COMPGROUPS.NET | Search | Post Question | Groups | Stream | About | Register

### 1D space FFT

• Email
• Follow

Hi all,

i have an instantanious velocity profile froma  jet cross section (1D) i have subtracted from this the convectional velocity of the profile (the mean) and the result is a profile of velocity fluctuation in the u direction at a given distance.  (data achieved by PIV technique)

The distance array has a 256 points (0.1072 e-3m to 0.2185m) the velocity profile also there for has the same number of points.  the change in d between samples is 0.854mm

i am using the fft of the velocity data myltiplied by the conjugate fft of the velocity data to only deal with the real parts.

ftu1 = fft(u1)*conj(fft(u1))

my x axis is calculated using,

n=length(dmm);  % dmm is imported data array
L= 218.5e-3;
k= [1/L : 1/L : n/L];

when i
plot (k, ftu1,'.');

i find a very large peak in the first bin,only after this peak (from the second bin to the end) is the data symmetrical.  i am unsure how and why this peak is there.  i am unsure weather this is due to to any spill overs or roll off (decrement). i am pretty knew to using faourier transforms.   i know matlab uses the entire length(x) as the default window function.

is it valid to simply remove this first data point or pad it with zero's.  since this first peak is not witnessed on the other side of the plot (other side of symmetry) i cannot determine this to be my dominant wave number.

Kind regards.
Neet.

 0

See related articles to this posting

On Nov 2, 9:46 am, "Neet Lad" <nits...@hotmail.com> wrote:
> Hi all,
>
> i have an instantanious velocity profile froma  jet cross section (1D) i =
have subtracted from this the convectional velocity of the profile (the mea=
n) and the result is a profile of velocity fluctuation in the u direction a=
t a given distance.  >(data achieved by PIV technique)

If you subtract the mean, the spectrum should be zero
at zero frequency.

> The distance array has a 256 points (0.1072 e-3m to 0.2185m) the velocity=
profile also there for has the same number of >points.  the change in d be=
tween samples is 0.854mm

N    =3D 256
dmin =3D 0.1072e-3
dmax =3D 0.2185
dd   =3D 0.854e-3

(dmax-dmin)/(N-1) =3D 0.85644e-3  % Not 0.854e-3
dmin+dd*(N-1)     =3D 0.21788     % Not 0.2185
(dmax-dmin)/dd     =3D 255.73     % Not 256

> i am using the fft of the velocity data myltiplied by the conjugate fft o=
f the velocity data to only deal with the real parts.
>
> ftu1 =3D fft(u1)*conj(fft(u1))

No.

That is the sum of the squares of the real
and imaginary parts. It seems to be a measure
of relative kinetic energy density.

if
U1 =3D fft(u1);
then
ftu1 =3D abs(U1).^2; % Not real(U1)

> my x axis is calculated using,
>
> n=3Dlength(dmm);  % dmm is imported data array
> L=3D 218.5e-3;
> k=3D [1/L : 1/L : n/L];

No.

x =3D dmin+dd*(N-1);
L =3D N*dd          % max(x)+ dd
dk =3D 1/L
k =3D dk*(0:N-1)

> when i
> plot (k, ftu1,'.');
>
>  i find a very large peak in the first bin,only after this peak (from the=
second bin to the end) is the data symmetrical.  i am unsure how and why t=
his peak is there.

It corresponds to the energy of the mean velocity
which should have been subtracted out.

>i am unsure weather this is due to to any spill overs or roll off (decreme=
nt). i am pretty knew to using faourier transforms.   i know matlab uses th=
e entire length(x) as the default window function.
>
> is it valid to simply remove this first data point or pad it with zero's.=
since this first peak is not witnessed on the other side of the plot (oth=
er side of symmetry) i cannot determine this to be my dominant wave number.
>

You are doing some thing wrong

1. Your distance numbers are not consistent
2. Your 0 wavelength spectrum value should be zero
if you subtracted the mean velocity

Hope this helps.

Greg

 0

On Nov 3, 2:09=A0am, Greg Heath <he...@alumni.brown.edu> wrote:
> On Nov 2, 9:46 am, "Neet Lad" <nits...@hotmail.com> wrote:
>
> > Hi all,
>
> > i have an instantanious velocity profile froma =A0jet cross section (1D=
) i have subtracted from this the convectional velocity of the profile (the=
mean) and the result is a profile of velocity fluctuation in the u directi=
on at a given distance. =A0>(data achieved by PIV technique)
>
> If you subtract the mean, the spectrum should be zero
> at zero frequency.

at zero wavenumber.

Hope this helps.

Greg

 0

2 Replies
631 Views

Similar Articles

11/30/2013 2:48:36 PM
page loaded in 3378232 ms. (0)

Similar Artilces:

Trailing space in meaning of space
Hi all, Just curiousity... I'm writing a set of macros which parses a string contaning only letters and spaces. Since I need to parse it literally, including blank spaces, and catcodes are irrelevant, I use \let and \meaning and then I read the letter with something like \def\split#1 #2 #3{#3}. What has amazed me is that the meaning of space has a trailing blank, so that I don't need to consider it as a special case. Crearly, this trailing space is intentional, but why? Javier ____________________________________________________________ Javier Bezos | TeX y tipograf... and then I read the letter with something > like \def\split#1 #2 #3{#3}. What has amazed me is > that the meaning of space has a trailing blank, so > that I don't need to consider it as a special case. > Crearly, this trailing space is intentional, but > why? Because not every space character is a space character! More exactly, a character token can have the same catcode as a normal space, but not the same character code. The trailing space is the character you gave \meaning. For the interested: TeX reads what you write in such a way that \uppercase or \lowercase is required

Server space?
Where can I go to get free or inexpensive web server space? I live in the U.S. For now, I'll only need 5-10 MB, but may want to expand. I have AOL 9.0. On that rate, what about a good .html editor for WinXP and WinVista? I don't need much .html programming, just mostly text with some pictures and maybe simple scripts. "Harry Potter" wrote ... > Where can I go to get free or inexpensive web server space? I live in > the U.S. For now, I'll only need 5-10 MB, but may want to expand. I > have AOL 9.0. On that rate, what about a good .html editor... can I go to get free or inexpensive web server space? =A0I live in > the U.S. =A0For now, I'll only need 5-10 MB, but may want to expand. =A0I > have AOL 9.0. =A0On that rate, what about a good .html editor for WinXP > and WinVista? =A0I don't need much .html programming, just mostly text > with some pictures and maybe simple scripts. tripod.com has free webpages, with a pagebuilder, etc... build.tripod.com only problem is it has advertisements on top... http://rich12345.tripod.com I recommend editing HTML by hand.. text you just type in.. graphics you put <img

Reuters http://atu.ca/d290b ...Electronic Arts has launched a new space horror story with "Dead Space" on Xbox 360, PlayStation 3 and PC. Set aboard an abandoned mining spaceship, the USG Ishimura, gamers must use an assortment of weapons to destroy the horrific alien Necromorphs that have killed the crew. "We have to constantly come up with new ways to scare the player and keep them guessing," said Glen Schofield, executive producer of "Dead Space" at Electronic Arts. "It takes thousands of iterations and trial and error, but the rewards of seeing gamers totally freak out because of what we've put in the game are totally worth it." San Francisco Chronicle review: http://atu.ca/b4d Amazon.com: http://atu.ca/DeadSpace

Colour space
-- I send my digital camera files to a Professional Lab for processing letting them do the colour correction. They prefer that I retain the colourspace that my camera sets. However they request that you do image resizing.

Hair space
\thinspace as {\kern ..16667em } (look in latex.ltx), so, assuming you want a hairspace that's half the width of a thinspace, you could use \def\hairspace{\kern .08333em } (or, the LaTeX way: \newcommand\hairspace{\kern .08333em }). Or you could use \kern directly for more fine-grained control. HTH, Igor P.S. I'm not sure if (and if yes, why) the space is necessary. -- http://cs.nyu.edu/~pechtcha/ |\ _,,,---,,_ pechtcha@cs.nyu.edu ZZZzz /,.-'' -. ;-;;,_ igor@watson.ibm.com |,4- ) )-,_. ,\ ( `'-' Igor Pechtchanski, Ph.D. '---''

Swap space ??
Hello I need some help - recently i getting strange error message (see below). For example I couldn,t start database engine. What i wrong. I suspect to law swap space but it's strange - i have never seen effects like this. Help me please (I'm not experienced solaris admin) Best Regards Mirek Adaptive Server Anywhere Stop Engine Utility Version 7.0.4.3513 an_inter_proc_sema::Initialize: failed to create shared memory File 'etc/iprocsem.c' at line #70 Aborting execution...Abort - core dumper bash-2.03# uname -a SunOS sun 5.8 Generic_117350-34 sun4u sparc SUNW,Sun-Fire-V250 bash-2.03# vmstat 5 procs memory page disk faults cpu r b w swap free re mf pi po fr de sr m1 m1 m1 m2 in sy cs us sy id 0 0 0 2283832 1553552 3 14 44 49 51 0 5 2 2 2 1 286 1681 829 3 0 96 0 0 0 448344 31584 2 74 615 537 538 0 35 19 9 10 56 617 861 1306 50 0 49 0 0 0 448408 31376 0 18 115 102 102 0 14 2 1 1 13 404 875 1206 50 0 50 0 0 0 442560 30728 18 278 412 1332 1370 0 221 17 10 10 35 636 1169 1310 53 1 46 0 0 0 418440 31128 1 272 88 2481 2523 0 316 7 4 3 22 617 1572 1271 65

Insufficient space
Hi experts, I want to deploy m-file logic on to a S3C2440A 32-BIT CMOS Micro-Controller which only have 1GB address space. There is a Linux Operating System and some application running on it, the space remaining is limited. Will I save much more space if I use mcc to create wrapper files in C or C++ than Java deployed from deploytool ? Did the mcc method require MCR (275MB) for client deployment ? Can MCR be bypassed ? May I know which method can minimize the most space and memory consumption ? Thanks Regards, Yow

texture space
There is an NVidia Normal mapping tool, which will convert an RGB image into a normal map. I think by default it uses OpenGL's texture coordinate system where s goes to the right of the image, t goes up and the origin is at the lower left corner. So the normal vectors would be relative to axes in these directions (plus the orthogonal axis to the st-plane). Direct3D uses a different texturing coordinate system: u goes to the right, v goes down the image and the origin is at the upper-left corner. My question is, if I were to use such a normal map that was generated in the opengl s

Space Game!
Wrote a game for Apple IIGS, uploaded on the site http://www.geocities.com/ltchean/space.html. It has star fields, space ship, asteroids, collision and explosion... The catch it - you will need Complete Pascal (or TML Pascal) - as I post it in source code format. This is to teach potential programmers how to write a game for Apple IIGS. It is intended to be simple and primary for teaching purpose only. You can see the screenshot in the URL above. I developed this using Sweet16 on an iMac, the speed might or might not be acceptable to a real Apple IIGS. But you are welcome to modify the source code to make it run at any speed you want. Enjoy! On Aug 25, 3:27 am, limtc <thyech...@gmail.com> wrote: > Wrote a game for Apple IIGS, uploaded on the sitehttp://www.geocities.com/ltchean/space.html. It has star fields, > space > ship, asteroids, collision and explosion... > The catch it - you will need Complete Pascal (or TML Pascal) - as I > post it in source code format. This is to teach potential programmers > how to write a game for Apple IIGS. It is intended to be simple and > primary for teaching purpose only. You can see the screenshot in the > URL

Space Camper
Look, there's an image of the new Space Camper on this Ebay auction: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=8434748351

projective space
My first question: Is the process of going from Euclidean space to Projective space, that is (x, y, z) --> (cx, cy, cz, c) for any c not zero, a similar idea as going from the real number x to the complex number (x, 0)? I just never really understood the relationship between Euclidean and Projective space (I've never studied projective geometry). Today I needed to obtain the 3D view space position of a point given its screen coordinates and normalized depth buffer values. I found out that if [x', y', z'] is the point in NDC space, and inv(P) is the inverse..., I would first need to multiply > by w, and then apply the inverse of P. But this wasn't the case. > Why? Let w' be the number whose multiplication you are missing. Assume you did multiply with it. Then (using your notation): w' [x', y', z', 1] inv(P) = w' [x, y, z, w] = [w' x, w' y, w' z, w' w] ~ [x / w, y / w, z / w, 1] Where ~ is for proportionality (geometric equality). Thus, same answer. -- http://kaba.hilvi.org Thanks. What about the first question: Is the process of going from Euclidean space to Projective space, that is (x, y

paging space
hi , i've working with aix 4.3.3 . after i'm booting the machine i've got this problem : hd6 Active = No i've add another paging paging01 and after rebooting i've got the same problem hd6 and paging01 Active = No . any one have an idea ? thanks ariec arieco@clalit.org.il <arieco@clalit.org.il> wrote: > i've working with aix 4.3.3 . > > after i'm booting the machine i've got this problem : > > hd6 Active = No > > i've add another paging paging01 and after rebooting i've got the same > problem hd6 and paging01 Ac

Enough Space
Hi, Due to memory constraints, the application image is placed in 2 different flash memory . The image in the Flash Memory is already of compressed format. In RAM, there is no enough space to accomodate both the parts together at the same time. How to overcome this scenario without increasing the RAM ? Is increasing the RAM , the only way to overcome this situation ? Thx in advans, Karthik Balaguru >Due to memory constraints, the application image is placed in 2 >different flash memory . The image in the Flash Memory is already of >compressed format. In RAM, there is no enough space to accomodate >both the parts together at the same time. How to overcome this >scenario without increasing the RAM ? >Is increasing the RAM , the only way to overcome this situation ? Use some kind of overlays, loading and decompressing the flash data to RAM on demand? This works if you're using RAM as a cache for an application image inflash, not if it contains runtime data not available elsewhere. It's often practical to do demand paging of code even without hardware support for memory management, because accesses are well-structured. -- mac the na�f

Window space to world space with matrices
Hi all! I'm writing an editor in which user can pan and zoom in/out a 2D view of a scene with mouse, and select items with Left MB. Panning and zooming works fine with my matrices. I'm having problems converting cursor position from window space (that is, 0-clientarea_width, 0-clientarea_height) to 'world' space. I store current view position (float tx, ty) and scale/zoom (float scale), and use them to construct a matrix for drawing and window-to-world space conversion. I'm using following code, but it only works when scale is 1.0 (ie. 1:1 ratio): void C2DView::OnLButtonDown(UINT nFlags, CPoint point) { CMatrix M; CPoint pt; M.m[0][0] = scale; M.m[1][1] = scale; M.m[2][2] = 1; // Z not used M.m[3][0] = tx; M.m[3][1] = ty; pt = M.TransformPoint(point); // pt.x and pt.y should now contain the cursor // position in world coordinates. } Is there something else that needs to be done? Dr. Proton <foo@isp.com> wrote: > I'm writing an editor in which user can pan and zoom in/out a 2D view > of a scene That's a 2D scene then, I take it? [...] > I'm using following code, but it only works when scale is 1.0 (ie. 1:1 > ratio): You

user space space slower performer than malloc space
code that writes blanks to the bytes of a user space appears to run 60% slower than the same code that writes blanks to an malloc allocated space. Any ideas why?? here are my timing results: clear user space. 16 meg 100 times. Begin 21.09.25 End 21.09.33 Elapsed 7294 milliseconds clear malloc space. 16 meg 100 times. Begin 21.09.33 End 21.09.37 Elapsed 4755 milliseconds here is my code that writes blanks to a user space: char* pSpace ; memset( &usrspc, ' ', sizeof(usrspc)) ; memcpy( usrspc.name, "TEST17C", 7 ) ; memcpy( usrspc.lib, "QTEMP", 5 ) ; memcpy( replace, "*YES", 4 ) ; sx = 16000000 ; pSpace = api_Quscrtus( conNull, usrspc, &sx, replace ) ; for( Ix = 0 ; Ix < 100 ; ++Ix ) { memset( pSpace, ' ', 16000000 ) ; } similar code that writes blanks to malloc allocated space: sx = 16000000 ; pSpace = malloc( sx ) ; for( nIx = 0 ; nIx < 100 ; ++nIx ) { memset( pSpace, ' ', 16000000 ) ; } Steve Richter wrote: > code that writes blanks to the bytes of a user space appears to run 60% > slower than the same code that writes blanks

sed double space until non-space character
Hi All How to sed ' s, ,| ,g' double space until non-space character ? e.g. FOR EACH : IF dfdfd THEN DO: asfasdfasdf. IF sdfsd THEN DO: s fa sfasf. IF dfdf THEN DO: asfasdf asfasf asasfasd. END. END. END. END. Result FOR EACH : | IF dfdfd THEN | DO: | | asfasdfasdf. | | IF sdfsd THEN | | DO: | | | s| fa sfasf. <------ should not replace after non-space character | | | IF dfdf THEN | | | DO: | | | | asfasdf | | | | asfasf | | | | asasfasd. | | | END. | | END. | END. END. 2009-04-23, 21:10(-07), moonhkt: [...] > How to sed ' s, ,| ,g' double space until non-space character ? [...] sed -e :1 -e 's/^ /| /' -e t1 -- St�phane Assume your input is in file.txt: sed 's/^$$*$$/\1\1/' file.txt On 4$B7n(B25$BF|(B, $B>e8a(B2$B;~(B48$BJ,(B, Hai Vu <haivu2...@gmail.com> wrote: > Assume your input is in file.txt: > sed 's/^$$*$$/\1\1/' file.txt Try two not work cat sed.txt | sed -e :1 -e 's/^ /| /' -e t1 FOR EACH : | IF dfdfd THEN | DO: | asfasdfasdf. | IF sdfsd THEN | DO: | s fa sfasf. | IF dfdf regular expression space and 2 byte space When receiving a particular string and if the string has a space/ 2 byte space with some trailing string. I want to remove the trailing string.$somestring = "some string"; $match_pattern = "/(.*)\s.*/iu"; preg_match_all($match_pattern, $somestring,$match ); echo $match[1][0] Looks like this only works for single byte space. How can I define the regular expressoin so that it finds the 2 bytes space. Thanks in advance. *** MD escribi�/wrote (Fri, 25 Aug 2006 21:25:41 GMT): > When receiving a particular string and if the string has a space/ 2 byte > space with some trailing string. > I want to remove the trailing string. > >$somestring = "some string"; > $match_pattern = "/(.*)\s.*/iu"; > > preg_match_all($match_pattern, $somestring,$match ); > echo $match[1][0] > > Looks like this only works for single byte space. > > How can I define the regular expressoin so that it finds the 2 bytes space. preg_replace('/ .*$/', '', some string"); // Not tested -- -+ http://alvaro.es - �lvaro G. Vicario - Burgos, Spain ++ Mi sitio sobre programaci�n web: http

PCI I/O space and memory space access
Hi all, I am quite new to vxworks and I would like an advice on a matter which is confusing me. I am trying to write a driver for a via 82c686 audio chip, on a standard pentium 3 bsp. I am not developing a plain vxworks driver, but instead I am using WindML "hardware abstraction layer" etc... There are some example drivers for Linux, based on OSS model, that are helping a lot but despite the large pile of docs I read, I am still confused about PCI I/O space mapping. During my attempts of driving the audio chip, I have verified that I can read the PCI configuration of the board ( memory base, irq etc), I can access various offsets and read/wirte values, but I haven't been able to access register in I/O space. My first attempt was to use the BAR0 value as a raw pointer to memory, then I realized ( thanks to previous posts on this group) that this was the wrong approach and that this region must be appropriately mapped to memory space in order to access it. But I am confused on how I should do this :S Can anyone point me in the right direction? Is there some WindRiver doc that cover this topic and that I missed? Thanks in advance! Giacomo Benelli You can try

/var out of disk space, but not...
HI. So I have a problem with my /var partition. I am unable to write to it and get "/var: write failed, file system is full" and "close failed: [Errno 28] No space left on device" when I do. If I look at disk usage using df, I get: Filesystem 1M-blocks Used Avail Capacity Mounted on /dev/ld0a 4585 2784 1571 63% / /dev/ld0f 4851 4617 -8 100% /var /dev/ld0e 9695 6129 3081 66% /usr /dev/ld0g 9695 2872 6337 31% /home /dev/ld0h 38788 9461 27386 25% /www kernfs 0 0 0 100% /kern procfs 0 0 0 100% /usr/pkg/emul/linux/proc elk:/www/staging 38788 10463 26384 28% /www/staging rhino:/www/production 268340 12743 241966 5% /www/production If I look at /var using du, I get: srvrs01# du -sPm /var 1125 /var Clearly there is a discrepancy here and I can't find anything to delete to free up the disk space. Any ideas on what is wrong and what I can do to fix it? Thanks