在ansys动力学分析中,怎么求质量阻尼和刚度阻尼?
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在ansys动力学分析中,怎么求质量阻尼和刚度阻尼?
在ansys动力学分析中,怎么求质量阻尼和刚度阻尼?
在ansys动力学分析中,怎么求质量阻尼和刚度阻尼?
质量阻尼与刚度阻尼一般是输入量,他们有一定的关联,很多时候是进行评估指定的,关系如下
Alpha damping and Beta damping are used to define Rayleigh damping constants α and β.The damping matrix (C) is calculated by using these constants to multiply the mass matrix (M) and stiffness matrix (K):
(C) = α(M) + β(K)
The ALPHAD and BETAD commands are used to specify α and β,respectively,as decimal numbers.The values of α and β are not generally known directly,but are calculated from modal damping ratios,ξi.ξi is the ratio of actual damping to critical damping for a particular mode of vibration,i.If ωi is the natural circular frequency of mode i,α and β satisfy the relation
ξi = α/2ωi + βωi/2
In many practical structural problems,alpha damping (or mass damping) may be ignored (α = 0).In such cases,you can evaluate β from known values of ξi and ωi,as
β = 2 ξi/ωi
Only one value of β can be input in a load step,so choose the most dominant frequency active in that load step to calculate β.
To specify both α and β for a given damping ratio ξ,it is commonly assumed that the sum of the α and β terms is nearly constant over a range of frequencies (see Figure 5.6:"Rayleigh Damping").Therefore,given ξ and a frequency range ωi to ωj,two simultaneous equations can be solved for α and β.