{"id":359950,"date":"2024-04-02T09:25:43","date_gmt":"2024-04-02T09:25:43","guid":{"rendered":"\/forum\/forums\/topic\/creation-of-a-matrix27-element-but-no-effect-on-the-result\/"},"modified":"2024-04-10T13:14:46","modified_gmt":"2024-04-10T13:14:46","slug":"creation-of-a-matrix27-element-but-no-effect-on-the-result","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/creation-of-a-matrix27-element-but-no-effect-on-the-result\/","title":{"rendered":"Creation of a MATRIX27 element, but no effect on the result"},"content":{"rendered":"

Hi there,<\/span><\/p>\n

I’m currently investigating the influence of a new type of bearing on the rotordynamic behavior of a rotor system. What is special about this bearing is that it has unsymmetrical stiffness and damping matrix in X, Y, ROTX and ROTY directions, and sometimes it has negative values of these dynamic properties, which means I cannot just use a general joint to model it. So I turned to creating a MATRIX27 element by inserting an APDL command snippet object. Here is my code, for example, to model the stiffness of the bearing:<\/span><\/p>\n

\/PREP7<\/span>
! define a node<\/span>
local,12,0,10,5,5,0,0,0 !CS definition            !  Defines a local coordinate system by a location and orientation.<\/span>
csys,0 ! Use a specific CS                    !  Activates a previously defined coordinate system.<\/span>
toffst,273.15,  ! Temperature offset from absolute zero<\/span>
*GET,NodeJ,NODE,,COUNT<\/span>
NodeJ = NodeJ + 1<\/span>
n,NodeJ,0,0,0,0,0,0<\/span>
d,NodeJ,UX,%_FIX%<\/span>
d,NodeJ,UY,%_FIX%<\/span>
d,NodeJ,UZ,%_FIX%<\/span>
d,NodeJ,ROTX,%_FIX%<\/span>
d,NodeJ,ROTY,%_FIX%<\/span>
*GET,KLid,ELEM,,COUNT<\/span>
KLid = KLid + 1<\/span>
DOF,UX,UY,UZ,ROTX,ROTY,ROTZ<\/span>
ET,KLid,27,0,2,4,1,      ! KOP(3) = 4 is Stiffness, = 5 is damping, = 2 is inertia output result<\/span>
r,KLid,4725.1761,3258.2165,0,-33261.2676,1626946.9728,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,-3258.2191,4725.1777,0,-1626946.5781,-33261.299,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,-15434.1567,89265.2558,0,-5182223.0717,625042.0062,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,-89265.2446,-15434.1487,0,-625040.2455,-5182222.0351,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span>
rmore,0,0,0,0,0,0,<\/span><\/p>\n

mat,KLid<\/span>
real,KLid<\/span>
type,KLid<\/span>
secnum,KLid  ! section ID<\/span>
MP,BETD,KLid,0.00000001,0,0,0,0<\/span>
EN,KLid,NodeJ,EPKL       ! define an element by the nodal connectivity<\/span><\/p>\n

\/SOLU<\/span><\/p>\n

It appears that the snippet successfully created the MATRIX27 element. When I set:<\/span><\/p>\n

ET,KLid,27,0,0,2,1,<\/span><\/p>\n

to model the mass matrix of the bearing, I can see that the mass summary in the Mechanical Solution Information has really changed (Type 68945 is the MATRIX27 element type):<\/p>\n

\n

***********  PRECISE MASS SUMMARY  ***********<\/span><\/p>\n

   TOTAL RIGID BODY MASS MATRIX ABOUT ORIGIN<\/span>
               Translational mass               |   Coupled translational\/rotational mass<\/span>
        0.10000E+06    0.0000        0.0000     |     0.0000       0.44899E-02   0.47978E-13<\/span>
         0.0000       0.10000E+06    0.0000     |   -0.44899E-02    0.0000       0.86666E-13<\/span>
         0.0000        0.0000       0.10000E+06 |   -0.47978E-13  -0.86666E-13    0.0000    <\/span>
     —————————————— | ——————————————<\/span>
                                                |         Rotational mass (inertia)<\/span>
                                                |    0.18592      -0.25673E-11  -0.59732E-11<\/span>
                                                |   -0.25673E-11   0.18592       0.46053E-11<\/span>
                                                |   -0.59732E-11   0.46053E-11   0.94659E-02<\/span><\/p>\n

   TOTAL MASS = 0.10000E+06<\/span>
     The mass principal axes coincide with the global Cartesian axes<\/span><\/p>\n

   CENTER OF MASS (X,Y,Z)=   0.86666E-18  -0.47978E-18   0.44899E-07<\/span><\/p>\n

   TOTAL INERTIA ABOUT CENTER OF MASS<\/span>
        0.18592      -0.25673E-11  -0.59732E-11<\/span>
       -0.25673E-11   0.18592       0.46053E-11<\/span>
       -0.59732E-11   0.46053E-11   0.94659E-02<\/span>
     The inertia principal axes coincide with the global Cartesian axes<\/span><\/p>\n

  *** MASS SUMMARY BY ELEMENT TYPE ***<\/span><\/p>\n

  TYPE      MASS<\/span>
     1  0.169594E-03<\/span>
 68945   100000.   <\/span><\/p>\n

 <\/p>\n

 <\/p>\n

However, the modal analysis results are the same compared to the results without the MATRIX27 element. Theoretically, if I create a MATRIX27 element with a stiffness matrix, the eigenfrequencies should be higher for the geometry that is radially and axially fixed on one side and founded with the bearing on the other side, and if I create a MATRIX27 element with a mass matrix, the eigenfrequencies should be lower. But no matter how I change the type of matrix or the values in the matrix. The results are always the same.<\/span><\/div>\n
 <\/div>\n
I also tried using the APDL command snippet object to create a generic joint, similar to the code I posted above. It works fine and gives the desired results. So I think it’s because of my lack of understanding of the MATRIX27 element, even though I have read the element reference of MATRIX27 carefully. Could you give me some advice about this element? Thanks in advance.<\/span><\/div>\n

Best regards,<\/span><\/p>\n

 <\/p>\n

Oliver<\/span><\/p>\n<\/div>\n","protected":false},"template":"","class_list":["post-359950","topic","type-topic","status-closed","hentry","topic-tag-Modal_Analysis-1","topic-tag-apdl","topic-tag-Matrix27-1","topic-tag-mechanical"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_subscription":["48109","20905"],"_bbp_author_ip":["96.7.218.223"]," _bbp_last_reply_id":["0"]," _bbp_likes_count":["0"],"_btv_view_count":["1171"],"_bbp_topic_status":["answered"],"_edit_lock":["1712050186:290635"],"_bbp_likes_count":["1"],"_bbp_topic_id":["359950"],"_bbp_forum_id":["27791"],"_bbp_engagement":["20905","48109"],"_bbp_voice_count":["2"],"_bbp_last_reply_id":["361164"],"_bbp_last_active_id":["361164"],"_bbp_last_active_time":["2024-04-08 16:45:33"]},"test":"zhengzhong-gaostud-tu-darmstadt-de"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/359950","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":2,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/359950\/revisions"}],"predecessor-version":[{"id":359952,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/359950\/revisions\/359952"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=359950"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}