一种评估自由场隔声测试中边缘衍射影响的数值分析模型

水声工程中,改善和提高自由场材料声学测试精度和可靠程度对水下航行器的声隐身设计具有非常重要的工程应用价值和现实意义。本文基于边界元和有限元方法对自由场材料隔声测试中存在的边缘衍射影响进行了数值评估模型研究,理论评估模型、分析条件和分析步骤均以实际测试为基础,并以水下钢板法向隔声测试为例计算分析了边缘衍射对轴向接收和偏轴向接收的影响程度和特点。研究表明,边缘衍射对自由场隔声测试的影响与样板几何尺寸和测试频率波长相对大小以及样板、声源和接收场点的空间几何配置等因素关系密切;与轴向接收相比,小角度偏轴向接收对抑制半波长与样板几何尺寸相当或远大于样板几何尺寸频段的边缘衍射影响较为有效,抑制效果与偏轴向距离及其相关轴向距离的选取有关。研究结果表明,该模型对更好地开展自由场材料隔声测试具有指导意义。

Pointwise Convergence of a Nonparametric Estimator of Regression in a Measurable Space Used in Contingent Valuation Method

The Contingent Valuation Method is used to evaluate individual preferences for a change concerning a public non-market resource or property. The objective is to build a nonparametric forecasting model of an individual＇s Willingness To Pay according to geographical location. Within this framework, an estimator （of type Nadaraya-Watson） is proposed for the regression of the variable related to geolocation. The specific characteristics of the location variable lead us to a more general regression model than the traditional models. Results are established for convergence of our estimator.

Numerical analysis and geotechnical assessment of mine scale model

Various numerical methods are available to model,simulate,analyse and interpret the results;however a major task is to select a reliable and intended tool to perform a realistic assessment of any problem.For a model to be a representative of the realistic mining scenario,a verified tool must be chosen to perform an assessment of mine roof support requirement and address the geotechnical risks associated with longwall mining.The dependable tools provide a safe working environment,increased production,efficient management of resources and reduce environmental impacts of mining.Although various methods,for example,analytical,experimental and empirical are being adopted in mining,in recent days numerical tools are becoming popular due to the advancement in computer hardware and numerical methods.Empirical rules based on past experiences do provide a general guide,however due to the heterogeneous nature of mine geology(i.e.,none of the mine sites are identical),numerical simulations of mine site specific conditions would lend better insights into some underlying issues.The paper highlights the use of a continuum mechanics based tool in coal mining with a mine scale model.The continuum modelling can provide close to accurate stress fields and deformation.The paper describes the use of existing mine data to calibrate and validate the model parameters,which then are used to assess geotechnical issues related with installing a new high capacity longwall mine at the mine site.A variety of parameters,for example,chock convergences,caveability of overlying sandstones,abutment and vertical stresses have been estimated.

Assessment of Numerical Models for Live Load Distribution in a Road Slab Bridge

This paper presents comparison of numerical models used in an analysis of a road bridge deck. The models were adapted for computing the live load distribution coefficients in composite concrete bridge deck. The load distribution method was chosen for assessment of the usability of different numerical model in slab bridge deck analysis. The goal of the study is to determine a simplest but still accurate numerical model to estimate live load effects on composite slab bridge. In the analysis, the well-established grillage approach was adapted for representation of the bridge deck as a basic model as well as more sophisticated three-dimensional models which was supposed to better represent the real behavior of the deck under concentrated wheel loads. The bridge deck was effectively modeled using beam and shell elements. The grillage method compares well with the finite-element method. This finding is allowed to establish simplification in numerical modeling of slab bridge decks for live load effect computations.