S O L U T I O N   O P T I O N S

PROBLEM DIMENSIONALITY. . . . . . . . . . . . .3-D
DEGREES OF FREEDOM. . . . . . UX   UY   UZ
ANALYSIS TYPE . . . . . . . . . . . . . . . . .STATIC (STEADY-STATE)
PRESTRESS EFFECTS CALCULATED. . . . . . . . . .YES
GLOBALLY ASSEMBLED MATRIX . . . . . . . . . . .SYMMETRIC .

                    S O L U T I O N   O P T I O N S

PROBLEM DIMENSIONALITY. . . . . . . . . . . . .3-D
DEGREES OF FREEDOM. . . . . . UX   UY   UZ
ANALYSIS TYPE . . . . . . . . . . . . . . . . .MODAL
   EXTRACTION METHOD. . . . . . . . . . . . . .BLOCK LANCZOS
NUMBER OF MODES TO EXTRACT. . . . . . . . . . .    10
MODAL EXTRACTION RANGE. . . . . . . . . . . . .  1.0000     TO   375.00
NORMALIZE MODES TO UNITY. . . . . . . . . . . .YES
GLOBALLY ASSEMBLED MATRIX . . . . . . . . . . .SYMMETRIC
NUMBER OF MODES TO EXPAND . . . . . . . . . . .    10
MODAL EXPANSION RANGE . . . . . . . . . . . . .  1.0000     TO   375.00
ELEMENT RESULTS CALCULATION . . . . . . . . . .ON

Hello Dan, For a pre-stressed modal, I believe you need nlgeom,on. Kind Regards,   Paul Troxler Senior Staff Engineer   BorgWarner Turbo Systems 1849 Brevard Road Arden, NC 28704 Tel: 828-650-7448   ptroxler@borgwarner.com -----Original Message----- >> ------------------------------ >> >> Message: 2 >> Date: Wed, 10 Aug 2022 14:23:53 +0000 >> From: "Bohlen, Dan (GE Aviation, US)" <dan.bohlen@ge.com> >> Subject: [Xansys] A basic prestressed modal run >> To: XANSYS Mailing List Home <xansys-temp@list.xansys.org> >> Message-ID: <055db1b30540403c88e1cc00c8f5ca6b@ge.com> >> Content-Type: text/plain; charset="us-ascii" >> >> Hi All, >> >> The last cyc symm modal was really for a friend. I'm working on something different. >> >> I have a cantilevered structure I'd like to do a small displacement, stress stiffened modal analysis. (No upcoord stuff - just prestress is what I want.) I believe I'm following the Ansys manual (I listing below.) I don't do this enough, but when I do the modal analysis - there's not a lot of confidence that its using the .emat from linear static run. I seem to get the same results as the no prestress modal run I made - no matter what load I put on it. >> >> Here's some of the output file..... >> >> Static prestress step output >> >> S O L U T I O N O P T I O N S >> >> PROBLEM DIMENSIONALITY. . . . . . . . . . . . .3-D >> DEGREES OF FREEDOM. . . . . . UX UY UZ >> ANALYSIS TYPE . . . . . . . . . . . . . . . . .STATIC (STEADY-STATE) >> PRESTRESS EFFECTS CALCULATED. . . . . . . . . .YES >> GLOBALLY ASSEMBLED MATRIX . . . . . . . . . . .SYMMETRIC . >> . >> . >> . *** LOAD STEP 1 SUBSTEP 1 COMPLETED. CUM ITER = 1 >> *** TIME = 1.00000 TIME INC = 1.00000 NEW TRIANG MATRIX >> >> >> *** ANSYS BINARY FILE STATISTICS >> BUFFER SIZE USED= 16384 >> 516.562 MB WRITTEN ON ELEMENT MATRIX FILE: run_modal_fx_spd_pre.emat >> 189.000 MB WRITTEN ON ELEMENT SAVED DATA FILE: run_modal_fx_spd_pre.esav >> 111.000 MB WRITTEN ON ASSEMBLED MATRIX FILE: run_modal_fx_spd_pre.full >> 130.500 MB WRITTEN ON RESULTS FILE: run_modal_fx_spd_pre.rst >> >> Then I do the modal >> >> >> S O L U T I O N O P T I O N S >> >> PROBLEM DIMENSIONALITY. . . . . . . . . . . . .3-D >> DEGREES OF FREEDOM. . . . . . UX UY UZ >> ANALYSIS TYPE . . . . . . . . . . . . . . . . .MODAL >> EXTRACTION METHOD. . . . . . . . . . . . . .BLOCK LANCZOS >> NUMBER OF MODES TO EXTRACT. . . . . . . . . . . 10 >> MODAL EXTRACTION RANGE. . . . . . . . . . . . . 1.0000 TO 375.00 >> NORMALIZE MODES TO UNITY. . . . . . . . . . . .YES >> GLOBALLY ASSEMBLED MATRIX . . . . . . . . . . .SYMMETRIC >> NUMBER OF MODES TO EXPAND . . . . . . . . . . . 10 >> MODAL EXPANSION RANGE . . . . . . . . . . . . . 1.0000 TO 375.00 >> ELEMENT RESULTS CALCULATION . . . . . . . . . .ON >> >> NO MENTION OF PRE-STRESS! ?? >> >> Here's the Ansys 18 help (I'm using Ansys 15) >> >> >> The procedure for performing a prestressed modal analysis from a linear base analysis is essentially the same as that of a standard modal analysis, except that you first need to prestress the structure by performing a static analysis: >> >> 1. Build the model and obtain a static solution with prestress effects turned on (PSTRES<file:///v:/aeapps/Ansys/v18_2_x64/Server/v182/commonfiles/help/en-us/help/ans_cmd/Hlp_C_PSTRES.html>,ON). The same lumped mass setting (LUMPM<file:///v:/aeapps/Ansys/v18_2_x64/Server/v182/commonfiles/help/en-us/help/ans_cmd/Hlp_C_LUMPM.html>) used here must also be used in the later prestressed modal analysis. Structural Static Analysis<file:///v:/aeapps/Ansys/v18_2_x64/Server/v182/commonfiles/help/en-us/help/ans_str/Hlp_G_STR2.html> describes the procedure to obtain a static solution. Use EMATWRITE<file:///v:/aeapps/Ansys/v18_2_x64/Server/v182/commonfiles/help/en-us/help/ans_cmd/Hlp_C_EMATWRITE.html>,YES if you want to look at strain energies from the modal analysis. >> >> This step can also be a transient analysis. If so, save the EMAT and ESAV files at the desired time point. >> >> 1. Enter the solution processor once again and obtain the modal solution, also with prestress effects activated (reissue PSTRES<file:///v:/aeapps/Ansys/v18_2_x64/Server/v182/commonfiles/help/en-us/help/ans_cmd/Hlp_C_PSTRES.html>,ON). Files Jobname.EMAT (if created) and Jobname.ESAV from the static analysis must be available. >> >> If another analysis is performed between the static and prestressed modal analyses, it is necessary to rerun the static analysis, or keep a copy of the EMAT file from the static analysis. >> Parts of my input file.... >> >> pstres,on >> !omeg,,783.09 ! 7478 RPM >> nsubs,1,1,1 >> nlgeom,off >> EMATWRITE,YES >> outres >> tref,70 >> !save >> pstres,on >> solve,,,,,noch >> >> fini >> /solu >> >> ! set up nodal diameter array >> nfreq=10 ! number of FREq to extract >> freqlo=1 ! FRE START >> freqhi=375 ! FRE CUT OFF >> pstres,on >> !upcoord,1,on >> antype,modal ! Modal analysis >> modopt,lanb,nfreq,freqlo,freqhi,,on ! Selects eigensolver, freq range 10-80,000 hz, on=scale to unity >> mxpand,nfreq,freqlo,freqhi,yes ! Specifies number of modes to expand >> >> I guess I can step up to the perturbation method............. >> >> Thanks, >> >> Dan Bohlen >> Senior Engineer, Stress Analysis >> STAR review chairman, collateral structures GE Aircraft Engines >> 1 Neumann Way >> Evendale, OH 45215 USA >> >> Build B90 Col. H5 cube BK35-251 >> M/D H358 Cell 513-917-3402 >> >> Building 200 Col. G3 cube BC088 Desk Phone 3-8816 >> >> "In God we trust, all others bring data." W Edwards Deming >> >>