【作者】 范相东；

【导师】 罗俊；

【作者基本信息】 华中科技大学 ， 理论物理， 2007， 硕士

【摘要】 万有引力常数G值的高精度绝对测量非常困难,在目前的各种基本物理常数测量值中,G值的精度是最低的,这除了与万有引力信号非常微弱、不可屏蔽以及在实验上极大程度地受到机械测量精度的限制外,还因为外界的干扰如温度波动,引力场的变化和地面振动也在很大程度上限制了G值测量精度的提高。本文围绕扭秤周期法测G中地面振动对扭秤实验的影响这一主题,通过计算机仿真模拟的方法计算了扭秤悬点在不同的外界激励下扭秤的响应特性,以及对最终扭秤周期稳定性的影响。计算表明,在随机白噪声的激励下引起扭秤周期的波动与目前实验数据相吻合,证实了目前周期波动的原因之一是由于地面振动造成的。在数值计算的基础上,推导出扭秤反常模式的解析表达式,找到了扭秤单摆模式与扭转模式之间的耦合关系,相比数值解,解析解可以给出反常模式与单摆幅度,频率以及扭秤自身结构参数之间的依赖关系,这可以对扭秤的设计给出指导意见:在不影响待测实验信号的前提下,将扭秤设计为对称结构如圆盘,可以显著降低地面振动对扭秤实验的影响;可以同步监测扭秤单摆模式的运动,通过解析解计算其对实验数据的影响并从中扣除。采取隔振措施是降低地面噪声的一种有效途径,建立了实验中一级和二级磁阻尼隔振系统的数学模型,计算了涡流损耗的阻尼因子与阻尼盘安放位置和形状之间的关系,并提出了改进和优化的意见。减小地面振动对扭秤的影响不仅有利于测G实验中周期稳定性的提高,而且对其他的扭秤实验精度的提高也很有帮助。更多还原

【Abstract】 The fact that the gravitational constant G is the least precisely determined constant among all the fundamental constants of nature shows that it still have many difficulties to improve the precision of determination of G. The difficulties in measuring G are mainly resulted from the extreme weakness of gravitational force and the measurement of the geometry of attracting and the attracted masses and the relative positions between them. Furthermore, the temperature drift, non-linear effect and seismic noise are also the reasons to limit the precision of G experiment.This paper mainly deals with the points about the effect of seismic noise on the determination of G. The response of the torsion pendulum when the support point is motivated by different force is simulated. The fluctuation of the period from the simulated data agrees well with the experiment data. The equation describing the dynamics of torsion balance and analysis solution has been proposed. We find the coupling between swing modes and the torsional mode. The analytic solutions show that the amplitude of this coupling mode depends on the amplitude of the swing modes and the frequency of the coupling mode is the linear combinations of the frequency in the two orthogonal directions in horizon. Our improved magnetic damper system can suppress the seismic noise, which is not only benefit for the determining G, but also can improve the precision of other gravitational experiment.更多还原