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1.
介质反射系数的反演方法及其计算机实现   总被引:1,自引:0,他引:1  
1 引言 本文考虑横向均匀的声波介质,利用脉冲平面波垂直入射,根据表面测量数据来直接反演介质的反射系数. 由于介质反射系数与介质声阻抗有着相互依赖的关系,人们以前的注意力都主要集中在声阻抗的反演问题上.如Syms讨论了解的存在性、唯一性等理论问题.张关泉从一维波动方程出发,研究了由阻抗反演声速的问题.顾桂定和张关泉就声阻抗的反演做过数值实验.Bube等人也对声阻抗反演问题进行过探讨. 本文从声波方程和应力—应变方程的联立方程组出发,导出一种直接反演介质反射系数的数值方法,不需要先求声阻抗,再由声阻抗求反射系数.值得指出的是利用这种方法可以导出一种非常有效的同时反演介质声速和密度的计算方法.详见文献[4]. 就本文提出的算法,利用SGI工作站做了大量数值实验,结果表明本算法稳定性好、精确度高.同时给出了由反射系数求声阻抗的例子.  相似文献   

2.
讨论三斜晶体介质半空间应力自由边界处三维平面波的传播.给出了1个寻找三维准P(qP)、准SV(qSV)和准SH(qSH)波的所有3个相速度解析表达式的方法.得出了三斜介质中qP、qSV、qSH波反射系数振幅比的三维闭式解,将其用于研究不同入射角时,对应的反射系数的数值变化,给出了不同极角和方位角时的图示.最后通过数值实例表明,与二维的情况相比较,三维各向异性对反射系数的影响更明显.  相似文献   

3.
本文就平板模型讨论核反应堆边界反射系数的辨识问题,在一边被墨体包围,介质非均匀,散射和裂变各向同性的情形下,我们给出了边界反射系数最佳辩识存在的充要条件,以及最佳辩识满足的必要条件。  相似文献   

4.
本文讨论介质的间断面和介质参数变化同时存在时,层系的反射系数问题.在地球物性参数反问题中,这样的模型更切合实际.第一部分给出层系反射系数的表达式;第二部分讨论有关的数学理论.  相似文献   

5.
宋德功  朱广田 《应用数学》1994,7(2):169-173
本文就平板模型讨论核反应堆边界反射系数的辨识问题。在一边被黑体包围,介质非均匀,散射和裂变各向同性的情形下,我们给出了边界反射系数是佳辨识存在的充要条件,以及最佳辨识满足的必要条件。  相似文献   

6.
使用线性粘滞的多孔弹性介质模型,解决在弹性介质和非饱和多孔弹性介质分界面上平面P波的反射与透射问题,这里的非饱和多孔介质中固体骨架被两种相互耦合的流体(液体和气体)所充满.通过势函数的方法得到了振幅反射系数与振幅透射系数.然后推导得到入射波与反射波、透射波之间能量转换情况.研究发现:用振幅比和能量比所表示的反射系数与透射系数是与入射角度、饱和度、入射频率以及上下层介质的弹性常数有关的方程式.数值计算通过图形的形式表达出来,而且入射角度、频率及饱和度对振幅和能量的反射与透射系数的影响分别进行了讨论.证明了在整个波的传播过程中分界处并没有发生能量的耗散.  相似文献   

7.
本文讨论了电子浓度呈双指数分布的等离子体鞘套的反射系数与穿透系数。用最小二乘法把鞘套的电子浓度分布参数拟合成双指数分布。由特殊函数来表示的波动方程的解被简化成初等函数,从而获得了物理概念清晰,便于数字计算的公式。用数字结果说明鞘套的反射系数和频率、电子浓度以及鞘套的厚度的关系。  相似文献   

8.
本文以飞行器再入大气层后的通信障碍为背景,考虑了两个问题:一、平面波入射到非均匀等离子体平面层上时的反射系数与传输系数,其中等离子体层的电子密度分布取非对称的双指数分布与正态分布;二、圆柱飞行器上开槽天线辐射的电磁波穿越径向非均匀等离子体鞘的远场方向图.文中给出了反射系数及传输系数的显式表示及若干以图或表格表示的数值结果.  相似文献   

9.
时频分析方法是沉积旋回判别中常用方法.不同时频分析方法时频谱对沉积旋回的刻画能力、模式判别精度和稳定性大为不同,因而有必要加以分析和甄别,优选出一种能准确反映沉积旋回频率变化趋势的时频分析方法.采用波动方程正演模拟方法对正旋回、反旋回、正反旋回、反正旋回共四种旋回地层进行正演模拟;选取广义S变换、小波变换、Wigner-Ville时频分布、仿射类时频分布(尺度图)计算地震记录的时频谱.考察不同时频分析方法对沉积旋回单元的判别极限,及其对噪声、突变层、反射系数突变、旋回单元组合方式变化的适应性.研究发现,时域波形特征与旋回模式有一一对应关系,但其判别稳定性差.在多种时频分析方法中,仿射类时频分布(尺度图)不仅能有效压制Wigner-Ville时频分布的交叉项干扰,同时对随机噪声的随机频率能量也有很好的压制作用.仿射类时频分布方法通过对频谱进行平滑,模糊瞬时频谱变化细节,突出主要频率变化趋势,使得主频受小层厚度突变、反射系数突变、旋回单元组合方式变化的影响小,具有很好的稳定性,在四种方法中具有最好的沉积旋回判别能力.  相似文献   

10.
本文在L~1空间研究平板几何中具有零边界的迁移方程,通过证明具有反射边界条件的迁移算子的预解式的范数对反射系数连续依赖,得到了反射边界迁移算子的预解式一致收敛于零边界迁移算子的预解式,进而得到零边界下谱界和增长界相等.  相似文献   

11.
《Optimization》2012,61(11):2307-2320
We discuss accelerated version of the alternating projection method which can be applied to solve the linear matrix inequality (LMI) problem. The alternating projection method is a well-known algorithm for the convex feasibility problem, and has many generalizations and extensions. Bauschke and Kruk proposed a reflection projection algorithm for computing a point in the intersection of an obtuse cone and a closed convex set. We carry on this research in two directions. First, we present an accelerated version of the reflection projection algorithm, and prove its weak convergence in a Hilbert space; second, we prove the finite termination of an algorithm which is based on the proposed algorithm and provide an explicit upper bound for the required number of iterations under certain assumptions. Numerical experiments for the LMI problem are provided to demonstrate the effectiveness and merits of the proposed algorithms.  相似文献   

12.
Based on Fermat’s principle and the automatic optimization mechanism in the propagation process of light,an optimal searching algorithm named light ray optimization is presented,where the laws of refraction and reflection of light rays are integrated into searching process of optimization.In this algorithm,coordinate space is assumed to be the space that is full of media with different refractivities,then the space is divided by grids,and finally the searching path is assumed to be the propagation path of light rays.With the law of refraction,the search direction is deflected to the direction that makes the value of objective function decrease.With the law of reflection,the search direction is changed,which makes the search continue when it cannot keep going with refraction.Only the function values of objective problems are used and there is no artificial rule in light ray optimization,so it is simple and easy to realize.Theoretical analysis and the results of numerical experiments show that the algorithm is feasible and effective.  相似文献   

13.
Dynkin has shown how subsystems of real root systems may be constructed. As the concept of subsystems of complex root systems is not as well developed as in the real case, in this paper we give an algorithm to classify the proper subsystems of complex proper root systems. Furthermore, as an application of this algorithm, we determine the proper subsystems of imprimitive complex proper root systems. These proper subsystems are useful in giving combinatorial constructions of irreducible representations of properly generated finite complex reflection groups.  相似文献   

14.
A new algorithm for the calculation of the electron state of superlattice was proposed. From the electron wave point of view, the reflection and interference of electron wave at the interface of superlattice were accounted for and the electron states of the superlattice were discussed. The electron energy levels calculated using this algorithm are in good agreement with experimental results.  相似文献   

15.
In this article we study symmetric subsets of Rauzy fractals of unimodular irreducible Pisot substitutions. The symmetry considered is reflection through the origin. Given an unimodular irreducible Pisot substitution, we consider the intersection of its Rauzy fractal with the Rauzy fractal of the reverse substitution. This set is symmetric and it is obtained by the balanced pair algorithm associated with both substitutions.  相似文献   

16.
A two-variable analogue of the descents monomials is defined and is shown to form a basis for the dense Garsia-Haiman modules. A two-variable generalization of a decomposition of a P-partition is shown to give the algorithm for the expansion into this descent basis. Some examples of dense Garsia-Haiman modules include the coinvariant rings associated with certain complex reflection groups.  相似文献   

17.
The use of a simple Stein-rule method is discussed for estimating the repayment probability of a new credit applicant. It is argued that this type of procedure could provide a superior algorithm when a multiperiod view of repayments is taken and when there is a desire to balance the categorised estimate from the common discriminant scoring procedure with a fairer reflection of the applicant's actual performance.  相似文献   

18.
To reduce the well-known jamming problem in global optimization algorithms, we propose a new generator for the simulated annealing algorithm based on the idea of reflection. Furthermore, we give conditions under which the sequence of points generated by this simulated annealing algorithm converges in probability to the global optimum for mixed-integer/continuous global optimization problems. Finally, we present numerical results on some artificial test problems as well as on a composite structural design problem.  相似文献   

19.
In this paper we rigorously show the existence of solutions of a matrix equation which arises in the design of micro electronical circuits. This equation was studied by Szidarovszky and Palusinsk [Appl. Math. Comput. 64, 115-119(1994)], who also presented an iterative algorithm for its solution. We show, via an example, that this algorithm could converge extremely slow in certian cases. The solution can then be used to minimize the reflection coefficients of the active signals.

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20.
The simplex algorithm of Nelder and Mead is extended to handle nonlinear optimization problems with constraints. To prevent the simplex from collapsing into a subspace near the constraints, a delayed reflection is introduced for those points moving into the infeasible region. Numerical experience indicates that the proposed algorithm yields good results in the presence of both inequality and equality constraints, even when the constraint region is narrow. We note that it may be possible to modify and improve the algorithm by trying out variants.  相似文献   

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