同济大学结构动力学简答题

同济大学结构动力学期末考试

1.What are the step-by-step methods for calculating structural dynamic

response? (有哪些方法)

Interpolation of excitation method

Central difference method

Newmark’s method

Wilson-method

State space method

2.Degree of freedom:

(1)The number of independent displacement required to define the

displaced positions of all the masses relative to their original positions is called the number degrees of freedom(DOFs) (chopra)

(2)The number of displacement quantities that must be considered to

represent the effects of all significant inertia force is called the number of freedoms of a system. Roy R. Craig

3.Effect of damping in vibration:

a)Natural frequency of damped system

b)Natural Period of damped system

c)Existence of damping will reduce the natural frequency

d)For normal structure

e)The displacement amplitude decays exponentially with time

f)The effect of damping is on the rate at which free vibration

decays

4.Mode Shape: it associates with frequency. And, it is deformed mode

of object at that frequency. Example: resonance occurred when , it makes the maximum deformation, different shape (deformation), different frequency.

Mode shape is the proportional relationship among the displacement of DOFs.

Mode shape is most likely to occur in the form of the deformation, and the first mode is the easiest one. Therefore, shape functions

are selected as close as possible to the mode shape to simplify the

analysis.

s of methods for determining the first several vibrations modes

of a MDOF system?

Superposition method

Rayleigh-Ritz method

Reyleigh method

Matrix iteration method

Jacobi iteration method

Subspace iteration method

Stodola iteration method

6.For SDOF system under harmonic loading, when the frequency ration

is very small the amplitude factor is close to 1, when becomes very large becomes very small, explain why?

1.单自由度系统承受谐波荷载，当频率比很小时，振幅放大系数

接近于1，当频率比很大时，振幅放大系数较小。请简要解释

原因。

The single-degree-of-freedom system bears harmonic load.

When the frequency ratio is small, the amplitude amplification coefficient is close to 1. When the frequency ratio is large, the amplitude amplification coefficient is small.Please briefly explain why.

2.“具有粘滞阻尼的系统，理论上其自由振动永远不会停止”，

这种说法是否正确？为什么？

Is it true that a system with viscous damping, in theory, will

never cease to vibrate freely? Why?

3.什么情况下多自由度体系的动力反应不能采用叠加法计算，需

要采用逐步法计算？

Under what circumstances can the dynamic response of a

multi-degree-of-freedom system not be calculated by the

superposition method, but by the stepwise method.

4.请举出土木工程领域避免和利用结构振动的各两个例子。

Please give two examples of avoiding and utilizing structural vibration in the field of civil engineering.

Civil Engineering