雙自由度系統(tǒng)ppt課件-資料下載頁
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【正文】 ratio of natural frequencies forced frequency ratio critical damping constant damping ratio 12 / mm??10 / kFst ??222 / mka ??112 / mkn ??naf ?? /?ng ?? /?nc mc ?22?ccc /2??Chapter 山東大學(xué)機械工程學(xué)院 50 ? the magnitude X1 and X2 can be expressed as ),(),(2211??????gffXgffXstst??Chapter 山東大學(xué)機械工程學(xué)院 51 Optimally Tuned Absorber ? all the curves intersect at points A and B regardless of the value of damping。 these points can be located by substituting the extreme cases of and into the above equations 0?? ???Chapter 山東大學(xué)機械工程學(xué)院 52 ? the most efficient vibration absorber is one for which the ordinates of the points A and B are equal。 this condition requires that the ratio of natural frequencies is given by ? the absorber satisfying the above condition is called the tuned vibration absorber（調(diào)頻或移頻動力吸振器） ? the optimal value of the damping ratio can be found by making the response curve as flat as possible at peaks A and B ? the function can be differentiated with respect to g to find the slope of ? by setting the slope equal to zero at points A and B two values of ξ (ξ A and ξB) can be obtained ??? 11fstX ?/1),(1 ?? gffstX ?/1Chapter 山東大學(xué)機械工程學(xué)院 53 ? the averaged value gives the optimal value for ξ ? the corresponding optimal (maximum) value of bees 3)1(83?????o p tstX ?/1??211 ??????????o p tstXChapter 山東大學(xué)機械工程學(xué)院 54 Design Aspects ? the harmonic excitation must be well know and not deviate much from its constant value ? the driving frequency can shift to one of the bined system’s resonant frequencies ? the driving frequency shifts can be quantified by examining the mass ratio μ defined as the ratio of the absorber mass to the primary mass mm a??? Mass ratio is too small, the bandwidth is narrow ? Mass ratio is too small, the absorber is too big Chapter 山東大學(xué)機械工程學(xué)院 55 Summary ? To understand: vibration isolator vs. vibration absorber, tuned vibration absorber, design parameters for tuned vibration absorber ? Examples to solve . RaoExamples , Problems , 46 Chapter 山東大學(xué)機械工程學(xué)院 56 拉哥朗日 （ Lagrange） 方程方法 第三章 多自由度系統(tǒng) 系統(tǒng)運動方程 自由度數(shù)目的增多，使建立微分方程進行振動分析變的復(fù)雜，因此需要采用 規(guī)范化、程序化， 甚至是 機械化 的方法建立系統(tǒng)的運動微分方程和進行振動分析。 剛度法和柔度法 Chapter 山東大學(xué)機械工程學(xué)院 57 無阻尼系統(tǒng)的自由振動 無阻尼系統(tǒng)的受迫振動 比例阻尼系統(tǒng)的振動 一般粘性阻尼系統(tǒng)的振動 Chapter 山東大學(xué)機械工程學(xué)院 58 固有振動的近似解和數(shù)值解 Dunkerley方法 Rayleigh方法 Ritz法 逆迭代法 其他迭代方法 動響應(yīng)的數(shù)值解 Chapter 山東大學(xué)機械工程學(xué)院 59 本章重要概念和理論 二自由度系統(tǒng)及其特點 耦合概念及其解耦 理解固有陣型的正交性 熟悉模態(tài)的概念 共振與反共振 動力吸振器
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