基于板材超声散射方法的研究

对于板材焊接接头常用的超声检测方法是脉冲反射法,而超声反射法对于一些垂直于入射面的面状缺陷难于检出,并且上下表面的缺陷有一定的盲区。基于这些局限性,研究超声散射法能够很好的解决。由于超声束近似球面散射,提出一种散射模型为斜发直收同侧。试验证明,采用这种方法能够容易识别垂直于入射面的面状缺陷。     

低场永磁MRI导引聚焦超声肿瘤消融系统的研究

研究了低场永磁磁共振(Magnetic Resonance Imaging,MRI)导引的高强度聚焦超声(High Intensity Focused Ultrasound,HIFU)系统,使两者融合为一体。把磁共振的磁体设计为U字形,这样HIFU治疗头就可以放置于磁共振开口的上方;同时,在磁兼容、磁共振的快速成像、磁共振的测温、相控阵换能器、HIFU的治疗计划等方面做了一些研究。研究结果表明,在低场永磁的磁共振导引下,可以实现系统的所有设计功能,系统定位的图像比上一代B超导引的HIFU清晰,提高了实用性。     

基于文化转译的参数化智造非遗竹编产品开发案例研究

目的 破解传统竹编技艺在当代传承中面临的文化脱节、工序费时、产品滞销三重困境,探索非遗活化的系统解决方案。方法 构建“文化转译-智造升级-价值共生”协同模型,基于Grasshopper参数化技术解构黄梅挑花纹样与地标建筑意象,研发双通道映射算法以实现非遗符号的智能转化;开发模块化编织模型革新生产体系,搭建高校、工坊与文旅场景的弹性协作网络。结果 竹编灯具的光影交互设计使挑花图案识别率达到82%,生产效能较传统模式提升300%,校准文化转译参数38项,孵化文旅场景应用IP,带动县域工坊订单量的增长。结论 研究证实数字技术能在保留手工痕迹的前提下重构非遗生产逻辑,赋予传统符号参与当代生活美学的生命力。竹编智造模式为乡土工艺的现代化转型提供了“脉络梳理-延续创新-生态融合”范本,证明非遗可作为城乡文化交融的创新介质。     

不同正则化方法在船舶辐射噪声计算中对比与试验研究

为研究不同背景下不同正则化参数方法在船舶辐射噪声评估中的适用性,降低辐射噪声计算误差,介绍了基于工况传递路径分析(OTPA)的船舶辐射噪声计算方法,讨论了奇异值分解(SVD)法、基于L-curve和广义交叉验证(GCV)的Tikhonov正则化方法在辐射噪声传递函数求解问题上的适用性,并进一步提出基于准最优(Q-O)判...     

空气耦合超声斜入射法检测固体火箭发动机脱粘缺陷及成像技术研究

为实现固体火箭发动机复合材料壳体粘接结构的非接触在役检测,该文采用空气耦合超声斜入射反射法进行研究。构建空气耦合超声斜入射检测系统,根据理论和实验确定有效的入射角范围并得出最佳入射角度,使用不同频率的探头在最佳入射角度下进行斜入射横波法反射法C扫描成像,最后用图像处理方法对缺陷进行定量表征,并与穿透法C扫描结果进行对比。结果表明：当遇到缺陷时,信号幅值会增大;两种检测频率下,12°为最佳入射角,且频率越大,信号的衰减越大;使用420 kHz探头检测时获得的C扫描图像质量高于250 kHz。通过混合滤波、改进的区域生长图像分割、Canny算子边缘提取以及形态学平滑处理和细化等方法,有效提取缺陷边缘,可实现缺陷的定量表征,420 kHz探头定量精度明显高于250 kHz,且缺陷尺寸越大,该方法结果与穿透法结果越吻合。     

Microwave imaging: Reconstructions from experimental data using conjugate gradient and enhancement by edge-preserving regularization

A method for reconstructing the complex permittivity profile of lossy dielectric objects from measured scattered far-field data is presented. An iterative reconstruction algorithm based on a conjugate gradient method is derived from an integral representation of the electric field and applying a moment method solution. Results obtained from experimental data are shown for both known and unknown targets. Then, a new regularization procedure is developed to enhance the quality of the reconstruction. This method, based on a Markov random fields approach, models the object to be reconstructed by homogeneous areas separated by borderlike discontinuities. Finally, the enhancement is shown by the reconstruction of a polystyrene square cylinder. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 337–342, 1997     

非对称矩阵结构系统固有值分析的广义逆迭代法

本文提出一种求解非对称矩阵结构的固有值的数值方法-通过广义的逆迭代过程把一个大型非对称的二次特征值问题简化为小型的标准特征值问题.算法不涉及复数运算,也不需把n阶的二次问题变换为2n阶的线性问题.迭代是在原n阶规模上进行,从而保持了系统各矩阵稀疏、带状的特点.节省了存储量和计算机时.数值实验表明本方法具有良好的稳定性和精度.     

Extension of moment-method solutions to vector scattering by three-dimensional non-linear dielectric objects in free space

In this paper, we explore the possibility of applying the moment method to determine the electromagnetic field distributions inside three-dimensional bounded non-linear dielectric objects of arbitrary shapes. The moment method has usually been employed to solve linear scattering problems. We start with an integral equation formulation, and derive a non-linear system of algebraic equations that allows us to obtain an approximate solution for the harmonic vector components of the electric field. Preliminary results of some numerical simulations are reported.     

First-order and second-order adjoint methods for parameter identification problems with an application to the elasticity imaging inverse problem

We devise a fast and reliable computational framework for the elasticity imaging inverse problem of detecting cancerous tumors in the human body using an output least-squares (OLS) approach. From a mathematical standpoint, this inverse problem requires identifying a parameter in a mixed variational problem. We develop, in a continuous setting, a first-order adjoint method and two second-order adjoint methods. The continuous formulae are then used to devise a scheme for an efficient computation of the gradient and the Hessian of the OLS objective. We give detailed numerical examples.     

涉及离散变量的函数统计矩点估计法

点估计法对于仅包含连续随机变量的函数和系统的随机分析具有原理简洁清晰、操作简单易行的优点,并可以直接给出除均值和标准差之外的其他低阶统计矩。然而,对于客观存在的或者是需处理为的涉及离散随机变量的系统,现有的点估计法无能为力。为解决这一问题,该文基于一般随机系统的形式解析解,导出了涉及离散变量函数和系统的统计矩估计的理论表达式;然后,将其与现有的点估计法相结合,给出了涉及离散变量的函数和系统的低阶矩估计的点估计法;最后,通过理论推导和算例分析两种方式验证了建议方法的合理性和有效性,且指出该方法对包含离散变量的一般工程随机系统分析的适用性。     

利用线性抽样方法重建Dirichlet边界条件声波散射区域

线性抽样方法是考虑一个第一类线性积分方程中的参数从区域内部趋近散射区域边界时,该方程的解趋近于无穷大。本文在此基础上就Dirichlet边界条件的声波反散射问题,利用积分方程理论严格证明了线性抽样方法对其的可用性,具体数值例子表明该方法是有效的。     

Parametric semi-blind deconvolution algorithm with Huber–Markov regularization for passive millimeter-wave images

Passive millimeter-wave (PMMW) images often suffer common problems of noise and blurring. A new method is proposed to estimate the instrument response function (IRF) and desired image simultaneously. The proposed variational model integrates the adaptive weight data term, image smooth term, and IRF smooth term. The major novelty of this work is that Huber–Markov regularization is adopted for PMMW image restoration, which can preserve structural details as well as suppress noise effectively. The IRF is parametrically formulated as a Gaussian-shaped function based on experimental measurements through the utilized PMMW imaging system. The alternation minimization iterative method is applied to achieve the IRF width and desired image. Comparative experimental results with some real PMMW images reveal that the proposed approach can effectively suppress noise, reduce ringing artifacts, and improve the spatial resolution.