光学观测中太阳夹角的分析与计算

对影响光学观测效果的太阳夹角计算方法进行了研究。首先给出了太阳夹角的定义及计算公式。然后重点研究了太阳视位置的计算方法,比较了几种赤纬角计算方法,给出了一种改进的时角计算方法,实现了高精度的太阳视位置计算,并对其计算精度进行了分析。最后提出了在实际光学观测应用中的太阳夹角计算算法。实验表明,太阳视位置计算精度比传统数值近似方法高一个数量级,能够满足光学观测中太阳光照分析的需要。     

船用增压锅炉的热平衡计算方法研究

研究了船用增压锅炉的热平衡计算方法。文章简要叙述了增压锅炉烟气侧的工作过程,重点分析了涡轮增压机组在不同锅炉负荷下功率、热力计算及热平衡计算方法。在实例计算部分,验证了增压机组的热损失数学表达式,并分析其计算结果,最终证明计算方法的正确性。     

任意倾斜角度下的永磁导轨感应磁场解析计算

平行移动式自稳定高温超导块材磁悬浮数值模拟计算包括永磁导轨感应磁场的计算。无限长的永磁轨道结构具有多样性。通过对称分布永磁轨道磁场的解析计算导出了任意倾斜角度下永磁轨道磁感应强度解析计算方法。采用此方法,成功计算出了多块交错排列的Halbach结构永磁轨道的感应磁场计算。采用该方法和商用Ansoft软件的有限元法分别对Halbach永磁轨道磁场进行了计算,对比计算结果表明,此方法是可行的,并且计算效率也远优于有限元法。     

温室内太阳净辐射量的计算方法

在现有理论及方法的基础上进行了相应推导 ,得出了进入温室内太阳净辐射量的计算方法。该计算方法可以为温室结构设计及能量计算提供理论依据。     

声学时域边界元法的时间卷积计算方法研究

核函数中保留Dirac函数的原型,形成关于时间的卷积积分,是声学时域边界元法中一种稳定、有效的时间数值积分计算方法 (CQ-BEM)。然而,传统CQ-BEM中卷积积分系数的获取有计算量大、耗时长,且对不同单元需要重新计算的问题,极大地降低了CQ-BEM法计算时域声场的效率。针对传统CQ-BEM积分系数计算效率低的问题,本文利用多项式展开定理给出了待求函数泰勒系数的解析表达与数值计算方法,建立了不同单元间待求系数的转换理论,可以在一次循环迭代内完成不同单元的积分系数的计算,大幅降低了计算量,提高了CQ-BEM方法的声场计算效率。脉动球源数值算例结果表明,在相同要求下,本文方法计算时间较传统方法减少50%以上,相对误差小5个数量级以上,且计算时间随单元数的增长率仅为传统方法的2.34%。因此,本文提出的系数计算方法能够有效提高CQ-BEM方法的时域声场计算效率,拓展了CQ-BEM在大型机电设备时域声场模拟的计算规模。     

消声器传递损失预测的边界元模态展开混合方法

将边界元法和解析方法结合形成一种混合方法用于计算消声器的传递损失,消声器被划分成若干个子结构,解析方法和边界元方法被分别用于计算规则结构和不规则结构的阻抗矩阵,不同子结构之间通过阻抗矩阵连接起来。为减少计算时间,采用一种基于模态配点法的简化方法。对单级膨胀腔、双级膨胀腔和穿孔管阻性消声器的传递损失进行了计算,混合方法计算结果与解析方法和三维数值方法计算结果吻合良好。分析了混合方法的计算效率并与传统子结构方法进行了比较,混合方法能明显节省计算时间。     

基于压缩感知的三维物体成像的简单计算方法

从压缩感知的原理入手,阐述了基于压缩感知的三维物体成像方法。为解决压缩感知三维物体成像计算量大的问题,重点提出了一种三维信息计算的简单方法。此方法通过两次压缩感知计算就可得到位于多个距离处的物体的三维信息,大大减少了计算量。对此方法进行了数值模拟,并分析了采样率的提高对于距离计算精度的影响;建立实际的三维成像系统,实验结果证明了这种方法的可行性。     

消声器传递损失预测的边界元模态展开混合方法

将边界元法和解析方法结合形成一种混合方法用于计算消声器的传递损失,消声器被划分成若干个子结构,解析方法和边界元方法被分别用于计算规则结构和不规则结构的阻抗矩阵,不同子结构之间通过阻抗矩阵连接起来。为减少计算时间,采用一种基于模态配点法的简化方法。对单级膨胀腔、双级膨胀腔和穿孔管阻性消声器的传递损失进行了计算,混合方法计算结果与解析方法和三维数值方法计算结果吻合良好。分析了混合方法的计算效率并与传统子结构方法进行了比较,混合方法能明显节省计算时间。      

核子CFP不同算法的计算量比较

对计算核子CFP的4种算法的计算量作了比较,结果表明:完备空间方法优于超完备空间方法,因子化方法优于未因子化方法,不同方法计算量差别很大。     

高温反应堆瞬发中子代时间计算

高温核反应堆在磁流体发电和核火箭等领域有良好的应用前景。高温反应堆具有堆芯温度高、结构复杂等特点,其中子物理性能参数的计算难度较大。研究了高温核反应堆瞬发中子代时间的计算方法,介绍了多种方法的计算原理和一种新型高温核反应堆的计算结果。研究表明,对于相同的反应堆模型,几种方法的计算结果符合较好,计算结果可信。     

The reconstruction of a spatially incoherent two-dimensional source in an acoustically rigid rectangular cavity

This paper applies Green's function modal expansion techniques to inverse source problems within an acoustically rigid rectangular cavity. In particular, solutions are developed for the reconstruction of a random spatially incoherent distributed source and a deterministic point source by using pressure-field measurements on adjacent walls. Such problems have seemingly not been addressed previously. Several example problems are studied in this paper. As is characteristic of inverse problems in general, numerical instabilities are encountered in the example problems addressed in this paper. These are linked to the notion of compactness in the forward operator, and dealt with using magnitude regularization and projections onto convex sets. The behavior of the example problems studied in this paper greatly deteriorates at frequencies near cavity resonances, particularly low frequency resonances (i.e., with ka < or = 2pi, where a is the smallest cavity dimension). Other results concerning the example problems are also given. A proof of compactness of an infinite rank version of the type of operator used in this paper is given in the Appendix. This proof implies that the convergence of the Green's function modal expansion in the kernel of the forward problem is related to the instability of the inverse problem. This implies that, if it suffices to know an integral of the source profile rather than the actual profile, the problem becomes more stable.     

An inverse problem in analytical dynamics

This paper presents an inverse problem in analytical dynamics. The inverse problem is to construct the Lagrangian when the integrals of a system are given. Firstly, the differential equations are obtained by using the time derivative of the integrals. Secondly, the differential equations can be written in the Lagrange equations under certain conditions and the Lagrangian can be obtained. Finally, two examples are given to illustrate the application of the result.     

A Proof of the Local Borg–Marchenko Theorem

In [2], [5] a “local” version of a basic uniqueness theorem in inverse spectral theory is given. This paper gives a simple proof of this theorem. Received: 6 November 2000 / Accepted: 8 November 2000     

求解非均匀介质中电场反问题的一个新方法

以由R³中多层介质电场的部分数据出发,确定R³中某一区域的形状为例,抽象为最优控制问题,证明了该问题的解的存在性。给出了有限元方法和图论相结合的新算法,根据这个算法,进行多种数值实验,得到了L²下各种计算结果。     

EFFECTIVE VIBRATION ANALYSIS OF IC ENGINES USING CYCLOSTATIONARITY. PART II—NEW RESULTS ON THE RECONSTRUCTION OF THE CYLINDER PRESSURES

This part addresses the feasibility of reconstructing the pressure trace in IC engine from non-intrusive structural vibration measurements by means of an optimal inverse filter. The problem is formally phrased into the general framework of cyclostationary processes introduced in Part I of this paper. It is proved that the optimal inverse filter is periodically varying. A number of guidelines are given for efficiently applying the proposed deconvolution scheme.     

Ultrasonic characterization of human cancellous bone using the Biot theory: inverse problem

This paper concerns the ultrasonic characterization of human cancellous bone samples by solving the inverse problem using experimental transmitted signals. The ultrasonic propagation in cancellous bone is modeled using the Biot theory modified by the Johnson et al. model for viscous exchange between fluid and structure. The sensitivity of the Young modulus and the Poisson ratio of the skeletal frame is studied showing their effect on the fast and slow wave forms. The inverse problem is solved numerically by the least squares method. Five parameters are inverted: the porosity, tortuosity, viscous characteristic length, Young modulus, and Poisson ratio of the skeletal frame. The minimization of the discrepancy between experiment and theory is made in the time domain. The inverse problem is shown to be well posed, and its solution to be unique. Experimental results for slow and fast waves transmitted through human cancellous bone samples are given and compared with theoretical predictions.     

A method of linearization for Painlevé equations: Painlevé IV, V

A method to linearize the initial value problem of the Painlevé equations IV, V is given. The procedure involves formulating a Riemann-Hilbert boundary value problem on intersecting lines for the inverse monodromy problem. This boundary value problem is reduced to a sequence of standard problems on single lines in a certain range of parameter space. Schlesinger transformations allow one to completely cover the parameter space. Special solutions are constructed from special cases of the Riemann problem as well.     

Quantum inverse scattering method and the Heisenberg ferromagnet

The quantum version of the inverse scattering method is formulated for the Heisenberg ferromagnet. The elements of the transition matrix for the corresponding auxiliary linear problem are the quantum analogue of the action-angle variables. In a continuous limit the model is shown to yield the quantum nonlinear Schrödinger equation.     

A new inverse approach for the equivalent gray radiative property of a non-gray medium using a modified zonal method and the complex-variable-differentiation method

Non-gray radiative properties of an absorbing, emitting, non-gray participating medium significantly increase the difficulty of solving the radiative transfer equation. This paper presents a new inverse approach for the equivalent gray radiative property of a non-gray medium. In this approach, the unknown equivalent gray radiative properties are treated as the optimization variables, and the errors to be minimized are the differences between the calculated temperatures and the measured ones. The measured data are simulated by solving the direct problem, in which a modified zonal method together with the Edwards exponential wide-band model is employed. In the inverse problem, the sensitivity coefficients are first calculated by the complex-variable-differentiation method, and then the least-square method and the Newton-Raphson iterative method are employed to minimize the target function. The effectiveness and efficiency of the inverse problem are demonstrated in an example, and another case is given to show the accuracy and potential of the proposed algorithm. The effects of the measurement error and the number of measurement points on the accuracy of the inverse analysis are also investigated in detail.     

Functional-analytical solution to an acoustic tomography problem, based on data from point transducers

A two-dimensional version of the functional-analytical algorithm for solving the inverse scattering problem is considered and modeled. Acoustic fields, transmitted and received by quasi-point transducers, are used as experimental data. The algorithm is mathematically rigorous and does not require either linearization of the models or iterations, making it attractive for a variety of applications in acoustic tomography.