来判别缺陷状况,该方法对缺陷的大小、性状等难以给出定量的结果,属于定性和半定量方法。在混凝土构件超声检测中引入层析成像技术,首先叙述层析成像的基本理论和算法,并在射线追踪过程中采用二阶段射线追踪方法,在反演过程中采用最小二乘法(LSQR)来保证计算的精度,通过工程实例可以说明采用超声波层析成像技术可提供整个构件测试断面上的完整信息,缺陷评估更直观、准确,信息量更丰富。     

射线追踪法的现状和展望

射线追踪法作为一种快速有效的波场近似计算方法,不仅对研究波在介质中的传播路径有重要意义,而且能快速反演并成像。在收集、研究国内外相关文献的基础上,介绍射线追踪法的现状及今后发展的展望。     

混凝土结构孔洞的高频弹性波散射

基于弹性波动理论,利用波函数展开法,对混凝土结构孔洞的高频弹性波散射问题进行了研究,给出了结构中弹性波波场分析解的表达式,分析了不同入射波频率情况下的散射波场特征。分析表明,入射波频率的改变对波的衰减特征有重要影响。     

超声波CT缺陷检测系统开发方法研究

在层析成像方法的基础上,设计采用超声波检测、射线追踪技术和层析成像反演技术的超声波层析成像缺陷检测系统,利用已有的用不同的Visual C++、Visual Basic、Fortran开发工具开发的功能模块,借助于软件工程的设计原则和面向对像的程序设计方法,将各自生成的功能模块集成为一体。系统具有丰富的图形交互环境和图形交互工具,用户只需利用图形交互环境和图形交互工具就可实现检测过程,通过试验验证了该系统可检测混凝土构件中缺陷的大小和形状。     

激发频率对钢筋混凝土声波CT反演精度的影响

采用数值模拟方法研究了激发频率对声波层析成像技术检测钢筋混凝土构件内缺陷反演精度的影响。利用有限元分析软件建立不同配筋率的钢筋混凝土模型,对弹性波在钢筋混凝土构件中的传播进行模拟和计算,在此基础上应用声波层析成像分析软件对其剖面成像,对比激发频率分别为100 k Hz和200 k Hz的声波层析成像反演结果。研究表明不同激发频率对声波层析成像技术检测不同配筋率混凝土缺陷具有一定影响,当激发频率为200 k Hz,且配筋率比较小时,声波层析成像技术对混凝土构件中孔洞缺陷与钢筋的检测比较敏感;而当激发频率为100 k Hz,且配筋率比较大时,声波层析成像技术能够定位混凝土构件内缺陷位置,伪像干扰小。     

一种快速水声目标波达方向估计方法

以基追踪为重构算法的水声目标波达方向估计方法在实际的应用中往往运算速度较慢,针对这一问题,在分析水声目标空间稀疏特性的基础上,结合压缩感知理论框架下波达方向估计的特点,提出一种快速水声目标波达方向估计方法。该方法通过逐步减小逼近参数的方式来得到l_0范数最优解,实现水声目标信号的波达方向估计。通过计算机仿真从成功率、运算时间、分辨角度等多个方面与基追踪算法进行比较分析,实验表明:在成功率和分辨角度上所提出算法与基追踪算法性能相当,但运算时间却仅仅是基追踪算法的1/11。     

弹性波CT关键技术与应用实例

本文首先对弹性波CT基本原理进行简要介绍,然后对弹性波CT关键技术进行较为详细的分析说明。提出椭圆约束方法实现更快速射线追踪,同时指出应用数据校正和误差控制等方法技术,能够有效提高解的唯一性和成像精度。最后通过应用实例对所述方法技术的正确性和实用性进行了充分验证。     

基于贝叶斯准则的双侧CT图像重建研究

对弹性波CT层析成像技术中增加检测点阵列的数量的问题进行了研究,提出了基于贝叶斯准则的缺陷识别方法,指出该方法达到了提高反演图像分辨率和缺陷判别的准确度的效果。     

An estimate of the time-varying temperature field of the main reflector and subreflector of the Shanghai 65 m radio telescope under solar illumination

The time-dependent temperature fields of the reflectors of the Shanghai 65 m radio telescope are investigated numerically, taking account of the non-uniform heating of the reflector surfaces due to solar illumination and the constantly changing ambient air temperature. This paper utilizes a ray casting algorithm to calculate the borderline separating the reflector areas in shadow and in sunshine, aiming to provide an accurate calculation of the solar energy absorbed. Then a ray tracing algorithm is utilized to calculate the total solar energy that is reflected by the main reflector area and received by the subreflector surface area. Finally, the solar energy is used as the main thermal load on the reflector surface to numerically examine the temperature distribution on both the main reflector and the subreflector. The results illustrate that the time-varying temperature fields of the reflectors of a radio telescope due to asymmetric solar illumination can be accurately simulated utilizing the ray casting algorithm and the ray tracing algorithm. The occurring periods and avoidance zones of the overheating of the subreflector are identified, among which the maximum temperature of the subreflector reaches 144.9°C. These dangerous observation zones should be avoided during the operation of the radio telescope.     

Optimization of the Geometries of Biconical Tapered Fiber Sensors for Monitoring the Early‐Age Curing Temperatures of Concrete Specimens

In this article, a geometrical optimization procedure using biconical tapered fiber sensors is proposed for monitoring the early‐age curing temperatures of concrete specimens. The geometries of the sensors are theoretically optimized by the ray‐tracing theory. The results of the theoretical analysis show that the performance of the sensors is heavily influenced by Evanescent Waves, which are due to the tunneling rays and are fully escaped by tapering the fiber. The effects of the geometrical parameters, including the taper ratios, taper lengths, and ray launch angles, as well as the surrounding temperatures, on the behavior of the sensors are studied numerically. The numerical results demonstrate that higher performance of the proposed optimized sensors can be achieved by a longer taper length and smaller taper ratio combined with an initial ray launching angle of 0.01 rad. An experimental study on early‐age curing temperature monitoring of concrete specimens with the biconical tapered fiber sensors was carried out. The experimental measurements agree well with the theoretical results.     

The central sunlighting system: development and validation of an optical prediction model

This article presents the development of a sufficiently accurate and reliable optical model to predict the lighting and thermal performance of the central sunlighting system (CSS). The model is based on the ray tracing technique to compute the amount of sunlight flux transmission through the light guide to interior spaces of buildings, and absorption of solar radiation within the components of the CSS, which may become solar heat gains indoors. The model is validated using a detailed ray tracing technique and field measurements carried out on a previous prototype. The validation results show that the model predictions are in good agreement with the ray tracing and measurement results. The model can be integrated in existing fenestration design tools, or in whole-building energy simulation software, with significantly lower calculation time compared to the full integration of suitable lighting simulation software.     

应变局部化带追踪模拟的复合单元方法与应用

利用复合单元技术考虑应变局部化带的影响，提出一种新的追踪应变局部化带发展的算法。通过直接降低材料参数来体现应变局部化带内软化的影响，对所有可能发生的应变局部化带的位置和方向进行记录与模拟；借用节理裂隙的统计方法拟合局部化带，得到破坏通道；然后重新对该破坏通道和原有网格信息进行复合单元的拓扑信息生成，并在此基础上重新进行计算，对局部化带发展追踪过程进行复核。该算法不要求追踪路径的连续性，并可充分考虑各局部化带间的相互影响。边坡算例证实所提出方法的可行性和可靠性，宝珠寺大坝的数值计算与模型试验的对比分析则说明提出的方法已具备解决实际工程问题的能力。     

Buckling and postbuckling behaviors of imperfect cylindrical shells subjected to torsion

Buckling and postbuckling behaviors of imperfect cylindrical shell subjected to torsion are investigated. The governing equations are based on the Karman–Donnell-type nonlinear differential equations. A boundary layer theory of shell buckling is applied to obtain the analytic solutions that meet the boundary conditions strictly. A singular perturbation technique is employed to determine the buckling loads and postbuckling equilibrium paths. Numerical results reveal that the current theory gives quite good estimates of the postbuckling paths of cylindrical shells. The effects of the geometric parameters on the buckling and postbuckling behaviors of the cylindrical shells are analyzed. It is confirmed that the postbuckling equilibrium paths of cylindrical shells subjected to torsion are unstable and the relatively shorter shells have higher postbuckling equilibrium paths. Finally, the effects of the initial imperfections on the buckling and postbuckling behaviors of the cylindrical shells are clarified. The illustrated results of the imperfect shells with different initial transverse deflections show that extremely small imperfections do indeed reduce the buckling loads and make the postbuckling equilibrium paths be lower. The buckling and postbuckling of cylindrical shells under torsion exhibit obvious imperfect sensitivity. Furthermore, the effects become greater following with the larger imperfections.     

Theoretical modelling and experimental evaluation of the optical properties of glazing systems with selective films

Transparent spectrally selective coatings and films on glass or polymeric substrates have become quite common in energy-efficient buildings, though their experimental and theoretical characterization is still not complete. A simplified theoretical model was implemented to predict the optical properties of multilayered glazing systems, including coating films, starting from the properties of the single components. The results of the simulations were compared with the predictions of a commercial simulation code which uses a ray tracing technique. Both models were validated thanks to several measurements carried out with a spectrophotometer on single and double sheet glazings with different films. Results show that both ray tracing simulations and the theoretical model provide good estimations of optical properties of glazings with applied films, especially in terms of spectral transmittance.     

结构非线性平衡路线跟踪算法的探讨

非线性静力稳定理论中一个比较重要的环节，就是结构亘线性平衡路线跟踪算法的选择。本文首先介绍了常用的结构非线性平衡路线跟踪算法，然后，对这些算法进行了比较，最后，简要说明了这些算法在程序实施时应注意的几个问题。     

Optimisation of building form for solar energy utilisation using constrained evolutionary algorithms

In this paper we describe a new methodology for optimising building and urban geometric forms for the utilisation of solar irradiation, whether by passive or active means. For this we use a new evolutionary algorithm (a hybrid CMA-ES/HDE algorithm) to search the user-defined parameter space, within defined constraints. The fitness function, solar irradiation, is predicted using the backwards ray tracing program RADIANCE in conjunction with a cumulative sky model for fast computation.Application of this technique to three very different scenarios suggest that the new method consistently converges towards an optimal solution. Furthermore, with respect to configurations subjectively chosen to be intuitively well performing, annual irradiation is increased by up to 20%; sometimes yielding highly non-intuitive but architecturally interesting forms.