斜入射下水中隐身夹芯复合材料附体结构声学设计

摘 要：将隐身夹芯复合材料代替附体结构钢质壳板,建立了斜入射条件下水中隐身夹芯复合材料结构的声学模型;从水声波动方程出发,推导了二维空间声波斜入射时的传递矩阵,及带空腔水附体结构的声反射系数和吸声系数表达式;对带空腔水附体结构模型进行了垂直入射声学试验,试验结果与传递矩阵法数值计算吻合较好;对试验模型进行了斜入射下声学性能数值计算,分析了入射角对反射系数和吸声系数的影响;考虑斜入射下夹芯层厚度、密度、损耗因子、及水层厚度等对隐身附体结构声学性能的影响,应用数值方法对水中隐身夹芯复合材料附体结构进行了声学设计,分析了各层材料参数和几何参数对隐身结构反射系数和吸声系数的影响规律。     

夹层复合材料在潜艇声隐身结构中的应用及其相关技术研究

本文对复合材料在潜艇声隐身结构中的应用情况进行了分析,对其材料、结构形式、作用效果等方面进行了详细阐述,提出了夹层吸声复合材料作为水下声隐身结构的发展趋势。然后利用数值计算的方法,对夹层复合材料的声学性能进行了分析,得到了夹层复合材料各层材料参数,如厚度、声特性阻抗和损耗等对声学性能的影响规律。最后,评估了典型局部结构壳板应用夹层复合材料后的力学性能和声隐身性能。结果表明,潜艇非耐压结构的壳板采用夹层复合材料可以满足结构的力学要求,与钢结构相比声隐身能力大大提高。     

不同厚度的双层碳团簇型微波隐身材料性能研究

通过微波隐身材料结构设计,对不同厚度的双层碳团簇型微波隐身材料在8.2～12.4GHz频率范围内的吸波性能进行了研究.发现对于不同的厚度要求,要使材料具有良好的吸波性能,应选用具有不同电导率σ的碳团簇型材料.对于总厚度为4mm的材料,反射峰值-31.0dB,有效带宽为3.74GHz;对于变换层为1mm、吸收层为2mm、总厚度为3mm的材料,最小反射率为-40.0dB,有效带宽3.8GHz;对于变换层和吸收层分别为1mm的材料,最小反射率达-33dB,有效带宽为3.3GHz.同时发现,当变换层和吸收层厚度相等时,材料的排列顺序不同,所得的吸收效果会存在很大差异,即材料的方向性显著,而当两者厚度不等时,材料的吸波性能基本与其排列顺序无关,方向性不显著.     

声学多层结构介质的研究进展

首先回顾了声学多层结构介质的研究历史,在此基础上简要介绍了近几年在声学多层结构介质特异声传输调控和原型声学功能器件方面的一些工作进展。从声学的角度,系统介绍了多层结构介质的有效介质理论,系统声学参数的各向异性近似,在声波隐身斗篷中的应用。通过严格散射理论推导和有限元数值模拟研究了声斗篷系统的近场声压分布和远场散射强度,发现该设计可在低频较宽的频带范围内显著降低被遮蔽区域的声散射截面;在此频率区间内,声信号散射截面随着频率的提高而增加,其截止频率由薄层厚度决定。最后对该领域的研究作了若干展望。     

某复合隐身涂层中雷达吸波涂层的测厚系统设计

针对“雷达+红外”复合隐身体系的结构特点和雷达吸波涂层的磁化特性,建立了某复合隐身涂层中雷达吸波涂层的磁力测厚模型,分析了测厚算法。结果表明,当复合隐身体系中红外涂层厚度+某底漆厚度远小于空气涂层厚度时,磁力测厚法可忽略红外涂层和某底漆厚度的影响,直接利用磁力大小与雷达吸波涂层厚度成正比的电磁学特性关系,测出雷达吸波涂层的厚度。本文作者还设计了磁力测厚传感器,开展了磁力测量试验。结果表明,该磁力测厚系统结构简单、测量结果精确。      

红外与雷达隐身涂层激光后向散射特性

研究了红外与雷达波隐身涂层的激光后向散射特性。研究结果表明:涂层的红外辐射率越小,激光后向反射率越大。从目标战术应用上考虑,通过对目标进行合理的迷彩图案设计,有可能实现红外与激光隐身兼容;从隐身原理和材料设计来考虑,完全可以做到雷达与激光隐身兼容;通过涂层表面结构微孔化,可使涂层激光后向反射率大大下降,而不影响雷达波隐身性能。      

潜艇典型结构的声振特性研究概况及声学设计构想

潜艇结构的振动与声辐射特性是声隐身研究的重点。对潜艇典型结构的声振特性研究现状进行综述,归纳总结典型结构声学设计的研究动态,论述开展结构声学设计的重要性和必要性,提出基于声学性能开展结构设计的流程及方法,为进一步研究潜艇结构声隐身设计提供参考。     

水下航行器声隐身性能快速评估研究

针对传统水下航行器声隐身性能评估方法计算时间长、实时性不强的缺点,将评估由数值计算问题变为基于多传感器信息融合的模式识别问题来解决。通过将RBF神经网络模型和LVQ神经网络模型相结合,提出了基于组合神经网络的水下航行器声隐身性能快速评估模型。利用加速度传感器测得壳体表面振动信息,抽取分析频段内每个频带的功率作为特征向量,通过组合神经网络模型进行识别分类,快速评估出航行器当前的声隐身状态。并利用水下双层加肋圆柱壳体模拟航行器舱段缩比模型,进行了水下声学试验,验证了方法的实时性和有效性。该评估方法计算速度快、评估正确率较高、通用性较强,可很好地应用于各类水下结构的声学状态评估。     

约束阻尼对二维声学黑洞薄板减振特性的影响

声学黑洞（Acoustic Black Holes,ABH）以结构厚度的幂律变化实现弹性波的汇聚,结合阻尼层能较好地抑制结构振动。为进一步实现结构的低频振动控制,将声学黑洞与约束阻尼复合,建立附加约束阻尼的二维声学黑洞薄板模型,采用数值方法计算加速度响应与结构损耗因子,研究二维声学黑洞板附加约束阻尼后的减振特性,并通过二维声学黑洞薄板振动试验开展验证,最后探究约束层材料、厚度及约束阻尼半径对声学黑洞板低频减振性能的影响规律。结果表明：相比于附加自由阻尼,约束阻尼使声学黑洞薄板在第一阶共振峰处的加速度导纳降低12.61 dB;当约束层厚度为截断厚度的2倍左右时,薄板整体可以达到较佳的减振效果。研究可为声学黑洞薄板结构的低频减振应用提供重要参考。     

多功能隐身纤维性能的研究

通过熔融纺丝制备了一种新型的红外/雷达多功能隐身纤维.本研究主要分析了纤维的热性能、力学性能、电性能和填料种类、含量、样品厚度和形态结构对纤维吸波性能的影响以及纤维的红隐身性能.研究表明随着粉体含量的增加纤维的力学性能、结晶度、熔融温度降低.随金属粉体含量的增加,纤维的质量比电阻率先降后升.复合粉体比单一粉体有较好的雷达吸收,金属粉体含量的增加有利于吸波性能的提高.皮层含有15%金属粉体的隐身纤维具有较好的红外隐身性能.隐身纤维大于10db的频宽可达2.39GHz,红外发射率可达0.62.本实验制备的隐身纤维材料有望成为一种极具发展潜力和工业价值的多功能隐身材料.     

Computational material design for acoustic cloaking

A topology optimization technique based on the topological derivative and the level set function is utilized to design/synthesize the microstructure of a pentamode material for an acoustic cloaking device. The technique provides a microstructure consisting of a honeycomb lattice composed of needle‐like and joint members. The resulting metamaterial shows a highly anisotropic elastic response with effective properties displaying a ratio between bulk and shear moduli of almost three orders of magnitude. Furthermore, in accordance with previous works in the literature, it can be asserted that this kind of microstructure can be realistically fabricated. The adoption of a topology optimization technique as a tool for the inverse design of metamaterials with applications to acoustic cloaking problems is one contribution of this paper. However, the most important achievement refers to the analysis and discussion revealing the key role of the external shape of the prescribed domain where the optimization problem is posed. The efficiency of the designed microstructure is measured by comparing the scattering wave fields generated by acoustic plane waves impinging on bare and cloaked bodies. Copyright © 2017 The Authors. International Journal for Numerical Methods in Engineering Published by John Wiley & Sons Ltd.     

A Numerical Study on AC Losses of a Double Layer Polygonal BSCCO Conductor by Finite Element Method

High-temperature superconductor (HTS) cables are candidates for power transmission cables in the near future. A cylindrical arrangement of HTS tapes for the cable has proved able to reduce the AC loss. Many studies on AC loss characteristics of HTS cables have been done, but few numerical models of the cable were verified by experiments. In this paper, a numerical model of the double-layer polygonal bismuth strontium calcium copper oxide (BSCCO) conductor is developed. Current density and magnetic field intensity distribution in the inner and outer layers are also investigated. The numerical results of the AC loss for different layer current distributions are identical with the experimental ones. Accordingly, the reliability of the numerical model is verified. By using this model, the influence of distance between the inner and outer layers, gap between two neighboring wires, and layer current distribution on AC losses of different layers is evaluated. The results show that increasing distance between layers and narrowing gap between wires are effective to reduce AC loss, while the unbalance of layer current distribution increases the AC loss of the double-layer conductor.     

Stresses in cross-ply laminated circular cylinders of axially variable thickness

Summary This paper presents the results from an analytical investigation of the behavior of composite circular cylinders subjected to internal and external surface loading. The present cylinder consists of a number of homogeneous ply groups of axially variable thickness. Each ply group forming a layer is treated as an individual thin elastic cylinder of generally orthotropic material with interfacial stresses on the inner and outer surfaces of the layer as boundary loading. The deformation and stresses in each layer can be expressed in terms of interfacial stresses along the exterior surfaces of each layer. All displacement and stresses throughout the composite cylinder can be determined subsequently after satisfying boundary conditions at the inside and outside surfaces of the cylinder in conjunction with the recurrence relationship among interfacial stresses. Numerical results are presented for different values of the inner-to-outer ratio, number of layers, stacking sequence, axially-variable-thickness parameter, and load factor. Based on the presented results, conclusions can be drawn concerning the cylinder behavior and its sensitivity to different parameter variations.     

Steam-side scale morphologies associated with scale exfoliation from ferritic steel T22

Abstract

Observations of steam-formed scales on type T22 ferritic steel reheater tubes have provided some insights into the scale morphologies associated with exfoliation. Measurements indicated that as the total thickness of the adherent scales increased, the ratio of the thicknesses of the main inner (Fe–Cr spinel) and outer (magnetite) layers increased continuously to a maximum of approximately 2.5. The often-assumed thickness ratio of 1.0 did not persist after a laminated structure of pairs of spinel and magnetite layers was developed in the main inner layer. The development of such multi-laminations appeared to be associated with a decrease in the rate of growth of the main outer, magnetite layer. In this particular set of samples, exfoliation occurred in scales of total thickness greater than approximately 270 μm, and involved separation of a single pair of oxide layers of similar thickness that consisted of the original outer magnetite layer and part of the original spinel layer. The scale lost in subsequent exfoliation events at essentially the same site consisted of a further pair of layers comprising the new magnetite layer re-grown after the initial event, and a further part of the original spinel layer. Exfoliation events did not appear to involve the whole of the spinel layer existing at that time, only the equiaxed region immediately subjacent to the magnetite and a portion of the laminated structure.     

Experimental investigation on the ballistic resistance of monolithic and multi-layered plates against ogival-nosed rigid projectiles impact

In this paper, the ballistic performance of single, two-, three- and four-layered steel plates impacted by ogival-nosed projectiles were experimentally investigated. Thin multi-layered plates arranged in various combinations of the same total thicknesses were normally impacted with the help of a gas gun. Ballistic limit velocity for each configuration target was obtained and compared based on the investigation of the effect of the air gap between layers, the number, order and thickness of layers on the ballistic resistance of targets. The results show that the thin monolithic targets have greater ballistic limit velocities than multi-layered targets if the total thickness less than a special value, and also the ballistic limit velocities of multi-layered targets decrease with the increase of the number of layers. Otherwise, the moderate thickness monolithic targets give lower ballistic limit velocities than multi-layered targets. Furthermore, the ballistic limit velocities of in-contact multi-layered targets are greater than those of spaced multi-layered targets. The order of layers affects the ballistic limit velocities of multi-layered targets, the ballistic resistance of the multi-layered targets is better when the first layer is thinner than the second layer.     

Novel multi-layer polymer-metal structures for use in ultrasonic transducer impedance matching and backing absorber applications

This paper presents a novel design principle for designing multilayer polymer-metal structures which are well suited for front surface impedance conversion (matching) and for back surface acoustic absorption. It is shown that a polymer layer with an outer metal layer, when loaded by a low impedance propagation medium, acts as an efficient impedance converter. The resulting impedance seen at the inner polymer surface is increased and the structure provides the same performance as a traditional quarter-wavelength matching layer. Experimental evidence is also shown for a double-matching scheme for a lead zirconate titanate (PZT) transducer using an inner polymer-metal multilayer and an outer polymer quarterwavelength layer, resulting in a 55% bandwidth at 2.6 MHz with air backing. Also, it is theoretically shown that multiple layers of a lossy polymer adhesive-metal structure produce low propagation velocity and high absorption. Experimental proof of this ultrasonic multilayer backing absorber is provided. Design theories based on both a simplified mass and spring model and a rigorous one-dimensional wave model have been developed and show fair agreement.     

声学覆盖层对潜艇抗水下爆炸能力的影响研究

为提高潜艇的隐身性能,潜艇壳体表面常敷设声学覆盖层结构.声学覆盖层常设有各类空腔等特殊结构形式,在受到水下爆炸冲击波时,空腔很容易产生变形并吸收能量,对潜艇的抗冲击性能产生影响.采用复合板单元的等效方法,针对敷设声学覆盖层的潜艇的抗冲击性能进行研究,得到了声学覆盖层对潜艇破坏环境、冲击环境的影响规律.研究表明,声学覆盖层将增加艇体结构对冲击波能量的吸收,使潜艇的破坏环境变坏,并使潜艇典型部位的设计冲击谱增大,但随着声学覆盖层的敷设方式不同,典型部位的设计冲击谱变化也各不相同.     

Free-space excitation of resonant cavities formed from cloaking metamaterial

We propose a new class of resonant electromagnetic structures, and study their response to free-space illumination. The structures consist of partial cylindrical shells that have the cloaking material properties proposed by Pendry et al. [Science 2006, 312, 1780]. These metamaterial shells have apertures that allow the propagation of incident irradiation into an interior resonant cavity. We use full wave time-harmonic analysis to study the field distribution inside the cavity, and show that an analogue of Whispering Gallery Modes (WGMs) can be efficiently excited via free-space illumination.     

覆盖层加筋板结构水下抗爆性能对比试验研究

为提高潜艇的隐身性能,潜艇壳体表面常敷设声学覆盖层结构。声学覆盖层常设有各类空腔等特殊结构形式,在受到水下爆炸冲击波时空腔产生变形并吸收能量,对潜艇的抗冲击性能产生影响。分别对不同覆盖层及无覆盖层的加筋平板试件开展水下抗爆炸性能对比性试验研究。通过试验获取各加筋平板试件典型部位的加速度、应变响应。比较不同覆盖层对加筋平板结构的实际抗冲效果,为今后声学覆盖层的抗冲设计和研究提供参考。