How can I add Non structural Mass to Solid elements?

Shoaib Shaikh_21072

There is an option for NSM for PShell elements. What would be the best option for PSolid elements to add non structural mass. Currently I'm using a CONM2 point mass that is distributed across a surface using 1D rigid elements. Is that the only/best way? It seems a little messy. 

Michele Macchioni

NSM

Subcase Information EntryThe NSM command can be used to select a non-structural mass set for mass generation.

Format

NSM = option

Example 1

In this example, NSM 12 is applied to the model for Subcase 1 and NSM 13 is applied to the model for Subcase 3. There is no non-structural mass applied to the model for Subcase 2:

SUBCASE 1 ANALYSIS=STATICS SPC = 1 LOAD = 2 NSM=12 	 SUBCASE 2 ANALYSIS=STATICS SPC = 3 LOAD = 4 	 SUBCASE 3 ANALYSIS=STATICS SPC = 5 LOAD = 5 NSM=13  BEGIN BULK NSM,12,PSOLID,3,0.3 NSM,13,PSOLID,3,0.7

Michele Macchioni

There are as well other option like NSMADD and so on.

Suggest to have a look at OptiStruct manual from which I just grabbed an extract

Hope this helps.

Regards

Michele

Shoaib Shaikh_21072

Hi Michele, 

 

Thank you for your reply. I'm only trying to apply this NSM to a part of the model. The methods above seem to apply it to the whole model when applied to a subcase. Is this correct or can I define the PSolid ID in this line below

 

BEGIN BULK NSM,12,PSOLID,3,0.3 NSM,13,PSOLID,3,0.7

and it would only apply to that particular property?<br /><br />

Regards

Shoaib

Michele Macchioni

Shoaib,

 

yes, NSM can be used to select a subset by property

NSM

Bulk Data EntryDefines non-structural mass per unit Length, per unit Area, or per unit Volume for a list of elements or properties.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
NSM	SID	TYPE	ID	VALUE	ID	VALUE	ID	VALUE
+	ID	VALUE	etc.	etc.	etc.	etc.	etc.	etc.

Example 1

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
NSM	4	PSHELL	155	0.06

Example 2

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
NSM	6	ELEMENT	12	0.03	13	0.06	14	0.03
+	18	0.02	36	0.03

Definitions

Field	Contents	SI Unit Example
SID	Non-structural mass set identification number. No default (Integer > 0)
TYPE	This can be one of the properties PSOLID, PSHELL, PCOMP, PBAR, PBARL, PBEAM, PBEAML, PROD, CONROD, PSHEAR, or PTUBE, in which case the list of IDs will refer to properties of the stated type, or it can be ELEMENT, in which case the list is of individual element IDs of elements that can have NSM. It can also be of type ELSET, in which case, it is an element SET ID. No default
ID	Property ID, Element ID, or Element Set ID depending on the TYPE definition. No default (Integer > 0)
VALUE	Non-structural mass per unit Length (1D elements), per unit Area (2D elements), or per unit Volume (3D elements). No default (Real)

PSiedlaczek

For me NSM looks promising as alternative to point masses. It can be defined for optistrup in hypermesh from Tools>Mass Trmimming panel. The single NSML can be applied to Load Step by selection NSM in subcase definition and works as expected. I have several NSMs in my model applied to sets of elements describing different types of weights.

however I have to change mass configuration between load cases.

In documentation I found that I should use NSMADD.
https://2021.help.altair.com/2021/hwdesktop/hm/topics/panels/help407.htm

I suppose definition from Load Collectors shall be used in some way. The problem is that I cannot find a path to efficiently apply created NSMADD to specific Load Cases. It does not appear in subcase definition NSM=.

How shall I define different mass configurations for sequence of load cases?

PSiedlaczek

I cannot believe how stupid definition of NSMADD in Altair HW is. From GUI of HyperMesh NSMADD cannot be applied to Subcase Information directly, where it should be possible according to documentation. But it can be achieved from GUI by trick, by changing SID of NSMADD to one selected in Subcase Information NSM.

see comments: https://2021.help.altair.com/2021.2/hwsolvers/os/topics/solvers/os/nsmadd_bulk_r.htm

I believe this is an source of 1M bugs, as no reference is tracked properly in GUI.

 

Martina Blazheska

PSiedlaczek said:

I cannot believe how stupid definition of NSMADD in Altair HW is. From GUI of HyperMesh NSMADD cannot be applied to Subcase Information directly, where it should be possible according to documentation. But it can be achieved from GUI by trick, by changing SID of NSMADD to one selected in Subcase Information NSM.

see comments: https://2021.help.altair.com/2021.2/hwsolvers/os/topics/solvers/os/nsmadd_bulk_r.htm

I believe this is an source of 1M bugs, as no reference is tracked properly in GUI.

 

It seems that NSMADD is treated as a load collector instead of as a group (like NSM is).

If you want to target all of the subcases with a single NSMADD, you can do this by creating a Case Control Card and choosing your NSMADD under the NSM checkbox:

Choosing a specific NSM group in the subcase will override the global case control NSM. If you want to do this, you need a LOADADD card, in which you will group your subcase specific loads and subcase specific NSMADD. Then use this LOADADD in the load field of the subcase.