敲击乐器弦振动的Matlab可视化模拟

敲击乐器能够演奏出优美动听的音调旋律,其敲击工具与弦振动之间存在着规律性数理关系,不同形状的锤击工具,产生的音调具有明显差异.利用数理方法推导出敲击乐器采用不同锤击工具(平面锤、余弦凸面锤、细棒锤)产生的弦振动波动方程,通过计算软件Matlad)实现对弦振动复杂的波动方程数值求解,以直观的图像形式对弦振动进行了可视化仿真模拟.     

蛋壳陶和玻璃杯的振动频率测定及音调对应

对振动的基本原理进行了阐述，利用手机软件，对4种不同的玻璃杯和一种蛋壳陶进行了固有振动频率的测量.实验中对玻璃杯以杯震碎的原理进行了分析并实际震碎了一种玻璃杯，同时利用不同水量的玻璃杯发声频率不同的原理，测量了不同水量玻璃杯对应的音乐音调.实验数据显示蛋壳陶的杯壁非常薄，展现了我国传统文化的魅力.研究的内容可以为玻璃杯振动声音的原理答疑解惑，也可以为如何震碎玻璃杯提供理论和实践的指导，同时依据本研究的内容，设计了两种音乐玻璃杯和音乐黑陶杯.     

影响"水杯编钟"音调变化的实验研究

利用微型麦克风和基于计算机声卡的虚拟频谱分析仪,实时采集水杯受击时的信号频谱图,通过对频谱图的分析获得水杯受击时的音调.利用Matlab对数据进行拟合得出水杯中不同体积水与受击时音调的关系.同时,研究了不同敲击点对音调的影响.     

脉冲敲击技术对PI微球表面粗糙度的影响

作为点火靶重要候选靶丸之一, 聚酰亚胺 (PI) 空心微球采用降解芯轴技术结合双单体气相沉积聚合法 (VDP) 制备. 在PI涂层过程中微球碰撞对表面质量影响较大, 为了减小碰撞提高表面质量, 选用筛网盘做样品盘, 激励方式由压电振动模式改为脉冲敲击模式进行对比. 实验数据表明微球运动过程中碰撞是引起表面质量变差的原因, 通过理论分析确认了筛网盘通过减少接触点可以减少微球与微球间、微球与样品盘间的碰撞, 并且将压电振动改为脉冲敲击模式可以减小微球碰撞次数. 脉冲敲击模式与压电振动模式相比, 其可控性、微球弹跳幅度、消除静电等方面均优于压电振动. 对于微球壁厚均匀性而言, 压电振动略好于脉冲敲击, 但相差较小. 单个微球的壁厚最大偏差前者为0.68 μm, 优于后者的0.73 μm; 单个微球壁厚平均值在同一批次内的最大起伏, 前者为0.26 μm, 优于后者0.57 μm. 白光干涉仪数据显示脉冲敲击起到了提高微球表面质量的作用, 其表面粗糙度Rq值由52–93 nm 减小到28–44 nm. 关键词： 脉冲敲击技术 聚酰亚胺靶丸 表面粗糙度 壁厚均匀性     

利用DIS数字化信息系统对高脚玻璃杯振动声现象的研究

对高脚玻璃酒杯杯沿受力F激励后杯壁发生振动的现象进行了研究,利用DIS声传感数字化信息系统采集振动频率,研究频率与振动有效质量之间的关系,结合振动理论研究其杯壁的受迫振动机理.     

对大气压实验的探索

1　问题提出　　科技活动课上 ,用杯子、易拉罐、火柴、橡皮筋、木板、塑料板、白纸、气球等材料 ,有几种方法可证明大气压的存在 .最简单的方法是 ,将杯子装满水 ,用纸盖上 ,手压着纸将杯子倒过来 ,松手后 ,纸便牢牢地贴着杯沿 .如果杯子不装满水 ,大气也进入了杯里 ,纸盖能否还贴着杯沿 ?2　第一次实验1 )实验目的 :探求杯中水量多少对纸张是否脱落的影响 .2 )实验方法 :通过改变杯中水量 ,观察纸张脱落情况 .3 )实验器材 :玻璃杯一个 (d =6cm,H =1 2 cm) ,纸张 6～ 7张 (1 0 cm× 1 0 cm)4 )实验步骤 :按照表 1改变水量观察纸张脱落情况…     

“水杯编钟”之振源及音程研究

通过实验证实对"水杯编钟"纵敲杯口、横敲杯壁时,分别是空气柱和杯体发声.查找出了部分文献认为纵敲杯口和横敲杯壁发声相同的这一不适结论的原因是模型错误和测量方法不同.实验还表明"水杯编钟"构成8度音程问题并非如通常认为的不能实现或很难实现.     

编磬振动特性的声全息研究

阐述了广义声全息成像的基本原理,对其中声源与其声场的变换关系进行了必要的推导与分析.运用这一原理及自制实验系统,对湖北省博物馆提供的单音磐及双音磐的振动特性进行了实验研究.首次获得单音磐的基频、谐频振模以及双音磬在不同敲击点激励时的两个基频振模.这对进一步研究磐的发声规律及声场特性具有重要意义.     

对“筷子提米”实验的改进

教材中和科普书籍中都有"筷子提米"这个小实验.在实验中,由于杯子内米粒与筷子之间的挤压,使杯子、筷子和米粒紧紧地挤在一起,这样杯子、筷子和米粒之间的摩擦力增大.将筷子向上提起,米粒和杯子由于摩擦力的作用阻碍筷子向上运动,结果反而将米粒和杯子一起提了起来.教材中设计的缺陷是:可操作性差.教学实践中不佳表现是:实验成功率不高,不能在短时间内完成实验;学生独立操作时甚至不能将米和杯子提起.许多教师都对实验进行过改进,不同程度地取得了一定的实验效果.下面给出一种改进方法,与其他改进相比,该改进简单易行,改进后的方法操作简便,极     

THz干涉测量用于障碍物后振动传感的研究

为探索THz干涉技术用于障碍物后振动传感的可行性,采用工作波长214.58 μm(对应频率约1.4 THz)的CO2激光器泵浦气体太赫兹源搭建了一套基于迈克尔逊干涉仪结构的THz干涉测量装置,实验研究了薄纸板遮挡后敲击目标镜产生的微小振动,利用相位分析法和频谱分析法对振动干涉信号进行处理,得到了振动位移随时间的变化以及...     

Chladni's clavicylinder and some imitations

Chladni's accomplishments in the field of instrument making were until recently not nearly as well-respected as his studies on the modes of vibration of plates and rods. However, he had developed his own friction instruments based on the glass harmonica, a popular instrument of his time. The instruments, which he partially built himself, had keys, which distinguished them from the glass harmonica. Additionally, these instruments differed from traditional keyboard instruments as they enabled the crescendo and decrescendo of individual notes after the key had been struck. Although Chladni's clavicylinder fascinated audiences and prompted imitations by many instrument makers, it was largely ignored by composers and pianists and therefore never became part of standard orchestration. The Museum of Musical Instruments of the University of Leipzig features three rare examples of friction instruments which have outlasted the centuries. These instruments were built according to the Chladni principle. After a thorough analysis, including the production of individual notes, these instruments will be presented in their cultural-historical as well as their technical context, followed by a discussion of their advantages and disadvantages. These originals exhibits allow for a conclusive comprehension of Chladni's ideas and his quest for new, unusual tone colors.     

含气泡液体中气泡振动的研究

研究了含气泡液体中单个气泡在驱动声场一定情况下的振动过程. 让每次驱动声场作用的时间特别短, 使气泡半径发生微小变化后再将其变化反馈到气泡群对驱动声场的散射作用中去, 从而可以得到某单个气泡周围受气泡散射影响后的声场, 接着再让气泡在该声场作用下做短时振动, 如此反复. 通过这样的方法, 研究了液体中单个气泡的振动情况并对其半径变化进行了数值模拟, 结果发现, 在液体中含有大量气泡的情况下, 某单个气泡的振动过程明显区别于液体中只有一个气泡的情况. 由于大量气泡和驱动声场的相互作用, 使气泡半径的变化存在多种不同的振动情况, 在不同的气泡大小和含量的情况下, 半径变化过程分别表现为: 在平衡位置附近振荡的过程; 周期性的空化过程; 一次空化过程后保持某一大小振荡的过程; 增长后维持某一大小振荡的过程等. 所以, 对于含气泡液体中气泡振动的研究, 在驱动声场一定的情况下, 必须考虑气泡含量的因素. 关键词： 含气泡液体 超声空化 散射 数值模拟     

近红外光谱分析技术在宝石研究中的应用

运用傅里叶变换红外光谱仪对常见宝石、玉石、有机宝石的近红外光谱进行分析研究以及谱峰归属。宝石的近红外光谱表明,宝石矿物中广泛存在不同类型水的合频、倍频吸收峰,也可出现能量较低的电子跃迁吸收峰,其中水分子组合频吸收峰位于5 200 cm-1±,OH的倍频吸收峰位于7 000 cm-1±,以5 898 cm-1±和7 849 cm-1±为中心的强宽吸收谱带为能量较低的电子跃迁吸收峰,并且当只有7 000 cm-1±出现时表明水以—OH的形式存在于宝石中,当5 200和7 000 cm-1±吸收峰同时存在则表明宝石矿物中水的存在形式既有水分子也有—OH。而有机宝石近红外光谱以7 000 cm-1± NH伸缩振动的一级倍频和5 200 cm-1± NH伸缩振动与酰胺Ⅱ的组合频为特征。但是,近红外光谱吸收峰的峰位、峰型、相对强度因有机宝石的品种不同而有所区别。苯环中CH的伸缩振动与弯曲振动组合频吸收峰(4 061和4 179 cm-1±)、CH伸缩振动与苯环骨架振动的组合频吸收峰(4 621和4 683 cm-1±)为经过有机物充填处理的宝玉石的特征谱峰,其中,与苯环有关的吸收峰,表示样品经过充填处理,指示样品中环氧树脂的存在。     

分子环境变化对振动退相时间影响的实验研究

物质分子振动退相时间测量是一种非标记无损分子检测方法, 用超连续谱时间分辨相干反斯托克斯拉曼散射方法可同时获得分子振动谱和退相时间. 实验以苯甲腈和甲醇为样品, 研究当分子环境变化时, 其主要振动谱的振动退相时间变化情况. 将苯甲腈与无水乙醇混合, 测量了苯甲腈分子1017, 2247和3085 cm^-1三个典型分子振动的退相时间随环境变化的规律, 并得到了变化后的振动退相时间. 测量了甲醇分子2851, 2960 cm^-1两个相邻分子振动的退相时间随环境的变化情况, 给出实验变化规律. 这种方法具有检测分子所处环境变化和分子相互作用的能力, 在生命科学、分子生物学和材料科学等研究领域中具有重要的应用前景.     

Difference thresholds for intensity perception of whole-body vertical vibration: effect of frequency and magnitude

Difference thresholds for seated subjects exposed to whole-body vertical sinusoidal vibration have been determined at two vibration magnitudes [0.1 and 0.5 ms(-2) root mean square (r.m.s.)] and at two frequencies (5 and 20 Hz). For 12 subjects, difference thresholds were determined using the up-and-down transformed response method based on two-interval forced-choice tracking. At both frequencies, the difference thresholds increased by a factor of five when the magnitude of the vibration increased from 0.1 to 0.5 ms(-2) r.m.s. The median relative difference thresholds, Weber fractions (deltaI/I), expressed as percentages, were about 10% and did not differ significantly between the two vibration magnitudes or the two frequencies. It is concluded that for the conditions investigated the difference thresholds for whole-body vibration are approximately consistent with Weber's Law. A vibration magnitude will need to be reduced by more than about 10% for the change to be detectable by human subjects; vibration measurements will be required to detect reductions of less than 10%.     

FEM calculation of an acoustic field in a sonochemical reactor

The spatial distribution of the acoustic amplitude in a sonochemical reactor has been numerically calculated using the finite element method (FEM). In the FEM program, the acoustic field in a sonochemical reactor is coupled with the vibration of the reactor's wall. The present calculations have revealed that the thin (thick) glass or stainless steel wall is nearly a free (rigid) boundary and that the glass wall is freer than the stainless steel wall. The influence of the attenuation coefficient of ultrasound on the acoustic field has also been studied in order to see the effect of bubbles on the acoustic field. As the attenuation coefficient increases, the vibration amplitude of the reactor's wall becomes smaller and the acoustic emission from the vibrating wall becomes weaker. The qualitative feature of the spatial pattern of sonochemiluminescence from an aqueous luminol solution has been reproduced by the calculation when the attenuation coefficient is in the range of 0.5-5m(-1). When the attenuation coefficient is less than about 0.05 m(-1), the standing wave pattern of an acoustic field in the liquid is very complex due to the acoustic emission from the vibrating wall. The present calculations have also revealed that some stripes of pressure antinodes have also been disconnected when the radius of the transducer is much smaller than the side length of the vibrating plate. The dependence of the acoustic field on the liquid height is also discussed.     

Atomistic finite element model for axial buckling and vibration analysis of single-layered graphene sheets

In this article, an atomistic model is developed to study the buckling and vibration characteristics of single-layered graphene sheets (SLGSs). By treating SLGSs as space-frame structures, in which the discrete nature of graphene sheets is preserved, they are modeled using three-dimensional elastic beam elements for the bonds. The elastic moduli of the beam elements are determined via a linkage between molecular mechanics and structural mechanics. Based on this model, the critical compressive forces and fundamental natural frequencies of single-layered graphene sheets with different boundary conditions and geometries are obtained and then compared. It is indicated that the compressive buckling force decreases when the graphene sheet aspect ratio increases. At low aspect ratios, the increase of aspect ratios will result in a significant decrease in the critical buckling load. It is also indicated that increasing aspect ratio at a given side length results in the convergence of buckling envelops associated with armchair and zigzag graphene sheets. The influence of boundary conditions will be studied for different geometries. It will be shown that the influence of boundary conditions is not significant for sufficiently large SLGSs.     

古编钟的声学特性

编钟是中国古代的重要乐器。通过对模型编钟振动方式、共振频率和声频谱的测量来分析编钟的声学特性,证实了编钟是发两个基音乐音的乐器。阐明了决定敲钟位置和古人调音方法的声学原理。用FFT做实际和模型编钟声的短时频谱分析。应用了信号处理中线性预测等方法来分析编钟声。实验表明用线性预测法计算基音频率是有足够高的准确度的。     

Modal analysis of circular plates with radial side cracks and in contact with water on one side based on the Rayleigh–Ritz method

In this paper, free vibrations of the baffled circular plates with radial side cracks and in contact with water on one side are investigated based on the Rayleigh–Ritz method. The completely free, simply supported and completely clamped boundary conditions are considered. Corner functions are introduced to describe the singularities at the crack tip. The motion of water is expressed by the velocity potential and the interaction between the water and the plate is derived in the form of an integral equation including the dynamic deformation of the cracked plate. The convergence studies are carried out and the numerical results show that the distinctions between the dry and wet mode shapes will be increased obviously excluding the first symmetric and antisymmetric modes when cracks appear. When the approximate methods based on the assumption that the wet modes are identical with the dry modes are adopted to calculate the eigenfrequencies, the errors of the results for cracked circular plates are larger than those for intact ones. The influences of the water on the symmetric and antisymmetric modes are different evidently, and the greatest reduction ratio of eigenfrequency and least difference between dry and wet mode are relative to the first symmetric mode. The verifications based on numerical simulation show that the proposed method is adequate for the investigation of free vibration of baffled circular plates with radial side cracks and in contact with water on one side.