Numerical optimization of the thickness distribution of three-dimensional structures with respect to their structural acoustic properties

This paper describes a numerical method to optimize the thickness distribution of three-dimensional structures with respect to various vibrational and structural properties. A combination of a commercially available finite element (FE) software package and additional user-written programs is used to modify the shape (but not the number of nodes and elements) of FE models of the structures to be optimized. The design variables are the structure's local thickness values at selected surface nodes. Possible objectives of the optimization include the minimization of the vibration level, the minimization of the structural mass, the maximization of the fundamental frequency, and the maximization of the difference between two arbitrarily chosen natural frequencies. The optimization procedure is applied to three example structures, namely, a rectangular plate, two plates joined at 90°, and a gearbox. Depending on the particular structure and on the choice of the objective function and constraints, the vibrational and structural properties can be substantially improved.     

PHYSIOLOGICAL MEASUREMENTS AS A BASIS OF WORK ORGANIZATION IN INDUSTRY

The measurement of the work-load in industry necessitates the use of reliable methods and of apparatus which is both robust and foolproof. Three methods are usually employed at our Institute: (1) an exact time-study covering the whole working day and including details of all accessory operations and all rest pauses; (2) the measurement of energy cost of work by the use of the respirometer developed at the Institute; (3) the measurement of pulse rate by means of the Muller pulse counter.

A number of examples are quoted of the use of these methods in several forging shops and in a motor car factory. The examples include instances of underloading and overloading of the worker, and the reasons and remedies are discussed.     

运输类大型飞机噪声适航测试方法应用

对研发过程中的新舟700系列飞机在内的涡桨运输类客机的噪声适航方法进行分析,对其瞬时声压级、有效感觉噪声级等算法进行研究.使用丹麦B&K公司的噪声分析产品PLUSE声学测试分析系统,采用基于静态测试预测噪声级的算法,“以机代台”对发动机静态数据进行分析.利用涡桨类飞机竞争机型庞巴迪DHC-8-400飞机已有的噪声数据,使用C#语言和Visual Studio 2013平台开发预测系统.最后利用SPSS软件进行置信区间的计算,验证数据的符合性.方法及竞争机型噪声数据可为今后上市的涡桨类运输飞机提供噪声适航研发依据.     

一种基于感声波纹结构的光学式声传感器

设计了一种基于硅MEMS敏感结构的光学式声传感器,其光学调制原理采用强度调制型,微敏感结构采用具有低应力波纹结构的感声薄膜芯片。对光纤与微敏感结构耦合技术进行实验研究,优化光学参数,并制作传感器样品。经实验测试,灵敏度达80mV/Pa。     

基于柔性测试技术的高精度水下声学采集与发射系统设计

水下声学采集与发射在水声测试系统中起着举足轻重的作用,以往的测试设备往往只针对水下水声信号的原始数据采集,而在岸基与水下系统的授时、定时以及同步性上缺乏可靠的技术手段予以保证,同时也存在测试功能针对性强、扩展性差等缺点;文章提出了基于柔性测试的高精度水下声学采集与发射技术,阐述了其基本的测试原理、关键技术实现以及软硬件实现方法,完成了岸基与水下测试系统授时误差小于200ns,定时同步误差小于100ns,最大6通道,每通道采样不小于200KS/s的水听器采集且同步2通道换能器任意波形输出的硬件功能,软件上实现了任务列表自动解析、基于岸基时间服务器的自动数据采集与发射功能,具有精度高、功能全面、智能化程序高等特点。     

Relationships between crack opening displacement,alloy variables,and crack detection sensitivity

Alloy grain size is known to influence both the propagation path and the closure stress of surface fatigue cracks in many alloys. The general trend is for the path to be more tortuous and the closure stress to be larger, the larger the grain size. By use of Ti Al-4V and Al 7075-T6, the effects of grain size on the nondestructive detection of surface cracks which might arise from closure stress and path irregularity variables were evaluated. Titanium specimens were inspected using an acoustic harmonic generation technique, and it was discovered that the major source of harmonic signals was grain sized crystallographic cracks. Harmonic signals were larger during fatigue in an 8-µm compared to a 4-µm grain sized alloy, as there were more grain sized cracks in the large grain material. Crack closure was found to be extremely important in determining the reflected acoustic amplitude obtained in inspecting small (100–1000 µm) cracks in Al 7075-T6 using a critical angle technique. Average received amplitudes were an order of magnitude smaller for cracks at zero load than for those opened by a tensile stress. The scatter in the reflected amplitude was also large, apparently as the result of variations in the degree of the closure from crack to crack. For the 7075 material, the important effect of larger grain size was to increase the irregularity of the crack path, making the small cracks more visible acoustically at azimuthal angles not normal to the crack plane.     

Time-resolved strain and deformation measurement on the vibrating saxophone reed

Single-reed musical instruments, such as the saxophone, generate sound through a complex interplay between the mechanics of the reed and the hydrodynamic and acoustic pressure in the instrument mouthpiece. To understand this complex mechanism, experimental data are lacking. This paper presents full-field, time-resolved measurements of strain and displacement of a vibrating saxophone reed, measured under mimicked realistic playing conditions. It is found that strain along the length axis of the reed is mainly expansive, except in a small zone near the tip where it becomes compressive when the reed touches the front edge of the mouthpiece. At the instant in the vibration phase where the reed touches the mouthpiece, significant bending and compressive strain appear along the direction perpendicular to the reed axis. Strain magnitudes in both directions are similar, with absolute values of 0.1%. Full-field strain maps reveal subtle characteristics which are not revealed by displacement measurements. Bi-axial bending and strain may be an essential component in reed mechanics, which up till now has been fully neglected in modelling.     

Surface acoustic wave measurements of surface cracks in ceramics

An investigation of scattering from surface cracks has been conducted. In particular, the change in the reflection coefficient of a Rayleigh wave incident on a surface indentation crack has been measured as the sample is stressed to fracture. The acoustic measurements have been correlated with the stable crack extension that precedes final failure. The crack extension behavior of as-indented specimens was found to differ appreciably from that of annealed specimens. Cracks in the annealed samples exhibited partial crack tip closure, but little stable extension, whereas cracks in the as-indented samples displayed both crack closure and irreversible crack growth. This behavior has been rationalized by invoking concepts based upon the residual stresses created by indentation.     

Raumakustische Zielgrößen und Maßnahmen zur Optimierung der kognitiven Leistungsfähigkeit sowie des akustischen Komforts in Mehrpersonenbüros

Lärm zählt zu den häufigsten Quellen von Beschwerden an Büroarbeitsplätzen. Insbesondere Gespräche von Mitarbeitern werden als störend erlebt. Darüber hinaus beeinträchtigt Bürolärm die Leistungsfähigkeit und das Befinden der Angestellten. Richtlinien und Normen berücksichtigen kaum die besondere Bedeutung sprachlicher Hintergrundgeräusche. Der Speech Transmission Index (STI), ein Maß für die Verständlichkeit von Sprache, wird aktuell als geeignete physikalische Führungsgröße zur Gestaltung offener Büroumgebungen diskutiert. Im Rahmen einer laborexperimentellen Untersuchung wird der Zusammenhang zwischen der Darbietung von Hintergrundschallen mit unterschied licher Sprachverständlichkeit (STI) und der kognitiven Leistungsfähigkeit sowie dem empfundenen akustischen Komfort von Probanden untersucht. Dabei zeigt sich ein starker Zusammenhang zwischen der Sprachverständlichkeit und Maßen kognitiver Leistungsfähigkeit sowie akustischem Komfort. Der STI kann daher als eine geeignete physikalische Führungsgröße zur Gestaltung offener Büroumgebungen betrachtet werden. Room acoustical set values and measures for optimization of cognitive performance and acoustic comfort in open‐plan offices. Noise is among the most frequently mentioned sources of complaint in open‐plan offices. Particularly conversations of colleagues are perceived as being annoying. In addition office noise is known to impair employees’ cognitive performance and wellbeing. Standards and norms hardly account for the special role of background speech. The Speech Transmission Index (STI), a measure of speech intelligibility, is assumed to be a suitable physical set value for the acoustical design of open‐plan offices. The results of a laboratory experiment are presented investigating the relationship between presentation of background speech varying in STI and cognitive performance as well as perceived acoustic comfort. A strong relationship between speech intelligibility and cognitive performance as well as acoustic comfort is found. Therefore the STI can be assumed to be a suitable physical set value for the acoustic design of open‐plan office.