ok, as I promise to solve the periodic condition problem for one of my collegues, so i decide give it a try.
http://www.cfd-online.com/Forums/fluent/28770-periodic-boundary-condition-shadow-pairs.html
use TUI: mesh/modify-zones/make-periodic choose your periodic boundary IDs as the input. Everything should go well and complete cells match on both sides should be found.
2014年10月22日星期三
2014年10月19日星期日
difference between fourier transform and wavelets
Haiz, sometimes when all the hope fade, you have to look for something which can cheers you up.
anyway, you still have to live for quite a long time.
so i move out the first step for digital signal processing
http://math.stackexchange.com/questions/279980/difference-between-fourier-transform-and-wavelets
et us say we are looking at the signal of the light emitted from a traffic light. So for some time it will be red, and for some time it will be green (ignore the yellow for now). If we take the Fourier transform of the observed frequency, we can say that
At some time the traffic light shows red. (We know frequency to infinite precision, and that the red part of the signal is non-zero.)
At some time the traffic light shows green.
But a functioning traffic light would have either red or green shown at a time, and not both. And if the traffic light malfunctions and shows both lights at the same time, we would still see from the Fourier transform
At some time the traffic light shows red.
At some time the traffic light shows green.
But if we take the wavelet transform we can sacrifice frequency precision to gain temporal information. So with the wavelet transform done on the working traffic light we may see
At parameter w which corresponds roughly to t(w) being 1 o'clock sharp and k(w) corresponding to red, the wavelet transform is large and non-zero. This can be taken to mean that sometime around 1 o'clock sharp (could be exactly 1 o'clock, could be 1 minute past, could be 30 second before) the light showed a color that is more or less red (could be a little bit purple, or maybe a little bit amber).
At parameter w which corresponds roughly to t(w) being 1 o'clock sharp and k(w) corresponding to green, the wavelet transform is almost zero. This can be taken to mean that at all the times around 1 o'clock (say plus or minus 2 minutes) the traffic light does not show any hint of green.
At parameter w which corresponds roughly to t(w) being five minutes past 1 and k(w) corresponding to green, the wavelet transform is large and non-zero. This would indicate that around 1:05 (maybe 1:06, or 1:04) the light shined greenish (could have a tinge of teal or a bit of yellow in it).
This would tell us that not only can the traffic light show both red and green lights, that at least at around 1 o'clock the light is working properly and only showing one light.
anyway, you still have to live for quite a long time.
so i move out the first step for digital signal processing
http://math.stackexchange.com/questions/279980/difference-between-fourier-transform-and-wavelets
et us say we are looking at the signal of the light emitted from a traffic light. So for some time it will be red, and for some time it will be green (ignore the yellow for now). If we take the Fourier transform of the observed frequency, we can say that
At some time the traffic light shows red. (We know frequency to infinite precision, and that the red part of the signal is non-zero.)
At some time the traffic light shows green.
But a functioning traffic light would have either red or green shown at a time, and not both. And if the traffic light malfunctions and shows both lights at the same time, we would still see from the Fourier transform
At some time the traffic light shows red.
At some time the traffic light shows green.
But if we take the wavelet transform we can sacrifice frequency precision to gain temporal information. So with the wavelet transform done on the working traffic light we may see
At parameter w which corresponds roughly to t(w) being 1 o'clock sharp and k(w) corresponding to red, the wavelet transform is large and non-zero. This can be taken to mean that sometime around 1 o'clock sharp (could be exactly 1 o'clock, could be 1 minute past, could be 30 second before) the light showed a color that is more or less red (could be a little bit purple, or maybe a little bit amber).
At parameter w which corresponds roughly to t(w) being 1 o'clock sharp and k(w) corresponding to green, the wavelet transform is almost zero. This can be taken to mean that at all the times around 1 o'clock (say plus or minus 2 minutes) the traffic light does not show any hint of green.
At parameter w which corresponds roughly to t(w) being five minutes past 1 and k(w) corresponding to green, the wavelet transform is large and non-zero. This would indicate that around 1:05 (maybe 1:06, or 1:04) the light shined greenish (could have a tinge of teal or a bit of yellow in it).
This would tell us that not only can the traffic light show both red and green lights, that at least at around 1 o'clock the light is working properly and only showing one light.
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