• Registered: 04-12-2017
  • Posts: 25

Topic: How to apply gravity?

Hello,

I am trying to apply gravity on my model but I am confused about that. I know I should use "Deadweight" command in my input file but how to decide the magnitude of this load?  Do I need to use 9.8/density of material? Thanks.

2 Reply by bp

  • bp
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  • From: Prague, Czech Rep.
  • Registered: 02-03-2007
  • Posts: 1,026

Re: How to apply gravity?

Hi,
the density is taken from material (keyword 'd'). You have to apply DeadWeight loading, where in the direction of the gravity you use the gravitational acceleration.
Example (2d simulation, gravity in x direction):

IsoLE 1 d 1. E 100.0 n 0.01  tAlpha 0.000012
DeadWeight 3 loadTimeFunction 1 Components 2 9.81 0. set 1

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  • Registered: 04-12-2017
  • Posts: 25

Re: How to apply gravity?

Hi Borek,

Thanks for your reply.

I was wondering if I use the density/d not 1 but the density of a real material, do I need still use 9.81 in the magnitude of DeadWeight? Thanks.



bp wrote:

Hi,
the density is taken from material (keyword 'd'). You have to apply DeadWeight loading, where in the direction of the gravity you use the gravitational acceleration.
Example (2d simulation, gravity in x direction):

IsoLE 1 d 1. E 100.0 n 0.01  tAlpha 0.000012
DeadWeight 3 loadTimeFunction 1 Components 2 9.81 0. set 1

4 Reply by KunZeng (edited by KunZeng 23-01-2018 20:37:56)

  • Registered: 04-12-2017
  • Posts: 25

Re: How to apply gravity?

And I tried to use "Set" to apply Deadweight but I got the error:

Error: (/home/kun/femdem/oofem/source/src/oofemlib/domain.C:819)
Domain :: instanciateYourself - Couldn't create crosssection: set
_______________________________________________________
stack trace:
  /home/kun/femdem/include/liboofem.so : oofem::Logger::writeELogMsg(oofem::Logger::logLevelType, char const*, int, char const*, ...)+0x1d7
  /home/kun/femdem/include/liboofem.so : oofem::Domain::instanciateYourself(oofem::DataReader*)+0x13c6
  /home/kun/femdem/include/liboofem.so : oofem::EngngModel::instanciateDomains(oofem::DataReader*)+0x51
  /home/kun/femdem/include/liboofem.so : oofem::EngngModel::instanciateYourself(oofem::DataReader*, oofem::InputRecord*, char const*, char const*)+0x236
  /home/kun/femdem/include/liboofem.so : oofem::InstanciateProblem(oofem::DataReader*, oofem::problemMode, int, oofem::EngngModel*, bool)+0x2ca
  /home/kun/femdem/include/liboofem.so : ()+0x2b962f
  /home/kun/femdem/include/liboofem.so : ()+0x37032c
  /home/kun/femdem/include/liboofem.so : ()+0x35594a
  /home/kun/femdem/include/liboofem.so : ()+0x34c3e3
  /usr/lib/x86_64-linux-gnu/libboost_python-py27.so.1.58.0 : boost::python::objects::function::call(_object*, _object*) const+0x26d
Total 1 error(s) and 0 warning(s) reported
oofem exit code 1

You can find my input file at attachment. Can you tell me where is problem I have? Thank you very much.

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  • From: Gothenburg, Sweden
  • Registered: 08-09-2009
  • Posts: 1,419

Re: How to apply gravity?

Errors like this (oofem tries to create a cross-section named "set") indicates that the number of sets and such aren't specified correctly in the domain specification. You'll have to specify "nset X" were X is the number of sets you have defined.

  • Registered: 04-12-2017
  • Posts: 25

Re: How to apply gravity?

Hi Borek and Mikael,

Thanks for your suggestion. I still have a question. Does the value of density affect the value of the deadweight for apply the gravity? I did a trial by letting a beam falling in the air without any restriction. Why the falling speed change if I change the value of the density(same deadweight: -9.81 in z direction)? Thanks.

Kun