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The Effect of Perforation on the Dynamics of a Flexible Panel 穿孔对柔性板动力学的影响
Q2 Physics and Astronomy Pub Date : 2014-09-17 DOI: 10.1155/2014/526045
A. Putra, Y. M. Cheah, N. Muhammad, A. Rivai, C. M. Wai
Introduction of holes into plate-like structures is commonly found as one of the practical noise control measures to reduce sound radiation. However, perforation also reduces the panel stiffness and hence increases its vibration. The discussion on this effect is lacking and hence this paper discusses the dynamics of a perforated panel from the results obtained from Finite Element (FE) model. Different hole geometries and arrangement are simulated to investigate their effect on the plate mobility. In general, it is found that increasing the perforation ratio increases the plate mobility. For a fixed perforation ratio, the mobility increases at high frequency (above 1 kHz) for a smaller hole density in the plate. The plate with holes concentrated at the middle shows the largest increase of vibration around the plate centre compared to those uniformly distributed or away from the middle and concentrated at the plate edges. This is because as the hole separation becomes smaller, the reduction of the global stiffness around the mid area of the plate becomes greater. This also corresponds to the finding here that the mobility is greater at the vicinity of the hole. Different conditions of the plate edges are found to give consistent trend of the effect of perforation.
在板状结构中引入孔是减少声辐射的一种实用的噪声控制措施。然而,穿孔也降低了面板的刚度,从而增加了面板的振动。由于缺乏对这种影响的讨论,因此本文从有限元模型得到的结果来讨论穿孔板的动力学。模拟了不同孔的几何形状和排列方式对板迁移率的影响。总的来说,发现增加穿孔比增加板的迁移率。在穿孔比固定的情况下,随着孔密度的减小,迁移率在高频(1khz以上)增加。孔集中在中间的板,与孔均匀分布或远离中间且孔集中在板边缘的板相比,在板中心周围的振动增加最大。这是因为随着孔间距的减小,板中部周围的整体刚度减小的幅度更大。这也对应于这里的发现,即在洞附近的迁移率更大。在不同的板边条件下,穿孔效应呈现一致的趋势。
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引用次数: 7
A Combined Softening and Hardening Mechanism for Low Frequency Human Motion Energy Harvesting Application 一种低频人体运动能量收集应用的软化与硬化联合机制
Q2 Physics and Astronomy Pub Date : 2014-09-07 DOI: 10.1155/2014/217032
K. Suhaimi, R. Ramlan, A. Putra
This paper concerns the mechanism for harvesting energy from human body motion. The vibration signal from human body motion during walking and jogging was first measured using 3-axes vibration recorder placed at various places on the human body. The measured signal was then processed using Fourier series to investigate its frequency content. A mechanism was proposed to harvest the energy from the low frequency-low amplitude human motion. This mechanism consists of the combined nonlinear hardening and softening mechanism which was aimed at widening the bandwidth as well as amplifying the low human motion frequency. This was realized by using a translation-to-rotary mechanism which converts the translation motion of the human motion into the rotational motion. The nonlinearity in the system was realized by introducing a winding spring stiffness and the magnetic stiffness. Quasi-static and dynamic measurement were conducted to investigate the performance of the mechanism. The results show that, with the right degree of nonlinearity, the two modes can be combined together to produce a wide flat response. For the frequency amplification, the mechanism manages to increase the frequency by around 8 times in terms of rotational speed.
本文研究了从人体运动中获取能量的机理。首先利用放置在人体不同部位的三轴振动记录仪测量人体在步行和慢跑时运动产生的振动信号。然后使用傅立叶级数对测量信号进行处理以研究其频率含量。提出了一种从人体低频低幅运动中获取能量的机制。该机构由非线性硬化和非线性软化相结合的机构组成,旨在拓宽带宽,放大人体低运动频率。这是通过使用平移-旋转机构实现的,该机构将人体运动的平移运动转换为旋转运动。通过引入卷绕弹簧刚度和磁刚度来实现系统的非线性。通过准静态和动态测量对机构的性能进行了研究。结果表明,在适当的非线性程度下,两种模态可以组合在一起产生宽的平坦响应。对于频率放大,该机构设法将频率增加约8倍的转速。
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引用次数: 7
Surface Wave Propagation in a Microstretch Thermoelastic Diffusion Material under an Inviscid Liquid Layer 无粘液体层下微拉伸热弹性扩散材料的表面波传播
Q2 Physics and Astronomy Pub Date : 2014-08-04 DOI: 10.1155/2014/518384
Rajesh Kumar, Sanjeev Ahuja, S. K. Garg
The present investigation deals with the propagation of Rayleigh type surface waves in an isotropic microstretch thermoelastic diffusion solid half space under a layer of inviscid liquid. The secular equation for surface waves in compact form is derived after developing the mathematical model. The dispersion curves giving the phase velocity and attenuation coefficients with wave number are plotted graphically to depict the effect of an imperfect boundary alongwith the relaxation times in a microstretch thermoelastic diffusion solid half space under a homogeneous inviscid liquid layer for thermally insulated, impermeable boundaries and isothermal, isoconcentrated boundaries, respectively. In addition, normal velocity component is also plotted in the liquid layer. Several cases of interest under different conditions are also deduced and discussed.
本文研究了瑞利型表面波在无粘液体层下的各向同性微拉伸热弹性扩散固体半空间中的传播。在建立数学模型的基础上,导出了表面波的紧致长期方程。在均匀无粘液体层下的微拉伸热弹性扩散固体半空间中,分别对绝热、不渗透边界和等温、等浓边界进行了不完美边界随弛豫时间的影响,用图形绘制了相速度和衰减系数随波数的色散曲线。此外,还绘制了液层的法向速度分量。并推导和讨论了不同条件下的几个有趣的例子。
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引用次数: 6
In Situ Measurement of Discomfort Curves for Seated Subjects in a Car on the Four-Post Rig 汽车四柱架上坐着受试者不适曲线的原位测量
Q2 Physics and Astronomy Pub Date : 2014-08-04 DOI: 10.1155/2014/239178
T. Ibicek, A. Thite
The aim of this study is to measure and quantify perceived intensity of discomfort due to vibration in a vehicle in situ considering complete vehicle dynamic behaviour. The shaker table based discomfort curves or the road test results may not accurately and universally indicate the true level of human discomfort in a vehicle. A new experimental method, using a seated human in a car on the four-post rig simulator, is proposed to quantify discomfort. The intensity of perception to vibration decreased with decreasing input and increasing frequency; the rate of change is different from the published literature; the difference is large for angular modes of inputs. Vehicle dynamic response is used to inform and analyse the results. The repeatability of the method and the fact that they are in situ measurements may eventually help reduce reliance on the road tests. Furthermore, discomfort curves obtained, subsequently, can be used in predictive models.
本研究的目的是测量和量化由于车辆振动引起的不适的感知强度,考虑到整车的动态行为。基于振动台的不舒服曲线或道路试验结果可能不能准确和普遍地表明人在车辆中的不舒服的真实水平。提出了一种新的实验方法,即在四柱钻机模拟器上使用坐着的人来量化不适。振动感知强度随输入的减小和频率的增加而减小;变化率与已发表的文献不同;对于输入的角模,差异很大。车辆动态响应用于通知和分析结果。该方法的可重复性和现场测量的事实最终可能有助于减少对道路测试的依赖。此外,所得的不适感曲线可用于预测模型。
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引用次数: 6
Prediction of Vibrational Behavior of Grid-Stiffened Cylindrical Shells 网格加筋圆柱壳的振动特性预测
Q2 Physics and Astronomy Pub Date : 2014-07-10 DOI: 10.1155/2014/242573
G. Rahimi, M. Hemmatnezhad, R. Ansari
A unified analytical approach is applied to investigate the vibrational behavior of grid-stiffened cylindrical shells with different boundary conditions. A smeared method is employed to superimpose the stiffness contribution of the stiffeners with those of shell in order to obtain the equivalent stiffness parameters of the whole panel. Theoretical formulation is established based on Sanders’ thin shell theory. The modal forms are assumed to have the axial dependency in the form of Fourier series whose derivatives are legitimized using Stoke's transformation. A 3D finite element model is also built using ABAQUS software which takes into consideration the exact geometric configuration of the stiffeners and the shell. The achievements from the two types of analyses are compared with each other and good agreement has been obtained. The Influences of variations in shell geometrical parameters, boundary condition, and changes in the cross stiffeners angle on the natural frequencies are studied. The results obtained are novel and can be used as a benchmark for further studies. The simplicity and the capability of the present method are also discussed.
采用统一的解析方法研究了不同边界条件下网格加筋圆柱壳的振动特性。采用涂布法将加劲肋的刚度贡献与壳体的刚度贡献叠加,得到整个板的等效刚度参数。理论公式是基于Sanders的薄壳理论建立的。假定模态形式具有轴向相关性,其导数使用斯托克变换合法化。利用ABAQUS软件建立了考虑加强筋和壳体精确几何结构的三维有限元模型。对两种分析结果进行了比较,得到了较好的一致性。研究了壳体几何参数、边界条件和交叉加强筋角度变化对固有频率的影响。所得结果新颖,可作为进一步研究的基准。讨论了该方法的简单性和性能。
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引用次数: 19
A Mathematical Images Group Model to Estimate the Sound Level in a Close-Fitting Enclosure 用数学图像群模型估计密闭环境中的声级
Q2 Physics and Astronomy Pub Date : 2014-06-12 DOI: 10.1155/2014/284362
Michael J. Panza
This paper describes a special mathematical images model to determine the sound level inside a close-fitting sound enclosure. Such an enclosure is defined as the internal air volume defined by a machine vibration noise source at one wall and a parallel reflecting wall located very close to it and acts as the outside radiating wall of the enclosure. Four smaller surfaces define a parallelepiped for the volume. The main reverberation group is between the two large parallel planes. Viewed as a discrete line-type source, the main group is extended as additional discrete line-type source image groups due to reflections from the four smaller surfaces. The images group approach provides a convergent solution for the case where hard reflective surfaces are modeled with absorption coefficients equal to zero. Numerical examples are used to calculate the sound pressure level incident on the outside wall and the effect of adding high absorption to the front wall. This is compared to the result from the general large room diffuse reverberant field enclosure formula for several hard wall absorption coefficients and distances between machine and front wall. The images group method is shown to have low sensitivity to hard wall absorption coefficient value and presents a method where zero sound absorption for hard surfaces can be used rather than an initial hard surface sound absorption estimate or measurement to predict the internal sound levels the effect of adding absorption.
本文描述了一种特殊的数学图像模型来确定密闭隔音箱内的声级。这种外壳被定义为由位于一面墙的机器振动噪声源和非常靠近它的平行反射墙所定义的内部风量,并作为外壳的外部辐射墙。四个较小的表面定义了一个平行六面体的体积。主要混响群在两个大的平行平面之间。作为一个离散的线型源,由于来自四个较小表面的反射,主组被扩展为额外的离散线型源图像组。图像组方法为硬反射表面的吸收系数为零的情况提供了收敛的解决方案。通过数值算例计算了外壁声压级和前壁高吸声的影响。这与一般的大房间漫射混响场封闭公式的结果进行了比较,计算了几个硬壁吸收系数和机器与前壁之间的距离。图像组法对硬壁吸收系数值的敏感性较低,并提出了一种可以使用硬表面零吸声而不是初始硬表面吸声估计或测量来预测增加吸收效果的内部声级的方法。
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引用次数: 2
Effect of Velocity and Time-Step on the Continuity of a Discrete Moving Sound Image 速度和时间步长对离散运动声像连续性的影响
Q2 Physics and Astronomy Pub Date : 2014-06-05 DOI: 10.1155/2014/950463
Y. Seki
As a basic study into 3-D audio display systems, this paper reports the conditions of moving sound image velocity and time-step where a discrete moving sound image is perceived as continuous motion. In this study, the discrete moving sound image was presented through headphones and ran along the ear-axis. The experiments tested the continuity of a discrete moving sound image using various conditions of velocity (0.25, 0.5, 0.75, 1, 2, 3, and 4 m/s) and time-step (0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, and 0.14 s). As a result, the following were required in order to present the discrete moving sound image as continuous movement. (1) The 3-D audio display system was required to complete the sound image presentation process, including head tracking and HRTF simulation, in a time shorter than 0.02 s, in order to present sound image movement at all velocities. (2) A processing time longer than 0.1 s was not acceptable. (3) If the 3-D audio display system only presented very slow movement (less than about 0.5 m/s), processing times ranging from 0.04 s to 0.06 s were still acceptable.
作为三维音频显示系统的基础研究,本文报道了离散运动声像被感知为连续运动的运动声像的速度和时间步长的条件。在本研究中,通过耳机呈现沿耳轴运行的离散运动声图像。实验使用不同的速度条件(0.25、0.5、0.75、1、2、3和4 m/s)和时间步长(0、0.02、0.04、0.06、0.08、0.10、0.12和0.14 s)来测试离散运动声图像的连续性。因此,为了将离散运动的声音图像呈现为连续运动,需要以下内容。(1)三维音频显示系统需要在小于0.02 s的时间内完成声音图像呈现过程,包括头部跟踪和HRTF模拟,以呈现各种速度下的声音图像运动。(2)处理时间超过0.1 s是不可接受的。(3)如果三维音频显示系统仅呈现非常缓慢的运动(小于0.5 m/s左右),处理时间在0.04 s ~ 0.06 s范围内仍然是可以接受的。
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引用次数: 0
Subband DCT and EMD Based Hybrid Soft Thresholding for Speech Enhancement 基于子带DCT和EMD的混合软阈值语音增强
Q2 Physics and Astronomy Pub Date : 2014-05-20 DOI: 10.1155/2014/765454
Erhan Deger, M. I. Molla, K. Hirose, N. Minematsu, Md. Kamrul Hasan
This paper presents a two-stage soft thresholding algorithm based on discrete cosine transform (DCT) and empirical mode decomposition (EMD). In the first stage, noisy speech is decomposed into eight frequency bands and a specific noise variance is calculated for each one. Based on this variance, each band is denoised using soft thresholding in DCT domain. The remaining noise is eliminated in the second stage through a time domain soft thresholding strategy adapted to the intrinsic mode functions (IMFs) derived by applying EMD on the signal obtained from the first stage processing. Significantly better SNR improvement and perceptual speech quality results for different noise types prove the superiority of the proposed algorithm over recently reported techniques.
提出了一种基于离散余弦变换(DCT)和经验模态分解(EMD)的两阶段软阈值算法。在第一阶段,将含噪语音分解为8个频带,并计算每个频带的特定噪声方差。基于该方差,在DCT域中使用软阈值对每个波段进行去噪。在第二阶段,通过时域软阈值策略来消除剩余的噪声,该策略适应于对第一阶段处理得到的信号应用EMD得到的本征模态函数(IMFs)。在不同噪声类型下显著提高信噪比和感知语音质量,证明了该算法优于最近报道的技术。
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引用次数: 5
Experimental Study for Vibration Behaviors of Locally Defective Deep Groove Ball Bearings under Dynamic Radial Load 动态径向载荷作用下局部缺陷深沟球轴承振动特性试验研究
Q2 Physics and Astronomy Pub Date : 2014-05-18 DOI: 10.1155/2014/271346
V. Patel, N. Tandon, R. Pandey
Rolling element bearings are used in many mechanical systems at the revolute joints for sustaining the dynamic loads. Thus, the reliable and efficient functioning of such systems critically depends on the good health of the employed rolling bearings. Hence, health monitoring of rolling bearings through their vibration responses is a vital issue. In this paper, an experimental investigation has been reported related to the vibration behaviours of healthy and locally defective deep groove ball bearings operating under dynamic radial load. The dynamic load on the test bearings has been applied using an electromechanical shaker. The vibration spectra of the healthy and defective deep groove ball bearings in time and frequency domains have been compared and discussed. Overall vibration increases in presence of local defects and dynamic radial load.
滚动轴承在许多机械系统的转动关节处用于承受动载荷。因此,这种系统的可靠和有效的功能关键取决于所使用的滚动轴承的良好健康。因此,通过振动响应对滚动轴承进行健康监测是一个至关重要的问题。本文对健康和局部缺陷深沟球轴承在动态径向载荷作用下的振动特性进行了实验研究。试验轴承上的动载荷是用机电激振器施加的。对健康和缺陷深沟球轴承的时域和频域振动谱进行了比较和讨论。局部缺陷和动态径向载荷的存在使整体振动增加。
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引用次数: 9
Vibration Analysis of Hollow Tapered Shaft Rotor 空心锥轴转子的振动分析
Q2 Physics and Astronomy Pub Date : 2014-04-28 DOI: 10.1155/2014/410851
P. Asdaque, R. Behera
Shafts or circular cross-section beams are important parts of rotating systems and their geometries play important role in rotor dynamics. Hollow tapered shaft rotors with uniform thickness and uniform bore are considered. Critical speeds or whirling frequency conditions are computed using transfer matrix method and then the results were compared using finite element method. For particular shaft lengths and rotating speeds, response of the hollow tapered shaft-rotor system is determined for the establishment of dynamic characteristics. Nonrotating conditions are also considered and results obtained are plotted.
轴或圆截面梁是旋转系统的重要部件,其几何形状在转子动力学中起着重要作用。考虑了等厚、等孔的空心锥形轴转子。采用传递矩阵法计算了临界转速或旋转频率条件,并用有限元法对计算结果进行了比较。在特定的轴长和转速下,确定空心锥形轴-转子系统的响应,建立其动态特性。还考虑了非旋转条件,并绘制了结果图。
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引用次数: 7
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Advances in Acoustics and Vibration
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