crash simulation

Altair Forum User

hello everybody,

i am doing a simulation of the crash of a square tube crashed by a solid plate.

i am interested in the reaction force by the tube throughout the crash distance.

i am using LSdyna solver...

i used the ascii output RCFORC but the result is not found as expected.

and i was suggested to use SECFORC as my output result.

can anyone please help me find out the difference of RCFORC and SECFORC.

thanks

sharad

Altair Forum User

hello everybody,

i am doing a simulation of the crash of a square tube crashed by a solid plate.

i am interested in the reaction force by the tube throughout the crash distance.

i am using LSdyna solver...

i used the ascii output RCFORC but the result is not found as expected.

and i was suggested to use SECFORC as my output result.

can anyone please help me find out the difference of RCFORC and SECFORC.

thanks

sharad

Definition from LS-DYNA Website:

Contact output

--------------------

There are numerous output files pertaining to contact which can be written by LS-DYNA. LSPOST can read these output files and plot the results.

The most common contact-related output file, RCFORC, is produced by including a *DATABASE_RCFORC command in the input deck. RCFORC is an ASCII file containing resultant contact forces for the slave and master sides of each contact interface. The forces are written in the global coordinate system. Note that RCFORC data is not written for single surface contacts as all the contact forces from such a contact come from the slave side (there is no master side) and thus the net contact forces are zero. To obtain RCFORC data when single surface contacts are used, one or more force transducers should be added via the *CONTACT_FORCE_TRANSDUCER_PENALTY command. A force transducer does not produce any contact forces and thus does not affect the results of the simulation. A force transducer simply measures contact forces produced by other contact interfaces defined in the model. One would typically assign a subset of the parts defined in a single surface contact to the slave side of a force transducer. No master side is defined. The RCFORC file would then report the resultant contact forces on that subset of parts. The ASCII output file NCFORC reports contact forces at each node. The command *DATABASE_NCFORC is required in the input deck to produce such a file. Further, one or more contact print flags must be set (see SPR and MPR on Card 1 of *CONTACT). Only those surfaces whose print flag is set to a value of 1 will have their nodal contact force output to the NCFORC file. By including a *DATABASE_SLEOUT command, contact interface energies are written to the ASCII ouput file SLEOUT. In cases where there are two or more contact interfaces in a model and the global statistics file (GLSTAT) indicates a problem with contact energy, such as a large negative value, the SLEOUT file is useful for isolating which contact interfaces are responsible. For general information on interpreting contact energies, see the LS-DYNA Theory Manual, Section 23.8.4. In some cases, it can be very useful to visualize contact surfaces and produce fringe plots of contact stress both in directions normal and tangential to the contact surface. To do this, a binary interface file must be written by (1) including a *DATABASE_BINARY_INTFOR command in the input deck, (2) setting one or more contact print flags as detailed above, and (3) including the option s=filename on the LS-DYNA execution line where filename is the intended name of the binary database. The database can be postprocessed using LS-POST.

Force Analysis

----------------

Forces can be obtained a variety of ways:

You can obtain interior forces and moments at a cross-section via the commands *DATABASE_CROSS_SECTION and *DATABASE_SECFORC. Note that when the 'set' option is used in defining a cross-section, a node set identifying the path of the cross-section AND at least one element set identifying the elements to ONE SIDE of the cross-section must be provided.

You can obtain externally applied forces on nodes or groups of nodes via the commands *DATABASE_NODAL_FORCE_GROUP and *DATABASE_NODFOR.

You can obtain forces associated with boundary conditions via the command *DATABASE_BNDOUT.

You can obtain forces specifically associated with *BOUNDARY_SPC by including the command *DATABASE_SPCFORC.

Resultant contact forces are written via the command *DATABASE_RCFORC. In the case of single surface contact, you would also need *CONTACT_FORCE_TRANSDUCER_(option) to extract resultant contact forces generated by the single surface contact.

Contact forces on individual nodes are written via *DATABASE_NCFORC. One or both of the 'print flags' SPR, MPR in *CONTACT must be set to 1 to identify the areas where nodal contact forces are to be extracted.

The data is written into the ASCII files SECFORC, NODFORC, BNDOUT, SPCFORC, RCFORC, and NCFORC.

Altair Forum User

Thank you,

that was helpful...

Altair Forum User

Hello I new member !!