13 Replies Latest reply on Jan 30, 2012 8:50 AM by sandeep pawar

    Natural frequency

    Ryszard Jackowicz

      Were to find SolidWorks Simulation egzample for calculation Natural Frequency for "Structure submerged in the water" ?

        • Re: Natural frequency
          Bill McEachern

          According to the AFNOR guide put out by Julien Boissat the software has no capability for dealing withthe added mass due to the presence of the water/fluid. However, I believe that the Geostar version may have this capability (ships with the Sim Premium product and is accessed from the CosmosM tool pick under the solidworks group in the start menu ). I know for sure that it supports an immersed pipe element. If you have this version you could search the help file. It would be a nice enhancement, and probably easy if it is already in GEOSTAR.

            • Re: Natural frequency
              sandeep pawar

              Hello Bill,

               

              How is Geostar different from SW Sim in terms of capabilities? I opened it once and it seemed to me that it was able to do low cycle fatigue (which SW Sim can not). Is that true? Hvae you used Geostar for any projects?

               

              Thanks.

               

              Sandeep

                • Re: Natural frequency
                  Bill McEachern

                  I have but not recently. I have never explored low cycle fatigue in the product so I can not comment one way or the other on that. It is your more or less typical "nodal" based conventional/traditional pre and post processor ala the old Ansys prep 7/ Patran from way back when. Well maybe not even that far back for Patran...... Someone sent me a copy of hte linear section of the theroretical manual the other day. I think I can send it along if some one wants is though I would have to check.

                  • Re: Natural frequency
                    Paul Kellner

                    Simulation is slowly implementing the capabilities of Cosmos/M. Cosmos/M does not use the terminology "decks" although it does produce a session file that can be edited and programmed to do parametric FEA without the help of a CAD program. In the day, Cosmos/M was meant to compete with ANSYS but with a GUI/menu/command hybrid interface.

                     

                    One capability that Cosmos/M has that will likely never be seen in Simulation is the ability to create hexahedral meshes which are less computationally intensive and sometimes more accurate with fewer dof than tet meshes.

                     

                    There are fluid elements in Cosmos/M.

                     

                    I would suspect that doing such an analysis would be problematic if the frequencies were so high that the speed of sound in the fluid was exceeded or if reflected waves somehow reinforced some mode or if cavitation was expected. On the other end of the spectrum you might need to do some kind of coupled aero-elastic type analysis with a CFD program.

                     

                    In the middle of these extremes you might just treat the fluid as additional damping.

                      • Re: Natural frequency
                        Kevin De Smet

                        Do you think we'll ever see the electromagnetic features of COSMOS/M in SolidWorks Simulation?

                        • Re: Natural frequency
                          Ryszard Jackowicz

                          I return to my original question "were to find egzample in Sim for Structural vibration in fluid". I understund that we dont have yet correct ?

                          As you point "in the midle of these extremes" we can treat the fluid as addirional damping, maybe "additional mass" Property of fluid insisde is easy to determined. More difficult is surronding fluid Some technical paper included added Masses in relation to cross section or shape of submerged structure.  For that immersed  structure is important wall thickness, shape, velocity of fluid  etc  This is manual calculationis in addition to calculation natural frequency without fluid.

                          But if we are going to use some combination of coefficients ..... i don,t like that.

                          Thanks Paul for your answer.

                            • Re: Natural frequency
                              Bill McEachern

                              the damping won't affect the fequency much but the added mass will. The damping will obviously attenuate the response quite a bit but not the fequencies of the response. The deal with this a lot in the computation of the natural frequency of "hull girders" - the hulls of large ships - not good to have it close to the wave encounter frequency even with all the damping. You may want to do a bit of literature search - as they probably have methods for estimating the frequencies of wetted structures.