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船舶声隐身性能由其自身的噪声量级确定,而管路系统的噪声又是船舶噪声的重要组成部分,由于管路噪声有其自身的特点,因此对于船舶声隐身性能的影响也具有其特殊性。结合工程实践分析船舶管路振动噪声与船舶总体声隐身特性的关联关系,得出管路的水动力噪声是影响船舶声纳平台区自噪声的主要干扰源之一的结论。围绕管路水动力噪声的生成特点,提出几点工作建议供同行参考。 相似文献
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目标跟踪是被动声纳系统的主要功能之一,跟踪器为目标运动分析和目标识别等后置处理提供输入数据。声纳操作员利用人脑独特的认知模式、先验知识和视觉的迹迹相关效应,能够很好地在声纳显示方位历程图上发现目标并录取跟踪。但实际应用中由于低信噪比、航迹交叉和转向等复杂多目标情形,声纳系统实现多目标自动跟踪十分困难。给出一种多目标自动跟踪的逻辑关联方法,利用被动声纳宽带波束输出数据,通过点迹与航迹关联、航迹评价管理和交叉处理等过程,可以较好实现多目标自动跟踪。试验数据的处理结果验证了所提方法的有效性,能够在声纳装备中得到工程应用。 相似文献
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声纳基阵信号模拟器是一种实用的、可近似仿真实际监测目标及使用环境的阵元级信号发生器。声纳基阵信号模拟器的使用将有效缩短数字式声纳的研制周期,大大减少湖试和海试的次数。文章中以通用信号阵列处理系统为运行环境,详细介绍了一种声纳基阵信号模拟器实时多任务系统的软件设计与开发过程,分析了该软件系统中所有基本任务的功能以及多任务之间的通信关系,并且最后给出了该实时多任务软件在通用信号处理机上的实现拓扑图。实践证明,该套软件功能完备,且具有很好的实时性和稳定性,非常适用于现代声纳工程领域。 相似文献
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SAS测绘率是大面积海底测绘的一个重要指标,多子阵的方法已经在常规单站SAS的实际系统中取得了良好的效果。针对双站合成孔径声纳(双站SAS)测绘速率受空间降采样率限制的问题,该本文首先给出了发射站固定的双站SAS模型,分析了该模型双站SAS的测绘率。为了提高双站SAS的测绘率,本文中提出了发射站固定下的多子阵双站合成孔径声纳成像方法,并给出了严格的数学模型,形成了多子阵双站SAS系统设计方案,提高了系统的测绘率。文章最后给出了基于波束形成逐点算法多子阵双站SAS的成像仿真,仿真结果验证了方法的有效性。 相似文献
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英国舰用和潜用声纳的最新发展 总被引:1,自引:0,他引:1
英国海军研究机构是世界上领先的水下应用研究机构之一。它得到能够研制和供应声纳系统的所有部份(包括换能器、拖曳基阵、数字信号处理、数据处理、显示设备、机械结构等)的国内工业的支持和补充,并不断在声纳领域推出新技术,提供新设备。本文根据英国军用声纳近期发展计划(包括出口声纳的安排),简介其舰用和潜用声纳的最新发展,并初步分析其发展特点。 相似文献
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0引言波束形成作为声纳系统的重要组成部分,直接影响着整体性能。通过优化波束形成权系数,为系统提高检测概率,精确定位、跟踪、识别搭建了良好的平台。然而这些优化设计都是在理想阵列流形的假设下进行的,权系数对误差比较敏感,如果实际的阵列流形发生失配时优化波束的效果将急剧降低。在体积阵中产生阵流形失配的原因有很多, 相似文献
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Microarray data often consist of a large number of genes and a small number of replicates. We have examined testing the null hypothesis of equality of mean for detecting differentially expressed genes. The p-value for each gene is often estimated using permutation samples not only for the target gene but also for other genes. This method has been widely used and discussed. However, direct use of the permutation method for the p-value estimation may not work well, because two types of genes are mixed in the sample; some genes are differentially expressed, whereas others are not. To overcome this difficulty, various methods for appropriately generating null permutation samples have been proposed. In this paper, we consider two classes of test statistics that are naturally modified to null statistics. We then obtain the uniformly most powerful (UMP) unbiased tests among these classes. If the underlying distribution is symmetric, the UMP unbiased test statistic is similar to that proposed by Pan (Bioinformatics 19:1333?C1340, 2003). Under another condition, the UMP unbiased test statistic has a different formula with one more degree of freedom and therefore is expected to give a more powerful test and a more accurate p-value estimation from a modified null statistic. In microarray data, because the number of replicates is often small, differences in the degree of freedom will produce large effects on the power of test and the variance of the p-value estimation. Some simulation studies and real data analyses are illustrated to investigate the performances of the methods. 相似文献
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Gillespie D 《Nano letters》2012,12(3):1410-1416
It is proposed that the layering of large ions at the wall/liquid interface of nanofluidic channels can be used to achieve high efficiency (possibly >50%) in the conversion of hydrostatic energy into electrical power. Large ions tend to produce peaks and troughs in their concentration profiles at charged walls, producing high concentrations far from the walls where the ions' pressure-driven velocity is high. This increases the streaming conductance and the energy conversion efficiency. 相似文献
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目标高分辨算法的性能优劣直接影响声纳、雷达的目标感知能力。考虑基于空间平滑思想的直接数据域算法,在干扰方向产生稳定的零陷。虚拟出期望信号并加入到接收数据中,将实际目标当作干扰,通过直接数据域自适应的方法在实际目标方向产生零陷:在波束图的左半部分适当位置虚拟一个期望信号,得到0°~90°的零陷分布图,在右半部分适当位置虚拟一个期望信号,得到90°~0°的零陷分布图,将这两部分零陷图组合后,取倒数得到实际功率谱图。该方法可以在单快拍、未知目标信号先验信息的情况下得到稳定、高分辨力的目标方位估计,并能够处理相干信号。仿真分析验证了算法的正确性和良好性能。 相似文献
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Jos M. A. Csar de S Renato M. Natal Jorge Robertt A. Fontes Valente Pedro M. Almeida Areias 《International journal for numerical methods in engineering》2002,53(7):1721-1750
The degenerated approach for shell elements of Ahmad and co‐workers is revisited in this paper. To avoid transverse shear locking effects in four‐node bilinear elements, an alternative formulation based on the enhanced assumed strain (EAS) method of Simo and Rifai is proposed directed towards the transverse shear terms of the strain field. In the first part of the work the analysis of the null transverse shear strain subspace for the degenerated element and also for the selective reduced integration (SRI) and assumed natural strain (ANS) formulations is carried out. Locking effects are then justified by the inability of the null transverse shear strain subspace, implicitly defined by a given finite element, to properly reproduce the required displacement patterns. Illustrating the proposed approach, a remarkably simple single‐element test is described where ANS formulation fails to converge to the correct results, being characterized by the same performance as the degenerated shell element. The adequate enhancement of the null transverse shear strain subspace is provided by the EAS method, enforcing Kirchhoff hypothesis for low thickness values and leading to a framework for the development of shear‐locking‐free shell elements. Numerical linear elastic tests show improved results obtained with the proposed formulation. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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Data reduction in non-null tests is difficult due to the presence of retrace error. We propose a simple yet effective data reduction approach for aspheric testing in a non-null interferometer. The new approach gives figure error of the aspheric by just subtracting the theoretical wavefront and first-order errors from the real wavefront obtained in the non-null interferometer. Precise prediction of the theoretical wavefront can be achieved by accurate calibration of the partial compensation system. The approach can be considered a generalization of the traditional data processing method in null tests, and errors that may affect its accuracy are discussed. A set of experiments have been carried out to demonstrate its validity and feasibility. 相似文献
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An omnibus test for spherical symmetry in ℝ2 is proposed, employing localized empirical likelihood. The thus obtained test statistic is distribution free under the null
hypothesis. The asymptotic null distribution is established and critical values for typical sample sizes, as well as the asymptotic
ones, are presented. In a simulation study, the good performance of the test is demonstrated. Furthermore, a real data example
is presented. 相似文献
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《Materials Science & Technology》2013,29(1):112-120
AbstractThe low temperature end of the hot ductility trough has been examined for steels which have been solution treated at ~1300°C before tensile testing in the temperature range of 1000–600°C. Failure in the trough in this region is intergranular ductile and occurs by strain intensification in the thin film of ferrite surrounding the prior austenite grain. The strain causes voiding to occur at the inclusions situated at the boundaries, the cavities gradually linking up to give failure. In steels which are solution treated before tensile testing, the depth of the trough is shown to be controlled by the volume fraction of the second phase particles, their size and the separation between the particles. Recovery in ductility on the low temperature side of the trough is solely dependent on being able to produce a sufficiently large quantity of ferrite to prevent strain concentration (~40%). Often this has to await the test temperature falling below the AR 3 in which case wide troughs are formed. However, if conditions are right, very narrow troughs can be produced in which the ferrite that is formed is deformation induced. The width of the trough at the low temperature end of the trough is shown to decrease with increase in strain rate, refinement of the austenite grain size, increase in cooling rate from the solution treatment temperature, decrease in the volume fraction of sulphides situated at the austenite grain boundaries and reduction in the Mn and C contents. The depth of the trough decreases in a similar manner with all these variables except for C and Mn, where for the former there is no effect and for the latter, increasing the Mn level reduces the depth. Narrow troughs on this side of the trough are dependent on being able to form deformation induced ferrite in sufficiently large amounts so as to improve the ductility at temperatures above the AR 3. A model is proposed to account for most of these observations. 相似文献
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This paper studies goodness-of-fit tests and specification tests for an extension of the Log-GARCH model, which is both asymmetric and stable by scaling. A Lagrange-multiplier test is derived for testing the extended Log-GARCH against more general formulations taking the form of combinations of Log-GARCH and exponential GARCH (EGARCH). The null assumption of an EGARCH is also tested. Portmanteau goodness-of-fit tests are developed for the extended Log-GARCH. An application to real financial data is proposed. 相似文献
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Michael Gorman Michael Hertz Garrick Louis Luna Magpili Mark Mauss Matthew Mehalik J.B. Tuttle 《工程教育杂志》2000,89(4):461-469
This paper describes an engineering graduate option in Systems Engineering designed to overcome some of the effects of specialization and compartmentalization by building a link between technical and ethical training. Students in this option produce case studies that emphasize ethical issues in the design process. The goal of the program is to turn out ethical professionals who are able to reflect on the moral implications of technology. The proposed approach uses realistic or real‐hypothetical hybrid case studies as a type of vicarious mentoring, and, when supplemented with readings in ethical theory and codes, may serve as a starting point for a deeper understanding of behavioral dilemmas. The developers of this approach are a multi‐disciplinary team from the Engineering School and the Darden Graduate School of Business Administration at the University of Virginia. The paper describes how the graduate option is structured and provides data on student outcomes. 相似文献
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Social networking platforms provide a vital source for disseminating
information across the globe, particularly in case of disaster. These platforms
are great mean to find out the real account of the disaster. Twitter is an example
of such platform, which has been extensively utilized by scientific community due
to its unidirectional model. It is considered a challenging task to identify eyewitness tweets about the incident from the millions of tweets shared by twitter users.
Research community has proposed diverse sets of techniques to identify eyewitness account. A recent state-of-the-art approach has proposed a comprehensive set
of features to identify eyewitness account. However, this approach suffers some
limitation. Firstly, automatically extracting the feature-words remains a perplexing
task against each feature identified by the approach. Secondly, all identified features were not incorporated in the implementation. This paper has utilized the language structure, linguistics, and word relation to achieve automatic extraction of
feature-words by creating grammar rules. Additionally, all identified features were
implemented which were left out by the state-of-the-art model. A generic
approach is taken to cover different types of disaster such as earthquakes, floods,
hurricanes, and wildfires. The proposed approach was then evaluated for all disaster-types, including earthquakes, floods, hurricanes, and fire. Based on the static
dictionary, the Zahra et al. approach was able to produce an F-Score value of
0.92 for Eyewitness identification in the earthquake category. The proposed
approach secured F-Score values of 0.81 in the same category. This score can
be considered as a significant score without using a static dictionary. 相似文献