# what is the meaning of the "alias erro"

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 February 23, 2006, 11:22 what is the meaning of the "alias erro" #1 ztdep Guest   Posts: n/a Hello: what is the meaning of the 'alias erro" in the spectral method! regards

 February 23, 2006, 12:12 Re: what is the meaning of the "alias erro" #2 scar Guest   Posts: n/a "alias erro" sounds like "aliasing error". An aliasing error can be seen as a contamination of the high modes that are not solved. An good reference is Canuto et al. Spectral methods in fluid mechanics

 February 25, 2006, 00:50 Re: what is the meaning of the "alias erro" #3 Wen Guest   Posts: n/a The simples explanation is like this: For example when you look at a fan spinning fast. You sometimes see a slowly rotating pattern, or even a slow rotation to the counter direction. And you are sure you the fan isn't spinning that slowly. So should you believe your eyes? The answer is no. Becasue your eyes has a limited response quickness, i.e. it takes at least 0.01 sec for you to form the image in your brain after you actually see the fan at location A. That means your eyes has low resolusion than necessary, or you can only reslove maximum frequency of 1/0.01 =100. If the fan is rotating at a speed faster than that, your measurement only show you a frequency smaller than 100. Hence the fast mode is aliased to (mapped to) the slow mode. And you will be interpreting a faster(high freq) motion as being a slow (low freq) mothion. If a system has both high freq and low freq at the same time. And your resolution is in the middle, then, you will see two low freq motions. That means the correct low freq motion is contaminated by the aliased (wrongly measured) high freq motion and the high freq motion is completely lost.

 February 26, 2006, 12:11 Re: what is the meaning of the "alias erro" #4 ztdep Guest   Posts: n/a thank you very much! your are a genius. i have understood it !

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