这样的冲击谱分析能做吗？

cnesim

任意一个结构件；
它的基础--（比如与震源对接的安装面）承受一个指定（比如X方向）的加速度冲击谱：
100hz，20g
500hz，100g
4000hz，100g
计算结构的位移、加速度、应力响应峰值分布


问题
1》哪位知道，hyperworks能算吗？

2》另外，如果能算，能否进行进一步进行优化设计？
（约束：结构上特定位置加速度峰值小于50g，目标：结构质量最小化）

cryber

LZ，建议你先试着做做，遇到问题，大家再一起讨论，不要上来问能不能做，有谁能说没做过的东西就能做或不能做（没有冒犯之意），

liminglaile

这个绝对可以做，而且我做过很多次了。我的工作内容有一部分就是做这个动态荷载的响应谱分析，我的项目的目标也是要求把谱的峰值控制在一个数值之下，同时保证最小的质量。具体的步骤没有必要细说了，因为HyperMesh自带的turtorials已经提供最详细的描述了，建议你先去参阅HyperMesh的教程：modal frequency response，以及相关的几个频率响应分析的教程，你便知道该怎样完成你手头的项目了。

其实绝大多数问题都是在HM的自带教程里已经详细介绍过了，可惜，懒汉太多。

cnesim

3# liminglaile 我想您一定是理解错了，我能提上面的问题，肯定是试过很多遍了！
我问的问题是冲击谱响应分析，不是频率响应分析？不知这位老师是如何做响应谱分析的？（不会是当做频率响应分析来做的吧，没有冒犯之意），如果不是按照频率响应分析做的，能否告知步骤，或者提供学习资料。
谢谢

cnesim

有关于冲击谱的问题希望交流，能否留个联系方式给我，我的email是366282033@qq.com

sunup

楼主自己没有搞清楚吧？你做冲击响应，是瞬态响应分析，不是频率响应分析

liminglaile

3# liminglaile  我想您一定是理解错了，我能提上面的问题，肯定是试过很多遍了！
我问的问题是冲击谱响应分析，不是频率响应分析？不知这位老师是如何做响应谱分析的？（不会是当做频率响应分析来做的吧，没有冒犯 ...
cnesim 发表于 2009-5-6 15:36

现在“老师”这个称呼基本上和“流氓”同一个含意了。哈哈！！！

另外，你的项目要求在HM的自带教程中都有涉及，而且都是很详细的步骤解释，你自己慢慢去看吧。我在上面所说的modal frequency response指的是动态荷载的设置在那个HM自带的modal frequency response里面讲述得很清楚了，而且也同时包括了如何察看你所需要的结构的位移、速度等等信息，全部都有，你需要足够的耐心。

另外，谢谢hg-boy支持！！！大家一起进步！！！为祖国服务！！！哈哈！！！

liminglaile

楼主自己没有搞清楚吧？你做冲击响应，是瞬态响应分析，不是频率响应分析
sunup 发表于 2009-5-6 18:10

对，还有那个transient的教程，都需要好好看看，就知道怎么做了。都是HM自带的，现成的。搂主要细心，还需要耐心。

cnesim

8# liminglaile MSC.NASTRAN高级动力学手册中是这样说的：
Shock spectra analysis and response spectrum analysis are methods used by many
engineers to estimate the maximum dynamic response of a structure. Most applications
involve complicated time-dependent loads or accelerations that excite the base of a
structure, such as an earthquake ground motion on a building or an explosive shock on a
small component in a ship. (Note that the only difference between shock and response
spectra is whether output displacements are measured in a fixed frame of reference or
relative to the base motion.)
The advantage of these methods over a conventional transient analysis is economy and
simplicity. The only major calculation step is obtaining a sufficient number of normal
modes to represent the entire frequency range of the input excitation and resulting
response. The disadvantage of the method is that the accuracy may be questionable and
the requirement of special input data in the MSC.Nastran solution sequences. In many
cases, a direct transient analysis with the actual excitation load will be more accurate, easier
to use, and faster.
The procedure involves two stages. First the applied loads or base excitations are
converted in a direct transient solution (SOL 109) into a spectrum table consisting of peak
response magnitudes for a set of single degree-of-freedom oscillators. Each oscillator is a
scalar spring/mass/damper having a different natural frequency and damping ratio. This
stage is optional since the shock spectrum data is frequently given in the contractual design
specifications or, in the case of earthquakes, is available through governmental agencies.
The second stage of the analysis consists of a modal analysis of the structure, data recovery,
and the response calculation that combines the modal properties of the analysis model
with the spectrum data of the applied loads. This stage is performed in a modal analysis
solution sequence (SOL 103). If a database was saved from the first stage, a restart will
provide the spectrum data automatically. Otherwise, the spectrum data must be supplied
in a direct tabular input (response versus natural frequency for several damping ratios).

cnesim

8# liminglaile
续......
Generating Response Spectra Curves
A response spectrum is generated as follows:
1. Assume that there is a series of small, single degree-of-freedom (SDOF) oscillators
each attached to the same location at the connection to the base structure. (In the
examples in the introduction to this section, the base structures are the building
and the spacecraft). These oscillators each have a different resonant frequency,
and all have the same modal damping ratio (2%, for example).
2. Apply a transient excitation to the base structure. Use the base structure’s
damping when computing the base structure’s transient response at the location
of the SDOF oscillators.
3. Use the base structure transient response as input to each SDOF oscillator.
Compute the magnitude of peak response of each SDOF oscillator, and plot the
peak response versus oscillator resonant frequency.
4. Change the modal damping ratio for the oscillators (to 5%, for example) and
repeat Steps 2 and 3 for the range of expected damping.
The response spectrum, therefore, depicts the maximum response magnitude of an SDOF system as a function of resonant frequency and damping.

Dynamic Response Predictions.

Once a spectrum is computed, it can be used for the
dynamic response analysis of an MSC.Nastran model of the component. For example, the
spectrum generated for a floor in a building that is subjected to an earthquake can then be
applied to a complex model of a piece of equipment attached to that floor. The peak
response of each mode of the equipment model is obtained from the spectrum, and these
peak responses are combined to create the overall response.

cnesim

8# liminglaile
续....

Consider the entire response spectrum process—generation and application—as a
two-step process.
Step 1 is generation of the response spectra
Step 2 is the application of the response spectra. For a given input, transient applied to the base structure (Step 1), the same stresses occur (Step 2) regardless of whether acceleration or displacement spectra were computed in Step 1. However, displacements and accelerations are different, because answers computed by using the absolute acceleration spectrum contain the rigid body contribution, whereas answers computed by using the relative displacement spectrum do not contain the rigid body contribution. Displacement and acceleration responses can be
made equal regardless of which spectra was used by using PARAM,LFREQ,0.01 (or some other small number) to remove the rigid body mode contribution from the answers.
Stresses and other element quantities are unaffected by the contribution of any rigid body modes. The same situation applies to relative velocity spectra as to relative displacement spectra.

第一步是讲如何生成冲击普
第二步：根据生成的谱计算结构的峰值响应
我的问题是：我已经有冲击普了，只进行第二部分工作。在NASTRAN 中我已经做过，现在希望在HW中做一下，并在hw中进行优化，使结构中特定部位的加速度峰值达到最小，或者控制在一定的范围内。

cnesim

6# sunup

生成谱的方法是瞬态响应分析，
根据普计算峰值响应在NASTRAN中是POOR MAN模态分析

请看我其它回复的帖子吧！！老哥

liminglaile

顶一下，莫生气，讨论问题要耐心。

另外，你需要的这种FEA分析我做过许多次，没问题。但是你性格太急躁。

cnesim

13# liminglaile
哈哈，见怪了！看来我真是有点急躁了，我在上面帖子中的语气好象不对，抱歉。
能否发一个您做过的简单实例学习一下呢？多谢！