用改装数字毫秒计研究气垫导轨上的振动

实验仪器: QG 150-79型气垫导轨、SSM-5G型数字毫秒计,并配用自制分频器. 将弹簧按图一与滑块相联,就构成了气轨上的谐振系统.谐振周期的表达式是M是滑块的质量,m是两弹簧的质量之和,K1、K2分别是两弹簧的劲度系数. 在滑块两侧附着阻尼磁块,就可以得到阻尼振动系统.阻尼振动振幅表达式是阻尼系数表达式是阻尼振动周期表达式是 目前各大专院校测量机械振动的周期,一般采用手动计时,多周期测量.这种方法不能用于研究阻尼振动.其原因有二:一是阻尼振动振幅不断变化,周期也不是想象的那样固定不变.多周期测量的结果,只能是许多不同周期的平…     

相位差法测受迫振动的阻尼系数

利用音叉在受迫阻尼振动中速度与驱动力之间的相位差测定了阻尼系数.该方法在系统的稳定状态下读数,克服了通常所用的振幅衰减方法中的不稳定性,可降低人为因素给测量带来的误差.     

简谐振动实验中相关物理量间的关系与能量守恒的研究

介绍了如何较为精确地在气垫导轨上测量滑块做简谐振动时的速度、周期、弹簧的等效质量和劲度系数等物理量。利用焦利氏秤对实验中的三对弹簧进行测量,通过逐差法计算得出弹簧的等效质量和劲度系数,其结果和气垫导轨实验所得结论符合较好。在此基础上,对实验中物理量之间的关系进行定量研究,得到周期与振幅无关、周期的平方与滑块的配重块质量呈线性关系。分析了气垫导轨测量速度产生误差的原因,在对测得的速度进行修正后,通过多组实验验证了简谐振动过程中机械能是守恒的。利用Origin软件绘制曲线描述物理量之间的关系和能量变化趋势,生动形象地展示了实验中存在的规律,有利于学生更好地理解实验结论,对实验教学效果有一定的促进作用。     

巧用光电门改进阻尼振动实验

在气垫导轨上阻尼振动研究的实验中,采用两个光电门分别测量阻尼振动的谐振子振动周期和半衰期,进而求出振动系统的粘滞性阻尼常量。该方法克服了传统实验中采用电子秒表测量谐振子做阻尼振动的半衰期时,因需要人眼观察和手动操作而导致测量误差大的问题,实现了对气垫导轨的粘滞性阻尼常量较为精确的测量。     

利用Tracker研究气垫导轨上弹簧振子运动

文章利用Tracker软件的自动追踪功能,对气垫导轨上弹簧振子的运动进行分析,得到滑块运动的数据及图像。在考虑弹簧质量的情况下,利用Tracker软件捕捉到的数据,定量地分析不同时段系统的机械能,验证在短时间段内弹簧振子系统的机械能守恒。在系统长时间的运动过程中,考虑系统中的能量损失,在Tracker分析得到滑块运动的v-t图形的基础上使用软件自带的拟合功能,对长时间段内滑块运动图像进行函数拟合,进而分析计算出气垫导轨上弹簧振子做阻尼振动的阻尼系数。     

气垫导轨上弹簧振子阻尼振动的数字化实验研究

对传统的气垫导轨上弹簧振子的简谐运动和阻尼振动的实验进行改进,同时利用DISLab位移传感器测量数据并结合MATLAB软件进行数据处理,能够方便精确地计算弹簧的弹性系数以及滑块与导轨间的阻尼常量,从而实现了物理实验的数字化。     

利用智能手机研究气垫导轨上的阻尼振动

在气垫导轨上探究弹簧振子的阻尼振动实验中, 一般采用半衰期法来测量黏性阻尼常量. 而半衰期通 常是依靠肉眼判断半衰点并利用手动控制电子秒表来测量的, 这种方法不仅误差大而且不易操作. 利用智能手机 传感器和S P ARK v u e软件, 通过绘制弹簧振子的“ 加速度 时间”图像来测量黏性阻尼常量, 既提高了实验精度也增 强了实验的可操作性     

条形挡光片测速的误差分析及修正方法

在利用气垫导轨装置及配件进行的各类实验中,速度作为一个基本的待测量,其准确测量有着重要的意义.通常利用MUJ-6B通用计数器记录不同类型挡光片经过光电门的遮光时间,用游标卡尺测得遮光距离从而得到速度值.本文从光电计时原理分析了使用U形挡光片、计时方式2不会出现系统误差,而使用条形挡光片、计时方式1会出现较大系统误差的原因.我们进一步利用气垫导轨上两弹簧连接滑块做简谐振动模型的理论公式推导出条形挡光片遮光时被光电门"吞掉"的宽度,进而得到了速度的修正公式.此外,通过气垫导轨上的动量守恒实验从另外一个角度验证了速度修正方法的正确性.     

基于Tracker软件研究竖直方向阻尼振动的居家实验

设计了基于Tracker软件研究竖直方向阻尼振动的居家实验.选用橡皮筋和水果自制振子模型,利用Tracker软件对自制橡皮筋振子的阻尼振动进行研究,绘制橡皮筋振子模型在竖直方向上做阻尼振动的“y t”图像,并通过数据拟合,计算出该阻尼振动的振幅、周期、圆频率、阻尼系数等,是利用生活物品进行大学物理实验的一次尝试.     

阻尼振幅究竟如何衰减

弹簧振子的阻尼振动是一种重要的振动模型。如果阻尼系数为v,振子速度为v,则在阻尼力(-vv)作用下,振子的位移x随时间t的变化为其中阻尼振动的圆频率。　　　　　　低于　无阻尼时的圆频率ω0.阻尼因子是振子质量),它满足低阻尼条件初位相,众所周知,阻尼振动不是严格意义上的周期性运动,不过我们仍把振子所能达到的最大距离称作振幅,只是能量的消耗使之衰减.然而几乎所有的教科书都认为(1)式中的A0是阻尼振幅衰减的起始值,并认为阻尼振幅按A0e-BT方式衰减①。按此意画成的与(1)式对应的位移-时间曲线就如(图一),其中虚线为A。e-’‘,表示振…     

Improvement of damping characteristics of structural members with high damping elastic inserts

The major objective of this work is to investigate theoretically the possibility of improving the damping capacities of structural members with the help of inserts of special high damping materials. The inserts have been considered to be both welded and press-fit to the members. It has been observed that the effectiveness of the press-fit inserts is much more than that of the welded inserts. In case of the welded inserts there exists an optimum size whereas for shrink-fit inserts best results are expected when the inserts are solid. It has been found that with such a method the damping capacity of a member can be considerably increased with no significant loss in static rigidity.     

Vibration and damping analysis of annular plates with constrained damping layer treatments

The natural frequencies and modal loss factors of annular plates with fully and partially constrained damping treatments are considered. The equations of free vibration of the plate including the transverse shear effects are derived by a discrete layer annular finite element method. The extensional and shear moduli of the viscoelastic material layer are described by the complex quantities. Complex eigenvalues are then found numerically, and from these, both frequencies and loss factors are extracted. The effects of viscoelastic layer stiffness and thickness, constraining layer stiffness and thickness, and treatment size on natural frequencies and modal loss factors are presented. Numerical results also show that the longer constrained damping treatment in radial length does not always provide better damping than the shorter ones.     

Radiation damping on cryoprobes

Radiation damping on 600 and 800 MHz cryoprobes was investigated. The phase angle β between a vector 90° phase shifted to the precessing magnetization and the rf field induced in the coil was found to depend markedly on whether an FID was being acquired or not. The magnitude of the radiation damping field was sufficiently strong to restore 95% of the equilibrium water magnetization of a 90% H2O sample in a 5 mm sample tube within about 5 ms following a 165° pulse. This can be exploited in water flip-back versions of NOESY and TOCSY experiments of proteins, but care must be taken to limit the effect of the radiation damping field from the water on the Ha protons. Long water-selective pulses can be applied only following corrections. We developed a program for correcting pulse shapes if β is non-zero. The WATERGATE scheme is shown to be insensitive to imperfections introduced by radiation damping.     

Hysteretic damping and causality

It is proven that linear oscillatory systems with hysteretic damping in the form of complex stiffness and/or complex elastic moduli satisfy the causality principle: the response of such a system to an arbitrary external force cannot appear earlier than the onset of the force. The proof, based on a rigorous solution to the problem of forced oscillations, is presented in detail for an oscillator with a complex stiffness, as well as in a brief explanation for a system with N mass. It is also shown that these systems are Lyapunov-unstable. A comparison is made to other linear hysteretic damping models.     

Rotational damping in ytterbium nuclei

We have made the first clear measurements of rotational damping widths in nuclei. In a mixture of three Yb nuclei, these widths are 300 +/- 60 keV between 1.2 and 1.5 MeV gamma-ray energy [approximately (37-57)Planck's constant]. Compound damping and motional narrowing are discussed in connection with these results.     

Power law damping parameter identification

The parameter estimation of a nonlinear power damping system is studied. The parameter identification method used here assumes a priori the equation of motion describing the system dynamics. The method, which is based on the measured data (acceleration), was applied to the free and forced vibrations.The identification procedure was found to be robust on the guessed value of parameters at the numerical experimentation. The parameter values were estimated with a good accuracy for both modes of system operation (free and forced) if only the measured time history was sampled at a high enough rate for the noise level contained within. It was shown that the steady state of the harmonically excited system is not the best region for the parameter identification with this method.During the experimentation the method was applied to the free vibrations in different media (air and water). The results obtained by the parameter identification method were compared to the ones obtained by separate tests and good agreement was found. The identification procedure was found to work fine for all models under consideration and the models' responses correspond well to the measured acceleration time histories.     

Dislocation damping in alkali halides

In the amplitude independent region the dislocation damping is attributed to either phonon-drag (Granato-Lücke theory) or to the compensating charge-cloud surrounding electrically charged dislocations (Robinson-Birnbaum theory). The experimental results for the dependence of the damping on temperature, frequency and dislocation charge are compared with the two theories. Since it is found that in some cases it is necessary to include both forms of damping, a more complete theory is developed which includes both terms.

In the amplitude dependent region the dislocation damping was thought to be due to the dislocations breaking away from pinning points or breaking through the compensating charge-cloud. Using the piezoelectric defect results for electrically charged dislocation in KCl the force-displacement hysteresis loop for the moving dislocations is determined together with the force-displacement curves for dislocations assuming phonon and charge-cloud damping. These results are found to be inconsistent with the “break away” models for amplitude dependence but instead to be consistent with the restoring force due to an elliptical compensation charge cloud, with a size proportional to the square root of the dislocation charge.