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April 24, 2014, 06:48 |
Craziest APDL mistery ever
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New Member
Enrique Cavlap
Join Date: Apr 2014
Posts: 1
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Hello everybody,
I have to say that I started using ANSYS APDL only a few months ago but this just doesn't make any sense to me... So I start using ANSYS 15.0 from the APDL Product Launcher... Simulation environment: ANSYS License: ANSYS Mechanical Add-on Modules: None And then I wrote this code to obtain the first five modal frequencies of a horizontal beam fixed at both ends: FINISH ! Exit from processor /CLEAR,NOSTART ! Clear database (not reading start145.ans) /FILNAME,AxialLoadEstimation,ON ! Change Jobname for the analysis (start new files) /Title,Axial Load Estimation for a steel bar with circular section !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! /PREP7 ! Enters mode creation preprocessor MatDens=1101 ! Material's Density (kg/m3) MatE=1.95e11 ! Material's Elastic Moduli (N/m2) MatPoisson=0.3 ! Material's Major Poisson's Ratio ! BeamLength=2.501999201 ! Length of the beam (m) SecRad=0.0075 ! Radius (m) ! AxForce=22400 ! Axial Force applied (N) ET,1,beam188 ! Define local element > type number 1 > beam188 ! Defines linear material properties MP,DENS,1,MatDens ! Density = 1101 kg/m3 MP,EX,1,MatE ! Elastic moduli = 1.95x10E11 N/m2 MP,PRXY,1,MatPoisson ! Major Poisson's ratio = 0.3 ! Create keypoints and line K,1,0,0,0 ! Keypoint 1 (0,0,0) K,2,BeamLength,0,0 ! Keypoint 2 (BeamLength,0,0) L,1,2,(BeamLength*100) ! Line between K1 and K2 with divisions by cm k,3,0,1,0 ! Keypoint 3 (0,1,0) [Orientation] SECTYPE,1,BEAM,CSOLID ! Circular solid beam section SECDATA,SecRad ! Radius=18.525mm (Diam=37.05mm) ! 8 div around circumference + 2 div through radius LATT,1,0,1,,3,,1 ! Associates element attributes with unmeshed lines ! MAT=1(beam188),0,TYPE=1(steel) ! KB=K3 KE= ! SECNUM=1(circular) LMESH,1 ! Generates nodes and line elements along Line 1 ! Definition of DoF constraints at nodes D,ALL,UZ,0 ! Neglect movement in z-axis D,ALL,ROTX,0 ! Neglect rotation in x-axis D,ALL,ROTY,0 ! Neglect rotation in y-axis D,1,UY,0 ! Neglect movement in y-axis D,2,UY,0 D,1,ROTZ,0 ! Neglect rotation in z-axis D,2,ROTZ,0 F,1,fx,-AxForce ! Specifies force load at node 1 F,2,fx,AxForce ! Specifies force load at node 2 ALLSEL !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! /SOLU ! Enter solution processor ANTYPE,STATIC ! Static analysis PSTRES,ON ! Specifies that prestress effects are calculated EMATWRITE,YES ! Forces the writing of all the element matrices to File.EMAT SOLVE ! Starts solution FINISH !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! /SOLU ! Enter solution processor ANTYPE,MODAL ! Modal analysis MODOPT,LANB,5 ! Extraction of 5 modes by Block Lanczos PSTRES,ON D,1,UX,0 ! Neglect movement in x-axis D,2,UX,0 SOLVE ! Starts solution FINISH !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! /POST1 ! Enter database results postprocessor SET,LIST ! Defines data set by scanning + listing each load step ! Extract modal frequencies !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I copy-paste this script and ANSYS gives me a first modal frequency of 78.140, but if I change the parameter BeamLength from 2.501999201 to 2.5019992, the frequency falls to 28.365!! Which is the frequency of the beam but unloaded... I don't know why by making the beam 0.000001 mm shorter the results change like this... Does anybody know what am I missing?? |
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