消声瓦声学性能计算方法研究

首先建立均匀圆柱腔中弹性波的计算模型,然后利用该模型建立复合过渡型声腔结构消声瓦吸声性能计算的理论模型,并应用这一理论模型计算分析现有声腔结构消声瓦及几种变形的声腔结构声腔结构形式的消声瓦的吸声性能,讨论材料环境温度和材料参数变化对吸声性能的影响,最后总结消声瓦声腔结构和不同材料参数对吸声性能影响的基本规律.     

消声瓦的吸声材料和结构对吸声性能影响的评估

对消声瓦的吸声机理作了概述,用我们提出的近似计算非均匀结构吸声器的材料等效物理参量方法,以及根据渐变吸收层声传输理论模型分别仿真了均匀材料、含实心粒子和空心粒子的复合材料构成的平板消声瓦和含空腔平板消声瓦随频率变化的吸声系数、各复合材料的特性阻抗和衰减系数,分析仿真结果阐明吸声材料和结构对消声瓦的吸声性能的影响,为优选吸声材料和结构提供某些参考依据.     

消声水池声场仿真研究

采用网格计算方法建立了消声水池声场的低频仿真分析模型,利用该模型对消声水池中三维声场进行了仿真分析,验证了其可靠性,并将分析结果与镜像声学方法计算进行了比较.通过分析得到不同频率不同吸声效果下消声水池声场的起伏程度等参数.     

消声水池声场的仿真计算

消声水池的声场计算对消声水池尺寸的确定和所敷设的吸声材料参数的选择十分重要。利用虚源方法建立了消声水池声场计算的声场模型,该模型考虑了二次反射、吸声系数随入射角变化、有指向性声源等多种情况。利用声场模型对水池的声场进行了计算,分别考虑了点声源、吸声系数随入射角变化、二次反射和指向性声源等情况。通过对不同条件下消声水池声场的计算仿真,分析了不同因素对水池自由场的影响,得到了具有一定应用价值的结论。     

脉冲爆震发动机微穿孔消声喷管研究

针对脉冲爆震发动机的噪声辐射特性,计算分析微穿孔板孔径、板厚、穿孔率、前后腔厚度等设计参数对单／双层微穿孔板吸声体共振频率、吸声系数的影响。设计并加工一组微穿孔消声喷管。实验研究发现：影双层微穿孔消声喷管对脉冲爆震发动机噪声辐射的降低都有一定的作用,双层结构优于单层结构;消声喷管越长,消声效果越好;发动机工作频率为20Hz时,300mm长双层微穿孔消声喷管可使噪声辐射峰值声压级降低2dB左右,脉冲声压级和声功率级降低4dB左右,声功率从1377．2W下降至542W。     

不同界面形状分层消声覆盖层声特性的实验研究

研究了不同界面形状的分层消声覆盖层的吸声性能。制备了三角形、半圆形、矩形和平面形等不同界面形状的分层消声覆盖层,并在声管中测试了其水声吸声系数。结果表明:在研究的频率范围内,非平面界面形状的分层消声覆盖层吸声性能优于平面界面形状的分层消声覆盖层的吸声性能,其中,半圆形界面形状的分层消声覆盖层吸声效果最好。原因在于声波在非平面界面上会发生波型转化,使声衰减能力弱的纵波转化为声衰减能力强的切变波,引起较大的剪切变形,入射波能量被大量地消耗。研究说明,合理设计分层消声覆盖层界面形状可以提高其水声吸声性能。     

消声水池用低频吸声尖劈的研制

在声学测量系统中 ,要求消声水池能在测量频段内达到近似自由场的声学环境 ,吸声尖劈可以对消声水池进行被动消声处理。本文介绍了一种能满足消声水池消声处理要求的低频吸声尖劈的设计要求、材料、结构设计、分布形式等     

中隔板对片式阻性消声器的影响分析

片式阻性消声器的消声能力决定于消声片的吸声系数,消声片内的中隔板对吸声系数影响的详细分析对消声器的设计和应用具有重要意义。应用传递矩阵法并结合声波在吸声材料中的传播理论,建立了片式阻性消声器内多层消声片的吸声系数计算模型,计算了消声器内不同消声通道的吸声系数,通过对比分析不同消声通道的吸声系数,讨论了中隔板对片式阻性消声器消声能力的影响。以实际消声器为例,通过计算吸声系数和实际的插入损失测试,对比两种结果,显示两者在随频率变化的趋势上吻合良好,验证了消声片内设置中隔板对消声器消声效果在不同频段具有不同的影响,在低频和较高频率范围内,中隔板具有积极作用,而对于中频段,中隔板具有消极作用。     

消声涂层的吸声性能

在选择合适的涂层基体的基础上,研究了在基体中掺入无机粉体填料的涂层的吸声系数.实验结果表明不同的材料基体、涂层填料的种类、粒径、形状极大地影响了消声涂层的吸声性能.同一种填料,用量增加,吸声系数升高.对材料组成进行优化后,合成了平均吸声系数达92.6%的样品.     

潜艇回声隐身效果评估方法

本文探讨了吸声材料的声压反射系数、吸声系数、回声降低(ER)与目标强度变化(△TS)等参数之间的解析关系。建立了敷瓦潜艇目标强度降低与声呐作用距离减小的数学表达式。按照＇当量原理＇对假想潜艇缩比模型裸体与敷瓦时的目标强度进行了测量。ER与△TS的实测值一致性很好。     

Covalent tethering of protruding arms for addressable DNA nanostructures

Functionalization of self-assembled DNA nanostructures is of fundamental importance for the realization of their application in nanotechnology and biosensing. Approaches reported so far suffer from lack of general applicability and usually require careful system design to avoid poor yields in the assembly of target structures. A novel approach well suited for fabrication of addressable DNA superstructures is reported here to generate DNA tile motifs. The method is based on the covalent linkage of a single-stranded protruding arm (covPA) to one of the oligomers forming the tile. Subsequent to assembly of tile motifs and superlattices, the covPA can be addressed by hybridization with complementary oligonucleotides or DNA-protein conjugates. The covPA can be located at arbitrary positions in a given tile motif without changing the general design and without compromising the structural integrity of the tile. The covPA strategy can also be readily extended to different PA sequences and multiple covPA arms can be linked to a tile. Superlattices obtained by self-assembly of covPA tiles reveal partial folding into double layers which possess an intrinsic order at the ultrastructural level. This phenomenon is likely associated with the increased flexibility of the covPA and might open up novel ways for DNA-based functionalization of solid surfaces and other applications of structural DNA nanotechnology.     

Computer-controlled optical scanning tile microscope

A new type of computer-controlled optical scanning, high-magnification imaging system with a large field of view is described that overcomes the commonly believed incompatibility of achieving both high magnification and a large field of view. The new system incorporates galvanometer scanners, a CCD camera, and a high-brightness LED source for the fast acquisition of a large number of a high-resolution segmented tile images with a magnification of 800x for each tile. The captured segmented tile images are combined to create an effective enlarged view of a target totaling 1.6 mm x 1.2 mm in area. The speed and sensitivity of the system make it suitable for high-resolution imaging and monitoring of a small segmented area of 320 microm x 240 microm with 4 microm resolution. Each tile segment of the target can be zoomed up without loss of the high resolution. This new microscope imaging system gives both high magnification and a large field of view. This microscope can be utilized in medicine, biology, semiconductor inspection, device analysis, and quality control.     

多视觉检测系统的定标

针对结构光视觉传感器所组成的多视觉测量系统，本文提出一种直接线性转换全局定标法，把各传感器的模块坐标归结到一个统一的用户坐标中。该系统用于轿车白车身有关参数的快速检测。标定后的系统对轿车进行检测，经与三坐标测量机测量结果比较，３σ＝０．５ｍｍ，完全满足车身公差±２ｍｍ的要求。     

基于统计能量法的隔声瓦减振性能仿真研究

在水下结构表面敷设隔声去耦材料是应用最广泛也是非常有效的一种提高舰船隐身性能的方法。基于统计能量法开展了隔声瓦对复杂锥柱结构水下振动的影响研究,讨论了隔声瓦敷设方式对复杂锥柱结构水下振动的影响,分析了阻尼损失系数对隔声瓦减振效果的影响。研究表明,隔声瓦敷设方式、阻尼损失系数对隔声瓦减振效果有较大影响:当隔声瓦敷设在结构振动主导传递途径上时,其对传递途径下游结构的振动抑制效果较为明显,而对于振源及传递途径上游结构振动的影响较小;隔声瓦减振效果随敷设密度的增大而增加,随阻尼损失系数的增大而有所降低。     

The response of layered aluminum nitride targets subjected to hypervelocity impact

This work presents both experimental and computational ballistic results of layered Aluminum Nitride (AlN) targets. An L/D = 6 tungsten penetrator is used to impact AlN targets at a nominal impact velocity of 2100m/s. The primary objective of this work is to determine the ballistic performance of layered ceramic targets to hypervelocity impact. Various layering configurations are investigated including separating the AlN ceramic layers by thin, low impedance, polymethyl methacrylate (PMMA). PMMA thicknesses of 1 mm, 0.5 mm and 0 mm are used. The number of AlN ceramic layers is also investigated. Target configurations of two, four, six, and twelve layers are considered. All targets consist of 76.2 mm of AlN. The experiments show that target resistance decreases when PMMA is added. Target resistance is also reduced when more layers are used. A secondary objective of this work is to evaluate the ballistic effect of reducing the lateral dimension of the ceramic tile (reduction in self-confinement). The experiments show reduced target resistance when the lateral tile size is decreased. Computations of selected experiments are presented to provide insight into the behavior of the AlN targets. The computations capture the effect of layering, PMMA separation and lateral tile size and provide insight into the behavior of the ceramic when used in these types of configurations.     

Error tolerant DNA self-assembly using (2k - 1)x(2k - 1) snake tile sets.

DNA self-assembly has been advocated as a possible technique for bottom-up manufacturing of scaffolds for computing systems in the nanoscale region. However, self-assembly is affected by different types of errors (such as growth and facet roughening) that severely limit its applicability. Different methods for reducing the error rate of self-assembly using tiles as basic elements have been proposed. A particularly effective method relies on snake tile sets that utilize a square block of even size (i.e., 2k x 2k tiles, k = 2, 3, . . .). In this paper, an odd-sized square block [i.e., (2k - 1) x (2k - 1)] is proposed as basis for the snake tile set. Compared with other tile sets, the proposed snake tile sets achieve a considerable reduction in error rate at a very modest reduction in growth rate. Growth and facet roughening errors are considered and analytical results are presented to prove the reduction in error rate compared with an even-sized snake tile set. Simulation results are provided.     

Error Tolerant DNA Self-Assembly Using ( $hbox{2}k-hbox{1}$)$times$( $hbox{2}k-hbox{1}$) Snake Tile Sets

DNA self-assembly has been advocated as a possible technique for bottom-up manufacturing of scaffolds for computing systems in the nanoscale region. However, self-assembly is affected by different types of errors (such as growth and facet roughening) that severely limit its applicability. Different methods for reducing the error rate of self-assembly using tiles as basic elements have been proposed. A particularly effective method relies on snake tile sets that utilize a square block of even size (i.e., 2k times 2k tiles, k = 2, 3,.. .). In this paper, an odd-sized square block [i.e., (2k -1) times (2k - 1)] is proposed as basis for the snake tile set. Compared with other tile sets, the proposed snake tile sets achieve a considerable reduction in error rate at a very modest reduction in growth rate. Growth and facet roughening errors are considered and analytical results are presented to prove the reduction in error rate compared with an even-sized snake tile set. Simulation results are provided.     

橡胶-地面石材摩擦性能的研究

基于橡胶摩擦学原理,采用水平拖拉方法在自制的简易摩擦测试装置上进行了橡胶-地面石材的摩擦性能实验,研究了法向荷栽、名义接触面积、静止接触时间对其摩擦性能的影响.结果表明,随着法向荷栽的增大,橡胶一地面石材的静摩擦因数有所减小,但减小的幅度逐渐减小;在同等低法向荷栽条件下,随着名义接触面积的增大或静止接触时间的延长,静摩擦因数均增大,表现出良好的线性相关性;但在同等中高法向荷栽条件下,静摩擦因数与名义接触面积不再符合简单的线性增长关系.     

Healing assessment of tile sets for error tolerance in DNA self-assembly

An assessment of the effectiveness of healing for error tolerance in DNA self-assembly tile sets for algorithmic/nano-manufacturing applications is presented. Initially, the conditions for correct binding of a tile to an existing aggregate are analysed using a Markovian approach; based on this analysis, it is proved that correct aggregation (as identified with a so-called ideal tile set) is not always met for the existing tile sets for nano-manufacturing. A metric for assessing tile sets for healing by utilising punctures is proposed. Tile sets are investigated and assessed with respect to features such as error (mismatched tile) movement, punctured area and bond types. Subsequently, it is shown that the proposed metric can comprehensively assess the healing effectiveness of a puncture type for a tile set and its capability to attain error tolerance for the desired pattern. Extensive simulation results are provided.     

基于YOLOv5的瓷砖表面缺陷检测

目的 针对目前的瓷砖表面人工缺陷检测效率低的问题,提出一种基于深度学习YOLOv5算法实现对生产线瓷砖表面缺陷的检测。方法 首先对数据集进行切图分割与数据增强处理,再通过labelimg对数据集进行数据标注,然后将数据集送入到优化后的YOLOv5网络模型进行迭代训练,并将最优权重用于测试。结果 通过实验对比,YOLOv5模型的检测准确率高于Faster RCNN、SSD、YOLOv4这3种模型,其检测平均准确度高于96%,平均检测时间为14ms。结论 表明该方法能够检测生产过程中的瓷砖缺陷问题,在瓷砖缺陷检测上有一定的先进性和实用性。