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11-18-2010 06:09 AM

For informations, it's better to consider the liquid as a virtual mass. Therefore, the virtual mass carrys on the tank's shell a hydrostatic pressure represented by MFLUID. But i don't know how to write this in the INPUT FILE (.DAT). Particularly in the case control together with in the main bulk and the DECK NASTRAN. I use the solution type SEMODES 103 RESPONSE SIMULATION, and the hydrostatic pressure takes part in the static subcase. At this moment, I just did a real pressure hydrostatic, id est it's represented by PLOADD4 like a force, but for modal analysis, it's not exact if I launch a calcul with this force. Indeed, we are not interested in the effects of hydrostatic pressure, but we are interested in frequential responses of the system.I need your help, if someone has some ideas or contacts, tell me.

NB : when i will have the MFLUID in the case control, Where I have to put MFLUID DEFINITION in the main bulk ? And HOW ?

Furthermore, I would to increase the disk memory, so I did the following statement :

$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$*

$* NASTRAN

$*

$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$*

INIT MASTER(S)

NASTRAN BUFFSIZE=32769

NASTRAN ITER=NO

$*

$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$*

$* FILE MANAGEMENT

$*

$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$*

ASSIGN SCR1='SCRATCH.SCR1'DELETE

ASSIGN SCR2='SCRATCH.SCR2'DELETE

ASSIGN DB1 ='SCRATCH.DB1'DELETE

ASSIGN DB2 ='SCRATCJ.DB2'DELETE

INIT SCRATCH LOGI=(SCR1(250000)),SCR300=(SCR2(250000)

INIT DBALL LOGI=(DB1(250000),DB2(250000)

$*

$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$*

$* EXECUTIVE CONTROL

$*

$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$*

ID,NASTRAN,nouveau1sim1-solution_2

SOL 103

TIME 999

DIAG 44

CEND

$*

Do you think it's enough to launch calcul with big models ? If not, could you give me another solution please.

I am waiting for your responses, and I am looking for your help.

Could you give me some help please ? Or may be we could call us.

Thank you for your attention and for your time.

Best regards.

Tibo

8 REPLIES

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11-18-2010 03:37 PM

Paul Blelloch, Ph.D.

Director, Aerospace Analysis

ATA Engineering, Inc.

11995 El Camino Real

San Diego, CA 92130

(858) 480-2065

Director, Aerospace Analysis

ATA Engineering, Inc.

11995 El Camino Real

San Diego, CA 92130

(858) 480-2065

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11-18-2010 03:44 PM

Paul Blelloch, Ph.D.

Director, Aerospace Analysis

ATA Engineering, Inc.

11995 El Camino Real

San Diego, CA 92130

(858) 480-2065

Director, Aerospace Analysis

ATA Engineering, Inc.

11995 El Camino Real

San Diego, CA 92130

(858) 480-2065

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11-18-2010 04:44 PM

I'm going to show what I have done for the hydrostatic pressure :

ECHO = NONE

BGSET = 100

SUBCASE 1

LOAD = 21

SUBCASE 2

LOAD = 100

SUBCASE 3

LOADSET = 103

METHOD = 103

STATSUB = 2

Now, for the MFLUID, I thought about the following sentence :

ECHO = NONE

BGSET = 100

MFLUID = ? (I don't know)

SUBCASE 1

LOAD = ? (for the MFLUID)

SUBCASE 2

LOAD = 100

SUBCASE 3

LOADSET = 103 (corresponding to the gravity)

METHOD = 103

STATSUB = 2

Now for the bulk data entries, what i have to pu for MFLUID ?

Should I put first of all MFLUID and characterics associated to the fluid and the surface, how can i do ? (I read the PDFs of SIEMENS, and it's not efficient for me) And for the second time, should I put LOAD correspondig to MFLUID so that the case control can understand what we refer to ?

Thank you in advance, you are really helpfull for me.

I am looking forward to read your response.

Regards

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11-18-2010 08:41 PM

SUBCASE 3

METHOD = 103

STATSUB = 2

MFLUID = 100

BEGIN BULK

MFLUID, 100, ....

ELIST,....

The mass has nothing to do with the static load, so the set ID for MFLUID has nothing to do with the set ID for the load.

Paul Blelloch, Ph.D.

Director, Aerospace Analysis

ATA Engineering, Inc.

11995 El Camino Real

San Diego, CA 92130

(858) 480-2065

Director, Aerospace Analysis

ATA Engineering, Inc.

11995 El Camino Real

San Diego, CA 92130

(858) 480-2065

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11-19-2010 02:42 AM

So If I put MFLUID in the case control, and that there was only Hydrostatic Pressure (H.P) in the static subcase, I have to dismiss the static subcase if i don't want to include the effect of static load, is that correct if i have no static subcase ? But if i keep the H.P in the static subcase, and in addition to that I put the MFLUID in the third subcase (modal subcase) is that correct ? Because I would like to include the effect of the static load. So, I'm going to show you what I think about what I have to do :

ECHO = NONE

BGSET = 100

SUBCASE 1

LOAD = 21

SUBCASE 2

LOAD = 100

SUBCASE 3

LOADSET = 103

METHOD = 103

STATSUB = 2

MFLUID = 100

After, there is the bulk data entries.

So, how can I point to the ELIST Card ?

And, how can i describe MFLUID for the free surface, liquid density ? Should I create a label number in the CAE INTERFACE ?

What is exactly ELIST ?

I know these questions are very stupid, but, in the Quick Reference Guide, and in the Installation Guide of NX NASTRAN, all these things are not really understandable.

I am really waiting for your response.

Thank you very much.

Friendly and Respectfully,

TIBO

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11-19-2010 09:16 AM

Director, Aerospace Analysis

ATA Engineering, Inc.

11995 El Camino Real

San Diego, CA 92130

(858) 480-2065

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11-19-2010 10:08 AM

Do you an example for the bulk data card for MFLUID and ELIST ?

Regards

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11-19-2010 01:29 PM - edited 10-01-2014 04:26 AM

The fluid/structure interface is defined with ELIST Bulk Data, which specify a set of wetted TRIA3 and QUAD4 elements that define the structural portion of the fluid boundary.

Each fluid volume is defined on an MFLUID Bulk Data input, which defines the fluid density, the ELISTs, and other boundaries.

A set of MFLUID volumes are requested in the case control request MFLUID = SID.

If pressure outputs are desired they will be printed if the case control request MPRES = is used to define a set of elements. The elements must also be active in an ELIST/MFLUID volume.

An example set of input data for a small problem is shown below:

Case Control

MFLUID = 25MPRES= ALLetc.Bulk Data

1 ,2 ,3 ,4 ,5 ,6 ,7 ,8 ,9 ,10$MFLUID, SID , CID , ZFS , RHO , ELIST1, ELIST2, PLANE1, PLANE2MFLUID , 25 , 0 , 115.4, .0246, 255 , , S$ELIST , ELID ,E1 , E2 , E3 , etc.ELIST , 255 , 1 , THRU , 25ETC...In the input above we have defined a fluid volume with a free surface normal to the basic z direction. The xz plane (PLANE1) is a plane of symmetry and the density is 0.0246. ELIST set 255 defines the positive faces of elements in the range 1 through 25 (missing numbers are allowed) as the structural/fluid boundary.

The connected elements may be wetted on one or both sides by the same volume. For instance a baffle plate extends partially into a tank and have two sides in the same fluid volume. If a plate completely separates the two parts of the tank, it is recommended that a separate volume be used for each side. Each side of an element should be listed on a separate ELIST.

Special terms are calculated if enclosed fluid volumes do not have a free surface or a plane of anti-symmetry. Otherwise, the incompressible fluid would produce a spurious low frequency mode with a mode shape corresponding to the volume change. This mode will not affect the structural response, but it is eliminated. Because the free surface allows the fluid volume to expand, it does not have these problems.

A free surface is defined as an x-y plane in any local rectangular coordinate system. The user simply specifies a value of z as the upper limit of the fluid volume. Different fluid volumes may have different levels and orientation. It is not required that the surface coincide with the element properties since partially wetted elements are allowed.

The virtual mass fluid option may be used in all NX Nastran dynamics solutions, including the following special approaches:

- Superelements – (Residual Only )

Nonlinear Analysis – (SOL 129)

Optimization – (does not create sensitivity matrices.)

Blas.

Figure 4-3. Virtual Mass Terminology

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