大尺寸薄膜型声学超材料复合结构低频宽带隔声性能研究EI北大核心CSCD

薄膜型声学超材料的提出与发展为使用轻薄结构有效解决低频噪声问题带来了希望。然而,受限于局域共振机理,单层的薄膜型声学超材料仅能够在极窄的频段范围内具备优异的低频隔声性能,很难满足舰船动力装备这类需要宽频段有效噪声的实际场景应用需求。通过将不同结构形式的多层薄膜型声学超材料进行复合,以期突破局域共振机理的窄带局限性,实现优异的低频宽带隔声性能。采用等效面密度概念,建立薄膜型声学超材料复合结构的隔声计算模型;基于双混响测试方法,开展多种复合方式的大尺寸薄膜型声学超材料复合结构的混响场激励隔声性能试验,验证隔声计算模型的有效性,比较并分析其低频宽带隔声性能。该研究工作为薄膜型声学超材料复合结构的隔声性能分析与实际工程应用提供一定参考价值。     

水声材料研发、测试及系统开发

水声材料研发专业组隶属于杭州应用声学研究所换能器与水下声系统研发中心和国防科技工业水声计量一级站,从事水声材料研发和校准测试技术研究工作,可提供声学结构设计、硫化灌注工艺、声学性能测试、测量系统设计和丌发、消声水池工程项目等技术服务,提供无硫橡胶吸声尖劈系列、无硫橡胶吸声圆锥系列、耐压吸声术尖劈、耐压宽带反声障板、耐压吸声障板、耐压隔声构件、去耦复合材料、透声包覆层材料等产品。     

两边支撑声学超材料板的低频宽带隔声性能研究

以电力变压器低频隔声为应用背景,提出了一种结构简单轻质的局域共振声学超材料板,它由在两边支撑框架上紧密粘贴高分子聚合物薄板制成,相比四边支撑超材料板,其具有更加优越的低频隔声能力。在声波垂直入射条件下,采用有限元仿真对其隔声特性进行研究,结果表明在248 Hz处出现了一个明显的隔声峰,隔声量达到了31 dB。为拓宽低频隔声频带,在超材料板上布置质量块,仿真结果表明在152~560 Hz范围内出现了三个密集的隔声峰,最高隔声量达26 dB,从而一定程度上实现宽频隔声效果;同时在120 Hz处出现了一个隔声量为18 dB的隔声峰。最后搭建了基于小型箱体的隔声实验平台,可以发现实验测试结果与仿真结果具有较好的一致性,从而验证了轻质声学超材料板良好的低频宽带隔声性能,说明了两边支撑声学超材料板具有广阔的工程化应用前景。     

消声瓦声学性能的大面积宽频带测量

本文利用水声计量测试最新研究成果-水声材料声学性能的自由场宽带压缩脉冲叠加法测量技术,在实验室对某型消声瓦(600×800×50mm)的声学性能进行了准确测量,测量频率范围为2kHz～20kHz.本文首先对测量系统和过程作简要的介绍;然后对声速和密度等参数已知的均匀材料样品进行了测量,并与理论计算进行比较,以核查测量系统的能力和性能;最后给出某型消声瓦的测量过程与具体测量结果.     

宽带水声参量阵指向性设计与实验验证

利用宽带水声参量阵可产生高指向性宽带低频声束,推导了宽带水声参量阵生成低频声束的自解调理论模型,对其换能器指向性进行了分析与设计,并研制出了宽带水声参量阵样机。测试结果表明：该样机产成的2 kHz声束的-3 dB指向性锐角约为2.6°,具有很好的指向性,且旁瓣抑制效果好,能够产生无旁瓣的高指向性低频声束。这为解决浅海水声通信的多途干扰、远程水声保密通信等问题提供了一条新思路。     

气垫隔声结构水中隔声性能分析

提出气垫隔声结构形式,与以橡胶阻尼材料为基体的隔声去耦瓦相比,气垫隔声结构具有孔隙率大的特点,能更好的隔声去耦。用解析方法分析无限、有限气垫隔声结构在水中的隔声性能,研究板厚与中间层特性声阻抗对隔声量的影响并分析无限结构与有限结构的差别。结果表明：在水中的隔声曲线中没有在空气中因“质量―弹簧―质量”共振造成的隔声低谷现象,且在低频时有限结构的隔声性能较好。行波管声学试验测试了气垫双层板结构的低频隔声性能,证实气垫隔声结构在水中的隔声效果和其在水中声学性能的正确性。     

带背腔薄膜型声学超材料低频隔声特性分析

为弥补传统材料难以有效控制低频噪声的不足,提出一种由弹性薄膜、穿孔质量环和背腔组成的薄膜型声学超材料,建立单元声固耦合有限元模型,分析其在10 Hz～700 Hz频段内的薄膜振动特性,探讨薄膜预应力、穿孔半径、背腔高度、附加质量和薄膜厚度对隔声性能的影响规律,并研究基于协同耦合隔声机理的多单元组合隔声效果。结果表明：薄膜与背腔和穿孔结构耦合能丰富薄膜在低频处的振动形式,较传统Helmholtz 共振腔和薄膜型声学超材料具有更宽的隔声频带;在考虑频段范围内存在6 个声衰减峰,背腔高度、薄膜厚度和预应力的改变可使第三和第四峰值产生明显频率偏移,多单元协同耦合可实现一定频率范围内的连续宽带隔声,分析结果可为低频噪声的轻质和宽带控制提供理论参考。     

一种带薄膜结构的Helmholtz腔声学超材料

为有效控制低频宽带噪声,设计了一种带薄膜结构的Helmholtz腔声学超材料。利用COMSOL软件对其透射特性进行详细分析,结果表明:不带膜的原本的Helmholtz腔结构其透射系数虽在低频范围内可以得到峰值,但其结构尺寸较大,且频带很窄,而文中设计的声学超材料结构的透射系数在低频范围可得到多个峰值,在相同结构尺寸下,与原本的Helmholtz腔结构相比,其固有频率向低频范围内偏移,因而提高了结构的低频隔声效果,拓宽了结构的隔声频率带宽。在此基础上进一步研究了声学超材料结构几何参数对透射系数的影响,优化了声学超材料的结构几何参数。     

水下声学超材料研究

声学超材料在空气中应用的研究已经很多,通过对其声学负参数的研究可以实现负折射、声隐身、波束控制以及超分辨成像等功能。声学超材料在空气中的良好应用也让更多的研究者们聚焦水下声学超材料(简称水声超材料)声聚焦、声透射等的研究,其在水下的研究涉及到流固耦合以及模式转换的影响,会更加复杂。水下研究的主要难题有尺度大、低频性能差、不耐静水压力等,针对此类问题,国内外研究者做了很多相关工作。水声超材料的发展历程经历了多个阶段。经典的局域共振型水声超材料的一系列优化措施是对实现水下宽带、低频吸声的探索;超晶格超表面复合结构的声二极管对实现噪声控制、声学通讯、目标探测等起到重要影响;其他比如水声隐身斗篷、水声学棱镜等应用也具有不错的前景。由此可见声学超材料在水下的研究潜力是巨大的。     

薄膜声学超材料降噪性能分析及设计

为了提升薄膜型声学超材料的隔声性能,首先采用模态叠加法和遗传优化算法实现一种反射型薄膜声学超材料单胞多参数结构优化设计;然后为了拓宽薄膜声学超材料单胞结构的隔声带宽,进一步提出一种能够实现低频宽带吸声的十字型薄膜声学超材料。结果表明:采用经过优化所得的反射型薄膜声学超材料可有效提高隔声带宽和离散频率的隔声量;并且十字型薄膜声学超材料单胞在510 Hz至820 Hz频带范围内平均吸声系数达到0.884,从而突破了薄膜声学超材料单胞仅在共振频率附近的窄带内具有优异吸声性能的限制。     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Effect of Permeable Crystalline Material on Steel Reinforcement Corrosion of Concrete

Permeable crystalline materialcan permeate into pores and cracks of concrete and catalyze the reaction between Ca(OH) 2and unhydrated cement to generate a great quantity needle non-soluble crystals, which can stop up the pores and cracks of concrete, and increase the impermeability of concrete. This paper reported the results of a study conducted to evaluate steel reinforcement corrosion of concrete specimens uncoated and coated with permeable crystalline material as well as mixed with the permeable crystalline material. The properties evaluated for corrosion test were water impermeability, water absorption, compressive strength and potential. The results of water impermeability, water absorption, compressive strength clearly showed that the permeable crystalline material could prohibit water, any soluble salts and moisture from penetrating the concrete to cause corrosion, leaking, and other problems, and it did increase the compressive strength, which was favorable for protection of corrosion of reinforcing steel. Moreover, it was concluded from the potential-time curve that the steel reinforcement of uncoated specimen was in the state of activation whereas that of other specimens coated and mixed with the permeable crystalline material was in the state of inactivation. Above all, it was indicated that the permeable crystalline materialis very effective to protect the steel reinforcement of concrete from corrosion.     

The Research and Application About "Dry Peeling Off" Technology for Airplane Surface Paint Layer

In this paper, the principle of spurting take off lacquer were introduced; and with orthogonal method the unsaturate polyester was prepared ;it was easy to peel airplane paint layer off with this material and equipment.     

Quality Study of Honeycomb Core Shaping Without Wax Stabilization

Sandwich panels utilizing honeycomb cores result in lightweight, high-strength units that are very rigid. Indeed, they give honeycomb panels the best strength-to-weight ratio of any construction type available. Conventionally, the wax is poured into the cell of the core to strengthen the structure and prevent the core from being crushed during milling. Much time and labor is required to wax, mill, and clean the cores. In this study, the process of pouring wax into the core was skipped. In other words, the cutter directly milled the core. Experiments showed that the compressive strength of the core produced without wax stabilization was only 3% lower than that of cores produced using the traditional method. In addition, the drum peel strengths of cores produced without wax stabilization were 38.4% higher than cores produced using the traditional method, in which residual wax seriously polluted the adhesive. It was also found that eliminating the wax process can reduce costs.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

In-process thermal treatment of polylactic acid in fused deposition modelling

Polylactic acid (PLA) is one of the most widely used open source fused filament fabrication materials due to its ease of extrusion, biodegradability, and mechanical strength. The mechanical strength of PLA largely depends on the proper growth of its semi-crystalline structure, which can be severely impaired by a low rate of crystallization, particularly in open source printers. This can be further aggravated by the non-uniform thermal distribution of heat that causes improper curing among the extruded beads of the printing material. As a result, PLA printed on open source printers does not achieve the best mechanical properties. This research, for the first time, proposes an additive-free solution implemented through a detailed set of experimentation to improve the curing rate through in-process temperature variations to cure the joints among the beads. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy is used to confirm the improvements in the bead joints. This work is conducted in two phases of experiments. In the first phase, a full factorial ANOVA is used to investigate various process parameters and the important variables are used in the second phase to print test specimens in four different sets.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.     

Early ironwork in Biscay: Survey,excavation, experimentation and materials characterization. An integral study of the mountainside ironworks (ferrerías de monte or “haizeolak”)

ABSTRACT

The production of iron in Biscay (Basque Country, Spain) has been a hallmark of this territory of the North of the Iberian Peninsula throughout its history. The Archaeology team of the Basque Country Mining Museum has spent 13 years, so far, studying the origins of this activity through the evidences left at the old pre-hydraulic iron production workshops known as mountainside ironworks (ferrerías de monte) or haizeolak. It has catalogued 170 archaeometallurgical sites of this type in Biscay, and the archeological excavation of some of them has led to the knowledge of the different stages of the production process that took place in these workshops. The team has also experimentally reproduced the work carried out in a mountainside ironworks from the High Middle Ages, and it has currently started the characterization process of this type of activity through the study of the collected materials.