激光测振方法在笔记本电脑振动实验中的应用

振动特性的测量和分析是鉴别相关部件工作可靠性的重要手段。常用的测振技术是接触式测量,但这种测试方法对于轻薄结构存在质量和刚度的附加问题,影响测量结果的准确性。笔记本电脑结构复杂、质量轻,宜采用非接触式测量。采用激光测振方法,首先对笔记本电脑结构进行实验模态分析。对于一台笔记本电脑来说,可能引起硬盘工作不稳定的部件包括扬声器、风扇、光驱、键盘等。改变输入条件,考察影响较为显著的扬声器和风扇两个部件与硬盘之间的影响关系与笔记本电脑结构振动分布情况,为结构布局的优化提供依据。     

调谐质量阻尼器用于改善硬盘驱动器读写头动臂的动力特性

通常计算机硬盘中的读写头动臂在3～4kHz的频率范围内有一个准刚性模态，这个准则性模态限制了伺服带宽进而限制了硬盘存储密度的提高。设计了一种调谐阻尼器结构来降低准刚性模态导致的振动，该阻尼器安装在音圈马达的线圈内部，结构简单，不影响动臂移动。所使用的阻尼材料取材于硬盘本身的密封橡胶，也避免了可能的气体污染。实验证明，该阻尼器能够很好地降低动臂在准刚性模态下的振动，因而有利于存储密度的提高。     

新品

影像航母华硕M60影音娱乐笔记本电脑参考价格:9688元人民币华硕新款影音娱乐专业笔记本电脑M60配备了1000GB硬盘,可以让你轻松储存约222张DVD影碟或125部1080p高清大片。高感光金属拉丝外观和ASUS背光LOGO的组合,16英寸16:9无边框屏幕、ATI HD4650、1GB DDR3显存、奥特蓝星扬声器、200万     

阻尼系数对音响系统的影响

音响系统中绝大多数的功放与扬声器的连接都是采用无源式分频连接方式,此种连接方式由于在功放和扬声器之间插入了CL分频网络,不仅会导致功放功率损耗增大,加大功放内阻,而且使功放的阻尼系数大大的损耗掉,直接影响功放与扬声器之间的阻尼匹配,从而导致低音浑浊不清,没有力度,影响整个音响系统。阻尼系数（DF）是指放大器对负载振荡衰减能力大小的一项指标,它等于扬声器的额定阻抗R与放大器输出端的内阻RO和线阻Rx之比,即从上式中可以看出,不管功放的内阻及功放与扬声器之间采用何种导线都对阻尼系数有影响。既然知道了无源…     

用TerraSonde音频测试仪优化扬声器系统

设计安装音响系统时，首先应该考虑和注意的是房间声学环境的设计和处理。然后依照房间的声学性能，设计、安装和调试扬声器系统。使系统达到最佳工作状态。应用基于计算机的测量系统TEF和其他方法，可为音响工程师提供大量数据，实现扬声器系统最佳化。但用这种传统的方法，需要较长的时间和丰富的经验，才能获得最好的结果。然而，常常有声学环境不理想又不能进一步做建筑声学处理的房间，要求工程师短期内完成扬声器系统的设计和优化。这时用传统的方法显然是不可能的。当优化扬声器系统时，不管系统简单还是复杂，至少有三个关键要素…     

一种基于流固耦合问题的低频散射声场预报方法EI北大核心CSCD

提出了一种流固耦合作用下的低频散射声场预报方法。从边界积分方程出发,推导弹性散射中流固耦合方程,通过引入附加质量、附加阻尼、附加压力概念实现解耦。将弹性散射表述为纯刚性散射项与二次辐射项的叠加,建立了刚性散射与弹性散射的联系。与辐射问题不同,散射中流体对结构的作用不仅表现为附加质量和附加阻尼,还存在一个与结构响应无关的压力项,且该压力项是二次辐射项的激励源。采用Fortran编写了边界元算法程序,用DMAP语言实现与Nastran的对接,形成了完整的散射声场预报方法,通过与理论结果对比,验证了预报方法的正确性。圆柱壳散射的计算结果表明:低频散射时弹性不可忽略;圆柱壳厚度对弹性散射强度和指向性有明显影响;肋骨对柱壳散射的影响与振动形式有关,环肋骨对以弯曲模态为主的弹性散射影响很小。     

测试参数对橡胶阻尼材料动态热机械分析结果的影响

通过对橡胶阻尼材料动态热机械性能进行测试,研究了测试频率、升温速率、测试模式等参数对测试结果的影响。结果表明:测试频率和升温速率都对测试结果有较大影响,橡胶阻尼材料的动态力学性能参数随着测试频率和升温速率的增大均向高温方向移动,为了更好地表征材料的阻尼性能,最好采用较低的升温速率;另外,测试模式的选择、静态力动态力以及振幅的设定都会影响测试结果的准确性。     

柔性动边界梁的弹塑性动力响应分析

实际工程中的梁结构并不是采用理想的刚性支承,而通常具有柔性动边界。该文建立了柔性动边界梁的计算模型,模型考虑了梁端有弹性支承、阻尼支承以及刚性块等情况,并利用有限差分方法对运动方程进行离散,研究分析了在动载作用下柔性动边界梁的弹塑性动力响应。研究表明:动边界对梁的变形和受力有很大的影响,与刚性支承相比,竖向弹性支承能够降低梁的振动频率,并且使梁的内力和相对位移幅值减小,从而提高结构的抗力,但提高抗力的效果与载荷作用时间的长短以及振动衰减的程度相关。     

边界粘弹性支承对矩形板强迫振动响应的影响

提出边界粘弹性支承对矩形板强迫振动响应影响的分析方法。该方法基于阻尼复模态分析,利用阻尼复模态的正交性,导出了板的完全解耦的模态方程;通过算例研究和讨论了粘弹性边界支承对板的振动响应的影响。     

三次非线性包装系统关键部件破损曲面研究

通过建立并分析二自由度的包装系统数学模型,提出了三次非线性包装系统关键部件在运输过程中破损边界曲面的评价方法。通过数学分析方法对三次非线性包装系统动力学方程进行求解,得到了破损边界曲线和破损边界曲面。运用数值分析分别讨论了破损边界受频率比、脉冲激励幅值和阻尼的影响规律。为运输包装的材料选择和结构设计提供了依据。     

A technique for measuring pole tip saturation of low inductance heads

Increasing the coercive force of a magnetic recording medium normally improves high density digital performance. However, in rigid disk systems, the head is not in intimate contact with the disk. In addition, the ferrites employed as head materials have much lower saturation magnetization than the metals normally used in other types of heads. Under these conditions, the head field may be inadequate to fully saturate recording media of higher than normal coercive force. In the development of the latest disk products, increasing the coercive force has not improved performance but has increased overwrite modulation. This situation has not been improved by increasing write current amplitude. Pole tip and core saturation of the record head has been suspected as the cause of these observations. This paper describes a method of characterizing saturation effects in low inductance heads such as those used with rigid disks. Evidence of the deterioration of performance due to pole tip and core saturation is shown from isolated pulse measurements on a rigid disk with NiZn and MnZn ferrite heads.     

用FPGA的直写硬盘图像记录技术

根据硬盘的工作原理,结合ATA标准,在分析现有图像记录系统的基础上,提出了一种由FPGA直接控制硬盘实现实时图像无损记录的存储技术。该技术最大限度地保存了原始图像信息,同时具有受计算机干预小、易于扩展升级、性价比高等优点。目前采用两块IDE硬盘时记录速度达到30Mb/s。     

Experimental studies of longitudinal and perpendicular high density recording

Single layer and double layer Co-Cr disks of various coercivities were sputter-deposited on rigid substrates and magnetic parameters measured. Record and playback properties were studied using both ferrite and thin film heads under identical system environments. A well optimized Ni-Co plated longitudinal disk was used as a benchmark throughout this investigation for direct comparison. With the objective of using "off the shelf" ring heads to bring up the perpendicular recording technology on rigid substrates, it was found that the performance of both our preliminary single and double layer Co-Cr perpendicular disks were at least as good as the well optimized longitudinal disk. The double layer disks have an added advantage of lower write current. Signal processing via Hilbert transform using both rectangular and Hamming windows was also studied and applied to the output waveforms.     

On backup policies for hard computer disks

The present study discusses backup policies for the files stored in a hard computer disk or hard computer disks. Two periodical backup policies are proposed both of which make a backup copy of files in a hard disk at age T, where ‘age’ refers to the elapsed time since the previous operation of making a backup copy or recovering from the hard disk failure. Under Policy I, all the files in the hard disk(s) are copied to the floppy disks or the magnetic tapes at every backup time. Under Policy II, a copy of the files created and/or updated since the previous backup time is added to the backup floppy disks or the magnetic tapes at the current backup time. For each policy, the expected cost per unit time over an infinite time span is formulated as an objective function. The existence of an optimal value of T minimizing the expected cost is examined. Numerical examples are also shown to illustrate the proposed backup policies. It is shown under Policy I that there always exists a positive finite optimal backup time, while the conditions under which an optimal backup time exists are clarified for Policy II.     

Design issues for practical rigid disk magnetoresistive heads

Some of the issues of magnetoresistive (MR) head design are discussed from the point of view of practical, high-reliability, low-cost, manufacturable heads for rigid disk files. The major advantages of MR heads over single element inductive thin-film heads are that the MR head gives an ideal, easy to equalize output waveshape, can be used on disks with high coercivities for high linear densities, and is less subject to stability problems at narrow trackwidths. The major advantages of MR heads over metal-in-gap ferrite heads are in narrow trackwidth and high-frequency potential. Disadvantages of MR heads in the rigid disk environment include concerns about reliability and, more specifically, possible environmental fragility, loss of performance due to imperfect alignment between the read and write elements and/or due to signal asymmetry, and the possibility of higher cost/price     

Two-dimensional scattering from an impenetrable cylindrical obstacle in an acoustic quarterspace

The problem of sound scattering by an infinitely long hard or soft circular cylindrical obstacle suspended near a rigid corner is investigated. The separation of variables technique, the appropriate wave field expansions and the method of images along with the translational addition theorem for cylindrical wave functions are used to derive a closed-form analytical solution in form of infinite series. The analytical results are illustrated with a numerical example in which the cylindrical obstacle is positioned near the rigid boundary of a water-filled acoustic quarter-space. The backscattering form function amplitude and spatial distribution of the total acoustic pressure are evaluated and discussed for representative values of the parameters characterizing the system. The effects of incident wave frequency, angle of incidence and proximity of the cylinder to the rigid boundary are examined. Limiting case involving an infinite cylinder in an acoustic halfspace is considered and fair agreement with a well-known solution is established.     

绿色建筑双叶结构轻质墙体隔声性能的试验研究

营造健康舒适的室内环境,对室内声舒适性有明确的要求。空气传声途径的隔声是反映建筑物声学质量最重要的物理量,控制建筑室内噪声水平已经成为室内环境设计的重要工作。本文研究了轻质墙体的隔声性能,重点分析了墙体中龙骨的类型、龙骨间距、空腔填充材料类型、填充材料厚度、面板层数和质量等对轻质结构墙体隔声性能的影响。测试结果表明,扩大独立面板尺寸,增大龙骨间距,墙体空腔填充岩棉或玻璃棉,增大面板层数或提高面板质量,避免结构性连接,对于优化改善双叶结构轻质墙体的隔声性能有积极效果。     

车载信息记录仪硬盘减振缓冲的研究

在车载环境下,冲击和振动会对工作中的硬盘造成传输中断甚至损坏。采用抗冲击振动性能强的硬盘以及合理的减振装置可以使设备稳定地工作。文中通过实验测试出某型号硬盘开启主动保护的激振频率的范围,针对实验数据及车载情况选用钢丝绳减振器,通过简化的动力学模型,确定了减振器型号以及隔振效率,并采用合理的安装方式,设计出结构简单,适应性强的硬盘隔振系统。     

头/盘界面均匀化Reynolds方程及其高效数值求解

当硬盘工作时,磁头滑块飞行在高速旋转的磁盘上方,头/盘界面产生了一层只有几个纳米的气膜,该气膜润滑方程为考虑气体稀薄效应的修正Reynolds方程。为了提高磁记录密度,人们正在考虑用离散磁道（Discrete Track Recording,DTR）磁盘取代传统的光滑磁盘。由于这种DTR磁盘表面磁道和沟槽的影响,在数值求解修正Reynolds方程的过程中,就需要足够多的离散网格来分辨出DTR磁盘表面几何形状,从而带来了计算效率问题。基于均匀化理论和修正Reynolds方程的线性流率（Linearized Flow Rate,LFR）模型,该文推导了一个适合分析DTR磁盘气体润滑特性的均匀化Reynolds方程,并采用有限体积法对均匀化Reynolds方程进行了求解和验证。其结果显示:相对于修正Reynolds方程,求解均匀化Reynolds方程只需要很少的离散网格,从而节省了大量的计算时间,大幅提高了计算效率,且两者压力分布、压力中心和承载力的最大相对误差都小于3.5%。     

声场分解的均匀圆阵实值MUSIC算法

经典方位角估计算法中未考虑阵列安装支架对阵列接收信号的影响,实际中阵列安装支架必然会对阵列接收信号产生影响。以环绕在刚性球上的均匀圆阵为阵列模型。在对声场特性的分析中将声学原理和阵列信号处理技术相结合,探讨了存在刚性球形障碍物时的声源方位角估计问题。首先从声学理论出发,分析了刚性球体散射声场及声场分解,讨论了刚性球体对圆阵响应的影响;进而结合阵列信号处理技术,在对声场分解所得到的特征波束空间,利用实值MUSIC算法实现了声源方位角估计。计算机仿真表明,该算法能较好地估计出空间多个声源的方位角,且计算量小,估计精度高,具有解相关声源的能力。