Low-frequency sound absorption design of underwater perforated structures and research on sound absorption prediction of phononic glass

水下低频宽带强吸声、高阻尼去耦材料对于艇体的隐蔽性具有重大意义。当材料的厚度限制在50mm以内时，传统的水下均质吸声材料可以在较高的频段实现有效吸声，但是难以实现千赫兹频段的有效吸声。虽然含空腔结构、含硬质高密度内核的局域共振结构的引入一定程度上实现了千赫兹频段的吸声，但是空腔结构的抗静水压力较弱；局域共振结构的密度较大，吸声频带较窄。为此，我们组提出了声子玻璃吸声材料的设计构想，实现了千赫兹之上频段的宽带强吸声，但是很难解决千赫兹以内频段的宽带强吸声。此外，声子玻璃材料作为一款新型的消声材料，其吸声性能预报问题一直没有解决，其隔振去耦性能也没有得到很好的研究。为此，本文引入了并联吸声的设计原理，通过多个类穿孔板结构的并联组合来解决千赫兹以内频段的宽带强吸声问题；通过引入改进的水下多孔吸声模型来解决声子玻璃的吸声预报问题；通过对声子玻璃材料样品的振动试验研究，探究了其静力与动力学特性，在此基础上设计了改进型艇用隔振基座并进行了试验研究。 首先是低频吸声问题。水下穿孔吸声结构有微孔型、内插型、孔加橡胶型等，文中首先对影响吸声效果的各个参数进行分析，获得了实现低频强吸声的参数特点。然后使用遗传算法研究了不同的约束条件下，穿孔结构实现低频吸声的组合参数。首先是对于不含橡胶的微孔型与内插型，使用遗传算法搜索确定了多个不同的组合，其可以实现100-1000Hz频段固定频点的强吸声，并对不同的组合进行了对比分析。然后对背腔含橡胶的结构进行搜索获得低频段内不同频点处的强吸声结构，并进行对比分析。 在实现单个结构固定频点强吸声的基础上，本文对穿孔类结构实现宽带吸声的并联结构进行研究，得出了实现并联宽带强吸声的两个条件：背腔隔开与使用欠阻尼单元。在此基础上，进一步研究了背腔中含有橡胶的并联单元的吸声效果，并与未含橡胶的并联单元的吸声效果进行对比分析。最后，利用遗传算法搜索获得了1000Hz以内频段，多种具有宽带强吸声效果的组合结构参数，实现了千赫兹频段内的宽带强吸声结构设计。 针对目前缺乏可用的多孔材料水下吸声预报模型的问题，本文将空气中的多孔声学方法发展到水声应用，建立起空气声与水声材料吸声之间的联系桥梁。本文首先对多孔板泡沫铝在空气中的吸声性能进行测试，利用遗传算法反演获得不同多孔声学模型下的非声学参数，并利用该参数对另一厚度的泡沫铝进行预测，将预测值与实验值对比分析研究反演获得非声学参数准确性。最后选择Pad&eacute;模型预测泡沫铝含硅油样品的吸声效果，并与泡沫铝中含不同种类聚氨酯材料进行对比分析，验证了预测模型的准确性，一定程度解决了多孔材料水下吸声结构的预报问题。 在水下消声与隔振去耦一体化设计中，本文主要通过试验验证了声子玻璃材料基座具有宽带的减、隔振能力与较强的静力承载能力，有望结合声子玻璃的宽带吸声性能，实现减振、去耦、消声一体化设计。 最后为设计主动可控的新型声呐罩结构，研究了拓扑声波导的特征。文中设计了两种声拓扑结构，一种为六角形单元结构，其可以根据参数的调节实现拓扑带宽的有效调控，相对带宽最大可超过 0.5，显著超过已知的结构；另一种为具有C2v对称性的长方形声子晶格结构，改变单元旋转角度可以实现结构的拓扑相变，利用相反拓扑相的结构可以构建稳健的拓扑声波导。该波导对缺陷与无序不敏感，为声拓扑绝缘体应用于水声通讯提供了参考。</p

铁矿粉烧结技术进展

在铁矿粉烧结过程中,需要充分把握铁矿粉的烧结行为和作用,考察其同化性、液相流动性、黏结相自身强度、连晶固结强度等烧结基础特性,有助于企业通过烧结优化配矿有效使用铁矿粉资源。近年来,国内外在铁矿粉烧结理论和技术方面取得了长足的进步,尤其体现在低温烧结、厚料层烧结技术的发展、褐铁矿使用技术的完善、预还原烧结的开发、镶嵌式烧结的设计、高温特性研究的不断深入等方面。这些技术的创新主要围绕如何高效利用铁矿粉资源进行,通常是源于资源的劣化和环境的恶化。然而,铁矿粉的优与劣其实是相对的,通过发挥其优势、抑制其劣势的方式,使得这种矿从劣质变为相对的＂优质＂,并通过这些新技术使其优点凸显、缺点被弥补,那么该矿的使用量、技术指标就能得到提高,也就具有＂优＂的品质。通过这些研究,实现了对劣质铁矿粉资源的高效利用。本文对此进行综述

铁矿粉烧结技术进展

在铁矿粉烧结过程中,需要充分把握铁矿粉的烧结行为和作用,考察其同化性、液相流动性、黏结相自身强度、连晶固结强度等烧结基础特性,有助于企业通过烧结优化配矿有效使用铁矿粉资源。近年来,国内外在铁矿粉烧结理论和技术方面取得了长足的进步,尤其体现在低温烧结、厚料层烧结技术的发展、褐铁矿使用技术的完善、预还原烧结的开发、镶嵌式烧结的设计、高温特性研究的不断深入等方面。这些技术的创新主要围绕如何高效利用铁矿粉资源进行,通常是源于资源的劣化和环境的恶化。然而,铁矿粉的优与劣其实是相对的,通过发挥其优势、抑制其劣势的方式,使得这种矿从劣质变为相对的&quot;优质&quot;,并通过这些新技术使其优点凸显、缺点被弥补,那么该矿的使用量、技术指标就能得到提高,也就具有&quot;优&quot;的品质。通过这些研究,实现了对劣质铁矿粉资源的高效利用。本文对此进行综述

铁矿粉烧结技术进展

在铁矿粉烧结过程中,需要充分把握铁矿粉的烧结行为和作用,考察其同化性、液相流动性、黏结相自身强度、连晶固结强度等烧结基础特性,有助于企业通过烧结优化配矿有效使用铁矿粉资源。近年来,国内外在铁矿粉烧结理论和技术方面取得了长足的进步,尤其体现在低温烧结、厚料层烧结技术的发展、褐铁矿使用技术的完善、预还原烧结的开发、镶嵌式烧结的设计、高温特性研究的不断深入等方面。这些技术的创新主要围绕如何高效利用铁矿粉资源进行,通常是源于资源的劣化和环境的恶化。然而,铁矿粉的优与劣其实是相对的,通过发挥其优势、抑制其劣势的方式,使得这种矿从劣质变为相对的＂优质＂,并通过这些新技术使其优点凸显、缺点被弥补,那么该矿的使用量、技术指标就能得到提高,也就具有＂优＂的品质。通过这些研究,实现了对劣质铁矿粉资源的高效利用。本文对此进行综述

新型轻质阻尼基座设计与隔振性能研究

为了减少船体振动与辐射噪声,采用声子玻璃和弧形衔接结构设计了一种新型轻质阻尼基座。然后用加速度振级落差表征其隔振性能,开展了水泵电机激励下的基座隔振性能试验研究,结果表明阻尼基座在20～10 000 Hz的频率范围具有显著的隔振效果,相较于同尺寸钢制基座,其振动落差总级可达12.93 dB。研究结果充分验证了本文设计的轻质阻尼基座具备高强度、高阻尼、宽频隔振的特点,在舰船机械设备等减振降噪领域具有广泛的潜在应用价值

Underwater acoustic metamaterial based on double Dirac cone characteristics in rectangular phononic crystals

We theoretically construct a rectangular phononic crystal (PC) structure surrounded by water with C-2v symmetry, and then place a steel rectangular scatterer at each quarter position inside each cell. The final complex crystal has two forms: the vertical type, in which the distance s between the center of the scatterer and its right-angle point is greater than 0.5a, and the transverse type, in which s is smaller than 0.5a (where a is the crystal constant in the x direction). Each rectangular scatterer has three variables: length L, width D, and rotation angle theta around its centroid. We find that, when L and D change and theta is kept at zero, there is always a linear quadruply degenerate state at the corner of the irreducible Brillouin zone. Then, we vary theta and find that the quadruply degenerate point splits into two doubly-degenerate states with odd and even parities. At the same time, the band structure reverses and undergoes a phase change from topologically non-trivial to topologically trivial. Then we construct an acoustic system consisting of a trivial and a non-trivial PC with equal numbers of layers, and calculate the projected band structure. A helical one-way transmission edge state is found in the frequency range of the body band gap. Then, we use the finite-element software Comsol to simulate the unidirectional transmission of this edge state and the backscattering suppression of right-angle, disorder, and cavity defects. This acoustic wave system with rectangular phononic crystal form broadens the scope of acoustic wave topology and provides a platform for easy acoustic operation

Band Gaps and Vibration Isolation of a Three-dimensional Metamaterial with a Star Structure

Elastic metamaterials have promising applications in wave control and vibration isolation, due to their extraordinary characteristics, e.g., negative Poisson ratio, band gaps, effective negative mass density and effective negative modulus. How to develop new functional metamaterials using a special structure has always been a hot topic in this field. In this study, a three-dimensional (3D) star structure is designed to construct metamaterials with both negative static and dynamic properties. The results show that the 3D star structure formed a wide band gap at lower frequency and had a negative Poisson's ratio. Different from conventional acoustic metamaterials, the main physical mechanism behind the low-frequency band gap of the 3D star structure is the resonance mode formed by the bending deformation of each rib plate, which made it easier to achieve effective isolation of low-frequency elastic waves with a low mass density. In addition, many structural parameters of the 3D star structure can be modulated to effectively adjust the band gap frequency by changing the angle between the concave nodes and aspect ratio. This study provides a new way to design the 3D acoustic metamaterials and develop the lightweight vibration isolation devices

Experimental research on sound absorption properties of impedance gradient composite with multiphase

In order to improve the sound absorption performance of the sound absorbing material in water, impedance gradient underwater sound absorbing composite with multiphase (IGCM) is prepared in this study. By superposing several layer materials of different impedance gradients, the mixture is poured in the mold layer by layer so that three kinds of IGCM with different mass density gradients of iron powder, tungsten powder and mixture of iron powder and tungsten powder are prepared. Under two operating conditions of the incident angle of 0&deg;and 20&deg;, the results show that the three IGCMs have good broadband absorption characteristics. The sound absorption frequency ranges of the three samples of IGCM under normal incident conditions are concentrated between 6kHz and 10kHz. The sound absorption performance of IGCM under oblique incidence is better than that under normal incidence, especially the IGCM with iron-tungsten powder, which could achieve wide-band strong sound absorption from 2kHz to 10kHz under the condition of oblique incident. The IGCM with iron-tungsten phase under sound wave&#39;s incident angle of 20 &deg; exhibits better sound absorption performance than the other two, which provides a theoretical reference for the design and manufacture of gradient sound absorbing materials.</p

Labyrinthine Structure with Subwavelength and Broadband Sound Insulation

In this text, the combination of spiral structure and zigzag channels is introduced to design labyrinthine structures, in which sound waves can propagate alternately in the clockwise and counterclockwise directions. Finite element method and S-parameter retrieval method are used to calculate band structures, effective parameters, and transmission properties of the structures. The influences of different structural parameters on their acoustic properties are also studied. These results show labyrinthine structures have multiple bandgaps in the range of 0 Hz-1000 Hz, and the proportion of bandgaps exceeds 33%, which indicates labyrinthine structures have good broadband properties. The normalized frequency of the lowest bandgaps is far smaller than 1, which indicates the structures take good control of sound waves on subwavelength scale. Combining units with different structural parameters can achieve better sound insulation. This research provides a new kind of space-coiling structure for low-frequency and broadband sound waves control, which have excellent application prospects

Broadband periodic and aperiodic acoustic topological insulator based on composite honeycomb structure

具有良好可重构性、良好缺陷兼容性及紧凑型的声学拓扑结构可能成为声学发展中一个有前景的方向.本文设计了一种可调谐、应用于空气声的二维宽带复合蜂窝形晶格结构,其元胞拥有两个变量:一个是中心圆的缩放参数s,另一个是&quot;花瓣&quot;图案围绕其质心的旋转角度q.研究发现当s为1.2, q为&plusmn;33&deg;时,在结构的布里渊区中心点出现四重简并态.在&plusmn;33&deg;两侧,能带会发生反转,体系经历拓扑相变;同时,结构的相对带隙宽带逐渐增加,其中q为0&deg;和60&deg;时,相对带宽分别为0.39和0.33.本研究还计算了由这两种转角的声子晶体组成的拼合结构的投影能带,发现在其体带隙中存在着边界态并验证了此拓扑边界的缺陷免疫特性.最后通过变化s,构建了一种非周期性双狄拉克锥型的声拓扑绝缘体并验证了其缺陷免疫性.本研究的体系相对带宽显著超过已知体系,将为利用声拓扑边界的声波器件微型化打下良好的基础.</p