Experimental investigation into dynamic axial impact responses of double hat shaped CFRP tubes

This paper aims to explore the dynamic responses and crashing characteristics of double hat shaped tubes made of weave carbon fiber reinforced plastic (CFRP). Experimental investigations were carried out into three different thicknesses and lengths of the composite tubes fabricated by the bladder molding process. Three distinct failure modes, classified as progressive end crushing, mid-length collapse and overlap opening, were observed in the dynamic crushing tests. Unlike continuous splaying fronds observed in the quasi-static tests, dynamic tests exhibited a number of fragment segments in the progressive end crushing mode. It is shown that the ply number was a critical parameter affecting the failure mode and energy absorption capability. The increase in ply number led to increases in the peak load and specific energy absorption (SEA); whereas the tubal length seemed insensitive to energy absorption capability. Compared to the quasi-static cases, the dynamic impact tests resulted in the higher peak load (increased from 46 % to 125 %) and lower SEA (reduced from 21 % to 33 %) for the tested tubes.     

Diagnostics for functional regression via residual processes

Methods of regression diagnostics for functional regression models are developed which relate a functional response to predictor variables that can be multivariate vectors or random functions. For this purpose, a residual process is defined by subtracting the predicted from the observed response functions. This residual process is expanded into functional principal components (FPC), and the corresponding FPC scores are used as natural proxies for the residuals in functional regression models. For the case of a univariate covariate, a randomization test is proposed based on these scores to examine if the residual process depends on the covariate. If this is the case, it indicates lack of fit of the model. Graphical methods based on the FPC scores of observed and fitted functions can be used to complement more formal tests. The methods are illustrated with data from a recent study of Drosophila fruit flies regarding life-cycle gene expression trajectories as well as functional data from a dose-response experiment for Mediterranean fruit flies (Ceratitis capitata).     

柔性直流系统短路故障网络阻抗建模与时频特性诊断方法研究

针对柔性直流系统直流侧短路故障诊断难题,文章从故障网络精确建模和暂态特征信号分析两个方面展开研究,并提出了阻抗网络暂态响应时频特性关联度的故障诊断方法。该方法通过向柔性直流系统线路入口处注入脉冲电压作为激励,实时提取所产生的暂态电流分量,经不同尺度的Mexican Hat变换得到时频能量序列,并构造反映故障网络暂态响应时频能量谱矩阵。同时,建立柔性直流系统精确模型,模拟不同故障点经不同大小电阻的短路故障,构建完整故障样本及其时频特征库,经相似度计算可选出与实测故障特征最相近的样本,确定故障点位置和估计短路电阻大小。最后,对上述原理方法进行算例分析,并与时域方法比较,结果表明文章所述诊断方法及其判据更为准确有效,相关原理正确可行。     

Linux主要发行版纵览

开源运动的蓬勃发展,催生出纷繁多样的Linux发行版本。本文收集了当前国内外几大主流Linux发行版本的最新信息,通过概括性的介绍,以帮助读者从中作出选择。     

泡沫铝部分填充薄壁梁弯曲吸能特性研究

为了研究泡沫铝填充帽型薄壁梁横向弯曲时的吸能特性,建立了泡沫铝填充双帽型薄肇粱的有限元模型,采用非线性有限元软件LS-DYNA进行了横向弯曲工况下的仿真.首先进行了空心帽型薄壁梁和泡沫铝填充帽型薄壁梁的横向弯曲仿真,分析了材料参数、几何参数对其比吸能(单位质量吸收的能量)的影响;然后为降低结构重量并保持薄壁梁吸能效果,对部分填充泡沫铝薄壁梁进行了横向弯曲仿真,考察了不同泡沫铝填充长度对结构吸能特性的影响.研究结果表明:填充泡沫铝后,帽型薄壁梁在横向弯曲中吸能特性有明显的改善;在吸收相同的能量时,泡沫铝填充薄壁梁的质量要比空心薄壁梁的质量少.