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Random response analysis,acceleration as input

Hello everyone,

I want to perform a random response analysis. I have PSD data in terms of acceleration. The component which I am going to analyze is fixed on one side rigidly and the other side is given acceleration input. I constrained the fixed side with SPCs and the gave the nodes of surface the as unit input of acceleration through SPCD and gave the ID of this load in RLOAD2 collector as exciteid and type as acceleration. I have referred the tutorial given.

But I am still getting an error no.186. I can't figure out the error. Is there something wrong with my acceleration input? Can I define acceleration in the format which I have mentioned above (on the surface that is).

Also can anyone tell me the difference between 'appliedload' and 'excitedload' in RANDPS with example?

Regards,

Bharat Hiranwale

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Rahul Rajan_21763

Hi,

Please find below some nice explanation for Random response analysis.

http://www.solidworks.in/sw/docs/Vibration_2010_ENG_FINAL.pdf

Requesting you to share the complete out file of your run.

1) For Base excitation, apply SPCD in FRF step

See thumbnail 1

2) You have to maintain consistent units, below table explains how to define base excitation for different units of PSD - Input

see thumbnail 2

3) The J and K entries determines whether the PSD is of auto correlation or cross correlation function.

For auto spectral density / Uncoupled PSDF, J = K, and X must be greater than zero and Y must be equal to zero and for cross spectral density / Coupled PSDF, the J will not be equal to K and in some cases J < K.

X and Y entries are the components of complex numbers, which means they are the real and imaginary parts and usually represents Cross-Spectrum PSD.

For a complex spectrum analysis, two RANDPS and TABRND1 entries are required. In the first RANDPS entry, you may have to set the real (X) component to non-zero and the imaginary (Y) component to zero. The TID on this RANDPS should point to table

TABRND1 with real component of cross-psd input.

In the second RANDPS entry, set the real (X) component to zero and imaginary (y) component to non-zero with TID pointing to TABRND1 table with imaginary component of cross-psd input.

I hope this helps

Regards

Rahul R

<?xml version="1.0" encoding="UTF-8"?>

hiranwale_bharat

Thanks Rahul.

I can not complete my run yesterday as it gave me error regarding .rs files.(I guess it was issue related to antivirus). Anyway thank you for the interest shown. I'll keep you posted for any new updates.

Regards,

Bharat Hiranwale

Rahul Rajan_21763

Thanks for the update.

Regards

Rahul R

hiranwale_bharat

Hello Rahul,

Regarding the statement you made

'For a complex spectrum analysis, two RANDPS and TABRND1 entries are required. In the first RANDPS entry, you may have to set the real (X) component to non-zero and the imaginary (Y) component to zero. The TID on this RANDPS should point to table

TABRND1 with real component of cross-psd input.'

In my case I have a PSD giving me 37 values of frequencies and corresponding values of their accelerations. As far as my understanding ,I guess that I don't have to use complex loading and should give X value as 1 and Y as 0 as it is uncoupled load.

Is my approach right?

Regards,

Bharat

hiranwale_bharat

Hello Rahul,

Please find the contents from .out file for Random response below in red color.

The problem is something like this.

There is a cylinder one circular face of which is to be fixed and other circular face has the acceleration input. So I fixed nodes on one face as SPC and applied acceleration through SPCD command on the nodes of the other face. I got the error as seen in the .OUT file.

Can you suggest any remedy on this problem?

Also can you tell me that if I have to perform Random analysis for a stipulated time(lets say for 50 seconds), then how to do it?

Regards
Bharat Hiranwale

Out file

NOTE # 9199
MSGLMT=STRICT is active, all messages will be printed.
You can suppress some less important warning messages by use of
MSGLMT=BRIEF or UNREF (in config file or in the input data).

1 PARAM(s) were set:
    G       ,     .06

*** WARNING # 4744
When using ADJUST on shell contacts it is safer to define MORIENT to be NORM or
REVNORM for CONTACT 2, so that the master pushout direction, which is
used by ADJUST, is more clearly defined.

Maximum adjustment distance of nodal coordinates for contact:
Contact        2, Grid    25072, Adj. Dist.= 1.0316E+00

*** ERROR # 186 ***
An SPCD component must be constrained by an SPC or SPC1 data.
      GRID ID = 56196
    component = 3
LOAD set ID = 3
   SPC set ID = 2
   subcase ID = 1

*** ERROR # 186 ***
An SPCD component must be constrained by an SPC or SPC1 data.
      GRID ID = 56197
    component = 3
LOAD set ID = 3
   SPC set ID = 2
   subcase ID = 1

*** ERROR # 186 ***
An SPCD component must be constrained by an SPC or SPC1 data.
      GRID ID = 56198
    component = 3
LOAD set ID = 3
   SPC set ID = 2
   subcase ID = 1

*** ERROR # 186 ***
An SPCD component must be constrained by an SPC or SPC1 data.
      GRID ID = 56200
    component = 3
LOAD set ID = 3
   SPC set ID = 2
   subcase ID = 1

*** ERROR # 186 ***
An SPCD component must be constrained by an SPC or SPC1 data.
      GRID ID = 56201
    component = 3
LOAD set ID = 3
   SPC set ID = 2
   subcase ID = 1

*** ERROR # 186 ***
An SPCD component must be constrained by an SPC or SPC1 data.
      GRID ID = 56262
    component = 3
LOAD set ID = 3
   SPC set ID = 2
   subcase ID = 1

*** ERROR # 186 ***
An SPCD component must be constrained by an SPC or SPC1 data.
      GRID ID = 56264
    component = 3
LOAD set ID = 3
   SPC set ID = 2
   subcase ID = 1

*** ERROR # 186 ***
An SPCD component must be constrained by an SPC or SPC1 data.
      GRID ID = 56266
    component = 3
LOAD set ID = 3
   SPC set ID = 2
   subcase ID = 1

*** ERROR # 186 ***
An SPCD component must be constrained by an SPC or SPC1 data.
      GRID ID = 56268
    component = 3
LOAD set ID = 3
   SPC set ID = 2
   subcase ID = 1

*** ERROR # 186 ***
An SPCD component must be constrained by an SPC or SPC1 data.
      GRID ID = 56270
    component = 3
LOAD set ID = 3
   SPC set ID = 2
   subcase ID = 1

*** More of ERROR messages # 186 were suppressed...

************************************************************************

OPTIMIZATION FILE AND PARAMETER INFORMATION :
---------------------------------------------

FEM model file               :
     C:/Users/polyengg5/Desktop/Bharat All Data/Polybond/TATA Power/hypermesh/Random trial/PSC1 Trial random _vertical.fem
Output files prefix          :
     C:/Users/polyengg5/Desktop/Bharat All Data/Polybond/TATA Power/hypermesh/Random trial/PSC1 Trial random _vertical
Model read from files:
    C:/Users/polyengg5/Desktop/Bharat All Data/Polybond/TATA Power/hypermesh/Random trial/PSC1 Trial random _vertical.fem

************************************************************************

************************************************************************

FINITE ELEMENT MODEL DATA INFORMATION :
---------------------------------------

Total # of Grids (Structural)        :     45738
Total # of Elements Excluding Contact:     38186
Total # of N2S Contact Elements      :      2610 (internally created CGAPG)
Total # of Degrees of Freedom        :    143127
Total # of Non-zero Stiffness Terms :   5538303

Element Type Information
------------------------

   CHEXA    Elements   :    36131
   CPENTA   Elements   :     2055

Load and Boundary Information
-----------------------------

   FORCE Sets        :         1
   SPC   Sets        :         1

Material and Property Information
---------------------------------

   PSOLID Cards      :         2
   MAT1   Cards      :         2

************************************************************************

************************************************************************

***** ERROR ENCOUNTERED BEFORE COMPLETING THE CHECK RUN *****
Current Memory (RAM)                                    :     100 MB
Estimated Minimum Memory (RAM) for the check run        :      92 MB

************************************************************************

This error occurs in module 'prpdrv'.

************************************************************************

RESOURCE USAGE INFORMATION
--------------------------

MAXIMUM MEMORY USED                                       100 MB
MAXIMUM DISK SPACE USED                                     1 MB

************************************************************************

************************************************************************

COMPUTE TIME INFORMATION
------------------------

EXECUTION STARTED                         Tue Jul 21 16:05:12 2015
EXECUTION COMPLETED                       Tue Jul 21 16:05:15 2015
ELAPSED TIME                                         00:00:02
CPU TIME                                             00:00:00

************************************************************************

*** PROGRAM STOPPED: FATAL ERROR(s) ENCOUNTERED.

                        ***** END OF REPORT *****

For Useful OptiStruct Tips and Tricks, go to the URL:
http://www.altairhyperworks.com/tips.aspx

************************************************************************
Following warning messages appeared too many times
and were suppressed:
     186
Total of 1355 repeat error message(s) were suppressed.
To see more messages use 'MSGLMT' control card in the data or config file.

************************************************************************

There were 1365 error messages during input processing.
The first message is repeated below:

*** ERROR # 186 ***
An SPCD component must be constrained by an SPC or SPC1 data.
       GRID ID = 56196
     component = 3
   LOAD set ID = 3
    SPC set ID = 2
    subcase ID = 1

************************************************************************

Altair Forum User

Hi,

Please refer the link below on how to use SPCD:

http://forum.altairhyperworks.com/index.php?/topic/13593-how-can-i-specify-an-enforced-displacement-in-a-subcase-or-loadstep-in-an-optistruct-input-deck/#entry24384

hiranwale_bharat

Hello Rahul,

Thank you for the link you shared. Hope it helps me.

I want to ask you about my approach towards the problem which is something as follows-

There is a cylinder one circular face of which is to be fixed and other circular face has the acceleration input. So I fixed nodes on one face as SPC and applied acceleration through SPCD command on the nodes of the other face.

I guess I am creating a SPC more than required. If i am giving my input through SPCD,then is it required to give one more SPC to replicate fixed constraint.

I will keep you updated regarding the process.

Regards,

Bharat Hiranwale

hiranwale_bharat

Hello Rahul,

about your link you shared in your last comment http://forum.altairh...eck/#entry24384

It seems that the first step mentioned is suitable for an example of Earthquake where your foundation or base of a building is getting excited.

But my problem is a bit different . It is like analysis of building feeling earthquake whose top most surface is also fixed.

A better example would be of a two wheeler suspension whose bottom portion is connected to the wheel and will feel the excitation due to road undulation. The other part of which will be connected rigidly to the frame or chassis.

So my problem is that,in the above two examples we will require two SPCs (one for fixed constraint[chassis or the top surface] and other for SPCD[for PSD]).

How can I do this in Random analysis?

Hope you understand my problem.

If you want to communicate mail me on this id: hiranwale_bharat@yahoo.co.in

Regards and thanks,

Bharat