Topology Optimization of Sound-Absorbing Materials for Two-Dimensional Acoustic Problems Using Isogeometric Boundary Element Method

In this work,an acoustic topology optimizationmethod for structural surface design covered by porous materials is proposed.The analysis of acoustic problems is performed using the isogeometric boundary elementmethod.Taking the element density of porousmaterials as the design variable,the volume of porousmaterials as the constraint,and the minimum sound pressure or maximum scattered sound power as the design goal,the topology optimization is carried out by solid isotropic material with penalization(SIMP)method.To get a limpid 0–1 distribution,a smoothing Heaviside-like function is proposed.To obtain the gradient value of the objective function,a sensitivity analysis method based on the adjoint variable method(AVM)is proposed.To find the optimal solution,the optimization problems are solved by the method of moving asymptotes(MMA)based on gradient information.Numerical examples verify the effectiveness of the proposed topology optimization method in the optimization process of two-dimensional acoustic problems.Furthermore,the optimal distribution of sound-absorbingmaterials is highly frequency-dependent and usually needs to be performed within a frequency band.

Sintering preparation of porous sound-absorbing materials from steel slag

Porous sound-absorbing materials were prepared from steel slag using waste expanded polystyrene（EPS） particles as pore former.The influences of the experimental conditions such as fly ash content,sintering temperature,sintering time,and pore former addition on the performance of the porous sound-absorbing materials were investigated.The results show that the porosity of the specimens can reach above 50.0%;the compressive strength and average sound-adsorption coefficient of the sintered specimens are above 3.0 MPa and 0.47,respectively.The optimum preparation conditions for the steel slag porous sound-absorbing materials are as follows：mass fraction of fly ash 50%,waste EPS particles 3.6 g,sintering temperature 1100℃,and sintering time 7.5h,which are determined by considering the properties of the sound-absorbing materials,energy consumption and cost.

Underwater Laser Welding/Cladding for High-performance Repair of Marine Metal Materials:A Review

With the rapid developments of marine resource exploitation,mounts of marine engineering equipment are settled on the ocean.When it is not possible to move the damaged equipment into a dry dock,welding operations must be performed in underwater environments.The underwater laser welding/cladding technique is a promising and advanced technique which could be widely applied to the maintenance of the damaged equipment.The present review paper aims to present a critical analysis and engineering overview of the underwater laser welding/cladding technique.First,we elaborated recent advances and key issues of drainage nozzles all over the world.Next,we presented the underwater laser processing and microstructural-mechanical behavior of repaired marine materials.Then,the newly developed powder-feeding based and wire-feeding based underwater laser direct metal deposition techniques were reviewed.The differences between the convection,conduction,and the metallurgical kinetics in the melt pools during underwater laser direct metal deposition and in-air laser direct metal deposition were illustrated.After that,several challenges that need to be overcame to achieve the full potential of the underwater laser welding/cladding technique are proposed.Finally,suggestions for future directions to aid the development of underwater laser welding/cladding technology and underwater metallurgical theory are provided.The present review will not only enrich the knowledge in the underwater repair technology,but also provide important guidance for the potential applications of the technology on the marine engineering.

A new clay-cement composite grouting material for tunnelling in underwater karst area

A new clay-cement composite grouting material (CCGM) for tunnelling in underwater karst area was developed through the excellent synergistic interactions among cement, clay, meta-aluminate and lignin. The probable formation mechanism of the material was proposed based on a series of experimental tests. The results show that with an optimal mass ratio (2:1:1:0.024) for water, cement, clay and additives, the obtained CCGM displayed an excellent grouting performance for karst in an underwater condition. Compared with neat cement grouts and clay-cement grouts, CCGM has faster gel time, lower bleeding rate and bulk shrinkage rate, greater initial viscosity, and a strong resistance to water dispersion. A successful engineering application indicates that CCGM not only fulfils a better grouting performance for karst in underwater conditions but also reduces the engineering cost and environmental pollution.

Parameter Study on a Composite Sound-Absorbing Structure Liner in Elevator Shafts

With the growing global environmental awareness,the development of renewable and green materials has gained increased worldwide interest to substitute conventional materials and are favorable for sustainable economic development.This paper proposed a novel eco-friendly sound absorbing structure(NSAS)liner for noise reduction in elevator shafts.The base layer integrated with the shaft walls is a damping gypsum mortarboard,and a rock wool board and a perforated cement mortarboard are used to compose the NSAS.Based on the acoustic impedance theory of porous materials and perforated panels,the sound absorption theory of the NSAS was proposed;the parameter effects of the rock wool board(flow resistivity,porosity,structure factor)and perforated panel(perforated rates,thickness,density,perforated diameter)on NSAS absorption were discussed theoretically for absorption improvement,and experiments were also conducted.Numerical results showed that the perforation rate,the thickness of the perforated plate,and the porosity,flow resistance,and volume density of the rock wool board played a key issue in the absorption performances of the NSAS.Experiments verified the accuracy of the proposed theoretical model.Wideband sound absorption performance of the NSAS at frequencies between 500–1600 Hz was achieved in both numerical analysis and experiments,and the sound absorption coefficient was improved to 0.72 around 1000 Hz after parameter adjustments.The NSAS proposed in this paper can also be made of other renewable materials with preferable structure strength and still has the potential to broaden the absorption bandwidth.It can provide a reference for controlling the elevator shaft noise.

Underwater Directional Acoustic Source Based on Pentamode Material

An underwater directional acoustic emitter is conceived with a highly anisotropic lattice material,whose acoustic characteristics manifest strong dependence on the orientation of the lattice material’s principal axis.Exploiting these features,a cylindrical structure made of such anisotropic lattice material is engineered to possess distinct impedance values in different directions,thereby facilitating wave emission along the principal axis while inducing reflection in other directions.Notably,through numerical simulations,it is demonstrated that the emission direction can be effectively manipulated by adjusting the principal axis orientation,concurrently enhancing the emitted power.In contrast to previous directional acoustic structures,the compact emitter presented in this study can get rid of the size-wavelength constraint,enabling effective control of low-frequency waves.

Oblique incidence properties of locally resonant sonic materials with resonance and Bragg scattering effects

A locally resonant sonic material （LRSM） is an elastic matrix containing a periodic arrangement of identical local resonators （LRs）, which can reflect strongly near their natural frequencies, where the wavelength in the matrix is still much larger than the structural periodicity. Due to the periodic arrangement, an LRSM can also display a Bragg scattering effect, which is a characteristic of phononic crystals. A specific LRSM which possesses both local resonance and Bragg scattering effects is presented. Via the layered-multiple-scattering theory, the complex band structure and the transmittance of such LRSM are discussed in detail. Through the analysis of the refraction behavior at the boundary of the composite, we find that the transmittance performance of an LRSM for oblique incidence depends on the refraction of its boundary and the transmission behaviors of different wave modes inside the composite. As a result, it is better to use some low-speed materials （compared with the speed of waves in surrounding medium） as the LRSM matrix for designing sound blocking materials in underwater applications, since their acoustic properties are more robust to the incident angle. Finally, a gap-coupled LRSM with a broad sub-wavelength transmission gap is studied, whose acoustic performance is insensitive to the angle of incidence.

水声材料声振特性的驻波管测量方法

提出了一种基于驻波管的测量方法,以获得水声材料在静水压条件下的声学和振动特性参数。设计了带有气压补偿功能的低频发射换能器,作为驻波管的声源,通过水柱将换能器的平面活塞振动耦合到水面下的被测样品。在被测样品背衬上安装加速度计,测量样品背面振速;同时在管壁中嵌入一对水听器,测量水柱声压。导出样品声波入射面的振速和声压,进而计算出样品前表面和背衬面之间的振速传递系数(去耦系数)、样品的输入阻抗和声压反射系数。建立低频驻波管测试系统,声管尺寸为内径300 mm、外径600 mm、高3 m,工作频率范围100~1000 Hz,利用水层样品和多层穿孔橡胶样品开展了实验研究。实验结果显示,测量数据与仿真计算数据吻合较好,验证了测量方法的有效性。

水声材料声学参数测试技术的进展

水声材料是水下声系统能力形成和发展的基础,其声学参数测试技术是确保水声材料构件功能实现的重要保障,然而目前水声材料构件的测试技术面临着低频拓展及高压拓展等方面带来的技术挑战。水声材料构件的声管测试技术可分为驻波管法、脉冲管法和行波管法,此3种方法在适用性方面相互补充,但存在测试构件尺寸小难以阐明结构的整体特性、构件与管壁间的缝隙造成测量失准的问题。自由场测试技术及压力罐测试技术是大面积水声材料测试的有效手段,但存在测试构件边缘衍射造成测量准确性降低的问题。对目前采用的水声材料测试技术及其研究现状进行了综述,讨论了各类测试技术存在的困难和挑战,并展望了水声材料构件测试技术未来的发展方向。

高分子基水下灌浆材料的研究进展

水下灌浆是水工建筑物修补加固的重要方法。相较于水泥基灌浆材料,高分子基灌浆材料具有黏度低、可灌性好、凝胶固化速率快和弹性好等优势,适用于细小裂缝和活动裂缝的快速修复。然而,目前常用的高分子基灌浆材料用于水下灌浆时,存在力学性能差、黏结强度差、耐久性差和成本高等不足。文中结合常用的高分子基灌浆材料,分析了水下灌浆的难点,并从树脂主剂、固化剂和助剂3个方面归纳了水下灌浆材料的改性策略。最后,指出了水下灌浆材料的未来发展方向是绿色化和自修复功能化,以更好地适应复杂的水下环境。

气凝胶复合材料在干式潜水服内胆隔热性能提升中的应用

为提升干式潜水服内胆的隔热性能,并探究气凝胶复合材料在潜水服内胆中的水下应用潜力。选择絮片型、发泡型及非织造布型气凝胶复合材料,采用绗缝工艺技术模拟材料在水下的受压状态,研究其在压缩状态下的隔热性能,然后,制作潜水服内胆,通过暖体假人实验及真人水下实验测试其隔热性能。结果表明,絮片型气凝胶复合材料的水下适用性优于絮片型新雪丽棉;发泡型及非织造布型气凝胶复合材料的热阻受压强影响小,也较适用于水下环境;在真人实验过程中,潜水员的核心温度始终大于37℃,证明所研制的气凝胶复合材料内胆具有良好的水下隔热效果。研究结果可为受压环境下防护服隔热材料的应用方法提供指导建议。

水下无人潜航器结构材料腐蚀研究进展

无人潜航器是人们开发、利用、探索海洋必不可少的工具之一,并具有广泛的军事应用前景。随着科学技术的不断进步和发展,无人潜航器不断地突破自己的极限工作深度,由于海洋环境的特殊性和复杂性,对其结构材料要求越来越高。基于国内外最新研究进展,综合分析了无人潜航器结构材料在海洋环境中的腐蚀因素,包括海水温度、pH值、含盐量、氯离子浓度和溶氧量等。针对无人潜航器结构材料在海洋环境中的腐蚀类型,探究了在特殊工作环境中水下无人潜航器结构材料发生腐蚀的原因。阐述了无人潜航器结构材料在海洋环境下的防腐蚀方法并对其未来防腐蚀技术的发展进行了展望。

海水老化下类填充微穿孔板结构水下吸声材料的性能及其寿命预测

针对现阶段潜艇用水下吸声材料的低厚度强低频吸声的性能诉求,基于三维间隔织物,将兼具多孔和共振吸声特性的类填充微穿孔板(F-MPPL)结构引入常规空心微珠填充水下吸声材料(HBF复合材料)中,设计出新型三相复合水下吸声材料(F-MPPL复合材料)。鉴于海中复杂环境对水下吸声材料声学性能的影响,采用人工海水浸泡的方法对F-MPPL复合材料进行海水老化,结果发现老化12个月后的F-MPPL复合材料平均吸声系数下降了13.6%。同时,基于海水老化下孔隙率和穿孔率的变化对最终宏观模型仿真结果的影响,对F-MPPL复合材料的水下吸声性能寿命进行预测发现,模型可准确预测材料吸声峰值的位置,但对材料吸声系数峰值的大小预测稍有偏差。研究结果可为各类水下吸声材料的吸声性能老化研究提供实践经验,并为F-MPPL结构在海水老化下的长期寿命预测及性能优化提供理论参考。

水下修复材料的黏结强度与变形性能研究进展

介绍了常用的几种水下修复材料的性能,分析了其作用机理,强调了黏结强度和变形性能的重要性,指出了各水下修复材料在接缝修复中存在的问题及优缺点,并提出了未来重点研究方向。

pH响应生物质功能材料的制备及其变色与油水分离应用

利用3-氨丙基三乙氧基硅烷对虾青素和2-羟基-1,4-萘醌进行偶联修饰,并引入棉纤维浆粕,通过抽滤-挤压的方式构筑pH响应生物质变色材料;采用红外光谱、X射线衍射分析和X-射线光电子能谱等检测手段对pH响应生物质变色材料进行性能表征;探究了其在不同酸碱性环境下的变色性能及变色可逆性。该变色材料对水相及油相展现出的不同润湿行为测试证明其具有突出的超亲水/水下超疏油性能,并展现出良好的油水分离效果。

深海水密连接器密封技术的发展现状

水密连接器是海洋装备关键通用配套器件之一,保证了深海探测器在对海洋资源探索过程中能量的供给以及信号的传输。本文介绍了水密连接器的发展历史、国内外水密连接器的种类、生产制造工艺和企业以及应用场景,着重阐述了水密连接器中封装绝缘材料与金属导体之间密封技术的研究进展。结合材料学科的特点,对橡胶型水密连接器、玻璃烧结型水密连接器和塑料型水密连接器三种类型水密连接器中绝缘材料的选择、密封成型工艺和研究进展进行综述,为全面了解水密连接器中密封技术提供了参考。最后对水密连接器的未来发展进行了展望。

基于多域特征提取的水下目标材料分类方法

针对水下目标材料的分类问题,提出了一种基于多域特征提取的水下目标材料分类方法.将目标回波信号的时域自回归(AR)系数、倒谱域特征、时频联合域的谱峰及谱峰频率相结合,实现了对金属、岩石、塑料、橡胶4类水下目标材料的分类,并利用消声水池的实测数据来验证该方法的有效性.结果表明,对于4类材料的仿真数据,所提方法的分类正确率均高于80%,且利用多域特征的效果明显优于利用单一特征.对于塑料和金属的实测数据,在信混比不小于0 dB时,所提方法的分类正确率可达80%以上.该方法对目标大小或形状等几何特征的差异具有较好的鲁棒性.

海底门声学计算及水下多孔介质材料降噪

分别建立船舶海底门的声场模型和声-固耦合模型,对海底门的声传递损失、结构湿模态进行计算,获取海底门降噪设计需避开的共振频率。建立海底门的流体模型,采用URANS和FW-H对流场及水动力噪声进行数值计算,云图显示格栅背面出现了显著的流动分离及压力脉动,且压力峰值条带沿着格栅对角线方向分布,频谱曲线显示海底门水动力噪声以低频为主。数值计算表明,当仅将海底门钢制格栅替换成水下多孔介质材料时降噪3.4 dB。共振频率计算及水下多孔介质材料应用为海底门声学设计提供了思路。

回填砂砾料地基振冲挤密加固处理及质量控制

振冲挤密加固处理主要通过振冲器的强烈振动使基础颗粒重新排列、孔隙减少,依靠振冲器的水平振动力,把回填的粗集料挤入周边介质并将孔内粗集料压实,从而提高地基承载力。广泛应用在各类土的液化处理、砂土以及湿陷性土等基础的加固处理,水下回填砂砾料基础由于砂砾料颗粒直径大、强度高,振冲挤密难以处理至设计深度,使用较少。

纳米二氧化硅改性不锈钢网用于油水分离

以正硅酸乙酯为原料,采用溶胶-凝胶法制备了硅溶胶,将硅溶胶与预沉积聚多巴胺(PDA)的不锈钢网(SSM)反应,采用分步沉积和原位生长法制备了超亲水-水下超疏油不锈钢网(SSM-PDA-SiO_(2))。采用FTIR、XRD、TG、SEM和接触角测量仪对其进行了测试。探究了硅溶胶反应时间对SSM-PDA-SiO_(2)亲水-疏油性能的影响,通过自重力驱动测试了其油水分离性能,考察了其循环分离性和力学稳定性。结果表明,PDA作为“桥梁”将纳米SiO_(2)沉积到SSM表面上,硅溶胶与SSM反应8 h制备的SSM-PDA-SiO_(2)-8具有最佳的亲水-疏油性能,水滴能在其表面60 ms内完全铺展,其对二氯甲烷等5种有机溶剂的水下油接触角在156.4°~160.9°之间,对二氯甲烷的滚动角为4.0°,表现出超亲水-水下超疏油特性。首次分离正庚烷/水的油水混合物水通量为40165 L/(m^(2)·h),分离效率99.3%,在50次分离循环时水通量为17728 L/(m^(2)·h),分离效率仍>98%。经过35次砂纸摩擦循环后,SSM-PDA-SiO_(2)-8保持了98%以上的分离效率。PDA的羟基、氨基等亲水基团提高了SSM-PDA-SiO_(2)的超亲水-水下超疏油特性,纳米SiO_(2)增加了其表面粗糙度。