FE-SEA方法在平台支持船噪声预报中的应用

平台支持船由于作业需要通常配备有动力定位系统,其在侧推工况下舱室噪声超标较为严重。针对这个问题采用计算流体力学(CFD)方法,得到侧推螺旋桨作用在导管上的脉动压力,并将时域计算结果转换成噪声计算的激励条件。采用有限元(FE)与统计能量分析(SEA)混合方法建立船体中频段FE-SEA耦合模型并建立船体高频段SEA模型,对某65 m AHTS船侧推工况下全频段(63 Hz~8000 Hz)舱室噪声进行预报,分析该船噪声分布规律及主要影响因素。并建立起全船的SEA模型,在中频段对比SEA与FE-SEA两种方法得到的舱室声压级频谱曲线,验证了使用混合模型的必要性。     

Numerical modeling of wave propagation in anisotropic viscoelastic laminated materials in transient regime: Application to modeling ultrasonic testing of composite structures

Composite laminate structures remain an important family of materials used in cutting-edge industrial areas. Building efficient numerical modeling tools for high-frequency wave propagation in order to represent ultrasonic testing experiments of these materials remains a major challenge. In particular, incorporating attenuation phenomena within anisotropic plies, and thin intermediate isotropic layers between the plies often represent significant obstacles for standard numerical approaches. In our work, we address both issues by proposing a systematic study of the fully discrete propagators associated to the Kelvin-Voigt, Maxwell, and Zener models, and by incorporating effective transmission conditions between plies using the mortar element method. We illustrate the soundness of our approach by proposing intermediate one-dimensional and two-dimensional numerical evidence, and we apply it to a more realistic configuration of a curved laminate composite structure in a three-dimensional setting.     

中国建筑声学的源流与脉络（1926 ～ 1986）

叙述了我国建筑声学早中期（1926—1986）的发展源流与脉络，主要是介绍有关的人物及其关系，为今后更深入的相关研究作一初步的梳理。     

建筑声学50年的回顾:贺马大猷教授90大寿

我国的建筑声学在马大猷教授奠定的基础上，20世纪50年代以来，无论在科研、设计、声学材料（结构）的研制和应用方面均有重大发展，在厅堂音质设计的某些领域内还取得了突破性的进展。本文仅就马大猷教授在建筑声学领域内做出的贡献，作简要的介绍。     

管网泄漏极性相关法定位研究

针对管网泄漏定位运算量大而不易实现在线检测的问题,设计一种运算快速、实时测量的定位方法。以泄漏液体的声学特性为依据,建立测漏模型,将捕获的信号离散化后极化处理,用极性相关法计算渡越时间,从而得到漏点到测点的距离。为验证极性相关法定位的可行性与可靠性,设计声学管网测漏仪。通过实验证明极性相关法能够有效提高相关函数的运算速度,易于在微处理芯片中进行实时分析,实现了工程中管网泄漏的在线定位测量。     

频率修正在超声变幅杆设计中的研究与应用

超声变幅杆在沿轴线方向作纵向振动时,由于存在泊松效应,纵向振动会引起变幅杆沿径向方向的横向振动。传统变幅杆在设计过程中,忽略横向振动的影响则会导致计算出的谐振频率高于实际频率。为了让变幅杆理论设计谐振频率与实际频率相符合,分别对简单圆柱杆和阶梯形变幅杆进行研究,推导出常用半径比范围内简单阶梯形变幅杆的频率修正公式,使其满足设计和使用要求,并可以减少能量传输过程中的能量损耗。     

A macro-element strategy based upon spectral finite elements and mortar elements for transient wave propagation modeling. Application to ultrasonic testing of laminate composite materials

Proposing efficient numerical modeling tools for high-frequency wave propagation in realistic configurations, such as the one appearing in ultrasonic testing experiments, is a major challenge, especially in the perspective of inversion loops or parametric studies. We propose a numerical methodology addressing this challenge and based upon the combination of the spectral finite element method and the mortar element method. From a prior decomposition of the scene of interest into “macro-elements,” we show how one can improve the performances of the standard finite element procedures in terms of memory footprint and computational load. Additionally, using this decomposition, we are able to efficiently reconstruct important modeling features on-the-fly, such as orientations of anisotropic materials or splitting directions of perfectly matched layers formulations, altogether in a robust and efficient manner. We believe that this strategy is particularly suitable for parametric studies and sensitivity analysis. We illustrate our strategy by simulating the propagation of an ultrasonic wave into an immersed and curved anisotropic laminate 3D specimen flawed with an internal circular delamination of varying size, thus showing the efficiency and the robustness of our approach.     

教室声学环境的分析及改善

对于教室内声学环境的要求,国内及国外一些有关规范都只停留在中频段(500～1 000 Hz)。这样的要求是不够的。在这样的声学环境中,教师健康和学生听课效果均受到影响。文章分析了达到优良室内声学环境的几个重要因素,着重减低低频噪声和控制低频混响时间。利用简单的吸声构件,得到几乎平直的混响时间频率特性。叙述了"掩蔽效应"对中、高频的影响并叙述了"哈斯效应"及在声学处理时要利用有利反射声的注意事项。为得到室内优良的音质环境,提出建议并给出工程实践结果的实例。     

Vertical oscillations of the thermocline caused by internal waves modify coldwater pelagic fish distribution: Results from a large stratified lake

Fishes typically occupy a species-specific temperature range, with their occupied depth being related to the lake’s temperature profile. When a fish’s preferred temperature range coincides with the thermocline, the location of their preferred thermal habitat is influenced by the rise and fall of internal waves, leading to possible changes in fish depth. These internal waves are common in large, stratified lakes, yet we do not know how they affect the spatial distribution and behavior of freshwater fishes. We conducted nighttime hydroacoustic surveys in a large, deep embayment of a large thermally stratified lake to observe whether pelagic fish respond to vertical oscillations of the thermocline caused by internal waves. The coldwater pelagic fish in our study (primarily cisco, Coregonus artedi) typically occupied a narrow vertical band approximately 5–8 m thick and temperatures between 10.8 ± 0.8–13.6 ± 1.6 °C (fishes sized 106–500 mm), just below the thermocline (centered around 15–17 °C). Importantly, the upper bound of fish depth varied in response to vertical thermocline movements associated with internal waves, suggesting fish respond to changes in their physical environment on timescales commensurate with basin-scale internal wave periods (hours to days), to remain within their preferred thermal habitat. Dissolved-oxygen levels were typically above avoidance thresholds of these fish, thus not likely exerting a strong influence on fish location. Our findings emphasize the need to account for internal waves when designing hydroacoustic and netting surveys, as thermocline movements can influence where fish are located.     

Detecting alkali-silica reaction: A multi-physics approach

A multi-physics approach for the assessment of alkali silica reaction (ASR) generates new foundational understanding of the nature of the reaction, which ultimately can be used for the development of techniques and tools for the assessment and monitoring of existing concrete structures. The approach combines two nondestructive evaluation techniques: (1) nonlinear acoustic measurements, which are sensitive to microcracking; and (2) microwave materials characterization measurements, which are sensitive to moisture including the transition of water from its free state in the pore solution to a bound state within accumulating ASR gel. Comparison with assessment of expansion and damage rating index obtained from petrographic analysis on standard mortar bars shows a correlation between all of the measures. Specifically, a strong correlation is found between the cumulative average nonlinearity parameter and expansion, and there is also agreement of the microwave measurements with the damage rating index.