Acoustic emission technique used for detecting early stages of precipitation during aging of Inconel 625

Aging behavior of Inconel 625 has been studied at 540 °C. The Ni₂(Cr,Mo) phase, found in this material only after a long service life, has been detected along with the γ^″ phase after a short aging. Acoustic emission technique has been found sensitive enough to detect early stages of precipitation.     

Global warming and carbon taxation Optimal policy and the role of administration costs

This paper develops a model relating CO₂ emissions to atmospheric concentrations, global temperature change and economic damages. For a variety of parameter assumptions, the model provides estimates of the marginal cost of emissions in various years. The optimal carbon tax is a function of the margical emission cost and the costs of administering the tax. This paper demonstrates that under any reasonable assumptions, the optimal carbon tax is zero for at least several decades.     

Numerical calculations of acoustic emission

Two computer programs which solve the partial differential equations for sound propagation numerically are applied to the study of problems in acoustic emission. The programs use finite difference and finite element techniques to calculate sound fields due to distributions of sources in complex geometries in two dimensions. The potential to handle more complex geometries and to model more realistic sources is the main advantage of these numerical calculations over the analytic calculations. The main disadvantage of the numerical techniques is the cost of obtaining results since a large main frame computer or supercomputer is required. Both numerical methods are found to agree well with analytic calculations using Green's functions. The finite difference method agrees very well with the analytic calculations but, in its current implementation, is much slower and contains more numerical noise compared to the finite element method. The finite element method has the additional advantage of being capable of handling more complex geometries than the finite difference method.     

Nonlinear response of an ideal gas bubble to ambient pressure change in a quiescent fluid

This paper is concerned with the small-amplitude oscillations of a bubble composed of an ideal gas in response to anabrupt change in the ambient pressure field. Specifically, we consider the bubble response to a pressure pulse and a pressure step in an otherwise quiescent fluid. The method of analysis employed in the present study is a standard two-timing expansion to eliminate a secular behavior encountered in the asymptotic expansion. In the impulse response the secularity is self-induced due solely to the nonlinearity of the problem whereas the secularity in the step response arises from the change in the equilibrium bubble volume caused by the ambient pressure change. The two-timing solution for each response shows that the secularity modifies the natural frequency of the radial oscillation. Further, the critical intensity of either the pressure pulse or the pressure step for existence of the steady-state bubble radius is determined from the frequency modulated solution and the stability of the bubble response is also discussed in terms of the bubble compressibility and heat transfer across the interface.     

ADCP在河道流量测验中的应用及误差分析

介绍了声学多普勒剖面仪（ADCP）流量测验原理、计算方法。对ADCP与传统测验方法在梧州站的比测试验进行分析,在中、低水流量相关关系较好,中、高水相关性较差,流量越大相对误差越大。探讨了ADCP流量测验中产生误差的原因,并对其误差提出了相应的解决对策。     

金沙江攀枝花江段入河排污口优化布设方法研究

针对目前入河排污口布设规划方法不完善的现状,以金沙江攀枝花江段为对象,以指标评分法为基础,综合水域纳污适宜性指标,排污口建设适宜性指标和排污口改造经济性指标,建立了入河排污口位置优化模型。以遗传算法为基础,以水功能区水质管理目标,水功能区纳污能力和区域排污需求量为限制条件,建立了入河排污口排污量规划模型。利用上述模型,优选出该江段15个最优排污单元,并计算出现状年和规划年15个规划排污口COD和NH3-N入河排污量分配方案,可满足地方经济发展的排污需求,同时也满足水功能区水质管理目标和纳污总量控制目标。     

无人水下航行器声自导技术研究

声自导技术的基础是波束形成技术,对波束形成技术的研究能够让我们更好地提高水下航行器的自动导引能力。本文首先对声自导系统的模型和基本职能进行了简单介绍,然后对波束形成技术和方位估计（参数估计）技术在无人水下航行器声自导技术上的应用进行了初步的研究,为我们将来发展新型无人水下航行器提供了一定的理论基础。     

声波测井中首波的物理机制

本文阐明了声波测井中的首波是波动方程的非线性效应,在井内外介质均为理想弹性体的情况下,导出了首波的解析表示式,指出它是一种共振模式,无轴向几何衰减。首波不是“临界、折射波至”,临界折射波不存在。几何声学不适用于声波测井。     

基于虚拟仪器的综合式无损检测系统

综合式无损检测系统是引入虚拟仪器概念，利用计算机系统的强大资源和LabVIEW软件，集超声、涡流和声阻三种探伤方法于一体的检测系统。实践应用证明，该系统可实现飞机探伤工作快速、机动和高效的要求，提高检测的可靠性。     

小波变换在声发射检测中的应用

在综合描述声发射信号特点和小波变换基本原理的基础上，结合实例介绍同时在时域和频域具有局部分析能力的信号处理方法-小波变换在声发射信号的特征提取、时频分析和噪声去除等方面的应用。